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

Peter Donaldson gauges the state of development of the various types of battery construction New connections M ost EV battery packs are built from groups of cells housed in modules interconnected within a case that provides structural support, thermal management, environmental protection and connectivity with the rest of the drivetrain, but this is not the only way to do it. There are potential benefits to eliminating modules and building packs up from cells inside the case, in what has become known as the cell-to- pack arrangement. A logical extension of this idea eliminates the dedicated case from the battery pack in the so-called cell- to-chassis concept. A third idea also discards the dedicated case but brings back the module, and is referred to as module-to-chassis construction. The point of all these is to improve the ratio of energy to weight and volume at pack level, and reduce the number of components in the pack and the manufacturing costs. One major and immediate effect of moving to cell-to-pack construction of batteries is on the cells themselves. According to one EV consultant cum battery systems developer and manufacturer we spoke to as part of the research for this article, the cells used are likely to be in prismatic or pouch format and larger, in terms of physical size as well as energy capacity. The main advantage of the cell- to-pack approach that flows from the use of fewer, larger cells is the smaller bill of materials and fewer interconnects, simplifying assembly and potentially increasing reliability. A Tesla battery pack might have 6000 cells, the consultant points out. “You break that down into maybe 16 modules on a Model S or four in a Model 3, and in either case that is a lot of interconnects, each of which is a potential point of failure. Going to cell- to-pack eradicates a lot of that, or at least minimises its impact.” Eliminating modules through cell- to-pack construction gets rid of all the associated structure in their side walls, tops and bases. That frees up more volume inside the case for the cells, increasing the volumetric energy density (kWh/litre) at pack level. While the lower parts count probably cuts costs by itself, it can also lead to fewer production steps, and potentially reduces the overall engineering effort required. Module-to-chassis could be seen as a stepping stone towards cell-to- chassis construction, the latter building individual cells directly into vehicle’s primary structure. The principal Williams’ FW-EVX platform incorporates cell-to-chassis battery architecture with cells in carbon fibre cases that contribute to strength and crashworthiness (Courtesy of Williams (d]anced Engineering) 64 Summer 2022 | E-Mobility Engineering