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

A battery sealing and thermal interface materials supplier notes that omitting battery module housings raises a number of issues, as they are important safety elements in battery packs. Additional safety measures are therefore required for cell-to-pack and cell-to-chassis pack designs that, for example, mitigate thermal propagation in case of a cell fire. “Battery modules are also important mechanical elements that ensure a stable position of battery cells, compensate for cell breathing and contribute to the overall mechanical integrity of the battery pack,” a company expert says. “Battery manufacturers have to develop new concepts that compensate for the omission of battery modules from a mechanical perspective.” Our specialist EV developer stresses that challenges present themselves in the design of the vehicle itself and in manufacture at different volumes. “From a design perspective, every vehicle has differing requirements, whether it’s a passenger vehicle, sportscar, last- mile delivery van or larger commercial truck, and the set of challenges vary depending on the application and the performance requirements,” the EV developer says. “You have to consider the volumes of vehicles you are looking to produce, how many batteries you are looking to build, and what the processes for those builds will be in a battery environment,” the developer adds. “At low volumes, for example with specialist sportscars or some commercial vehicles that undergo body conversions, you typically have a very labour-intensive build process, so a more complicated battery build process is acceptable because the assembly methodology allows for that. “If you are producing vehicles in the hundreds, thousands or tens of thousands of units per year you need a heavily automated solution. You need a very clear understanding of the requirements, not just from a technical and performance perspective but also from a commercial point of view.” A developer of lithium metal batteries argues that the biggest challenge that has to be overcome is traditional thinking about how vehicles, including their battery packs, are manufactured, from raw materials through to just-in- time delivery of major subsystems. “To be viable, cell-to-pack and cell-to-chassis systems must be more productive across several metrics, including development effort, safety, total cost, assembly time and performance,” a company expert says. “With that in mind, the cost-benefit analysis should be holistic and advantages are efficiency of packaging, structural performance and weight reduction in the resulting vehicle, says one specialised EV developer. “Effectively, you are reducing the replication of structural performance,” a company expert says. “If you have a large standalone battery pack within any vehicle chassis, you effectively need a very large void to accommodate it, which is structurally inefficient. You end up building additional structural strength into the battery case itself and, you have to reinforce the chassis structure where the battery pack bolts into it. “When you remove that large void from the chassis you can design the primary structure in a much more efficient way, using less material and with more direct control of load paths.” A battery developer adds that cell- to-chassis construction also allows for better weight distribution. “If you’ve got a single mass pack effectively mounted into the chassis in a specific number of locations, you can’t really distribute the weight in the same way,” a company expert says. “Direct cell-to-chassis allows for optimisation of weight distribution.” Inevitably, there are challenges with these approaches to battery design, and a senior engineer with a vehicle technology and engineering services company highlighted meeting safety requirements while delivering maximum performance with respect to cell-to- pack designs in particular. “From this perspective, moving the pack to be more of a structural part of the vehicle, and removing the modules, can remove certain failure mode mitigations around cell venting and propagation,” an expert from the company says. Cooling also needs to be managed differently when taking this approach, and welding processes have to be reimagined for production solutions. Battery pack with a cell-to-pack design and prismatic cells, illustrating the option of using fewer but larger cells than typically in packs based on cylindrical cells (Courtesy of Henkel) Summer 2022 | E-Mobility Engineering 65 Focus | Cell-to-pack batteries