Stability and safety of polyethylene-oxide solid-state batteries with optimized cathodes at elevated temperatures

Polymer-based all-solid-state batteries (ASSBs) are approaching practical energy storage applications, but many systems still require elevated temperatures to achieve sufficient ionic transport. In polyethylene-oxide (PEO)-based cells, operation around 70 ° C is commonly recommended, creating a trade-off between electrochemical performance and mechanical stability. Since real application battery packs may experience dynamic thermal profiles and short-term deviations from ideal operating conditions, defining operational, degradation and safety temperature limits is essential for thermal management and system-level design. In this work, the electrical and thermal stability of PEO-based ASSBs is investigated in fourteen laboratory-scale pouch cells incorporating previously optimized 700 kg mol −1 PEO composite cathodes. Electrical stability was evaluated through OCV measurements, electrochemical impedance spectroscopy (EIS), and cycling experiments, while thermal stability was assessed by accelerating rate calorimetry (ARC) and thermogravimetric analysis (TGA). The results show that the cells remain operational up to approximately 100 ° C, defining a “soft abuse” region between 70 and 100 ° C where functionality is preserved despite showing signs of degradation. Above 100 ° C, a transition to a “hard abuse” regime is observed, characterized by a progressive electrical instability and degradation. Self-heating reactions are not observed until approximately 150 ° C, providing a separation of 50 ° C between the first electrical instability at 100 ° C and the onset of exothermic degradation. These findings establish key operational and safety temperature boundaries for the investigated optimized PEO-based ASSBs, providing engineering-relevant inputs for defining safe operating strategies, thermal management system design and pack construction criteria for next-generation polymer-based solid-state energy storage systems.