Oxalate co-precipitation synthesis of LiNi0.6Co0.2Mn0.2O2 for low-cost and high-energy lithium-ion batteries

Abstract

A facile oxalate co-precipitation method combined with solid-state sintering is used to synthesize layered LiNi0.6Co0.2Mn0.2O2 (NCM-622) as a low-cost cathode material for lithium ion batteries. Homogeneous Ni-Co-Mn oxalate precursors were obtained by adding oxalic acid into mixed metal acetates without the need of rigorous control of co-precipitation parameters. The effects of sintering temperature on the morphology, structure and electrochemical properties of the synthesized NCM-622 are studied. An intermediate sintering temperature of 850 °C is found to favor the integrity of the layered structure by compromising the solid-state reaction and Li loss, leading to a low degree of cation mixing. The as-synthesized NCM-622 delivers a capacity of 152 mA h g−1 after 100 cycles at 1 C (93.2% retention), and shows excellent rate capability with 76.8 mA h g−1 at 10 C, which is competitive to the materials prepared by the mainstream hydroxide co-precipitation method. Moreover, a solution-based surface modification was employed to further improve the cathode through self-adsorption of Al(OH)3 using Al2(SO4)3 precursor in order to form a Al2O3 coating. The facial surface modification has significantly improved the performance of NCM-622 under normal and high voltage conditions.