Improvement of the high-rate discharge capability of phosphate-doped spinel LiMn2O4 by a hydrothermal method

Micrometer-scale pristine and phosphate-doped spinel LiMn2O4 materials with homogeneous size distribution were synthesized by a one-step hydrothermal method. The composition, structure and morphology of the as-prepared samples were characterized using inductively coupled plasma atomic emission spectroscopy (ICP-AES), chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of phosphate doping on the structural and electrochemical properties of spinel LiMn2O4 was investigated by Fourier transform infrared (FT-IR) spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The phosphate-doped LiMn2O4 cathode (with a molar ratio of PO43−:LiMn2O4 = 1.5%) exhibits good high-rate discharge capability with 94 mAh/g at a current density of 2960 mA/g. The analyses demonstrate that compared with the pristine LiMn2O4 sample, the phosphate-doped samples have a relatively large Li-ion diffusion coefficient and smaller charge-transfer resistance due to the increase of the unit cell volume of spinel LiMn2O4 caused by the doping of phosphate.