Sturcture And Composition Design Of Carbon/Molybdenum Sulfide Composite Colloid Particles And Research Of Their Electrochemical Performance

In recent years,the popular:ity of portable electronic devices and energy electric vehicles has objectively helped to alleviate the growing energy crisis and environmental pollution.Lithium-ion batteries are widely used because of their high energy density and long cycle performance.However,commercial anode graphite materials have a low theoretical specific capacity(372 mA h g-1),which is hard to meet the growing needs of people.Therefore,exploring and researching electrode materials with high specific capacity,low cost and environmental friendliness is crucial to alleviating the energy crisis and the future development of lithium-ion batteries.In this thesis,layered molybdenum sulfide(MoS2)was selected to prepare lithium ion battery anode material.MoS2 is a graphite-like two-dimensional layered structure.The layers are connected by weak van der Waals force.Therefore,MoS2 is easily embedded and removed for lithium ions.It's an excellent anode material(theoretical specific capacity 670 mA h g'1).Yet,the poor electrical conductivity of MoS2 is not satisfactory,which is attributed to its semiconductor properties and volume expansion problems,resulting in a decreased electrochemical performance.To solve this problem,we designed a simple hydrothermal synthesis of monodisperse hollow sandwich type SiO2@C@MoS2 microspheres,a core-shell structure of Fe3O4@C@MoS2 composites and hollow sandwich TiO2@C@MoS2 microspheres.The morphology and crystal structure were investigated by means of SEM,TEM,XRD,XPS and Raman.We designed and synthesized SiO2@C@MoS2,Fe3O4@C@MoS2 and TiO2@C@MoS2 composite materials through SiO2@PDA@MoS2,?-Fe2O3@PDA@MoS2 and PS@TiO2@PDA@MoS2 materials respectively,annealing in N2 atmosphere at 800 ?,600 ? and 800 ? for 2 h.In their structure,the surface-anchored MoS2 nanosheets have excellent lithium ion intercalation ability;the middle carbon interlayer is a nitrogen-doped carbon layer formed by carbonization of polydopamine(PDA),which has excellent conductivity and it can effectively bind the surface-anchored MoS2 nanosheets.The hollow cage-like SiO2 and the partially etched Fe3O4 inner layer structure itself have a high theoretical specific capacity and a low discharge platform,and the hollow and core-shell structures can alleviate the volume expansion effect in the process of deintercalating lithium ions.TiO2 has stable physicochemical properties.Based on this synergistic coating strategy,our composites exhibit excellent electrochemical performance when applied to lithium ion battery anode materials:(1)When the current density is 0.2 A g'1,SiO2@C@MoS2,the initial capacity is 1039 mA h g-1,the initial coulombic efficiency is as high as 82.7%.The SiO2@C@MoS2 has capacity of 600.4 mA h g-1 at 1 A g-1 after 300 cycles.(2)The initial capacity of Fe3O4@C@MOS2 at 0.2 A g-1current density is 1335.5 mA h g-1,the initial coulombic efficiency is 80.5%,and the capacity remains 686.5 mA h g-1 after 150 cycles at 0.2 A g-1.(3)When the current density is 0.1 A g-1,the initial capacity of TiO2@C@MoS2 is 1642.4 mA h g-1,the initial Coulombic efficiency is 80.7%,and the capacity retains 611.9 mA h g-1 at 1 A g-1 after 550 cycles.The electrochemical properties and cycle stability of these three composite electrode materials at different magnifications are far superior to the comparative samples C@MoS2,Fe3O4@C and TiO2@C materials.