Engineer making rechargeable batteries with layered nanomaterials
A
Kansas State University researcher is developing more efficient ways to save costs,
time and energy when creating nanomaterials and lithium-ion batteries. Gurpreet
Singh, assistant professor of mechanical and nuclear engineering, and his
research team have published two recent articles on newer, cheaper and faster
methods for creating nanomaterials that can be used for lithium-ion batteries.
In the past year, Singh has published eight articles -- five of which involve
lithium-ion battery research.
"We
are exploring new methods for quick and cost-effective synthesis of
two-dimensional materials for rechargeable battery applications," Singh
said. "We are interested in this research because understanding lithium
interaction with single-, double- and multiple-layer-thick materials will
eventually allow us to design battery electrodes for practical applications.
This includes batteries that show improved capacity, efficiency and longer
life."
For the
latest research, Singh's team created graphene films that are between two and
10 layers thick. Graphene is an atom-thick sheet of carbon. The researchers
grew the graphene films on copper and nickel foils by quickly heating them in a
furnace in the presence of controlled amounts of argon, hydrogen and methane
gases. The team has been able to create these films in less than 30 minutes.
Their work appears in the January issue of ACS-Applied Materials and Interfaces
in an article titled "Synthesis of graphene films by rapid heating and
quenching at ambient pressures and their electrochemical
characterization."
The
research is significant because the researchers created these graphene sheets
by quickly heating and cooling the copper and nickel substrates at atmospheric
pressures, meaning that scientists no longer need a vacuum to create
few-layer-thick graphene films and can save energy, time and cost, Singh said.
The
researchers used these graphene films to create the negative electrode of a
lithium-ion cell and then studied the charge and discharge characteristics of
this rechargeable battery. They found the graphene films grown on copper did
not cycle the lithium ions and the battery capacity was negligible. But
graphene grown on nickel showed improved performance because it was able to
store and release lithium ions more efficiently.
"We
believe that this behavior occurs because sheets of graphene on nickel are
relatively thick near the grain boundaries and stacked in a well-defined manner
-- called Bernal Stacking -- which provides multiple sites for easy uptake and
release of lithium ions as the battery is discharged and charged," Singh
said.
In a second
research project, the researchers created tungsten disulfide nanosheets that
were approximately 10 layers thick. Starting with bulk tungsten disulfide
powder -- which is a type of dry lubricant used in the automotive industry --
the team was able to separate atomic layer thick sheets of tungsten disulfide
in a strong acid solution. This simple method made it possible to produce
sheets in large quantities. Much like graphene, tungsten disulfide also has a
layered atomic structure, but the individual layers are three atoms thick.
The
researchers found that these acid-treated tungsten disulfide sheets could also
store and release lithium ions but in a different way. The lithium is stored
through a conversion reaction in which tungsten disulfide dissociates to form
tungsten and lithium sulfide as the cell is discharged. Unlike graphene, this
reaction involves the transfer of at least two electrons per tungsten atom.
This is important because researchers have long disregarded such compounds as
battery anodes because of the difficulty associated with adding lithium to
these materials, Singh said. It is only recently that the conversion
reaction-based battery anodes have gained popularity.
"We
also realize that tungsten disulfideis a heavy compound compared to
state-of-the-art graphite used in current lithium-ion batteries," Singh
said. "Therefore tungsten disulfide may not be an ideal electrode material
for portable batteries."
The research appeared in a recent issue of the Journal of Physical Chemistry Letters.
Both
projects are important because they can help scientists create nanomaterials in
a cost-effective way. While many studies have focused on making graphene using
low-pressure chemical processes, little research has been tried using rapid
heating and cooling at atmospheric pressures, Singh said. Similarly, large
quantities of single-layer and multiple-layer thick sheets of tungsten
disulfide are needed for other applications.
"Interestingly,
for most applications that involve this kind of battery research and corrosion
prevention, films that are a few atoms thick are usually sufficient,"
Singh said. "Very high quality large area single-atom-thick films are not
a necessity."
Other
Kansas State University researchers involved in the projects include Romil Bhandavat
and Lamuel David, both doctoral students in mechanical engineering, India, and
Saksham Pahwa, a visiting undergraduate student, India. The graphene research
involved University of Michigan researchers, including Zhaohui Zhong, assistant
professor of electrical engineering and computer science, andGirish Kulkarni,
doctoral candidate in electrical engineering.
Singh's
work has been supported by the National Institute of Standards and Technology
and the Kansas National Science Foundation Experimental Program to Stimulate
Competitive Researchprogram.
Singh
plans future research to study how these layered nanomaterials can create
better electrodes in the form of heterostructures, which are essentially
three-dimensional stacked structures involving alternating layers of graphene
and tungsten or molybdenum disulfide.
Source: Kansas State University
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