Intrinsic Role of Cationic Substitution in Tuning Li/Ni Mixing in High-Ni Layered Oxides

Nickel-rich transition-metal (TM) layered oxides, particularly those with high Ni content, attract worldwide interest for potential use as high-capacity cathodes in next-generation Li-ion batteries. However, as Ni loading increases, Li and Ni sitting at octahedra tend to mix, resulting in reduced electrochemical activity, which has been one major obstacle to their practical applications. Herein, we investigate the kinetic and thermodynamic aspects of Li/Ni mixing in LiNi0.7MnxCo0.3–xO2 (0 ≤ x ≤ 0.3) as they are synthesized, through quantitative determination of structural ordering and comparison to ab initio calculations. Results from this study elucidate the role of Co/Mn-substitution in tuning Li/Ni ordering, intrinsically through local magnetic interaction. Specifically, Co substitution facilitates Li/Ni ordering by relieving the intra-plane magnetic frustration and reducing the inter-plane super-exchange (SE) interaction; in contrast, Mn exacerbates magnetic frustration and strengthens SE, thereby aggravating Li/Ni mixing. These findings highlight the interplay between local magnetic interaction and cationic ordering, which has yet to be fully investigated for the needs of designing high-Ni layered cathodes and, broadly, TM-based oxides for various applications.