LiNi1/3Co1/3Mn1/3O2 coated by Al2O3 from urea homogeneous precipitation method: improved Li storage performance and mechanism exploring

Layered LiNi1/3Co1/3Mn1/3O2 has been successfully coated with a uniform Al2O3 film through an homogeneous precipitation method with urea as a precipitant. The bare and Al2O3-coated LiNi1/3Co1/3Mn1/3O2 samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and electrochemical charge/discharge tests. For the 1 % Al2O3-coated LiNi1/3Co1/3Mn1/3O2 sample, XRD results show that it possesses the best hexagonal layered crystal structure with the lowest cation mixing among all samples, and SEM and TEM images show a uniform and amorphous Al2O3 layer (similar to 13 nm) formed on the LiNi1/3Co1/3Mn1/3O2 surface. Compared with bare sample, it exhibits superior electrochemical performance including the highest initial coulombic efficiency (92.1 %), high discharge capacity (202.6 mAh g(-1) at 0.1 C), excellent cycling performance (92 % at the 100th cycle, 0.5 C), and rate performance. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) are used to aid to reveal the functional mechanism, and the results show that the improving on the electrochemical performance after Al2O3 coating can be attributed to the suppressed electrolyte (LiPF6 or solvents) decomposition reaction on the cathode/electrolyte interface and thus reduced interfacial impedance value and impedance growth speed with cycling.