Co-precipitation synthesis of nickel-rich cathodes for Li-ion batteries

The preparation of Ni-rich cathode materials is challenging due to the Ni2+ ion sensitivity to oxidation during synthesis. The synthesis conditions during the manufacture of Ni-rich materials such as LiNi0.8Mn0.1Co0.1O2 (NMC811) therefore require stringent control. The co-precipitation step, applied in the synthesis of the metal hydroxide precursor, determines the secondary particle assembly formation, where it is typically desirable to produce uniform, spherical, ∼10μm-diameter structures. A stirred tank reactor is often employed to maintain a constant temperature of 60 °C and a controlled pH of between 10.5 and 11.5 in an inert atmosphere to maintain a high Ni2+/Ni3+ ion ratio. This promotes the formation of an NMC hydroxide precursor (NixMnyCoz(OH)2) which is typically milled with a lithium salt and calcined to form LiNixMnyCozO2 with a layered α-NaFeO2 crystalline structure. This review outlines some of the critical synthetic parameters for the formation of spherical secondary assemblies of metal hydroxide precursors for nickel-rich layered cathodes.