Pumping Iron (and Air) to Store Energy

January 22, 2023

Popular Mechanics:

If you want to store energy, lithium-ion batteries are really the only game in town. It’s why you’ll find them in consumer products from electric cars, smartphones, and everything in between. In fact, lithium is so vital to humanity’s green energy future that people are trying to figure out how to get more of it as soon as humanly possible. 

But what might work for your laptop isn’t the best storage idea for power grids where energy output is measured in megawatts. Lithium-ion batteries are only great at expending energy over a short period, the compound lithium isn’t exactly readily available, and if you’ve ever seen a Tesla engulfed in flames, you know they can explode. 

Now, Form Energy, a Massachusetts-based energy company, thinks it has the solution: iron-air batteries. And the company is willing to put $760 million behind the idea by building a new manufacturing facility in West Virginia.

Each iron-air battery is about the size of a washer/dryer set and holds 50 iron-air cells, which are then surrounded by an electrolyte (similar to the Duracell in your TV remote). Using a principle called “reverse rusting,” the cells “breathe” in air, which transforms the iron into iron oxide (aka rust) and produces energy. To charge it back up, a current reverses the oxidation and turns the cells back into iron. 

NASA first started experimenting with iron-air batteries back in the late 1960s, and it’s obvious why this next-gen storage system has engineers excited. For one, iron-air batteries solve a few of lithium’s biggest shortcomings right off the bat. As their name suggests, these batteries use primarily iron, the fourth most abundant element on Earth, and … well … air.

Secondly, and most importantly, iron-air batteries would be 10 times cheaper, perform better, and last 17 times longer. Right now, these batteries’ primary task would be to bridge the gap when utilities need more power during peak hours, and as green energy eats up a bigger share of the energy pie, they could also crucially store excess energy on sunny days to shore up supply when the clouds roll in. Lithium-ion only provides approximately four hours of storage, whereas iron-air could deliver up to 100 hours—a full four days to bridge those energy gaps. 

The downsides to iron-air batteries? They’re big and also slow to recharge, which is likely why lithium-ion will remain the battery of choice for electric cars and smartphones. Form Energy also says these iron-air batteries will form “power blocks” where iron-air batteries handle long load times, while lithium-ion batteries take care of spikes in demand. 

With construction starting this year, Form Energy hopes its West Virginia factory will start producing its first batteries as early as 2024. Energy’s Iron Age is only just beginning.


13 Responses to “Pumping Iron (and Air) to Store Energy”

  1. tildeb Says:

    Oh good grief. Not only is the lithium reference to all things battery grossly out of date but – just like the sun rising in the east – Tesla is mentioned only in negative reference with lithium batteries that have caught fire. Nowhere does the article reference that Tesla is ALREADY making iron phosphate batteries for both the Model 3 and Model Y and they are ALREADY on the market. (Tesla is ALREADY making storage batteries with iron.) Nope, everyone MUST make some negative comment about Tesla first – as if gaining street cred or bona fides or something to get published? – and then tout late comers as if they are ground breakers. This kind of article is pure narrative and highly biased against a company that has already brought the idea successfully to market and ignore this success entirely.

    • rhymeswithgoalie Says:

      I agree there was no need to refer to Tesla fires when it has long been an issue with laptop fires and other devices that require special safety notices for checked bags on planes or package delivery.

      Just a note that LFP (lithium iron phosphate batteries) are not at all the same as the Form Energy iron-air (or “rust”) batteries. Rust batteries operate at a different scale and application space than EV and e-toy batteries.

      Lithium iron phosphate (LFP) batteries are less energy dense than Li+ (NMC), but they are cheaper and safer. Thermal runaway for Li+ batteries (what Tesla originally used) is 210°C while LFP doesn’t hit thermal runaway until 270%deg;C.

      Form Energy’s iron-air batteries do not have a risk of thermal runaway.

  2. Anthony O'Brien Says:

    Lithium ion batteries biggest feature is their energy stored to weight factor, which is not relevant to most non mobile uses.

    Speed of charge/discharge of lithium ion batteries is well below that of capacitors, but better than many other batteries.

    Lithium ion batteries self discharge. A fully charged battery will go flat over time. Not as fast as a capacitor but faster than other batteries.

    Lots of reasons why lithium ion may not be the best for grid power storage, but may still have a place in the mix.

    Iron oxide batteries will be expensive to start, but as production ramps up should be much cheaper than lithium. But will it be cheaper than second use EV batteries.

