November 13, 2015

Electrochemistry to satisfy mass demand

      Electronmicroscopical image of Pyrite nanocrystals, which make up the cathode
in the fool’s gold battery (photo: Empa)

(November 13, 2015)  Super environmentally friendly: the “fool’s gold battery”

High-performance lithium ion batteries face a major problem: Lithium will eventually start to run out as batteries are deployed in electric cars and stationary storage units. Researchers from Empa and ETH Zurich have now discovered an alternative: the “fool’s gold battery”. It consists of iron, sulfur, sodium and magnesium – all elements that are in plentiful supply. This means that giant storage batteries could be built on the cheap and used stationary in buildings or next to power plants, for instance.

There is an urgent need to search for low-priced batteries to store electricity. Intermittency of green electricity is affecting the power grids, calling for stationary storage units to be connected into a smart grid., Electric cars are of increasing popularity, but are still to explensive. Efficient lithium ion batteries we know are not suitable for large-scale stationary storage of electricity; they are just too expensive 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. 

The key to success: pyrite (fool’s gold) as a cathode material.
(photo: JJ Harrison/

Safe, durable and affordable

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. Nanocrystals made of pyrite – more commonly known as fool’s gold – serve as the cathode. 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, calling for further optimization.

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