Study On Lithium Storage And Sodium Storage Performance And Modification Of Niobium-based Oxide

The rapid development of consumer electronics and electric vehicle industry has made people's requirements for energy storage batteries more and more high.The energy storage battery not only has the characteristics of long cycle,low cost,safety and pollution,but also meets people's high Requirements for use of power,high energy density batteries.Among them,Niobium-based oxide Nb2O5 has been widely studied as a negative electrode material for lithium/sodium batteries due to its good cycle stability and special Lithium ion intercalation/deintercalation mechanism,but low electron conductivity and ion diffusion coefficient reduce the reversible capacity of Nb2O5,which limits the application of materials under high capacity conditions.Like Nb2O5,TiNb2O7 also has good structural stability and suitable charge/discharge plateau,but the high band gap also makes TiNb2O7 material have poor conductivity.Therefore,this paper designs the appropriate modification scheme to improve the conductivity of the material,and thus improve the charge and discharge performance of the material.The main work content and research situation are as follows:(1)The Nb2O5 precursor material with lamellar flower structure was synthesized by hydrothermal method.The SEM characterization confirmed that the microflower structure was formed by a single nanosheet with a thickness of about 30 nm.The overall dispersal of flowers was good and the structure was regular.The electrochemical properties of Nb2O5 calcined at different temperatures were compared and analyzed.The Nb2O5 obtained at 600°C calcination had higher charge-discharge specific capacity,201.2 mAh/g at 1 C and 147.0 mAh/g at 10 C,which was attributed to the material's own crystal structure and the apparent nanosheet-like structure,the nanosheet has a larger specific surface area,while there were more interstitial sites in the T-phase structure which are beneficial to ion diffusion.The synergy of the ions made the diffusion of ions at a large rate more rapid,and the electrochemical performance of the material was also superior.(2)The pure phase Nb2O5 calcined at the optimum temperature was hydrogenated,and the mechanism of lithium storage and sodium storage was further explored.Electrochemical tests showed that the electrochemical properties of the material after hydrogenation modification were significantly improved in lithium/sodium electricity.The specific charge capacities of the hydrogenated modified materials in lithium battery were 136.6 mAh/g at 30 C and 103.3 mAh/g at 50 C,respectively,which were significantly higher than the charge-discharge ratio of unmodified materials.Electrochemical kinetic analysis of the materials before and after modification showed that the hydrogenated modified material had smaller transfer impedance and higher ion diffusion coefficient(1.38×10~-1616 cm~2/s),and the existence of oxygen vacancies also increased the proportion of Pseudo-capacitive Current in the process of lithium ion de/intercalation.For sodium,the material exhibited the same electrochemical performance as lithium,which confirmed that by forming surface oxygen vacancies,the material electrode reaction rate and the charge transfer capability can be enhanced.(3)The composite modification of the reduced graphene oxide of TiNb2O7material was carried out,and the electrochemical performance of the composite material in sodium ion battery was investigated.The SEM image showed that TiNb2O7 nanoparticles with a size of about 100 nm were uniformly attached to the surface of the reduced graphene oxide sheet,and no obvious agglomeration occurs.According to the electrochemical properties and the Electrochemical Impedance Spectroscopy,the composite had better electron conduction and ion conductivity than the pure phase TiNb2O7.The charge specific capacity of the composite is 201.1mAh/g at 0.2 C and 151.6 mAh/g at 0.5 C,respectively,which was higher than the charge-discharge ratio capacity of the pure phase material,indicating that the reduction of graphene oxide doping was effective to improve the conductivity of the material.