|
Researchers with the U.S. Department of Energy Lawrence Berkeley National
Laboratory (Berkeley Lab) have created a graphene and tin nanoscale composite
material for high-capacity energy storage in renewable lithium ion batteries.
By encapsulating tin between sheets of graphene, the researchers constructed a
new, lightweight “sandwich” structure that should bolster battery performance.
“For an electric vehicle, you need a lightweight battery that can be charged
quickly and holds its charge capacity after repeated cycling,” says Yuegang
Zhang, a staff scientist with Berkeley Lab’s Molecular Foundry, in the
Inorganic Nanostructures Facility, who led this research. “Here, we’ve shown
the rational design of a nanoscale architecture, which doesn’t need an additive
or binder to operate, to improve battery performance.”
Graphene is a single-atom-thick, “chicken-wire” lattice of carbon atoms with
stellar electronic and mechanical properties, far beyond silicon and other
traditional semiconductor materials. Previous work on graphene by Zhang and his
colleagues has emphasized electronic device applications.
In this study, the team assembled alternating layers of graphene and tin to
create a nanoscale composite. To create the composite material, a thin film of
tin is deposited onto graphene. Next, another sheet of graphene is transferred
on top of the tin film. This process is repeated to create a composite material,
which is then heated to 300 C (572 F) in a hydrogen and argon environment.
During this heat treatment, the tin film transforms into a series of pillars,
increasing the height of the tin layer.
“The formation of these tin nanopillars from a thin film is very particular
to this system, and we find the distance between the top and bottom graphene
layers also changes to accommodate the height change of the tin layer,” says
Liwen Ji, a post-doctoral researcher at the Foundry. Ji is the lead author and
Zhang the corresponding author of a paper reporting the research in Energy
and Environmental Science.
The change in height between the graphene layers in these new nanocomposites
helps during electrochemical cycling of the battery, as the volume change of
tin improves the electrode’s performance. In addition, this accommodating
behavior means the battery can be charged quickly and repeatedly without
degrading—crucial for rechargeable batteries in electric vehicles.
“We have a large battery program here at Berkeley Lab, where we are capable
of making highly cyclable cells. Through our interactions in the Carbon Cycle
2.0 program, the Materials Science Division researchers benefit from quality
battery facilities and personnel, along with our insights in what it takes to
make a better electrode,” says coauthor Battaglia, program manager in the
Advanced Energy Technology department of Berkeley Lab’s Environmental and
Energy Technologies Division. “In return, we have an outlet for getting these
requirements out to scientists developing the next generation of materials.”
