Synthesis and characterization of concentration-gradient LiNi0.6Co0.2Mn0.2O2 cathode material for lithium ion batteries

Spherical Ni0.6Co0.2Mn0.2(OH)2 precursor with the concentration of Ni and Mn changed in opposite was prepared by co-precipitation. Then, well-ordered spherical LiNi0.6Co0.2Mn0.2O2 was synthesized by sintering the mixture of as-prepared precursor and LiOH⋅H2O first calcined at 550 °C for 4 h in air, followed at 820 °C for 12 h 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. The concentration-gradient material had a superior electrochemical performances compared to conventional homogeneous LiNi0.6Co0.2Mn0.2O2 material, demonstrated by the results of C-V and EIS. The results of charge and discharge test demonstrated that the concentration-gradient LiNi0.6Co0.2Mn0.2O2 cathode material sintered at 820 °C delivered an initial discharge capacity of 174.3 mA h g−1 at 1 C rate between 2.8 and 4.3 V and more than 93.1% of that was retained after 100 cycles. Besides, this material also exhibited excellent rate capability and high voltage cut-off and temperature performance.