Effect of vanadium doping on electrochemical performance of LiMnPO4 for lithium-ion batteries

A series of LiMn1-x V (x) PO4 samples have been synthesized successfully via a conventional solid-state reaction method. The active materials are characterized by x-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy. The electrochemical performances of the samples are tested using cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge measurement techniques. It is confirmed that the samples are in single phase when the content of vanadium (x) is lower than 0.05. If that content is higher than 0.1, the samples are shown to contain an additional conductive phase of Li3V2(PO4)(3). The vanadium doping significantly enhances the electrochemical properties of LiMnPO4. It is underlined that the optimal ratio for a low-vanadium doping with the best electrochemical performance is 0.1 and this material exhibits a corresponding initial charge and discharge capacity of 98.9 and 98.1 mAh g(-1) at 0.1 C under 50 A degrees C. The capacity retention is higher than 99 % after 30 cycles. The dramatic electrochemical improvement of the LiMnPO4 samples is ascribed to the strengthened ability of lithium-ion diffusion and enhanced electronic conductivity for the V-doped samples.