Nanoflowers Improve Ultracapacitors

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.

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 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.

So far, ultracapacitors have been limited to niche applications that require high power and quick, repetitive recharging. For example, the devices provide quick bursts of power to buses, trucks, and light-rail trains over short stretches, and braking replenishes them. If they could store more energy, however, they could be a powerful, long-lasting replacement for batteries in hybrid-electric vehicles and portable electronics.

How great would it be if we could replace batteries with ultracapacitors that recharged in an instant and never needed to be replaced? With each breakthrough like this one, that possibility becomes a little bit bigger.

via Technology Review