A Better Energizer

An ultracapacitor is what really keeps going and going. . . .

By Alex Stone|Sunday, May 28, 2006

If you've ever had a cell phone suddenly die on you, you know that batteries are the weak link in mobile electronics. That's why MIT electrical engineer Joel Schindall thinks the time is ripe for capacitors. "They are better than batteries in almost every way, except in the amount of energy they store," he says. Schindall and his research group have licked that limitation.

Unlike batteries, which produce voltage from a chemical reaction, capacitors store electricity between a pair of metal plates. The larger the area of the plates, and the smaller the space between them, the more energy a capacitor can hold. Schindall's group had a radical idea: Cover the plates with millions of microscopic filaments known as carbon nanotubes. The tiny tubes vastly expand the surface area, creating a perfect sponge for electricity. "Now we can expect to store an amount of energy that is comparable to what batteries store," he says.

A capacitor-powered cell phone could be charged in minutes or seconds instead of hours. And since capacitors can be reused indefinitely, environmental waste from discarded batteries would become a thing of the past. Schindall says battery-free bliss may be less than five years away.

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