Energy Storage Publications

Hyung-Seok Lim, Won-Jin Kwak, Sujong Chae, Sungun Wi, Linze Li, Jiangtao Hu, Jinhui Tao, Chongmin Wang, Wu Xu, Ji-Guang Zhang."Stable Solid Electrolyte Interphase Layer Formed by Electrochemical Pretreatment of Gel Polymer Coating on Li Metal Anode for Lithium–Oxygen Batteries."ACS Energy Letters 6 (9), 3321-3331 (September 2021).
Abstract: Lithium–oxygen (Li–O₂) batteries exhibit the highest theoretical specific energy density among candidates for next-generation energy storage systems, but the instabilities of Li metal anode (LMA), air electrode, and electrolyte largely limit the practical applications of these batteries. Herein, we report an effective method to protect the LMA against side reactions between the LMA and the crossover contaminants such as highly reactive oxygen moieties. A solid electrolyte interphase (SEI) layer rich in inorganic components is formed on the LMA coated with poly(ethylene oxide) thin film through an in situ electrochemical precharging step under oxygen atmosphere. This uniformly distributed SEI layer interacts with the flexible polymer matrix and forms a submicrometer-sized gel-like polymer layer. This polymer-supported SEI layer leads to much longer cycle life (1₃0 vs 6₅ cycles) as compared to that of pristine cells under the same testing conditions. It is also very effective to stabilize the LMA/electrolyte interphase with a redox mediator.

Bethel Tarekegne, Rebecca O'Neil, Jeremy Twitchell."Energy Storage as an Equity Asset."Current Sustainable/Renewable Energy Reports 8, 149-155 (September 2021).
Abstract: This review offers a discussion on how energy storage deployment advances equitable outcomes for the power system. It catalogues the four tenets of the energy justice concept—distributive, recognition, procedural, and restorative—and shows how they relate to inequities in energy affordability, availability, due process, sustainability, and responsibility. Energy storage systems have been deployed to support grid reliability and renewable resource integration, but there is additional emerging value in considering the connections between energy storage applications and equity challenges in the power system. Through a thorough review of the energy justice and energy transitions literature, this paper offers the equity dimensions of storage project design and implementations. Emerging energy programs and projects are utilizing energy storage in pursuit of improved equity outcomes. Future research and policy design should integrate energy justice principles to align storage penetration with desired equity outcomes.

Charlie Vartanian, Matt Paiss, Vilayanur Viswanathan, Jaime Kolln, David Reed."Review of Codes and Standards for Energy Storage Systems."Current Sustainable/Renewable Energy 8, 138-148 (September 2021).
Abstract: This article summarizes key codes and standards (C&S) that apply to grid energy storage systems. The article also gives several examples of industry efforts to update or create new standards to remove gaps in energy storage C&S and to accommodate new and emerging energy storage technologies. While modern battery technologies, including lithium ion (Li-ion), increase the technical and economic viability of grid energy storage, they also present new or unknown risks to managing the safety of energy storage systems (ESS). This article focuses on the particular challenges presented by newer battery technologies. Prior publications about energy storage C&S recognize and address the expanding range of technologies and their unique characteristics. However, there remains significant need and opportunity for researchers to add to the knowledge base that informs the development of technical references and standards, and ultimately, the application of published standards for the effective and safe design and use of modern ESS.

Patrick Balducci, Kendall Mongird, Mark Weimar."Understanding the Value of Energy Storage for Power System Reliability and Resilience Applications."Current Sustainable/Renewable Energy Reports 8, 131-137 (September 2021).
Abstract: The need for energy storage in the electrical grid has grown in recent years in response to a reduced reliance on fossil fuel baseload power, added intermittent renewable investment, and expanded adoption of distributed energy resources. While the methods and models for valuing storage use cases have advanced significantly in recent years, the value of enhanced resilience remains an open research question. The findings of the recent research indicate that energy storage provides significant value to the grid, with median benefit values for specific use cases ranging from under $10/kW-year for voltage support to roughly $100/kW-year for capacity and frequency regulation services. While the value of lost load is used widely to estimate the benefits of mitigating short-duration outages, reaching as high as $719/kilowatt-year, there is no consensus when it comes to monetizing the value of improving grid resilience. This paper presents a use case taxonomy for energy storage and uses the taxonomy to conduct a meta-analysis of an extensive set of energy storage valuation studies. It reviews several approaches for monetizing reliability and resiliency services and presents a proposed approach for valuing resiliency for energy storage investments.

Xiang Li, Peiyuan Gao, Yun-Yu Lai, J. David Bazak, Aaron Hollas, Heng-Yi Lin, Vijayakumar Murugesan, Shuyuan Zhang, Chung-Fu Cheng, Wei-Yao Tung, Yueh-Ting Lai, Ruozhu Feng, Jin Wang, Chien-Lung Wang, Wei Wang, Yu Zhu."Symmetry-breaking design of an organic iron complex catholyte for a long cyclability aqueous organic redox flow battery."Nature Energy 6, 873-881 (September 2021).
Abstract: The limited availability of a high-performance catholyte has hindered the development of aqueous organic redox flow batteries (AORFB) for large-scale energy storage. Here we report a symmetry-breaking design of iron complexes with 2,2′-bipyridine-4,4′-dicarboxylic (Dcbpy) acid and cyanide ligands. By introducing two ligands to the metal centre, the complex compounds (M4[Fe^II(Dcbpy)₂(CN)₂], M = Na, K) exhibited up to a 4.2 times higher solubility (1.22 M) than that of M₄[Fe^II(Dcbpy)₃] and a 50% increase in potential compared with that of ferrocyanide. The AORFBs with 0.1 M Na_4M/[Fe^II(Dcbpy)₂(CN)₂] as the catholyte were demonstrated for 6,000 cycles with a capacity fading rate of 0.00158% per cycle (0.217% per day). Even at a concentration near the solubility limit (1 M Na₄[Fe^II(Dcbpy)₂(CN)₂]), the flow battery exhibited a capacity fading rate of 0.008% per cycle (0.25% per day) in the first 400 cycles. The AORFB cell with a nearly 1:1 catholyte:anolyte electron ratio achieved a cell voltage of 1.2 V and an energy density of 12.5 Wh l^–1.

Ismael A. Rodriguez-Perez, Hee-Jung Chang, Matthew Fayette, Bhuvaneswari M. Sivakumar, Daiwon Choi, Xiaolin Li, David Reed."Mechanistic investigation of redox processes in Zn–MnO₂ battery in mild aqueous electrolytes."Journal of Materials Chemistry A 9 (36), 20766-20775 (August 2021).
Abstract: Zinc–MnO₂ based batteries have acquired attention for grid-level applications, due to impressive theoretical performance, cost effectiveness and intrinsic safety. However, there are still many challenges that remain elusive due to the complex and controversial mechanisms of operation that hinder commercialization. In this work, the detailed redox processes that occur at the cathode during Zn–MnO₂ battery operation are elucidated. Using a blend of structural and electrochemical techniques, the redox pairs that occur during operation are mechanistically studied while also showcasing the true impact of the electrolyte additive (0.1 M MnSO₄) in a 1 M ZnSO₄ electrolyte. An electrochemical quartz-crystal microbalance (EQCM) has been leveraged to reveal the effect of zinc hydroxy sulfate salt (Zn₄SO₄(OH)₆·nH₂O) and zinc manganese oxide (Zn_xMn_yO_z) dissolution/deposition, which are believed to be major components during discharge and charge conditions. These results provide insight not currently available, allowing a holistic view of the electrochemical reaction mechanisms during battery operation.

Xin He, Dominic Bresser, Stefano Passerini, Florian Baakes, Ulrike Krewer, Jeffrey Lopez, Christopher Thomas Mallia, Yang Shao-Horn, Isidora Cekic-Laskovic, Simon Wiemers-Meyer, Fernando A. Soto, Victor Ponce, Jorge M. Seminario, Perla B. Balbuena, Hao Jia, Wu Xu, Yaobin Xu, Chongmin Wang, Birger Horstmann, Rachid Amine, Chi-Cheung Su, Jiayan Shi, Khalil Amine, Martin Winter, Arnulf Latz, Robert Kostecki."The passivity of lithium electrodes in liquid electrolytes for secondary batteries."Nature Reviews Materials (August 2021).
Abstract: Rechargeable Li metal batteries are currently limited by safety concerns, continuous electrolyte decomposition and rapid consumption of Li. These issues are mainly related to reactions occurring at the Li metal–liquid electrolyte interface. The formation of a passivation film (that is, a solid electrolyte interphase) determines ionic diffusion and the structural and morphological evolution of the Li metal electrode upon cycling. In this Review, we discuss spontaneous and operation-induced reactions at the Li metal–electrolyte interface from a corrosion science perspective. We highlight that the instantaneous formation of a thin protective film of corrosion products at the Li surface, which acts as a barrier to further chemical reactions with the electrolyte, precedes film reformation, which occurs during subsequent electrochemical stripping and plating of Li during battery operation. Finally, we discuss solutions to overcoming remaining challenges of Li metal batteries related to Li surface science, electrolyte chemistry, cell engineering and the intrinsic instability of the Li metal–electrolyte interface.

Alasdair J. Crawford, Daiwon Choi, Patrick J. Balducci, Venkat R. Subramanian, Vilayanur V. Viswanathan."Lithium-ion battery physics and statistics-based state of health model."Journal of Power Sources 501, 230032 (July 2021).
Abstract: A pseudo-2d model using COMSOL Multiphysics® software simulates performance degradation of Li-ion batteries when subjected to peak shaving grid service. Multiple degradation pathways are considered, including solid electrolyte interphase (SEI) formation and breakdown, cathode dissolution and its effect on SEI formation. The model is validated by simulating commercial cell performance. We develop a global model simulating performance across all chemistries, along with a model treating chemistries individually. There is good agreement between these two models for various optimization parameters such as SEI equilibrium potential, cathode dissolution exchange current density, solvent diffusivity in the SEI and SEI ionic conductivity. To circumvent time constraints related to the COMSOL model, a 0d global model is developed, which fits data well. Good agreement for various optimization parameters is obtained among the COMSOL global & individual chemistry models and the 0-d model. A top-down, statistics-based model using current, voltage, and anode expansion rate as degradation predictors is developed using insights from the physics-based model. This model predicts degradation for multiple grid services and electric vehicle drive cycles with high accuracy and provides the pathway to develop an efficient battery management system combining machine learning and findings from computationally intensive physics-based algorithms.

Birger Horstmann, Jiayan Shi, Rachid Amine, Martin Werres, Xin He, Hao Jia, Florian Hausen, Isidora Cekic-Laskovic, Simon Wiemers-Meyer, Jeffrey Lopez, Diego Galvez-Aranda, Florian Baakes, Dominic Bresser, Chi-Cheung Su, Yaobin Xu, Wu Xu, Peter Jakes, Rudiger A. Eichel, Egbert Figgemeier, Ulrike Krewer, Jorge M. Seminario, Perla B. Balbuena, Chongmin Wang, Stefano Passerini, Yang Shao-Horn, Martin Winter, Khalil Amine, Robert Kostecki, Arnulf Latz."Strategies towards enabling lithium metal in batteries: interphases and electrodes."Energy & Environmental Science (July 2021).
Abstract: Despite the continuous increase in capacity, lithium-ion intercalation batteries are approaching their performance limits. As a result, research is intensifying on next-generation battery technologies. The use of a lithium metal anode promises the highest theoretical energy density and enables use of lithium-free or novel high-energy cathodes. However, the lithium metal anode suffers from poor morphological stability and Coulombic efficiency during cycling, especially in liquid electrolytes. In contrast to solid electrolytes, liquid electrolytes have the advantage of high ionic conductivity and good wetting of the anode, despite the lithium metal volume change during cycling. Rapid capacity fade due to inhomogeneous deposition and dissolution of lithium is the main hindrance to the successful utilization of the lithium metal anode in combination with liquid electrolytes. In this perspective, we discuss how experimental and theoretical insights can provide possible pathways for reversible cycling of two-dimensional lithium metal. Therefore, we discuss improvements in the understanding of lithium metal nucleation, deposition, and stripping on the nanoscale. As the solid–electrolyte interphase (SEI) plays a key role in the lithium morphology, we discuss how the proper SEI design might allow stable cycling. We highlight recent advances in conventional and (localized) highly concentrated electrolytes in view of their respective SEIs. We also discuss artificial interphases and three-dimensional host frameworks, which show prospects of mitigating morphological instabilities and suppressing large shape change on the electrode level.

Peiyuan Gao, Haiping Wu, Xianhui Zhang, Hao Jia, Ju-Myung Kim, Mark H. Engelhard,Chaojiang Niu, Zhijie Xu, Ji-Guang Zhang, Wu Xu."Optimization of Magnesium-Doped Lithium Metal Anode for High Performance Lithium Metal Batteries through Modeling and Experiment."Angewandte Chemie International 60 (30), 16506-16513, (July 2021).
Abstract: Lithium (Li)-magnesium (Mg) alloy with limited Mg amount, which can also be called Mg-doped Li (Li-Mg), has been considered as a potential alternative anode for high energy density rechargeable Li metal batteries. However, the optimum doping-content of Mg in Li-Mg anode and the mechanism of the improved performance are not well understood. Herein, density functional theory (DFT) calculations are used to investigate the effect of Mg amount in Li-Mg anode. The Li-Mg with about 5 wt. % Mg (abbreviated as Li-Mg5) has the lowest absorption energy of Li, thus all the surface area can be “controlled” by Mg atoms, leading to the smooth and continuous deposition of Li on the surface around the Mg center. A localized high concentration electrolyte enables Li-Mg5 to exhibit the best cycling stability in Li metal batteries with high-loading cathode and lean electrolyte under 4.4 V high-voltage, which is approaching the demand of practical application. This electrolyte also helps generate an inorganic-rich solid electrolyte interphase, which leads to smooth, compact and less corrosion layer on the Li-Mg5 surface. Both theoretical simulations and experimental results prove that Li-Mg5 has optimum Mg content and gives best battery cycling performance.

Haiping Wu, Peiyuan Gao, Hao Jia, Lianfeng Zou, Linchao Zhang, Xia Cao, Mark H. Engelhard, Mark E. Bowden, Michael S. Ding, Jiangtao Hu, Dehong Hu, Sarah D. Burton, Kang Xu, Chongmin Wang, Ji-Guang Zhang, Wu Xu."A Polymer-in-Salt Electrolyte with Enhanced Oxidative Stability for Lithium Metal Polymer Batteries."ACS Applied Materials & Interfaces 13 (27), 31583-31593 (July 2021).
Abstract: The lithium (Li) metal polymer battery (LMPB) is a promising candidate for solid-state batteries with high safety. However, high voltage stability of such a battery has been hindered by the use of polyethylene oxide (PEO), which oxidizes at a potential lower than 4^V versus Li. Herein, we adopt the polymer-in-salt electrolyte (PISE) strategy to circumvent the disadvantage of the PEO–lithium bis(fluorosulfonyl)imide (LiFSI) system with EO/Li ≤ 8 through a dry ball-milling process to avoid the contamination of the residual solvent. The obtained solid-state PISEs exhibit distinctly different morphologies and coordination structures which lead to significant improvement in oxidative stability. P(EO)₁LiFSI has a low melting temperature, a high ionic conductivity at 60 °C, and an oxidative stability of ∼4.5^V versus Li/Li⁺. With an effective interphase rich in inorganic species and a good stability of the hybrid polymer electrolyte toward Li metal, the LMPB constructed with Li||LiNiSub>1/3Co_1/3Mn_1/3O₂ can retain 74.4% of capacity after 186 cycles at 60 °C under the cutoff charge voltage of 4.3^V. The findings offer a promising pathway toward high-voltage stable polymer electrolytes for high-energy-density and safe LMPBs.

Hee-Jung Chang, Ismael A. Rodriguez-Perez, Matthew Fayette, Nathan L. Canfield, Huilin Pan, Daiwon Choi, Xiaolin Li, David Reed."Effects of water-based binders on electrochemical performance of manganese dioxide cathode in mild aqueous zinc batteries."Carbon Energy 3: (3), 473-481 (July 2021).
Abstract: In the majority of rechargeable batteries including lithium-ion batteries, polyvinylidene fluoride (PVdF) binders are the most commonly used binder for both anode and cathode. However, using PVdF binder requires the organic solvent of N-methyl-2-pyrrolidone which is expensive, volatile, combustible, toxic, and has poor recyclability. Therefore, switching to aqueous electrode processing routes with non-toxic binders would provide a great leap forward towards the realization of ideally fully sustainable and environmentally friendly electrochemical energy storage devices. Various water-soluble binders (aqueous binders) were characterized and compared to the performance of conventional PVdF. Our study demonstrates that the electrochemical performance of Zn/MnO₂ aqueous batteries is significantly improved by using sodium carboxymethyl cellulose (CMC) binder. In addition, CMC binders offer desirable adhesion, good wettability, homogeneous material distribution, and strong chemical stability at certain pH levels (3.5–5) without any decomposition for long-cycle life.

Bhuvaneswari M. Sivakumar, Venkateshkumar Prabhakaran, Kaining Duanum, Edwin Thomsen, Brian Berland, Nicholas Gomez, David Reed, Vijayakumar Murugesan."Long-Term Structural and Chemical Stability of Carbon Electrodes in Vanadium Redox Flow Battery."ACS Applied Energy Materials 4: (6), 6074-6081 (June 2021).
Abstract: Predicting the performance decay in carbon electrodes is critical to maximizing the longevity of redox flow battery (RFB) systems. This study investigates the effect of long-term cycling (over 8000 cycles) on the structural and chemical evolution of carbon electrodes. We find that the microstructural aspects such as graphitic stacking order and interlayer spacing along with overall morphological construct remain largely unchanged even after the prolonged cycling process. Conversely, significant changes in surface chemistry such as the evolution of functional groups and point defects are evident from our combined multimodal spectroscopic and computational analysis. The X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis reveal chemical absorption of chloride counter anions at point defects within the graphitic surface. Additionally, our results suggest that vanadium cation plays an important role in counter anion–carbon surface interaction and subsequently the surface chemistry evolutions. Our findings provide insights about surface chemical evolution that is critical for predicting electrode performance and longevity of RFB.

Xiaowen Zhan, Minyuan M. Li, J. Mark Weller, Vincent L. Sprenkle, Guosheng Li."Recent Progress in Cathode Materials for Sodium-Metal Halide Batteries."Materials 14: (12), 3260 (June 2021).
Abstract: Transitioning from fossil fuels to renewable energy sources is a critical goal to address greenhouse gas emissions and climate change. Major improvements have made wind and solar power increasingly cost-competitive with fossil fuels. However, the inherent intermittency of renewable power sources motivates pairing these resources with energy storage. Electrochemical energy storage in batteries is widely used in many fields and increasingly for grid-level storage, but current battery technologies still fall short of performance, safety, and cost. This review focuses on sodium metal halide (Na-MH) batteries, such as the well-known Na-NiCl₂ battery, as a promising solution to safe and economical grid-level energy storage. Important features of conventional Na-MH batteries are discussed, and recent literature on the development of intermediate-temperature, low-cost cathodes for Na-MH batteries is highlighted. By employing lower cost metal halides (e.g., FeCl₂, and ZnCl₂, etc.) in the cathode and operating at lower temperatures (e.g., 190 °C vs. 280 °C), new Na-MH batteries have the potential to offer comparable performance at much lower overall costs, providing an exciting alternative technology to enable widespread adoption of renewables-plus-storage for the grid.

Ruozhu Feng, Xin Zhang, Vijayakumar Murugesan, Aaron Hollas, Ying Chen, Yuyan Shao, Eric Walter, Nadeesha P. N. Wellala, Litao Yan, Kevin M. Rosso, Wei Wang."Reversible ketone hydrogenation and dehydrogenation for aqueous organic redox flow batteries." Science 372: (6544), 836-840 (May 2021).
Abstract: Aqueous redox flow batteries with organic active materials offer an environmentally benign, tunable, and safe route to large-scale energy storage. Development has been limited to a small palette of organics that are aqueous soluble and tend to display the necessary redox reversibility within the water stability window. We show how molecular engineering of fluorenone enables the alcohol electro-oxidation needed for reversible ketone hydrogenation and dehydrogenation at room temperature without the use of a catalyst. Flow batteries based on these fluorenone derivative anolytes operate efficiently and exhibit stable long-term cycling at ambient and mildly increased temperatures in a nondemanding environment. These results expand the palette to include reversible ketone to alcohol conversion but also suggest the potential for identifying other atypical organic redox couple candidates.

J. David Bazak, Allison R. Wong, Kaining Duanmu, Kee Sung Han, David Reed, Vijayakumar Murugesan."Concentration-Dependent Solvation Structure and Dynamics of Aqueous Sulfuric Acid Using Multinuclear NMR and DFT."Journal of Physical Chemistry B 125 (19), 5089-5099 (May 2021).
Abstract: Sulfuric acid is a ubiquitous compound for industrial processes, and aqueous sulfate solutions also play a critical role as electrolytes for many prominent battery chemistries. While the thermodynamic literature on it is quite well-developed, comprehensive studies of the solvation structure, particularly molecular-scale dynamical and transport properties, are less available. This study applies a multinuclear nuclear magnetic resonance (NMR) approach to the elucidation of the solvation structure and dynamics over wide temperature (−10 to 50 °C) and concentration (0–18 M) ranges, combining the ¹⁷O shift, line width, and T₁ relaxation measurements, 33S shift and line width measurements, and ¹H pulsed-field gradient NMR measurements of proton self-diffusivity. In conjunction, these results indicate a crossover between two regimes of solvation structure and dynamics, occurring above the concentration associated with the deep eutectic point (∼4.5 ^M), with the high-concentration regime dominated by a strong water–sulfate correlation. This description was borne out in detail by the activation energy trends with increasing concentration derived from the relaxation of both the H₂O/H₃O⁺ and H₂SO₄/HSO₄^-;/SO₄2^2-17O resonances and the 1H self-diffusivity. However, the 17O chemical shift difference between the H₂O/H₃O⁺ and H₂SO₄/HSO₄^2-resonances across the entire temperature range is nevertheless strikingly linear. A computational approach coupling molecular dynamics simulations and density functional theory NMR shift calculations to reproduce this trend is presented, which will be the subject of further development. This combination of multinuclear, dynamical NMR, and computational methods, and the results furnished by this study, will provide a platform for future studies on battery electrolytes where aqueous sulfate chemistry plays a central role in the solution structure.

Junhua Song, Kang Xu, Nian Liu, David Reed, Xiaolin Li."Crossroads in the renaissance of rechargeable aqueous zinc batteries." Materials Today 45: 191-212 (May 2021).
Abstract: Aqueous zinc batteries dominate the primary battery market with alkaline chemistries and recently have been rejuvenated as rechargeable devices to compete for grid-scale energy storage applications. Tremendous effort has been made in the past few years and improved cyclability has been demonstrated in both alkaline, neutral, and mild acidic systems. In this review/perspective, we will elucidate the merits of rechargeable aqueous zinc batteries through side-by-side comparison to Li-ion batteries, examine the challenges and progress made in the pursuit of highly rechargeable alkaline and mild acidic batteries, and finally provide a holistic forward look at the technology. The focus is placed on static closed cell designs, while flow batteries and open systems like zinc-air batteries will not be included due to space constraint.

Nimat Shamim, Edwin C. Thomsen, Vilayanur V. Viswanathan, David Reed, Vincent Sprenkle, Guosheng Li."Evaluating ZEBRA Battery Module under the Peak-Shaving Duty Cycles."Materials 14: (9), 2280 (April 2021).
Abstract: With the recent rapid increase in demand for reliable, long-cycle life, and safe battery technologies for large-scale energy-storage applications, a battery module based on ZEBRA battery chemistry is extensively evaluated for its application in peak shaving duty cycles. First, this module is tested with a full capacity cycle consisting of a charging process (factory default) and a discharging process with a current of 40 A. The battery energy efficiency (discharge vs. charge) is about 90%, and the overall energy efficiency is 80.9%, which includes the auxiliary power used to run the battery management system electronics and self-heating to maintain the module operating temperature (265 °C). Generally, because of the increased self-heating during the holding times that exist for the peak shaving duty cycles, the overall module efficiency decreases slightly for the peak-shaving duty cycles (70.7–71.8%) compared to the full-capacity duty cycle. With a 6 h, peak-shaving duty cycle, the overall energy efficiency increases from 71.8% for 7.5 kWh energy utilization to 74.1% for 8.5 kWh. We conducted long-term cycling tests of the module at a 6 h, peak-shaving duty cycle with 7.5 kWh energy utilization, and the module exhibited a capacity degradation rate of 0.0046%/cycle over 150 cycles (>150 days).

Biwei Xiao, Yichao Wang, Sha Tan, Miao Song, Xiang Li, Yuxin Zhang, Feng Lin, Kee Sung Han, Fredrick Omenya, Khalil Amine, Xiao-Qing Yang, David Reed, Yanyan Hu, Gui-Liang Xu, Enyuan Hu, Xin Li, Xiaolin Li. "Vacancy‐Enabled O3 Phase Stabilization for Manganese‐Rich Layered Sodium Cathodes."Angewandte Chemie International Edition60 (15), 8258-8267 (April 2021).
Abstract: Manganese‐rich layered oxide materials hold great potential as low‐cost and high‐capacity cathodes for Na‐ion batteries. However, they usually form a P2 phase and suffer from fast capacity fade. In this work, an O3 phase sodium cathode has been developed out of a Li and Mn‐rich layered material by leveraging the creation of transition metal (TM) and oxygen vacancies and the electrochemical exchange of Na and Li. The Mn‐rich layered cathode material remains primarily O3 phase during sodiation/desodiation and can have a full sodiation capacity of ca. 220 mAh g⁻¹. It delivers ca. 16 mAh g⁻¹ specific capacity between 2–3.8 V with >86 % retention over 250cycles. The TM and oxygen vacancies pre‐formed in the sodiated material enables a reversible migration of TMs from the TM layer to the tetrahedral sites in the Na layer upon de‐sodiation and sodiation. The migration creates metastable states, leading to increased kinetic barrier that prohibits a complete O3‐P3 phase transition.

Di Wu, Xu Ma."Modeling and Optimization Methods for Controlling and Sizing Grid-Connected Energy Storage: A Review." Current Sustainable/Renewable Energy Reports (March 2021).
Abstract: Energy storage is capable of providing a variety of services and solving a multitude of issues in today’s rapidly evolving electric power grid. This paper reviews recent research on modeling and optimization for optimally controlling and sizing grid-connected battery energy storage systems (BESSs). Open issues and promising research directions are discussed. Recent studies on BESS dispatch, evaluation, and sizing focus on advanced modeling and optimization methods to maximize stacked value streams from multiple services. BESS models have been improved to better represent operational characteristics or capture degradation effects. Different solution methods and optimization techniques have been proposed to improve the benefits and cost-effectiveness of BESSs, using deterministic approaches prevalently but with impressive progress in modeling and addressing uncertainties. Recent progress in BESS scheduling and sizing better supports planning and operational decision-making in different use cases, which is highly important to advance the deployment of BESSs. Additional research is required to properly model the trade-off between short-term benefits and service life with multiple degradation effects explicitly considered in the decision-making process. Advanced methods are to be developed for effectively determining optimal BESS sizes that maximize overall benefits within a varying lifetime considering diversified system conditions, as well as uncertainties at planning and operational stages.

Di Wu, Xu Ma, Patrick Balducci, Dhruv Bhatnagar."An economic assessment of behind-the-meter photovoltaics paired with batteries on the Hawaiian Islands." Applied Energy 286 (March 2021).
Abstract: Due to natural variability and uncertainty, the ever-increasing penetration of solar generation in Hawaii presents challenges to power grid operators to maintain reliable system operation. Demand response (DR) has the potential to be a cost-effective tool for Hawaii to reach its aggressive renewable energy goals while maintaining the reliability of power grids. The Hawaii Public Utilities Commission has approved the Hawaiian Electric Company’s revised portfolio of DR programs. The companies have released a grid services purchase agreement and subscribed an initial tranche of load into their DR programs. This paper presents innovative analytical methods and comprehensive economic assessment for distributed photovoltaics (PV) paired with battery energy storage systems (BESSs) for two new DR programs, including fast frequency response and capacity grid service. Optimal dispatch and sizing methods are proposed for the paired system considering different tariff schedules and PV compensation programs across five islands. It was found that while the best resource configuration and potential economic benefits vary with tariff structure, a BESS paired with PV can be optimally dispatched to generate multiple value streams simultaneously. Compensation from DR programs is an important value stream to help increase the cost-effectiveness of the integrated system.

Xia Cao, Peiyuan Gao, Xiaodi Ren, Lianfeng Zhu, Mark H. Engelhard, Bethany E. Matthews, Jingtao Hu, Chaojiang Niu, Dianying Liu, Bruce W. Arey, Chongmin Wang, Jie Xiao, Jun Liu, Wu Xu, Ji-Guang Zhang."Effects of fluorinated solvents on electrolyte solvation structures and electrode/electrolyte interphases for lithium metal batteries." Proceedings of the National Academy of Sciences (PNAS) 118 (9), no. e2020357118 (March 2021).
Abstract: Electrolyte is very critical to the performance of the high-voltage lithium (Li) metal battery (LMB), which is one of the most attractive candidates for the next-generation high-density energy-storage systems. Electrolyte formulation and structure determine the physical properties of the electrolytes and their interfacial chemistries on the electrode surfaces. Localized high-concentration electrolytes (LHCEs) outperform state-of-the-art carbonate electrolytes in many aspects in LMBs due to their unique solvation structures. Types of fluorinated cosolvents used in LHCEs are investigated here in searching for the most suitable diluent for high-concentration electrolytes (HCEs). Nonsolvating solvents (including fluorinated ethers, fluorinated borate, and fluorinated orthoformate) added in HCEs enable the formation of LHCEs with high-concentration solvation structures. However, low-solvating fluorinated carbonate will coordinate with Li⁺ ions and form a second solvation shell or a pseudo-LHCE which diminishes the benefits of LHCE. In addition, it is evident that the diluent has significant influence on the electrode/electrolyte interphases (EEIs) beyond retaining the high-concentration solvation structures. Diluent molecules surrounding the high-concentration clusters could accelerate or decelerate the anion decomposition through coparticipation of diluent decomposition in the EEI formation. The varied interphase features lead to significantly different battery performance. This study points out the importance of diluents and their synergetic effects with the conductive salt and the solvating solvent in designing LHCEs. These systematic comparisons and fundamental insights into LHCEs using different types of fluorinated solvents can guide further development of advanced electrolytes for high-voltage LMBs.

Ju-Myung Kim, Xianhui Zhang, Ji-Guang Zhang, Arumugam Manthiram, Ying Shirley Meng, Wu Xu."A review on the stability and surface modification of layered transition-metal oxide cathodes." Materials Today (February 2021).
Abstract: An ever-increasing market for electric vehicles (EVs), electronic devices and others has brought tremendous attention on the need for high energy density batteries with reliable electrochemical performances. However, even the successfully commercialized lithium (Li)-ion batteries still face significant challenges with respect to cost and safety issues when they are used in EVs. From a cathode material point of view, layered transition-metal (TM) oxides, represented by LiMO₂ (M = Ni, Mn, Co, Al, etc.) and Li-/Mn-rich xLi2MnO₃·(1–x)LiMO₂, have been considered as promising candidates because of their high theoretical capacity, high operating voltage, and low manufacturing cost. However, layered TM oxides still have not reached their full potential for EV applications due to their intrinsic stability issues during electrochemical processes. To address these problems, a variety of surface modification strategies have been pursued in the literature. Herein, we summarize the recent progresses on the enhanced stability of layered TM oxides cathode materials by different surface modification techniques, analyze the manufacturing process and cost of the surface modification methods, and finally propose future research directions in this area.

Vijayakumar Murugesan, Zimin Nie, Xin Zhang, Peiyuan Gao, Zihua Zhu, Qian Huang, Litao Yan, David Reed, Wei Wang."Accelerated design of vanadium redox flow battery electrolytes through tunable solvation chemistry."Cell Reports Physical Science 2 (2), 100323 (February 2021).
Abstract: Operational stability of electrolytes is a persistent impediment in building redox flow battery technology. Stabilizing multiple vanadium oxidation states in aqueous solution is a primary challenge in designing reliable large-scale vanadium redox flow batteries (VRBs). Here we demonstrate that rationally selected ionic additives can stabilize the aqua vanadium solvate structures through preferential bonding and molecular interactions despite their relatively low concentrations (≤0.1 M). The competing cations (NH₄⁺ and Mg²⁺) and bonding anions (SO₄²⁻, PO₄³⁻, and Cl⁻) introduced by bi-additives are used to tune the vanadium solvation chemistry and design an optimal electrolyte for VRB technology. Such molecular engineering of VRB electrolytes results in enhancement of the operational temperature window by 180% and energy density by more than 30% relative to traditional electrolytes. This work demonstrates that tunable solvation chemistry is a promising pathway to engineer an optimal electrolyte for targeted electrochemical systems.

Xiang Liu, Biwei Xiao, Amine Daali, Xinwei Zhou, Zhou Yu, Xiang Li, Yuzi Liu, Liang Yin, Zhenzhen Yang, Chen Zhao, Likun Zhu, Yang Ren, Lei Cheng, Shabbir Ahmed, Zonghai Chen, Xiaolin Li, Gui-Liang Xu, Khalil Amine."Stress- and Interface-Compatible Red Phosphorus Anode for High-Energy and Durable Sodium-Ion Batteries."ACS Energy Letters 6, 547-556 (February 2021).
Abstract: Sodium-ion batteries are promising candidates for energy storage application, but the absence of high-capacity and low-cost anode materials significantly limits their practical specific energy and cost. Red phosphorus (RP) possesses a high theoretical specific capacity but suffers from large volume change, low electronic conductivity, and unstable solid-electrolyte interphase (SEI). Herein, a hierarchical micro/nanostructured antimony-doped RP/carbon anode was developed, which demonstrates extraordinary electrochemical performance with high initial Coulombic efficiency of ∼90%, high areal capacity (∼1.7 mAh cm^–2), and good cycle stability and rate capability. Combined experimental and computational studies consistently revealed that such a unique structural design can dramatically accommodate the mechanical stress and moreover effectively restrain the undesired decomposition of electrolyte solvents regardless of electrolyte formulation, resulting in superior structural integrity and thin and robust SEI formation during cycling. The present finding has offered an alternative strategy for stress management and interface engineering on high-capacity alloying-based anode materials.

Haiping Wu, Hao Jia, Chongmin Wang, Ji-Guang Zhang, Wu Xu."Recent Progress in Understanding Solid Electrolyte Interphase on Lithium Metal Anodes." Advanced Energy Materials 11 (5), 2003092 (February 2021).
Abstract: Lithium metal batteries (LMBs) are one of the most promising candidates for next‐generation high‐energy‐density rechargeable batteries. Solid electrolyte interphase (SEI) on Li metal anodes plays a significant role in influencing the Li deposition morphology and the cycle life of LMBs. However, a thorough understanding on the mechanisms of SEI formation and evolution is still inadequate. In this review, the progress in understanding structures, properties, and influencing factors of SEI, as well as efficient strategies of tailoring SEI are focused upon. First, the compositions, models, and recent progress in characterizing atomic structures of SEI are summarized. Second, the properties of SEI, including electronic conduction, ionic conduction, stability, and mechanical properties are elucidated. Structures and properties of SEI are greatly affected by multiple factors, thus interactions between these factors and SEI are systematically discussed. Correlations of SEI with Li deposition morphology, rate capability, and cycle life are further summarized. Moreover, efficient strategies of tailoring SEI with desired properties, including in situ SEI and ex situ SEI, are also reviewed. Finally, future directions, including in‐operando techniques, multi‐modality approaches for characterization of SEI, and artificial intelligence assisted understanding of correlations between electrolyte components and SEI properties are proposed.

Xia Cao, Hao Jia, Wu Xu, Ji-Guang Zhang."Review—Localized High-Concentration Electrolytes for Lithium Batteries." Journal of Electrochemical Society 168, no. 1, artical no. 010522 (January 2021).
Abstract: The conventional LiPF₆/carbonate-based electrolytes have been widely used in graphite (Gr)-based lithium (Li) ion batteries (LIBs) for more than 30 years because a stable solid electrolyte interphase (SEI) layer forms on the graphite surface and enables its long-term cycling stability. However, few of these electrolytes are stable under the more stringent conditions needed with a Li metal anode (LMA) and other anodes, such as silicon (Si), which exhibit large volume changes during charge/discharge processes. Many different approaches have been developed lately to stabilize Li metal batteries (LMBs) and Si-based LIBs. From this aspect, localized high-concentration electrolytes (LHCEs) have unique advantages: not only are they stable in a wide electrochemical window, they can also form stable SEI layers on LMA and Si anode surfaces to enable their long-term cycling stability. The ultrathin SEI layer formed on a Gr anode can also improve the safety and high-rate operation of conventional LIBs. In this paper, we give a brief summary of our recent work on LHCEs, including their design principle and applications in both LMBs and LIBs. A perspective on the future development of LHCEs is also discussed.

Minyuan M. Li, Xiaochuan Lu, Xiaowen Zhan, Mark H. Engelhard, Jeffrey F. Bonnett, Evgueni Polikarpov, Keeyoung Jung, David M. Reed, Vincent Sprenkle, Guosheng Li."High performance sodium-sulfur batteries at low temperature enabled by superior molten Na wettability."Chemical Communications 57 (1) 45-48 (January 2021).
Abstract: Reducing the operating temperature of molten sodium-sulfur batteries (~350 °C) is critical to create safe and cost-effective devices for large-scale energy storage. By raising the surface treatment temperature with lead acetate trihydrate, we can significantly improve sodium wettability on ß"-Al₂O₃ solid electrolyte at a low temperature of 120 °C, previously unattained. In turn, the Na S cell can reach a capacity as high as 520.2mAh/g and stable cycling over 1000 cycles at 120 °C, which is slightly higher than the melting point of sodium (98 °C). Analyzing surfaces treated at different temperatures, the deposited Pb particles show similar morphologies but distinct compositions, inferring a strong correlation between passivation and performance.

Xia Cao, Lianfeng Zou, Bethany E. Matthews, Linchao Zhang, Xinzi He, Xiaodi Ren, Mark H. Engelhard, Sarah D. Burton, Patrick Z. El-Khoury, Hyung-Seok Lim, Chaojiang Niu, Hongkyung Lee, Chungsheng Wang, Bruce W. Arey, Chongmin Wang, Jie Xiao, Jun Liu, Wu Xu, Ji-Guang Zhang."Optimization of fluorinated orthoformate based electrolytes for practical high-voltage lithium metal batteries."Energy Storage Materials 34, 76-84 (January 2021).
Abstract: Lithium (Li) metal batteries (LMBs) have been revitalized in recent years in response to the increasing demand for high energy density batteries. However, the instability of Li metal anode (LMA) is still a critical barrier that limits large scale applications of these batteries. This work optimizes tris(2,2,2-trifluoroethyl) orthoformate (TFEO) based electrolytes and reveals the fundamental mechanisms behind their stability towards both LMA and cathodes. It is also found that the optimized composition of the electrolytes is sensitive to the electrolyte amount used in the batteries due to the consumption of the salt during the cycling process. The optimized TFEO based electrolytes create highly effective solid electrolyte interphase and cathode electrolyte interphase, which prevent continuous electrode/electrolyte side reactions and significantly prolong the cycle life of LMBs with a NMC811 cathode under very challenging conditions (4.2 mAh cm⁻² cathode loading, 50 µm Li and lean electrolyte of 3 g (Ah)⁻¹). The design principles discovered in this work provide guidance for further development of electrolytes for the stable operation of high energy density LMBs.

Maitri Uppaluri, Akshay Subramaniam, Lubhani Mishra, Vilayanur Viswanathan, Venkat R. Subramanian."Can a Transport Model Predict Inverse Signatures in Lithium Metal Batteries Without Modifying Kinetics?"Journal of Electrochemical Society 167, number 16, article number 160547 (December 2020).
Abstract: In this study, a one-dimensional transport model is developed and analyzed to predict the inverse overpotential signature observed during lithium metal electrodeposition. This simple approach predicts inverse signatures stemming from the competing interplay between moving boundary rates and mass transfer limitations. The numerical scheme used for the present model simulations is presented in detail which has been further used to study the effect of design parameters on the prevalence and strength of inverse signatures. It was found that the proposed model and the analysis is more pertinent to thick lithium symmetric cells, commonly used for in-depth fundamental studies.

Qian Huang, Bin Li, Chaojie Song, Zhengming Jiang, Alison Platt, Khalid Fatih, Christina Bock, Darren Jang, David Reed. "In Situ Reliability Investigation of All-Vanadium Redox Flow Batteries by a Stable Reference Electrode."Journal of Electrochemical Society 165, number 16, article number 160541 (December 2020).
Abstract: Redox flow batteries (RFBs) have been studied over the past several decades as a promising candidate for stationary energy storage applications. It is therefore important to understand the reliability of RFBs and the mechanisms that cause degradation with time. Contributions from individual electrodes are difficult to separate especially for long-term cycle testing due to the lack of a stable reference electrode. In our work, the reliability and degradation mechanisms of an all-vanadium RFB were investigated by a stable reference electrode based on the dynamic hydrogen electrode (DHE). The newly developed DHE reference electrode demonstrated high accuracy and long-term stability that enables in situ monitoring of individual electrode signals over hundreds of cycles in a vanadium RFB. This approach enables the full cell degradation to be separated into contributions from the cathode and anode. The cathode and anode were found to play quite different roles in the increase in overpotential of the vanadium RFB during long-term cycling. The anode reaction limited both the charge and discharge capacity over 100 cycles. The negative side also appeared to be the rate limiting factor throughout cycling as determined by EIS measurement. The cathode contributed to the performance degradation as cycling exceeded 50 cycles.

Xiaodi Ren, Xianhui Zhang, Zulipiya Shadike, Lianfeng Zou, Hao Jia, Xia Cao, Mark H. Engelhard, Bethany E. Matthews, Chongmin Wang, Bruce W. Arey, Xiao-Qing Yang, Jun Liu, Ji-Guang Zhang, Wu Xu."Designing Advanced In Situ Electrode/Electrolyte Interphases for Wide Temperature Operation of 4.5 V Li||LiCoO₂ Batteries." Advanced Materials 32 (49), no. 2004898 (December 2020).
Abstract: High‐energy‐density batteries with a LiCoO₂ (LCO) cathode are of significant importance to the energy‐storage market, especially for portable electronics. However, their development is greatly limited by the inferior performance under high voltages and challenging temperatures. Here, highly stable lithium (Li) metal batteries with LCO cathode, through the design of in situ formed, stable electrode/electrolyte interphases on both the Li anode and the LCO cathode, with an advanced electrolyte, are reported. The LCO cathode can deliver a high specific capacity of ≈190 mAh g⁻¹ and show greatly improved cell performances under a high charge voltage of 4.5 V (even up to 4.55 V) and a wide temperature range from −30 to 55 °C. This work points out a promising approach for developing Li||LCO batteries for practical applications. This approach can also be used to improve the high‐voltage performance of other batteries in a broad temperature range.

Tzu-Ling Chen, Rui Sun, Carl Willis, Bert Krutzer, Brian F. Morgan, Frederick L. Beyer, Kee Sung Han, Vijayakumar Murugesan, Yossef A. Elabd."Impact of ionic liquid on lithium ion battery with a solid poly(ionic liquid) pentablock terpolymer as electrolyte and separator."Polymer 209, 122975 (November 2020).
Abstract: In this study, the physical, transport, mechanical, morphological, and electrochemical properties of a ternary blend solid polymer electrolyte (SPE) (poly(ionic liquid) (PIL) multiblock polymer, lithium salt, and ionic liquid (IL)) were systematically investigated as a function of IL concentration. With increasing IL concentration, the conductive volume increases along with the polymer chain segmental mobility. This facilitates high ionic conductivity, while the mechanical modulus exhibits a percolation threshold. Surprisingly, at higher IL concentrations, there is a reduction in the lithium cation mobility as evidenced by pulsed-field gradient nuclear magnetic resonance, which coincides with an increased overpotential evidenced by lithium metal stripping and plating. Stable lithium ion battery cycling durability (over 100 cycles at room temperature) is demonstrated with the ternary blend SPE as the electrolyte and separator. This work provides valuable insights into the design of new SPEs with both high ionic conductivity and improved battery stability.

Xiaodi Ren, Peiyuan Gao, Lianfeng Zou, Shuhong Jiao, Xia Cao, Xianhui Zhang, Hao Jia, Mark H. Engelhard, Bethany E. Matthews, Haiping Wu, Hongkyung Lee, Chaojiang Niu, Chongmin Wang, Bruce W. Arey, Jie Xiao, Jun Liu, Ji-Guang Zhang, Wu Xu."Role of inner solvation sheath within salt–solvent complexes in tailoring electrode/electrolyte interphases for lithium metal batteries."Proceedings of the National Academy of Sciences of the United States of America 117 (46) 28603-28613 (November 2020).
Abstract: Functional electrolyte is the key to stabilize the highly reductive lithium (Li) metal anode and the high-voltage cathode for long-life, high-energy-density rechargeable Li metal batteries (LMBs). However, fundamental mechanisms on the interactions between reactive electrodes and electrolytes are still not well understood. Recently localized high-concentration electrolytes (LHCEs) are emerging as a promising electrolyte design strategy for LMBs. Here, we use LHCEs as an ideal platform to investigate the fundamental correlation between the reactive characteristics of the inner solvation sheath on electrode surfaces due to their unique solvation structures. The effects of a series of LHCEs with model electrolyte solvents (carbonate, sulfone, phosphate, and ether) on the stability of high-voltage LMBs are systematically studied. The stabilities of electrodes in different LHCEs indicate the intrinsic synergistic effects between the salt and the solvent when they coexist on electrode surfaces. Experimental and theoretical analyses reveal an intriguing general rule that the strong interactions between the salt and the solvent in the inner solvation sheath promote their intermolecular proton/charge transfer reactions, which dictates the properties of the electrode/electrolyte interphases and thus the battery performances.

Ji-Guang Zhang, Wu Xu, Jie Xiao, Xia Cao, Jun Liu."Lithium Metal Anodes with Nonaqueous Electrolytes." Chemical Reviews 120 (24), 13312-13348 (December 2020).
Abstract: High-energy rechargeable lithium (Li) metal batteries (LMBs) with Li metal anode (LMA) were first developed in the 1970s, but their practical applications have been hindered by the safety and low-efficiency concerns related to LMA. Recently, a worldwide effort on LMA-based rechargeable LMBs has been revived to replace graphite-based, Li-ion batteries because of the much higher energy density that can be achieved with LMBs. This review focuses on the recent progress on the stabilization of LMA with nonaqueous electrolytes and reveals the fundamental mechanisms behind this improved stability. Various strategies that can enhance the stability of LMA in practical conditions and perspectives on the future development of LMA are also discussed. These strategies include the use of novel electrolytes such as superconcentrated electrolytes, localized high-concentration electrolytes, and highly fluorinated electrolytes, surface coatings that can form a solid electrolyte interphase with a high interfacial energy and self-healing capabilities, development of “anode-free” Li batteries to minimize the interaction between LMA and electrolyte, approaches to enable operation of LMA in practical conditions, etc. Combination of these strategies ultimately will lead us closer to the large-scale application of LMBs which often is called the “Holy Grail” of energy storage systems.

Chenxi Qian, Jie Zhao, Yongming Sun, Hye Ryoung Lee, Langli Luo, Meysam Makaremi, Sankha Mukherjee, Jiangyan Wang, Chenxi Zu, Meikun Xia, Chongmin Wang, Chandra Veer Singh, Yi Cui, and Geoffrey A. Ozin."Electrolyte-Phobic Surface for the Next-Generation Nanostructured Battery Electrodes." Nanoletters 20 (10) 7455-7462 (October 2020).
Abstract: Nanostructured electrodes are among the most important candidates for high-capacity battery chemistry. However, the high surface area they possess causes serious issues. First, it would decrease the Coulombic efficiencies. Second, they have significant intakes of liquid electrolytes, which reduce the energy density and increase the battery cost. Third, solid-electrolyte interphase growth is accelerated, affecting the cycling stability. Therefore, the interphase chemistry regarding electrolyte contact is crucial, which was rarely studied. Here, we present a completely new strategy of limiting effective surface area by introducing an “electrolyte-phobic surface”. Using this method, the electrolyte intake was limited. The initial Coulombic efficiencies were increased up to ∼88%, compared to ∼60% of the control. The electrolyte-phobic layer of Si particles is also compatible with the binder, stabilizing the electrode for long-term cycling. This study advances the understanding of interphase chemistry, and the introduction of the universal concept of electrolyte-phobicity benefits the next-generation battery designs.

Hui Wang, Yuyan Shao, Huilin Pan, Xuefei Feng, Ying Chen, Yi-Sheng Liu, Eric D. Walter, Mark H. Engelhard, Kee Sung Han, Tao Deng, Guoxi Ren, Dongping Lu, Xiaochuan Lu, Wu Xu, Chunsheng Wang, Jun Feng, Karl T. Mueller, Jinghua Guo, Ji-Guang Zhang."A lithium-sulfur battery with a solution-mediated pathway operating under lean electrolyte conditions."Nano Energy 76 (October 2020).
Abstract: Lithium-sulfur (Li–S) battery is one of the most promising candidates for the next generation energy storage systems. However, several barriers, including polysulfide shuttle effect, the slow solid-solid surface reaction pathway in the lower discharge plateau, and corrosion of Li anode still limit its practical applications, especially under the lean electrolyte condition required for high energy density. Here, we propose a solution-mediated sulfur reduction pathway to improve the capacity and reversibility of the sulfur cathode. With this method, a high coulombic efficiency (99%) and stable cycle life over 100 cycles were achieved under application-relevant conditions (S loading: 6.2 mg cm⁻²; electrolyte to sulfur ratio: 3 mL_{E gs}⁻¹; sulfur weight ratio: 72 wt%). This result is enabled by a specially designed Li₂S_4-rich electrolyte, in which Li₂S is formed through a chemical disproportionation reaction instead of electrochemical routes. A single diglyme solvent was used to obtain electrolytes with the optimum range of Li₂S₄ concentration. Operando X-ray absorption spectroscopy confirms the solution pathway in a practical Li–S cell. This solution pathway not only introduces a new electrolyte regime for practical Li–S batteries, but also provides a new perspective for bypassing the inefficient surface pathway for other electrochemical processes.

Yaobin Xu, Haiping Wu, Hao Jia, Mark H. Engelhard, Ji-Guang Zhang, Wu Xu, Chongmin Wang."Sweeping potential regulated structural and chemical evolution of solid-electrolyte interphase on Cu and Li as revealed by cryo-TEM."Nano Energy 76: Number 105040 (October 2020).
Abstract: A fundamental understanding of solid-electrolyte interphase (SEI) is paramount importance for controlling the cycling performance of rechargeable lithium metal batteries. The structural and chemical evolution of SEI with respect to electrochemical operating condition remains barely established. Here we develop a unique method for imaging the evolution of SEI formed on the Cu foil under sweeping electrochemical potential. By using cryogenic TEM imaging combined with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy electronic structure analyses, we reveal that, for the vinylene carbonate (VC)-free electrolyte, the SEI formed at 1.0 V is a monolithic amorphous structure, which evolves to amorphous matrix embedded with Li₂O particles as the voltage decreases to 0 V. In the case of VC-containing electrolyte, the SEI is featured by an amorphous matrix with Li₂O particles from 1.0 V to 0 V. The thickness of SEI formed on Cu foil increases with decreasing voltage. Associated with the localized charge modulation by the surface topographic feature and defects in the Cu foil, the SEI layer shows direct spatial correlation with these structural defects in the Cu. In addition, upon Li deposition, the SEI formed on the Li metal has similar thickness with, but different composition from the SEI formed on the Cu foil at 0 V. Those results provide insight toward SEI engineering for enhanced cycling stability of Li metal.

Un-Hyuck Kim, Geon-Tae Park, Byoung-Ki Son, Gyeong Won Nam, Jun Liu, Liang-Yin Kuo, Payam Kaghazchi, Chong S. Yoong, Yang-Koo Sun."Heuristic solution for achieving long-term cycle stability for Ni-rich layered cathodes at full depth of discharge." Nature Energy 5, 860-869 (November 2020).
Abstract: The demand for energy sources with high energy densities continues to push the limits of Ni-rich layered oxides, which are currently the most promising cathode materials in automobile batteries. Although most current research is focused on extending battery life using Ni-rich layered cathodes, long-term cycling stability using a full cell is yet to be demonstrated. Here, we introduce Li[Ni_0.90Co_0.09Ta_0.01]O2, which exhibits 90% capacity retention after 2,000 cycles at full depth of discharge (DOD) and a cathode energy density >850 Wh kg−1. In contrast, the currently most sought-after Li[Ni_0.90Co_0.09Al_0.01]O2 cathode loses ~40% of its initial capacity within 500 cycles at full DOD. Cycling stability is achieved by radially aligned primary particles with [003] crystallographic texture that effectively dissipate the internal strain occurring in the deeply charged state, while the substitution of Ni³⁺ with higher valence ions induces ordered occupation of Ni ions in the Li slab and stabilizes the delithiated structure.

Patrick Balducci, Kendall Mongird, Di Wu, Dexin Wang, Vanshika Fotedar, Robert Dahowski."An Evaluation of the Economic and Resilience Benefits of a Microgrid in Northampton, Massachusetts."Energies 13 (18), 4802 (September 2020).
Abstract: Recent developments and advances in distributed energy resource (DER) technologies make them valuable assets in microgrids. This paper presents an innovative evaluation framework for microgrid assets to capture economic benefits from various grid and behind-the-meter services in grid-connecting mode and resilience benefits in islanding mode. In particular, a linear programming formulation is used to model different services and DER operational constraints to determine the optimal DER dispatch to maximize economic benefits. For the resiliency analysis, a stochastic evaluation procedure is proposed to explicitly quantify the microgrid survivability against a random outage, considering uncertainties associated with photovoltaic (PV) generation, system load, and distributed generator failures. Optimal coordination strategies are developed to minimize unserved energy and improve system survivability, considering different levels of system connectedness. The proposed framework has been applied to evaluate a proposed microgrid in Northampton, Massachusetts that would link the Northampton Department of Public Works, Cooley Dickenson Hospital, and Smith Vocational Area High School. The findings of this analysis indicate that over a 20-year economic life, a 441 kW/441 kWh battery energy storage system, and 386 kW PV solar array can generate $2.5 million in present value benefits, yielding a 1.16 return on investment ratio. Results of this study also show that forming a microgrid generally improves system survivability, but the resilience performance of individual facilities varies depending on power-sharing strategies.

Raymond R. Unocic, Katherine L. Jungjohann, B. Layla Mehdi, Nigel D. Browning, Chongmin Wang."In situ electrochemical scanning/transmission electron microscopy of electrode–electrolyte interfaces."MRS Bulletin 45 (9) 738-745 (September 2020).
Abstract: Insights into the dynamics of electrochemical processes are critically needed to improve our fundamental understanding of electron, charge, and mass transfer mechanisms and reaction kinetics that influence a broad range of applications, from the functionality of electrical energy-storage and conversion devices (e.g., batteries, fuel cells, and supercapacitors), to materials degradation issues (e.g., corrosion and oxidation), and materials synthesis (e.g., electrodeposition). To unravel these processes, in situ electrochemical scanning/transmission electron microscopy (ec-S/TEM) was developed to permit detailed site-specific characterization of evolving electrochemical processes that occur at electrode–electrolyte interfaces in their native electrolyte environment, in real time and at high-spatial resolution. This approach utilizes “closed-form” microfabricated electrochemical cells that couple the capability for quantitative electrochemical measurements with high spatial and temporal resolution imaging, spectroscopy, and diffraction. In this article, we review the state-of-the-art instrumentation for in situ ec-S/TEM and how this approach has resulted in new observations of electrochemical processes.

Lili Shi, Seong-Min Bak, Zulipiya Shadike, Chengqi Wang, Chaojiang Niu, Paul Northrup, Hongkyung Lee, Arthur Y. Baranovskiy, Cassidy S. Anderson, Jian Qin, Shuo Feng, Xiaodi Ren, Dianying Liu, Xiao-Qing Yang, Fei Gao, Dongping Lu, Jie Xiao, Jun Liu."Reaction heterogeneity in practical high-energy lithium–sulfur pouch cells."Energy & Environmental Science 10 (13) 3620-3632 (September 2020).
Abstract: The lithium–sulfur (Li–S) battery is a promising next-generation energy storage technology because of its high theoretical energy and low cost. Extensive research efforts have been made on new materials and advanced characterization techniques for mechanistic studies. However, it is uncertain how discoveries made on the material level apply to realistic batteries due to limited analysis and characterization of real high-energy cells, such as pouch cells. Evaluation of pouch cells (>1 A h) (instead of coin cells) that are scalable to practical cells provides a critical understanding of current limitations which enables the proposal of strategies and solutions for further performance improvement. Herein, we design and fabricate pouch cells over 300 W h kg⁻¹, compare the cell parameters required for high-energy pouch cells, and investigate the reaction processes and their correlation to cell cycling behavior and failure mechanisms. Spatially resolved characterization techniques and fluid-flow simulation reveal the impacts of the liquid electrolyte diffusion within the pouch cells. We found that catastrophic failure of high-energy Li–S pouch cells results from uneven sulfur/polysulfide reactions and electrolyte depletion for the first tens of cycles, rather than sulfur dissolution as commonly reported in the literature. The uneven reaction stems from limited electrolyte diffusion through the porous channels into the central part of thick cathodes during cycling, which is amplified both across the sulfur electrodes and within the same electrode plane. A combination of strategies is suggested to increase sulfur utilization, improve nanoarchitectures for electrolyte diffusion and reduce consumption of the electrolytes and additives.

Xiaowen Zhan, Jeffrey F. Bonnett, Mark H. Engelhard, David M. Reed, Vincent L. Sprenkle, Guosheng Li."A High‐Performance Na–Al Battery Based on Reversible NaAlCl₄ Catholyte."Advanced Energy Materials Article number 2001378 (September 2020).
Abstract: This work demonstrates a high‐capacity and safe Na–Al battery pairing a sodium metal anode and reversible NaAlCl₄ catholyte for grid scale energy storage applications. The energy‐rich Na anode allows the full use of the aluminum cathode, resulting in a full‐cell capacity of 308 mAh g⁻¹ at a discharge voltage of 1.6 V. Benefiting from the use of a β″‐alumina solid electrolyte, molten sodium anode, and reversible Al deposition/stripping from NaAlCl4 catholyte, the battery presents a stable Coulombic efficiency of 100% and energy efficiency of ≈95%. At a rate of C/3 (6.77 mA cm⁻²), the cell maintains 282 mAh g⁻¹ (447 Wh kg⁻¹) after 200 cycles with an excellent capacity retention of 97.6%. Moreover, pathways to build Na‐anode‐free cells from the discharged state under dry air are elucidated, which further extends the feasibility of this battery for stationary storage applications. These findings are expected to provide a new platform for the development of practical aluminum batteries.

M.S. Lee, K.S. Han, J. Lee, Y. Shin, T.C. Kaspar, Y. Chen, M.H. Engelhard, K.T. Mueller, V. Murugesan."Defect-induced anisotropic surface reactivity and ion transfer processes of anatase nanoparticles."Materials Today Chemistry 17 (September 2020).
Abstract: Surface reactivity and ion transfer processes of anatase TiO₂ nanocrystals were studied using lithium bis(trifluoromethylsulfone)imide (LiTFSI) as a probing molecule. Analysis of synthesized anatase TiO₂ by electron microscopy reveals aggregated nanoparticles (average size ~8 nm) with significant defects (holes and cracks). With the introduction of LiTFSI salt, the Li⁺-adsorption propensity towards the surface along the anatase (100) step edge plane is evident in both x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) analysis. Ab initio molecular dynamics (AIMD) analysis corroborates the site-preferential interaction of Li⁺ cations with oxygen vacancies and the thermodynamically favorable transport through the (100) step edge plane. Using ⁷Li nuclear magnetic resonance (NMR) chemical shift and relaxometry measurements, the presence of Li⁺ cations near the interface between TiO₂ and the bulk LiTFSI phase was identified, and subsequent diffusion properties were analyzed. The lower activation energy derived from NMR analysis reveals enhanced mobility of Li⁺ cations along the surface, in good agreement with AIMD calculations. On the other hand, the TFSI^– anion interaction with defect sites leads to CF₃ bond dissociation and subsequent generation of carbonyl fluoride-type species. The multimodal spectroscopic analysis including NMR, electron paramagnetic resonance (EPR), and x-ray photoelectron spectroscopy (XPS) confirms the decomposition of TFSI– anions near the anatase surface. The reaction mechanism and electronic structure of interfacial constituents were simulated using AIMD calculations. Overall, this work demonstrates the role of defects at the anatase nanoparticle surface on charge transfer and interfacial reaction processes.

Matthew Fayette, Hee-Jung Chang, Ismael A. Rodriguez-Perez, Xiaolin Li, David Reed."Electrodeposited Zinc-Based Films as Anodes for Aqueous Zinc Batteries."ACS Applied Materials & Interfaces 12 (38) 42763-42772 (August 2020).
Abstract: Zinc-based batteries have attracted extensive attention in recent years, due to high safety, high capacities, environmental friendliness, and low cost compared to lithium-ion batteries. However, the zinc anode suffers primarily from dendrite formation as a mode of failure in the mildly acidic system. Herein, we report on electrochemically deposited zinc (ED Zn) and copper–zinc (brass) alloy anodes, which are critically compared with a standard commercial zinc foil. The film electrodes are of commercially relevant thicknesses (21 and 25 μM). The electrodeposited zinc-based anodes exhibit low electrode polarization (∼0.025 V) and stable cycling performance in 50 cycle consecutive experiments from 0.26 to 10 mA cm^–2 compared to commercial Zn foil. Coulombic efficiencies at 1 mA cm^–2 were over 98% for the electrodeposited zinc-based materials and were maintained for over 100 cycles. Furthermore, full cells with an electrodeposited Zn/brass anode, electrolytic manganese dioxide (EMD) cathode, in 1 M ZnSO₄ + 0.1 M MnSO₄ delivered capacities of 96.3 and 163 mAh g^–1, respectively, at 100 mA g^–1 compared to 92.1 mAh g^–1 for commercial Zn. The electrodeposited zinc-based anodes also show better rate capability, delivering full cell capacities of 35.9 and 47.5 mAh g^–1 at a high current of up to 3 A g^–1. Lastly, the electrodeposited zinc-based anodes show enhanced capacity for up to 100 cycles at 100 mA g^–1, making them viable anodes for commercial use.

