Nano-Structured Surface Engineering for Enhanced Thermal Interfaces in Electric Vehicle Battery Cooling Systems

High-performance lithium-ion batteries in electric vehicles (EVs) generate substantial heat during high-rate charging and discharging, which can cause local overheating, accelerated capacity degradation, and, in extreme cases, thermal runaway. Conventional cooling approaches, such as air cooling and indirect liquid cooling, often struggle to maintain uniform temperature while adding weight and complexity to the design. As EVs power densities increase, advanced thermal management strategies are needed to ensure safety and efficiency. This study investigates the use of nanostructured copper tube surfaces to enhance condensation heat transfer as a compact and passive solution for two-phase battery thermal management systems (BTMS). Copper tubes (Ø6.35 mm, 200 mm length) were chemically etched to produce superhydrophilic surfaces, while superhydrophobic variants were obtained by further coating with polydimethylsiloxane (PDMS). Condensation tests were performed in saturated steam (~80 °C) with chilled water at 10 °C flowing inside the tubes. Results showed that the superhydrophobic surface achieved the highest thermal performance, with an average temperature difference of 2.94 °C, compared to 1.61 °C for the superhydrophilic and 1.16 °C for the untreated copper. The findings demonstrate that micro/nano-scale surface engineering can significantly improve condensation heat transfer, offering promising potential for integration into lightweight and compact EVs battery cooling systems.