`Freeze-thaw battery' is adept at preserving its energy
Molten-salt battery marks step toward seasonal storage of grid-scale
energy

Date:
April 5, 2022
Source:
DOE/Pacific Northwest National Laboratory
Summary:
Scientists have created a battery designed for the electric
grid that locks in energy for months without losing much storage
capacity. It's a step toward batteries that can be used for seasonal
storage: saving renewable energy in one season, such as the spring,
and spending it in another, like autumn.



FULL STORY ========================================================================== Scientists have created a battery designed for the electric grid that
locks in energy for months without losing much storage capacity.


==========================================================================
The development of the "freeze-thaw battery," which freezes its energy
for use later, is a step toward batteries that can be used for seasonal storage: saving energy in one season, such as the spring, and spending
it in another, like autumn.

The prototype is small, about the size of a hockey puck. But the potential usefulness of the science behind the device is vast, foretelling a
time when energy from intermittent sources, like sunshine and wind,
can be stored for a long time. The work by scientists at the Department
of Energy's Pacific Northwest National Laboratory was published online
March 23 in Cell Reports Physical Science.

"Longer-duration energy storage technologies are important for increasing
the resilience of the grid when incorporating a large amount of renewable energy," said Imre Gyuk, director of Energy Storage at DOE's Office of Electricity, which funded the work. "This research marks an important
step toward a seasonal battery storage solution that overcomes the self-discharge limitations of today's battery technologies." Harnessing
and packaging nature's energy Renewable sources ebb and flow with
nature's cycles. That makes it difficult to include them in a reliable,
steady stream of electricity. In the Pacific Northwest in the spring,
for instance, rivers heavy with runoff power hydroelectric dams to the
max just as winds blow fiercely down the Columbia Gorge. All that power
must be harnessed immediately or stored for a few days at most.



==========================================================================
Grid operators would love to harness that springtime energy, store it
in large batteries, then release it late in the year when the region's
winds are slow, the rivers are low, and demand for electricity peaks.

The batteries would also enhance utilities' ability to weather a power
outage during severe storms, making large amounts of energy available
to be fed into the grid after a hurricane, a wildfire or other calamity.

"It's a lot like growing food in your garden in the spring, putting the
extra in a container in your freezer, and then thawing it out for dinner
in the winter," said first author Minyuan "Miller" Li.

The battery is first charged by heating it up to 180 degrees Celsius,
allowing ions to flow through the liquid electrolyte to create chemical
energy. Then, the battery is cooled to room temperature, essentially
locking in the battery's energy. The electrolyte becomes solid and the
ions that shuttle energy stay nearly still. When the energy is needed,
the battery is reheated and the energy flows.

The freeze-thaw phenomenon is possible because the battery's electrolyte
is molten salt -- a molecular cousin of ordinary table salt. The material
is liquid at higher temperatures but solid at room temperature.



==========================================================================
The freeze-thaw concept dodges a problem familiar to anyone who has let
their car sit unused for too long: a battery that self-discharges as it
sits idle. A fast discharge rate, like that of batteries in most cars
or laptops, would hamper a grid battery designed to store energy for
months. Notably, the PNNL freeze-thaw battery has retained 92 percent
of its capacity over 12 weeks.

In other words, the energy doesn't degrade much; it's preserved, just
like food in a freezer.

Ordinary ingredients a plus The team avoided rare, expensive and highly reactive materials. Instead, the aluminum-nickel molten-salt battery is
chock full of Earth-abundant, common materials. The anode and cathode are
solid plates of aluminum and nickel, respectively. They're immersed in a
sea of molten-salt electrolyte that is solid at room temperature but flows
as a liquid when heated. The team added sulfur -- another common, low-cost element -- to the electrolyte to enhance the battery's energy capacity.

One of the biggest advantages of the battery is the composition of
a component, called a separator, placed between the anode and the
cathode. Most higher- temperature molten-salt batteries require a ceramic separator, which can be more expensive to make and susceptible to breakage during the freeze-thaw cycle. The PNNL battery uses simple fiberglass,
possible because of the battery's stable chemistry. This cuts costs and
makes the battery sturdier when undergoing freeze-thaw cycles.

"Reducing battery costs is critical. That is why we've chosen common,
less- expensive materials to work with, and why we focused on removing
the ceramic separator," said corresponding author Guosheng Li, who led
the study.

The battery's energy is stored at a materials cost of about $23 per
kilowatt hour, measured before a recent jump in the cost of nickel. The
team is exploring the use of iron, which is less expensive, in hopes of bringing the materials cost down to around $6 per kilowatt hour, roughly
15 times less than the materials cost of today's lithium-ion batteries.

The battery's theoretical energy density is 260 watt-hours per kilogram -
- higher than today's lead-acid and flow batteries.

Researchers point out that batteries designed for seasonal storage would
likely charge and discharge just once or twice a year. Unlike batteries designed to power electric cars, laptops or other consumer devices,
they don't need to last hundreds or thousands of cycles.

"You can start to envision something like a large battery on a 40-foot
tractor- trailer parked at a wind farm," said coauthor Vince Sprenkle,
senior strategic advisor at PNNL. "The battery is charged in the spring
and then the truck is driven down the road to a substation where the
battery is available if needed during the summer heat." Battelle,
which operates PNNL, has filed for a patent on the technology.


========================================================================== Story Source: Materials provided by
DOE/Pacific_Northwest_National_Laboratory. Original written by Tom
Rickey. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Minyuan M. Li, Xiaowen Zhan, Evgueni Polikarpov, Nathan L. Canfield,
Mark
H. Engelhard, J. Mark Weller, David M. Reed, Vincent L. Sprenkle,
Guosheng Li. A freeze-thaw molten salt battery for seasonal
storage. Cell Reports Physical Science, 2022; 100821 DOI:
10.1016/j.xcrp.2022.100821 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220405084551.htm

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