Considering aluminium or steel for your electric vehicle’s battery enclosure? How about a composite instead? In the United States, the Environmental Protection Agency (EPA) says that for every 100 pounds (45kg) of weight taken out of a vehicle, the fuel economy is increased by 1-2%. Let’s consider how composite EV battery enclosures could support the overall lightweighting mission, and provide additional structural benefits compared with the traditional metal offerings. Battery enclosures for EVs, also called frames, boxes or housings, have the primary purpose of holding and protecting the battery cells. They come in different shapes and sizes, and much like other vehicle parts, are an arena for several materials fighting for prominence. Aluminium and steel are traditional material choices. Yet, composites could provide an improved alternative, which will significantly improve the performance of the EVs.
The hurdles ahead for electric vehicles
Mass EV adoption is currently held back by range anxiety — concerns that vehicles won’t be able to travel far enough on a single charge. To alleviate this, there is an unquestionable need for safe, lightweight and cost-effective EVs. For these EVs to make it in the market, the components that form them must also possess these qualities. If a part can be made using a lighter material without compromising safety and function, then it’s a no-brainer for designers and material selectors in original equipment manufacturer and system supplier businesses. In some instances, switching from metal to composite doesn’t just match previous functionality, it surpasses it by bringing in additional benefits. This is demonstrated in the case of EV battery enclosures, as composites offer weight reduction, improved insulation, reduced noise, vibration and harshness. Let’s look closer at each characteristic.
Composites offer EV weight reduction
This is arguably the main driver in choosing composites, as a weight saving of up to 40% can be achieved if the enclosure is made from a pure composite material rather than aluminium. A lighter battery box has a positive knock-on effect on the entire vehicle. With a lighter vehicle weight, smaller batteries (or reduced engine sizes for hybrids) are required to haul the vehicle. This positive spiral results in reduced vehicle cost and range anxiety, which will play a big role in the mass adoption of EVs.
No need for separate insulation systems
Aside from being a lighter material in their own right, composites take away the need for a separate insulation system, which reduces weight even further, as well as helping to streamline the supply and value chain. With metal battery enclosures, an added insulation system around the material is required to keep the batteries in operational temperatures. Due to the insulating properties of composites, these materials already do a good job of preventing heat transfer, without the need to add more weight-increasing parts in the system.
Electric vehicles with lowered NVH
While not a safety-critical factor, a quieter vehicle is a more commercially viable vehicle. NVH is the result of vibration or noise, which is transmitted and radiated acoustically in the cabin. NVH is less with composites than with metals, as the former have inherent damping properties. This is true for the battery enclosures as well as other vehicle parts and could mean the difference between a luxury driving experience and a less comfortable one.
Boosted EV safety
Looking at the wider vehicle, composite battery casing can be designed as part of the vehicle body structure, not only protecting the battery, but also the passengers of the vehicle. The strength and stiffness properties of composites outweigh those of aluminium or steel, providing better crash safety. This integration will require close collaboration between the battery enclosure suppliers and chassis designers, but offers a real possibility to boost vehicle safety.
High-volume production is essential in reducing overall costs. It is possible to use continuous manufacturing methods such as pultrusion to produce EV battery box components. Pultrusion as a process enables composite manufacturers to pack in more fibres in the same cross section, compared with other composite manufacturing methods, allowing stronger, but lighter parts to be made.
Remember, the fibres are the part that carries the load in the material. Working closely with the composite manufacturer allows designers to precisely engineer the fibre content and alignments to achieve the best possible strength and weight properties at the best price point.
What’s next for composite EV battery enclosures?
If OEMs are going to reap the energy economy returns of light-weighting that the EPA predicted, composites will no doubt play their role. This could be a much bigger role than simply reducing the mass of the vehicle, but also improving crash safety, driving dynamics and experience as well as overall strength of the vehicle. Range anxiety remains one of the key hurdles that the EV sector must overcome, and thinking outside of the conventional material choices for battery enclosures are essential steps to reducing vehicle weight and reaping fuel economy returns.
• The author is Jari Sopanen, transportation segment owner at Exel Composites