Tech Briefs Magazine - May 2022 - 45

Power & Energy
Decreasing Anode Corrosion in Metal-Air Batteries
An oil displacement system to mitigate open-circuit corrosion in metal-air and
metal-seawater batteries.
Massachusetts Institute of Technology, Cambridge, MA
M
etal-air batteries can be used in a
variety of applications ranging from
range extenders for electric vehicles to
emergency power systems. Metal-seawater
batteries are primarily used for
underwater applications ranging from
torpedoes to underwater unmanned vehicles.
A team of researchers at the Department
of Mechanical Engineering,
MIT, has developed an oil displacement
system to mitigate open-circuit corrosion
in metal-air and metal-seawater batteries.
Metal-air/seawater batteries have high
gravimetric energy densities; however,
open-circuit (OC) anode corrosion causes
severe capacity fade when the battery
is shut off. Previous technologies focus on
chemical mitigation methods (i.e., changing
electrode or electrolyte composition),
which provide insufficient corrosion mitigation
and power density. Other mechanical
corrosion mitigation methods require
flushing the cell, which increases the volume
of tanks required for the system. The
proposed technology implements a system
that displaces the electrolyte with oil when
the battery is off to prevent OC corrosion.
The main elements of the system include
a metal-air cell, a tank of mineral
oil and electrolyte, and a separate tank
of water. Pumps and pipes move liquids
between these three parts. The device
displaces corrosive electrolyte from the
anode surface by pumping oil into the
cell. In comparison to other mechanical
corrosion mitigation methods, this oil displacement
method increases volumetric
energy density by 15 percent. Additionally,
a liquid that has a different density
than the electrolyte, is immiscible in the
electrolyte, nonconducting, inviscid, and
nonreactive with the other system components
could replace the oil in this system.
For more information, contact tlo-inquiries
@mit.edu; 617-253-6966.
High-Power Direct Borohydride Fuel Cells
These fuel cells have twice the operating voltage as hydrogen fuel cells.
Washington University in St. Louis, MO
E
lectrification of the transportation
sector is critical to future energy and
environmental resilience and will require
high-power fuel cells (either standalone
or in conjunction with batteries)
to facilitate the transition to electric vehicles,
from cars and trucks to boats and
airplanes.
Liquid-fueled fuel cells are an attractive
alternative to traditional hydrogen
fuel cells because they eliminate the
need to transport and store hydrogen.
They can help to power unmanned underwater
vehicles, drones, and, eventually,
electric aircraft - all at significantly
lower cost. These fuel cells could also
serve as range-extenders for current battery-powered
electric vehicles, thus advancing
their adoption.
Engineers have developed high-power
direct borohydride fuel cells (DBFCs)
that operate at double the voltage of
conventional hydrogen fuel cells. The
research team identified an optimal
range of flow rates, flow field architectures,
and residence times that enable
high-power operation. This approach addresses
key challenges in DBFCs; namely,
Tech Briefs, May 2022
1.2
1
0.8
0.6
0.4
0.2
1.2
PPD (W cm-2)
1
0.8
0.6
0.4
0.2
2006 2007 2008
2010 2012 2012 2015 2016 2019 This
work
A summary of open circuit voltages of the representative DBFC performance in green and current
density at 1.5 V in orange. DBFCs with peak power density at high voltage (>1 V) are represented
by blue columns and those with peak power density at low voltage (<1 V) are represented by black
columns. The present work is highlighted by the yellow column. (Photo: Ramani Lab)
proper fuel and oxidant distribution and
the mitigation of parasitic reactions.
The team has demonstrated a single-cell
operating voltage of 1.4 or greater,
double that obtained in conventional
hydrogen fuel cells, with peak powers
approaching 1 watt/cm2
. Doubling the
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voltage would allow for a smaller, lighter,
more efficient fuel cell design, which
translates to significant gravimetric and
volumetric advantages when assembling
multiple cells into a stack for commercial
use. Their approach is broadly applicable
to other classes of liquid/liquid fuel cells.
45
Current density at 1.5 V (A cm-2)
OCV (V)
2.2
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
TB Power Energy 0522_1.indd 45
Cov
ToC
4/20/22 12:06 PM
Current density at 1.5 V (mA cm-2)
Peak power density (PPD) (W cm-2)
OCV (V)

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Tech Briefs Magazine - May 2022

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