Study Of Class Graphene-Coated Graphite Oxide Anode Material For Lithium-Ion Batteries

As we know, graphite has been widely used in lithium ion battery anode material owing to its many advantages, such as low expansion characteristics, high security, high stability, abundant raw materials, low cost and etc.. However, graphite is also embracing a variety of challenges in the electronic area. To put it differently, if a battery bearing such disabilities, for example, low specific capacity, along with the poor rate performance and the low first coulomb efficiency as well, it will gradually become fall to meet the developing needs and progression expectation of the lithium ion battery. This decade witnesses a rapid developing requirement for advanced lithium ion batteries capability standard, following with the constantly growing high-performance graphite anode material. To achieve escalation of electrochemical performance of graphite anode material, the oxidation modification and carbon-covering of graphite had been being under a limelight of the academic circles. This is because oxidization of carbon electrode materials could provide with relative superior structure which carrying less inappropriate sp³ hybridization and the fragile chain-like pattern. In fact, compare with raw material, graphite oxide?GO?, oxidized from high-purity graphite, will rain benefits on elevating the lithium battery capacity, via increasing the endurance of the graphite structure while irreversible capacity decreased, and specific capacity of graphite material, thereby, will be increased as a whole. Also, initial Coulomb efficiency can be promoted by planting oxygen atom between the layers, expanding the distance of graphite sheets, contributing to shape a thin and even SEI film, and improving the stability of the graphite material finally. In addition, GO after carbon-coating procedure, can obtain smoother surface, which tend to form a more compact SEI film, enhancing the first Coulomb efficiency of this materials consequently. From what has been stated above, the theme of this thesis is the preparation of high-performance graphite anode materials by the oxidation modification and carbon covering.In this paper, high purity graphite as raw materials, GO is prepared by using the non-toxic and pollution-free liquid phase hydrogen peroxide oxidation style or gas phase air oxidation style to oxidize high purity graphite respectively. Then the liquid acrylonitrile oligomer?LPAN? as the carbon source, the LPAN and graphite oxide are mixed with water as solvent. Eventually after high temperature carbon covering, the class graphene coated graphite oxide lithium ion anode materials is prepared.Firstly, high-purity graphite as an active substance, acetylene black as a conductive agent, the SA, PVDF, CMC traditional anode material binders and SBR emulsion/CMC binder are respectively made into half-cell in order to test electrochemical performance. Test results indicate that according to the material quality ratio of high purity graphite:CMC:SBR: acetylene black = 93:3:3:1, water as a solvent and SBR emulsion/CMC as a binder to make a pole piece which forms the thinner SEI film, better film uniformity and higher initial coulombic efficiency by constant current charge and discharge test. In addition, using quality ratio of active substances: CMC: SBR: acetylene black = 93:3:3:1 as anode material for coating, which can greatly reduce the amount of binder and acetylene black to save a number of costs.Then, through the study of graphite oxidation process and the preparation technology of class graphene, the following conclusions can be drawn. The optimum conditions for air oxidation style to prepare class graphene-coated graphite oxide lithium ion battery anode materials are as follows. The oxidation is carried out under air at 350 ? for 4 h. The additional quality of LPAN is 25% of graphite oxide. Pre-oxidation temperature is 220 ?, whose holding time is 3 h. Its coating temperature is 1000 ? with the holding time for 4 h. Nevertheless, the optimum conditions for hydrogen peroxide oxidation style to prepare class graphene-coated graphite oxide anode materials are as follows. The added ratio of high purity graphite and?30 wt.%? hydrogen peroxide is 1 g:40 m L. Graphite oxidation temperature is 80 ? with its oxidation time for 2 h. The rest sintered coating process is same as the preparation method of the air oxidation style.Finally, through a series of tests and analyses, it is found that class graphene-coated graphite oxide lithium ion battery anode material C/O₂-350?-LPAN-1000 ?, which is prepared by simple and convenient gas-phase air oxidation style, has obvious advantages of electrochemical performance. Its high specific capacity is 493.7 m Ahg-1. It has a high initial coulomb efficiency that is 90%. Besides, its cycling stability, cycle efficiency and rate capability are good. In contrast, the class graphene-coated graphite oxide lithium ion battery cathode material C/H₂O₂-LPAN-1000 ?, which is prepared by the non-toxic and pollution-free liquid phase hydrogen peroxide oxidation style, has more excellent electrochemical properties, such as its wonderful cycling stability, great cycle efficiency, good rate capability, etc.. Besides, it has the higher initial coulomb efficiency that is 90.9%. What is more important is that it owns higher specific capacity for 541.7 m Ahg-1. After compared with the two materials, result is gotten that the class graphene-coated graphite oxide lithium ion battery anode material C/H₂O₂-LPAN-1000 ? has higher specific capacity, larger initial coulomb efficiency, better cycle efficiency, more durable cycle stability and higher rate capability, which is far exceeding the commercial graphite of lithium ion anode material. Therefore, it exhibits enormous potential for application of the lithium ion battery anode materials in the future.