Research On Rate Performance Of Flake Graphite Anode Material Of Lithium Ion Battery

The influence of particle size on the graphite electrochemical performance wasstudied. The natural flake graphite was modified by following methods: surfaceoxidization、surface carbon coating、combination of former two methods to improvethe rate performance and cycle performance of graphite.Several methods were used to measure the structure and properties of graphite, suchas SEM、XRD、CV and charge-discharge testing, the results shown that smaller particlesize of graphite has better performance. Three different particle size of graphites11μm、17μm and20μm are studied, and when the average particle size is17μm, the graphitehas best rate performance. The capacities of the graphite are362.4mAh/g、331.7mAh/g、282.2mAh/g、134.5mAh/g、88.3mAh/g and29.9mAh/g corresponding to the rates0.1C、0.2C、0.5C、1C、2C and5C.The natural flake graphite was oxidized by H2SO4+H2O2, and then expanded in400℃for5h. The oxidation didn’t change the structure of graphite, but it increased thed002of graphite, this is conducive to the lithium ion intercalation and de-intercalationbetween graphite layers. The oxidation also decreased cycle performance of graphite.The capacities of graphite, which is oxidized for1h, are368.9mAh/g、349.0mAh/g、333.9mAh/g、184.6mAh/g、119.3mAh/g and36.2mAh/g corresponding to the rates0.1C、0.2C、0.5C、1C、2C and5C. And after150cycles in1C rate, its capacity retentionis68.5%, which is higher than natural graphite’s74.4%. The oxidation of naturalgraphite improved its rates performance, but decreased its cycle performance.The carbon coated graphite was prepared by impregnating graphite in a mixture ofphenolic resin and ethyl acetate, and then stirring in80℃, followed by carbonization.The results show that carbon coated of graphite doesn’t change its structure. When themass ratio of carbon and graphite is5:95, the sample that obtained has higher capacity.The capacity of carbon-coated graphite are368.4mAh/g、352.0mAh/g、345.2mAh/g、232.5mAh/g、141.4mAh/g and43.9mAh/g corresponding to the rates0.1C、0.2C、0.5C、1C、2C and5C, and after150cycles in1C, its capacity retention is83.2%.,which is improved8.8%relative to natural graphite.The natural graphite was oxidized in H2SO4+H2O2solution for1h and then carboncoated. The modified graphite has better cycle performance and higher capacity in different rates. The capacities of modified graphite are348.9mAh/g、281.1mAh/g151.8mAh/g and50.1mAh/g corresponding to the rates0.5C、1C、2C and5C, whichincreases66.7mAh/g、146.6mAh/g and63.5mAh/g relative to natural graphite. After150cycles in1C, its capacity retention is83.8%, which increases9.4%relative tonatural graphite.