Spectroscopic Investigation of Li3PS4-LiI Sulfide-Based Glass-Ceramic Solid Electrolytes after Moisture Exposure

Abstract

Sulfide-based solid electrolytes (SEs) have been extensively studied because of their high lithium-ion conductivities. Among the solid electrolytes, glass or glass-ceramic SEs have suitable thermoplastic characteristics for battery manufacturing processes. However, sulfide-based SEs react strongly with moisture, resulting in toxic H2S gas generation and reduced lithium-ion conductivity. Although the effects of moisture exposure on sulfide-based SEs have been investigated by some researchers, related studies are scarce and further research is required. In this study, X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were performed to investigate the structural changes in a glass-ceramic sulfide-based SE, viz., Li3PS4-0.2LiI before and after exposure to moisture, focusing on the changes in the surface chemical species, adsorbed H2O, and related species. In addition, SE samples exposed to moist air were subjected to recovery treatment by vacuum heating. XPS and DRIFTS analyses revealed that the main reason for the decrease in the lithium-ion conductivity of the glass-ceramic SE after moisture exposure is the adsorption of water onto the SE surface and/or its hydration. In particular, the H2O layer adsorbed to the SE surface physically and/or chemically decreases the lithium-ion conductivity at the grain boundaries (i.e., SE/SE interface), although the bulk conduction is maintained.