Enhanced electrochemical property of FePO 4 -coated LiNi 0.5 Mn 1.5 O 4 as cathode materials for Li-ion battery

Abstract Pristine LiNi 0.5 Mn 1.5 O 4 and FePO 4 -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 LiNi 0.5 Mn 1.5 O 4 and FePO 4 -coated one. All materials show similar morphologies with uniform particle distribution with small particle size, and FePO 4 coating does not affect the morphology of LiNi 0.5 Mn 1.5 O 4 material. EDS mapping and HRTEM show that FePO 4 may be successfully wrapped around the surfaces of LiNi 0.5 Mn 1.5 O 4 particles, and provides an effective coating layer between the electrolyte and the surface of LiNi 0.5 Mn 1.5 O 4 particles. FePO 4 (1 wt%)-coated LiNi 0.5 Mn 1.5 O 4 cathode shows the highest discharge capacity at high rate (2 C) among all samples. After 80 cycles, the reversible discharge capacity of FePO 4 (1 wt%) coated LiNi 0.5 Mn 1.5 O 4 is 117 mAh g −1 , but the pristine one only has 50 mAh g −1 . FePO 4 coating is an effective and controllable way to stabilize the LiNi 0.5 Mn 1.5 O 4 /electrolyte interface, and avoids the direct contact between LiNi 0.5 Mn 1.5 O 4 powders and electrolyte, then suppresses the side reactions and enhances the electrochemical performance of the LiNi 0.5 Mn 1.5 O 4 .