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.

We report the synthesis of a low-cost carbon/sulfur nanocomposite using Ketjen black (KBC) as the carbon framework, encapsulated by thin graphene sheets using a simple process that relies on binding a functionalized KBC/S nanoparticle surface with graphene oxide (GO), which is reduced in situ. A slight excess of GO is employed to create a second layer of graphene wrapping around the KBC/S. This g-KBC/S sulfur cathode exhibits excellent cyclability over 200 cycles where the average stabilized fade rate is only 0.026% or 1.1 mAh g(-1) per cycle. This excellent performance is primarily attributed to the wrapped, internally porous architecture. The large pore volume, small pore diameter, and uniform nanoparticle size of the mesoporous KBC array provides an ideal frame for the fabrication of a homogeneous C/S composite, whereas the graphene/GO sheets serve as an external chemical and physical barrier that inhibits polysulfide diffusion.

In article number 1501636, Linda Nazar and co‐workers demonstrate the nature of the interaction between metal oxides and polysulfides, with an aim to explore materials with the ability to chemically entrap polysulfides. 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, which is essential for the design of high performance Li‐S cells.

Composite electrodes of a-TiS 3 /S/carbon (Ketjen black; KB) with high capacity were prepared by mechanical milling from a-TiS 3 and S/KB composites. The composites were fabricated into coin type liquid cells and all-solid-state cells and operated as rechargeable batteries at room temperature. The reversible capacity of the coin type liquid cells decreased from 484 to 33 mAh g −1 over 50 chargedischarge cycles, because the polysulfides formed from the redox reactions of a-TiS 3 /S dissolved in the liquid electrolyte. On the other hand, the all-solid-state cells showed higher reversible capacity and better cyclability than the coin type liquid cells. In order to improve their cycle performance, solid electrolyte (SE) powders were added to the composite electrodes to serve as lithium-ion conduction paths to the active materials. The cell using the a-TiS 3 /S/KB composite with 30 wt% SE exhibited the highest reversible capacity of about 850 mAh g −1 at the 1st cycle and retained a reversible capacity of about 650 mAh g −1 after the 50th cycle. Owing to their relatively high sulfur content, composite positive electrodes of a-TiS 3 /S/KB are attractive positive electrodes with high capacities for all-solid-state lithium secondary batteries.Conventional lithium-ion batteries using organic liquid electrolytes have been used extensively as power sources for mobile devices and personal computers. 1,2 Increasingly, they have been scaled up for use in large applications for electric vehicles and smart grids. 3 However, traditional lithium ion batteries containing a transition metal oxide cathode and a graphite anode are not able to satisfy energy density demands for many applications. 4,5 Sulfur is one of the most promising positive electrode materials because of its high theoretical specific capacity of 1672 mAh g −1 , which is at least 5 times higher than that of the transition metal oxides such as LiCoO 2 . 6,7 In addition, sulfur has many other advantages of low cost, abundant resource and environmental friendliness. However, pronounced capacity fading during cycling of lithium-sulfur batteries has been a major challenge that has thwarted their practical use. 8,9 The poor cycle life is attributable to the dissolution of intermediate lithium polysulfides (Li 2 S n , n = 4-8) 10-12 formed during charge-discharge into organic liquid electrolytes. The volumetric expansion and contraction of sulfur during cycling and the insulating nature of sulfur and lithium sulfide are also drawback for sulfur electrodes. A well-designed sulfur electrode to solve these issues is required. Current approaches focus on confining sulfur active materials in porous nanostructures to capture lithium polysulfides during charge-discharge reactions. [13][14][15][16][17][18][19][20][21][22][23][24] Various sulfur/carbon composites have been studied as positive electrodes in Li/S batteries. For example, a sulfur-porous hollow carbon composite electrode showed the reversible capacity of 974 mAh g −1 after 100 cycles. 13 Sulfur/carbon nanotube composit...