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In Li–S batteries, the insulating nature of sulfur and Li 2 S causes enormous challenges, such as high polarization and low active material utilization. The nucleation of the solid discharge product, Li 2 S, during the discharge cycle, and the activation of Li 2 S in the subsequent charge cycle, cause a potential challenge that needs to be overcome. Moreover, the shuttling of soluble lithium polysulfide intermediate species results in active material loss and early capacity fade. In this study, we have used thiourea as an electrolyte additive and showed that it serves as both a redox mediator to overcome the Li 2 S activation energy barrier and a shuttle inhibitor to mitigate the notorious polysulfide shuttling via the investigation of thiourea redox activity, shuttle current measurements and study of Li 2 S activation. The steady-state shuttle current of the Li–S battery shows a 6-fold drop when 0.02 M thiourea is added to the standard electrolyte. Moreover, by adding thiourea, the charge plateau for the first cycle of the Li 2 S based cathodes shifts from 3.5 V (standard ether electrolyte) to 2.5 V (with 0.2 M thiourea). Using this additive, the capacity of the Li–S battery stabilizes at ∼839more »mA h g −1 after 5 cycles and remains stable over 700 cycles with a low capacity decay rate of 0.025% per cycle, a tremendous improvement compared to the reference battery that retains only ∼350 mA h g −1 after 300 cycles. In the end, to demonstrate the practical and broad applicability of thiourea in overcoming sulfur-battery challenges and in eliminating the need for complex electrode design, we study two additional battery systems – lithium metal-free cells with a graphite anode and Li 2 S cathode, and Li–S cells with simple slurry-based cathodes fabricated via blending commercial carbon black/S and a binder. We believe that this study manifests the advantages of redox active electrolyte additives to overcome several bottlenecks in the Li–S battery field.« less

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)more »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.« less