Researchers at Chalmers, in collaboration with Carbon Nexus at Deakin University, have shown how the manufacturing process can tailor carbon fiber's multifunctional properties. An important step in the development of structural batteries.
Carbon fiber is best known for being a very strong and light construction material but can also store energy electrochemically. This multi-functionality can be used to make what are known as structural batteries. The carbon fiber then functions both as a construction material and energy storage at the same time. This means significant weight savings.
Carbon fiber's properties vary depending on the process parameters and what precursor that is being used. Some types of carbon fiber can be very stiff, but have a far too low electrochemical storage capacity, and vice versa. To be able to build efficient structural batteries, you therefore need carbon fiber that combines a sufficiently high electrochemical storage capacity together with sufficiently good mechanical properties. The better the combined properties, the more efficient the structural battery.
It is well known which manufacturing parameters affect carbon fiber's mechanical properties, but relatively little about its electrochemical storage capacity. An important step in the development of structural batteries is therefore to understand how the manufacturing process can be tuned to optimize the multifunctional properties of the carbon fiber.
The first step in carbon fiber manufacturing takes place by spinning organic polymers, which are held together by carbon atoms, into a plastic fiber thread. The polymeric precursor comes almost exclusively from oil, although other types of material can be used. In this study, a yarn of commercial polyacrylonitrile (PAN) fiber was used. In the next step, the plastic fiber thread is pulled through several ovens in what is known as the stabilization and oxidation process. The plastic fiber thread can be pulled with varying amounts of tension, which affects the microstructure.
"Best multifunctional performance occurred at medium tensile stress. It gave almost a maximum electrochemical capacity together with a relatively good stiffness. The study shows that the electrochemical capacity is affected by both amorphous and crystalline phases, that is the disordered and ordered states of the atoms. Simply, it's about making as well-balanced microstructural compromise as possible based on the intended area of use", says Johanna Xu, researcher at the Department of Industrial and Materials Science, Chalmers.
The multifunctional properties that the researchers have achieved are on a par with certain types of commercial carbon fiber available today. However, there is very limited public knowledge on how the manufacturing process affects the multifunctional properties.
"What’s special about the study is that we show how the process can be controlled to optimize the multifunctional properties. In our continued research, we will also study the influence of temperature in the carbonization process, which is the next step in manufacturing", says Johanna Xu.
Leif Asp has been researching carbon fiber for a long time, and has seen an increased interest in recent years when it comes to structural batteries.
"I have definitely noticed an increased interest in structural batteries. There are more and more researchers in the field and the efforts are getting bigger. It also creates opportunities for more joint projects where we can utilize each other's strengths. Our fantastic collaboration with Carbon Nexus and Deakin University is a good example of that, says Leif Asp," professor at the Department of Industry and Materials Science, Chalmers.
Facts
The results are presented in: Effect of tension during stabilization on carbon fiber multifunctionality for structural battery composites - ScienceDirect
Authors of the study: Johanna Xu, Claudia Creighton, Marcus Johansen, Fang Liu, Shanghong Duan, David Carlstedt, Pablo Mota-Santiago, Peter Lynch, Leif E. Asp
The carbon fibers were manufactured in Australia at Carbon Nexus, Deakin university which is one of the few independent research facilities with the latest technology.