Preparation And Properties Of TiO₂-based Materials With Oxygen Vacancies For Lithium-ion Battery Anode

Lithium-ion batteries have been widely used in the fields of consumer electronics,electric vehicles and large-scale energy storage due to its excellent electrochemical properties.In particular,with the swift and violen development of emerging industries such as artificial intelligence,wearable equipment,flexible display and robot in recent years,it has a more promising future.As one of the core of lithium-ion batteries,negative electrode has always been a hot spot of research.Served as anode materials for lithium-ion batteries,the anatase TiO₂ possesses good cycling stability and safety performance.Nevertheless,poor electronic conductivity and sluggish Li⁺diffusivity in crystal lattice of the anatase TiO₂ materials confine its electrochemical properities tremendously.In this thesis,we research TiO₂ based materials containing oxygen vacancies preparaed by different approaches and its impact for electrochemical performance when used as anode materials.Anatase TiO₂ nanosheets were synthesized by a simple hydrothermal approach,and then anatase TiO_2-x with different oxygen vacancy concentration were prepared by hydrothermal reduction of hydrazine aqueous solution at different volume fraction.We investigate that how oxygen vacancy influence the performance of the battery.The results show that compared with the pure anatase TiO₂nanosheets,the TiO_2-x with oxygen vacancies has better electrochemical performance.Furthermore,the specific capacity,cycle and rate performance of TiO_2-x-1%material is the best when the volume fraction of hydrazine hydrate is 1%.Using graphene oxide as carbon source,TiO₂@RGO nanocomposite material was prepared by a one-step hydrothermal synthesis.Subsequently,we obtain TiO₂@RGO-H composites containing oxygen vacancy by heating TiO₂@RGO in the H₂ atmosphere at 500°C and synergistic effect of oxygen vacancy and reduction graphene oxide in the TiO₂@RGO-H composites on the electrochemical performance of the batteries was studied.The results show that the charge and discharge capacity of TiO₂@RGO-H composites can reach 135.3 mAh g^-1 and 135.5 mAh g^-1 at 200mA g^-1 respectively after 200 cycles.Simultaneously,the coulombic efficiency and capacity retention rate is 99.85%and 79.3%,accordingly.Anatase TiO₂-R with nanorod-like structure was prepared by hydrothermal process firstly and then we obtain TiO_2-x-R nanorods containing oxygen vacancy by reducing TiO₂-R in 1 M aqueous sodium borohydride at room temperature.The influence of different structure and morphology of anatase TiO₂and oxygen vacancy on the electrochemical performance of lithium ion battery was researched.The test results show that the initial charge and discharge specific capacity of TiO_2-x-R material is 156.8mAh g^-1 and 197.3 mAh g^-1 at 1 C,respectively.In the meantime,its initial coulombic efficiency is79.5%.The charge specific capacity of the lithium-ion battery is 95.4 mAh g^-1 and the capacity rention rate is about 60.8%after 50 cycles.