The effect of Co₃O₄ & LiCoO₂ cladding layer on the high rate and storage property of high nickel material LiNi_0.8Co_0.15Al_0.05O₂ by simple one-step wet coating method

Highlights: •Co₃O₄ & LiCoO₂ complex layer with nutty-cake structure improves the rate and storage performance of LiNi_0.8Co_0.15Al_0.05O₂. •Lithium impurity on NCA surface can be synchronously transformed to LiCoO₂ when coating Co₃O₄. •LiCoO₂ with the similar structure to LiNiO₂ tightly immobilizes Co₃O₄ layer on NCA surface. -- Abstract: Co₃O₄ & LiCoO₂ complex cladding layer with nutty-cake structure effectively improves high rate and storage properties of high nickel material LiNi_0.8Co_0.15Al_0.05O₂ (NCA), using a simple one-step wet-coating process, and the degradation of NCA is successfully restrained. The structure and morphology of samples are demonstrated by X-ray diffraction (XRD), scanning electron microscope (SEM), and field-emission high resolution transmission electron microscope (FEHRTEM). The elemental composition and distribution are determinate by energy dispersive spectrometer (EDS). In comparison with pristine NCA, 0.25 wt.% Co₃O₄-modified NCA has a better electrochemical performance with more capacity of approximate 30 mAh g⁻¹ at 1C after 150 cycles. At 5C and 10C, it also exhibits better capacity retentions and higher capacities. After exposed to the air for 100 days, 0.25 wt. % Co₃O₄-modified NCA still shows better electrochemical performance than pristine NCA stored at the same condition. The improved comprehensive performance of Co₃O₄ & LiCoO₂ coated NCA is related with the facile coating method in which Co₃O₄ is formed and the lithium impurity on NCA surface is consumed to produce LiCoO₂ concurrently during calcining process. The reaction mechanism of Co₃O₄ & LiCoO₂ composite layer is analyzed using the cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS).