Next-Generation Flow Battery Design Sets Records

If they are scaled up to the size of a football field or more, 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.

Why Do We Need New Kinds of Flow Batteries?
Large-scale energy storage provides a kind of insurance policy against disruption to our electrical grid. When severe weather or high demand hobble the ability to supply electricity to homes and businesses, energy stored in large-scale flow battery facilities can help minimize disruption or restore service. The need for these flow battery facilities is only expected to grow, as electricity generation increasingly comes from renewable energy sources, such as wind, solar and hydroelectric power. Intermittent power sources such as these require a place to store energy until it’s needed to meet consumer demand.

While there are many flow battery designs and some commercial installations, existing commercial facilities rely on mined minerals such as vanadium that are costly and difficult to obtain. That’s why research teams are seeking effective alternative technologies that use more common materials that are easily synthesized, stable and non-toxic.

“We cannot always dig the Earth for new materials,” said Imre Gyuk, director of energy storage research at DOE’s Office of Electricity. “We need to develop a sustainable approach with chemicals that we can synthesize in large amounts—just like the pharmaceutical and the food industries.”

The work on flow batteries is part of a large program at PNNL to develop and test new technologies for grid-scale energy storage that will be accelerated with the opening of PNNL’s Grid Storage Launchpad in 2024.

A Benign “Sugar Water” Sweetens the Pot for an Effective Flow Battery
The PNNL research team that developed this new battery design includes researchers with backgrounds in organic and chemical synthesis. These skills came in handy when the team chose to work with materials that had not been used for battery research, but which are already produced for other industrial uses.

“We were looking for a simple way to dissolve more fluorenol in our water-based electrolyte,” said Ruozhu Feng, the first author of the new study. “The β-cyclodextrin helped do that, modestly, but it’s real benefit was this surprising catalytic ability.”

The researchers then worked with co-author Sharon Hammes-Schiffer of Yale University, a leading authority on the chemical reaction underlying the catalytic boost, to explain how it works.

As described in the research study, the sugar additive accepts positively charged protons, which helps balance out the movement of negative electrons as the battery discharges. The details are a bit more complicated, but it’s like the sugar sweetens the pot to allow the other chemicals to complete their chemical dance.

The study is the next generation of a PNNL-patented flow battery design first described in the journal Science in 2021. There, the researchers showed that another common chemical, called fluorenone, is an effective flow battery component. But that initial breakthrough needed improvement because the process was slow compared with commercialized flow battery technology. This new advance makes the battery design a candidate for scale up, the researchers say.

At the same time, the research team is working to further improve the system by experimenting with other compounds that are similar to β-cyclodextrin but smaller. Like honey, β-cyclodextrin addition also makes the liquid thicker, which is less than ideal for a flowing system. Nonetheless, the researchers found its benefits outweighed its drawbacks.

The research team has applied for U.S. patent protection for their new battery design.

Karyn Hede is senior science communicator and media relations advisor at PNNL. The article was originally posted to the website of the Pacific Northwest National Laboratory (PNNL).