Ke Lu, Bomin Li, Xiaowen Zhan, Fan Xia, Olusola J. Dahunsi, Siyuan Gao, David M. Reed, Vincent L. Sprenkle, Guosheng Le, Yingwen Cheng."Elastic Na_xMoS₂-Carbon-BASE Triple Interface Direct Robust Solid–Solid Interface for All-Solid-State Na–S Batteries."Nano Letters 20:(9), 6837-6844 (August 2020).
Abstract: The developments of all-solid-state sodium batteries are severely constrained by poor Na-ion transport across incompatible solid–solid interfaces. We demonstrate here a triple Na_xMoS₂-carbon-BASE nanojunction interface strategy to address this challenge using the β″-Al₂O₃ solid electrolyte (BASE). Such an interface was constructed by adhering ternary Na electrodes containing 3 wt % MoS₂ and 3 wt % carbon on BASE and reducing contact angles of molten Na to ∼45°. The ternary Na electrodes exhibited twice improved elasticity for flexible deformation and intimate solid contact, whereas Na_xMoS₂ and carbon synergistically provide durable ionic/electronic diffusion paths, which effectively resist premature interface failure due to loss of contact and improved Na stripping utilization to over 90%. Na metal hosted via triple junctions exhibited much smaller charge-transfer resistance and 200 h of stable cycling. The novel interface architecture enabled 1100 mAh/g cycling of all-solid-state Na–S batteries when using advanced sulfur cathodes with Na-ion conductive PEO_10-NaFSI binder and Na_xMo₆S₈ redox catalytic mediator.

Yaobin Xu, Haiping Wu, Hao Jia, Ji-Guang Zhang, Wu Xu, Chongmin Wang."Current Density Regulated Atomic to Nanoscale Process on Li Deposition and Solid Electrolyte Interphase Revealed by Cryogenic Transmission Electron Microscopy."ACS Nano 14 (7): 8766-8775 (July 2020).
Abstract: Current density has been perceived to play a critical rule in controlling Li deposition morphology and solid electrolyte interphase (SEI). However, the atomic level mechanism of the effect of current density on Li deposition and the SEI remains unclear. Here based on cryogenic transmission electron microscopy (TEM) imaging combined with energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) electronic structure analyses, we reveal the atomic level correlation of Li deposition morphology and SEI with current density. We discover that increasing current density leads to increased overpotential for Li nucleation and growth, leading to the transition from growth-limited to nucleation-limited mode for Li dendrites. Independent of current density, the electrochemically deposited Li metal (EDLi) exhibits crystalline whisker-like morphology. The SEI formed at low current density (0.1 mA cm^–2) is monolithic amorphous; while, a current density of above 2 mA cm^–2 leads to a mosaic structured SEI, featuring an amorphous matrix with Li₂O and LiF dispersoids, and the thickness of the SEI increases with the increase of current density. Specifically, the Li₂O particles are spatially located at the top surface of the SEI, while LiF is spatially adjacent to the Li–SEI interface. These results offer possible ways of regulating crucial microstructural and chemical features of EDLi and SEI through altering deposit conditions and consequently direct correlation with battery performance.

Ying Chen, Nicholas R. Jaegers, Hui Wang, Kee Sung Han, Jian Zhi Hu, Karl T. Mueller, Vijayakumar Murugesan."Role of Solvent Rearrangement on Mg²⁺ Solvation Structures in Dimethoxyethane Solutions using Multimodal NMR Analysis."Journal of Physical Chemistry Letters 11: 6443-6449 (July 2020).
Abstract: One of the main impediments faced for predicting emergent properties of a multivalent electrolyte (such as conductivity and electrochemical stability) is the lack of quantitative analysis of ion–ion and ion–solvent interactions, which manifest in solvation structures and dynamics. In particular, the role of ion–solvent interactions is still unclear in cases where the strong electric field from multivalent cations can influence intramolecular rotations and conformal structural evolution (i.e., solvent rearrangement process) of low permittivity organic solvent molecules on solvation structure. Using quantitative ¹H, ¹⁹F, and ¹⁷O NMR together with ¹⁹F nuclear spin relaxation and diffusion measurments, we find an unusual correlation between ion concentration and solvation structure of Mg(TFSI)₂ salt in dimethoxyethane (DME) solution. The dominant solvation structure evolves from contact ion pairs (i.e., [Mg(TFSI)(DME)_1–2]⁺) to fully solvated clusters (i.e., [Mg(DME)₃]²⁺) as salt concentration increases or as temperature decreases. This transition is coupled to a phase separation, which we study here between 0.06 and 0.36 M. Subsequent analysis is based on an explanation of the solvent rearrangement process and the competition between solvent molecules and TFSI anions for cation coordination.

Won-Jin Kwak, Sujong Chae, Ruozhu Feng, Peiyuan Gao, Jeffrey Read, Mark H. Engelhard, Lirong Zhong, Wu Xu, Ji-Guang Zhang."Optimized Electrolyte with High Electrochemical Stability and Oxygen Solubility for Lithium–Oxygen and Lithium–Air Batteries."ACS Energy Letters 5 (7): 2182-2190 July 2020).
Abstract: Lithium–oxygen (Li–O₂) batteries with high reversibility require a stable electrolyte against the side reactions with Li-metal anode and reactive oxygen species. Moreover, an electrolyte that can effectively utilize the low partial pressure of oxygen in the atmosphere has significant effect on the practical application of Li–air batteries. In this study, a localized high-concentration electrolyte (LHCE) was developed using 1H,1H,₅H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE) as a diluent, which satisfies all these conditions simultaneously. The OTE-based LHCE exhibits much improved electrochemical performance in Li–O₂ batteries and Li–air batteries in comparison to the conventional electrolyte and high-concentration electrolyte. The design principles of this electrolyte also provide important guidelines for research to further develop new electrolytes for Li–O₂ and Li–air batteries.

Saul Perez Beltran, Xia Cao, Ji-Guang Zhang, Perla B. Balbuena."Localized High Concentration Electrolytes for High Voltage Lithium–Metal Batteries: Correlation between the Electrolyte Composition and Its Reductive/Oxidative Stability." Chemistry of Materials 32 (14) 5973-5984 (July 2020).
Abstract: We demonstrate a first-principles screening methodology as an effective tool to explore electrolyte formulations for the new generation of high energy density rechargeable batteries. We study the liquid structure and electronic properties in dilute electrolytes, high concentration electrolytes (HCE), and localized high concentration electrolytes (LHCE), with focus on electrolyte formulations based on lithium bis(fluorosulfonyl)imide (LiFSI), dimethyl carbonate (DMC), and bis(2,2,2-trifluoroethyl) ether (BTFE) as a diluent. We describe the solvation complexes in the dilute electrolyte and explore structural changes triggered by the increase in lithium salt concentration for HCEs and the diluent effects in LHCEs. In HCE formulations, there is a 4-fold coordination environment of lithium-ions as in the dilute electrolyte, but the number of lithium-ion interactions with O atoms from FSI^- anions dominates. In these solutions, the ability of the FSI– anions to interact with multiple lithium-ions allows complex 3^D network formation and influences the reductive/oxidative behavior of the electrolyte. Interestingly, in LHCEs, the BTFE diluent molecules do not change the 3^D solution structure when diluting the HCE formulation from 5.49 to ₃.8₃ M. However, there is a composition threshold where the structural and electronic behavior may change. We show that diluting the HCE electrolyte with BTFE down to 1.77 M breaks the three-dimensional solution structure into an island-like solvation complex. We relate these structural changes to the electronic properties of the electrolytes finding a causal relationship between the reductive/oxidative behavior and the lithium–oxygen interaction mechanisms in the solvated complexes. The coordination with lithium-ions lowers the electrolyte LUMO and HOMO levels: the higher is the number of interactions with lithium-ions, the more likely the solvent molecule, FSI^- anion, or diluent molecule is to be reduced and the less likely it is to become oxidized. The evolution of the solvated ion structure in HCE and LHCE suggests a close connection to a corresponding change in the lithium-ion transport mechanisms for these electrolytes.

Jie Xiao, Qiuyan Li, Yujing Bi, Mei Cai, Bruce Dunn, Tobias Glossman, Jun Liu, Tetsuya Osaka, Ryuta Sugiura, Bingbin Wu, Jihui Yang, Ji-Guang Zhang, M. Stanley Whittingham."Understanding and applying coulombic efficiency in lithium metal batteries."Nature Energ (June 2020).
Abstract: Coulombic efficiency (CE) has been widely used in battery research as a quantifiable indicator for the reversibility of batteries. While CE helps to predict the lifespan of a lithium-ion battery, the prediction is not necessarily accurate in a rechargeable lithium metal battery. Here, we discuss the fundamental definition of CE and unravel its true meaning in lithium-ion batteries and a few representative configurations of lithium metal batteries. Through examining the similarities and differences of CE in lithium-ion batteries and lithium metal batteries, we establish a CE measuring protocol with the aim of developing high-energy long-lasting practical lithium metal batteries. The understanding of CE and the CE protocol are broadly applicable in other rechargeable metal batteries including Zn, Mg and Na batteries.

Zhe Peng, Xia Cao, Peiyuan Gao, Haiping Jia, Xiaodi Ren, Swadipta Roy, Zhendong Li, Yun Zhu, Weiping Xie, Dianying Liu, Qiuyan Li, Deyu Wang, Wu Xu, Ji-Guang Zhang."High‐Power Lithium Metal Batteries Enabled by High‐Concentration Acetonitrile‐Based Electrolytes with Vinylene Carbonate Additive."Advanced Functional Materials 30 (24)Number 2001285 (June 2020).
Abstract: To enable next‐generation high‐power, high‐energy‐density lithium (Li) metal batteries (LMBs), an electrolyte possessing both high Li Coulombic efficiency (CE) at a high rate and good anodic stability on cathodes is critical. Acetonitrile (AN) is a well‐known organic solvent for high anodic stability and high ionic conductivity, yet its application in LMBs is limited due to its poor compatibility with Li metal anodes even at high salt concentration conditions. Here, a highly concentrated AN‐based electrolyte is developed with a vinylene carbonate (VC) additive to suppress Li⁺ depletion at high current densities. Addition of VC to the AN‐based electrolyte leads to the formation of a polycarbonate‐based solid electrolyte interphase, which minimizes Li corrosion and leads to a very high Li CE of up to 99.2% at a current density of 0.2 mA cm^‐2. Using such an electrolyte, fast charging of Li||NMC333 cells is realized at a high current density of 3.6 mA cm^‐2, and stable cycling of Li||NMC622 cells with a high cathode loading of 4 mAh cm^‐2 is also demonstrated.

Lynn Trahey, Fikile R. Brushett, Nitash P. Balsara, Gerbrand Ceder, Lei Cheng, Yet-Ming Chiang, Nathan T. Hahn, Brian J. Ingram, Shelley D. Minteer, Jeffrey S. Moore, Karl T. Mueller, Linda F. Nazar, Kristin A. Persson, Donald J. Siegel, Kang Xu, Kevin R. Zavadil, Venkat Srinivasan, George W. Crabtree."Energy storage emerging: A perspective from the Joint Center for Energy Storage Research."Proceedings of the National Academy of Sciences 117 (23) 12550-12557 (June 2020).
Abstract: Energy storage is an integral part of modern society. A contemporary example is the lithium (Li)-ion battery, which enabled the launch of the personal electronics revolution in 1991 and the first commercial electric vehicles in 2010. Most recently, Li-ion batteries have expanded into the electricity grid to firm variable renewable generation, increasing the efficiency and effectiveness of transmission and distribution. Important applications continue to emerge including decarbonization of heavy-duty vehicles, rail, maritime shipping, and aviation and the growth of renewable electricity and storage on the grid. This perspective compares energy storage needs and priorities in 2010 with those now and those emerging over the next few decades. The diversity of demands for energy storage requires a diversity of purpose-built batteries designed to meet disparate applications. Advances in the frontier of battery research to achieve transformative performance spanning energy and power density, capacity, charge/discharge times, cost, lifetime, and safety are highlighted, along with strategic research refinements made by the Joint Center for Energy Storage Research (JCESR) and the broader community to accommodate the changing storage needs and priorities. Innovative experimental tools with higher spatial and temporal resolution, in situ and operando characterization, first-principles simulation, high throughput computation, machine learning, and artificial intelligence work collectively to reveal the origins of the electrochemical phenomena that enable new means of energy storage. This knowledge allows a constructionist approach to materials, chemistries, and architectures, where each atom or molecule plays a prescribed role in realizing batteries with unique performance profiles suitable for emergent demands.

Kee Sung Han, Zhou Yu, Hui Wang, Paul C. Redfern, Lin Ma, Lei Cheng, Ying Chen, Jian Zhi Hu, Larry A. Curtiss, Kang Xu, Vijayakumar Murugesan, Karl T. Mueller."Origin of Unusual Acidity and Li⁺ Diffusivity in a Series of Water-in-Salt Electrolytes."Journal of Physical Chemistry B 124 (25): 5284-5291 (June 2020).
Abstract: Superconcentrated aqueous electrolytes (“water-in-salt” electrolytes, or WiSEs) enable various aqueous battery chemistries beyond the voltage limits imposed by the Pourbaix diagram of water. However, their detailed structural and transport properties remain unexplored and could be better understood through added studies. Here, we report on our observations of strong acidity (pH 2.4) induced by lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) at superconcentration (at 20 mol/kg). Multiple nuclear magnetic resonance (NMR) and pulsed-field gradient (PFG) diffusion NMR experiments, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations reveal that such acidity originates from the formation of nanometric ion-rich structures. The experimental and simulation results indicate the separation of water-rich and ion-rich domains at salt concentrations ≥5 m and the acidity arising therefrom is due to deprotonation of water molecules in the ion-rich domains. As such, the ion-rich domain is composed of hydrophobic −CF₃ (of TFSI^–) and hydrophilic hydroxyl (OH^–) groups. At 20 m concentration, the tortuosity and radius of water diffusion channels are estimated to be ∼10 and ∼1 nm, respectively, which are close to values obtained from hydrated Nafion membranes that also have hydrophobic polytetrafluoroethylene (PTFE) backbones and hydrophilic channels consisting of SO₃^– ion cluster networks providing for the transport of ions and water. Thus, we have discovered the structural similarity between WiSE and hydrated Nafion membranes on the nanometer scale.

Xiaowen Zhan, Xiaochuan Lu, David M. Reed, Vincent L. Sprenkle, and G. Li."Emerging soluble organic redox materials for next-generation grid energy-storage applications."MRS Communications 10 (2):215-229 (June 2020).
Abstract: Because of their structural versatility, fast redox reactivity, high storage capacity, sustainability, and environmental friendliness, soluble organic redox molecules have emerged as materials that have potential for use in energy-storage systems. Considering these advantages, this paper reviews recent progress in implementing such materials in aqueous soluble organic redox flow batteries and organic alkali metal/air batteries. We identify and discuss major challenges associated with molecular structures, cell configurations, and electrochemical parameters. Hopefully, we provide a general guidance for the future development of soluble organic redox materials for emerging energy-storage devices used in the electricity grid.

Biwei Xiao."Intercalated water in aqueous batteries."Carbon Energy 2 (2):251-264 (May 2020).
Abstract: The unprecedentedly growing demand for energy storage devices in recent years calls for diversified chemistries with unique advantages. When it comes to safety and cost, aqueous battery systems have attracted tremendous attention. Owing to its small size, high polarity, and hydrogen bonding, water in the electrode materials, either in the form of structural water or cointercalated hydrated cations, drastically change the electrochemical behavior through multiple aspects. This review discusses the roles of water in aqueous batteries from how water molecules coordinate with cations to examples of water‐mediated reactions in different types of host materials.

Yulun Zhang, Yuxiao Lin, Lingfeng He, Vijayakumar Murugesan, Gorakh Pawar, Bhuvana M. Sivakumar, Hanping Ding, Dong Ding, Boryann Liaw, Eric J. Dufek, and Bin Li."Dual Functional Ni₃S₂@Ni Core–Shell Nanoparticles Decorating Nanoporous Carbon as Cathode Scaffolds for Lithium–Sulfur Battery with Lean Electrolytes."dACS Applied Energy Materials3 (5):4173-4179 (May 2020).
Abstract: Lithium–sulfur batteries are very promising for next-generation energy storage. However, most studies use flooded electrolytes to achieve a high specific capacity at the expense of lowering the specific energy. Understanding lithium–sulfur battery performance with lean electrolytes is highly desirable. Herein, a modified Pechini method is developed to synthesize a nanoporous carbon host decorated with Ni₃S₂@Ni particles. Such a cathode delivers enhanced specific capacities with extended cycling life in lean electrolytes, due to the dual functions of the Ni₃S₂ shell, which can both facilitate reaction kinetics and promote electrolyte wetting. This work highlights a strategy to rationally design cathodes for high-energy lithium–sulfur batteries.

Di Wu, Xu Ma, Sen Huang, Tao Fu, Patrick Balducci."Stochastic optimal sizing of distributed energy resources for a cost-effective and resilient Microgrid."Energy 198 (May 2020).
Abstract: Recent developments and advances in distributed energy resources (DERs) make them more affordable, accessible, and prevalent in microgrids. Research on designing and operating a microgrid with various DERs has received increasing attention during the past few years. This paper proposes a two-stage stochastic mixed-integer programming method for jointly determining optimal sizes of various DERs, considering both economic benefits and resilience performance. The proposed method explicitly models the interaction between DER sizing at the planning stage and hourly or sub-hourly microgrid dispatch at the operating stage in both grid-connected and island modes, considering stochastic grid disturbances, load, and renewable generation. A formulation method is then proposed to convert the stochastic sizing problem to an equivalent mix-integer linear programming problem, which can be efficiently solved even with a large number of system operating conditions. Using the proposed stochastic sizing method, a resource planning analysis for a military base in the U.S. is presented. It is found that the proposed method can effectively determine the optimal DER sizes to meet a required resilience goal at the maximum net-benefit. Impacts of several key factors including tariff rates, discount rate, and survivability level on optimal DER sizes are analyzed through case studies.

Ji Chen, Xiulin Fan, Qin Li, Hongbin Yang, M. Reza Khoshi, Yaobin Xu, Sooyeon Hwang, Long Chen, Xiao Ji, Chongyin Yan, Huixin He, Chongmin Wang, Eric Garfunkel, Dong Su, Oleg Borodin, Chunsheng Wang."Electrolyte design for LiF-rich solid–electrolyte interfaces to enable high-performance microsized alloy anodes for batteries."Nature Energy 5: 386-397 (May 2020).
Abstract: Lithium batteries with Si, Al or Bi microsized (>10 µm) particle anodes promise a high capacity, ease of production, low cost and low environmental impact, yet they suffer from fast degradation and a low Coulombic efficiency. Here we demonstrate that a rationally designed electrolyte (2.0 M LiPF₆ in 1:1 v/v mixture of tetrahydrofuran and 2-methyltetrahydrofuran) enables 100 cycles of full cells that contain microsized Si, Al and Bi anodes with commercial LiFePO₄ and LiNi_0.8Co_0.15Al_0.05O₂ cathodes. Alloy anodes with areal capacities of more than 2.5 mAh cm⁻² achieved >300 cycles with a high initial Coulombic efficiency of >90% and average Coulombic efficiency of >99.9%. These improvements are facilitated by the formation of a high-modulus LiF–organic bilayer interphase, in which LiF possesses a high interfacial energy with the alloy anode to accommodate plastic deformation of the lithiated alloy during cycling. This work provides a simple yet practical solution to current battery technology without any binder modification or special fabrication methods.

Hansen Wang, Xia Cao, Hanke Gu, Yayuan Liu, Yanbin Li, Zewen Zhang, William Huang, Hongxia Wang, Jiangyan Wang, Wu Xu, Ji-Guang Zhang, Yi Cui."Improving Lithium Metal Composite Anodes with Seeding and Pillaring Effects of Silicon Nanoparticles."ACS Nano 14 (4): 4601-4608 (April 2020).
Abstract: Metallic lithium (Li) anodes are crucial for the development of high specific energy batteries yet are plagued by their poor cycling efficiency. Electrode architecture engineering is vital for maintaining a stable anode volume and suppressing Li corrosion during cycling. In this paper, a reduced graphene oxide “host” framework for Li metal anodes is further optimized by embedding silicon (Si) nanoparticles between the graphene layers. They serve as Li nucleation seeds to promote Li deposition within the framework even without prestored Li. Meanwhile, the Li_xSi alloy particles serve as supporting “pillars” between the graphene layers, enabling a minimized thickness shrinkage after full stripping of metallic Li. Combined with a Li compatible electrolyte, a 99.4% Coulombic efficiency over ∼600 cycles is achieved, and stable cycling of a Li||NMC₅₃2 full cell for ∼380 cycles with negligible capacity decay is realized.

Junhua Song, Kuan Wang, Jianming Zheng, Mark H. Engelhard, Biwei Xiao, Enyuan Hu, Zihua Zhu, Chongmin Wang, Manling Sui, Yuehe Lin, David Reed, Vincent Sprenkle, Pengfei Yan, Xiaolin Li."Controlling Surface Phase Transition and Chemical Reactivity of O3-Layered Metal Oxide Cathodes for High-Performance Na-Ion Batteries."ACS Energy Letter 5 6: 1718-1725 (April 2020).
Abstract: O3-layered metal oxides are promising cathode materials for high-energy Na-ion batteries (SIBs); however, they suffer from fast capacity fade. Here, we develop a high-performance O3-NaNi_0.68Mn_0.22Co_0.10O₂ cathode for SIBs toward practical applications by suppressing the formation of a rock salt layer at the cathode surface with an advanced electrolyte. The cathode can deliver a high specific capacity of ∼196 mAh g^–1 and demonstrates >80% capacity retention over 1000 cycles. NaNi_0.68Mn_0.22Co_0.10O₂ hard carbon full-cells with practical loading (>2.5 mAh cm^–2) and lean electrolyte (∼40 μL) demonstrate ∼82% capacity retention after 450 cycles. A 60 mAh single-layer pouch cell has also been fabricated and demonstrated stable performance. This work represents a significant leap in SIB development and brings new insights to the development of advanced layered metal oxide cathodes for alkaline-ion batteries.

Jan Alam, Patrick Balducci, Kevin Whitener, Steve Cox."Energy Storage Control Capability Expansion: Achieving Better Technoeconomic Benefits at Portland General Electric's Salem Smart Power Center."IEEE Power and Energy Magazine 18 (2) (March 2020).
Abstract: The value proposition for energy storage systems (ESSs) is a key topic for creating and advancing its acceptance within the electric power sector, particularly for electric utilities. Although ESS as a technology is gaining popularity within the electric utility industry, its anticipated value streams are not fully understood, quantified, and demonstrated. The unavailability of suitable demonstration sites/projects, the lack of a deep understanding of available economic opportunities, and the deployment complexities associated with pursuing those opportunities are some of the reasons that complicate its value demonstration. The lessons learned from holistic demonstration projects covering key steps, e.g., economic value stream identification, evaluation, and its subsequent realization via suitable control strategies, could help electric utilities learn to manage ESS adoption challenges better.

Ying Chen, Nicholas R. Jaegers, Kee Sung Han, Hui Wang, Robert P. Young, Garvit Agarwal, Andrew S. Lipton, Rajeev S. Assary, Nancy M. Washton, Jian Zhi Hu, Karl T. Mueller, Vijayakumar Murugesan."Probing Conformational Evolution and Associated Dynamics of Mg(N(SO₂CF₃)₂)₂·Dimethoxyethane Adduct Using Solid-State ¹⁹F and 1H NMR."Journal of Physical Chemistry C 124 (9):4999-5008 (March 2020).
Abstract: Bis(trifluoromethanesulfonimide) or TFSI is widely used as a counter anion in electrolyte design due to its structural flexibility and chemical stability. We studied the conformational variations and associated dynamics of TFSI in adduct of Mg(TFSI)₂ with dimethoxyethane (DME), a solvate crystalline material using solid-state ¹H and ¹⁹F NMR. TFSI molecular motion in this solvate structure falls within the timescale of the ¹⁹F NMR experiment, yielding spectroscopic signatures for unique TFSI conformers under the coordination environment of Mg²⁺ cation. Within the temperature range of −5 to 82 °C, we observe nine distinct TFSI sites in both crystalline and disordered regions using ¹⁹F NMR, reflecting complexity of structural and dynamics of TFSI anions within solvate structure. The four distinguishable sites in the disordered region for the two CF₃ groups of the same TFSI molecule are identified using chemical shift analysis. The exchange rate constants from site to site are calculated through variable temperature ¹⁹F NMR and two-dimensional (2D) exchange spectroscopy (EXSY) experiments, along with respective activation enthalpies using Eyring’s formulation. The flip rate of CF₃ around the S–C bond is estimated as ∼15 s^–1 at 8 °C with ΔH≠ ∼ 22 kJ/mol, but the rotation of the entire TFSI is 4.8 s^–1 at 8 °C with a significantly greater ΔH≠ = 98 ± 10 kJ/mol. Furthermore, the slow conversion of trans to cis conformers at a lower temperature (T ≤ 1 °C) in the crystalline region is monitored, with a conversion rate of ∼2 × 10^–5 s^–1 at −5 °C. Density functional theory (DFT)-based calculations were performed to support further the assignment of experimental chemical shifts, and the activation energy E_a = 21.1 kJ/mol obtained for the cis to trans transition is consistent with experimental values. The combined set of ¹⁹F and ¹H under both one-dimensional (1D) and 2D NMR methods demonstrated here can be further used for examining electrode–electrolyte interfaces to probe the motions of various constituents that can enable detailed studies of interfacial processes and dynamics. Ultimately, such studies will aid in the design and discovery of interfacial constructs in which directed defect chemistry, chemical moiety distribution, and nanostructure are employed to drive efficient charge transport.

Xiaowen Zhan, Mark E. Bowden, Xiaochuan Lu, Jeffery F. Bonnett, Teresa Lemmon, David M. Reed, Vincent L. Sprenkle, and Guosheng L. " A Low‐Cost Durable Na‐FeCl₂ Battery with Ultrahigh Rate Capability " Advanced Energy Materials (March 2020).
Abstract:Na‐based batteries have long been regarded as an inexpensive, sustainable candidate for large‐scale stationary energy storage applications. Unfortunately, the market penetration of conventional Na‐NiCl₂ batteries is approaching its limit for several reasons, including limited rate capability and high Ni cost. Herein, a Na‐FeCl₂ battery operating at 190 °C is reported that allows a capacity output of 116 mAh g^-1 at an extremely high current density of 33.3 mA cm^-2 (≈0.6C). The superior rate performance is rooted in the intrinsically fast kinetics of the Fe/Fe²⁺ redox reaction. Furthermore, it is demonstrated that a small amount of Ni additive (10 mol%) effectively mitigates capacity fading of the Fe/NaCl cathode caused by Fe particle pulverization during long‐term cycling. The modified Fe/Ni cathode exhibits excellent cycling stability, maintaining a discharge energy density of over 295 Wh kg^-1 for 200 cycles at 10 mA cm^-2 (≈C/5).

Zhan X., J.P. Sepulveda, X. Lu, J.F. Bonnett, N.L. Canfield, T.L. Lemmon, and K. Jung.D. Reed, V. Sprenkle, G. Li. " Elucidating the role of anionic chemistry towards high-rate intermediate-temperature Na-metal halide batteries." Energy Storage Materials 24:177-187 (January. 2020).
Abstract:Sodium (Na)-based battery technologies that are economical (because Na is abundant) and have long cycle life are gaining importance for large-scale energy storage applications. Among the widely studied Na-based battery systems, intermediate-temperature (IT) Na-metal halide (Na-MH) batteries have demonstrated several advantages over conventional high-temperature Na batteries, including superior battery safety, lower operating temperature and manufacturing cost, potentially longer cycle life, and easier assembly. However, the rate performance of IT Na-MH batteries is inevitably affected by the lower operating temperature. In pursuit of faster charge-transfer reaction kinetics, we extended our studies of cathode materials beyond the extensively investigated NiCl2 to NiBr2 (NaBr/Ni) and NiI2 (NaI/Ni) compounds. We systematically investigated the synergetic effects of anion chemistry on the electrochemical properties. Surprisingly, among three tested cathodes, the NaBr/Ni cathode showed the highest energy density of 174 Wh/kg at 33.3 mA/cm2 (~0.8C), which is 2.5 and 1.9 times higher than those of NaCl/Ni and NaI/Ni cells. We explored the underlying enhancement mechanism in great detail via multiple structural characterization and electrochemical techniques. The sodium-halide salt dissolution in molten NaAlCl4 was found to be the determining factor in rate improvement. Our findings will greatly advance IT Na-MH battery technologies and pave the way towards fundamental understanding of reaction kinetics for high-temperature batteries in general.

Yaobin Xu, Haiping Wu, Yang He, Qingsong Chen, Ji-Guang Zhang, Wu Xu, Chongmin Wang."Atomic to Nanoscale Origin of Vinylene Carbonate Enhanced Cycling Stability of Lithium Metal Anode Revealed by Cryo-Transmission Electron Microscopy."Nano Letters 20 (1):418-425 (January 2020).
Abstract: Batteries using lithium (Li) metal as the anode are considered promising energy storage systems because of their high specific energy densities. The crucial bottlenecks for Li metal anode are Li dendrites growth and side reactions with electrolyte inducing safety concern, low Coulombic efficiency (CE), and short cycle life. Vinylene carbonate (VC), as an effective electrolyte additive in Li-ion batteries, has been noticed to significantly enhance the CE, whereas the origin of such an additive remains unclear. Here we use cryogenic transmission electron microscopy imaging combing with energy dispersive X-ray spectroscopy elemental and electron energy loss spectroscopy electronic structure analyses to reveal the role of the VC additive. We discovered that the electrochemically deposited Li metal (EDLi) in the VC-containing electrolyte is slightly oxidized with the solid electrolyte interphase (SEI) being a nanoscale mosaic-like structure comprised of organic species, Li₂O and Li₂CO₃, whereas the EDLi formed in the VC-free electrolyte is featured by a combination of fully oxidized Li with Li₂O SEI layer and pure Li metal with multilayer nanostructured SEI. These results highlight the possible tuning of crucial structural and chemical features of EDLi and SEI through additives and consequently direct correlation with electrochemical performance, providing valuable guidelines to rational selection, design, and synthesis of additives for new battery chemistries.

Bingbin Wu, Yang Yang, Dianying Liu, Chaojiang Niu, Mark Gross, Lorraine Seymour, Hongkyung Lee, Phung M. L. Le,Thanh D.Vo, Zhiqun Daniel Deng, Eric J. Dufek, M. Stanley Whittingham, Jun Liu, and Jie Xiao. " Good Practices for Rechargeable Lithium Metal Batteries. " Journal of The Electrochemical Society 166, 16: A4141-A4149 (December. 2019).
Abstract:High-energy rechargeable lithium metal batteries have been intensively revisited in recent years. Since more researchers started to use pouch cell as the platform to study the fundamentals at relevant scales, safe testing and handling of lithium metal and high-energy lithium metal batteries have become critical. Cautions and safety procedures are needed when handling cycled pouch cells with pulverized lithium metal particles inside. From cell design, electrode preparation, cell fabrication to testing procedure, this work aims to discuss the possible root causes that may initiate cell internal short circuit and raise safety concerns. Safe transfer, disassembly and disposal of cycled Li metal pouch cells are also discussed. The insights provided in this article are applicable for the research on high-energy lithium-ion batteries as well and may inspire more safety strategies to accelerate research innovation by using large-format batteries as the testing vehicle and conduct the research safely. 

Xiaoqin Zang, Litao Yan, Yang Yang, Huilin Pan, Zimin Nie, Ki Won Jung,Zhiqun Daniel Deng, and Wei Wang."Monitoring the State‐of‐Charge of a Vanadium Redox Flow Battery with the Acoustic Attenuation Coefficient: An In Operando Noninvasive Method."Small Methods (December 2019).
Abstract: Redox flow battery technology has been increasingly recognized as a promising option for large‐scale grid energy storage. Access to high‐fidelity information on the health status of the electrolyte, including the state‐of‐charge (SOC), is vital to maintaining optimal and economical battery operation. In this study, an ultrasonic probing cell that can be used to measure SOC in real time is designed. This unprecedented, new measurement approach overcomes the influence of varying temperatures by measuring the acoustic attenuation coefficient of the redox flow battery electrolyte online and noninvasively. The new approach is used to estimate the SOC of a vanadium redox flow battery in operando from measured acoustic properties. The accuracy of the SOC estimated from the acoustic properties is validated against SOC calculated by the titration method. The results show that the acoustic attenuation coefficient is a robust parameter for SOC monitoring, with a maximum error of 4.8% and extremely low sensitivity to temperature, while sound speed appears to be less accurate in the benchmark‐inference method, with a maximum error of 22.5% and high sensitivity to temperature. The acoustic measurement approach has great potential for inexpensive real‐time SOC monitoring of redox flow battery operations.

Jie Bao, Vijayakumar Murugesan, Carl Justin Kamp, Yuyan Shao, Litao Yan, Wei Wang."Machine Learning Coupled Multi‐Scale Modeling for Redox Flow Batteries."Advanced Theory and Simulations 3 (2):article number 1900167 (November 2019).
Abstract: The framework of a multi‐scale model that couples a deep neural network, a widely used machine learning approach, with a partial differential equation solver and provides understanding of the relationship between the pore‐scale electrode structure reaction and device‐scale electrochemical reaction uniformity within a redox flow battery is introduced. A deep neural network is trained and validated using 128 pore‐scale simulations that provide a quantitative relationship between battery operating conditions and uniformity of the surface reaction for the pore‐scale sample. Using the framework, information about surface reaction uniformity at the pore level to combined uniformity at the device level is upscaled. The information obtained using the framework and deep neural network against the experimental measurements is also validated. Based on the multi‐scale model results, a time‐varying optimization of electrolyte inlet velocity is established, which leads to a significant reduction in pump power consumption for targeted surface reaction uniformity but little reduction in electric power output for discharging. The multi‐scale model coupled with the deep neural network approach establishes the critical link between the micro‐structure of a flow‐battery component and its performance at the device scale, thereby providing rationale for further operational or material optimization.

Zhe Peng, Junhua Song,Liyuan Huai, Biwei Xiao, Lianfeng Zou, Guomin Zhu, Abraham Martinez, et al, Deyu Wang, Wu Xu, and Ji-Guang Zhang. " Enhanced Stability of Li Metal Anodes by Synergetic Control of Nucleation and the Solid Electrolyte Interphase " Advanced Energy Materials, 9(42): 1901764 (November 2019).
Abstract:Use of a protective coating on a lithium metal anode (LMA) is an effective approach to enhance its coulombic efficiency and cycling stability. Here, a facile approach to produce uniform silver nanoparticle‐decorated LMA for high‐performance Li metal batteries (LMBs) is reported. This effective treatment can lead to well‐controlled nucleation and the formation of a stable solid electrolyte interphase (SEI). Ag nanoparticles embedded in the surface of Li anodes induce uniform Li plating/stripping morphologies with reduced overpotential. More importantly, cross‐linked lithium fluoride‐rich interphase formed during Ag+ reduction enables a highly stable SEI layer. Based on the Ag‐LiF decorated anodes, LMBs with LiNi1/3Mn1/3Co1/3O2 cathode (≈1.8 mAh cm−2) can retain >80% capacity over 500 cycles. The similar approach can also be used to treat sodium metal anodes. Excellent stability (80% capacity retention in 10 000 cycles) is obtained for a Na||Na3V2(PO4)3 full cell using a Na‐Ag‐NaF/Na anode cycled in carbonate electrolyte. These results clearly indicate that synergetic control of the nucleation and SEI is an efficient approach to stabilize rechargeable metal batteries.

Haiping Wu ,Yaobin Xu, Xiaodi Ren. Bin Liu, Mark H. Engelhard, Michael S. Ding, Patrick Z. El‐Khoury, Linchao Zhang, Qiuyan Li, Kang Xu, Chongmin Wang, Ji‐Guang Zhang, and Wu Xu. " Polymer‐in‐“Quasi‐Ionic Liquid” Electrolytes for High‐Voltage Lithium Metal Batteries." Advanced Energy Materials 9, 41:1902108 (November 2019).
Abstract:Due to the limited oxidation stability (<4 V) of ether oxygen in its polymer structure, polyethylene oxide (PEO)‐based polymer electrolytes are not compatible with high‐voltage (>4 V) cathodes, thus hinder further increases in the energy density of lithium (Li) metal batteries (LMBs). Here, a new type of polymer‐in‐“quasi‐ionic liquid” electrolyte is designed, which reduces the electron density on ethereal oxygens in PEO and ether solvent molecules, induces the formation of stable interfacial layers on both surfaces of the LiNi1/3Mn1/3Co1/3O2 (NMC) cathode and the Li metal anode in Li||NMC batteries, and results in a capacity retention of 88.4%, 86.7%, and 79.2% after 300 cycles with a charge cutoff voltage of 4.2, 4.3, and 4.4 V for the LMBs, respectively. Therefore, the use of “quasi‐ionic liquids” is a promising approach to design new polymer electrolytes for high‐voltage and high‐specific‐energy LMBs.

Xiao J. " How lithium dendrites form in liquid batteries. " Science 366 , 6464: 426-427 (October. 2019).
Abstract:Conventional rechargeable lithium (Li)–ion batteries generally use graphite as the anode, where Li ions are stored in the layered graphite. However, the use of Li metal as the anode is now being reconsidered. These next-generation battery technologies could potentially double the cell energy of conventional Li-ion batteries (1). Rechargeable Li metal batteries were commercialized more than four decades ago but were in use only briefly because of safety concerns (2). With the advancements of electrolyte (3, 4), electrode architecture (5), and characterization techniques (6) in recent years, a better fundamental understanding of the interfacial reactions during charging and discharging that dictate cell performance has developed and inspired a reevaluation of the use of Li metal anodes in rechargeable batteries.

Jian Zhi Hu, Nicholas R. Jaegers, Ying Chen, Kee Sung Han, Hui Wang, Vijayakumar Murugesan, Karl T. Mueller."Adsorption and Thermal Decomposition of Electrolytes on Nanometer Magnesium Oxide: An in Situ ¹³C MAS NMR Study."ACS Applied Materials & Interfaces 11 (42):38689-38696 (October 2019).
Abstract: Mg batteries have been proposed as potential alternatives to lithium-ion batteries because of their lower cost, higher safety, and enhanced charge density. However, the Mg metal readily oxidizes when exposed to an oxidizer to form a thin MgO passivation surface layer that blocks the transport of Mg²⁺ across the solid electrode–electrolyte interface (SEI). In this work, the adsorption and thermal decomposition of diglyme (G2) and electrolytes containing Mg(TFSI)₂ in G2 on 10 nm-sized MgO particles are evaluated by a combination of in situ ¹³C single-pulse, surface-sensitive ¹H–¹³C cross-polarization (CP) magic-angle spinning (MAS) nuclear magnetic resonance, and quantum chemistry calculations. At 180 °C, neat G2 decomposes on MgO to form surface-adsorbed −OCH₃ groups that are captured as a distinctive peak located at about 50 ppm in the CP/MAS spectrum. At low Mg(TFSI)₂ salt concentration, the main solvation structure in this electrolyte is solvent-separated ion pairs without extensive Mg–TFSI contact ion pairs. G2, likely including a small amount of G2-solvated Mg²⁺, adsorbs onto the MgO surface. At high Mg(TFSI)₂ salt concentrations, contact ion pairs between Mg and TFSI are formed extensively in the solution with the first solvation shell containing one pair of Mg–TFSI and two G2 molecules and the second solvation shell containing up to six G2 molecules, namely, MgTFSI(G2)₂(G2)₆⁺. In the presence of MgO, MgTFSI(G2)₂(G2)₆⁺ adsorbs onto the MgO surface. At 180 °C, the MgO surface stimulates a desolvation process converting MgTFSI(G2)₂(G2)₆⁺ to MgTFSI(G2)₂⁺ and releasing G2 molecules from the second solvation shell of the MgTFSI(G2)₂(G2)₆⁺ cluster into the solution. MgTFSI(G2)₂⁺ and MgTFSI(G2)₂(G2)₆⁺ tightly adsorb onto the MgO surface and are observed by ¹H–¹³C CP/MAS experiments. The results contained herein show that electrolyte composition has a directing role in the species present on the electrode surface, which has implications on the structures and constituents of the solid–electrolyte interface on working electrodes and can be used to better understand its formation and the failure modes of batteries.

Yang He, Xiaodi Ren, Yaobin Xu, Mark H. Engelhard, Xiaolin Li, Jie Xiao, Jun Liu, Ji-Guang Zhang, Wu Xu, and Chongmin Wang. " Origin of lithium whisker formation and growth under stress." Nature Nanotechnology, 14, 1042-1047 (October. 2019).
Abstract:Lithium metal has the lowest standard electrochemical redox potential and very high theoretical specific capacity, making it the ultimate anode material for rechargeable batteries. However, its application in batteries has been impeded by the formation of Li whiskers, which consume the electrolyte, deplete active Li and may lead to short-circuit of the battery. Tackling these issues successfully is dependent on acquiring sufficient understanding of the formation mechanisms and growth of Li whiskers under the mechanical constraints of a separator. Here, by coupling an atomic force microscopy cantilever into a solid open-cell set-up in environmental transmission electron microscopy, we directly capture the nucleation and growth behaviour of Li whiskers under elastic constraint. We show that Li deposition is initiated by a sluggish nucleation of a single crystalline Li particle, with no preferential growth directions. Remarkably, we find that retarded surface transport of Li plays a decisive role in the subsequent deposition morphology. We then explore the validity of these findings in practical cells using a series of carbonate-poisoned ether-based electrolytes. Finally, we show that Li whiskers can yield, buckle, kink or stop growing under certain elastic constraints.

Zheng Y., F.A. Soto, V. Ponce, J. Seminario, X. Cao, J. Zhang, and P.B. Balbuena. " Localized high concentration electrolyte behavior near a lithium–metal anode surface." Journal of Materials Chemistry A 43:25047-25055 (October. 2019).
Abstract:Wide-scale practical application of rechargeable lithium–metal batteries remains a significant challenge due to dendrite growth. To overcome this challenge, electrolytes must be designed to allow for the formation of protective solid electrolyte interphase (SEI) layers on the highly reactive lithium–metal anode (LMA) surfaces. Recently, novel localized high-concentration electrolytes (LHCEs) were introduced as a potential solution to enable dendrite-free cycling of LMAs, by using an inert solvent to “dilute” the high concentration electrolytes. Ideally, the diluent itself does not dissolve the salt but is miscible with the solvent to form a localized high concentrated salt/solvent cluster surrounded by the diluent. However, detailed structure and potential surface reactions that may take place in LHCE environment are not yet clear. In this work, we investigated the reactivity of 1 M lithium bis(fluorosulfonyl)imide (LiFSI) in a mixture of dimethoxyethane (DME)/tris(2,2,2-trifluoroethyl)orthoformate (TFEO) (1 : 3 by mol) electrolyte near a Li metal surface based on density functional theory and ab initio molecular dynamics (MD) simulations. Selected liquid interfacial configurations were obtained from classical MD simulations. Our results indicate that when salt and TFEO molecules are close to each other and to the surface, fluoride anions resulting from the fast salt anion decomposition can trigger a cascade of reactions that lead to the decomposition of TFEO. However, if the Li cation is initially solvated by DME and the anion forming a complex, the stability of the anion increases significantly. The Li solvated structure is implied in the LHCE concept; however statistically the larger amount of TFEO molecules suggest also the first scenario leading to TFEO decomposition. Therefore, the broader implication of our simulations is that the defluorination of TFEO may contribute, together with the anion decomposition, to the observed rapid formation of a stable SEI on the surface of the lithium metal; consequently, favorably affecting the stability of LMAs during battery operation.

Ning Kang, Yuxiao Lin, Li Yang, Dongping Lu, Jie Xiao, Yue Qi, Mei Cai."Cathode porosity is a missing key parameter to optimize lithium-sulfur battery energy density."Nature Communications Article number 4597 (October 2019).
Abstract: While high sulfur loading has been pursued as a key parameter to build realistic high-energy lithium-sulfur batteries, less attention has been paid to the cathode porosity, which is much higher in sulfur/carbon composite cathodes than in traditional lithium-ion battery electrodes. For high-energy lithium-sulfur batteries, a dense electrode with low porosity is desired to minimize electrolyte intake, parasitic weight, and cost. Here we report the profound impact on the discharge polarization, reversible capacity, and cell cycling life of lithium-sulfur batteries by decreasing cathode porosities from 70 to 40%. According to the developed mechanism-based analytical model, we demonstrate that sulfur utilization is limited by the solubility of lithium-polysulfides and further conversion from lithium-polysulfides to Li₂S is limited by the electronically accessible surface area of the carbon matrix. Finally, we predict an optimized cathode porosity to maximize the cell level volumetric energy density without sacrificing the sulfur utilization.

X.Cao, X. Ren, L. Zou, M.H. Engelhard, W. Huang, H. Wang, and B.E. Matthews, H. Lee, C. Niu, B. W. Arey, Y. Cui, C. Wang, J. Xiao, J. Liu, W.Xu, and J. Zhang. " Monolithic solid–electrolyte interphases formed in fluorinated orthoformate-based electrolytes minimize Li depletion and pulverization. " Nature Energy 4,796–805 (September. 2019).
Abstract:Lithium (Li) pulverization and associated large volume expansion during cycling is one of the most critical barriers for the safe operation of Li-metal batteries. Here, we report an approach to minimize the Li pulverization using an electrolyte based on a fluorinated orthoformate solvent. The solid–electrolyte interphase (SEI) formed in this electrolyte clearly exhibits a monolithic feature, which is in sharp contrast with the widely reported mosaic- or multilayer-type SEIs that are not homogeneous and could lead to uneven Li stripping/plating and fast Li and electrolyte depletion over cycling. The highly homogeneous and amorphous SEI not only prevents dendritic Li formation, but also minimizes Li loss and volumetric expansion. Furthermore, this new electrolyte strongly suppresses the phase transformation of the LiNi0.8Co0.1Mn0.1O2 cathode (from layered structure to rock salt) and stabilizes its structure. Tests of high-voltage Li||NMC811 cells show long-term cycling stability and high rate capability, as well as reduced safety concerns.

Ke Lu, Siyuan Gao, Guosheng Li, Jacob Kaelin, Zhengcheng Zhang, Yingwen Cheng."Regulating Interfacial Na-Ion Flux via Artificial Layers with Fast Ionic Conductivity for Stable and High-Rate Na Metal Batteries."ACS Materials Letters 1: 303-309 (August 2019).
Abstract: Metallic Na electrodes are promising anodes for low-cost and high-energy density batteries due to their natural abundance and high specific capacity. Unfortunately, they are extremely reactive and spontaneously form unstable solid-electrolyte interphases, which lead to critical challenges including growth of dendritic/mossy Na structures and fast degradation. We report here the design of artificial interphase films that have intrinsic high Na⁺-ion conductivity, which enable protected Na electrodes with simultaneously improved surface stability and redox kinetics. They were prepared from Mo₆S₈ films, which transform to Na_xMo₆S₈ (x ≈ 16) through an in-situ sodiation process when pressed onto Na metal. The protected Na electrodes were stable in dry air for days and exhibited 2.5 times higher exchange current density compared with pristine Na electrodes. They enabled symmetric batteries with stable cycling for 1200 h at 0.5 mA cm^–2 and fast Na metal batteries with substantially improved high-rate performance and robust durability for 1000 cycles.

Yonggang Yao, Zhennan Huang, Pengfei Xie, Lianping Wu, Lu Ma, Tangyuan Li, Zhenqian Pang, Miaolun Jiao, Zhiqiang Liang, Jinlong Gao, Yang He, Dylan Jacob Kline, Michael R. Zachariah, Chongmin Wang, Jun Lu, Tianpin Wu, Teng Li, Chao Wang, Reza Shahbazian-Yassar, and Liangbing Hu " High Temperature Shockwave Stabilized Single Atoms. Nature Nanotechnology 14,9:851-857 (August. 2019).
Abstract:The stability of single-atom catalysts is critical for their practical applications. Although a high temperature can promote the bond formation between metal atoms and the substrate with an enhanced stability, it often causes atom agglomeration and is incompatible with many temperature-sensitive substrates. Here, we report using controllable high-temperature shockwaves to synthesize and stabilize single atoms at very high temperatures (1,500–2,000 K), achieved by a periodic on–off heating that features a short on state (55 ms) and a ten-times longer off state. The high temperature provides the activation energy for atom dispersion by forming thermodynamically favourable metal–defect bonds and the off-state critically ensures the overall stability, especially for the substrate. The resultant high-temperature single atoms exhibit a superior thermal stability as durable catalysts. The reported shockwave method is facile, ultrafast and universal (for example, Pt, Ru and Co single atoms, and carbon, C3N4 and TiO2 substrates), which opens a general route for single-atom manufacturing that is conventionally challenging.

Yoon B., J. Park, J. Lee, S. Kim, X. Ren, Y. Lee, H. Kim,H. Lee, and M. Ryou. " High-Rate Cycling of Lithium-Metal Batteries Enabled by Dual-Salt Electrolyte-Assisted Micro-Patterned Interfaces." ACS Applied Materials & Interfaces 11,  35: 31777-31785 (August. 2019).
Abstract:We present a synergistic strategy to boost the cycling performance of Li-metal batteries. The strategy is based on the combined use of a micropattern (MP) on the surface of the Li-metal electrode and an advanced dual-salt electrolyte (DSE) system to more efficiently control undesired Li-metal deposition at higher current density (∼3 mA cm^–2). The MP-Li electrode induces a spatially uniform current distribution to achieve dendrite-free Li-metal deposition beneath the surface layer formed by the DSE. The MP-Li/DSE combination exhibited excellent synergistic rate capability improvements that were neither observed with the MP-Li system nor for the bare Li/DSE system. The combination also resulted in the Li||LiMn₂O₄ battery attaining over 1 000 cycles, which is twice as long at the same capacity retention (80%) compared with the control cells (MP-Li without DSE). We further demonstrated extremely fast charging at a rate of 15 C (19.5 mA cm^–2).

Ji-Guang. " Anode-less." Nature Energy A 4:637-638 (August. 2019).
Abstract:A conventional lithium-ion battery makes use of both an anode and a cathode. Now, a new design of batteries with no anodes in their initial state is shown to be promising for practical applications.

Jeonghun Oh, Hearin Jo, Hongkyung Lee, Hee-Tak Kim, Yong Min Lee, Myung-Hyun Ryou."Polydopamine-treated three-dimensional carbon fiber-coated separator for achieving high-performance lithium metal batteries."Journal of Power Sources 430: 130-136 (August 2019).
Abstract: The development of safe and high-performance lithium (Li) metal anodes has been a challenging issue that has not been addressed for decades. In this study, we have developed a thermally stable polydopamine-treated three-dimensional (3D) carbon fiber-coated separator (P3D-CFS) using an economical and environment-friendly process. P3D-CFS has a conductive coating layer that is used as a 3D hosting structure, which does not cause morphological changes in the Li metal anode. As a result, the unit cells (LiMn₂O₄/Li metal) employing P3D-CFS improve the cycle performance and rate capability compared to commercial polyethylene (PE) separators. P3D-CFS maintained 83.1% of the initial discharge capacity at the 400th cycle, whereas bare PE maintains only 74.3% of the initial discharge capacity after the 250th cycle (C/2 = 0.5 mA cm⁻²). P3D-CFS maintains 42.8% of the initial discharge capacity at a 7C rate (7 mA cm⁻²), whereas only 0.19% is maintained by bare PE under the same condition. Owing to the thermally stable properties of P3D-CFS, the open-circuit voltage of the unit cells (LiMn₂O₄/graphite) that employed P3D-CFS is maintained for over 60 min at 140 °C, whereas the unit cells that employed bare PE show a sudden voltage drop after only 3 min.

Lianfeng Zou, Jianyu Li, Zhenyu Liu, Guofeng Wang, Arumugam Manthiram, Chongmin Wang."Lattice doping regulated interfacial reactions in cathode for enhanced cycling stability."Nature Communications 10, Article number 3447 (August 2019).
Abstract: Interfacial reactions between electrode and electrolyte are critical, either beneficial or detrimental, for the performance of rechargeable batteries. The general approaches of controlling interfacial reactions are either applying a coating layer on cathode or modifying the electrolyte chemistry. Here we demonstrate an approach of modification of interfacial reactions through dilute lattice doping for enhanced battery properties. Using atomic level imaging, spectroscopic analysis and density functional theory calculation, we reveal aluminum dopants in lithium nickel cobalt aluminum oxide are partially dissolved in the bulk lattice with a tendency of enrichment near the primary particle surface and partially exist as aluminum oxide nano-islands that are epitaxially dressed on the primary particle surface. The aluminum concentrated surface lowers transition metal redox energy level and consequently promotes the formation of a stable cathode-electrolyte interphase. The present observations demonstrate a general principle as how the trace dopants modify the solid-liquid interfacial reactions for enhanced performance.

Xiaodi Ren, Lianfeng Zou, Xia Cao, Mark H. Engelhard, Wen Liu, Sarah D. Burton, Hongkyung Lee, Chaojiang Niu, Bethany E. Matthews, Zihua Zhu, Chongmin Wang, Bruce W. Arey, Jie Xiao, Jun Liu, Ji-Guang Zhang."Enabling High-Voltage Lithium-Metal Batteries under Practical Conditions."Joule 3 (7): 1662-1676 (July 2019).
Abstract: High-energy-density Li-metal batteries are promising next-generation energy-storage systems. However, their development is greatly restricted because of the lack of functional electrolytes that can work efficiently on both the reactive Li anode and the aggressive cathodes under practical conditions, where high-voltage, high-loading cathode, thin Li anode and lean electrolyte are all indispensable. Here, we chose ether as the base solvent, which has intrinsic good cathodic but poor anodic stabilities and redesigned the electrolyte in a localized high-concentration electrolyte (LHCE) formulation to build the protective interphases onto both the anode and the cathode, simultaneously. Ether-based LHCE can effectively suppress side reactions, resulting in stable cycling of Li||NMC811 cells under voltages up to 4.5 V and under practical conditions. This electrolyte design provides critical insights for future electrolyte development for practical high-energy-density Li-metal batteries.

Haiping Jia, Lianfeng Zou, Peiyuan Gao, Xia Cao, Wengao Zhao, Yang He, Mark H. Engelhard Sarah D. Burton, Hui Wang , Xiaodi Ren, Qiuyan Li, Ran Yi, Xin Zhang, Chongmin Wang, Zhijie Xu, Xiaolin Li, Ji‐Guang Zhang, and Wu Xu.  " High‐Performance Silicon Anodes Enabled By Nonflammable Localized High‐Concentration Electrolytes. Advanced Energy Materials 9 (31): 1900784 (July. 2019).
Abstract:Silicon anodes are regarded as one of the most promising alternatives to graphite for high energy‐density lithium‐ion batteries (LIBs), but their practical applications have been hindered by high volume change, limited cycle life, and safety concerns. In this work, nonflammable localized high‐concentration electrolytes (LHCEs) are developed for Si‐based anodes. The LHCEs enable the Si anodes with significantly enhanced electrochemical performances comparing to conventional carbonate electrolytes with a high content of fluoroethylene carbonate (FEC). The LHCE with only 1.2 wt% FEC can further improve the long‐term cycling stability of Si‐based anodes. When coupled with a LiNi0.3Mn0.3Co0.3O2 cathode, the full cells using this nonflammable LHCE can maintain >90% capacity after 600 cycles at C/2 rate, demonstrating excellent rate capability and cycling stability at elevated temperatures and high loadings. This work casts new insights in electrolyte development from the perspective of in situ Si/electrolyte interphase protection for high energy‐density LIBs with Si anodes.

Jiaxin Zheng,Yaokun Ye,Tongchao Liu,Yinguo Xiao, Chongmin Wang, Feng Wang, Feng Pan. " Ni/Li Disordering in Layered Transition Metal Oxide: Electrochemical Impact, Origin, and Control." Accounts of Chemical Research 52 8:2201-2209 (June. 2019).
Abstract:Lithium ion batteries (LIBs) not only power most of today’s hybrid electric vehicles (HEV) and electric vehicles (EV) but also are considered as a promising system for grid-level storage. Large-scale applications for LIBs require substantial improvement in energy density, cost, and lifetime. Layered lithium transition metal (TM) oxides, in particular, Li(NixMnyCoz)O2 (NMC, x + y + z = 1) are the most promising candidates as cathode materials with the potential to increase energy densities and lifetime, reduce costs, and improve safety. In order to further boost Li storage capacity, a great deal of attention has been directed toward developing Ni-rich layered TM oxides. However, structural disorder as a result of Ni/Li exchange in octahedral sites becomes a critical issue when Ni content increases to high values, as it leads to a detrimental effect on Li diffusivity, cycling stability, first-cycle efficiency, and overall electrode performance. Increasing effort has been dedicated to improving the electrochemical performance of layered TM oxides via reduction of cationic mixing. Therefore, it is important to summarize this research field and provide in-depth insight into the impact of Ni/Li disordering on electrochemical characteristics in layered TM oxides and its origin to accelerate the future development of layered TM oxides with high performance.

Chaojiang Niu, Huilin Pan, Wu Xu, Jie Xiao, Ji-Guang Zhang, Langli Luo, Chongmin Wang, Donghai Mei, Jiashen Meng, Xuanpeng Wang, Ziang Liu, Liqiang Mai, Jun Liu."Self-smoothing anode for achieving high-energy lithium metal batteries under realistic conditions."Nature Nanotechnology 14: 594-601 (June 2019).
Abstract: Despite considerable efforts to stabilize lithium metal anode structures and prevent dendrite formation, achieving long cycling life in high-energy batteries under realistic conditions remains extremely difficult due to a combination of complex failure modes that involve accelerated anode degradation and the depletion of electrolyte and lithium metal. Here we report a self-smoothing lithium–carbon anode structure based on mesoporous carbon nanofibres, which, coupled with a lithium nickel–manganese–cobalt oxide cathode with a high nickel content, can lead to a cell-level energy density of 350–380 Wh kg⁻¹ (counting all the active and inactive components) and a stable cycling life up to 200 cycles. These performances are achieved under the realistic conditions required for practical high-energy rechargeable lithium metal batteries: cathode loading ≥4.0 mAh cm⁻², negative to positive electrode capacity ratio ≤2 and electrolyte weight to cathode capacity ratio ≤3 g Ah⁻¹. The high stability of our anode is due to the amine functionalization and the mesoporous carbon structures that favour smooth lithium deposition.

Twitchell JB."A Review of State-Level Policies on Electrical Energy Storage."Current Sustainable/Renewable Energy Reports 6 (2): 35-41 (June 2019).
Abstract: Since California adopted its energy storage mandate in 2013, 14 other states have developed energy storage policies designed to encourage adoption or reduce barriers. This paper reviews those efforts to identify what types of policies are being developed, the underlying goals and rationale behind different approaches, and the early outcomes of those policies. State activity related to energy storage has accelerated in recent years, and numerous policies have emerged. Generally, those policies take one of two approaches: facilitating operational experience with energy storage by ensuring its presence on the grid, or enabling future deployments by removing or reducing barriers. Through detailed review of state policy actions, this paper explores the drivers, design, and implementation of these five specific types of energy storage policy. A taxonomy of state policies related to energy storage is presented, as well as recent research findings that support the different approaches and specific examples of how, where, and why those policies have been implemented. Finally, early impacts of these policies are considered.

Biwei Xiao, Kuan Wang, Gui-Liang Xu, Junhua Song, Zonghai Chen, Khalil Amine, David Reed, Maling Sui, Vincent Sprenkle, Yang Ren, Pengfei Yan, Xiaolin Li."Revealing the Atomic Origin of Heterogeneous Li‐Ion Diffusion by Probing Na."Advanced Materials 31 (29): 1005889 (May 2019).
Abstract: Tracing the dynamic process of Li‐ion transport at the atomic scale has long been attempted in solid state ionics and is essential for battery material engineering. Approaches via phase change, strain, and valence states of redox species have been developed to circumvent the technical challenge of direct imaging Li; however, all are limited by poor spatial resolution and weak correlation with state‐of‐charge (SOC). An ion‐exchange approach is adopted by sodiating the delithiated cathode and probing Na distribution to trace the Li deintercalation, which enables the visualization of heterogeneous Li‐ion diffusion down to the atomic level. In a model LiNi_1/3Mn_1/3Co_1/3O₂ cathode, dislocation‐mediated ion diffusion is kinetically favorable at low SOC and planar diffusion along (003) layers dominates at high SOC. These processes work synergistically to determine the overall ion‐diffusion dynamics. The heterogeneous nature of ion diffusion in battery materials is unveiled and the role of defect engineering in tailoring ion‐transport kinetics is stressed.

Gyujin Song, Jun Young Cheong, Chanhoon Kim, Langli Luo, Chihyun Hwang, Sungho Choi, Jaegeon Ryu, Sungho Kim, Hyun-Kon Song, Chongmin Wang, II-Doo Kim, Soojin Park."Atomic-scale combination of germanium-zinc nanofibers for structural and electrochemical evolution."Nature Communications 10, Article number 2364 (May 2019).
Abstract: Alloys are recently receiving considerable attention in the community of rechargeable batteries as possible alternatives to carbonaceous negative electrodes; however, challenges remain for the practical utilization of these materials. Herein, we report the synthesis of germanium-zinc alloy nanofibers through electrospinning and a subsequent calcination step. Evidenced by in situ transmission electron microscopy and electrochemical impedance spectroscopy characterizations, this one-dimensional design possesses unique structures. Both germanium and zinc atoms are homogenously distributed allowing for outstanding electronic conductivity and high available capacity for lithium storage. The as-prepared materials present high rate capability (capacity of ~ 50% at 20 C compared to that at 0.2 C-rate) and cycle retention (73% at 3.0 C-rate) with a retaining capacity of 546 mAh g⁻¹ even after 1000 cycles. When assembled in a full cell, high energy density can be maintained during 400 cycles, which indicates that the current material has the potential to be used in a large-scale energy storage system.

Jaegeon Ryu, Ji Hui Seo, Gyujin Song, Keunsu Choi, Dongki Hong, Chongmin Wang, Hosik Lee, Jun Hee Lee, Soojin Park."Infinitesimal sulfur fusion yields quasi-metallic bulk silicon for stable and fast energy storage."Nature Communications 10, Article number 2351 (May 2019).
Abstract: A fast-charging battery that supplies maximum energy is a key element for vehicle electrification. High-capacity silicon anodes offer a viable alternative to carbonaceous materials, but they are vulnerable to fracture due to large volumetric changes during charge–discharge cycles. The low ionic and electronic transport across the silicon particles limits the charging rate of batteries. Here, as a three-in-one solution for the above issues, we show that small amounts of sulfur doping (<1 at%) render quasi-metallic silicon microparticles by substitutional doping and increase lithium ion conductivity through the flexible and robust self-supporting channels as demonstrated by microscopy observation and theoretical calculations. Such unusual doping characters are enabled by the simultaneous bottom-up assembly of dopants and silicon at the seed level in molten salts medium. This sulfur-doped silicon anode shows highly stable battery cycling at a fast-charging rate with a high energy density beyond those of a commercial standard anode.

