These batteries ditch the lithium for something much cheaper: iron

[Illustration: Daniel Salo/Fast Company]

Form Energy’s iron air batteries rust and ‘derust’ iron to store power.


The number of wind farms in the U.K. has more than quadrupled since 2010. But last year, when a “wind drought” over more than a week meant that it was suddenly much less windy than usual, the country had to scramble to buy extra power made from fossil fuels.

It’s one example of renewable energy’s biggest challenge: When the sun isn’t shining and the wind isn’t blowing, the grid still needs a source of power. Lithium-ion batteries—like the giant batteries that Tesla has installed in Australia—can store the energy generated by renewables, but are too expensive for long-term storage.

To move completely away from fossil fuels, the grid needs a different solution. Form Energy, one startup working in that space, thinks that iron—which is cheap and abundant—is the key to building better batteries. The company’s “iron-air” batteries, which cost less than a tenth of lithium-ion batteries, can affordably store energy for days.

[Photo: courtesy Form Energy]

“It became very clear that although lithium-ion was cheap, and continues to get cheaper—and will be deployed at large scales on the grid—it was still too expensive to go after the biggest opportunity and the biggest opportunity on the grid, which was being able to be cheap enough so you can fully replace coal plants, natural gas plants, with renewable,” says Form Energy CEO Mateo Jaramillo, who launched the startup in 2017 after leaving Tesla.

Dealing with intermittent renewable energy for a few hours, or overnight, isn’t as hard, Jaramillo says. But backing up that power for days, or even weeks is much more difficult. When he left Tesla, he didn’t know what technology could solve the problem or whether it would be possible to quickly bring it to market.

The team considered multiple possibilities for the technology, building an analytic platform to compare the options in detail. “The problem that we were going after is a very large problem, and it’s a very large market,” he says. “So any option we were considering had to be able to scale to meet the size of the challenge—thousands of terawatt-hours capability. And it also had to be safe. It had to be fundamentally cheap, fundamentally scalable, and fundamentally safe.”

[Image: courtesy Form Energy]

Iron-air batteries, they concluded, made the most sense, and had been proven to work in earlier tests at universities. Each of the company’s batteries, roughly the size of a washing machine, pulls in oxygen and converts iron inside to rust, and then charges by using electricity to “unrust,” turning the rust back into iron. As the iron rusts again, it generates a current. When rust happens naturally on something like a wrought-iron fence, it’s a “one-way battery,” Jaramillo says. “By providing electricity to that anode, we’re essentially driving off that rust and returning the iron back to its metallic state.”

[Photo: courtesy Form Energy]

Unlike lithium, iron is one of the most abundant elements on Earth and available on every continent. Companies like Tesla are beginning to incorporate iron into their lithium batteries to replace other rare minerals, like cobalt. An iron-air battery discharges power slowly, so it isn’t a good fit for an electric car, but it works well for dispensing energy over days to the electric grid. For the grid, it will make sense both to have technology that can quickly respond to provide boosts of power, like lithium-ion batteries, and something like iron-air batteries to store power over longer periods.

The company’s first pilot, with a utility in Minnesota, will launch next year, with 1.5 megawatts of storage. Larger pilots will follow in 2024 “in the tens of megawatts scale, and then going from there, quickly, to the hundreds of megawatts scale,” Jaramillo says. The company, which now has around 200 employees, will be scaling up from R&D to large-scale manufacturing and is working on detailed studies to prove to financing companies how the technology performs and how durable it should be, so it can get very low-cost capital to build it. “We’re developing infrastructure,” he says. “And if you want to deploy a lot of infrastructure, you have to be able to finance it like infrastructure.”


Adele Peters is a staff writer at Fast Company who focuses on solutions to some of the world’s largest problems, from climate change to homelessness. Previously, she worked with GOOD, BioLite, and the Sustainable Products and Solutions program at UC Berkeley, and contributed to the second edition of the bestselling book “Worldchanging: A User’s Guide for the 21st Century.” More

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