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

Abstract

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 degrees 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 degrees C (2C) and 50.5 degrees 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.