Depth-dependent valence stratification driven by oxygen redox in lithium-rich layered oxide

Abstract

Lithium-rich nickel-manganese-cobalt (LirNMC) layered material is a promising cathode for lithium-ion batteries thanks to its large energy density enabled by coexisting cation and anion redox activities. It however suffers from a voltage decay upon cycling, urging for an in-depth understanding of the particle-level structure and chemical complexity. In this work, we investigate the Li1.2Ni0.13Mn0.54Co0.13O2 particles morphologically, compositionally, and chemically in three-dimensions. While the composition is generally uniform throughout the particle, the charging induces a strong depth dependency in transition metal valence. Such a valence stratification phenomenon is attributed to the nature of oxygen redox which is very likely mostly associated with Mn. The depth-dependent chemistry could be modulated by the particles’ core-multi-shell morphology, suggesting a structural-chemical interplay. These findings highlight the possibility of introducing a chemical gradient to address the oxygen-loss-induced voltage fade in LirNMC layered materials.

Multiphase, Multiscale Chemomechanics at Extreme Low Temperatures: Battery Electrodes for Operation in a Wide Temperature Range

“…We first investigate the degree of the depth‐dependence for the cracks with different origins (Figure 3c). While the cycling‐induced damage is more severe over the core region of the particle, in good agreement with a number of reported experimental observations, [ 16,17 ] the low‐temperature‐induced cracks exhibit a rather flat depth‐dependence profile. Although the high‐resolution images offer a great amount of structural details, it could be overwhelming to the visual assessment.…”

Laboratory X-ray Microscopy Study of Microcrack Evolution in a Novel Sodium Iron Titanate-Based Cathode Material for Li-Ion Batteries

“…In addition, gradients of the chemical potential or the concentration of elements in a (large) particle might significantly accelerate the intragranular fracture processes [13,48]. However, to address the SOC heterogeneity in the particles, the 3d-metal charge state has to be quantified in a spatially resolved manner by applying high-resolution spectroscopic techniques such as X-ray absorption spectromicroscopy or spectrotomography [49][50][51]. Although it is not possible with state-of-the-art laboratory nano-XCT tools because of the use of characteristic X-rays (Cu-Kα), the developed electrochemical operando cell is well suited to X-ray absorption spectroscopy studies.…”

Structural and chemical evolution in layered oxide cathodes of lithium-ion batteries revealed by synchrotron techniques

“…The first example is a recent study by Zhang et al. on the depth-dependent redox stratification effect in a Li-rich NMC (Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 ) cathode [ 73 ]. The complexity in this material lies with the co-existing and intertwined cation and anion redox reactions upon charging to high voltage.…”

“…(a) The depth-dependent redox stratification effect in a Li-rich NMC (Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 ) cathode. Adapted with permission from [ 73 ], Copyright 2020, Springer Nature. (b) The inhomogeneous redox and lattice strain in cycled LiNi 0.8 Mn 0.1 Co 0.1 O 2 particle.…”

“…In general, these novel computational methods can greatly assist battery researchers and synchrotron scientists in reducing large-scale experimental data and extracting scientifically important information. Machine learning approaches have been used to guide high-throughput synchrotron experiments for material screening [ 81 ], to conduct classification and dimension reduction for chemical imaging data for capturing undesired side reactions in batteries [ 76 , 82 , 83 ], to assist with battery imaging data processing, segmentation and quantification [ 73 , 84 ] and to construct a numerical model for battery failure and lifetime prediction [ 85 , 86 ].…”