Enhanced electrochemical property of FePO4-coated LiNi0.5Mn1.5O4 as cathode materials for Li-ion battery

Pristine LiNi0.5Mn1.5O4 and FePO4-coated one with Fd-3m space groups were prepared by a sol-gel method. The structure and performance were studied by X-ray diffraction (XRD) rietveld refinement, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectrometer (EDS) mapping, electrochemical impedance spectroscopy (EIS) and charge-discharge tests, respectively. The lattice parameters of all samples almost remain the same from the Rietveld refinement, revealing that the crystallographic structure has no obvious difference between pristine LiNi0.5Mn1.5O4 and FePO4-coated one. All materials show similar morphologies with uniform particle distribution with small particle size, and FePO4 coating does not affect the morphology of LiNi0.5Mn1.5O4 material. EDS mapping and HRTEM show that FePO4 may be successfully wrapped around the surfaces of LiNi0.5Mn1.5O4 particles, and provides an effective coating layer between the electrolyte and the surface of LiNi0.5Mn1.5O4 particles. FePO4 (1wt%)-coated LiNi0.5Mn1.5O4 cathode shows the highest discharge capacity at high rate (2C) among all samples. After 80 cycles, the reversible discharge capacity of FePO4 (1wt%) coated LiNi0.5Mn1.5O4 is 117mAhg-1, but the pristine one only has 50mAhg-1. FePO4 coating is an effective and controllable way to stabilize the LiNi0.5Mn1.5O4/electrolyte interface, and avoids the direct contact between LiNi0.5Mn1.5O4 powders and electrolyte, then suppresses the side reactions and enhances the electrochemical performance of the LiNi0.5Mn1.5O4.