50 January/February 2024 | E-Mobility Engineering substrate film passes between the gravure roll and the backing roll, the coating material in the engraved cells is transferred onto the substrate. The engraved pattern determines the thickness and distribution of the coating. Coatings for cooling plates are almost always sprayed on or deposited electrostatically, notes Dean at Parker Lord. “This ensures more uniform coverage on large parts with interesting geometries.” He notes that overspray from the company’s Sipiol UV dielectric coating is collected for reuse during the application process. “Cylindrical cells are a good option for roll coating because of their flat surface and relatively small surface area.” With dielectric coatings, the main application technologies are electrodeposition coating (e-coating), powder coating and UV-cured liquid coatings, or some combination of these, explains Munro at PPG. In general, e-coats are applied as liquids. The coating material is contained in a bath and is given a positive electrical charge, while the parts dipped into the bath are given a negative charge. The attraction between the charges ensures that the coating sticks to the parts. E-coat application systems require significant manufacturing space, can be capital-intensive, and make it difficult to change coating material. “But it is a very robust system” Munro notes, “providing uniform coverage of complex parts and shapes, high productivity, typically smaller maintenance cost in the long run, and great usage of material with minimal solid waste. In essence, e-coat systems are great for large production components such as lids, trays, frame plates, module racking, or anything of that sort.” The next major option is powder coating, which can be fully automated with robotics or inline spraying. As with e-coating, powder coatings are typically electrostatic processes, and they also have a significant manufacturing footprint, although some reductions can be achieved through the use of IR curing systems, Munro notes. One of the drawbacks of powder coating is that the complex shapes of some components causes them to form Faraday cages, which shield some areas from the electrostatic charge, resulting in some areas not receiving the coating as intended. “The benefits of powder coating far outweigh most of the negatives, though,” Munro argues. “They have great mechanical properties, ensuring components hold up over the battery’s lifetime, offer high utilisation of the coating material through recycling, and are applicable to many different part types and shapes within the pack, including lids, treys, frame plates, module racking and cooling tubes,” he says. “We coat millions of cooling tubes with our ENVIROCRON® Dielectric PRO.” UV cured coatings are the newest option for applying dielectric coatings to battery components but have some drawbacks. These include limited options among equipment suppliers along with an early focus on cell applications, which today limits the technology’s suitability for other components. Also their mechanical properties are not as robust as those of powder or e-coats, Munro reports. “UV coatings do a few things really well though,” he adds. “Those are fast, high-volume production along with the ability to coat filled battery cells, which other systems are unable to do safely. They also offer significantly lower energy costs compared with some of the other methods, which benefits manufacturers who are attempting to maximise throughput. “What’s consistent across all of these application methods is that they’re highly automated,” Munro adds. “That can drive us to very high efficiencies and first-run rates on the production of these types of materials.” He emphasises that PPG tailors its coating solutions to customers’ preferences and established capital assets and supply chains. “Anywhere we can take advantage of things that are already deployed, it’s just going to help them progress far more rapidly to scale.” Near term predictions In the realm of promising new coating technologies, Dr Knecht points to Henkel’s conductive electrode coatings for cells. Parker Lord’s Dean reckons that the limitations of PET films and powder coatings will lead to more adoption of coatings applied as liquids for dielectric protection. “The volumes, throughput, cost, and more demanding OEM requirements around voltage, durability, and multifunctionality will drive this adoption.” With dielectric coatings, Munro at PPG anticipates much greater use of UV-cured materials because they are solids, their application consumes relatively little energy and yields faster throughput when coating filled cells. “This is the next large movement in coatings for the battery pack, along with fire protection considerations.” Insight | Battery coatings Exposure to UV light initiates a chemical reaction that causes a monomer to form a cross-linked polymer with the aid of a photo-initiator chemical, the final polymer consisting of a threedimensional network of interconnected molecules (Image courtesy of Parker Lord)
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