The heart of the electric vehicle (EV) is its battery, which has been the primary focus of R&D efforts over the past decade. Not so obvious a research target but equally important is where the battery lives.
The battery box houses the cells and protects them from dust, water, and impact. These cases can also provide structural support for the cells and incorporate thermal management for optimised performance. As a protective enclosure, they make a pivotal contribution to vehicle safety but also pose significant design challenges in terms of performance, weight, cost, and manufacturing. This is where the collaborative research project ALuminium Intensive Vehicle Enclosures (ALIVE) has made promising developments.
The project kicked off in 2020 with the aim of developing improved structural aluminium battery enclosures for EVs. Led by aluminium specialist Constellium’s University Technology Center (UTC) at Brunel University London, consortium partners also included BMW, Volvo, EXPERT Technologies Group, Innoval Technology, Powdertech, and WMG (University of Warwick). The £15m (US$19m) project was half funded by UK government subsidies through its Advanced Propulsion Centre.
“The main problem was that today’s battery box manufacturing lines are bespoke to a single design,” explains Martin Jarrett, Technology Director for Constellium’s Automotive Structures & Industry business unit and UTC leader. “There isn’t much ability to share technology across different vehicle models or brands. At the same time, they are also highly capital intensive. We launched the ALIVE Project to tackle just that.”
The target was a modular and scalable aluminium battery box design that could be used for a range of different vehicles. Harnessing the same basic technology in a flexible way could open the door to lower manufacturing costs and greater supply chain resilience. By the time the project concluded in May 2024, the team had a solution with some impressive metrics.
Flexible, cheap, light
The battery enclosure designs and associated manufacturing technologies developed under ALIVE enabled weight savings of 12% to 35% compared to existing OEM aluminium and steel designs, respectively, while meeting or exceeding performance targets. That’s down to a combination of joining and forming technologies and Constellium’s family of high-strength and high-crash alloys, Constellium HSA6 and Constellium HCA6.
The team also realised huge advances in terms of production costs. “We’ve demonstrated that we can produce battery boxes—both structural and non-structural—with 35-50% less capital than the equivalent standard battery box production,” Jarrett tells Automotive World. Structural battery packs serve as part of the vehicle’s load-bearing structure while non-structural ones do not.
“In the initial months of the project in 2020 and 2021, there was a lot of development from the OEMs in terms of cell-to-module and cell-to-pack designs,” he notes. The different design approaches require various levels of structural integrity from the box itself, and the ALIVE solution’s design needed to be flexible enough to accommodate all options.
“What started off as basically a fully structural battery box with integrated side cells suddenly became a non-structural battery box, where the side cells were displaced into the architecture of the vehicle,” Jarrett explains. “As a consequence, we also developed innovative side cell technology.”
Today’s aluminium-extruded side cells tend to be large, multi-cell hollows, which can be made on a limited number of extrusion presses around the world. The team explored how they could produce side cells by extrusion on smaller presses, using a dual material approach. This consisted of a very strong inner material to protect the batteries joined to an outer portion made of more ductile material to absorb energy in a crash. “This gives us a much more flexible approach to side cell production,” he emphasises.
Another important aspect to the solution stems from the use of a U-frame made from a freeform bender. “It negates what you would normally see in a battery box, where the front is stretch-bent, cut, and welded,” states Jarrett. “With our approach, we eliminate all those step by producing a single profile and joining it at the one end.” This reduces the number of welds and fabrication steps, as well as the opportunity for potential leak paths frequently found at that front end, where the stretch-bent part is joined to the horizontals. “The weld there can often be problematic, but we managed to overcome that,” he points out.
From passenger cars to heavy trucks
This particular project focussed on passenger vehicles, working to design specifications for consortium partners BMW and Volvo, but the technology is transferrable to any OEM and any vehicle. “It’s basically a skateboard type design, but we’ve also taken that concept and developed it into more upright, chest-type battery boxes that can be used for larger vehicles, including heavy trucks and off-road vehicles,” says Jarrett. “They require a much larger battery box, but the idea and the concepts that have been designed through the ALIVE Project allow us to grow vertically and horizontally, so we can then accommodate much bigger battery capacities.”
The team is currently prototyping its designs for OEMs which, for now, remain unidentified. A battery box prototyping line is up and running in the UK, and the plan is to promote the technology to more industry players and eventually launch mass production. Building on the learning from ALIVE, Constellium has begun a follow-on collaborative R&D project exploring aluminium recycling within battery boxes.
For suppliers, the ability to provide different battery box designs off the same equipment could go far in improving their resiliency in an unpredictable market. EV sales projections have not played out as many expected, and the past year has seen several big name automakers dial back their production plans and launch schedules. A supplier that can only provide the battery box for one particular vehicle could find itself in a very risky situation if that original forecast doesn’t play out. “Our solution allows for greater flexibility when it comes to some of the EV production forecasts,” he points out.
By lowering the manufacturing costs of this pivotal component, savings could trickle down to the EV sticker price. There have long been calls for more affordable electric models, and this could contribute. “By helping the supply chain, we are making EVs more of an economic possibility for consumers,” Jarrett concludes. He estimates these new battery boxes could find their way into a production car within the next five years.
