Impact of Manganese on the Cycling Performance of Ni-Rich LiNi_1–<i>x</i>Mn_<i>x</i>O₂ Cathodes

Ni-rich LiNi1–xMnxO2 (NM, x ≤ 0.4) cathodes with high Mn levels have garnered particular attention due to their cost-effectiveness and enhanced safety for lithium-ion batteries, yet their cycling performance remains unsatisfactory. Herein, we investigate the relationship among structure characteristics, cycling performance, and Mn content, revealing that the cycling performance of NM cathodes is associated with Mn-level controlled cation ordering within their structures. Specifically, except for the inherent Li+/Ni2+ disorder, higher Mn levels in NM cathodes tend to disrupt the Ni2+/Mn4+ ordering, resulting in phase segregation and the formation of Mn-enriched regions with Mn3+/Mn3+ pairs. Distorted [Mn3+O6] octahedra, weak interactions between Mn3+ ions, and Mn3+ dissolution in the Mn-enriched regions are detrimental to the structural stability of NM cathodes, thus leading to inferior cycling performance. This study provides a profound understanding of Mn roles in Co-free Ni-rich cathodes and highlights the significance of maintaining cation ordering to achieve high-performance NM cathodes.