Effect of electrode surface treatment on carbon fiber based structural supercapacitors: Electrochemical analysis, mechanical performance and proof-of-concept

Abstract

Supercapacitors based on carbon fiber reinforced polymer (CFRPs) were studied and the influence of surface treatment on mechanical and electrochemical properties was explored. Electrodes were prepared by deposition of graphene nanoplatelets (GNPs) combined with different binders (PVDF and PVA) onto the surface of a carbon fiber fabric. A significant decrease in the Interlaminar Shear Strength (ILSS) is observed when comparing the solid polymer electrolyte to the structural resin (around 50 %). Moreover, the addition of any binder promotes a decrease in the ILSS due to lower interfacial properties (around 20 % when compared to the GNP-coated condition). Electrochemical impedance spectroscopy (EIS) analysis proves that the structural capacitor can be fitted with an equivalent circuit consisting of R-CPE series elements. An increase of the bulk resistance was observed when using a binder (29.7 and 22.7 kΩ) when compared to the GNP-only-coated (10.2 kΩ). For this reason, the structural supercapacitor with the best properties was the GNP-only-coated one with a specific capacitance and coulombic efficiency, calculated by Galvanostatic charge-discharge (GCD), of 5.2 mF/g, showing also high stability of electrochemical properties over time. Energy storage capability was successfully demonstrated by a proof of concept consisting of powering a LED after a short charge time of the device.