Stabilization of gamma sulfur at room temperature to enable the use of carbonate electrolyte in 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 Li2S without the formation of intermediate polysulfides, therefore eliminating irreversible side reactions and improving cycling stability. 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 gamma-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 Li2S 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 gamma-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.

Automated summary

This study investigates the stability of lithium sulfur batteries in carbonate electrolyte. The authors found that monoclinic gamma-sulfur on activated carbon nanofibers converts to Li2S without the formation of intermediate polysulfides, leading to improved cycling stability.