Published on November 15th, 2015 | by Tina Casey29
“Unthinkable” Energy Storage Combo Leverages Fool’s Gold
November 15th, 2015 by Tina Casey
The energy storage field could be in for a transformation if a team of researchers from Switzerland is on the right track. They’re hot on the trail of a battery deploying the humble crystalline material fool’s gold — aka iron pyrite — with the aim of pulling off a twofer. The new pyrite battery would enable low-cost, large-scale energy storage at power plants and other facilities, thus freeing up global supplies of lithium for small-scale use, including electric vehicle batteries.
Lithium supply is a key issue for the growing EV and stationary energy storage markets. Though lithium-ion battery technology is a proven and efficient solution, as these markets grow, the cost of lithium could surge, so the hunt is on for cheaper, more abundant materials to take over.
From Geological Joke To Energy Storage Hero
Iron pyrite is a common sulfide material easily mistaken for gold by the uninitiated due to its yellowish appearance. Pyrite has many industrial applications, and the US battery company Energizer is apparently the first to use pyrite in a single-use consumer battery in tandem with lithium.
Deploying pyrite in rechargeable batteries presents a different set of challenges, and that’s the task undertaken by Switzerland’s Laboratory for Thin Films and Photovoltaics at the leading research institution Empa (Empa is the German acronym for Swiss Federal Laboratories for Materials Science and Technology).
Dubbed “unthinkable” by Empa’s press office, the new energy storage solution consists of a magnesium anode and a cathode made of pyrite nanocrystals, with an electrolyte of magnesium and sodium ions.
Here’s the rundown from Empa:
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.
As Empa notes, all of the materials used in the new battery — iron, magnesium, sodium, and sulfur — are among the most abundant on Earth’s crust by mass, ranging from 4th to 15th place. In contrast, lithium clocks in around number 33.
That doesn’t sound too bad, but consider that fully half of the world’s known lithium reserves are concentrated in Bolivia and the supply chain begins to look a little dicey.
Here in the US, the Obama Administration has been eyeballing just such supply chain issues related to renewable energy and energy storage. In 2013, the Administration launched the Critical Materials Institute under the Energy Department to address supply chain bottlenecks, including the development of abundant, low-cost substitutes for lithium (that includes using iron pyrite for solar cells, btw).
Manufacturing costs are another consideration, and the Empa team has that angle covered, too. The idea would be to manufacture iron sulfide nanocrystals by grinding iron and sulfur using existing ball-mill technology.
No Fool’s Gold For You, Electric Vehicles…
In terms of energy density, pyrite is a weak player, so to be clear, the Empa team is not proposing that a pyrite battery that would compete in the EV market, or in the emerging small-scale residential or commercial energy storage market. They’re talking about energy storage on the scale of terrawatts.
Of course, a terrawatt-scale solution is not particularly useful or cost-effective across the board. However, it could be enormously useful in countries like Switzerland, where a good deal of the country’s existing hydropower potential is untapped due to lack of storage.
Historically, the country has relied on nuclear energy, and the Empa team anticipates that a low-cost terrawatt-scale energy storage solution could replace the entire annual production of one if its nuclear plants.
The next step for the team is to increase the voltage of the battery by refining the electrolytes.
The next step also involves finding a private sector angel to help push things along, so if you’re sitting on a pile of dough and you want to invest in the post-lithium economy, give them a ring over there at the Laboratory for Thin Films and Photovoltaics.
…At Least, Not Right Now
While the Empa team is focusing on large-scale pyrite-enabled systems, researchers over at Vanderbilt University in the US are working at the opposite end of the scale, adding pyrite to small “button-type” lithium batteries used in watches, LED flashlights, and other smaller-than-a-smartphone devices with pyrite.
The aim is to come up with a rechargeable energy storage formula that improves on the Energizer disposable pyrite/lithium battery.
The key obstacle to recharge-ability is the tendency of nanoscale pyrite crystals to interact chemically with the electrolytes. To prevent the unwanted reaction, you can use larger or “bulk” iron pyrite, but then the energy storage results are less than optimal because the iron is farther from the surface of the crystal. In contrast, using nanoscale or “quantum dot” pyrite would move the iron right up to the surface, allowing the sulfurs to react with lithium (or sodium, as the case may be).
The Vanderbilt team tinkered with a number of different combinations until they hit a sweet spot by deploying nanocrystals of about 4.5 nanometers on button batteries.
The pyrite assist involves a kind of shape-shifting process in the material itself, which does not take place in conventional lithium batteries. Here’s how one researcher describes it:
Storing lithium or sodium in conventional battery materials is like pushing chocolate chips into the cake and then pulling the intact chips back out. With the interesting materials we’re studying, you put chocolate chips into vanilla cake and it changes into a chocolate cake with vanilla chips.
Based on their results, the team envisions a mobile energy storage future based on engineered nanomaterials, in which charging takes a matter of seconds and discharge stretches over days, with a lifespan extending over tens of thousands of cycles.
That could be somewhere far off in the sparkling green future, but on the other hand, look how far EV battery technology has come in the last ten years or so.