Energy storage is the key to balancing the challenges of renewable energy, particularly the variable output and the mismatch between peak power generation times and peak demand. With high power output, large energy storage capacity, and the ability to switch between charge and discharge modes quickly, flow batteries are a great match for solar, wind and other renewable energy sources.
New R&D is targeting one expensive component in flow batteries: the membrane that separates the positive and negative electrolytes. Accounting for up to 44% of the cost, it is typically made with a perfluorocarbon material which has one supplier, Chemours (a spinoff of Dupont). In addition to being expensive, organic membranes create potentially environmentally harmful byproducts.
Ionic Windows, a start-up from University of Washington, is developing a replacement made from cheap, safe, widely available silica gel.
Ionic Windows has developed a hybrid organic-inorganic proton-conducting membrane by borrowing technology from the food packaging industry. In its process, the silica gel is liquified, dipped in a paper mold, exposed to an acid bath to create nanopores, and then dried.
“We took a step back and starting asking what was really required to make a successful membrane.” says Dr. Greg Newbloom, CEO. “We identified a few key attributes and bet that we could get there with inorganic materials”. The company experimented with anodized aluminum oxide, which resulted in a effective model for the silica gel process. “Silica is a particularly good fit for membranes because it is a highly stable material—great for strongly oxidizing battery chemistries—with demonstrated potential to create all sorts of nanostructures. But it’s also dirt cheap, which is important for commercial applications.”
Ionic Windows currently has working prototypes measuring up to 60 cm^2. Commercial flow batteries use membranes on the order of 1000 cm^2, so the company believes it is six to nine months away from customer trials. “Our biggest technical hurdle is brittleness,” explains Newbloom. “It’s an intrinsic disadvantage of inorganic materials and has prevented the commercialization of high performance inorganic membrane technology in the past,”
Once it overcomes the hurdle, Ionic Windows expects to be able to produce membranes at a cost of $50/m2, about 1/5 the cost of perfluorocarbon membranes. The company estimates that flow battery manufacturers will see a capital cost reduction of up to 25%.
Cost reductions like these can help accelerate the adoption of reflow batteries, and companion renewable energy sources, by utilities, industry and microgrids.
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