Another nanotechnology route to better ultracapacitors for energy storage

http://www.foresight.org/nanodot/?p=2849
Chemically modified graphene has found in manganese oxide nanoflower/carbon nanotube array a rival nanotech material to improve energy storage using ultracapacitors. From “Nanoflowers Improve Ultracapacitors: A novel design could boost energy storage“, and article in Technology Review written by Prachi Patel-Predd and found via KurzweilAI.net:

Imagine a cell-phone battery that recharges in a few seconds and that you would never have to replace. That’s the promise of energy-storage devices known as ultracapacitors, but at present, they can store only about 5 percent as much energy as lithium-ion batteries. An advance by researchers at the Research Institute of Chemical Defense, in China, could boost ultracapacitors’ ability to store energy.

A capacitor consists of two electrodes with opposite charges, often separated by an insulator that keeps electrons from jumping directly between them. The researchers have developed an electrode that can store twice as much charge as the activated-carbon electrodes used in current ultracapacitors. The new electrode contains flower-shaped manganese oxide nanoparticles deposited on vertically grown carbon nanotubes.

The electrodes deliver five times as much power as activated-carbon electrodes, says Hao Zhang, lead author of the Nano Letters paper [abstract] describing the new work. The electrode’s longevity also compares with that of activated-carbon electrodes, Zhang says: discharging and recharging the electrodes 20,000 times reduced the capacitor’s energy-storage capacity by only 3 percent.

…Ultracapacitors can store millions of times more energy than the tiny capacitors used in electronic circuits.

But their performance still pales beside that of batteries, which store energy using chemical reactions. “If I gave you a cell phone with an ultracapacitor battery, you’d never replace the battery, and you could recharge it in a few seconds, but it would only last half an hour,” says Joel Schindall, an electrical-engineering professor at MIT.

…”The way of growing manganese oxide on carbon nanotube arrays is new and has produced beautiful structures,” says Yury Gogotsi, a materials-science and engineering professor at Drexel University. Gogotsi says that combining the high conductivity of the carbon nanotubes with the charge-storage capacity of manganese oxide is an attractive approach. But, he adds, “it is not practical for large volume, such as automotive applications, because the use of carbon nanotube arrays and tantalum foil makes them expensive.”

Indeed, says Schindall, cost could be the main barrier to ultracapacitors with nanostructured electrodes. “They’ve found a way to grow these structures,” he says, “but now they’ve got to be able to grow them densely enough and economically enough to be practical.”

—Jim

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