New Design for Iron Flow Battery Could Aid Electric Grid
In the 1970’s, scientists at the National Aeronautics and Space Administration (NASA) developed the first iron flow batteries using an iron/chromium system for photovoltaic applications. Over the next decade, these unique systems, which combine charged iron with an aqueous liquid energy carrier, were improved upon for large-scale energy storage. But Guosheng Li, a senior scientist at the Department of Energy’s Pacific Northwest National Laboratory (PNNL), said the storage systems were not true flow batteries, but rather hybrid systems.
“With these conventional iron flow batteries, the liquid is on the cathode, and they use a fully dissolved catholyte. But on the anode side, they take advantage of iron plating,” Li said. “We wanted to find a way to make the battery full flow, entirely soluble, and remove the iron plating so that we could improve upon the original design.”
A flow battery exchanges ions between liquid anodes and cathodes, called anolyte and catholyte. Image: PNNL
During the COVID-19 pandemic, Li and colleagues were charged with coming up with new ways to store energy generated by renewable sources such as wind and solar energy power. The goal was to design a flow battery that could use Earth-abundant materials—and create back-up storage for the U.S. electrical grid.
The first step was to find an electrolyte that could bind and store charge iron in a liquid complex. The group determined that a common phosphonate chemical, nitrogenous triphosphonate, nitrilotri-methylphosphonic acid (NTMPA), which is already widely used in water treatment facilities to prevent corrosion, could do the trick.
PNNL battery researcher Gabriel Nambafu assembles a test flow battery apparatus. (Photo by Andrea Starr/PNNL)
“Our first-generation phosphonate NTMPA can bind and store charged iron in the liquid complex in mild operating conditions with near-neutral pH and environmental benignity,” Li said. “And unlike other flow battery materials, it’s something we can source domestically.”
Flow batteries charge through electrochemical reactions. The battery circulates the liquid electrolyte, in this case the NTMPA, which charge and discharge electrons via a redox reaction. When the battery is hooked up to an external circuit, that energy can be used provide power as needed.
What’s advantageous about flow batteries compared to other types of energy storage devices is that they are easily scalable. The larger the electrolyte supply tank, the more energy that can be stored within the battery.
When asked about the biggest challenges involved with designing this new type of iron flow battery, Li said making the iron soluble so it can interact with the electrolyte was one. But he and his team also spent a good amount of time working to come up with the right voltage potential to make the battery work.
Discover the Benefits of ASME Membership
“We chose a conventional iron, ferrocyanide, as a catholyte,” he said. “We had to then strategically design a material that has a good voltage offset so that you can have a good voltage output.”
When testing the new design at lab-scale, the researchers were able to reach energy density up to 9 watt-hours per liter, or 9 kWh per cubic meter. While it is not as energy dense as commercialized vanadium-based systems, which reach energy density at 25 watt-hours per liter, Li said his team is working on making targeted improvements.
“We want to improve voltage output and to do that we need to make the anolyte potential lower,” he said. “NTMPA was a good starting point, but the potential is a little bit high, which means the output will be a little bit low.”
More from ASME.org: Improved Power for Rested Batteries
Li continued, “No one had ever thought about this complex before. It gives us some good ideas of what we need to do in order to lower the redox potential as we design a new ligand or complex, or perhaps change some of the operating conditions to make the voltage output larger.”
That said, Li is very excited about the potential of new iron flow batteries for renewable energy storage. All materials needed for this type of iron flow battery are easily sourced within the United States and can be safely used in urban and suburban environments near energy consumers, so they can help serve as backup energy storage for the country’s electrical grids.
Improvement in Battery Technology: Breakthrough Could Make for Long-Range EVs
“The new iron flow battery is a good candidate for longer duration batteries, with discharge over 10-20 hours,” he said. “And we have improved on this old design because of a fundamental understanding of both the battery and the material design. By engaging in a deep dive into the materials, we discovered things we didn’t know before. Sometimes it can lead a way to a whole new field. And I believe, as we make progress on this design, it can open up a new door for a flow battery field in the future.”
Kayt Sukel is a technology and business writer in Houston.
“With these conventional iron flow batteries, the liquid is on the cathode, and they use a fully dissolved catholyte. But on the anode side, they take advantage of iron plating,” Li said. “We wanted to find a way to make the battery full flow, entirely soluble, and remove the iron plating so that we could improve upon the original design.”
A flow battery exchanges ions between liquid anodes and cathodes, called anolyte and catholyte. Image: PNNL
The first step was to find an electrolyte that could bind and store charge iron in a liquid complex. The group determined that a common phosphonate chemical, nitrogenous triphosphonate, nitrilotri-methylphosphonic acid (NTMPA), which is already widely used in water treatment facilities to prevent corrosion, could do the trick.
PNNL battery researcher Gabriel Nambafu assembles a test flow battery apparatus. (Photo by Andrea Starr/PNNL)
Flow batteries charge through electrochemical reactions. The battery circulates the liquid electrolyte, in this case the NTMPA, which charge and discharge electrons via a redox reaction. When the battery is hooked up to an external circuit, that energy can be used provide power as needed.
What’s advantageous about flow batteries compared to other types of energy storage devices is that they are easily scalable. The larger the electrolyte supply tank, the more energy that can be stored within the battery.
When asked about the biggest challenges involved with designing this new type of iron flow battery, Li said making the iron soluble so it can interact with the electrolyte was one. But he and his team also spent a good amount of time working to come up with the right voltage potential to make the battery work.
Discover the Benefits of ASME Membership
“We chose a conventional iron, ferrocyanide, as a catholyte,” he said. “We had to then strategically design a material that has a good voltage offset so that you can have a good voltage output.”
When testing the new design at lab-scale, the researchers were able to reach energy density up to 9 watt-hours per liter, or 9 kWh per cubic meter. While it is not as energy dense as commercialized vanadium-based systems, which reach energy density at 25 watt-hours per liter, Li said his team is working on making targeted improvements.
“We want to improve voltage output and to do that we need to make the anolyte potential lower,” he said. “NTMPA was a good starting point, but the potential is a little bit high, which means the output will be a little bit low.”
More from ASME.org: Improved Power for Rested Batteries
Li continued, “No one had ever thought about this complex before. It gives us some good ideas of what we need to do in order to lower the redox potential as we design a new ligand or complex, or perhaps change some of the operating conditions to make the voltage output larger.”
That said, Li is very excited about the potential of new iron flow batteries for renewable energy storage. All materials needed for this type of iron flow battery are easily sourced within the United States and can be safely used in urban and suburban environments near energy consumers, so they can help serve as backup energy storage for the country’s electrical grids.
Improvement in Battery Technology: Breakthrough Could Make for Long-Range EVs
“The new iron flow battery is a good candidate for longer duration batteries, with discharge over 10-20 hours,” he said. “And we have improved on this old design because of a fundamental understanding of both the battery and the material design. By engaging in a deep dive into the materials, we discovered things we didn’t know before. Sometimes it can lead a way to a whole new field. And I believe, as we make progress on this design, it can open up a new door for a flow battery field in the future.”
Kayt Sukel is a technology and business writer in Houston.
As renewable energy gains momentum, oil and natural gas continue to remain primary global energy sources. This collection delves into latest digital trends enabling breakthroughs in energy transformation.