B11-O-11Atomic-scale Tracking Cation Diffusion in Lithium Manganese Oxide

Abstract

Solid-state phase transition are ubiquitous and of critical importance to numerous technological applications, including energy conversion and storage systems. These transition processes involve local atomic displacements or long-range atom migration without adding/reducing any atoms. For example, in perovskite ferroelectrics the oxygen octahedron shift and/or rotation results in a first order phase transition-polarization switching [ 1 ]. Investigating the dynamic processes of phase transformation in solids is critical to gain insights to understanding the fundamental physical properties of functional materials and benefiting industrial technologies. Here, we track full atoms motion/shift in lithium manganese oxide during a phase transition from spinel to rocksalt by using atomically resolved aberration corrected scanning transmission electron microscopy and spectroscopy. We find that given energy the transition metal cations can readily hop between oxygen tetrahedral and octahedral sites in lithium manganese oxide similar to lithium diffusion behavior, leaving the anion structure framework almost unchanged. During phase transition, the transition metal cation migration path, intermediate state, migration length, and atomic structure of phase boundaries are discovered and the mechanism is discussed. Our observations help us to understand the past experimental phenomena and provide useful information to stabilize the structure of electrode materials and thus improve the life of lithium ion batteries.