The Design, Synthesis Of The Core-shell Metal Oxide Nanocomposites And The Research On Its Lithium Storage Properties

As early as a few decades ago, rechargeable lithium ion batteries（LIBS） is infocus, because it is considered to be one of the most important green energy storagetechnology.Recently, the demand of the higher capacity, higher power density, bettercycle performance, and better rate capbility LIBS has been raised, particularly in theapplication of hybrid vehicles.Graphit，as one of the most commonly used commercialanode materials, due to its low theoretical capacity of372mAh g-1, the poor high-rateperformance, and the security problems of itself, has been unable to meet the increasingdemand.Due to its high theoretical capacity,transition metal oxides is considered to be themost promising material which can take the place of graphite.However，it will inducegreat volume expansion in the process of Lithium inserting(it s generally considered tobe300%).These materials usually show short cycling life.So,in order to improve theperformance of these materials,people usually use the following twomethods: Making these materials to be nanostructures (nanorods, nano films,etc.). Coating with other materials (The most commonly used material is carbon.)Forinstance, Due to its high theoretical capacity (1007mAh g-1), chemical and thermalstability, natural abundance, low cost, environmental benignity and the advantage ofbeing easily to made nanostructures with suitable size,we select Fe2O3as the core andcoat it with other materials.The carbon shell usually shows poor safety performancewhen it is overcharged. So we select TiO2with high safety performance, outstandingrate capability and no volume expansion as the shell to coat Fe2O3. The compositematerial with one dimensional mesoporous core-shell nanostructures shows stable reversible capacity as high as~860mAh g-1at high current density of1A g-1,excellent cyclic stability with ultralong cycling life over1000cycles.Due to its porousstructure,the material also shows excellent photocatalytic activities in both UV andvisible light region.After80min, up to90%of MO has been degraded by theheterogeneous photocatalyst, exhibiting its excellent photocatalytic activity. Inaddition,it delivers apparently enhanced photocatalytic activity on MO degradationunder visible light, which photodegrades70%of MO after irradiation of6hours.The main work are：⑴The synthesis of materials： Prepair the precurs FeOOH from FeCl3in Hydrothermal Synthesis method； Prepair the precurs FeOOH@TiO2core-shell nanorods in St ber method； Mesoporous core-shell nanocomposites with porous Fe2O3nanorods as the coreand porous TiO2as the shell are synthesized by calcination treatment of FeOOH@TiO2coreshell nanorods.⑵Characterization and performance testing of materials：Characterization and testing of the electrochemical properties:The sample is characterized by powder X-ray powder diffraction (XRD, PhilipsX’-pert X-ray diffractometer, Cu Kα radiation:λ=0.154056nm), scanning electronmicroscope (SEM, JEOL JSM-7500F scanning electron microscope) equipped with anenergy dispersive spectroscopy (EDS) probe, and transmission electron microscope(TEM, JEOL JEM-2100). N2adsorption/desorption isotherms of the product aremeasured at77K using Micromeritics Co. Ltd., Tristar. The total specific surface area isdetermined with the multipoint Braunauer-Emmett-Teller (BET) method.The sample istested by LAND battery testing system.Characterization of the photocatalytic performance:The as-obtained samples are investigated with scanning electron microscope(SEM, JEOL JSM-7500F) equipped with an energy dispersive spectroscopy (EDS)probe for the element analysis, transmission electron microscope (TEM, JEOLJEM-2100), and powder X-ray powder diffraction (XRD, Philips X’-pert X-raydiffractometer,). N2adsorption-desorption isotherms of the product are measured at77K using Micromeritics Co. Ltd., Tristar. The total specific surface area is determinedwith the multipoint Braunauer-Emmett-Teller (BET) method. UV-visiblediffuse-reflectance spectra (DRS) are obtained on a Cary-500UV-Vis-NIRspectrometer with BaSO4powder as the internal standard to obtain the optical properties of the samples over the wavelength range of300-800nm.Photoluminescence (PL) spectra are recorded with a Hitachi F-2700FluorescenceSpectrophotometer at room temperature. The sample is evaluated with the degradationof methyl orange (MO), which is a typical model pollutant, in aqueous solution underthe irradiation of both visible and UV light.