The lithium-sulfur battery is receiving intense interest because its theoretical energy density exceeds that of lithium-ion batteries at much lower cost, but practical applications are still hindered by capacity decay caused by the polysulfide shuttle. Here we report a strategy to entrap polysulfides in the cathode that relies on a chemical process, whereby a hostmanganese dioxide nanosheets serve as the prototype-reacts with initially formed lithium polysulfides to form surface-bound intermediates. These function as a redox shuttle to catenate and bind 'higher' polysulfides, and convert them on reduction to insoluble lithium sulfide via disproportionation. The sulfur/manganese dioxide nanosheet composite with 75 wt% sulfur exhibits a reversible capacity of 1,300 mA h g À 1 at moderate rates and a fade rate over 2,000 cycles of 0.036%/cycle, among the best reported to date. We furthermore show that this mechanism extends to graphene oxide and suggest it can be employed more widely.

The lithium‐sulfur battery is a compelling energy storage system because its high theoretical energy density exceeds Li‐ion batteries at much lower cost, but applications are thwarted by capacity decay caused by the polysulfide shuttle. Here, proof of concept and the critical metrics of a strategy to entrap polysulfides within the sulfur cathode by their reaction to form a surface‐bound active redox mediator are demonstrated. It is shown through a combination of surface spectroscopy and cyclic voltammetry studies that only materials with redox potentials in a targeted window react with polysulfides to form active surface‐bound polythionate species. These species are directly correlated to superior Li‐S cell performance by electrochemical studies of high surface area oxide cathodes with redox potentials below, above, and within this window. Optimized Li‐S cells yield a very low fade rate of 0.048% per cycle. The insight gained into the fundamental surface mechanism and its correlation to the stability of the electrochemical cell provides a bridge between mechanistic understanding and battery performance essential for the design of high performance Li‐S cells.

A sulfur electrode exhibiting strong polysulfide chemisorption using a porous N, S dual-doped carbon is reported. The synergistic functionalization from the N and S heteroatoms dramatically modifies the electron density distribution and leads to much stronger polysulfide binding. X-ray photoelectron spectroscopy studies combined with ab initio calculations reveal strong Li(+) -N and Sn (2-) -S interactions. The sulfur electrodes exhibit an ultralow capacity fading of 0.052% per cycle over 1100 cycles.

present in DMSO solutions of lithium polysulfi des (neither S 4 ·− or S 2 ·− were detected). This was also the only radical species observed by Barchasz et al. [ 12 ] upon discharge of a sulfur electrode in tetraethylene glycol dimethyl ether (TEGDME). None of these studies, however, gives a quantitative estimate of the free radical content in the electrolyte, as compared with the various S n 2− dianions. Is the S 3 ·− radical prominent upon cycling in Li-S cells using dimethoxyethane (DME) and 1,3-dioxolane (DOL) solvents? In this event, could its reactivity be held responsible-through electrolyte decomposition-for capacity fading over extended cycling? If not, could the practical capacity of a Li-S cell be augmented by favoring free radicals by tuning the dielectric characteristics of the electrolyte?Herein, we assess the effect of sulfur radical species formed upon cycling of Li-S cells; in particular S 3 ·− . Based on our unequivocal observation of sulfur radicals in a Li-S cell by X-ray absorption near edge structure (XANES)-for the fi rst time under operating conditions-using an EPD solvent (DMA), we show that radicals are not stabilized in glyme-based electrolytes. However, we do show that S 3 ·− reacts with DOL at elevated temperatures, while DME remains intact. In contrast, the much greater dissociation of the anion precursor, S 6 2− , to the trisulfur radical in donor solvents such as DMA and DMSO-where trisulfur is in high concentration but nonreactive-surprisingly and importantly allows the full utilization of both sulfur and Li 2 S. The effective solvation of the latter results in the complete absence of an overpotential on charge. Chemical incompatibility between the lithium metal negative electrode and EPDsolvents can be overcome with anode protection, demonstrating their applicability as electrolytes for the Li-S or Li 2 S batteries in hybrid cells.

A versatile, cost-effective electrochemical analysis strategy is described that determines the specific S(n)(2-) adsorptivity of materials, and allows prediction of the long-term performance of sulphur composite electrodes in Li-S cells. Measurement of nine different materials with varying surface area, and hydrophobicity using this protocol determined optimum properties for capacity stabilization.