Researchers at the Georgia Institute of Technology in the U.S. have developed a compact flow battery cell configuration that reduces the size of the cell by 75% and correspondingly reduces the size and the cost of the entire flow battery.

With zinc-iodide chemistry, the battery could run for more than 220 hours, or for more than 2,500 cycles at off-peak conditions.

It could also potentially reduce the cost from $800 to less than $200 per kWh by using recycled electrolytes.

The team published their findings in Proceedings of the National Academy of Sciences and said their work could revolutionize how major commercial buildings to residential homes are powered.

Flow batteries get their name from the flow cell where electron exchange happens. Their conventional design, the planar cell, requires bulky flow distributors and gaskets, increasing size and cost but decreasing overall performance. The cell itself is also expensive

Compact flow batteries 

The researchers pointed out flow batteries can smooth out the fluctuations, arising from inconsistent solar or wind power which often faces difficulty to achieve a reliable power grid.

To reduce both footprint and cost, the researchers focused on improving the flow cell’s volumetric power density.

The team turned to a configuration commonly used in chemical separation and made use of a fiber-shaped filter membrane known as hollow fiber.

This resulted in a space-saving design that could mitigate pressure across the membranes that ions pass through without needing additional support infrastructure.

“We were aware of the advantages that hollow fibers imparted on separation membranes and set out to realize those same advantages in the battery field,” said Ryan Lively, a researcher on the project.

Applying the concept, the researchers were able to develop a “sub-millimeter, bundled microtubular” SMBT membrane that reduced the membrane-to-membrane distance by nearly 100 times.

This bundling design of the membrane became the key to maximizing the flow of batteries’ potential.

The microtubular membrane worked as an electrolyte distributor simultaneously without the need for large supporting materials while the bundled microtubes created a shorter distance between electrodes and membranes, thereby increasing the volumetric power density.

The SBMT cells could also be applied to different energy storage systems like electrolysis and fuel cells and could be strengthened further, the researchers said.

Powering the battery

The researchers used four different chemistries; vanadium, zinc-bromide, quinone-bromide, and zinc-iodide to validate their battery configuration.

Zinc iodide was identified as the most energy-dense option, making it the most effective for residential units.

The researchers also said it offered advantages when compared to lithium; as it has less of a supply chain issue and can be turned into zinc oxide and dissolved in acid, making it easily recyclable.

The team is working on commercialization, focusing on developing batteries with different chemistries like vanadium and scaling up their size.

Eventually, they hope to deploy the battery in Georgia Tech’s 1.4 MW microgrid in Tech Square, a project that tests microgrid integration into the power grid and offers a living laboratory for professors and students.

Last year, researchers at the Chinese Academy of Sciences (CAS) claimed to have built a stable kilowatt-scale aqueous redox flow battery with high-performance organic redox-active molecules for renewable storage.

In the same month, researchers at the University of Sydney claimed to have developed a new, low-cost sodium-sulfur battery with four times the energy capacity of lithium-ion batteries.

Image: Georgia Institute of Technology