Liquid immersion thermal management of lithium-ion batteries for electric vehicles: An experimental study

The thermal and electrical performance of lithium-ion batteries subjected to liquid immersion cooling conditions in a dielectric fluid has been experimentally investigated in this study. A single 26650 LiFePO4 cylindrical cell is completely immersed in Novec 7000 and charged and discharged at onerous maximum rates of up to 4C and 10C, respectively, where C can be defined as the measure of the rate at which a cell is charged or discharged relative to its rated capacity. Immersion cooling offers high rates of heat transfer from the cell's surface, in particular when the saturation temperature of the fluid is exceeded, and two-phase conditions are established. At a preheated liquid pool temperature of 33 ± 0.5 °C for discharge rates ≥ 2C, subcooled boiling conditions develop, with the cell's temperature rise limited to 3.6 °C at the end of 10C discharge. Furthermore, for 4C charging under the same preheating conditions, the cell's temperature rise does not exceed 1 °C. Superior performance is observed under two-phase immersion cooling conditions in comparison to both single phase liquid immersion and natural convection air cooling for the same charge and discharge rates. Excellent thermal homogenisation across the cell is also determined, with a maximum axial temperature difference of 0.25 °C and 1 °C for 4C charging and 10C discharging respectively.