Researchers make next-generation, high-toughness battery component


Date:
June 18, 2020
Source:
Brown University
Summary:
By combining a ceramic material with graphene, engineers have made
what they say is the toughest solid electrolyte built to date.



FULL STORY ==========================================================================
A team of Brown University researchers has found a way to double the
toughness of a ceramic material used to make solid-state lithium ion
batteries. The strategy, described in the journal Matter, could be useful
in bringing solid- state batteries to the mass market.


========================================================================== "There's huge interest in replacing the liquid electrolytes in current batteries with ceramic materials because they're safer and can provide
higher energy density," said Christos Athanasiou, a postdoctoral
researcher in Brown's School of Engineering and lead author of the
research. "So far, research on solid electrolytes has focused on
optimizing their chemical properties. With this work, we're focusing
on the mechanical properties, in the hope of making them safer and more practical for widespread use." The electrolyte is the barrier between
a battery's cathode and anode through which lithium ions flow during
charging or discharging. Liquid electrolytes work pretty well -- they're
found in most batteries in use today -- but they have some problems. At
high currents, tiny filaments of lithium metal can form inside the electrolytes, which cause batteries to short circuit. And since liquid electrolytes are also highly flammable, those shorts can lead to fires.

Solid ceramic electrolytes aren't flammable, and there's evidence that
they can prevent the formation of lithium filaments, which could enable batteries to operate at higher currents. However, ceramics are highly
brittle materials that can fracture during the manufacturing process
and during use.

For this new study, the researchers wanted to see if infusing a
ceramic with graphene -- a super-strong carbon-based nanomaterial --
could increase the material's fracture toughness (a material's ability
to withstand cracking without falling apart) while maintaining the
electronic properties needed for electrolyte function.

Athanasiou worked with Brown engineering professors Brian Sheldon and
Nitin Padture, who for years have used nanomaterials to toughen ceramics
for use in the aerospace industry. For this work, the researchers made
tiny platelets of graphene oxide, mixed them with powder of a ceramic
called LATP, and then heated the mixture to form a ceramic-graphene
composite.

Mechanical testing of the composite showed a more than two-fold increase
in toughness compared to the ceramic alone. "What's happening is that
when crack starts in a material, the graphene platelets essentially
hold the broken surfaces together so that more energy is required for
the crack to run," Athanasiou said.

Experiments also showed that the graphene didn't interfere with the
electrical properties of the material. The key was making sure the
right amount of graphene was added to the ceramic. Too little graphene
wouldn't achieve the toughening effect. Too much would cause the material
to become electrically conductive, which is not desired in an electrolyte.

"You want the electrolyte to conduct ions, not electricity," Padture said.

"Graphene is a good electrical conductor, so people may think
we're shooting ourselves in the foot by putting a conductor in our
electrolyte. But if we keep the concentration low enough, we can keep
the graphene from conducting, and we still get the structural benefit."
Taken together, the results suggest that nanocomposites could provide a
path forward to making safer solid electrolytes with mechanical properties
to be used in everyday applications. The group plans to continue working
to improve the material, trying nanomaterials other than graphene and
different types of ceramic electrolyte.

"To our knowledge, this is the toughest solid electrolyte that anyone has
made to date," Sheldon said. "I think what we've shown is that there's
a lot of promise in using these composites in battery applications."
Other co-authors on the paper were Mok Yun Jin and Cristina Ramirez. The
work was supported by the U.S. Department of Energy (DE-SC0018113).


========================================================================== Story Source: Materials provided by Brown_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Christos E. Athanasiou, Mok Yun Jin, Cristina Ramirez, Nitin
P. Padture,
Brian W. Sheldon. High-Toughness Inorganic Solid Electrolytes
via the Use of Reduced Graphene Oxide. Matter, 2020; DOI:
10.1016/j.matt.2020.05.003 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200618124801.htm

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