A battery that runs on air

Redox flow batteries are very energy efficient, and theoretically quite easy to scale up. But at the moment, they’re too expensive to use widely.

Now a team of UK chemists have figured out a way to make redox flow batteries with much cheaper materials – in fact, one of their materials is air.

Their prototype battery is 50-100 times cheaper than current commercial batteries in terms of energy stored – but still much more expensive in terms of power output. Nevertheless, the researchers believe that more research will allow them to bring this cost down too.

Redox flow batteries have two electrolytes separated by a porous membrane. Power is created as the electrolytes flow through the membrane.

The researchers’ innovation, published in Nature Communications, is to use a gas electrolyte and a liquid electrolyte – and a second membrane to keep the whole project stable.

“Our dual-membrane approach is very exciting as it opens up many new possibilities for both this and other batteries,” says co-author Professor Nigel Brandon, dean of Imperial College London’s Faculty of Engineering, UK.

Specifically, their battery uses a polysulphide solution as the liquid electrolyte, and air as the gas. The two fluids are separated by a solution of sodium hydroxide, bordered by two membranes. This allows both electrolytes to flow from side to side without affecting the battery’s performance.

And, in even better news, all of the materials involved are cheap.

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A cost analysis by the researchers estimates that their new battery materials will result in a cost of roughly A$3.50 per kilowatt hour – between 50 and 100 times cheaper than conventional batteries, like lead-acid and lithium-ion.

Unfortunately, the battery prototype still isn’t very powerful – that is, it doesn’t discharge energy very efficiently. This means that the power cost of the battery is more like $2,300 per kilowatt, which is far above commercial costs.

But the researchers are confident they can bring this down.

“To make this cost-effective for large-scale storage, a relatively modest improvement in performance would be required, which could be achieved by changes to the catalyst to increase its activity or by further improvements in the membranes used,” explains Brandon.

If these improvements are made, the researchers are in talks with the university’s spinoff company RFC Power Ltd about commercialising the research.

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