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  1. 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 andpost-mortemspectroscopy/ 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.

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  2. Sulfur and selenium based rechargeable batteries have attracted great attention due to their high gravimetric/volumetric energy densities owing to multielectron conversion reactions. Over the last few years, rationally designed nanomaterials have played a crucial role in the continuous growth of these battery systems. In this context, electrospun nanostructures are of paramount interest for the development of these rechargeable secondary batteries due to their high surface area to volume ratio and good mechanical stability. Here, a systematic and comprehensive review of the recent advances in the development of electrospun nanostructures as novel materials for next generation sulfur and selenium based lithium and sodium batteries is presented. In this review, we highlight the recent progress made in Li–S, RT Na–S, Li–S x Se y , RT Na–S x Se y , Li–Se and RT Na–Se batteries using electrospun carbon, polymers or heterostructures with tailored textural properties, compositions and surface functionalities (polysulfide trapping capability and catalytic activity) in cathodes, interlayers, separator coatings, and electrolyte membranes. The emphasis is placed on various synthesis strategies to design advanced electrospun nanostructures with tunable structural properties and the impact of these features on capacity, rate capability and long-term cycling. Moreover, we have introduced the ‘fraction of (electrochemically) active cathode (FAC)’ as a parameter to highlight the advantages of free-standing electrospun nanostructures compared to their non-electrospun or slurry-cast electrospun counterparts. Furthermore, current challenges and prospects in the use of electrospun nanostructures in each battery system are also discussed. We believe that this review will provide new opportunities in the field of advanced sulfur and selenium based rechargeable batteries using electrospun nanostructures. 
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