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

you just need to know the rules,” he says. “You give plenty of space around the high-voltage interconnects, and you follow an architecture that has safety principles built in.” Thermal management e ects While the cell-to-pack concept has some impacts on thermal management, they are not fundamental. “In general, most modules are loaded onto a cold plate, and cell-to-pack would be no different,” the lithium metal battery developer notes. “In the case of prismatic can cells, they can be placed directly onto a cold plate and held in place with a thermally conductive adhesive. The vehicle technology and engineering services specialist says, “I would add that by removing the module, it’s clear that failure to design a safe cell-to-cell propagation prevention method will probably cause a more severe failure, without the module to provide containment, particularly when coupled with larger format cells. “Therefore, our thermal strategies have been designed from the ground up to ensure we go back to first engineering principles. We then accelerate our deployment of a given solution by using our strong intellectual property in this space. Now more than ever, we also leverage our control systems capability to ensure we are able to detect potential failures far in advance of a physical event.” While the impact on thermal management cannot be clearly generalised, says the adhesives, sealants and thermal interface materials expert, the effect on overall cooling requirements is expected to be low, and on cooling plate design it is expected to be moderate. However, the effect on the use of thermal interface materials could be more significant, particularly with prismatic cell designs. “As the cells are required to provide enhanced structural stability within the battery pack, conventional thermal gap fillers can be replaced by thermally conductive adhesives,” he says. With the omission of modules, the propagation of a thermal runway can be faster and more severe in cell-to-pack batteries, and needs to be addressed by additional safety measures, he adds. Further, larger cell designs are often seen in cell-to-pack concepts that can also lead to more severe thermal runaway events as more energy can be released. Thermal runaway prevention is expected to become more important in cell-to-pack designs by means of cell-to-cell heat shield materials, for example. The specialist EV builder notes that the effects of module-to-chassis and cell-to-chassis construction on thermal management can be application- specific. The company has developed a low-volume sports coupe with a module-to-chassis battery system with air cooling, for example. Air-based thermal management is sufficient when performance requirements are low, he says, while there are several ways of providing thermal management with liquid heat transfer media. These include hard- piped solutions, expanding enclosures that fully encapsulate individual modules or by immersion. “From a design point of view, how you integrate those will depend on the type of cell or module you’re using and the thermal challenges you’re presented with,” he adds. “There is some really interesting work being done around the immersed solutions at the moment. One of the significant issues with them, however, is that you end up with a very high-mass dielectric fluid. “The reality is that some of these technologies are well-developed. In our case, a module-to-chassis approach is proven in the coupe we have developed, and the platform can be used as the basis for a wide range of alternative applications, be they passenger or commercial. Full immersion of a pack, however, is still at a relatively low technical and manufacturing readiness level and needs significant work to understand the real-world benefits. Air cooling for the coupe’s module- to-chassis battery was chosen because it chimes well with the company’s philosophy. “What we are trying to do is ‘lightweight’ the EV,” its builder says. “The bonded aluminium and multi- material structure mean that we end up with a very light vehicle platform. “In the case of the coupe, we have a full vehicle that weighs under 1000 kg with a 40 kWh battery capacity. By reducing mass, we are seeing benefits at system levels throughout the While Tesla’s Model Y has the structural battery pack, the skateboard architecture of the Model X illustrates why making the pack as strong as possible can be desirable (Courtesy of Tesla) Summer 2022 | E-Mobility Engineering 71 Focus | Cell-to-pack batteries