A High‐Safety Solid‐State Thermally Responsive Separator‐Electrolyte Structure for Flexible Energy Storage Devices

ABSTRACT In the era of energy development, electrochemical energy storage devices are widely used for their high‐power density and long cycle life. However, rapid ion transport can cause excessive heat, accelerating degradation and raising safety risks. To address this, a high strength integrated smart separator‐electrolyte structure based on poly (N‐isopropylacrylamide) (PNIPAAm) is developed. The assembled supercapacitor achieves 81% capacitance retention after 5000 cycles at 1 A g −1 . By incorporation of hydrophilic (N‐vinylpyrrolidone) NVP monomer and high concentration salts, the hydrogen bonding network is precisely regulated, giving the structure exceptional mechanical robustness and anti‐freezing performance, enabling stable operation under deformation and extreme conditions. Leveraging the reversible phase transition of PNIPAAm, the electrolyte dynamically closes ion channels upon heating and reopens them upon cooling, achieving automatic shutdown and self‐recovery of device operation. Above 60°C, the electrolyte rapidly suppresses ionic transport (100% capacity loss), with full function recovery after cooling. In addition, the color change of the exclamation mark pattern on the outer packaging allows for quick and accurate identification of the overheating status. The synergistic integration of thermal responsiveness and visual alerting ensures ultra‐safe operation and provides a promising strategy for enhancing the operational safety of next‐generation flexible energy storage devices.