Characterizing the Structural Change of Na₃PS₄ Solid Electrolytes in a Humid N₂ Atmosphere

Abstract

Sulfide solid electrolytes (SSEs) show a higher ionic conductivity than oxide solid electrolytes. However, SSEs generally exhibit a moisture-sensitive nature. This study focused on the degradation mechanisms of SSEs in a humid N2 atmosphere, and Na3PS4 (NPS) was selected as the SSE. The structural changes during exposure to humidified N2 were monitored using a system comprising an X-ray diffractometer, a humidity regulator, and an H2S sensor. Structural evaluations revealed that the exposed NPS was a hydrate, and it was recovered to the NPS crystal phase by the removal of adsorbed/hydrated water molecules using regenerating treatments, such as heating at 200 °C or drying under reduced pressure with/without heating. The regenerated NPS showed an ionic conductivity of 5.3 × 10–5 S cm–1 at 25 °C, which is 40 times that of the exposed NPS. These results suggest that exposed NPS can be structurally and conductively regenerated to the NPS crystal phase using regeneration treatments.