Sodium- and potassium-based batteries could be key for smart grid of the future

Sodium- and potassium-based batteries hold promise for cheap energy storage
Matthew Boebinger, a graduate student at Georgia Tech, and Matthew McDowell, an assistant professor in the George W. Woodruff School of Mechanical Engineering and the School of Materials Science and Engineering, used an electron microscope to observe chemical reactions in a battery-simulated environment. Credit: Rob Felt, Georgia Tech

From electric cars that travel hundreds of miles on a single charge to chainsaws as mighty as gas-powered versions, new products hit the market each year that take advantage of recent advances in battery technology.

But that growth has led to concerns that the world's supply of , the metal at the heart of many of the new rechargeable batteries, may eventually be depleted.

Now researchers at the Georgia Institute of Technology have found new evidence suggesting that batteries based on and hold promise as a potential alternative to lithium-based batteries.

"One of the biggest obstacles for sodium- and potassium-ion batteries has been that they tend to decay and degrade faster and hold less energy than alternatives," said Matthew McDowell, an assistant professor in the George W. Woodruff School of Mechanical Engineering and the School of Materials Science and Engineering.

"But we've found that's not always the case," he added.

For the study, which was published June 19 in the journal Joule and was sponsored by the National Science Foundation and the U.S. Department of Energy, the research team looked at how three different ions—lithium, sodium, and potassium—reacted with of sulfide, also called pyrite and fool's gold.

Watch lithium ions shatter a pyrite molecule, simulating the process of battery degradation. Credit: Brice Zimmerman, Georgia Tech

As batteries charge and discharge, ions are constantly reacting with and penetrating the particles that make up the battery electrode. This reaction process causes large volume changes in the electrode's particles, often breaking them up into small pieces. Because sodium and are larger than lithium, it's traditionally been thought that they cause more significant degradation when reacting with particles.

In their experiments, the reactions that occur inside a battery were directly observed inside an electron microscope, with the iron sulfide particles playing the role of a battery electrode. The researchers found that iron sulfide was more stable during reaction with sodium and potassium than with lithium, indicating that such a battery based on sodium or potassium could have a much longer life than expected.

The difference between how the different ions reacted was stark visually. When exposed to lithium, iron sulfide particles appeared to almost explode under the . On the contrary, the iron sulfide expanded like a balloon when exposed to the sodium and potassium.

"We saw a very robust reaction with no fracture—something that suggests that this material and other materials like it could be used in these novel batteries with greater stability over time," said Matthew Boebinger, a graduate student at Georgia Tech.

The study also casts doubt on the notion that large volume changes that occur during the electrochemical reaction are always a precursor to particle fracture, which causes electrode failure leading to battery degradation.

Sodium- and potassium-based batteries hold promise for cheap energy storage
Matthew Boebinger, a graduate student at Georgia Tech, observing video footage of a chemical reaction between sodium and iron sulfide. Credit: Rob Felt, Georgia Tech

The researchers suggested that one possible reason for the difference in how the different ions reacted with the iron sulfide is that the lithium was more likely to concentrate its reaction along the particle's sharp cube-like edges, whereas the reaction with sodium and potassium was more diffuse along all of the surface of the iron sulfide particle. As a result, the iron particle when reacting with sodium and potassium developed a more oval shape with rounded edges.

While there's still more work to be done, the new research findings could help scientists design battery systems that use these types of novel materials.

"Lithium batteries are still the most attractive right now because they have the most energy density—you can pack a lot of energy in that space," McDowell said. "Sodium and potassium batteries at this point don't have more density, but they are based on elements a thousand times more abundant in the earth's crust than lithium. So they could be much cheaper in the future, which is important for large scale energy storage—backup power for homes or the energy grid of the future."


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More information: Matthew G. Boebinger, David Yeh, Michael Xu, B. Casey Miles, Baolin Wang, Marc Papakyriakou, John A. Lewis, Neha P. Kondekar, Francisco Javier Quintero Cortes, Sooyeon Hwang, Xiahan Sang, Dong Su, Raymond R. Unocic, Shuman Xia, Ting Zhu, and Matthew T. McDowell, "Avoiding Fracture in a Conversion Battery Material through Reaction with Larger Ions," (Joule, June 2018). DOI: 10.1016/j.joule.2018.05.015
Provided by Georgia Institute of Technology
Citation: Sodium- and potassium-based batteries could be key for smart grid of the future (2018, June 19) retrieved 17 December 2018 from https://techxplore.com/news/2018-06-sodium-potassium-based-batteries-cheap-energy.html
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Jun 19, 2018
one hundredth the cost with half the capacity would be a great deal.

Jun 20, 2018
Can these new batteries exceed the 200W-h per liter of other types?

Jun 20, 2018
"Can these new batteries exceed the 200W-h per liter of other types?"

That is not relevant as size isn't really an issue for mass storage batteries. Mass storage needs to be cheap and durable above all. This is where sodium and potassium shine.

Generally you can look at the electronegativity of the involved element to figure out what makes a more energy dense battery. Lithium is better than Sodium (or potassium) in that regard.

You can figure electronegativity by looking at the table of elements. The further up and the further right you go the larger it is. (Approximately. There are exceptions).

Optimally we'd build something like Fluor-ion batteries for maximum energy density (theoretical limit about 8 times that of Li-ion), but since Fluor is an incredibly reactive element (read: unsafe) we should probably pass.
Though once in a while someone does try to bring one to market for specialized (read: military) purposes.

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