Properties of electrochemical double-layer capacitors with carbon-nanotubes-on-carbon-fiber-felt electrodes

Abstract

Carbon nanotube (CNT) layers deposited on carbon fiber cloth (CFC) materials have been studied as electrodes of electrochemical double layer capacitors (EDLCs), in particular, the electrochemical performance and cycle stability of symmetric EDLCs in an organic electrolyte (tetraethyl-ammonium-fluoroborate in acetonitrile). Due to the large surface area of carbon-fibers, the CNT mass loading can be as high as 18 mg/cm2 which is magnitudes larger than that of what can be deposited on aluminium or nickel metal sheets. The area normalized double layer capacitance of CNT/CFC electrodes in the above organic electrolytes were found to be in the range of 100–400 mF/cm2, and the specific capacitances were 18–48 F/g. These latter values are below the achievable values of single-wall CNT of 80 F/g; the lower values can be attributed to the presence of multi-walled CNTs of some quantities, having lower accessible surface area. The energy density of CNT/CFC supercapacitors is 0.8–1.5 Wh/kg, while the power density varies between 5 and 20 kW/kg calculated on electrode level. Excellent cycling stability of EDLCs built with CNT-on carbon felt electrodes has been demonstrated up to 1 million cycles, which is due to the inert nature of substrate causing the absence of corrosion process and high mass load of CNT.