E-Mobility Engineering 019 | In conversation: Stephen Lambert l WAE EVR l Battery case materials focus l Quality control insight l Clipper Automotive Clipper Cab digest l Optimising battery chemistries insight l Powertrain testing focus

36 modular design to stop thermal runaway propagation (TRP) before the casing has to contain it. Ideally, thermal runaway can be prevented at the cell level, then at a group of cells, then a bigger group of cells. There are several barriers to preventing propagation before it reaches the casing. This is part of the Failure Modes and Effects Analysis, but so far it has not been the critical decider for material choice. Regulation 100.3 in the Automotive Regulatory Guide requires giving occupants a 5-minute warning before there is fire outside the battery case, so the aim is to prevent getting to that point. This requires looking at the materials choices and the gas venting path. There is a major challenge for battery cases for low-volume automotive platforms, which are difficult to electrify as it is not cost-effective to create a cell-to-case design by creating a brand new cell. The best use of space has to be achieved in other ways, and the modular approach allows the modules to be as big as possible within that space. The load case is built into the design of the case platform, maximising the size of the module. This minimises There is no filler in cell-to-case designs that are in direct contact with the cooling plate; the thermal path is between the cell and the cooling plate. Then there is foamor potting that is structural, with the adhesive including an FR additive. This has higher structural properties with low density tominimise the weight by using polyurethanematerial. Some customers are looking only for structural strength, others require the structural strength with FR properties, but both need a high application rate. As this approach is a new development, battery architecture designers are still looking for the right way to go. With thermal propagation, there is the question of whether the flame retardant needs to be added to the foam or if another technology should be used. For example, foam potting is used for cylindrical cells, while for prismatic and pouch cells, fire protection pads or compression pads are used to compensate for swelling. This provides flexibility in the foam for movement and swelling, but it needs fast curing with one application rather than application in layers. The initial curing has to take only a fewminutes to allow for additional processes, while the full curing process needs a full day. Recycling Two sides to the materials question are emerging. There’s the performance and cost of the battery case now, and the recycling issues at the end of the vehicle life in 20 years’ time. Designers want to be certain that the cases can be recycled effectively. One design assumption for the cases is that at the end of the 20 years, the recycling processes will not be energy-intensive, but the worst case is that the cases will have to be shredded for recycling. That means the main consideration is the combination of adhesives and materials, as their interaction can cause problems in that shredding process. For example, composites such as carbon fibre-reinforced plastic are difficult to shred. Discontinuous carbon fibre and recycled carbon fibre might be easier for recycling and can replace structural and non-structural components to replace plastic components in automotive designs, but they are not cost-effective for case designs. So the design of the case means considering how to take the case apart, and not using materials that are hard to recycle while still ensuring safe performance. In a modular case, most of the materials are set in the battery platform. These include the plastic carriers, the adhesives and the busbars, all with a UL94 rating of V-0. The battery casing is part of the vehicle integration, so each vehicle designer comes with different needs. The case can be highly structural or not at all, the weight can be the top priority or perhaps range is more critical. Modular battery case designs with thermoplastics can provide an increase in energy density of more than 30% versus other designs, as this approach makes optimum use of the space available. There are several opportunities with a Focus | Battery case materials Gap fillers now have more requirements for the structural properties and to provide high thermal conductivity (Courtesy of Henkel) May/June 2023 | E-Mobility Engineering