In Situ Local Resistance Analysis of Mechanical Degradation in All‐Solid‐State Batteries

All-solid-state lithium-ion batteries (ASSLIBs) have attracted considerable attention as next-generation energy storage devices owing to their safety and high-energy density. The electronic transport properties of cathode composites employing inorganic solid electrolytes depend strongly on their microstructural characteristics. Although mechanical failure due to the loss of interparticle contact between cathode active materials directly affects the electron transport pathways, it has been largely overlooked as a critical degradation mechanism in ASSLIBs. In this study, an in situ local resistance analysis technique based on scanning spreading resistance microscopy was developed to visualize changes in the local electronic resistance distribution within ASSLIBs. In situ observations of cathode composites during charging revealed electrical isolation of some cathode active materials during the initial stages of charging, followed by an increase in interparticle contact resistance at higher charging potentials. Furthermore, electrochemical simulations based on a three-dimensional model qualitatively described the evolution of the experimental voltage profiles, highlighting mechanical degradation due to the interparticle contact loss between cathode active materials. The method proposed herein provides novel insights into mechanically induced electronic contact loss in active materials that cannot be evaluated by conventional topographical and morphological analyses.