Chaojiang Niu, Hongkyung Lee, Shuru Chen, Qiuyan Li, Jason Du, Wu Xu, Ji-Guang Zhang, M. Stanley Whittingham, Jie Xiao, Jun Liu."High-energy lithium metal pouch cells with limited anode swelling and long stable cycles."Nature Energy 4: 551-559 (May 2019).
Abstract: Lithium metal anodes have attracted much attention as candidates for high-energy batteries, but there have been few reports of long cycling behaviour, and the degradation mechanism of realistic high-energy Li metal cells remains unclear. Here, we develop a prototypical 300 Wh kg⁻¹ (1.0 Ah) pouch cell by integrating a Li metal anode, a LiNi_0.6Mn_0.2Co_0.2O₂ cathode and a compatible electrolyte. Under small uniform external pressure, the cell undergoes 200 cycles with 86% capacity retention and 83% energy retention. In the initial 50 cycles, flat Li foil converts into large Li particles that are entangled in the solid-electrolyte interphase, which leads to rapid volume expansion of the anode (cell thickening of 48%). As cycling continues, the external pressure helps the Li anode maintain good contact between the Li particles, which ensures a conducting percolation pathway for both ions and electrons, and thus the electrochemical reactions continue to occur. Accordingly, the solid Li particles evolve into a porous structure, which manifests in substantially reduced cell swelling by 19% in the subsequent 150 cycles.

Zhe Peng, Feihong Ren, Shanshan Yang, Muqin Wang, Jie Sun, Deyu Wang, Wu Xu, Ji-Guang Zhang."A highly stable host for lithium metal anode enabled by Li₉Al₄-Li₃N-AlN structure."Nano Energy 59: 110-119 (May 2019).
Abstract: Lithium (Li) metal battery is one of the ideal candidates for the next-generation high-energy-density batteries, but its practical application is still plagued by its large volume change, low coulombic efficiency (CE), and safety issues related to dendrite growth. This work describes a potential solution to these issues using a cross-linked Li₉Al₄-Li₃N-AlN (LLA) structure as a stable host for Li metal anode. The in situ-formed uniform Li₉Al₄ and Li₃N sites on AlN nano-clusters can suppress dendrite growth during the Li plating/stripping process. The intrinsic lithiophilicity of Li₉Al₄ sites with adjacent Li₃N attracts Li⁺ ions for fast migration and uniform plating/stripping. These unique features lead to dimensional stability of Li@LLA composite anodes (1540 mAh g⁻¹ and 1600 mAh cm⁻³). High-rate, high-capacity cycling of Li metal anodes has been maintained with a CE of ~98% in carbonate-based electrolytes. High capacity retention of 90.1% is achieved for a Li@LLA||LiNi_0.8Co_0.1Mn_0.1O₂ full cell at the 200th cycle. Therefore, the LLA structure with a simple fabrication process could be a promising candidate to enhance the safety of next-generation Li metal batteries.

Pengfei Yan, Jianming Zheng, Zhen-Kun Tang, Arun Devaraj, Guoying Chen, Khalil Amine, Ji-Guang Zhang, Li-Min Liu, Chongmin Wang."Injection of oxygen vacancies in the bulk lattice of layered cathodes."Nature Nanotechnology 14: 602-608 (April 2019).
Abstract: Surfaces, interfaces and grain boundaries are classically known to be sinks of defects generated within the bulk lattice. Here, we report an inverse case by which the defects generated at the particle surface are continuously pumped into the bulk lattice. We show that, during operation of a rechargeable battery, oxygen vacancies produced at the surfaces of lithium-rich layered cathode particles migrate towards the inside lattice. This process is associated with a high cutoff voltage at which an anionic redox process is activated. First-principle calculations reveal that triggering of this redox process leads to a sharp decrease of both the formation energy of oxygen vacancies and the migration barrier of oxidized oxide ions, therefore enabling the migration of oxygen vacancies into the bulk lattice of the cathode. This work unveils a coupled redox dynamic that needs to be taken into account when designing high-capacity layered cathode materials for high-voltage lithium-ion batteries.

Bin Liu, Wu Xu, Lingli Luo, Jianming Zheng, Xiaodi Ren, Hui Wang, Mark H. Engelhard, Chongmin Wang, Ji-Guang Zhang."Highly Stable Oxygen Electrodes Enabled by Catalyst Redistribution through an In Situ Electrochemical Method."Advanced Energy Materials 9 (15): 1803598 (April 2019).
Abstract: In this work, for the first time an in situ electrochemical pretreatment approach to fabricate a highly reversible oxygen electrode with redistributed ultrafine RuO₂ catalysts on a carbon nanotube (CNT) matrix is reported. The optimally pretreated RuO₂/CNT oxygen electrodes demonstrate an extremely stable cycling life, 800 times with non‐Li metal anode, under a capacity‐limited protocol of 800 mAh g⁻¹ in an ether‐based electrolyte in an O₂ environment. The highly stable activity of ultrafine RuO₂ catalysts in oxygen reduction and evolution processes originates from the synergetic effect of greatly reduced size of catalyst (<2 nm) and uniform redistribution of catalyst particles after the in situ electrochemical pretreatment process. The pretreatment method discovered in this work can not only significantly enhance the activity/efficiency of the catalysts used for air electrodes but can also be widely applied to other electro‐catalysis systems.

Shuru Chen, Chaojing Niu, Hongkyung Lee, Qiuyan Li, Lu Yu, Wu Xu, Ji-Guang Zhang, Eric J. Dufek, M. Stanley Whittingham, Shirley Meng, Jie Xiao, Jun Liu."Critical Parameters for Evaluating Coin Cells and Pouch Cells of Rechargeable Li-Metal Batteries."Joule 3 (4): 1094-1105 (April 2019).
Abstract: Lithium-metal anode has regained broad interest because of the steadily increasing demand for high-energy batteries. In this paper, we first investigate and demonstrate how the cycle performance of Li-metal batteries varied depending on the critical experimental parameters of coin cells, such as the electrolyte amount, Li-metal thickness, and the cathode loading. We then design and build a representative Li-metal pouch cell with specific energy of 300 Wh/kg to provide an effective validation of electrode materials and accurate cell performance evaluations. Finally, we propose a set of coin-cell parameters and testing conditions for the battery research community to bridge the gap between fundamental research and practical adoption of new ideas or materials and to expedite their full integration into realistic battery systems.

Xiaodi Ren, Lianfeng Zou, Shuhong Jiao, Donghai Mei, Mark H. Engelhard, Qiuyan Li, Hongkyung Lee, Chaojiang Niu, Brian D. Adams, Chongmin Wang, Jun Liu, Ji-Guang Zhang, Wu Xu."High-Concentration Ether Electrolytes for Stable High-Voltage Lithium Metal Batteries."ACS Energy Letters 4 (4), 896-902 (April 2019).
Abstract: High-voltage (>4.3 V) rechargeable lithium (Li) metal batteries (LMBs) face huge obstacles due to the high reactivity of Li metal with traditional electrolytes. Despite their good stability with Li metal, conventional ether-based electrolytes are typically used only in <4.0 V LMBs because of their limited oxidation stability. Here we report high-concentration ether electrolytes that can induce the formation of a unique cathode electrolyte interphase via the synergy between the salt and the ether solvent, which effectively stabilizes the catalytically active cathodes and preserves their structural integrity under high voltages. Eventually, LMBs can retain 92% capacity after 500 cycles at 4.3 V with very limited Li consumption. More importantly, such ether electrolytes enable stable battery cycling not only under voltages as high as 4.5 V but also on highly demanding Ni-rich layered cathodes. These findings significantly expand knowledge of ether electrolytes and provide new perspectives of electrolyte design for high-energy-density LMBs.

Runwei Mo, Fan Li, Xinyi Tan, Pengcheng Xu, Ran Tao, Gurong Shen, Xing Lu, Fang Liu, Li Shen, Bin Xu, Qiangfeng Xiao, Xiang Wang, Chongmin Wang, Jinlai Li, Ge Wang, Yunfeng Lu."High-quality mesoporous graphene particles as high-energy and fast-charging anodes for lithium-ion batteries."Nature Communications 10, Article number 1474 (April 2019).
Abstract: The application of graphene for electrochemical energy storage has received tremendous attention; however, challenges remain in synthesis and other aspects. Here we report the synthesis of high-quality, nitrogen-doped, mesoporous graphene particles through chemical vapor deposition with magnesium-oxide particles as the catalyst and template. Such particles possess excellent structural and electrochemical stability, electronic and ionic conductivity, enabling their use as high-performance anodes with high reversible capacity, outstanding rate performance (e.g., 1,138 mA h g⁻¹ at 0.2 C or 440 mA h g⁻¹ at 60 C with a mass loading of 1 mg cm⁻²), and excellent cycling stability (e.g., >99% capacity retention for 500 cycles at 2 C with a mass loading of 1 mg cm⁻²). Interestingly, thick electrodes could be fabricated with high areal capacity and current density (e.g., 6.1 mA h cm⁻² at 0.9 mA cm⁻²), providing an intriguing class of materials for lithium-ion batteries with high energy and power performance.

Vijayakumar Murugesan, Jong Soo Cho, Niranjan Govind, Amity Andersen, Matthew J. Olszta, Kee Sung Han, Guosheng Li, Hongkyung Lee, David M. Reed, Vincent L. Sprenkle, Sungjin Cho, Satish K. Nune, Daiwon Choi."Lithium Insertion Mechanism in Iron Fluoride Nanoparticles Prepared by Catalytic Decomposition of Fluoropolymer."ACS Applied Energy Materials 2 (3): 1832-1843 (March 2019).
Abstract: Metal fluorides with high redox potential and capacity from strong metal–fluoride bond and conversion reaction make them promising cathodic materials. However, detailed lithium insertion and extraction mechanisms have not yet been clearly understood and explained. Here we report low-temperature synthesis of electrochemically active FeF₃/FeF₂ nanoparticles by catalytic decomposition of a fluoropolymer [perfluoropolyether (PFPE)] using a hydrated iron oxalate precursor both in air and in inert atmosphere. Freshly synthesized FeF₃ nanoparticle delivered specific capacity above 210 mAh/g with decent cycling performance as a Li-ion battery cathode. Both in situ and ex situ characterization techniques were used to investigate the detailed PFPE decomposition and fluorination mechanisms leading to FeF₃/FeF₂ formation as well as the lithium insertion mechanism in a FeF₃ cathode. Specifically, a detailed understanding was investigated using thermogravimetry–mass spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, nuclear magnetic resonance, transmission electron microscopy, scanning electron microscopy/energy dispersive spectroscopy, and X-ray absorption near-edge structure. The novel synthesis route developed not only offers access to electrochemically active metal fluorides but also offers a catalytic approach for decomposing highly inert fluoropolymers for environmental protection.

Jun Liu, Zhenan Bao, Yi Cui, Eric J. Dufek, John B. Goodenough, Peter Khalifah, Qiuyan Li, Bor Yann Liaw, Ping Liu, Arumugam Manthiram, Y. Shirley Meng, Venkat R. Subramanian, Michael F. Toney, Vilayanur V. Viswanathan, M. Stanley Whittingham, Jie Xiao, Wu Xu, Jihui Yang, Xiao-Qing Yang, Ji-Guang Zhang."Pathways for practical high-energy long-cycling lithium metal batteries."Nature Energy 4, 180-186 (March 2019).
Abstract: State-of-the-art lithium (Li)-ion batteries are approaching their specific energy limits yet are challenged by the ever-increasing demand of today’s energy storage and power applications, especially for electric vehicles. Li metal is considered an ultimate anode material for future high-energy rechargeable batteries when combined with existing or emerging high-capacity cathode materials. However, much current research focuses on the battery materials level, and there have been very few accounts of cell design principles. Here we discuss crucial conditions needed to achieve a specific energy higher than 350 Wh kg⁻¹, up to 500 Wh kg⁻¹, for rechargeable Li metal batteries using high-nickel-content lithium nickel manganese cobalt oxides as cathode materials. We also provide an analysis of key factors such as cathode loading, electrolyte amount and Li foil thickness that impact the cell-level cycle life. Furthermore, we identify several important strategies to reduce electrolyte-Li reaction, protect Li surfaces and stabilize anode architectures for long-cycling high-specific-energy cells.

Yuliang Cao, Matthew Li, Jun Lu, Jun Liu, Khalil Amine."Bridging the academic and industrial metrics for next-generation practical batteries."Nature Nanotechnology 14, 200-207 (March 2019).
Abstract: Batteries have shaped much of our modern world. This success is the result of intense collaboration between academia and industry over the past several decades, culminating with the advent of and improvements in rechargeable lithium-ion batteries. As applications become more demanding, there is the risk that stunted growth in the performance of commercial batteries will slow the adoption of important technologies such as electric vehicles. Yet the scientific literature includes many reports describing material designs with allegedly superior performance. A considerable gap needs to be filled if we wish these laboratory-based achievements to reach commercialization. In this Perspective, we discuss some of the most relevant testing parameters that are often overlooked in academic literature but are critical for practical applicability outside the laboratory. We explain metrics such as anode energy density, voltage hysteresis, mass of non-active cell components and anode/cathode mass ratio, and we make recommendations for future reporting. We hope that this Perspective, together with other similar guiding principles that have recently started to emerge, will aid the transition from lab-scale research to next-generation practical batteries.

Jinhong Lee, Yun-Jung Kim, Hyun Soo Jin, Hyungjun Hoh, Hobeom Kwack, Hyunwon Chu, Fangmin Ye, Hongkyung Lee, Hee-Tak Kim."Tuning Two Interfaces with Fluoroethylene Carbonate Electrolytes for High-Performance Li/LCO Batteries."ACS Omega 4 (2), 3220-3227 (February 2019).
Abstract: Various electrolytes have been reported to enhance the reversibility of Li-metal electrodes. However, for these electrolytes, concurrent and balanced control of Li-metal and positive electrode interfaces is a critical step toward fabrication of high-performance Li-metal batteries. Here, we report the tuning of Li-metal and lithium cobalt oxide (LCO) interfaces with fluoroethylene carbonate (FEC)-containing electrolytes to achieve high cycling stability of Li/LCO batteries. Reversibility of the Li-metal electrode is considerably enhanced for electrolytes with high FEC contents, confirming the positive effect of FEC on the stabilization of the Li-metal electrode. However, for FEC contents of 50 wt % and above, the discharge capacity is significantly reduced because of the formation of a passivation layer on the LCO cathodes. Using balanced tuning of the two interfaces, stable cycling over 350 cycles at 1.5 mA cm^–2 is achieved for a Li/LCO cell with the 1 M LiPF₆ FEC/DEC = 30/70 electrolyte. The enhanced reversibility of the Li-metal electrode is associated with the formation of LiF and polycarbonate in the FEC-derived solid electrolyte interface (SEI) layer. In addition, electrolytes with high FEC contents lead to lateral Li deposition on the sides of Li deposits and larger dimensions of rodlike Li deposits, suggesting the elastic and ion-conductive nature of the FEC-derived SEI layer.

Vaithiyalingam Shutthanandan, Manjula Nandasiri, Jianming Zheng, Mark H. Engelhard, Wu Xu, Suntharampillai Thevuthasan, Vijayakumar Murugesan."Applications of XPS in the Characterization of Battery Materials."Journal of Electron Spectroscopy and Related Phenomena 231:2-10 (February 2019).
Abstract: Technological development requires reliable power sources where energy storage devices are emerging as a critical component. Wide range of energy storage devices, Redox-flow batteries (RFB), Lithium ion based batteries (LIB), and Lithium-sulfur (LSB) batteries are being developed for various applications ranging from grid-scale level storage to mobile electronics. Material complexities associated with these energy storage devices with unique electrochemistry are formidable challenge which needs to be address for transformative progress in this field. X-ray photoelectron spectroscopy (XPS) - a powerful surface analysis tool - has been widely used to study these energy storage materials because of its ability to identify, quantify and image the chemical distribution of redox active species. However, accessing the deeply buried solid-electrolyte interfaces (which dictates the performance of energy storage devices) has been a challenge in XPS usage. Herein we report our recent efforts to utilize the XPS to gain deep insight about these interfaces under realistic conditions with varying electrochemistry involving RFB, LIB and LSB.

Amity Andersen, Nav Nidhi Rajput, Kee Sung Han, Huilin Pan, Niranjan Govind, Kristin A. Persson, Karl T. Mueller, Vijayakumar Murugesan."Structure and Dynamics of Polysulfide Clusters in a Nonaqueous Solvent Mixture of 1,3-Dioxolane and 1,2-Dimethoxyethane."Chemistry of Materials 31 (7): 2308-2319 (February 2019).
Abstract: Molecular clustering and associated dynamic processes of lithium polysulfide species were unraveled using classical molecular dynamics and ab initio metadynamics calculations. The spectroscopic signatures of polysulfide clusters were analyzed using a multimodal analysis including experimental and computational nuclear magnetic resonance (NMR) and X-ray absorption spectroscopies. Lithium polysulfide solutes (Li₂S₄, Li₂S₆, and Li₂S₈) and their mixtures in a 1,3-dioxolane and 1,2-dimethoxyethane (DOL/DME) solvent undergo aggregation driven by intramolecular lithium–sulfur (Li–S) interactions, leading to distributions of cluster sizes, which could critically influence the functioning of lithium–sulfur batteries. Representative polysulfide clusters with systematic increases in molecular size were extracted from the classical molecular dynamics trajectories for subsequent structural and spectroscopic property calculations using density functional theory analysis. Structural analysis of these clusters reveals progressively decreasing solvent involvement in Li⁺ coordination varying from Li₂S₄ to Li₂S₈, with more pronounced variation and changes in DME compared with those in DOL. These observations are reflected in the analysis of the experimental and theoretical ⁷Li and ¹⁷O NMR chemical shifts and pulsed field gradient-NMR diffusion measurements. A comparison of experimental and theoretical S K-edge X-ray absorption near edge spectra shows that relatively large lithium sulfide chain clusters are likely to occur in the DOL/DME-solvated lithium sulfide systems. Ab initio metadynamics simulations and NMR analysis indicate that Li⁺ solvated by only the solvent can occur through Li⁺ dissociation from sulfide chains. However, the occurrence of “sulfide-free” Li⁺ is a minor mechanism compared with the dynamic aggregation and shuttling processes of polysulfide solvates in DOL/DME-based electrolytes of Li–S batteries. Overall, atomistic insights gained about clustering and lithium exchange dynamics will be critical for the predictive understanding of the polysulfide shuttling and nucleation process that dictates the Li–S battery performance.

Shidong Song, Limei Yu, Yanli Ruan, Jian Sun, Butian Chen, Wu Xu, Ji-Guang Zhang."Highly efficient Ru/B₄C multifunctional oxygen electrode for rechargeable LiO₂ batteries."Journal of Power Sources 413: 11-19 (February 2019).
Abstract: Irreversible parasitic reactions and the resulting accumulation of insulating side products are main barriers for practical application of rechargeable lithium–oxygen (LiO₂) batteries. Therefore, it is critical to develop multifunctional oxygen electrodes suitable for oxygen reduction reaction, oxygen evolution reaction, and decomposition of side reaction products. Here we report the application of ultrafine ruthenium on boron carbide (Ru/B₄C) with highly efficient multifunctional activities as carbon-free oxygen electrodes for LiO₂ batteries. Li₂CO₃ and LiOH can be completely decomposed by Ru/B₄C at 4.0 V and 4.1 V, respectively, within the stability window of the electrolyte. A LiO₂ battery using the Ru/B₄C oxygen electrode achieves low overpotentials for LiO₂ reactions, and excellent cycling performance under the capacities of 300 and 500 mAh g⁻¹Ru/B₄C. In-situ gas chromatography analysis reveals that O₂ is the major gas product during charging. Only a negligible amount of CO₂ is observed in the first charging process. Therefore, Ru/B₄C can be a very promising oxygen-electrode material for LiO₂ batteries and Li–air batteries operated in ambient air.

Dana Jin, Sangjin Choi, Woosun Jang, Aloysius Soon, Jeongmin Kim, Hongjae Moon, Wooyoung Lee, Younki Lee, Sori Son, Yoon-Cheol Park, Hee-Jung Chang, Guosheng Li, Keeyoung Jung, Wooyoung Shim."Bismuth Islands for Low-Temperature Sodium-Beta Alumina Batteries."ACS Applied Materials & Interfaces 11 (3):2917-2924 (January 2019).
Abstract: Wetting of the liquid metal on the solid electrolyte of a liquid metal battery controls the operating temperature and performance of the battery. Liquid sodium electrodes are particularly attractive because of their low cost, natural abundance, and geological distribution. However, they wet poorly on a solid electrolyte near its melting temperature, limiting their widespread suitability for low-temperature batteries to be used for large-scale energy storage systems. Herein, we develop an isolated metal-island strategy that can improve sodium wetting in sodium-beta alumina batteries that allows operation at lower temperatures. Our results suggest that in situ heat treatment of a solid electrolyte followed by bismuth deposition effectively eliminates oxygen and moisture from the surface of the solid electrolyte, preventing the formation of an oxide layer on the liquid sodium, leading to enhanced wetting. We also show that employing isolated bismuth islands significantly improves cell performance, with cells retaining 94% of their charge after the initial cycle, an improvement over cells without bismuth islands. These results suggest that coating isolated metal islands is a promising and straightforward strategy for the development of low-temperature sodium-β alumina batteries.

Biwei Xiao, Teofilo Rojo, Xiaolin Li."Hard Carbon as Sodium‐Ion Battery Anodes: Progress and Challenges."ChemSusChem 12 (1):133-144 (January 2019).
Abstract: Hard carbon (HC) is the state‐of‐the‐art anode material for sodium‐ion batteries due to its excellent overall performance, wide availability, and relatively low cost. Recently, tremendous effort has been invested to elucidate the sodium storage mechanism in HC, and to explore synthetic approaches that can enhance the performance and lower the cost. However, disagreements remain in the field, particularly on the fundamental questions of ion transfer and storage and the ideal HC structure for high performance. This Minireview aims to provide an analysis and summary of the theoretical limitations of HC, discrepancies in the storage mechanism, and methods to improve the performance. Finally, future research on developing ideal structured HCs, advanced electrolytes, and optimized electrolyte–electrode interphases are proposed on the basis of recent progress.

Junhua Song, Dongdong Xiao, Jaiping Jia, Guomin Zhu, Mark Engelhard, Biwei Xiao, Shuo Feng, Dongsheng Li, David Reed, Vincent Sprenkle, Yuehe Lin, Xiaolin Li."A comparative study of pomegranate Sb@C yolk–shell microspheres as Li and Na-ion battery anodes."Nanoscale 11 (1): 348-355 (January 2019).
Abstract: Alloy-based nanostructure anodes have the privilege of alleviating the challenges of large volume expansion and improving the cycling stability and rate performance for high energy lithium- and sodium-ion batteries (LIBs and SIBs). Yet, they face the dilemma of worsening the parasitic reactions at the electrode–electrolyte interface and low packing density for the fabrication of practical electrodes. Here, pomegranate Sb@C yolk–shell microspheres were developed as a high-performance anode for LIBs and SIBs with controlled interfacial properties and enhanced packing density. Although the same yolk–shell nanostructure (primary particle size, porosity) and three-dimensional architecture alleviated the volume change induced stress and swelling in both batteries, the SIBs show 99% capacity retention over 200 cycles, much better than the 78% capacity retention of the LIBs. The comparative electrochemical study and X-ray photoelectron spectroscopy characterization revealed that the different SEIs, besides the distinct phase transition mechanism, played a critical role in the divergent cycling performance.

Hongkyung Lee, Hyung-Seok Lim, Xiaodi Ren, Lu Yu, Mark H. Engelhard, Kee Sung Han, Jinhong Lee, Hee-Tak Kim, Jie Xiao, Jun Liu, Wu Xu, Ji-Guang Zhang."Detrimental Effects of Chemical Crossover from the Lithium Anode to Cathode in Rechargeable Lithium Metal Batteries."ACS Energy Letters 3 (12), 2921-2930 (December 2018).
Abstract: Interfacial stability is one of the crucial factors for long-term cyclability of lithium (Li) metal batteries (LMBs). While cross-contamination phenomena have been well-studied in Li-ion batteries (LIBs), similar phenomena have rarely been reported in LMBs. Here, we investigated cathode failure triggered by chemical crossover from the anode in LMBs. In contrast to LIBs, the cathode in LMBs suffers more significant capacity fading, and its capacity cannot be fully recovered by replacing the Li anode. In-depth surface characterization reveals severe deterioration related to the accumulation of highly resistive polymeric components in the cathode–electrolyte interphase. The soluble byproducts generated by extensive electrolyte decomposition at the Li metal surface can diffuse toward the cathode side, resulting in severe deterioration of the cathode and separator surfaces. A selective Li-ion permeable separator with a polydopamine coating has been developed to mitigate the detrimental chemical crossover and enhance the cathode stability.

Jian Zhi Hu, Nicholas R. Jaegers, Mary Y Hu, Karl T. Mueller."In situ and ex situ NMR for battery research."Journal of Physics: Condensed Matter 30 (46) (November 2018).
Abstract: A rechargeable battery stores readily convertible chemical energy to operate a variety of devices such as mobile phones, laptop computers, electric automobiles, etc. A battery generally consists of four components: a cathode, an anode, a separator and electrolytes. The properties of these components jointly determine the safety, the lifetime, and the electrochemical performance. They also include, but are not limited to, the power density and the charge as well as the recharge time/rate associated with a battery system. An extensive amount of research is dedicated to understanding the physical and chemical properties associated with each of the four components aimed at developing new generations of battery systems with greatly enhanced safety and electrochemical performance at a significantly reduced cost for large scale applications. Advanced characterization tools are a prerequisite to fundamentally understanding battery materials. Considering that some of the key electrochemical processes can only exist under in situ conditions, which can only be captured under working battery conditions when electric wires are attached and current and voltage are applied, make in situ detection critical. Nuclear magnetic resonance (NMR), a non-invasive and atomic specific tool, is capable of detecting all phases, including crystalline, amorphous, liquid and gaseous phases simultaneously and is ideal for in situ detection on a working battery system. Ex situ NMR on the other hand can provide more detailed molecular or structural information on stable species with better spectral resolution and sensitivity. The combination of in situ and ex situ NMR, thus, offers a powerful tool for investigating the detailed electrochemistry in batteries.

Xiaochuan Lu, Hee-Jung Chang, Jeffery F. Bonnett, Nathan L. Canfield, Keeyoung Jung, Vincent L. Sprenkle, Guosheng Li."An Intermediate-Temperature High-Performance Na–ZnCl₂ Battery."ACS Omega 3 (11): 15702-15708 (November 2018).
Abstract: The Na−β-alumina battery (NBB) is one of the most promising energy storage technologies for integrating renewable energy resources into the grid. In the family of NBBs, Na–NiCl₂ battery has been extensively studied during the past decade because it has a lower operating temperature, better safety, and good battery performance. One of the major issues with the Na–NiCl₂ battery is material cost, which is primarily from Ni metal in the battery cathode. As an alternative, Zn is much cheaper than Ni, and replacing Ni with Zn in the cathode can significantly reduce the cost. In this work, we investigate the performance and reaction mechanism for a Na–ZnCl₂ battery at 190 °C. Two-step reversible reactions are identified. During the first step of charging, NaCl reacts with Zn to produce a ribbon-type Na₂ZnCl₄ layer. This layer is formed at the NaCl–Zn interface rather than covering the surface of the Zn particles, which leads to an excellent cell rate capability. During the second step, the produced Na₂ZnCl₄ is gradually consumed to form ZnCl₂ on the surface of Zn particles. The formed ZnCl₂ covers most of the surface area of the Zn particles and shows a limited rate capability compared to that of the first step. We conclude that this limited performance of the second step is due to the passivation of Zn particles by ZnCl₂, which blocks the electron pathway of the NaCl–Zn cathodes.

Kuber Mishra, Wu Xu, Mark Engelhard, Ruiguo Cao, Jie Xiao, Ji-Guang Zhang, Xiao-Dong Zhou."The Effect of Solvent on the Capacity Retention in a Germanium Anode for Lithium Ion Batteries."Journal of Electrochemical Conversion and Storage 15 (4)041012 (November 2018).
Abstract: A thin and mechanically stable solid electrolyte interphase (SEI) is desirable for a stable cyclic performance in a lithium ion battery. For the electrodes that undergo a large volume expansion, such as Si, Ge, and Sn, the presence of a robust SEI layer can improve the capacity retention. In this work, the role of solvent choice on the electrochemical performance of Ge electrode is presented by a systematic comparison of the SEI layers in ethylene carbonate (EC)-based and fluoroethylene carbonate (FEC)-based electrolytes. The results show that the presence of FEC as a cosolvent in a binary or ternary solvent electrolyte results in an excellent capacity retention of ∼85% after 200 cycles at the current density of 500 mA g−1; while EC-based electrode suffers a rapid capacity degradation with a capacity retention of just 17% at the end of 200 cycles. Post analysis by an extensive use of X-ray photoelectron spectroscopy (XPS) was carried out, which showed that the presence of Li₂O in FEC-based SEIs was the origin for the improved electrochemical performance.

Hongkyung Lee, Shuru Chen, Xiaodi Ren, Abraham Martinez, Vaithiyalingam Shutthanandan, Vijayakumar Murugesan, Kee Sung Han, Qiuyan Li, Jun Liu, Wu Xu, Ji-Guang Zhang."Electrode Edge Effects and the Failure Mechanism of Lithium‐Metal Batteries."ChemSusChem 11 (21) 3821-3828 (November 2018).
Abstract: The very high specific capacity of Li metal makes it an ideal anode for high‐energy batteries. However, Li dendrite growth and the formation of isolated (or “dead”) Li during repeated Li plating/stripping processes leads to a low coulombic efficiency (CE). In this work, we discovered, for the first time, that electrode edge effects play an important role in the failure of Li‐metal batteries. The dead Li formed on the edge of Cu substrate was systematically investigated through SEM, energy‐dispersive X‐ray (EDX) spectroscopy, and 2D X‐ray photoelectron spectroscopy (XPS). To minimize the Li loss at the edge of the Cu exposed to pressure‐free space, a modified Li∥Cu cell configuration with a Cu electrode smaller than Li metal is preferred. It was clearly demonstrated that using an electrode configuration with a minimal open space or pressure‐free space across electrodes can reduce accumulation of dead Li during cycling and increase Li CE. This phenomenon was also verified in Li‐metal batteries (Li∥LiNi_1/3Mn_1/3Co_1/3O₂) and should be considered in the design of practical Li‐metal batteries.

Yun-Jung Kim, Hyun S. Jin, Dong-Hyun Lee, Jaeho Choi, Wonhee Jo, Hyungjun Noh, Jinhong Lee, Hyunwon Chu, Hobeom Kwack, Fangmin Ye, Hongkyung Lee, Myung-Hyun Ryou, Hee-Tak Kim."Guided Lithium Deposition by Surface Micro‐Patterning of Lithium‐Metal Electrodes."ChemElectroChem 5 (21), 3169-3175 (November 2018).
Abstract: Uncontrolled lithium (Li) deposition has hampered the evolution of Li‐metal electrode‐based Li‐batteries. In this work, we report the differences of a guided Li deposition with a size change of the square hole micro‐patterns carved on the Li‐metal surface with two different dimensions using a simple stamping method. Li deposition is preferentially initiated on the top edge for the smaller pattern and on the bottom for the larger pattern. Although the two patterns lead to a more uniform utilization of the Li, the larger pattern shows a higher cycling stability within a LiFePO₄/Li cell than that of the smaller one indicating that initiating the Li deposition from the bottom of the hole is more efficient in confining the deposited Li. Based on the impedance analysis of the compressed Li electrodes, we suggest that the guided Li deposition on the bottom of the hole is attributed to a large contrast in the resistance of native surface passivation layer between the top and hole surfaces. This improved understanding can further advance guided Li deposition induced by surface patterns for high performance Li‐metal batteries.

Ming-Shan Wang, Zhi-Qiang Wang, Ran Jia, Yi Yang, Fang-Yu Zhu, Zhen-Liang Yang, Yun Huang, Xing Li, Wu Xu."Facile electrostatic self-assembly of silicon/reduced graphene oxide porous composite by silica assist as high performance anode for Li-ion battery."Applied Surface Science 456: 379-389 (October 2018).
Abstract: Silicon(Si)/graphene composite has been regarded as one of the most promising candidates for next generation anode materials with high power and energy density in lithium ion batteries. Introduction of graphene in Si anodes could improve the electronic conductivity, suppress the severe volume expansion of Si, and facilitate the formation of stable solid electrolyte interphase, etc. However, traditionally mechanical mixing of Si and graphene cannot realize uniform distribution of Si particles on the graphene sheets, which would largely weaken the effectiveness of the graphene in the composite. In this work, nano-Si/reduced graphene oxide porous composite (p Si/rGO) has been fabricated by a facile electrostatic self-assembly approach via using SiO₂ as the sacrificial template. Compared with the simply mechanically mixed nano-Si and rGO (Si/rGO), the nano-Si particles could be more uniformly dispersed among the rGO sheets in the p Si/rGO, which significantly increases its electronic conductivity. Moreover, the drastic volume expansion of nano-Si during repeated lithiation/delithiation cycles also has been effectively accommodated by the large number of pores left after removing the SiO₂ template in the composite. Thus, the p Si/rGO presented largely enhanced electrochemical performances, showing a high reversible capacity up to 1849 mA h g⁻¹ at 0.2 A g⁻¹ with good capacity retention, and high rate capability (535 mA h g⁻¹ at 2 A g⁻¹).

Pengcheng Xu, Congxin Xie, Chenhui Wang, Qinzhi Lai, Wei Wang, Huamin Zhang, Xianfeng Li."A membrane-free interfacial battery with high energy density."Chemical Communications 82 (54):11262-11629 (October 2018).
Abstract: A new concept of the membrane-free interfacial battery based on a biphasic system was proposed for the first time. An aqueous ZnBr₂ solution was used as a negative electrolyte, while Br₂ in CCl₄ served as a positive electrolyte. This interfacial Zn/Br₂ battery demonstrated a very impressive performance with a CE of 96% and an EE of 81% at a current density of 15 mA cm⁻².

Hee-Jung Chang, Xiaochuan Lu, Jeffery F. Bonnett, Nathan L. Canfield, Keesung Han, Mark H. Engelhard, Keeyoung Jung, Vincent L. Sprenkle, Guosheng Li."Decorating β′′-alumina solid-state electrolytes with micron Pb spherical particles for improving Na wettability at lower temperatures."Journal of Materials Chemistry A 6 (40)19703-19711 (October 2018).
Abstract: Overcoming poor physical contact is one of the most critical hurdles for batteries using solid-state electrolytes. In particular, overpotential from the liquid–solid interface between molten sodium and a β′′-alumina solid-state electrolyte (BASE) in a sodium–metal halide (Na–MH) battery could be enormous at lower operating temperatures (<200 °C) due to intrinsically poor Na wetting on the BASE surface. In this work, we describe how surface modification with lead acetate trihydrate (LAT) at different temperatures affects Na wetting on BASEs. LAT treatment conducted at a temperature of 400 °C (under a nitrogen gas atmosphere) shows significantly better Na wettability and battery performance than treatments at lower temperatures. The formation of a unique morphology—micron-sized Pb spherical particles—is observed on the surface of the BASE LAT treated at 400 °C. We also observed evolution of the Na wetting configuration from a Cassie drop, to a Wenzel drop, and finally to a sunny-side-up drop, which is clearly different from the Young–Dupré relation, with increasing the contact-angle measurement temperature. We conclude that formation of a thin Na penetrating film (sunny-side-up shape) on Pb-decorated BASEs is crucial for achieving good battery performance at lower operating temperatures. The new observations and fundamental understanding of Na wetting reported here will provide excellent guidance for improving cell performance in general and will further promote development of practical Na–MH battery technologies for large-scale energy storage applications.

Jinhua Huang, Zheng Yang, Vijayakumar Murugesan, Eric Walter, Aaron Hollas, Baofei Pan, Rajeev S. Assary, Ilya A. Shkrob, Xiaoling Wei, Zhengcheng Zhang."Spatially Constrained Organic Diquat Anolyte for Stable Aqueous Flow Batteries."ACS Energy Letters 3 (10) 2533-2538 (October 2018).
Abstract: Redox-active organic materials (ROMs) are becoming increasingly attractive for use in redox flow batteries as promising alternatives to traditional inorganic counterparts. However, the reported ROMs are often accompanied by challenges, including poor solubility and stability. Herein, we demonstrate that the commonly used diquat herbicides, with solubilities of >2 M in aqueous electrolytes, can be used as stable anolyte materials in organic flow batteries. When coupled with a ferrocene-derived catholyte, the flow cells with the diquat anolyte demonstrate long galvanic cycling with high capacity retention. Notably, the mechanistic underpinnings of this remarkable stability are attributed to the improved π-conjugation that originated from the near-planar molecular conformations of the spatially constrained 2,2′-bipyridyl rings, suggesting a viable structural engineering strategy for designing stable organic materials.

Liang Yin, Gerard S. Mattei, Zhou Li, Jianming Zheng, Wengao Zhao, Fredrick Omenya, Chengcheng Fang, Wangda Li, Jianyu Li, Qiang Xie, Ji-Guang Zhang, M. Stanley Whittingham, Ying Shirley Meng, Arumugam Manthiram, Peter G. Khalifah."Extending the limits of powder diffraction analysis: Diffraction parameter space, occupancy defects, and atomic form factors."Review of Scientific Instruments 89 (9), article number 093002 (September 2018).
Abstract: Although the determination of site occupancies is often a major goal in Rietveld refinement studies, the accurate refinement of site occupancies is exceptionally challenging due to many correlations and systematic errors that have a hidden impact on the final refined occupancy parameters. Through the comparison of results independently obtained from neutron and synchrotron powder diffraction, improved approaches capable of detecting occupancy defects with an exceptional sensitivity of 0.1% (absolute) in the class of layered NMC (Li[Ni_xMn_yCo_z]O₂) Li-ion battery cathode materials have been developed. A new method of visualizing the diffraction parameter space associated with crystallographic site scattering power through the use of f* diagrams is described, and this method is broadly applicable to ternary compounds. The f* diagrams allow the global minimum fit to be easily identified and also permit a robust determination of the number and types of occupancy defects within a structure. Through a comparison of neutron and X-ray diffraction results, a systematic error in the synchrotron results was identified using f* diagrams for a series of NMC compounds. Using neutron diffraction data as a reference, this error was shown to specifically result from problems associated with the neutral oxygen X-ray atomic form factor and could be eliminated by using the ionic O²⁻ form factor for this anion while retaining the neutral form factors for cationic species. The f* diagram method offers a new opportunity to experimentally assess the quality of atomic form factors through powder diffraction studies on chemically related multi-component compounds.

Enyue Zhao, Kaihui Nie, Xiqian Yu, Yong-Sheng Hu, Fangwei Wang, Jie Xiao, Hong Li, Xuejie Huang."Advanced Characterization Techniques in Promoting Mechanism Understanding for Lithium–Sulfur Batteries."Advanced Functional Materials 23 (38): 1707543 (September 2018).
Abstract: Due to their numerous advantages, such as high specific capacity, lithium–sulfur batteries (Li–S batteries) have attracted much attention as next‐generation energy storage systems. To meet future needs for commercial application, Li–S batteries will require both improved cycle life and high energy density. It is of critical importance to understand the fundamental mechanisms in Li–S systems to further improve the overall battery performance. Various advanced characterization techniques, over the past few years, have proven their important role in promoting the mechanism understanding for Li–S batteries. Here, the recent progress of mechanism understanding, including redox reactions, Li polysulfides dissolution, etc., in Li–S systems based on the advanced characterization techniques is reviewed. Special focus is placed on how these advanced characterization techniques are being employed and what characteristic or capability they possess. The importance of the combination of multiple characterization techniques, differences between ex situ and in situ experimental methods, as well as effects of characterization conditions in Li–S batteries are also discussed.

Lu Yu, Shuru Chen, Hongkyung Lee, Linchao Zhang, Mark H. Engelhard, Qiuyan Li, Shuhong Jiao, Jun Liu, Wu Xu, Ji-Guang Zhang."A Localized High-Concentration Electrolyte with Optimized Solvents and Lithium Difluoro(oxalate)borate Additive for Stable Lithium Metal Batteries."ACS Energy Letters 3 (9) 2059-2067 (September 2018).
Abstract: We report a carbonate-based localized high-concentration electrolyte (LHCE) with a fluorinated ether as a diluent for 4-V class lithium metal batteries (LMBs), which enables dendrite-free Li deposition with a high Li Coulombic efficiency (∼98.5%) and much better cycling stability for Li metal anodes than previously reported dimethyl carbonate-based LHCEs at lean electrolyte conditions. This electrolyte consists of 1.2 M lithium bis(fluorosulfonyl)imide (LiFSI) in a cosolvent mixture of ethylene carbonate (EC)/ethyl methyl carbonate (EMC) with bis(2,2,2-trifluoroethyl) ether (BTFE) as the diluent and 0.15 M lithium difluoro(oxalate)borate (LiDFOB) as an additive. A Li||LiNi_1/3Mn_1/3Co_1/3O₂ battery with a high areal loading of 3.8 mAh cm^–2 maintains 84% of its initial capacity after 100 cycles. The enhanced stability can be attributed to the robust solid–electrolyte interface (SEI) layer formed on the Li metal anode, arising from the preferential decomposition of LiDFOB salt and EC solvent molecules.

Shuhong Jiao, Xiaodi Ren, Ruiguo Cao, Mark H. Engelhard, Yuzi Liu, Dehong Hu, Donghai Mei, Jianming Zheng, Wengao Zhao, Qiuyan Li, Ning Liu, Brian D. Adams, Cheng Ma, Jun Liu, Ji-Guang Zhang, Wu Xu."Stable cycling of high-voltage lithium metal batteries in ether electrolytes."Nature Energy 3: 739-746 (September 2018).
Abstract: The key to enabling long-term cycling stability of high-voltage lithium (Li) metal batteries is the development of functional electrolytes that are stable against both Li anodes and high-voltage (above 4 V versus Li/Li⁺) cathodes. Due to their limited oxidative stability ( <4 V), ethers have so far been excluded from being used in high-voltage batteries, in spite of their superior reductive stability against Li metal compared to conventional carbonate electrolytes. Here, we design a concentrated dual-salt/ether electrolyte that induces the formation of stable interfacial layers on both a high-voltage LiNi_1/3Mn_1/3Co_1/3O₂ cathode and the Li metal anode, thus realizing a capacity retention of >90% over 300 cycles and ~80% over 500 cycles with a charge cut-off voltage of 4.3 V. This study offers a promising approach to enable ether-based electrolytes for high-voltage Li metal battery applications.

Wentao Duan, Bin Li, Dongping Lu, Xiaoliang Wei, Zimin Nie, Vijayakumar Murugesan, James P. Kizewski, Aaron Hollas, David Reed, Vincent Sprenkle, Wei Wang."Towards an all-vanadium redox flow battery with higher theoretical volumetric capacities by utilizing the VO²⁺/V³⁺ couple."Journal of Energy Chemistry 27 (5): 1381-1385 (September 2018).
Abstract: An all-vanadium redox flow battery with V(IV) as the sole parent active species is developed by accessing the VO²⁺/V³⁺ redox couple. These batteries, referred to as V4RBs, possess a higher theoretical volumetric capacity than traditional VRBs. Copper ions were identified as an effective additive to boost the battery performance.

Biwei Xiao, Fernando Soto, Meng Gu, Kee Sung Han, Junhua Song, Hui Wang, Mark H. Engelhard, Vijayakumar Murugesan, Karl T. Mueller, David Reed, Vincent Sprenkle, Perla B. Balbuena, Xiaolin Li."Lithium‐Pretreated Hard Carbon as High‐Performance Sodium‐Ion Battery Anodes."Advanced Energy Materials 8 (24) 1801441 (August 2018).
Abstract: Hard carbon (HC) is the state‐of‐the‐art anode material for sodium‐ion batteries (SIBs). However, its performance has been plagued by the limited initial Coulombic efficiency (ICE) and mediocre rate performance. Here, experimental and theoretical studies are combined to demonstrate the application of lithium‐pretreated HC (LPHC) as high‐performance anode materials for SIBs by manipulating the solid electrolyte interphase in tetraglyme (TEGDME)‐based electrolyte. The LPHC in TEGDME can 1) deliver > 92% ICE and ≈220 mAh g⁻¹ specific capacity, twice of the capacity (≈100 mAh g⁻¹) in carbonate electrolyte; 2) achieve > 85% capacity retention over 1000 cycles at 1000 mA g⁻¹ current density (4 C rate, 1 C = 250 mA g⁻¹) with a specific capacity of ≈150 mAh g⁻¹, ≈15 times of the capacity (10 mAh g⁻¹) in carbonate. The full cell of Na₃V₂(PO₄)₃‐LPHC in TEGDME demonstrated close to theoretical specific capacity of ≈98 mAh g⁻¹ based on Na₃V₂(PO₄)₃ cathode, ≈2.5 times of the value (≈40 mAh g⁻¹) with nontreated HC. This work provides new perception on the anode development for SIBs.

Shuru Chen, Jianming Zheng, Lu Yu, Xiaodi Ren, Mark H. Engelhard, Chaojiang Niu, Hongkyung Lee, Wu Xu, Jie Xiao, Jun Liu, Ji-Guang Zhang."High-Efficiency Lithium Metal Batteries with Fire-Retardant Electrolytes."Joule 2 (8), 1548-1558 (August 2018).
Abstract: A safe electrolyte for 4-V class lithium metal batteries (LMBs) was reported by diluting a fire-retardant high-concentration electrolyte (HCE) with an electrochemically “inert” and poorly solvating fluorinated ether. Named localized high-concentration electrolyte (LHCE), it inherits the merits from the HCE but dramatically overcomes its disadvantages. The fire-retardant LHCE enables dendrite-free and stable cycling of a Li metal anode with high Coulombic efficiency of up to 99.2% and greatly enhances the cycling stability of Li||NMC622 batteries for more than 600 cycles. The excellent electrochemical performances of the LHCE is ascribed to the well-reserved, locally concentrated solvation structures and its improved interfacial reaction kinetics and stability. These findings open up a new avenue for developing highly stable and safe electrolyte systems for high-energy-density LMBs for practical applications.

Xiaodi Ren, Shuru Chen, Hongkyung Lee, Donghai Mei, Mark H. Engelhard, Sarah D. Burton, Wengao Zhao, Jianming Zheng, Qiuyan Li, Michael S. Ding, Marshall Schroeder, Judith Alvarado, Kan Xu, Y. Shirley Meng, Jun Liu, Ji-Guang Zhang, Wu Xu."Localized High-Concentration Sulfone Electrolytes for High-Efficiency Lithium-Metal Batteries."Chem 4 (8), 1877-1892 (August 2018).
Abstract: For high-voltage rechargeable lithium (Li)-metal batteries (LMBs), electrolytes with good stabilities on both the highly oxidative cathodes and the highly reductive Li-metal anodes are urgently desired. Sulfones have excellent oxidative stability, yet their high viscosity, poor wettability, and, in particular, incompatibility with Li anodes greatly hinder their applications in LMBs. Here, we demonstrate that a high Li Coulombic efficiency (CE) of 98.2% during repeated Li plating and stripping cycles can be realized in concentrated lithium bis(fluorosulfonyl)imide (LiFSI)-tetramethylene sulfone electrolyte. More importantly, the localized high-concentration electrolyte, formed by the dilution of the high-concentration electrolyte with a non-solvating fluorinated ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, solves the viscosity and wettability issues, further improves Li CE (98.8%), and improves the high-voltage (4.9 V) performance of LMBs with effective Al protection.

Guosheng Li."Turning Cooler."Nature Energy (August 2018).
Abstract: Harsh operating conditions, such as high temperatures, hinder the grid-scale application of liquid metal batteries (LMBs). Now, their operating temperature is shown to be substantially lowered thanks to a lithium-ion-conducting solid-state electrolyte. Stationary energy storage systems consisting of large-scale rechargeable batteries are increasingly considered as one of the most important components to effectively integrate intermittent renewable sources such as wind and solar into reliable and resilient next-generation grids^1,2. Because there is less restriction on the energy footprint for stationary energy storage systems than portable devices, the high-temperature liquid metal battery (LMB)³ is now facing great opportunities after nearly four decades of dormancy^4,5. Traditional LMBs are typically constructed with molten metal electrodes and molten salt electrolytes that separate the two liquid electrodes (Fig. 1a). As LMBs need to maintain their liquid state under operation, the minimum cell operating temperature is generally above 450 °C, which is determined by the melting points of the electrode and electrolyte materials (Fig. 1c)^3,6. Now, writing in Nature Energy, Hui Wu, Yi Cui and co-workers from China and the United States report using a lithium (Li)-ion-conducting solid-state electrolyte (SSE) to enable operating LMBs at a temperature of merely 240 °C.

Haiping Jia, Jianming Zheng, Junhua Song, Langli Luo, Ran Yi, Luis Estevez, Wengao Zhao, Rajankumar Patel, Xiaolin Li, Ji-Guang Zhang."A novel approach to synthesize micrometer-sized porous silicon as a high performance anode for lithium-ion batteries."Nano Energy 50: 589-597 (August 2018).
Abstract: Porous structured silicon (p-Si) has been recognized as one of the most promising anodes for Li-ion batteries. However, many available methods to synthesize p-Si are difficult to scale up due to their high production cost. Here we introduce a new approach to obtain spherical micrometer-sized silicon with unique porous structure by using a microemulsion of the cost-effective of silica nanoparticles and magnesiothermic reduction method. The spherical micron-sized p-Si particles prepared by this approach consist of highly aligned nano-sized silicon and exhibit a tap density close to that of bulk Si particles. They have demonstrated significantly improved electrochemical stability compared to nano-Si. Well controlled void space and a highly graphitic carbon coating on the p-Si particles enable good stability of the structure and low overall resistance, thus resulting in a Si-based anode with high capacity (~1467 mAh g⁻¹ at 2.6 A g⁻¹), enhanced cycle life (370 cycles with 83% capacity retention), and high rate capability (~650 mAh g⁻¹ at 11A g⁻¹). This approach may also be generalized to prepare other hierarchical structured high capacity anode materials for constructing high energy density lithium ion batteries.

Keeyoung Jung, Hee-Jung Chang, Jeffery F. Bonnett, Nathan L. Canfield, Vincent L. Sprenkle, Guosheng Li."An advanced Na-NiCl₂ battery using bi-layer (dense/micro-porous) β″-alumina solid-state electrolytes."Journal of Power Sources 396: 297-303 (August 2018).
Abstract: Sodium metal halide (Na-MH) batteries present tremendous opportunities for grid scale energy storage applications. In this work, we describe an advanced Na-MH battery operating at 190 °C using a bi-layer (thin dense/thick porous layers) β″-alumina solid-state electrolyte (BASE). The novel design of the bi-layer BASE promotes high Na-ion transportation by reducing the Na+ ion path length. The excellent battery performances are achieved with a stable capacity retention of 350 W h/kg up to >350 cycles (∼6 months). Moreover, owing to the thin dense layer of BASE, the round trip energy efficiency (or discharging energy density) of the tested battery shows an ∼8% increase compared to that of state of the art Na-MH battery reported in the literature. Results from this work clearly demonstrate that advanced Na-MH batteries using bi-layer BASEs can have significant impacts on improving battery performances at lower operating temperatures, and further stretch its feasibility in stationary energy storage applications.

Wengao Zhao, Lianfeng Zou, Jianming Zheng, Haiping Jia, Junhua Song, Mark H. Engelhard, Chongmin Wang, Wu Xu, Yong Yang, Ji-Guang Zhang."Simultaneous Stabilization of LiNi_0.76Mn_0.14Co_0.10O₂ Cathode and Lithium Metal Anode by Lithium Bis(oxalato)borate as Additive."ChemSusChem 11 (13), 2211-2220 (July 2018).
Abstract: The long‐term cycling performance, rate capability, and voltage stability of lithium (Li) metal batteries with LiNi_0.76Mn_0.14Co_0.10O₂ (NMC76) cathodes is greatly enhanced by lithium bis(oxalato)borate (LiBOB) additive in the LiPF6‐based electrolyte. With 2% LiBOB in the electrolyte, a Li∥NMC76 cell is able to achieve a high capacity retention of 96.8% after 200 cycles at C/3 rate (1 C=200 mAg^-1), which is the best result reported for a Ni‐rich NMC cathode coupled with Li metal anode. The significantly enhanced electrochemical performance can be ascribed to the stabilization of both the NMC76 cathode/electrolyte and Li‐metal‐anode/electrolyte interfaces. The LiBOB‐containing electrolyte not only facilitates the formation of a more compact solid–electrolyte interphase on the Li metal surface, it also forms a enhanced cathode electrolyte interface layer, which efficiently prevents the corrosion of the cathode interface and mitigates the formation of the disordered rock‐salt phase after cycling. The fundamental findings of this work highlight the importance of recognizing the dual effects of electrolyte additives in simultaneously stabilizing both cathode and anode interfaces, so as to enhance the long‐term cycle life of high‐energy‐density battery systems.

Pengcheng Shi, Linchao Zhang, Hongfa Xiang, Xin Liang, Yi Sun, Wu Xu."Lithium Difluorophosphate as a Dendrite-Suppressing Additive for Lithium Metal Batteries."Applied Materials & Interfaces 10 (26): 22201-22209 (July 2018).
Abstract: The notorious lithium (Li) dendrites and the low Coulombic efficiency (CE) of Li anode are two major obstacles to the practical utilization of Li metal batteries (LMBs). Introducing a dendrite-suppressing additive into nonaqueous electrolytes is one of the facile and effective solutions to promote the commercialization of LMBs. Herein, Li difluorophosphate (LiPO₂F₂, LiDFP) is used as an electrolyte additive to inhibit Li dendrite growth by forming a vigorous and stable solid electrolyte interphase film on metallic Li anode. Moreover, the Li CE can be largely improved from 84.6% of the conventional LiPF₆-based electrolyte to 95.2% by the addition of an optimal concentration of LiDFP at 0.15 M. The optimal LiDFP-containing electrolyte can allow the Li||Li symmetric cells to cycle stably for more than 500 and 200 h at 0.5 and 1.0 mA cm^–2, respectively, much longer than the control electrolyte without LiDFP additive. Meanwhile, this LiDFP-containing electrolyte also plays an important role in enhancing the cycling stability of the Li||LiNi_1/3Co_1/3Mn_1/3O₂ cells with a moderately high mass loading of 9.7 mg cm^–2. These results demonstrate that LiDFP has extensive application prospects as a dendrite-suppressing additive in advanced LMBs.

Jianming Zheng, Pengfei Yan, Luis Estevez, Chongmin Wang, Ji-Guang Zhang."Effect of calcination temperature on the electrochemical properties of nickel-rich LiNi_0.76Mn_0.14Co_0.10O₂ cathodes for lithium-ion batteries."Nano Energy 49: 538-548 (July 2018).
Abstract: High energy density, nickel (Ni)-rich, layered LiNi_xMn_yCo_zO₂ (NMC, x ≥ 0.6) materials are promising cathodes for lithium-ion batteries. However, several technical challenges, such as fast capacity fading and high voltage instability, hinder their large-scale application. Herein, we identified an optimum calcining temperature range for the Ni-rich cathode LiNi_0.76Mn_0.14Co_0.10O₂(NMC76). NMC76 calcined at 750–775 °C exhibits a high discharge capacity (~215 mAh g⁻¹ when charged to 4.5 V) and retains ca. 79% of its initial capacity after 200 cycles. It also exhibits an excellent high-rate capability, delivering a capacity of more than 160 mAh g⁻¹ even at a 10 C rate. The high performance of NMC76 is directly related to the optimized size of its primary particles (100–300 nm) (which constitute the spherical secondary particles of >10 µm) and cation mixing. Higher calcination temperature (≥800 °C) leads to rapid increase of primary particle size, poor cycling stability, and inferior rate capability of NMC76 due to severe micro-strain and -crack formation upon repeated lithium-ion de/intercalations. Therefore, NMC76 calcined at 750–775 °C is a very good candidate for the next generation of Li ion batteries.

Damien Saurel, Brahim Orayech, Biwei Xiao, Daniel Carriazo, Xiaolin Li, Teófilo Rojo."From Charge Storage Mechanism to Performance: A Roadmap toward High Specific Energy Sodium‐Ion Batteries through Carbon Anode Optimization."Advanced Energy Materials 8 (17) 1703268 (June 2018).
Abstract: While sodium‐ion batteries (SIBs) represent a low‐cost substitute for Li‐ion batteries (LIBs), there are still several key issues that need to be addressed before SIBs become market‐ready. Among these, one of the most challenging is the negligible sodium uptake into graphite, which is the keystone of the present LIB technology. Although hard carbon has long been established as one of the best substitutes, its performance remains below that of graphite in LIBs and its sodium storage mechanism is still under debate. Many other carbons have been recently studied, some of which have presented capacities far beyond that of graphite. However, these also tend to exhibit larger voltage and high first cycle loss, leading to limited benefits in terms of full cell specific energy. Overcoming this concerning tradeoff necessitates a deep understanding of the charge storage mechanisms and the correlation between structure, microstructure, and performance. This review aims to address this by drawing a roadmap of the emerging routes to optimization of carbon materials for SIB anodes on the basis of a critical survey of the reported electrochemical performances and charge storage mechanisms.

Junhua Song, Biwei Xiao, Yuehe Lin, Kang Xu, Xiaolin Li."Interphases in Sodium‐Ion Batteries."Advanced Energy Materials 8 (17) 1703082 (June 2018).
Abstract: Sodium‐ion batteries (SIBs) as economical, high energy alternatives to lithium‐ion batteries (LIBs) have received significant attention for large‐scale energy storage in the last few years. While the efforts of developing SIBs have benefited from the knowledge learned in LIBs, thanks to the apparent proximity between Na‐ions and Li‐ions, the unique physical and chemical properties of Na‐ions also distinctly differ themselves from Li‐ions. It is expected that SIBs have drastically different electrode material structure, solvation–desolvation behavior, electrode–electrolyte interphase stabilities, ion transfer properties, and hence electrochemical performance of batteries. In this review, the authors comprehensively summarize the current understanding of the anode solid electrolyte interphase and cathode electrolyte interphase in SIBs, with an emphasis on how the tuning of the stability and ion transfer properties of interphases fundamentally determines the reversibility and efficiency of electrochemical reactions. Through these carefully screened references, the authors intend to reveal the intrinsic correlation between the properties/functionalities of the interphases and the electrochemical performance of batteries.

Wenhao Ren, Dongna Liu, Congli Sun, Xuhui Yao, Jian Tan, Chongmin Wang, Kangning Zhao, Xuanpeng Wang, Qi Li, Liqiang Mai."Nonhierarchical Heterostructured Fe₂O₃/Mn₂O₃ Porous Hollow Spheres for Enhanced Lithium Storage."Small 14 (26), 1800659 (May 2018).
Abstract: High capacity transition‐metal oxides play significant roles as battery anodes benefiting from their tunable redox chemistry, low cost, and environmental friendliness. However, the application of these conversion‐type electrodes is hampered by inherent large volume variation and poor kinetics. Here, a binary metal oxide prototype, denoted as nonhierarchical heterostructured Fe₂O₃/Mn₂O₃ porous hollow spheres, is proposed through a one‐pot self‐assembly method. Beyond conventional heteromaterial, Fe₂O₃/Mn₂O₃ based on the interface of (104)_Fe2O3 and (222)_Mn2O3 exhibits the nonhierarchical configuration, where nanosized building blocks are integrated into microsized spheres, leading to the enhanced structural stability and boosted reaction kinetics. With this design, the Fe₂O₃/Mn₂O₃ anode shows a high reversible capacity of 1075 mA h g⁻¹ at 0.5 A g⁻¹, an outstanding rate capability of 638 mA h g⁻¹ at 8 A g⁻¹, and an excellent cyclability with a capacity retention of 89.3% after 600 cycles.

Dongping Lu, Qiuyan Li, Jian Liu Jianming Zheng, Yuxing Wang, Seth Ferrara, Jie Xiao, Ji-Guang Zhang, Jun Liu."Enabling High-Energy-Density Cathode for Lithium–Sulfur Batteries."Applied Materials & Interfaces 10 (27) 23094-23102 (June 2018).
Abstract: High-energy lithium–sulfur (Li–S) battery is built on high loading and dense sulfur electrodes. Unfortunately, these electrodes usually suffer from a low sulfur utilization rate and limited cycle life due to the gap in scientific knowledge between the fundamental research and the application at relevant scales. In this work, effects of electrode porosity on the electrode energy density, cell cycling stability, Li anode interface, and electrolyte/sulfur ratio were investigated on the basis of high-loading sulfur electrodes. Using electrodes with sulfur loading of 4 mg cm^–2 and thickness at ∼60 μm, a high energy density of over 1300 Wh L^–1 has been obtained at electrode level, which provides a decent basis for high-energy Li–S cell development. In addition, Li–S cells with the high-loading and dense electrodes demonstrate promising cycling stability (∼80% capacity retention for 200 cycles). These significant improvements are contributed by the synergistic effects of dense sulfur cathode, improved electrode wetting, and suppressed quick growth of the interphase layer on Li-metal anode. This study sheds light on rational design of sulfur cathode for balanced cell energy density and cycling life.

Jian Liu, Dongping Lu, Jianming Zheng, Pengfei Yan, Biqiong Wang, Xueliang Sun, Yuyan Shao, Chongmin Wang, Jie Xiao, Ji-Guang Zhang, Jun Liu."Minimizing Polysulfide Shuttle Effect in Lithium-Ion Sulfur Batteries by Anode Surface Passivation."Applied Materials & Interfaces 10 (26) 21965-21972 (June 2018).
Abstract: Lithium-ion sulfur batteries use nonlithium materials as the anode for extended cycle life. However, polysulfide shuttle reactions still occur on the nonmetal anodes (such as graphite and Si), and result in undesirable low Coulombic efficiency. In this work, we used Al₂O₃ layers coated by atomic layer deposition (ALD) technique to suppress the shuttle reactions. With the optimal thickness of 2 nm Al₂O₃ coated on graphite anode, the Coulombic efficiency of the sulfur cathode was improved from 84% to 96% in the first cycle, and from 94% to 97% in the subsequent cycles. As a result, the discharge capacity of the sulfur cathode was increased to 550 mAh g^–1 in the 100th cycle, as compared with 440 mAh g^–1 when the pristine graphite anode was used. The Al₂O₃ passivation layer minimizes the formation of insoluble sulfide (Li₂S₂, Li₂S) on the surface of graphite anode and improves the efficiency and capacity retention of the graphite-sulfur batteries. The surface passivation strategy could also be used in other sulfur based battery systems (with Li, Si, and Sn anodes), to minimize side reactions and enable high-performance sulfur batteries.

