On the performance of supercapacitors with electrodes based on carbon nanotubes and carbon activated material - A review

Supercapacitors or electrochemical double-layer capacitors (EDLCs) have capacitance value up to thousands of Farads at the same size as for conventional capacitors. At such capacitance value EDLCs are of interest for electrical energy storage. The specific energy of commercial supercapacitors is limited to 5-6 Wh/kg, whereas for batteries the lower limit is 35-40 Wh/kg. Nonetheless other advantages of supercapacitors make them already useful in conjunction with batteries in power applications. Main results related to supercapacitor performance improvement available in literature are presented. Research efforts have been done to increase the specific capacitance of supercapacitor electrodes based on activated or porous carbon material, already used in commercial products. By using available activated carbon with a specific surface area reaching 3000 m(2)/g, specific capacitance values up to 300 F/g have been reported for the investigated experimental supercapacitors. Nonetheless, further optimization of activated carbon properties and its use in supercapacitor electrodes is required for 300 F/g and higher value. By addition of metallic oxides or conductive polymers in the activated carbon used for EDLC electrodes, specific capacitance enhancement takes place. Carbon nanotubes used in experimental supercapacitor electrodes resulted in specific capacitance as high as 180 F/g but higher electrical conductivity and consequently, specific power than in the case of activated carbon was observed. Addition of a small percent of carbon nanotubes in the activated carbon for electrodes results in performance improvement (higher capacitance and conductivity). Nevertheless, high cost of carbon nanotubes prevents their use in commercial products. (C) 2007 Elsevier B.V. All rights reserved.