Tungsten Disulfide Catalysts Supported on a Carbon Cloth Interlayer for High Performance Li–S Battery

The capacity limitations of insertion‐compound cathodes has motivated interest in a sulfur cathode for a rechargeable battery cell with a metallic‐lithium anode; but irreversible capacity loss owing to solubility of intermediate Li₂S_x (x = 2–8) polysulfides in the organic‐liquid electrolytes used has prevented practical application. A dual‐function cathode structure consisting of layered tungsten disulfide (WS₂) supported both on the cathode current collector and on a carbon cloth interlayer (CCl) gives excellent performance in a lithium half‐cell by providing strong adsorption of the soluble Li₂S_x on the WS₂ with fast access to electrons from the current collector via a blocking carbon cloth interlayer.     

Reductive Dechlorination of Tetrachloroethene Following Abiotic Versus Biotic Reduction of Hexavalent Chromium

A feasibility evaluation identified chemical reduction and biostimulation as a potential remedy for a plume containing hexavalent chromium (Cr(VI)) and tetrachloroethene (PCE) at an industrial site in southern California. The objectives of this laboratory study were to determine the stoichiometry of calcium polysulfide (CaS_x) reaction with Cr(VI) in the presence of sediment, the effect of CaS_x on the potential for in situ biological reductive dechlorination of PCE, and the potential to reduce Cr(VI) and PCE by addition of only an electron donor. Approximately 1 L of CaS_x solution (containing 50 g S^2-/L) was required per 1000 L of groundwater containing 45 mg/L of Cr(VI) (i.e., 1.8 mol S^2- per mol Cr(VI)). The sediment also exerted a sulfide demand (≥0.38 g S^{2 -} per kg sediment), but at a slower rate than the Cr(VI). In microcosms prepared with lactate, corn syrup, soybean oil, or methanol, but no CaS_x, the Cr(VI) was biologically reduced in the treatments with lactate and corn syrup, but much more slowly than with CaS_x. Even after 20 months of incubation, no significant reductive dechlorination of PCE occurred in any of the microcosms, including those in which the Cr(VI) was removed with CaS_x. Bioaugmentation was tested with the microcosms that received lactate and corn syrup (following 20 months of incubation), using an enrichment culture that actively dechlorinates trichloroethene. PCE dechlorination began within 1 month in the lactate-only treatment; in the corn syrup-amended treatment, PCE dechlorination occurred in only one of the three bottles. However, no PCE dechlorination occurred following bioaugmentation of the lactate and corn syrup microcosms that were initially treated with CaS_x, indicating that CaS_x (and/or its reaction products) exerted a negative impact on the chlororespiring microbes. This outcome highlights the need to evaluate sites on a case-by-case basis when in situ chemical treatment is applied prior to microbial reductive dechlorination.     

Genomic properties of Marine Group A bacteria indicate a role in the marine sulfur cycle

Marine Group A (MGA) is a deeply branching and uncultivated phylum of bacteria. Although their functional roles remain elusive, MGA subgroups are particularly abundant and diverse in oxygen minimum zones and permanent or seasonally stratified anoxic basins, suggesting metabolic adaptation to oxygen-deficiency. Here, we expand a previous survey of MGA diversity in O₂-deficient waters of the Northeast subarctic Pacific Ocean (NESAP) to include Saanich Inlet (SI), an anoxic fjord with seasonal O₂ gradients and periodic sulfide accumulation. Phylogenetic analysis of small subunit ribosomal RNA (16S rRNA) gene clone libraries recovered five previously described MGA subgroups and defined three novel subgroups (SHBH1141, SHBH391, and SHAN400) in SI. To discern the functional properties of MGA residing along gradients of O₂ in the NESAP and SI, we identified and sequenced to completion 14 fosmids harboring MGA-associated 16S RNA genes from a collection of 46 fosmid libraries sourced from NESAP and SI waters. Comparative analysis of these fosmids, in addition to four publicly available MGA-associated large-insert DNA fragments from Hawaii Ocean Time-series and Monterey Bay, revealed widespread genomic differentiation proximal to the ribosomal RNA operon that did not consistently reflect subgroup partitioning patterns observed in 16S rRNA gene clone libraries. Predicted protein-coding genes associated with adaptation to O₂-deficiency and sulfur-based energy metabolism were detected on multiple fosmids, including polysulfide reductase (psrABC), implicated in dissimilatory polysulfide reduction to hydrogen sulfide and dissimilatory sulfur oxidation. These results posit a potential role for specific MGA subgroups in the marine sulfur cycle.     

