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Iron-air batteries may prove a cheap, eco-friendly solution for energy storage


August 8, 2012

Dr. Narayan is testing one of his new batteries by using it to power a small fan (Photo: Dietmar Quistorf/USC)

Dr. Narayan is testing one of his new batteries by using it to power a small fan (Photo: Dietmar Quistorf/USC)

Revamping a concept that was first explored forty years ago, researchers at the University of Southern California (USC) are putting the final touches on a patent-pending design for cheap, rechargeable, high energy density iron-air batteries. Because of their unique features, the batteries look particularly well-suited to the kind of large-scale energy storage that could accelerate the adoption of renewable energy sources.

The quest for a cheap, environmentally friendly rechargeable battery stretches back for decades. For one, lithium-ion batteries were first proposed in the seventies, and only recent advances in materials technology have made this technology into one of the most common, high-performing solutions for today's portable electronics.

Now, a team of USC researchers may have found the key to resuscitating yet another design first proposed around the same time – the iron-air battery.

In the context of battery design, iron has more than a few perks: it is durable, it packs good amounts of energy per unit of mass, it is easily recycled and, last but not least, it is very cheap – in commercial quantities, it only costs around US$1/kg (2.2 lb).

Iron-air batteries were a prime candidate for electric vehicles and military applications after the "oil crisis" that started in 1973. However, research stopped abruptly only years later, when scientists realized that iron-air batteries presented a serious and seemingly insurmountable limitation: whenever the battery was being charged, a wasteful process of hydrolysis drained away about half of the battery's energy.

Back to the present, where researchers at USC have finally found a solution to this wasteful problem. They learned that adding a small amount of bismuth sulfide into the battery shut down the harmful reaction and reduced the waste of energy more than tenfold, from fifty down to just four percent. (Other possible choice materials such as lead or mercury were discarded because, even though they could have worked just as well, they wouldn't have been as safe.)

Another crucial strength of the system is the remarkably simple, cost-effective design of its iron electrode. The researchers combined iron powder with a polyethylene binder, heating the mix to obtain a "pressed-plate" electrode that is simple to make and has high specific energy. With this technology, a battery storing a kWh of energy – the equivalent of 24 new iPad batteries – would require only about $3 worth (3 kg/6.6 lb) of iron powder.

This cheaper iron electrode is driving costs down significantly, and the researchers are targeting an aggressive $100 per kWh for their batteries. For reference, research firm Lux Research puts the cost of lithium-ion batteries at roughly around $600/kWh and says their cost will decrease quite slowly, dropping below the $400/kWh mark no earlier than in 2020.

The iron-air battery is exhibiting very promising durability, with a target life of 5,000 charge-discharge cycles. Even more importantly, the batteries seem to retain good performance when they are being drained quickly: at a two-hour rate of discharge, the batteries are showing a twenty-fold increase in capacity compared to commercially available electrodes.

All in all, this battery design seems well-suited to meet the demands of fast-paced, large-scale energy storage applications, and could supply the ideal "energy grid buffer" for renewable but intermittent energy sources like solar and wind power.

A paper describing the battery was published on a recent issue of the Journal of the Electrochemical Society.

Sources: USC, Lux Research

About the Author
Dario Borghino Dario studied software engineering at the Polytechnic University of Turin. When he isn't writing for Gizmag he is usually traveling the world on a whim, working on an AI-guided automated trading system, or chasing his dream to become the next European thumbwrestling champion. All articles by Dario Borghino

Is this technology more/less dense than current lithium cells? Will it mean less/more weight in an automotive application?


Wasn't it Edison who came up with this battery? The moneytards have screwed us for years this is clearly a case of business killing the environment for cash. Ive always wondered what the human body needs iron for.


I would also like to know the weight ratio. Will it be better or worse than current lithium batteries?

Rasto Ha

Converting scrap metal old vehicles into new energy storage, now that's renewable!


re; MasterG

Edison improved the nickle-iron battery.

At the center of every red blood cell there is an Atom of iron with out it the cell can not carry oxygen.


At last a 12 year life battery.


the weight is significantly better than lithium ion but as far as im aware the number of recharges of these is only in the hundreds, while lithium ion is in the thousands.

David Anderton

I recall an article a couple of weeks ago highlighting a commercial operation that manufactures iron air batteries. They might have even had some arp-e funding. My hat's off to USC scientists if they have accomplished what this article claims. This was in fact Edison's idea.... but apparently they've improved it significantly. Back to the future.


