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

Sulfide-based solid electrolytes(SEs) have been extensivelystudiedbecause of their high lithium-ion conductivities. Among the solidelectrolytes, glass or glass-ceramic SEs have suitable thermoplasticcharacteristics for battery manufacturing processes. However, sulfide-basedSEs react strongly with moisture, resulting in toxic H2S gas generation and reduced lithium-ion conductivity. Although theeffects of moisture exposure on sulfide-based SEs have been investigatedby some researchers, related studies are scarce and further researchis 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-ceramicsulfide-based SE, viz., Li3PS4-0.2LiI beforeand after exposure to moisture, focusing on the changes in the surfacechemical species, adsorbed H2O, and related species. Inaddition, SE samples exposed to moist air were subjected to recoverytreatment by vacuum heating. XPS and DRIFTS analyses revealed thatthe main reason for the decrease in the lithium-ion conductivity ofthe glass-ceramic SE after moisture exposure is the adsorption ofwater onto the SE surface and/or its hydration. In particular, theH(2)O layer adsorbed to the SE surface physically and/orchemically decreases the lithium-ion conductivity at the grain boundaries(i.e., SE/SE interface), although the bulk conduction is maintained.