The Si/C composite materials were prepared by ball milling method, and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The result displayed that Si in the Si/C composite materials still maintained a good crystal structure and uniformly dispersed in carbon black matrix. The first discharge capacity was 3393 mAh/g, and 4 cycles later still retained 1000 mAh/g, showing better charge-discharge cycle performance. Electrochemical impedance spectroscopy test indicated that there appeared three semicircles respectively representing the impedance of contact problems, solid electrolyte interface film (SEI film), charge transfer and phase transformation in the first lithiation, and their evolutive principles were also investigated.

Key words: lithium ion battery, silicon anode, electrochemical impedance spectroscopy, SEI film, phase transformation