Nanowire battery holds 10 times the charge of existing ones
Date: Tuesday, December 18, 2007 @ 23:08:18 MST
Stanford researchers have found a way to use silicon nanowires to
reinvent the rechargeable lithium-ion batteries that power laptops,
iPods, video cameras, cell phones, and countless other devices.
The new version, developed through research led
by Yi Cui, assistant professor of materials science and engineering,
produces 10 times the amount of electricity of existing lithium-ion,
known as Li-ion, batteries. A laptop that now runs on battery for two
hours could operate for 20 hours, a boon to ocean-hopping business
"It's not a small improvement," Cui said. "It's a revolutionary development."
The breakthrough is described in a paper, "High-performance lithium
battery anodes using silicon nanowires," published online Dec. 16 in Nature Nanotechnology, written by Cui, his graduate chemistry student Candace Chan and five others.
The greatly expanded storage capacity could make Li-ion batteries
attractive to electric car manufacturers. Cui suggested that they could
also be used in homes or offices to store electricity generated by
rooftop solar panels.
"Given the mature infrastructure behind silicon, this new technology can be pushed to real life quickly," Cui said.
The electrical storage capacity of a Li-ion battery is limited by
how much lithium can be held in the battery's anode, which is typically
made of carbon. Silicon has a much higher capacity than carbon, but
also has a drawback.
Silicon placed in a battery swells as it absorbs positively charged
lithium atoms during charging, then shrinks during use (i.e., when
playing your iPod) as the lithium is drawn out of the silicon. This
expand/shrink cycle typically causes the silicon (often in the form of
particles or a thin film) to pulverize, degrading the performance of
Cui's battery gets around this problem with
nanotechnology. The lithium is stored in a forest of tiny silicon
nanowires, each with a diameter one-thousandth the thickness of a sheet
of paper. The nanowires inflate four times their normal size as they
soak up lithium. But, unlike other silicon shapes, they do not
Research on silicon in batteries began three decades ago. Chan
explained: "The people kind of gave up on it because the capacity
wasn't high enough and the cycle life wasn't good enough. And it was
just because of the shape they were using. It was just too big, and
they couldn't undergo the volume changes."
Then, along came silicon nanowires. "We just kind of put them together," Chan said.
For their experiments, Chan grew the nanowires on a stainless steel
substrate, providing an excellent electrical connection. "It was a
fantastic moment when Candace told me it was working," Cui said.
Cui said that a patent application has been filed. He is
considering formation of a company or an agreement with a battery
manufacturer. Manufacturing the nanowire batteries would require "one
or two different steps, but the process can certainly be scaled up," he
added. "It's a well understood process."
Source: Stanford University