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

• Published in: Nature energy 2021-06, Vol.6 (6), p.642-652
• Main Authors: Csernica, Peter M., Kalirai, Samanbir S., Gent, William E., Lim, Kipil, Yu, Young-Sang, Liu, Yunzhi, Ahn, Sung-Jin, Kaeli, Emma, Xu, Xin, Stone, Kevin H., Marshall, Ann F., Sinclair, Robert, Shapiro, David A., Toney, Michael F., Chueh, William C.
• Format: Article
• Language: English
• Subjects: 639/301/299; 639/301/299/891; 639/301/930/328; batteries; Economics and Management; Electrodes; Energy; Energy Policy; ENERGY STORAGE; Energy Systems; Flux density; Heterogeneity; Hypoxia; Lithium; Lithium-ion batteries; materials for energy and catalysis; microscopy; Oxygen; Rechargeable batteries; Renewable and Green Energy; Vacancies; X ray absorption
• ISSN: 2058-7546; 2058-7546
• DOI: 10.1038/s41560-021-00832-7

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 Li 1.18– x Ni 0.21 Mn 0.53 Co 0.08 O 2– δ electrodes to quantitatively profile the oxygen deficiency over cycling at the nanoscale. The oxygen deficiency penetrates into the bulk of individual primary particles (~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 (~5 μm) 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. Oxygen release in Li-rich layered oxides is of both fundamental and practical interest in batteries, but a varied mechanistic understanding exists. Here the authors evaluate the extent of oxygen release over extended cycles and present a comprehensive picture of the phenomenon that unifies the current explanations.