The automotive industry tends toward tradition and incremental change, which is why the development of effective electric vehicles (EVs) has been so challenging. Still, the momentum toward their development is gaining by the day and with these innovations come the inevitable challenges associated with them.
One of the most significant challenges facing the development of EVs is how to keep the batteries cool enough to function at peak performance throughout the life of the vehicle. Initially, original equipment manufacturers (OEMs) tried to air-cool batteries but, as performance and safety demands increased, they have moved towards water-glycol cooling systems instead.
While these systems are a significant improvement over air-cooling, the water-glycol cooling systems still present challenges as EV batteries strive to charge faster and operate more safely. The question facing EV OEMs today is what technology will provide the most effective cooling system in the future as these vehicles become more prevalent on the roads. To answer that question, we must first examine the differences between internal combustion engine (ICE) vehicles and EV motors and their electrical hardware.
ICE vs. EV
ICE vehicles generate a significant amount of waste heat. On average, an ICE vehicle uses about 40% of its heat to keep engine components running. The other 60% of the generated heat exits the vehicle via the exhaust or is used for other purposes ranging from heating the vehicle’s cabin to running its catalytic system. While it is a thermally-inefficient system, the waste heat doesn’t affect vehicle drivability or performance.
In an EV, however, excess heat is much more of a problem as heat can damage the sensitive electrical equipment vital to keeping the vehicle in working order. Even though EVs systems can run up to 90% efficient and generate much less heat, the damage that can be done to their power system is much more devastating.
Overheated batteries, for example, can age quickly, diminishing their range, power and overall efficiency. In addition, heat can damage some electric motor components and power electronics, causing unacceptable breakdowns that are often expensive to fix. Finally, uncontrolled heat generation could lead to safety issues, in cases of thermal runaway.
To understand why new technology is so crucial to the future development of EV systems, it’s important to examine how the industry has cooled its batteries in the past and how most EVs keep their batteries from overheating currently.
History of EV Battery Thermal Management
Early cooling systems for EVs were inadequate and resulted in warranty claims, shortened battery life and longer charging times. Limitations of these early cooling systems prevented OEMs from introducing “fast-charging” technology because of the heat it would generate. Consumers looking for quicker charging times grew impatient with the original EVs’ slow charging times and the lack of effective cooling prevented that from changing.
To deal with the overheating issue, which degrades the battery, most of today’s EV manufacturers have turned to the technology they were most familiar with from their ICE offerings: a water-glycol cooling system. Tubes filled with the water-glycol mixture snake their way through the battery pack in the EV and keep temperatures at between 20 to 32 degrees Celsius, which is the ideal operating temperature for the batteries.
While this form of active cooling has allowed faster charging speeds and extends the battery life, it does have its own shortcomings. The heat doesn’t dissipate as readily as it could otherwise because it must travel from the battery pack through the cooling jacket to reach the coolant. In other words, while water-glycol cooling is more performant than air-cooling, it is still not an ideal system. It doesn’t cool effectively enough to enable the rapid charging that will be necessary if EVs are to make a difference in today’s automotive marketplace.
That’s why the emerging technology of immersion cooling is so exciting. Though no EV OEM is currently using larger scale immersion cooling technology, some proof of concept and niche applications are already in the market and many industry stakeholders working closely to further develop the technology, which is likely to be more largely as soon as 2025 and beyond.
The Advantages of Immersion Cooling
At the simplest level, immersion cooling is exactly what it sounds like: a system that contains liquid with a battery pack immersed in it. No cooling jacket is needed and the dielectric fluid comes into direct contact with the battery. This enables faster cooling and safer operation. Following are some of the advantages of immersion cooling:
- Allows XFC (Extra-Fast Charging) charging in under 10 minutes (typical charge is 10 - 80% SoC)
- Improved battery thermal control
- Improved heat-transfer performance by a factor of 20
- Reduced potential for thermal runaway
- Extended battery lifetime
Battery simulations of high-speed charging have been conducted to see how significant the difference is when charging a battery at a rate greater than 3C. Immersed-cooled batteries reduced peak temperature by 5% versus water glycol systems.
Based on initial testing, it becomes increasingly clear that immersion cooling is a superior battery thermal management technology that will become standard to cool high-performance EV batteries in the future. As the technology emerges into real-world applications, it becomes worthwhile to partner with companies that understand how to formulate effective, durable and safe dielectric fluids for each specific EV battery system.
As immersion cooling for EV batteries becomes more prevalent throughout the industry, the fluids that will be used in the process will have to evolve as well. It’s important to find a partner who can work in tandem to develop the Battery Thermal Management Fluid (BTMF) at the same time as the OEMs/Tier One Suppliers develop the Battery Thermal Management Systems (BTMS) to keep them one step ahead of their competitors.
For more information on immersion cooling, contact us or visit the Electrification section of Lubrizol360.