Mechanochemical Synthesis and Characterization of Metastable Hexagonal Li4SnS4 Solid Electrolyte

A new crystalline lithium-ion conducting material, Li4SnS4 with an ortho-composition, was prepared by a mechanochemical technique and subsequent heat treatment. Synchrotron X-ray powder diffraction was used to analyze the crystal structure, revealing a space group of P63/mmc and cell parameters of a = 4.01254(4) Å and c = 6.39076(8) Å. Analysis of a heat-treated hexagonal Li4SnS4 sample revealed that both lithium and tin occupied either of two adjacent tetrahedral sites, resulting in fractional occupation of the tetrahedral site (Li, 0.375; Sn, 0.125). The heat-treated hexagonal Li4SnS4 had an ionic conductivity of 1.1 × 10–4 S cm–1 at room temperature and a conduction activation energy of 32 kJ mol–1. Moreover, the heat-treated Li4SnS4 exhibited a higher chemical stability in air than the Li3PS4 glass-ceramic.