Synthesis and ionic conductivity of an argyrodite-type Li6SbS5I electrolyte

Sulfide-based lithium ionic conductors show high conductivity. Many studies have focused on improving conductivity and understanding their migration mechanisms. Argyrodite-type Li6PS5X (X = Cl, Br, I) electrolytes with P cations are among the main subjects of research regarding the substitution of anions and cations. In this study, argyrodite-type thioantimonate electrolytes were prepared to extend the compositions of argyrodite-type electrolytes and study their mechanisms of ion conduction. An argyrodite-type crystal precipitated in the composition of Li6SbS5I, but was not obtained in the composition of Li6SbS5X (X = Cl, Br). This could be explained by the difference in size between the SbS4 tetrahedra and halide anions. Argyrodite-type Li6SbS5I displayed a conductivity of 2.1 × 10−6 S cm−1 at 25 °C, which was higher than that of Li6PS5I. Comparing these crystal structures, only the lattice parameters differed, and the site positions and occupancies were almost identical. However, the pathways limiting 3D migration were intra-cage jumps within Li6SbS5I and inter-cage jumps within Li6PS5I, based on their bond valence-based energy landscapes. The bottleneck sizes for ionic conduction in Li6SbS5I is better than that of Li6PS5I. This difference was due to the lattice parameters derived from the SbS4 and PS4 tetrahedra. This study reveals a strategy to predict the producibilities and increase the conductivities of argyrodite-type electrolytes.