The Preparation And Electrochemical Performance Studies Of Mesocarbon Microbeads

The development of lithium ion batteries and carbon anode materials, especially MCMBs, are reviewed in detail. The synthesis and properties of anode materials are studied by using various electrochemical methods in combination with Brunauer-Emmer-Teller (BET) surface area measurement, powder X-ray diffraction (XRD), inductively coupled plasma (ICP) spectroscopy, particle size analysis, and so on. The whole process of producing technique of lithium ion batteries is also developed.Mesocarbon microbeads are prepared from coal tar via polymerization, separation, carbonization and graphitization. By controlling pyridine insoluble in coal tar and using optimized conditions of polymerization, the MCMBs are prepared which possess good spherical shape and narrow particle size distribution without sieving. In comparison with previous methods, the MCMBs prepared by us can be directly used as anode material in practical lithium ion batteries with simplified technics and lower costs.The graphitized MCMBs prepared by us have higher packing density, lower specific surface area, lower irreversible capacity and excellent cycling behavior in comparison with commercial MCMBs. It has 92.32% coulomb efficiency at first cycle and still keeps 94.87% of first discharge capacity after 100 cycles. The kinetics behaviors of carbon electrode are studied by means of linear sweep voltammetry and chronoamperometry measurements. It is found that the exchange current density and diffusion coefficient of lithium increase with the increase of content of Li intercalating into carbon electrodes. The diffusion coefficient of Li for MCMBs is 5.58x10-9cm2-s-l higher than that of Li for synthetic graphite, which is 6.32xl0-10cm2 S-1.The doping and coating MCMBs have been studied in detail. It is found that boron doping improves the degree of graphitization of samples from 88.4% to 93.0%, and the samples keep 96.7% of capacity at first cycle after 20 cycles. The rate performance of the Ni-coated electrode isABSTRACTimproved significantly, which has 30mAh-g"1 capacities higher than uncoated MCMBs at 2C discharge current. After being held at 25% humidity for 12h, the Ag-coated MCMBs still have 316.4mAh-g"1 in the first charge-discharge cycle and have excellent cycle ability which keep 95.8% of discharge capacity at the first cycle after 20 cycles. At the same condition, the uncoated MCMBs just keep 74.6% of the first discharge capacity. Cu coating have the same effect as the Ag coating about sensitive to humidity, but the coated Cu is easily oxided on air. Cu-Ag alloy is provided with normal temperature antioxygenic property in air. The coated MCMBs still have excellent electrochemical performance after being held at high humidity. The MCMBs with mild oxidation have 361.5mAh-g~1 of discharge capacity and excellent cycling behavior. The oxidation method can be well controlled and is promising for industry.A simple theoretical model is presented to simulate the galvanostatic discharge behavior of MCMBs. This mathematical model taking into account its properties gives the insights of the physical processes occurring within the intercalation host and to predict theoretically the behavior of the intercalation host. The discharge profiles, exchange current and diffusion coefficient of lithium are predicted by using this model, and the predicted values are consistent with experimental results. This in turn can lead to a better development and design of the intercalation materials.Optimized process for the production of lithium ion batteries is developed. Some prepared materials are used as anodes of lithium ion batteries, and 053048 type batteries with 710mAh of discharge capacity are prepared. Batteries with B-doped MCMBs anode have excellent cycling behavior that keep 92.9% of the first discharge capacity after 300 cycles. And batteries with mild oxidation MCMBs anode have improved the large current discharge characteristic. The capacity at 2C rate discharge current is 87.5% of the capacity at 0.2C rate discharge current.Lithium ion batteries with 1...