Preparation And Electrochemical Performance Of Natural Flake Graphite Spheroidized Micropowder Based Anode For Lithium-ion Battery

Natural flake graphite has been used as a raw material for the production of lithium-ion battery anodes,and its production process usually includes steps such as spheroidization,purification,and surface coating modification.The spheroidization step usually produces a large number of micropowders with fine particles and large specific surface area,which are mostly used as raw materials for the production of low value-added products such as lubricants and refractories.In order to realize the high-value utilization of spheroidized graphite micropowder,this thesis starts with the research of wet purification process,and conducts research on the preparation of high-performance negative electrode materials for lithium-ion batteries using it as raw material.The effects of different coating and granulation methods on the properties of spheroidized micropowder were mainly discussed.The main research contents and conclusions obtained in this paper are as follows:(1)The spheroidized micropowder was purified by a step-by-step purification process of hydrofluoric acid treatment followed by hydrochloric acid and the one-step purification process of a mixed acid of hydrofluoric acid and hydrochloric acid.It is shown that the two methods can effectively remove impurities in the micropowder.Comparing the two purification processes,when the purification effect is not much different,the one-step acid method requires less acid,the leaching time is short,and the overall process is shortened.The fixed carbon content of the material reaches 99.72%.(2)Firstly,the purified micropowder is granulated and coated by liquid phase method using the solution obtained by dissolving asphalt in tetrahydrofuran as a granulation coating agent.When the amount of asphalt in the coating solution was 10%,the tap density of the prepared carbon-coated micropowder was 15.5%higher than that before coating,reaching 0.537 g/cm~3.The specific surface area decreased to 8.70 m~2/g from 11.76 m~2/g before coating.The coulombic efficiency for the first time increased by about 5%compared with that before coating,reaching90.95%.Although liquid phase coating can improve the comprehensive properties of micropowders,the products obtained by coating still have problems such as low tap density.(3)The purified micropowder was processed by granulation coating by mechanofusion method.When the coating asphalt content is 10%,the specific surface area of carbon-coated micropowder is 5.02 m~2/g,the tap density is 0.902 g/cm~3,and the first Coulomb efficiency is 91.36%.By further reducing the heating rate of the carbonization process,the problem of uneven carbonization in the carbonization process of the coated pitch can be solved,and better coating effect and uniform particles can be obtained.Under the optimal carbonization temperature regime,the obtained material has a tap density of 0.922 g/cm~3,a D50 of 11.67μm,a specific surface area of 3.15 m~2/g,and a first Coulomb efficiency of93.12%.After 200 cycles at a rate of 0.5C,there is still a capacity retention rate of 85%,and after 400 cycles at a rate of 0.2C,the capacity retention rate is still 79%,indicating that the material has good cycle stability.