Researchers who are developing 'structural' batteries made of carbon fibre composite say the technology could cut energy usage and weight in electric cars by allowing the vehicle's battery to function as both a power source and part of the structure of the vehicle.
A team at Chalmers University of Technology in Sweden has published research on how new types of batteries, made of carbon fibre (as seen in the picture above) could help reduce the weight of electric vehicles and extend their driving range by doubling up as part of the car's structure – like the roof or bonnet.
“Structural batteries offer potential to achieve weight savings of up to 20% by just replacing the roof of an electric vehicle with a structural battery,” the researchers said in the paper published in the journal Advanced Materials.
"We have succeeded in creating a battery made of carbon fibre composite that is as stiff as aluminium and energy-dense enough to be used commercially,” said Chalmers researcher Richa Chaudhary. “Just like a human skeleton, the battery has several functions at the same time.”
The battery is based on a composite material and has carbon fibre as both the positive and negative electrodes, where the positive electrode is coated with lithium iron phosphate. Previously the core of the positive electrode was made of an aluminium foil. In the anode the carbon fibre acts as a reinforcement, as well as an electrical collector and active material. In the cathode it acts as a reinforcement, current collector, and as a scaffolding for the lithium to build on, the researchers said.
The carbon fibre conducts the electron current, which the researcher said reduced the need for current collectors made of copper or aluminium which reduces the overall weight. In the battery, the lithium ions are transported between the battery terminals through a semi-solid electrolyte, instead of a liquid one; the team note this is “challenging” when it comes to getting high power and more research is needed, although they point out the design does contribute to increased safety in the battery cell, through a reduced risk of fire.
Structural battery research has been going on for many years at Chalmers; the team published their first results in 2018 on how stiff, strong carbon fibres could store electrical energy chemically. Since then, the research group has further developed its concept.
In 2021 the team developed battery had an energy density of 24 watt-hours per kilogramme (Wh/kg) and has now increased that to 30 Wh/kg. While this is still much lower than what existing lithium-ion batteries can offer, the researchers note that when the battery is part of the construction an electric car, for example, the overall weight of the vehicle is greatly reduced which means not as much energy is required to run it.
"Investing in light and energy-efficient vehicles is a matter of course if we are to economise on energy and think about future generations. We have made calculations on electric cars that show that they could drive for up to 70 percent longer than today if they had competitive structural batteries," says research leader Leif Asp.
The research team has increased the stiffness of the structural battery cell has increased its stiffness – specifically the elastic modulus – from 25 GPa to 70 GPa. This, they said, means that the material can carry loads just as well as aluminium, but with a lower weight.
However, the team said there is still a lot of engineering work to be done before the battery cells can be taken from lab manufacturing on a small scale to being produced on a large scale. The researchers said that batteries for devices such as phones or laptops would be the first step, or components such as electronics in cars that could be powered by structural batteries.
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