钒改性锂离子电池正极材料LiFe0.5Mn0.5PO4/C 电化学性能

采用高温固相反应,以NH4VO3为钒源合成了化学计量式为(1-x)LiFe0.5Mn0.5PO4-xLi3V2(PO4)3/C(x=0,0.1,0.2,0.25,1)的钒改性磷酸锰铁锂正极材料.电化学测试表明钒改性能明显提高磷酸锰铁锂材料的充放电性能,其中x=0.2时得到的0.8LiFe0.5Mn0.5PO4-0.2Li3V2(PO4)3/C(标记为LFMP-LVP/C)材料电化学性能最好,其0.1C倍率时的放电比容量为141mAh·g-1.X射线衍射(XRD)分析指出LFMP-LVP/C材料的微观结构为橄榄石型LiFe0.5Mn0.5PO4/C和NASICON型Li3V2(PO4)3组成的双相结构.能量色射X射线谱(EDS)分析结果指出,Fe、Mn、V、P元素在所合成材料中的分布非常均匀,表明所制备材料成分的均一性.Li3V2(PO4)3改性使材料的电导率明显提高.LiFe0.5Mn0.5PO4的电导率为1.9×10-8S·cm-1,而LFMP-LVP材料电导率提高到2.7×10-7S·cm-1.与纯Li3V2(PO4)3的电导率(2.3×10-7S·cm-1)相近.电化学测试表明钒改性使LFMP-LVP/C材料充放电过程电极极化明显减小,从而电化学性能得到显著提高.本文工作表明Li3V2(PO4)3改性可成为提高橄榄石型磷酸盐锂离子电池正极材料电化学性能的一种有效方法.

Electrochemical Performance of Vanadium Modified LiFe0.5Mn0.5PO4/C Cathode Materials for Lithium-Ion Batteries

Vanadium modified LiFe0.5Mn0.5PO4/C cathode materials with a nominal composition of (1-x)LiFe0.5Mn0.5PO4-xLi3V2(PO4)3/C (x=0,0.1,0.2,0.25,1) were prepared by a solid-state reaction using NH4VO3 as the vanadium source.The electrochemical performance of the LiFe0.5Mn0.5PO4-based compounds improved upon vanadium modification.The 0.8LiFe0.5Mn0.5PO4-0.2Li3V2(PO4)3/C (LFMP-LVP/C) sample exhibited the highest discharge capacity of 141 mAh·g-1 at 0.1C rate.X-ray diffraction analyses revealed a dual phase of the LFMP-LVP/C composite with the coexistence of an olivine-type LiFe0.5Mn0.5PO4/C phase and a NASICON-type Li3V2(PO4)3 phase.Energy dispersive X-ray spectroscopy (EDS) analysis indicates a uniform distribution of Fe,Mn,V,and P in the composite.The electronic conductivity of LFMP-LVP was found to be 2.7×10-7 S·cm-1,which is much higher than the value (1.9×10-8 S·cm-1) of LiFe0.5Mn0.5PO4 and similar to the value (2.3×10-7 S·cm-1) of pure Li3V2(PO4)3.Vanadium modification remarkably reduced the electrode polarization of the LFMP-LVP/C cathode during the charge-discharge procedure.This suggests that vanadium modification is an effective method to improve the electrochemical performance of olivine-type cathode materials.