Stabilization of gamma sulfur at room temperature to enable the use of carbonate electrolyte in Li-S batteries

This past decade has seen extensive research in lithium-sulfur batteries with exemplary works mitigating the notorious polysulfide shuttling. However, these works utilize ether electrolytes that are highly volatile severely hindering their practicality. Here, we stabilize a rare monoclinic γ-sulfur phase within carbon nanofibers that enables successful operation of Lithium-Sulfur (Li-S) batteries in carbonate electrolyte for 4000 cycles. Carbonates are known to adversely react with the intermediate polysulfides and shut down Li-S batteries in first discharge. Through electrochemical characterization and post-mortem spectroscopy/ microscopy studies on cycled cells, we demonstrate an altered redox mechanism in our cells that reversibly converts monoclinic sulfur to Li 2 S without the formation of intermediate polysulfides for the entire range of 4000 cycles. To the best of our knowledge, this is the first study to report the synthesis of stable γ-sulfur and its application in Li-S batteries. We hope that this striking discovery of solid-to-solid reaction will trigger new fundamental and applied research in carbonate electrolyte Li-S batteries. Lithium sulfur batteries are an emerging energy storage medium, but their stability in carbonate electrolyte remains hampered by side-reactions. Here, the authors show that as-produced monoclinic gamma-sulfur on activated carbon nanofibers converts to Li 2 S without the formation of intermediate polysulfides, therefore eliminating irreversible side reactions and improving cycling stability.