Study On The Preparation, Microstructure And Lithium Storage Performance Of Iron-titanium Bimetallic Oxide

With the development of society,the demand for energy is increasing.The traditional energy has limited resources,and can easily cause environmental pollution,thus it is gradually replaced by other clean energy.Lithium ion batteries(LIBs)stand out from the new energy sources because of their high energy density and environmental protection.Anode material,as one of the important part of LIBs,determines the whole battery performance.However,the low theoretical specific capacity of the anode material in traditional LIBs seriously limits its applications.As a new type of anode material for LIBs,transition metal oxides(TMOs)have attracted more attention due to their high specific capacity,abundant resources and safety in use.However,when the TMOs are used as the anode material,there are some problems in the charge-discharge process,such as poor cycle stability and conductivity.Therefore,the construction of high-performance TMOs anode materials is of great significance for the application and development of LIBs.In this thesis,the composition,microstructure and stability of Fe2TiO5 were studied,and its electrochemical properties and lithium storage mechanism were explored.(1)Fe2TiO5 nanoparticles(NPs),Fe2TiO5/TiO2 and Fe2TiO5/Fe2O3 mixture were prepared by a solvothermal method.The effects of components on electrochemical properties were systematically investigated.It is found that the reversible specific capacity of Fe2TiO5 NPs is 810.4 mAh g-1 after 200 cycles,which is higher than that of Fe2TiO5/TiO2(340.8 mAh g-1)or Fe2TiO5/Fe2O3(214.2 mAh g-1).In addition,Fe2TiO5 NPs show the best rate performance among the three materials.(2)The effects of electron-beam irradiation on the morphology and microstructure stability of Fe2TiO5 NPs produced by a solvothermal method,with or without the addition of polyvinyl-pyrrolidone(PVP)were studied by in-situ transmission electron microscopy.For the Fe2TiO5 NPs produced without adding PVP,their structure and morphology show no obvious changes under electron beam irradiation.However,for the Fe2TiO5 NPs produced with PVP,they undergo three distinct stages of morphological evolution under the electron beam irradiation,namely,layer exfoliation,local pulverization,and amorphization.The different behaviors are attributed to the fact that PVP can generate oxygen vacancies in Fe2TiO5.The thermal effect and knock-on collision caused by the electron beam play a dominant role in the morphological changes of Fe2TiO5 NPs produced with PVP.(3)The electrochemical properties of Fe2TiO5 NPs prepared with and without PVP were investigated.The Fe2TiO5 NPs produced with PVP demonstrate better electrochemical performance than those produced without PVP,which is ascribed to the fact that the addition of PVP results in more oxygen vacancies in Fe2TiO5 NPs.These oxygen vacancies can provide more active sites in the reaction,which is conducive to promoting the diffusion of Li+and the transfer of charge,so as to improve the conductivity of Fe2TiO5 materials.Moreover,the existence of oxygen vacancy can alleviate the structural deformation of Fe2TiO5 NPs electrode in the charge-discharge process,thus improving the cycle stability of the electrode material.