Persistent and partially mobile oxygen vacancies in Li-rich layered oxides

Increasing the energy density of layered oxide battery electrodes is challenging as accessing high states of delithiation often triggers voltage degradation and oxygen release. Here we utilize transmission-based X-ray absorption spectromicroscopy and ptychography on mechanically cross-sectioned Li1.18-xNi0.21Mn0.53Co0.08O2-delta electrodes to quantitatively profile the oxygen deficiency over cycling at the nanoscale. The oxygen deficiency penetrates into the bulk of individual primary particles (similar to 200 nm) and is well-described by oxygen vacancy diffusion. Using an array of characterization techniques, we demonstrate that, surprisingly, bulk oxygen vacancies that persist within the native layered phase are indeed responsible for the observed spectroscopic changes. We additionally show that the arrangement of primary particles within secondary particles (similar to 5 mu m) causes considerable heterogeneity in the extent of oxygen release between primary particles. Our work merges an ensemble of length-spanning characterization methods and informs promising approaches to mitigate the deleterious effects of oxygen release in lithium-ion battery electrodes.

Automated summary

Utilizing transmission-based X-ray absorption spectromicroscopy and ptychography, the study quantitatively profiles oxygen deficiency in layered oxide battery electrodes at the nanoscale. It reveals that oxygen vacancies in the bulk of individual particles and their diffusion are responsible for spectroscopic changes. Additionally, the arrangement of particles within secondary particles causes heterogeneity in oxygen release.