ELECTROMOBILITY Cooling systems - Four methods to keep EVs cool
Battery technology is developing rapidly. However, lithium-ion (Li-ion) batteries are by far the most commonly used in electric cars and other alternative mobility options today. They may seem safe but the potential is there for catastrophe if they aren’t kept cool.
To keep batteries in check for electrified mobility options, cooling systems have been developed. Some may seem very similar to cooling systems in traditional petrol-engine vehicles while others are unique. All have the same purpose: to prevent battery failure.
Why cooling systems in battery-powered vehicles are necessary
In December of 2016, a Texas recycling plant had a serious and all-consuming fire when a discarded smartphone battery was crushed. It’s a minute fraction of the size of an EV’s battery, yet it can have dire consequences.
Thermal runaway can happen in EV batteries as well which are much, much larger. Typically, it’s due to a collision that pierces the Li-ion battery pack or while it’s charging. A BMW i3 caught fire while charging in Spain, luckily not causing damage to anything but the vehicle. The energy contained in an EVs battery pack is immense. A cooling system prevents the battery from overheating, keeping you safe while you drive around in it.
Four types of cooling systems exist to moderate the heat generated by EV batteries:
Fin cooling system
Early designs in electrification used cooling fins to dissipate heat. That’s the case with early plug-in hybrid models like the Chevrolet Volt. Li-ion cells sandwich the aluminum cooling fin to aid in even temperatures across the cells.
Fin cooling makes use of surface area to disperse heat. The larger the surface area, the more air heat the fins can absorb from the batteries and disperse into the atmosphere. While functional for smaller batteries on cars and especially electronics, fin cooling could not keep up with the rigors of modern long-range, high-capacity Li-ion battery packs.
Air cooling system
Again used mostly in early designs, air cooling is the simplest style of cooling system around. The premise is all about passing as much air over the battery pack as possible. Heat transfers from the battery into the less-dense air, then carried off into the atmosphere. The early Nissan Leaf design used air cooling.
Air cooling is particularly ineffective in hot climates where the ambient temperature is higher than the desired operating range. Safety concerns like thermal runaway become much more real, not to mention the operating range is severely reduced.
Indirect liquid cooling system
The most common way to cool EVs currently is with indirect liquid cooling systems. In this design, a series of pipes are routed through and/or around the battery pack much like a cooling system on an ICE vehicle. The fluid, typically glycol, is excellent at storing heat that is transferred from the warmer battery pack and circulating it to a heat exchanger like a radiator. This is the style used in EVs manufactured by Tesla, BMW, Jaguar, and Chevrolet, plus others.
Although the indirect cooling system is most common, it isn’t without its own issues. Fluid leaks inside the battery pack, for example, could be dangerous and there are environmental concerns regarding glycol disposal. For now, it remains the most desirable solution.
Direct liquid cooling system
The optimum cooling performance occurs when the coolant is in direct contact with the battery’s cells. A direct liquid cooling system would be able to absorb heat most efficiently, regulating the battery’s temperature precisely. However, the coolant would be required to be non-conducting so there would not be an electrical hazard.
Currently, no EVs use direct cooling systems but that could change soon. Developers such as XING Mobility and M&I Materials are leading the charge to get these non-conducting coolants into use in the auto industry.