5D X-Ray Nanodiffraction Reveals Nanoscale Structural Deformation in NMC Cathode Materials
Authors: Zhou Tao , Liu Tongchao , Huang Weiyuan , Yu Lei , Wang Jing , Wen Jianguo , Cai Zhonghou , Holt Martin , Amine Khalil 
Published: December 2024

Ni-rich layered oxide cathodes LiNixCoyMn1-x-yO2 (NMC, x>0.5) are promising candidates for next-generation lithium-ion batteries thanks to their high capacity and low cost. The main issue that limits their large-scale commercialization is the capacity degradation, which is exacerbated by the chemical and mechanical instabilities introduced from further increasing the Ni content and the higher delithiation states. The chemical and mechanical instabilities are primarily studied with x-ray absorption (e.g. XANES) and diffraction (e.g. HEXRD) techniques, which provide statistically averaged information on thousands of cathode particles with streamlined data acquisition and data analysis routines.

X-ray nanodiffraction complements the aforementioned techniques with spatially resolved information on individual particles. A 5-dimensional dataset (2D in the real space and 3D in the reciprocal space) is acquired for each particle, providing a detailed yet complex perspective on the mechanical instabilities. With results from a few recent studies, we show, below, how different ways of reducing the 5D data space can lead to the discovery of specific nanoscale structure deformation inaccessible to most other methods.

For a core-shell NMC polycrystal cathode aimed to enhance the cycling stability, we show that the lattice parameter of the secondary particle matches that expected of the designed compositional gradient. Reversing the compositional gradient results in stress during growth as inferred from the remnant lattice rotation observed at the boundary between neighboring primary particles [1]. For a study on the effect of aging, we show the formation of an oxide layer on the surface of single crystal NMC cathodes. A reduced 5D rocking curve indicates that the oxide layer induces a tensile strain on the order of 10-2. The strain measured with nanodiffraction is about 100 times higher than what was measured with HEXRD, the latter being an underestimation averaged over the entirety of the largely unstrained particles [2].

Lattice rotation is a prevalent lattice deformation in battery materials commonly associated with the formation of defects. Compared to the overwhelming scientific interest on the lattice strain, the importance of lattice rotation is often overlooked when it comes to mechanical instabilities. With 5D analysis on the lattice rotation, we show a dominating mode of structural degradation in the form of a twisting motion along the long axis of the nanoparticles [3]. More recently, we were able to further link the unrecoverable parts of lattice rotation to the mechanical failure of single crystal cathodes [4].

[1] Tongchao Liu, Lei Yu, Jun Lu, Tao Zhou, Xiaojing Huang, Zhonghou Cai, Alvin Dai, Jihyeon Gim, Yang Ren, Xianghui Xiao, Martin V. Holt, Yong S. Chu, Ilke Arslan, Jianguo Wen & Khalil Amine. Nature Communications volume 12, Article number: 6024 (2021)

[2] Lei Yu, Jing Wang, Tao Zhou, Junxiang Liu, Weiyuan Huang, Tianyi Li, Tongchao Liu, Jianguo Wen, Khalil Amine, in preparation.

[3] Lei Yu, Alvin Dai, Tao Zhou, Weiyuan Huang, Jing Wang, Tianyi Li, Lu Ma, Xianghui Xiao, Mingyuan Ge, Rachid Amine, Steven Ehrlich, Jianguo Wen, Tongchao Liu, Khalil Amine, under review in Nature Communications.

[4] Weiyuan Huang, Tongchao Liu, Lei Yu, Jing Wang, Tao Zhou, Junxiang Liu, Tianyi Li, RachidAmine, Xianghui Xiao, Mingyuan Ge, Lu Ma, Steven N. Ehrlich, Martin V. Holt, Jianguo Wen, Khalil Amine, accepted in Science.