Oxygen Vacancy Regulated TiNb₂O7 Compound And Investigations On Its Enhanced Electrochemical Performance As Anode Materials In Li-ion Batteries

The energy crisis and environmental pollution are increasingly becoming huge challenges for human sustainable development.To solve these problems,promoting the research and development of new energy technologies has become a development strategy vigorously pursued by various countries.Energy storage equipment is the key to new energy technology.Compared with traditional lead storage batteries and nickel-cadmium batteries,lithium-ion batteries have the advantages of high energy density,long cycle life,no memory effect,and environmental friendliness,so it is currently the most ideal energy storage equipment.However,lithium-ion batteries based on graphite anodes have become increasingly difficult to meet the requirements of new smart devices and electric vehicles for larger capacity and higher power density of energy storage equipment.Therefore,the development of a new generation of lithium-ion battery anode materials has become a research hotspot today.TiNb2O7 as an embedded anode material,benefits from its unique ReO3structure on the shear plane.It has a small volume change during charge and discharge,and the lithium compound has excellent thermal stability,so it has good cycle stability.The existence of channels for intercalation of lithium ions between the shear units makes them have good rate performance at the same time.However,TiNb2O7 itself has poor electrical conductivity,which affects its performance when used as a negative electrode material for lithium ion batteries.At present,there are two main methods for the modification of TiNb2O7:one is to construct special micro-morphology by means such as electrostatic spinning,strengthen the contact between the electrolyte and the material,and shorten the lithium ion intercalation pathway to improve the electrochemical performance of TiNb2O7.The second is to compound TiNb2O7 with a material with good conductivity to improve its conductivity,such as surface carbon coating.The disadvantages of these two methods are that the technology is complicated,the cost is increased,and the effective load of the negative electrode material is reduced,thus the electrochemical characteristics of the materials might be damaged.In order to avoid the shortcomings of the above methods and explore a simple and effective new method to improve the electrochemical performance of materials.In this paper,supercritical fluid treatment is used to introduce oxygen vacancies in TiNb2O7 compound,and the mechanism of improving the electrochemical performance of materials after introducing oxygen vacancies is studied in detail.The main work and conclusions of this study are as follows:after hydrothermal treatment of niobium chloride and titanium isopropoxide in a molar ratio of Nb and Ti in TiNb207,the precursor is obtained by centrifugation.Two kinds of samples with oxygen vacancies are obtained by calcining the precursor in argon atmosphere and supercritical ethanol treatment of pure phase TiNb2O7.XRD,HRTEM SEM,BET and other testing methods proved that the crystal structure and micro morphology of the two oxygen vacancy samples are consistent with those of the pure phase samples.XPS and ESR tests proved that supercritical ethanol treatment introduced more oxygen vacancies in the material than calcination in argon atmosphere.The conventionally synthesized TiNb2O7 and two kinds of oxygen vacancy regulated samples were prepared into half-cell and tested for electrochemical performance.It is found that with the increase of oxygen vacancies,the rate performance and cycle stability of the samples were significantly improved.In order to study the mechanism of the oxygen vacancies to improve the electrochemical performance of TiNb2O7,the conductivity of the powder sample,the impedance of the half-cell system and the pseudocapacitance capacitance are tested.The results show that the existence of oxygen vacancies generates an adaptive built-in electric field on the surface of the material,which improves the material's electrical conductivity and enhances the capacitance control during the charge and discharge process of the material,so that samples with more oxygen vacancies have better cycle stability performance,higher reversible capacity and better rate performance.The work in this thesis proves that supercritical ethanol treatment of TiNb2O7 can effectively introduce oxygen vacancies and significantly improve the cycle performance and rate performance of the material.Such method is facile,quick,effective and environmental benign.This work would provide a new strategy and approach for enhancing the electrochemical performance of multi-component oxides as electrode materials.