Preparation and Electrochemical Performance of Na⁺-stabilized Layered LiNi_0.6Co_0.2Mn_0.2O₂ Cathode Material for Lithium-ion Batteries

Na-doped Li_0.98Na_0.02Ni_0.6Co_0.2Mn_0.2O₂ cathode material was synthesized through a simple oxalate co-precipitation. Powder X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), energy dispersive X-ray spectroscopy(EDS), inductively coupled plasma-atomic emission spectrometry(ICP-AES), electrochemical impedance spectroscopy(EIS) and galvanostatic charge-discharge tests were employed to analyze the particle morphology, crystal structure and electrochemical properties of the as-prepared materials. Results indicate that the Na-stabilized sample has a more ordered α-NaFeO₂ structure(space group R3m), reduced Li⁺/Ni²⁺ cation mixing and enlarged Li layer spacing, which facilitates the fast insertion and extraction of Li⁺ ions in the bulk structure. Electrochemical results confirm that the Na-stabilized sample has excellent cycling stability and high rate performance. After 100 cycles at 1C between 2.7 V and 4.3 V, the cathode delivers a discharge capacity of 146 mA·h/g with capacity retention of 95.4%. At 0.1C, 0.2C, 0.5C, 1C, 3C, 5C, 10C and 20C, the specific capacities of the material are 181, 168, 162, 155, 143, 136, 126 and 113 mA·h/g, respectively. The Na-doping method is facile and feasible, which can provide some valuable reference for synthesizing other high rate and high capacity layered anode/cathode oxides.