Carbon fibers could soon become part of the energy system for the next generation of structural batteries.
Researchers from Chalmers University of Technology in Sweden have discovered that carbon fibers can directly store energy by working as battery electrodes, which could ultimately contribute to an overall weight-reduction in future aircrafts and vehicles.
While carbon fiber has predominantly been used as a reinforcing material, the researchers found that it has the ability to perform more tasks, including storing energy.
After examining the microstructure of different types of commercially available carbon fibers, the researchers found that carbon fibers with small and poorly oriented crystals have good electrochemical properties, but a lower stiffness in relative terms.
However, carbon fibers with large, highly oriented crystals have a greater stiffness with electrochemical properties that are too low to use for structural batteries.
The type of carbon fibers best suited to store energy have a slightly higher stiffness than steel, while those with poor electrochemical properties are just over twice as rigid as steel.
“We now know how multifunctional carbon fibers should be manufactured to attain a high energy storage capacity, while also ensuring sufficient stiffness,” Leif Asp, a professor of Material and Computational Mechanics at Chalmers University of Technology, said in a statement. “A slight reduction in stiffness is not a problem for many applications such as cars.
“The market is currently dominated by expensive carbon fiber composites whose stiffness is tailored to aircraft use,” he added. “There is therefore some potential here for carbon fiber manufacturers to extend their utilization.”
Scientists need to find a way to significantly reduce the weight of passenger aircrafts in order to be powered by electricity. The weight of electric vehicles also need to be reduced to extend the driving distances possible for each battery charge.
“A car body would then be not simply a load-bearing element, but also act as a battery,” Asp said. “It will also be possible to use the carbon fiber 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,” he added.
According to Asp, in order for this new process to be suitable for the aviation industry, they may have to increase the thickness of the carbon fiber composites to compensate for the reduced stiffness of structural batteries, which would also increase the energy storage capacity.
“The key is to optimize vehicles at system level – based on the weight, strength, stiffness and electrochemical properties,” he said. “That is something of a new way of thinking for the automotive sector, which is more used to optimizing 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,” Asp added. “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.”
The study was published in Multifunctional Materials.