Tailoring the Pore Size of a Polypropylene Separator with a Polymer Having Intrinsic Nanoporosity for Suppressing the Polysulfide Shuttle in Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are being considered as one of the most promising candidates for the development of next‐generation energy storage technologies. Although much progress has been made over the past decade, the development of Li–S batteries is still held back by a crucial polysulfide‐shuttle problem. To address this critical issue, an approach to reduce the pore size of the separator is presented here, to prevent the penetration of soluble polysulfide species. A polymer with intrinsic nanoporosity (PIN) is developed within the micrometer‐scale pores of a polypropylene separator. The framework of polypropylene acts as a skeleton to sustain reliable mechanical properties with the thin membrane. Upon the formation of PIN in the pores, the polypropylene separator maintains its thickness. With the thin PIN–polypropylene membrane, the Li–S cells can be operated with a relatively high sulfur loading. The PIN allows the transport of Li⁺ ions, but suppresses the penetration of the polysulfide species. The Li–S batteries with the PIN‐modified polypropylene separator exhibit enhanced cycling performance.     

Hybrid Lithium‐Sulfur Batteries with an Advanced Gel Cathode and Stabilized Lithium‐Metal Anode

The insulating nature of sulfur, polysulfide shuttle effect, and lithium‐metal deterioration cause a decrease in practical energy density and fast capacity fade in lithium‐sulfur (Li‐S) batteries. This study presents an integrated strategy for the development of hybrid Li‐S batteries based on a gel sulfur cathode, a solid electrolyte, and a protective anolyte composed of a highly concentrated salt electrolyte containing mixed additives. The dense solid electrolyte completely blocks polysulfide diffusion, and also makes it possible to investigate the cathode and anode independently. This gel cathode effectively traps the polysulfide active material while maintaining a low electrolyte to sulfur ratio of 5.2 mL g^?1. The anolyte effectively protects the Li metal and suppresses the consumption of liquid electrolyte, enabling stable long‐term cycling for over 700 h in Li symmetric cells. This advanced design can simultaneously suppress the polysulfide shuttle, protect Li metal, and reduce the liquid electrolyte usage. The assembled hybrid batteries exhibit remarkably stable cycling performance over 300 cycles with high capacity. Finally, surface‐sensitive techniques are carried out to directly visualize and probe the interphase formed on the surface of the Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) pellet, which may help stabilize the solid–liquid interface.     

Novel spironolactone-analogs as impurities in spironolactone

Six novel spironolactone-analogs steroids (3-8) were isolated from spironolactone by using various chromatographic methods. Their structures were elucidated by spectrometric analysis. Two of the analogs (3 and 7) were confirmed by X-ray crystallography. The A-ring of compounds 3-7 is opened at C-2C-3 bond, and compound 7 is an organic polysulfide, which has a rare, nine-membered ring with a five sulfur atom bridge.     

Effect of biologically produced sulfur on gas absorption in a biotechnological hydrogen sulfide removal process

Absorption of hydrogen sulfide in aqueous suspensions of biologically produced sulfur particles was studied in a batch stirred cell reactor, and in a continuous set-up, consisting of a lab-scale gas absorber column and a bioreactor. Presence of biosulfur particles was found to enhance the absorption rate of H(2)S gas in the mildly alkaline liquid. The mechanism for this enhancement was however found to depend on the type of particles used. In the gently stirred cell reactor only small hydrophilic particles were present (d(p) < 3 microm) and the enhancement of the H(2)S absorption rate can be explained from the heterogeneous reaction between dissolved H(2)S and solid elemental sulfur to polysulfide ions, S(x) (2-). Conditions favoring enhanced H(2)S absorption for these hydrophilic particles are: low liquid side mass transfer (k(L)), high sulfur content, and presence of polysulfide ions. In the set-up of gas absorber column and bioreactor, both small hydrophilic particles and larger, more hydrophobic particles were continuously produced (d(p) up to 20 microm). Here, observed enhancement could not be explained by the heterogeneous reaction between sulfide and sulfur, due to the relatively low specific particle surface area, high k(L), and low [S(x) (2-)]. A more likely explanation for enhancement here is the more hydrophobic behavior of the larger particles. A local increase of the hydrophobic sulfur particle concentration near the gas/liquid interface and specific adsorption of H(2)S at the particle surface can result in an increase in the H(2)S absorption rate.     

