context: The FIB-SEM tomography and electrochemical testing results together strongly suggest that the severe mechanical degradation is the main cause of the rapid capacity fade in the SSB composite electrode, particularly in later cycles. In current study, the crack development is mostly observed near the cathode/solid electrolyte interface, which suggests that the cathode particle volume change is the origin of the mechanical failure during cycling. Thus, minimizing this mechanical degradation is critical to extending the cycle life of SSBs.