Chemical stability of Li4PS4I solid electrolyte against hydrolysis

Sulfide solid electrolytes in the Li3PS4-LiI system are promising for all-solid-state batteries owing to their high ionic conductivity in the order of 10(-4) S cm(-1) and electrochemical stability. Nonetheless, the low chemical stability tendency of sulfide-based materials under ambient atmosphere is a critical issue due to the generation of toxic H2S gas. In this study, the chemical stability of Li4PS4I (Li3PS4-LiI) solid electrolyte under ambient atmosphere was investigated and compared with that of Li3PS4 to analyze the effect of the incorporation of LiI on the chemical stability of sulfide-based electrolytes. No generation of H2S gas was detected in the Li4PS4I solid electrolyte after an exposure of 60 min to the ambient atmosphere with high relative humidity of 40%. The hydrolysis suppression is attributed to the formation of LiI center dot H2O, acting as a protective barrier between PS43- units in the electrolyte and H2O molecules in air. The structural reversibility of Li4PS4I by simple drying at 180 degrees C was confirmed and the solid electrolyte exhibited an ionic conductivity of 10(-4) S cm(-1) at room temperature, similar to that of the sample before the exposure to the ambient atmosphere.