The electrical response of carbon fibre reinforced electrodes in structural power composites under cyclic compaction

Multifunctional structural power composites (SPCs) provide a lightweighting solution for conventional electrochemical energy storage, while offering additional mechanical capability. This work studied the anisotropic electrical response of woven carbon fibre (WCF) reinforced structural supercapacitor electrodes, i.e., plain weave, spread tow, and carbon aerogel (CAG) modified spread tow fabrics, under cyclic compaction. Experimental results show that 1 MPa compaction increased in-plane conductivity by over 60 % and out-of-plane conductivity by at least five-fold for all fabrics tested. Numerical studies revealed that the intra-yarn fibre volume fraction is a critical factor for both in-plane and out-of-plane electrical performance. The predicted in-plane conductivity of woven fabrics presents a linear relationship with the intra-yarn fibre volume fraction, following a modified rule of the mixtures (ROMs). For the out-of-plane conduction, a larger number of percolating paths formed with more fibre-to-fibre contacts and fibre clusters under a higher fibre volume fraction, thus promoting the out-of-plane conductivity. Additionally, CAG modification formed a conductive CAG skin over the fabric surface, which largely reduced the in-plane electrical anisotropy of WCFs. In principle, reducing the intra-yarn free volume of WCF-reinforced electrodes provides a route towards significantly improving the electrical performance of SPCs and serves as a guidance for subsequent encapsulation and multifunctional design.