To improve the thermal management efficiency of vehicular lithium-ion batteries, Nano-Graphite (NG) and Nano-Aluminum (NA) were added to Paraffin (PA) to prepare Nano-Composite Phase Change Materials (NCPCM). Based on combinatorial mathematics modeling, the influence of different mass ratios of NCPCM’s physical parameters such as thermal conductivity and latent heat of phase change on battery thermal management efficiency was studied. Experimental analysis of thermal management of car lithium-ion batteries was conducted using RGO/BN/PA CPCM, RT44HC/CF CPCM and NCPCM3 under slow charge to fast charge conditions. Results show that at a 3.5 C discharge rate, NCPCM3 with a thermal conductivity of 2.1 W/(m·K) and a latent heat of 206.18 J/g could reduce the maximum temperature and maximum temperature difference of the car lithium-ion battery pack to 44.2 ℃ and 4.4 ℃ respectively. Further improvement of the thermal performance parameters of NCPCM did not significantly improve its thermal management performance. NCPCM3 shows significantly better battery thermal management efficiency than RGO/BN/PA CPCM and RT44HC/CF CPCM, ensuring normal operating temperature for the car lithium-ion battery pack.