    • rhymeswithgoalie Says:

      There’s a fundamental scaling approach in designing systems that people have used for centuries that depends on the cost difference between a fast response and a long-term response.

      In human commercial systems, stocking items for quick shelf access in retail facilities is the most expensive, then the boxed items in the back room on big racks, then the cheapest is the warehouse that stores the material in bulk. The access times, the margins and the availability vary in these classic systems.

      The analogous system in computers is cost trade-off to access data/storage: Registers on board the processor chip are the most “expensive” storage, followed by (say) fast-access RAM on the motherboard, followed by the hard drive. Beyond that is the Cloud (and in older systems archived data that takes the longest to access was typically stored on cheap magnetic tape that required a robot arm to fetch out of its silo and put in a drive, like a jukebox).

      Likewise, I’d expect power/storage scaling to follow much the same engineering trade-off model: Power plants and grid-scale batteries would have fast-response front ends linked with slower, more massive power sources on line. Of course it should eventually all be standardized black-box components that should plug-n-play with comparably standardized control software.

  3. Anthony O'Brien Says:

    Sports car fires are more common than Tesla fires. Ferrari had a problem with the 457, Lamborghini had a problem with the Aventador. As a driver, or passenger, the Tesla fires are not of any more concern than an equivalent petrol car.

    However long past the point of either escape, or death, of the occupants EV fires are a huge concern for fire fighters. In an fixed storage industrial system these concerns are entirely manageable, but do need too be managed.

    And the new Tesla batteries are lithium iron phosphate LiFePO4. Not the same battery.

    • greenman3610 Says:

      The technology is rapidly moving past this “batteries catch fire” story.
      I’m old enough to remember when a couple of Apple MacBooks caught fire on the assembly line – around 2000 or so –
      I wish I’d bought 10k of Apple stock right on that day..

    • Gingerbaker Says:

      And wasn’t it the Chevy Bolt that had to be massively recalled and batteries changed – because of fires? They even recommended that customers not park their Bolt in their garages?

  4. jimbills Says:

    Kudos on ‘pumping iron’. Good ‘un.

    Funny how this thread has become about one little throwaway line in the article, but if this is indeed a tech that can help BOTH the storage issue and lithium supply, I don’t see a need for kvetching. It’s a rare bit of tech news that might actually be a win/win.

    • tildeb Says:

      What you call the throw away line – one inserted very much on purpose – is used as a negative comparison to elevate the safety of iron when, in fact, it reveals that PM’s role informing the public about advanced battery research and application including the use of iron is throwing away Tesla’s impactful contribution to this end. That’s neither fair nor balanced. This skewed framing should raise the issue of why in the minds of readers and indicate we’re receiving a narrative rather than good journalism. Lithium is an important component but only one component and so Tesla is also researching many other kinds and compositions. Tesla focuses on what works at scale and efficiency and is the kind of company that has and will pivot quickly should better alternatives arise. This is a corporate virtue rarely if ever used to balance the negative press constantly used to vilify the world’s leading alternative/renewable energy technology company, one that actually brings real world solutions to real world problems to market.

      • jimbills Says:

        Most readers know that it’s not just Tesla vehicles that catch fire. Combustibility, though, is a universal problem with lithium battery tech, and the author had to mention it. The author didn’t have to mention Tesla by name, granted, but perhaps they did so only because Tesla is the most famous example.

        I’d suggest that you’re such a Tesla fanboy that you’re reading way too much into this, but fine – the author as well as PM are part of the media cabal intent on destroying Tesla’s reputation and denying them any credit for iron battery technology.


        All this doesn’t change the fact that lithium supplies are desperately needed and anything that reduces total lithium demand (including companies besides Tesla) might be helpful in bringing ‘real world solutions’, too:

        • tildeb Says:

          In regards to being a ‘fanboy’, I am bullish on Tesla compared to legacy automakers and startups when it comes to switching energy away from fossil fuels in transportation. In this regard, I think it is extremely counterproductive if not downright foolish to cast Tesla as some kind of bad guy character in the car business. This opinion I try to base on the best information I can find. This is why I think it’s a major story that someone who tears apart vehicles for insightful commentary and legitimate criticism and who once was very hard on Tesla vehicles for just these causes – Sandy Munro – has become a far greater Tesla ‘fanboy’ today than I am and EV expert. He calls Tesla’s vertically integrated approach to designing and manufacturing EVs to be “engineering at the speed of thought.” This month old video captures his reasons starting at 1:20 and he is an automotive EV expert that I have always found worth listening to.

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