Potassium-insertion in polyacrylonitrile-based carbon fibres for multifunctional energy storage, morphing, and strain-sensing

Abstract

By increasing the number of functions a structure performs it is possible to save weight and volume on a systems level. Ion-insertion in carbon fibres (CFs) is a way to create multifunctional structures for energy storage, morphing, and strain-sensing. Previous studies have focussed on lithium- and sodium-insertion to create multifunctionality. However, with a larger ionic radius and a chemistry more amenable to insertion in polyacrylonitrile (PAN)-based CFs, potassium-insertion is a promising way forward. Here, a study is conducted to examine potassium-insertion in intermediate modulus PAN-based CFs for multifunctionality. Electrochemical cycling shows a maximum reversible capacity of 170 mAh/g, with ex-situ mechanical testing showing a small impact on the CFs’ mechanical properties post-cycling. Operando measurements show a maximum reversible CF expansion during potassium-insertion of 0.24%, and analytical modelling illustrates that such strains can generate significant deformations in a morphing structure. A voltage-strain coupling of 0.26 V/unit strain is also found. Results are compared with previous work on lithium- and sodium-insertion, with the conclusion that potassium-insertion is more promising than sodium-insertion, but less so than lithium-insertion for multifunctional structures.