Study on the effect of immersion thermal management for high-current rate fast charging of 21700 Li-ion batteries

During high-rate fast charging, power batteries will generate significant heat. Therefore, it is more necessary to have an efficient thermal management system. This paper presents a thermal behavior simulation model for a 21700 NCM Li-ion ternary battery module, obtaining the onset temperature of each stage of the overheating decomposition reaction. On this basis, we developed an immersion cooling model for the battery module. And its cooling effect at different spacing (5-20 mm) and two different flow rate ranges (5-20 mm/s and 40-200 mm/s) in the fast charging process is simulated and analyzed. The results show that a 5 mm spacing exhibits a good heat transfer effect at low flow rates, while a flow rate of at least 20 mm/s is required for stable boiling heat transfer. In the high flow rate range, decreasing spacing or increasing flow rate will both reduce the temperature and temperature difference of batteries. Compared to 20 mm spacing and 40 mm/s flow rate, 5 mm spacing and 200 mm/s flow rate reduce temperature and temperature difference of batteries by 9.3 degrees C and 14.9 degrees C, respectively. Finally, the addition of the disturbing structure enhances coolant flow uniformity while minimally increasing flow pressure drop, and increases the heat flux by 157 W/m(2), thereby further optimizing the cooling effectiveness.