Four methods to keep electric vehicle batteries cool

For battery performance and lifespan, keeping the battery pack within the right temperature range is key. We'll tell you more about the different battery cooling methods for electric vehicle batteries that a used and the up and downsides of these methods.

1. Air cooling

By running air through the battery pack batteries can be cooled. For example, Nissan uses this technology to cool the batteries of the Nissan Leaf. They circulate the air from inside the car through the battery pack. With this system the batteries can be cooled but can also be heated during cold winter days. A downside to this system is that the temperature of the air inside the vehicle is also the temperature with which the batteries get cooled. When you turn up the heat inside the car because you are cold, the batteries get heated as well. This is sometimes not ideal, especially when high power is requested.

Another way of cooling the batteries with air, is by guiding the outside air through ducts to the battery pack in the vehicle. In this case, the temperature of the batteries will fluctuate with the fluctuation of the temperature outside. During hot summer days, the batteries will rise in temperature as well. This is again a problem for high power application since the risk of overheating the battery increases.

In most low to medium power applications, air cooling is sufficient. The power demanded from the drivetrain is not that high causing the battery temperature to stay around the surrounding temperature. Even when high power is demanded occasionally, air cooling will still be enough because the batteries will have more than enough time to cool down after a short high-power demand.

When the demanded power gets higher, the air cooling system will not be sufficient anymore. Let us look at some other types of cooling systems.

2. Liquid cooling

Liquid cooling is the most popular way of cooling a battery pack. A liquid cooling system consists of a lot more components then for example an air-cooling system. These components do make it possible to improve the cooling performance by upgrading the components.

Electric vehicle manufacturers like Tesla and Audi use liquid cooling in their battery packs. This cooling system is a separate cooling system which only cools the battery pack, the motor and controller are cooled with a second liquid cooling system because of the temperature differences between the components. The battery pack needs to stay below 60 degrees Celsius, causing the temperature of the cooling fluid to stay as low as possible. The temperature of the motor and controller can reach temperatures as high as 140 degrees Celsius.

When those three components share the same cooling system, the battery pack will be heated by the motor and controller. A separate cooling system for the battery pack is necessary.

Liquid cooling is the most favorite solution for almost every battery pack. Whether it is a low power or high-power application, liquid cooling has the most advantages. With low power applications, the battery pack can be nursed so it will always operate at the right temperature. With high power applications the battery pack can be cooled to the maximum. The temperature of the cooling system must be kept as low as possible to enable maximum power for the longest time possible.

Besides all these cooling advantages, the battery pack can be heated as well by adding a heating element in the cooling system.

As said before, the cooling system of the battery pack and the cooling system of the motor and controller need to be separated. These two cooling systems can occasionally be combined to heat the battery pack when needed by the motor and controller. Tesla uses this method for example. They can heat the battery pack with the heat generated by the motor and controller. This is very useful during cold winter days.

3. Cooling with heat conducting materials

Heat conducting materials, such as heat pipes can be used to withdraw heat from the battery pack. This is a slower way of cooling the batteries then when using liquid cooling. Also, metals like aluminum and copper are heat conducting materials. Unfortunately, this way of cooling is only one part of the cooling system instead of a complete one. When using this as the only cooling system, the heat conducting material needs to be very large. The heat conducting material has a certain heat capacity. This is the amount of heat that a material can absorb per weight of the material. For a large withdrawal of heat from the battery pack, the heat conducting material would need to be massive.

This means that this way of cooling will need to be combined with another cooling system such as the two systems mentioned earlier. The heat conducting material will guide the heat to the other cooling system.

4. Submersion cooling

Another way of cooling a battery pack with liquid is to submerge the complete battery pack in the cooling fluid. This technology is already used in the world of supercomputers. However, this method is very expensive.

Another downside is that the amount of fluid used has a certain heat capacity. As explained before, this is the amount of heat that a material can absorb. By submerging the entire battery pack in a fluid, the fluid can only cool as much as the heat capacity allows it to. In other words, the fluid heats up together with the battery pack. The fluid just slows this process down.

In high-power applications this method of cooling will need to be combined with other types of cooling systems. For example, the housing can be made of aluminum which conducts heat very well. When air passes alongside this housing, the battery pack and the fluid inside can be cooled.

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