Multimodal Analysis of Short- and Medium-Term Degradation in Multilayered All-Solid-State Batteries

All-solid-state batteries (ASSBs) using oxide-type solid electrolytes (SEs) have attracted attention, owing to their high chemical stability and intrinsic safety. However, large-scale fabrication remains challenging because of their low sintering density and insufficient solid–solid contact between particles. Recently, multilayered ASSBs constructed by alternately stacking the electrode and SE layers have been commercialized, but their degradation behavior during charge–discharge cycling remains unclear. In this study, multilayered ASSBs were examined for the short- and medium-term degradation behaviors during charge–discharge cycling. A multimodal analysis, combining scanning electron microscopy (SEM) and Raman spectroscopy, was employed to observe cross sections in the pristine state and after cycling. The charge–discharge profiles exhibited discontinuous changes in voltage plateaus and capacities at 303, 313, and 323 K, whereas a monotonic decrease in capacity was observed at 333 K. SEM revealed the formation of a decomposition layer, particularly at 303 K, suggesting the degradation of the SE and the electrode active material. Raman spectroscopy further clarified significant peak shifts at the SE/electrode interfaces, reflecting a collapsed structure of the SE and supporting the SEM observations. Overall, multilayered oxide-type ASSBs undergo decomposition at the interfaces and within the electrode layer, leading to discontinuous capacity changes at lower temperatures during cycling.