Technology that allows vehicle body shells to serve as batteries may be a step closer to reality. Researchers at the Chalmers University of Technology claim to have produced a working "structural battery" that can both hold a charge and, as the name says, act as part of a vehicle's structure.

The battery is made from carbon fiber, which is already used for both body panels and monocoques, albeit primarily in high-end supercars and race cars. Carbon fiber is attractive to automakers and race-car builders because it's both lightweight and strong, but researchers have also shown that it can serve as an electrode and conductor, according to a Chalmers press release.

In the test battery, carbon fiber serves as the negative electrode, while the positive electrode is a lithium-iron-phosphate-coated aluminum foil. They're separated by a fiberglass fabric, which also houses the electrolyte.

Researchers have been working on structural batteries since 2007, and Volvo investigated this idea more than a decade ago. But this is the first with the potential to meet real-world targets for electrical properties and strength, researchers claim.

McLaren P1’s MonoCage carbon fiber monocoque

McLaren P1’s MonoCage carbon fiber monocoque

"Previous attempts to make structural batteries have resulted in cells with either good mechanical properties or good electrical properties," Leif Asp, a Chalmers professor and project leader, said in a statement. "But here, using carbon fiber, we have succeeded in designing a structural battery with both competitive energy storage capacity and rigidity."

At 24 watt-hours per kilogram, energy density is only about 20% that of current lithium-ion cells, researchers admitted. They expect the potential weight savings from the use of carbon fiber and elimination of heavy standalone battery packs will require less energy, though. The batteries could also be used in other applications, such as electric bicycles and consumer electronics, researchers suggested.

Carbon fiber itself takes more energy to make but studies have shown saves CO2 emissions over the vehicle lifetime. However, finding a way to produce the material on a large scale for mass-market vehicles has proven difficult.

Such technology, if it might be used, and if it can pass muster for safety, might be the key to solving a difficult tradeoff between lowering vehicle mass and raising battery pack size.