Tech Briefs Magazine - June 2024 - 33

An All-Liquid Iron Flow Battery for Better Energy Storage
A new design provides a pathway to a safe, economical, water-based, flow battery made
with Earth-abundant materials.
Pacific Northwest National Laboratory, Richland, WA
A
commonplace chemical used in water treatment facilities has
been repurposed for large-scale energy storage in a new battery
design by researchers at the Department of Energy's Pacific
Northwest National Laboratory. The design provides a pathway to
a safe, economical, water-based, flow battery made with Earth-abundant
materials. It provides another pathway in the quest to incorporate
intermittent energy sources such as wind and solar energy into
the nation's electric grid.
The researchers reported in Nature Communications that their
iron-based battery exhibited remarkable cycling stability over 1,000
consecutive charging cycles, while maintaining 98.7 percent of its
maximum capacity. For comparison, previous studies of similar
iron-based batteries reported degradation of the charge capacity
two orders of magnitude higher, over fewer charging cycles.
Iron-based flow batteries designed for large-scale energy storage
have been around since the 1980s, and some are now commercially
available. What makes this battery different is that it stores energy
in a unique liquid chemical formula that combines charged iron
with a neutral-pH phosphate-based liquid electrolyte, or energy
carrier. Crucially, the chemical, called nitrogenous triphosphonate,
nitrilotri-methylphosphonic acid or NTMPA, is commercially
available in industrial quantities because it is typically used to inhibit
corrosion in water treatment plants.
" We were looking for an electrolyte that could bind and store
charged iron in a liquid complex at room temperature and mild
operating conditions with neutral pH, " said Senior Author Guosheng
Li. " We are motivated to develop battery materials that are
Earth-abundant and can be sourced domestically. "
Flow batteries can serve as backup generators for the electric
grid. Flow batteries are one of the key pillars of a decarbonization
strategy to store energy from renewable energy resources. Their
advantage is that they can be built at any scale, from the lab-bench
scale, as in the PNNL study, to the size of a city block.
In the near term, grid operators are looking to locate battery
energy storage systems (BESS) in urban or suburban areas near
energy consumers. Often, city planners must grapple with consumer
safety concerns. The type of aqueous flow battery reported here
could help alleviate safety concerns.
" A BESS facility using the chemistry similar to what we have developed
here would have the advantage of operating in water at
neutral pH, " said Author Aaron Hollas. " In addition, our system
uses commercially available reagents that haven't been previously
investigated for use in flow batteries. "
The team reported that its initial design can reach energy density,
a key design feature, up to nine watt-hours per liter (Wh/L). In
comparison, commercialized vanadium-based systems are more
than twice as energy dense, at 25 Wh/L. Higher energy density
batteries can store more energy in a smaller square footage, but a
system built with Earth-abundant materials could be scaled to provide
the same energy output.
" Our next step is to improve battery performance by focusing on
aspects such as voltage output and electrolyte concentration, which
will help to increase the energy density, " said Li. " Our voltage output
is lower than the typical vanadium flow battery output. We are
working on ways to improve that. "
PNNL researchers plan to scale-up this and other new battery
technologies at a new facility called the Grid Storage Launchpad
(GSL) opening at PNNL in 2024.
For more information, contact Karyn Hede at karyn.hede@
pnnl.gov; 509-375-2144.
Lead Author and Battery Researcher Gabriel Nambafu assembles a test
flow battery apparatus. (Image: Andrea Starr, Pacific Northwest National
Laboratory)
Tech Briefs, June 2024
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