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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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⁺.

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.

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.

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.

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.

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.

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.

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.

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.