Research Of Graphite Anode Material With LPAN Coating

In this thesis graphite anode material had been coated by a graphene-like material to produce composite material, which was tested by X-ray power diffraction, Scanning electron microscopy, Transmission Electron Microscopy, Raman spectrum, Thermogravimetric Analyzer and Electrochemical charge and discharge test. The holding time, synthesis temperature and the proportion of LPAN were studied respectively to understand how these conditions affect the performance of graphite anode material. The following achievements are included:1. The sintering temperature of LPAN was researched. Firstly, the TG test of LPAN was performed, in order to find out the carbonization temperature range of LPAN. After sintering at different temperatures, the samples were tested by X-ray power diffraction and Raman spectra analysis to know the basic properties of grapheme-like material. At last, the electrochemical performance of grapheme-like material sintered with different temperature was tested. So, what was found was that the LPAN possessed grapheme-like structure after sintering at a certain temperature.2. The basic performance of high purity graphite, as well as its electrochemical performance was studied. According to X-ray power diffraction and the pictures of Scanning electron microscopy of high purity graphite, the layer spacing of graphite d002 could be calculated as 0.32841nm and the lamellar structure of graphite before the electrochemical charging and discharging test could be clearly observed. After the electrochemical charging and discharging test, the solid electrolyte interphase (SEI) layer appearance of electrode material would be entirely different when different binder (SA or PVDF) was used. The electrochemical performance of the graphite was better when SA used as binder, the formation of SEI layer in pole piece was uniform, which could help improve the first coulombic efficiency of battery. After the performance of electrochemical test, the coulombic efficiency of high purity graphite was 85% and its discharge capacity was 400mAh/g.3. The holding time, synthesis temperature and the proportion of LPAN were studied to produce modified graphite. According to X-ray power diffraction, pictures of Scanning electron microscopy and Transmission Electron Microscopy, it could be confirmed that LPAN coating at the surface of graphite uniformly was able to promote the stability of the laminated structure of the graphite. Compared with the pure graphite anode materials, the discharge capacity of the graphite-base anode material which was prepared by sintering graphite coated with 10% proportion of LPAN at 1000℃ for 4h reached to 490mAh/g,450mAh/g、400mAh/g、310mAh/g and 230mAh/g at 0.1C、0.5C、1.0C、3.0C and 5.0C, respectively. After being coated, the coulombic efficiency of the graphite anode material had improved. The coulombic efficiency of high purity graphite and the graphite anode material coated with LPAN was 85% and 88%. What’s more, the Specific Capacity of the graphite anode material coated with LPAN could still be stabilized at 490mAh/g.4. The effect on surface oxidation of graphite by different methods, such as gaseous phase oxidation and liquid phase oxidation, was studied. According to TG diagrams of graphite, there is a weight loss after 550℃ in oxygen. The oxidation temperature range of the high purity graphite was defined. And also according to X-ray power diffraction, Scanning electron microscopy, Transmission Electron Microscopy and EDS pictures of graphite oxide, the sample differed from normal graphite, which contained many tiny pieces of graphite. The sample oxidized under 350℃ had more serious defect degree, which had better performance in the first Coulombic Efficiency and Specific Capacity.5. What had been researched was that the Electrochemical performance of the oxidation graphite-base anode material, which was prepared by sintering oxidation graphite coated with 10% proportion of LPAN at 1000℃ for 4h, was better than pure graphite anode material. It was clearly found that the LPAN coating graphite could improve the cycle performance and rate performance of oxidation graphite. And surface oxidation of graphite could promote the first Coulomb Efficiency and Specific Capacity. The electrochemical performance of oxidized high purity graphite in 350℃ coated with 10% of LPAN sintered in 1000℃ could exceed the theoretical Specific Capacity of graphite. The Specific Capacity of modified graphite that was synthesized by this method was 510mAh/g after 300 cycle, and the first Coulombic Efficiency was 91%.