| The key problem of lithium-ion battery lies in anode materials. And it gives priority to carbon material in the industrialization. The needle coke, which is low-cost, was modified by the way of surface treatment which was attempted to improve coulometer efficiency, and results showed excellent electrochemical performance of the composite material in this paper.The composite needle coke was made by solidifying phenolic resin on the surface. The method adopted was named as heat-filtrate in the thesis. First of all, the sequence of graphitization and coating should be decided, and then the size of the grain was found out. The results from electrochemical performance showed that the sample, graphitized before coating with particle diameter between 20μm and 25μm, was not fit for lithium-ion battery anode material because its first discharging capacity was 282 mAh·g-1 and the initial efficiency was 71.7%. However, another sample graphitized after coating, particle diameter scale of which was from 15μm to 20μm, was got well. The capacity could reach 321.1 mAh·g-1 and the efficiency was 84.3% in the first cycle. As the conditions mentioned above, we can produce a series of composite materials which were different in the content of coating quantity when the proportion of resin and coke was changed. According to XRD (X-ray diffraction), SEM (scanning electron microscopy), galvanostatic charge/discharge and CV (cycle voltammetry), the results showed the best performance of the composite material while the proportion of resin to coke was 1:3. The reversible capacity was kept at 410.1 mAh·g-1 and the coulomb efficiency was 91.2% in the first cycle. In a word, the composite materials made in this work have bright future in the commercial produce on a large scale.
|
PDF Full Text Request