Nanoscale Mapping of Transition Metal Ordering in Individual LiNi0.5Mn1.5O4 Particles Using 4D-STEM ACOM Technique

TL;DR

This study employs 4D-STEM to achieve nanoscale mapping of transition metal ordering in individual LiNi0.5Mn1.5O4 particles, revealing how annealing conditions influence local ordering and providing insights into the material's electrochemical performance.

Contribution

First direct nanoscale observation and quantification of transition metal ordering in LiNi0.5Mn1.5O4 particles using 4D-STEM, linking local structure to processing conditions.

Findings

Ordered spinel structure is consistent throughout individual particles.

Extent of ordering varies with annealing conditions.

Boundary between highly-ordered and low-ordered particles identified.

Abstract

The electrochemical performance of the spinel LiNi0.5Mn1.5O4, a high-voltage positive electrode material for Li-ion batteries, is influenced by the transition metal arrangement in the octahedral network, leading to disordered (Fd m S.G.) and ordered3 (P4332 S.G.) structures. However, widely used techniques lack the spatial resolution necessary to elucidate the ordering phenomenon at the particle scale. Using the 4D-STEM technique, we present the first direct observation of ordering distribution in individual LiNi0.5Mn1.5O4 particles with nanometric spatial resolution. We propose a quantification method for the local degree of ordering based on the ratio of ordered to disordered spinel lattices along the particle thickness extracted from electron diffraction spot intensities. In an ordered spinel LiNi0.5Mn1.5O4, the transition metal ordering is consistently observed throughout the primary particle. However, the extent of ordering in the spinel phase depends on its distribution at the particle scale, a factor influenced by the annealing conditions. The 4D-STEM analysis elucidates the boundary between highly-ordered and low-ordered LiNi0.5Mn1.5O4 particles.