| Graphene is an excellent carbon nanomaterial with an extremely large specific surface area,excellent photoelectric properties and mechanical strength.In recent years,progress has been made in the growth of graphene on the surface of non-catalytic planar substrates such as various oxides,dielectrics,and semiconductors.However,due to the complexity of the surface of the micro-nanoparticles?size,geometry,roughness,defects,surface chemistry,etc.?,the growth of graphene on the particles is still a less accessible area.At present,the methods for preparing graphene/nanoparticle composite structures are mainly divided into two types:wet method and dry method.Among them,the wet method forms a graphene/nanoparticle composite by reacting graphene oxide?GO?or reduced graphene oxide?RGO?in water or an organic solvent to react with an organic/inorganic metal salt precursor.The wet process is simple,easy to achieve mass production,low cost,and diversified product structure,but the quality of the prepared graphene is not high,and it is difficult to avoid the problem of stacking graphene.The dry method is chemical vapor deposition?CVD?,which can directly grow graphene on the surface of the particles,greatly improving the conductivity of the powder.However,direct growth of graphene by CVD method generally requires higher temperature?800-1000°C?,and the uniformity of graphene growth and preparation efficiency problems need to be solved.Based on this,this paper uses traditional CVD method and innovative fluidized bed-microwave plasma chemical vapor deposition?FB-PCVD?to directly grow graphene on the surface of negative electrode particles,and explores the graphene composite anode material.Electrochemical performance.In this thesis,the Si@G core-shell composite with controllable graphene thickness was prepared by conventional CVD method with ethanol as carbon source and controlled growth time.The effects of graphene coating thickness on the morphology,structure and electrochemical properties of Si@G composites were investigated by XRD,SEM,TEM,Raman and TGA physical characterization and constant current charge and discharge tests.The results show that the thicker graphene shell,although reducing the specific capacity of the composite and the first coulombic efficiency,can significantly improve the electrochemical stability.When the graphene shell is about12 nm thick,the specific capacity of charge after 10 cycles reaches 1069.8 mAh g-1,and the cycle retention is 81.2%;while the pure Si sample is only 23.5%.This is attributed to the buffering of graphene to silicon volume effects and its excellent electrical conductivity.On the other hand,in order to solve the shortcomings of high growth temperature and poor uniformity of graphene when graphene is grown on particles by conventional CVD method,this paper uses FB-PCVD method to form a fluidized sample under the action of methane and argon.Graphene uniformly coated titanium dioxide nanoparticles were prepared by microwave plasma at a shorter time and at a lower temperature.The results show that the coating of highly conductive graphene can effectively improve the electrical conductivity and structural stability of the original TiO2,thereby improving its electrochemical performance.The specific capacity of the TiO2-G composite after cycling for 320 cycles at a current density of 100 mA·g-1 was 166.4 mAh g-1,while the original TiO2 was only 32.8 mAh g-1.Although graphene composites are used in commercial lithium/sodium ion batteries for a long distance,the growth conditions and processes of graphene grown on granule substrates are studied,and graphene composites are used in the field of electrochemistry.The excellent performance is very practical for subsequent research. |
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