用响应面法优化了低温碳热还原合成LiFePO4/C的工艺,用中心组合设计研究了蔗糖用量、焙烧温度、焙烧时间和低温反应温度四因素对放电比容量的影响。结果表明,放电比容量与四因素关系符合二次模型,焙烧温度和蔗糖量以及两者的交互作用对放电比容量影响较为显著,各个因素的二次方影响高度显著。由模型得出的最优操作条件为:焙烧温度718℃;焙烧时间10.88 h;蔗糖量0.866 g g 1LiFePO4;热处理温度105℃。该条件下LiFePO4/C的实际放电比容量为140.6 mA h g 1,与模型预测值142.03 mA h g 1无显著差异。
以LiH2PO4、LiF和V2O5为原料,蔗糖为还原剂,用碳热还原法合成了Li3V2[(PO4)1–xFx]3/C(x=0、0.02、0.05、0.08、0.10和0.15),并用X射线衍射、Fourier变换红外光谱、循环伏安、交流阻抗谱和恒流充放电技术研究了F–掺杂对材料结构和电化学性能的影响。结果表明:F–掺杂Li3V2(PO4)3/C与纯Li3V2(PO4)3/C均为单斜结构,但少量的F–掺杂可提高电极反应可逆程度和电导率,降低电荷传递阻抗;在所得的F–掺杂材料中,Li3V2[(PO4)0.95F0.05]3/C具有较好的电化学性能。在3.0～4.2 V(vs.Li/Li+)循环时,电极的0.5 C放电容量为124.4 mA h/g,50次循环后容量保持率为98.5%,15 C下的放电容量为84.7 mA h/g,50次循环后容量保持率为97.4%,而Li3V2(PO4)3/C的仅为59.2 mA h/g和89.0%。
LiNi0.5Mn1.5O4 was synthesized by combustion synthesis(UCS) using urea as fuel.X-ray diffraction and scanning electron microscope measurements showed that the spinel structure LiNi0.5Mn1.5O4 with the space group Fd3m was formed during urea combustion.Both structure and particle size could be adjusted by the amount of urea and the heat treatment temperature used in the UCS.For the LiNi0.5Mn1.5O4 sample prepared with a urea/Li molar ratio of 0.57 and a heat treatment temperature of 900 C,the particle-size distribution fell in a narrow range of 1-2 m.Electrochemical tests indicated that this LiNi0.5Mn1.5O4 sample delivered a discharge capacity of 133.6 mAh/g with a capacity retention rate of 99.6% after 20 cycles at 0.5 C.
