Electrochemistry to satisfy mass demand: the pyrite battery
High-performance lithium ion batteries face a major problem: Lithium will eventually start to run out. 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 in buildings, for instance.
There is an urgent need to search for low-priced batteries to store electricity: Increasingly large waves of fluctuating green electricity are affecting the power grids as a growing number of electrical devices and even power-hungry electric cars are plugged into the mains. The balance between supply and demand is becoming increasingly more difficult. However, the efficient lithium ion batteries we know are not suitable for large-scale temporary storage; they are just too expensive, too fragile and the 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.
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 in the anode is far safer than lithium, so the battery can't explode. And the test battery in the lab already withstood 40 charging and discharging cycles without comprising its performance, which suggests that it is an extremely durable system.
The biggest advantage, however, is the fact that all the ingredients for this kind of battery are very affordable and in plentiful supply: Iron sulfide nanocrystals, for instance, can be produced by grinding dry metallic iron with sulfur in special mills. Magnesium is 1,000 times more common in the earth's crust than lithium. One kilogram costs around 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.
Storing the electricity produced annually at Leibstadt Nuclear Power Plant
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 recently 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. "The battery's full potential has not been exhausted yet," says Kovalenko, who teaches as a professor at ETH Zurich's Department of Chemistry and Applied Biosciences alongside his research at Empa. "If we refine the electrolytes, we're bound to be able to increase the electric voltage of the sodium-magnesium hybrid cell even further."