Scientists from Chungbuk National University in South Korea have presented a new cooling system for 4680 format lithium-ion batteries, which are used in modern electric vehicles, including the new Tesla model. This solution combines the operating principles of a heat pipe and two-phase immersion cooling, providing for efficient heat removal from batteries without pumps and other active elements, solely through the natural circulation of liquid between the evaporation and condensation zones.
The 4680 format is one of the most important technological advances in the field of batteries. It provides high energy density and makes it easier to assemble battery modules. However, these elements generate a lot of heat, especially during fast charging or intensive operation. Temperatures can exceed the safe threshold of 60°C, accelerating battery wear, reducing battery capacity and increasing the risk of overheating. Conventional cooling systems (air or liquid ones) often fail under such loads, especially at high currents.
The South Korean researchers have proposed an original solution: a sealed chamber containing batteries and a small amount of cooling liquid. When heated, the liquid evaporates, rising to condense on the cooling plate and then seeping down the walls or through a special porous wick. This creates a closed two-phase heat removal cycle. The entire system, which operates passively without external energy sources, is simple, reliable and silent.
The key element of this design is the wick, which helps the liquid come back to the evaporation zone. The scientists tested six wicks, differing in material (polyurethane, cellulose, combined fabric) and shape. The best efficiency was demonstrated by a wick made of mixed fabric with a crown geometry, which allowed steam to freely escape upwards. This configuration (Wick 5) maintained the temperature at 47°C with a thermal load of 85 W, providing a minimum temperature difference across the surface (2.8°C) and a low thermal resistance (0.26°C/W), which indicates that the system is stable and operates in a uniform fashion.
The results were further confirmed by computer models created using the AMESim and ANSYS Fluent engineering software. The simulation made it possible not only to evaluate the system’s operation under conditions that are difficult to reproduce in the laboratory, but also to determine the optimal parameters. The most stable operation was observed when 30–40% of the chamber was filled with liquid. At a smaller volume, the liquid quickly evaporates and the wick dries out. At a larger volume, circulation gets disrupted and evaporation becomes less effective. The scientists also found that with a thermal load above 155 W, the system fails due to accumulating steam, which disrupts the phase heat exchange process.
The biggest advantage of this system is its simplicity and efficiency. It does not require complex equipment and can operate with a minimum volume of liquid. The compact and modular design makes it possible to shorten the distance between batteries without the risk of overheating. Amid increasing electric vehicle production, where every millimeter and every gram is crucial, this solution might prove especially useful.
In the future, the scientists plan to adapt the system to work with dielectric (non-conductive) liquids, which will make it completely safe for use in real battery modules. They are also planning to develop more precise models that take into account the microstructure of wicks and the peculiarities of heat exchange in porous materials.
