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    Iron-air batteries

    Also known as iron-air battery, multi-day storage, Form Energy battery

    Iron-air batteries store electricity by turning iron into rust while discharging and back into iron while charging, aiming for multi-day storage of up to 100 hours.[1][2] US developer Form Energy began delivering its first pilot system in 2026 and has agreements including a 300 MW / 30 GWh project tied to a Google data center in Minnesota.[3][4]

    Editor reviewedUpdated Batteries and energy storageEnergy and climateScience
    Key facts

    How it works

    An iron-air battery “breathes” oxygen. When discharging it converts iron metal to rust, and when charging an electric current turns the rust back into iron, a process Form Energy calls reversible rusting.[1] The cell uses iron, water and air with a water-based, non-flammable electrolyte. Form says the design has no mechanism for thermal runaway.[5] The system can store and discharge energy for up to 100 hours.[2] Typical lithium-ion grid batteries provide one to eight hours.[6]

    Why multi-day storage matters

    Lithium-ion batteries cover daily cycles well and have become cheap, with stationary packs at 70 dollars per kilowatt-hour in 2025.[7] Iron-air developers aim at a different job, storage over several days, using iron, water and air.[2][5]

    Projects and timeline

    • Cambridge, Minnesota. Great River Energy and Form Energy broke ground in August 2024 on a 1.5 MW pilot, then expected online by late 2025.[8] By March 2026 Form had begun delivering the system and expected the full project online during 2026.[3]
    • Crusoe. On 24 March 2026 Form and Crusoe announced an agreement for 12 GWh of iron-air storage for AI data centers. Deliveries start in 2027 from Form Factory 1 in Weirton, West Virginia.[9]
    • Xcel Energy and Google. A 2026 Google-Xcel agreement includes a 300 MW / 30 GWh Form system, described as the largest battery project by energy capacity announced to date.[4] Form’s chief executive said the first modules should ship by the end of 2028.[10]

    How it compares

    Iron-air competes for long-duration work with flow-batteries, which scale energy by enlarging electrolyte tanks and are typically offered with 2 to 18 hours of discharge.[11][12] Iron-air targets much longer discharge, up to 100 hours.[2] Its materials, iron, water and air, avoid the vanadium supply concerns of flow batteries and the lithium price swings of lithium-ion.[5][13][14]

    What to watch

    The key test is whether the Cambridge pilot reaches commercial operation and performs as promised, because the much larger contracts depend on the same technology.[3][4] The pilot has already slipped from its original late-2025 target.[8]

    Questions readers ask

    How does an iron-air battery work?

    When discharging it takes in oxygen from the air and converts iron to rust; charging converts the rust back to iron. Form Energy calls this reversible rusting.[1]

    How long can it supply power?

    Form Energy says up to 100 hours, far longer than typical lithium-ion grid batteries, which provide one to eight hours.[2][6]

    Is any iron-air battery running yet?

    As of March 2026, Form Energy had begun delivering its first commercial pilot system in Minnesota, with the full project expected online in 2026. It was originally expected by late 2025.[3][8]

    What is the 30 GWh project?

    A 300 MW / 30 GWh Form Energy system in a Google-Xcel Energy agreement, described as the largest battery project by energy capacity announced to date. First modules are expected to ship by the end of 2028.[4][10]

    Sources

    Each numbered claim is a statement we checked against the sources listed with it. Status shows how well established it is.

    1. [1]

      Form Energy's iron-air battery works by reversible rusting - while discharging it breathes in oxygen from the air and converts iron to rust, and while charging an electric current converts the rust back to iron. confirmedas of 2026-10-10

    2. [2]

      Form Energy says its iron-air system can store and discharge energy for up to 100 hours. confirmedas of 2026-10-10

    3. [3]

      As of March 2026 Form Energy had begun delivering its first commercial pilot system in Minnesota, with the full project expected online in 2026. confirmedas of 2026-03-24

    4. [4]

      A 2026 agreement between Google and Xcel Energy includes a 300 MW / 30 GWh Form Energy iron-air battery, described as the largest battery project by energy capacity announced to date. confirmedas of 2026-03-04

    5. [5]

      Form Energy's battery uses iron, water and air with a water-based, non-flammable electrolyte, and the company says it has no mechanism for thermal runaway. confirmedas of 2026-10-10

    6. [6]

      Battery storage provides short-term flexibility to the power system, typically for periods of one to eight hours. confirmedas of 2024-04-25

    7. [7]

      Battery pack prices for stationary storage fell to 70 US dollars per kilowatt-hour in 2025, 45% lower than in 2024. confirmedas of 2025-12-09

    8. [8]

      In August 2024 Great River Energy and Form Energy broke ground on a 1.5 MW multi-day iron-air storage project in Cambridge, Minnesota, then expected to operate by late 2025. confirmedas of 2024-08-15

    9. [9]

      On 24 March 2026 Form Energy and Crusoe announced an agreement for 12 gigawatt-hours of iron-air storage for AI data centers, with deliveries from 2027 built at Form Factory 1 in Weirton, West Virginia. confirmedas of 2026-03-24

    10. [10]

      Form Energy's chief executive said the company expects to ship the first modules for the Xcel-Google project by the end of 2028. reportedas of 2026-03-04

    11. [11]

      Flow battery energy capacity is raised by enlarging the electrolyte tanks and power by enlarging the reactor, so the two can be sized separately. confirmedas of 2023-04-07

    12. [12]

      Invinity offers vanadium flow battery configurations with discharge durations of 2 to 18 hours. confirmedas of 2026-10-10

    13. [13]

      Vanadium is widespread but dilute and hard to extract, production is concentrated in Russia, China and South Africa, and its prices are high and volatile. confirmedas of 2023-04-07

    14. [14]

      Lithium prices at the start of 2026 were more than twice their level a year earlier, and cobalt prices also doubled over the year. confirmedas of 2026-10-10

    15. [15]

      CATL says it has ranked first globally in EV battery usage for nine consecutive years and first in storage battery deliveries for five consecutive years. confirmedas of 2026-10-10

    Revision history (1)
    1. Page created.

    Created Oct 10, 2026. Last reviewed by an editor on Oct 10, 2026. Next scheduled review: Jan 10, 2027.

    Cite this page

    "Iron-air batteries." ContentLora, updated Oct 10, 2026. https://contentlora.com/wiki/iron-air-batteries

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