镁离子掺杂对LiFePO4/C材料电池性能的影响

通过PVA(聚乙烯醇)包覆工艺利用固相法合成了镁离子掺杂的LiFePO₄/C.材料的高温电导率特征曲线和电阻率与掺杂含量变化的曲线表明，材料中由于Mg离子的掺杂，使得其导电机制由n型半导体向p型半导体转换.在镁离子掺杂原子百分含量为0.3％(x)下，研究了材料的结晶性能随烧成温度的变化.973 K下合成材料具有良好的微观结构，材料的亚微米颗粒和PVA裂解产生的碳黑形成了粒径在10 μm左右的团簇体.在循环伏安特性曲线中，存在两个小的肩峰,表明在循环过程中，锂离子可以通过由掺杂产生的锂空位进行插入和脱出.材料在0.1 C的充放电速率下，首次充放电曲线具有平稳的电压平台和较大的充放电容量.当充放电速率为0.5 C时，材料仍然具有大于120 mA•h•g^－1的充放电容量；经过100次循环后，基本上没有发现材料的循环容量衰减的情况.

Influence of Mg Ion Doping on the Battery Properties of LiFePO4/C

LiFePO₄/C doped by Mg ion was obtained by solid phase reaction synthesis route with PVA (polyvinyl alcohol) coating processing. Conduction properties at different temperatures and resistivity change at different dopant contents indicate that conduction mechanism of LiFePO₄ will change from n type to p type along with the increasing of doping content. Crystallization of LiFePO₄/C with the dopant content of 0.3％(x) at different synthesis temperatures was characterized. For the sample synthesized at 973 K, the particles with a diameter of several hundred nanometers together with carbon decomposed by PVA formed secondary particles with a diameter of 10 micrometer. Along with curves of cyclic voltammetry, two shoulder-peaks showed that another way for lithium ion extraction/ insertion in cathode existed. When batteries were cycled at a rate of 0.1 C, the charge and discharge curves showed flat work voltages and large capacities. When the charge-discharge rate was increased to 0.5 C, LiFePO₄ covered by carbon and doped by Mg ion showed capacity of more than 120 mA•h•g^－1. After 100 cycles, the capacity fade was neglectable.