Fundamental insights into static immersion cooling of large-scale lithium-ion Batteries: Thermal behavior, heat transfer mechanisms, and multivariable analysis

Immersion cooling has emerged as a promising thermal management solution for lithium-ion batteries (LIBs), offering superior heat dissipation compared to conventional methods. However, most existing research predominantly focused on small-scale, low-power batteries, leaving a critical gap in understanding static immersion cooling (SIC) for large-scale batteries. In this study, a dedicated experimental platform was developed to systematically investigate the thermal control performance of cooling methods, immersion heights, battery placements, ambient temperatures, and dielectric fluid types (transformer oil, silicone oil, and fluorinated liquids). The results indicate that fully immersing the LIB in transformer oil reduces the battery maximum temperature by 30–35 % compared to natural air convection, while maintaining heat dissipation rate of 45–60 %. Under high discharge rates (5 C), the battery temperature can be effectively kept below the 60 °C safety threshold. Furthermore, the natural convection patterns in the fluid and heat transfer characteristics were analyzed. It is found that fluid natural convection may increase the temperature difference when the battery is immersed upright, whereas an inverted configuration could improve temperature uniformity. Besides, among the tested dielectric fluids, fluorinated liquid exhibits superior performance, achieving a heat dissipation rate of 54.13 %, attributed to its high heat capacity and low viscosity. This research provides fundamental insights into SIC mechanisms, advancing the design of efficient immersion thermal management technology for applications in electric vehicles and grid-scale energy storage systems.