Highly concentrated LiTFSI – EC electrolytes for Li metal batteries

Concentrated electrolytes have the potential to increase the stability for batteries with lithium metal anodes. In this study, liquid electrolytes were created by mixing ethylene carbonate (EC), a solid at room temperature, with a high concentration of LiTFSI salt. The binary LiTFSI:EC highly concentrated electrolytes have the benefit of extremely low volatility as compared to conventional organic electrolytes and also allow for cycling vs. Li metal anodes. Using a LiTFSI:EC electrolyte with molar ratio 1:6, the coulombic efficiency for Li plating/stripping on Cu is 97% at a current density of 1 mA·cm−2 with a 2 mAh·cm−2 capacity, pointing to a practically useful performance. In a full cell set-up using a commercial LiFePO4 (LFP) cathode, the efficiency is maintained, proving compatibility. In comparison to other carbonate electrolytes, there is less accumulation of decomposition products on the surface of a cycled Li film, which in part explains the improved cycle life. In all, this electrolyte system sh...