America Is Building the World’s Biggest Battery—And It Will Run on Rust (ft. Form Energy)

With long sandy beaches, glassy lakes, gentle rolling mountains, and carpets of pine, few states in the U.S. host as much moody, natural allure as the state of Maine—and now the Pine Tree State is hoping to notch yet another accolade. While not exactly a natural wonder of sorts, this record-breaking first will nonetheless help preserve what makes Maine—and all of Earth’s natural spaces—special.

Soon Maine will be home to the world’s largest clean-energy battery. It will be able to store 8,500 megawatt-hours of energy, which can power 85 megawatts for up to 100 hours. One megawatt is enough to power 670 homes on average, according to an environmental engineering professor at Rice University, Daniel Cohan for CBS Austin.

With plans to build on the site of a former paper mill in the small town of Lincoln in northern Maine, this new battery project is one piece of a nationwide energy makeover that’s retooling old energy infrastructure, abandoned factories, and forgotten mines into the very foundation of the U.S. green energy revolution. But even among these “repurposed energy” projects, the battery being built in Maine is one of the most important, because when it’s operational in 2028, it’ll provide New England with multi-day clean energy storage—essentially back-up power for when the wind isn’t blowing and the Sun isn’t shining.

And it’s all thanks to the power of rust.

The mind behind this green energy megaproject is Form Energy, a Massachusetts-based company leveraging iron-air research developed by MIT materials scientist and co-founder Yet-Ming Chiang, Ph.D. The idea of harnessing rust’s potential to create long-term energy storage isn’t new—NASA first developed the idea back in the 1960s. But creating an iron-air battery that’s robust enough and cheap enough at around $20 per kilowatt-hour is Form Energy’s major breakthrough.

“If we take a lithium-ion battery pack, the cost of that pack today is about $200 kilowatt-hours. In order to do multi-day storage, we need to have battery packs that cost one-tenth or less,” Yet-Ming Chiang told PBS in 2023. “Air is still free, and iron is one of the most widely produced, lowest cost materials in the world.”

Put simply, iron-air batteries contain an iron anode and an air-breathing cathode. When power is needed (particularly during those cold New England winters), the oxygen in the air oxidizes the iron, which releases electrons and provides power. When renewable energy is plentiful, the batteries reverse this oxidation process via an electric current that essentially transforms the rust back into iron and breathes out oxygen.