Synthesis and characterization of full concentration-gradient LiNi0.7Co0.1Mn0.2O2 cathode material for lithium-ion batteries

Spherical Ni0.7Co0.1Mn0.2(OH)2 precursor with the content of Ni decreasing gradually from the core to the surface of the particle and the content of Co and Mn increasing was prepared by co-precipitation from sulfate solutions using NaOH and NH4OH as precipitation and complexing agents. Then, well-ordered spherical LiNi0.7Co0.1Mn0.2O2 particles was synthesized by sintering the mixture of as-prepared precursor and LiOH·H2O in flowing oxygen. Their structural and electrochemical properties were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), charge-discharge test, cyclic voltammetry (C-V) method and electrochemical impedance spectroscopy (EIS) test. EDXS results indicated that the concentration of Ni, Co and Mn changed gradually inside out of the particle. The full concentration-gradient (FCG) material had better electrochemical performances compared to homogeneous LiNi0.7Co0.1Mn0.2O2, confirmed by the results of C-V and EIS. The results of charge-discharge tests demonstrated that the FCG-LiNi0.7Co0.1Mn0.2O2 material sintered at 810 °C delivered an initial discharge capacity of 179.1 mA h g−1 at 1 C rate between 2.8 and 4.3 V and more than 94.0% of that was retained after 100 cycles. Besides, it also exhibited excellent rate capability and high voltage and temperature performance, with a high capacity of 155.9 mA h g−1 even at 10 C rate.