Preparation Of New Composite Carriers Based On Molybdenum Disulfide And Their Application In Cathode Of Lithium-sulfur Batteries

Lithium sulfur batteries（LSBs）have been considered as promising candidates for large-scale high energy density devices due to the potentially high energy density(1675 m Ah g^-1),high theoretical specific capacity(2600 wh kg^-1),low cost and environment-friendly.Despite the promising features,the performance of LSBs is far below the requirement of industrial use.The challenges of LSBs include low suffur utilization,low culombic efficiency and instability during charging and discharging process,which is likely due to the insulating nature of sulfur and discharge product（Li₂S）,high solubility of polysulphide,shuttle effects,volumetric changes in the electrodes,and the growth of lithium dendrites in the negative electrode,etal.A variety of polar inorganic materials with unique catalytic activity（such as metal sulfide,metal nitride,metal oxide and metal carbide）have been applied to the modification of sulfur cathode to improve the electrochemical performance of LSBs.They can improve the interaction between cathode materials and lithium polysulfide（Li PSs）and catalyze the transformation of active substances,so as to inhibit the"shuttle effect".In recent years,molybdenum disulfide（Mo S₂）has shown great potential as a LSBs catalytic material because of its excellent chemical stability and high electrocatalytic activity.At present,there are still some obstacles for the use of Mo S₂ in LSBs,such as nano lamellar aggregation and insufficient conductivity.In order to overcome these shortcomings,Mo S₂ has been embedded into carbon-based materials by in-situ synthesis to construct two highly conductive three-dimensional-interconnected structure with specific morphology and surface modification.The main research work is as follows:（1）Through the alkyne coupling and hydrothermal reactions,Hs GDY/Mo S₂/Ni₃S₂ three-dimensional-interconnected nanostructures was constructed in situ on the nickel foam collector.The composite electrode material catalyzed the conversion of Li PSs while fixing sulfur efficiently,and effectively speeded up the redox kinetics of Li PSs.The three-dimensional interconnected hydrogen substituted graphdiyne（Hs GDY）carbon framework has microporous,mesoporous and macroporous structures,which can effectively adsorb Li PSs while alleviating volume expansion.After Mo S₂/Ni₃S₂ doping,a large number of exposed terminal alkynes and sulfur sites catalyzed the conversion of Li PSs through synergetic catalysis,effectively accelerate the redox kinetics of Li PSs,and inhibited the"shuttle effect".The LSBs based on the three-dimensional interconnected composite cathode has specific capacities of 1224.6 m Ah g^-1 for the first discharge at 0.1 C and 486.9 m Ah g^-1after 500 cycles at 2 C.（2）V₂C mxene/Mo S₂ heterostructure was constructed by a hydrothermal method.The Mo S₂formed a three-dimensional-interconnected structure on the surface and interlayer of V₂C MXene,and the excellent electrical conductivity of V₂C MXene was retained.At the same time,the vertical ion transport rate of the composites increased,thus achieving rapid Li⁺diffusion.In the process of etching precursor V₂Al C,a large number of functional groups were formed.The combination of functional groups and polar Mo S₂ provided significant sites for the adsorption and catalysis of Li PSs,which can effectively restrain the shuttle effect and improve the specific capacity and cycle life of the battery.The LSBs based on the three-dimensional interconnected composite cathode has a first discharge specific capacity of 1246.3 m Ah g^-1 at0.1 C.The discharge specific capacity remains at 740.8 m Ah g^-1 after 300 cycles.