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. Li4SnS4 electrolytes can overcome some of these weaknesses and show the suppressed evolution of H2S 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 Li4SnS4 in humid N2. X-ray structural analysis revealed that Li4SnS4 was hydrated to Li4SnS4·4H2O without generating H2S 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 H2S gas. These findings will aid in the design of moisture-resistant sulfide materials.