<p>Polymer electrolytes, recognized for their favorable interfacial compatibility, excellent processability and low cost, are regarded as promising materials for next-generation batteries. Despite significant advancements in improving the ionic conductivity and overall electrochemical performance of polymer electrolytes, safety concerns regarding polymer-based batteries exist, i.e., the thermal runaway may occur under extreme operating conditions. This risk is attributed to the inherent flammability of most polymer materials and the release of combustible gases during thermal decomposition at elevated temperatures, thereby exacerbating fire propagation and intensification. In this review, we systematically summarize thermal runaway mechanisms and propose corresponding optimization strategies, focusing on polymer electrolyte innovations, such as thermally stable, thermo-responsive, and non-flammable polymer electrolytes, in combination with thermally resistant interphase engineering. This review provides a comprehensive analysis of recent advances in polymer electrolyte technology and offers a roadmap for the rational design of materials and interfaces for next-generation batteries.</p>