Enhanced electrochemical performance of manganese-doped β-LiVOPO4 cathode materials for lithium-ion batteries

LiV1-xMnxOPO4 (0 ≤ x ≤ 0.2) cathode materials have been first synthesized by substituting V4+ in β-LiVOPO4 with Mn4+ ion using a common solid-state method. Effects of Mn doping on the structures, morphology, and electrochemical properties of β-LiVOPO4 were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), and various electrochemical methods such as galvanostatic charge–discharge tests, cyclic voltammograms (CV), and electrochemistry impedance spectroscopy (EIS) as well. Of the compositions investigated, the LiV0.96Mn0.04OPO4 materials present the best electrochemical characteristics with the first discharge capacity of 150.0 and 148.7 mAh/g kept after 30 cycles at 0.2 C, while the value for β-LiVOPO4 is only 135.5 and 123.6 mAh/g, respectively. It is clearly demonstrated that the improvement in electrochemical properties of β-LiVOPO4 may be a result from the reduced charge transfer resistance, the increased lithium-ion diffusion, and phase conversion due to Mn doping.