Imaging cathode materials using Bragg Coherent X-ray Diffraction

Abstract

The performance and longevity of lithium-ion batteries depend critically on the structural and electrochemical dynamics of their constituent materials, particularly cathodes. Among these, LiCoO₂ (LCO) is a benchmark material known for its high energy density. However, the structural evolution of LCO during electrochemical cycling, including strain, defects, and domain formation, remains poorly understood, largely due to the limitations of conventional imaging techniques in resolving nanoscale dynamics non-destructively.

This thesis leverages Bragg Coherent X-ray Diffraction Imaging (Bragg CDI), a powerful, non-destructive technique, to probe the three-dimensional structural and strain dynamics of nanocrystalline LCO cathodes. By combining traditional phasing methods with machine learning-based strain reconstruction tools, and further enhancing data interpretation with advanced analysis techniques, this work provides unprecedented insights into the nanoscale behaviour of LCO under varying electrochemical and electric field conditions.

The study reveals that during electrochemical cycling, LCO nanocrystals exhibit dynamic domain behaviour, including the formation and expansion of domains at the crystal edges in the charged state, followed by fragmentation into smaller domains bounded by dislocations. These processes are reversed during discharge, with domains shrinking and reassembling as the crystal approaches its discharged state. Additionally, under applied electric fields, polarised domains and significant phase changes are observed, with the field inducing phase uniformity along its direction. Notably, a migrating dislocation near the crystal edge exhibits depth invariance across varying field magnitudes, aligning with the domain expansion limit observed during cycling.

These findings contribute to a deeper understanding of the structural and electrochemical interplay in LCO cathodes, offering valuable insights into the mechanisms underlying performance degradation and suggesting pathways for improving battery design and functionality.

More information

Identifiers

ORCID for David Alexandru Serban: orcid.org/0000-0003-4335-4522

ORCID for Marcus Newton: orcid.org/0000-0002-4062-2117

ORCID for Andrew Cruden: orcid.org/0000-0003-3236-2535

Catalogue record

Export record