A facile process for coating amorphous FePO4 onto LiNi0.8Co0.15Al0.05O2 and the effects on its electrochemical properties

Ni-rich layered LiNi0.8Co0.15Al0.05O2 is coated with amorphous FePO4 in an ethanol-based colloidal solution. X-ray diffraction (XRD) measurements indicate that the coated sample is pure hexagonal phase without any crystalline FePO4 in it. Additionally, the lattice parameters a and c are not influenced by the coating layer. The morphologies of the samples are characterized by scanning electron microscope (SEM) analysis. Compared with the pristine sample, the FePO4-coated one shows no change on morphology. However, an amorphous FePO4 coating layer can be observed through transmission electron microscope (TEM) analysis. Moreover, energy dispersive spectrometer (EDS) elemental mappings results confirm that the FePO4 uniformly coats on the host material. By electrochemical characterizations, it is proved that the capacity retention of the FePO4-coated sample is much higher than that of the pristine one. After 100 charge-discharge cycles at 2 C rate, the pristine and FePO4-coated samples exhibit the capacity retentions of 70.7% and 88.3%, respectively. Furthermore, the impedance increasing during charge-discharge cycles is slowed down by the FePO4 coating layer.