Sulfide-based solid electrolyte, all-solid secondary battery including the same, and method of preparing the sulfide-based solid electrolyte

A method of preparing a sulfide solid electrolyte, the method comprising:

• providing a mixture comprising
• a starting material composition comprising elements P, S, and Li, and
• a lithium compound comprising a halogen element;
• and
• treating the mixture to prepare the sulfide solid electrolyte,
• wherein the sulfide solid electrolyte comprises
• an ionic conductor comprising a PS43− unit, a P2S64− unit, and a P2S74− unit, and
• the 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
• wherein 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% .

A sulfide solid electrolyte, comprising:

• an ionic conductor comprising a PS43− unit, a P2S64− unit, and a P2S74− unit;
• and
• a lithium compound comprising a halogen element, wherein an amount of the lithium compound is about 3 weight percent to about 22 weight percent with respect to the total weight of the sulfide solid electrolyte,
• 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%, and
• wherein the sulfide solid electrolyte is a reaction product of a starting material composition comprising the elements P, S, and Li, and the lithium compound containing the halogen element.