Enhanced Thermal Performance of Cylindrical Li‐Ion Cells Using Fin‐Assisted Multi‐Phase Change Materials for Efficient Heat Dissipation and Uniform Temperature Control

ABSTRACT This study examines the thermal behavior of Li‐ion batteries (LIB) under high discharge rates, emphasizing the necessity of an efficient battery thermal management system (BTMS) employing phase change materials (PCMs). Without any thermal regulation, the battery temperatures rose sharply to 66.16°C, 74.8°C, and 82.40°C at 3 C , 4 C , and 5 C discharge rates, respectively—well above the safe operating threshold. Incorporating a PCM‐based BTMS significantly mitigated this rise, lowering the maximum temperatures to 29.69°C, 30.74°C, and 31.78°C, corresponding to reductions of approximately 55.12%, 58.91%, and 61.43%. Among the four PCMs tested (RT‐28, RT‐31, RT‐33, and RT‐35), RT‐28 demonstrated superior thermal performance, exhibiting the lowest temperature rise and the highest energy absorption (1.9 kJ at 5 C ), compared to RT‐31 (1.7 kJ). At 5 C , RT‐28 achieved a liquid fraction of 51.17%, while RT‐31 reached a liquid fraction of 44.48%. Over time, thermal resistance increased for RT‐28, RT‐31, and RT‐33, with RT‐31 peaking at 3.95 mΩ, whereas RT‐35 remained nearly constant at 3.80 mΩ. These results highlight that selecting PCMs with phase change temperatures closely matching the battery's operational range can effectively enhance safety, suppress thermal runaway, and improve performance in high‐power applications such as electric vehicles (EVs) and renewable energy systems.