| Cover Story - Wednesday, January 2, 2008
New battery lasts 10 times as long
Silicon Valley legacy of innovation continues — with silicon
by Arden Pennell
Imagine rarely having to recharge the battery of your new, all-electric car. Saving gas is just one potential benefit of a new battery that lasts 10 times longer than standard models, creator and Stanford University researcher Yi Cui said.
"It can be used in laptops. You can do international flights without charging up" or it can be used in iPods or cell phones, said Cui, an assistant professor in the Materials Science and Engineering Department.
Cui and colleagues announced the break-through battery last month, capping two years of research, he said.
The notion of a battery based on nanotechnology came about when Cui got to Stanford in 2005.
"I was very excited when this idea was demonstrated to work for the first time," Cui said.
The new battery generates 10 times as much energy as traditional batteries by getting around the tendency of silicon to break down through normal use, he said.
In standard lithium-ion batteries, the silicon expands during charging as it absorbs lithium ions, then shrinks during use as the tiny particles flow back out.
The expand-and-contract cycle causes silicon, which is in the shape of particles or layers, to degrade. But Cui's new battery uses a forest of tiny silicon wires to store ions, he said.
The nanowires, each with a diameter of one-thousandth the thickness of a sheet of paper, grow to four times their normal size but don't fracture as other silicon shapes do, he said.
With silicon intact, the battery keeps going — including in electric-car engines, a use Cui is particularly excited about.
"You don't need to burn gasoline. You can use the battery. It has high enough energy to drive really long distances," he said.
He plans to run more lab tests to determine the battery's exact duration, but it could hit commercial markets in as little as five years, he said.
He plans to either start his own company or license the technology to others, he said.
And with abundant supply and pre-existing technology, it shouldn't cost too much, he said.
"Silicon is really abundant, the second most abundant element. The semiconductor industry is mature. [So] the cost is low," he said.
As the region's nickname implies, silicon played a crucial local role in high-tech innovations as an ideal material for semiconductors and later computer chips.
But nanotechnology, or the ability to make such small objects, is only about a decade old, Cui said.
"In previous research, they couldn't solve this problem" of preventing silicon breakage, because the pieces were too large, he said.
And while silicon has the highest known charge capacity, or ability to store lithium ions, that potential could not be unlocked earlier due to its tendency to wear out, Cui and others said in a letter describing their findings.
Cui has received phone calls from all over the world since the letter's publication online in the journal Nature Nanotechnology, he said.
Staff Writer Arden Pennell can be e-mailed at apennell@paweekly.com. | 
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