Graphene-based Metal Oxide/sulfide Composite Material Preparation And Electrochemical Performance Research

Metal oxide and sulfide anode materials were limited their large-scale applications in lithium-ion batteries due to their poor electrical conductivity and volume expansion effects during charge and discharge.In this thesis,a graphene/metal oxide?MO_x?/tungsten disulfide?WS₂?composite was prepared.The structure,morphology and electrochemical lithium storage properties of the composite were studied in detail.We discussed the contact interface and binding mechanism between the MO_x?WS₂?and the graphite.The nanocomposite had good electronic conductivity and effectively buffers the volume expansion caused by the MO_x?MS₂?materials during the charge and discharge process,so it exhabited excellent rate performance and long cycle life.The specific research content and results are as follows:?1?Using ammonium metatungstate as the tungsten source,graphene oxide as the carrier,deionized water as the solvent and thiourea as the sulfur source,a mixture of graphene oxide and ammonium metatungstate was prepared by simple stirring,ultrasound and drying.rGO@WO₃ and rGO@WS₂ composites were prepared from precursor composites,followed by hydrazine hydrate reduction and high temperature treatment.The scanning electron microscope?SEM?,transmission electron microscope?TEM?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?were used to characterize the rGO@WO₃ and rGO@WS₂ composite materials.Electrochemical tests showed that the corresponding rGO@WO₃ composite material has better cycle performance when the ratio of WO₃ to graphene oxide is 2:1.The specific capacity of discharge after 200 cycles of charge and discharge at a current density of 100m A g^-1?0.1C?is 450mAh g^-1,the corresponding rGO@WS₂ composite material has better rate performance when the ratio of WS₂ to graphene oxide is 4:1 and has a specific discharge capacity of 400mAh g^-1 at a current density of 1C.?2?rGO@WO₃-(Co_xNi_1-x)WO₄ composite materials and rGO@Co-Ni-WS₂ composite material with different contents cobalt and nickel were prepared by using the same preparation method,they were characterized by SEM and TEM,MOx exists between the layers or surface of the graphene structure in rGO@WO₃-?CoxNi₁-x?WO₄ composite material.When MOx is combined with graphene,it can buffer the volume expansion of MOx during charge and discharge.Tungsten disulfide nanosheets are stacked on top of each other and evenly distributed in the graphene structure in the rGO@Co-Ni-WS₂ composite material.For rGO@Co-Ni-WS₂ material,a small amount of metal element doping can greatly improve the conductivity of WS₂ itself.When WS₂ is combined with graphene,the good structural stability of graphene can be used as a carrier for WS₂ and prevent the re-stacking of WS₂nanosheets.Electrochemical performance tests show that the rGO@WO₃-?CoxNi₁-x?WO₄composite material and rGO@Co-Ni-WS₂ composite material have excellent rate performance and cycle performance,and the discharge specific capacity of the two composite materials will increase by the increase of cycle the number of times.After 100 cycles at a current density of 0.1C,they have a discharge specific capacitance of?800 mAh g^-1 and?700 mAh g^-1,respectively.In addition,the rGO@Co-Ni-WS₂ composite material has high specific discharge capacity after 200 cycles,showing excellent cycle durability.