Application of Carbon Nanotubes for Resolving Issues and Challenges on Electrochemical Capacitors

In electrochemical capacitors electrode is the key factor to determine the energy density and power density; hence the selection of electrode materials is the most crucial part. The specific energy of commercial supercapacitors is limited to 5–6 Wh kg−1, whereas for batteries the lower limit is 35–40 Wh kg−1. In this chapter, the type of electrochemical capacitors, the storage principles, and the characteristics of composite electrode based on carbon nanotubes and carbon-based materials, transition metal oxides, and conducting polymers are briefly discussed. The composites combine the large pseudocapacitance with the fast charging/discharging double-layer capacitance and excellent mechanical properties of the carbon nanotubes. Most of the commercially available devices use carbon electrodes and organic electrolytes, and research efforts have been done to increase the specific capacitance of supercapacitor electrodes based on carbon nanotubes. Composite electrodes based on carbon nanotubes exhibit excellent electronic conductivity, electrochemical charge-storage properties, fast charge/discharge switching, and specific power making them promising electrode materials for high-power supercapacitors due to their unique properties of carbon nanotubes.