Two weeks ago, Form Energy, a Massachusetts startup with celebrity founders and funders, attracted much battery industry attention by publicizing an exotic “iron-air battery,” a long-lasting technology it said was so cheap that it would undercut natural gas in electricity generation.

Today, a new paper by researchers at Carnegie Mellon University, provided first to The Electric, generally validates Form’s cost claims—but there are caveats:

· On paper, Form’s battery would cost about $25 per kilowatt-hour to make, according to the Carnegie Mellon paper. That would be a fifth to a quarter that of standard nickel-manganese-cobalt and lithium-iron phosphate technology, and just a bit more than the $20/kWh that Form claims.

· But the cost is still up to 10 times higher than that of a natural gas-based power system, according to an estimate in a March paper in Nature Energy.

· And even if iron-air’s cost were $1/kWh, it could still be far more expensive than natural gas in the other main category of stationary storage—the enabling system that must be built around any fuel or battery. One reason is that iron loses a great deal of its energy to inefficiencies in actual use and would likely require a much larger battery than NMC or LFP. As a result, its cost in a stationary system could far exceed the $1,000 per kilowatt level typical of a natural gas system.

Form has said it is driving down its costs and will be ready for the market in 2025.

As a concept, the iron air battery goes back more than a half century: On Oct. 20, 1967, The New York Times reported that the research division of General Telephone and Electronics had come up with what GTE called “the most advanced battery of its type developed to date.” In the brief account, Lee Davenport, head of the GTE lab, described an experimental iron-air battery with six times the energy density of lead acid, then and now the standard battery in combustion vehicles. In a conference the next year, two GTE researchers called iron air a potential battery for NASA space systems, but it does not appear to have ever gotten out of the lab for NASA or anyone else.

Form launched in 2017, backed by Breakthrough Energy Ventures, whose investors include Bill Gates and Jeff Bezos, and more recently ArcelorMittal, the steel company. Form’s CEO is Mateo Jaramillo, who previously developed Tesla’s Powerwall stationary battery, and its chief scientist is Yet-Ming Chiang, a co-founder in the past of A123 Systems and 24M, two prominent lithium-ion startups (Chiang is the guest today for the inaugural Live Chat With The Electric.). Last month, Jaramillo and Chiang came out of stealth and said they had been working on an iron-air battery that would last 100 hours.

What sets an iron-air battery apart is both the cheapness of iron, one of the most plentiful metals on the planet, and how it works. In a lithium-ion battery, power for your phone, laptop or EV is created when atoms of lithium shuttle back and forth between the two electrodes during charge and discharge. In iron air, there are instead several steps in the shuttling process: for starters, the cathode is made of oxygen, rather than the metals and minerals contained in NMC or LFP. When the battery is discharging, the oxygen mixes with water and changes to hydroxide. It then passes to the anode, where it meets iron and changes into iron hydroxide, and from that to magnetite—rust. When you charge to use your device, the battery goes through all these steps in reverse.

The Carnegie Mellon paper, co-written by Venkat Viswanathan, a mechanical engineering professor, and Shashank Sripad and Dilip Krishnamurthy, two of his doctoral candidates, assembled a generic iron air battery that would last 150 hours.

According to Sripad’s calculations, the raw iron-air materials would be around $4/kWh, far lower than the $36/kWh cost of the metals in NMC622. That is because the form of iron used in the battery is essentially rust—or “dust” as Sripad put it. The rest of the $25/kWh cost is for the battery pack, an oxygen compressor and filter, a fire suppression system, and manufacturing, Sripad told me.

On its face, the 100-hour battery stationary battery is equivalent to the “million-mile” electric vehicle battery, which I wrote about Sunday. Just as it’s not clear to many why anyone would want an EV battery that lasts five to seven decades, some people responded to Form’s announcement by questioning the mass-market for a four-day stationary battery.

But the way to think about such long-duration stationary storage is similar to why long range in EVs makes sense even though very few people will drive 300 or 400 miles straight. Just as many people are wary of EVs for fear of ending up with an exhausted EV battery on a lonely road at midnight in a snowstorm, they also worry about dependence on solar and wind if they confront an extended period of cloudy, windless days, or a power outage triggered by extreme weather. Form and other makers of long-duration storage figure such anxiety could be alleviated by a safety margin of a few days in which their refrigerator will still run and the lights stay on.

A previous version of this article incorrectly reversed "charge" and "discharge" in the explanation of how iron-air batteries work.

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About Steve LeVine

Steve LeVine is editor of The Electric. Previously, he worked at Axios, Quartz and Medium, and before that The Wall Street Journal and The New York Times. He is the author of The Powerhouse: America, China and the Great Battery War, and is on Twitter @stevelevine

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