This study investigates phase change materials (PCMs) for lithium battery thermal management. A PCM cooling model was developed and experimentally validated, showing ≤1.5 K temperature error and ≤5% PCM melting simulation deviation. A non-uniform battery arrangement was proposed to optimize temperature distribution. Key PCM parameters (melting point, conductivity, latent heat) were analyzed for thermal performance. A hybrid liquid-PCM cooling system was designed and optimized via an entropy-weighted TOPSIS-NSWOA strategy. At 4 C discharge, the optimized system achieved 311.41 K maximum temperature (5.89 K reduction) and 4.71 K temperature difference, meeting 18 650 battery safety standards. The findings guide PCM selection and integrated thermal management design, balancing heat dissipation and temperature uniformity