Tech Briefs Magazine - February 2022 - 38

Power & Energy
molecular architecture of the material
makes it possible to simultaneously
achieve high power, high capacitance,
and low-temperature characteristics.
When the team investigated the
mechanism of charge transfer in this
class of compounds, it turned out that
they have two directions of development:
First, they can be used as protective
layers in conjunction with traditional
Li-ion battery materials. Second, they
can become an active component of
electrical storage materials.
In the first phase of development,
the team tested the concept of a new
material, mixing individual
components
that simulate the conducting
chain with redox-active nitroxyl-containing
polymers. It was important to
ensure that all parts of the structure
worked together and reinforced each
other. After that, the stage of substance
synthesis began, which involved sensitive
components that can easily collapse
at the slightest mistake.
Of the several polymers obtained,
only one was found to be stable and
efficient. The main chain of the new
material is formed by complexes of
nickel with ligands called " salen. " A stable
free radical was attached to it
through covalent bonds capable of
rapid oxidation and reduction (charge
and discharge).
The new battery could excel in situations
where very fast charging is
required or when operating at low temperatures.
It contains fewer metals that
can cause environmental harm; nickel is
present in a small amount in the polymer
but there is much less of it than in
Li-ion batteries.
For more information, contact Polina
Vyacheslavovna Ogorodnikova at pressa@
spbu.ru.
Eliminating Corrosion Extends Life of Lightweight
Batteries
A new design could extend the shelf-life of single-use metal-air batteries for electric vehicles,
off-grid storage, and other applications.
Massachusetts Institute of Technology, Cambridge, MA
etal-air batteries are one of the lightest
and most compact types of batteries,
but when not in use, they degrade
quickly, as corrosion eats away at their
metal electrodes. While typical rechargeable
lithium-ion batteries only lose about
5 percent of their charge after a month of
storage, they are too costly, bulky, or heavy
for many applications. Primary (nonrechargeable)
aluminum-air batteries are
much less expensive and more compact
and lightweight, but they can lose 80 percent
of their charge a month.
A new design overcomes the problem
of corrosion in aluminum-air batteries by
introducing an oil barrier between the
aluminum electrode and the electrolyte
- the fluid between the two battery electrodes
that eats away at the aluminum
when the battery is on standby. The oil is
rapidly pumped away and replaced with
electrolyte as soon as the battery is used.
As a result, the energy loss is cut to just
0.02 percent a month - more than a
thousand-fold improvement.
The system uses a thin membrane
placed between the battery electrodes.
When the battery is in use, both sides of
the membrane are filled with a liquid electrolyte,
but when the battery is put on
standby, oil is pumped into the side closest
to the aluminum electrode, protecting the
aluminum surface from the electrolyte on
the other side of the membrane.
The battery system also takes advantage
of a property of aluminum called
38
Cov
M
The proof-of-concept battery lasted through 24 days of use and standby cycles, compared to just
three days for a comparable battery without the new protective system in place. (Photo: MIT)
" underwater oleophobicity " - that is,
when aluminum is immersed in water, it
repels oil from its surface. As a result,
when the battery is reactivated and electrolyte
is pumped back in, the electrolyte
easily displaces the oil from the
aluminum surface, which restores the
power capabilities of the battery. The
result is an aluminum-air prototype with
a much longer shelf-life than that of conventional
aluminum-air batteries.
When the battery was repeatedly used
and then put on standby for one to two
days, the new design lasted 24 days,
while the conventional design lasted for
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only three. Aluminum, in addition to
being very inexpensive, can store and
deliver more energy per pound than
almost anything else.
Aluminum-air batteries have been
used as range extenders for electric vehicles
to supplement built-in rechargeable
batteries and are sometimes used as
power sources in remote locations or for
some underwater vehicles. With a longer
shelf-life, the use of aluminum-air batteries
could extend to other applications.
For more information, contact Karl-Lydie
Jean-Baptiste at kjeanbap@mit.edu; 617253-1682.
Tech
Briefs, February 2022

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Tech Briefs Magazine - February 2022

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