A new computational model and experimental data from carbon fiber-based composite battery electrodes could pave the way for high-performance structural components with energy storage capabilities, according to researchers [Carlstedt et al., Composites Science and Technology 220 (2022) 109283, https://doi.org/10.1016/j.compscitech.2022.109283]. Such innovative multifunctional materials could be crucial to the realization of lightweight all-electric aircraft in the future.
“We wanted to realize structural battery composites with multifunctional performance,” explains first author of the study, David Carlstedt of Chalmers University of Technology. “[But] to do so, we needed computational models to guide our work.”
Together with colleagues at Hamburg University of Applied Sciences, the researchers first created composite electrode lamina from commercial carbon fibers embedded in a structural polymer matrix consisting of a solid porous vinyl-ester based skeleton saturated with a lithium-containing liquid electrolyte, building on earlier work [e.g., Johannisson et al., Composites Science and Technology 168 (2018) 81-87, https://doi.org/10.1016/j.compscitech.2018.08.044]. The carbon fibers perform a dual role. On one hand, the fibers store electrical energy in the form of chemical energy by accepting lithium ions from the electrolyte during charging. The ions are released during discharging, enabling the carbon fibers to work as battery electrodes. Simultaneously, the carbon fibers provide structural support to the porous polymer matrix. This dual functionality allows the exploitation of carbon fiber-based composites as structural batteries.
The team investigated the composite’s electro-chemo-mechanical performance as a material and in terms of its battery performance. Simultaneously, they used a computational modelling framework to predict the composite’s properties and compared the predictions with experimental data. The electrode thickness, electrolyte transport properties and applied current all significantly affect the electrochemical performance of the composite, according to their findings, while fiber expansion during lithiation creates mechanical strain within the material.
“[These] coupled electro-chemo-mechanical processes occur simultaneously and affect each other,” points out Carlstedt. “The mechanical load will affect the open cell potential and the state of lithiation will affect the fiber moduli and volume.”
The team are now working on balancing these factors and improving the combined electrochemical and mechanical performance by reducing the separator and electrode thickness and improving transport properties of the structural polymer electrolyte, for example, to boost power output.
“The novelty [of our approach] stems from the fact that the carbon fiber electrodes allow for new and innovative designs,” says Carlstedt. “For example, in addition to making a battery with the ability to sustain mechanical loads, the fibers also allow for curved shapes of the battery/material.”
The carbon fiber composite is also promising for strain sensing and could be applied more generally in conventional battery design. The computational approach could be explored with other battery designs.
Schematic illustration of the carbon fiber/structural battery electrolyte electrode. The structural battery electrolyte consists of two phases: a solid phase corresponding to a mechanically robust porous polymer network and a liquid phase containing a Li-salt liquid electrolyte. The liquid phase in the porous polymer network enables ion transport between the electrodes, while the solid phase can distribute mechanical loads. The hierarchical structure of the composite electrode is shown in (c) at different length scales.