Multi-Objective Optimization of a Hybrid Phase Change Material-Air Battery Thermal Management System to Maximize Energy Density and Thermal Performance

Abstract The exponential rise of electric vehicles demands lightweight, high-density battery packs; a robust battery thermal management system (BTMS) inherently compromises both gravimetric (ρEG) and volumetric (ρEV) energy densities. This study addresses this tradeoff by optimizing forced air + phase change material (PCM)-based hybrid BTMS using Response Surface Methodology (RSM). The objective functions include maximizing ρEG and ρEV while minimizing maximum surface temperature (TS,Max), temperature difference (ΔTS), and fan power (P). The design variables include cell spacing (A), aluminum-shell contact angle (B), and air velocity (C). The optimization is performed under constant heat generation corresponding to a 2C charge rate at an ambient temperature of 35 °C to represent adverse conditions. The optimized configuration is then evaluated under cyclic operation with constant 2C charging and variable discharge rates based on a modified Indian driving cycle. RSM results indicate that cell spacing is the dominant parameter in reducing ΔTS, while both cell spacing and air velocity significantly influence TS,Max. The optimal configuration (A = 5.7 mm, B = 123.9 deg, and C = 1.35 m/s) satisfies the constraints TS,Max < 50 °C and ΔTS < 5 °C, yielding TS,Max = 49.4 °C and ΔTS = 4.5 °C. The optimized BTMS contributes less than 10% to the total pack weight and achieves module-level energy densities of ρEG = 160.4 Wh/kg and ρEV = 245.7 Wh/l using a staggered cell arrangement. The results demonstrate effective thermal regulation under cyclic conditions with minimal compromise in energy densities.