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Nanotechnology
Transforms Lithium-ion Batteries
Stanford University
February 4, 2008
Palo Alto, CA -- Nanotechnology could make today’s
lithium-ion batteries a thing of the past. Researchers at
Stanford University (Palo Alto, CA) have developed a way to
use silicon nanowires to improve the rechargeable battery
technology commonly used in cordless tools and other
devices. The new technology produces 10 times the amount of
electricity of existing lithium-ion batteries. |
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Traditionally, the electrical storage
capacity of a lithium-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 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.
The Stanford battery gets around this problem by using
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.
“It’s not a small improvement,” claims Yi Cui, an assistant
professor of materials science and engineering. “It’s a
revolutionary development. Given the mature infrastructure
behind silicon, this new technology can be pushed to real
life quickly.
“Manufacturing the nanowire batteries would require one or
two different steps, but the process can certainly be scaled
up,” adds Cui. “It’s a well understood process.”
The greatly expanded storage capacity could make lithium-ion
batteries attractive to electric car manufacturers.
According to Cui, they could also be used in homes or
offices to store electricity generated by rooftop solar
panels.
Research on silicon in batteries began 3 decades ago.
“[But], people gave up on it because the capacity wasn’t
high enough and the cycle life wasn’t good enough,” says
Cui. “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. For their experiments, Cui
and his colleagues grew the
nanowires on a stainless steel substrate, which provided an
excellent electrical connection. |
