Thermal performance of direct two-phase refrigerant cooling for lithium-ion batteries in electric vehicles

•Direct two-phase refrigerant cooling is proposed for batteries in electric vehicles.•Thermal performance of the refrigerant cooling is measured under vehicle conditions.•The most effective performance is observed at the vapor quality of 0.85.•The cell temperature limit of 45 °C is satisfied under harsh environments.•During aging, the refrigerant cooling provides 16.1% higher battery capacity. The lithium-ion battery has been considered as a power source of electric vehicles (EVs). An efficient battery thermal management system is essential for lithium-ion batteries with high cooling performance and long lifetime. The objective of this study is to investigate the performance improvement of a novel direct two-phase refrigerant cooling over a conventional liquid cooling for traction batteries of EVs. Based on full-scale experiments under actual vehicle conditions, the thermal performance of the two-phase refrigerant cooling is compared with that of the conventional liquid cooling with the same outer size. The two-phase refrigerant cooling satisfies the maximum cell temperature limit of 45 °C even under harsh environmental conditions. During aging, the two-phase refrigerant cooling provides 16.1% higher battery capacity and 15.0% lower internal resistance compared with the liquid cooling under harsh environmental conditions. Overall, the two-phase refrigerant cooling is considered a preferred alternative to the conventional liquid cooling owing to its reliable performance even with a simple and lightweight structure.