Fig. and Supplementary Fig. show the distribution of the maximum principle stress at the cathode/solid-electrolyte interface, for both single crystal and polycrystalline particles exposed to various discharge rates. A high tensile stress persists at the interface, irrespective of whether a single crystal or polycrystalline cathode is considered. Moreover, the comparative analysis under different discharge rates in Fig. reveals that the reduction of the discharge rate is not a solution for alleviating this persistent tensile stress at interfaces. However, Fig. shows that reducing the Young's modulus of the solid electrolytes instead, through the utilization of polymerbased or sulfide solid electrolytes, effectively alleviates the high tensile stress at the interface and enhances the overall mechanical stability. Moreover, Fig. shows the effect of electrochemical cycling on the evolution of interfacial stress in composite cathodes. The NMC cathode was initially discharged at 1 C to a cut-off voltage of 3 V and then immediately charged at 1 C. Fig. shows that the interface between cathodes and electrolytes underwent significantly higher tensile stress upon charge than discharge. In composite cathodes with oxide electrolytes, the average interfacial stress increased from 378 MPa upon discharge to 580 MPa upon charge at the same state of lithiation.