Sulfur (S) has seen itself in the center of several new developments in the field of battery engineering as the material is often touted for its high energy capacity; new research from Drexel University seems set on cementing sulfur’s status in the field, as new findings from their research show that batteries may stand to benefit a lot from adapting a rare kind of sulfur called “gamma” sulfur.
Technically, this rare form of sulfur is called monoclinic gamma-phase sulfur, and its rarity is at least partly due to the fact that this particular sulfur form is hard to come by. Known production pathways in forming “gamma sulfur” are within oil wells or at high-temperature environments in laboratory settings.
Drexel scientists wanted to create a way to confine sulfur in a carbon-based electrode to be used in batteries, given sulfur’s unfortunate penchant for forming unwanted polysulfides during the electrochemical reactions that happen inside lithium-sulfur (Li-S) batteries.
The hope was that by confining the sulfur within the carbon mesh, they would be able to limit the sulfur’s exposure to the carbonate electrolyte that all too often lead to polysulfide formation—especially given the fact that polysulfide buildup often leads to deteriorating battery performance and even failure.
However, Drexel researchers found themselves with a pleasant surprise as they attempted to use vapor deposition onto a carbon (C) nanofiber mesh to try and incorporate sulfur into its structure; instead of simply seeing sulfur locked inside, they instead found the rare “gamma sulfur” locked within the carbon nanofiber mesh—and it just so happens that gamma sulfur was unreactive to the carbonate electrolyte, meaning no polysulfides to worry about. Their radical new battery technology was published as a paper in the journal Communications Chemistry.
“At first, it was hard to believe that this is what we were detecting because in all previous research monoclinic sulfur has been unstable under 95 °C (203 °F),” said co-author Rahul Pai. “In the last century there have only been a handful of studies that produced monoclinic gamma sulfur and it has only been stable for 20-30 minutes at most. But we had created it in a cathode that was undergoing thousands of charge-discharge cycles without diminished performance – and a year later, our examination of it shows that the chemical phase has remained the same.”
“Having a cathode that works with the carbonate electrolyte that they’re already using is the path of least resistance for commercial manufacturers,” added Drexel’s Department of Chemical and Biological Engineering George B. Francis Chair professor Dr. Vibha Kalra in a Drexel University press release. “So rather than pushing for the industry adoption of a new electrolyte, our goal was to make a cathode that could work in the pre-existing Li-ion electrolyte system.”
The resulting gamma sulfur battery remained stable across 4,000 charge-discharge cycles across about one year of testing, with the prototype battery possessing triple the capacity of a standard lithium-ion battery.
Finally, Dr. Kalra said to New Atlas: “While we are still working to understand the exact mechanism behind the creation of this stable monoclinic sulfur at room temperature, this remains an exciting discovery and one that could open a number of doors for developing more sustainable and affordable battery technology.”
References
- Breakthrough in cathode chemistry clears path for lithium-sulfur batteries’ commercial viability. (2022, February 10). Drexel News; Drexel University. http://drexel.edu/news/archive/2022/February/lithium-sulfur-cathode-carbonate-electrolyte
- Lavars, N. (2022, February 11). Rare form of sulfur offers a key to triple-capacity EV batteries. New Atlas. https://newatlas.com/energy/rare-form-sulfur-lithium-ion-battery-triple-capacity/
- Pai, R., Singh, A., Tang, M. H., & Kalra, V. (2022). Stabilization of gamma sulfur at room temperature to enable the use of carbonate electrolyte in Li-S batteries. Communications Chemistry, 5(1), 1–11. https://doi.org/10.1038/s42004-022-00626-2
