Correlative Operando X-Ray Imaging and Diffraction Revealing Mechanical Failure Pathways in Sulfide-Based All-Solid-State Batteries

All-solid-state batteries (ASSBs) based on sulfide solid electrolytes and lithium metal anodes promise high energy density and enhanced safety. However, their practical implementation is hindered by coupled electro-chemo-mechanical instabilities. Here, we combine operando X-ray computed tomography (XCT), operando X-ray diffraction (XRD), and pressure monitoring to elucidate degradation mechanisms in LiNi0.8Co0.1Mn0.1O2 (NCM811) | Li6PS5Cl (LPSC) | Li cells under realistic cycling conditions. By directly correlating particle- and stack-level morphological evolution with lattice-scale structural and strain dynamics, we establish a multiscale understanding of failure processes. Operando XCT reveals reversible volume changes of the NCM composite cathode during (de-)lithiation. Spatially resolved operando XRD uncovers heterogeneous lithiation fronts and depth-dependent electrochemical activity across the cathode thickness, while also identifying a partial release of internal microstrain at the NCM|LPSC interface associated with oxidative decomposition of LPSC. At the LPSC|Li interface, XCT visualizes crack propagation, lithium infiltration into the solid electrolyte, and interfacial void formation, ultimately leading to mechanical disconnection and soft short-circuiting. Notably, these mechanically induced degradation phenomena exhibit partial reversibility during cycling. The presence of soft shorts is independently confirmed by characteristic cell pressure reversals. This multimodal operando framework provides critical insight into degradation pathways and establishes design principles for mechanically robust sulfide-based ASSBs.