Ultrathin Hydrated Salt Gel with High Thermal Storage Density and Switchable Low Thermal Conductivity to Suppress Battery Thermal Runaway Propagation

We present a hydrated salt polymer gel (TCM51/PAMPS) that combines a thermal switch with high-capacity thermal storage to suppress lithium-ion battery thermal runaway propagation. The gel shifts from a conductive state (0.52 W/(m·K)) to an insulating state (0.056 W/(m·K)) upon heating, while storing 1828 kJ/kg via phase change and decomposition. Nail penetration–induced thermal runaway tests on the cell packs show that the gel can effectively prevent propagation and maintain adjacent cell temperatures at relatively low levels. In contrast, ceramic fiber aerogel only delays thermal runaway and may fail to fully suppress propagation even under full coverage. This dual absorption-insulation mechanism actively limits heat transfer and establishes a low-temperature environment, outperforming static insulators. The material’s scalability and robust performance offer a promising route for safer high-energy battery systems in electric vehicles and stationary storage. • A hydrated salt polymer gel achieves dual heat-absorption and thermal switching. • Provides 1828 kJ//kg of heat absorption, 1.25× the vaporization enthalpy of water. • Thermal conductivity drops from 0.52 to 0.056 W/(m·K) upon carbonization. • A 2 mm gel layer prevents 51 Ah cell packs thermal runaway in all configurations.