First-Principles Insights into the Role of Coordination Polyhedron Size on Mn Ion Migration within Li2-xMnO3 Layered Cathode Material

Abstract

Li-rich cathode materials are promising cathode materials for lithium-ion batteries. However, the Mn ion migration in Li-rich cathode materials during charge–discharge cycles significantly impedes their practical application. In this study, a systematical investigation has been carried out to reveal the Mn ion migration mechanisms in Li_2-xMnO₃ by using first-principles calculations. It is found that the Mn migration energy increases with increasing Li⁺ extraction from Li₂MnO₃. Conversely, the Li_Mn anti-site formation energy declines with the extraction of more Li⁺ from Li₂MnO₃. The migration energy decreases under the tensile strain along the c- and b-axes. Further investigations reveal that the Mn ion migration energy is determined by MnO₆ coordination polyhedron. Specifically, a larger MnO₆ coordination polyhedron volume would result in lower migration energy, highlighting the coordination polyhedron size as a pivotal factor in the suppression of Mn ion migration. This study offers an in-depth understanding of transition metal ion migration phenomena, providing theoretical guidance for devising strategies to mitigate Mn migration in Li-rich materials.