i3 - January/February 2017 - 27

that such batteries could have a long useful
lifetime. And because these batteries could
be installed and operated just like conventional solid lithium-ion batteries, without
any of the auxiliary components needed
in the past, they could be easily adapted
to existing installations or conventional
battery pack designs for cars, electronics or
even grid-scale power storage.
The MIT team expects to move from
this lab-scale proof of concept to a
practical prototype within about a year.
Another challenge for those exploring
Li-air battery chemistries is after a few
charging cycles the carbon electrode
would become corroded and the electrolytic fluid would decompose. But no
one knew exactly why. Now scientists
from the Munich Technical University
(TUM) and the Jülich Research Center
have found the reason for this behavior:
during the charging process, highly
reactive "singlet oxygen" an extremely
reactive substance, is generated. This
oxygen corrodes surrounding materials within fraction of seconds, the
researchers discovered. It also decomposes electrolytic fluid.
The researchers hope to find a mechanism to prevent the formation of singlet
oxygen during charging. One of the most
C TA . t e c h / i 3

promising approaches is by replacing
the lithium cobalt oxide cathode with
carbon particles.
Another team, led by Dr. Kyeongjae
Cho, a professor of materials science and
engineering in the Erik Jonsson School of
Engineering and Computer Science at the
University of Texas, Dallas, along with his
graduate student Yongping Zheng, discovered new catalyst materials for Li-air
batteries that could jumpstart efforts at
expanding battery capacity.
Their research, published in the
journal Nature Energy, focuses on the
electrolyte catalysts inside the battery,
which, when combined with oxygen,
create chemical reactions that form the
basis of the battery's energy capacity.
They report that soluble-type catalysts
possess significant advantages over
conventional solid catalysts, exhibiting
much higher efficiency. They found that
only certain organic materials can be
utilized as a soluble catalyst. Cho and
Zheng have collaborated with researchers
at Seoul National University in Korea
to create a new catalyst for the Li-air
battery called dimethylphenazine, which
possesses higher stability and increased
voltage efficiency.
The researchers say with this new

SE I
In a "thermal
REA
runaway"
situation
additional
heat increases
the reaction
rate until the
cell erupts in
T
flames.

N REACTION RATE

N R AT E

it is waterproof,
working up to five
minutes while
submerged.
The research
team is working
to improve the
electrodes to limit
corrosion, on the
configuration of
cell assemblies
and to optimize
the structure of
the battery.

CTI O

layers in close
electrical contact.
This prototype
battery is reported
to have withstood
more than 1,000
bending and
twisting actions
while powering a
set of LEDs. They
claim these batteries can be recharged 90 times
and as a bonus,

HEA

tional batteries
was replaced by a
soft flexible polymer gel. When
this assembly
was complete,
the researchers
gently heated
the outer rubber
layer, causing it
to shrink wrap
the rest of the
components and
packing the

E XOTHER

REA

Researchers at the Changchun Institute of Applied Chemistry in China have come
up with flexible Li-air cells for wearables.
Source: CIAC

The liquid inside most
lithium-ion batteries is highly
flammable. If the battery shortcircuits, either by puncturing
the thin sheet of plastic
separating the positive and
negative sides of the battery or
because of impurities - it can
heat up the liquid electrolyte -
and possibly, result in a fire.
Overcharging is another
culprit. Lithium-ion batteries
have circuitry inside to prevent
overcharging and short
circuits, but if this circuitry is
damaged, the battery could
become overheated, resulting
in a process known as "thermal
runaway." Basically, the battery
generates heat, causing
reactions that generate more

heat, until it erupts in flames.
One advantage of the MIT Li-air
variation is that the battery
cannot be overcharged,
because the reaction is selflimiting. The new battery is
protected because when
overcharged, the reaction
shifts to a different form that
prevents further activity. The
researchers claim they have
overcharged the battery for 15
days, to 100 times its capacity,
without any damage.

INC

NO
OVERCHARGING
ISSUES

MI C

catalyst the Li-air battery should become
a more practical energy storage solution.
But it could take five to 10 years before
their research translates into new batteries that can be used in consumer
devices and electric vehicles.
Another new study published in the
Journal of The Electrochemical Society
(JES) also focuses on catalyst materials
and could represent a fundamental step
forward in advancing Li-air technology
through more efficient electrode reactions
in the battery. The study details a cathode
catalyst composed of three transition
metals (manganese, nickel, and cobalt),
which can create the right oxidation state
during battery cycling. K.M. Abraham of
Northeastern University, co-author of the
study, says it represents a fundamental step
forward in advancing Li-air that could
lead to more efficient electrode reactions.
Li-air is highly researched, but there
are still barriers to be overcome before
it can go into full-fledged practical use,
Abraham notes. He thinks there will
be some limited use in the near future
in specialty applications, but it could
be five years or more before it becomes
a fully used technology. Just in time
for 5G phones and autonomous
electric vehicles. n
JANUARY/FEBRUARY 2017

27
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