Solid-state batteries (SSBs) present a promising technology for next-generation batteries. Interface delamination between storage particles and solid electrolytes contributes to greater impedance for Li transfer and capacity loss in SSBs. Electrolyte cracking would cause degradation of the ionic or electronic conductivity of electrolytes. To investigate these failure mechanisms, we developed a 3D electro‑chemo‑mechanical phase-field fracture model for solid-state cathodes. Our simulations show that unstable interfacial delamination is highly probable during lithium extraction. Furthermore, electrolyte cracking can happen quite readily, and the electrolyte can break into several parts in only one insertion half cycle and even the appearance of full delamination [1]. We systematically examined the effects of active material volume fraction, electrolyte stiffness, and crack patterns on interfacial stability and electrolyte cracking. The results indicate that thinner and softer electrolytes improve resistance to delamination, consistent with analytical predictions and experimental evidence. Conversely, thicker and softer electrolytes enhance resistance to electrolyte cracking, which also aligns with theoretical and experimental observations [2]. We also find that discrete interfacial cracks composed of multiple segments can mitigate debonding during extraction, in agreement with analytical solutions. Moreover, electrolyte cracking is effectively suppressed when defects are located away from both interfaces and external boundaries during insertion [3]. Based on these insights, we propose design guidelines for mechanically stable solid‑state cathodes: using softer electrolytes, maintaining active material volume fractions between 50% and 60%, controlling crack patterns, and reducing particle size. These strategies collectively help to suppress both interfacial delamination and electrolyte cracking.