i3 - January/February 2017 - 26

battery can be cycled, and optimizing the
complex chemical reactions that occur
during charge and discharge to boost
battery performance.
But there have been major breakthroughs moving Li-air battery
technology from a laboratory curiosity
closer to practical implementation. Here
are a few examples.
Commercial batteries are self-contained
but this has not been the case for lithiumair batteries, early versions of which
adopted a so-called "open-cell" design to
get enough air in to the reaction point.
This oxygen was then released again

The energy density of new battery chemistries
such as Li-air could approach 1kWhr/kg.

NEW TECHNOLOGIES

100 Wh Kg-1

Flight (?)
SUPER
BATTERY

Local Grid
Storage

Metal-Air
Metal-Sulphur
Flow Batteries
upcoming...

Long Range HDV

Long Range EV
500 Wh Kg-1

REVOLUTIONARY
CHANGE

l 2020
Mid Range EV
Stand-Alone
Storage
Small Grid
Stabilization
Short Range HDV
l 2017

250 Wh Kg-1

SAFER
AND
GREENER
CELLS

Li-Ion
200 Wh Kg-1
Short Range EV
Na-Ion
HEV
Mg-Ion
Smartphones
Cordless
150 Wh Kg-1
Tools
Laptops
l TODAY PRESENT TECHNOLOGIES

APPLICATION

ENERGY

Source: Helmholtz Institut Ulm
26

JANUARY/FEBRUARY 2017

CHEMISTRIES

Flexible
Lithium-Air
Batteries For
Wearables
There is growing
interest in
wearable sensors
and flexible
displays that need
power. Traditional
lithium-ion
batteries, which
are hard and rigid,
do not fit the bill.
Until recently,
neither did Li-air

batteries since
conventional Liair cathodes are
typically made of
rigid materials,
such as ceramics
encased in
fiberglass. If the
battery is flexed,
the electrolyte-a
liquid-would leak
out. This problem
is compounded
when oxygen
reacts with lithium
at the cathode to
produce lithium

to the atmosphere during the reverse
reaction in the charging cycle. Open
systems require the consistent intake
of oxygen from the environment, while
closed systems do not - making them
safer and more efficient.
In the open process, the oxygen also
changes states from gaseous to solid
and back again during charging and
discharging, resulting in huge volume
changes (gases occupy more volume
than solids) and placing a great deal of
mechanical stress on the cell, disrupting
electrical conduction paths and possibly
causing it to fail prematurely.
The Li-air batteries developed in the
lab since the 1970s also wasted much of
the injected energy as heat and degraded
relatively quickly. To avoid damaging the
cell they required expensive extra components to scrub out water from the humid
incoming air and filter carbon dioxide
from the air that fed the batteries.
By making cells that contain their
own oxygen, rather than relying on
the proportion of oxygen in the air,
MIT Professor Ju Li and his team of
researchers (including members from
Argonne National Laboratory and Peking
University in Beijing), created a much
more practical self-contained design. In

peroxide, a solid
that builds up and
pushes out the
electrolyte, killing
the battery cell.
But if researchers
at the Changchun
Institute of Applied
Chemistry in China
have their way,
next generation
Li-air batteries could power
everything from
clothing packed
with light-emitting
diodes (LEDs) to

roll-up tablets.
Unlike conventional Li-air batteries, consisting of
an anode and cathode made of hard
materials, they
made the anode
from concentric
lithium layers and
the cathode was
constructed using
a flexible porous
mesh of carbon
and nickel. The
liquid electrolyte
used in conven-

the MIT approach the oxygen remains
inside the cell and in a solid state at all
times - the oxygen becomes bound to
the lithium to form a glass-like material.
These molecules are encased in a matrix
of cobalt oxide, forming what researchers
call "nanolithia" - nanostructures that act
as a catalyst for the chemical reactions
that take place in the cell.
This reduces the voltage loss by a factor
of five, according to the researchers, so
only eight percent of the electrical energy
is turned into heat. This development
could lead to faster charging for cars,
as heat removal from the battery pack
becomes less of a safety concern.
In cycling tests, a lab version of the new
battery was put through 120 chargingdischarging cycles, and showed less than
a two percent loss of capacity, indicating

e--

Previous
approaches to
Li-air batteries
required O2
intake and
expulsion
during the
discharge and
charge cycles.

discharging

Li

Li+

e--

O2

O2

LixO2

charging

Li

Li+

e--

O2

LixO2

e--

I T I S I N N O VAT I O N

O2
i3 - January/February 2017

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