Synthesis of Si and tin-doped Si powders via gas-phase sodium reduction for Li-ion batteries

Pure silicon nano-powder was successfully synthesized via gas-phase sodium reduction of silicon tetrachloride, exhibiting 100% conversion of the reactants and achieving >95% yield of the final product. The interactions of the process conditions and tin-doping with the particle morphology were investigated. The produced powders were analyzed by nitrogen adsorption, transmission and scanning electron microscopy, X-ray diffraction, inert gas fusion analysis and glow discharge mass spectroscopy. The washed polycrystalline silicon particles had a BET surface area in the range of 23-44 m(2)/g. The silicon aciniform aggregates consisted of relatively homogeneous primary particles in the range of 20-100 nm. The silicon was protected by a 2-3 nm thick passivation layer established during the washing step resulting in an oxygen content of less than 3 wt.%. Electrochemical testing demonstrated a high inherent capacity for the pure Si powders. The initial capacity and 1st cycle charge efficiency of Si-containing anode electrodes was dependent on the initial powder surface area. The highest capacity was achieved for Si powders with intermediate BET surface area of 28.5 m(2)/g and cells with this anode material delivered capacity of 2651 mA h/g (normalized to Si) and 82.4% efficiency at first charge. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan.