Preparation And Electrochemical Performance Of Sulfide Composites For Cathode Of Lithium-sulfur Battery

Lithium-sulfur battery has become a promising energy storage device due to its advantages of high energy density,low cost,safety and environmental protection,and has become one of the choices to meet the development needs of electric vehicles.However,there are several major factors hindering the development and application of lithium-sulfur batteries:poor conductivity of the positive sulfur electrode,capacity loss due to shuttle effects,and volume changes during circulation.Therefore,it is necessary to develop the main material and design the structure of the positive electrode.The metal-organic skeleton materials（MOFs）have broad application prospects in adsorption,separation,catalysis,ion conduction and energy storage due to their adjustable pore structure and ultra-high specific surface area.Metal sulfide has strong polarity,interacts with Li PSs,and generally has good electrical conductivity,which can meet the rapid conduction of electrons on the electrode.CoS₂ has a high conductivity of 6700S/cm in transition metal sulfide,moreover,the polar adsorption and catalytic capacity of Li PSs are excellent.Carbon nanotubes can enhance the conductivity of the system,large specific surface area and so on.Therefore,this topic designed to prepare cobalt disulfide composite material using MOFs as template and carbon nanotubes as positive electrode of lithium sulfur battery.Specific work is as follows:（1）ZIF-67@CNT was prepared by in-situ composite,and CoS₂@CNT/C polyhedral composite was prepared by carbonization and vulcanization,and the optimal addition amount of CTAB and CNT was explored.CTAB,as a surfactant,regulates the particle size of the polyhedron,and CNT enhances the electrical conductivity of the system.When the battery is loaded with 75wt%sulfur as a positive electrode,the maximum specific discharge capacity is1154.3m A h/g at 0.2C.After 100 cycles,the capacity is 764 m A h/g,and the capacity retention rate is 66.2%.（2）In order to improve the cycling performance of the electrode,another metal was introduced to obtain bimetallic sulfide Zn S/CoS₂@CNT@C,which can provide more active sites.In addition,the optimal amount of CTAB addition was explored.As the positive electrode of Li-sulfur battery,the maximum specific discharge capacity of the composite at 0.2C is 1171 m A h/g,and the reversible specific capacity is 851 m A h/g after 100 cycles,and the capacity retention rate is 72.6%.（3）In this paper,ZIF-67 nanosheet was used as template,Co₁-CoS₂@CNT@C two-dimensional nanosheet composite was synthesized by carbonization and vulcanization after co-precipitation,and single-atom Co was successfully prepared with Zn as sacrificant,which not only enhanced the conductivity of the material,but also improved the adsorption and catalytic ability of the material to Li PSs.The optimal addition amount of Zn（NO₃）₂ was also explored.When the composite material is used in the positive electrode of lithium sulfur battery,when the amount of Zn（NO₃）₂is 0.15g,it still has 73.2%capacity retention rate after 100 cycles at 0.2C.When the current density is 1C,the reversible specific capacity of 473.3m Ah g^-1 is still available after 495 cycles,and the average capacity decay rate per cycle is only 0.029%.