Battery Power - May/June 2013 - (Page 30)
Research & Development
Hybrid Ribbons a Gift for Powerful Batteries
Mike Williams, Senior Media Relations Specialist
Rice University
Hybrid ribbons of vanadium oxide (VO2) and graphene may
accelerate the development of high-power lithium-ion batteries suitable for electric cars and other demanding applications.
The Rice University lab of materials scientist Pulickel Ajayan
determined that the well-studied material is a superior cathode
for batteries that could supply both high energy density and
significant power density.
The ribbons created at Rice are thousands of times thinner than a sheet of paper, yet have potential that far outweighs
current materials for their ability to charge and discharge very
quickly. Cathodes built into half-cells for testing at Rice fully
charged and discharged in 20 seconds and retained more than 90
percent of their initial capacity after more than 1,000 cycles.
Graphene-coated
ribbons of vanadium
oxide, seen in a scanning electron microscope
image, might be the best
electrode for lithium-ion
batteries yet tested, according to researchers at
Rice University. Image by
Ajayan Group
“This is the direction battery research is going, not only
for something with high energy density but also high power
density,” Ajayan said. “It’s somewhere between a battery and a
supercapacitor.”
The ribbons also have the advantage of using relatively
abundant and cheap materials. “This is done through a very
simple hydrothermal process, and I think it would be easily scalable to large quantities,” he said.
Ajayan said vanadium oxide has long been considered a
material with great potential, and in fact vanadium pentoxide
has been used in lithium-ion batteries for its special structure
and high capacity. But oxides are slow to charge and discharge,
due to their low electrical conductivity. The high-conductivity
graphene lattice that is literally baked in solves that problem
nicely, he said, by serving as a speedy conduit for electrons and
channels for ions.
The atom-thin graphene sheets bound to the crystals take
up very little bulk. In the best samples made at Rice, fully
84 percent of the cathode’s weight was the lithium-slurping
VO2, which held 204 milliamp hours of energy per gram. The
researchers, led by Rice graduate student Yongji Gong and lead
author Shubin Yang, said they believe that to be among the best
overall performance ever seen for lithium-ion battery electrodes.
30
Battery Power • March/April 2013
Hydrothermal processing of vanadium pentoxide and
graphene oxide creates graphene-coated ribbons of
crystalline vanadium oxide, which show great potential as ultrafast charging and discharging electrodes
for lithium-ion batteries. (Credit: Ajayan Group)
“One challenge to production was controlling the conditions
for the co-synthesis of VO2 ribbons with graphene,” Yang said.
The process involved suspending graphene oxide nanosheets
with powdered vanadium pentoxide (layered vanadium oxide,
with two atoms of vanadium and five of oxygen) in water and
heating it in an autoclave for hours. The vanadium pentoxide
was completely reduced to VO2, which crystallized into ribbons,
while the graphene oxide was reduced to graphene, Yang said.
The ribbons, with a web-like coating of graphene, were only
about 10 nanometers thick, up to 600 nanometers wide and tens
of micrometers in length.
“These ribbons were the building blocks of the threedimensional architecture,” Yang said. “This unique structure
was favorable for the ultrafast diffusion of both lithium ions and
electrons during charge and discharge processes. It was the key
to the achievement of excellent electrochemical performance.”
In testing the new material, Yang and Gong found its capacity for lithium storage remained stable after 200 cycles even at
high temperatures (167°F) at which other cathodes commonly
decay, even at low charge-discharge rates.
“We think this is real progress in the development of cathode
materials for high-power lithium-ion batteries,” Ajayan said,
suggesting the ribbons’ ability to be dispersed in a solvent might
make them suitable as a component in the paintable batteries
developed in his lab.
The work was funded by the US Army Research Office and
the Office of Naval Research through a Multidisciplinary University Research Initiative grant and a National Science Foundation Graduate Research Fellowship grant.
www.BatteryPowerOnline.com
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Table of Contents for the Digital Edition of Battery Power - May/June 2013
Polaris Battery Labs and Carestream Tollcoating Form Alliance
Intelligent Enumerating Battery Charger Provides Safe and Fast Charge for Mobile Equipment
Shippers of Lithium Batteries and Equipment Experience Delays as New Air Transport Requirements Take Effect
A New Method for Maintaining the Charge of VRLA Batteries in Telecommunications Standby Systems
Battery Power 2013 Conference Preview
Batteries
ICs & Semiconductors
Charging & Testing
Components & Materials
Industry News
Research & Development
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