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A D V A N C E D
M A T E R I A L S
&
P R O C E S S E S | F E B R U A R Y / M A R C H
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SMALL SCALE LITHIUM
FEATURES SURPRISING
STRENGTH
A team of researchers from
Caltech, Pasadena, Calif., and Carnegie
Mellon University, Pittsburgh, mea-
sured the strength of lithium metal at
the nano- and microscale, a first that
could ultimately lead to improved lith-
ium-ion battery performance. Using a
special vacuum chamber at Caltech,
the team formed pillars of single-crystal
lithium a few micrometers tall and just
a few nanometers to micrometers in
diameter. They discovered that at this
size, lithium is up to 100 times stronger
than indicated by previous measure-
ments at a larger scale. Additionally,
researchers found that the stiffness of
lithium dendrites—needlelike branch-
ing structures that advance into a
battery, causing it to short-circuit or
even explode—varied by as much as a
factor of four according to their crystal-
lographic orientation.
Until now, attempts to physically
curb the growth of lithium dendrites
have involved a solid electrolyte sand-
wiched between the cathode and anode
to serve as a physical barrier; however,
the electrolytes used thus far have not
been able to withstand the force of the
growing dendrites. Now that research-
ers know what they’re up against, a
stronger solid electrolyte can be devel-
oped to keep the lithium dendrites in
check. caltech.edu, cmu.edu.
NEW METAL-OXIDE FILMS
PATTERNED ON GRAPHENE
Researchers from Brown Univer-
sity, Providence, R.I., developed a new
method for making ultrathin textured
metal-oxide films that have improved
properties as catalysts and electrodes.
The scientists placed stacks of wrinkled
graphene sheets in a water-based solu-
tion containingpositively chargedmetal
ions. The negatively charged graphene
pulled the ions into the spaces between
the sheets, and the particles bonded
together, creating thin sheets of metal
that followed the wrinkle patterns of
the graphene. When the graphene was
oxidized away, the texturedmetal-oxide
film remained. The process works with
a variety of metal oxides—zinc, alumi-
num, manganese, and copper oxides—
which are too stiff to be textured with
the methods the team previously devel-
oped to deform graphene films.
In the experiments that followed,
researchers demonstrated improved
properties of the new films. Wrinkled
manganese oxide, when used as a bat-
tery electrode, had a charge-carrying
capacity four times higher than a planar
sheet, and crumpled zinc oxide filmwas
four times more reactive than a planar
film in a photocatalytic reaction—re-
ducing a dye dissolved in water under
ultraviolet light. The process represents
more than just bolstered performance,
according to Po-Yen Chen, a postdoc-
toral researcher. “Based on what we
learned from making the metal-oxide
films, we can start to think about using
this method to make new 2D materi-
als that are otherwise unstable in bulk
solution,” he explains. “With our con-
finement method, we think it’s possi-
ble.
NANOTECHNOLOGY
BRIEF
The world nanomaterials market is forecast to reach $55,016 million by 2022, registering a CAGR of 20.7% from 2016 to
2022, according to a new report available from Report Buyer, London. Heavy investment in R&D activities by
government organizations is expected to propel market growth.
A micrometer-sized pillar of lithium.
Images courtesy of J. Greer Laboratory/
Caltech.
Diagrams of a lithium-ion battery. When
the battery is connected and charge
is flowing (at right), small needles of
lithiummetal grow, which can destroy
the battery.
Using graphene sheets as tiny templates,
researchers developed a method of
making metal-oxide films with intricate
surface textures. Courtesy of Hurt/Wong
Labs, Brown University.