<p>Paraffin (PA) is a common phase change material, which is widely used in battery thermal management systems (BTMS) because of its high latent heat and temperature uniformity, simple system structure, and no increase in battery energy consumption. In this work, sulfur-free expanded graphite (EG) is prepared by oxidation intercalation without H₂SO₄ in the preparation process, which avoids the harm to devices caused by the S element. The sulfur-free EG exhibits a high expanded volume of 324 mL·g⁻¹, which can adsorb PA well to prevent leakage. When the mass filling ratio of EG is 5.0%, EG/PA-5.0 composite films show high latent heat of phase transition (253.08 J·g⁻¹), and thermal conductivity (2.56 W·m⁻¹·K⁻¹). EG/PA films are attached to the external surface of the lithium iron phosphate battery for a heat dissipation performance test. When the discharge rate is 1C at room temperature, the surface temperature and maximum temperature difference between temperature measurement points of the battery with EG/PA-5.0 film are 32.1°C and 1.2°C. After charge-discharge at 1C for 100 cycles, the thermal properties of EG/PA remain basically unchanged, and it has good cycle stability. The simulation results are in good agreement with the actual temperature changes of the battery at different discharge rates. This work indicates that sulfur-free EG/PA composite has a good application prospect in BTMS of the power batteries.</p>