Energy Storage Publications

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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