First-Principles Studies of Structural Evolutions in Cathode Materials LiMO₂ (M=Co, Mn, Ni)

Abstract

Understanding the structural inconsistency of LiMO2 (M = Co, Mn, Ni) is crucial for developing high-performance NCM batteries. Here we explore the structural evolutions of stoichiometric LiMO2 using the first-principles calculations combined with the cluster expansion method. We automatically obtain the ground state structures of the stochiometric LiMO2 by just considering the cation orderings in the quasi rock-salt structures and the following structural relaxations due to both the atomic size mismatches and the Jahn-Teller distortions. We point out that, on the one hand, the cation orderings are mainly determined by the nearest, the second nearest, and the third nearest cation interactions and can be obtained from the ‘phase diagram’ which we have built using the relative strengths of effective cluster interaction (ECI). On the other hand, the structural relaxations are dominated by the crystal field splitting (CFS) energies, i.e., structures with larger CFS energies are more stable. By calculating the effective cluster interactions and CFS energies for various structures of LiMO2, we clearly show how ECI and CFS play roles in determining the structural evolution mechanism of these systems.