Effective ultrafast charging of electric cars with a new type of cooled battery
Freudenberg Sealing Technologies has conducted a comprehensive study to investigate how typical polymer materials of seals and other components behave in such cooling fluids.
During “supercharging” of an electric car, as well as during extreme power output, the traction battery heats up considerably. The resulting temperatures can exceed the performance of current liquid cooling systems. Novel cooling strategies counter this: The battery cells are embedded directly in a specially developed cooling medium that effectively dissipates the heat.
More and more electric cars can fill up with fresh energy at a fast-charging facility. With a charging power of several hundred kilowatts, this fills the battery to 80% within half an hour, for example. The amount of energy flowing into the battery in this process is two to three times higher than in the opposite direction when energy is released even under high-performance conditions – for example, when an electric sports car drives through the Nürburgring North Loop. This operating state is called “supercharging.” During this process, the battery heats up considerably. If the cooling system is inadequate, this can have a negative impact on its power consumption and service life, among other things. Conventional liquid cooling systems, which cool complete battery cell systems from the outside, are reaching their limits. For this reason, automotive manufacturers are increasingly developing a new type of liquid cooling system that embeds cells and their electrical arresters in the cooling medium (“battery immersion cooling”): The medium flows directly around the individual cells and effectively dissipates the released heat.
Suitability of polymer materials in immersion cooling systems
The cooling media used in such systems have different chemical properties than previously used media. For example, they must be electrically insulating due to direct cell contact. Vehicle manufacturers are investigating several classes of cooling media, some of which are new and have very different chemical properties.
As essential components for such cooling systems, the chemical properties of sealing elements must be matched to the cooling media. Components such as connecting elements, cell spacers and media reservoirs must also be matched. In order to obtain a broad database for specific customer inquiries, Freudenberg Sealing Technologies’ material pre-development experts therefore conducted a comprehensive study to investigate the suitability of polymer materials for media used in “immersion cooling” systems.
The materials relevant to the company were exposed to different fluids. Among the fluids tested were isoparaffinic oils and ester-based oils specified and widely used for battery direct cooling. In addition to the most common fluids, the materials professionals also looked at types that fluid manufacturers’ development departments are currently working on.
Mutual effects of materials and fluids
The findings were quite surprising, depending on the fluid, says materials developer Dr. Tobias Möller. “The behavior of some novel fluids differs significantly from classic fluids. Nevertheless, we were able to identify suitable materials. Our guiding questions were: What swelling do the fluids generate in the polymer materials? And conversely, do the materials affect the fluids? The experimental conditions were challenging.”
Standardized test specimens made of the polymer materials were immersed in the fluids for a defined duration. To account for long-term effects and to accelerate the immersion, the temperature was considerably higher than is usual and desirable in battery systems. Key physical properties of the test specimens were then determined, such as volume, weight, recovery, elongation at break, and hardness, which are crucial for the full functionality of a seal over its entire service life.
“The study has brought great clarity. Now we have a comprehensive overview of how the tested polymer materials behave in typical cooling circuits. This is an excellent basis for developing future series seals and spacer elements,” summarizes Dr. Boris Traber, head of the company’s global materials pre-development. “We also now know more details about the fluids. All in all, Freudenberg Sealing Technologies can provide well-founded answers to specific customer inquiries and deliver reliable products as usual, also for this new cooling technology.”
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