THERMAL MANAGEMENT AND PHASE CHANGE HEAT TRANSFER CHARACTERISTICS OF LiFePO₄ BATTERIES BY COOLING PHASE CHANGE MATERIALS

The cycle life and thermal safety of lithium-iron-phosphate (LiFePO₄) batteries are important factors restricting the popularization of new energy vehicles. The study aims to prevent battery overheating, prolong the cycle life of power batteries and improve their thermal safety by discussing the heat production of LiFePO4 batteries to solve the problem of temperature rise in the natural-convection environment and cut the energy consumption in the liquid cooling system. A numerical simulation and experiment are employed to study the heat production characteristics of LiFePO4 batteries and the heat transfer characteristics of the system, with its PCM and coupling PCM of paraffin and expanded graphite), channel liquid, and micro-channel PCM coupling cooled to control the temperature of the batteries. The results show that the temperature goes higher with the discharge rate during discharge. Since it has large internal component values, LiFePO4 produces more heat at the beginning and end of discharge. When the battery pack is discharged at 1C and 2C rates, the mass-flow rates are 1.8 ⋅ 10⁻³ kg/s and 3.6 ⋅ 10⁻³ kg/s, the temperature can be controlled at most 40 °C, and the temperature difference less than 3 °C, respectively. Paraffin is composed of expanded graphite, and the thermal conductivity of the composite heat storage PCM (phase change heat storage materials) is 24 times of that of pure paraffin. Therefore, cooling the active liquid and coupled PCM can improve the cooling efficiency and has a good effect on solving the problem of temperature rise and energy consumption reduction. The research provides a reference for the thermal energy management of LiFePO₄ batteries, providing a method of cooling PCM of LiFePO₄ batteries.