Researchers at the Georgia Institute of Technology found evidence suggesting that batteries based on sodium and potassium hold promise as a potential alternative to lithium-based batteries in order to accommodate an increased demand for energy storage and a global depletion of lithium resources.
As new battery technology emerges due to the rapid growth of the electric vehicle and renewable energy markets, the demand for energy storage with advantages in cost, cyclability and energy density is increasing.
Lithium batteries are currently preferred over sodium- and potassium-based batteries because they possess the most energy density. However, sodium and potassium battery systems offer the advantage of decreased material costs.
“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,” said Matthew McDowell, an assistant professor in the George W. Woodruff School of Mechanical Engineering and the School of Materials Science and Engineering.
Because sodium and potassium ions are much larger than lithium, it’s traditionally been thought that they cause more significant degradation when reacting with particles and decay faster than their lithium counterpart. Now, researchers have found that’s not always the case.
The study, which was sponsored by the National Science Foundation and the U.S. Department of Energy, looked at how the three different ions--lithium, sodium, and potassium--reacted with particles of iron sulfide, also called pyrite and fool’s gold.
In their experiments, the reactions that occurred 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 electron microscope. 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 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.
While there's still more work to be done on the topic, the new research findings could help scientists design battery systems that use these types of novel materials.
(Video Source: Georgia Institute of Technology)