Oleic acid-assisted preparation of LiMnPO4 and its improved electrochemical performance by Co doping

LiMnPO4, with a particle size of 50-150 nm, was prepared by oleic acid-assisted solid-state reaction. The materials were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The electrochemical properties of the materials were investigated by galvanostatic cycling. It was found that the introduction of oleic acid in the precursor led to smaller particle size and more homogeneous size distribution in the final products, resulting in improved electrochemical performance. The electrochemical performance of the sample could be further enhanced by Co doping. The mechanism for the improvement of the electrochemical performance was investigated by Li-ion chemical diffusion coefficient ((D) over tilde (Li)) and electrochemical impedance spectroscopy measurements. The results revealed that the (D) over tilde (Li) values of LiMnPO4 measured by cyclic voltammetry method increase from 9.2x10(-18) to 3.0 x 10(-17) cm(2) s(-1) after Co doping, while the charge transfer resistance (R-ct) can be decreased by Co doping.