A dual-halogen electrolyte for protective-layer-free all-solid-state lithium batteries

Halide-type solid electrolytes (SEs) have emerged as a new class of promising Li+ conductors due to their high ionic conductivity, good deformability and excellent oxidation stability. Nevertheless, to move a step closer to the application in all-solid-state lithium batteries (ASSLBs), the poor compatibility against metal anode for halide SEs needs to be addressed. Herein, a dual-halogen trigonal SE, Li2ZrCl6-xFx is developed. With the proper incorporation of F, the SE can maintain high ionic conductivity and considerable moisture stability. Moreover, protective-layer-free ASSLBs prepared from the single SE and high-voltage cathode materials LiCoO2 can be reversibly cycled in the voltage window of 2.52–4.32 V (versus Li+/Li) with a high initial coulombic efficiency of 95.57%, and maintain 76% of the initial capacity after 70 cycles. The good electrochemical performance is originated from the in-situ formed interface protective layer between SE and Li alloy, as demonstrated by X-ray photoelectron spectroscopy and computational characterizations. This work indicates that developing mixed halogen-based SEs is a cost-effective way to improve the stability of halide SEs against alkali metal anode, and could accelerate the application for high-voltage ASSLBs.