Design of Dielectric Fluid Immersion Cooling System for Efficient Thermal Management of Lithium‐Ion Battery Packs

ABSTRACT Heat generation during fast charging and discharging of lithium‐ion batteries (LIBs) remains a significant challenge, potentially leading to overheating, reduced performance, or thermal runaway. Traditional battery thermal management systems (BTMS), such as air‐based cooling and indirect liquid cooling using cold plates, often result in high thermal gradients—both vertically within cells and horizontally across battery packs—especially under high‐current discharge rates. To address these issues, this study introduces and evaluates a steady‐state convection‐based ester‐oil immersion cooling (EOIC) technique for LIBs. Numerical simulations based on the Newman, Tiedemann, Gu and Kim model, aligned with multi‐scale multi‐dimensional principles, were performed on both a single 18650 cylindrical cell and a 4S2P battery pack. Experimental validations were conducted under 2C and 3C discharge rates at 25°C ambient temperature. The EOIC system demonstrated a temperature reduction of up to 13°C in the 18650 cell and 15°C in the 4S2P pack at 3C discharge compared to natural air convection and achieved ≤ 10°C thermal gradient across cells in the battery pack. The simulation results closely matched experimental data, with a maximum deviation of only 2°C, confirming the model's reliability. Moreover, EOIC outperformed conventional mineral oil‐based immersion cooling in both cooling effectiveness and temperature uniformity. These findings confirm EOIC as a promising passive BTMS approach, ensuring improved safety, performance, and thermal stability for LIBs in electric vehicle applications.