On the evaluation of composite phase change materials for passive thermal management of lithium-ion batteries

Effective thermal management is essential for the safe operation of lithium-ion batteries under varying discharge conditions. This study experimentally investigates a passive battery thermal management system (BTMS) using paraffin-based phase change material (PCM) and graphite-enhanced composite PCM (CPCM). Graphite contents of 4.0%, 6.4%, 8.0%, and 12.0 wt% were evaluated under discharge currents of 2–10 A over 300 s, with battery surface temperatures compared for no-BTMS, PCM, and CPCM configurations. Thermophysical properties were measured, and a theoretical energy balance was used to estimate battery heat generation. The findings demonstrate that the battery pack without BTMS exhibits the highest temperature rise under all tested conditions, while paraffin-based PCM effectively reduces the rate of temperature rise. Graphite addition further enhances heat transport and delays thermal saturation. At 8 A, the CPCM system reduced battery-retained sensible heat by approximately 60% ± 9 pp compared with the no-BTMS case, versus 44% ± 9 pp for pure PCM. The results highlight the trade-off between enhanced thermal conductivity and reduced latent heat capacity with increasing graphite content. A supplementary replicated campaign at elevated initial temperatures (≈30–35 °C) confirmed that the 6.4 wt% CPCM, with its higher latent-heat capacity, provides better temperature control than the 8.0 wt% formulation as melting is approached.