Effects of Coprecipitation Conditions on the Electrochemical Properties of Cobalt‐Free LiNi0.9Mn0.1‐xAlxO2 Cathodes

Abstract Commercializing high‐nickel, cobalt‐free cathodes, such as LiNi 0.9 Mn 0.1‐x Al x O 2 (NMA‐90), hinges on effectively incorporating Al 3+ during the hydroxide coprecipitation reaction. However, Al 3+ coprecipitation is nontrivial as Al 3+ possesses unique precipitation properties compared to Ni 2+ and Mn 2+ , which impact the final precursor morphology and consequently the cathode properties. In this study, the nuance of Al 3+ coprecipitation and its influence on the cycling stability of NMA with increasing Al 3+ content is elucidated. While low reaction pH and ammonia concentration are suitable for producing Al‐free LiNi 0.9 Mn 0.1 O 2 (NM‐90) effectively, the same coprecipitation environment leads to porous precursor morphology and poor cycle life in Al‐containing LiNi 0.9 Mn 0.08 Al 0.02 O 2 (NMA‐900802) and LiNi 0.9 Mn 0.05 Al 0.05 O 2 (NMA‐900505). By systematically increasing the reaction pH and ammonia concentration for the Al‐containing compositions, the precursor morphology becomes denser and the cathode cycling stability is greatly improved. It is hypothesized that the improvement in cycling stability stems from the reduction in Al(OH) 3 nucleation, which promotes hydroxide particle growth with optimal Al 3+ incorporation into the cathode lattice.