A new technology to create electrochemical double-layer supercapacitors is provided using carbon nanotubes as electrodes of the storage medium. This invention allows efficient transport between the capacitor electrodes through the porous nature of the nanotubes, and has a low interface resistance between the electrode material and the collector. Carbon nanotubes directly grown on a metal surface are used to improve the supercapacitor performance. The nanotubes offer a high surface area and usable porosity for a given volume and mass, both of which are highly desirable for supercapacitor operation.
The growth of MWCNT and/or single-wall carbon nanotube (SWCNT) towers is done directly on polished, ultra-smooth alloy substrates containing iron or nickel, such as nichrome, kanthal, and stainless steel. The growth process for generating a MWCNT tower array requires heating the collector metal substrate in an inert argon gas atmosphere to 750 °C. After thermal equilibration, 1,000 sccm of 8/20 ethylene/Hs gas flow results in the growth of carbon nanotube towers. Two such electrodes separated by a membrane are packaged properly, after soaking into an aqueous or organic electrolyte, to create a supercapacitor cell. The supercapacitors provide high power densities not possible with conventional batteries while attempting to provide reasonable energy density as well. In addition, the supercapacitors charge very rapidly, in about a couple of minutes or under.