Form Energy Irons Out Bugs in Long Storage Battery

March 30, 2023


When Billy Woodford and his friends set out to build a new kind of battery that could replace a coal plant, their breakthrough technology took inspiration from the disposable hand-warming sacks that spectators use at football stadiums. The battery’s key ingredient: rust.

Woodford’s startup, Form Energy Inc., went into business in 2017 with a clear and ambitious goal. The battery needed to soak up renewable energy during the day and release it at night, and to keep running after sunset and on windless days. A lithium-ion battery, like those in EVs and smartphones, would work, but no utility can afford to run that type of battery on the grid for more than a few hours. Utilities need one that will also be cheap enough to deploy for 100 hours or more. “You can have pretty much any battery do any duration on the grid,” says Mateo Jaramillo, who worked at Tesla Inc. before co-founding Form and is today its chief executive officer. (Woodford is chief technology officer.) “It always comes down to cost.”

Form’s five co-founders, who also include Yet-Ming Chiang, Ted Wiley and Marco Ferrara, started by spitballing ideas for materials, discarding most as soon as they came up. Some suggestions had already been commercialized, like flow batteries using materials such as vanadium and big vats of liquid. But a 100-hour battery could rely only on dirt-cheap, abundant elements, and the short list eventually came down to iron and sulfur. Because it’s the easier material to handle, iron won.

Woodford then turned to an unlikely source for inspiration: the disposable hand warmers he used on cold days growing up in Pennsylvania. Crushing these little sacks filled with crystals begins a process of rusting iron—it essentially reacts with oxygen to form iron oxide—that’s sped up with chemicals. The reaction releases energy in the form of heat. Woodford and Chiang, Form’s science brains, thought that with the right setup they could use the same reaction to release energy as electrons instead.

Jaramillo wasn’t convinced. “I thought I was going to disprove the idea,” he says. “You might as well prove it’s a terrible idea first, rather than finding out later.”

Except the idea wasn’t terrible. After thousands of experiments, Woodford’s bet on hand warmers is at the heart of Form’s battery. The company, based in Somerville, Massachusetts, has raised almost $900 million from the likes of the Bill Gates-led Breakthrough Energy Ventures and inked partnerships with Georgia Power, Great River Energy and Xcel Energy. Next comes construction of a $760 million battery-manufacturing facility in West Virginia, which the company says it wants to have up and running by the end of 2024.

For now, the only place to see Form’s iron-battery breakthrough in action is a testing center in a warehouse in Berkeley, California. “If you’re watching from the outside, it’s not high entertainment—not exactly charismatic megafauna,” Jaramillo warns visitors as he walks past a plastic box the size of a small refrigerator. “But in order to get to the cost targets that we’re going after, it can’t afford to look like much.”

At a commercial scale, Form’s battery will be made up of many of those plastic boxes, packed inside shipping containers and parked close to transmission cables. And if you look closely, it’s possible to see some action: Each box contains black liquid bubbles, not unlike Coca-Cola degassing in a giant milk container. What you’re seeing is rust in action, perhaps the most unusual strategy Form has used. Chemically speaking, the process in the plastic boxes is iron mixing with oxygen to form iron oxides (better known as rusted iron) alongside the electricity generation. The process can be reversed, too. Add electricity back in, and it’s possible to separate the iron out while releasing oxygen. If it wasn’t reversible, it would be one expensive battery that continuously rusted iron to generate electricity.

The chemical reaction behind Form’s approach is relatively simple, but building a battery that can be charged or discharged hundreds of times is not. Rust, for example, isn’t one chemical; it’s usually a mixture of iron oxides, and converting each one back to iron requires different conditions.

Inevitably, there are unwanted side reactions. One, which produces hydrogen, requires occasional topping up with water; another traps carbon dioxide from the air, reducing the life span of the battery. And even once it’s achieved commercial scale, there’s no guarantee Form’s battery will work perfectly or solve all the challenges that come with transitioning the grid away from fossil fuels. The company has two more years to, er, iron out the kinks before commercial deployments come due.

From the start, Form’s goal has been to build something that would work as well as a lithium-ion battery at one-seventh the cost (about $20 per kilowatt-hour). It’s an achievement that would bring powering the grid with 100% renewables into the realm of affordability. Although the first battery projects Form builds will be more expensive than that, opting for iron makes the goal of beating lithium-ion’s price by a big margin believable, particularly as a demand-driven lithium shortage further highlights iron’s abundance. The more iron-air batteries the company builds, the cheaper each one will become.

“It’s fairly easy to make a terrible iron-air battery,” Jaramillo says. “It is very hard to make that chemistry perform at its highest level and at the lowest cost.”


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