Carbon fiber as we know it is one of the most impressive materials in our toolkit. Its incredible lightness and strength has seen it take hold in everything from competitive cycling, to supercar design to cutting edge aircraft. But could it also play a role in energy storage? One team of scientists has been exploring the possibilities, and say that carefully engineered forms of the material do indeed boast the necessary electrochemical properties, raising some interesting possibilities for weight-saving vehicle design.
The research was carried out at Sweden's Chalmers University of Technology and started with a pretty simple premise. Carbon fiber has already been shown to have potential as an electrode material in experimental batteries, while its mechanical properties are well established, so can these two attributes be combined in the one multipurpose material?
Carbon fiber manufactured for structural purposes is generally engineered to be as stiff as possible, but these materials leave a lot to be desired in terms of electrochemical capacity. Conversely, carbon fiber with good electrochemical abilities tends to offer a much lower stiffness.
In what they say was an unexplored field of research, the scientists set out to find a carbon fiber that can fit both bills. This meant studying the microstructures in different types of commercially available carbon fibers, looking at how the crystals within were sized and arranged. They discovered that carbon fibers with greater stiffness had large, highly oriented crystals, while less stiff carbon fiber had small and poorly oriented crystals.
This new knowledge, the researchers say, provides a basis for the pursuit of carbon fibers that hit the sweet spot, offering both useful electrochemical properties and required stiffness. And as study author Leif Asp explains, there is a bit of room to move in the current crop of commercially available carbon fibers.
"We now know how multifunctional carbon fibers should be manufactured to attain a high energy storage capacity, while also ensuring sufficient stiffness," he says. "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. There is therefore some potential here for carbon fiber manufacturers to extend their utilization."
Because weight is so critical in vehicle design and the fuel efficiency of the finished product, the scientists are already imagining how this new material, if developed to become part of the energy system, could shake things up. The researchers are already working with the automotive and aviation industries to explore these possibilities for structural batteries.
"A car body would then be not simply a load-bearing element, but also act as a battery," he says. "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."
The research was published in the journal Multifunctional Materials.
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