Reasearch On Fabrication And Modification Of Niobium-based Oxide For Electrochemical Energy Storage

Lithium-ion battery with the advantage of long cycle life,high energy density,safety has become the most attracted energy storage device.Due to its high power and excellent cycling performance,Li₄Ti₅O₁₂ has been extensively studied as a negative electrode material for lithium ion battery,however,its lower specific capacity limits its application.Compared with Li4Ti5O12,niobium-based oxide with high specific capacity and similar intercalation lithium potential is expected to become a new type of power lithium-ion battery anode material.However,its poor conductivity restricts the use of niobium-based oxides.Therefore,this paper aims to improve the conductivity of the material through the combination with graphene and carbon coating,and thus enhance the electrochemical performance.The specific research contents are as follows:The Nb3O7F material was prepared by hydrothermal method and further modified with graphene.The influence of graphene content on the electrochemical performance was studied.Results show that when the mass ratio of Nb₃O₇F and graphene is 8 to 1,the sample exhibits the best electrochemical performance.At a discharge current density of 2000 mA·g^-1,the specific capacity of the sample reaches 95.7 mAh·g^-1,while the pure Nb₃O₇F is only 36.1mAh·g^-1.Furthermore,the capacity retention is 73.7%under 500 mA·g^-1 current density over500 cycles,indicating that the introduction of graphene contributes to improve the overall electrochemical properties of Nb₃O₇F.The ZnNb2O6 material was prepared by the solid-phase method and the carbon shell coating was obtained by using glucose as the carbon source.The result shows that the carbon is successfully coated on the surface of ZnNb₂O₆.When the mass ratio of ZnNb₂O₆ and glucose is 10 to 1,the electrochemical performance is the best.At the current density of 2000mA·g^-1,the specific capacity of sample can reach 85.2 mAh·g^-1,the specific capacity of the electrode is 170.9 mAh·g^-1 after 1000 charge-discharge cycles at a current density of 500mA·g^-1 with a capacity retention of 84.4%,indicating that the material has good cycling stability after carbon coating.The nano-sized ZnNb₂O₆ material was prepared by hydrothermal method.Compared with the micron-sized ZnNb2O6 materials obtained by the solid-phase method,the nano-ZnNb₂O₆ has better rate performance and cycling performance.When the current density is 50,100,200,500,1000 and 2000 mA·g^-1,the specific capacity is 303.5,214.9,183.3,134.9,105.8 and 72.9 mAh·g^-1,respectively.At 500 mA·g^-1,the capacity loss is 15.2%after 1000 charge-discharge cycles.The results show that the smaller size of the material has better electrochemical performance.The TiNb₂O₇ material was prepared by solvothermal method.Co-coating of TiNb₂O₇with C and N using glucosamine hydrochloride as carbon and nitrogen source was studied.The results indicated C and N were found uniformally distributed on TiNb₂O₇ surface.The electrochemical tests of TiNb₂O₇ with different coating amounts showed that when the mass ratio of TiNb₂O₇ and the glucosamine hydrochloride is 20 to 1,the electrochemical performance is the best,and the discharge capacity at 0.1C,0.2C,0.5C,1C,2C and 5C rate is268.9,251.5,236.7,223.9,202.5 and 184.1 mAh·g^-1,respectively.The capacity retention rate is 90%over 500 cycles at 5C,indicating that co-coating with C and N can improve TiNb₂O₇rate performance and cycling performance.