Porphyrin‐Derived Graphene‐Based Nanosheets Enabling Strong Polysulfide Chemisorption and Rapid Kinetics in Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries hold great promise as a next‐generation battery system because of their extremely high theoretical energy density and low cost. However, ready lithium polysulfide (LiPS) diffusion and sluggish redox kinetics hamper their cyclability and rate capability. Herein, porphyrin‐derived graphene‐based nanosheets (PNG) are proposed for Li–S batteries, which are achieved by pyrolyzing a conformal and thin layer of 2D porphyrin organic framework on graphene to form carbon nanosheets with a spatially engineered nitrogen‐dopant‐enriched skin and a highly conductive skeleton. The atomic skin is decorated with fully exposed lithiophilic sites to afford strong chemisorption to LiPSs and improve electrolyte wettability, while graphene substrate provides speedy electron transport to facilitate redox kinetics of sulfur species. The use of PNG as a lightweight interlayer enables efficient operation of Li–S batteries in terms of superb cycle stability (cyclic decay rate of 0.099% during 300 cycles at 0.5 C), good rate capability (988 mAh g^?1 at 2.0 C), and impressive sulfur loading (areal capacity of 8.81 mAh cm^?2 at a sulfur loading of 8.9 mg cm^?2). The distinct interfacial strategy is expected to apply to other conversion reaction batteries relying on dissolution–precipitation mechanisms and requiring interfacial charge‐ and mass‐transport‐mediation concurrently.     

Tethered Molecular Sorbents: Enabling Metal‐Sulfur Battery Cathodes

A rechargeable battery that uses sulfur at the cathode and a metal (e.g., Li, Na, Mg, or Al) at the anode provides perhaps the most promising path to a solid‐state, rechargeable electrochemical storage device capable of high charge storage capacity. It is understood that solubilization in the electrolyte and loss of sulfur in the form of long‐chain lithium polysulfides (Li₂S_x, 2 < x < 8) has hindered development of the most studied of these devices, the rechargeable Li‐S battery. Beginning with density‐functional calculations of the structure and interactions of a generic lithium polysulfide species with nitrile containing molecules, it is shown that it is possible to design nitrile‐rich molecular sorbents that anchor to other components in a sulfur cathode and which exert high‐enough binding affinity to Li₂S_x to limit its loss to the electrolyte. It is found that sorbents based on amines and imidazolium chloride present barriers to dissolution of long‐chain Li₂S_x and that introduction of as little as 2 wt% of these molecules to a physical sulfur‐carbon blend leads to Li‐S battery cathodes that exhibit stable long‐term cycling behaviors at high and low charge/discharge rates.     

Plasma‐Enhanced Atomic Layer Deposition of Ultrathin Oxide Coatings for Stabilized Lithium–Sulfur Batteries

One of the most challenging problems in the development of lithium–sulfur batteries is polysulfide dissolution, which leads to cell overcharge and low columbic efficiency. Here, we propose the formation of a thin conformal Li‐ion permeable oxide layer on the sulfur‐carbon composite electrode surface by rapid plasma enhanced atomic layer deposition (PEALD) in order to prevent this dissolution, while preserving electrical connectivity within the individual electrode particles. PEALD synthesis offers a fast deposition rate combined with a low operating temperature, which allows sulfur evaporation during deposition to be avoided. After PEALD of a thin layer of aluminium oxide on the surface of electrode composed of large (ca. 10 μm in diameter) S‐infiltrated activated carbon fibers (S‐ACF), significantly enhanced cycle life is observed, with a capacity in excess of 600 mA·h·g^?1 after 300 charge–discharge cycles. Scanning electron microscopy (SEM) shows a significant amount of redeposited lithium sulfides on the external surface of regular S‐ACF electrodes. However, the PEALD alumina‐coated electrodes show no lithium sulfide deposits on the fiber surface. Energy dispersive spectroscopy (EDS) studies of the electrodes’ chemical composition further confirms that PEALD alumina coatings dramatically reduce S dissolution from the cathodes by confining the polysulfides inside the alumina barrier.     

Petaled Molybdenum Disulfide Surfaces: Facile Synthesis of a Superior Cathode for QDSSCs

Quantum dot sensitized solar cells (QDSSCs) are in need of a highly active, stable, and inexpensive cathode material for practical devices. Here, a new, facile, hydrothermal preparation of nanostructured MoS₂ is shown. Grown directly from a planar Mo metal foil, the MoS₂ films have a petaled morphology that exposes a large number of catalytically active Mo edge sites, and are highly active for the electrochemical reduction of water and aqueous polysulfide. Preliminary results of its performance in solar devices are further presented, demonstrating superior QDSSC efficiency compared to the use of Pt cathodes.     

