Researchers from Empa and ETH Zurich have discovered an alternative to the lithium ion battery chemistry with the “fool’s gold battery”. They believe the prime potential lies in giant storage batteries that could be built at low cost and used for stationary storage in buildings or next to power plants. Maybe not for electric vehicles or portable electronics just yet.

A fool’s gold battery consists of iron, sulfur, sodium and magnesium – all elements that are low cost and in plentiful supply. Lithium will eventually start to price even higher as batteries are deployed in electric cars and stationary storage units. For high performance lithium ion batteries basic supply issues are a major cost problem.

Pyrite nanocrystals under the electron microscope, which make up the cathode in the fool’s gold battery. Image Credit: Empa. Click image for the largest view.

Pyrite nanocrystals under the electron microscope, which make up the cathode in the fool’s gold battery.  Image Credit: Empa.    Click image for the largest view.

There is an urgent need to find and develop low-priced batteries to store electricity. The intermittency of wind and solar electricity is affecting the power grid, a situation calling for stationary storage units to be connected into a smart grid. Electric cars are of increasing popularity, but are still to expensive. Today’s efficient lithium ion batteries are not suitable for large-scale stationary storage of electricity, they are just too expensive because precious lithium is too scarce. A cheap alternative is called for – a battery made of inexpensive ingredients that are available in abundance. But electrochemistry is a tricky business: Not everything that’s cheap can be used to make a battery.

Maksym Kovalenko, Marc Walter and their colleagues at Empa’s Laboratory for Thin Films and Photovoltaics have now managed to pull off the unthinkable. By combining a magnesium anode with an electrolyte made of magnesium and sodium ions with nanocrystals made of pyrite – more commonly known as fool’s gold – to serve as the cathode, they have a working battery.

Pyrite is crystalline iron sulfide. The sodium ions from the electrolyte migrate to the cathode during discharging. When the battery is recharged, the pyrite re-releases the sodium ions. This so-called sodium-magnesium hybrid battery already works in the lab and has several advantages: The magnesium as the anode is far safer than highly flammable lithium. And the test battery in the lab already withstood 40 charging and discharging cycles without compromising its performance, suggesting further optimization would be useful.

The biggest advantage, however, is the fact that all the ingredients for this kind of battery are easily affordable and in plentiful supply. Iron sulfide nanocrystals, for instance, can be produced by grinding dry metallic iron with sulfur in conventional ball-mills. Iron, magnesium, sodium, and sulfur hold the 4th, 6th, 7th and 15th places by the abundance in the Earth’s crust (by mass). One kilogram of magnesium costs at most four Swiss francs, which makes it 15 times cheaper than lithium. There are also savings to be made when it comes to constructing the cheap batteries. Lithium ion batteries require relatively expensive copper foil to collect and conduct away the electricity. For the fool’s gold battery, however, inexpensive aluminum foil is perfectly sufficient.

Today the researchers primarily see potential in their development for large network storage batteries. The fool’s gold battery is not suitable for electric cars – its output is too low. But wherever it boils down to costs, safety and environmental friendliness, the technology is a plus.

In their paper published in the journal Chemistry of Materials, the Empa researchers propose batteries with terawatts of storage capacity. Such a battery might be used to temporarily store the annual production from the Swiss nuclear power station in Leibstadt, for instance.

Kovalenko, who teaches as a professor at ETH Zurich’s Department of Chemistry and Applied Biosciences alongside his research at Empa said, “The battery’s full potential has not been exhausted yet. If we refine the electrolytes, we’re bound to be able to increase the electric voltage of the sodium-magnesium hybrid cell even further and to extend its cycling life. We also look for investors willing to support research into such post-Li-ion technologies and bring them to the market.”

The Swiss folks may be exploring a little understatement, too. The technology is already closing in on lead acid, carbon and alkaline technology and half way to lithium ion cell voltages, in the first working lab sample. The technology might not seem real exciting, but the materials costs are going to set off a revolution if the commercial scale step works out well.

Old enough to remember how fast alkaline batteries eclipsed carbon batteries? Duracell and Energizer might want to be checking in with these Swiss folks. A “Gold Rechargeable” at a low price might be a battery sales gold mine.


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