SOLID ION CONDUCTOR, SOLID ELECTROLYTE INCLUDING THE SOLID ION CONDUCTOR, ELECTROCHEMICAL CELL INCLUDING THE SOLID ION CONDUCTOR, AND PREPARATION METHOD OF THE SAME

A compound represented by the Formula 1 and having an argyrodite-type crystal structure: LiM1M2PSM3 Formula 1 wherein M1 is at least one element of Group 2 or Group 11 of the periodic table, M2 is at least one metal element other than Li of Group 1 of the periodic table, M3 is at least one element of Group 17 of the periodic table, and wherein 4≤a≤8, 0