Synthesis And Characterization Of Composite Nano-silicon Anode Materials For Lithium Ion Battery

Silicon possessed the highest theoretical capacity (4200 mAh/g) of all known anode material and is suggested as a promsing anode material for the next generation lithium ion batteries. However, the process of lithium insertion into and extraction from silicon is accompanied by a huge volume change (up to 300%), which induces a strong stress in Si anode and causes the pulverization of silicon active center and the rapid capacity fading. The preparation of nanosize Si materials is an effective method to alleviate the volume effect. Nano composition containing a large number of Si nanowires was fabricated and researched in this work.In this dissertation, A nano Si composite anode material was prepared by secondary chemical vapor deposition based on the mechanism of vapor-liquid-solid process. The interaction between the experimental conditions and the electrochemical properties of the as-prepared deposites was investigated systematically. The reaction process factors, including the reaction atmosphere, the deposition temperature, the gas pressure and the flow rate, were researched and optimized in details. The morphologies and microstructure of the materials wre tested by XRD, Raman and SEM, and the electrochemical properties was investigated by constant current discharging, cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) at the room temperature.The silicon composite film with excellent electrochemical performance was obtained at 500℃with SiH4/H2 as the reaction gas at the flow rate of 0.25 l/min. Nano silicon composite materials with mixed-architectural network structure composed of Si nanowires and Si nanoparticles and Au-Si nanoparticles was synthezied under the optimized processing. The first discharge capacity of the composite electrode was 3071.8 mAh/g and the coulomb efficiency was up to 90.37% during the first cycle. The coulomb efficiency was maintained at above 95% in the following 20th cycles.The results suggested that the composite structure with connected nanowires is an effective way to improve the electrochemcial performance of silcion anode materials..