Power to weight ratios don't really matter for utility storage applications. All that matters is durability, and capacity/$. If they can really produce a battery that is 6x cheaper than lithium ions, this could make renewable resources our primary power generation technology.

William McCluskey

MasterG is correct- Edison nickel-iron battery was "current" in the 1900's for electric cars. See "nickel-iron battery" in Wikipedia for details. They were manufactured up to 1975 for stationary applications like railroad signals. Main advantage was economy, but they had relatively low power density.


The weight ratio will be worse... Much! worse, but who cares. The tech is not for cars, its for the power grid. Imagine a battery the size of a cargo container, which the power company can place at a sub station, now imagine 10s of thousands of them.

Iron is needed for blood... Google: Hemoglobin.


Lithium vs. Iron. Weight is not nearly as important as safety.


This is wonderful news. I hope it actually hits the market. As they say, there's many a slip betwixt cup and lip.

One other point -- and I apologize in advance for nitpicking -- "perk" is not a synonym for "benefit" or "advantage" in this context. Perk is short for perquisite, a word with a very specific connotation. Perks are privileges or emoluments associated with someone's rank, position or job.


The weight of 3kg of iron powder for 1kwh of battery means overall battery with plastic binder, plastic casing, wires etc may well almost double, so target might be 5-6kg overall weight for a battery of 1kwh (IMHO).

I currently use commercial LiPo in automotive use, and its weight (including hard casing etc) is about 6.6kg per kwh. In comparison, original Prius NiMH battery was 1.87kwh weighing c 57kg resulting in 30.5kg per kwh. Subsequent Prius models are still NiMH.

Mitsubishi MIEV claims 7km range per kwh, while Tesla claims 6.5km. So with current commercially-available batteries, you can get 1km range from 1kg of battery. Many commute vehicles only need 150km range, which is only 150kg - not much more than carrying an extra passenger. The issue is more cost per km of range. Commercial LiPo is already down to c$300/kwh which is c$40 per km of range (c$60 per mile of range).

I am not seeking to denigrate the research reported here, as any weight and cost savings are to be welcomed. But I simply note that LiPo packs are already at weight and cost that justifies electric vehicle use... so we should not wait. Unfortunately, by the time an auto company has 'handled' the batteries, they are marked up 100%, which lessens the economics at present. It would be good to have some standard ISO sizes and voltages, so end-users can buy batteries separately. In a car at present the only 'good value' elements are 12v battery, tyres etc - because they are standard specs. All proprietary items, from a small piece of trim to a car ignition controller costs a fortune in comparison.

[But caution is needed, as many of the no-name LiPo packs are 'seconds' coming out of same factories in China, but which are then marketed on eBay with a new sticker slapped on battery, claiming same specs.] Graeme Harrison (prof at-symbol post.harvard.edu)

Graeme Harrison

I've homebrewed some NiFe edison type batteries but they never seem to work as well as the proponents claim.

Plante lead-acid, on the other hand are quite easy to make and store. They are big and heavy but they easily provide enough power for everything we do. Everything stationary, anyway.

Now to get me some Bismuth Sulfide yummy.


I've home brewed some lithium ion batteries but they never seem to work as well as Panasonic claims. Does that say the chemistry is not good or that you haven't spent 20 years making these cells? A NiFe cell is not the same as a FeO cell, now if we only had some real information other then the fact that it is cheaper.


So there you have it. All the new battery technology is beyond the home brewer. We all have to pay whatever these manufacturers decide, which as the good professor has pointed out is a ripoff. Maybe old Slowburn is right batteries are a waste of money. If this new FeO technology is proprietary then I'm not interested.


For several posters here, some responses.

First, this article is not about a new take on the Edison cell (Nickel-Iron) it is an air breathing battery. It uses oxygen from the air to convert iron in an electrolyte solution into something like rust.

As it is rechargeable, it has an internal mechanism to reverse the process, depositing iron back on the anode. The cathode is a permeable membrane exposed to the air.

Second, it has a mid range power density. That is based on the density of the anode and cathode. The anode is an iron plate, probably with a copper mesh inside to provide better conductivity. The cathode, is a conductive semi-permeable membrane. the battery, like a lead acid cell is also filled with water and some electrolyte solution. Iron is heavier than lithium, but lighter than lead. The cathode end, is really just a bit of plastic with air inside it. That makes the total battery lighter than you might think, but it's still a chunk of iron.

