NaHCO_3对水热合成磷酸铁锂的组织结构与性能的影响

Effect of NaHCO_3 on microstructure and performance of lithium ion phosphate

以Li2CO3、NaHCO3、FeC2O4·2H2O和NH4H2PO4为原料,采用水热法制备LiFePO4,溶液中几种离子的物质的量比n(Li1+):n(Na+):n(Fe2+):n(PO43+)为1:x:1:1(x=0、0.1、0.2、0.3和0.5)。采用聚乙烯醇为碳源,对LiFePO4粉末进行高温碳化包覆处理,得到LiFePO4/C复合正极材料。利用X射线衍射(XRD)、扫描电镜(SEM)、拉曼光谱、激光粒度仪和恒流充放电技术研究水热溶液中NaHCO3的浓度x对LiFePO4的形貌和电性能的影响。结果表明:LiFePO4的粒度随NaHCO3浓度增加而减小,x从0增加到0.5时LiFePO4的粒度从8.08μm降低至3.06μm;当x=0和0.1时水热反应后存在未反应完的草酸亚铁杂质,当x=0.2、0.3和0.5时,LiFePO4粉末为纯相;当x=0.5时粉末表现出良好的电化学性能,其振实密度达到1.15 g/cm3,室温下0.1C倍率下放电的放电比容量达到144.1(mA·h)/g,1C倍率下放电的放电比容量保持在118.2(mA·h)/g。

LiFePO4 was synthesized by hydrothermal process using Li2CO3、NaHCO3、FeC2O4·2H2O and NH4H2PO4 as raw materials. And the molar ration of Li1＋：Na＋：Fe2＋：PO43＋is 1：x：1：1 （ x= 0, 0.1, 0.2, 0.3 and 0.5 ）. Adding polyvinyl alcohol, LiFePO4/C was obtained during the high temperature process. The effect of different concentration of NaHCO3 on microstructure and electrochemical properties of LiFePO4 and LiFePO4/C was investigated by the methods of X-ray Diffraction （XRD）, scanning electron microscope （SEM）, Raman spectra, laser granularity analysis and constant current charge-discharge experiments. The results shown that no impurities exist in the LiFePO4 synthesized when x ranging from 0.2 to 0.5 . And the particle size of these samples decreases from 8.08μm（x=0） to 3.08μm（x=0.5）. When x=0.5,the cells perform excellent electrochemical properties, and whose tap density is 1.15 g·cm-3 and discharge specific capacity is 144.1 （mA·h）/g at 0.1C and 118.2 （mA·h）/g at 1C under room temperature, respectively.