A material derived from trees could potentially replace liquid electrolytes in next-generation batteries.
From:
Brown University
October 21, 2021 -- In pursuit of
batteries that deliver more power and operate more safely, researchers are
working to replace the liquids commonly used in today's lithium ion batteries
with solid materials. Now, a research team from Brown University and the
University of Maryland has developed a new material for use in solid-state
batteries that's derived from an unlikely source: trees.
In research published in the
journal Nature, the team demonstrates a solid ion conductor that
combines copper with cellulose nanofibrils -- polymer tubes derived from wood.
The paper-thin material has an ion conductivity that is 10 to 100 times better
than other polymer ion conductors, the researchers say. It could be used as
either a solid battery electrolyte or as an ion-conducting binder for the
cathode of an all-solid-state battery.
"By incorporating copper with
one-dimensional cellulose nanofibrils, we demonstrated that the normally
ion-insulating cellulose offers a speedier lithium-ion transport within the
polymer chains," said Liangbing Hu, a professor in the University of
Maryland's Department of Materials Science and Engineering. "In fact, we
found this ion conductor achieved a record high ionic conductivity among all
solid polymer electrolytes."
The work was a collaboration between Hu's
lab and the lab of Yue Qi, a professor at Brown's School of Engineering.
Today's lithium ion batteries, which are
widely used in everything from cellphones to cars, have electrolytes made from
lithium salt dissolved in a liquid organic solvent. The electrolyte's job is to
conduct lithium ions between a battery's cathode and anode. Liquid electrolytes
work pretty well, but they have some downsides. At high currents, tiny
filaments of lithium metal, called dendrites, can form in the electrolyte
leading to short circuits. In addition, liquid electrolytes are made with
flammable and toxic chemicals, which can catch fire.
Solid electrolytes have the potential to
prevent dendrite penetration and can be made from non-flammable materials. Most
of the solid electrolytes investigated so far are ceramic materials, which are
great at conducting ions but they're also thick, rigid and brittle. Stresses
during manufacturing as well as charging and discharging can lead to cracks and
breaks.
The material introduced in this study,
however, is thin and flexible, almost like a sheet of paper. And its ion
conductivity is on par with ceramics.
Qi and Qisheng Wu, a senior research
associate at Brown, performed computer simulations of the microscopic structure
of the copper-cellulose material to understand why it is able to conduct ions
so well. The modeling study revealed that the copper increases the space
between cellulose polymer chains, which normally exist in tightly packed
bundles. The expanded spacing creates what amount to ion superhighways through
which lithium ions can zip by relatively unimpeded.
"The lithium ions move in this
organic solid electrolyte via mechanisms that we typically found in inorganic
ceramics, enabling the record high ion conductivity," Qi said. "Using
materials nature provides will reduce the overall impact of battery manufacture
to our environment."
In addition to working as a solid
electrolyte, the new material can also act as a cathode binder for a
solid-state battery. In order to match the capacity of anodes, cathodes need to
be substantially thicker. That thickness, however, can compromise ion
conduction, reducing efficiency. In order for thicker cathodes to work, they
need to be encased in an ion-conducting binder. Using their new material as a binder,
the team demonstrated what they believe to be one of the thickest functional
cathodes ever reported.
The researchers are hopeful that the new
material could be a step toward making bringing solid state battery technology
to the mass market.
The research at Brown University was
supported by the National Science Foundation (DMR-2054438).
https://www.sciencedaily.com/releases/2021/10/211021175142.htm
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