Electrochemical Characteristics of Si/C/CNT Composites for Anode Material of Lithium Ion Battery

Abstract

In recent years, lithium ion battery has been widely used on portable electronic devices and electric/hybrid vehicles because of its high energy density and cycling stability. As an anode material for the lithium ion battery, Silicon(Si) is getting attention for its high theoretical specific capacity (about 4200mAh/g) and its proper potential range for lithium insertion and extraction. However, Si has properties that could be obstacles for its practical use as the lithium ion battery anode. Si not only has a low intrinsic electric conductivity but also undergoes severe volume changes during the lithium ion insertion/extraction process which results in pulverization of the electrode materials, causing the capacity to fade. To overcome these problems and enhance the electric conductivity, we synthesized Silicon/Carbon/CNT composites as an anode material. Si/C/CNT composites were prepared by the fabrication processes including the synthesis of SBA-15, magnesiothermic reduction of SBA-15 to obtain Si/MgO by ball milling, carbonization of phenolic resin with CNT and HCl etching. The prepared Si/C/CNT composites were analysed by BET, XRD, FE-SEM and TGA. Among the SBA-15 samples synthesized with reaction temperatures between 50°C and 70°C, the SBA-15 of 60°C showed the largest specific surface area. Also the electrochemical performances of Si/C/CNT composites as the anode electrode were investigated by constant current charge/discharge test, cyclic voltammetry and leakage tests in the electrolyte of LiPF6 dissolved in organic solvents(EC:DMC:EMC=1:1:1 vol%). The coin cell using Si/C/CNT composite(Si:CNT=97 :3 in weight) has better capacity(1,440 mAh/g) than that of other composition coin cells. Also, it is found that Si/C/CNT composite(Si:CNT=97:3 in weight) electrode shows improved cycling performance and electric conductivity.