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Lithium-ion batteries power everything from phones to electricity grids but their lifespan is incredibly short, plus they're difficult to recycle. Now, researchers at Harvard University have found a solution, literally.

The team has developed a so-called flow battery which stores energy in liquid solutions. This solution modifies the molecules in electrolytes, ferrocene and viologen to make them stable, water-soluble, and stop them degrading over time. Dissolved in water, the molecules lose just one per cent of capacity for every 1,000 charging cycle. The battery is non-toxic, non-corrosive and lasts for far longer than current Lithium-ion models – estimated at a decade, rather than months.


Batteries of this type are often used as a storage solution for renewable, unpredictable energy sources such as wind and solar, but require regular electrolyte maintenance.

“Because we were able to dissolve the electrolytes in water, this is a long-lasting battery that you could put in your basement,” said Roy Gordon, professor of chemistry and materials science at Harvard University who co-led the research. “If spilt on the floor, it wouldn’t eat the concrete and since the medium is noncorrosive, you can use cheaper materials to build the components of the batteries, like the tanks and pumps.”

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The research is hoping to crack a Department of Energy goal of building a battery that can store energy for less than $100 (£80) per kilowatt-hour. If achieved, this would make stored renewable energy competitive with traditional power plants. “If you can get anywhere near this cost target then you change the world,” said Michael Aziz, professor of materials and energy technologies at Harvard.


Crucial to the development of the new battery was research into why current versions degrade so quickly, even in neutral solutions. Having identified that molecule viologen in the negative electrolyte was decomposing, the team was able to modify its molecular structure to make it more stable. Work then began to make ferrocene, used as the positive electrolyte, soluble too.

“Aqueous soluble ferrocenes represent a whole new class of molecules for flow batteries,” said Aziz. The neutral make-up of the solution should also lower the cost of the membrane needed to separate the two sides of the battery, while also making it less toxic. Harvard has filed patents related to the breakthrough for “innovations in flow battery technology”.

The research was published in the journal ACS Energy Letters.