E-Mobility Engineering 016 l Aurora Powertrains eSled dossier l In Conversation: Thomas de Lange l Automated manufacturing focus l Torque sensing insight l Battery Show Europe 2022 report l Sodium batteries insight l User interfaces focus

that for VW’s ID3 have ratios of around 35 to 37%. Cylindrical cells are at the lower end of that range, while prismatic cells are a bit better, but prismatics have a lower energy density because they contain voids. “With a three-in-one construction, we are targeting ratios of up to 60% with pouch cells,” Giaume said. The key idea was the creation of a plastic sandwich strong enough to form part of the module structure, through which a dielectric fluid can be circulated. The fluid provides direct cooling of the electrical connector plates, which are analogous to busbars inside the module and are connected at right angles to the current collector plates in each cell via the tabs. In many battery designs, the tabs are the parts that get the hottest. “Cells are very anisotropic in terms of thermal conductivity,” Giaume said. “That’s because of the [metal] current collectors that run along the length and height of the cell, especially in pouch cells, but through the thickness there is very little, so we extract heat from these preferential directions to optimise thermal management.” Using a 3D-printed electrically inert demonstrator, Giaume showed us how the basic ‘mini-module’ unit is assembled, in this case using pouch cells. The ends are formed as sandwich plates designed to be injection moulded from an aromatic polyamide material such as DuPont’s Zytel HTN, which has a high glass-transition temperature that gives it very stable mechanical properties from -40 ºC to +80 ºC. The sandwich structure is completed by aluminium outer skins, making the end piece a hybrid construction in material terms and a very stiff torsion box structurally. A key enabler of the concept is the chemical bond that forms between the aluminium electrical connector plate and the polyamide on the end piece when the two components are welded together, which takes about 45 seconds, Giaume said. The bond is enabled by a water- based proprietary coating that activates the surface of the aluminium and allows it to ‘pick up’ the molecules of polyamide as it melts. “This can achieve around 60 MPa of lap shear strength, which is two to three times stronger than any adhesive,” he said. The sides of the mini-module are formed by a pair of pressure plates that are bolted to the end pieces. These side plates compress the cells and also contain fluid passages and space for BMS circuit boards and sensors. A flexible foam between the cells allows for expansion and contraction as they charge and discharge. Aluminium top and bottom plates complete the mini- module, forming another very rigid torsion box. The three-in-one modules can be stacked vertically, horizontally and end to end to form mega-modules and complete packs. Where two modules meet end to end they share a single end piece, which handles structural loads, cooling and electrical connection for both of them. “So, in the volume of a conventional 60 kWh battery you could pack almost 95 kWh. It’s all about packaging,” Giaume said. Henkel revealed two new thermal coatings for battery packs at the show: the epoxy-based Loctite EA9400 and the water-based Loctite FPC5060. Both materials are designed to be applied to the inside of a battery pack lid. “If there is a thermal event, their job is to keep the heat and fire inside the battery,” Asa Persson explained. The epoxy material will keep the outside of the pack lid about 700 °C cooler than the inside, for example. “You have a lower temperature on the other side of the battery lid than with the water-based product, but in tests they have both shown the ability to withstand an 1100 °C fire for up to 10 minutes,” Persson said. The single-component FPC5060 takes the form of a beige inorganic paste created by the aqueous synthetic resin dispersion method, and the cured coating does not produce smoke or fumes when exposed to heat. It is sprayed onto the part, and a 4 mm-thick coat cures at room temperature in 24 hours, or less if heat is applied. “We know short curing times are essential for OEMs, so we are looking at ways to reduce them,” Persson noted. The two-component EA9400 is applied using a flat stream process, and after 60 minutes the battery lid is ready to be transported to the next station on the assembly line. After 120 minutes it can be loaded onto a carrier/truck, while after 180 minutes it is touch-dry. Although initially intended for the inside of a battery pack lid, EA9400 can be used wherever heat needs to be kept away from critical parts. “Thinking of new applications, you could coat the corners near the tyres and wheels, and you can also coat surfaces vertically as well as horizontally,” Persson added. Applied to the outside of the battery box, EA9400 can also provide corrosion protection to the aluminium, while using it underneath could protect the battery from grass fires, with which all EV OEMs need to comply, Persson pointed out. /enkel»s fire resistant coatings for applications sucO as tOe inside of Iattery pack lids oɈer tOe cOoice of epoxy Iased or water Iased formulas Winter 2022 | E-Mobility Engineering 49 ShowReport | Battery Show Europe 2022