Solid electrolyte production method

A method of producing a solid electrolyte comprising a lithium element, a sulfur element, a phosphorus element and a halogen element, said method comprising a first step of mixing two or more compounds satisfying (1) and a complexing agent 1 satisfying (2), and a second step of further mixing in a complexing agent 2 satisfying (3) after the first step:

• (1) a compound containing one or more selected from the group consisting of a lithium element, a sulfur element, a phosphorus element and a halogen element;
• (2) a complexing agent 1 capable of forming a complex containing Li3PS4 and a halogen element, wherein the complexing agent 1 contains a nitrogen element;
• (3) a complexing agent 2 other than the complexing agent 1, capable of forming a complex containing Li3PS4, wherein the complexing agent 2 contains an oxygen element;
• and
• wherein said two or more compounds satisfying (1), taken together, comprise all of a lithium element, a sulfur element, a phosphorus element and a halogen element.