A Novel Flame‐Retardant Solid‐Solid Phase Change Material for High‐Rate Cycling and Thermal Runaway Protection in Battery Thermal Safety System

The increasing energy density of battery storage systems highlights crucial thermal safety issues. Composite phase change materials (CPCMs) exhibit immense potential for temperature regulation. However, their widespread application is restricted by inherent flammability, low thermal conductivity, and susceptibility to leakage. We developed a multifunctional solid‐solid flame‐retardant CPCM via two‐step chemical crosslinking, strong hydrogen bonding, and an intumescent flame‐retardant system comprising an “acid‐nitrogen‐carbon” source. This innovatively resolves the trade‐off between flame retardancy and the deterioration of phase‐change/mechanical properties. While maintaining a high latent heat (100.8 J/g), high thermal conductivity (1.6 W/(m·K)), and favorable mechanical flexibility, it concurrently exhibits exceptional flame retardancy. It achieves the highest V‐0 rating in the UL‐94 standard, with a total heat release (THR) and total smoke production (TSP) limited to only 35.43 MJ/m 2 and 0.53 m 2 , respectively. In lithium‐ion batteries under a 3C discharge rate, they maintain the maximum temperature and temperature difference below 45°C and 3.7°C. Crucially, leveraging synergistic flame retardancy and excellent heat dissipation, they address the critical challenge of mitigating the propagation of battery thermal runaway. This work provides a novel strategy for battery thermal management, integrating efficient heat dissipation and thermal runaway isolation.