WPI Research Publication

FALL 2012

WPI Research is the research magazine of Worcester Polytechnic Institute. It contains news and features about graduate research in the arts and sciences, business, and engineering, along with notes about new grants, books, and faculty achievements.

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Recharging Energy Storage Yan Wang, director of the Electrochemical Energy Labora- tory, is attempting to perform some magic of his own: by of- fering a novel spin on a type of rechargeable fuel cell called a flow battery, Wang hopes to help take wind and solar power mainstream. In a conventional flow battery, electrolytes are stored in external tanks and pumped across a membrane in a cen- tral chamber to generate the chemical reactions that store or release electrical energy. Flow batteries don't need elec- trodes, which simplifies their design. Because they require less physical packaging material, they are more compact and cheaper to manufacture than ordinary batteries. And they are easy to scale since, as Wang explains, "the total energy is not limited by your battery size." Need more capacity? Just build bigger tanks. That makes flow batteries the leading candidate for storing the energy generated by wind turbines and solar cells for use across an electrical grid when the sun isn't shining and the wind isn't blowing. But current flow battery designs have their limitations. For one thing, the metals used to make the electrolytes are not very soluble, resulting in low energy density. And while existing flow batteries store energy more cheaply than ordinary recharge- ables (Wang says flow battery storage costs $300–$500 per kilowatt hour, compared with $1,000 per kilowatt hour for standard lithium-ion batteries), they aren't cheap enough to be commercially viable. The U.S. Department of Energy, for example, has set a goal of $100 per kilowatt hour for grid storage. Wang aims to meet that goal by doing away with conventional electrolyte solutions en- tirely. Instead, he wants to fill his flow batteries with thick suspensions of undissolved nickel and zinc particles. Because they are mostly metal, those dark, gooey suspen- sions (Wang has dubbed them "Worcester crude") possess 10 times the energy density of other electrolytes, and are much cheaper to produce. And because the suspensions Yan Wang, center, and graduate student Qina Sa watch graduate student Zhangfeng Zheng prepare samples in the glove box in Wang's battery research lab. The team has developed a novel design for flow batteries, which are used for energy storage in power grids. The design uses thick suspensions of metal particles. [13]

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