Numerical Investigation and Comparative Analysis of Passive Thermal Management Systems for Li-Ion Batteries.

Thermal management of lithium-ion batteries is critical for safe and efficient electric vehicle operation. This study presents a numerical investigation of passive thermal management systems for a single 18650 cylindrical battery cell using Ansys Fluent. Two studies were conducted: a steady-state geometric comparison of bare cell, rectangular fins, and Fibonacci fins, and a transient analysis of Fibonacci fins integrated with phase change material n-eicosane across multiple C-rates. Steady-state results show that Fibonacci fins achieve equivalent thermal performance to rectangular fins while offering a 24% more compact assembly footprint. In the transient study, PCM showed negligible effect at 1C as cell temperature did not reach the melting threshold. At 2C, 2.5C, and 3C, PCM reduced maximum temperature by 8.08K, 16.55K, and 24.89K respectively. At 5C, cell temperature reached 372.42K confirming passive cooling is insufficient at extreme discharge rates. Results confirm that Fibonacci fin and PCM combination provides effective passive thermal management for lithium-ion batteries at moderate C-rates.