Self-healing Battery Prototype
Stanford postdoctoral researcher Chao Wang holds a container of self-healing polymer that can be applied to silicon electrodes to keep them from cracking and falling apart during battery operation.
Left: An electron micrograph shows cracks left in a self-healing polymer coating due to swelling of its silicon electrode during charging. Right: Five hours later, the smaller cracks have healed.
Science: Your next gen smartphone could bring in self-healing battery electrode. Scientists just invented it.
Scientists invent self-healing
battery electrode.
Researchers have
made the first battery electrode that heals itself, opening a new and
potentially commercially viable path for making the next generation of lithium
ion batteries for electric cars, cell phones and other devices. The secret is a
stretchy polymer that coats the electrode, binds it together and spontaneously
heals tiny cracks that develop during battery operation, said the team from
Stanford University and the Department of Energy's (DOE) SLAC National
Accelerator Laboratory.
They reported the
advance in the Nov. 19 issue of Nature Chemistry.
"Self-healing
is very important for the survival and long lifetimes of animals and
plants," said Chao Wang, a postdoctoral researcher at Stanford and one of
two principal authors of the paper. "We want to incorporate this feature
into lithium ion batteries so they will have a long lifetime as well."
Chao developed the
self-healing polymer in the lab of Stanford Professor Zhenan Bao, whose group
has been working on flexible electronic skin for use in robots, sensors,
prosthetic limbs and other applications. For the battery project he added tiny
nanoparticles of carbon to the polymer so it would conduct electricity.
"We found
that silicon electrodes lasted 10 times longer when coated with the
self-healing polymer, which repaired any cracks within just a few hours,"
Bao said.
Their capacity for
storing energy is in the practical range now, but we would certainly like to
push that," said Yi Cui, an associate professor at SLAC and Stanford who
led the research with Bao. The electrodes worked for about 100 charge-discharge
cycles without significantly losing their energy storage capacity. "That's
still quite a way from the goal of about 500 cycles for cell phones and 3,000
cycles for an electric vehicle," Cui said, "but the promise is there,
and from all our data it looks like it's working."
Researchers
worldwide are racing to find ways to store more energy in the negative
electrodes of lithium ion batteries to achieve higher performance while
reducing weight. One of the most promising electrode materials is silicon; it
has a high capacity for soaking up lithium ions from the battery fluid during
charging and then releasing them when the battery is put to work.
But this high capacity comes at a price: Silicon electrodes swell to
three times normal size and shrink back down again each time the battery
charges and discharges, and the brittle material soon cracks and falls apart,
degrading battery performance. This is a problem for all electrodes in
high-capacity batteries, said Hui Wu, a former Stanford postdoc who is now a
faculty member at Tsinghua University in Beijing, the other principal author of
the paper.
To make the
self-healing coating, scientists deliberately weakened some of the chemical
bonds within polymers – long, chain-like molecules with many identical units.
The resulting material breaks easily, but the broken ends are chemically drawn
to each other and quickly link up again, mimicking the process that allows
biological molecules such as DNA to assemble, rearrange and break down.
Researchers in
Cui's lab and elsewhere have tested a number of ways to keep silicon electrodes
intact and improve their performance. Some are being explored for commercial
uses, but many involve exotic materials and fabrication techniques that are
challenging to scale up for production.
The self-healing
electrode, which is made from silicon microparticles that are widely used in
the semiconductor and solar cell industry, is the first solution that seems to
offer a practical road forward, Cui said. The researchers said they think this
approach could work for other electrode materials as well, and they will
continue to refine the technique to improve the silicon electrode's performance
and longevity.
Summary:
This invention could help bring about the next generation of lithium ion batteries for electric cars, mobile phones and a number of other battery-powered devices.
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