Thermal management of composite phase change material capsule-based lithium-ion battery packs under forced convection

Effective thermal management is essential for ensuring the safety and reliability of lithium-ion battery packs under transient and high-power operating conditions. This study proposes a capsule-based battery thermal management strategy incorporating composite phase change material (CPCM) and systematically evaluates its thermal performance under controlled forced-convection environments. A battery module composed of sixteen 18,650 cells arranged in a nonuniform 4543 capsule configuration is designed, where each cell is encapsulated by layered 3D-printed sheaths filled with either pure paraffin wax or CPCM (consisting of paraffin wax mixed with 2 wt% nano carbon black). A coupled numerical-experimental framework is employed, combining three-dimensional transient simulations with wind tunnel experiments at inlet air speeds ranging from natural convection to strong forced convection. Both average and maximum temperatures of individual capsules are analyzed to capture thermal stabilization behavior, temperature uniformity, and peak temperature suppression. The results show that increasing air speed significantly accelerates thermal stabilization, while further increases provide diminishing cooling benefits due to internal heat transfer limitations. Compared with paraffin wax, CPCM consistently improves temperature uniformity and reduces average temperature levels across the module. Differences in maximum temperature are influenced by ambient conditions; however, CPCM demonstrates superior internal heat spreading and latent heat buffering, leading to a more stable thermal response. These findings highlight the importance of capsule-level thermal regulation and simultaneous evaluation of average and maximum temperature metrics. The proposed capsule-based CPCM-assisted strategy offers a scalable and effective solution for advanced lithium-ion battery thermal management.