Thermal Management Mode for
Pure Electric Vehicles: Battery Immersion Cooling
Air-cooled systems are the most widely used because they are simple in design, inexpensive and have no leakage problems. Air cooling is divided into active type with forced convection and passive type with natural convection. The small heat capacity (Cp = 1.006 kJ/kgK at standard temperature) and low thermal conductivity of air compared to media such as liquids make it unlikely that air cooling will be the technology of choice for the next generation of electric vehicles with larger battery packs and faster charging rates.
Liquid cooling can be categorized into indirect and direct approaches. Compared to air, coolant has greater heat capacity and higher thermal conductivity. Indirect liquid cooling is currently one of the most common solutions for battery thermal management due to balanced temperature control. The most commonly used coolant is a mixture of water and ethylene glycol. The principle of indirect cooling is to allow the coolant to flow through channels on the bottom or side of the cell/cell module to transfer heat out of the system.
The cooling effect can be improved by using specific thermal interface materials (TIM). The disadvantage of indirect liquid cooling compared to air cooling is the complexity of the system. More components as well as channels/lines may lead to more failures, extra weight and leakage problems.
Another emerging cooling technology is direct liquid cooling, also called immersion cooling, which completely submerges the cell in a dielectric liquid. This is a non-conductive liquid with a high resistance to electrical breakdown. The introduction of this technology means that the complexity of the battery process and component design can be greatly reduced, as well as helping to reduce the weight and size of the system and significantly improving the stability and balance of the battery temperature control. Immersion cooling allows the battery to be heated or cooled as needed without the use of heat exchangers, which brings significant gains in efficiency. Immersion cooling of EV batteries is still in its infancy, but some use cases have already emerged, such as Faraday Future's patented full immersion cell system, the immersion cooling technology of the Dakar Rally car Audi RS Q e-tron, or the IMMERSIO™ system by former employees of Panasonic and Tesla.
