All-Solid-State Garnet Type Lithium-Sulfur Battery Enabled by Inorganic Interfacial Engineering and 3D Electrolyte Architectures

Current progress in Lithium-Sulfur (Li-S) batteries using garnet electrolytes have involved use of flammable liquid or polymer catholytes to achieve stable cycling due to poor ionic conduction properties of sulfur and the poor interface between sulfur cathodes and LLZO. However, this compromises the safety of “solid-state” batteries. In this work, we propose a novel design which coats our sulfur cathode (Li-S redox material: sulfurized polyacrylonitrile, SPAN) with lithium bis(fluorosulfonyl)imide (LiFSI) to improve SPAN/SPAN and cathode/LLZO interfaces and to provide ionic conductivity in the composite cathode. The LiFSI salt has an ionic conductivity of 1.2×10^-4 S/cm at 60 Celsius degree and 1.9×10^-5 S/cm at 22 Celsius degree, and it is stable in the charge/discharge electrochemical window of SPAN. LiFSI creates Li+ ionic conductive pathways which enhance Li⁺ ion transport kinetics through the cathode and its interface with LLZO. With our thin bilayer LLZO architecture^1,2 we are the first to demonstrate an all-solid-state garnet Li-S batteries that achieved an average discharge capacity of 1400 mAh/g at 0.167 mA/cm² for over 40 cycles and 437 mAh/g at a discharge current density of 0.84 mA/cm² for over 200 cycles both at 60 Celsius degree, using a sulfur mass loading of 1 mg/cm². With a new 3D column architecture, we extended sulfur loading to 7mg/cm² and achieved an exceptionally high discharge capacity of 1569 mAh/g at 0.03C (~0.35 mA/cm²) at 60 Celsius degree using our all-solid-state garnet Li-S battery design, which corresponding to an energy density of 338 Wh/kg and 797 Wh/L.<br/><br/>References:<br/>1. B. Liu, L. Zhang, S. Xu, D. W. McOwen, Y. Gong, C. Yang, G. R. Pastel, H. Xie, K. Fu, J. Dai, C. Chen, E. D. Wachsman, L. Hu, Energy Storage Mater. 14, 376–382 (2018).<br/>2. K. Fu, Y. Gong, G. T. Hitz, D. W. McOwen, Y. Li, S. Xu, Y. Wen, L. Zhang, C. Wang, G. Pastel, J. Dai, B. Liu, H. Xie, Y. Yao, E. D. Wachsman, L. Hu, Energy Environ. Sci. 10, 1568–1575 (2017).