Abstract: The present invention relates to a sulfide-based solid electrolyte for an all-solid lithium secondary battery, and to a method for preparing the sulfide-based solid electrolyte. The present invention has an effect of providing a sulfide-based solid electrolyte that has excellent stability with respect to lithium metal and has excellent ion conductivity, while having high crystallinity. The present invention has an effect of providing a method for preparing a sulfide-based solid electrolyte that has excellent stability with respect to lithium metal and has excellent ion conductivity, while having high crystallinity even when heat-treated at a low temperature.

Abstract: A sulfide solid electrolyte includes: an ionic conductor including a PS43? unit, a P2S64? unit, and a P2S74? unit; and a lithium compound containing a halogen element, wherein a molar ratio of the P2S64? unit to the PS43? unit is about 1:1 to about 5:1, and a molar amount of the P2S74? unit with respect to the total molar amount of the PS43? unit, the P2S64? unit, and the P2S74? unit is greater than 0 to about 60%.