Enhanced safety of high-power lithium-ion batteries using thermally conductive and flame-retardant shape-stabilized PCM

Lithium–ion batteries in electric vehicles and energy storage systems are highly vulnerable to excessive heat generation, leading to performance degradation and thermal runaway. To address these challenges, shape-stabilized phase change materials (SSPCMs) incorporating expanded graphite (EG) and epoxy resin (ER) were developed to improve thermal conductivity, structural stability, and flame resistance. The EG–ER synergy is the key innovation: EG establishes a continuous in-plane heat-spreading network and forms an oxygen-blocking barrier upon heating, while ER immobilizes the PCM and promotes char, yielding transient-only ignition and self-extinguishing under 30 s flame. Nine SSPCMs with different PCM/EG/ER ratios were fabricated and systematically evaluated in terms of thermal conductivity, latent heat, shape stability, and flammability. Overall, the optimal composition (80 wt% PCM, 10 wt% EG, 10 wt% ER) exhibited excellent thermal performance and retained its structure after five thermal cycles at 150 °C. FT–IR analysis and flame tests confirmed chemical integrity and self-extinguishing behavior, attributed to the oxygen barrier effect of EG. When integrated into cylindrical 18,650 cells, the SSPCM effectively suppressed temperature rise under discharge rates from 1C to 5C. In a 2S2P battery pack, it maintained surface temperatures at 37.2 °C (2C) and 50.5 °C (4C). Compared with air cooling, it reduced peak temperature by up to 40 % and achieved 16.8 % and 33.1 % reductions compared to pure PCM and silicone oil, respectively. These findings demonstrate that the proposed SSPCM not only provides high thermal conductivity and flame retardancy but also offers a reliable passive cooling solution. This approach has strong potential for enhancing the safety and performance of high-power lithium–ion batteries in electric vehicles and energy storage systems.