The solid-state batteries must be able to operate within a wide range of charging and discharging times, ranging from ultra-fast pulses to slow discharging over the course of multiple days. The various compositional strains imposed by these different (dis)charging rates can significantly affect the evolution of grain-level stress and strain responses in composite cathodes. Key to solving the challenges of the cathode/electrolyte interface and crystal defect formation in cathodes is a clear understanding of the chemo-mechanics of the composite cathodes across battery-relevant length scales and strain rates. High-resolution transmission electron microscopy (HRTEM) experiments and atomic-scale simulations reveal that dislocations resulting from heterogeneous Li intercalation can trigger irreversible migration of TM ions into octahedral sites in the Li layer and subsequent structural degradation . Chemo-mechanical simulations using cohesive zone models and phase-field damage models have advanced the understanding of the microscopic mechanical fracture behaviour in electrode materials . However, the assessment of how microstructure and (dis)charging protocols affect the formation of crystal defects and defect-induced structural degradation at the grain level in composite cathodes remains Fig. Schematic view of electrochemical reaction, Li intercalation, structural degradation, and lattice defect types in composite cathodes of solid-state battery cells: point defects (zero-dimensional (0D) defects), dislocations (one-dimensional (1D) defects) and interfaces (two-dimensional(2D) defects). Key to solving the challenges of the cathode/electrolyte interface, crystal defect formation, and structural degradation in cathodes is a clear understanding of the chemo-mechanics of the composite cathodes across battery-relevant length scales. Non-uniform volume changes resulting from Li intercalation and the crystalline anisotropy of primary cathode particles lead to high stress, contact loss, and crystal defect accumulation, in particular dislocations and stacking faults. The presence of crystal defects can markedly reduce the energy barriers to remove lattice oxygen, which triggers Li/TM ion mixing and structural degradation. The large compositional strains in cathodes result in contact mechanics problems between cathodes and solid electrolyte.