Study Of Preparation And Electrochemical Performance Of Si/C Composites As Anode Materials For Li-ion Battery

Silicon is expected to become one of the candidate anode materials replacinggraphite, because of its high theoretical specific capacity (4200mAh/g) and richresources. However, the low conductivity, huge volume expansion and poor cyclingperformance of silicon severely restrict its commercial application. Carbon materialscan be used as "buffer base" of silicon electrode because of its good ionic and electronicconductivity, good scalability and elasticity and small volume change during charge anddischarge. In addition, lithium intercalation potential of silicon and graphite is close.Therefore, composite prepared from silicon and carbon should be had high capacity andexcellent cycling performance as anode material for lithium-ion battery.In this study, polyaniline and starch were used as carbon source, nano silicon wasas the silicon source, silicon/carbon composites were prepared by different methods.(1) Using aniline and nano silicon as the raw materials, silicon/carbon compositeanode materials were prepared by emulsion polymerization and pyrolysis. Fouriertransform infrared spectroscopy and X-ray diffraction were used to character thestructure of samples in this study. And the effects of preparation conditions (i.g., massratio of silicon/aniline) on the electrochemical performance of composite anodematerials were studied. The results indicate that the surface of nano-silicon wassuccessfully coated by polyaniline, the composite anode materials show high specificcapacity and good cycling performance under the conditions that silicon/aniline ratio is1:2, composite anode material: Super p: CMC is85:5:10, and citric acid and KOHbuffer solution at pH=3as solvent. Its reversible capacity reaches1031mAh/g after20cycles.(2) Using potato starch and nano silicon as the raw material, silicon/carboncomposite was prepared by pyrolysis and milling method. The influencing mechanismof preparation conditions (i.g., milling time, silicon/carbon ratio, pH of solvent andkinds of binders) were discussed. The results show that composite exhibite the bestelectrochemical performance under the conditions that silicon/graphite ratio is4:8,milling time is10h, active material: conductive graphite: CMC is85:5:10and citric acidand KOH buffer solution at pH=3as solvent. The first charge and discharge capacity ofcomposite is1347mAh/g and934mAh/g, respectively, and charge and dischargecapacity is as high as1034.08mAh/g and985.34mAh/g after20cycles. It is because that starch-based carbon coated can effectively alleviate the volume expansion of siliconduring charge. On the other hand, grafting esterification reaction occurs between siliconnano-particles and CMC, which can allow the electrode to maintain good integrity inthe charge-discharge process.