Surface Surgery of the Nickel-Rich Cathode Material LiNiCoAlO: Toward a Complete and Ordered Surface Layered Structure and Better Electrochemical Properties.

A complete and ordered layered structure on the surface of LiNiCoAlO (NCA) has been achieved via a facile surface-oxidation method with NaSO. The field-emission transmission electron microscopy images clearly show that preoxidation of the hydroxide precursor can eliminate the crystal defects and convert Ni(OH) into layered β-NiOOH, which leads to a highly ordered crystalline NCA, with its (006) planes perpendicular to the surface in the sintering process. X-ray photoelectron spectroscopy and Raman shift results demonstrate that the contents of Ni and Co ions are reduced with preoxidization on the surface of the hydroxide precursor. The level of Li/Ni disordering in the modified NCA determined by the peak intensity ratio I/I in X-ray diffraction patterns decreases. Thanks to the complete and ordered layered structure on the surface of secondary particles, lithium ions can easily intercalate/extract in the discharging-charging process, leading to greatly improved electrochemical properties.