Formation Process of Halogen-Rich Argyrodite: Elemental Disordering of Atomic Arrangement at the 4a and 4d Sites in a Heat Treatment

Sulfide-based solid electrolytes are increasingly recognized as crucial materials for the practical application of all-solid-state batteries. In particular, halogen-rich argyrodites, featuring hybrid doping with chlorine and bromine, demonstrate that the Li-ion conductivity is influenced by the degree of elemental disorder among chlorine, bromine, and sulfur at the anion sites (4a, 4d). This study employed in situ XRD/PDF during the annealing process of sample synthesis to investigate the formation of disorder at these anion sites. Initially, a sulfur-rich argyrodite phase formed at lower annealing temperatures (200–320 °C). Subsequently, in the higher temperature range (320–460 °C), lithium halide amorphization and thermal diffusion led to the formation of a halogen-rich argyrodite phase. This phase is characterized by the substitution of sulfur with halogen at the 4a/4d sites in argyrodites.