Which cooling system works best in electric vehicles?

Battery thermal management system is still a subject of much research. As engineers constantly reflect on how our automobile engines work, our understanding of them will change and develop in the next few years.

There are several ways to cool electric vehicle batteries using phase change materials, heat sinks, air or liquid coolants

1. Phase change materials absorb heat energy by transforming solid into liquid. When the phase changes, the material can absorb a lot of heat, but the temperature change is very small. Phase change material cooling system can meet the cooling requirements of battery pack, but the volume change during phase change limits its application.

2. The surface area of automobile radiator shall be increased to improve the heat transfer rate. Heat is transferred from the battery pack to the heat sink through conduction, and from the heat sink to the air through convection. Fins have high thermal conductivity and can achieve the cooling target, but they add a lot of extra weight to the battery pack. The use of fins has been very successful in the electronic field. Traditionally, they have been used as an additional cooling system for internal combustion engine vehicles. The use of heat sinks to cool electric vehicle batteries is no longer popular because the extra weight of the heat sinks outweighs the benefits of cooling

3. Air cooling uses convection principle to transfer heat from the battery pack. When air flows over the surface, it will take away the heat emitted by the battery pack. Air cooling is simple and feasible, but compared with liquid cooling, it is not efficient and relatively rough. Air cooling was used in earlier versions of electric vehicles, such as the Nissan Leaf. With the use of electric vehicles becoming more and more popular, pure air cooling battery packs have appeared safety problems, especially in hot climates. Other car manufacturers, such as Tesla, insist that liquid cooling is the safest method

4. Liquid coolant has higher thermal conductivity and heat capacity than air (the ability to store heat in the form of its bonds), so it has very effective performance and its own advantages, such as compact structure and easy layout. Among these options, the liquid coolant will provide the best performance to maintain the battery pack at the correct temperature range and uniformity. The liquid cooling system also has safety problems related to leakage and handling, because ethylene glycol can cause danger to the environment if not handled properly. Tesla, Jaguar and BMW are currently using these systems.

5. A research team from the National Renewable Energy Laboratory of the United States and the National Active Distribution Network Technology Research Center of China compared four different cooling methods for lithium-ion bag batteries: air cooling, indirect liquid cooling, direct liquid cooling and fin cooling. The results show that the air cooling system needs 2 to 3 times more energy than other methods to maintain the same average temperature; The indirect liquid cooling system has the lowest maximum temperature rise; The fin cooling system adds about 40% of the extra weight of the battery. When the four cooling methods have the same volume, the weight of the battery is the largest. Indirect liquid cooling is more practical than direct liquid cooling, although its cooling performance is slightly lower.