Synthesis and electrochemical properties of silicon/carbon composites prepared by high temperature pyrolysis

Silicon/carbon composites as anode materials for lithium batteries with high power capacity were synthesized by a high temperature pyrolysis method. The performances of the silicon/carbon composites were investigated by X-ray diffraction,thermogravimetric analysis,scanning electron microscopy,transmission electron microscopy,galvanostatic cell cycling,and cyclic voltammetry. It is found that the silicon/carbon composites consist of silicon,carbon and few silicon dioxide phases,and the carbon content is about 39%. Electrochemical cycling tests of button cells show that the specific capacity is far more than that of carbon materials. The initial charge capacity of the silicon/carbon composites is 768 m Ah·g^-1 at a current of 0.2 m A and the initial coulombic efficiency is 75.6%.After 70 cycles the reversible specific capacity is 529.0 m Ah·g^-1 and the average capacity deterioration rate of each cycle is 0.44%.These improvements can be attributed to the introduction of carbon in the Si/C composites and carbon coatings on the Si surface,which provide a rapid lithium transport pathway,reduce the cell impedance and stabilize the electrode structure during charge/discharge cycles.