Chemical Vapor Deposition Of CNWs And Electrochemical Performance Of MnO₂/CNWs Electrodes

As an energy storage device,lithium ion battery has the advantages of high energy density,no memory effect,safety and long service life,so it has become one of the most widely used energy devices.In the field of electrochemistry,nano carbon materials have great potential,but the theoretical capacity of carbon materials is low,which can not meet people’s demand for efficient energy storage equipment.Metal compounds have attracted the attention of researchers because of their high theoretical capacity,safety and environmental protection.However,when metal compounds are used as electrode materials,they tend to expand in the charging and discharging process,leading to rapid capacity decay,which seriously limits the development of metal compounds as anode materials.In this paper,carbon nanowall and manganese dioxide particles are combined as anode material of lithium ion battery,and the advantages of the two materials are combined to conduct the following research.In this paper,hot wire chemical vapor deposition method was used to prepare carbon nanowall film in methane and hydrogen atmosphere with titanium as the substrate,and Mn O2/CNWs composite electrode was obtained by deposition of manganese dioxide particles on the carbon nanowall film by electrodeposition.Carbon nanowalls were grown on titanium sheets by chemical vapor deposition.The optimum temperature for carbon nanowalls was investigated by controlling the distance between hot wire and substrate to adjust growth temperature.By analyzing the SEM morphology and Raman spectrum,it can be concluded that the carbon nanowall cannot grow effectively at a lower temperature,and the nucleation rate and growth rate of the carbon nanowall will be improved at a higher temperature,but the defects of the film will increase accordingly.When the growth temperature is about 510 ℃,carbon nanowall films with uniform distribution,good quality and fewer graphene layers can be obtained.The effects of gas ratio on the structure and electrochemical properties of the thin films were studied by adjusting the concentration of carbon source at appropriate growth temperature.As the carbon concentration decreases,the length of the carbon nanowall increases,the density of the wall decreases,and the mass of the film increases.The number of graphene layers reflected in the nanowall changes from multiple layers to fewer layers.When the ratio of methane to hydrogen is 1:2,high quality carbon nanowall films can be obtained.Under this condition,the reversible specific capacity of the prepared electrode can reach 199.9 m Ah/g after 100 cycles at the current density of 100 m A/g,showing strong stability.With attached carbon nano titanium plate of the wall for the collection of fluid,using cyclic voltammograms sedimentary manganese dioxide particles,carbon nanotubes wall film as the carrier,can make the manganese dioxide particle uniform distribution at the top of the wall carbon nanotubes,SEM topography and XPS spectrum analysis it is concluded that the appropriate negative voltage can make the deposit of the surface of the manganese dioxide produces a large number of holes.The results show that when the voltage window is-1～1.5 V,the Mn O2 particles with uniform distribution and certain pore structure can be obtained by deposition 10 cycles.The reversible specific capacity of the prepared Mn O2/CNWs composite electrode can reach 533 m Ah/g after 100 cycles at 100 m A/g current density.Manganese dioxide particles deposited by cyclic voltammetry can obviously improve the capacitive properties of carbon materials,and also show good stability as composite materials.