Renewable energy is key to achieving a net-zero energy world. One question that commonly arises is how can energy from clean but intermittent power sources, such as solar and wind, be stored and distributed in a lasting way? On July 10, the Department of Energy’s Pacific Northwest National Laboratory (PNNL) announced that researchers had developed a record-setting flow battery that maintained its capacity to store and release energy for more than a year of continuous charge and discharge. The next-generation battery design relies on a novel catalyst to boost its longevity and capacity: the common food additive β-cyclodextrin, a simple sugar that derives from starch.
The researchers, which included chemists, material scientists, mathematicians, and long-time PNNL battery researcher and principal investigator Wei Wang, optimized the ratio of chemicals in the battery system until it achieved 60% more peak power. They cycled the battery for more than year, stopping only once due to a plastic tubing failure, and observed almost no loss of the battery’s ability to recharge.
The β-cyclodextrin additive also sped up the electrochemical reaction that stored and released the flow battery energy through homogeneous catalysis, meaning the sugar was dissolved in a liquid solution rather than applied as a solid to a surface.
“This is a brand new approach to developing flow battery electrolyte,” Wang said in the PNNL news release. “We showed that you can use a totally different type of catalyst designed to accelerate the energy conversion. And further, because it is dissolved in the liquid electrolyte it eliminates the possibility of a solid dislodging and fouling the system.”
A flow battery consists of two external chambers containing a negative anolyte solution that charges through an electrochemical reaction and a positive catholyte solution that balances the positive and negative charges during the battery’s charge and discharge. The battery stores that energy in chemical bonds until an external circuit is connected, whereby it releases the energy to power electrical devices. A flow battery differs from a solid-state battery because liquid is constantly circulating to supply the electrolyte.
Animation by Sara Levine / Pacific Northwest National Laboratory
What makes flow batteries promising in decarbonization strategies is their ability to scale from the lab bench to a city block, according to the release. Flow batteries the size of a football field or greater can serve as a backup generator for the electric grid.
Furthermore, this research uses a common, stable, and nontoxic additive in its innovative battery rather than mined materials, such as vanadium, which are expensive and difficult to obtain, according to PNNL’s release. “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 research team has applied for a patent for its battery design, which may be eligible for licensing. As scientists often do, the team is already looking to improve the system by experimenting with compounds similar to β-cyclodextrin, but smaller to limit the increase in viscosity of the battery chamber liquid, which needs to circulate constantly.
PNNL expects its work on flow batteries and grid-scale energy storage research will be accelerated when the laboratory opens its Grid Storage Launchpad in 2024.
The study received support from the DOE Office of Electricity through its Energy Storage Division and from the Energy Storage Materials Initiative at PNNL. Other contributors include the Center for Molecular Electrocatalysis at PNNL, which helped explained the boost in battery capacity through mathematical calculations; and the Environmental Molecular Sciences Laboratory, also located at PNNL.
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