The Si/Cu and Si/Cu/graphite composites were synthesized by mechanical ball milling. The phases of composites were analyzed with X-ray diffraction. Their charge-discharge performance of the composite as negative electrodes in Li-ion batteries were tested and the formation process of solid electrolyte interface/interphase (SEI) was discussed by cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS). The results show that the materials prepared by ball milling are the composites consisting of Si and CU3Si alloy. During cycling the composite electrodes suffer from cracking which cause the large particles pulverize. Therefore, it facilitates the further formation of SEI film on the surface of newly formed particles. The initial reversible capacity and efficiency of composites are improved and the cycle cycleability is enhanced obviously after the ball milling of Si/Cu composite with graphite. The Si/Cu/graphite composite electrode has an initial reversible capacity of 420 mAh g(-1) and a charge-discharge efficiency of 65%. (c) 2007 Elsevier B.V. All rights reserved.