Preparation And Electrochemical Performance Study Of Sulfur Carrier Materials Based On Transition Metal Sulfides For Lithium-sulfur Battery

The depletion of fossil fuels and the increasingly serious environmental issue have stimulated the demand and exploration of various clean and renewable energy technologies.The search for efficient,sustainable and stable energy that can be stored is undoubtedly a research hotspot in the new energy field.Lithium-sulfur batteries have aroused wide concern in the electrochemical energy storage and conversion areas due to their high energy,low cost,and no pollution.Experiments show that reasonable regulation of the sulfur content and utilization of the cathode can effectively improve the electrochemical performance of lithium-sulfur batteries.Consequently,the design and construction of sulfur carriers in lithium-sulfur batteries is one of the key approaches to optimize their performance.Nevertheless,the electrochemical performance of lithium-sulfur batteries is affected by factors such as the electronic insulation of active materials and discharge end products,and the volume expansion and dissolution of intermediate products during the conversion process,which hinders the commercialization of lithium-sulfur batteries.Rationally designing a highly conductive sulfur support structure material to buffer volume expansion,adsorb lithium polysulfide（Li PS）,and catalyze the kinetics of conversion reactions is an important research topic to obtain high-performance lithium-sulfur batteries.The main work of this paper is to prepare transition metal sulfides as sulfur carriers for lithium-sulfur batteries.The specific research contents are as follows:（1）The sea urchin-like precursor was prepared by a simple hydrothermal method,and then a sulfur source and cetyltrimethylammonium bromide（CTAB）were introduced for the second hydrothermal treatment.During the hydrothermal vulcanization process,the needle-like structure was transformed into a sheet-like structure,resulting in the preparation of Co S microspheres with abundant mesopores.The voids between the radial fan-shaped sheet structures provide buffer space for the activity to shrink and expand the volume of polysulfides.The highly conductive Co S can realize electron transfer during redox process and effectively adsorb Li PS.（2）Porous CoMoS₃ microspheres and sheet-like Co S composites were prepared as sulfur support materials for lithium-sulfur batteries.Among them,CoMoS₃ as a bimetallic sulfide provides abundant active sites to catalyze sulfur redox reactions.The highly conductive sheet-like Co S has a strong adsorption effect on polysulfides.The fast charge transfer capability and enhanced redox kinetics originate from the synergistic adsorption of the two catalytic polysulfides.Electrochemical tests show that the initial discharge specific capacity of CoMoS₃/Co S/S at 0.1 C is 1080 m Ah g^-1,which remains 708 m Ah g^-1 after 200cycles.（3）A mixed solution of polyacrylonitrile,polyvinylpyrrolidone polymer and cobalt-molybdenum oxide was used as the electrospinning solution.Under the action of the high-voltage electric field,the bead-string structure is formed by spinning.After high-temperature vulcanization heat treatment,a bead-string conductive three-dimensional network structure of carbon fiber wrapped CoMoS₃/Mo S₂ nanospheres（CMS@CNF）was formed.High-temperature vulcanized carbon nanofibers can achieve rapid electron and Li⁺transfer.Porous CoMoS₃/Mo S₂ nanospheres（CMS）can significantly alleviate the dissolution and diffusion of polysulfides and catalyze the redox reactions between various sulfides.The CMS@CNF/S composite material is used as the sulfur carrier for lithium-sulfur batteries,and the capacity decay rate per cycle is only 0.088% after 600 cycles at 1 C.