Nanotube Capacitors As Battery Substitutes?

Lynne Kiesling

Check out this very cool idea for reinventing capacitors with nanotubes to provide energy storage for portable devices. The capacitor, a 300-year-old technology for modulating current flow by storing small amounts of energy, stores energy via electrodes that separate a charge and thus maintain potential. But it can only store energy in proportion to the surface area of the electrodes, so the way to reinvent the capacitor is to figure out a way to increase the electrode surface area.

Rechargable and disposable batteries use a chemical reaction to produce energy. “That’s an effective way to store a large amount of energy,” he says, “but the problem is that after many charges and discharges … the battery loses capacity to the point where the user has to discard it.”

But capacitors contain energy as an electric field of charged particles created by two metal electrodes. Capacitors charge faster and last longer than normal batteries. The problem is that storage capacity is proportional to the surface area of the battery’s electrodes, so even today’s most powerful capacitors hold 25 times less energy than similarly sized standard chemical batteries.

The researchers solved this by covering the electrodes with millions of tiny filaments called nanotubes. Each nanotube is 30,000 times thinner than a human hair. Similar to how a thick, fuzzy bath towel soaks up more water than a thin, flat bed sheet, the nanotube filaments on increase the surface area of the electrodes and allow the capacitor to store more energy. Schindall says this combines the strength of today’s batteries with the longevity and speed of capacitors.

“It could be recharged many, many times perhaps hundreds of thousands of times, and … it could be recharged very quickly, just in a matter of seconds rather than a matter of hours,” he says.

This kind of research could prove extremely valuable, because it focuses on a way to increase the amount of storage in a given physical area. One of the challenges facing batteries and fuel cells is getting them to be useful storage technologies while being small enough to be practical and user-friendly; recall the article I mentioned last Sunday that discussed methanol cartridge prototype laptops.

Reinventing old technologies is great.