Iron cathodes could slash costs, sustainability issues

Chemists are suggesting a relatively abundant metal could hold the key to more sustainable battery technology amid the intense demand for resources by industries in the green energy transition.

A collaboration between several US universities and published in the journal Science Advances offers up iron as a solution to the challenge of batteries needing rare metals like cobalt and nickel.

Cathodes in lithium-ion batteries made from cobalt and nickel present several challenges. First, these materials are less abundant. Both, for instance, make up less than 0.01% of the elements in Earth’s crust.

Compare that to iron, which makes up around 5%.

That Oregon State University (OSU) led study was developed with US$3m funding from the US Department of Energy to develop a high-energy density battery that is more sustainable and less demanding of rare earth metals.

Cathodes in existing batteries account for about half of the manufacturing costs and are responsible for receiving electrons from an external circuit during the electrochemical process that generates electricity. In lithium-ion batteries, lithium ions travel through the battery’s electrolyte towards the cathode from the anode as energy is discharged.

But developing an iron-based cathode industry could have a relatively affordable cathode material available says Xiulei “David” Ji, a chemistry professor at OSU.

Li, who led the study, says the iron cathode battery his team has developed could slash costs and help keep the battery manufacturing industry going as rare metals become more finite.

“We’ve transformed the reactivity of iron metal, the cheapest metal commodity,” Ji says.

“Our electrode can offer a higher energy density than the state-of-the-art cathode materials in electric vehicles. And since we use iron, whose cost can be less than a dollar per kilogram – a small fraction of nickel and cobalt, which are indispensable in current high-energy lithium-ion batteries – the cost of our batteries is potentially much lower.

“Our iron-based cathode will not be limited by a shortage of resources; we will not run out of iron till the sun turns into a red giant.”

It’s hoped that using a solid solution of fluorine and phosphate ions to facilitate the conversion of commercial iron powder, lithium fluoride and lithium phosphate into iron salts in the electrochemical process will help to ‘break’ the energy ceiling that traditional batteries are beginning to reach.

“We’re not using some more expensive salt in conjunction with iron – just those the battery industry has been using and then iron powder,” Ji says. “To put this new cathode in applications, one needs to change nothing else – no new anodes, no new production lines, no new design of the battery. We are just replacing one thing, the cathode.”

Ji notes that storage efficiency is still poor in the prototype but expects further investment from the industry will result in a better product that is more sustainable in terms of both extraction and recycling than current cathode metals. 

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