Solid electrolyte

A method of producing a crystallized solid electrolyte wherein the solid electrolyte has a peak in a peak region of 75.0 ppm or more and 80.0 ppm or less in a 31P-NMR spectrum, the method comprising:

• producing a solid electrolyte from a raw material and a compound comprising a halogen element;
• and
• heating the solid electrolyte to obtain the crystallized solid electrolyte;
• wherein the raw material comprises:
• (i) lithium sulfide and phosphorus sulfide, (ii) sulfur and phosphorus, (iii) phosphorus sulfide and sulfur, or (iv) phosphorus sulfide, sulfur, and phosphorus.