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“Nanoscoops” Could Spark New Generation of Electric Automobile Batteries
New Nanoengineered Batteries Developed at
Rensselaer Exhibit Remarkable Power Density, Charging More Than
40 Times Faster Than Today’s Lithium-ion
Batteries
Researchers at Rensselaer Polytechnic
Institute developed an entirely new type of nanomaterial
that could enable the next generation of high-power
rechargeable lithium (Li)-ion batteries for electric
automobiles, laptop computers, mobile phones, and other
devices. The material, called a “nanoscoop” because it
resembles a cone with a scoop of ice cream on top, is
shown in the above scanning electron microscope image.
Nanoscoops can withstand extremely high rates of charge
and discharge that would cause today’s Li-ion batteries
to rapidly deteriorate and fail.
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An entirely new type of nanomaterial developed at Rensselaer
Polytechnic Institute could enable the next generation of
high-power rechargeable lithium (Li)-ion batteries for electric
automobiles, as well as batteries for laptop computers, mobile
phones, and other portable devices.
The new material, dubbed a “nanoscoop” because its shape
resembles a cone with a scoop of ice cream on top, can
withstand extremely high rates of charge and discharge that
would cause conventional electrodes used in today’s Li-ion
batteries to rapidly deteriorate and fail. The nanoscoop’s
success lies in its unique material composition, structure, and
size.
The Rensselaer research team, led by Professor Nikhil Koratkar,
demonstrated how a nanoscoop electrode could be charged and
discharged at a rate 40 to 60 times faster than conventional
battery anodes, while maintaining a comparable energy density.
This stellar performance, which was achieved over 100
continuous charge/discharge cycles, has the team confident that
their new technology holds significant potential for the design
and realization of high-power, high-capacity Li-ion
rechargeable batteries.
“Charging my laptop or cell phone in a few minutes, rather
than an hour, sounds pretty good to me,” said Koratkar, a
professor in the Department of Mechanical,
Aerospace, and Nuclear Engineering at Rensselaer. “By using
our nanoscoops as the anode architecture for Li-ion
rechargeable batteries, this is a very real prospect. Moreover,
this technology could potentially be ramped up to suit the
demanding needs of batteries for electric automobiles.”
Batteries for all-electric vehicles must deliver high power
densities in addition to high energy densities, Koratkar said.
These vehicles today use supercapacitors to perform
power-intensive functions, such as starting the vehicle and
rapid acceleration, in conjunction with conventional batteries
that deliver high energy density for normal cruise driving and
other operations. Koratkar said the invention of nanoscoops may
enable these two separate systems to be combined into a single,
more efficient battery unit.
Results of the study were detailed in the paper
“Functionally Strain-Graded Nanoscoops for High Power Li-Ion
Battery Anodes,” published Thursday by the journal Nano
Letters. See the full paper at: http://pubs.acs.org/doi/abs/10.1021/nl102981d
The anode structure of a Li-ion battery physically grows and
shrinks as the battery charges or discharges. When charging,
the addition of Li ions increases the volume of the anode,
while discharging has the opposite effect. These volume changes
result in a buildup of stress in the anode. Too great a stress
that builds up too quickly, as in the case of a battery
charging or discharging at high speeds, can cause the battery
to fail prematurely. This is why most batteries in today’s
portable electronic devices like cell phones and laptops charge
very slowly – the slow charge rate is intentional and designed
to protect the battery from stress-induced damage.
The Rensselaer team’s nanoscoop, however, was engineered to
withstand this buildup of stress. Made from a carbon (C)
nanorod base topped with a thin layer of nanoscale aluminum
(Al) and a “scoop” of nanoscale silicon (Si), the structures
are flexible and able to quickly accept and discharge Li ions
at extremely fast rates without sustaining significant damage.
The segmented structure of the nanoscoop allows the strain to
be gradually transferred from the C base to the Al layer, and
finally to the Si scoop. This natural strain gradation provides
for a less abrupt transition in stress across the material
interfaces, leading to improved structural integrity of the
electrode.
The nanoscale size of the scoop is also vital since
nanostructures are less prone to cracking than bulk materials,
according to Koratkar.
“Due to their nanoscale size, our nanoscoops can soak
and release Li at high rates far more effectively than the
macroscale anodes used in today’s Li-ion batteries,” he said.
“This means our nanoscoop may be the solution to a critical
problem facing auto companies and other battery manufacturers –
how can you increase the power density of a battery while still
keeping the energy density high?”
A limitation of the nanoscoop architecture is the relatively
low total mass of the electrode, Koratkar said. To solve this,
the team’s next steps are to try growing longer scoops with
greater mass, or develop a method for stacking layers of
nanoscoops on top of each other. Another possibility the team
is exploring includes growing the nanoscoops on large flexible
substrates that can be rolled or shaped to fit along the
contours or chassis of the automobile.
Along with Koratkar, authors on the paper are
Toh-Ming Lu, the R.P. Baker Distinguished Professor of Physics and associate
director of the Center for
Integrated Electronics at Rensselaer; and Rahul Krishnan, a
graduate student in the Department of Materials
Science and Engineering at Rensselaer.
This study was supported by the National Science Foundation
(NSF) and the New York State Energy Research
and Development Authority (NYSERDA).
For more information on Koratkar’s research at Rensselaer,
visit:
For more information on Lu’s research at Rensselaer,
visit:
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Published
January 4,
2011 |
Contact: Michael Mullaney
Phone: (518) 276-6161
E-mail: mullam@rpi.edu |
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