Fluoride‐rich Sulfide Solid Electrolyte With Ultrahigh Air Stability for All‐Solid‐State Batteries

Abstract Argyrodites are among the most promising sulfide‐based solid electrolytes (SEs) due to their high ionic conductivity and ductility. However, the poor atmospheric stability of sulfide‐based SEs caused by the side reaction with moisture, which generates toxic H 2 S gas and degrades its high ionic conductivity and low electronic conductivity, has limited the commercialization of ASSBs. Herein, the preparation of sulfide‐based SEs consisting of a Li 6 PS 5 Cl (LPSCl) core and fluoride‐rich LPSCl shell are described using a facial fluorine treatment following an annealing process to improve atmospheric stability. Most importantly, with the benefit of a fluoride‐rich LPSCl shell, the prepared SE exhibits well‐kept low electronic conductivity even after exposure to an atmosphere with 20% relative humidity at 25 °C, resulting in an improvement in electrochemical properties without short‐circuiting. These results indicate that the fluoride‐rich LPSCl shell effectively suppresses side reactions with moisture and mitigates the extent of irreversible side reactions. These experimental results and associated first‐principles density functional theory (DFT) models profoundly understand the enhanced air stability of F‐LPSCl. Full cells employing an air‐exposed F‐LPSCl exhibit an enhanced initial discharge capacity of 168.5 mAh g −1 at 0.05 C, cycling stability at 0.3 C over 500 cycles, and rate capability.