Operando real-space imaging of a structural phase transformation in a high-voltage electrode

TL;DR

This study uses operando Bragg Coherent Diffractive Imaging to visualize nanoscale phase transformations in a high-voltage battery electrode, revealing interface evolution and dislocation dynamics that influence electrochemical performance.

Contribution

It demonstrates the application of operando BCDI to directly observe phase transformation mechanisms in battery materials at the nanoscale.

Findings

Direct observation of nucleation and growth of Li-rich phase

Evolution from curved to planar interface driven by dislocation dynamics

Negligible kinetic limitations even at fast discharge rates

Abstract

Discontinuous solid-solid phase transformations play a pivotal role in determining properties of rechargeable battery electrodes. By leveraging operando Bragg Coherent Diffractive Imaging (BCDI), we investigate the discontinuous phase transformation in LixNi0.5Mn1.5O4 within a fully operational battery. Throughout Li-intercalation, we directly observe the nucleation and growth of the Li-rich phase within the initially charged Li-poor phase in a 500 nm particle. Supported by the microelasticity model, the operando imaging unveils an evolution from a curved coherent to planar semi-coherent interface driven by dislocation dynamics. We hypothesize these dislocations exhibit a glissile motion that facilitates interface migration without diffusion of host ions, leaving the particle defect-free post-transformation. Our data indicates negligible kinetic limitations impacting the transformation kinetics, even at discharge rates as fast as C/2. This study underscores BCDI's capability to provide operando insights into nanoscale phase transformations, offering valuable guidance for electrochemical materials design and optimization.