Correlative ADF-EDS-EELS Tomography Maps 3D Valence State Dynamics in LiNi1/3Co1/3Mn1/3O2 Battery Cathodes

Understanding how battery cathodes degrade is crucial for improving energy storage, and recent work by Jaewhan Oh, Sunggu Kim, and Chaehwa Jeong, alongside Jason Manassa, Jonathan Schwartz, and Sangmoon Yoon, presents a significant advance in visualising these processes. The team developed a new method that simultaneously maps the atomic structure, chemical composition, and electronic states of battery materials in three dimensions, offering unprecedented insight into degradation mechanisms. Applying this technique to lithium nickel manganese cobalt oxide particles, researchers observe that while chemical changes occur evenly throughout the material, alterations in electronic states and the segregation of elements concentrate at the surface. This discovery reveals a complex interplay between bulk and surface-level degradation, demonstrating that cathode failure is not simply a matter of phase transitions, but is actively driven by ion movement and material dissolution, ultimately establishing nanoscale inhomogeneity and valence gradients as key contributors to battery failure.

Understanding how battery cathodes and other functional materials degrade requires simultaneous knowledge of structural, chemical, and electronic changes in three dimensions. Scientists have developed a new multi-modal correlative microscopy approach, combining scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy-loss spectroscopy, to achieve nanoscale 3D characterisation. This method directly correlates structural, chemical, and electronic information within a single volume of material, overcoming limitations of sequential analysis techniques. The team demonstrated this capability by investigating lithium-rich layered oxide cathode materials, revealing that oxygen vacancy formation and manganese dissolution are key degradation pathways. These processes lead to the formation of core-shell structures and the loss of electrochemical performance. This correlative microscopy approach represents a significant advancement in materials characterisation, offering a powerful tool for understanding degradation phenomena in a wide range of functional materials.

Beam Stability Verification and Data Calibration

Supplementary figures demonstrate beam stability, confirming that observed changes are due to material evolution, not instrument-induced damage. Representative tomographic tilt series images visually illustrate the data collected. Inductively Coupled Plasma Optical Emission Spectrometry provides bulk chemical analysis, serving as a ground truth for comparison with spatially resolved data. Supplementary movies provide dynamic visualizations of the 3D data, allowing for intuitive understanding of the spatial distribution of chemical composition, valence states, and structural features. This data ensures the accuracy and reliability of the findings.

Nanoscale Cathode Degradation Mapped in 3D

This work presents a breakthrough in characterizing battery cathode degradation through simultaneous three-dimensional mapping of atomic structure, chemical composition, and valence states. Scientists developed a novel technique, ADF-EDS-EELS tomography, to visualize nanoscale changes within NCM111 particles during electrochemical cycling. This method allows for correlated 3D imaging of atomic structure, composition, and electronic structure within a single low-dose STEM tilt series acquisition, revealing previously unseen degradation processes. Experiments tracked the evolution of NCM111 cathodes through 50, 100, and 200 electrochemical cycles, demonstrating capacity loss after each cycle.

Atomic-resolution measurements confirmed structural phase transitions, progressing from a layered structure to spinel-like and ultimately to a rock-salt structure. Reconstructed 3D chemical composition maps, validated using fused multi-modal tomography, revealed a homogeneous distribution of oxygen and transition metals in pristine and partially cycled particles, with only minor local segregation near the surface. However, the fully cycled particle exhibited a notably inhomogeneous distribution of transition metals, consistent with the transition to a rock-salt structure. Quantitative analysis of valence states revealed that while chemical composition evolved uniformly, valence state changes and transition metal inhomogeneity were strongly surface-localized and depth-dependent. These findings establish valence state gradients and nanoscale inhomogeneity as active contributors to cathode failure, highlighting the roles of ion migration and dissolution-driven segregation. This correlative 3D platform opens new opportunities for studying redox-driven transformations in fields such as heterogeneous catalysis.

Surface and Bulk Degradation in Cathode Materials

Applying this simultaneous imaging technique to lithium nickel manganese cobalt oxide particles at different stages of charge-discharge cycling, scientists have revealed nanoscale degradation processes with unprecedented spatial and chemical detail. The findings demonstrate that while the overall chemical composition remains uniform throughout the particle, changes in valence states and the concentration of transition metal inhomogeneity are strongly focused near the surface. This coexistence of bulk and surface-driven degradation reveals a complex interplay of mechanisms, moving beyond simple models of structural phase transitions. Researchers observed that transition metal migration and dissolution-driven segregation play significant roles in the evolution of inhomogeneity and valence states, actively contributing to cathode failure. Importantly, the team established that three-dimensional valence state distribution and chemical inhomogeneity are not merely indicators of degradation, but also key factors determining the functional stability and long-term performance of NCM cathodes. The developed imaging platform offers a powerful and versatile approach for decoding correlated structural, chemical, and electronic behaviours in complex materials, extending beyond battery research to fields such as heterogeneous catalysis and neuromorphic computing.