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-xLi(3)V(2)(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 0.8LiFe(0.5)Mn(0.5)PO(4)-0.2Li(3)V(2)(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 2.7x10(-7) S . cm(-1), which is much higher than the value (1.9x10(-8) S . cm(-1)) of LiFe0.5Mn0.5PO4 and similar to the value (2.3 x 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.