The ‘Redox Flow’ Battery Poised to Solve the Electricity Storage Problem

As part of their work towards cracking the problem of renewable energy storage, these researchers have developed a new version of a “redox flow” battery. 

This type of battery is a well-known design that has been around for quite some time now. It stores electricity in solutions, sorts electrons, and uses power only when it is required. The latest iteration of this battery improves upon previous ones by using materials that are both inexpensive and readily available, making it accessible and easier to deploy on a wider scale.

How a Redox Flow Battery Works

In the battery, a positive and negative chemical are stored in separate tanks. These chemicals are pumped in and out of a chamber where they then exchange ions across a membrane, flowing one way to charge and the flowing in the other way to discharge. Although these systems have used expensive and dangerous materials for their electrolytes in the past, such as vanadium and bromine dissolved in acid, recent designs have brought us more organic alternatives. 

Sourcing Organic Materials 

In its latest design, the USC research team—who reported their findings in the Journal of the Electrochemical Society—used a waste product from the mining industry alongside an organic material that can be made from carbon-based feedstocks, including CO2, and is already used in other redox flow batteries. 

Sri Narayan, chemistry professor and the study’s lead author, said: "We have demonstrated an inexpensive, long-life, safe and eco-friendly flow battery attractive for storing the energy from solar and wind energy systems at a mass-scale,"

A diagram detailing the function of the redox flow battery developed by USC researchers. Image used courtesy of USC

Overcoming the Storage Hurdle

Energy storage is one of renewable power’s biggest hurdles. This is because when energy is being generated by wind turbines or solar panels, demand is not always high, and this leads to a surplus that has nowhere to go in the absence of a viable storage solution. And it is this problem—finding or developing a viable storage solution—which the USC researchers are trying to solve. 

They focused their efforts on the redox flow battery because it is a proven technology that has already been used in a limited number of applications. It makes use of fluids to store electrochemical energy, sorting electrons and recombining via reduction and oxidation before releasing them to generate electricity when it is needed. 

Large-Scale Energy Storage by Reusing Products

In its latest iteration of the battery, the USC researchers used different fluids: an iron sulfate solution, the mining industry waste product which is plentiful and inexpensive, and anthraquinone disulfonic acid (AQDS), an organic material that is already used in existing redox flow batteries due to its stability and energy storage potential. 

This is the first time that the two compounds have been used together for large-scale energy storage.

An Eco-friendly and Renewable Energy Storage Solution

In testing, the USC researchers found that the iron-AQDS redox flow battery could cycle hundreds of times without exhibiting any power loss. In contrast to competing technologies, this is a major improvement because durability is important for large-scale use.

It is thought by the research team that the redox flow battery could be used as a long-term renewable energy storage system. To date, Narayan said, “there has been no economically viable, eco-friendly solution to energy storage that can last for 25 years."

“Lithium-ion batteries do not have the long-life and vanadium-based batteries uses expensive, relatively toxic materials limiting large-scale use. Our system is the answer to this challenge. We foresee these batteries used in residential, commercial and industrial buildings to capture renewable energy."