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 reactants used are liquid bromine and hydrogen fuel, which is cheap, but also has had issues with breaking down the membrane in other flow batteries. By taking out the membrane they were able to speed up energy storage and extend the life of the battery.
“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.”
As we bring more renewable technologies like wind and solar into the grid, affordable and reliable energy storage is increasingly important. While solar and wind energy output varies based on weather conditions, large scale energy storage systems can smooth out the power delivery from those technologies by storing any excess energy when it's produced and using it when the output is lower or demand is higher.
“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.