USC develops better redox flow battery

USC scientists have developed a new battery that could solve the electricity storage problem that has limited widespread use of renewable energy.

The technology is an improvement on known designs that store electricity in a solution, sort the electrons and release the energy when needed. Redox flow batteries have been around for a while, but USC researchers have built a better version based on low-cost and readily available materials.

“We have developed an inexpensive, long-life, safe and environmentally friendly flow battery that can store energy from solar and wind systems on a large scale,” said Sri Narayan, professor of chemistry and co-director of the USC Rock Hydrocarbon Institute and lead author of the study.

The research was published recently in the Journal of the Electrochemical Society.

Energy storage is a big hurdle for renewable energy because there isn't always a coincidence of electricity demand when wind turbines and solar cells are generating electricity. There are many challenges in finding a viable storage solution, which is what USC scientists are trying to solve. They looked at redox flow batteries because they are already used in some cases. It uses fluids to store electrochemical energy, sorting and recombining electrons through reduction and oxidation, and releasing them to generate electricity when needed.

Image credit: University of Southern California

The key innovation achieved by the USC scientists is that they used different liquids: an iron sulfate solution and an acid. Iron sulfate is a waste product from mining and is cheap. Anthraquinone disulfonic acid (AQDS) is an organic material that has been used in some redox flow batteries due to its stability, solubility and energy storage potential. While the two compounds are well known, this is the first time they have been combined to demonstrate their potential for large-scale energy storage. Tests conducted in the USC laboratory proved that the battery has major advantages over competitors.

First, iron sulfate is cheap and abundant, with a dime buying about 2.2 pounds, and mass production of AQDS costs only about $1.60 per pound. At these prices, the material cost of the battery developed by scientists at the University of Southern California is $66 per kilowatt-hour; if produced on a large scale, the cost of electricity would be less than half that of redox batteries using vanadium, which is more expensive and more toxic.

Second, the researchers found that, unlike existing technologies, the iron-AQDS battery can be cycled, or recharged, hundreds of times with little loss of power. The durability of energy storage systems is important for large-scale use.

The technology also has storage advantages over lithium-ion batteries . The proliferation of consumer electronics and electric vehicles powered by lithium- ion batteries has created a scarcity of the element, driving up costs. In turn, those economic benefits make other, cheaper energy storage options more attractive, the study said. Lithium-ion batteries also don't last as long because they need to be recharged, as most people who have charged their phones and laptops know.

The use of renewable energy is growing but is limited by energy storage constraints. Storing just 20% of the current solar and wind energy would require 7,000 gigawatt-hours of storage capacity. One gigawatt-hour of electricity is enough to power 700,000 homes for one hour.

"Until now, there has been no economically viable, environmentally friendly energy storage solution that can last for 25 years," Narayan said. "Lithium-ion batteries have a short lifespan, while vanadium-based batteries use expensive, relatively toxic materials, limiting large-scale use. We envision these batteries being used in residential, commercial and industrial buildings to harvest renewable energy."