A common food and drug additive has shown it can boost the capacity and longevity of a next-generation battery design in a record-setting experiment.
A research team from the Department of Energy’s Pacific Northwest National Laboratory reports that the flow battery, a design optimized for electrical grid energy storage, maintains its capacity to store and release energy for more than a year. which is continuously charging and discharging.
The study, recently published in the journal Joule, detailed the first use of a dissolved simple sugar called β-cyclodextrin, a starch derivative, to improve battery longevity and capacity. In a series of experiments, the scientists optimized the ratio of chemicals in the system until it achieved 60 percent higher power.
Then, they repeatedly cycled the battery for over a year, stopping the experiment only when the plastic tubing failed. During all the time, the current battery hardly has any activity to recharge. This is the first laboratory-scale flow battery experiment to report more than a year of continuous use with minimal capacity loss.
The β-cyclodextrin additive is also the first to accelerate the electrochemical reaction that stores and then releases the flow of energy in the battery, in a process called homogeneous catalysis. This means that the sugar does its work while dissolved in solution, rather than as a solid applied to a surface.
“This is a new method of developing a flow battery electrolyte,” said Wei Wang, a longtime battery researcher at PNNL and the study’s principal investigator. “We have shown that you can use a completely different type of catalyst designed to accelerate the conversion of energy. And in addition, because it is dissolved in the liquid electrolyte it eliminates the possibility of a solid dislodging and fouling of the system .”
What is a flow battery?
As their name suggests, flow batteries have two chambers, each filled with a different liquid. Batteries charge through an electrochemical reaction and store energy in chemical bonds. When connected to an external circuit, they release that energy, which can power electrical devices. Flow batteries differ from solid-state batteries because they have two external liquid supply tanks that constantly circulate through them to provide the electrolyte, which is like a “blood supply” for in the system. The larger the electrolyte supply tank, the more energy can be stored in the battery flow.
If they are scaled 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 main pillars of a decarbonization strategy to store energy from renewable energy resources. Their advantage is that they can be built on any scale, from lab-bench scale, like the PNNL study, to the size of a city block.
Why do we need new types of running batteries?
Large-scale energy storage provides a kind of insurance policy against disruption to our electrical grid. When severe weather or high demand disrupts the ability to supply electricity to homes and businesses, the energy stored in multiple battery storage facilities can help minimize disruption or restore service. The demand for these battery flow facilities is expected to grow, as electricity generation increasingly comes from renewable energy sources, such as wind, solar and hydroelectric power. Intermittent power sources like this require a place to store the energy until it is needed to meet the needs of consumers.
While there are many battery flow designs and some commercial installations, existing commercial facilities rely on mined minerals such as vanadium which are expensive and difficult to obtain. That’s why research teams are looking for effective alternative technologies that use more common materials that are easy to synthesize, stable and non-toxic.
“We don’t always dig in the Earth for new materials,” said Imre Gyuk, director of energy storage research at the DOE’s Office of Electricity. “We need to develop a sustainable approach to chemicals that we can synthesize in large quantities—like in the pharmaceutical and food industries.”
Work on flow batteries is part of a larger PNNL program to develop and test new technologies for grid-scale energy storage that will be accelerated by the opening of PNNL’s Grid Storage Launchpad in 2024.
A poor ‘sugar water’ sweetens the pot for an effective draining battery
The PNNL research team developing this new battery design includes researchers with backgrounds in organic and chemical synthesis. These skills come in handy when the team chooses to work with materials that have not yet been used for battery research, but that have been developed for other industrial uses.
“We are looking for a simple way to dissolve more fluorenol in our water-based electrolyte,” said Ruozhu Feng, the first author of the new study. “β-cyclodextrin helps do that, moderately, but it’s real benefit is this surprising catalytic ability.”
The researchers then worked with co-author Sharon Hammes-Schiffer of Yale University, a leading authority on the chemical reactions that underlie the catalytic boost, to explain how it works.
As described in the research study, the sugar additive accepts protons with a positive charge, which helps balance the movement of negative electrons as the battery discharges. The details are a bit more complicated, but it’s like sugar sweetening the pot to allow 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, researchers have shown that another common chemical, called fluorenone, is an effective flow battery component. But that initial development required a lot of work because the process was slow compared to commercial flow battery technology. This new development makes the battery design a candidate for scaling, the researchers said.
At the same time, the research team worked to further improve the system by experimenting with other compounds similar to β-cyclodextrin but smaller. Like honey, the addition of β-cyclodextrin also makes the liquid thicker, which is not very good for a flowing system. However, researchers have found that its benefits outweigh its drawbacks.
Understanding the complex chemistry occurring within the new flow battery design required the expertise of many scientists, including Ying Chen, Xin Zhang, Peiyuan Gao, Ping Chen, Sebastian Mergelsberg, Lirong Zhong, Aaron Hollas, Yangang Lian, Vijayakumar Murugesan, Qian Huang, Eric Walter and Yuyan Shao at PNNL, and Benjamin JG Rousseau and Hammes-Schiffer at Yale, in addition to Feng and Wang.
The research team has applied for US patent protection for their new battery design.
Ruozhu Feng et al, Proton-regulated alcohol oxidation for high-capacity ketone-based flow battery anolyte, Joule (2023). DOI: 10.1016/j.joule.2023.06.013
Provided by the Pacific Northwest National Laboratory
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