Synthesis of Li(Ni0.6Co0.2Mn0.2)O2 with sodium DL-lactate as an eco-friendly chelating agent and its electrochemical performances for lithium-ion batteries

Abstract

(Ni0.6Co0.2Mn0.2)(OH)2 precursor has been successfully prepared using hydroxide co-precipitation method. The thermodynamic model of hydroxide co-precipitation with sodium DL-lactate as an eco-friendly chelating agent is proposed. The microstructures of (Ni0.6Co0.2Mn0.2)(OH)2 precursors and Li(Ni0.6Co0.2Mn0.2)O2 cathode materials are investigated using X-ray diffractometer and scanning electronic microscopy, while the electrochemical performances of Li(Ni0.6Co0.2Mn0.2)O2 cathode materials are measured using a charge–discharge test. The influences of pH value on the structure and morphological and electrochemical performances of Li(Ni0.6Co0.2Mn0.2)O2 cathode materials have been discussed in detail. The results show that the sample at pH = 11.5 exhibits the best lamellar structure and lowest cation mixing, while the sample at pH = 11.0 delivers the most uniform and full particles and possesses the highest initial charge–discharge performance of 183.4 mAh/g and the best coulombic efficiency of 77.9% at the voltage range of 3.0–4.3 V. Even after 100 cycles, its discharge capacity still remains 165.2 mAh/g with the best retention rate of 90.1%. Furthermore, the sample at pH = 11.0 delivers the highest discharge capacity at each current density. Even if discharged at 5C (1000 mA/g), the capacity of 115.6 mAh/g has been achieved. The sample at pH = 11.0 exhibits the highest Li-ion diffusion coefficients (2.072 × 10−12 cm2/s).