Episode 1: Carbon fiber-based structural battery serves multiple functions

In this podcast episode, MRS Bulletin’s Laura Leay interviews Leif Asp of Chalmers University of Technology about his group’s development of an all-carbon fiber-based structural battery. The negative electrode uses carbon fiber and, for the positive electrode, the carbon fiber is coated with lithium iron phosphate. In both cases the carbon fiber takes on the roles of mechanical reinforcement and current collection. This work was published in a recent issue of Advanced Materials.

Transcript

LAURA LEAY: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on hot topics in materials research. My name is Laura Leay. Lithium ion batteries are currently in widespread use but their energy density still doesn’t compare to more traditional means of powering transportation. One challenge for their use in these applications is that they add to the mass of a vehicle. New developments of a multifunctional battery show that it’s possible to have a battery that can also carry a structural load. Whereas previous experiments have used carbon fiber for the positive electrode, the new type of battery uses carbon fiber to construct both electrodes, oriented to impart strength and stiffness in one direction. The negative electrode uses carbon fiber without further treatment but for the positive electrode, the carbon fiber was coated with lithium iron phosphate, or LFP. In both cases the carbon fiber takes on the roles of mechanical reinforcement and current collection. For the untreated negative electrode the carbon fiber performs a third function. Professor Leif Asp, from Chalmers University of Technology in Sweden, explains.

LEIF ASP: We have two electrodes that are based on the carbon fibers but only one case – negative electrode – are the fibers actually the active material. In the positive side they are coated with a cation material as the active material, but it serves still as reinforcement and current collectors.

LAURA LEAY: The electrolyte is a semi-solid composite. A solution of monomers and electrolyte is heated, causing the monomers to polymerize into a glassy network with the electrolyte filling a network of pores. The polymer allows mechanical load transfer to the carbon fiber electrodes.  Different separators were used between the two electrodes. This latest research is encouraging, demonstrating an energy density of 30 Watt-hours per kilogram and stability over up to 1000 cycles. This performance, particular the energy density, is likely to improve but the remarkable mechanical properties of this all-carbon fiber battery demand attention.

LEIF ASP: We can expect this to increase, to at least double, within reasonable years. So I would say that we can end up with maybe 40-50% of the conventional LFP-based battery but of course one has to realize this comes with additional mechanical load carrying capability. The modulus of this is actually a stiffer response than you would get from aluminum. So this is the combination of performances that we are after.

LAURA LEAY: This means that future electrified transport options could be designed differently; the design would need to consider how structural components can also be replaced with the battery. To consider how well it would perform as a structural component requires assessment on a case-by-cases basis depending on the mechanical load. This necessitates multifunctional analysis at a systems level where both power requirements and mechanical performance are considered. Refining different components of the battery could lead to improvements in performance both in terms of electrical performance and mechanical. 

LEIF ASP: Within the year we will see 100 GPa modulus – 30% higher than aluminum – and maybe 60 Wh/kg. I think that’s doable. I think over 100 Wh/kg is doable. Strength over 700 MPa is also doable. We are working on the cost of making the carbon fibers for the negative electrode. We are working on replacing some of the fibers used in the positive to get even higher modulus. We’re looking at making the coating on the structural battery positive electrode more ductile.

LAURA LEAY: Some of these materials swell and contract during charge/discharge cycles which can induce stress. Professor Asp’s team is now working on multiscale models to understand these changes. These advances involve a multidisciplinary team which includes electrochemists, materials and mechanical engineers, electron microscopists and physicists working together creatively. 

LEIF ASP: We all meet in this field and together try to develop this. It’s super-exciting getting to work in such a diverse team.

LAURA LEAY: This work was published in a recent issue of Advanced Materials. My name is Laura Leay from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on X, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.