Nanocapacitors with Big-Energy Storage

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http://www.technologyreview.com/energy/22297/

Monday, March 16, 2009

Nanocapacitors with Big-Energy Storage

Nanopore arrays combine high power and storage capacity.

By Katherine Bourzac

The ultimate electronic energy-storage device would store plenty of energy but also charge up rapidly and provide powerful bursts when needed. Sadly, today's devices can only do one or the other: capacitors provide high power, while batteries offer high storage.

Now researchers at the University of Maryland have developed a kind of capacitor that brings these qualities together. The research is in its early stages, and the device will have to be scaled up to be practical, but initial results show that it can store 100 times more energy than previous devices of its kind. Ultimately, such devices could store surges of energy from renewable sources, like wind, and feed that energy to the electrical grid when needed. They could also power electric cars that recharge in the amount of time that it takes to fill a gas tank, instead of the six to eight hours that it takes them to recharge today.

There are many different kinds of batteries and capacitors, but in general, batteries can store large amounts of energy yet tend to charge up slowly and wear out quickly. Capacitors, meanwhile, have longer lifetimes and can rapidly discharge, but they store far less total energy. Electrochemists and engineers have been working to solve this energy-storage problem by http://www.technologyreview.com/energy/22280/">boosting batteries' power and http://www.technologyreview.com/business/22062/?a=f">increasing capacitors' storage capacity.

Sang Bok Lee, a chemistry professor, and Gary Rubloff, a professor of engineering and director of the Maryland NanoCenter, created nanostructured arrays of electrostatic capacitors. Electrostatic capacitors are the simplest kind of electronic-energy-storage device, says Rubloff. They store electrical charge on the surface of two metal electrodes separated by an insulating material; their storage capacity is directly proportional to the surface area of these sandwich-like electrodes. The Maryland researchers boosted the storage capacity of their capacitors by using nanofabrication to increase their total surface area. Their electrodes work in the same way as ones found in conventional capacitors, but instead of being flat, they are tubular and tucked deep inside nanopores.

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Nanopore power: Arrays of capacitors built inside nanopores are shown here in a scanning electron micrograph image overlaid with an illustration that shows their design. The pores are etched into an aluminum substrate (dark yellow). The capacitors form two thin layers of metal (blue) separated by a layer of insulating material (light yellow).
Credit: A. James Clark School of Engineering, University of Maryland

http://www.nature.com/nnano/journal/vaop/ncurrent/abs/nnano.2009.37.html