Effect analysis on integration efficiency and safety performance of a battery thermal management system based on direct contact liquid cooling

We design and fabricate a novel lithium-ion battery system based on direct contact liquid cooling to fulfill the application requirement for the high-safety and long-range of electric vehicles. By the immersion in the flowing silicone oil to achieve the highly efficient heat exchange, the NCM811 cells can be grouped without gap, and thereby the battery system achieves maximum volume efficiency. The mass and volume integration ratio of the battery system are 91% and 72%, respectively, which are 1.1 and 1.5 times that of the tube-based indirect liquid contact cooling system, respectively. Specifically, the temperature increment of the cells during 1C discharge does not exceed 13 ℃, and the dynamic temperature difference is less than 8.8 ℃. The results from simulation show that the maximum temperature rise and maximum temperature difference of the direct contact liquid cooling system are only 20%–30% of the indirect contact liquid cooling system. Particularly, the system can effectively prevent the thermal runaway propagation without any additional measures, owing to the high heat dissipation rate and oxygen isolation. The research has led to the successful construction of an oil-immersed battery system with high integration ratio and excellent safety, which provides a feasible solution for the demand of the high safety and high specific energy of the electric vehicle battery system.