LiFePO_4正极材料的合成与电化学性能研究

Study on the synthesis of LiFePO_4 cathode and its electrochemical performance

采用固相反应合成了LiFePO4正极材料,研究了抑制Fe2+氧化以及产物粒径长大对产物充放电性能的影响。制备样品分别用XRD、FT-IR、SEM进行表征。在添加20%乙炔黑、纯氮气氛下、600℃烧结24h可制得单一物相的LiFePO4粉末。在2.5～4.3V(vs.Li)范围内,测量了不同扫描速度(0.06、0.1、0.2mV/s)对循环伏安的影响。结果表明制备材料有良好的Li+脱嵌性能、LiFePO4中的Fe2+/Fe3+氧化还原反应是一个准可逆体系。在2.7～4.0V(vs.Li)范围内,以15mA/g电流密度放电,首次放电比容量可达到147mAh/g,且电压平台好,放电反应表现出典型的两相行为。

LiFePO4 powders were synthesized following solid reaction. The influence of avoiding oxidation of Fe^2＋ and undesirable particle growth on the charge/discharge performance of the as-prepared samples was investigated. The materials were characterized by X-ray powder diffraction, FT-IR spectroscopy, scanning electron microscopy. A single phase of LiFePO4 powder can be synthesized by sintering precursor（adding 20% C） in flowing pure nitrogen at 600℃ for 24 h, The effect of the scanning rate on the cycle voltammograms was measured at 0.06, 0.1, 0.2 mV/s between 2.5 and 4.3 V（vs. Li）. The results meant that the prepared material has good reversibility for Lit extration/insertion and that the Fe^2＋/Fe^3＋ redox reaction in LiFePO4 is a quasi-reversible system. A specific capacity of 147 mAh/g was delivered when first discharging at room temperature under 15 mA/g between 2.7 and 4.0 V （vs. Li）. The shapes of the discharge curves, which had flat potential plateau, suggested that the discharge reaction proceeds as a typical two-phase reaction.