E-Mobility Engineering 014 l InoBat Auto dossier l In Conversation: Brandon Fisher l Battery monitoring focus l Supercapacitor applications insight l Green-G ecarry digest l Lithium-sulphur batteries insight l Cell-to-pack batteries focus

include stakeholders from battery cell engineering, battery pack engineering, vehicle assembly, purchasing and logistics. The analysis should study the entire EV production process rather than being limited to a direct one-to- one comparison of cell-to-pack or cell-to-chassis versus module-to-pack assembly construction.” Physical integration impacts In terms of physical integration of the battery into the vehicle, the cell-to- pack approach may seem very similar to traditional cell-to-module-to-pack construction, but it still requires careful consideration. “Much of our activity in this area is looking at how we can use the cells to give structure to the overall vehicle performance, through a detailed, virtual characterisation from the cells to the systems,” notes one vehicle technology and engineering services specialist. “Through physical testing to correlate the models, we are able to analyse various scenarios to provide the best solution for a given application.” He emphasises that with one fewer barrier – the module structure – to protect the cells in crash scenarios, there has to be much more focus on the interaction between the cells, the battery case and the vehicle structure to ensure a safe and practical solution. “It would be wasteful to create additional volume for cells, if only to allocate it to larger walls around the battery enclosure due to poor understanding of how the impact deforms the structure. Again, this can be managed through strong modelling techniques.” Further challenges, he adds, are encountered as the battery system enclosure interacts with more of the chassis and vehicle system elements, such as seating anchors in the Tesla Model Y, for example. The structural impact of the cell- to-chassis approach is much greater. “New solutions must be developed that ensure a safe placement of the battery cells inside the vehicle chassis over the full lifetime,” an adhesives, sealants and thermal interface materials expert notes. “Current design concepts range from using special cell carriers to hold the cells in place, mechanical elements at the side, bottom or top of the battery pack, and most important new adhesives to allow a strong and reliable connection of battery cells to the bottom or cooling plate in the vehicle,” the expert adds. “Further developments address novel insulating coatings for prismatic cell cans that can be used instead of conventional polymer foils and improve the bonding between the cell and the cooling plate.” The structural battery pack in Tesla’s Model Y can be seen as an example of the cell-to-chassis philosophy because, as the name suggests, the pack is a key load bearing member of the vehicle’s chassis, and it can be configured with or without modules. Cell-to-pack construction also has implications for the shape of battery packs, argues the EV consultant and battery systems manufacturer, which is a consequence of using much larger cells. “The downside of that is that the lowest common denominator is a fixed shape, a problem that does not exist with 21700 cylindrical cells, for example, as you can make the pack any shape you like because they are quite small cells,” the consultant says. “When you jump up to modules, there are again quite a lot of ways in which you can change their layout, so you have some flexibility, but when you go to cell-to-pack – if you use very large cells – you lose most of that flexibility.” While this is not really a problem for vehicles whose battery packs are large rectangular slabs, he says, for EVs derived from IC engine platforms the structure can be very restrictive, as it forces designers to shape the pack to fit the available space. However, EVs based on IC engine- powered platforms are likely to be rare in future. One approach to cell-to-chassis construction implies the need for cells whose construction can add to the structural strength of the vehicle, the EV consultant adds. “My interpretation is that you literally don’t have any other supporting structure.” These cells might be very large and strong enough to form a structural element of the frame, in the way some motorcycle engines are. “I don’t think that’s ever going to happen, and I don’t know any cell manufacturers or designers who ever want that to happen,” the consultant says. Focus | Cell-to-pack batteries Battery packs with a cell-to-pack design and cylindrical cells typically have a terminal at each end of the cell, which can complicate the task of making cell-to-cell electrical connections (Courtesy of Henkel) 66 Summer 2022 | E-Mobility Engineering