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

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.