Experimental studies on two-phase immersion liquid cooling for Li-ion battery thermal management

The thermal management of lithium-ion batteries (LIBs) has become a critical topic in the energy storage and automotive industries. Among the various cooling methods, two-phase submerged liquid cooling is known to be the most efficient solution, as it delivers a high heat dissipation rate by utilizing the latent heat from the liquid-to-vapor phase change. In this study, a novel two-phase liquid immersion system was proposed, and the cooling performance of an 18650 LIB was investigated to evaluate the effects of thermal management on the performance of the battery pack. Four cooling strategies, namely natural, forced convection, mineral oil (single-phase), and SF33 fluid (two-phase) cooling, were compared under different discharge rates and dynamic load conditions. The results suggest that two-phase immersion cooling with SF33 fluid was highly effective to keep the cell temperature under 34 °C under all tested conditions, and the temperature change of the battery did not exceed 5 °C. A large amount of heat from the battery during high C discharge was absorbed by the boiling of SF33, allowing it to effectively maintain the cell temperature in an optimal temperature range (33–34 °C). Finally, the mechanism of pool heat transfer was determined through visual analysis. Initially, small bubbles appeared near the wires and battery terminals, which acted as gasification cores. Subsequently, small bubbles arose around the surface of the battery body, most of which grew to reach the interface. Eventually, the vapor condensed near the top condenser coils. This study provides a foundation for the further development of direct two-phase liquid-cooling technology, which can be an effective method for enhancing the life and safety of LIBs.