Third, the greatest power density I have seen is the aluminum-air battery. These are not rechargeable, however. They are totally recyclable, just not rechargeablle Al=O batteries are used in satellites and some military applications. they would give an electric car teh greatest range of any current battery, but instead of recharging, you would have to replace the battery. A fully discharged battery has a paste like gel of aluminum hydroxide in it. That aluminum oxide/hydroxide can then be processed into first aluminum oxide, then into aluminum by first heating it, then using the standard aluminum refining process. The electrolyte is a simple salt water solution. For storage, you drain out the water, as the battery has a substantial leakage through the water while filled.

This battery will have some fraction of the power storage that an aluminum air battery has. If it is more than half that of an Al-O battery, then it could be a very good choice for a station battery.

As a practicing Engineer there are several questions I would like to ask before or recommending using such a system.

What is the cycle efficiency? in an Edison Cell, the cycle efficiency is below 50%. That is why they fell out of favor. You had to put twice as much power in as you could get out. Cycle efficiency for a lead acid cell is around 80%, as is a Lithium cell.

What are the maintenance needs and costs. In most metal-air batteries, the electrolyte is exposed to atmosphere, so that frequent labor is required to counter the effects of evaporation and/or electrolyte loss.

What are the maximum discharge rates and times? this determines how fast I can get the stored energy out of the battery.

What is the shelf life of a fully charged battery? of a fully discharged battery? All batteries have some internal leakage. That is why they have a 'shelf life'. What is the period of time that the battery can hold it's charge? Full charge, 80% charge from full charge, 50% charge from full charge? This question will tell me how long between full power states I can still use the battery to provide 'peaking power'. It will also be an important factor in determining the size of the battery bank. For a solar installation, a battery usually needs to provide a minimum of three days backup power.

What are the off-gassing products and quantities? Most battery systems, including sealed cells such as lead acid and lithium ion/Lithium Metal Halide cells off-gas hydrogen. Some also will off-gas chlorine or other hazardous or toxic chemicals. This will impact the storage location requirements and limitations. Some of these considerations will also determine if the installation will be required to be a hazardous location, or if the site will need to be classified after it is used for a period of time.

What are the environmental requirements? Maximum and minimum temperatures, clearance for dissipation of internal heat losses, etc.

Given this information, I could as an Engineer, provide the calculations I would need to design a battery based power storage facility. I would also then be able to calculate total cost and lifetime cost, and thus determine if it is economically feasible.

Given the information in this article, there is not enough information available to tell if it is worth doing or not.


The point of patents is to allow a new company to get up to speed or to actually get R & D dollars back motivating the R & D in the first place. Whining that it is propriety is failing to look at the big picture. 18 or so years later patents will be up and competition can start. Still, I don't think we will be paying monopoly prices because there are competing battery technologies.

Standardization and interchangeability I am absolutely for. May not be so easy as there are different battery characteristics and electronics to regulate charging and discharging. It might be possible to include that stuff in the battery unit and have a standard output/input that any electric car can use. Still, the gov would have to do some good design to get that in a form that is not limiting to design and performance of cars in the future.

I think we are too early to standardize. There is just too much downside. Could easily cripple the industry before it gets started.

We don't even know for sure if batteries are the way to go. Double-layer capacitors have only been around since 1966. I suspect there is still a lot of room for development and they have some very nice attributes that batteries don't have like exceedingly long lives. Fast charge/discharge, high voltage. But they have issues that need solved: holding a charge for a while, holding enough energy, the danger for someone unqualified to mess with because of the very fast discharge.

There are also contraptions somewhere between batteries and capacitors. Maybe one of those is the best solution.


So where do I buy these? : )

Justin Bell

"Given the information in this article, there is not enough information available to tell if it is worth doing or not" - YetanotherBob is right.

Not much point arguing the toss RE weight and economics when there's no tech info to hand.

And yet to contradict myself somewhat, I'm still concerned that they use a medium like polyethylene for construction. If you're starting out trying to make a tool that will help us shift away from the fossil economy, perhaps it would be better to choose a renewably-sourced polymer? I guess we can worry about that when the FeO batteries are on the shelves (ha!).

Chris Hooley
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