| Lithium-sulfur batteries are one of the most promising next-generation energy storage systems due to their high theoretical specific capacity and outstanding theoretical energy density,as well as abundant reserves,environment-friendly of cathode sulfur active materials.However,a series of problems,such as the poor conductivity of elemental sulfur and the final discharge product,the volume expansion problem of the sulfur during discharge,and the"shuttle effect"of lithium polysulfide,etc.,have severely restricted the commercial development of lithium-sulfur batteries.In addition,the slow redox kinetics of the intermediate product lithium polysulfide is another important issue.In view of the main problems of the above,this article aims to improves the electrochemical performance of the battery by enhancing the conductivity of the sulfur cathode,inhibiting the dissolution of lithium polysulfide.And achieved periodic results.The main work of this article includes:1.Synthesis of CoS2/CNTs-S composite cathode material.Co S2/CNTs composites were synthesized in situ by hydrothermal method using acidified CNTs as the substrate,cobalt acetate tetrahydrate?Co?Ac?2×4H2 O?as the cobalt source and carbon disulfide?CS2?as the sulfur source.And then,high temperature melting method was used to combine with sulfur to obtainCo S2/CNTs-S composite cathode material.The three-dimensionally interconnected CNTs have good electrical conductivity and a highly porous structure,which is conducive to the rapid transport of electrons and buffer the volume expansion problem of sulfur during the discharge process.Moreover,the abundantCo S2 nanoparticles not only help chemically capture soluble lithium polysulfide,but also enhance the redox reaction kinetics of lithium polysulfide.Because of these synergistic advantages,Co S2/CNTs-S cathodes have achieved excellent electrochemical performance,including high discharge specific capacity,excellent rate capability,and outstanding cycle stability.Co S2/CNTs-S cathode exhibits a remarkable initial capacity of 1031m Ah g-1at1.0 C rate,and 570m Ah g-1is maintained after 500 cycles with a low capacity fading of 0.089%per cycle.Even at 2.0 C,theCo S2/CNTs-S electrode still exhibits excellent electrochemical performance(an outstanding discharge capacity of733m Ah g-1is still achieved after 150 cycles,with a capacity decay of 0.13%per cycle).2.Synthesis of S@Co-NCHS composite cathode material.Co-NCHS composite was synthesized by stirring at normal temperature and calcining at high temperature,which use polystyrene?PS?microspheres as a template,dopamine hydrochloride as a carbon source,and cobalt chloride hexahydrate?Co Cl2×6H2 O?as a cobalt source.And then,high temperature melting method was used to combine with sulfur to obtain S@Co-NCHS composite cathode material.The hollow carbon spheres can provide space for the storage of active material sulfur,greatly alleviate the volume change of elemental sulfur during the charge and discharge process,and physical limit the"shuttle effect"of lithium polysulfide.In addition,the doped nitrogen atoms and uniformly dispersed cobalt nanoparticles provide enough chemisorption sites for soluble lithium polysulfide,which can better inhibit the shuttle of lithium polysulfide.Besides,cobalt nanoparticles can also serve as catalyst to promote redox reaction kinetics of lithium polysulfide.Thanks to the synergistic effects of carbon spherical shells,uniformly dispersed cobalt nanoparticles and nitrogen doping,S@Co-NCHS cathode material has significantly improved the specific capacity,coulombic efficiency and cycle stability of lithium-sulfur batteries.S@Co-NCHS cathode exhibits a remarkable initial discharge capacity of 1307m Ah g-1at 0.2 C.Even under 3.0 C,the discharge specific capacity remains 624m Ah g-1,showing a high rate performance.And at 1.0 C,the specific capacity of465m Ah g-1is maintained after 800 cycles with a low capacity fading of 0.062%per cycle. |
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