Battery performance is crucial to the continued advancement of electric vehicle (EV) design. One of the fundamental challenges in creating a battery pack is the effective management of heat generated during the battery’s charge and discharge cycles.
A basic principle of physics is that heat can be transferred in three ways: radiation (the outward propagation of infrared waves), convection (the movement of molecules in liquids or gasses from hot areas to colder areas), and conduction (transfer of energy via direct contact with an adjoining body). When comparing the efficacy of each method, it is helpful to think of cooking as an example. Cooking food using solar radiation would be ineffective (assuming no devices were used to concentrate the solar rays). Similarly, cooking with a blow dryer, which uses a motor to force fluid motion, would be impractical. But by placing a pan directly on a stove burner and using conduction, heat is transferred very efficiently and food quickly cooks.
The same concept holds for batteries: transferring heat is best accomplished using conduction. We see evidence of this fact with our cell phone batteries, which depend upon radiation for their heat to dissipate into the open air—the phones can become excessively hot and will shut down. Fans rely on convection to cool the central processing units (CPUs) in computers. But again, the effectiveness is limited, as we see when computers get too warm while doing the hard work of, say, streaming videos or playing games.
Currently, some leading car manufacturers use EV battery pack designs that employ radiant methods of heat dissipation. The result is poor temperature distribution that results in hot spots and EVs that are limited in the performance they can offer—making them disadvantaged in the marketplace. A majority of the latest generation of EVs and upcoming prototypes, however, are turning to conductive, liquid-cooled methods for thermal management.
For optimal conductivity, every cook knows that a pan’s bottom must maintain close contact with the stove burner, and again, it’s a similar story for electric vehicle batteries: the battery pack must be in close contact with a cooling plate. To the naked eye, these surfaces within the battery assembly appear to be quite smooth and in perfect contact. At the microscopic level, however, both surfaces have peaks and valleys that create roughness, entrap air and prevent ideal contact.
Battery manufacturers use thermal interface materials (TIMs) to displace the air and fill in the gaps between the two substrates. The two most commonly used TIMs are cure-in-place, liquid-dispensed gap fillers, and pre-cured thermal pads.
Parker LORD’s CoolTherm™ liquid-dispensed gap fillers are made specifically for the automotive industry. They feature high thermal conductivity with low viscosity and help to wick away heat. As a specialized product, they are a more economical choice for car manufacturers than gap fillers which meet a range of specs across multiple industries. CoolTherm™ gap fillers help manufacturers economize in another way: liquid dispensed into the gap area will flow into all of the microscopic spaces, allowing for looser tolerance for both design and manufacturing. Decreasing tolerances by just one millimeter can add substantial cost to the battery pack’s metal housing…but manufacturers can save money by relaxing tolerances for those metal-to-metal connections and achieve the same amount of heat transfer by using gap fillers in the extra space.
Contact us today and learn how to save money while improving EV battery performance!