Macro-coating and micro-impregnation enabled hydrated salt composites for battery thermal safety systems

The increasing energy density of lithium-ion batteries in electric vehicles and energy-storage systems is intensifying thermal-safety challenges, particularly the risk of thermal-runaway initiation and propagation under high-rate operating conditions. To address these critical issues, in this research, we have designed a double-layer- encapsulated, modified, hydrated-salt composite phase-change material (SPHE2-UVPCM) for battery thermal management. This material, SPHE2-UV, employs sodium thiosulfate pentahydrate and sodium acetate trihydrate as the phase-change matrix, integrated within a dual-scale encapsulation architecture. Microscopically, hydrophilic fumed silica and expanded graphite collaboratively construct combine to form a porous confinement scaffold that provides nucleation sites and salt immobilization. Macroscopically, a UV-curable resin coating forms an impervious barrier to ensure mechanical integrity. Systematic characterization confirmed near-zero supercooling and enhanced thermal conductivity reaching 2.74 W m−1 K−1 in SPHE2-UV, concurrently while simultaneously delivering a latent heat of 138.87 J g−1 and a water-vaporization enthalpy of crystallized water measuring 509.69 J g−1. The hierarchical encapsulation enables cyclic stability with a 96.6 % retention of latent heat after 80 cycles and with superior leak resistance, with more than 96 % of the mass retained at 150 °C. In battery-module testing, this composite material maintains the maximum temperature of the battery module below 50 °C and suppresses the temperature differential to 4.5 °C at a 3C discharge rate. Additionally, this research has also proven that thermal runaway can be contained effectively under simulated-abuse conditions. The unique dual-scale encapsulation architecture developed in this research thus provides a novel solution to the long-standing challenges of leakage and supercooling in hydrated-salt PCMs, while simultaneously delivering the integrated functions of thermal regulation, flame retardance, and thermal-runaway inhibition, which are key requirements for next-generation battery thermal-management systems.