Study On Synthesis And Electrochemical Performances Of Metal Sulfide Composites Electrode Materials

With the increasing demand for energy in the 21 st century,the corresponding high-efficiency energy storage device has been regarded as a strategic technology for the popularization of secondary energy in modern technological society.As an important electrochemical energy storage device at present,supercapacitors have high electrochemical stability,long cycle life and the ability of rapid charge and discharge.The energy storage efficiency can be improved by forming an electrochemical double layer charge or a pseudocapacitance surface redox reaction.And the supercapacitor with high energy density and high power density is becoming the research hotspot of clean energy in the world.Many researchers are working on developing new and excellent electrode materials.Among the transition metal sulfide compounds,molybdenum disulfide,a typical graphene-like two-dimensional layered compound,has arousedextensive interest due to its large specific surface area and good electrical conductivity.When the size of molybdenum disulfide is reduced to the nanoscale level,compared with the bulk molybdenum disulfide,the nano-molybdenum disulfide has larger specific surface area,stronger adsorption capacity and higher reactivity.Due to the unique physical and chemical properties of quantum scale effect,their properties are preserved.However,the single molybdenum disulfide nanomaterials also have the problems of poor electronic conductivity,poor stability and low specific capacity.To this end,we design molybdenum disulfide nanomaterials with different morphologies and structures,and further optimizes the properties of molybdenum disulfide composite functional materials by introducing high conductivity carbon-based functional materials such as graphene and carbon nanotubes.In this paper,we have successfully synthesized three-dimensional monoor few-layered molybdenum disulfide nanosheet/nitrogen-doped graphene composite aerogel electrode materials,and multi-wall carbon nanotube interconnected molybdenum disulfide/carbon nanoflower conductive network composite electrode materials,all of which have shown better electrochemical properties than those reported in the current literature.The main works are listed as follows:1.Two-dimensional mono-or few-layered molybdenum disulfide nanosheets were prepared by one-step hydrothermal and liquidexfoliation.Next,one-step hydrothermal method was used to combine few layers of molybdenum disulfide nanosheets with graphene containing nitrogen source to construct a three-dimensional porous aerogel material.After a series of morphology and structure characterization,the electrode material has a large surface area,which effectively prevent the accumulation and agglomeration of molybdenum disulfide nanosheets and form a stable conductive network structure for the rapid transport of ions and electrons.The electrochemical test showed that the composites have a higher specific capacity and better stability.At the current density of 1 A/g,the specific capacity can reach 532 F/g,and the capacitance could be maintained at 93.6%at the current desity of 10 A/g of 10,000 cycles.The synthesized composite aerogels electrode materials are assembled into symmetrical supercapacitor,which has high energy density and power density.2.Multiwalled carbon nanotubes interconnected molybdenum disulfide/carbon nanoflower composite electrode materials were prepared by one-step hydrothermal method.Carbon nanotubes are used as the interconnecting medium to obtain a stable conductive network.In order to compare and verify the functions of carbon nanotubes,the characterization and electrochemical tests were carried out under the same conditions with or without the addition of carbon nanotubes.It has shown that carbon nanotubes,as electronic pathways,are conducive to rapid electron transport,effectively reducing the stacking of molybdenum disulfide nanosheets in compositematerials,increasing the active specific surface area,providing a suitable channel for rapid ion transport,and improving the stability of composite materials.The composites can reach 318 F/g at a current density of 1 A/g,and maintain a capacitance of 91.7% even after 3,000 cycles at a large current density of 10 A/g.