Flow battery paves way for cheaper, large scale energy storage

The prototype device has been shown to generate three times as much power per square centimetre as other membraneless systems, including lithium-ion batteries. The breakthrough is expected to pave the way toward cheaper, large scale energy storage. "This technology has as much promise as anything else being explored for storage, if not more," noted Cullen Buie, an assistant professor of mechanical engineering at MIT. "Contrary to previous opinions that membraneless systems are purely academic, this system could potentially have a large practical impact." The device created by Buie and his team relies on a phenomenon called laminar flow, whereby 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 in the battery consist of a liquid bromine solution and hydrogen fuel. The group chose to work with bromine because the chemical is relatively inexpensive and available in large quantities. However, because fuel cell designs based on hydrogen and bromine have largely had mixed results (hydrobromic acid tends to eat away at a battery's membrane), the team decided to simply take the membrane out. The researchers estimate that their flow battery could produce energy costing as little as $100 per kilowatt hour — a goal that the US Department of Energy believes would be economically attractive to utility companies. "You can do so much to make the grid more efficient if you can get to a cost point like that," Buie added. "Most systems are easily an order of magnitude higher, and no one's ever built anything at that price."