METHOD FOR PRODUCING SULFIDE SOLID ELECTROLYTE

A method for producing a sulfide solid electrolyte includes a firing step of firing a raw material containing LiS in a hydrogen sulfide-containing atmosphere at a temperature of 300° C. or higher, LiS having a purity of 50 to 90% by mass at the start of firing. The LiS may contain impurities including at least one of LiOH, LiO, LiHCO, and LiCO. In the firing step, it is preferable that a concentration of a hydrogen sulfide in the hydrogen sulfide-containing atmosphere is 50 volume % or more. It is preferable that the raw material further contains PSand LiX (X represents at least one type of elemental halogen), and the sulfide solid electrolyte has an argyrodite-type crystal structure.