Carbon fibre vehicle chassis shown to store energy like a battery
Carbon fibre vehicle bodies have been shown to work as battery electrodes and directly store energy like a battery in a study from Chalmers University of Technology, Sweden.
This opens up new opportunities for structural batteries, where the carbon fibre becomes part of the energy system. In particular the researchers said such a system could contribute to a significant weight-reduction in the aircraft and vehicles of the future.
Passenger aircraft need to be much lighter than they are today in order to be powered by electricity. A reduction in weight is also very important for vehicles in order to extend the driving distance per battery charge.
“A car body would then be not simply a load-bearing element, but also act as a battery,” said Chalmers professor Leif Asp. “It will also be possible to use the carbon fibre for other purposes such as harvesting kinetic energy, for sensors or for conductors of both energy and data. If all these functions were part of a car or aircraft body, this could reduce the weight by up to 50 per cent.”
The researchers studied the microstructure of different types of commercially available carbon fibres. They discovered that carbon fibres with small and poorly oriented crystals have good electrochemical properties but a lower stiffness in relative terms. If you compare this with carbon fibres that have large, highly oriented crystals, they have greater stiffness, but the electrochemical properties are too low for use in structural batteries.
“We now know how multifunctional carbon fibres should be manufactured to attain a high energy storage capacity, while also ensuring sufficient stiffness,” Asp says. “A slight reduction in stiffness is not a problem for many applications such as cars. The market is currently dominated by expensive carbon fibre composites whose stiffness is tailored to aircraft use. There is therefore some potential here for carbon fibre manufacturers to extend their utilisation.”
In the study, the types of carbon fibre with good electrochemical properties had a slightly higher stiffness than steel, whereas the types whose electrochemical properties were poor were just over twice as rigid as steel.
For the aviation industry, it may be necessary to increase the thickness of carbon fibre composites, to compensate for the reduced stiffness of structural batteries Asp explained. This would, in turn, also increase their energy storage capacity.
“The key is to optimise vehicles at system level – based on the weight, strength, stiffness and electrochemical properties. That is something of a new way of thinking for the automotive sector, which is more used to optimising individual components.”
“Structural batteries may perhaps not become as efficient as traditional batteries, but since they have a structural load-bearing capability, very large gains can be made at system level. In addition, the lower energy density of structural batteries would make them safer than standard batteries, especially as they would also not contain any volatile substances.”