Linking Void and Interphase Evolution to Electrochemistry in Solid-State Batteries Using Operando X-Ray Tomography

Despite progress in solid-state battery engineering, our understanding of the chemo-mechanical phenomena that govern electrochemical behavior and stability at solid-solid interfaces remains limited compared to solid-liquid interfaces. Here, we use operando synchrotron X-ray computed microtomography to investigate the evolution of lithium/solid-state electrolyte interfaces during battery cycling, revealing how the complex interplay between void formation, interphase growth, and volumetric changes determines cell behavior. Void formation during lithium stripping is directly visualized in symmetric cells, and the loss of contact at the interface between lithium and the solid-state electrolyte (Li₁₀SnP₂S₁₂) is found to be the primary cause of cell failure. Reductive interphase formation within the solid-state electrolyte is simultaneously observed, and image segmentation reveals that the interphase is redox-active upon charge. At the cell level, we postulate that global volume changes and loss of stack pressure occur due to partial molar volume mismatches at either electrode. These results provide new insight into how chemo-mechanical phenomena can impact cell performance, which is necessary to understand for the development of solid-state batteries.