Preparation Of Niobium-based Oxide And Its Application In Lithium Storage And Photocatalysis

Niobium oxide is widely used in energy storage and photocatalysis due to its excellent physical and chemical properties.However,the low intrinsic electron conductivity of niobium base oxide as anode material for lithium ion battery affects its electrochemical performance.As a photocatalyst,its wide band gap leads to its narrow optical response range.In order to improve the lithium storage and photocatalytic performance of niob-based oxides,this paper improved the lithium storage and photocatalytic performance of niob-based oxides from two aspects:preparation and modification.The main content of this paper is as follows:（1）.The precursor of T-Nb₃O₇F phase composed of nano-sheets was prepared by hydrothermal method using HF as morphology regulator and F source,and then the flower-like F-Nb₂O₅ was synthesized by topological conversion.Micron flower-like F-Nb₂O₅ was assembled from single crystal nanosheets with a thickness of about 20 nm and a size of about 1μm×2μm,with an average size of about 5μm and 97%（100）crystal surfaces exposed.The band gap of F-Nb₂O₅ is reduced to 2.87 eV by F atom doping,which improves its electrical conductivity.The special exposed crystal surface,the synergistic effect of F atom doping and the three-dimensional multistage structure make F-Nb₂O₅ have high Li⁺ion diffusion coefficient and excellent pseudocapacitance characteristics,so that it has excellent electrochemical performance:The high reversible specific capacity of 132.7mAh g^-1 can be provided even after 1500 cycles at 10 C magnification,and the capacity retention rate is 81.5%.（2）.Three-dimensional sea urchin-like MoNb₁₂O₃₃ microspheres were prepared by simple hydrothermal method and subsequent annealing process.The urchin-like microspheres were assembled from one-dimensional radially oriented nanorods with a diameter of about 50 nm and a diameter of about 3μm.CV and EIS tests show that MoNb₁₂O₃₃ has high pseudo capacitance,low charge transfer resistance and high lithium ion diffusion coefficient.The sea urchin MoNb₁₂O₃₃ microspheres showed excellent electrochemical performance as anode material for lithium-ion batteries:the specific capacity of the microspheres could still reach 168 mAh g-1 even at 20 C over the ratio,and the capacity retention rate reached 90%after 500 cycles at 10 C.In addition,the whole battery assembled with the commercial LiNi_0.5Mn_0.3Co_0.2O₂ also showed excellent electrochemical performance:the reversible capacity of 120 mAh g-1 was maintained after2500 cycles at 10 C.（3）.Ti₂Nb₁₀O₂₉ mesoporous microspheres were prepared by solvothermal method,and then Ti₂Nb₁₀O₂₉@F-C composites were prepared using PVDF as carbon and fluorine sources.Ti₂Nb₁₀O₂₉@F-C composite materials are composed of many interconnected nanoparticles with the size of 50-120 nm,with an average size of about 1～1.5μm mesoporous microspheres,with large pore volume and specific surface area.Due to the synergistic effect of the large surface area and the coating of the F-doped carbon layer,Ti₂Nb₁₀O₂₉@F-C composites show excellent electrochemical performance:even at the ultra-high current density of 30 C,the reversible specific capacity can still reach 211 mAh g^-1,which is 66mAh g^-1higher than that of Ti₂Nb₁₀O₂₉.In addition,the anode assembly for Ti₂Nb₁₀O₂₉@F-C LiNi_0.5Mn_0.3Co_0.2O₂||TNO@F-all cells showed excellent electrochemical performance:in 0.5,1,2,5 and 10 C reversible capacity respectively 209,196,176,141 and111 mAh g^-1;After 500 cycles at 10 C rate,the capacity remained at 64%.（4）.The prepared F-Nb₂O₅,sea urchin MoNb₁₂O₃₃ and Ti₂Nb₁₀O₂₉@F-C were used as photocatalysts to degrade Rhodamine-B.The results showed that F-Nb₂O₅ had the highest degradation rate of 99.5%of Rhodamine-B solution,which showed good photocatalytic activity.However,MoNb₁₂O₃₃ and Ti₂Nb₁₀O₂₉@F-C are not ideal as photocatalysts.