Overview

High Voltage Aqueous Batteries

State-of-the-art Lithium-ion batteries (LIBs) face safety and environmental concerns due to utilization of the flammable organic electrolyte. Aqueous electrolytes are a natural replacement, however, they are limited by the narrow electrochemical stability window (~1.23V). We proposed a highly-concentrated aqueous electrolyte, named Water-in-Salt electrolyte (WiSE), whose electrochemical stability window was expanded to ~3.0 V with the formation of an electrode/electrolyte interphase, far exceeding what is typically obtained from aqueous electrolytes. The surface of the electrode is kinetically protected while operating beyond the thermodynamic limit of water. Based on WiSE and its derivates, we have achieved the further expansion of the aqueous window, which allows for more energetic electrode couples to deliver higher energy density. The successful fabrication of this brand-new class of aqueous Li-ion battery chemistry will significantly reshape the energy storage landscape.

 Representative publications:

  • L. Suo, D. Oh, Y. lin, Z. Zhuo,O. Borodin, T. Gao, F. Wang, A. Kushima, Z. Wang,H. Kim, Y. Qi, W. Yang, F. Pan, J. Li, Ju; K. Xu, C. Wang, How Solid-Electrolyte-Interphase Forms in Aqueous Electrolytes, Journal of the American Chemical Society2017, 139, 18670−18680.

  • C. Yang, J.Chen, T. Qing, X. Fan, W. Sun, A. v. Cresce, M. S. Ding, M.A. Schroeder, N. Eidson, C. Wang, K. Xu, “4.0 V Aqueous Li-ion Batteries,” Joule2017, 1, 122–132.

  • L. Suo, O. Borodin, T. Gao, M. Olguin, J. Ho, X. Fan, C. Luo, C. Wang, K. Xu. Water-in-Salt Electrolyte Enables High Voltage Aqueous Li-ion Chemistries. Science2015, 350, 938.

All-Solid-State Batteries

All-solid-state batteries hold great promise to improve the safety of today’s lithium ion batteries. However, the performance of the all-solid-state batteries are largely limited by the interfacial resistance between electrode and electrolyte. The energy density of all-solid-state batteries cannot compete with the conventional liquid-electrolyte batteries unless lithium metal is used as the anode. We are interested in understanding the origins of high interfacial resistance between solid electrodes and electrolyte. We demonstrated that the electrochemical stability window of solid electrolytes are overestimated from the conventional measurements, and we proposed to use the Li/electrolyte/electrolyte+carbon cell to approach the intrinsic electrochemical stability of solid electrolytes. By taking advantage of the reversible decomposition of solid electrolyte, we were able to make a battery from a single material, a revolutionary concept to eliminate the highly resistive interface. Meanwhile, the decomposition of the solid electrolytes may also lead to large interfacial resistance. We then extended our understandings about the electrode/electrolyte interface to realize high-performance all-solid-state batteries by interphase engineering and nanostructure design of electrode composite. We are also working on lithium metal anode for all-solid-state batteries, particularly on lithium dendrite suppression.

Representative publications:

Multivalent Batteries

Due to their high natural abundance in the earth crust, large capacity and environmental compatibility,  Mg, Al, Ca and Zn metals serve as promising alternatives for Li as battery anodes. However, the electrochemistry based on multivalent-ions is significantly different from that of lithium-ion. For example, the kinetics and the stability of intercalation and conversion chemistry in cathode materials, composition of the solid electrolyte interface, the reversibility and morphology of metal stripping and deposition, electrochemical stability of the electrolyte, and so forth are just a few of the differences from monovalent-ion battery chemistries. The research and development of these systems is still in its infancy, our work focuses on finding appropriate cathode materials and developing novel electrolytes to enhance the energy density and cycle stability of multivalent batteries.

Representative publications:

Organic Active Materials

Organic electrode materials offering the advantages of lightweight, abundance, low cost, sustainability and recyclability are promising for sustainable alkali-ion batteries. However, the low conductivity, high solubility and large volume change inhibit the development of organic electrode materials. To overcome these challenges, our work focuses on investigating the role of particle size, thin film coating, electrolyte, self-healing effect, and electron-donating/withdrawing functional groups in organic batteries. We are also interested in developing new organic materials based on carbonyl, imine and azo groups for long lifetime and fast charge/discharge organic batteries, and performing the fundamental study for the reaction mechanism and kinetics with in situ and ex situ techniques.

Representative publications:

  • C. Luo, O. Borodin, X. Ji, S. Hou, K.J. Gaskell, X. Fan, J. Chen, T. Deng, R. Wang, J. Jiang, C. Wang, Azo compounds as a family of organic electrode materials for alkali-ion batteries, Proceedings of the National Academy of Sciences2018, 115, 2004-2009.

  • Chao Luo, Xiulin Fan, Zhaohui Ma, Tao Gao, Chunsheng Wang, “Self-healing Chemistry between Organic Material and Binder for Stable Sodium Ion Batteries,” Chem, Accepted

  • C. Luo, R. Huang, R. Kevorkyants, M. Pavanello, H. He, C. Wang. Self-assembled Organic Nanowires for High Power Density Lithium Ion Batteries. Nano Letters, 2014, 14, 1596–1602.

Electrolyte for High-voltage Lithium Batteries

The electrolyte is the culprit for poor battery performance under aggressive electrochemistries in lithium based battery and innovation is in absolute demand to keep up with the advancement of cathode materials and application of high capacity anode (such as lithium metal and silicon). The modern Li-ion batteries are exclusively based on ethylene carbonate (EC) electrolytes, which stabilize the graphite anode via formation of an SEI without impeding (de)lithiation. However, these EC-based electrolytes do not have sufficient anodic stability to sustain the aggressive cathode materials for the next generation battery chemistries, such as 4.4 V LiNi0.8Mn0.1Co0.1O2 (NMC 811) and > 5.0 V high voltage cathodes. Besides, these EC-based electrolytes are not stable against the Li metal anode due to the intrinsic reactivity of carbonyl functionality (C=O), confining the columbic efficiency of Li plating/striping to a constantly low level (< 90%). The inefficient plating and stripping also accompanies the detrimental Li dendrite formation. Our work focuses on developing novel non-aqueous electrolytes for highly reversible and high-energy Li battery systems.

Representative publications:

  • X. Fan,† L. Chen,† O. Borodin, X. Ji, J. Chen, S. Hou, T. Deng, J. Zheng, C. Yang, S. Liou, K. Amine, K. Xu, C. Wang, Non-flammable Electrolyte Enables Li-Metal Batteries with Aggressive Cathode Chemistries, Nature Nanotechnology2018, Accepted.

  • X. Fan,† E. Hu,† X. Ji, Y. Zhu, F. Han, S. Hwang, J. Liu, S. Bak, Z. Ma, T. Gao, S.-C. Liou, J. Bai, X.-Q. Yang, Y. Mo, K. Xu, D. Su, C Wang, High Energy-Density and Reversibility of Iron Fluoride Cathode Enabled Via an Intercalation-Extrusion Reaction, Nature Communications2018, Accepted.

  • X. Fan, L. Chen, X. Ji, T. Deng, S. Hou, J. Chen, J. Zheng, F. Wang, J. Jiang, K. Xu, C. Wang, “Highly fluorinated interphases enable high voltage Li metal batteries” Chem2018, 4, 174-185

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