Atomic-Scale Revealing the Structure Distribution between LiMO2 and Li2MnO3 in Li-Rich and Mn-Based Oxide Cathode Materials

Abstract

Lithium-rich and manganese-based oxide (LRMO) cathode materials are regarded as promising cathode materials for lithium-ion batteries with anionic redox characteristics and higher specific energy density. However, the complex initial structure and complicated reaction mechanism of LRMO is controversial. Herein, the reaction mechanism and unusual electrochemical phenomena are reconsidered after proposing the concept of structure distribution between Li2MnO3 and LiMO2 structures. The initial structure states show different types of composition characteristics of Li2MnO3 and LiMO2, including “large and isolated distribution” and “uniformly dispersed distribution” characteristics, as summarized by multiple aberration correction scanning transmission electron microscopy observations at the atomic-scale for cross sectional samples. Based on the density functional theory calculations, X-ray absorption spectroscopy, and atomic-scale observations during the different voltage states, the results accordingly suggest that the distribution characteristic is the essential cause of the unusual behavior in LRMO. It governs the reaction behavior, leading to the changes in electronic structure of O2p and TM3d, and the maintenance of layered structure, reversibility of the anionic redox, as well as, the voltage hysteresis. This work constructs the interrelationships of electrochemical behavior—distribution characteristic—reaction mechanism, contributing to the further application of LRMO materials in the electric vehicle market.