March 16, 2009

Nano holes make fast electricity storage

Start with closely spaced microscopic holes, line them with layers of metal only a few nanometers thick and you have a superfast electricity storage device.

The device is an array of nanoscale electrostatic capacitors formed in close, regularly spaced holes in a thin film of aluminum oxide. The holes are lined with metal, insulator and metal layers totaling 25 nanometers.

The electrostatic capacitor holds 0.7 watt hours per kilogram -- 10 times as much as other nanostructured electrostatic capacitors and almost as much as the widely used but slower electric double layer capacitors.

Electrostatic capacitors store electricity as charges on the surfaces of metal electrodes. This makes them the fastest type of capacitor. The densely-packed nanotube structure gives the device it's greater capacity.

The electrostatic capacitor could be a lower-cost alternative to electric double layer capacitors for electric vehicles. Capacitors are paired with high-capacity batteries in electric vehicles. The battery provides bulk storage and the capacitor burst power for quick acceleration and a way to capture braking energy.

Research paper:
Nanotubular Metal-Insulator-Metal Capacitor Arrays for Energy Storage
Nature Nanotechnology, published online March 15, 2009

Researchers' homepages:
Parag Banerjee
Israel Perez
Laurent Henn-Lecordier
Sang Bok Lee
Gary W. Rubloff

Related stories and briefs:
Nanomaterial promises record fast batteries -- related research

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