Form Energy closes $240m financing round toward commercialisation of iron-air battery

by John Shepherd
The basic principle of the iron-air battery's operation is reversible rusting. Image: Form Energy
Form Energy has announced the close of a $240m (£174m) Series D financing round as it moves to expand deployment of its rechargeable iron-air battery technology.

The company’s first project, with Minnesota-based utility Great River Energy, is expected to go online in 2023 – followed by bigger systems for wider deployment in 2024.

Form’s latest funding round was led by ArcelorMittal’s XCarb innovation fund, with participation from asset firm TPG’s Rise Climate Fund.


Form’s first commercial product is a rechargeable iron-air battery capable of delivering electricity for 100 hours at system costs, which the company claims is competitive with conventional power plants "and less than one-tenth the cost of lithium-ion”.
The front-of-the-meter battery can be used continuously over a multi-day period and will enable a reliable, secure, and fully renewable electric grid year-round, Form said.

The basic principle of operation is reversible rusting. While discharging, the battery breathes in oxygen from the air and converts iron metal to rust. While charging, the application of an electrical current converts the rust back to iron and the battery breathes out oxygen.


Each of Form’s individual batteries are about the size of a washing machine. Each of these modules is filled with a water-based, non-flammable electrolyte, "similar to the electrolyte used in AA batteries”. Inside the liquid electrolyte are stacks of between 10 and 20 metre-scale cells, which include iron electrodes and air electrodes.

Form said that in its least dense configuration, a 1 MW system would require about an acre of land, while higher density configurations can achieve >3MW/acre.

Meanwhile, Form and ArcelorMittal on developing iron materials that ArcelorMittal would non-exclusively supply for Form’s battery systems. Form said it intends to source the iron domestically and manufacture the battery systems near where they will be sited.