Application of Spatiotemporal Thermal Energy Storage Phase Change Materials in Batteries Thermal Management

ABSTRACT Thermal management of lithium‐ion batteries is crucial for both performance and safety, yet existing solutions struggle to address heating and cooling demands simultaneously across a wide temperature range. Here, we design a eutectic phase change material based on sodium acetate trihydrate and urea (SAT‐Urea) that combines a suitable phase transition temperature (≈34.1°C), high phase change enthalpy (232.7 J g ^{− 1} ), and a supercooling degree exceeding 64°C, enabling spatiotemporal thermal energy storage. Density functional theory and molecular dynamics simulations reveal that Na ⁺ ‐centered solvation cages formed by acetate, water, and urea, together with a highly dynamic, competitive hydrogen‐bond network, suppress nucleation and stabilize the deeply supercooled state down to −30°C. Further incorporation into a carboxymethyl cellulose matrix yields a shape‐stable composite (SAT‐Urea‐CMC) with good cycling stability. When applied to 18650 cells, SAT‐Urea‐CMC provides bidirectional thermal regulation: at 25°C, it reduces the cell surface temperature by up to 17.9°C during 3C discharge; at −12°C, pre‐triggered crystallization elevates the operating temperature, lowers internal resistance, and increases discharge capacity by more than 12.5%. This work demonstrates a lightweight, passive material platform for spatiotemporal battery thermal management in both hot and cold environments.