Aaron Hollas, Xiaoliang Wei, Vijayakumar Murugesan, Zimin Nie, Bin Li, David Reed, Jun Liu, Vincent Sprenkle & Wei Wang."A biomimetic high-capacity phenazine-based anolyte for aqueous organic redox flow batteries."Nature Energy 3: 508-514 (June 2018).
Abstract: Aqueous soluble organic (ASO) redox-active materials have recently attracted significant attention as alternatives to traditional transition metal ions in redox flow batteries (RFB). However, reported reversible capacities of ASO are often substantially lower than their theoretical values based on the reported maximum solubilities. Here, we describe a phenazine-based ASO compound with an exceptionally high reversible capacity that exceeds 90% of its theoretical value. By strategically modifying the phenazine molecular structure, we demonstrate an increased solubility from near-zero with pristine phenazine to as much as 1.8 M while also shifting its redox potential by more than 400 mV. An RFB based on a phenazine derivative (7,8-dihydroxyphenazine-2-sulfonic acid) at its near-saturation concentration exhibits an operating voltage of 1.4 V with a reversible anolyte capacity of 67 Ah l⁻¹ and a capacity retention of 99.98% per cycle over 500 cycles.

Aaron Hollas, Xiaoliang Wei, Vijayakumar Murugesan, Zimin Nie, Bin Li, David Reed, Jun Liu, Vincent Sprenkle, Wei Wang."A biomimetic high-capacity phenazine-based anolyte for aqueous organic redox flow batteries."Nature Energy3: 508-514 (June 2018).
Abstract: Aqueous soluble organic (ASO) redox-active materials have recently attracted significant attention as alternatives to traditional transition metal ions in redox flow batteries (RFB). However, reported reversible capacities of ASO are often substantially lower than their theoretical values based on the reported maximum solubilities. Here, we describe a phenazine-based ASO compound with an exceptionally high reversible capacity that exceeds 90% of its theoretical value. By strategically modifying the phenazine molecular structure, we demonstrate an increased solubility from near-zero with pristine phenazine to as much as 1.8 M while also shifting its redox potential by more than 400 mV. An RFB based on a phenazine derivative (7,8-dihydroxyphenazine-2-sulfonic acid) at its near-saturation concentration exhibits an operating voltage of 1.4 V with a reversible anolyte capacity of 67 Ah l⁻¹ and a capacity retention of 99.98% per cycle over 500 cycles.

Patrick J. Balducci, M. Jan E. Alam, Trevor D. Hardy, Di Wu."Assigning value to energy storage systems at multiple points in an electrical grid."Energy & Environmental Science (June 2018).
Abstract: The ability to define the potential value that energy storage systems (ESSs) could generate through various applications in electric power systems, and an understanding of how these values change due to variations in ESS performance and parameters, market structure, utility structures, and valuation methodologies is highly important in advancing ESS deployment. This paper presents a taxonomy for assigning benefits to the use cases or services provided by ESSs, defines approaches for monetizing the value associated with these services, assigns values, or more precisely ranges of values, to major ESS applications by region based on a review of an extensive set of literature, and summarizes and evaluates the capabilities of several available tools currently used to estimate value for specific ESS deployments.

Xing Li, Jianming Zheng, Xiaodi Ren, Mark H. Engelhard, Wengao Zhao, Qiuyan Li, Ji-Guang Zhang, Wu Xu."Dendrite‐Free and Performance‐Enhanced Lithium Metal Batteries through Optimizing Solvent Compositions and Adding Combinational Additives."Advanced Energy Materials 8 (15) 1703022 (May 2018).
Abstract: The instability of lithium (Li) metal anodes due to dendritic growth and low Coulombic efficiency (CE) hinders the practical application of high‐energy‐density Li metal batteries. Here, the systematic studies of improving the stability of Li metal anodes and the electrochemical performance of Li metal batteries through the addition of combinational additives and the optimization of solvent compositions in dual‐salt/carbonate electrolytes are reported. A dendrite‐free and high CE of 98.1% for Li metal anode is achieved. The well‐protected Li metal anode and the excellent cyclability and rate capability of the 4‐V Li metal batteries are obtained. This is attributed to the formation of a robust, denser, more polymeric, and higher ionic conductive surface film on the Li metal anode via the electrochemical reductive decompositions of the electrolyte components and the ring‐opening polymerization of additives and cyclic carbonate solvents. The key findings of this work indicate that the optimization of solvent compositions and the manipulation of additives are facile and effective ways to enhance the performances of Li metal batteries.

Bin Liu, Ji-Guang Zhang, Wu Xu. "Advancing Lithium Metal Batteries."Joule2 (5):833-845 (May 2018).
Abstract: Lithium (Li)-ion batteries have been widely used as power sources for portable electronic devices and are emerging into transportation and grid applications, but the energy density of the state-of-the-art Li-ion batteries will reach its theoretical limit soon, and new battery designs are urgently needed to satisfy the increasing demand for high-energy-density batteries. In this regard, Li metal anode material has attracted worldwide attention because of its many merits. Although practical applications of Li metal anodes are still limited by several challenges, such as dendrite growth and low coulombic efficiency, rapid development of new materials and electrode designs in recent years has overcome many bottlenecks in this field and hastened the practical applications of high-energy-density and high-performance rechargeable Li metal batteries. In this Perspective, recent significant progress on stabilization of Li metal anodes for Li metal batteries is highlighted. We also present a perspective on future directions and possibilities to better address the existing challenges of Li metal anodes and Li metal batteries.

Hui Wang, Brian D. Adams, Huilin Pan, Liang Zhang, Kee Sung Han, Luis Estevez, Dongping Lu, Haiping Jia, Jun Feng, Jinghua Guo, Kevin R. Zavadil, Yuyan Shao, Ji-Guang Zhang."Tailored Reaction Route by Micropore Confinement for Li–S Batteries Operating under Lean Electrolyte Conditions."Advanced Energy Materials 8 (21): 1800590 (May 2018).
Abstract: Lithium‐sulfur (Li–S) batteries are one of the most promising alternative energy storage systems beyond Li‐ion batteries. However, the sluggish kinetics of the nucleation and growth of the solid discharge product of Li₂S/Li₂S₂ in the lower discharge plateau has been recently identified as a critical hurdle for attaining high specific capacity in Li–S batteries with high sulfur loadings under lean electrolyte conditions. Herein, a new strategy of breaking the charge‐transport bottleneck by successful generation of experimentally verified stable Li₂S₂ and a reservoir of quasi‐solid lithium polysulfides within the micropores of activated carbon fiber cloth as a high‐sulfur‐loading host is proposed. The developed Li–S cell is capable of delivering a highly sustainable areal capacity of 6.0 mAh cm⁻² under lower electrolyte to sulfur ratios (<3.0 mL_E g_S⁻¹). Micropore confinement leads to generation of solid Li₂S₂ that enables high utilization of the entire electroactive area by its inherent self‐healing capacity. This strategy opens a new avenue for rational material designs for Li–S batteries under lean electrolyte condition.

Zhaoxin Yu, Shun-Li Shang, Yue Gao, Daiwei Wang, Xiaolin Li, Ki-Kui Liu, Donghai Wang."A quaternary sodium superionic conductor - Na_10.8Sn_1.9PS_11.8."Nano Energy 47: 325-330 (May 2018).
Abstract: Sulfide-based Na-ion conductors are promising candidates as solid-state electrolytes (SSEs) for fabrication of solid-state Na-ion batteries (NIBs) because of their high ionic conductivities and low grain boundary resistance. Currently, most of the sulfide-based Na-ion conductors with high conductivities are focused on Na₃PS₄ phases and its derivatives. It is desirable to develop Na-ion conductors with new composition and crystal structure to achieve superior ionic conductivities. Here we report a new quaternary Na-ion conductor, Na_10.8Sn_1.9PS_11.8, exhibiting a high ionic conductivity of 0.67 mS cm⁻¹ at 25 °C. This high ionic conductivity originates from the presence of a large number of intrinsic Na-vacancies and three-dimensional Na-ion conduction pathways, which has been confirmed by single-crystal X-ray diffraction and first-principles calculations. The Na_10.8Sn_1.9PS_11.8 phase is further evaluated as an electrolyte in a Na-Sn alloy/TiS₂ battery, demonstrating its potential application in all-solid-state NIBs.

Daiwon Choi, Prashanth H. Jampani, J.R.P. Jayakody, Steven G. Greenbaum, Prashant N. Kumta."Synthesis, surface chemistry and pseudocapacitance mechanisms of VN nanocrystals derived by a simple two-step halide approach."Materials Science and Engineering: B 230: 8-19 (April 2018).
Abstract: Chloroamide precursors generated via a simple two-step ammonolysis reaction of transition metal chloride in the liquid phase at room temperature were heat treated in ammonia at moderate temperature to yield nano-sized VN crystallites. Grain growth inhibited by lowering the synthesis temperature (≈400 °C) yielded agglomerated powders of spherical crystallites of cubic phase of VN with particle sizes as small as 6 nm in diameter. X-ray diffraction, FTIR, mass spectroscopy (MS), and nuclear magnetic resonance (NMR) spectroscopy assessed the ammonolysis and nitridation reaction of the VCl4-NH3 system. X-ray Rietveld refinement, the BET technique and high-resolution transmission microscopy (HRTEM), energy dispersive X-ray (EDX) and thermogravimetric analysis (TGA) helped assess the crystallographic and microstructural nature of the VN nanocrystals. The surface chemistry and redox reaction leading to the gravimetric pseudo-capacitance value of (≈855 F/g) measured for the VN nanocrystals was determined and validated using FTIR, XPS and cyclic voltammetry analyses.

Jian Zhi Hu, Nav Nidhi Rajput, Chuan Wan, Yuyan Shao, Xuchu Deng, Nicholas R. Jaegers, Mary Hu, Yingwen Chen, Yongwoo Shin, Joshua Monk, Zhong Chen, Zhaohai Qin, Karl Todd Mueller, Jun Liu, Kristin A. Persson."²⁵Mg NMR and computational modeling studies of the solvation structures and molecular dynamics in magnesium based liquid electrolytes."Nano Energy 46: 436-446 (April 2018).
Abstract: There is increasing evidence that the solvation structure of the active components in a liquid electrolyte solution strongly impacts the performance in electrochemical applications. In this work, the nanoscale solvation structures and dynamics of Mg(BH₄)₂ and Mg(TFSI)₂ dissolved in diglyme (DGM) at various concentrations and ratios of Mg(BH₄)₂/Mg(TFSI)₂ were investigated using a combination of natural abundance ²⁵Mg NMR, quantum chemistry calculations of ²⁵Mg NMR chemical shifts, classical molecular dynamics (MD) calculations, and electrochemical performance tests. By mixing two competing Mg salts, we were able to reduce the strong covalent interactions between Mg²⁺ and BH₄– anions. A small increase is observed in the coordination number of Mg-TFSI and a significant increase in the interaction of Mg²⁺ ions with glymes. Through a combination of NMR, DFT and MD simulations, various stable species around 1 nm in size were detected in the mixed salt solution, which play key roles in the enhanced electrochemical performance of the mixed electrolyte. It is established that for the neat Mg(TFSI)₂ in DGM electrolyte at dilute concentrations the TFSI- is fully dissociated from Mg²⁺. At higher concentrations, Mg²⁺ and TFSI- are only partially dissociated as contact ion pairs are formed. In contrast, at 0.01 M Mg(BH₄)₂ (saturated concentration) in DGM, the first solvation shell of a Mg²⁺ ion contains two BH₄- anions and one DGM molecule, while the second solvation shell consists of five to six DGM molecules. An exchange mechanism between the solvation structures in the combined electrolyte containing both Mg(BH₄)₂ and Mg(TFSI)₂ in DGM was found to result in the observation of a single ²⁵Mg NMR peak. This exchange is responsible for an increase in uncoordinated anions, as well as improved stability and ionic conductivity as compared to single anion solution. Solvent molecule rearrangement and direct Mg-ion exchange between the basic solvation structures are hypothesized as likely reasons for the exchange. We elucidate that the solvent rearrangement is energetically much more favorable than direct Mg-ion hopping and is thus suggested as the dominant exchange mechanism.

Li X ,Tang Y ,Wang M ,Zhu C ,Zhao W ,Zheng J ,Lin Y ,Song J  2018. "Self-supporting activated carbon/carbon nanotube/reduced graphene oxide flexible electrode for high performance supercapacitor" Carbon 129:236-244. (April 2018).

Abstract: A self-supporting and flexible activated carbon/carbon nanotube/reduced graphene oxide (AC/CNT/RGO) film has been rationally designed for constructing high- performance supercapacitor. The AC/CNT/RGO film is prepared by anchoring the AC particles with a 3D and porous framework built by hierarchically weaving the 1 D CNT and 2D RGO using their intrinsic van der Waals force. The CNT network is beneficial for improving the electronic conductivity of the electrode, while the AC particles could effectively suppress the aggregation of RGO and CNT due to their blocking effect. The synergistic effects among the AC, CNT and RGO validate the AC/CNT/RGO as a promising electrode for supercapacitor, exhibiting greatly enhanced electrochemical performances in comparison with the pure RGO film, pure CNT film and AC electrode. The AC/CNT/RGO electrode delivers a high specific capacitance of 101 F g-1 at the current density of 0.2 A g-1, offering a maximum energy density of 30.0 W h kg-1 in organic electrolyte at the cut-off voltage range of 0.001~3.0 V. The findings of this work open a new avenue for the design of self-supporting electrodes for the development of flexible and light weight energy storage supercapacitor.

Xing Li, Kangjia Zhang, David Mitlin, Zhenzhong Yang, Mingshan Wang, Yao Tang, Fei Jiang, Yingge Du, Jianming Zheng."Fundamental Insight into Zr Modification of Li- and Mn-Rich Cathodes: Combined Transmission Electron Microscopy and Electrochemical Impedance Spectroscopy Study."Chemistry of Materials 30 (8) 2566-2573 (April 2018).
Abstract: While zirconium-based coatings are known to improve the cycling stability of a number of lithium ion battery cathodes, the microstructural origin of this enhancement remains uncertain. Here we combine advanced transmission electron microscopy (high-resolution transmission electron microscopy, high-angle annular dark field, electron energy loss spectroscopy, and energy-dispersive X-ray spectroscopy) with electrochemical impedance analysis to provide new insight into the dramatic role of Zr surface modification on the electrochemical performance of Li- and Mn-rich (LMR) cathodes (Li[Li_0.2Ni_0.13Co0.13Mn_0.54]O₂). It is demonstrated that a Zr-based rock-salt structure layer with a thickness of 1–2 nm is formed on the surface of the LMR. This layer is effective in suppressing the deleterious phase transformation of LMR from initial layered composite combining Li₂MO₃ and LiMO₂ to the disordered rock-salt phase, leading to an enhanced long-term cycling performance and rate capability. Electrochemical impedance spectroscopy analysis demonstrates that the Zr coating does not affect the cathode electrolyte interface (CEI), with the surface film impedance (R_sf) being virtually identical in both cases after 100 cycles, at 45.1 versus 45.6 Ω. Conversely, the Zr coating tremendously stabilizes the cathode interfacial structure. The charge-transfer impedance (R_ct) in the baseline unmodified LMR increases from 34.2 Ω at cycle 3 to 729.2 Ω at cycle 100. For the Zr-modified specimen, R_ct increases dramatically less, from 19.7 to 76.9 Ω. The key finding of this study is then that Zr is actively incorporated into the structure of the cathode but does not affect CEI stability. This fundamental result should guide future surface modification strategies for a range of cathode materials.

Zheng H ,Xie Y ,Xiang H ,Shi P ,Liang X ,Xu W."A bifunctional electrolyte additive for separator wetting and dendrite suppression in lithium metal batteries.". Electrochimica Acta 270:62-69. (April 2018).
Abstract: Reformulation of electrolyte systems and improvement of separator wettability are vital to electrochemical performances of rechargeable lithium (Li) metal batteries, especially for suppressing Li dendrites. In this work we report a bifunctional electrolyte additive that improves separator wettability and suppresses Li dendrite growth in LMBs. A triblock polyether (Pluronic P123) was introduced as an additive into a commonly used carbonate-based electrolyte. It was found that addition of 0.2~1% (by weight) P123 into the electrolyte could effectively enhance the wettability of polyethylene separator. More importantly, the adsorption of P123 on Li metal surface can act as an artificial solid electrolyte interphase layer and contribute to suppress the growth of Li dendrites. A smooth and dendritic-free morphology can be achieved in the electrolyte with 0.2% P123. The Li||Li symmetric cells with the 0.2% P123 containing electrolyte exhibit a relatively stable cycling stability at high current densities of 1.0 and 3.0 mA cm-2.

Liu B ,Xu W ,Tao J ,Yan P ,Zheng J ,Engelhard M H,Lu D ,Wang C ,Zhang J. "Enhanced Cyclability of Lithium-Oxygen Batteries with Electrodes Protected by Surface Films Induced via In-Situ Electrochemical Process" Advanced Energy Materials 8(11).(April,2018)
Abstract: Although the rechargeable lithium–oxygen (Li–O₂) batteries have extremely high theoretical specific energy, the practical application of these batteries is still limited by the instability of their carbon‐based air‐electrode, Li metal anode, and electrodes, toward reduced oxygen species. Here a simple one‐step in situ electrochemical precharging strategy is demonstrated to generate thin protective films on both carbon nanotubes (CNTs), air‐electrodes and Li metal anodes simultaneously under an inert atmosphere. Li–O₂ cells after such pretreatment demonstrate significantly extended cycle life of 110 and 180 cycles under the capacity‐limited protocol of 1000 mA h g⁻¹ and 500 mA h g⁻¹, respectively, which is far more than those without pretreatment. The thin‐films formed from decomposition of electrolyte during in situ electrochemical precharging processes in an inert environment, can protect both CNTs air‐electrode and Li metal anode prior to conventional Li–O₂ discharge/charge cycling, where reactive reduced oxygen species are formed. This work provides a new approach for protection of carbon‐based air‐electrodes and Li metal anodes in practical Li–O₂ batteries, and may also be applied to other battery systems.

Kuber Mishra, Jianming Zheng, Rajankumar Patel, Luis Estevez, Haiping Jia, Langli Luo, Patrick Z. El-Khoury, Xiaolin Li, Xiao-Dong Zhou, Ji-Guang Zhang."High performance porous Si@C anodes synthesized by low temperature aluminothermic reaction."Electrochimica Acta 269: 509-516 (April 2018).
Abstract: A low temperature (210°C) aluminothermic reaction process using a eutectic mixture of AlCl₃ and ZnCl₂ as the mediator has been developed to synthesize porous silicon (Si) as an anode for lithium (Li)-ion battery applications. With carbon pre-coating on the porous SiO₂ precursor, carbon coated porous Si (p-Si@C) core-shell structured anodes could be obtained with architecture and morphology similar to that of the porous SiO₂ precursor. The carbon coating network not only facilitates the electron and Li⁺ ion transportation, but also offers good mechanical support minimizing the particle pulverization that is associated with the large volume change of Si during lithiation/delithiation. As a result, p-Si@C anode demonstrates a high specific capacity of ∼2100 mAh g⁻¹ at the current density of 1.2 A g⁻¹ and significantly improved capacity retention of ∼89% over 250 cycles, which is much better than that of p-Si. Therefore, p-Si@C is promising anode for high-energy-density Li-ion batteries. The similar low temperature synthesis approach can also be used to prepare other functional materials.

Wengao Zhao, Jianming Zheng, Lianfeng Zou, Haiping Jia, Bin Liu, Hui Wang, Mark H. Engelhard, Chongmin Wang, Wu Xu, Yong Yang, Ji-Guang Zhang."High Voltage Operation of Ni‐Rich NMC Cathodes Enabled by Stable Electrode/Electrolyte Interphases."Advanced Energy Materials8 (19), 1800297 (March 2018).
Abstract: The lithium (Li) metal battery (LMB) is one of the most promising candidates for next‐generation energy storage systems. However, it is still a significant challenge to operate LMBs with high voltage cathodes under high rate conditions. In this work, an LMB using a nickel‐rich layered cathode of LiNi_0.76Mn_0.14Co_0.10O₂ (NMC76) and an optimized electrolyte [0.6 m lithium bis(trifluoromethanesulfonyl)imide + 0.4 m lithium bis(oxalato)borate + 0.05 m LiPF₆ dissolved in ethylene carbonate and ethyl methyl carbonate (4:6 by weight)] demonstrates excellent stability at a high charge cutoff voltage of 4.5 V. Remarkably, these Li||NMC76 cells can deliver a high discharge capacity of >220 mA h g⁻¹ (846 W h kg⁻¹) and retain more than 80% capacity after 1000 cycles at high charge/discharge current rates of 2C/2C (1C = 200 mA g⁻¹). This excellent electrochemical performance can be attributed to the greatly enhanced structural/interfacial stability of both the Ni‐rich NMC76 cathode material and the Li metal anode using the optimized electrolyte.

Li X, J Tao, D Hu, MH Engelhard, W Zhao, J Zhang, and W Xu. 2018. "Stability of Polymeric Separators in Lithium Metal Batteries in a Low Voltage Environment." Journal of Materials Chemistry A. 6(12):5006-5015. (March, 2018)
Abstract: The separator is an important component in rechargeable lithium (Li) metal batteries, however, less attention has been focused on it. In this work, several representative separators, such as polyethylene, polypropylene, and such polyolefin separators with coatings of ceramic and polymeric materials, were selected to assemble into Li||Cu and Li||Li coin cells to test the Coulombic efficiency values of Li metal and the cycling stability in a low voltage environment less than 1 V. Moreover, two representative electrolytes of LiPF6 and LiTFSI-LiBOB in carbonate solvent mixture were also employed to systematically study their interactions with the separators in Li metal cells. It was found that the separators could largely affect the Coulombic efficiency values and cycling stability of Li metal cells, especially when using the LiPF6 electrolyte, which is probably due to the effect of the trace amount of HF in the LiPF6 electrolyte. Among these separators, polyethylene separator is the most stable one with Li metal. This work gave some reasonable explanations for the above phenomena, which could provide references for Li metal battery studies when employing Li||Cu and Li||Li cells conducted in the low voltage environment.

Shuru Chen, Jianming Zheng, Donghai Mei, Kee Sung Han, Mark H. Engelhard, Wengao Zhao, Wu Xu, Jun Liu, Ji-Guang Zhang."High‐Voltage Lithium‐Metal Batteries Enabled by Localized High‐Concentration Electrolytes."Advanced Materials30 (21) 1706102 (March 2018).
Abstract:Rechargeable lithium‐metal batteries (LMBs) are regarded as the “holy grail” of energy‐storage systems, but the electrolytes that are highly stable with both a lithium‐metal anode and high‐voltage cathodes still remain a great challenge. Here a novel “localized high‐concentration electrolyte” (HCE; 1.2 m lithium bis(fluorosulfonyl)imide in a mixture of dimethyl carbonate/bis(2,2,2‐trifluoroethyl) ether (1:2 by mol)) is reported that enables dendrite‐free cycling of lithium‐metal anodes with high Coulombic efficiency (99.5%) and excellent capacity retention (>80% after 700 cycles) of Li||LiNi_1/3Mn_1/3Co_1/3O₂ batteries. Unlike the HCEs reported before, the electrolyte reported in this work exhibits low concentration, low cost, low viscosity, improved conductivity, and good wettability that make LMBs closer to practical applications. The fundamental concept of “localized HCEs” developed in this work can also be applied to other battery systems, sensors, supercapacitors, and other electrochemical systems.

Alasdair J. Crawford, Qian Huang, Michael C.W. Kintner-Meyer, Ji-Guang Zhang, David M. Reed, Vincent L. Sprenkle, Vilayanur V. Viswanathan, Daiwon Choi."Lifecycle comparison of selected Li-ion battery chemistries under grid and electric vehicle duty cycle combinations."Journal of Power Sources 380: 185-193 (March 2018).
Abstract: Li-ion batteries are expected to play a vital role in stabilizing the electrical grid as solar and wind generation capacity becomes increasingly integrated into the electric infrastructure. This article describes how two different commercial Li-ion batteries based on LiNi_0.8Co_0.15Al_0.05O₂ (NCA) and LiFePO₄ (LFP) chemistries were tested under grid duty cycles recently developed for two specific grid services: (1) frequency regulation (FR) and (2) peak shaving (PS) with and without being subjected to electric vehicle (EV) drive cycles. The lifecycle comparison derived from the capacity, round-trip efficiency (RTE), resistance, charge/discharge energy, and total used energy of the two battery chemistries are discussed. The LFP chemistry shows better stability for the energy-intensive PS service, while the NCA chemistry is more conducive to the FR service under the operating regimes investigated. The results can be used as a guideline for selection, deployment, operation, and cost analyses of Li-ion batteries used for different applications.

Saurel, D; Orayech, B; Xiao, B; Carriazo, D; Li,X;Rojo T. "'From Charge Storage Mechanism to Performance: A Roadmap toward High Specific Energy Sodium‐Ion Batteries through Carbon Anode Optimization" Advanced Energy Materials.  (March, 2018)
Abstract: While sodium‐ion batteries (SIBs) represent a low‐cost substitute for Li‐ion batteries (LIBs), there are still several key issues that need to be addressed before SIBs become market‐ready. Among these, one of the most challenging is the negligible sodium uptake into graphite, which is the keystone of the present LIB technology. Although hard carbon has long been established as one of the best substitutes, its performance remains below that of graphite in LIBs and its sodium storage mechanism is still under debate. Many other carbons have been recently studied, some of which have presented capacities far beyond that of graphite. However, these also tend to exhibit larger voltage and high first cycle loss, leading to limited benefits in terms of full cell specific energy. Overcoming this concerning tradeoff necessitates a deep understanding of the charge storage mechanisms and the correlation between structure, microstructure, and performance. This review aims to address this by drawing a roadmap of the emerging routes to optimization of carbon materials for SIB anodes on the basis of a critical survey of the reported electrochemical performances and charge storage mechanisms.

Jinhua Huang, Wentao Duan, Jingjing Zhang, Ilya A. Shkrob, Rajeev S. Assary, Baofei Pan, Chen Liao, Zhengcheng Zhang, Xiaoliang Wei, Lu Zhang."Substituted thiadiazoles as energy-rich anolytes for nonaqueous redox flow cells."Journal of Materials Chemistry A 6 (15): 6251-6254 (March 2018).
Abstract: Understanding structure–property relationships is essential for designing energy-rich redox active organic molecules (ROMs) for all-organic redox flow batteries. Herein we examine thiadiazole ROMs for storage of negative charge in the flow cells. These versatile molecules have excellent solubility and low redox potentials, allowing high energy density to be achieved. By systematically incorporating groups with varying electron accepting/withdrawing ability, we have examined substituent effects on their properties of interest, including redox potentials, calendar lives of charged ROMs in electrolyte, and the flow cell cycling performance. While the calendar life of energized fluids can be tuned in a predictable fashion over a wide range, the improvements in the calendar life do not automatically translate into the enhanced cycling performance, indicating that in addition to the slow reactions of charged species in the solvent bulk, there are other parasitic reactions that occur only during the electrochemical cycling of the cell and can dramatically affect the cycling lifetime.

Chang HJ ,Lu X ,Bonnett J F,Canfield N L,Son S ,Park YC ,Jung K ,Sprenkle V L,Li G. "'Ni-less' Cathodes for High Energy Density, Intermediate Temperature"Advanced Materials Interfaces. 1701592 (March, 2018)
Abstract: Among various battery technologies being considered for stationary energy storage applications, sodium–metal halide (Na–MH) batteries have become one of the most attractive candidates because of the abundance of raw materials, long cycle life, high energy density, and superior safety. However, one of issues limiting its practical application is the relatively expensive nickel (Ni) used in the cathode. In the present work, the focus is on efforts to develop new Ni‐based cathodes, and it is demonstrated that a much higher specific energy density of 405 Wh kg⁻¹ (16% higher than state‐of‐the‐art Na–MH batteries) can be achieved at an operating temperature of 190 °C. Furthermore, 15% less Ni is used in the new cathode formula than that in conventional Na–NiCl₂ batteries. Long‐term cycling tests also show stable electrochemical performance for over 300 cycles with excellent capacity retention (≈100%). The results in this work indicate that these advances can significantly reduce the raw material cost associated with Ni (a 31% reduction) and promote practical applications of Na–MH battery technologies in stationary energy storage systems.

Brian D. Adams, Jianming Zheng, Xiaodi Ren, Wu Xu, Ji-Guang Zhang."Accurate Determination of Coulombic Efficiency for Lithium Metal Anodes and Lithium Metal Batteries."Advanced Energy Materials 8 (7): (March 2018).
Abstract: Lithium (Li) metal is an ideal anode material for high energy density batteries. However, the low Coulombic efficiency (CE) and the formation of dendrites during repeated plating and stripping processes have hindered its applications in rechargeable Li metal batteries. The accurate measurement of Li CE is a critical factor to predict the cycle life of Li metal batteries, but the measurement of Li CE is affected by various factors that often lead to conflicting values reported in the literature. Here, several parameters that affect the measurement of Li CE are investigated and a more accurate method of determining Li CE is proposed. It is also found that the capacity used for cycling greatly affects the stabilization cycles and the average CE. A higher cycling capacity leads to faster stabilization of Li anode and a higher average CE. With a proper operating protocol, the average Li CE can be increased from 99.0% to 99.5% at a high capacity of 6 mA h cm⁻² (which is suitable for practical applications) when a high-concentration ether-based electrolyte is used.

Ye F, H Noh, JH Lee, H Lee, and HT Kim.Ye F, H Noh, JH Lee, H Lee, and HT Kim."Li2S/Carbon Nanocomposite Strips from a Low-Temperature Conversion of Li2SO4 as High-Performance Lithium-Sulfur Cathodes." Journal of Materials Chemistry A 6(15): 6617-6624 (March 2018).
Abstract:Carbothermal conversion of Li2SO4 provides a cost-effective strategy to fabricate high-capacity Li2S cathodes, however, Li2S cathodes derived from Li2SO4 at high temperatures (> 800 oC), having high crystallinity and large crystal size, result in a low utilization of Li2S. Here, we report a Li2SO4/poly(vinyl alcohol)-derived Li2S/Carbon nanocomposite (Li2S@C) strips at a record low temperature of 635 oC. These Li2S@C nanocomposite strips as a cathode shows a low initial activation potential (2.63 V), a high initial discharge capacity (805 mAh g-1 Li2S) and a high cycling stability (0.2 C and 1 C). These improvedresults could be ascribed to the nano-sized Li2S particles as well as their low crystallinity due to the PVA-induced carbon network and the low conversion temperature, respectively. An XPS analysis reveals that the C=C and C=O bonds derived from the carbonization of PVA can promote the conversion of Li2SO4 at the low temperature.

Yu L, NL Canfield, S Chen, H Lee, X Ren, MH Engelhard, Q Li, J Liu, W Xu, and J Zhang."Enhanced Stability of Li Metal Anode by using a 3D Porous Nickel Substrate." ChemElectroChem 5 (5): 761-769 (March 2018).
Abstract:Lithium (Li) metal is considered the “holy grail” anode for high energy density batteries, but its applications in rechargeable Li metal batteries are still hindered by the formation of Li dendrites and low Coulombic efficiency for Li plating/stripping. An effective strategy to stabilize Li metal is by embedding Li metal anode in a three-dimensional (3D) current collector. Here, a highly porous 3D Ni substrate is reported to effectively stabilize Li metal anode. Using galvanostatic intermittent titration technique combined with scanning electron microscopy, the underlying mechanism on the improved stability of Li metal anode is revealed. It is clearly demonstrated that the use of porous 3D Ni substrate can effectively suppress the formation of “dead” Li and forms a dense surface layer, whereas a porous “dead” Li layer is accumulated on the 2D Li metal which eventually leads to mass transport limitations. X-ray photoelectron spectroscopy results further revealed the compositional differences in the solid-electrolyte interphase layer formed on the Li metal embedded in porous 3D Ni substrate and the 2D copper substrate.

Li X ,Zhang K ,Wang M ,Liu Y ,Qu M ,Zhao W ,Zheng J  2018. "Dual functions of zirconium modification on improving the electrochemical performance of Ni-rich LiNi0.8Co0.1Mn0.1O2" Sustainable Energy & Fuels 2(2):413-421. (February 2018).
Abstract: Trace amount of Zirconium (Zr) has been adopted to modify the crystal structure and surface of the Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material. During cycling at 1.0C, the Zr-modified NCM811 shows an improved capacity retention of 92% after 100 cycles, higher than 75% for pristine NMC811. In addition, the Zr-modified NCM811 is capable of delivering a discharge capacity of 107 mAh g-1 at 10.0C rate, much higher than 28 mAh g-1 delivered by pristine material. These improved electrochemical performances are ascribed to the dual functions of Zr modification. On one hand, part of the Zr enters the crystal lattice, which is beneficial for reducing the Li/Ni cation mixing and enhancing the crystal stability of the cathode. On the other hand, the rest of the Zr forms a 1~2 nm thick coating layer on the surface of the NCM811 cathode, which effectively prevents the direct contact between NCM and the electrolyte, thus suppressing the detrimental interfacial reactions. Therefore, the Zr-modified LiNi0.8Co0.1Mn0.1O2 exhibited significantly enhanced cycling stability and charging/discharging rate capability in comparison with the untreated counterpart.

Huilin Pan, Kee Sung Han, Mark H. Engelhard, Ruiguo Cao, Junzheng Chen, Ji-Guang Zhang, Karl T. Mueller, Yuyan Shao, Jun Liu."Addressing Passivation in Lithium–Sulfur Battery Under Lean Electrolyte Condition."Advanced Functional Materials 1707234 (February 2018).
Abstract: Reducing the electrolyte amount is critical for the high specific energy of lithium–sulfur (Li–S) batteries in practice. The reduced electrolyte condition (a so‐called “lean electrolyte”) raises a complex situation for sulfur redox reactions since the reactions rely on the electrolyte mediation. The insulating nature of discharge product Li₂S and its uncontrollable accumulation (passivation) at the cathode interface is one of the major challenges for stable cycling of a Li–S battery under lean electrolyte condition. In this study, it is presented that the NH₄TFSI additive in electrolyte solution greatly alleviates the passivation issue in Li–S batteries under lean electrolyte conditions. The ammonium additive enhances the dissociation of Li₂S and largely reduces the insoluble and large Li₂S particles in the sulfur cathodes, which facilitate the reversible and sustainable redox reactions of sulfur. Therefore, the cycle life of Li–S batteries under lean electrolyte conditions is significantly improved. In addition, it is found that the morphology of Li anodes is dependent on the cathode structures. An ammonium additive enables homogeneous surface of cathode and Li anode and extended cycle life.

Ming-Shan Wang, Zhi-Qiang Wang, Zhou Chen, Zhen-Liang Yang, Zhi-Liang Tang, Hong-Yu Luo, Yun Huang, Xing Li, Wu Xu."One dimensional and coaxial polyaniline@tin dioxide@multi-wall carbon nanotube as advanced conductive additive free anode for lithium ion battery."Chemical Engineering Journal 334: 162-171 (February 2018).
Abstract: In this paper, we design a novel one dimensional and coaxial polyaniline@tin dioxide@multi-wall carbon nanotube (PANI@SnO₂@MWCNT) composite as advanced conductive additive free anode material for the lithium ion battery. The SnO₂ nanoparticles (∼5 nm) are firstly fixed on the conductive MWCNT skeleton by self-assembling the nano-sized SnO₂ particles on the surface of MWCNT with the assist of surfactant P123 then followed by in-situ coating a flexible layer of PANI with excellent electron and lithium ion conductivity. The one dimensional and coaxial PANI@SnO₂@MWCNT can effectively accommodate the volume expansion of SnO₂ nanoparticles during lithiating and delithiating via the wrapping of the flexible coating layer of PANI and the buffer of the one dimensional MWCNT. Moreover, the electronic and lithium ionic conductivities of the composite are also obviously improved by the synergistic action between the PANI and MWCNT. As a result, the PANI@SnO₂@MWCNT composite exhibits an excellent rate capacity and stable cycling performance even without the adding of the conductive additive.

Shaofang Fu, Junhua Song, Chengzhou Zhu, Gui-Liang Xu, Khalil Amine, Chengjun Sun, Xiaolin Li, Mark H Engelhard, Dan Du, Yuehu Lin."Ultrafine and highly disordered Ni₂Fe₁ nanofoams enabled highly efficient oxygen evolution reaction in alkaline electrolyte."Nano Energy44: 319-326 (February 2018).
Abstract: Nickel iron hydroxides are the most promising non-noble electrocatalysts for oxygen evolution reaction (OER) in alkaline media. By in situ reduction of metal precursors, compositionally controlled three-dimensional Ni_xFe_y nanofoams (NFs) are synthesized with high surface area and uniformly distributed bimetallic networks. The resultant ultrafine and highly disordered amorphous Ni₂Fe₁ NFs exhibit extraordinary electrocatalytic performance toward OER and overall water splitting in alkaline media. At a potential as low as 1.42 V (vs. RHE), Ni₂Fe₁ NFs can deliver a current density of 10 mA/cm² and show negligible activity loss after 12 h stability test. Even at large current flux of 100 mA/cm², an ultralow overpotential of 0.27 V is achieved, which is about 0.18 V more negative than benchmark RuO₂. Both ex-situ Mӧssbauer spectroscopy and X-ray Absorption Spectroscopy reveal a phase separation and transformation for the Ni₂Fe₁ catalyst during OER process. The evolution of oxidation state and disordered structure of Ni₂Fe₁ might be a key to the high catalytic performance for OER.

Li X ,Zheng J ,Engelhard M H,Mei D ,Li Q ,Jiao S ,Liu N ,Zhao W ,Zhang J ,Xu W. "Effects of Imide–Orthoborate Dual-Salt Mixtures in Organic Carbonate Electrolytes on the Stability of Lithium Metal Batteries " ACS Applied Materials Interfaces 10(3):2469-2479. (January, 2018)

Abstract: The effects of lithium imide and lithium orthoborate dual-salt electrolytes of different salt chemistries in carbonate solvents on the cycling stability of Li metal batteries were systematically and comparatively investigated. Two imide salts (LiTFSI and LiFSI) and two orthoborate salts (LiBOB and LiDFOB) were chosen for this study and compared with the conventional LiPF6 salt. The cycling stability of the Li metal cells with the electrolytes follows the order from good to poor as LiTFSI-LiBOB > LiTFSI-LiDFOB > LiPF6 > LiFSI-LiBOB > LiFSI-LiDFOB, indicating that LiTFSI behaves better than LiFSI and LiBOB over LiDFOB in these four dual-salt mixtures. The LiTFSI-LiBOB can effectively protect the Al substrate and form a more robust surface film on Li metal anode, while the LiFSI-LiBOB results in serious corrosion to the stainless steel cell case and a thicker and looser surface film on Li anode. Computational calculations indicate that the chemical and electrochemical stabilities also follow the order of LiTFSI-LiBOB > LiTFSI-LiDFOB > LiFSI-LiBOB > LiFSI-LiDFOB. The key findings of this work emphasize that the salt chemistry is critically important for enhancing the interfacial stability of Li metal anode and should be carefully manipulated in the development of high performance Li metal batteries.

Shuhong Jiao, Jianming Zheng, Qiuyan Li, Xing Li, Mark H. Engelhard, Ruiguo Cao, Ji-Guang Zhang, Wu Xu."Behavior of Lithium Metal Anodes under Various Capacity Utilization and High Current Density in Lithium Metal Batteries."Joule 2 (1) 110-124 (January 2018).
Abstract: Lithium (Li) metal batteries (LMBs) have recently attracted extensive interest in the energy-storage field after silence from the public view for several decades. However, many challenges still need to be overcome before their practical application, especially those that are related to the interfacial instability of Li metal anodes. Here, we reveal for the first time that the thickness of the degradation layer on the metallic Li anode surface shows a linear relationship with Li areal capacity utilization up to 4.0 mAh cm⁻² in a practical LMB system. The increase in Li capacity utilization in each cycle causes variations in the morphology and composition of the degradation layer on the Li anode. Under high Li capacity utilization, the current density for charge (i.e., Li deposition) is identified to be a key factor controlling the corrosion of the Li metal anode. These fundamental findings provide new perspectives for the development of rechargeable LMBs.

Yuxing Wang, Dongping Lu, Mark Bowden, Patrick Z. ElKhoury, Kee Sung Han, Zhiqun Daniel Deng, Jie Xiao, Ji-Guang Zhang, Jun Liu."Mechanism of Formation of Li₇P₃S₁₁ Solid Electrolytes through Liquid Phase Synthesis."Chemistry of Materials 30 (3) 990-997 (January 2018).
Abstract: Crystalline Li₇P₃S₁₁ is a promising solid electrolyte for all solid-state lithium/lithium ion batteries. A controllable liquid phase synthesis of Li₇P₃S₁₁ is more desirable than conventional mechanochemical synthesis, but recent attempts suffer from reduced ionic conductivities. Here we elucidate the mechanism of formation of crystalline Li₇P₃S₁₁ synthesized in the liquid phase [acetonitrile (ACN)]. We conclude that crystalline Li₇P₃S₁₁ forms through a two-step reaction: (1) formation of solid Li₃PS₄·ACN and amorphous “Li₂S·P₂S₅” phases in the liquid phase and (2) solid-state conversion of the two phases. The implication of this two-step reaction mechanism for morphology control and the transport properties of liquid phase synthesized Li₇P₃S₁₁ is identified and discussed.

Zheng J ,Chen S ,Zhao W ,Song J ,Engelhard M H,Zhang J  2018. " Extremely Stable Sodium Metal Batteries Enabled by Localized High-Concentration Electrolytesigh Concentration Electrolytes" ACS Energy Letters 3(2):315-321. (January, 2018)
Abstract: Sodium (Na) metal is a promising anode for Na ion batteries. However, the high reactivity of Na metal with electrolytes and the low Na metal cycling efficiency have limited its practical application in rechargeable Na metal batteries. High concentration electrolytes (HCE, ≥4 M) consisting of sodium bis(fluorosulfonyl)imide (NaFSI) and ether solvent could ensure the stable cycling of Na metal with high coulombic efficiency, but suffer from high viscosity, poor wetting ability, and high salt cost. Here, we report that the salt concentration could be significantly reduced (≤ 1.5 M) by diluting with a hydrofluoroether (HFE) as ‘inert’ diluent, which maintains the solvation structures of HCE, thereby forming a localized high concentration electrolyte (LHCE). A LHCE (2.1 M NaFSI/DME-BTFE (solvent molar ratio 1:2)) has been demonstrated to enable the dendrite-free Na deposition with high coulombic efficiency of  > 99%, fast-charging (20C) and stable cycling (90.8% retention after 40,000 cycles) of Na||Na3V2(PO4)3 batteries.

Xiaodi Ren, Yaohui Zhang, Mark H. Engelhard, Qiuyan Li, Ji-Guang Zhang, Wu Xu."Guided Lithium Metal Deposition and Improved Lithium Coulombic Efficiency through Synergistic Effects of LiAsF₆ and Cyclic Carbonate Additives."ACS Energy Letters 3: 14-19 (January 2018).
Abstract: Spatial and morphology control over lithium (Li) metal nucleation and growth, as well as improving Li Coulombic efficiency (CE), are among the most challenging issues for rechargeable Li metal batteries. Here, we report that LiAsF₆ and cyclic carbonate additives such as vinylene carbonate (VC) or fluoroethylene carbonate (FEC) can work synergistically to address these challenges. It is revealed that LiAsF₆ can be reduced to Li_xAs alloy and LiF, which act as nanosized seeds for Li growth and form a robust solid electrolyte interface layer. The addition of VC or FEC not only enables the uniform distribution of Li_xAs seeds but also improves the flexibility of the solid electrolyte interface layer. As a result, highly compact, uniform, and dendrite-free Li film with vertically aligned column structure can be obtained with increased Li CE, and the Li metal batteries using the electrolyte with both LiAsF₆ and cyclic carbonate additives can have improved cycle life.

Hongkyung Lee, Xiaodi Ren, Chaojiang Niu, Lu Yu, Mark H. Engelhard, Inseong Cho, Myung-Hyun Ryou, Hyun Soo Jin, Hee-Tak Kim, Jun Liu, Wu Xu, Ji-Guang Zhang."Suppressing Lithium Dendrite Growth by Metallic Coating on a Separator."Advanced Functional Materials 27 (45) 1704391 (December 2017).
Abstract: Lithium (Li) metal is one of the most promising candidates for the anode in high‐energy‐density batteries. However, Li dendrite growth induces a significant safety concerns in these batteries. Here, a multifunctional separator through coating a thin electronic conductive film on one side of the conventional polymer separator facing the Li anode is proposed for the purpose of Li dendrite suppression and cycling stability improvement. The ultrathin Cu film on one side of the polyethylene support serves as an additional conducting agent to facilitate electrochemical stripping/deposition of Li metal with less accumulation of electrically isolated or “dead” Li. Furthermore, its electrically conductive nature guides the backside plating of Li metal and modulates the Li deposition morphology via dendrite merging. In addition, metallic Cu film coating can also improve thermal stability of the separator and enhance the safety of the batteries. Due to its unique beneficial features, this separator enables stable cycling of Li metal anode with enhanced Coulombic efficiency during extended cycles in Li metal batteries and increases the lifetime of Li metal anode by preventing short‐circuit failures even under extensive Li metal deposition.

Jianming Zheng, Pengfei Yan, Jiandong Zhang, Mark H. Engelhard, Zihua Zhu, Bryant J. Polzin, Steve Trask, Jie Xiao, Chongmin Wang, Jiguang Zhang."Suppressed oxygen extraction and degradation of LiNi _x Mn _y Co _z O₂ cathodes at high charge cut-off voltages."Nano Research 10 (12) 4221-4231 (December 2017).
Abstract: The capacity degradation mechanism in lithium nickel–manganese–cobalt oxide (NMC) cathodes (LiNi_1/3Mn_1/3Co_1/3O₂ (NMC₃₃₃) and LiNi_0.4Mn_0.4Co_0.2O₂ (NMC₄₄₂)) during high-voltage (cut-off of ₄.8 V) operation has been investigated. In contrast to NMC₄₄₂, NMC₃₃₃ exhibits rapid structural changes including severe micro-crack formation and phase transformation from a layered to a disordered rock-salt structure, as well as interfacial degradation during high-voltage cycling, leading to a rapid increase of the electrode resistance and fast capacity decline. The fundamental reason behind the poor structural and interfacial stability of NMC₃₃₃ was found to be correlated to its high Co content and the significant overlap between the Co^3+/4+ t_2g and O²⁻ 2p bands, resulting in oxygen removal and consequent structural changes at high voltages. In addition, oxidation of the electrolyte solvents by the extracted oxygen species generates acidic species, which then attack the electrode surface and form highly resistive LiF. These findings highlight that both the structural and interfacial stability should be taken into account when tailoring cathode materials for high voltage battery systems.

Qiuyan Li, Dongping Lu, Jianming Zhang, Shuhong Jiao, Langli Luo, Chongmin Wang, Kang Xu, Ji-Guang Zhang, Wu Xu."Li⁺-Desolvation Dictating Lithium-Ion Battery’s Low-Temperature Performances."ACS Applied Materials & Interfaces9 (49): 42761-42768 (November 2017).
Abstract: Lithium (Li) ion battery has penetrated almost every aspect of human life, from portable electronics, vehicles, to grids, and its operation stability in extreme environments is becoming increasingly important. Among these, subzero temperature presents a kinetic challenge to the electrochemical reactions required to deliver the stored energy. In this work, we attempted to identify the rate-determining process for Li⁺ migration under such low temperatures, so that an optimum electrolyte formulation could be designed to maximize the energy output. Substantial increase in the available capacities from graphite∥LiNi_0.80Co_0.15Al_0.05O₂ chemistry down to −40 °C is achieved by reducing the solvent molecule that more tightly binds to Li⁺ and thus constitutes a high desolvation energy barrier. The fundamental understanding is applicable universally to a wide spectrum of electrochemical devices that have to operate in similar environments.

J. Zhang, Z. Yang, I. A. Shkrob, R. S. Assary, S. Tung, B. Silcox, W. Duan, J. Zhang, C. Liao, Z. Zhang, W. Wang, L. A. Curtiss, L. Thompson, X. Wei, L. Zhang. " Annulated dialkoxybenzenes as catholyte materials for nonaqueous redox flow batteries: achieving high chemical stability through bicyclic substitution " Advanced Energy Materials. 2017, 7, 1701272. (November 2017).
Abstract: 1,4-Dimethoxybenzene derivatives are materials of choice for use as catholytes in non-aqueous redox flow batteries, as they exhibit high open-circuit potentials and excellent electrochemical reversibility. However, chemical stability of these materials in their oxidized form needs to be improved. Disubstitution in the arene ring is used to suppress parasitic reactions of their radical cations, but this does not fully prevent ring-addition reactions. By incorporating bicyclic substitutions and ether chains into the dialkoxybenzenes, a novel catholyte molecule, 9,10-bis(2-methoxyethoxy)-1,2,3,4,5,6,7,8-octahydro-1, 4:5,8- dimethanenoanthracene (BODMA), is obtained and exhibits greater solubility and superior chemical stability in the charged state. A hybrid flow cell containing BODMA is operated for 150 charge–discharge cycles with a minimal loss of capacity.

Shuhong Jiao, Jianming Zheng, Qiuyan Li, Xing Li, Mark H. Engelhard, Ruiguo Cao, Ji-Guang Zhang, and Wu Xu. "Behavior of Lithium Metal Anodes under Various Capacity Utilization and High Current Density in Lithium Metal Batteries " Joule 2018, 2,1-15 (Nov. 2017 online).  

Abstract:Lithium (Li) metal batteries (LMBs) have recently attracted extensive interest in the energy-storage field after silence from the public view for several decades. However, many challenges still need to be overcome before their practical application, especially those that are related to the interfacial instability of Li metal anodes. Here, we reveal for the first time that the thickness of the degradation layer on the metallic Li anode surface shows a linear relationship with Li areal capacity utilization up to 4.0 mAh cm⁻² in a practical LMB system. The increase in Li capacity utilization in each cycle causes variations in the morphology and composition of the degradation layer on the Li anode. Under high Li capacity utilization, the current density for charge (i.e., Li deposition) is identified to be a key factor controlling the corrosion of the Li metal anode. These fundamental findings provide new perspectives for the development of rechargeable LMBs.

Xuefeng Wang, Minghao Zhang, Judith Alvarado, Shen Wang, Mahsa Sina, Bingyu Lu, James Bouwer, Wu Xu, Jie Xiao, Ji-Guang Zhang, Jun Liu, Ying Shirley Meng."New Insights on the Structure of Electrochemically Deposited Lithium Metal and Its Solid Electrolyte Interphases via Cryogenic TEM." Nano Letters17 (12): 7606-7612 (November 2017).
Abstract:Lithium metal has been considered the “holy grail” anode material for rechargeable batteries despite the fact that its dendritic growth and low Coulombic efficiency (CE) have crippled its practical use for decades. Its high chemical reactivity and low stability make it difficult to explore the intrinsic chemical and physical properties of the electrochemically deposited lithium (EDLi) and its accompanying solid electrolyte interphase (SEI). To prevent the dendritic growth and enhance the electrochemical reversibility, it is crucial to understand the nano- and mesostructures of EDLi. However, Li metal is very sensitive to beam damage and has low contrast for commonly used characterization techniques such as electron microscopy. Inspired by biological imaging techniques, this work demonstrates the power of cryogenic (cryo)-electron microscopy to reveal the detailed structure of EDLi and the SEI composition at the nanoscale while minimizing beam damage during imaging. Surprisingly, the results show that the nucleation-dominated EDLi (5 min at 0.5 mA cm–2) is amorphous, while there is some crystalline LiF present in the SEI. The EDLi grown from various electrolytes with different additives exhibits distinctive surface properties. Consequently, these results highlight the importance of the SEI and its relationship with the CE. Our findings not only illustrate the capabilities of cryogenic microscopy for beam (thermal)-sensitive materials but also yield crucial structural information on the EDLi evolution with and without electrolyte additives.

Xinxin Cao, Anqiang Pan, Sainan Liu, Jiang Zhou, Site Li, Guozhong Cao, Jun Liu, Shuquan Liang."Chemical Synthesis of 3D Graphene‐Like Cages for Sodium‐Ion Batteries Applications."Advanced Energy Materials7 (20) 1700797 (October 2017).
Abstract: Sodium (Na) super ion conductor structured Na₃V₂(PO₄)₃ (NVP) is extensively explored as cathode material for sodium‐ion batteries (SIBs) due to its large interstitial channels for Na⁺ migration. The synthesis of 3D graphene‐like structure coated on NVP nanoflakes arrays via a one‐pot, solid‐state reaction in molten hydrocarbon is reported. The NVP nanoflakes are uniformly coated by the in situ generated 3D graphene‐like layers with the thickness of 3 nm. As a cathode material, graphene covered NVP nanoflakes exhibit excellent electrochemical performances, including close to theoretical reversible capacity (115.2 mA h g⁻¹ at 1 C), superior rate capability (75.9 mA h g⁻¹ at 200 C), and excellent cyclic stability (62.5% of capacity retention over 30000 cycles at 50 C). Furthermore, the 3D graphene‐like cages after removing NVP also serve as a good anode material and deliver a specific capacity of 242.5 mA h g⁻¹ at 0.1 A g⁻¹. The full SIB using these two cathode and anode materials delivers a high specific capacity (109.2 mA h g⁻¹ at 0.1 A g⁻¹) and good cycling stability (77.1% capacity retention over 200 cycles at 0.1 A g⁻¹).

Han, K. S.; Chen, J.; Cao, R.; Rajput, N. N.; Murugesan, V.; Shi, L.; Pan, H.; Zhang, J.-G.; Liu, J.; Persson, K. A.; Mueller, K. T. " Effects of Anion Mobility on Electrochemical Behaviors of Lithium–Sulfur Batteries " Chemistry of Materials. 29(21): 9023-9029 (Oct. 2017).
Abstract: The electrolyte is a crucial component of lithium–sulfur (Li–S) batteries, as it controls polysulfide dissolution, charge shuttling processes, and solid-electrolyte interphase (SEI) layer formation. Experimentally, the overall performance of Li–S batteries varies with choice of solvent system and Li-salt used in the electrolyte, and a lack of predictive understanding about the effects of individual electrolyte components inhibits the rational design of electrolytes for Li–S batteries. Here we analyze the role of the counteranions of common Li salts (such as TfO^–, FSI^–, TFSI^–, and TDI^–) when dissolved in DOL/DME (1:1 by vol.) for use in Li–S batteries. The evolution of ion–ion and ion–solvent interactions due to various anions was analyzed using ¹⁷O NMR and pulsed-field gradient (PFG) NMR and then correlated with electrochemical performance in Li–S cells. These data reveal that the formation of the passivation layer on the anode and the loss of active materials from the cathode (evidenced by polysulfide dissolution) are related to anion mobility and affinity with lithium polysulfide, respectively. For future electrolyte design, anions with lower mobility and weaker interactions with lithium polysulfides may be superior candidates for increasing the long-term stability of Li–S batteries.

Bin Liu, Wu Xu, Jianming Zheng, Pengfei Yan, Eric D. Walter, Nancy Isern, Mark E. Bowden, Mark H. Engelhard, Sun Tai Kim, Jeffrey Read, Brian D. Adams, Xiaolin Li, Jaephil Cho, Chongmin Wang, and Ji-Guang Zhang. "Temperature Dependence of the Oxygen Reduction Mechanism in Nonaqueous Li–O2 Batteries " ACS Energy Letters 2017, 2(11) 2525-2530 (Oct. 2017).

Abstract:The temperature dependence of the oxygen reduction mechanism in nonaqueous Li–O₂ batteries is investigated within the temperature range of −20 to 40 °C. The discharge capacity of the Li–O₂ battery first decreases from 7492 mAh g^–1 at 40 °C to 2930 mAh g^–1 at 0 °C and then increases sharply with a further decrease in temperature and reaches a very high capacity of 17 716 mAh g^–1 at −20 °C at 0.1 mA cm^–2. The lifetime of superoxide intermediates and the solution pathway were found to play a dominant role in the discharge of the Li–O₂ battery in the temperature range of −20 to 0 °C, but the electrochemical kinetics of oxygen reduction and the surface pathway dominate the discharge behavior of the Li–O₂ batteries between 0 and 40 °C. This work will broaden the fundamental understanding of the oxygen reduction process in the Li–O₂ battery, especially at different temperatures.

Pan, H.; Li, B.; Mei, D.; Nie, Z.; Shao, Y.; Li, G.; Li, X. S.; Han, K. S.; Mueller, K. T.; Sprenkle, V.; Liu, J. " Controlling Solid–Liquid Conversion Reactions for a Highly Reversible Aqueous Zinc–Iodine Battery" ACS Energy Letters 2:2674-2680 (Oct. 2017).

Abstract: Aqueous rechargeable batteries are desirable for energy storage because of their low cost and high safety. However, low capacity and short cyclic life are significant obstacles to their practical applications. Here, we demonstrate a highly reversible aqueous zinc–iodine battery using encapsulated iodine in microporous carbon as the cathode material by controlling solid–liquid conversion reactions. We identified the factors influencing solid–liquid conversion reactions, e.g., the pore size, surface chemistry of carbon host, and solvent effect. Rational manipulation of the competition between the adsorption in carbon and solvation in electrolytes for iodine species is responsible for the high reversibility and cyclic stability. The zinc–iodine battery delivers a high capacity of 174.4 mAh g^–1 at 1C, stable cyclic life over 3000 cycles with ∼90% capacity retention, and negligible self-discharge. We believe that the principles for stabilizing the zinc–iodine system could provide new insight for other conversion systems such as lithium–sulfur systems.

Brian D. Adams, Emily V. Carino, Justin G. Connell, Kee Sung Han, Ruiguo Cao, Junzheng Chen, Jianming Zheng, Qiuyan Li, Karl T. Mueller, Wesley A. Henderson, Ji-Guang Zhang. " Long Term Stability of Li-S Batteries Using High Concentration Lithium Nitrate Electrolytes" Nano Energy. 2017, 607-617.(Oct. 2017).
Abstract: The lithium-sulfur (Li-S) battery is a very promising candidate for the next generation of energy storage systems required for electrical vehicles and grid energy storage applications due to its very high theoretical specific energy (2500 W h kg−1). However, low Coulombic efficiency (CE) during repeated Li metal plating/stripping has severely limited the practical application of rechargeable Li-S batteries. In this work, a new electrolyte system based on a high concentration of LiNO3 in diglyme (G2) solvent is developed which enables an exceptionally high CE for Li metal plating/stripping and thus high stability of the Li anode in the sulfur-containing electrolyte. The tailoring of electrolyte properties for the Li anode has proven to be a highly successful strategy for improving the capacity retention and cycle life of Li-S batteries. This electrolyte provides a CE of greater than 99% for over 200 cycles of Li plating/stripping. In contrast, the Li anode cycles for less than 35 cycles (with a high CE) in the state-of-the-art 1 M LiTFSI + 0.3 M LiNO3 in 1,3-dioxolane:1,2-dimethoxyethane (DOL:DME) electrolyte under the same conditions. The stable Li anode enabled by the new electrolyte may accelerate the applications of high energy density Li-S batteries in both electrical vehicles and large-scale grid energy storage markets.

Junhua Song, Pengfei Yan, Langli Luo, Xingguo Qi, Xiaohui Rong, Jianming Zheng, Biwei Xiao, Shuo Feng, Chongmin Wang, Yong-Sheng Hu, Yuehe Lin, Vincent L. Sprenkle, Xiaolin Li."Yolk-shell structured Sb@C anodes for high energy Na-ion batteries."Nano Energy 40: 504-511 (October 2017).
Abstract: Despite great advances in sodium-ion battery developments, the search for high energy and stable anode materials remains a challenge. Alloy or conversion-typed anode materials are attractive candidates of high specific capacity and low voltage potential, yet their applications are hampered by the large volume expansion and hence poor electrochemical reversibility and fast capacity fade. Here, we use antimony (Sb) as an example to demonstrate the use of yolk-shell structured anodes for high energy Na-ion batteries. The Sb@C yolk-shell structure prepared by controlled reduction and selective removal of Sb₂O₃ from carbon coated Sb₂O₃ nanoparticles can accommodate the Sb swelling upon sodiation and improve the structural/electrical integrity against pulverization. It delivers a high specific capacity of ~ 554 mAh g⁻¹, good rate capability (315 mhA g⁻¹ at 10 C rate) and long cyclability (92% capacity retention over 200 cycles). Full-cells of O3-Na_0.9[Cu_0.22Fe_0.30Mn_0.48]O₂ cathodes and Sb@C-hard carbon composite anodes demonstrate a high specific energy of ~ 130 Wh kg⁻¹ (based on the total mass of cathode and anode) in the voltage range of 2.0–4.0 V, ~ 1.5 times energy of full-cells with similar design using hard carbon anodes.

Lu, X, HJ Chang, JF Bonnett, NL Canfield, K Jung, VL Sprenkle, G Li. "Effect of cathode thickness on the performance of planar Na-NiCl₂ battery." Journal of Power Sources 365: 456-462 (Oct. 2017).
Abstract:Na-beta alumina batteries (NBBs) are one of the most promising technologies for renewable energy storage and grid applications. Commercial NBBs are typically constructed in tubular designs, primarily because of their ease of sealing. However, planar designs are considered superior to tubular counterparts in terms of power output, cell packing, ease of assembly, and thermal management. In this paper, the performance of planar NBBs has been evaluated at an intermediate temperature. In particular, planar Na-NiCl₂ cells with different cathode loadings and thicknesses have been studied at 190°C. The effects of the cathode thickness, charging current, and discharging power output on the cell capacity and resistance have been investigated. More than 60% of theoretical cell capacity was retained with constant discharging power levels of 200, 175, and 100 mW/cm² for 1x, 2x, and 3x cathode loadings, respectively. The cell resistance with 1x and 2x cathode loadings was dominated by ohmic resistance with discharging currents up to 105 mA/cm², while for 3x cathode loading, it was primarily dominated by ohmic resistance with currents less than 66.67 mA/cm² and by polarization resistance above 66.67 mA/cm².

Pan, H., Chen, J., Cao, R., Vijay, M., Rajput, N.N., Han, K.S., Persson, K., Estevez, L., Engelhard, M.H., Zhang, J.G., Mueller, K.T., Cui, Y., Shao, Y., Liu, J. " Non-encapsulation Approach for High Performance Li-S Batteries through Controlled Nucleation and Growth" Natrue Energy. 2017, 2,813-820 (Sept. 2017).
Abstract: High-surface-area, nanostructured carbon is widely used for encapsulating sulfur and improving the cyclic stability of Li–S batteries, but the high carbon content and low packing density limit the specific energy that can be achieved. Here we report an approach that does not rely on sulfur encapsulation. We used a low-surface-area, open carbon fibre architecture to control the nucleation and growth of the sulfur species by manipulating the carbon surface chemistry and the solvent properties, such as donor number and Li⁺ diffusivity. Our approach facilitates the formation of large open spheres and prevents the production of an undesired insulating sulfur-containing film on the carbon surface. This mechanism leads to ~100% sulfur utilization, almost no capacity fading, over 99% coulombic efficiency and high energy density (1,835 Wh kg⁻¹ and 2,317 Wh l⁻¹). This finding offers an alternative approach for designing high-energy and low-cost Li–S batteries through controlling sulfur reaction on low-surface-area carbon. 

