Spray-assisted synthesis of ant-cave-structured Ni-rich cathode microspheres with Li-reactive coating layer for high-performance Li-ion batteries

Abstract

In this study, a spray-assisted synthetic method for preparation of Ni-rich Li [NixCoyMn1-x-y]O2 (NCM) cathode microspheres is introduced. Unlike the co-precipitation method, which necessitates pH control, the use of complexing agent, and further lithiation step, the spray-assisted approach can produce Li-containing precursors with homogeneous elemental distribution in a few seconds. To overcome the high energy density loss arising from the morphological traits of the hollow/porous microspheres produced from the spray process, a two-step spraying methodology is adopted. Planetary ball milling efficiently pulverizes the spray-pyrolyzed product, which is then dispersed in an aqueous solution to form colloids. Spray drying and subsequent oxidation of the colloidal solution yield ant-cave-structured NCM microspheres with fine primary particles. By simply changing the stoichiometry of the metal salts dissolved in the aqueous solution, NCM cathodes with the desired composition (NCM622 and NCM811) are obtained. Additionally, a Li-reactive coating layer is introduced on the surface of the fine particles comprising NCM microspheres by a 10-min gas-phase coating method. The delicate design of NCM622 cathode with a coating layer enables stable cycle performance (capacity retention of 82.0 % after the 150th cycle) and high rate capability (136.8 mA h g−1 at 10 C) when operated under high-voltage conditions (2.5–4.5 V).