Automotive Electronics

Organic Flow Batteries for Grid-Scale Energy Storage

Researchers at the University of Southern California (USC) have developed a water-based organic battery that is long lasting and built from cheap, eco-friendly components. The new battery, which uses no metals or toxic materials, is intended for use in power plants, where it can make the energy grid more resilient and efficient by creating a large-scale means to store energy for use as needed. This is similar to an announcement from Harvard scientists and engineers earlier this year, who also demonstrated a new type of battery that could fundamentally transform the way electricity is stored on the grid, making power from renewable energy sources such as wind and solar far more economical and reliable.

"The batteries last for about 5,000 recharge cycles, giving them an estimated 15-year life span," said Sri Narayan, professor of chemistry at the USC Dornsife College of Letters, Arts and Sciences and corresponding author of a paper describing the new batteries that was published online by the Journal of the Electrochemical Society on June 20. "Lithium ion batteries degrade after around 1,000 cycles and cost 10-times more to manufacture."

The USC team's breakthrough centered on the electroactive materials. While previous battery designs have used metals or toxic chemicals, Narayan and Prakash wanted to find an organic compound that could be dissolved in water. Such a system would create a minimal impact on the environment and would likely be cheap, they figured. Through a combination of molecule design and trial-and-error, the scientists found that certain naturally occurring quinones - oxidized organic compounds - fit the bill. Quinones are found in plants, fungi, bacteria and some animals, and are involved in photosynthesis and cellular respiration.

"These are the types of molecules that nature uses for energy transfer," Narayan said. Currently, the quinones needed for the batteries are manufactured from naturally occurring hydrocarbons. In the future, the potential exists to derive them from carbon dioxide, Narayan said.

Narayan collaborated with G.K. Surya Prakash, professor of chemistry and director of the USC Loker Hydrocarbon Research Institute, as well as USC's Bo Yang, Lena Hoober-Burkhardt and Fang Wang. "Such organic flow batteries will be game-changers for grid electrical energy storage in terms of simplicity, cost, reliability and sustainability," Prakash said.

The batteries could pave the way for renewable energy sources to make up a greater share of the nation's energy generation. Solar panels can only generate power when the sun's shining, and wind turbines can only generate power when the wind blows. That inherent unreliability makes it difficult for power companies to rely on them to meet customer demand. With batteries to store surplus energy, which can be doled out as needed, that sporadic unreliability could cease to be an issue.

" 'Mega-scale' energy storage is a critical problem in the future of renewable energy," Narayan said. The new battery is based on a redox flow design - similar in design to a fuel cell, with two tanks of electroactive materials dissolved in water. The solutions are pumped into a cell containing a membrane between the two fluids with electrodes on either side releasing energy. The design has the advantage of decoupling power from energy. The tanks of electroactive materials can be made as large as needed - increasing the total amount of energy the system can store - or the central cell can be tweaked to release that energy faster or slower, altering the amount of power (energy released over time) that the system can generate.

The Harvard battery was designed, built, and tested in the laboratory of Michael J. Aziz, Gene and Tracy Sykes Professor of Materials and Energy Technologies at the Harvard School of Engineering and Applied Sciences (SEAS). Roy G. Gordon, Thomas Dudley Cabot Professor of Chemistry and Professor of Materials Science, led the work on the synthesis and chemical screening of molecules. Alán Aspuru-Guzik, Professor of Chemistry and Chemical Biology, used his pioneering high-throughput molecular screening methods to calculate the properties of more than 10,000 quinone molecules in search of the best candidates for the battery.

The new flow battery developed by the Harvard team already performs as well as vanadium flow batteries, with chemicals that are significantly less expensive, and with no precious metal electrocatalyst.

“The whole world of electricity storage has been using metal ions in various charge states but there is a limited number that you can put into solution and use to store energy, and none of them can economically store massive amounts of renewable energy,” Gordon said. “With organic molecules, we introduce a vast new set of possibilities. Some of them will be terrible and some will be really good. With these quinones we have the first ones that look really good.”

Aspuru-Guzik noted that the project is very well aligned with the White House Materials Genome Initiative. “This project illustrates what the synergy of high-throughput quantum chemistry and experimental insight can do,” he said. “In a very quick time period, our team honed in to the right molecule. Computational screening, together with experimentation, can lead to discovery of new materials in many application domains.”

Quinones are abundant in crude oil as well as in green plants. The molecule that the Harvard team used in its first quinone-based flow battery is almost identical to one found in rhubarb. The quinones are dissolved in water, which prevents them from catching fire.

To back up a commercial wind turbine, a large storage tank would be needed, possibly located in a below-grade basement, said co-lead author Michael Marshak, a postdoctoral fellow at SEAS and in the Department of Chemistry and Chemical Biology. Or if you had a whole field of turbines or large solar farm, you could imagine a few very large storage tanks.

The same technology could also have applications at the consumer level, Marshak said. “Imagine a device the size of a home heating oil tank sitting in your basement. It would store a day’s worth of sunshine from the solar panels on the roof of your house, potentially providing enough to power your household from late afternoon, through the night, into the next morning, without burning any fossil fuels.”

“The Harvard team’s results published in Nature demonstrate an early, yet important technical achievement that could be critical in furthering the development of grid-scale batteries,” said ARPA-E Program Director John Lemmon. “The project team’s result is an excellent example of how a small amount of catalytic funding from ARPA-E can help build the foundation to hopefully turn scientific discoveries into low-cost, early-stage energy technologies.”

Team leader Aziz said the next steps in the project will be to further test and optimize the system that has been demonstrated on the bench top and bring it toward a commercial scale. “So far, we’ve seen no sign of degradation after more than 100 cycles, but commercial applications require thousands of cycles,” he said. He also expects to achieve significant improvements in the underlying chemistry of the battery system. “I think the chemistry we have right now might be the best that’s out there for stationary storage and quite possibly cheap enough to make it in the marketplace,” he said. “But we have ideas that could lead to huge improvements.”

By the end of the three-year development period, Connecticut-based Sustainable Innovations, LLC, a collaborator on the project, expects to deploy demonstration versions of the organic flow battery contained in a unit the size of a horse trailer. The portable, scaled-up storage system could be hooked up to solar panels on the roof of a commercial building, and electricity from the solar panels could either directly supply the needs of the building or go into storage and come out of storage when there’s a need. Sustainable Innovations anticipates playing a key role in the product’s commercialization by leveraging its ultra-low cost electrochemical cell design and system architecture already under development for energy storage applications.

“You could theoretically put this on any node on the grid,” Aziz said. “If the market price fluctuates enough, you could put a storage device there and buy electricity to store it when the price is low and then sell it back when the price is high. In addition, you might be able to avoid the permitting and gas supply problems of having to build a gas-fired power plant just to meet the occasional needs of a growing peak demand.”

University of Southern California , Sustainable Innovations, LLC , Harvard School of Engineering and Applied Sciences
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