Preparation Of One-Dimensional Carbon-Based Nanostructure Composites For Electrochemical Energy Storage

Energy is an essential material basis for human survival and development.With the rapid exhaustion of non-renewable fossil fuels and aggravation of environment problems,the development of renewable and clean energy such as,wind,solar,biomass,tide and geothermal is becoming more and more important.So,a largescale energy storage system becomes extremely necessary to modulate intermittent renewable resources and integrate them into the grid safely and smoothly.Among various kinds of energy storage device,lithium/sodium ion batteries with the advantages of high energy density,long cycle life,low cost and environmental friendly have become the potential batteries for grid energy storage and electric cars.Anode material is an indispensable constituent part of lithium ion battery,which determines the overall performance of the lithium ion battery to a large extent.Carbon nanomaterials have many unique properties in morphology,electrical conductivity and mechanical properties,but their specific capacity is low.Therefore,carbon nanocomposites based on electrostatic spinning technology are considered as an ideal choice for new electrochemical energy storage device electrode materials.In this thesis,we prepared porous TiO₂@NC coaxial nanotubes and Sb/CNFs nanocomposites.While studying the battery performance of the materials,we also paid attention to the energy storage mechanism and reaction mechanism of the materials,laying a solid foundation for the subsequent development of high-capacity electrode materials.The main research content and innovation points are as follows:(1)The porous TiO₂@NC coaxial nanotubes were firstly prepared by a template method and polymerization/carbonization technique.Firstly,PAN was prepared by electrospinning technique as a template.An amorphous TiO₂ layer was uniformly coated on the surface of PAN nanofibers via a situ-hydrolysis process of Ti(OBu)₄under high-humidity atmosphere.Next,the PAN templates underwent pyrolysis in air as well as the anatase TiO₂ nanotubes formed.Afterwards,conductive PPy layer was deposited on the TiO₂ nanotubes to yield coaxial TiO₂@PPy nanotubes.Finally,the resultant TiO₂@PPy nanotubes were treated at400°C in argon atmosphere.TiO₂@NC coaxial nanotubes were successfully obtained.As applied for lithium ion batteries anode material,It was found that the as-obtained TiO₂@NC anode exhibited remarkable electrochemical specific capacity values of 480 mAhg^-1 and 235mAhg^-1 at current densities of 0.1 Ag^-1 and 0.5 Ag^-1,respectively,which was much higher than bare TiO₂ and TiO₂@polypyrrole(TiO₂@PPy)electrode.Conductive N-doped porous carbon coating with large specific surface area can improve electronic conduction,increase lithium diffusion pathways,and refrain from aggregation and volume change.(2)Sodium ion battery has similar physical and chemical properties to lithium ion battery,but compared with lithium ion resource with higher cost,sodium in the earth's crust has more abundant reserves and lower cost,so sodium ion battery as a lithium ion battery alternative battery has attracted a lot of people's research interest.Sb/CNF nanocomposites were further prepared by electrostatic spinning.Reasonable structural design,Sb uniform embedded in carbon nanotubes,in order to determine the optimal composition of the optimization of Sb content.In addition,potassium antimony tartrate contains K⁺,which is used as a pore-forming agent to improve the porosity and specific surface area of carbon fiber.The abundant pore structure in Sb/CNF composite can offer electrolyte effortless access to contact the embedded Sb nanocrystals,thus promote the play of active materials to a greater extent in energy-storage applications.It was found that the as-obtained Sb/CNFs anode exhibited remarkable electrochemical specific capacity values of 462 mAh g^-1 and 404 mAhg^-1 at current densities of 0.1 Ag^-1 and 0.5 Ag^-1,respectively.In addition,electrolyte transports in different pore sizes were given to verify this phenomenon by molecular dynamic simulations.