Leif Asp, a materials scientist at the Chalmers University of Technology in Sweden, has been at the forefront of structural battery research for the past decade. In 2010, Asp, Greenhalgh, and a team of European scientists collaborated on Storage, a project that aimed to build structural batteries and integrate them into a prototype hybrid Volvo. “At that time, I didn’t think it would have much impact on society, but as we moved along it struck me that this could be a very useful idea,” says Asp, who characterizes the conventional battery as a “structural parasite.” He says the main benefit of structural batteries is that they reduce the amount of energy an EV needs to drive the same distance—or it can increase its range. “We need to focus on energy efficiency,” says Asp. In a world where most electricity is still produced with fossil fuels, every electron counts in the fight against climate change.

During the three-year project, the Storage team successfully integrated commercial lithium-ion batteries into a plenum cover, a passive component that regulates air intake into the engine. It wasn’t the car’s main battery, but a smaller secondary pack that supplied electricity to the air-conditioning, stereo, and lights when the engine temporarily turned off at a stop light. This was the first proof of concept for a structural battery that was integrated into the body of a working car and was essentially a small-scale version of what Tesla is trying to achieve.

But sandwiching a bunch of conventional Li-ion cells into the body of a car isn’t as efficient as making the car’s body serve as its own battery. During the Storage collaboration, Asp and Greenhalgh also developed a structural supercapacitor that was used as a trunk lid. A supercapacitor is similar to a battery but stores energy as electrostatic charge, rather than a chemical reaction. The one made for the Volvo trunk consisted of two layers of carbon fiber infused with iron oxide and magnesium oxide, separated by an insulating layer. The whole stack was wrapped in laminate and molded into the shape of the trunk.

Supercapacitors don’t hold nearly as much energy as a battery, but they’re great at rapidly delivering small amounts of electric charge. Greenhalgh says that they’re also easier to work with and were a necessary stepping stone toward accomplishing the same thing with a battery. The Volvo was a proof of concept that structural energy storage was viable in an EV, and the success of the Storage project generated a lot of hype about structural batteries. But despite that enthusiasm, it took a few years to procure more funding from the European Commission to push the technology to the next level. “This is a very challenging technology and something that’s not going to be solved with a few million pounds thrown at it,” says Greenhalgh of the financing difficulties. “We got a lot more funding, and now it’s really starting to snowball.”

This summer, Asp, Greenhalgh, and a team of European researchers wrapped up a three-year research project called Sorcerer that had the goal of developing structural lithium-ion batteries for use in commercial aircraft. Aviation is arguably the killer app for structural energy storage. Commercial aircraft produce a lot of emissions, but electrifying passenger jets is a major challenge because they require so much energy. Jet fuel is terrible for the environment, but it’s about 30 times more energy-dense than state-of-the-art commercial lithium-ion cells. In a typical 150-passenger aircraft, that means you’d need about 1 ton of batteries per person. If you tried to electrify this jet with existing cells, the plane would never get off the ground.