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Nanometer makes for greatest performance in batteries
Category : General 15 Mar 2010 08:01 AM | Industry News
In the new experiments, each of these electrically and thermally conductive nanotubes was coated with a layer of a reactive fuel that can produce heat by decomposing. This fuel was then ignited at one end of the nanotube using either a laser beam or a high-voltage spark, and the result was a fast-moving thermal wave traveling along the length of the carbon nanotube like a flame speeding along the length of a lit fuse. Heat from the fuel goes into the nanotube, where it travels thousands of times faster than in the fuel itself. As the heat feeds back to the fuel coating, a thermal wave is created that is guided along the nanotube. With a temperature of 3,000 kelvins, this ring of heat speeds along the tube 10,000 times faster than the normal spread of this chemical reaction. The heating produced by that combustion, it turns out, also pushes electrons along the tube, creating a substantial electrical current.
According to the researchers, unlike normal batteries, these nanotubes never lose their stored energy if they are left unused. For the study, Michael Strano of the Massachusetts Institute of Technology and his colleagues coated their nanotubes with cyclotrimethylene trinitramine. One property that nanotubes have is that they conduct heat very, very well along their length, up to a hundred times faster than in metals.
The scientists used a laser or an electric spark to set off the reaction in a bundle of coated carbon nanotubes, and lensed the results with a high-speed camera. However, they discovered the process created a useful voltage - a phenomenon they call "thermopower waves". Their nanotube bundles carry, gram for gram, up to 100 times more energy than a standard lithium-ion battery.
The conventional fuel cell has been around since the 1800s but corrosive fuels, catalytic deactivation and complexity have been a hurdle. From an engineering standpoint, thermopower waves could be a very simple alternative.
The researchers also plan to pursue another aspect of their theory: that by using different kinds of reactive materials for the coating, the wave front could oscillate, thus producing an alternating current. That would open up a variety of possibilities, Strano says, because alternating current is the basis for radio waves such as cell phone transmissions, but present energy-storage systems all produce direct current.