A study led by Chalmers University of Technology, Sweden, has shown that such structural batteries can significant reduce the weight of electric aircraft and vehicles.
“A car body would then be not simply a load-bearing element, but also act as a battery,” said Leif Asp, Professor of Material and Computational Mechanics at Chalmers University of Technology. “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 percent.”
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. Compared to 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,” said Asp. “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 are just over twice as rigid as steel.
The researchers are collaborating with both the automotive and aviation industries, where it may be necessary to increase the thickness of carbon fibre composites to compensate for the reduced stiffness of structural batteries. 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,” he said. “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.”
Graphitic microstructure and performance of carbon fibre Li-ion structural battery electrodes was published in the journal Multifunctional Materials.
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