Study On Preparation And Properties Of Silicon/Carbon Composite Anode Material

To enhance and improve the first charge-discharge efficiency, cycle life and high rate performance of the silicon anode materials,the Si/C composite materials was prepared by ball-milling and spray drying method, and the preparation process and conditions were studied in detail in this paper. The Si/C composite materials crystal structure, surface morphology, electrochemical properties and microstructure of dynamics has been studied through X-ray diffraction(XRD), Scanning Electron Microscopy(SEM), Transmission Electron Microscopy(TEM), Charge/Discharge performance, Cyclic Voltammetry and Electrochemical Impedance Spectroscopy(EIS).First the Si/C composite was prepared by ball-milling method,the optimal process conditions were obtained:the ball-milling time of preparation of nano silicon is 4h;the ball-milling time of preparation of precursor is 3h;pyrolysis condition is 600℃×6h. The influence of graphite content, the graphite matrix and the coating carbon source on the properties of Si/C composite was further studied,the research results show that Si/C composite has the reasonable structure and good electrochemical performance when the content of graphite was 60%.Then expanded graphite was used as base, the first charge-discharge efficiency was increased to 80.1%. At the same time,excellent cycle and high-rate performance were obtained,the capacity retention rate was 70.8% after 200 cycles in the 100 m A/g current density. Even at 200 m A/g,400 m A/g and 600 m A/g current density the discharge specific capacity reached 615.5 m Ah/g,535.5 m Ah/g and 460 m Ah/g respectively after 250 cycles.Based on the electrode plate morphlogy analysis found that the stability of electrode structure had been greatly improved.At last,phenolic resin was used as coating carbon resource, silicon particles had better dispersion effect.At 1000 ℃, the best comprehensive properties of material was achieved,the first discharge specific capacity was 838.1 m Ah/g,the first coulombic efficiency was 73.1% and the capacity retention was 89.7% after 100 cycles.Second, the Si/C composite was prepared by spray drying method.The results showed that, the high rate performance was greatly improved, the diffusion rate of lithium ion was 1.89×10-12cm2/s calculated by cyclic voltammetry method, it is a higher level in the same kind study. Then the ratio of the ball and material was increased, the test results showed that the capacity retention rate were 85.1% from 10 to 200 cycles at 100 m A/g current density, and the capacity retention rate was 76.3% after 300 cycles at 200 m A/g current density. Through electrode morphology analysis concluded that the stability of electrode structure was excellent. Finally,phenolic resin was used as coating carbon source,the first charge-discharge efficiency was improved and Si/C composite had good cycling performance.