Preparation And Electrochemical Performance Of Vanadium Oxide-based Microspheres

Vanadium oxides have been studied as the electrode materials for rechargeable LIBs because of its low cost,abundance,special layered or open-framework structure as well as its high special capacity and power density.V2O5 and V2O3 were studied as the electrode materials in LIBs in this thesis,including the synthesis of hierarchical V2O5 and V2O3 microspheres and their modified electrode materials of Al2O3/V2O5 by doping and V2O3/C by carbon coating,morphology and the electrochemical performances.The main results are as follows:1)The monodisperse hierarchical V2O5 hollow microspheres were synthesized by a template-free microthermal solvothermal method,followed by calcination at 400 ?,for the first time using VO(acac)2 as raw material.The diameters of the hollow microspheres are around 400-550 nm with the shell thickness of 55 nm,in which the building blocks are the nanosheets with the length of 80-130 nm,the width of 50-80 nm and the thickness of 10-25 nm.These hollow microspheres show excellent electrochemical performance.The discharge capacity can reach 284.2 and 239.7 mA h g-1 at 0.2 and 0.5 C,respectively.The capacities remain 87%and 83%,respectively after 30 cycles at room temperature.2)The uniform hierarchical Al2O3/V2O5 hollow microspheres with good dispersibility were synthesized by a template-free microthermal solvothermal method,combined with calcination at 450 ?,using VO(acac)2 and Al(O-i-Pr)3 as raw materials.The hollow microspheres are constructed by the nanorods with the widths of 30-70 nm and 50-110 nm in length,with the diameter of the microspheres of 300-450 nm and the shell thickness of 40-65 nm.The composite material exhibits improved cycling stability by doping the Al2O3 especially at high rates(1 and 2 C).The capacity of the sample with the Al(O-i-Pr)3 addition of 0.0167 g remains above 87%after 30 cycles at room temperature.3)The monodisperse V2O3/C microspheres were synthesized by a simple template-free solvothermal method,followed by 600 ? calcination under N2/H2 atmosphere,using VO(acac)2 and glucose as raw materials.The diameters of those microspheres are around 200-450 nm,in which the building blocks are the nanoparticles with the diameter of 10-70 nm.The composite microspheres were utilized in LIBs as an anode material for the first time.After the carbon coating,the composite material exhibits improved electrochemical performance,including enhanced capacity and cyclability.The capacity of those microspheres remains above 66%after 40 cycles at the current densities of 500 mA g-1.