Supercapacitor could make electric car viable.
Hiawatha Bray - Boston Globe - June 26, 2006
Honda FCX’s Ultracapacitor based power storage system.
Scientists at the Massachusetts Institute of Technology think they're on the verge of making traditional batteries obsolete.
The researchers are working on a new device that uses carbon nanotubes to store and release electrical energy in a system that could carry as much power as today's lead or lithium batteries.
But unlike the rechargeable batteries used on today's cellphones and laptop computers, these devices could be recharged hundreds of thousands of times before wearing out.
And instead of taking hours to recharge, they could be powered up in about the same time it takes to fill up a gas tank.
Electronics professor Joel Schindall drives a Toyota hybrid car, which uses an electric battery to reduce gasoline consumption. But Schindall would prefer an all-electric car, and he thinks his team's research could finally make such vehicles practical.
In a basement laboratory at MIT, Schindall and his colleagues are using acetylene gas to deposit carbon nanotubes on pieces of silicon. Schindall says that the technology isn't much different from the kind used to produce microchips, and so mass production shouldn't be too difficult. Still, he said, ``It's one thing to postulate it, but that's a long way from being commercially viable and competitive in price." Schindall says he hopes to have a finished example by the fall.
The device being developed at MIT's Laboratory for Electromagnetic and Electronic Systems isn't a battery, but a capacitor - a device that's already used in nearly every electronic product on the planet. When plugged into an electrical circuit, a capacitor briefly stores incoming electricity, they releases it at a predictable rate. Capacitors can't store very much power, compared to traditional batteries. But while it takes hours to recharge a battery, capacitors charge almost instantly. And while most batteries can only be recharged a few hundred or thousand times before wearing out, capacitors can be recharged hundreds of thousands of times.
During the 1960s, scientists discovered that they could make more powerful capacitors by coating their electrodes with finely ground charcoal - a form of carbon. The charcoal crystals greatly increased the surface area of each electrode, allowing it to collect a greater electrical charge.
Since then, scientists have learned how to grow carbon nanotubes - extremely thin fibers of pure carbon. Schindall and his colleagues realized that millions of tiny nanotubes would do a much better job than ground charcoal in expanding an electrode's surface area. And if the nanotube-coated electrodes were made large enough, you could build a capacitor that could work like a battery with enough power to drive a device for hours.
Not everybody is convinced that Schindall's super capacitors will deliver as much power as he claims.
Andrew Burke, research engineer at the Institute of Transportation Studies at the University of California at Davis, said that the new capacitors would have to be many times more powerful than any previously created. "I have a lot of respect for those guys, but I have not seen any data," Burke said. "Until I see the data, I'm inclined to be skeptical."
Even if Schindall's capacitors work, he doubts they'll transform the electronics industry overnight. Companies have too much invested in today's battery systems, and it would take years before carbon nanotube capacitors could be mass-produced.
"I think that in five years, you could see limited use," Schindall said. "Then in 10 years, you begin to see the cost crossover point," when capacitors become as cheap as standard rechargeable batteries.