Dual-stage Thermal Storage and Flame-Retardant Thermal Insulation of Hydrated Salt Composite for Battery Thermal Safety Systems

Lithium-ion batteries (LIBs) have become the cornerstone of global clean energy transition with their superior energy density and long cycle life. However, the escalating energy density of LIBs intensifies critical thermal safety concerns, including severe heat accumulation and uncontrollable thermal runaway propagation. The organic phase change materials (PCMs) are limited by inherent flammability and low latent heat, whereas inorganic hydrated salts suffer from intractable supercooling and liquid leakage. To address these bottlenecks, this study develops a hydrated-salt composite PCM (CPCM) employing sodium sulfate decahydrate as the matrix, encapsulated within a synergistic framework of expanded graphite and porous calcium silicate. The optimized CPCM features a dual-stage heat storage mechanism by leveraging vaporization enthalpy, it delivers a phase-change enthalpy of 140.5 J g−1 and the remarkable total heat-storage density of 879.0 J g−1, while maintaining excellent cyclic stability. Notably, the optimized CPCM demonstrates superior flame retardancy, achieving a UL-94 V-0 rating. In flame-exposure tests, the material acts as an exceptional flame-insulating barrier, maintaining an impressively low back-side temperature of merely 30.2 °C even under direct burner exposure. In a module comprising five series-connected 23 Ah prismatic lithium iron phosphate (LiFePO4) cells, SPEC10 limits the maximum temperature to 57.6 °C at 2C discharge rate, representing reductions of 5.2 °C and 5.0 °C relative to the organic flame-retardant CPCM (FRCPCM) and the hydrated salt CPCM (SPE5) modules, respectively. Furthermore, it provides a robust thermal shock protection with heating plates reaching 200 °C by 8000 s. This multifunctional CPCM serves as a promising material candidate for enhancing the thermal safety of battery management systems.