Mechanochemical Synthesis and Characterization of\nMetastable Hexagonal Li<sub>4</sub>SnS<sub>4</sub> Solid Electrolyte

A new crystalline\nlithium-ion conducting material, Li₄SnS₄ with\nan <i>ortho</i>-composition, was prepared\nby a mechanochemical technique and subsequent heat treatment. Synchrotron\nX-ray powder diffraction was used to analyze the crystal structure,\nrevealing a space group of <i>P</i>6₃/<i>mmc</i> and cell parameters of <i>a</i> = 4.01254(4)\nÅ and <i>c</i> = 6.39076(8) Å. Analysis of a heat-treated\nhexagonal Li₄SnS₄ sample revealed that both\nlithium and tin occupied either of two adjacent tetrahedral sites,\nresulting in fractional occupation of the tetrahedral site (Li, 0.375;\nSn, 0.125). The heat-treated hexagonal Li₄SnS₄ had an ionic conductivity of 1.1 × 10^–4 S\ncm^–1 at room temperature and a conduction activation\nenergy of 32 kJ mol^–1. Moreover, the heat-treated\nLi₄SnS₄ exhibited a higher chemical stability\nin air than the Li₃PS₄ glass-ceramic.