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

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.