Effects of Coprecipitation Conditions on the Electrochemical Properties of Cobalt‐Free LiNi_0.9Mn_0.1‐xAl_xO₂ Cathodes

Abstract Commercializing high‐nickel, cobalt‐free cathodes, such as LiNi_0.9Mn_0.1‐xAl_xO₂ (NMA‐90), hinges on effectively incorporating Al³⁺ during the hydroxide coprecipitation reaction. However, Al³⁺ coprecipitation is nontrivial as Al³⁺ possesses unique precipitation properties compared to Ni²⁺ and Mn²⁺, which impact the final precursor morphology and consequently the cathode properties. In this study, the nuance of Al³⁺ coprecipitation and its influence on the cycling stability of NMA with increasing Al³⁺ content is elucidated. While low reaction pH and ammonia concentration are suitable for producing Al‐free LiNi_0.9Mn_0.1O₂ (NM‐90) effectively, the same coprecipitation environment leads to porous precursor morphology and poor cycle life in Al‐containing LiNi_0.9Mn_0.08Al_0.02O₂ (NMA‐900802) and LiNi_0.9Mn_0.05Al_0.05O₂ (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 Al³⁺ incorporation into the cathode lattice.