Cleantech uses ‘reversable rusting’ to develop 100-hour battery

A MASSACHUSETTS energy firm has developed an iron-based battery that can store electricity for four days using a novel method called “reverse rusting”.

Form Energy’s iron-air batteries can output electricity by using oxygen to convert iron metal into rust, and then reverse this reaction by expelling the oxygen when they need to charge.

The technology, first developed by NASA in the 1960s, has proven popular as a form of renewable energy storage in the US.

Form has already established projects in several states, and secured US$405m from its recent funding round, taking its total investment to US$1.2bn.

A spokesperson for the company said: “For the electric grid long-duration energy storage (LDES) batteries have huge potential. For multi-day periods, it is helpful to have a battery that is capable of dispatching a lot of energy but dispatching it slowly.”

They added: “These funds will accelerate the expansion of our iron-air battery manufacturing operations and the deployment of the battery systems, as well as support continued R&D.”

Long-duration batteries

Iron-air batteries tend to have an discharge efficiency of around 50%. This is low compared to lithium-ion batteries, which have a discharge efficiency of around 80%.

However, iron-air batteries have the advantage of long duration, with systems like Form’s lasting for around 100 hours per fuel cycle, while lithium-ion batteries typically last around eight hours per cycle.

Research has shown that LDES could be an effective system for maintaining energy supply and demand for large-scale renewable energy, namely wind and solar.

Form says that its technology has been made to “complement” short-duration lithium-ion batteries and their usage on the grid, with the iron-air system intended for use and specific points in the year where renewable generation is low.

Scaling challenges

Scaling the technology for electricity grids will take a regulatory overhaul in technological adaptation, according to Form.

A spokesperson said: “Existing markets were designed with entirely different resources and a largely combustion-driven grid in mind.

“Grid planners need new modelling tools that identify the investments necessary to maintain reliability across the hour to hour, day to day, week to week, season to season, and year to year variability that characterises high renewables grids.”

The UK Science and Technology Committee published a report earlier this year on LDES and its use in UK renewables, with the government currently consulting on a LDES business model with a cap-and-floor mechanism.

The US Department of Energy will invest US$505m into LDES projects that are capable of delivering electricity for ten or more hours, via the Bipartisan Infrastructure Law.

Form’s recent funding boost will filter into the company’s deployment of its pilot project, the Cambridge Energy Storage Project, in Cambridge, Minnesota.

The 1.5MW/150 MWh energy storage project is expected to operational by late 2025.

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Correction: this article previously stated that Form Energy's iron batteries can output electricity by using oxygen to convert iron metal into air. This has been corrected to clarify that oxygen is used to convert iron metal into rust.