Revealing Roles of Co and Ni in Mn‐Rich Layered Cathodes

Abstract Pressing demand for reducing the dependence of the costly Co and Ni elements has recently made Mn‐rich layered oxides much more attractive as potential cathodes for rechargeable lithium‐ion batteries. Although the Co and Ni effects in Ni‐rich cathodes are investigated in detail, there is still a serious lack of fundamental understandings of the influences of the Co and Ni substitution on the structural and electrochemical properties of the Mn‐rich layered cathodes. Here, Co‐substituted, Co and Ni co‐substituted, and Ni‐substituted Mn‐rich layered cathodes Li(Mn, Ni, Co)O 2 are consciously designed to explore the roles of Co and Ni. These results elucidate that Co 4+ is destructive for the structural stability of Mn‐rich cathodes due to the increased instability in the lattice oxygen, especially at high potentials, thereby delivering poor cycling stability, while Ni substitution of Co introduces Li/Ni mixing to enhance the lattice oxygen stability and suppress phase segregation and irreversible phase transition, leading to much improved cycling stability. These findings complement the elemental chemistry of the Co‐, Ni‐, and Mn‐based layered oxide cathodes, and benefit the development of Co‐free Mn‐rich layered cathode materials for future rechargeable lithium‐ion batteries.