Monday, June 19, 2006

Super Battery

Ever wish you could charge your cellphone or laptop in a few seconds rather than hours? As this ScienCentral News video explains, researchers at the Massachusetts Institute of Technology are developing a battery that could do just that, and also might never need to be replaced.

The Past is Future

As our portable devices get more high-tech, the batteries that power them can seem to lag behind. But Joel Schindall and his team at M.I.T. plan to make long charge times and expensive replacements a thing of the past--by improving on technology from the past.

They turned to the capacitor, which was invented nearly 300 years ago. Schindall explains, "We made the connection that perhaps we could take an old product, a capacitor, and use a new technology, nanotechnology, to make that old product in a new way."

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 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 technology has broad practical possibilities, affecting any device that requires a battery. Schindall says, "Small devices such as hearing aids that could be more quickly recharged where the batteries wouldn't wear out; up to larger devices such as automobiles where you could regeneratively re-use the energy of motion and therefore improve the energy efficiency and fuel economy."

Nanotube filaments on the battery's electrodes image: MIT/Riccardo Signorelli

Schindall thinks hybrid cars would be a particularly popular application for these batteries, especially because current hybrid batteries are expensive to replace.

Schindall also sees the ecological benefit to these reinvented capacitors. According to the Environmental Protection Agency, more than 3 billion industrial and household batteries were sold in the United States in 1998. When these batteries are disposed, toxic chemicals like cadmium can seep into the ground.

"It's better for the environment, because it allows the user to not worry about replacing his battery," he says. "It can be discharged and charged hundreds of thousands of times, essentially lasting longer than the life of the equipment with which it is associated."

Schindall and his team aren't the only ones looking back to capacitors as the future of batteries; a research group in England recently announced advances of their own. But Schindall's groups expects their prototype to be finished in the next few months, and they hope to see them on the market in less than five years.

Schindall's research was featured in the May 2006 edition of Discover Magazine and presented at the 15th International Seminar on Double Layer Capacitors and Hybrid Energy Storage Devices in Deerfield Beach, Florida on December 2005. His research is funded by the Ford-MIT Consortium.

by Victor Limjoco



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