掺氟-富锂磷酸亚铁锂正极材料的电化学性能

Electrochemical performance of F-doped and Li-rich lithium iron phosphate

采用固相烧结法于700℃烧结制备了具有橄榄石结构(空间群Pmnb)的微米掺氟-富锂磷酸亚铁锂。通过X粉末衍射仪、充放电循环、扫描电子显微镜、循环伏安等现代测试手段表征了制备样品的电化学性能。实验结果表明:掺氟增大了样品的晶胞。在制备的掺氟样和未掺氟富锂磷酸亚铁锂样中,在2 C倍率电流下,理论组成为Li1.15FePO4F0.15的微米样品的第1循环和第30循环的放电比容量分别为115.1 mAh/g和109.6 mAh/g。掺氟显著改善了磷酸亚铁锂的大电流放电性能,使磷酸亚铁锂的电荷传递阻抗减小。

Series of F-doped and Li-rich lithium iron phosphates with a olivine structure,composed of the micrometer size particles,were synthesized by a solid state process at 700 ℃.X-ray powder diffraction,charge-discharge cycles,cyclic voltammogram,SEM and other advanced techniques were employed to study the electrochemical performances of the as-prepared samples.The experimental results indicate that the crystal cell of the fluoride doped lithium iron phosphate are larger than that of undoped sample.The sample with a theoretical composition of Li1.15FePO4F0.15 exhibits a capacity of 115.1 mAh·g-1 in the 1st cycle and 109.6 mAh·g-1 in the 30th cycle at 2 C rate,which exhibits the best electrochemical performance in the as-synthesized fluoride doped samples and undoped sample.The fluoride doping obviously improves the discharge performance of lithium iron phosphates at high rate,and decrease the charge transfer resistance of the fluoride doped sample than those of undoped sample.