Research Of Synthesis And Properties Of Silicon Copper/Carbon Composite Anode For Lithium Ion Batteries

Silicon-based anode materials have become a focus because of its high theoretical capacity. But the huge volume changes of silicon before and afer lithium insertion results in unstable electrode structure and poor cycle performance. Based on previous research, Si-Cu and Si-Cu/C composites were synthesized by mechanical ball milling and high temperature solid phase method. The binder, conductive agent and annealing condition were optimized, and the electrochemical properties of the composites were researched.Si-Cu omposite, which was prepared by mechanical alloying method, have an initial reversible capacity of 232 mAh·g^-1. The cycle performance and initial efficiency were poor. Si-Cu composites were also synthesized by high temperature solid phase method with different proportion of Si and Cu. XRD results showed that Si-Cu composite was composed of Si, Cu and Cu₃Si. SEM photos showed that silicon particles were evenly wrapped by nanosized copper particles. Si-Cu composite, which has a proportion of 3:3:4 of SiO, CuO and Al, has the best electrochemical properties. The initial reversible capacity is about 200 mAh·g^-1 and the cycle performance is relatively better.Si-Cu/C composites were prepared by ball milling and high temperature porolysis method. Si-Cu/C composites with SiO as silicon source exhibited that it consisted of several types of Si-Cu alloy and amorphous carbon. The proportion of Si and Cu in the composites was researched. SiO₃CuO₃Al6/C composite showed better electrochemical property, the reversible capacity was 300mAhg^-1 and remained stable even after 100 cycles. Si-Cu/C composites with nanosized Si as silicon source were also researched using the mole ratio of Si and Cu of 9:1, 8:2, 7:3 and 6:4. XRD results showed that the composites included Si and Cu₃Si, the alloy phase improved the conductivity of the composites. The results of electrochemical tests indicated that the properties of Si₉-Cu₁/C composites had an initial reversible capacity of 500 mAh·g^-1 and the capacity retention was 81% after 50 cycles.The binder, conductive agent and annealing conditions of Si₉-Cu₁/C composites electrodes were optimized. The electrode, which consisted of Si₉-Cu₁/C composites with SiO as silicon source, 35mass% coating carbon, acetylene black conductive agent and PVDF binder, was vacuum dried at 80℃and then annealed at 200℃under Ar atmosphere. The reversible capacity and cycle performance were greatly improved. The initial reversible capacity was about 1000 mAh·g^-1 and still remained 500 mAh·g^-1 after 250 cycles.