H. Wang, D. Lin, Y. Liu, Y. Li, Y. Cui. " Ultrahigh-current density anodes with interconnected Li metal reservoir through overlithiation of mesoporous AlF3 framework" Sci. Adv. e170130 (Sept. 2017).
Abstract:Lithium (Li) metal is the ultimate solution for next-generation high–energy density batteries but is plagued from commercialization by infinite relative volume change, low Coulombic efficiency due to side reactions, and safety issues caused by dendrite growth. These hazardous issues are further aggravated under high current densities needed by the increasing demand for fast charging/discharging. We report a one-step fabricated Li/Al₄Li₉-LiF nanocomposite (LAFN) through an “overlithiation” process of a mesoporous AlF₃ framework, which can simultaneously mitigate the abovementioned problems. Reaction-produced Al₄Li₉-LiF nanoparticles serve as the ideal skeleton for Li metal infusion, helping to achieve a near-zero volume change during stripping/plating and suppressed dendrite growth. As a result, the LAFN electrode is capable of working properly under an ultrahigh current density of 20 mA cm⁻² in symmetric cells and manifests highly improved rate capability with increased Coulombic efficiency in full cells. The simple fabrication process and its remarkable electrochemical performances enable LAFN to be a promising anode candidate for next-generation lithium metal batteries.

X. Wei, W. Pan, W. Duan, A. Hollas, Z. Yang, B. Li, Z. Nie, J. Liu, D. Reed, W. Wang, V. Sprenkle. "Materials and Systems for Organic Redox Flow Batteries: Status and Challenges " ACS Energy Letters 2017, 2,(9),2187-2204. (Aug. 2017).
Abstract: Redox flow batteries (RFBs) are propitious stationary energy storage technologies with exceptional scalability and flexibility to improve the stability, efficiency, and sustainability of our power grid. The redox-active materials are the key component for RFBs with which to achieve high energy density and good cyclability. Traditional inorganic-based materials encounter critical technical and economic limitations such as low solubility, inferior electrochemical activity, and high cost. Redox-active organic materials (ROMs) are promising alternative “green” candidates to push the boundaries of energy storage because of the significant advantages of molecular diversity, structural tailorability, and natural abundance. Here, the recent development of a variety of ROMs and associated battery designs in both aqueous and nonaqueous electrolytes are reviewed. The critical challenges and potential research opportunities for developing practically relevant organic flow batteries are discussed.

X. Wei, W. Pan, W. Duan, A. Hollas, Z. Yang, B. Li, Z. Nie, J. Liu, D. Reed, W. Wang, V. Sprenkle. "Materials and Systems for Organic Redox Flow Batteries: Status and Challenges " ACS Energy Letters 2017, 2,(9),2187-2204. (Aug. 2017).
Abstract:Redox flow batteries (RFBs) are propitious stationary energy storage technologies with exceptional scalability and flexibility to improve the stability, efficiency, and sustainability of our power grid. The redox-active materials are the key component for RFBs with which to achieve high energy density and good cyclability. Traditional inorganic-based materials encounter critical technical and economic limitations such as low solubility, inferior electrochemical activity, and high cost. Redox-active organic materials (ROMs) are promising alternative “green” candidates to push the boundaries of energy storage because of the significant advantages of molecular diversity, structural tailorability, and natural abundance. Here, the recent development of a variety of ROMs and associated battery designs in both aqueous and nonaqueous electrolytes are reviewed. The critical challenges and potential research opportunities for developing practically relevant organic flow batteries are discussed.

Wu D, M Kintner-Meyer, T Yang, P Balducci. "Analytical sizing methods for behind-the-meter battery storage." Journal of Energy Storage 12: 297-304 (Aug. 2017).
Abstract:In behind-the-meter application, battery storage system (BSS) is used to reduce a commercial or industrial customer's payment for electricity use, including energy and demand charges. The potential value of BSS in payment reduction and the optimal size can be determined by formulating and solving standard mathematical programming problems. In such mathematical programming methods, users input system information such as load profiles, energy/demand charge rates, and battery characteristics to construct a standard programming problem, which typically involves a large number of constraints and decision variables. The problems are then solved by optimization solvers to obtain numerical solutions. Such kind of methods cannot directly link the obtained optimal battery sizes to input parameters and requires case-by-case analysis. In this paper, we present an objective quantitative analysis of costs and benefits for customer-side BSS, and thereby identify key factors that affect optimal sizing. We then develop simple but effective guidelines for determining the most cost-effective battery size. The proposed analytical sizing methods are innovative, and provide engineering insights on how the optimal battery size varies with system characteristics. We illustrate the proposed methods using practical building load profile and utility rate. The obtained results are compared with the ones using mathematical programming based methods for validation.

Michael S. Ding, Qiuyan Li, Xing Li, Wu Xu, Kang Xu."Effects of Solvent Composition on Liquid Range, Glass Transition, and Conductivity of Electrolytes of a (Li, Cs)PF₆ Salt in EC-PC-EMC Solvents."Journal of Physical Chemistry C 121 (21): 11178-11183 (May 2017).
Abstract: Electrolytes of 1 M LiPF₆ (lithium hexafluorophosphate) and 0.05 M CsPF₆ (cesium hexafluorophosphate) in EC-PC-EMC (ethylene carbonate-propylene carbonate-ethyl methyl carbonate) solvents of varying solvent compositions were studied for the effects of solvent composition on the lower limit of liquid range, glass transition temperature (as a reflection of viscosity), and electrolytic conductivity. In addition, a ternary phase diagram of EC-PC-EMC was constructed, and crystallization temperatures of EC and EMC were calculated to assist the interpretation and understanding of the change of liquid range with solvent composition. A function based on the Vogel–Fulcher–Tammann equation was fitted to the conductivity data in their entirety and was plotted as conductivity surfaces in solvent composition space for more direct and clear comparisons and discussions. Changes of viscosity and dielectric constant of the solvents with their composition, in relation to those of the solvent components, were found to be underlying many of the processes studied.

Cho SJ, MJ Uddin, PK Alaboina, SS Han, MI Nandasiri, YS Choi, E Hu, KW Nam, AM Schwarz, SK Nune, JS Cho, KH Oh, D Choi. "Exploring Lithium Deficiency in Layered Oxide Cathode for Li-Ion Battery." Advanced Sustainable Systems 1 (7) (June 2017).
Abstract:The ever-growing demand for high capacity cathode materials is on the rise since the futuristic applications are knocking on the door. Conventional approach to developing such cathode relies on the lithium-excess materials to operate the cathode at high voltage and extract more lithium-ion. Yet, they fail to satiate the needs because of their unresolved issues upon cycling such as, for lithium manganese-rich layered oxides-their voltage fading, and for as nickel-based layered oxides-the structural transition. Here, in contrast, lithium-deficient ratio is demonstrated as a new approach to attain high capacity at high voltage for layered oxide cathodes. Rapid and cost effective lithiation of a porous hydroxide precursor with lithium deficient ratio is acted as a driving force to partially convert the layered material to spinel phase yielding in a multiphase structure (MPS) cathode material. Upon cycling, MPS reveals structural stability at high voltage and high temperature and results in fast lithium-ion diffusion by providing a distinctive solid electrolyte interface (SEI) chemistry-MPS displays minimum lithium loss in SEI and forms a thinner SEI. MPS thus offers high energy and high power applications and provides a new perspective compared to the conventional layered cathode materials denying the focus for lithium excess material.

K. Shah, N. Balsara, S. Banerjee, M. Chintapalli, A. P. Cocco, W. K. S. Chiu, I. Lahiri, S. Martha, A. Mistry, P. P. Mukherjee, V. Ramadesigan, C. S. Sharma, V. R. Subramanian, S. Mitra, and A. Jain. "State of the Art and Future Research Needs for Multiscale Analysis of Li-Ion Cells " J. Electrochem. En. Conv. Stor. 2017, 14 (2) 020801-17 (May. 2017).
Abstract: The performance, safety, and reliability of Li-ion batteries are determined by a complex set of multiphysics, multiscale phenomena that must be holistically studied and optimized. This paper provides a summary of the state of the art in a variety of research fields related to Li-ion battery materials, processes, and systems. The material presented here is based on a series of discussions at a recently concluded bilateral workshop in which researchers and students from India and the U.S. participated. It is expected that this summary will help understand the complex nature of Li-ion batteries and help highlight the critical directions for future research.

Manjula I. Nandasir, Luis E. Camacho-Forero, Ashleigh M. Schwarz, Vaithiyalingam Shutthanandan, Suntharampillai Thevuthasan, Perla B. Balbuena, Karl T. Mueller, Vijayakumar Murugesan. "In Situ Chemical Imaging of Solid-Electrolyte Interphase Layer Evolution in Li–S Batteries."Chemistry of Materials 29 (11):4728-4737 (May 2017).
Abstract: Parasitic reactions of electrolyte and polysulfide with the Li-anode in lithium sulfur (Li–S) batteries lead to the formation of solid-electrolyte interphase (SEI) layers, which are the major reason behind severe capacity fading in these systems. Despite numerous studies, the evolution mechanism of the SEI layer and specific roles of polysulfides and other electrolyte components are still unclear. We report an in situ X-ray photoelectron spectroscopy (XPS) and chemical imaging analysis combined with ab initio molecular dynamics (AIMD) computational modeling to gain fundamental understanding regarding the evolution of SEI layers on Li-anodes within Li–S batteries. A multimodal approach involving AIMD modeling and in situ XPS characterization uniquely reveals the chemical identity and distribution of active participants in parasitic reactions as well as the SEI layer evolution mechanism. The SEI layer evolution has three major stages: the formation of a primary composite mixture phase involving stable lithium compounds (Li2S, LiF, Li2O, etc.) and formation of a secondary matrix type phase due to cross interaction between reaction products and electrolyte components, which is followed by a highly dynamic monoanionic polysulfide (i.e., LiS5) fouling process. These new molecular-level insights into the SEI layer evolution on Li-anodes are crucial for delineating effective strategies for the development of Li–S batteries.

Jinhong Lee, Jongchan Song, Hongkyung Lee, Hyungjun Noh, Yun-Jung Kim, Sung Hyun Kwon, Seung Geol Lee, Hee-Tak Kim."A Nanophase-Separated, Quasi-Solid-State Polymeric Single-Ion Conductor: Polysulfide Exclusion for Lithium–Sulfur Batteries."ACS Energy Letters 2 (5): 1232-1239 (April 2017).
Abstract: Formation of soluble polysulfide (PS), which is a key feature of lithium sulfur (Li–S) batteries, provides a fast redox kinetic based on a liquid–solid mechanism; however, it imposes the critical problem of PS shuttle. Here, we address the dilemma by exploiting a solvent-swollen polymeric single-ion conductor (SPSIC) as the electrolyte medium of the Li–S battery. The SPSIC consisting of a polymeric single-ion conductor and lithium salt-free organic solvents provides Li ion hopping by forming a nanoscale conducting channel and suppresses PS shuttle according to the Donnan exclusion principle when being employed for Li–S batteries. The organic solvents at the interface of the sulfur/carbon composite and SPSIC eliminate the poor interfacial contact and function as a soluble PS reservoir for maintaining the liquid–solid mechanism. Furthermore, the quasi-solid-state SPSIC allows the fabrication of a bipolar-type stack, which promises the realization of a high-voltage and energy-dense Li–S battery.

Chen, J., Henderson, W.A., Pan, H., Perdue, B.R., Cao, R., Hu, J. Z., Wan, C., Han, K.S., Mueller, K.T., Zhang, J.G., Shao, Y., Liu, J. " Improving Lithium–Sulfur Battery Performance Under Lean Electrolyte Through Nanoscale Confinement in Soft Swellable Gels" Nano Letters. 2017, 17, (5) 3061-3067 (April 2017).
Abstract: Li–S batteries have been extensively studied using rigid carbon as the host for sulfur encapsulation, but improving the properties with a reduced electrolyte amount remains a significant challenge. This is critical for achieving high energy density. Here, we developed a soft PEO₁₀LiTFSI polymer swellable gel as a nanoscale reservoir to trap the polysulfides under lean electrolyte conditions. The PEO₁₀LiTFSI gel immobilizes the electrolyte and confines polysulfides within the ion conducting phase. The Li–S cell with a much lower electrolyte to sulfur ratio (E/S) of 4 g_E/g_S (3.3 mL_E/g_S) could deliver a capacity of 1200 mA h/g, 4.6 mA h/cm², and good cycle life. The accumulation of polysulfide reduction products, such as Li₂S, on the cathode, is identified as the potential mechanism for capacity fading under lean electrolyte conditions.

Duan, W, J Huang, JA Kowalski, IA Shkrob, M Vijayakumar, E Walter, B Pan, Z Yang, JD Milshtein, B Li, C Liao, Z Zhang, W Wang, J Liu, JS Moore, FR Brushett, L Zhang, X Wei. "“Wine-Dark Sea” in an Organic Flow Battery: Storing Negative Charge in 2,1,3-Benzothiadiazole Radicals Leads to Improved Cyclability."ACS Energy Letters 2 (5): 1156-1161 (April 2017).
Abstract: Redox-active organic materials (ROMs) have shown great promise for redox flow battery applications but generally encounter limited cycling efficiency and stability at relevant redox material concentrations in nonaqueous systems. Here we report a new heterocyclic organic anolyte molecule, 2,1,3-benzothiadiazole, that has high solubility, a low redox potential, and fast electrochemical kinetics. Coupling it with a benchmark catholyte ROM, the nonaqueous organic flow battery demonstrated significant improvement in cyclable redox material concentrations and cell efficiencies compared to the state-of-the-art nonaqueous systems. Especially, this system produced exceeding cyclability with relatively stable efficiencies and capacities at high ROM concentrations (>0.5 M), which is ascribed to the highly delocalized charge densities in the radical anions of 2,1,3-benzothiadiazole, leading to good chemical stability. This material development represents significant progress toward promising next-generation energy storage.

Wan C ,Xu S ,Hu M Y,Cao R ,Qian J ,Qin Z ,Liu J ,Mueller K T,Zhang J ,Hu J Z. "Multinuclear NMR Study of the Solid Electrolyte Interface Formed in Lithium Metal Batteries" Applied Materials & Interfaces 9 (17): 14741-14748 (April 2017).
Abstract: The composition of the solid electrolyte interphase (SEI) layers formed in Cu|Li cells using lithium bis(fluorosulfonyi)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 1,2-dimethoxyethane (DME) electrolytes is determined by a multinuclear solid-state MAS NMR study at high magnetic field. It is found that the “dead” metallic Li is largely reduced in the SEI layers formed in a 4 M LiFSI–DME electrolyte system compared with those formed in a 1 M LiFSI–DME electrolyte system. This finding relates directly to the safety of Li metal batteries, as one of the main safety concerns for these batteries is associated with the “dead” metallic Li formed after long-term cycling. It is also found that a large amount of LiF, which exhibits superior mechanical strength and good Li+ ionic conductivity, is observed in the SEI layer formed in the concentrated 4 M LiFSI–DME and 3 M LiTFSI–DME systems but not in the diluted 1 M LiFSI–DME system. Quantitative 6Li MAS NMR results indicate that the SEI associated with the 4 M LiFSI–DME electrolyte is denser than those formed in the 1 M LiFSI–DME and 3 M LiTFSI–DME systems. These studies reveal the fundamental mechanisms behind the excellent electrochemical performance associated with higher concentration LiFSI–DME electrolyte systems.

Wonhee Jo, Hong Suk Kang, Jaeho Choi, Hongkyung Lee, Hee-Tak Kim."Plasticized Polymer Interlayer for Low-Temperature Fabrication of a High-Quality Silver Nanowire-Based Flexible Transparent and Conductive Film."Applied Materials & Interfaces 9 (17): 15114-15121 (April 2017).
Abstract: Silver nanowires (AgNWs) are one of the most promising materials to replace commercially available indium tin oxide in flexible transparent conductive films (TCFs); however, there are still numerous problems originating from poor AgNW junction formation and improper AgNW embedment into transparent substrates. To mitigate these problems, high-temperature processes have been adopted; however, unwanted substrate deformation prevents the use of these processes for the formation of flexible TCFs. In this work, we present a novel poly(methyl methacrylate) interlayer plasticized by dibutyl phthalate for low-temperature fabrication of AgNW-based TCFs, which does not cause any substrate deformation. By exploiting the viscoelastic properties of the plasticized interlayer near the lowered glass-transition temperature, a monolithic junction of AgNWs on the interlayer and embedment of the interconnected AgNWs into the interlayer are achieved in a single-step pressing. The resulting AgNW-TCFs are highly transparent (∼92% at a wavelength of 550 nm), highly conductive (<90 Ω/sq), and environmentally and mechanically robust. Therefore, the plasticized interlayer provides a simple and effective route to fabricate high-quality AgNW-based TCFs.

Chang HJ ,Lu X ,Bonnett J F,Canfield N L,Son S ,Park YC ,Jung K ,Sprenkle V L,Li G. "Development of intermediate temperature sodium nickel chloride rechargeable batteries using conventional polymer sealing technologies." Journal of Power Sources 348: 150-157 (April 2017).
Abstract:Developing advanced and reliable electrical energy storage systems is critical to fulfill global energy demands and stimulate the growth of renewable energy resources. Sodium metal halide batteries have been under serious consideration as a low cost alternative energy storage device for stationary energy storage systems. Yet, there are number of challenges to overcome for the successful market penetration, such as high operating temperature and hermetic sealing of batteries that trigger an expensive manufacturing process. Here we demonstrate simple, economical and practical sealing technologies for Na-NiCl₂ batteries operated at an intermediate temperature of 190°C. Conventional polymers are implemented in planar Na-NiCl₂ batteries after a prescreening test, and their excellent compatibilities and durability are demonstrated by a stable performance of Na-NiCl₂ battery for more than 300 cycles. The sealing methods developed in this work will be highly beneficial and feasible for prolonging battery cycle life and reducing manufacturing cost for Na-based batteries at elevated temperatures (<200°C).

Li Y ,An Q ,Cheng Y ,Liang Y ,Ren Y ,Sun CJ ,Dong H ,Tang Z ,Li G ,Yao Y. "A high-voltage rechargeable magnesium-sodium hybrid battery." Nano Energy 34: 188-194 (April 2017).
Abstract:Growing global demand of safe and low-cost energy storage technology triggers strong interests in novel battery concepts beyond state-of-art Li-ion batteries. Here we report a high-voltage rechargeable Mg-Na hybrid battery featuring dendrite-free deposition of Mg anode and Na-intercalation cathode as a low-cost and safe alternative to Li-ion batteries for large-scale energy storage. A prototype device using a Na₃V₂(PO₄)₃ cathode, a Mg anode, and a Mg-Na dual salt electrolyte exhibits the highest voltage (2.60 V vs. Mg) and best rate performance (86% capacity retention at 10C rate) among reported hybrid batteries. Synchrotron radiation-based X-ray absorption near edge structure (XANES), atomic-pair distribution function (PDF), and high-resolution X-ray diffraction (HRXRD) studies reveal the chemical environment and structural change of Na₃V₂(PO₄)₃ cathode during the Na ion insertion/deinsertion process. XANES study shows a clear reversible shift of vanadium K-edge and HRXRD and PDF studies reveal a reversible two-phase transformation and V-O bond length change during cycling. The energy density of the hybrid cell could be further improved by developing electrolytes with a higher salt concentration and wider electrochemical window. This work represents a significant step forward for practical safe and low-cost hybrid batteries.

Jianming Zheng, Joshua Lochala, Alexander Kwok, Zhiqun Daniel Deng, Jie Xiao."Research Progress towards Understanding the Unique Interfaces between Concentrated Electrolytes and Electrodes for Energy Storage Applications."Advanced Science 4 (8) (March 2017).
Abstract: The electrolyte is an indispensable component in all electrochemical energy storage and conversion devices with batteries being a prime example. While most research efforts have been pursued on the materials side, the progress for the electrolyte is slow due to the decomposition of salts and solvents at low potentials, not to mention their complicated interactions with the electrode materials. The general properties of bulk electrolytes such as ionic conductivity, viscosity, and stability all affect the cell performance. However, for a specific electrochemical cell in which the cathode, anode, and electrolyte are optimized, it is the interface between the solid electrode and the liquid electrolyte, generally referred to as the solid electrolyte interphase (SEI), that dictates the rate of ion flow in the system. The commonly used electrolyte is within the range of 1-1.2 M based on the prior optimization experience, leaving the high concentration region insufficiently recognized. Recently, electrolytes with increased concentration (>1.0 M) have received intensive attention due to quite a few interesting discoveries in cells containing concentrated electrolytes. The formation mechanism and the nature of the SEI layers derived from concentrated electrolytes could be fundamentally distinct from those of the traditional SEI and thus enable unusual functions that cannot be realized using regular electrolytes. In this article, we provide an overview on the recent progress of high concentration electrolytes in different battery chemistries. The experimentally observed phenomena and their underlying fundamental mechanisms are discussed. New insights and perspectives are proposed to inspire more revolutionary solutions to address the interfacial challenges.

Rajput NN ,Murugesan V ,Shin Y ,Han KS ,Lau KC ,Chen J ,Liu J ,Curtiss L A,Mueller K T,Persson K A. "Elucidating the Solvation Structure and Dynamics of Lithium Polysulfides Resulting from Competitive Salt and Solvent Interactions" Chemistry of Materials 29 (8): 3375-3379 (March 2017).
Abstract: Designing optimal electrolytes is key to enhancing the performance of energy storage devices,especially relating to cycle life, efficiency, and stability. Specifically, for future beyond-Li ion energy storage, there is still ample room for electrolyte improvements. Among the candidates for higher gravimetric energy storage, the Li−S battery is considered quite promising, owing to its theoretical specific energy density (2600 Wh/kg) and specific capacity (1675 mAh/g) and significantly lower cost as compared to state-of-art lithium-ion batteries.2−4 However, despite these attractive attributes, successful commercialization of Li−S batteries is currently hindered by poor cycling performance and capacity retention that is primarily caused by the parasitic reactions between the Li metal anode and dissolved polysulfide (PS) species from the cathode during the cycling process.

Vijayakumar, M., Han, K.S., Hu, J., Mueller, K.T. " Molecular Level Structure and Dynamics of Electrolytes Using 17O Nuclear Magnetic Resonance Spectroscopy " eMagRes. 2017, 3, 71-82 (March. 2017).
Abstract: Electrolytes help harness the energy from electrochemical processes by serving as solvents and transport media for redox-active ions. Molecular-level interactions between ionic solutes and solvent molecules – commonly referred to as solvation phenomena – give rise to many functional properties of electrolytes such as ionic conductivity, viscosity, and stability. It is critical to understand the evolution of solvation phenomena as a function of competing counterions and solvent mixtures to predict and design the optimal electrolyte for a target application. Probing oxygen environments is of great interest as oxygens are located at strategic molecular sites in battery solvents and are directly involved in inter- and intramolecular solvation interactions. NMR signals from ¹⁷O nuclei in battery electrolytes offer nondestructive bulk measurements of isotropic shielding, electric field gradient tensors, and transverse and longitudinal relaxation rates, which are excellent means for probing structure, bonding, and dynamics of both solute and solvent molecules. This article describes the use of ¹⁷O NMR spectroscopy in probing the solvation structures of various electrolyte systems ranging from transition metal ions in aqueous solution to lithium cations in organic solvent mixtures.

Bin Liu, Wu Xu, Pengfei Yan, Sun Tai Kim, Mark H. Engelhard, Xiuliang Sun, Donghai Mei, Jaephil Cho, Chongmin Wang, Ji-Guang Zhang."Stabilization of Li Metal Anode in DMSO-Based Electrolytes via Optimization of Salt–Solvent Coordination for Li–O₂ Batteries."Advanced Energy Materials 7 (14) (March 2017).
Abstract: The conventional electrolyte of 1 m lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in dimethyl sulfoxide (DMSO) is unstable against the Li metal anode and therefore cannot be used directly in practical Li–O₂ batteries. Here, we demonstrate that a highly concentrated electrolyte based on LiTFSI in DMSO (with a molar ratio of 1:3) can greatly improve the stability of the Li metal anode against DMSO and significantly improve the cycling stability of Li–O₂ batteries. This highly concentrated electrolyte contains no free DMSO solvent molecules, but only complexes of (TFSI−)_a-Li⁺-(DMSO)_b (where a + b = 4), and thus enhances their stability with Li metal anodes. In addition, such salt–solvent complexes have higher Gibbs activation energy barriers than the free DMSO solvent molecules, indicating improved stability of the electrolyte against the attack of superoxide radical anions. Therefore, the stability of this highly concentrated electrolyte at both Li metal anodes and carbon-based air electrodes has been greatly enhanced, resulting in improved cycling performance of Li–O₂ batteries. The fundamental stability of the electrolyte in the absence of free-solvent against the chemical and electrochemical reactions can also be used to enhance the stability of other electrochemical systems.

D. Lin, J. Zhao, J. Sun, H. Yao, Y. Liu, K. Yan, Y. Cui. "Three-dimensional stable lithium metal anode with nanoscale lithium islands embedded in ionically conductive solid matrix" Proc. Natl. Acad.Sci. 114: 4613-4618(Mar.2017).
Abstract:Rechargeable batteries based on lithium (Li) metal chemistry are attractive for next-generation electrochemical energy storage. Nevertheless, excessive dendrite growth, infinite relative dimension change, severe side reactions, and limited power output severely impede their practical applications. Although exciting progress has been made to solve parts of the above issues, a versatile solution is still absent. Here, a Li-ion conductive framework was developed as a stable “host” and efficient surface protection to address the multifaceted problems, which is a significant step forward compared with previous host concepts. This was fulfilled by reacting overstoichiometry of Li with SiO. The as-formed Li_xSi–Li₂O matrix would not only enable constant electrode-level volume, but also protect the embedded Li from direct exposure to electrolyte. Because uniform Li nucleation and deposition can be fulfilled owing to the high-density active Li domains, the as-obtained nanocomposite electrode exhibits low polarization, stable cycling, and high-power output (up to 10 mA/cm²) even in carbonate electrolytes. The Li–S prototype cells further exhibited highly improved capacity retention under high-power operation (∼600 mAh/g at 6.69 mA/cm²). The all-around improvement on electrochemical performance sheds light on the effectiveness of the design principle for developing safe and stable Li metal anodes.

Chang HJ ,Canfield N L,Jung K ,Sprenkle V L,Li G. "Advanced Na-NiCl₂ Battery Using Nickel-Coated Graphite with Core-Shell Microarchitecture." ACS Applied Materials & Interfaces 9 (13): 11609-11614 (March 2017).
Abstract:Stationary electric energy storage devices (rechargeable batteries) have gained increasing prominence due to great market needs, such as smoothing the fluctuation of renewable energy resources and supporting the reliability of the electric grid. With regard to raw materials availability, sodium-based batteries are better positioned than lithium batteries due to the abundant resource of sodium in Earth's crust. However, the sodium-nickel chloride (Na-NiCl₂) battery, one of the most attractive stationary battery technologies, is hindered from further market penetration by its high material cost (Ni cost) and fast material degradation at its high operating temperature. Here, we demonstrate the design of a core�shell microarchitecture, nickel-coated graphite, with a graphite core to maintain electrochemically active surface area and structural integrity of the electron percolation pathway while using 40% less Ni than conventional Na-NiCl₂ batteries. An initial energy density of 133 Wh/kg (at ~C/4) and energy efficiency of 94% are achieved at an intermediate temperature of 190°C.

Jianming Zheng, Mark H. Engelhard, Donghai Mei, Shuhong Jiao, Bryant J. Polzin, Ji-Guang Zhang, Wu Xu."Electrolyte additive enabled fast charging and stable cycling lithium metal batteries."Nature Energy 2, Article number: 17012 (March 2017).
Abstract: Batteries using lithium (Li) metal as anodes are considered promising energy storage systems because of their high energy densities. However, safety concerns associated with dendrite growth along with limited cycle life, especially at high charge current densities, hinder their practical uses. Here we report that an optimal amount (0.05 M) of LiPF₆ as an additive in LiTFSI–LiBOB dual-salt/carbonate-solvent-based electrolytes significantly enhances the charging capability and cycling stability of Li metal batteries. In a Li metal battery using a 4-V Li-ion cathode at a moderately high loading of 1.75 mAh cm⁻², a cyclability of 97.1% capacity retention after 500 cycles along with very limited increase in electrode overpotential is accomplished at a charge/discharge current density up to 1.75 mA cm⁻². The fast charging and stable cycling performances are ascribed to the generation of a robust and conductive solid electrolyte interphase at the Li metal surface and stabilization of the Al cathode current collector.

Shidong Song, Wu Xu, Ruiguo Cao, Langli Luo, Mark H. Engelhard, Mark E. Bowden, Bin Liu, Luis Estevez, Chongmin Wang, Ji-Guang Zhang."B₄C as a stable non-carbon-based oxygen electrode material for lithium-oxygen batteries."Nano Energy 33: 195-204 (March 2017).
Abstract: Lithium-oxygen (Li-O₂) batteries have extremely high theoretical specific capacities and energy densities when compared with Li-ion batteries. However, the instability of both electrolyte and carbon-based oxygen electrode related to the nucleophilic attack of reduced oxygen species during oxygen reduction reaction and the electrochemical oxidation during oxygen evolution reaction are recognized as the major challenges in this field. Here we report the application of boron carbide (B₄C) as the non-carbon based oxygen electrode material for aprotic Li-O₂ batteries. B₄C has high resistance to chemical attack, good conductivity, excellent catalytic activity and low density that are suitable for battery applications. The electrochemical activity and chemical stability of B₄C are systematically investigated in an aprotic electrolyte. Li-O₂ cells using B₄C-based air electrodes exhibit better cycling stability than those using carbon nanotube- and titanium carbide-based air electrodes in the electrolyte of 1 M lithium trifluoromethanesulfonate in tetraglyme. The performance degradation of B₄C-based electrode is mainly due to the loss of active sites on B₄C electrode during cycles as identified by the structure and composition characterizations. These results clearly demonstrate that B₄C is a very promising alternative oxygen electrode material for aprotic Li-O₂ batteries. It can also be used as a standard electrode to investigate the stability of electrolytes.

Soto F A,Yan P ,Engelhard M H,Marzouk A ,Wang C ,Liu J ,Sprenkle V L,El-Mellouhi F ,Balbuena P B,Li X. "Tuning the Solid Electrolyte Interphase for Selective Li- and Na-Ion Storage in Hard Carbon." Advanced Materials 29 (18): 1606860 (March 2017).
Abstract:Solid-electrolyte interphase (SEI) films with controllable properties are highly desirable for improving battery performance. In this paper, a combined experimental and theoretical approach is used to study SEI films formed on hard carbon in Li- and Na-ion batteries. It is shown that a stable SEI layer can be designed by precycling an electrode in a desired Li- or Na-based electrolyte, and that ionic transport can be kinetically controlled. Selective Li- and Na-based SEI membranes are produced using Li- or Na-based electrolytes, respectively. The Na-based SEI allows easy transport of Li ions, while the Li-based SEI shuts off Na-ion transport. Na-ion storage can be manipulated by tuning the SEI layer with film-forming electrolyte additives, or by preforming an SEI layer on the electrode surface. The Na specific capacity can be controlled to < 25 mAh g^-1;= 1/10 of the normal capacity (250 mAh g^-1). Unusual selective/preferential transport of Li ions is demonstrated by preforming an SEI layer on the electrode surface and corroborated with a mixed electrolyte. This work may provide new guidance for preparing good ion-selective conductors using electrochemical approaches.

Tianyuan Ma, Gui-Liang Xu, Yan Li, Li Wang, Xiangming He, Jianming Zheng, Jun Liu, Mark H. Engelhard, Peter Zapol, Larry A. Curtiss, Jacob Jorne, Khalil Amine, Zonghai Chen."Revisiting the Corrosion of the Aluminum Current Collector in Lithium-Ion Batteries."Journal of Physical Chemistry Letters 8 (5): 1072-1077 (February 2017).
Abstract: The corrosion of aluminum current collectors and the oxidation of solvents at a relatively high potential have been widely investigated with an aim to stabilize the electrochemical performance of lithium-ion batteries using such components. The corrosion behavior of aluminum current collectors was revisited using a home-build high-precision electrochemical measurement system, and the impact of electrolyte components and the surface protection layer on aluminum foil was systematically studied. The electrochemical results showed that the corrosion of aluminum foil was triggered by the electrochemical oxidation of solvent molecules, like ethylene carbonate, at a relative high potential. The organic radical cations generated from the electrochemical oxidation are energetically unstable and readily undergo a deprotonation reaction that generates protons and promotes the dissolution of Al³⁺ from the aluminum foil. This new reaction mechanism can also shed light on the dissolution of transitional metal at high potentials.

Duan, W, RS Vemuri, D Hu, Z Yang, X Wei. "A Protocol for Electrochemical Evaluations and State of Charge Diagnostics of a Symmetric Organic Redox Flow Battery." Journal of Visualized Experiments 120 (Feb. 2017).
Abstract: Redox flow batteries have been considered as one of the most promising stationary energy storage solutions for improving the reliability of the power grid and deployment of renewable energy technologies. Among the many flow battery chemistries, non-aqueous flow batteries have the potential to achieve high energy density because of the broad voltage windows of non-aqueous electrolytes. However, significant technical hurdles exist currently limiting non-aqueous flow batteries to demonstrate their full potential, such as low redox concentrations, low operating currents, under-explored battery status monitoring, etc. In an attempt to address these limitations, we recently reported a non-aqueous flow battery based on a highly soluble, redox-active organic nitronyl nitroxide radical compound, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). This redox material exhibits an ambipolar electrochemical property, and therefore can serve as both anolyte and catholyte redox materials to form a symmetric flow battery chemistry. Moreover, we demonstrated that Fourier transform infrared (FTIR) spectroscopy could measure the PTIO concentrations during the PTIO flow battery cycling and offer reasonably accurate detection of the battery state of charge (SOC), as cross-validated by electron spin resonance (ESR) measurements. Herein we present a video protocol for the electrochemical evaluation and SOC diagnosis of the PTIO symmetric flow battery. With a detailed description, we experimentally demonstrated the route to achieve such purposes. This protocol aims to spark more interests and insights on the safety and reliability in the field of non-aqueous redox flow batteries.

Shidong Song, Wu Xu, Jianming Zheng, Langli Luo, Mark H. Engelhard, Mark E. Bowden, Bin Liu, Chongmin Wang, Ji-Guang Zhang."Complete Decomposition of Li₂CO₃ in Li–O₂ Batteries Using Ir/B₄C as Noncarbon-Based Oxygen Electrode."Nano Letters 17 (3): 1417-1424 (February 2017).
Abstract: Instability of carbon-based oxygen electrodes and incomplete decomposition of Li₂CO₃ during charge process are critical barriers for rechargeable Li–O₂ batteries. Here we report the complete decomposition of Li₂CO₃ in Li–O₂ batteries using the ultrafine iridium-decorated boron carbide (Ir/B₄C) nanocomposite as a noncarbon based oxygen electrode. The systematic investigation on charging the Li₂CO₃ preloaded Ir/B₄C electrode in an ether-based electrolyte demonstrates that the Ir/B₄C electrode can decompose Li₂CO₃ with an efficiency close to 100% at a voltage below 4.37 V. In contrast, the bare B₄C without Ir electrocatalyst can only decompose 4.7% of the preloaded Li₂CO₃. Theoretical analysis indicates that the high efficiency decomposition of Li₂CO₃ can be attributed to the synergistic effects of Ir and B₄C. Ir has a high affinity for oxygen species, which could lower the energy barrier for electrochemical oxidation of Li₂CO₃. B₄C exhibits much higher chemical and electrochemical stability than carbon-based electrodes and high catalytic activity for Li–O₂ reactions. A Li–O₂ battery using Ir/B₄C as the oxygen electrode material shows highly enhanced cycling stability than those using the bare B₄C oxygen electrode. Further development of these stable oxygen-electrodes could accelerate practical applications of Li–O₂ batteries.

Dongping Lu, Jinhui Tao, Pengfei Yan, Wesley A. Henderson, Qiuyan Li, Yuyan Shao, Monte L. Helm, Oleg Borodin, Gordon L. Graff, Bryant Polzin, Chongmin Wang, Mark Engelhard, Ji-Guang Zhang, James J. De Yoreo, Jun Liu, Jie Xiao."Formation of Reversible Solid Electrolyte Interface on Graphite Surface from Concentrated Electrolytes."Nano Letters 17 (3):1602-1609 (February 2017).
Abstract: Li-ion batteries (LIB) have been successfully commercialized after the identification of ethylene-carbonate (EC)-containing electrolyte that can form a stable solid electrolyte interphase (SEI) on carbon anode surface to passivate further side reactions but still enable the transportation of the Li⁺ cation. These electrolytes are still utilized, with only minor changes, after three decades. However, the long-term cycling of LIB leads to continuous consumption of electrolyte and growth of SEI layer on the electrode surface, which limits the battery’s life and performance. Herein, a new anode protection mechanism is reported in which, upon changing of the cell potential, the electrolyte components at the electrode-electrolyte interface reorganize reversibly to form a transient protective surface layers on the anode. This layer will disappear after the applied potential is removed so that no permanent SEI layer is required to protect the carbon anode. This phenomenon minimizes the need for a permanent SEI layer and prevents its continuous growth and therefore may lead to largely improved performance for LIBs.

Li B, Liu, J. "Progress and directions in low-cost redox-flow batteries for large-scale energy storage." National Science Review 4 (1): 91-105 (Jan. 2017).
Abstract:Compared to lithium-ion batteries, redox-flow batteries have attracted widespread attention for long-duration, large-scale energy-storage applications. This review focuses on current and future directions to address one of the most significant challenges in energy storage: reducing the cost of redox-flow battery systems. A high priority is developing aqueous systems with low-cost materials and high-solubility redox chemistries. Highly water-soluble inorganic redox couples are important for developing technologies that can provide high energy densities and low-cost storage. There is also great potential to rationally design organic redox molecules and fine-tune their properties for both aqueous and non-aqueous systems. While many new concepts begin to blur the boundary between traditional batteries and redox-flow batteries, breakthroughs in identifying/developing membranes and separators and in controlling side reactions on electrode surfaces also are needed.

Jianming Zheng, Seungjun Myeong, Woongrae Cho, Pengfei Yan, Jie Xiao, Chongmin Wang, Jaephil Cho, Ji-Guang Zhang."Li- and Mn-Rich Cathode Materials: Challenges to Commercialization."Advanced Energy Materials 7 (6):1601284 (December 2016).
Abstract: The lithium- and manganese-rich (LMR) layered structure cathodes exhibit one of the highest specific energies (≈900 W h kg⁻¹) among all the cathode materials. However, the practical applications of LMR cathodes are still hindered by several significant challenges, including voltage fade, large initial capacity loss, poor rate capability and limited cycle life. Herein, we review the recent progress and in depth understandings on the application of LMR cathode materials from a practical point of view. Several key parameters of LMR cathodes that affect the LMR/graphite full-cell operation are systematically analyzed. These factors include the first-cycle capacity loss, voltage fade, powder tap density, and electrode density. New approaches to minimize the detrimental effects of these factors are highlighted in this work. We also provide perspectives for the future research on LMR cathode materials, focusing on addressing the fundamental problems of LMR cathodes while keeping practical considerations in mind.

Fu S ,Zhu C ,Song J ,Engelhard M H,Li X ,Zhang P ,Xia H ,Du D ,Lin Y. "Template-directed synthesis of nitrogen- and sulfur-codoped carbon nanowire aerogels with enhanced electrocatalytic performance for oxygen reduction." Nano Research 10 (6): 1888-1895 (Dec. 2016).
Abstract:Heteroatom doping, precise composition control, and rational morphology design are efficient strategies for producing novel nanocatalysts for the oxygen reduction reaction (ORR) in fuel cells. Herein, a cost-effective approach to synthesize nitrogen- and sulfur-codoped carbon nanowire aerogels using a hard templating method is proposed. The aerogels prepared using a combination of hydrothermal treatment and carbonization exhibit good catalytic activity for the ORR in alkaline solution. At the optimal annealing temperature and mass ratio between the nitrogen and sulfur precursors, the resultant aerogels show comparable electrocatalytic activity to that of a commercial Pt/C catalyst for the ORR. Importantly, the optimized catalyst shows much better long-term stability and satisfactory tolerance for the methanol crossover effect. These codoped aerogels are expected to have potential applications in fuel cells.

Shamie J S,Liu C H,Shaw L L,Sprenkle V L. "New Mechanism for the Reduction of Vanadyl Acetylacetonate to Vanadium Acetylacetonate for Room Temperature Flow Batteries." ChemSusChem 10 (3): 533-540 (Dec. 2016).
Abstract:In this study, a new mechanism for the reduction of vanadyl acetylacetonate, VO(acac)₂, to vanadium acetylacetonate, V(acac)₃, is introduced. V(acac)₃ has been studied for use in redox flow batteries (RFBs) for some time; however, contamination by moisture leads to the formation of VO(acac)₂. In previous work, once this transformation occurs, it is no longer reversible because there is a requirement for extreme low potentials for the reduction to occur. Here, we propose that, in the presence of excess acetylacetone (Hacac) and free protons (H⁺), the reduction can take place between 2.25 and 1.5 V versus Na/Na⁺ via a one-electron-transfer reduction. This reduction can take place in situ during discharge in a novel hybrid Na-based flow battery (HNFB) with a molten Na-Cs alloy as the anode. The in situ recovery of V(acac)₃ during discharge is shown to allow the Coulombic efficiency of the HNFB to be =100% with little or no capacity decay over cycles. In addition, utilizing two-electron-transfer redox reactions (i.e., V³⁺/V⁴⁺ and V²⁺/V³⁺ redox couples) per V ion to increase the energy density of RFBs becomes possible owing to the in situ recovery of V(acac)₃ during discharge. The concept of in situ recovery of material can lead to more advances in maintaining the cycle life of RFBs in the future.

Han KS ,Rajput NN ,Vijayakumar M ,Wei X ,Wang W ,Hu J Z,Persson K A,Mueller K T. "Preferential Solvation of an Asymmetric Redox Molecule" Journal of Physical Chemistry C 120 (49): 27834-27839 (Nov. 2016).
Abstract: The fundamental correlations between solubility and solvation structure for the electrolyte system comprising N-(ferrocenylmethyl)-N,N-dimethyl-N-ethylammonium bistrifluoromethylsulfonimide (Fc1N112-TFSI) dissolved in a ternary carbonate solvent mixture is analyzed using combined NMR relaxation and computational methods. Probing the evolution of the solvent–solvent, ion–solvent and ion–ion interactions with an increase in solute concentration provides a molecular level understanding of the solubility limit of the Fc1N112-TFSI system. An increase in solute concentration leads to pronounced Fc1N112-TFSI contact-ion pair formation by diminishing solvent–solvent and ion–solvent type interactions. At the solubility limit, the precipitation of solute is initiated through agglomeration of contact-ion pairs due to overlapping solvation shells.

Murugesan, V, Q Luo, R Lloyd, Z Nie, X Wei, B Li, VL Sprenkle, JD Londono, M Unlu, W Wang. "Tuning the Perfluorosulfonic Acid Membrane Morphology for Vanadium Redox-Flow Batteries."ACS Applied Materials and Interfaces 8 (50): 34327-34334 (Nov. 2016).
Abstract: The microstructure of perfluorinated sulfonic acid proton-exchange membranes such as Nafion significantly affects their transport properties and performance in a vanadium redox-flow battery (VRB). In this work, Nafion membranes with various equivalent weights ranging from 1000 to 1500 are prepared and the morphology-property-performance relationship is investigated. NMR and small-angle X-ray scattering studies revealed their composition and morphology variances, which lead to major differences in key transport properties related to proton conduction and vanadium-ion permeation. Their performances are further characterized as VRB membranes. On the basis of this understanding, a new perfluorosulfonic acid membrane is designed with optimal pore geometry and thickness, leading to higher ion selectivity and lower cost compared with the widely used Nafion 115. Excellent VRB single-cell performance (89.3% energy efficiency at 50 mA·cm-2) was achieved along with a stable cyclical capacity over prolonged cycling.

Park, M, J Ryu, W Wang, J Cho. "Material design and engineering of next-generation flow-battery technologies." Nature Review Materials 2 (Nov. 2016).
Abstract: Spatial separation of the electrolyte and electrode is the main characteristic of flow-battery technologies, which liberates them from the constraints of overall energy content and the energy/power ratio. The concept of a flowing electrolyte not only presents a cost-effective approach for large-scale energy storage, but has also recently been used to develop a wide range of new hybrid energy storage and conversion systems. The advent of flow-based lithium-ion, organic redox-active materials, metal-air cells and photoelectrochemical batteries promises new opportunities for advanced electrical energy-storage technologies. In this Review, we present a critical overview of recent progress in conventional aqueous redox-flow batteries and next-generation flow batteries, highlighting the latest innovative alternative materials. We outline their technical feasibility for use in long-term and large-scale electrical energy-storage devices, as well as the limitations that need to be overcome, providing our view of promising future research directions in the field of redox-flow batteries.

Sookyung Jeong, Xiaolin Li, Jianming Zheng, Pengfei Yan, Ruiguo Cao, Hee Joon Jung, Chongmin Wang, Jun Liu, Ji-Guang Zhang."Hard carbon coated nano-Si/graphite composite as a high performance anode for Li-ion batteries."Journal of Power Sources 329: 323-329 (October 2016).
Abstract: With the ever-increasing demands for higher energy densities in Li-ion batteries, alternative anodes with higher reversible capacity are required to replace the conventional graphite anode. Here, we demonstrate a cost-effective hydrothermal carbonization approach to prepare a hard carbon coated nano-Si/graphite (HC-nSi/G) composite as a high performance anode for Li-ion batteries. In this hierarchical structured composite, the hard carbon coating not only provides an efficient pathway for electron transfer, but also alleviates the volume variation of Si during charge/discharge processes. The HC-nSi/G composite electrode shows excellent performance, including a high specific capacity of 878.6 mAh g⁻¹ based on the total weight of composite, good rate performance, and a decent cycling stability, which is promising for practical applications.

Mehdi, BL, A Stevens, J Qian, C Park, W Xu, WA Henderson, J Zhang, KT Mueller, ND Browning. "The Impact of Li Grain Size on Coulombic Efficiency in Li Batteries."Scientific Reports 6: Article number 34267 (Oct. 2016).
Abstract: One of the most promising means to increase the energy density of state-of-the-art lithium Li-ion batteries is to replace the graphite anode with a Li metal anode. While the direct use of Li metal may be highly advantageous, at present its practical application is limited by issues related to dendrite growth and low Coulombic efficiency, CE. Here operando electrochemical scanning transmission electron microscopy (STEM) is used to directly image the deposition/stripping of Li at the anode-electrolyte interface in a Li-based battery. A non-aqueous electrolyte containing small amounts of H₂O as an additive results in remarkably different deposition/stripping properties as compared to the “dry” electrolyte when operated under identical electrochemical conditions. The electrolyte with the additive deposits more Li during the first cycle, with the grain sizes of the Li deposits being significantly larger and more variable. The stripping of the Li upon discharge is also more complete, i.e., there is a higher cycling CE. This suggests that larger grain sizes are indicative of better performance by leading to more uniform Li deposition and an overall decrease in the formation of Li dendrites and side reactions with electrolyte components, thus potentially paving the way for the direct use of Li metal in battery technologies.

Cheng, Y, HJ Chang, H Dong, D Choi, VL Sprenkle, J Liu, Y Yao, G Li. "Rechargeable Mg-Li hybrid batteries: status and challenges."Journal of Materials Research 31 (20) :3125-3141 (Oct. 2016).
Abstract: A magnesium-lithium (Mg-Li) hybrid battery consists of an Mg metal anode, a Li⁺ intercalation cathode, and a dual-salt electrolyte with both Mg²⁺ and Li⁺ ions. The demonstration of this technology has appeared in literature for few years and great advances have been achieved in terms of electrolytes, various Li cathodes, and cell architectures. Despite excellent battery performances including long cycle life, fast charge/discharge rate, and high Coulombic efficiency, the overall research of Mg-Li hybrid battery technology is still in its early stage, and also raised some debates on its practical applications. In this regard, we focus on a comprehensive overview of Mg-Li hybrid battery technologies developed in recent years. Detailed discussion of Mg-Li hybrid operating mechanism based on experimental results from literature helps to identify the current status and technical challenges for further improving the performance of Mg-Li hybrid batteries. Finally, a perspective for Mg-Li hybrid battery technologies is presented to address strategic approaches for existing technical barriers that need to be overcome in future research direction.

Wang Y, P Yan, J Xiao, X Lu, J Zhang, VL Sprenkle. "Effect of Al2O3 on the sintering of garnet-type Li6.5La3Zr1.5Ta0.5O12."Solid State Ionics 294: 108-115 (Oct. 2016).
Abstract:It is widely recognized that Al plays a dual role in the fabrication of garnet-type solid electrolytes, i.e., as a dopant that stabilizes the cubic structure and a sintering aid that facilitates the densification. However, the sintering effect of Al2O3 has not been well understood so far because Al is typically "unintentionally" introduced into the sample from the crucible during the fabrication process. In this study, we have investigated the sintering effect of Al on the phase composition, microstructure, and ionic conductivity of Li_6.5La₃Zr_1.5Ta_0.5O₁₂ by using an Al-free crucible and intentionally adding various amounts of y-Al₂O₃. It was found that the densification of Li_6.5La₃Zr_1.5Ta_0.5O₁₂ occurred via liquid-phase sintering, with evidence of morphology change among different compositions. Among all of the compositions, samples with 0.05mol Al per unit formula of garnet oxide (i.e., 0.3wt% Al₂O₃) exhibited the optimal microstructure and the highest total ionic conductivity of 5x10^-4Scm^-1 at room temperature.

Choi D, C Zhu, S Fu, D Du, MH Engelhard, Y Lin. "Electrochemically Controlled Ion-exchange Property of Carbon Nanotubes/Polypyrrole Nanocomposite in Various Electrolyte Solutions." Electroanalysis 29 (3): 929-936 (Sept. 2016).
Abstract: The electrochemically controlled ion-exchange properties of multi-wall carbon nanotube (MWNT)/electronically conductive polypyrrole (PPy) polymer composite in the various electrolyte solutions have been investigated. The ion-exchange behavior, rate and capacity of the electrochemically deposited polypyrrole with and without carbon nanotube (CNT) were compared and characterized using cyclic voltammetry (CV), chronoamperometry (CA), electrochemical quartz crystal microbalance (EQCM), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It has been found that the presence of carbon nanotube backbone resulted in improvement in ion-exchange rate, stability of polypyrrole, and higher anion loading capacity per PPy due to higher surface area, electronic conductivity, porous structure of thin film, and thinner film thickness providing shorter diffusion path. Chronoamperometric studies show that electrically switched anion exchange could be completed more than 10 times faster than pure PPy thin film. The anion selectivity of CNT/PPy film is demonstrated using X-ray photoelectron spectroscopy (XPS).

Fu, S, C Zhu, J Song, MH Engelhard, X Li, D Du, Y Lin. "Highly Ordered Mesoporous Bimetallic Phosphides as Efficient Oxygen Evolution Electrocatalysts."ACS Energy Letters 1 (4) :792-796 (Sept. 2016).
Abstract: Oxygen evolution from water using earth-abundant transition-metal-based catalysts is of importance for the commercialization of water electrolyzers. Herein, we report a hard templating method to synthesize transition metal phosphides with uniform shape and size. By virtue of the structural feature, synergistic effects among metals, and the in situ formed active species, the as-prepared phosphides with optimized composition present enhanced electrocatalytic performance toward the oxygen evolution reaction in alkaline solution. In detail, the catalyst with optimized composition reaches a current density of 10 mA/cm² at a potential of 1.511 V vs a reversible hydrogen electrode, which is much lower than that of a commercial RuO₂ catalyst. Our work offers a new strategy to optimize the catalysts for water splitting by controlling the morphology and composition.

Li X, P Yan, MH Engelhard, AJ Crawford, V Viswanathan, C Wang, J Liu, VL Sprenkle. "The importance of solid electrolyte interphase formation for long cycle stability full-cell Na-ion batteries."Nano Energy 27: 664-672 (Sept. 2016).
Abstract: Na-ion battery, as an alternative high-efficiency and low-cost energy storage device to Li-ion battery, has attracted wide interest for electrical grid and vehicle applications. However, demonstration of a full-cell battery with high energy and long cycle life remains a significant challenge. Here, we investigated the role of solid electrolyte interphase (SEI) formation on both cathodes and anodes and revealed a potential way to achieve long-term stability for Na-ion battery full-cells. Pre-cycling of cathodes and anodes leads to preformation of SEI, and hence mitigates the consumption of Na ions in full-cells. The example full-cell of Na0.44MnO2-hard carbon with pre-cycled and capacity-matched electrodes can deliver a specific capacity of ~116 mAh/g based on Na0.44MnO2 at 1 C rate (1 C=120 mA/g). The corresponding specific energy is ~313 Wh/kg based on the cathode. Excellent cycling stability with ~77% capacity retention over 2000 cycles was demonstrated at 2 C rate. Our work represents a leap forward in Na-ion battery development.

Wei X, W Duan, J Huang, L Zhang, B Li, DM Reed, W Xu, VL Sprenkle. "A High-Current, Stable Nonaqueous Organic Redox Flow Battery."ACS Energy Letters 1: 705-711 (Sept. 2016).
Abstract:Nonaqueous redox flow batteries are promising in pursuit of high energy density storage systems owing to the broad voltage windows (>2 V) but currently are facing key challenges such as limited cyclability and rate performance. To address these technical hurdles, here we report the nonaqueous organic flow battery chemistry based on N-methylphthalimide anolyte and 2,5-di-tert-butyl-1-methoxy-4-[2'-methoxyethoxy]benzene catholyte, which harvests a theoretical cell voltage of 2.30 V. The redox flow chemistry exhibits excellent cycling stability under both cyclic voltammetry and flow cell tests upon repeated cycling. A series of Daramic and Celgard porous separators are evaluated in this organic flow battery, which enable the cells to be operated at greatly improved current densities as high as 50 mA·cm^-2 compared to those of other nonaqueous flow systems. The stable cyclability and high-current operations of the organic flow battery system represent significant progress in the development of promising nonaqueous flow batteries.

Huang, J, B Pan, W Duan, X Wei, RS Assary, L Su, FR Brushett, L Cheng, C Liao, MS Ferrandon, W Wang, Z Zhang, AK Burrell, LA Curtiss, IA Shkrob, JS Moore, L Zhang. "The lightest organic radical cation for charge storage in redox flow batteries." Scientific Reports 6: Article number 32102 (Aug. 2016).
Abstract: In advanced electrical grids of the future, electrochemically rechargeable fluids of high energy density will capture the power generated from intermittent sources like solar and wind. To meet this outstanding technological demand there is a need to understand the fundamental limits and interplay of electrochemical potential, stability, and solubility in low-weight redox-active molecules. By generating a combinatorial set of 1,4-dimethoxybenzene derivatives with different arrangements of substituents, we discovered a minimalistic structure that combines exceptional long-term stability in its oxidized form and a record-breaking intrinsic capacity of 161 mAh/g. The nonaqueous redox flow battery has been demonstrated that uses this molecule as a catholyte material and operated stably for 100 charge/discharge cycles. The observed stability trends are rationalized by mechanistic considerations of the reaction pathways.

Qian, J, BD Adams, J Zheng, W Xu, WA Henderson, J Wang, ME Bowden, S Xu, JZ Hu, J Zhang. "Anode-Free Rechargeable Lithium Metal Batteries." Advanced Functional Materials 26 (39): 7094-7102 (Aug. 2016).
Abstract: Anode-free rechargeable lithium (Li) batteries (AFLBs) are phenomenal energy storage systems due to their significantly increased energy density and reduced cost relative to Li-ion batteries, as well as ease of assembly because of the absence of an active (reactive) anode material. However, significant challenges, including Li dendrite growth and low cycling Coulombic efficiency (CE), have prevented their practical implementation. Here, an anode-free rechargeable lithium battery based on a Cu||LiFePO₄ cell structure with an extremely high CE (>99.8%) is reported for the first time. This results from the utilization of both an exceptionally stable electrolyte and optimized charge/discharge protocols, which minimize the corrosion of the in situly formed Li metal anode.

Cheng, L, LA Curtiss, KR Zavadil, AA Gewirth, Y Shao, KG Gallagher. "Sparingly Solvating Electrolytes for High Energy Density Lithium–Sulfur Batteries." ACS Energy Letters 1 (3): 503-509 (July 2016).
Abstract: Moving to lighter and less expensive battery chemistries compared to contemporary lithium-ion requires the control of energy storage mechanisms based on chemical transformations rather than intercalation. Lithium–sulfur (Li/S) has tremendous theoretical specific energy, but contemporary approaches to control this solution-mediated, precipitation–dissolution chemistry require large excesses of electrolyte to fully solubilize the polysulfide intermediates. Achieving reversible electrochemistry under lean electrolyte operation is the most promising path for Li/S to move beyond niche applications to potentially transformational performance. An emerging Li/S research area is the use of sparingly solvating electrolytes and the creation of design rules for discovering new electrolyte systems that fundamentally decouple electrolyte volume from sulfur and polysulfide reaction mechanism. This Perspective presents an outlook for sparingly solvating electrolytes as a key path forward for long-lived, high energy density Li/S batteries including an overview of this promising new concept and some strategies for accomplishing it.

Bin Liu, Pengfei Yan, Wu Xu, Jianming Zheng, Yang He, Langli Luo, Mark E. Bowden, Chongmin Wang, Ji-Guang Zhang."Electrochemically Formed Ultrafine Metal Oxide Nanocatalysts for High-Performance Lithium–Oxygen Batteries."Nano Letters 16 (8): 4932-4939 (July 2016).
Abstract: Lithium–oxygen (Li–O₂) batteries have an extremely high theoretical specific energy density when compared with conventional energy-storage systems. However, practical application of the Li–O₂ battery system still faces significant challenges. In this work, we report a new approach for synthesis of ultrafine metal oxide nanocatalysts through an electrochemical prelithiation process. This process reduces the size of NiCo₂O₄ (NCO) particles from 20–30 nm to a uniformly distributed domain of ∼2 nm and significantly improves their catalytic activity. Structurally, the prelithiated NCO nanowires feature ultrafine NiO/CoO nanoparticles that are highly stable during prolonged cycles in terms of morphology and particle size, thus maintaining an excellent catalytic effect to oxygen reduction and evolution reactions. A Li–O₂ battery using this catalyst demonstrated an initial capacity of 29 280 mAh g^–1 and retained a capacity of >1000 mAh g^–1 after 100 cycles based on the weight of the NCO active material. Direct in situ transmission electron microscopy observations conclusively revealed the lithiation/delithiation process of as-prepared NCO nanowires and provided in-depth understanding for both catalyst and battery chemistries of transition-metal oxides. This unique electrochemical approach could also be used to form ultrafine nanoparticles of a broad range of materials for catalyst and other applications.

Pan, H, KS Han, M Vijayakumar, J Xiao, R Cao, J Chen, J Zhang, KT Mueller, Y Shao, J Liu. "Ammonium Additives to Dissolve Lithium Sulfide through Hydrogen Binding for High-Energy Lithium–Sulfur Batteries."Applied Materials & Interfaces 9 (5): 4290-4295 (July 2016).
Abstract: In rechargeable Li–S batteries, the uncontrollable passivation of electrodes by highly insulating Li₂S limits sulfur utilization, increases polarization, and decreases cycling stability. Dissolving Li₂S in organic electrolyte is a facile solution to maintain the active reaction interface between electrolyte and sulfur cathode, and thus address the above issues. Herein, ammonium salts are demonstrated as effective additives to promote the dissolution of Li₂S to 1.25 M in DMSO solvent at room temperature. NMR measurements show that the strong hydrogen binding effect of N–H groups plays a critical role in dissolving Li₂S by forming complex ligands with S2– anions coupled with the solvent’s solvating surrounding. Ammonium additives in electrolyte can also significantly improve the oxidation kinetics of Li₂S, and therefore enable the direct use of Li₂S as cathode material in Li–S battery system in the future. This provides a new approach to manage the solubility of lithium sulfides through cation coordination with sulfide anion.

Hongfa Xiang, Pengcheng Shi, Priyanka Bhattacharya, Xilin Chen, Donghai Mei, Mark E. Bowden, Jianming Zheng, Ji-Guang Zhang, Wu Xu."Enhanced charging capability of lithium metal batteries based on lithium bis(trifluoromethanesulfonyl)imide-lithium bis(oxalato)borate dual-salt electrolytes."Journal of Power Sources 318: 170-177 (June 2016).
Abstract: Rechargeable lithium (Li) metal batteries with conventional LiPF₆-carbonate electrolytes have been reported to fail quickly at charging current densities of about 1.0 mA cm⁻² and above. In this work, we demonstrate the rapid charging capability of Li||LiNi_0.8Co_0.15Al_0.05O₂ (NCA) cells can be enabled by a dual-salt electrolyte of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(oxalato)borate (LiBOB) in a carbonate solvent mixture. The cells using the LiTFSI-LiBOB dual-salt electrolyte significantly outperform those using the LiPF₆ electrolyte at high charging current densities. At the charging current density of 1.50 mA cm⁻², the Li||NCA cells with the dual-salt electrolyte can still deliver a discharge capacity of 131 mAh g⁻¹ and a capacity retention of 80% after 100 cycles. The Li||NCA cells with the LiPF6 electrolyte start to show fast capacity fading after the 30th cycle and only exhibit a low capacity of 25 mAh g⁻¹ and a low retention of 15% after 100 cycles. The reasons for the good chargeability and cycling stability of the cells using the LiTFSI-LiBOB dual-salt electrolyte can be attributed to the good film-formation ability of the electrolyte on the Li metal anode and the highly conductive nature of the sulfur-rich interphase layer.

Xuyong Feng, Hailin Zou, Hongfa Xiang, Xin Guo, Tianpei Zhou, Yucheng Wu, Wu Xu, Pengfei Yan, Chongmin Wang, Ji-Guang Zhang, Yan Yu."Ultrathin Li₄Ti₅O₁₂ Nanosheets as Anode Materials for Lithium and Sodium Storage."ACS Applied Materials & Interfaces 8 (26): 16718-16726 (June 2016).
Abstract: Ultrathin Li₄Ti₅O₁₂ (LTO) nanosheets with ordered microstructures were prepared via a polyether-assisted hydrothermal process. Pluronic P123, a polyether, can impede the growth of Li₂TiO₃ in the precursor and also act as a structure-directing agent to facilitate the (Li_1.81H_0.19)Ti₂O₅·2H₂O precursor to form the LTO nanosheets with the ordered microstructure. Moreover, the addition of P123 can suppress the stacking of LTO nanosheets during calcining of the precursor, and the thickness of the nanosheets can be controlled to be about 4 nm. The microstructure of the as-prepared ultrathin and ordered nanosheets is helpful for Li⁺ or Na⁺ diffusion and charge transfer through the particles. Therefore, the ultrathin P123-assisted LTO (P-LTO) nanosheets show a rate capability much higher than that of the LTO sample without P123 in a Li battery with over 130 mAh g^–1 of capacity remaining at the 64C rate. For intercalation of larger size Na⁺ ions, the P-LTO still exhibits a capacity of 115 mAh g^–1 at a current rate of 10 C and a capacity retention of 96% after 400 cycles.

