Synthesis,Structure And Properties Of Li₃VO₄ Anode For Lithium Ion Batteries

Traditional batteries could not meet the needs of the market with the rapid development of electronic products and electronic vehicle industries.Thus,it's especially important to do research and development on higher energy density lithium ion batteries.Anode is the key part of a lithium ion battery,which has already had broad attention.Nowadays,both of the commercial anodes,graphite and Li4Ti5O12 material,have unsolved problems.Li dendrites are easily formed on the surface of graphite,and the electrochemical performance at high current density is unsatisfactory.Li4Ti5O12 material has a high potential platform and low theoretical specific capacity,leading to a low energy density.Li3VO4 anode material has a high theoretical specific capacity of 394 mAh·g-1,a proper potential for Li+ insertion/de-insertion and a good rate capacity.Therefore,the study about Li3VO4 is significant.In this thesis,the synthesis routes and calcined temperatures were studied to find out the best conditions.In-situ techniques such as in-situ XRD and in-situ EIS were used to study the structure changes and interface properties of Li3VO4 anode during the initial cycle.Mn element was mixed within Li3VO4 material to get a new anode material of Li3V1-xMnxO4,which could improve the capacity.Find out the reason for improving capacities and study the influence of Mn element by CV,in-situ XRD and in-situ EIS.Here are the main results:1.The best synthesis route was sol-gel method,and the best calcined temperatures was 550?.This kind of Li3VO4 material had the best electrochemical performance.2.The lithium storage behaviors of the prepared Li3VO4 material were studied by in-situ XRD and in-situ EIS techniques.In-situ EIS experiment was performed during PITT process to discuss the formation of the solid electrolyte interface(SEI)on the Li3VO4 and the kinetics of lithium ion diffusion.The results showed that the irreversible process of phase II was one of the significant reasons for the low initial coulombic efficiency,as well as the formation of SEI.3.The addition of Mn element lead to a new phase Li2MnO3.It is proved that Li3V0.93Mn0.07O4 had the best improvement of the electrochemical performance.The reason for the capacity improvement was probably the direct contribution of Mn element.The intercalation/de-intercalation of Li+was proved by the changes of structure observed by in-situ XRD experiment.The result of in-situ EIS experiment showed that Mn element had little influence on the diffusion coefficient of Li+ and the solid electrolyte interphase,while promoted the charge transform process.