Abstract
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 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 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.
Highlights
This past decade has seen extensive research in lithium-sulfur batteries with exemplary works mitigating the notorious polysulfide shuttling
The thermogravimetric analysis (TGA) curve shows mild initial weight loss below 100 °C associated with evaporation of adsorbed moisture
While the higher-rate lower-temperature weight loss suggests evaporation of exposed unconfined sulfur, the lower-rate higher-temperature loss can be attributed to sulfur confined in micro/mesopores
Summary
This past decade has seen extensive research in lithium-sulfur batteries with exemplary works mitigating the notorious polysulfide shuttling. They proposed that the confinement within sub-nano pores prevented the formation of larger sulfur allotropes (S5–8) and possibly resulted in small sulfur allotropes (S2–4) only, which in turn converted to Li2S without the intermediate polysulfides (Li2S8, Li2S6...) They showed stable capacity (with single discharge plateau) in carbonate electrolytes for up to 200 cycles. Fu et al synthesized carbon/sulfur cathodes with sulfur confined in sub-nanometer carbon pores (0.4–1 nm)[26] Their material exhibited single plateau discharge and stable reversible capacity for 100 cycles in carbonate electrolyte. They proposed that the small pore size forced the de-solvation of lithium ions and resulted in solid-state lithiation and de-lithiation of confined S8 molecules. The development of unconfined high loading sulfur cathodes in Li–S batteries employing carbonatebased electrolytes can revolutionize the field of high energy density practical batteries
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