MIT's Renewable "Flow Battery" Could Store Solar And Wind Power On Large-Scale And Even Cheaper

MIT's Renewable Flow Battery Could Store Solar And Wind Power On Large-Scale And Even Cheaper

Researchers at Massachusetts Institute of Technology (MIT) have developed a battery that could bring us reliable and cheap large scale energy storage. Based on flow battery technology, the researchers took out the costly membrane and created a battery that has a power density that is an order of magnitude higher than lithium-ion batteries and three times greater than other membrane-less systems.

MIT reports, "The device stores and releases energy in a device that relies on a phenomenon called laminar flow: Two liquids are pumped through a channel, undergoing electrochemical reactions between two electrodes to store or release energy. Under the right conditions, the solutions stream through in parallel, with very little mixing. The flow naturally separates the liquids, without requiring a costly membrane."

The battery reactants are liquid bromine and hydrogen; the chemical reaction reduces liquid bromine to hydrobromic acid at a solid graphite electrode while hydrogen is oxidized at a porous graphite electrode. The strong chemical reaction between the hydrogen and bromine enables the battery to store more energy per unit volume than other flow batteries, MIT said. Reversible hydrogen-bromine reactions have been used in other flow batteries, but corrosive properties eventually cause conventional ion-exchange membranes to fail. MIT's membraneless setup is designed to solve that problem.

A diagram of a vanadium flow battery

Large-scale flow batteries could enable solar and wind systems to store energy as its produced and then meter it out as it is needed during times of peak demand. The economies of scale are right, too, since liquid bromine and hydrogen fuel are both widely available and relatively inexpensive in large quantities, "with more than 243,000 tons produced each year in the United States."

“Here, we have a system where performance is just as good as previous systems, and now we don’t have to worry about issues of the membrane,” says Martin Bazant, a professor of chemical engineering. “This is something that can be a quantum leap in energy-storage technology.”

“Energy storage is the key enabling technology for renewables,” says Cullen Buie, an assistant professor of mechanical engineering. “Until you can make [energy storage] reliable and affordable, it doesn’t matter how cheap and efficient you can make wind and solar, because our grid can’t handle the intermittency of those renewable technologies.”

MIT says, "Braff built a prototype of a flow battery with a small channel between two electrodes. Through the channel, the group pumped liquid bromine over a graphite cathode and hydrobromic acid under a porous anode. At the same time, the researchers flowed hydrogen gas across the anode. The resulting reactions between hydrogen and bromine produced energy in the form of free electrons that can be discharged or released.

The researchers were also able to reverse the chemical reaction within the channel to capture electrons and store energy — a first for any membraneless design."

Now that the team's experiments have lined up with their computer models, they're focused on scaling up the technology and seeing how it performs. They predict that the technology will be able to produce energy costing as little as $100/kWh, which would make it the cheapest large scale energy storage system built yet.