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

Focus | Cell-to-pack batteries Acknowledgements The author would like to thank Ian Goodman at Goodman Wolfe Consulting, Dr Tobias Knecht at Henkel Neil Yates at Watt Electric Vehicle Company, Pete Bishop at Silver Power Systems, James Hoxey at Williams Advanced Engineering, and Mark Niedzwiecki at Sion Power for their help with researching this article. vehicle. For example, the thermal loading of moving something weighing 1000 kg is much smaller than that generated by moving something that weighs 2000 kg.” Interconnects and the BMS The battery developer working with the EV builder stresses that in any battery pack there are really two interconnects to consider, the first being the high- voltage, high-power system for the traction motors, the second being the sensing and control network for the BMS. “When you have a system based on modules, the monitoring aspect can be effectively distributed through the module,” he says. “You might have a circuit board in each module for the temperature and voltage measurement, and that has a single Can bus connection that talks back to the master part of the BMS. “The high-power connections will be made via bolted connections or via a large pin on the connector. Those modules are typically identical, so they can be easily assembled in manufacturing and can be replaced during a refurbishment or repair of the pack. “In a cell-to-pack or cell-to-chassis design, the interconnects for the cells are either welded or bolted, depending on the cell format. They might be connected in groups if they are small cylindrical cells, groups of cells in parallel, fitted into the chassis or pack. The BMS will have its own ‘octopus’ of cables running out to the individual cells. “If you look at it from a logical perspective, the wiring diagrams would look the same but the physical implementation would be different between the systems.” Serviceability and replacement The lithium metal battery maker cautions that cell-to-chassis designs can make battery servicing difficult. “The battery enclosure portion of the vehicle chassis must be removable to be able to access and service the battery pack, and having an easily removable battery also facilitates battery swapping,” the company expert says. He stresses that the vehicle OEM must develop a strategy and requirements for servicing. For example, this would involve determining which components are serviceable, identifying the least replaceable unit, and deciding what the training requirements for technicians are. Another key decision is whether each dealership services the battery, or whether it should go to a regional repair facility. While adhesives can ensure strong, reliable fixing of cells to the chassis, repair, replacement and recycling are major challenges with this kind of battery architecture, the sealants and adhesives expert says. “The development of adhesive and mechanical concepts that allow a simple disassembly of the battery after reaching end-of-life or battery failure is a pivotal task.” Growing maturity The technical maturity of these architectures is progressing quickly, with cell-to-pack much further along. Multiple automotive OEMs and cell manufacturers have announced the introduction of their cell-to-pack and cell-to-chassis battery concepts to the market, with Tesla’s structural battery pack, BYD’s Blade battery and CATL’s cell-to-pack designs being the most prominent examples, the sealants and adhesives expert notes. “While early examples focused mostly on the safer LFP cell chemistry, recent announcements also include nickel-rich layered oxides that are considered harder to handle,” he says. “That clearly indicates the rising maturity of cell- to-pack technology. Following BYD’s cell-to-pack market introduction in its Han [luxury saloon] in 2020, more automotive OEMs are expected to announce development of novel cell- to-pack concepts.” The long, slim cells in BYD’s Blade battery are designed to optimise battery pack structure, enabling more than 50% better use of space than a conventional battery architecture (Courtesy of BYD) 72 Summer 2022 | E-Mobility Engineering