Influence of copper addition for silicon–carbon composite as anode materials for lithium ion batteries

Abstract

A series of porous Si–C and Si–C/Cu composites have been successfully fabricated by a simple sol–gel and pyrolysis process. In the Si–C/Cu composites, nanoscale Si and Cu particles are homogeneously dispersed in the pyrolyzed carbon matrix. Furthermore, Cu₃Si phase has formed during the carbonization process confirmed by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). As an anode material for lithium ion batteries, the Si–C/Cu2 composite exhibits a high initial discharge capacity of 2234 mA h g⁻¹ and a reversible discharge capacity of 947 mA h g⁻¹ after 100 cycles at the current density of 100 mA g⁻¹, respectively. With the current density gradually increasing to 1000 mA g⁻¹, the composite shows an average capacity of 848 mA h g⁻¹, exhibiting superior rate capability. The excellent cycling stability and rate discharge performance of the Si–C/Cu2 composite can be attributed to the improved conductivity owing to the addition of Cu, and the nanoporous structures as well as the formation of Cu₃Si, which both have good buffer effect to release volume expansion and maintain the integrity of the electrode during the charge–discharge cycles.