Swedish researchers have produced a battery made of ultra-lightweight materials, including carbon fibre that works as an electrode, a conductor, and a load-bearing structure, in a breakthrough that could pave the way for lighter, more efficient electric cars and planes.
The breakthrough in the long-running quest to develop “massless energy storage” was reported late last month, as the result of a collaboration between Chalmers University of Technology and KTH Royal Institute of Technology, both in Sweden.
The technology works using types of carbon fibre which, as well as being stiff and strong, have a good ability to store electrical energy chemically – a discovery that was named by Physics World as one of 2018’s ten biggest scientific breakthroughs, according to Science Daily.
“Previous attempts to make structural batteries have resulted in cells with either good mechanical properties, or good electrical properties,” said Leif Asp, Professor at Chalmers and leader of the project.
“But here, using carbon fibre, we have succeeded in designing a structural battery with both competitive energy storage capacity and rigidity.”
The battery uses carbon fibre as a negative electrode, and a lithium iron phosphate-coated aluminium foil as the positive electrode. The carbon fibre acts as a host for the lithium and stores the energy, but also conducts electrons, removing the need for copper and silver conductors and further reducing the weight.
The two electrode materials are separated by a fibreglass fabric in a structural electrolyte matrix, which serves to transport the lithium ions between the two electrodes of the battery, while also transferring mechanical loads between carbon fibres and other parts.
Science Daily reports that the structural battery presented by the team of researchers has properties that far exceed anything yet seen, in terms of electrical energy storage, stiffness and strength, offering a multifunctional performance 10 times higher than previous prototypes.
Even with this improved performance, however, the researchers’ battery currently has an energy density of 24 Wh/kg, which translates to roughly 20 per cent capacity compared to comparable lithium-ion batteries currently available.
But the team argues that – using the example of electric cars – since the weight of the vehicles can be greatly reduced, less energy would be required to drive them. The study notes that in a Tesla model S (85 kWh), the battery weighs around 25% of the total vehicle weight.
“Current battery systems add weight with no contribution to the system’s structural performance,” the introduction to the research paper says.
“For electric vehicles to be more efficient, and for all‐electric aircraft to evolve, total energy storage must be increased while maintaining or reducing weight.”
To this end, a new project is being financed by the Swedish National Space Agency to increase the performance of the team’s structural battery further, replacing the aluminium foil with carbon fibre as a load-bearing material in the positive electrode, providing both increased stiffness and energy density.
The new project, which is expected to be completed within two years, will also replace the fibreglass separator with an ultra-thin variant, providing a much greater effect and faster charging cycles.
Leif Asp, who will lead this project too, estimates that such a battery could reach an energy density of 75 Wh/kg and a stiffness of 75 GPa, making it about as strong as aluminium, but with a comparatively much lower weight.
“The next generation structural battery has fantastic potential,” said Asp in comments to Science Daily. “We are really only limited by our imaginations here. 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.”