Cheng Y, L Luo, L Zhong, J Chen, B Li, W Wang, SX Mao, C Wang, VL Sprenkle, G Li, J Liu. "Highly Reversible Zinc-Ion Intercalation into Chevrel Phase Mo6S8 Nanocubes and Applications for Advanced Zinc-Ion Batteries."ACS Applied Materials and Interfaces 8 (22):13673-13677 (June 2016).
Abstract: This work describes the synthesis of Chevrel phase Mo6S8 nanocubes and its application as the anode material for rechargeable Zn-ion batteries. Mo6S8 can host Zn(2+) ions reversibly in both aqueous and nonaqueous electrolytes with specific capacities around 90 mAh/g, and exhibited remarkable intercalation kinetics and cyclic stability. In addition, we assembled full cells by integrating Mo6S8 anodes with zinc-polyiodide (I(-)/I3(-))-based catholytes, and demonstrated that such full cells were also able to deliver outstanding rate performance and cyclic stability. This first demonstration of a zinc-intercalating anode could inspire the design of advanced Zn-ion batteries.

Li B, J Liu, Z Nie, W Wang, DM Reed, J Liu, P McGrail, VL Sprenkle. "Metal-Organic Frameworks as Highly Active Electrocatalysts for High-Energy Density, Aqueous Zinc-Polyiodide Redox Flow Batteries." Nano Letters 16 (7): 4335-4340 (June 2016).
Abstract: The new aqueous zinc-polyiodide redox flow battery (RFB) system with highly soluble active materials as well as ambipolar and bifunctional designs demonstrated significantly enhanced energy density, which shows great potential to reduce RFB cost. However, the poor kinetic reversibility and electrochemical activity of the redox reaction of I₃-/I- couples on graphite felts (GFs) electrode can result in low energy efficiency. Two nanoporous metal-organic frameworks (MOFs), MIL-125-NH₂ and UiO-66-CH₃, that have high surface areas when introduced to GF surfaces accelerated the I₃-/I- redox reaction. The flow cell with MOF-modified GFs serving as a positive electrode showed higher energy efficiency than the pristine GFs; increases of about 6.4% and 2.7% occurred at the current density of 30 mA/cm² for MIL-125-NH₂ and UiO-66-CH₃, respectively. Moreover, UiO-66-CH₃ is more promising due to its excellent chemical stability in the weakly acidic electrolyte. This letter highlights a way for MOFs to be used in the field of RFBs.

Estevez L, DM Reed, Z Nie, AM Schwarz, MI Nandasiri, JP Kizewski, W Wang, EC Thomsen, J Liu, J Zhang, VL Sprenkle, B Li. "Tunable oxygen functional groups as electrocatalysts on graphite felt surfaces for all-vanadium flow batteries."ChemSusChem 9 (12): 1455-1461 (May 2016).
Abstract: A dual oxidative approach using O2 plasma followed by treatment with H2O2 to impart oxygen functional groups onto the surface of a graphite felt electrode. When used as electrodes for an all-vanadium redox flow battery (VRB) system, the energy efficiency of the cell is enhanced by 8.2 % at a current density of 150 mA cm-2 compared with one oxidized by thermal treatment in air. More importantly, by varying the oxidative techniques, the amount and type of oxygen groups was tailored and their effects were elucidated. It was found that O-C=O groups improve the cells performance whereas the C-O and C=O groups degrade it. The reason for the increased performance was found to be a reduction in the cell overpotential after functionalization of the graphite felt electrode. This work reveals a route for functionalizing carbon electrodes to improve the performance of VRB cells. This approach can lower the cost of VRB cells and pave the way for more commercially viable stationary energy storage systems that can be used for intermittent renewable energy storage.

Shen F, W Luo, J Dai, Y Yao, M Zhu, E Hitz, Y Tang, Y Chen, VL Sprenkle, X Li, L Hu. "Ultra-Thick, Low-Tortuosity, and Mesoporous Wood Carbon Anode for High-Performance Sodium-Ion Batteries."Advanced Energy Materials 6 (14) (May 2016).
Abstract: Pyrolysis of earth-abundant wood yields to ultra-thick, low-tortuosity, and mesoporous carbon anodes for sodium-ion batteries. Such a low-tortuosity and porous structure promotes electrolyte diffusion and provides fast transport channels for Na ions, which enables a high areal capacity.

Prabhakaran V ,Mehdi B L,Ditto J J,Engelhard M H,Wang B ,Gunaratne KD D,Johnson D C,Browning N D,Johnson G E,Laskin J. "Rational design of efficient electrode–electrolyte interfaces for solid-state energy storage using ion soft landing" Nature Communications 7 (April 2016).
Abstract: The rational design of improved electrode–electrolyte interfaces (EEI) for energy storage is critically dependent on a molecular-level understanding of ionic interactions and nanoscale phenomena. The presence of non-redox active species at EEI has been shown to strongly influence Faradaic efficiency and long-term operational stability during energy storage processes. Herein, we achieve substantially higher performance and long-term stability of EEI prepared with highly dispersed discrete redox-active cluster anions (50 ng of pure ∼0.75 nm size molybdenum polyoxometalate (POM) anions on 25 μg (∼0.2 wt%) carbon nanotube (CNT) electrodes) by complete elimination of strongly coordinating non-redox species through ion soft landing (SL). Electron microscopy provides atomically resolved images of a uniform distribution of individual POM species soft landed directly on complex technologically relevant CNT electrodes. In this context, SL is established as a versatile approach for the controlled design of novel surfaces for both fundamental and applied research in energy storage.

Crawford, A, E Thomsen, D Reed, D Stephenson, V Sprenkle, J Liu, V Viswanathan. "Development and validation of chemistry agnostic flow battery cost performance model and application to nonaqueous electrolyte systems." International Journal of Energy Research 40 (12): 1611-1623 (April 2016).
Abstract: A chemistry agnostic cost performance model is described for a nonaqueous flow battery. The model predicts flow battery performance by estimating the active reaction zone thickness at each electrode as a function of current density, state of charge, and flow rate using measured data for electrode kinetics, electrolyte conductivity, and electrode-specific surface area. Validation of the model is conducted using a 4 kW stack data at various current densities and flow rates. This model is used to estimate the performance of a nonaqueous flow battery with electrode and electrolyte properties used from the literature. The optimized cost for this system is estimated for various power and energy levels using component costs provided by vendors. The model allows optimization of design parameters such as electrode thickness, area, flow path design, and operating parameters such as power density, flow rate, and operating SOC range for various application duty cycles. A parametric analysis is done to identify components and electrode/electrolyte properties with the highest impact on system cost for various application durations. A pathway to 100$ kW h⁻¹ for the storage system is identified. Copyright © 2016 John Wiley & Sons, Ltd.

Dong H, Y Li, Y Liang, G Li, CJ Sun, Y Ren, Y Lu, Y Yao. "A magnesium-sodium hybrid battery with high operating voltage."Chemical Communications 52: 8263-8266 (April 2016).
Abstract: We report a high performance magnesium-sodium hybrid battery utilizing a magnesium-sodium dual-salt electrolyte, a magnesium anode, and a Berlin green cathode. The cell delivers an average discharge voltage of 2.2 V and a reversible capacity of 143 mA h g-¹. We also demonstrate the cell with an energy density of 135 W h kg-¹ and a high power density of up to 1.67 kW kg-¹.

Cao, R, J Chen, KS Han, W Xu, D Mai, P Bhattacharya, MH Engelhard, KT Mueller, J Liu, J Zhang. "Effect of the Anion Activity on the Stability of Li Metal Anodes in Lithium-Sulfur Batteries." Advanced Functional Materials 26 (18): 3059-3066 (March 2016).
Abstract: With the significant progress made in the development of cathodes in lithium-sulfur (Li-S) batteries, the stability of Li metal anodes becomes a more urgent challenge in these batteries. Here the systematic investigation of the stability of the anode/electrolyte interface in Li-S batteries with concentrated electrolytes containing various lithium salts is reported. It is found that Li-S batteries using LiTFSI-based electrolytes are more stable than those using LiFSI-based electrolytes. The decreased stability is because the N–S bond in the FSI− anion is fairly weak and the scission of this bond leads to the formation of lithium sulfate (LiSO_x) in the presence of polysulfide species. In contrast, in the LiTFSI-based electrolyte, the lithium metal anode tends to react with polysulfide to form lithium sulfide (LiS_x), which is more reversible than LiSO_x formed in the LiFSI-based electrolyte. This fundamental difference in the bond strength of the salt anions in the presence of polysulfide species leads to a large difference in the stability of the anode-electrolyte interface and performance of the Li-S batteries with electrolytes composed of these salts. Therefore, anion selection is one of the key parameters in the search for new electrolytes for stable operation of Li-S batteries.

Chen, J, KS Han, WA Henderson, KC Lau, M Vijayakumar, T Dzwiniel, H Pan, LA Curtiss, J Xiao, KT Mueller, Y Shao, J Liu. "Restricting the Solubility of Polysulfides in Li-S Batteries Via Electrolyte Salt Selection."Advanced Energy Materials 6 (11) (March 2016).
Abstract: Lithium 2-trifluoromethyl-4,5-dicyanoimidazole as a supporting salt in electrolytes achieves a reduced Li₂S₈ solubility by tuning the chemical production to Li₄S₈ dimer. Ab initio molecular dynamics and nuclear magnetic resonance calculation confirms the solvation structure radius increase by 20%. Combined with Li₂S₈ and LiNO₃, the electrolyte can demonstrate a stable 300 cycling battery of practical sulfur loading.

Deng, X, M Hu, X Wei, W Wei, KT Mueller, Z chen, JZ Hu. "Nuclear magnetic resonance studies of the solvation structures of a high-performance nonaqueous redox flow electrolyte." Journal of Power Sources 308: 172-179 (March 2016).
Abstract: Understanding the solvation structures of electrolytes is important for developing nonaqueous redox flow batteries that hold considerable potential for future large scale energy storage systems. The utilization of an emerging ionic-derivatived ferrocene compound, ferrocenylmethyl dimethyl ethyl ammonium bis(trifluoromethanesulfonyl)imide (Fc1N112-TFSI), has recently overcome the issue of solubility in the supporting electrolyte. In this work, ¹³C, ¹H and ¹⁷O NMR investigations were carried out using electrolyte solutions consisting of Fc1N112-TFSI as the solute and the mixed alkyl carbonate as the solvent. It was observed that the spectra of ¹³C experience changes of chemical shifts while those of ¹⁷O undergo linewidth broadening, indicating interactions between solute and solvent molecules. Quantum chemistry calculations of both molecular structures and chemical shifts (¹³C, ¹H and ¹⁷O) are performed for interpreting experimental results and for understanding the detailed solvation structures. The results indicate that Fc1N112-TFSI is dissociated at varying degrees in mixed solvent depending on concentrations. At dilute solute concentrations, most Fc1N112+ and TFSI− are fully disassociated with their own solvation shells formed by solvent molecules. At saturated concentration, Fc1N112+-TFSI- contact ion pairs are formed and the solvent molecules are preferentially interacting with the Fc rings rather than interacting with the ionic pendant arm of Fc1N112-TFSI.

Duan, W, RS Vemuri, JD Milshtein, S Laramie, RD Dmello, J Huang, L Zhang, D Hu, M Vijayakumar, W Wang, J Liu, RM Darling, L Thompson, K Smith, JS Moore, FR Brushett, X Wei. "A symmetric organic-based nonaqueous redox flow battery and its state of charge diagnostics by FTIR." Journal of Materials Chemistry A 4: 5448-5456 (March 2016).
Abstract: Redox flow batteries have shown outstanding promise for grid-scale energy storage to promote utilization of renewable energy and improve grid stability. Nonaqueous battery systems can potentially achieve high energy density because of their broad voltage window. In this paper, we report a new organic redox-active material for use in a nonaqueous redox flow battery, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) that has high solubility (>2.6 M) in organic solvents. PTIO exhibits electrochemically reversible disproportionation reactions and thus can serve as both anolyte and catholyte redox materials in a symmetric flow cell. The PTIO flow battery has a moderate cell voltage of ∼1.7 V and shows good cyclability under both cyclic voltammetry and flow cell conditions. Moreover, we demonstrate that FTIR can offer accurate estimation of the PTIO concentration in electrolytes and determine the state of charge of the PTIO flow cell, suggesting FTIR as a powerful online battery status sensor. This study is expected to inspire more insights in this under-addressed area of state of charge analysis aiming at operational safety and reliability of flow batteries.

Wan, C, MY Hu, O Borodin, J Qian, Z Qin, J Zhang, JZ Hu. "Natural abundance ¹⁷O, ⁶Li NMR and molecular modeling studies of the solvation structures of lithium bis(fluorosulfonyl)imide/1,2-dimethoxyethane liquid electrolytes."Journal of Power Sources 307: 231-243 (March 2016).
Abstract: Natural abundance ¹⁷O and⁶Li NMR experiments, quantum chemistry and molecular dynamics studies were employed to investigate the solvation structures of Li+ at various concentrations of LiFSI in DME electrolytes. It was found that the chemical shifts of both ¹⁷O and ⁶Li changed with the concentration of LiFSI, indicating the changes of solvation structures with concentration. For the quantum chemistry calculations, the coordinated cluster LiFSI(DME)₂ forms at first, and its relative ratio increases with increasing LiFSI concentration to 1 M. Then the solvation structure LiFSI(DME) become the dominant component. As a result, the coordination of forming contact ion pairs between Li+ and FSI− ion increases, but the association between Li+ and DME molecule decreases. Furthermore, at LiFSI concentration of 4 M the solvation structures associated with Li+(FSI−)₂(DME), Li+₂(FSI−)(DME)₄ and (LiFSI)₂(DME)₃ become the dominant components. For the molecular dynamics simulation, with increasing concentration, the association between DME and Li+ decreases, and the coordinated number of FSI− increases, which is in perfect accord with the DFT results.

Jianming zheng, Pengfei Yan, Ruiguo Cao, Hongfa Xiang, Mark H. Engelhard, Bryant J. Polzin, Chongmin Wang, Ji-Guang Zhang, Wu Xu."Effects of Propylene Carbonate Content in CsPF₆-Containing Electrolytes on the Enhanced Performances of Graphite Electrode for Lithium-Ion Batteries."ACS Applied Materials & Interfaces 8 (8):5715-5722 (February 2016).
Abstract: The effects of propylene carbonate (PC) content in CsPF₆-containing electrolytes on the performances of graphite electrode in lithium half cells and in graphite∥LiNi_0.80Co_0.15Al_0.05O₂ (NCA) full cells are investigated. It is found that the performance of graphite electrode is significantly affected by PC content in the CsPF₆-containing electrolytes. An optimal PC content of 20% by weight in the solvent mixtures is identified. The enhanced electrochemical performance of graphite electrode can be attributed to the synergistic effects of the PC solvent and the Cs⁺ additive. The synergistic effects of Cs⁺ additive and appropriate amount of PC enable the formation of a robust, ultrathin, and compact solid electrolyte interphase (SEI) layer on the surface of graphite electrode, which is only permeable for desolvated Li⁺ ions and allows fast Li⁺ ion transport through it. Therefore, this SEI layer effectively suppresses the PC cointercalation and largely alleviates the Li dendrite formation on graphite electrode during lithiation even at relatively high current densities. The presence of low-melting-point PC solvent improves the sustainable operation of graphite∥NCA full cells under a wide temperature range. The fundamental findings also shed light on the importance of manipulating/maintaining the electrode/electrolyte interphasial stability in various energy-storage devices.

Jianming Zheng, Pengfei Yan, Donghai Mei, Mark H. Engelhard, Samuel S. Cartmell, Bryant J. Polzin, Chongmin Wang, Ji-Guang Zhang, Wu Xu."Highly Stable Operation of Lithium Metal Batteries Enabled by the Formation of a Transient High-Concentration Electrolyte Layer."Advanced Energy Materials 6 (8) (February 2016).
Abstract: Lithium (Li) metal has been extensively investigated as an anode for rechargeable battery applications due to its ultrahigh theoretical specific capacity and the lowest redox potential. However, significant challenges including dendrite growth and low Coulombic efficiency are still hindering the practical applications of rechargeable Li metal batteries. It is demonstrated that long-term cycling of Li metal batteries can be realized by the formation of a transient high-concentration electrolyte layer near the surface of Li metal anode during high rate discharge process. The highly concentrated Li⁺ ions in this transient layer will immediately be solvated by the available solvent molecules and facilitate the formation of a stable and flexible solid electrolyte interphase (SEI) layer composed of a poly(ethylene carbonate) framework integrated with other organic/inorganic lithium salts. This SEI layer largely suppresses the corrosion of Li metal anode attacked by free organic solvents and enables the long-term operation of Li metal batteries. The fundamental findings in this work provide a new direction for the development of Li metal batteries that could be operated at high current densities for a wide range of applications.

Kumar G R,Savariraj D A,Karthick S N,Selvam S ,Balamuralitharan B ,Kim HJ ,Viswanathan K K,Vijayakumar M ,Prabakar K. "Phase transition kinetics and surface binding states of methylammonium lead iodide perovskite" Phys. Chem. Chem. Phys. 18: 7284-7297 (Feb. 2016).
Abstract: We have presented a detailed analysis of the phase transition kinetics and binding energy states of solution processed methylammonium lead iodide (MAPbI3) thin films prepared at ambient conditions and annealed at different elevated temperatures. It is the processing temperature and environmental conditions that predominantly control the crystal structure and surface morphology of MAPbI3 thin films. The structural transformation from tetragonal to cubic occurs at 60 °C with a 30 minute annealing time while the 10 minute annealed films posses a tetragonal crystal structure. The transformed phase is greatly intact even at the higher annealing temperature of 150 °C and after a time of 2 hours. The charge transfer interaction between the Pb 4f and I 3d oxidation states is quantified using XPS.

Bin Liu, Ji-Guang Zhang, Guozhen Shen."Pursuing two-dimensional nanomaterials for flexible lithium-ion batteries."Nano Today 11 (1):82-97 (February 2016).
Abstract: Stretchable/flexible electronics provide a foundation for various emerging applications that beyond the scope of conventional wafer/circuit board technologies due to their unique features that can satisfy a broad range of applications such as wearable devices. Stretchable electronic and optoelectronics devices require the bendable/wearable rechargeable Li-ion batteries, thus these devices can operate without limitation of external powers. Various two-dimensional (2D) nanomaterials are of great interest in flexible energy storage devices, especially Li-ion batteries. This is because 2D materials exhibit much more exposed surface area supplying abundant Li-insertion channels and shortened paths for fast lithium ion diffusion. Here, we will review the recent developments on the flexible Li-ion batteries based on two dimensional nanomaterials. These researches demonstrated advancements in flexible electronics by incorporating various 2D nanomaterials into bendable batteries to achieve high electrochemical performance, excellent mechanical flexibility as well as electrical stability under stretching/bending conditions.

Cheng Y, D Choi, KS Han, KT Mueller, J Zhang, VL Sprenkle, J Liu, G Li. "Toward the design of high voltage magnesium-lithium hybrid batteries using dual-salt electrolytes." Chemical Communications 52: 5379-5382 (Feb. 2016).
Abstract: We report a design of high voltage magnesium-lithium (Mg-Li) hybrid batteries through rational control of the electrolyte chemistry, electrode materials and cell architecture. Prototype devices with a structure of Mg-Li/LiFePO₄ (LFP) and Mg-Li/LiMn₂O₄ (LMO) have been investigated. A Mg-Li/LFP cell using a dual-salt electrolyte 0.2 M [Mg₂Cl₂(DME)₄][AlCl₄]₂ and 1.0 M LiTFSI exhibits voltages higher than 2.5 V (vs. Mg) and a high specific energy density of 246 W h kg^-1 under conditions that are amenable for practical applications. The successful demonstrations reported here could be a significant step forward for practical hybrid batteries.

Choi D, X Li, WA Henderson, Q Huang, SK Nune, JP Lemmon, VL Sprenkle. "LiCoPO₄ cathode from a CoHPO₄xH₂O nanoplate precursor for high voltage Li-ion batteries." Heliyon 2 (2) (Feb. 2016).
Abstract: A highly crystalline LiCoPO₄/C cathode material has been synthesized without noticeable impurities via a single step solid-state reaction using CoHPO₄xH₂O nanoplate as a precursor obtained by a simple precipitation route. The LiCoPO₄/C cathode delivered a specific capacity of 125 mAhg-¹ at a charge/discharge rate of C/10. The nanoplate precursor and final LiCoPO₄/C cathode have been characterized using X-ray diffraction, thermogravimetric analysis - differential scanning calorimetry (TGA-DSC), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) and the electrochemical cycling stability has been investigated using different electrolytes, additives and separators.

Hu, JZ, Z Zhao, MY Hu, J Feng, X Deng, X Chen, W Xu, J Liu, J Zhang. "In situ⁷Li and ¹³³Cs nuclear magnetic resonance investigations on the role of Cs⁺ additive in lithium-metal deposition process." Journal of Power Sources 304: 51-59 (Feb. 2016).
Abstract: Cesium ion (Cs+) has been reported to be an effective electrolyte additive to suppress Li dendrite growth which prevents the application of lithium (Li) metal as an anode for rechargeable Li batteries. In this work, we investigated the effect of Cs+ additive on Li depositions using quantitative in situ⁷Li and ¹³³Cs nuclear magnetic resonance (NMR) with planar symmetric Li cells. It's found that the addition of Cs+ can significantly enhance both the formation of well aligned Li nanorods and reversibility of the Li electrode. In situ¹³³Cs NMR directly confirms that Cs+ migrates to Li electrode to form a positively charged electrostatic shield during the charging process. Much more electrochemical “active” Li was found in Li films deposited with Cs+ additive, while more electrochemical “dead” and thicker Li rods were identified in Li films deposited without Cs+. Combining the in situ and the previous ex-situ results, a Li deposition model has been proposed to explain these observations.

Li G, X Lu, JY Kim, KD Meinhardt, HJ Chang, NL Canfield, VL Sprenkle. "Advanced intermediate temperature sodium-nickel chloride batteries with ultra-high energy density." Nature Communications 7:10683 (Feb. 2016).
Abstract: Sodium-metal halide batteries have been considered as one of the more attractive technologies for stationary electrical energy storage, however, they are not used for broader applications despite their relatively well known redox system. One of the roadblocks hindering market penetration is the high operating temperature. Here we demonstrate that planar sodium-nickel chloride batteries can be operated at an intermediate temperature of 190°C with ultra-high energy density. A specific energy density of 350 Wh kg ^-1, higher than that of conventional tubular sodium-nickel chloride batteries (280°C), is obtained for planar sodium-nickel chloride batteries operated at 190°C over a long-term cell test (1,000 cycles), and it attributed to the slower particle growth of the cathode materials at the lower operating temperature. Results reported here demonstrate that planar sodium-nickel chloride batteries operated at an intermediate temperature could greatly benefit this traditional energy storage technology by improving battery energy density, cycle life and reducing material costs.

Reed DM, EC Thomsen, B Li, W Wang, Z Nie, BJ Koeppel, VL Sprenkle. "Performance of a low cost interdigitated flow design on a 1 kW class all vanadium mixed acid redox flow battery." Journal of Power Sources 306: 24-31 (Feb. 2016).
Abstract: Three flow designs were operated in a 3-cell 1 kW class all vanadium mixed acid redox flow battery. The influence of electrode surface area and flow rate on the coulombic, voltage, and energy efficiency and the pressure drop in the flow circuit will be discussed and correlated to the flow design. Material cost associated with each flow design will also be discussed.

Wang W, VL Sprenkle. "Energy storage: Redox flow batteries go organic."Nature Chemistry 8 (3): 204-206 (Feb. 2016).
Abstract: Access to sustainable and affordable energy is the foundation for the economic growth and future prosperity of our society. Given the drive to also reduce the carbon footprint associated with traditional fossil-based electricity generation, renewable resources could provide a clean and sustainable energy future. However, while the amount of energy produced from renewable resources such as solar and wind is steadily increasing, and the generation costs continuously falling, it still only represents a small fraction of current energy production. One big issue is the intermittent and fluctuating nature of energy produced from renewables and this will threaten the stability of the grid when the energy share from these resources surpasses 20% of the overall energy capacity¹. Electrical energy storage is a potentially cost-effective approach to solving this problem and would be beneficial for renewable energy integration, balancing the mismatch between supply and demand, as well as improving the overall reliability and efficiency of the grid.

Jianming Zheng, Pengfei Yan, Wang Hay Kan, Chongmin Wang, Arumugam Manthiram."A Spinel-Integrated P2-Type Layered Composite: High-Rate Cathode for Sodium-Ion Batteries."Journal of the Electrochemical Society 163 (3):A584-A591 (January 2016).
Abstract: Sodium-ion batteries (SIB) are being intensively investigated, owing to the natural abundance and low cost of Na resources. However, the SIBs still suffer from poor rate capability due to the large ionic radius of Na⁺ ion and the significant kinetic barrier to Na⁺-ion transport. Here, we present an Fd-3m spinel-integrated P2-type layered composite (P2 + Fd-3m) material as a high-rate cathode for SIBs. The P2 + Fd-3m composite material Na_0.50Ni_1/6Co_1/6Mn_2/3O₂ shows significantly enhanced discharge capacity, energy density, and rate capability as compared to the pure P2-type counterpart. The composite delivers a high capacity of 85 mA h g⁻¹ when discharging at a very high current density of 1500 mA g⁻¹ (10 C rate) between 2.0 and 4.5 V, validating it as a promising cathode candidate for high-power SIBs. The superior performance is ascribed to the improved kinetics in the presence of the integrated-spinel phase, which facilitates fast electron transport to coordinate with the timely Na⁺-ion insertion/extraction. The findings of this work also shed light on the importance of developing lattice doping, surface coating, and electrolyte additives to further improve the structural and interfacial stability of P2-type cathode materials and fully realize their practical applications in sodium-ion batteries.

Bin Liu, Wu Xu, Pengfei Yan, Xiuliang Sun, Mark E. Bowden, Jeffrey Read, Jiangfeng Qian, Donghai Mei, Chongmin Wang, Ji-Guang Zhang."Enhanced Cycling Stability of Rechargeable Li–O₂ Batteries Using High-Concentration Electrolytes."Advanced Functional Materials 26 (4):605-613 (December 2015).
Abstract: The stability of electrolytes against highly reactive, reduced oxygen species is crucial for the development of rechargeable Li–O₂ batteries. In this work, the effect of lithium salt concentration in 1,2-dimethoxyethane (DME)-based electrolytes on the cycling stability of Li–O₂ batteries is investigated systematically. Cells with highly concentrated electrolyte demonstrate greatly enhanced cycling stability under both full discharge/charge (2.0–4.5 V vs Li/Li⁺) and the capacity-limited (at 1000 mAh g⁻¹) conditions. These cells also exhibit much less reaction residue on the charged air-electrode surface and much less corrosion of the Li-metal anode. Density functional theory calculations are used to calculate molecular orbital energies of the electrolyte components and Gibbs activation energy barriers for the superoxide radical anion in the DME solvent and Li⁺–(DME) _n solvates. In a highly concentrated electrolyte, all DME molecules are coordinated with salt cations, and the C–H bond scission of the DME molecule becomes more difficult. Therefore, the decomposition of the highly concentrated electrolyte can be mitigated, and both air cathodes and Li-metal anodes exhibit much better reversibility, resulting in improved cyclability of Li–O₂ batteries.

Liu L, X Wei, Z Nie, VL Sprenkle, W Wang. "A Total Organic Aqueous Redox Flow Battery Employing a Low Cost and Sustainable Methyl Viologen Anolyte and 4-HO-TEMPO Catholyte." Advanced Energy Materials 6(3):1-8 (Dec. 2015).
Abstract: Increasing worldwide energy demands and rising CO2 emissions have motivated a search for new technologies to take advantage of renewables such as solar and wind energies. Redox flow batteries (RFBs) with their high power density, high energy efficiency, scalability (up to MW and MWh), and safety features are one suitable option for integrating such energy sources and overcoming their intermittency. However, resource limitation and high system costs of current RFB technologies impede wide implementation. Here, a total organic aqueous redox flow battery (OARFB) is reported, using low-cost and sustainable methyl viologen (MV, anolyte) and 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (4-HO-TEMPO, catholyte), and benign NaCl supporting electrolyte. The electrochemical properties of the organic redox active materials are studied using cyclic voltammetry and rotating disk electrode voltammetry. The MV/4-HO-TEMPO ARFB has an exceptionally high cell voltage, 1.25 V. Prototypes of the organic ARFB can be operated at high current densities ranging from 20 to 100 mA cm2, and deliver stable capacity for 100 cycles with nearly 100% Coulombic efficiency. The MV/4-HO-TEMPO ARFB displays attractive technical merits and thus represents a major advance in ARFBs.

Oleg Borodin, Marco Olguin, P. Ganesh, Paul R.C. Kent, Joshua L. Allen, Wesley A. Henderson."Competitive lithium solvation of linear and cyclic carbonates from quantum chemistry."Physical Chemistry Chemical Physics 18: 164-175 (November 2015).
Abstract: AbstractThe composition of the lithium cation (Li⁺) solvation shell in mixed linear and cyclic carbonate-based electrolytes has been re-examined using Born–Oppenheimer molecular dynamics (BOMD) as a function of salt concentration and cluster calculations with ethylene carbonate:dimethyl carbonate (EC:DMC)–LiPF₆ as a model system. A coordination preference for EC over DMC to a Li⁺ was found at low salt concentrations, while a slightly higher preference for DMC over EC was found at high salt concentrations. Analysis of the relative binding energies of the (EC)_n(DMC)_m–Li⁺ and (EC)_n(DMC)_m–LiPF₆ solvates in the gas-phase and for an implicit solvent (as a function of the solvent dielectric constant) indicated that the DMC-containing Li⁺ solvates were stabilized relative to (EC₄)–Li⁺ and (EC)₃–LiPF₆ by immersing them in the implicit solvent. Such stabilization was more pronounced in the implicit solvents with a high dielectric constant. Results from previous Raman and IR experiments were reanalyzed and reconciled by correcting them for changes of the Raman activities, IR intensities and band shifts for the solvents which occur upon Li⁺ coordination. After these correction factors were applied to the results of BOMD simulations, the composition of the Li⁺ solvation shell from the BOMD simulations was found to agree well with the solvation numbers extracted from Raman experiments. Finally, the mechanism of the Li⁺ diffusion in the dilute (EC:DMC)LiPF₆ mixed solvent electrolyte was studied using the BOMD simulations.

Savariraj D A,Rajendrakumar G ,Selvam S ,Karthick S N,Balamuralitharan B ,Kim HJ ,Viswanathan K K,Vijayakumar M ,Prabakar K. "Stacked Cu1.8S nanoplatelets as counter electrode for quantum dot-sensitized solar cell" RCS Advances 5: 100560-100567 (Nov. 2015).
Abstract: It is found that the electrocatalytic activity of Cu2−xS thin films used in quantum dot-sensitized solar cells (QDSSCs) as counter electrode (CE) for the reduction of polysulfide electrolyte depends on the surface active sulfide and disulfide species and the deficiency of Cu. The preferential bonding between Cu2+ and S2−, leading to the selective formation of a Cu1.8S stacked platelet-like morphology, is determined by the cetyl trimethyl ammonium bromide surfactant and deposition temperature; the crab-like Cu–S coordination bond formed dictates the surface area to volume ratio of the Cu1.8S thin films and their electrocatalytic activity. The Cu deficiency enhances the conductivity of the Cu1.8S thin films, which exhibit near-infrared localized surface plasmon resonance due to free carriers, and UV-vis absorption spectra show an excitonic effect due to the quantum size effect. When these Cu1.8S thin films were employed as CEs in QDSSCs, a robust photoconversion efficiency of 5.2% was obtained for the film deposited at 60 °C by a single-step chemical bath deposition method.

Liu B, Xu W, Yan P, Bhattacharya P, Cao R, Bowden ME, Engelhard MH, Wang CM, Zhang JG."In-Situ-Grown ZnCo2O4 on Single-Walled Carbon Nanotubes as Air Electrode Materials for Rechargeable Lithium-Oxygen Batteries."ChemSusChem 8 (21): 3697-703 (November 2015).
Abstract: The development of highly efficient catalysts is critical for the practical application of lithium-oxygen (Li-O2) batteries. Nanosheet-assembled ZnCo2O4 (ZCO) microspheres and thin films grown in-situ on single-walled carbon nanotube (ZCO/SWCNT) composites as high-performance air electrode materials for Li-O2 batteries are reported. The in-situ grown ZCO/SWCNT electrodes delivered high discharge capacities, decreased the onset of the oxygen evolution reaction by 0.9 V during the charging process, and led to longer cycling stability. These results indicate that in-situ grown ZCO/SWCNT composites can be used as highly efficient air electrode materials for oxygen reduction and evolution reactions. The enhanced catalytic activity displayed by the uniformly dispersed ZCO catalyst on nanostructured electrodes is expected to inspire further development of other catalyzed electrodes for Li-O2 batteries and other applications.

Lu X, G Li, JY Kim, KD Meinhardt, VL Sprenkle. "Enhanced sintering of ß"-Al_2/O₃/YSZ with the sintering aids of TiO₂ and MnO₂." Journal of Power Sources 295:167-174 (Nov. 2015).
Abstract: ß"-Al₂O3 has been the dominated choice for the electrolyte materials of sodium batteries because of its high ionic conductivity, excellent stability with the electrode materials, satisfactory mechanical strength, and low material cost. To achieve adequate electrical and mechanical performance, sintering of ß"-Al₂O₃ is typically carried out at temperatures above 1600°C with deliberate efforts on controlling the phase, composition, and microstructure. Here, we reported a simple method to fabricate ß"-Al₂O₃/YSZ electrolyte at relatively lower temperatures. With the starting material of boehmite, single phase of ß"-Al₂O₃ can be achieved at as low as 1200°C. It was found that TiO₂ was extremely effective as a sintering aid for the densification of ß"-Al₂O₃ and similar behavior was observed with MnO₂ for YSZ. With the addition of 2 mol% TiO₂ and 5 mol% MnO₂, the ß"-Al₂O₃/YSZ composite was able to be densified at as low as 1400°C with a fine microstructure and good electrical/mechanical performance. This study demonstrated a new approach of synthesis and sintering of ß"-Al₂O₃/YSZ composite, which represented a simple and low-cost method for fabrication of high-performance ß"-Al₂O₃/YSZ electrolyte.

Reed DM, EC Thomsen, B Li, W Wang, Z Nie, BJ Koeppel, JP Kizewski, VL Sprenkle. "Stack Developments in a kW Class All Vanadium Mixed Acid Redox Flow Battery at the Pacific Northwest National Laboratory." Journal of the Electrochemical Society 163 (1):A5211-A5219 (Nov. 2015).
Abstract: Over the past several years, efforts have been focused on improving the performance of kW class all vanadium mixed acid redox flow battery stacks with increasing current density. The influence of the Nafion membrane resistance, an interdigitated design to reduce the pressure drop in the electrolyte circuit, the temperature of the electrolyte, and the electrode structure will be discussed and correlated to the electrical performance. Improvements to the stack energy efficiency and how those improvements translate to the overall system efficiency will also be discussed.

Wei X, G Xia, BW Kirby, EC Thomsen, B Li, Z Nie, GG Graff, J Liu, VL Sprenkle, W Wang. "An Aqueous Redox Flow Battery Based on Neutral Alkali Metal Ferri/ferrocyanide and Polysulfide Electrolytes." Journal of The Electrochemical Society 163(1):A5150-A5153 (Nov. 2015).
Abstract: We have demonstrated a new ferri/ferrocyanide - polysulfide (Fe/S) flow battery, which employs less corrosive, relatively environmentally benign neutral alkali metal ferri/ferrocyanide and alkali metal polysulfides as the active redox couples. A cobalt nanoparticle - decorated graphite felt was used at the polysulfide side as the catalyst. Excellent electrochemical performance was successfully acquired in the Fe/S flow cells with high cell efficiencies (99% coulombic efficiency and ~74% energy efficiency) and good cycling stability over extended charge/discharge operations. The positive half-cell appears to be the performance - limiting side in the Fe/S flow battery determined by using a carbon cloth probe. The inexpensive redox materials and possibly cell part materials can lead to reduced capital cost, making the Fe/S flow battery a promising cost-effective energy storage technology.

Liang Xiao, Xilin Chen, Ruiguo Cao, Jiangfeng Qian, Hongfa Xiang, Jianming Zheng, Ji-Guang Zhang, Wu Xu."Enhanced performance of Li|LiFePO₄ cells using CsPF₆ as an electrolyte additive."Journal of Power Sources 293: 1062-1067 (October 2015).
Abstract: The practical application of lithium (Li) metal anode in rechargeable Li batteries is hindered by both the growth of Li dendrites and the low Coulombic efficiency (CE) during repeated charge/discharge cycles. Recently, we have discovered that CsPF₆ as an electrolyte additive can significantly suppress Li dendrite growth and lead to highly compacted and well aligned Li nanorod structures during Li deposition on copper substrates. In this paper, the effect of CsPF₆ additive on the performance of rechargeable Li metal batteries with lithium iron phosphate (LFP) cathode is further studied. Li|LFP coin cells with CsPF₆ additive in electrolytes show well protected Li anode surface, decreased resistance, enhanced rate capability and extended cycling stability. In Li|LFP cells, the electrolyte with CsPF₆ additive shows excellent long-term cycling stability (at least 500 cycles) at a charge current density of 0.5 mA cm⁻² without internal short circuit. At high charge current densities, the effect of CsPF₆ additive becomes less significant. Future work needs to be done to protect Li metal anode, especially at high charge current densities and for long cycle life.

Crawford A, V Viswanathan, D Stephenson, W Wang, EC Thomsen, DM Reed, B Li, PJ Balducci, M Kinter-Meyer, VL Sprenkle. "Comparative analysis for various redox flow batteries chemistries using a cost performance model." Journal of Power Sources 293: 388-399 (Oct. 2015).
Abstract: The total energy storage system cost is determined by means of a robust performance-based cost model for multiple flow battery chemistries. Systems aspects such as shunt current losses, pumping losses and various flow patterns through electrodes are accounted for. The system cost minimizing objective function determines stack design by optimizing the state of charge operating range, along with current density and current-normalized flow. The model cost estimates are validated using 2-kW stack performance data for the same size electrodes and operating conditions. Using our validated tool, it has been demonstrated that an optimized all-vanadium system has an estimated system cost of < $350 kWh^-1 for 4-h application. With an anticipated decrease in component costs facilitated by economies of scale from larger production volumes, coupled with performance improvements enabled by technology development, the system cost is expected to decrease to 160 kWh^-1 for a 4-h application, and to $100 kWh^-1 for a 10-h application. This tool has been shared with the redox flow battery community to enable cost estimation using their stack data and guide future direction.

Cheng, Y, Y Shao, LR Parent, ML Sushko, G Li, PV Sushko, ND Browning, C Wang, J Liu. "Interface Promoted Reversible Mg Insertion in Nanostructured Tin–Antimony Alloys."Advanced Materials 27 (42): 6598-6605 (Sept. 2015).
Abstract: An interface promoted approach is developed for guiding the design of stable and high capacity materials for Mg batteries using SnSb alloys as model materials. Experimental and theoretical studies reveal that the SnSb alloy has exceptionally high reversible capacity (420 mA h g⁻¹), excellent rate capability, and good cyclic stability for hosting Mg ions due to the stabilization/promotion effects of the interfaces between the multicomponent phases generated during repeated magnesiation–demagnesiation.

Hongfa Xiang, Donghai Mei, Pengfei Yan, Priyanka Bhattacharya, Sarah D. Burton, Arthur von Wald Cresce, Ruiguo Cao, Mark H. Engelhard, Mark E. Bowden, Zihua Zhu, Bryant J. Polzin, Chongmin Wang, Kang Xu, Ji-Guang Zhang, Wu Xu."The Role of Cesium Cation in Controlling Interphasial Chemistry on Graphite Anode in Propylene Carbonate-Rich Electrolytes."ACS Applied Materials & Interfaces 7 (37): 20687-20695 (September 2015).
Abstract: Despite the potential advantages it brings, such as wider liquid range and lower cost, propylene carbonate (PC) is seldom used in lithium-ion batteries because of its sustained cointercalation into the graphene structure and the eventual graphite exfoliation. Here, we report that cesium cation (Cs⁺) directs the formation of solid electrolyte interphase on graphite anode in PC-rich electrolytes through its preferential solvation by ethylene carbonate (EC) and the subsequent higher reduction potential of the complex cation. Effective suppression of PC-decomposition and graphite-exfoliation is achieved by adjusting the EC/PC ratio in electrolytes to allow a reductive decomposition of Cs⁺-(EC)_m (1 ≤ m ≤ 2) complex preceding that of Li⁺-(PC)_n (3 ≤ n ≤ 5). Such Cs⁺-directed interphase is stable, ultrathin, and compact, leading to significant improvement in battery performances. In a broader context, the accurate tailoring of interphasial chemistry by introducing a new solvation center represents a fundamental breakthrough in manipulating interfacial reactions that once were elusive to control.

Cosimbescu L, X Wei, M Vijayakumar, W Xu, ML Helm, SD Burton, CM Sorensen, J Liu, VL Sprenkle, W Wang. "Anion-Tunable Properties and Electrochemical Performance of Functionalized Ferrocene Compounds." Scientific Reports 5:14117 (Sept. 2015).
Abstract:We report a series of ionically modified ferrocene compounds for hybrid lithium-organic non-aqueous redox flow batteries, based on the ferrocene/ferrocenium redox couple as the active catholyte material. Tetraalkylammonium ionic moieties were incorporated into the ferrocene structure, in order to enhance the solubility of the otherwise relatively insoluble ferrocene. The effect of various counter anions of the tetraalkylammonium ionized species appended to the ferrocene, such as bis(trifluoromethanesulfonyl)imide, hexafluorophosphate, perchlorate, tetrafluoroborate, and dicyanamide on the solubility of the ferrocene was investigated. The solution chemistry of the ferrocene species was studied, in order to understand the mechanism of solubility enhancement. Finally, the electrochemical performance of these ionized ferrocene species was evaluated and shown to have excellent cell efficiency and superior cycling stability.

Liang Xiao, Jie Xiao, Xiqian Yu, Pengfei Yan, Jianming Zheng, Mark Engelhard, Priyanka Bhattacharya, Chongmin Wang, Xiao-Qing Yang, Ji-Guang Zhang. "Effects of structural defects on the electrochemical activation of Li₂MnO₃."Nano Energy 16: 143-151 (September 2015).
Abstract: Structural defects, e.g. Mn³⁺/oxygen non-stoichiometry, largely affect the electrochemical performance of both Li₂MnO₃ and lithium-rich manganese-rich (LMR) layered oxides with Li₂MnO₃ as one of the key components. Herein, Li₂MnO₃ samples with different amount of structural defects of Mn3+/oxygen non-stoichiometry are prepared. The results clearly demonstrate that the annealed Li₂MnO₃ (ALMO), quenched Li₂MnO₃ (QLMO), and quenched Li2MnO3 milled with Super P (MLMO) all show pure C2/m monoclinic phase with stacking faults. MLMO shows the largest amount of Mn³⁺, followed by the QLMO and then the ALMO. The increased amount of Mn³⁺ in Li₂MnO₃ (such as sample MLMO) facilitates the activation of Li₂MnO₃ and leads to the highest initial discharge specific capacity of 167.7 mA h g⁻¹ among the samples investigated in this work. However, accelerated activation of Li₂MnO₃ also results in faster structural transformation to spinel-like phase, leading to rapid capacity degradation. Therefore, the amount of Mn³⁺ needs to be well controlled during synthesis of LMR cathode in order to reach a reasonable compromise between the initial activity and long-term cycling stability. The findings of this work could be widely applied to explain the effects of Mn³⁺ on different kinds of LMR cathodes.

Zhu, Z, Y Zhou, P Yan, RS Vemuri, W Xu, R Zhao, X Wang, S Thevuthasan, DR Baer, CM Wang. "In Situ Mass Spectrometric Determination of Molecular Structural Evolution at the Solid Electrolyte Interphase in Lithium-Ion Batteries." Nano Letters 15 (9): 6170-6176 (Aug. 2015).
Abstract: Dynamic structural and chemical evolution at solid–liquid electrolyte interface is always a mystery for a rechargeable battery due to the challenge to directly probe a solid–liquid interface under reaction conditions. We describe the creation and usage of in situ liquid secondary ion mass spectroscopy (SIMS) for the first time to directly observe the molecular structural evolution at the solid–liquid electrolyte interface for a lithium (Li)-ion battery under dynamic operating conditions. We have discovered that the deposition of Li metal on copper electrode leads to the condensation of solvent molecules around the electrode. Chemically, this layer of solvent condensate tends to be depleted of the salt anions and with reduced concentration of Li+ ions, essentially leading to the formation of a lean electrolyte layer adjacent to the electrode and therefore contributing to the overpotential of the cell. This observation provides unprecedented molecular level dynamic information on the initial formation of the solid electrolyte interphase (SEI) layer. The present work also ultimately opens new avenues for implanting the in situ liquid SIMS concept to probe the chemical reaction process that intimately involves solid–liquid interface, such as electrocatalysis, electrodeposition, biofuel conversion, biofilm, and biomineralization.

Lu X, ME Bowden, VL Sprenkle, J Liu. "A Low Cost, High Energy Density, and Long Cycle Life Potassium-Sulfur Battery for Grid-Scale Energy Storage." Advanced Materials 27(39):5915-5922 (Aug. 2015).
Abstract:A potassium-sulfur battery using K⁺-conducting beta-alumina as the electrolyte to separate a molten potassium metal anode and a sulfur cathode is presented. The results indicate that the battery can operate at as low as 150°C with excellent performance. This study demonstrates a new type of high-performance metal-sulfur battery that is ideal for grid-scale energy-storage applications.

Dongping Lu, Pengfei Yan, Yuyan Shao, Qiuyan Li, Seth Ferrara, Huilin Pan, Gordon L. Graff, Bryant Polzin, Chongmin Wang, Ji-Guang Zhang, Jun Liu, Jie Xiao."High performance Li-ion sulfur batteries enabled by intercalation chemistry."Chemical Communications 51: 13454-13457 (July 2015).
Abstract: AbstractThe unstable interface of lithium metal in high energy density Li sulfur (Li–S) batteries raises concerns of poor cycling, low efficiency and safety issues, which may be addressed by using intercalation types of anode. Herein, a new prototype of Li-ion sulfur battery with high performance has been demonstrated by coupling a graphite anode with a sulfur cathode (2 mA h cm⁻²) after successfully addressing the interface issue of graphite in an ether based electrolyte.

Canfield NL, JY Kim, JF Bonnett, RL Pearson III, VL Sprenkle, J Kung. "Effects of fabrication conditions on mechanical properties and microstructure of duplex ß"-Al₂O₃ solid electrolyte." Materials Science and Engineering: B 197: 43-50 (July 2015).
Abstract:Na-beta batteries are an attractive technology as a large-scale electrical energy storage for grid applications. However, additional improvements in performance and cost are needed for wide market penetration. To improve cell performance by minimizing polarizations, reduction of electrolyte thickness was attempted using a duplex structure consisting of a thin dense electrolyte layer and a porous support layer. In this paper, the effects of sintering conditions, dense electrolyte thickness, and cell orientation on the flexural strength of duplex BASEs fabricated using a vapor phase approach were investigated. It is shown that sintering at temperatures between 1500 and 1550°C results in fine grained microstructures and the highest flexural strength after conversion. Increasing thickness of the dense electrolyte has a small impact on flexural strength, while the orientation of load such that the dense electrolyte is in tension instead of compression has major effects on strength for samples with a well-sintered dense electrolyte.

Deng X, MY Hu, X Wei, W Wang, Z Chen, J Liu, JZ Hu. "Natural abundance ¹⁷O nuclear magnetic resonance and computational modeling studies of lithium based liquid electrolytes." Journal of Power Sources 285: 146-155 (July 2015).
Abstract:Natural abundance ¹⁷O NMR measurements were conducted on electrolyte solutions consisting of Li[CF₃SO₂NSO₂CF₃] (LiTFSI) dissolved in the solvents of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and their mixtures at various concentrations. It was observed that ¹⁷O chemical shifts of solvent molecules change with the concentration of LiTFSI. The chemical shift displacements of carbonyl oxygen are evidently greater than those of ethereal oxygen, strongly indicating that Li⁺ ion is coordinated with carbonyl oxygen rather than ethereal oxygen. To understand the detailed molecular interaction, computational modeling of ¹⁷O chemical shifts was carried out on proposed solvation structures. By comparing the predicted chemical shifts with the experimental values, it is found that a Li⁺ ion is coordinated with four double bond oxygen atoms from EC, PC, EMC and TFSI anion. In the case of excessive amount of solvents of EC, PC and EMC the Li⁺ coordinated solvent molecules are undergoing quick exchange with bulk solvent molecules, resulting in average ¹⁷O chemical shifts. Several kinds of solvation structures are identified, where the proportion of each structure in the liquid electrolytes investigated depends on the concentration of LiTFSI.

Qian, J, W Xu, P Bhattacharya, M Engelhard, WA Henderson, Y Zhang, J Zhang. "Dendrite-free Li deposition using trace-amounts of water as an electrolyte additive." Nano Energy 15: 135-144 (July 2015).
Abstract:Residual water (H₂O) presents in nonaqueous electrolytes has been widely regarded as a detrimental factor for lithium (Li) batteries. This is because H₂O is highly reactive with the commonly used LiPF₆ salt leading to the formation of HF which subsequently corrodes battery materials. In this work, we demonstrate that a controlled trace-amount of H₂O (25–50 ppm) can be an effective electrolyte additive for achieving dendrite-free Li metal deposition in LiPF_6-based electrolytes, while avoid detrimental effects. Detailed analyses revealed that the trace amount of HF derived from the decomposition reaction of LiPF₆ with H₂O is electrochemically reduced during the initial Li deposition process to form a uniform and dense LiF-rich solid electrolyte interphase (SEI) layer on the surface of the substrate. This LiF-rich SEI layer leads to a uniform distribution of the electric field on the substrate surface thereby enabling uniform and dendrite-free Li deposition. Meanwhile, the detrimental effect of HF on the other cell components is diminished due to the consumption of the HF in the LiF formation process. Microscopic analysis reveals that the as-deposited, dendrite-free Li films exhibit a self-aligned and highly-compact Li nanorod structure which is consistent with a vivid blue color due to structural coloration. These findings clearly demonstrate a novel approach to control the nucleation and grow processes of Li metal films using a well-controlled, trace-amount of H₂O, as well as illuminate the effect of H₂O on other electrodeposition processes.

Reed DM, ED Thomsen, W Wang, Z Nie, B Li, X Wei, BJ Koeppel, VL Sprenkle. "Performance of Nafion^® N115, Nafion^® NR-212, and Nafion^® NR-211 in a 1 kW class all vanadium mixed acid redox flow battery."Journal of Power Sources 285:425-430 (July 2015).
Abstract:Three Nafion^® membranes of similar composition but different thicknesses were operated in a 3-cell 1 kW class all vanadium mixed acid redox flow battery. The influence of current density on the charge/discharge characteristics, coulombic and energy efficiency, capacity fade, operating temperature and pressure drop in the flow circuit will be discussed and correlated to the Nafion^® membrane thickness. Material costs associated with the Nafion^® membranes, ease of handling the membranes, and performance impacts will also be discussed.

Wei X, W Xu, J Huang, L Zhang, ED Walter, CW Lawrence, M Vijayakumar, WA Henderson, TL Liu, L Cosimbescu, B Li, VL Sprenkle, W Wang. "Radical Compatibility with Nonaqueous Electrolytes and Its Impact on an All-Organic Redox Flow Battery." Angewandte Chemie 54 (30):8684-8687 (July 2015).
Abstract:Nonaqueous redox flow batteries hold the promise of achieving higher energy density because of the broader voltage window than aqueous systems, but their current performance is limited by low redox material concentration, cell efficiency, cycling stability, and current density. We report a new nonaqueous all-organic flow battery based on high concentrations of redox materials, which shows significant, comprehensive improvement in flow battery performance. A mechanistic electron spin resonance study reveals that the choice of supporting electrolytes greatly affects the chemical stability of the charged radical species especially the negative side radical anion, which dominates the cycling stability of these flow cells. This finding not only increases our fundamental understanding of performance degradation in flow batteries using radical-based redox species, but also offers insights toward rational electrolyte optimization for improving the cycling stability of these flow batteries.

Pengfei Yan, Jianming Zheng, Jie Xiao, Chongmin Wang, Ji-Guang Zhang."Recent advances on the understanding of structural and composition evolution of LMR cathodes for Li-ion batteries."Frontiers in Energy Research (June 2015).
Abstract: Lithium-and-manganese-rich (LMR) cathode materials have been regarded as very promising for lithium (Li)-ion battery applications. However, their practical application is still limited by several barriers such as their limited electrochemical stability and rate capability. In this work, we present recent progress on the understanding of structural and compositional evolution of LMR cathode materials, with an emphasis being placed on the correlation between structural/chemical evolution and electrochemical properties. In particular, using Li[Li_0.2Ni_0.2Mn_0.6]O₂ as a typical example, we clearly illustrate the structural characteristics of pristine materials and their dependence on the material-processing history, cycling-induced structural degradation/chemical partition, and their correlation with electrochemical performance degradation. The fundamental understanding that resulted from this work may also guide the design and preparation of new cathode materials based on the ternary system of transitional metal oxides.

Kerisit, S, M Vijayakumar, KS Han, KT Mueller. "Solvation structure and transport properties of alkali cations in dimethyl sulfoxide under exogenous static electric fields." Journal of Chemical Physics 142 (22) 224502 (June 2015).
Abstract:A combination of molecular dynamics simulations and pulsed field gradient nuclear magnetic resonance spectroscopy is used to investigate the role of exogenous electric fields on the solvation structure and dynamics of alkali ions in dimethyl sulfoxide (DMSO) and as a function of temperature. Good agreement was obtained, for select alkali ions in the absence of an electric field, between calculated and experimentally determined diffusion coefficients normalized to that of pure DMSO. Our results indicate that temperatures of up to 400 K and external electric fields of up to 1 V nm⁻¹ have minimal effects on the solvation structure of the smaller alkali cations (Li⁺ and Na⁺) due to their relatively strong ion-solvent interactions, whereas the solvation structures of the larger alkali cations (K⁺, Rb⁺, and Cs⁺) are significantly affected. In addition, although the DMSO exchange dynamics in the first solvation shell differ markedly for the two groups, the drift velocities and mobilities are not significantly affected by the nature of the alkali ion. Overall, although exogenous electric fields induce a drift displacement, their presence does not significantly affect the random diffusive displacement of the alkali ions in DMSO. System temperature is found to have generally a stronger influence on dynamical properties, such as the DMSO exchange dynamics and the ion mobilities, than the presence of electric fields.

Kim JY, NL Canfield, JF Bonnett, VL Sprenkle, K Jung, I Hong. "A Duplex ß"-Al2O3 Solid Electrolyte Consisting of A Thin Dense Layer and A Porous Substrate."Solid State Ionics 278: 192-197 (June 2015).
Abstract:To improve the performance of Na-beta batteries at intermediate temperatures (≤200°C) where much improved cyclability and reduced degradation can be achieved, there is a need to lower the resistance/polarization coming from BASEs while maintaining good strength. In this paper, the concept of a duplex BASE consisting of a thin dense electrolyte and a porous support was proposed as a solution to achieve low area-specific resistance while maintaining good mechanical strength. The effects of various factors including porosity, composition, and the homogeneity of ingredients on the flexural strength of duplex BASEs were examined. In summary, lower porosity, higher YSZ content in the structure, and the attrition milling of powders resulted in improved strength. The area-specific resistance measurement exhibited that the resistance of duplex BASEs was mainly originated from a dense layer. Overall, the maximum strength of 260 MPa and the ASR value of 0.31 cm2 (at 350°C) was achieved from a duplex BASE consisting of a 50 µm thick dense layer (Al2O3: YSZ = 7:3 in volume) and a 500 µm thick porous support (Al2O3: YSZ = 4:6 in volume with 19% open porosity). The effects of various factors on the properties of duplex BASEs will be explained in details.

Li G, X Lu, JY Kim, V Viswanathan, KD Meinhardt, MH Engelhard, VL Sprenkle. "An Advanced Na-FeCl₂ ZEBRA Battery for Stationary Energy Storage Application." Advanced Energy Materials 5(12) (June 2015).
Abstract:In article number 1500357, Guosheng Li, Jin Y. Kim, and co-workers report a remarkably reliable Na-FeCl₂ ZEBRA battery for stationary energy storage applications. The removal of surface oxide passivation layers on iron particles is critical and it is attributed to polysulfide species generated from sulfur-based additives through polysulfide reactions. The Na-FeCl₂ cells presented can be assembled at the discharge state (NaCl + Fe powder) without handling highly hazardous materials such as anhydrous FeCl₂ and metallic sodium.

Shamie JS, C Liu, LL Shaw, VL Sprenkle. "Room Temperature, Hybrid Sodium-Based Flow Batteries with Multi-Electron Transfer Redox Reactions." Scientific Reports 5, article number 11215 (June 2015).
Abstract:We introduce a new concept of hybrid Na-based flow batteries (HNFBs) with a molten Na alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane for grid-scale energy storage. Such HNFBs can operate at ambient temperature, allow catholytes to have multiple electron transfer redox reactions per active ion, offer wide selection of catholyte chemistries with multiple active ions to couple with the highly negative Na alloy anode, and enable the use of both aqueous and non-aqueous catholytes. Further, the molten Na alloy anode permits the decoupled design of power and energy since a large volume of the molten Na alloy can be used with a limited ion-exchange membrane size. In this proof-of-concept study, the feasibility of multi-electron transfer redox reactions per active ion and multiple active ions for catholytes has been demonstrated. The critical barriers to mature this new HNFBs have also been explored.

Jianming Zheng, Pengfei Yan, Meng Gu, Michael J. Wagner, Kevin A. Hays, Junzheng Chen, Xiaohong Li, Chongmin Wang, Ji-Guang Zhang, Jun Liu, Jie Xiao."Interfacial reaction dependent performance of hollow carbon nanosphere – sulfur composite as a cathode for Li-S battery."Frontiers in Energy Research (May 2015).
Abstract: Lithium-sulfur (Li-S) battery is a promising energy storage system due to its high energy density, cost effectiveness, and environmental friendliness of sulfur. However, there are still a number of technical challenges, such as low Coulombic efficiency and poor long-term cycle life, impeding the commercialization of Li-S battery. The electrochemical performance of Li-S battery is closely related with the interfacial reactions occurring between hosting substrate and active sulfur species, which are poorly conducting at fully oxidized and reduced states. Here, we correlate the relationship between the performance and interfacial reactions in the Li-S battery system, using a hollow carbon nanosphere (HCNS) with highly graphitic character as hosting substrate for sulfur. With an appropriate amount of sulfur loading, HCNS/S composite exhibits excellent electrochemical performance because of the fast interfacial reactions between HCNS and the polysulfides. However, further increase of sulfur loading leads to increased formation of highly resistive insoluble reaction products (Li₂S₂/Li₂S), which limits the reversibility of the interfacial reactions and results in poor electrochemical performances. These findings demonstrate the importance of the interfacial reaction reversibility in the whole electrode system on achieving high capacity and long cycle life of sulfur cathode for Li-S batteries.

Wei X, B Li, W Wang. "Porous Polymeric Composite Separators for Redox Flow Batteries." Polymer Reviews 55(2):247-272 (May 2015).
Abstract:Currently, the most commonly used membranes in redox flow batteries (RFB) are ion-exchange membranes. In particular, in all vanadium flow battery systems (VRB), perfluorinated polymers such as Nafion^® are widely used, owing to their high proton conductivity and chemical stability; however, the extremely high cost of currently available membranes has limited the commercialization of VRB technology. Recently, low-cost porous polymeric composite separators (e.g., polytetrafluoroethylene [PTFE]/silica), as an alternative to traditional ion-exchange membranes, have attracted a great deal of interest because of their significantly lower cost. Porous separators prepared from various polymer materials and inorganic fillers have demonstrated comparable electrochemical performances to that of Nafion^® in flow battery tests with different redox chemistries. This paper provides a review of porous separators for flow battery applications. In addition to discussions of separator material selection and preparation methods, we also emphasize the electrochemical performance of various flow battery systems, especially the capacity fade mechanism that is closely related to ion-transport across porous separator.

Pan, H, X Wei, WA Henderson, Y Shao, J Chen, P Bhattacharya, J Xiao, J Liu. "On the Way Toward Understanding Solution Chemistry of Lithium Polysulfides for High Energy Li–S Redox Flow Batteries." Advanced Energy Materials 5 (16)(Apr. 2015).
Abstract:Lithium–sulfur (Li–S) redox flow battery (RFB) is a promising candidate for high energy large-scale energy storage application due to good solubility of long-chain polysulfide species and low cost of sulfur. Here, the fundamental understanding and control of lithium polysulfide chemistry are studied to enable the development of liquid phase Li–S redox flow prototype cells. These differ significantly from conventional static Li–S batteries targeting for vehicle electrification. A high solubility of the different lithium polysulfides generated at different depths of discharge and states of charge is required for a flow battery in order to take full advantage of the multiple electron transitions. A new dimethyl sulfoxide based electrolyte is proposed for Li–S RFBs, which not only enables the high solubility of lithium polysulfide species, especially for the short-chain species, but also results in excellent cycling with a high Coulombic efficiency. The challenges and opportunities for the Li–S redox flow concept have also been discussed in depth.

Wei X, W Xu, J Huang, L Zhang, E Walter, C Lawrence, M Vijaykumar, WA Henderson, T Liu, L Cosimbescu, B Li, V Sprenkle, W Wang. "Radical Compatibility with Nonaqueous Electrolytes and Its Impact on an All-Organic Redox Flow Battery."Angewandte Chemie 54 (30): 8684-8687 (Apr. 2015).
Abstract:Nonaqueous redox flow batteries hold the promise of achieving higher energy density because of the broader voltage window than aqueous systems, but their current performance is limited by low redox material concentration, cell efficiency, cycling stability, and current density. We report a new nonaqueous all-organic flow battery based on high concentrations of redox materials, which shows significant, comprehensive improvement in flow battery performance. A mechanistic electron spin resonance study reveals that the choice of supporting electrolytes greatly affects the chemical stability of the charged radical species especially the negative side radical anion, which dominates the cycling stability of these flow cells. This finding not only increases our fundamental understanding of performance degradation in flow batteries using radical-based redox species, but also offers insights toward rational electrolyte optimization for improving the cycling stability of these flow batteries.

