Correlation between Local Structure and Reaction Mechanism in Disordered Rock-Salt-Type Lithium–Manganese Oxides

Abstract

First-principles (FP) calculations of disordered rock-salt-type lithium–manganese oxides were performed by assuming a quasi-random structure model with the composition of Li16Mn16O32. The effects of randomness in the crystal structure and the changes in local atomic configurations during the Li extraction process on electronic structures, phase stability, and electrochemical properties were investigated by the FP calculations. The calculations indicate that the randomness of local atomic configurations, which originates from the disordered structure, makes it possible for Mn and O sites to take on a variety of electronic states. Analyses of densities of states, magnetic moments of Mn atoms, and Bader charges indicate the possibility that not only Mn but also oxygen atoms contribute to the redox reaction. The migration of Li and Mn is found to appear from octahedral to tetrahedral sites at a high state of charge. The FP calculations suggest that the change in local atomic configurations and electronic structures causes the transition in voltage profiles from sloping to 3 V plateau shape as the cycle progresses, which is characteristic of spinel-related positive electrode materials.