Degradation of an argyrodite-type sulfide solid electrolyte by a trace of water: A spectroscopic analysis

Sulfide-based solid electrolytes have gained attention for application in solid-state lithium batteries, due to their high ionic conductivities, suitable mechanical properties, and wide electrochemical windows. However, the sulfide in these materials is very hygroscopic, and can react with traces of water, thus generating toxic H2S gas. This reduces the lithium-ion conductivity, which plays an important role in solid state batteries. On the contrary, it has also been found that the conductive performance of a sulfide solid electrolyte exposed to water can be partially recovered by a suitable heat treatment. In this study, multiple spectroscopic analyses using X-ray photoelectron spectroscopy, Raman spectroscopy, nuclear magnetic resonance spectroscopy, and diffuse reflectance infrared Fourier-transform spectroscopy were performed on an argyrodite-type sulfide solid electrolyte to elucidate the degradation mechanism under a small amount of moisture, as in a dry room, as well as the recovery mechanism of a degraded sample by vacuum heat treatment. We found that the degradation behavior of the PS43− unit and the adsorption/desorption of water molecules on the surface of the electrolyte were correlated with the lithium-ion conductivity.