Electrochemical performance of vanadium modified LiFe 0.5Mn 0.5PO 4/C cathode materials for lithium-ion batteries

Abstract

Vanadium modified LiFe 0.5Mn 0.5PO 4/C cathode materials with a nominal composition of (1-x)LiFe 0.5Mn 0.5PO 4-xLi 3V 2(PO 4) 3/C (x=0, 0.1, 0.2, 0.25, 1) were prepared by a solid-state reaction using NH 4VO 3 as the vanadium source. The electrochemical performance of the LiFe 0.5Mn 0.5PO 4-based compounds improved upon vanadium modification. The 0.8LiFe 0.5Mn 0.5PO 4-0.2Li 3V 2(PO 4) 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 LiFe 0.5Mn 0.5PO 4/C phase and a NASICON-type Li 3V 2(PO 4) 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 LiFe 0.5Mn 0.5PO 4 and similar to the value (2.3 × 10 -7 S·cm -1) of pure Li 3V 2(PO 4) 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. © Editorial office of Acta Physico-Chimica Sinica.