Cao, R, W Xu, D Lu, J Xiao, J Zhang. "Anodes for Rechargeable Lithium-Sulfur Batteries." Advanced Energy Materials 5 (16)(Apr. 2015).
Abstract:With the significant progress that has been made toward the development of cathode materials and electrolytes in lithium-sulfur (Li-S) batteries in recent years, the stability of the anode in Li-S batteries has become one of the more urgent challenges in order to reach long-term stability of Li-S batteries. In Li-S batteries, a passivation layer is easily formed on the metallic Li anode surface because of the presence of polysulfides and electrolyte additives. Although the passivation layer on the Li metal anode can significantly suppress Li dendrite growth and improve the safety of Li-S batteries, continuous corrosion of the Li metal anode eventually leads to battery failure due to the increased cell impedance and the depletion of electrolyte. Here, the recent developments on the protection of the Li metal anode in Li-S batteries are reviewed. Various strategies used to minimize the corrosion of Li anodes and to reduce its impedance increase are analyzed. Other alternative anodes used in sulfur-based rechargeable batteries are also discussed.

Chen J, D Wu, E Walter, M Engelhard, P Bhattacharya, H Pan, Y Shao, F Gao, J Xiao, J Liu. "Molecular-confinement of polysulfides within mesoscale electrodes for the practical application of lithium sulfur batteries."Nano Energy 13: 267-274 (Apr. 2015).
Abstract:Nitrogen-doped porous carbon (NPC) and multi-wall carbon nanotubes (MWCNT) have been frequently studied to immobilize sulfur in lithium–sulfur (Li–S) batteries. However, neither NPC nor MWCNT itself can effectively confine the soluble polysufides if cathode thickness e.g. sulfur loading is increased. In this work, NPC was combined with MWCNTs to construct an integrated host structure to immobilize sulfur at a relevant scale. The function of doped nitrogen atoms was revisited and found to effectively attract sulfur radicals generated during the electrochemical process. The addition of MWCNT facilitated the uniform coating of sulfur nanocomposites to a practically thickness and homogenized the distribution of sulfur particles in the pristine electrodes, while NPC provided sufficient pore volume to trap the dissolved polysulfides species. More importantly, the difficulty of electrode wetting, a critical challenge for thick sulfur cathodes, is also mitigated after the adoption of MWCNT, leading to a high areal capacity of ca. 2.5 mA h/cm² with a capacity retention of 81.6% over 100 cycles.

Cheng Y, RM Stolley, KS Han, Y Shao, BW Arey, NM Washton, KT Mueller, ML Helm, VL Sprenkle, J Liu, G Li. "Highly Active Electrolytes for Rechargeable Mg Batteries Based on [Mg₂(μ-Cl)2]2+ Cation Complex in Dimethoxyethane. "Physical Chemistry Chemical Physics 17: 13307-13314 (Apr. 2015).
Abstract:A novel [Mg₂(μ-Cl)₂]²⁺ cation complex, which is highly active for reversible Mg electrodeposition, was identified for the first time in this work. This complex was found to be present in electrolytes formulated in dimethoxyethane (DME) through dehalodimerization of non-nucleophilic MgCl₂ by reacting with either Mg salts (such as Mg(TFSI)₂, TFSI = bis(trifluoromethane)sulfonylimide) or Lewis acid salts (such as AlEtCl₂ or AlCl₃). The molecular structure of the cation complex was characterized by single crystal X-ray diffraction, Raman spectroscopy and NMR. The electrolyte synthesis process was studied and rational approaches for formulating highly active electrolytes were proposed. Through control of the anions, electrolytes with an efficiency close to 100%, a wide electrochemical window (up to 3.5 V) and a high ionic conductivity (>6 mS cm^-1) were obtained. The understanding of electrolyte synthesis in DME developed in this work could bring significant opportunities for the rational formulation of electrolytes of the general formula [Mg₂(μ-Cl)₂][anion]_x for practical Mg batteries.

Yu, X, H Pan, Y Zhou, P Northrup, J Xiao, S Bak, M Liu, KW Nam, D Qu, J Liu, T Wu, XQ Yang. "Direct Observation of the Redistribution of Sulfur and Polysufides in Li–S Batteries During the First Cycle by In Situ X-Ray Fluorescence Microscopy." Advanced Energy Materials 5 (16) (March 2015).
Abstract:A novel in situ X-ray fluorescence microscopy combined with X-ray absorption spectroscopy technique is reported to investigate the Li–S batteries during electrochemical cycling. The evolution of morphology changes of the electrode is monitored in real time using the X-ray fluorescence images, while the changes of the sulfur chemical state are characterized simultaneously using the X-ray absorption spectroscopy spectra.

Welch D A,Mehdi B L,Hatchell H J,Faller R ,Evans J E,Browning N D. "Using molecular dynamics to quantify the electrical double layer and examine the potential for its direct observation in the in-situ TEM." Advanced Structural and Chemical Imagining 1 (1) (March 2015).
Abstract: Understanding the fundamental processes taking place at the electrode-electrolyte interface in batteries will play a key role in the development of next generation energy storage technologies. One of the most fundamental aspects of the electrode-electrolyte interface is the electrical double layer (EDL). Given the recent development of high spatial resolution in-situ electrochemical fluid cells for scanning transmission electron microscopy (STEM), there now exists the possibility that we can directly observe the formation and dynamics of the EDL. In this paper we predict electrolyte structure within the EDL using classical models and atomistic Molecular Dynamics (MD) simulations. Classical models are found to greatly differ from MD in predicted concentration profiles. It is thus suggested that MD must be used in order to accurately predict STEM images of the electrode-electrolyte interface. Using MD and image simulation together for a high contrast electrolyte (the high atomic number CsCl electrolyte), it is determined that, for a smooth interface, concentration profiles within the EDL should be visible experimentally. When normal experimental parameters such as rough interfaces and low-Z electrolytes (like those used in Li-ion batteries) are considered, observation of the EDL appears to be more difficult.

Xiao J ,Hu J Z,Chen H ,Vijayakumar M ,Zheng J ,Pan H ,Walter E D,Hu M Y,Deng X ,Feng J ,Liaw BY ,Gu M ,Deng Z ,Lu D ,Xu S ,Wang C M,Liu J. "Following the Transient Reactions in Lithium–Sulfur Batteries Using an In Situ Nuclear Magnetic Resonance Technique." Nano Letters 15 (5): 3309-3316 (March 2015).
Abstract:A fundamental understanding of electrochemical reaction pathways is critical to improving the performance of Li–S batteries, but few techniques can be used to directly identify and quantify the reaction species during disharge/charge cycling processes in real time. Here, an in situ ⁷Li NMR technique employing a specially designed cylindrical microbattery was used to probe the transient electrochemical and chemical reactions occurring during the cycling of a Li–S system. In situ NMR provides real time, semiquantitative information related to the temporal evolution of lithium polysulfide allotropes during both discharge/charge processes. This technique uniquely reveals that the polysulfide redox reactions involve charged free radicals as intermediate species that are difficult to detect in ex situ NMR studies. Additionally, it also uncovers vital information about the ⁷Li chemical environments during the electrochemical and parasitic reactions on the Li metal anode. These new molecular-level insights about transient species and the associated anode failure mechanism are crucial to delineating effective strategies to accelerate the development of Li–S battery technologies.

Dongping Lu, Jianming Zheng, Qiuyan Li, Xi Xie, Seth Ferrara, Zimin Nie, Layla B. Mehdi, Nigel D. Browning, Ji-Guang Zhang, Gordon L. Graff, Jun Liu, Jie Xiao."High Energy Density Lithium–Sulfur Batteries: Challenges of Thick Sulfur Cathodes."Advanced Energy Materials 5 (16)(March 2015).
Abstract: High energy and cost-effective lithium sulfur (Li–S) battery technology has been vigorously revisited in recent years due to the urgent need of advanced energy storage technologies for green transportation and large-scale energy storage applications. However, the market penetration of Li–S batteries has been plagued due to the gap in scientific knowledge between the fundamental research and the real application need. Here, a facile and effective approach to integrate commercial carbon nanoparticles into microsized secondary ones for application in high loading sulfur electrodes is proposed The slurry with the integrated particles is easily cast into electrode laminates with practically usable mass loadings. Uniform and crack-free coating with high loading of 2–8 mg cm⁻² sulfur are successfully achieved. Based on the obtained thick electrodes, the dependence of areal specific capacity on mass loading, factors influencing electrode performance, and measures used to address the existing issues are studied and discussed.

Shao Y ,Rajput NN ,Hu J Z,Hu M Y,Liu T L.,Wei Z ,Gu M ,Deng X ,Xu S ,Han KS ,Wang J ,Nie Z ,Li G ,Zavadil K ,Xiao J ,Wang C M,Henderson W A,Zhang J ,Wang Y ,Mueller K T,Persson K A,Liu J. "Nanocomposite polymer electrolyte for rechargeable magnesium batteries." Nano Energy 12: 750-579 (March 2015).
Abstract:Nanocomposite polymer electrolytes present new opportunities for rechargeable magnesium batteries. However, few polymer electrolytes have demonstrated reversible Mg deposition/dissolution and those that have still contain volatile liquids such as tetrahydrofuran (THF). In this work, we report a nanocomposite polymer electrolyte based on poly(ethylene oxide) (PEO), Mg(BH₄)₂ and MgO nanoparticles for rechargeable Mg batteries. Cells with this electrolyte have a high coulombic efficiency of 98% for Mg plating/stripping and a high cycling stability. Through combined experiment-modeling investigations, a correlation between improved solvation of the salt and solvent chain length, chelation and oxygen denticity is established. Following the same trend, the nanocomposite polymer electrolyte is inferred to enhance the dissociation of the salt Mg(BH₄)₂ and thus improve the electrochemical performance. The insights and design metrics thus obtained may be used in nanocomposite electrolytes for other multivalent systems.

Vijayakumar M, N Govind, B Li, X Wei, Z Nie, S Thevuthasan, VL Sprenkle, W Wang. "Aqua-vanadyl ion interaction with Nafion^® membranes."Frontiers in Energy Research 3, article number 10 (March 2015).
Abstract:Lack of comprehensive understanding about the interactions between Nafion membrane and battery electrolytes prevents the straightforward tailoring of optimal materials for redox flow battery applications. In this work, we analyzed the interaction between aqua-vanadyl cation and sulfonic sites within the pores of Nafion membranes using combined theoretical and experimental X-ray spectroscopic methods. Molecular level interactions, namely, solvent share and contact pair mechanisms are discussed based on vanadium and sulfur K-edge spectroscopic analysis.

Mehdi, BL, J Qian, E Nasybulin, C Park, DA Welch, R Faller, H Mehta, WA Henderson, W Xu, CM Wang, JE Evans, J Liu, J Zhang, KT Mueller, ND Browning. "Observation and Quantification of Nanoscale Processes in Lithium Batteries by Operando Electrochemical (S)TEM." <Nano Letters 15 (3): 2168-2173 (Feb. 2015).
Abstract:An operando electrochemical stage for the transmission electron microscope has been configured to form a “Li battery” that is used to quantify the electrochemical processes that occur at the anode during charge/discharge cycling. Of particular importance for these observations is the identification of an image contrast reversal that originates from solid Li being less dense than the surrounding liquid electrolyte and electrode surface. This contrast allows Li to be identified from Li-containing compounds that make up the solid-electrolyte interphase (SEI) layer. By correlating images showing the sequence of Li electrodeposition and the evolution of the SEI layer with simultaneously acquired and calibrated cyclic voltammograms, electrodeposition, and electrolyte breakdown processes can be quantified directly on the nanoscale. This approach opens up intriguing new possibilities to rapidly visualize and test the electrochemical performance of a wide range of electrode/electrolyte combinations for next generation battery systems.

Qian J, WA Henderson, W Xu, P Bhattacharya, M Engelhard, O Borodin, J Zhang. "High rate and stable cycling of lithium metal anode."Nature Communications 6: Article number 6362 (Feb. 2015).
Abstract:Lithium metal is an ideal battery anode. However, dendrite growth and limited Coulombic efficiency during cycling have prevented its practical application in rechargeable batteries. Herein, we report that the use of highly concentrated electrolytes composed of ether solvents and the lithium bis(fluorosulfonyl)imide salt enables the high-rate cycling of a lithium metal anode at high Coulombic efficiency (up to 99.1%) without dendrite growth. With 4 M lithium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane as the electrolyte, a lithium|lithium cell can be cycled at 10 mA cm⁻² for more than 6,000 cycles, and a copper|lithium cell can be cycled at 4 mA cm⁻² for more than 1,000 cycles with an average Coulombic efficiency of 98.4%. These excellent performances can be attributed to the increased solvent coordination and increased availability of lithium ion concentration in the electrolyte. Further development of this electrolyte may enable practical applications for lithium metal anode in rechargeable batteries.

Li B, Z Nie, M Vijayakumar, G Li, J Liu, VL Sprenkle, W Wang. "Ambipolar zinc-polyiodide electrolyte for a high-energy density aqueous redox flow battery." Nature Communications 6 article number 6303 (Feb. 2015).
Abstract:Redox flow batteries are receiving wide attention for electrochemical energy storage due to their unique architecture and advantages, but progress has so far been limited by their low energy density (~25Whl^-1). Here we report a high-energy density aqueous zinc-polyiodide flow battery. Using the highly soluble iodide/triiodide redox couple, a discharge energy density of 167Whl^-1 is demonstrated with a near-neutral 5.0 M Znl₂ electrolyte. Nuclear magnetic resonance study and density functional theory-based simulation along with flow test data indicate that the addition of an alcohol (ethanol) induces ligand formation between oxygen on the hydroxyl group and the zinc ions, which expands the stable electrolyte temperature window to from -20 to 50°C, while ameliorating the zinc dendrite. With the high-energy density and its benign nature free from strong acids and corrosive components, zinc-polyiodide flow battery is a promising candidate for various energy storage applications.

Jianming zheng, Pinghong Xu, Meng Gu, Jie Xiao, Nigel D. Browning, Pengfei Yan, Chongmin Wang, Ji-Guang Zhang."Structural and Chemical Evolution of Li- and Mn-Rich Layered Cathode Material."Chemistry of Materials 27 (4):1381-1390 (January 2015).
Abstract: Lithium (Li)- and manganese-rich (LMR) layered-structure materials are very promising cathodes for high energy density lithium-ion batteries. However, the voltage fading mechanism in these materials as well as its relationships to fundamental structural changes is far from being sufficiently understood. Here we report the detailed phase transformation pathway in the LMR cathode (Li[Li_0.2Ni_0.2Mn_0.6]O₂) during cycling for samples prepared by the hydrothermal assisted (HA) method. It is found that the transformation pathway of the LMR cathode is closely correlated to its initial structure and preparation conditions. The results reveal that the LMR cathode prepared by the HA approach experiences a phase transformation from the layered structure (initial C2/m phase transforms to R3‾m phase after activation) to a LT-LiCoO₂ type defect spinel-like structure (with the Fd3‾m space group) and then to a disordered rock-salt structure (with the Fm3‾m space group). The voltage fade can be well correlated with Li ion insertion into octahedral sites, rather than tetrahedral sites, in both defect spinel-like and disordered rock-salt structures. The reversible Li insertion/removal into/from the disordered rock-salt structure is ascribed to the Li excess environment that permits Li percolation in the disordered rock-salt structure despite the increased kinetic barrier. Meanwhile, because of the presence of a large quantity of oxygen vacancies, a significant decrease in the Mn valence is detected in the cycled particle, which is below that anticipated for a potentially damaging Jahn-Teller distortion (+3.5). Clarification of the phase transformation pathway, cation redistribution, oxygen vacancy and Mn valence change provides unique understanding of the voltage fade and capacity degradation mechanisms in the LMR cathode. The results also inspire us to further enhance the reversibility of the LMR cathode via improved surface structural stability.

Qiang Wang, Jianming Zhang, Eric Walter, Huilin Pan, Dongping Lu, Pengjian Zuo, Honghao Chen, Z. Daniel Deng, Bor Yann Liaw, Xiqian Yu, Xiaoqing Yang, Ji-Guang Zhang, Jun Liu, Jie Xiao."Direct Observation of Sulfur Radicals as Reaction Media in Lithium Sulfur Batteries."Journal of the Electrochemical Society 162 (3): A474-A478 (January 2015).
Abstract: Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge processes follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials and the electrochemical characteristics of the cell, it is revealed that the chemical and electrochemical reactions in Li-S cell are driving each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new perspectives to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.

Wei X ,Cosimbescu L ,Xu W ,Hu J Z,Vijayakumar M ,Feng J ,Hu M Y,Deng X ,Xiao J ,Liu J ,Sprenkle V L,Wang W. "Towards High-Performance Nonaqueous Redox Flow Electrolyte Via Ionic Modification of Active Species." Advanced Energy Materials 5 (1): 1400678 (Jan. 2015).
Abstract:Nonaqueous redox flow batteries are emerging flow-based energy storage technologies that have the potential for higher energy densities than their aqueous counterparts because of their wider voltage windows. However, their performance has lagged far behind their inherent capability due to one major limitation of low solubility of the redox species. Here, a molecular structure engineering strategy towards high performance nonaqueous electrolyte is reported with significantly increased solubility. Its performance outweighs that of the state-of-the-art nonaqueous redox flow batteries. In particular, an ionic-derivatized ferrocene compound is designed and synthesized that has more than 20 times increased solubility in the supporting electrolyte. The solvation chemistry of the modified ferrocene compound. Electrochemical cycling testing in a hybrid lithium–organic redox flow battery using the as-synthesized ionic-derivatized ferrocene as the catholyte active material demonstrates that the incorporation of the ionic-charged pendant significantly improves the system energy density. When coupled with a lithium-graphite hybrid anode, the hybrid flow battery exhibits a cell voltage of 3.49 V, energy density about 50 Wh L⁻¹, and energy efficiency over 75%. These results reveal a generic design route towards high performance nonaqueous electrolyte by rational functionalization of the organic redox species with selective ligand.

Liu, T, JT Cox, D Hu, X Deng, J Hu, MY Hu, J Xiao, Y Shao, K Tang, J Liu. "A fundamental study on the [(μ-Cl)3Mg2(THF)6]+ dimer electrolytes for rechargeable Mg batteries." Chemical Communications 51: 2312-2315 (Jan. 2015).
Abstract:The long sought solvated [MgCl]+ species in the Mg-dimer electrolytes was characterized by soft mass spectrometry. The presented study provides an insightful understanding on the electrolyte chemistry of rechargeable Mg batteries.

Parent LR, Y Cheng, PV Sushko, Y Shao, J Liu, CM Wang, ND Browning. "Realizing the Full Potential of Insertion Anodes for Mg-Ion Batteries Through the Nanostructuring of Sn." Nano Letters 15 (2): 1177-1182 (Dec. 2014).
Abstract:Magnesium is of great interest as a replacement for lithium in next-generation ion-transfer batteries but Mg-metal anodes currently face critical challenges related to the formation of passivating layers during Mg-plating/stripping and anode–electrolyte–cathode incompatibilities.1−6 Alternative anode materials have the potential to greatly extend the spectrum of suitable electrolyte chemistries2,7 but must be systematically tailored for effective Mg²⁺ storage. Using analytical (scanning) transmission electron microscopy ((S)TEM) and ab initio modeling, we have investigated Mg²⁺ insertion and extraction mechanisms and transformation processes in β-SnSb nanoparticles (NPs), a promising Mg-alloying anode material. During the first several charge–discharge cycles (conditioning), the β-SnSb particles irreversibly transform into a porous network of pure-Sn and Sb-rich subparticles, as Mg ions replace Sn atoms in the SnSb lattice. After electrochemical conditioning, small Sn particles/grains (<33 ± 20 nm) exhibit highly reversible Mg-storage, while the Sb-rich domains suffer substantial Mg trapping and contribute little to the system performance. This result strongly indicates that pure Sn can act as a high-capacity Mg-insertion anode as theoretically predicted,8 but that its performance is strongly size-dependent, and stable nanoscale Sn morphologies (<40 nm) are needed for superior, reversible Mg-storage and fast system kinetics.

Li G, X Lu, JY Kim, MH Engelhard, JP Lemmon, and VL Sprenkle. "The Role of FeS in Initial Activation and Performance Degradation of Na-NiCl2 Batteries." Journal of Power Sources 272:398-403 (Dec 2014).
Abstract: The role of iron sulfide (FeS) in initial cell activation and degradation in the Na-NiCl2 battery was investigated in this work. The research focused on identifying the effects of the FeS level on the electrochemical performance and morphological changes in the cathode. The x-ray photoelectron spectroscopy study along with battery tests revealed that FeS plays a critical role in initial battery activation by removing passivation layers on Ni particles. It was also found that the optimum level of FeS in the cathode resulted in minimum Ni particle growth and improved battery cycling performance. The results of electrochemical characterization indicated that sulfur species generated in situ during initial charging, such as polysulfide and sulfur, are responsible for removing the passivation layer. Consequently, the cells containing elemental sulfur in the cathode exhibited similar electrochemical behavior during initial charging compared to that of the cells containing FeS.

Wei X, W Xu, M Vijayakumar, L Cosimbescu, TL Liu, VL Sprenkle, and W Wang. "TEMPO-based Catholyte for High Energy Density Nonaqueous Redox Flow Batteries." Advanced Materials 26(45):7649-7653 (Dec 2014).
Abstract:A TEMPO-based non-aqueous electrolyte with the TEMPO concentration as high as 2.0 _M is demonstrated as a high-energy-density catholyte for redox flow battery applications. With a hybrid anode, Li|TEMPO flow cells using this electrolyte deliver an energy efficiency of ca. 70% and an impressively high energy density of 126 W h L^-1.

Zhang Y ,Qian J ,Xu W ,Russell S M,Chen X ,Nasybulin E ,Bhattacharya P ,Engelhard M H,Mei D ,Cao R ,Ding F ,Cresce A V,Xu K ,Zhang J. "Dendrite-Free Lithium Deposition with Self-Aligned Nanorod Structure." Nano Letters 14 (12): 6889-6896 (Nov. 2014).
Abstract:Suppressing lithium (Li) dendrite growth is one of the most critical challenges for the development of Li metal batteries. Here, we report for the first time the growth of dendrite-free lithium films with a self-aligned and highly compacted nanorod structure when the film was deposited in the electrolyte consisting of 1.0 M LiPF₆ in propylene carbonate with 0.05 M CsPF₆ as an additive. Evolution of both the surface and the cross-sectional morphologies of the Li films during repeated Li deposition/stripping processes were systematically investigated. It is found that the formation of the compact Li nanorod structure is preceded by a solid electrolyte interphase (SEI) layer formed on the surface of the substrate. Electrochemical analysis indicates that an initial reduction process occurred at ∼2.05 V vs Li/Li⁺ before Li deposition is responsible for the formation of the initial SEI, while the X-ray photoelectron spectroscopy indicates that the presence of CsPF₆ additive can largely enhance the formation of LiF in this initial SEI. Hence, the smooth Li deposition in Cs⁺- containing electrolyte is the result of a synergistic effect of Cs⁺ additive and preformed SEI layer. A fundamental understanding on the composition, internal structure, and evolution of Li metal films may lead to new approaches to stabilize the long-term cycling stability of Li metal and other metal anodes for energy storage applications.

Adams B D,Black R ,Radtke C ,Williams Z ,Mehdi B L,Browning N D,Nazar L F. "The Importance of Nanometric Passivating Films on Cathodes for Li–Air Batteries" ACS Nano 8 (12): 12483-12493 (Nov. 2014).
Abstract: Recently, there has been a transition from fully carbonaceous positive electrodes for the aprotic lithium oxygen battery to alternative materials and the use of redox mediator additives, in an attempt to lower the large electrochemical overpotentials associated with the charge reaction. However, the stabilizing or catalytic effect of these materials can become complicated due to the presence of major side-reactions observed during dis(charge). Here, we isolate the charge reaction from the discharge by utilizing electrodes prefilled with commercial lithium peroxide with a crystallite size of about 200–800 nm. Using a combination of S/TEM, online mass spectrometry, XPS, and electrochemical methods to probe the nature of surface films on carbon and conductive Ti-based nanoparticles, we show that oxygen evolution from lithium peroxide is strongly dependent on their surface properties. Insulating TiO2 surface layers on TiC and TiN - even as thin as 3 nm–can completely inhibit the charge reaction under these conditions. On the other hand, TiC, which lacks this oxide film, readily facilitates oxidation of the bulk Li2O2 crystallites, at a much lower overpotential relative to carbon. Since oxidation of lithium oxygen battery cathodes is inevitable in these systems, precise control of the surface chemistry at the nanoscale becomes of upmost importance.

Jianming Zhang, Meng Gu, Jie Xiao, Bryant J. Polzin, Pengfei Yan, Xilin Chen, Chongmin Wang, Ji-Guang Zhang."Functioning Mechanism of AlF3 Coating on the Li- and Mn-Rich Cathode Materials."Chemistry of Materials 26 (22): 6320-6327 (October 2014).
Abstract: We report systematic studies of the microstructural changes of uncoated and AlF₃-coated Li-rich Mn-rich (LMR) cathode materials (Li_1.2Ni_0.15Co_0.10Mn_0.55O₂) before and after cycling using a combination of aberration-corrected scanning/transmission electron microscopy (S/TEM) and electron energy loss spectroscopy (EELS). TEM coupled with EELS provides detailed information about the crystallographic and electronic structure changes that occur after cycling, thus revealing the fundamental improvement mechanism of surface coating. The results demonstrate that the surface coating reduces oxidation of the electrolyte at high voltage, suppressing the accumulation of a thick solid electrolyte interface (SEI) layer on electrode particle surface. Surface coating significantly enhances the stability of the surface structure and protects the electrode from severe etching/corrosion by the acidic species in the electrolyte, reducing the formation of etched surfaces and corrosion pits. Moreover, surface coating alleviates the undesirable voltage fade by mitigating layered to spinel-like phase transformation in the bulk region of the material. These fundamental findings may also be widely applied to explain the functioning mechanisms of other surface coatings used in a broad range of electrode materials.

Han, KS, NN Rajput, X wei, W Wang, JZ Hu, KA Persson, KT Mueller. "Diffusional motion of redox centers in carbonate electrolytes" Journal of Physical Chemistry 141(10): 104509 (Sept. 2014).
Abstract: Ferrocene (Fc) and N-(ferrocenylmethyl)-N,N-dimethyl-N-ethylammonium bistrifluoromethyl-sulfonimide (Fc1N112-TFSI) were dissolved in carbonate solvents and self-diffusion coefficients (D) of solutes and solvents were measured by (1)H and (19)F pulsed field gradient nuclear magnetic resonance (NMR) spectroscopy. The organic solvents were propylene carbonate (PC), ethyl methyl carbonate (EMC), and a ternary mixture that also includes ethylene carbonate (EC). Results from NMR studies over the temperature range of 0-50 °C and for various concentrations (0.25-1.7 M) of Fc1N112-TFSI are compared to values of D simulated with classical molecular dynamics (MD). The measured self-diffusion coefficients gradually decreased as the Fc1N112-TFSI concentration increased in all solvents. Since TFSI(-) has fluoromethyl groups (CF3), D(TFSI) could be measured separately and the values found are larger than those for D(Fc1N112) in all samples measured. The EC, PC, and EMC have the same D in the neat solvent mixture and when Fc is dissolved in EC/PC/EMC at a concentration of 0.2 M, probably due to the interactions between common carbonyl structures within EC, PC, and EMC. A difference in D (D(PC) < D(EC) < D(EMC)), and both a higher E(a) for translational motion and higher effective viscosity for PC in the mixture containing Fc1N112-TFSI reflect the interaction between PC and Fc1N112(+), which is a relatively stronger interaction than that between Fc1N112(+) and other solvent species. In the EC/PC/EMC solution that is saturated with Fc1N112-TFSI, we find that D(PC) = D(EC) = D(EMC) and Fc1N112(+) and all components of the EC/PC/EMC solution have the same E(a) for translational motion, while the ratio D(EC/PC/EMC)/D(Fc1N112) is approximately 3. These results reflect the lack of available free volume for independent diffusion in the saturated solution. The Fc1N112(+) transference numbers lie around 0.4 and increase slightly as the temperature is increased in the PC and EMC solvents. The trends observed for D from simulations are in good agreement with experimental results and provide molecular level understanding of the solvation structure of Fc1N112-TFSI dissolved in EC/PC/EMC.

Vijayakumar, M., Nie, Z., Walter, E., Hu, J., Liu, J., Sprenkle, V. and Wang, W. "Understanding Aqueous Electrolyte Stability through Combined Computational and Magnetic Resonance Spectroscopy: A Case Study on Vanadium Redox Flow Battery Electrolytes." ChemPlusChem doi: 10.1002/cplu.201402139 (Sept 2014).
Abstract: Commercial sodium-sulphur or sodium-metal halide batteries typically need an operating temperature of 300-350°C, and one of the reasons is poor wettability of liquid sodium on the surface of beta alumina. Here we report an alloying strategy that can markedly improve the wetting, which allows the batteries to be operated at much lower temperatures. Our combined experimental and computational studies suggest that addition of caesium to sodium can markedly enhance the wettability. Single cells with Na-Cs alloy anodes exhibit great improvement in cycling life over those with pure sodium anodes at 175 and 150°C. The cells show good performance even at as low as 95°C. These results demonstrate that sodium-beta alumina batteries can be operated at much lower temperatures with successfully solving the wetting issue. This work also suggests a strategy to use liquid metals in advanced batteries that can avoid the intrinsic safety issues associated with dendrite formation.

Cheng Y, LR Parent, Y Shao, CM Wang, VL Sprenkle, G Li, and J Liu. "Facile Synthesis of Chevrel Phase Nanocubes and their Applications for Multivalent Energy Storage." Chemistry of Materials 26(17):4904-4907. doi:10.1021/cm502306c (Aug 2014).
Abstract: The Chevrel phases (CPs, MxMo6T8, M=metal, T=S or Se) are capable of rapid and reversible intercalation of multivalent ions and are the most practical cathode materials for rechargeable magnesium batteries. For the first time, we report a facile method for synthesizing Mo6S8 nanoparticles and demonstrate that these nanoparticles have significantly better Mg2+ intercalation kinetics compared with microparticles. The results described in this work could inspire the synthesis of nanoscale CPs, which could substantially impact their application.

Wei X, L Cosimbescu, W Xu, JZ Hu, M Vijayakumar, J Feng, MY Hu, X Deng, J Xiao, J Liu, VL Sprenkle, and W Wang. "Towards High Performance Nonaqueous Redox Flow Electrolyte Via Ionic Modification of Active Species." Advanced Energy Materials (1400678), doi:DOI: 10.1002/aenm.201400678 (Aug 2014).
Abstract: Nonaqueous redox flow batteries are emerging flow-based energy storage technologies that have the potential for higher energy densities than their aqueous counterparts because of their wider voltage windows. However, their performance has lagged far behind their inherent capability due to one major limitation of low solubility of the redox species. Here, a molecular structure engineering strategy towards high performance nonaqueous electrolyte is reported with significantly increased solubility. Its performance outweighs that of the state-of-the-art nonaqueous redox flow batteries. In particular, an ionic-derivatized ferrocene compound is designed and synthesized that has more than 20 times increased solubility in the supporting electrolyte. The solvation chemistry of the modified ferrocene compound. Electrochemical cycling testing in a hybrid lithium-organic redox flow battery using the as-synthesized ionic-derivatized ferrocene as the catholyte active material demonstrates that the incorporation of the ionic-charged pendant significantly improves the system energy density. When coupled with a lithium-graphite hybrid anode, the hybrid flow battery exhibits a cell voltage of 3.49 V, energy density about 50 Wh L-1, and energy efficiency over 75%. These results reveal a generic design route towards high performance nonaqueous electrolyte by rational functionalization of the organic redox species with selective ligand.

X. Lu, G. Li, J.Y. Kim, D. Mei, J.P. Lemmon, and V.L. Sprenkle, "Liquid-metal electrode to enable ultra-low temperature sodium–beta alumina batteries for renewable energy storage." Nat. Commun. 5:4578 (Aug 2014).
Abstract: Commercial sodium–sulphur or sodium-metal halide batteries typically need an operating temperature of 300–350°C, and one of the reasons is poor wettability of liquid sodium on the surface of beta alumina. Here we report an alloying strategy that can markedly improve the wetting, which allows the batteries to be operated at much lower temperatures. Our combined experimental and computational studies suggest that addition of caesium to sodium can markedly enhance the wettability. Single cells with Na-Cs alloy anodes exhibit great improvement in cycling life over those with pure sodium anodes at 175 and 15°C. The cells show good performance even at as low as 95°C. These results demonstrate that sodium–beta alumina batteries can be operated at much lower temperatures with successfully solving the wetting issue. This work also suggests a strategy to use liquid metals in advanced batteries that can avoid the intrinsic safety issues associated with dendrite formation.

Eduard Nasybulin, Wu Xu, B. Layla Mehdi, Edwin Thomsen, Mark H. Engelhard, Robert C. Masse, Priyanka Bhattacharya, Meng Gu, Wendy Bennett, Zimin Nie, Chongmin Wang, Nigel D. Browning, Ji-Guang Zhang. "Formation of Interfacial Layer and Long-Term Cyclability of Li–O2 Batteries."ACS Applied Materials & Interfaces 6 (16):14141-14151 (July 2014).
Abstract: The long-term operation of Li–O₂ batteries under full discharge/charge conditions is investigated in a glyme-based electrolyte. The formation of stable interfacial layer on the electrode surface during the initial cycling stabilizes reaction products at subsequent cycling stages as demonstrated by quantitative analyses of the discharge products and the gases released during charging. There is a quick switch from the predominant formation of Li₂O₂ to the predominant formation of side products during the first few cycles. However, after the formation of the stable interfacial layer, the yield of Li₂O₂ in the reaction products is stabilized at about 33–40%. Extended cycling under full discharge/charge conditions is achievable upon selection of appropriate electrode materials (carbon source and catalyst) and cycling protocol. Further investigation on the interfacial layer, which in situ forms on air electrode, may increase the long-term yield of Li₂O₂ during the cycling and enable highly reversible Li–O₂ batteries required for practical applications.

Nasybulin E N,Xu W ,Mehdi B L,Thomsen E C,Engelhard M H,Masse R C,Bhattacharya P ,Gu M ,Bennett W D,Nie Z ,Wang C M,Browning N D,Zhang J. "Formation of Interfacial Layer and Long-Term Cyclability of Li-O₂ Batteries." ACS Applied Materials & Interfaces 6 (16): 14141-14151 (July 2014).
Abstract:The long-term operation of Li–O₂ batteries under full discharge/charge conditions is investigated in a glyme-based electrolyte. The formation of stable interfacial layer on the electrode surface during the initial cycling stabilizes reaction products at subsequent cycling stages as demonstrated by quantitative analyses of the discharge products and the gases released during charging. There is a quick switch from the predominant formation of Li₂O₂ to the predominant formation of side products during the first few cycles. However, after the formation of the stable interfacial layer, the yield of Li₂O₂ in the reaction products is stabilized at about 33–40%. Extended cycling under full discharge/charge conditions is achievable upon selection of appropriate electrode materials (carbon source and catalyst) and cycling protocol. Further investigation on the interfacial layer, which in situ forms on air electrode, may increase the long-term yield of Li₂O₂ during the cycling and enable highly reversible Li–O₂ batteries required for practical applications.

Du Y ,Gu M ,Varga T ,Wang C M,Bowden M E,Chambers S A .  "Strain Accommodation by Facile WO6 Octahedral Distortion and Tilting during WO3 Heteroepitaxy on SrTiO3(001)" Applied Materials & Interfaces 6 (16):14253-14258 (July 2014)
Abstract: In this work, we demonstrate that WO6 octahedra in tungsten trioxide (WO3) undergo an unusually large degree of distortion and tilting to accommodate interfacial strain. This motion strongly impacts nucleation, structure, and defect formation during the epitaxial growth of WO3 on SrTiO3(001). A metastable tetragonal phase can be stabilized by heteroepitaxy and a thickness-dependent phase transition (tetragonal to monoclinic) is observed. In contrast to misfit dislocation formation, facile WO6 octahedral deformation gives rise to three types of planar defects. The thicknesses of affected regions can range from several to tens of nanometers with graded lattice parameters, allowing the strain from interfacial lattice mismatch to be relieved gradually. These atomically resolved, unique interfacial defects may significantly alter the electronic, electrochromic, and mechanical properties of WO3 epitaxial films.

Cao R ,Walter E D,Xu W ,Nasybulin E N,Bhattacharya P ,Bowden M E,Engelhard M H,Zhang J. "The Mechanisms of Oxygen Reduction and Evolution Reactions in Nonaqueous Lithium–Oxygen Batteries." ChemSusChem 7 (9):2436-2440 (July 2014).
Abstract:A fundamental understanding of the mechanisms of both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in nonaqueous lithium–oxygen (Li–O₂) batteries is essential for the further development of these batteries. In this work, we systematically investigate the mechanisms of the ORR/OER reactions in nonaqueous Li–O₂ batteries by using electron paramagnetic resonance (EPR) spectroscopy, using 5,5-dimethyl-pyrroline N-oxide as a spin trap. The study provides direct verification of the formation of the superoxide radical anion (O₂^.−) as an intermediate in the ORR during the discharge process, while no O₂^.− was detected in the OER during the charge process. These findings provide insight into, and an understanding of, the fundamental reaction mechanisms involving oxygen and guide the further development of this field.

Xiaolin Li, Meng Gu, Shenyang Hu, Rhiannon Kennard, Pengfei Yan, Xilin Chen, Chongmin Wang, Michael J. Sailor, Ji-Guang Zhang, Jun Liu. "Mesoporous silicon sponge as an anti-pulverization structure for high-performance lithium-ion battery anodes."Nature Communications 5: Article number 4105 (July 2014).
Abstract: Nanostructured silicon is a promising anode material for high-performance lithium-ion batteries, yet scalable synthesis of such materials, and retaining good cycling stability in high loading electrode remain significant challenges. Here we combine in-situ transmission electron microscopy and continuum media mechanical calculations to demonstrate that large (>20 μm) mesoporous silicon sponge prepared by the anodization method can limit the particle volume expansion at full lithiation to ~30% and prevent pulverization in bulk silicon particles. The mesoporous silicon sponge can deliver a capacity of up to ~750 mAh g^-1 based on the total electrode weight with >80% capacity retention over 1,000 cycles. The first cycle irreversible capacity loss of pre-lithiated electrode is >5%. Bulk electrodes with an area-specific-capacity of ~1.5 mAh cm^-2 and ~92% capacity retention over 300 cycles are also demonstrated. The insight obtained from this work also provides guidance for the design of other materials that may experience large volume variation during operations.

Anqiang Pan, Yaping Wang, Wu Xu, Zhiwei Nie, Shuquan Liang, Zimin Nie, Chongmin Wang, Guozhong Cao, Ji-Guang Zhang. "High-performance anode based on porous Co₃O₄ nanodiscs."Journal of Power Sources 255: 125-129 (June 2014).
Abstract: In this article, two-dimensional, Co₃O₄ hexagonal nanodiscs are prepared using a hydrothermal method without surfactants. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been employed to characterize the structural properties. As revealed by the SEM and TEM experiments, the thickness of our as-fabricated Co₃O₄ hexagonal nanodiscs is about 20 nm, and the pore diameters range from several nanometers to 30 nm. As an anode for lithium-ion batteries, porous Co₃O₄ nanodiscs exhibit an average discharge voltage of ∼1 V (vs. Li/Li⁺) and a high specific charge capacity of 1161 mAh g⁻¹ after 100 cycles. They also demonstrate excellent rate performance and high Columbic efficiency at various rates. These results indicate that porous Co₃O₄ nanodiscs are good candidates as anode materials for lithium-ion batteries.

BR Chalamala, T Soundappan, GR Fisher, MA Anstey, VV Viswanathan, ML Perry. "Redox Flow Batteries: An Engineering Perspective." Proceedings of the IEEE 102 (6): 976 - 999 (June 2014).
Abstract:Redox flow batteries are well suited to provide modular and scalable energy storage systems for a wide range of energy storage applications. In this paper, we review the development of redox-flow-battery technology including recent advances in new redox active materials, cell designs, and systems, all from the perspective of engineers interested in applying this technology. We discuss cost, performance, and reliability metrics that are critical for deployment of large flow-battery systems. The technology, while relatively young, has the potential for significant improvement through reduced materials costs, improved energy efficiency, and significant reduction in the overall system costs.

Yingwen Cheng, Yuyan Shao, Ji-Guang Zhang, Vincent L. Sprenkle, Jun Liu and Guosheng Li, "High performance batteries based on hybrid magnesium and lithium chemistry" Chem. Commun., 2014, 50, 9644-9646 (June 2014).
Abstract: This work studied hybrid batteries assembled with a Mg metal anode, a Li+ ion intercalation cathode and a dual-salt electrolyte containing Mg2+ and Li+ ions. We show that such hybrid batteries were able to combine the advantages of Li and Mg electrochemistry. They delivered outstanding rate performance (83% capacity retention at 15 C) with superior safety and stability (B5% fade for 3000 cycles).

J.T. Vaughey, Gao Liu, Ji-Guang Zhang."Stabilizing the surface of lithium metal."MRS Bulletin 39 (5): 429-435 (May 2014).
Abstract: The success of high capacity energy storage systems based on lithium (Li) batteries relies on the realization of the promise of Li-metal anodes. Li metal has many advantageous properties, including an extremely high theoretical specific capacity (3860 mAh g^–1), the lowest electrochemical potential (–3.040 V versus standard hydrogen electrode), and low density (0.59 g cm^–3), which, all together, make it a very desirable electrode for energy storage devices. However, while primary Li batteries are used for numerous commercial applications, rechargeable Li-metal batteries that utilize Li-metal anodes have not been as successful. This article discusses the properties of Li metal in the absence of surface stabilization, as well as three different approaches currently under investigation for stabilizing the surface of Li metal to control its reactivity within the electrochemical environment of a Li-based battery.

Mehdi B L,Gu M ,Parent L R,Xu W ,Nasybulin E N,Chen X ,Unocic R R,Xu P ,Welch D A,Abellan P ,Zhang J ,Liu J ,Wang C M,Arslan I ,Evans J E,Browning N D. "In-situ electrochemical transmission electron microscopy for battery research." Microscopy & Microanalysis 20 (2): 484-492 (April 2014).
Abstract:The recent development of in-situ liquid stages for (scanning) transmission electron microscopes now makes it possible for us to study the details of electrochemical processes under operando conditions. As electrochemical processes are complex, care must be taken to calibrate the system before any in-situ/operando observations. In addition, as the electron beam can cause effects that look similar to electrochemical processes at the electrolyte/electrode interface, an understanding of the role of the electron beam in modifying the operando observations must also be understood. In this paper we describe the design, assembly, and operation of an in-situ electrochemical cell, paying particular attention to the method for controlling and quantifying the experimental parameters. The use of this system is then demonstrated for the lithiation/delithiation of silicon nanowires.

Jianming Zheng, Meng Gu, Arda Genc, Jie Xiao, Pinghong Xu, Xilin Chen, Zihua Zhu, Wenbo Zhao, Lee Pullan, Chongmin Wang, Ji-Guang Zhang. "Mitigating Voltage Fade in Cathode Materials by Improving the Atomic Level Uniformity of Elemental Distribution."Nano Letters 14 (5): 2628-2635 (April 2014).
Abstract: Lithium- and manganese-rich (LMR) layered-structure materials are very promising cathodes for high energy density lithium-ion batteries. However, their voltage fading mechanism and its relationships with fundamental structural changes are far from being well understood. Here we report for the first time the mitigation of voltage and energy fade of LMR cathodes by improving the atomic level spatial uniformity of the chemical species. The results reveal that LMR cathodes (Li[Li_0.2Ni_0.2M_0.6]O₂) prepared by coprecipitation and sol–gel methods, which are dominated by a LiMO₂ type R3‾m structure, show significant nonuniform Ni distribution at particle surfaces. In contrast, the LMR cathode prepared by a hydrothermal assisted method is dominated by a Li₂MO₃ type C2/m structure with minimal Ni-rich surfaces. The samples with uniform atomic level spatial distribution demonstrate much better capacity retention and much smaller voltage fade as compared to those with significant nonuniform Ni distribution. The fundamental findings on the direct correlation between the atomic level spatial distribution of the chemical species and the functional stability of the materials may also guide the design of other energy storage materials with enhanced stabilities.

Vijayakumar M ,Govind N ,Walter E D,Burton S D,Shukla A K,Devaraj A ,Xiao J ,Liu J ,Wang C M,Karim A M,Thevuthasan S. "Molecular structure and stability of dissolved lithium polysulfide species." Phys. Chem. Chem. Phys. 16: 10923-10932 (March 2014).
Abstract:The ability to predict the solubility and stability of lithium polysulfide is vital in realizing longer lasting lithium–sulfur batteries. Herein we report combined experimental and computational analyses to understand the dissolution mechanism of lithium polysulfide species in an aprotic solvent medium. Multinuclear NMR, variable temperature ESR and sulfur K-edge XAS analyses reveal that the lithium exchange between polysulfide species and solvent molecules constitutes the first step in the dissolution process. Lithium exchange leads to de-lithiated polysulfide ions (S_n²⁻) which subsequently form highly reactive free radicals through dissociation reaction (S_n²⁻ → 2S_n2^˙−). The energy required for the dissociation and possible dimer formation reactions of the polysulfide species is analyzed using density functional theory (DFT) based calculations. Based on these findings, we discuss approaches to optimize the electrolyte in order to control the polysulfide solubility.

Jianming Zheng, Jie Xiao, Meng Gu, Pengjian Zuo, Chongmin Wang, Ji-Guang Zhang. "Interface modifications by anion receptors for high energy lithium ion batteries." Journal of Power Sources 250: 313-318 (March 2014).
Abstract: Li-rich, Mn-rich (LMR) layered composite has attracted extensive interests because of its highest energy density among all cathode candidates for lithium ion batteries (LIB). However, capacity degradation and voltage fading remain the major challenges for LMR cathodes prior to their practical applications. Here, we demonstrate that anion receptor, tris(pentafluorophenyl)borane ((C₆F₅)₃B, TPFPB), substantially enhances the stability of electrode/electrolyte interface and thus improves the cycling stability of LMR cathode Li[Li_0.2Ni_0.2Mn_0.6]O₂. In the presence of 0.2 M TPFPB, Li[Li_0.2Ni_0.2Mn_0.6]O₂ shows an improved capacity retention of 76.8% after 500 cycles. It is proposed that TPFPB effectively confines the highly active oxygen species released from structural lattice through its strong coordination ability and high oxygen solubility. The electrolyte decomposition caused by the oxygen species attack is therefore largely mitigated, forming reduced amount of byproducts on the cathode surface. Additionally, other salts such as insulating LiF derived from electrolyte decomposition are also soluble in the presence of TPFPB. The collective effects of TPFPB mitigate the accumulation of parasitic reaction products and stabilize the interfacial resistances between cathode and electrolyte during extended cycling, thus significantly improving the cycling performance of Li[Li_0.2Ni_0.2Mn_0.6]O₂.

Abellan Baeza P ,Mehdi B L,Parent L R,Gu M ,Park C ,Xu W ,Zhang Y ,Arslan I ,Zhang J ,Wang C M,Evans J E,Browning N D. "Probing the Degradation Mechanisms in Electrolyte Solutions for Li-Ion Batteries by in Situ Transmission Electron Microscopy" Nano Letters 14 (3): 1293-1299 (Feb. 2014).
Abstract:Development of novel electrolytes with increased electrochemical stability is critical for the next generation battery technologies. In situ electrochemical fluid cells provide the ability to rapidly and directly characterize electrode/electrolyte interfacial reactions under conditions directly relevant to the operation of practical batteries. In this paper, we have studied the breakdown of a range of inorganic/salt complexes relevant to state-of-the-art Li-ion battery systems by in situ (scanning) transmission electron microscopy ((S)TEM). In these experiments, the electron beam itself caused the localized electrochemical reaction that allowed us to observe electrolyte breakdown in real-time. The results of the in situ (S)TEM experiments matches with previous stability tests performed during battery operation and the breakdown products and mechanisms are also consistent with known mechanisms. This analysis indicates that in situ liquid stage (S)TEM observations could be used to directly test new electrolyte designs and identify a smaller library of candidate solutions deserving of more detailed characterization. A systematic study of electrolyte degradation is also a necessary first step for any future controlled in operando liquid (S)TEM experiments intent on visualizing working batteries at the nanoscale.

Ran Yi, Jinkui Feng, Dongping Lu, Mikhail Gordin, Shuru Chen, Daiwon Choi, Donghai Wang, "GeO_x/Reduced Graphene Oxide Composite as an Anode for Li-ion Batteries: Enhanced Capacity via Reversible Utilization of Li₂O along with Improved Rate Performance" Advanced Functional Materials, 24, p.1059-1066 (Feb 2014).
Abstract: A self-assembled GeO_x/reduced graphene oxide (GeO_x/RGO) composite, where GeO_x nanoparticles are grown directly on reduced graphene oxide sheets, is synthesized via a facile one-step reduction approach and studied by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, electron energy loss spectroscopy elemental mapping, and other techniques. Electrochemical evaluation indicates that incorporation of reduced graphene oxide enhances both the rate capability and reversible capacity of GeO_x, with the latter being due to the RGO enabling reversible utilization of Li₂O. The composite delivers a high reversible capacity of 1600 mAh g^-1 at a current density of 100 mA g^-1, and still maintains a capacity of 410 mAh g^-1 at a high current density of 20 A g^-1. Owing to the flexible reduced graphene oxide sheets enwrapping the GeO_x particles, the cycling stability of the composite is also improved significantly. To further demonstrate its feasibility in practical applications, the synthesized GeO_x/RGO composite anode is successfully paired with a high voltage LiN_i0.5Mn_1.5O₄ cathode to form a full cell, which shows good cycling and rate performance.

Viswanathan VV, AJ Crawford, DE Stephenson, S Kim, W Wang, B Li, GW Coffey, EC Thomsen, GL Graff, PJ Balducci, MCW Kintner-Meyer, and VL Sprenkle. 2014. "Cost and Performance Model for Redox Flow Batteries." Journal of Power Sources, 247:1040-1051. doi:10.1016/j.jpowsour.2012.12.023 (Feb 2014).
Abstract: A cost model is developed for all vanadium and iron-vanadium redox flow batteries. Electrochemical performance modeling is done to estimate stack performance at various power densities as a function of state of charge and operating conditions. This is supplemented with a shunt current model and a pumping loss model to estimate actual system efficiency. The operating parameters such as power density, flow rates and design parameters such as electrode aspect ratio and flow frame channel dimensions are adjusted to maximize efficiency and minimize capital costs. Detailed cost estimates are obtained from various vendors to calculate cost estimates for present, near-term and optimistic scenarios. The most cost-effective chemistries with optimum operating conditions for power or energy intensive applications are determined, providing a roadmap for battery management systems development for redox flow batteries. The main drivers for cost reduction for various chemistries are identified as a function of the energy to power ratio of the storage system.

Xilin Chen, Xiaolin Li, Donghai Mei, Ju Feng, Mary Y Hu, Jianzhi Hu, Mark Engelhard, Jianming Zheng, Wu Xu, Jie Xiao, Jun Liu, Ji-Guang Zhang. "Reduction Mechanism of Fluoroethylene Carbonate for Stable Solid–Electrolyte Interphase Film on Silicon Anode." ChemSusChem 7 (2): 549-554 (Feb. 2014).
Abstract: Fluoroethylene carbonate (FEC) is an effective electrolyte additive that can significantly improve the cycling ability of silicon and other anode materials. However, the fundamental mechanism of this improvement is still not well understood. Based on the results obtained from ⁶Li NMR and X-ray photoelectron spectroscopy studies, we propose a molecular-level mechanism for how FEC affects the formation of solid electrolyte interphase (SEI) film: 1)FEC is reduced through the opening of the five-membered ring leading to the formation of lithium poly(vinyl carbonate), LiF, and some dimers; 2)the FEC-derived lithium poly(vinyl carbonate) enhances the stability of the SEI film. The proposed reduction mechanism opens a new path to explore new electrolyte additives that can improve the cycling stability of silicon-based electrodes.

G, Li, X. Lu, J.Y. Kim, J.P. Lemmon, and V.L. Sprenkle, "Improved cycling behavior of ZEBRA battery operated at intermediate temperature of 175°C," Journal of Power Sources, 249 (2014) 414-417 (Jan. 2014).
Abstract: Operation of the sodium-nickel chloride battery at temperatures below 200°C reduces cell degradation and improves cyclability. One of the main technical issues with operating this battery at intermediate temperatures such as 175°C is the poor wettability of molten sodium on β"”-alumina solid electrolyte (BASE), which causes reduced active area and limits charging. In order to overcome the poor wettability of molten sodium on BASE at 175°C, a Pt grid was applied on the anode side of the BASE using a screen printing technique. Cells with their active area increased by metallized BASEs exhibited deeper charging and stable cycling behavior.

Jiuchun Jiang, Wei Shi, Jianming Zheng, Pengjian Zuo, Jie Xiao, Xilin Chen, Wu Xu, Ji-Guang Zhang. "Optimized Operating Range for Large-Format LiFePO₄/Graphite Batteries." Journal of the Electrochemical Society 161 (3): A336-A341 (Dec. 2013).
Abstract: Long-term cycling performances of LiFePO₄/graphite batteries have been investigated in different state-of-charge (SOC) ranges. It is found that batteries cycled in the medium SOC range exhibit superior cycling stability over those cycled at both ends of the SOC ranges. A variety of characterization techniques, including galvanostatic intermittent titration technique (GITT) analysis, model-based parameter identification, electrochemical impedance spectroscopy analysis, and entropy change test, were used to investigate the performance difference of the batteries cycled in different SOC ranges. The results reveal that batteries at the end of SOC exhibit much higher polarization impedance than those within the medium-SOC range. This result can be attributed to the significant structural change of the cathode and anode materials as revealed by the large entropy change within these SOC regions. Identification of the best operating conditions for LiFePO₄/graphite batteries will significantly extend their cycle life. The general control principle obtained in this work, such as modulating the charge/discharge current to minimize the impedance extremes can also be used in the operation control of other battery systems.

Sacci R L,Dudney N J,More K L,Parent L R,Arslan I ,Browning N D. "Direct visualization of initial SEI morphology and growth kinetics during lithium deposition by in situ electrochemical transmission electron microscopy."Chemical Communications 17: 2104-2107 (Dec. 2013).
Abstract: Deposition of Li is a major safety concern existing in Li-ion secondary batteries. Here we perform the first in situ high spatial resolution measurement coupled with real-time quantitative electrochemistry to characterize SEI formation on gold using a standard battery electrolyte. We demonstrate that a dendritic SEI forms prior to Li deposition and that it remains on the surface after Li electrodissolution.

B Li, M Gu, Z Nie, X Wei, C Wang, V Sprenkle, and W Wang, "Nanorod Niobium Oxide as Powerful Catalysts for an All Vanadium Redox Flow Battery", Nano Letters, 2014, 14, 158-165 (Dec 2013).
Abstract: A powerful low-cost electrocatalyst, nanorod Nb₂O₅, is synthesized using hydrothermal method with monoclinic phases and simultaneously deposited on the surface of graphite felt (GF) electrode in an all vanadium flow battery (VRB). Cyclic voltammetry (CV) study confirmed that Nb₂O₅ has catalytic effects towards redox couples of V(II)/V(III) at the negative side and V(IV)/V(V) at the positive side to facilitate the electrochemical kinetics of the vanadium redox reactions. Because of poor conductivity of Nb₂O₅, the performance of the Nb₂O₅ loaded electrodes is strongly dependent on the nanosize and uniform distribution of catalysts on GFs surfaces. Accordingly, optimal amounts of W-doped Nb₂O₅ nanorods with minimum agglomeration and improved distribution on GFs surfaces are established by adding water-soluble compounds containing tungsten (W) into the precursor solutions. The corresponding energy efficiency is enhanced by ~10.7% at high current density (150 mA.cm^-2) as compared with one without catalysts. Flow battery cyclic performance also demonstrates the excellent stability of the as prepared Nb₂O₅ catalyst enhanced electrode. These results suggest that Nb₂O₅-based nanorods, replacing expensive noble metals, uniformly decorating GFs holds great promise as high-performance electrodes for VRB applications.

Eduard Nasybulin, Wu Xu, Mark H. Engelhard, Zimin Nie, Xiaohong S. Li, Ji-Guang Zhang. "Stability of polymer binders in Li–O₂ batteries."Journal of Power Sources 243: 899-907 (Dec. 2013).
Abstract: The stability of various polymer binders was systematically investigated in the oxygen-rich environment required for the operation of Li–O₂ batteries. Due to the coverage on air electrode surface by the discharge products and decomposition products of the electrolyte during the discharge process of Li–O₂ batteries, the binder in the air electrode is hard to be detected making the evaluation of its stability problematic. Therefore, stability of the binder polymers against the reduced oxygen species generated during the discharge process was investigated by ball milling the polymers with KO₂ and Li₂O₂, respectively. Most of the studied polymers are unstable under these conditions and their decomposition mechanisms are proposed according to the analyzed products. Polyethylene was found to exhibit excellent stability when exposed to superoxide and peroxide species and is suggested as a robust binder for air electrodes. In addition, the binding strength of the polymer significantly affects the discharge performance of Li–O₂ batteries.

Jie Xiao, Xiqian Yu, Jianming zheng, Yungang Zhou, Fei Gao, Xilin Chen, Jianming Bai, Xiao-Qing Yang, Ji-Guang Zhang. "Interplay between two-phase and solid solution reactions in high voltage spinel cathode material for lithium ion batteries."Journal of Power Sources 242: 736-741 (Nov. 2013).
Abstract: Lithium ion batteries (LIBs) are attracting intensive interests worldwide because of their potential applications in transportation electrification and utility grid. The intercalation compounds used in LIBs electrochemically react with Li⁺ ions via single or multiple phase transitions depending on the nature of the material structure as well as the synthesis and operating conditions. For LiNi_0.5Mn_1.5O₄ high voltage spinel, a promising candidate positive electrode material for LIBs, there are three spinel-structured phases sequentially appeared through two successive two-phase reactions during the delithiation/lithiation processes. Here we demonstrate, experimentally and theoretically, that through elemental substitution, the solid solution ranges for both the first and second phases are significantly extended during the electrochemical charge–discharge process. This type of structural changes with more solid solution regions facilitate fast Li⁺ diffusion by reducing the number of phase boundaries that Li⁺ ions have to overcome and resulted in less shrinkage of the unit cells at the end of charge process. This work unravels the fundamental interactions between structural and electrochemical properties by using spinel as the platform, which may be widely adopted to explain or tailor the properties of materials for energy storage and conversion.

G. Li, X. Lu, J.Y. Kim, J.P. Lemmon, and V.L. Sprenkle, "Cell Degradation of a Na-NiCl₂ (ZEBRA) Battery," Journal of Materials Chemistry A, 47 (2013) 14935 - 14942 (Nov 2013).
Abstract: In this work, the parameters influencing the degradation of a Na-NiCl₂ (ZEBRA) battery were investigated. Planar Na-NiCl₂ cells using β"”-alumina solid electrolyte (BASE) were tested with different C-rates, Ni/NaCl ratios, and capacity windows, in order to identify the key parameters for the degradation of Na-NiCl₂ battery. The morphology of NaCl and Ni particles were extensively investigated after 60 cycles under various test conditions using a scanning electron microscope. A strong correlation between the particle size (NaCl and Ni) and battery degradation was observed in this work. Even though the growth of both Ni and NaCl can influence the cell degradation, our results indicate that the growth of NaCl is a dominant factor in cell degradation. The use of excess Ni seems to play a role in tolerating the negative effects of particle growth on degradation since the available active surface area of Ni particles can be still sufficient even after particle growth. For NaCl, a large cycling window was the most significant factor, of which effects were amplified with decrease in Ni/NaCl ratio.

Gu M ,Parent L R,Mehdi B L,Unocic R R,Mcdowell M T,Sacci R L,Xu W ,Connell J G,Xu P ,Abellan Baeza P ,Chen X ,Zhang Y ,Perea D E,Evans J E,Lauhon L ,Zhang J ,Liu J ,Browning N D,Cui Y ,Arslan I ,Wang C M. "Demonstration of an Electrochemical Liquid Cell for Operando Transmission Electron Microscopy Observation of the Lithiation/Delithiation Behavior of Si Nanowire Battery Anodes." Nano Letters 13 (12): 6106-6112 (Nov. 2013).
Abstract:Over the past few years, in situ transmission electron microscopy (TEM) studies of lithium ion batteries using an open-cell configuration have helped us to gain fundamental insights into the structural and chemical evolution of the electrode materials in real time. In the standard open-cell configuration, the electrolyte is either solid lithium oxide or an ionic liquid, which is point-contacted with the electrode. This cell design is inherently different from a real battery, where liquid electrolyte forms conformal contact with electrode materials. The knowledge learnt from open cells can deviate significantly from the real battery, calling for operando TEM technique with conformal liquid electrolyte contact. In this paper, we developed an operando TEM electrochemical liquid cell to meet this need, providing the configuration of a real battery and in a relevant liquid electrolyte. To demonstrate this novel technique, we studied the lithiation/delithiation behavior of single Si nanowires. Some of lithiation/delithation behaviors of Si obtained using the liquid cell are consistent with the results from the open-cell studies. However, we also discovered new insights different from the open cell configuration—the dynamics of the electrolyte and, potentially, a future quantitative characterization of the solid electrolyte interphase layer formation and structural and chemical evolution.

Shao Y ,Liu T L.,Li G ,Gu M ,Nie Z ,Engelhard M H,Xiao J ,Lu D ,Wang C M,Zhang J ,Liu J. "Coordination Chemistry in magnesium battery electrolytes: how ligands affect their performance." Scientific Reports 3 (Nov. 2013).
Abstract:Magnesium battery is potentially a safe, cost-effective, and high energy density technology for large scale energy storage. However, the development of magnesium battery has been hindered by the limited performance and the lack of fundamental understandings of electrolytes. Here, we present a study in understanding coordination chemistry of Mg(BH₄)₂ in ethereal solvents. The O donor denticity, i.e. ligand strength of the ethereal solvents which act as ligands to form solvated Mg complexes, plays a significant role in enhancing coulombic efficiency of the corresponding solvated Mg complex electrolytes. A new electrolyte is developed based on Mg(BH₄)₂, diglyme and LiBH₄. The preliminary electrochemical test results show that the new electrolyte demonstrates a close to 100% coulombic efficiency, no dendrite formation, and stable cycling performance for Mg plating/stripping and Mg insertion/de-insertion in a model cathode material Mo6S8 Chevrel phase.

