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 travelers.
"It's not a small improvement," Cui said. "It's a
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 the battery.
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 fracture.
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."