SOLID ION CONDUCTOR COMPOUND, SOLID ELECTROLYTE INCLUDING SOLID ION CONDUCTOR COMPOUND, ELECTROCHEMICAL CELL INCLUDING SOLID ION CONDUCTOR COMPOUND, AND METHOD OF PREPARING SOLID ION CONDUCTOR COMPOUND

A compound represented by Formula 1 and having an argyrodite-type crystal structure: LiM1PSM2M3 Formula 1 In Formula 1, M1 is at least one metal element of Group 1 to Group 15 of the periodic table, except Li, M2 is SO, M3 is at least one element of Group 17 of the periodic table; and 4≤x≤8, 0≤v