Enhancing Heat Dissipation in Cylindrical Battery Packs via Phase Change Materials Embedded with TiO₂/Fe₃O₄ Nanoparticles

Efficient thermal management is critical to ensuring the safety, performance, and lifespan of lithium-ion battery packs operating at high C-rates. This study presents a systematic experimental investigation of a passive battery thermal management system based on phase change materials (PCM) enhanced with thermally conductive nanoparticles (TiO₂ and Fe₃O₄). Five cooling configurations—air cooling, pure PCM, PCM–TiO₂ (0.25 vol%), PCM–Fe₃O₄ (0.25 vol%), and PCM–Fe₃O₄ (0.125 vol%)—were evaluated using a cylindrical 18650 battery module (5S × 4P) under operating conditions ranging from 0.75C to 1.75C at an ambient temperature of 27°C. The results demonstrate that conventional air cooling exhibits the poorest thermal performance, with maximum temperatures reaching 75–78°C at high C-rates. In contrast, PCM-based systems significantly suppress temperature rise, reducing peak temperatures to approximately 55°C (∼30% reduction). The incorporation of nanoparticles further enhances heat dissipation, with the PCM–TiO₂ system achieving a reduction of ∼33–34%, while the PCM–Fe₃O₄ (0.25 vol%) configuration delivers the best performance, achieving a maximum temperature reduction of ∼35–36% and improved thermal uniformity with temperature gradients limited to 4–7°C. Importantly, enhanced thermal regulation directly contributes to improved electrochemical performance, including increased voltage stability and extended discharge duration under high-load conditions. Unlike conventional hybrid cooling systems, the proposed approach offers a simple, fully passive, and energy-efficient solution that requires no pumps or external power. These findings highlight the strong potential of nanoparticle-enhanced PCM systems, particularly PCM–Fe₃O₄ composites, for practical implementation in electric vehicles and high-power energy storage applications.