Johanna Xu (left) and Leif Asp (right) from Chalmers University of Technology examine a newly manufactured structural battery cell. Photo: Marcus Folino, Chalmers University of Technology.
Johanna Xu (left) and Leif Asp (right) from Chalmers University of Technology examine a newly manufactured structural battery cell. Photo: Marcus Folino, Chalmers University of Technology.

Researchers at Chalmers University of Technology in Sweden have produced a structural battery that performs 10 times better than all previous versions. The battery contains carbon fiber that serves simultaneously as an electrode, conductor and load-bearing material. This latest breakthrough, reported in a paper in Advanced Energy & Sustainability Research, paves the way for essentially 'massless' energy storage in vehicles and other technology.

The batteries in today's electric vehicles constitute a large part of their weight, without fulfilling any load-bearing function. A structural battery, on the other hand, is one that works as both a power source and as part of the structure – for example, in a car body. This is termed 'massless' energy storage, because in essence the battery's weight vanishes when it becomes part of the load-bearing structure. Calculations show that this type of multifunctional battery could greatly reduce the weight of an electric vehicle.

The development of structural batteries at Chalmers University of Technology has proceeded through many years of research, including previous discoveries with certain types of carbon fiber. In addition to being stiff and strong, carbon fibers also have a good ability to store electrical energy chemically.

The first attempt to produce a structural battery was made in 2007, but it has so far proven difficult to manufacture batteries that possess both good electrical and mechanical properties. Now, researchers from Chalmers, in collaboration with researchers at KTH Royal Institute of Technology in Stockholm, Sweden, report a structural battery with properties that far exceed anything yet seen, in terms of electrical energy storage, stiffness and strength. Its multifunctional performance is 10 times higher than previous structural battery prototypes.

The battery has an energy density of 24Wh/kg, approximately 20% of the capacity of comparable lithium-ion batteries currently available. But since structural batteries can help to reduce the weight of electric vehicles, less energy will be required to drive them, and lower energy density also results in increased safety. With a stiffness of 25GPa, the structural battery can readily compete with many commonly used construction materials.

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

The new battery has a negative electrode made of carbon fiber and a positive electrode made of a lithium iron phosphate-coated aluminium foil; these electrodes are separated by a fiberglass fabric in an electrolyte matrix. Despite their success in creating a structural battery 10 times better than all previous ones, the researchers did not choose these materials to try to break records – rather, they wanted to investigate and understand the effects of material architecture and separator thickness.

A new project, financed by the Swedish National Space Agency, is now underway, where the performance of this structural battery will be enhanced yet further. The aluminium foil will be replaced with carbon fiber as a load-bearing material in the positive electrode, providing both increased stiffness and energy density. The fiberglass separator will be replaced with an ultra-thin variant, which will give a much greater effect – as well as faster charging cycles. The new project is expected to be completed within two years.

Leif Asp, who is leading this project as well, estimates that such a battery could reach an energy density of 75Wh/kg and a stiffness of 75GPa. This would make it about as strong as aluminium, but with a much lower weight.

"The next generation structural battery has fantastic potential," says Asp. "If you look at consumer technology, it could be quite possible within a few years to manufacture smartphones, laptops or electric bicycles that weigh half as much as today and are much more compact."

In the longer term, it is absolutely conceivable that electric cars, electric planes and satellites will be designed with and powered by structural batteries. "We are really only limited by our imaginations here," says Asp. "We have received a lot of attention from many different types of companies in connection with the publication of our scientific articles in the field. There is understandably a great amount of interest in these lightweight, multifunctional materials."

This story is adapted from material from Chalmers University of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.