Synthesis Of Transition Metal Dichalcogenides/Carbon Nanocomposites With Study On Their Performances As Anodes Of Lithium Ion Batteries

Transition metal dichalcogenides and carbon materials with their unique structures,the physical and chemical properties have potential application in lithium ion battery anode materials field.At the same time,the study reveals that the composite of these two kinds of materials can greatly enhance the synergy between them,applying it to the cathode material shows a high reversible lithium storage capacity,good cycling stability and excellent high rate charge and discharge cycle performance.Hybrid of transition metal dichalcogenides?MoS₂,SnS₂?and graphene,carbon sphere of carbon were designed,and the influence of the crystal structure and surface morphology of the composite that using as lithium ion battery cathode material on the electrochemical performances has been studied.The first chapter introduced the background and significance of this paper;the second chapter presents the experiment method,drug reagents,experimental apparatus and test instrument have been used during the synthesizing experiment;it introduces the main work during my studying for master degree from the third chapter to the fifth chapter.The mian content and conclusion of the paper is as follows:1.MoS₂/GF composites were synthesized by hydrothermal method using graphene oxide?GO?,sodium molybdate and thiourea as raw materials with assistance of different cationic surfactants(C₁₄TAB,C₁₆TAB,C₁₈TAB).The investigation of as-prepared samples by X-ray diffraction and scanning electron microscopy demonstrate that the composites have presented different morphologies and microstructures due to the effects of the cationic surfactants.Electrochemical performances for reversible Li lithium storage of the composites indicate that the capacities,cycling stability and rate capability were influenced by different morphologies and microstructures.Comparison to C₁₆TAB and C18 TAB assistance,the composite synthesized with C14 TAB assistance delivered a high first discharge capacity of 955 mAh/g and reversible capacity of 751 mAh/g after 50 cycles with excellent rate capability.The improvement in the electrochemical performances of the composites synthesized with C14 TAB assistance is attributed to its special particle-on-sheet structure and synergistic interactions between graphene and MoS₂.2.The carbon spheres were prepared with the dehydration of glucose,and MoS₂/C composites were synthesized by developing MoS₂ nanosheets on the carbon spheres with assistance of L-cysteine.From the characterization of XRD and SEM,it was found that Mo S2/Carbon composites have a special core-shell structure with the diameter among 450-500 nm,and the shell of MoS₂ is composed of self assembled layered thin nanosheets.From the measurement of electrochemical performances,it is found that Mo S2/Carbon composites are superior to bare MoS₂ in high first charge and discharge capacity,cycling stability and rate capability due to the robust structure and promoted synergy which were brought by unique core-shell structure.MoS₂/Carbon composites delivered a first discharge capacity of 696.6 m Ah/g with coulombic efficiency of 83% and reversible capacity of 624 mAh/g after 30 cycles.3.SnS₂/GNS composites were synthesized by hydrothermal method with different mole ratio of Sn S2 and graphene under the help of L-cysteine.From the characterization of XRD and SEM,it was found that the size of SnS₂ of SnS₂/GNS-1,SnS₂/GNS-2,SnS₂/GNS-4 composites is continuous decrease,which indicates that the increasing of the amount of graphene can inhibit the growth of SnS₂ with multiple direction.From the measurement of electrochemical performances,it is found that SnS₂/GNS-4 composites delivered a first discharge capacity of 1285.8 mAh/g with coulombic efficiency of 83.3% and reversible capacity of 766.4 mAh/g after 50 cycles.The improvement in the electrochemical performances of SnS₂/GNS-4 composites is attributed to sufficient amount of graphene facilitate inself to form three-dimensional structure and regulate the size of SnS₂ to form nanoparticles.