Highly Stable Lithium–Sulfur Batteries Based on Laponite Nanosheet‐Coated Celgard Separators

Lithium–sulfur (Li–S) batteries are of great interest due to their high theoretical energy density. However, one of the key issues hindering their real world applications is polysulfide shuttle, which results in severe capacity decay and self‐discharge. Here, a laponite nanosheets/carbon black coated Celgard (LNS/CB‐Celgard) separator to inhibit polysulfide shuttle and to enhance the Li⁺ conductivity simultaneously is reported. The polysulfide shuttle is efficiently inhibited through strong interactions between the O active sites of the LNS and polysulfides by forming the Li···O and O? S bonds. Moreover, the separator features high Li⁺ conductivity, fast Li⁺ diffusion, excellent electrolyte wettability, and high thermal stability. Consequently, the Li–S batteries with the LNS/CB‐Celgard separator and the pure S cathode show a high initial reversible capacity of 1387 mA h g^?1 at 0.1 C, high rate performance, superior cycling stability (with a capacity decay rate of 0.06% cycle^?1 at 0.2 C and 0.028% cycle^?1 at 1.0 C over 500 cycles), and ultralow self‐discharge. The separator could also enhance the performance of other batteries such as the LiFePO₄/separator/Li battery. This work sheds a new light on the design and preparation of novel separators for highly stable Li–S batteries via a “green” and cost‐effective approach.     

Novel 2D Sb2S3 Nanosheet/CNT Coupling Layer for Exceptional Polysulfide Recycling Performance

2D layer‐structured materials are considered a promising candidate as a coupling material in lithium sulfur batteries (LSBs) due to their high surface‐volume ratio and abundant active binding sites, which can efficiently mitigate shuttling of soluble polysulfides. Herein, an electrochemical Li intercalation and exfoliation strategy is used to prepare 2D Sb₂S₃ nanosheets (SSNSs), which are incorporated onto a separator in LSBs as a new 2D coupling material for the first time. The cells containing a rationally designed separator which is coated with an SSNS/carbon nanotube (CNT) coupling layer deliver a much improved specific capacity with a remarkable 0.05% decay rate for over 200 cycles at a current density of 2 C. The capability of the SSNSs to entrap polysulfides through their favorable interfacial functionality and the high electrical conductivity of the CNT network facilitates recycling of active materials. The first‐principle calculations verify the important roles of SSNSs, which demonstrate ideal binding strengths (1.33–2.14 eV) to entrap Li₂S_x as well as a low‐energy barrier (189 meV) for Li diffusion. These findings offer new insights into discovering novel coupling layers for high‐performance LSBs and shed new light on the application of 2D layer‐structured materials in energy storage systems.     

Polysulfide‐Shuttle Control in Lithium‐Sulfur Batteries with a Chemically/Electrochemically Compatible NaSICON‐Type Solid Electrolyte

A NaSICON‐type Li⁺‐ion conductive membrane with a formula of Li_{1+ x} Y _x Zr_{2? x} (PO₄)₃ (LYZP) (x = 0–0.15) has been explored as a solid‐electrolyte/separator to suppress polysulfide‐crossover in lithium‐sulfur (Li‐S) batteries. The LYZP membrane with a reasonable Li⁺‐ion conductivity shows both favorable chemical compatibility with the lithium polysulfide species and exhibits good electrochemical stability under the operating conditions of the Li‐S batteries. Through an integration of the LYZP solid electrolyte with the liquid electrolyte, the hybrid Li‐S batteries show greatly enhanced cyclability in contrast to the conventional Li‐S batteries with the porous polymer (e.g., Celgard) separator. At a rate of C/5, the hybrid Li ||LYZP|| Li₂S₆ batteries developed in this study (with a Li‐metal anode, a liquid/LYZP hybrid electrolyte, and a dissolved lithium polysulfide cathode) delivers an initial discharge capacity of ≈1000 mA h g^?1 (based on the active sulfur material) and retains ≈90% of the initial capacity after 150 cycles with a low capacity fade‐rate of <0.07% per cycle.     

Rationalizing Electrocatalysis of Li–S Chemistry by Mediator Design: Progress and Prospects

The lithium–sulfur (Li–S) battery is regarded as a next‐generation energy storage system due to its conspicuous merits in high theoretical capacity (1672 mAh g^?1), overwhelming energy density (2600 Wh kg^?1), and the cost‐effectiveness of sulfur. However, the practical application of Li–S batteries is still handicapped by a multitude of key challenges, mainly pertaining to fatal lithium polysulfide (LiPS) shuttling and sluggish sulfur redox kinetics. In this respect, rationalizing electrocatalytic processes in Li–S chemistry to synergize the entrapment and conversion of LiPSs is of paramount significance. This review summarizes recent progress and well‐developed strategies of the mediator design toward promoted Li–S chemistry. The current advances, existing challenges, and future directions are accordingly highlighted, aiming at providing in‐depth understanding of the sulfur reaction mechanism and guiding the rational mediator design to realize high‐energy and long‐life Li–S batteries.