Want a Solar-Powered Home? Here's a New Battery That Won't Ignite

As solar panels and wind turbines spread worldwide, they'll need batteries to store power for times when they don't produce it. Harvard debuts a promising prototype.

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Harvard researchers have built a flow battery that stores energy in linquid tanks and uses only non-toxic, non-corrosive, non-flammable materials.

If you dream of an off-grid house powered by the sun, plan on a battery to store energy for cloudy days—ideally, one that won’t catch fire. Harvard researchers might have just the fix.

In the race to build the battery of the future, they’re unveiling a unique option. They say their flow battery is the first made with cheap, non-toxic, non-corrosive, non-flammable, high-performance materials.

“It is a huge step forward. It opens this up for anyone to use,” says Michael Aziz,  Harvard University engineering professor and co-author of a study published Thursday in the journal Science. Because the battery is safe and non-corrosive, he says, it’s well suited for both businesses and homes, adding: “This is chemistry I’d be happy to put in my basement.”

As climate change accelerates the push for clean power, energy storage has emerged as the holy grail of renewables, and its research has taken off in the last five years. The reason’s simple: solar panels and wind turbines produce intermittent power that needs to be stored for use when the sun doesn’t shine or the wind doesn’t blow.

The lithium-ion battery, introduced by Sony more than two deades ago for personal electronics, has limits. It can be pricey, especially for larger uses, and flammable. It’s caused a few electric cars to catch fire, and bulk shipments have even ignited cargo planes.

So researchers are tweaking the lithium battery and looking for alternatives. Some, like the Harvard researchers, have received funding from the U.S. Department of Energy, to explore not only new chemical mixes but also nanosized components. (Read about itsy-bitsy batteries.)

Aziz’s team has focused on flow batteries, which—unlike traditional solid-state ones—store energy in external liquid tanks. The bigger the tanks, the more energy stored. Most such batteries use metals such as vanadium that can be costly and corrosive.

The Harvard scientists built a prototype last year that instead uses organic molecules known as quinones. While it performs well and has been licensed to a company in Europe, it still contains bromine, which can be toxic and volatile. So this year, the team replaced the bromine with a non-toxic and non-corrosive ion called ferrocyanide.

How flow battery works

"It sounds bad because it has the word 'cyanide' in it," Michael Marshak, who discovered the new recipe while a Harvard post-doctoral fellow, says in a university announcement of the findings.  "Cyanide kills you because it binds very tightly to iron in your body. In ferrocyanide, it's already bound to iron, so it's safe,” says Marshak, now assistant professor of chemistry at the University of Colorado Boulder, adding it’s commonly used as a food additive and fertilizer.

“This work breaks new ground in demonstrating organic molecules as the active ingredients,” says George Crabtree, director of Argonne National Laboratory's Joint Center for Energy Storage Research. He says it’s “noteworthy and promising,” adding the battery “just begins to scratch the surface of this rich playing field.”

Another battery expert not involved in the Harvard research also sees its merit. “It’s scalable, it’s inherently safe” and potentially cheap, says Robert Savinell, engineering professor at Case Western Reserve University. He expects it could be commercialized soon, within a decade, but it still needs more testing.

Aziz agrees. “We need to prove the molecules aren’t decomposing over thousands and thousands of cycles,” he says, noting his team extrapolated on shorter durations. He expects such testing will occur within a year, but Harvard will probably license the technology before it’s done.

“This could happen pretty quickly,” says Aziz, noting several companies have already approached him. How quickly, he says, will depend on whether the licensee is a startup or an established battery manufacturer.

Others, including Elon Musk with his Tesla Gigafactory in Nevada, are rushing to mass-produce batteries for cars, homes and businesses. As solar and wind capacity soars, Aziz expects a lot of competition in energy storage. (Find out about the  surprising countries where renewables are taking off.)

Yet given the potential size of the market, he says even the cheapest battery probably won’t be made fast enough to saturate demand.

The story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.

On Twitter: Follow Wendy Koch and get more environment and energy coverage at NatGeoEnergy.

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