Thermal performance of lithium-ion battery tabs under liquid immersion cooling conditions

The thermal performance of the electrode terminals or tabs of a 26650 LiFePO₄ cylindrical lithium-ion battery under direct contact liquid immersion cooling conditions is experimentally investigated during charging and discharging, highlighting their contribution to the overall heat transfer from the battery which has not been examined previously. High rates of heat transfer occur from the terminal surfaces for complete immersion in Novec 7000 due to the battery’s anisotropic thermophysical properties, coupled with additional heating from the electrical connections. The establishment of two-phase conditions for initial bulk fluid temperatures of 33 °C ± 0.5 °C further augments the heat transfer, providing greater thermal uniformity across the entire battery as nucleate boiling is induced on the terminal surfaces. Vigorous vapour bubble growth and departure limits the temperature difference between the terminals and the bulk fluid, indicative of the heat transfer intensity, with values two to three times lower than those observed under natural convection liquid immersion conditions. For the discharge rate of 10C, the phase change restricts the temperature difference between the positive and negative terminals and the bulk fluid to a maximum of 3.5 °C and 5 °C respectively. A corresponding cell thermal inhomogeneity of 2.2 °C is maintained, minimising accelerated electrochemical material degradation. Similar performance is exhibited during charging at the rate of 4C, restricting the temperature difference between the positive and negative terminals and the bulk fluid to a maximum of 1.4 °C and 2.2 °C respectively, and the cell thermal inhomogeneity to 1 °C.