METHOD OF PREPARING SOLID ELECTROLYTE AND ALL-SOLID BATTERY INCLUDING SOLID ELECTROLYTE PREPARED BY THE METHOD

A method of preparing a solid electrolyte and an all-solid battery including a solid electrolyte prepared by the method, the method including: contacting a first solvent and a first starting material comprising an alkali metal, sulfur, phosphorus, an element M, or a combination thereof to form a first solution; precipitating a first precursor from the first solution; contacting a second solvent, the first precursor, and a second starting material comprising an alkali metal, sulfur, phosphorus, an element M, or a combination thereof to form a second solution; precipitating a second precursor from the second solution; and heat treating the second precursor to prepare the solid electrolyte, wherein the element M comprises an element of Group 14 of the Periodic Table of the Elements, and the element M and the alkali metal in the first starting material and the second starting material are the same or different.