As one important component of sulfur cathodes, the carbon host plays a key role in the electrochemical performance of lithium‐sulfur (Li‐S) batteries. In this paper, a mesoporous nitrogen‐doped carbon (MPNC)‐sulfur nanocomposite is reported as a novel cathode for advanced Li‐S batteries. The nitrogen doping in the MPNC material can effectively promote chemical adsorption between sulfur atoms and oxygen functional groups on the carbon, as verified by X‐ray absorption near edge structure spectroscopy, and the mechanism by which nitrogen enables the behavior is further revealed by density functional theory calculations. Based on the advantages of the porous structure and nitrogen doping, the MPNC‐sulfur cathodes show excellent cycling stability (95% retention within 100 cycles) at a high current density of 0.7 mAh cm‐2 with a high sulfur loading (4.2 mg S cm‐2) and a sulfur content (70 wt%). A high areal capacity (≈3.3 mAh cm‐2) is demonstrated by using the novel cathode, which is crucial for the practical application of Li‐S batteries. It is believed that the important role of nitrogen doping promoted chemical adsorption can be extended for development of other high performance carbon‐sulfur composite cathodes for Li‐S batteries. The nitrogen‐doped mesoporous carbon material is found to chemically adsorb sulfur, and the related mechanism is revealed by experimental survey and density functional theory calculation. Taking full advantages of chemical adsorption of sulfur, MPNC‐S cathode delivered an excellent capacity retention (95% within 100 cycles), high Coulombic efficiency (>96%), as well as high areal capacity of above 3 mAh cm‐2.
We report the synthesis of a graphene–sulfur composite material by wrapping poly(ethylene glycol) (PEG) coated submicrometer sulfur particles with mildly oxidized graphene oxide sheets decorated by carbon black nanoparticles. The PEG and graphene coating layers are important to accommodating volume expansion of the coated sulfur particles during discharge, trapping soluble polysulfide intermediates, and rendering the sulfur particles electrically conducting. The resulting graphene–sulfur composite showed high and stable specific capacities up to ∼600 mAh/g over more than 100 cycles, representing a promising cathode material for rechargeable lithium batteries with high energy density.
Flexible nanostructured reduced graphene oxide–sulfur (rGO–S) composite films are fabricated by synchronously reducing and assembling GO sheets with S nanoparticles on a metal surface. The nanostructured architecture in such composite films not only provides effective pathways for electron transport, but also suppresses the diffusion of polysulfides. Furthermore, they can serve as the cathodes of flexible Li–S batteries.
The polysulfide ions formed during the first reduction wave of sulfur in Li–S battery were determined through both and derivatization of polysulfides. By comparing the cyclic voltammetric results with and without the derivatization reagent (methyl triflate) as well as the and derivatization results under potentiostatic condition, derivatization was found to be more appropriate than its counterpart, since subsequent fast chemical reactions between the polysulfides and sulfur may occur during the timeframe of procedures. It was found that the major polysulfide ions formed at the first reduction wave of elemental sulfur were the and species, while the widely accepted reduction products of and for the first reduction wave were in low abundance.
In order to address the challenges associated with lithium–sulfur batteries with high energy densities, various approaches, including advanced designs of sulfur composites, electrolyte engineering, and functional separators, are lately introduced. However, most approaches are effective for sulfur cathodes with limited sulfur contents, i.e., <80 wt%, imposing a significant barrier in realizing high energy densities in practical cell settings. Here, elemental sulfur‐mediated synthesis of a perfluorinated covalent triazine framework (CTF) and its simultaneous chemical impregnation with elemental sulfur via SNAr chemistry are demonstrated. SNAr chemistry facilitates the dehalogenation and nucleophilic addition reactions of perfluoroaryl units with nucleophilic sulfur chains, achieving a high sulfur content of 86 wt% in the resulting CTF. The given sulfur‐impregnated CTF, named SF‐CTF, exhibits a specific capacity of 1138.2 mAh g−1 at 0.05C, initial Coulombic efficiency of 93.1%, and capacity retention of 81.6% after 300 cycles, by utilizing homogeneously distributed sulfur within the micropores and nitrogen atoms of triazine units offering high binding affinity toward lithium polysulfides. Elemental sulfur‐mediated trimerization of aromatic nitriles along with perfluoroaryl‐elemental sulfur SNAr chemistry leads to preparation of sulfur‐embedded covalent triazine frameworks with a high sulfur content of 86 wt% and exceptional electrochemical performance when tested as a cathode material in lithium–sulfur batteries, 93.1% initial Coulombic efficiency, and a specific capacity of 1138.2 mAh g−1.
Three‐dimensional metal carbide MXene/reduced graphene oxide hybrid nanosheets are prepared and applied as a cathode host material for lithium–sulfur batteries. The composite cathodes are obtained through a facile and effective two‐step liquid‐phase impregnation method. Owing to the unique 3 D layer structure and functional 2 D surfaces of MXene and reduced graphene oxide nanosheets for effective trapping of sulfur and lithium polysulfides, the MXene/reduced graphene oxide/sulfur composite cathodes deliver a high initial capacity of 1144.2 mAh g−1 at 0.5 C and a high level of capacity retention of 878.4 mAh g−1 after 300 cycles. It is demonstrated that hybrid metal carbide MXene/reduced graphene oxide nanosheets could be a promising cathode host material for lithium–sulfur batteries. Composite cathodes: Metal carbide MXene/reduced graphene oxide hybrid nanosheets are applied as cathode host materials for lithium–sulfur batteries. With their unique 3 D layer structure and functional 2 D surfaces for the effective trapping of sulfur and lithium polysulfides, the composite cathodes deliver a high initial capacity (1144.2 mAh g−1 at 0.5 C) and excellent capacity retention (878.4 mAh g−1 after 300 cycles), so are promising candidates for application in lithium–sulfur batteries (see figure).