New Iron-Air Battery Technology Adds Multiday Storage to Renewables

Battery energy storage.
Published On
Aug 13, 2021

Like the Energizer bunny himself, the quest to improve large-scale battery efficiency never winds down. The search for breakthrough materials has led to some surprising possibilities. A few years ago, researchers at the University of Maryland developed a chemistry based on wood, and Vancouver, Canada-based Zinc8 Energy Solutions developed recharge technology for zinc-air batteries.

Recently, the ongoing pursuit of the perfect battery turned up the latest power storage method, as another innovator announced it had developed a battery based on an unlikely element: this battery runs on rust.

More specifically, the battery uses the unique properties of iron. Somervile, Mass.-based storage innovator, Form Energy Inc. announced a major milestone in its development of a utility-scale battery product that relies on the chemistry of iron and air, in what it calls “reverse rusting.”

Simply put, while charging, the application of an electrical current splits apart the iron and oxygen molecules in rust (iron oxide). This converts the rust to pure iron, and the battery emits or “breathes out” the oxygen. When discharging, the battery does the opposite—it absorbs or “breathes in” oxygen from the air and converts the iron metal to rust.

The technology offers a number of advantages. At the top of the list is the plentiful supply of iron. According to the American Chemistry Society, iron is the most abundant element, by mass, on Earth.

Combining this with the equally abundant, safe and inexpensive elements of just air and water, Form Energy has developed its first commercial product capable of delivering electricity for 100 hours at system costs competitive with conventional power plants and at less than 1/10th the cost of lithium-ion batteries.

The company says the long-duration storage offered by the iron-air battery will be a breakthrough for renewable energy by allowing solar and wind power to compensate for their daily variability.

According to CEO and co-founder, Mateo Jaramillo, the implications are significant. By making renewable energy available when and where it's needed, even during multiple days of extreme weather or grid outages, Jaramillo says the battery is "tackling the biggest barrier to deep decarbonization."

About the Author

Rick Laezman

Freelance Writer

Rick Laezman is a Los Angeles-based freelance writer who has been covering renewable power for more than 10 years. He may be reached at

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