Thermoresponsive Gel Polymer Electrolytes Enabled by Retained Double Bonds for Thermal Shutdown in Lithium‐Ion Batteries

Gel polymer electrolytes offer the advantage of simultaneously maintaining high ionic conductivity and improved safety, yet they remain ineffective in suppressing thermal runaway under elevated temperatures. Herein, we report a thermoresponsive gel polymer electrolyte (TGPE) enabled by retained double bonds that provides an intrinsic thermal shutdown through retained double bonds. The TGPE is constructed by polymerizing triallyl isocyanurate (TAIC) with pentaerythritol tetraacrylate (PETEA) at 60 °C, forming a partially cross‐linked network with abundant unreacted C=C bonds. Upon overheating above 115 °C, these residual bonds undergo rapid secondary cross‐linking within 15 min, converting the electrolyte from an ion‐conductive gel into a dense ion‐blocking gel. This transition sharply increases internal resistance, suppresses ionic transport, and results in nearly zero capacity with a current reduction exceeding 90%. Under normal operation, the TGPE exhibits high ionic conductivity (0.54 mS cm −1 at 30 °C), a wide electrochemical stability window up to 4.35 V versus Li + /Li, and stable cycling performance with 89.3% capacity retention after 500 cycles in Li||LiFePO 4 cells. More importantly, the autonomous thermal shutdown significantly delays thermal runaway, increasing the triggering temperature ( T 2 ) from 108.7 to 146.3 °C in 3.0 Ah Graphite||LiFePO 4 pouch cells and from 114.9 to 135.9 °C in 1.0 Ah SiC||NCM811 cells. This bond‐retention‐activated densification strategy offers a scalable route toward intrinsically safe lithium‐ion batteries by balancing electrochemical performance and thermal safety.