Thermal-hydraulic enhancement of immersion-cooled cylindrical lithium-ion battery modules using end-face copper layers and arc-shaped inlet deflectors

Immersion cooling delivers high heat transfer efficiency and promising application potential for lightweight and compact liquid cooling systems of vehicle lithium-ion batteries. However, conventional single-inlet/single-outlet cooling configurations may lead to non-uniform coolant distribution and localized heat accumulation near battery end faces, whereas introducing additional ports increases structural complexity and sealing requirements. To address these problems, this study proposes a novel passive scheme combining end-face heat conduction layers and built-in arc-shaped deflectors. A numerical model using dielectric fluid is established to investigate how key parameters affect the thermo-hydraulic performance of battery modules. Under the 2C discharging condition, the synergistic configuration with a flow rate of 2 L/min, 2 mm copper layers and 12 mm full-span deflectors exhibits comparatively competitive overall performance among all cases simulated in this work. Compared with the baseline, the maximum temperature drops from 36.63 ℃ to 30.60 ℃ by 16.46 %, and the maximum temperature difference falls to 3.86 ℃ with a 64.62 % reduction. The total pressure drop only rises by 16.15 %. This design enhances temperature regulation and uniformity with a minor hydraulic penalty. By jointly enhancing lateral heat spreading and regulating the coolant flow field, the proposed passive structure suppresses localized hot spots and improves temperature uniformity without introducing additional ports. It retains a compact single-inlet/single-outlet architecture and provides a practical design strategy for immersion thermal management of vehicle lithium-ion battery modules.