New Catalyst May Make Lithium Sulfur Batteries Practical

Gwangju Institute of Science and Technology (GIST) scientists have discovered a new catalyst material’s ability to significantly improve lithium-sulfur battery life, opening doors to their near-future practical commercial realization.

Lithium-sulfur batteries, given their light weight and theoretical high capacities, are a promising alternative to conventional lithium-ion batteries for large-scale energy storage systems, drones, electric vehicles, etc. But at present, they suffer from poor battery life, limiting their applicability.

At the heart of most electronics today are rechargeable lithium-ion batteries (LIBs). But their energy storage capacities are not enough for large-scale energy storage systems (ESSs). Lithium-sulfur batteries (LSBs) could be useful in such a scenario due to their higher theoretical energy storage capacity. They could even replace LIBs in other applications like drones, given their light weight and lower cost.

But the same mechanism that is giving them all this power is keeping them becoming a widespread practical reality. Unlike LIBs, the reaction pathway in LSBs leads to an accumulation of solid lithium sulfide (Li₂S₆) and liquid lithium polysulfide (LiPS), causing a loss of active material from the sulfur cathode (positively charged electrode) and corrosion of the lithium anode (negatively charged electrode). To improve battery life, scientists have been looking for catalysts that can make this degradation efficiently reversible during use.

In a new study published in ChemSusChem, scientists from GIST, Korea, report their breakthrough in this endeavor. “While looking for a new electrocatalyst for the LSBs, we recalled a previous study we had performed with cobalt oxalate (CoC₂O₄) in which we had found that negatively charged ions can easily adsorb on this material’s surface during electrolysis. This motivated us to hypothesize that CoC₂O₄ would exhibit a similar behavior with sulfur in LSBs as well,” explained Prof. Jaeyoung Lee from GIST, who led the study.

To test their hypothesis, the scientists constructed an LSB by adding a layer of CoC₂O₄ on the sulfur cathode.

Sure enough, observations and analyses revealed that CoC₂O₄‘s ability to adsorb sulfur allowed the reduction and dissociation of Li₂S₆ and LiPS. Further, it suppressed the diffusion of LiPS into the electrolyte by adsorbing LiPS on its surface, preventing it from reaching the lithium anode and triggering a self-discharge reaction. These actions together improved sulfur utilization and reduced anode degradation, thereby enhancing the longevity, performance, and energy storage capacity of the battery.

Impressed by these findings, Prof. Lee envisions an electronic future governed by LSBs, which LIBs cannot realize. “LSBs can enable efficient electric transportation such as in unmanned aircrafts, electric buses, trucks and locomotives, in addition to large-scale energy storage devices,” he observes. “We hope that our findings can get LSBs one step closer to commercialization for these purposes.”

A higher capacity, lower weight, less expensive battery would certainly be very welcomed by consumers. It does seem that these scientists have gotten this battery chemistry a fresh start. While it is still very early in the lithium sulfur story, it now looks like the story is going to continue. With lithium at a high price, perhaps the economic incentive alone is enough to get more progress underway.

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