Thermal management of lithium-ion batteries under high ambient temperature and rapid discharging using composite PCM and liquid cooling

To improve the thermal performance of the lithium-ion battery at a high ambient temperature of 40 °C and high discharge rate of 5C, a hybrid cooling system composed of composite phase change material (RT44HC/expanded graphite) and counterflow liquid cooling is designed for a battery module with 25 cylindrical batteries. A numerical study is carried out to investigate the influences on the maximum temperature and temperature uniformity of the battery module by different parameters, such as composite phase change material thicknesses, coolant flow directions, expanded graphite mass fractions, coolant velocities and coolant temperatures. The results show that the mass fraction of expanded graphite has an optimal value of 12% in this work, corresponding to the limitations of maximum temperature and temperature difference by 45.25 °C and 3.49 °C, respectively. In addition, compared with the parallel flow direction, the counterflow flow direction scheme possesses better thermal performance. Increasing the coolant velocity can reduce the maximum temperature to a certain extent, but the reduction trend levels off accompanied with a large pressure drop, so a low velocity balancing between the performance and power consumption is preferred. Furthermore, the lower coolant temperature will increase the temperature difference. Therefore, a high inlet temperature should be preferred as close to the ambient temperature. The present hybrid cooling configuration can handle rapid discharging of 5C even under a high ambient environment, which shows outstanding thermal performance and effectively improves the thermal safety of batteries.