Vijayakumar M, W Wang, Z Nie, VL Sprenkle, and JZ Hu. "Elucidating the Higher Stability of Vanadium (V) Cations in Mixed Acid Based Redox Flow Battery Electrolytes." Journal of Power Sources 241:173-177. doi:10.1016/j.jpowsour.2013.04.072 (Nov 2013).
Abstract:The Vanadium (V) cation structures in mixed acid based electrolyte solution were analysed by density functional theory (DFT) based computational modelling and ⁵¹V and ³⁵Cl Nuclear Magnetic Resonance (NMR) spectroscopy. The Vanadium (V) cation exists as di-nuclear [V₂O₃Cl₂.6H₂O]²⁺ compound at higher vanadium concentrations (=1.75M). In particular, at high temperatures (>295K) this di-nuclear compound undergoes ligand exchange process with nearby solvent chlorine molecule and forms chlorine bonded [V₂O₃Cl₂.6H₂O]²⁺ compound. This chlorine bonded [V₂O₃Cl₂.6H₂O]²⁺ compound might be resistant to the de-protonation reaction which is the initial step in the precipitation reaction in Vanadium based electrolyte solutions. The combined theoretical and experimental approach reveals that formation of chlorine bonded [V₂O₃Cl₂.6H₂O]²⁺ compound might be central to the observed higher thermal stability of mixed acid based Vanadium (V) electrolyte solutions.

Xu W ,Wang J ,Ding F ,Chen X ,Nasybulin E N,Zhang Y ,Zhang J. "Lithium metal anodes for rechargeable batteries" Energy & Environmental Science 7: 513-537 (Oct. 2013).
Abstract:Lithium (Li) metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mA hg^-1), low density (0.59 g cm^-3) and the lowest negative electrochemical potential (−3.040 V vs. the standard hydrogen electrode). Unfortunately, uncontrollable dendritic Li growth and limited Coulombic efficiency during Li deposition/stripping inherent in these batteries have prevented their practical applications over the past 40 years. With the emergence of post-Li-ion batteries, safe and efficient operation of Li metal anodes has become an enabling technology which may determine the fate of several promising candidates for the next generation energy storage systems, including rechargeable Li–air batteries, Li–S batteries, and Li metal batteries which utilize intercalation compounds as cathodes. In this paper, various factors that affect the morphology and Coulombic efficiency of Li metal anodes have been analyzed. Technologies utilized to characterize the morphology of Li deposition and the results obtained by modelling of Li dendrite growth have also been reviewed. Finally, recent development and urgent need in this field are discussed.

Jianming Zheng, Wei Shi, Meng Gu, Jie Xiao, Pengjian Zuo, Chongmin Wang, Ji-Guang Zhang. "Electrochemical Kinetics and Performance of Layered Composite Cathode Material Li[Li_0.2Ni_0.2Mn_0.6]O₂." Journal of the Electrochemical Society 160 (11): A2212-A2219 (Oct. 2013).
Abstract: Lithium-rich, manganese-rich (LMR) layered composite cathode material Li[Li_0.2Ni_0.2Mn_0.6]O₂synthesized by a co-precipitation method delivers a high discharge capacity of 281 mAh g−1 at a low current density of C/25. However, significant increase of cell polarization and decrease of discharge capacity are observed at voltage below 3.5 V with increasing current densities. Galvanostatic intermittent titration technique (GITT) analysis and electrochemical impedance spectroscopy (EIS) measurements demonstrate that lithium ion intercalation/de-intercalation reactions into/out of this material are kinetically controlled by Li₂MnO₃ component and its activated MnO₂ component. The relationship between the electrochemical kinetics and rate performance as well as cycling stability has been systematically investigated. High discharge capacity of 149 mAh g⁻¹ can be achieved at 10 C charge rate and C/10 discharge rate, indicating that the LMR cathode could withstand high charge rate (except initial activation process), which is very promising for practical applications. The results also reveal that the continuous formation of poorly conducting spinel phase is responsible for the capacity fading of LMR cathodes.

B Li, Q Luo, X Wei, Z Nie, E Thomsen, B Chen, V Sprenkle, and W Wang, "Capacity Decay Mechanism of Microporous Separator-Based All-Vanadium Redox Flow Batteries and its Recovery", ChemSusChem, 2014, 7, 577-584 (Oct 2013).
Abstract: The results of the investigation of the capacity decay mechanism of vanadium redox flow batteries with microporous separators as membranes are reported. The investigation focuses on the relationship between the electrochemical performance and electrolyte compositions at both the positive and negative half-cells. Although the concentration of total vanadium ions remains nearly constant at both sides over cycling, the net transfer of solution from one side to the other and thus the asymmetrical valance of vanadium ions caused by the subsequent disproportionate self-discharge reactions at both sides lead to capacity fading. Through in situ monitoring of the hydraulic pressure of the electrolyte during cycling at both sides, the convection was found to arise from differential hydraulic pressures at both sides of the separators and plays a dominant role in capacity decay. A capacity-stabilizing method is developed and was successfully demonstrated through the regulation of gas pressures in both electrolyte tanks.

Gu M ,Kushima A ,Shao Y ,Zhang J ,Liu J ,Browning N D,Li J ,Wang C M. "Probing the Failure Mechanism of SnO₂ Nanowires for Sodium-Ion Batteries." Nano Letters 13 (11): 5203-5211 (Sept. 2013).
Abstract:Nonlithium metals such as sodium have attracted wide attention as a potential charge carrying ion for rechargeable batteries. Using in situ transmission electron microscopy in combination with density functional theory calculations, we probed the structural and chemical evolution of SnO₂ nanowire anodes in Na-ion batteries and compared them quantitatively with results from Li-ion batteries (Huang, J. Y.; et al. Science 2010, 330, 1515−1520). Upon Na insertion into SnO₂, a displacement reaction occurs, leading to the formation of amorphous NaxSn nanoparticles dispersed in Na2O matrix. With further Na insertion, the Na_xSn crystallized into Na₁₅Sn₄ (x = 3.75). Upon extraction of Na (desodiation), the Na_xSn transforms to Sn nanoparticles. Associated with the dealloying, pores are found to form, leading to a structure of Sn particles confined in a hollow matrix of Na₂O. These pores greatly increase electrical impedance, therefore accounting for the poor cyclability of SnO₂. DFT calculations indicate that Na⁺ diffuses 30 times slower than Li⁺ in SnO₂, in agreement with in situ TEM measurement. Insertion of Na can chemomechanically soften the reaction product to a greater extent than in lithiation. Therefore, in contrast to the lithiation of SnO₂ significantly less dislocation plasticity was seen ahead of the sodiation front. This direct comparison of the results from Na and Li highlights the critical role of ionic size and electronic structure of different ionic species on the charge/discharge rate and failure mechanisms in these batteries.

Jie Xiao, Jianming Zheng, Xiaolin Li, Yuyan Shao, Ji-Guang Zhang. "Hierarchically structured materials for lithium batteries."Nanotechnology 24 (42) (Sept. 2013).
Abstract: The lithium-ion battery (LIB) is one of the most promising power sources to be deployed in electric vehicles, including solely battery powered vehicles, plug-in hybrid electric vehicles, and hybrid electric vehicles. With the increasing demand for devices of high-energy densities (>500 Wh kg⁻¹), new energy storage systems, such as lithium–oxygen (Li–O₂) batteries and other emerging systems beyond the conventional LIB, have attracted worldwide interest for both transportation and grid energy storage applications in recent years. It is well known that the electrochemical performance of these energy storage systems depends not only on the composition of the materials, but also on the structure of the electrode materials used in the batteries. Although the desired performance characteristics of batteries often have conflicting requirements with the micro/nano-structure of electrodes, hierarchically designed electrodes can be tailored to satisfy these conflicting requirements. This work will review hierarchically structured materials that have been successfully used in LIB and Li–O₂ batteries. Our goal is to elucidate (1) how to realize the full potential of energy materials through the manipulation of morphologies, and (2) how the hierarchical structure benefits the charge transport, promotes the interfacial properties and prolongs the electrode stability and battery lifetime.

Soowhan Kim, Edwin Thomsen, Guanguang Xia, Zimin Nie, Jie Bao, Kurtis Recknagle, Wei Wang, Vilayanur Viswanathan, Qingtao Luo, Xiaoliang Wei, Alasdair Crawford, Greg Coffey, Gary Maupin, Vincent Sprenkle. "1 kW/1 kWh advanced vanadium redox flow battery utilizing mixed acid electrolytes". Journal of Power Sources 237 (2013) 300-309 (Sept 2013).
Abstract: This paper reports on the recent demonstration of an advanced vanadium redox flow battery (VRFB) using a newly developed mixed acid (sulfuric and hydrochloric acid) supporting electrolyte at a kW scale. The developed prototype VRFB system is capable of delivering more than 1.1 kW in the operation range of 15~85% state of charge (SOC) at 80 mA cm^-2 with an energy efficiency of 82% and energy content of 1.4 kWh. The system operated stably without any precipitation at electrolyte temperatures >45°C. At similar electrolyte temperatures, tests with a conventional sulfuric acid electrolyte suffered from precipitation after 80 cycles. By operating stably at elevated temperatures (>40°C), the mixed acid system enables significant advantages over the conventional sulfate system, namely; 1) high stack energy efficiency due to better kinetics and lower electrolyte resistance, 2) lower viscosity resulting in reduced pumping losses, 3) lower capital cost by elimination of heat exchanger, 4) higher system efficiency and 5) simplified system design and operation. Demonstration of the prototype stack with the mixed acid electrolyte has been shown to lower the cost of conventional VRFB systems for large-scale energy storage applications.

X. Wei, Q. Luo, B. Li, Z. Nie, E. Miller, J. Chambers, V. Sprenkle, and W. Wang. "Performance Evaluation of Microporous Separator in Fe/V Redox Flow Battery." ECS Transactions 45(26):17-24. (Sept 2013).
Abstract: The newly developed Fe/V redox flow battery has demonstrated attractive cell performance. However, the deliverable energy density is relatively low due to the reduced cell voltage. To compensate this disadvantage and compete with other redox flow battery systems, cost reduction of the Fe/V system is necessary. This paper describes evaluation of hydrocarbon-based Daramic^® microporous separators for use in the Fe/V system. These separators are very inexpensive and have exceptional mechanical properties. Separator B having ion exchange capacity demonstrated excellent capacity retention capability, and exhibited energy efficiency above 65% over a broad temperature range of 5-50°C and at current densities up to 80mA/cm². Therefore, this separator shows great potential to replace the expensive Nafion^® membrane. This will drive down the capital cost and make the Fe/V system a promising low-cost energy storage technology.

W Xu, X Chen, W Wang, D Choi, F Ding, J Zheng, Z Nie, YJ Choi, J Zhang, and Z Yang. "Simply AlF3-treated Li₄Ti₅O₁₂ composite anode materials for stable and ultrahigh power lithium-ion batteries."Journal of Power Sources 236 (2013), 169 -174. (Aug 2013).
Abstract: The commercial Li₄Ti₅O₁₂ (LTO) is successfully modified by AlF₃ via a low temperature process. After being calcined at 400°C for 5 h, AlF₃ reacts with LTO to form a composite material, which mainly consists of Al₃+ and F- co-doped LTO with small amounts of anatase TiO₂. Al³⁺ and F- co-doped LTO demon- strates ultrahigh rate capability comparing to the pristine LTO. Since the amount of the byproduct TiO₂ is relatively small, the modified LTO electrodes retain the main voltage characteristics of LTO with a minor feature similar to those of anatase TiO₂. The doped LTO anodes deliver slightly higher discharge capacity and maintain the excellent long-term cycling stability when compared to the pristine LTO anode. Therefore, Al³⁺ and F- co-doped LTO composite material synthesized at low temperature is an excellent stable and ultra-high power lithium-ion batteries.

Jianming Zheng, Meng Gu, Jie Xiao, Pengjian Zuo, Chongmin Wang, Ji-Guang Zhang. "Corrosion/Fragmentation of Layered Composite Cathode and Related Capacity/Voltage Fading during Cycling Process."Nano Letters 13 (8): 3824-3830 (June 2013).
Abstract: The Li-rich, Mn-rich (LMR) layered structure materials exhibit very high discharge capacities exceeding 250 mAh g^–1 and are very promising cathodes to be used in lithium ion batteries. However, significant barriers, such as voltage fade and low rate capability, still need to be overcome before the practical applications of these materials. A detailed study of the voltage/capacity fading mechanism will be beneficial for further tailoring the electrode structure and thus improving the electrochemical performances of these layered cathodes. Here, we report detailed studies of structural changes of LMR layered cathode Li[Li_0.2Ni_0.2Mn_0.6]O₂ after long-term cycling by aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The fundamental findings provide new insights into capacity/voltage fading mechanism of Li[Li_0.2Ni_0.2Mn_0.6]O₂. Sponge-like structure and fragmented pieces were found on the surface of cathode after extended cycling. Formation of Mn²⁺ species and reduced Li content in the fragments leads to the significant capacity loss during cycling. These results also imply the functional mechanism of surface coatings, for example, AlF₃, which can protect the electrode from etching by acidic species in the electrolyte, suppress cathode corrosion/fragmentation, and thus improve long-term cycling stability.

Dongyang Chen, Soowhan Kim, Vincent Sprenkle, Michael A. Hickner. "Composite blend polymer membranes with increased proton selectivity and lifetime for vanadium redox flow batteries". Journal of Power Sources 231 (2013) 301-306. (Jun 2013).
Abstract: Composite membranes based on blends of sulfonated fluorinated poly(arylene ether) (SFPAE) and poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-co-HFP)) were prepared with varying P(VDF-co-HFP) content for vanadium redox flow battery (VRFB) applications. The properties of the SFPAE-P(VDF-co-HFP) blends were characterized by atomic force microscopy, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The water uptake, mechanical properties, thermal properties, proton conductivity, VO²⁺] permeability and VRFB cell performance of the composite membranes were investigated in detail and compared to the pristine SFPAE membrane. It was found that SFPAE had good compatibility with P(VDF-co-HFP) and the incorporation of P(VDF-co-HFP) increased the mechanical properties, thermal properties, and proton selectivity of the materials effectively. An SFPAE composite membrane with 10 wt.% P(VDF-co-HFP) exhibited a 44% increase in VRFB cell lifetime as compared to a cell with a pure SFPAE membrane. Therefore, the P(VDF-co-HFP) blending approach is a facile method for producing low-cost, high-performance VRFB membranes.

Xiaochuan Lu, Guosheng Li, Jin Y Kim, John P. Lemmon, Vincent L Sprenkle, Zhenguo Yang, "A novel low-cost sodium-zinc chloride battery." Energy & Environmental Science 6(6): 1837-1843 (Jun 2013).
Abstract: The sodium-metal halide (ZEBRA) battery has been considered as one of the most attractive energy storage systems for stationary and transportation applications. Even though Na-NiCl2 battery has been widely investigated, there is still a need to develop a more economical system to make this technology more attractive for commercialization. In the present work, a novel low-cost Na-ZnCl2 battery with a planar β"-Al2O3 solid electrolyte (BASE) was proposed, and its electrochemical reactions and battery performance were investigated. Compared to the Na-NiCl2 chemistry, the ZnCl2-based chemistry was more complicated, in which multiple electrochemical reactions including liquid-phase formation occurred at temperatures above 253°C. During the first stage of charge, NaCl reacted with Zn to form Na in the anode and Na2ZnCl4 in the cathode. Once all the residual NaCl was consumed, further charging led to the formation of a NaCl-ZnCl2 liquid phase. At the end of charge, the liquid phase reacted with Zn to produce solid ZnCl2. To identify the effects of liquid-phase formation on electrochemical performance, button cells were assembled and tested at 280°C and 240°C. At 280°C where the liquid phase formed during cycling, cells revealed quite stable cyclability. On the other hand, more rapid increase in polarization was observed at 240°C where only solid-state electrochemical reactions occurred. SEM analysis indicated that the stable performance at 280°C was due to the suppressed growth of Zn and NaCl particles, which were generated from the liquid phase during discharge of each cycle.

Jianming Zheng, Jie Xiao, Zimin Nie, Ji-Guang Zhang. "Lattice Mn³⁺ Behaviors in Li₄Ti₅O₁₂/LiNi_0.5Mn_1.5O₄ Full Cells."Journal of Electrochemical Society 160 (8): A1264-A1268 (May 2013).
Abstract: High voltage spinels LiNi_0.5Mn_1.5O₄ (LNMO) with different contents of residual lattice Mn³⁺ have been evaluated in full cells using Li₄Ti₅O₁₂ (LTO) as anode. Greatly improved cycling stability has been observed for all spinels in LTO-limited full cell, compared with those in LNMO-limited ones, while the underlying mechanisms are quite different. “Shallow cycling” of LNMO in LTO-limited cells does not require complete transition to the third cubic phase, reducing the phase boundaries that Li⁺ has to overcome and thus improving the cell performances. However, in LNMO-limited cells, influences of lattice Mn³⁺ are more easily exemplified in the Li⁺ deficient environment and superior electrochemical performance are observed for spinel with higher content of lattice Mn³⁺.

Bin Li, Liyu Li, Wei Wang, Zimin Nie, Baowei Chen, Xiaoliang Wei, Qingtao Luo, Zhenguo Yang, and Vincent Sprenkle. "Fe/V Redox Flow Battery Electrolyte Investigation and Optimization". Journal of Power Sources 229 (2013) 1-5. (May 2013).
Abstract: The recently invented iron (Fe)/vanadium (V) redox flow battery (IVB) system has attracted increasing attention because of its long-term cycling stability and low-cost membrane/separator. In this paper, we describe our extensive matrix study of factors such as electrolyte composition; state of charge (SOC), and temperature that influence the stability of electrolytes in both positive and negative half-cells. During the study, an optimized electrolyte that can be operated in a temperature range from -5°C to 50°C without precipitation is identified. Fe/V flow cells using the optimized electrolyte and low-cost separator exhibit satisfactory cycling performance at different temperatures. Efficiencies, capacities, and energy densities of flow batteries at various temperatures are studied.

X. Wei, Z Nie, Q Luo, B Li, V. Sprenkle, and W. Wang, "Polyvinyl Chloride/Silica Nanoporous Composite Separator for All-Vanadium Redox Flow Battery Applications." Journal of the Electrochemical Society, 160(8):A1215 - A1218, 2013. (May 2013).
Abstract: We demonstrate application of a commercial nanoporous polyvinyl chloride (PVC)/silica separator in an all-vanadium redox flow battery (VRB) as a low-cost alternative to expensive Nafion^® membranes. This hydrophilic separator is composed of silica particles enmeshed in a PVC matrix that creates unique porous structures. These nano-scale pores with an average pore size of 45nm and a porosity of 65% serve as ion transport channels that are critically important for flow battery operation. The VRB flow cell using the PVC/silica separator produces excellent electrochemical performance in a mixed-acid VRB system with average energy efficiency (EE) of 79% at the current density of 50mAcm^-2. This separator affords the VRB flow cell with excellent rate capability with its EE higher than that of Nafion^® membrane at current densities above 100mAcm^-2. With this separator, the EE of the VRB flow cell exhibits great tolerance to temperature fluctuations in the typical operational temperature range of the mixed-acid VRB system. More importantly, the flow cell using the separator demonstrates an excellent capacity retention over cycling, which enables the VRB system to operate in the long term with minimal electrolyte maintenance.

D Reed, G Coffey, E Mast, N Canfield, J Mansurov, X Lu, VL Sprenkle. "Wetting of sodium on ß-Al₂O₃/YSZ composites for low temperature planar sodium-metal halide batteries". Journal of Power Sources 227: 94-100 (Apr 2013).
Abstract:Wetting of Na on ß-Al₂O₃/YSZ composites was investigated using the sessile drop technique. The effects of moisture and surface preparation were studied at low temperatures. Electrical conductivity of Na/ß-Al₂O₃/YSZ/Na cells was also investigated at low temperatures and correlated to the wetting behavior. The use of planar ß-Al₂O₃ substrates at low temperature with low cost polymeric seals is realized due to improved wetting at low temperature and conductivity values consistent with the literature.

Eduard Nasybulin, Wu Xu, Mark H. Engelhard, Xiaohong S. Li, Meng Gu, Dehong Hu, Ji-Guang Zhang. "Electrocatalytic properties of poly(3,4-ethylenedioxythiophene) (PEDOT) in Li-O₂ battery."Electrochemistry Communications 29: 63-66 (April 2013).
Abstract: The catalytic activity of poly(3,4-ethylenedioxythiophene) (PEDOT) was investigated during oxygen reduction/evolution reactions in Li–O₂ batteries. PEDOT was prepared by in situ chemical polymerization of 3,4-ethylenedioxythiophene monomer in carbon matrix. PEDOT significantly reduces the overvoltage of the charging process in a Li–O₂ battery. The electrocatalytic effect of PEDOT can be attributed to its redox activity. Apparently, PEDOT acts as a mediator in electron transfer during discharge and charge processes.

Jianming Zheng, Jie Xiao, Wu Xu, Xilin Chen, Meng Gu, Xiaohong Li, Ji-Guang Zhang. "Surface and structural stabilities of carbon additives in high voltage lithium ion batteries."Journal of Power Sources 227: 211-217 (April 2013).
Abstract: The stabilities of different conductive carbon additives have been systematically investigated in high voltage lithium ion batteries. It is found that the higher surface area of conductive additives leads to more parasitic reactions initiating from different onset voltages. A closer inspection reveals that for the low surface area carbon such as Super P, PF₆⁻ anions reversibly intercalate into carbon structure at around 4.7 V. For high surface area carbons, in addition to the electrolyte decomposition, the oxidation of functional groups at high voltage further increases the irreversible capacity and Li⁺ ion consumption. Coulombic efficiency, irreversible capacity and cycling stability observed by using different carbon additives are correlated with their structure and surface chemistry, thus providing information for predictive selection of carbon additives in different energy storage systems.

X. Wei, Z. Nie, Q. Luo, B. Li, B. Chen, K. Simmons, V. Sprenkle, W. Wang, "Nanoporous Polytetrafluoroethylene/Silica Composite Separator as a High-Performance All-Vanadium Redox Flow Battery Membrane". Advanced Energy Materials, 3, 1215-1220, 2013. (Apr 2013).
Abstract:A novel low-cost nanoporous polytetrafluoroethylene (PTFE)/silica composite separator has been prepared and evaluated for its use in an all-vanadium redox flow battery (VRB). The separator consists of silica particles enmeshed in a PTFE fibril matrix. It possesses unique nanoporous structures with an average pore size of 38 nm and a porosity of 48%. These pores function as the ion transport channels during redox flow battery operation. This separator provides excellent electrochemical performance in the mixed-acid VRB system. The VRB using this separator delivers impressive energy efficiency, rate capability, and temperature tolerance. In addition, the flow cell using the novel separator also demonstrates an exceptional capacity retention capability over extended cycling, thus offering excellent stability for long-term operation. The characteristics of low cost, excellent electrochemical performance and proven chemical stability afford the PTFE/silica nanoporous separator great potential as a substitute for the Nafion membrane used in VRB applications.

B. Li, M. Gu, Z. Nie, Y. Shao, Q. Luo, X. Wei, X. Li, J. Xiao, C. Wang, V. Sprenkle, and W. Wang, "Bismuth Nanoparticle Decorating Graphite Felt as a High-Performance Electrode for an All-Vanadium Redox Flow Battery". Nano Letters, 13, 1330-1335, 2013. (Feb 2013).
Abstract: Employing electrolytes containing Bi3+, bismuth nanoparticles are synchronously electrodeposited onto the surface of a graphite-felt electrode during operation of an all-vanadium redox flow battery (VRFB). The influence of the Bi nanoparticles on the electrochemical performance of the VRFB is thoroughly investigated. It is confirmed that Bi is only present at the negative electrode and facilitates the redox reaction between V(II) and V(III). However, the Bi nanoparticles significantly improve the electrochemical performance of VRFB cells by enhancing the kinetics of the sluggish V(II)/V(III) redox reaction, especially under high power operation. The energy efficiency is increased by 11% at high current density (150 mA.cm-2) owing to faster charge transfer as compared with one without Bi. The results suggest that using Bi nanoparticles in place of noble metals offers great promise as high-performance electrodes for VRFB application.

Q Luo, L Li, W Wang, Z Nie, X Wei, B Li, B Chen, Z Yang, and VL Sprenkle. "Capacity Decay and Remediation of Nafion-based All-Vanadium Redox Flow Batteries". ChemSusChem 6(2) 268-274. (Feb 2013).
Abstract: The relationship between the electrochemical performance of vanadium redox flow batteries (VRB) and electrolyte compositions has been investigated, and the reasons for capacity decay over charge-discharge cycling have been analyzed and are discussed in this paper. The results show that the reasons for capacity fading over real charge-discharge cycling include not only the imbalanced vanadium active species, but also the asymmetrical valence of vanadium ions in positive and negative electrolytes. The asymmetrical valence of vanadium ions leads to the SOC range to decrease in positive electrolyte and increase in negative electrolyte, respectively. As a result, the higher SOC range in negative half-cells further aggravate the capacity fading by creating a higher over-potential and possible hydrogen evolution. Based on this finding, we developed two methods for restoring the lost capacity; thereby enabling long-term operation of VRBs to be achieved without the substantial loss of energy resulting from periodic remixing of electrolytes.

W Wang, Q Luo, B Li, X Wei, L Li, and Z Yang. "Recent Progress in Redox Flow Battery Research and Development".Advanced Functional Materials 23 (8), 970-986.(Feb 2013).
Abstract: With the increasing need to seamlessly integrate renewable energy with the current electricity grid, which itself is evolving into a more intelligent, efficient, and capable electrical power system, it is envisioned that energy-storage systems will play a more prominent role in bridging the gap between current technology and a clean sustainable future in grid reliability and utilization. Redox flow battery technology is a leading approach in providing a well-balanced approach for current challenges. In this paper, we review recent progress in the research and development of redox flow battery technology, including cell-level components of electrolytes, electrodes, and membranes. Our review focuses on new redox chemistries for both aqueous and non-aqueous systems.

X. Lu, JP Lemmon, JY Kim, VL Sprenkle, and ZG Yang. "High Energy Density Na-S/NiCl2 Hybrid Battery." Journal of Power Sources 224 (2013) 312- 316. (Feb 2013).
Abstract: High temperature (250-350°C) sodium-beta alumina batteries (NBBs) are attractive energy storage devices for renewable energy integration and other grid related applications. Currently, two technologies are commercially available in NBBs, e.g., sodium-sulfur (Na-S) battery and sodium-metal halide (ZEBRA) batteries. In this study, we investigated the combination of these two chemistries with a mixed cathode. In particular, the cathode of the cell consisted of molten NaAlCl4 as a catholyte and a mixture of Ni, NaCl and Na2S as active materials. During cycling, two reversible plateaus were observed in cell voltage profiles, which matched electrochemical reactions for Na-S and Na-NiCl2 redox couples. An irreversible reaction between sulfur species and Ni was identified during initial charge at 280°C, which caused a decrease in cell capacity. The final products on discharge included Na2Sn with 1< n < 3, which differed from Na2S3 found in traditional Na-S battery. Reduction of sulfur in the mixed cathode led to an increase in overall energy density over ZEBRA batteries. Despite of the initial drop in cell capacity, the mixed cathode demonstrated relatively stable cycling with more than 95% of capacity retained over 60 cycles under 10mA/cm2. Optimization of the cathode may lead to further improvements in battery performance.

Eduard Nasybulin, Wu Xu, Mark H. Engelhard, Zimin Nie, Sarah D. Burton, Lelia Cosimbescu, Mark E. Gross, Ji-Guang Zhang. "Effects of Electrolyte Salts on the Performance of Li–O₂ Batteries."Journal of Physical Chemistry C 117 (6): 2635-2645 (Jan. 2013).
Abstract: The effects of lithium salts on the performance of Li–O₂ batteries and the stability of salt anions in the O₂ atmosphere during discharge/charge processes were systematically investigated by studying seven common lithium salts in tetraglyme as electrolytes for Li–O₂ batteries. The discharge products of Li–O₂ reactions were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, and nuclear magnetic resonance spectroscopy. The performance of Li–O₂ batteries was strongly affected by the salt used in the electrolyte. Lithium tetrafluoroborate (LiBF₄) and lithium bis(oxalato)borate (LiBOB) decomposed and formed LiF and lithium oxalate, respectively, as well as lithium borates during discharge of Li–O₂ batteries. In the case of other salts, including lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTf), lithium hexafluorophosphate (LiPF₆), lithium perchlorate (LiClO₄), and lithium bromide (LiBr), the discharge products mainly consisted of Li₂O₂ and carbonates with minor signs of decomposition of LiTFSI, LiTf, and LiPF₆. LiBr and LiClO₄ showed the best stability during the discharge process. For the cycling performance, LiTf and LiTFSI were the best among the studied salts. In addition to the instability of lithium salts, decomposition of tetraglyme solvent was a more significant factor contributing to the limited cycling stability. Thus, a more stable nonaqueous electrolyte including organic solvent and lithium salt still needs to be further developed to reach a fully reversible Li–O₂ battery.

Wang W, D Choi, and Z Yang."Li-Ion Battery with LiFePO4 Cathode and Li₄Ti₅O₁₂ Anode for Stationary Energy Storage". Metallurgical and Materials Transactions A, Physical Metallurgy and Materials Science 44A(1 Supplement): 21-25. (Jan 2013).
Abstract: Li-ion batteries based on commercially available LiFePO₄ cathode and Li₄Ti₅O₁₂ anode were investigated for potential stationary energy storage applications. The full cell that operated at flat 1.85 V demonstrated stable cycling up to 200 cycles followed by a rapid fade. A Li-ion full cell with Ketjen black modified LiFePO₄ cathode and an unmodified Li₄Ti₅O₁₂ anode exhibited negligible fade after more than 1200 cycles with a capacity of ~130 mAh/g at C/2. The improved stability, along with its cost-effectiveness, environmental benignity, and safety, make the LiFePO₄/Li₄Ti₅O₁₂ combination Li-ion battery a promising option for storing renewable energy.

X Lu, BW Kirby, W Xu, G Li, JY Kim, JP Lemmon, VL Sprenkle, and ZG Yang. "Advanced Intermediate-Temperature Na-S Battery." Energy & Environmental Science 6(1) (2013) 299 - 306. (Jan 2013).
Abstract: In this study, we reported an intermediate-temperature (~150°C) sodium-sulfur (Na-S) battery. With a reduced operating temperature, this novel battery can potentially reduce the cost and safety issues associated with the conventional high-temperatures (300~350°C) Na-S battery. A dense β"-Al2O3 solid membrane and tetraglyme were utilized as the electrolyte separator and catholyte solvent in this battery. Solubility tests indicated that cathode mixture of Na2S4 and S exhibited extremely high solubility in tetraglyme (e.g., > 4.1 M for Na2S4 + 4 S). CV scans of Na2S4 in tetraglyme revealed two pairs of redox couples with peaks at around 2.22 and 1.75 V, corresponding to the redox reactions of polysulfide species. The discharge/charge profiles of the Na-S battery showed a slope region and a plateau, indicating multiple steps and cell reactions. In-situ Raman spectra during battery operation suggested that polysulfide species were formed in the sequence of Na2S5 + S → Na2S5 + Na2S4 → Na2S4 + Na2S2 during discharge and in a reverse order during charge. This battery showed dramatic improvement in rate capacity and cycling stability over room-temperature Na-S batteries, which makes it extremely attractive for renewable energy integration and other grid related applications.

GS Li, XC Lu, CA Coyle, JY Kim, JP Lemmon, VL Sprenkle, and ZG Yang. "Novel ternary molten salt electrolytes for intermediate-temperature sodium/nickel chloride batteries."Journal of Power Sources 220, 193 -198. (Dec 2012).
Abstract: The sodium-nickel chloride (ZEBRA) battery is typically operated at relatively high temperature (250~350°C) to achieve adequate electrochemical performance. Reducing the operating temperature in the range of 150 to 200°C can lead to enhanced cycle life by suppressing temperature related degradation mechanisms. The operation at these intermediate temperatures also allows for lower cost materials of construction such as elastomeric sealants and gaskets. To achieve adequate electrochemical performance at lower operating temperatures requires an overall reduction in ohmic losses associated with temperature. This includes reduction in the ohmic resistance of β"-alumina solid electrolyte (BASE) and the incorporation of low melting point molten salt as the secondary electrolyte. In present work, planar-type Na/NiCl2 cells with a thin flat BASE (600 μm) and low melting point secondary electrolyte were evaluated at reduced temperatures. Molten salts used as secondary electrolytes were fabricated by the partial replacement of NaCl in the standard secondary electrolyte (NaAlCl4) with other lower melting point alkali metal salts such as NaBr, LiCl, and LiBr. Electrochemical characterization of these ternary molten salts demonstrated improved ionic conductivity and sufficient electrochemical window at reduced temperatures. Furthermore, Na/NiCl2 cells with 50 mol% NaBr-containing secondary electrolyte exhibited reduced polarizations at 175°C compared to the cell with the standard NaAlCl4 catholyte. The cells also exhibited stable cycling performance even at 150°C.

Q Luo, L Li, Z Nie, W Wang, X Wei, B Li, B Chen, Z Yang. "In-situ investigation of vanadium ion transport in redox flow battery." Journal of Power Sources 218 (2012) 15-30 (Nov 2012).
Abstract: Flow batteries with vanadium and iron redox couples as the electroactive species were employed to investigate the transport behavior of vanadium ions in the presence of an electric field. It was shown that the electric field accelerated the positive-to-negative and reduced the negative-to-positive transport of vanadium ions in the charging process and affected the vanadium ion transport in the opposite way during discharge. In addition, a method was designed to differentiate the concentration-gradient-driven vanadium ion diffusion and electric-field-driven vanadium ion migration. A simplified mathematical model was established to simulate the vanadium ion transport in real charge-discharge operation of the flow battery. The concentration gradient diffusion coefficients and electric-migration coefficients of V²⁺, V³⁺, VO²⁺, and VO₂⁺ across a NAFION^® membrane were obtained by fitting the experimental data.

X Wei, L Li, Q Luo, Z Nie, W Wang, B Li, GG Xia, E Millar, J Chambers, Z Yang. "Microporous separators for Fe/V redox flow batteries." (2013) Journal of Power Sources 218 (2012) 39-45 (Nov 2012).
Abstract: The Fe/V redox flow battery has demonstrated promising performance with distinct advantages over other redox flow battery systems. Due to the less oxidative nature of the Fe(III) species, hydrocarbon-based ion exchange membranes or separators can be used. Daramic^® microporous polyethylene separators were tested on Fe/V flow cells using sulfuric/chloric mixed acid-supporting electrolytes. Among them, separator C exhibited good flow cell cycling performance with satisfactory repeatability over a broad temperature range of 5-50°C. Energy efficiency (EE) of C remains around 70% at current densities of 50-80 mA.cm^-2 in temperatures ranging from room temperature to 50°C. The capacity decay problem could be circumvented through hydraulic pressure balancing by means of applying different pump rates to the positive and negative electrolytes. Stable capacity and energy were obtained over 20 cycles at room temperature and 40°C. These results show that extremely low-cost separators ($1-20/m²) are applicable in the Fe/V flow battery system with acceptable energy efficiency. This represents a remarkable breakthrough: a significant reduction of the capital cost of the Fe/V flow battery system, which could further its market penetration in grid stabilization and renewable integration.

D Stephenson, S Kim, F Chen, E Thomsen, V Viswanathan, W Wang, VL Sprenkle. "Electrochemical Model of the Fe/V Redox Flow Battery."Journal of the Electrochemical Society 159 (12): A1993-A2000 (Oct 2012).
Abstract: A zero-dimensional electrochemical model of the Fe/V redox flow battery (RFB) is presented that can model RFB performance at low flow rates (<0.5 mL min^-1 cm^-2) and varied temperatures. The electrochemical model is appropriate for practical RFBs and provides good agreement with experimental data. In addition, a proposed non-ideal electrode model is introduced that accounts for higher voltage losses at low flow rates. Semi-quantitative operation strategies and electrode design guidelines can be obtained from the model. We found that ohmic losses associated with the electrolyte were dominating our electrode losses, which means operating the cell at higher temperature will reduce electrolyte ohmic losses and viscosity, thus leading to higher system efficiency. Thinner electrodes than the 4.5-mm-thick felt used in this study should reduce ohmic losses as well as pumping losses if the same space velocity is maintained. This electrochemical model can be easily incorporated into system-level and cost models, which will help in system optimization, system control, and pump selection and help avoid potential risks of large scale RFB system development.

W Wang, L Li, Z Nie, B Chen, Q Luo, Y Shao, X Wei, F Chen, G Xia, Z Yang. "A new hybrid redox flow battery with multiple redox couples." Journal of Power Sources 216 (2012), 99-103. (Oct 2012).
Abstract: A redox flow battery using V⁴⁺/V⁵⁺ vs. V²⁺/V³⁺ and Fe²⁺/Fe³⁺ vs. V²⁺/V³⁺ redox couples in chloric/sulfuric mixed acid supporting electrolyte was investigated for potential stationary energy storage applications. The Fe/V hybrid redox flow cell using mixed reactant solutions and operated within a voltage window of 0.5~1.7 V demonstrated stable cycling over 100 cycles with energy efficiency ~80% and negligible capacity fading at room temperature. A 66% improvement in the energy density of the Fe/V hybrid cell was achieved compared with the previously reported Fe/V cell using only Fe²⁺/Fe³⁺ vs. V²⁺/V³⁺ redox couples.

X Lu, GS Li, JY Kim, JP Lemmon, VL Sprenkle, and ZG Yang. "The effects of temperature on the electrochemical performance of sodium-nickel chloride batteries." Journal of Power Sources 215 (2012), 288-295. (Oct 2012).
Abstract: The sodium-nickel chloride (ZEBRA) battery is typically operated at relatively high temperatures (≥ 300°C) to achieve adequate electrochemical performance. In the present study, the effects of operating temperature on the electrochemical performance of planar-type sodium-nickel chloride batteries were investigated in order to evaluate the feasibility of the battery operation at low temperatures (≥ 200°C). Electrochemical test results revealed that the battery was able to be cycled at C/3 rate at as low as 175°C despite the higher cell polarization at the reduced temperature. Overall, low operating temperature resulted in a considerable improvement in the stability of cell performance. Cell degradation was negligible at 175°C, while 55% increase in end-of-charge polarization was observed at 280°C after 60 cycles. SEM analysis indicated that the performance degradation at higher temperatures was related to the particle growth of both nickel and sodium chloride in the cathode. The cells tested at lower temperatures (e.g., 175 and 200°C), however, exhibited a sharp drop in cell voltage at the end of discharge due to the diffusion limitation, possibly caused by the limited ionic conductivity of NaAlCl4 melt or the poor wettability of sodium on the β"-Al2O3 solid electrolyte (BASE). Therefore, improvements in the ionic conductivity of a secondary electrolyte and sodium wetting as well as reduction in the ohmic resistance of BASE are required to further enhance the battery performance at low temperatures.

Jianming Zheng, Jie Xiao, Xiqian Yu, Libor Kovarik, Meng Gu, Fredrick Omenya, Xilin Chen, Xiao-Qing Yang, Jun Liu, Gordon L. Graff, M. Stanley Whittingham, Ji-Guang Zhang. "Enhanced Li⁺ ion transport in LiNi_0.5Mn_1.5O₄ through control of site disorder." Physical Chemistry Chemical Physics 14: 13515-13521 (Sept. 2012).
Abstract: High voltage spinel LiNi_0.5Mn_1.5O₄ is a very promising cathode material for lithium ion batteries that can be used to power hybrid electrical vehicles (HEVs). Through careful control of the cooling rate after high temperature calcination, LiNi_0.5Mn_1.5O₄ spinels with different disordered phase and/or Mn³⁺ contents have been synthesized. It is revealed that during the slow cooling process (<3 °C min⁻¹), oxygen deficiency is reduced by the oxygen intake, thus the residual Mn³⁺ amount is also decreased in the spinel due to charge neutrality. In situ X-ray diffraction (XRD) demonstrates that the existence of a disordered phase fundamentally changes the spinel phase transition pathways during the electrochemical charge–discharge process. The presence of an appropriate amount of oxygen deficiency and/or Mn³⁺ is critical to accelerate the Li⁺ ion transport within the crystalline structure, which is beneficial to enhance the electrochemical performance of LiNi_0.5Mn_1.5O₄. LiNi_0.5Mn_1.5O₄ with an appropriate amount of disordered phase offers high rate capability (96 mAh g⁻¹ at 10 °C) and excellent cycling performance with 94.8% capacity retention after 300 cycles. The fundamental findings in this work can be widely applied to guide the synthesis of other mixed oxides or spinels as high performance electrode materials for lithium ion batteries.

Xilin Chen, Wu Xu, Jie Xiao, Mark H. Engelhard, Fei Deng, Donghai Mei, Dehong Hu, Jian Zhang, Ji-Guang Zhang."Effects of cell positive cans and separators on the performance of high-voltage Li-ion batteries."Journal of Power Sources 213: 160-168 (Sept. 2012).
Abstract:The effects of different cell positive cans and separators on first-cycle Coulombic efficiency and long-term cycling stability of a high-voltage spinel cathode are investigated systematically. Compared to stainless steel (SS) positive cans, aluminum (Al)-clad SS-316 positive cans are much more resistant to oxidation at high voltages; therefore, the initial Coulombic efficiency of the batteries with Al-clad can is improved by more than 13%. Among the five separators studied in this work, the polyethylene (PE) separator exhibits the best electrochemical stability. The cells using LiCr_0.05Ni_0.45Mn_1.5O₄ as the cathode, an Al-clad positive can, and a PE separator exhibits a first-cycle Coulombic efficiency of about 90% and a capacity fading of only 0.01% per cycle.

Xilen Chen, Xiaolin Li, Fei Ding, Wu Xu, Jie Xiao, Yuliang Cao, Praveen Meduri, Jun Liu, Gordon L. Graff, Ji-Guang Zhang. "Conductive Rigid Skeleton Supported Silicon as High-Performance Li-Ion Battery AnodesConductive Rigid Skeleton Supported Silicon as High-Performance Li-Ion Battery Anodes."Nano Letters 12 (8): 4124-4130 (July 2012).
Abstract: A cost-effective and scalable method is developed to prepare a core–shell structured Si/B₄C composite with graphite coating with high efficiency, exceptional rate performance, and long-term stability. In this material, conductive B₄C with a high Mohs hardness serves not only as micro/nano-millers in the ball-milling process to break down micron-sized Si but also as the conductive rigid skeleton to support the in situ formed sub-10 nm Si particles to alleviate the volume expansion during charge/discharge. The Si/B₄C composite is coated with a few graphitic layers to further improve the conductivity and stability of the composite. The Si/B₄C/graphite (SBG) composite anode shows excellent cyclability with a specific capacity of ∼822 mAh·g^–1 (based on the weight of the entire electrode, including binder and conductive carbon) and ∼94% capacity retention over 100 cycles at 0.3 C rate. This new structure has the potential to provide adequate storage capacity and stability for practical applications and a good opportunity for large-scale manufacturing using commercially available materials and technologies.

Cao Y, L Xiao, ML Sushko, W Wang, b Schwenzer, J Xiao, Z Nie, LV Saraf, Z Yang, J Liu. "Sodium Ion Insertion in Hollow Carbon Nanowires for Battery Applications." Nano Letters 12 (7): 3783-3787 (June 2012).
Abstract: Hollow carbon nanowires (HCNWs) were prepared through pyrolyzation of a hollow polyaniline nanowire precursor. The HCNWs used as anode material for Na-ion batteries deliver a high reversible capacity of 251 mAh g^-1 and 82.2% capacity retention over 400 charge-discharge cycles between 1.2 and 0.01 V (vs Na⁺/Na) at a constant current of 50 mA g^-1 (0.2 C). Excellent cycling stability is also observed at an even higher charge-discharge rate. A high reversible capacity of 149 mAh g^-1 also can be obtained at a current rate of 500 mA g^-1 (2C). The good Na-ion insertion property is attributed to the short diffusion distance in the HCNWs and the large interlayer distance (0.37 nm) between the graphitic sheets, which agrees with the interlayered distance predicted by theoretical calculations to enable Na-ion insertion in carbon materials.

Wang W, W Xu, L Cosimbescu, D Choi, L Li, and Z Yang. "Anthraquinone with Tailored Structure for Nonaqueous Metal-Organic Redox Flow Battery." Chemical Communications 48(53):6669-6671. (May 2012).
Abstract: A nonaqueous, hybrid metal-organic redox flow battery based on tailored anthraquinone structure is demonstrated to have an energy efficiency of ~82% and a specific discharge energy density similar to these of aqueous redox flow batteries, which is due to the significantly improved solubility of anthraquinone in supporting electrolytes.

Jie Xiao, Xilin Chen, Peter V. Sushko, Maria L. Sushko, Libor Kovarik, Jijun Feng, Zhiqun Deng, Jianming Zheng, Gordon L. Graff, Zimin Nie, Daiwon Choi, Jun Liu, Ji-Guang Zhang, M.Stanley Whittingham."High-Performance LiNi_0.5Mn_1.5O₄ Spinel Controlled by Mn³⁺ Concentration and Site Disorder."Advanced Materials 24 (16): 2109-2116 (April 2012).
Abstract:The complex correlation between Mn³⁺ ions and the disordered phase in the lattice structure of high voltage spinel, and its effect on the charge transport properties, are revealed through a combination of experimental study and computer simulations. Superior cycling stability is achieved in LiNi_0.45Cr_0.05Mn_1.5O₄ with carefully controlled Mn³⁺ concentration. At 250th cycle, capacity retention is 99.6% along with excellent rate capabilities.

Xiaolin Li, Praveen Meduri, Xilin Chen, Wen Qi, Mark H. Engelhard, Wu Xu, Fei Ding, Jie Xiao, Wei Wang, Chongmin Wang, Ji-Guang Zhang, Jun Liu."Hollow core–shell structured porous Si–C nanocomposites for Li-ion battery anodes."Journal of Materials Chemistry 22: 11014-11017 (April 2012).
Abstract:Hollow core–shell structured porous Si–C nanocomposites with void space up to tens of nanometres are designed to accommodate the volume expansion during lithiation for high-performance Li-ion battery anodes. An initial capacity of ∼760 mA h g⁻¹ after formation cycles (based on the entire electrode weight) with ∼86% capacity retention over 100 cycles is achieved at a current density of 1 A g⁻¹. Good rate performance is also demonstrated.

Wang W, Z Nie, B Chen, F Chen, Q Luo, X Wei, G Xia, M Skyllas-Kazacos, L Li, and Z Yang. "A New Fe/V Redox Flow Battery Using Sulfuric/Chloric Mixed Acid Supporting Electrolyte." Advanced Energy Materials 2(4): 487-493. (Feb. 2012).
Abstract: A redox flow battery using Fe²⁺/Fe³⁺ and V²⁺/V³⁺ redox couples in chloric/sulfuric mixed-acid supporting electrolyte was investigated for potential stationary energy storage applications. The Fe/V redox flow cell using mixed reactant solutions operated within a voltage window of 0.5~1.35 V with a nearly 100% utilization ratio and demonstrated stable cycling over 100 cycles with energy efficiency > 80% and no capacity fading at room temperature. A 25% improvement in the discharge energy density of the Fe/V cell was achieved compared with the previous reported Fe/V cell using pure chloride-acid supporting electrolyte. Stable performance was achieved in the temperature range between 0°C and 50°C as well as using a microporous separator as the membrane. The improved electrochemical performance makes the Fe/V redox flow battery a promising option as a stationary energy storage device to enable renewable integration and stabilization of the electric grid.

Wu Xu, Adam Read, Phillip K. Koech, Dehong Hu, Chongmin Wang, Jie Xiao, Asanga B. Padmaperuma, Gordon L. Graff, Jun Liu, Ji-Guang Zhang."Factors affecting the battery performance of anthraquinone-based organic cathode materials."Journal of Materials Chemistry 22: 4032-4039 (Jan. 2012).
Abstract:Two organic cathode materials based on the poly(anthraquinonyl sulfide) structure with different substitution positions were synthesized and their electrochemical behavior and battery performance were investigated. The substitution positions on the anthraquinone structure, the type of binders for electrode preparation, and electrolyte formulations have been found to have significant effects on the performance of batteries containing these organic cathode materials. The polymer with less steric hindrance at the substitution positions has higher capacity, longer cycle life and better high-rate capability. Polyvinylidene fluoride binder and ether-based electrolytes are favorable for the high capacity and long cycle life of the anthraquinonyl organic cathodes.

Zhang J, L Li, Z Nie, B Chen, M Vijayakumar, S Kim, W Wang, B Schwenzer, J Liu, and Z Yang. "Effects of additives on the stability of electrolytes for all-vanadium redox flow batteries." Journal of Applied Electrochemistry 41(10 - Special Issue S1):1215-1221. (Oct 2011).
Abstract: The stability of the electrolytes for all-vanadium redox flow battery was investigated with ex-situ heating/cooling treatment and in situ flow-battery testing methods. The effects of inorganic and organic additives have been studied. The additives containing the ions of potassium, phosphate, and polyphosphate are not suitable stabilizing agents because of their reactions with V(V) ions, forming precipitates of KVSO₆ or VOPO₄. Of the chemicals studied, polyacrylic acid and its mixture with CH₃SO₃H are the most promising stabilizing candidates, which can stabilize all the four vanadium ions (V²⁺, V³⁺, VO²⁺, and VO₂⁺) in electrolyte solutions up to 1.8 M. However, further effort is needed to obtain a stable electrolyte solution with >1.8 M V⁵⁺ at temperatures higher than 40°C.

J Xiao, NA Chernova, S Upreti, X Chen, Z Li, Z Deng, D Choi, W Xu, Z Nie, GL Graff, J Liu, MS Whittingham, J Zhang."Electrochemical performances of LiMnPO₄ synthesized from non-stoichiometric Li/Mn ratio."Journal of Physical Chemistry Chemical Physics 13: 18099-18106 (Sept. 2011).
Abstract:In this paper, the influences of the lithium content in the starting materials on the final performances of as-prepared Li_xMnPO₄ (x hereafter represents the starting Li content in the synthesis step which does not necessarily mean that Li_xMnPO₄ is a single phase solid solution in this work) are systematically investigated. It has been revealed that Mn₂P₂O₇ is the main impurity when Li < 1.0 while Li₃PO₄ begins to form once x > 1.0. The interactions between Mn₂P₂O₇ or Li₃PO₄ impurities and LiMnPO₄ are studied in terms of the structural, electrochemical, and magnetic properties. At a slow rate of C/50, the reversible capacity of both Li_0.5MnPO₄ and Li_0.8MnPO₄ increases with cycling. This indicates a gradual activation of more sites to accommodate a reversible diffusion of Li⁺ ions that may be related to the interaction between Mn₂P₂O₇ and LiMnPO₄ nanoparticles. Among all of the different compositions, Li_1.1MnPO₄ exhibits the most stable cycling ability probably because of the existence of a trace amount of Li₃PO₄ impurity that functions as a solid-state electrolyte on the surface. The magnetic properties and X-ray absorption spectroscopy (XAS) of the MnPO₄·H₂O precursor, pure and carbon-coated Li_xMnPO₄ are also investigated to identify the key steps involved in preparing a high-performance LiMnPO₄.

Wang W, S Kim, B Chen, Z Nie, J Zhang, G Xia, L Li, and Z Yang. "A New Redox Flow Battery Using Fe/V Redox Couples in Chloride Supporting Electrolyte." Energy & Environmental Science 4(10):4068-4073. (June 2011).
Abstract: A new redox flow battery using Fe²⁺/Fe³⁺ and V²⁺/V³⁺ redox couples in chloride-supporting electrolyte was proposed and investigated for potential stationary energy storage applications. The Fe/V redox flow cell using mixed reactant solutions operated within a voltage window of 0.5~1.35 V with a nearly 100% utilization ratio and demonstrated stable cycling with energy efficiency around 80% at room temperature. Stable performance was also achieved in the temperature range between 0°C and 50°C. The improved stability and electrochemical activity over a broader temperature range over the current technologies (such as Fe/Cr redox chemistry) potentially eliminate the necessity of external heat management and use of catalysts, making the Fe/V redox flow battery a promising option as a stationary energy storage device to enable renewable integration and stabilization of the electrical grid.

Anqiang Pan, Ji-Guang Zhang, Guozhong Cao, Shuquan Liang, Chongmin Wang, Zimin Nie, Bruce W. Arey, Wu Xu, Dawei Liu, Jie Xiao, Guosheng Li, Jun Liu."Nanosheet-structured LiV₃O₈ with high capacity and excellent stability for high energy lithium batteries."Journal of Materials Chemistry 21: 10077-10084 (May 2011).
Abstract:Highly stable LiV₃O₈ with a nanosheet-structure was successfully prepared using polyethylene glycol (PEG) polymer in the precursor solution as the structure modifying agent, followed by calcination in air at 400 °C, 450 °C, 500 °C, and 550 °C. These materials provide the best electrochemical performance ever reported for LiV₃O₈ crystalline electrodes, with a specific discharge capacity of 260 mAh g^-1 and no capacity fading over 100 cycles at 100 mA g^-1. The excellent cyclic stability and high specific discharge capacity of the material are attributed to the novel nanosheets structure formed in LiV₃O₈. These LiV₃O₈ nanosheets are good candidates for cathode materials for high-energy lithium battery applications.

Anqiang Pan, Daiwon Choi, Ji-Guang Zhang, Shuquan Liang, Guozhong Cao, Zimin Nie, Bruce W. Arey, Jun Liu."High-rate cathodes based on Li₃V₂(PO₄)₃ nanobelts prepared via surfactant-assisted fabrication."Journal of Power Sources 196 (7):3646-3649 (April 2011).
Abstract:In this work, we have synthesized monoclinic Li₃V₂(PO₄)₃ nanobelts via a single-step, solid-state reaction process in a molten hydrocarbon. The as-prepared Li₃V₂(PO₄)₃ nanoparticles have a unique nanobelt shape and are ∼50-nm thick. When cycled in a voltage range between 3.0 V and 4.3 V at a 1C rate, these unique Li₃V₂(PO₄)₃ nanobelts demonstrate a specific discharge capacity of 131 mAh g⁻¹ (which is close to the theoretical capacity of 132 mAh g⁻¹) and stable cycling characteristics.

Schwenzer B, S Kim, M Vijayakumar, Z Yang, J Liu. "Correlation of structural differences between Nafion/polyaniline and Nafion/polypyrrole composite membranes and observed transport properties."Journal of Membrane Science 327 (1-2): 11-19 (Apr. 2011).
Abstract:Polyaniline/Nafion and polypyrrole/Nafion composite membranes, prepared by chemical polymerization, are studied by scanning electron microscopy, infrared and nuclear magnetic resonance spectroscopy. Differences in vanadium ion diffusion through the membranes and in the membranes' area specific resistance are linked to analytical observations that polyaniline and polypyrrole interact differently with Nafion. Polypyrrole, a weakly basic polymer, binds less strongly to the sulfonic acid groups of the Nafion membrane. Infrared spectroscopy results suggest that the hydrophobic polymer aggregates in the center of the Nafion channel rather than attaching to the hydrophilic walls containing sulfonic acid groups. This results in a drastically elevated membrane resistance and only slightly decreased vanadium ion diffusion compared to a Nafion membrane. Polyaniline, on the other hand, polymerizes along the sides of the Nafion pores and on the membrane surface, binding tightly to the sulfonic acid groups of Nafion, polyaniline's greater basicity possibly causing the difference in polymerization behavior. This leads to a more effective reduction in vanadium ion transport across the polyaniline/Nafion membranes and the increase in membrane resistance is less severe. The performance of selected polypyrrole/Nafion composite membranes is tested in a static vanadium redox cell. Increased coulombic efficiency, compared to a cell employing a pure Nafion membrane, further confirms the reduced vanadium ion transport through the composite membranes.

Li L, S Kim, W Wang, M Vijayakumar, Z Nie, B Chen, J Zhang, G Xia, JZ Hu, GL Graff, J Liu, and Z Yang. "A Stable Vanadium Redox-Flow Battery with High Energy Density for Large-scale Energy Storage." Advanced Energy Materials 1(3):394-400. (March 2011).
Abstract: The all-vanadium redox flow battery is a promising technology for large-scale renewable and grid energy storage, but is limited by the low energy density and poor stability of the vanadium electrolyte solutions. A new vanadium redox flow battery with a significant improvement over the current technology is reported in this paper. This battery uses sulfate-chloride mixed electrolytes, which are capable of dissolving 2.5 M vanadium, representing about a 70% increase in energy capacity over the current sulfate system. More importantly, the new electrolyte remains stable over a wide temperature range of -5 to 50°C, potentially eliminating the need for electrolyte temperature control in practical applications. This development would lead to a significant reduction in the cost of energy storage, thus accelerating its market penetration.

Yang Z, J Zhang, MCW Kintner-Meyer, X Lu, D Choi, JP Lemmon, and J Liu. "Electrochemical Energy Storage for Green Grid." Chemical Reviews 111(5):3577 -3613. (March 2011).
Abstract: Electrochemical Energy Storage (EES) is an established, valuable approach for improving the reliability and overall use of the entire power system (generation, transmission, and distribution [T&D]). Sited at various T&D stages, EES can be employed for providing many grid services, including a set of ancillary services such as (1) frequency regulation and load following (aggregated term often used is balancing services), (2) cold start services, (3) contingency reserves, and (4) energy services that shift generation from peak to off -peak periods. In addition, it can provide services to solve more localized power quality issues and reactive power support.

Deyu Wang, Jie Xiao, Wu Xu, Zimin Nie, Chongmin Wang, Gordon L. Graff, Ji-Guang Zhang."Preparation and electrochemical investigation of Li₂CoPO₄F cathode material for lithium-ion batteries."Journal of Power Sources 196 (4): 2241-2245 (Feb. 2011).
Abstract:In this paper, we report the electrochemical characteristics of a novel cathode material, Li₂CoPO₄F, prepared by solid-state reactions. The solid-state reaction mechanism involved in synthesizing the Li₂CoPO₄F also is analyzed in this paper. When cycled between 2.0 V and 5.0 V during cyclic voltammetry measurements, the Li₂CoPO₄F samples present one, fully reversible anodic reaction at 4.81 V. When cycled between 2.0 V and 5.5 V, peaks occurring at 4.81 V and 5.12 V in the first anodic scan evolved to one broad oxidative, mound-like pattern in subsequent cycles. Correspondingly, the X-ray diffraction (XRD) pattern of the Li₂CoPO₄F electrode discharged from 5.5 V to 2.0 V is slightly different from the patterns exhibited by a fresh sample and the sample discharged from 5.0 V to 2.0 V. This difference may correspond to a structural relaxation that appears above 5 V. In the constant current cycling measurements, the Li₂CoPO₄F samples exhibited a capacity as high as 109 mAh g^-1 and maintained a good cyclability between 2.0 V and 5.5 V vs. Li/Li⁺. XRD measurements confirmed that the discharged state is Li₂CoPO₄F. Combining these XRD results and electrochemical data proved that up to 1 mol Li⁺ is extractable when charged to 5.5 V.

Wu Xu, Nathan L. Canfield, Deyu Wang, Jie Xiao, Zimin Nie, Ji-Guang Zhang."A three-dimensional macroporous Cu/SnO₂ composite anode sheet prepared via a novel method."Journal of Power Sources 195 (21): 7403-7408 (Nov. 2010).
Abstract:A three-dimensional macroporous Cu/SnO₂ composite anode sheet for lithium ion batteries was prepared via a novel method that is based on selective reduction of metal oxides at appropriate temperatures. SnO₂ particles were imbedded on the Cu particles within the three-dimensionally interconnected Cu substrate, and the whole composite sheet was used directly as an electrode without adding extra conductive carbons and binders. Compared with the SnO₂-based electrode prepared via the conventional tape-casting method on Cu foil, the porous Cu/SnO₂ composite electrode shows significantly improved battery performance. This methodology produces limited wastes and is also adaptable to many other materials. It is a promising approach to make macroporous electrode for Li-ion batteries.

Jie Xiao, Wu Xu, Deyu Wang, Daiwon Choi, Wei Wang, Xiaolin Li, Gordon L. Graff, Jun Liu, Ji-guang Zhang."Stabilization of Silicon Anode for Li-Ion Batteries."Journal of the Electrochemical Society 157 (10): A1047-A1051 (Aug. 2010).
Abstract:Micrometer-sized Si particles with nanopore structures were investigated as anode material for Li-ion batteries. The porous structure of Si helps accommodate the large volume variations that occur during the Li insertion/extraction processes. To improve the electronic integrity of the Si-based anode, a two-step process was utilized. First, chemical vapor deposition (CVD) was used to enhance the electronic conductivity of individual Si particles by depositing a uniform carbon coating on both the exterior surfaces and the pores. Next, the electronic contact among silicon particles was improved by adding Ketjenblack (KB) carbon, which exhibits an elastic, chainlike structure that maintains a stable electronic contact among silicon particles during cycling. Using this approach, an anode with a reversible capacity of more than 1600 mAh/g after 30 cycles was obtained. The combination of the nanopore structure, CVD-coated carbon on the Si surface, and the elastic carbon (KB) among the silicon particles provides a cost-effective approach to utilize the large micrometer-sized Si particles in Li-ion batteries.

Wu Xu, NL Canfield, D Wang, J Xiao, Z Nie, XS Li, WD Bennett, CC Bonham, J Zhang. "An Approach to Make Macroporous Metal Sheets as Current Collectors for Lithium-Ion Batteries."Journal of the Electrochemical Society 157 (7): A765-A769 (May 2010).
Abstract:A simple method and approach is described to produce macroporous metal sheets as current collectors for lithium-ion batteries. This method is based on slurry blending, tape casting, sintering, and reducing of metal oxides and produces a uniform macroporous metal sheet. As an example, a macroporous copper sheet was prepared and used as the current collector for a silicon thin-film anode material. Such a porous copper substrate allows Si to have a much better adhesion, lower electrical contact resistance, higher capacity, capacity retention, and longer cycle life than on surface-roughened Cu foil and smooth Cu foil. This methodology produces very limited wastes and is also adaptable to many other materials such as Ni porous sheets at an industrial-scale production that is easy to be achieved.

Jie Xiao, Wu Xu, Daiwon Choi, Ji-Guang Zhang."Synthesis and Characterization of Lithium Manganese Phosphate by a Precipitation Method."Journal of the Electrochemical Society 157 (2): A142-A147 (Dec. 2010).
Abstract:LiMnPO₄ is synthesized from MnPO₄•H₂O precursor precipitated via a spontaneous reaction. These MnPO₄•H₂O nanoplates react quickly with the lithium source and form a pure phase of LiMnPO₄ that has good electrochemical properties. Thermogravimetric analysis was used to determine the optimum synthesis temperature. The crystallization of LiMnPO₄ occurs before 438°C. After full nucleation at 550°C, the samples exhibit a discharge capacity of 115 mAh/g^-1 (C/20 rate, 2.5-4.4 V) in the first cycle. The Coulombic efficiency is maintained at near 100% after the first few cycles. When the synthesis temperature decreases to 350°C, the particle size of the LiMnPO₄ is further reduced to 10-50 nm with a reversible capacity of more than 90 mAh g^-1. For 550°C synthesized LiMnPO₄, 73% of the initial capacity was retained at the 60th cycle. After high rate (5C) discharge, the reversible capacity of the LiMnPO₄ can be recovered to nearly the original value of 110 mAh g^-1 at the C/20 rate. This precipitation method is a cost effective approach for manufacturing high performance LiMnPO₄ cathode materials.