‘Massless’ energy storage solution comes from Sweden

It contains carbon fibre that serves simultaneously as an electrode, conductor, and load-bearing material. This research breakthrough paves the way for essentially ‘massless’ energy storage in vehicles and other technology.

‘Massless’ energy storage

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 multi-functional battery could greatly reduce the weight of an electric vehicle.

The first attempt to make a structural battery was made in 2007, but it has so far proven difficult to manufacture batteries with both good electrical and mechanical properties.

Now the development has taken a real step forward, with researchers from Chalmers, in collaboration with KTH Royal Institute of Technology in Stockholm. Presenting a structural battery with properties that far exceed anything yet seen, in terms of electrical energy storage, stiffness and strength. Its multifunctional performance is ten times higher than previous structural battery prototypes.

The battery has an energy density of 24 Wh/kg, meaning approximately 20 percent capacity compared to comparable lithium-ion batteries currently available. But since the weight of the vehicles can be greatly reduced, less energy will be required to drive an electric car. And with a stiffness of 25 GPa, the structural battery can really compete with many other commonly used construction materials.

Selection of materials

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

Now, a new project, financed by the Swedish National Space Agency, is underway, where the performance of the structural battery will be increased yet further. The aluminium foil will be replaced with carbon fibre as a load-bearing material in the positive electrode, providing both increased stiffness and energy density. The fibreglass 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 too, estimates that such a battery could reach an energy density of 75 Wh/kg and a stiffness of 75 GPa. This would make the battery about as strong as aluminium, but with a comparatively much lower weight.

Collaboration is key

The project is run in collaboration between Chalmers University of Technology and KTH Royal Institute of Technology, Sweden’s two largest technical universities. The battery electrolyte has been developed at KTH. The project involves researchers from five different disciplines: material mechanics, materials engineering, lightweight structures, applied electrochemistry and fibre and polymer technology.

Funding has come from the European Commission’s research program Clean Sky II, as well as the US Airforce.