| The silicon monoxide and natural graphite composite anode material was studied for lithium- ion battery. As anode material of lithium- ion battery, natural graphite has a stable cycling performance,but its theoretical capacity is only 372 m Ah/g.The silicon monoxide has a high theoretical capacity,but its cycling performance is poor because of its volume effect in the process of lithium intercalation and deintercalation. Therefore, this paper will fabricates the composite material of natural graphite and silicon monoxide, then use mild expansion and carbon coating to improve the cycling performance of the composite anode material, reduce the first irreversible capacity, make it not only has high specific capacity,but good cycle performance. Structural and morphology changes were characterized by using XRD and SEM,respectively;C V and galvanostatic charge-discharge tests were carried out to evaluate the electrochemistry performance of the as-prepared composite anode materials.Fabricating mild expanded graphite by liquid phase oxidation intercalation reaction and high temperature treatment,use hydrogen peroxide as oxidant, organic acid and inorganic acid as intercalation agents,. After the mild expansion treatment, the interlayer spacing of graphite is increased, the reversible capacity is improved, the rate performance and cycling performance of the graphite is better than that of natural graphite. Formic acid is the most appropriate intercalation agents through analisis, its mild expanded graphite has reversible specific capacity 351 m Ah/g, 344 m Ah/g, 328 m Ah/g, 290 m Ah/g,180 m Ah/g, 59 m Ah/g at 0.1C, 0.2C, 0.5C, 1C, 2C, 5C respectively. The liquid phase reaction time was also optimized, determine the appropriate reaction time was 4h. Under this condition, mild expanded graphite has appropriate interlayer spacing, micro morphology, which conducive to the electrochemistry performance of the materials.The silicon monoxide / graphite composite anode material was prepared by ball milling.the silicon monoxide material was studied at first. Its reversible capacity is 844.0m Ah/g for the first cycle, coulomb efficiency is 43.6%,and the capacity retention rate is only 24.4% at 5 cycle. The influence of different composite ratio and different milling time on the electrochemistry performance of the composite anode materials were studied. The composite anode material which silicon monoxide’s mass ratio is 15% has good performance, its reversible capacity is 447.94 m Ah/g for the first cycle, at 40 times cycle, the capacity maintain rate is 71.2%. With the increase of the milling time, the first cycle coulomb efficiency of the material is decreased, big current discharge performance is decreased.so the milling time of 7h is the most suitable. At the same time, the silicon monoxide/mild expanded graphite composite material was studied, the reversible capacity are 454 m Ah/g, 361 m Ah/g and 165 m Ah/g,at 0.1C, 0.2C and 2C respectively. Compared with silicon monoxide /natural graphite composite anode material, reversible capacity improved 1%, 6%, 15% respectively.Use pitch as the carbon source, the carbon coating of the silicon monoxide / graphite composite material was carried out with the method of solid phase mixing and high temperature treatment, the mass ratio of the coating carbon was 15%. After carbon coating process,the composite materials’ first cycle coulomb efficiency is raised, reversible capacity is increased, cycling performance is improved obviously, especially the big current discharge performance is improved. The reversible capacity of silicon monoxide / mild expanded graphite / carbon composite anode material are 469 m Ah/g, 346 m Ah/g, 236 m Ah/g and 117 m Ah/g at 0.1C, 1C, 2C and 5C respectively.Compared to the un-carbon coating composite material, the reversible capacity are increased by 4%,22%, 43% and 112% respectively. |
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