Polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) have good ionic conductivity and flexibility, and is a key component of all-solid-state lithium batteries (ASSLBs). Therefore, the mechanical integrity of PEO-based SPEs during cell operation needs to be urgently evaluated. Here, we conducted a series of tensile and shear adhesion performance tests on PEO₁₆–LiTFSI electrolyte and LiFePO₄ electrode adhesion samples at various temperatures and quenching rates. Based on the interface performance data and the elastic–viscoplastic material model of the PEO–LiTFSI electrolyte, a comprehensive electrochemical–mechanical model was established to analyze the stress in the cell and evaluate the mechanical integrity of the PEO₁₆–LiTFSI electrolyte and SPE/cathode interface. The experimental results show that the adhesion strength of the SPE and cathode decreases significantly with increasing operating temperature and quenching rate. The simulation study indicates that the mechanical properties of the SPE can be fully utilized to a certain extent by increasing the quenching rate. In addition, appropriately increasing the operating temperature helps maintain the mechanical integrity of the SPE during cell operation. However, increasing the quenching rate and operating temperature will reduce the interface bonding properties between the SPE and the cathode, resulting in an increased probability of mechanical failure at the SPE/cathode interface. To suppress this negative effect, a design scheme to maintain the structural integrity of the PEO-based polymer electrolyte is proposed by using the C-rate and the SPE thickness as control parameters, which can assist in engineering design and safe operation of Li/PEO₁₆–LiTFSI/LiFePO₄ for ASSLBs.