Hydration and Dehydration Behavior of Li₄SnS₄ for Applications as a Moisture-Resistant All-Solid-State Battery Electrolyte

All-solid-state batteries are promising energy storage devices owing to their high safety and energy density. Sulfide-based solid electrolytes have high ionic conductivities and are ductile. Although sulfide electrolytes are candidates for all-solid-state batteries, they are moisture-sensitive. Li 4 SnS 4 electrolytes can overcome some of these weaknesses and show the suppressed evolution of H 2 S gas in a humid environment. However, the suppression mechanism is unclear, making the design of moisture-resistant sulfide electrolytes challenging. Therefore, we investigated the structural changes of Li 4 SnS 4 in humid N 2 . X-ray structural analysis revealed that Li 4 SnS 4 was hydrated to Li 4 SnS 4 ·4H 2 O without generating H 2 S gas. Furthermore, the hydrate could be reversibly dehydrated by heat treatment to the original sulfide, suggesting that the formation of stable hydrates suppresses the generation of H 2 S gas. These findings will aid in the design of moisture-resistant sulfide materials.