Nanotubes juice super batteries

Capacitors store electric charge, and supercapacitors are capable of delivering a large amount of energy in a short time -- something that is beyond regular batteries.

Researchers at the University of California at Davis and Mytitek Incorporated have found a relatively simple and inexpensive way to form a new type of thin film supercapacitor from multi-wall carbon nanotubes.

Carbon nanotubes are rolled-up sheets of carbon; multi-wall carbon nanotubes are sets of nested nanotubes. Nanotubes make good electrodes for super capacitors because they are highly conductive and have large surface areas for trapping electric charges.

The nanotube capacitors could eventually be used in electric and hybrid vehicles, space applications, cell phones, and lightweight electronic fuses; they would be especially appropriate for providing the needed surge of startup power for fuel cells, according to the researchers.

The researchers' prototype supercapacitor produced a power density of 30 kilowatts per kilogram, which is seven and a half times the power of today's commercial supercapacitors, according to the researchers. Other researchers have achieved power densities of 20 kilowatts per kilogram, but they use more expensive single-wall carbon nanotubes and a fabrication process that required heating, according to the researchers.

The process to make the multi-wall nanotube supercapacitor film is simple, and thus potentially inexpensive. The researchers deposited high concentrations of nanotubes suspended in liquid on nickel films and dried them at room temperature. The nanotubes ended up densely packed and partially aligned.

The super capacitors could be ready for practical use within one to five years, according to the researchers. The work appeared in the February 1, 2005 issue of Nanotechnology.