Thermal Management of Lithium-Ion Battery Packs for Electric Vehicles: Comparative Analysis of Air Cooling, Liquid Cooling, and Phase Change Material Hybrid Strategies for Capacity Retention and Cycle Life

The thermal management system of a lithium-ion battery pack is the single most influential design factor for battery cycle life, safety, and energy availability in electric vehicles, as the electrochemical degradation rate of lithium-ion cells follows an approximately exponential Arrhenius relationship with temperature — halving or doubling with every approximately 10°C decrease or increase above the optimal operating range of 15–45°C. This paper presents a comprehensive comparative study of five battery thermal management system (BTMS) strategies — forced air cooling, indirect liquid cooling via cold plate, direct liquid cooling, phase change material (PCM) combined with liquid cooling hybrid, and direct immersion cooling — applied to a 20.48 kWh lithium iron phosphate (LFP) battery pack (16S4P, 51.2 V, 400 Ah, 64 prismatic cells) representative of a small electric passenger vehicle application in Indian conditions. Thermal simulations using ANSYS Fluent CFD coupled with an equivalent circuit battery model are validated against experimental measurements on a 16-cell test assembly with forced air and liquid cooling capability. Temperature distribution during 1C and 2C discharge at 25°C ambient, temperature uniformity index (standard deviation of cell temperatures), cooling system power consumption, cell cycle life projection based on accelerated degradation testing, and 10-year total cost of ownership are compared across all five strategies. Results demonstrate that the PCM + liquid cooling hybrid achieves the lowest maximum cell temperature (40°C at 1C discharge), best temperature uniformity (ΔT = 3.8°C), and longest projected cycle life (2420 cycles to 80% SOH) at 1C discharge, while requiring 33.3% less cooling power than pure liquid cooling. For Indian urban EV operating conditions, with typically 1–1.5C average discharge rates and ambient temperatures of 28–42°C in summer, the PCM + liquid hybrid is identified as the preferred BTMS strategy for maximising battery calendar life and maintaining driving range stability throughout the 10-year vehicle life.