Preparation and electrochemical properties of silicon copper alloy for high performance anode

Abstract

To improve the electrochemical performance of silicon-based anode materials, herein, silicon-copper (Si-Cu) incompatible alloy anode material were prepared via facile chemical reduction and ball milling methods. Subsequently, nitrogen-doped carbon-coated Si-Cu alloy (Si-Cu/N-C) composites were prepared via in-situ polymerization with aniline in the high-temperature calcinations process. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were performed to analyze the physical characterization of these materials. Besides, the electrochemical performance of the catalysis was studied by constant current charging and discharging, cyclic voltammetry and electrochemical AC impedance spectroscopy (EIS). Electrochemical tests demonstrate that Si-Cu anode performs a high electrocatalytic activity when the ratio of Si to Cu is 1.5∶1 and the ball milling time is 7 h. The anode exhibits an initial discharge capacity of 1 018.6 mAh/g and a capacity of 499.2 mAh/g after 100 cycles. After the coating modification, TEM result shows that this composite anode material possesses a core-shell structure. When the coating mass of N-doped carbon is 0.45, the Si-Cu/N-C electrode exhibits an initial discharge capacity of 1 147.7 mAh/g and maintains a specific capacity of 857.9 mAh/g after 100 cycles. Furthermore, the capacity retention rate of Si-Cu/N-C anode increases by 10.8% as compared with that of Si-Cu. The improved electrochemical performance after modification is attributed to the unique core-shell structure of Si-Cu/N-C. On the one hand, the N-doped carbon coating layer not only improves the conductivity, but also reduces the contact resistance between the electrolyte and electrode. On the other hand, the nitrogen doping of Si-Cu/N-C composite can increase the active site of lithium storage on the surface, reduce lithium storage potential and form a stable solid electrolyte interface (SEI) film during the cycling process.