A key challenge for automotive manufacturers is the need to reduce weight in order to extend the driving distance per battery charge. But at the same time safety cannot be compromised: electrical vehicles need to comply with established standards, particularly those involving frontal crashes.
Carbon fibre, which was originally employed for use in structural composites, is known to provide the most lightweight structural solutions by its unrivalled specific stiffness and strength. However, this material can also be used to store electrical energy.
Leif Asp, professor of material and computational mechanics at Chalmers University of Technology, says that “… we now know how multifunctional carbon fibres should be manufactured to attain a high energy storage capacity, while also ensuring sufficient stiffness. 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.”
The mechanical and electrochemical properties of carbon fibre are coupled through a piezo-electrochemical effect, which makes it possible to harvest electrical kinetic energy from a vehicle movements. The use of this type of multifunctional material opens up new opportunities for multifunctional structural batteries, where the carbon fibre becomes part of the energy system, which in turn can lead to a significant weight-reduction, up to 50%, in the vehicles of the future.
Asp headed up a multidisciplinary group of researchers who recently published a study on how the microstructure of carbon fibres affects their electrochemical properties – that is, their ability to operate as electrodes in a lithium-ion battery. So far this has been an unexplored research field.
The researchers studied the microstructure of different types of commercially available carbon fibres. They found that 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.
According to Asp, structural batteries may not become as efficient as traditional batteries. However, the key is to optimise vehicles at the system level – based on the weight, strength, stiffness and electrochemical properties. That is a new way of thinking for the automotive sector, which is more used to optimising individual components.
Report by freelance technology writer, Bob Emmerson