"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."
Ultracapacitor Nanotech Breakthrough
This sentence encapsulates well both the enormous promises and the big problem of ultracapacitors. Thankfully, engineers and researchers haven't said their last word. They are working out on squeezing out more storage capacity into capacitors, and the latest breakthrough has to do with "Nanoflowers"...There are two main paths that have been explored to boost the storage capacity of capacitors: Increasing the surface area of the electrodes (f.ex. with activated carbon, or carbon nanotubes) and using better charge-storing materials (f.ex. manganese oxide and conducting polymers).
The Best of Both Worlds
The beauty of the new electrode design, published in Nano Letters and reported in Technology Review, is that it combines the two methods:
First, the researchers grow an array of carbon nanotubes on a foil made from the metal tantalum, which is commonly used in capacitors. Then they grow 100-nanometer-wide flower-shaped nanoparticles directly on the array. The nanotubes grow more or less vertically, but they're not very stiff and tend to fall across each other. The nanoflowers grow mostly at the junctions of multiple nanotubes and have a large surface area (236 square meters per gram) compared with typical particles of manganese oxide. [...]
When current flows through the tantalum foil, charges quickly get transferred to and stored in the manganese oxide: the electrode stores twice as much charge as the same volume of activated carbon. The nanotubes' high conductivity could also give them a greater power output than current ultracapacitors have, the researchers say.
Another one of the benefits of capacitors in general, including this new design, is that they can be cycled a lot. After 20,000 cycles, it only lost 3% of its charge capacity.
As with many technologies still in the lab, these new ultracapacitors are still too expensive to be used in high volumes (in electric cars, for example). Researchers are looking into ways of producing the right materials in high quantities and at low prices, and we wish them the best of luck.
Via Technology Review
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