Surface Reaction of Argyrodite-Type Sulfide Solid Electrolyte in Air with a Dew Point of −20°C

Sulfide solid electrolytes are expected to be used for practical all solid-state batteries because they combine high formability with high ionic conductivity. However, unlike oxide and organic solid electrolytes, sulfide solid electrolytes have problems such as toxic hydrogen sulfide generation and conductivity degradation due to even slight moisture. In this study, we investigated the details of the denaturation of argyrodite-type sulfide solid electrolyte (ASSE) by a small amount of water, with the aim of further increasing the water resistance of ASSE. The denaturation of ASSE in air with moisture at the dew point −20 °C, which is comparable to a typical dry room environment, was already reported; EIS and XRD revealed only the surface of ASSE degraded by moisture in the air. Surface analysis was also conducted and revealed that surface degraded components such as Li2CO3, Li2SO4 are formed on the surface. In this study, the effects of oxygen and carbon dioxide were also examined in addition to water. Details of the denaturation was investigated using XRD, XPS, IR and Raman. This investigation revealed that the denaturant is formed only on the surface by moisture, that the denaturant is oxidized by oxygen, and that Li2CO3 is formed by carbon dioxide. More details will be discussed at the meeting site.