Title.
Hierarchically Heterogeneous Electro-Chemo-Mechanical Coupling Effects in Composite Battery Electrodes
Authors.
Yang Yang1,†, Kejie’s Student2,†, Kai Zhang3,4,†, Sang-Jun Lee3,†, Linqin Mu5, Crystal K. Walters5, Stephanie Spence5, Zhengrui Xu5, Chenxi Wei3, Qingxi Yuan4, Young-Sang Yu6, Xianghui Xiao7, Piero Pianetta3, Peter Cloetens1, Jun-Sik Lee3, Kejie Zhao2,*, Feng Lin5,*, Yijin Liu3,*
Abstract.
Multiscale electro-chemo-mechanical interplay governs the local structural and chemical evolution, which is fundamental to the global electrochemical properties in batteries. Cycling batteries under kinetically limited conditions induces state of charge (SoC) heterogeneity, builds up mechanical stress, and provokes morphological breakdown. These processes prevail in most battery electrodes and ultimately determine the device-level battery performance. Understanding these processes at many length scales can inform designing materials and electrodes that allow for large areal capacity, fast charging, and effective utilization of active compounds. In this study, we investigated the electro-chemo-mechanical interplay in layered oxide cathodes using hard x-ray phase contrast tomography that simultaneously covers over a thousand active particles with nanometric spatial resolution, enabling an unprecedented statistical analysis that reveals the electrode-level SoC analysis. Coupled with nanoscale x-ray spectro-microscopy and electron microscopy, we reconstruct the morphological and chemical transformations in the layered oxide cathode under fast charging conditions and, subsequently, elucidate two stages of the chemomechanical transformation at the single particle level: 1) the host material’s local lattice structural transition and 2) liquid electrolyte infiltration that forms new diffusion pathway for lithium ions. Resulted from the evolving mismatch between the local electrical and ionic conductivity, there is a depth-dependent chemomechanical response at the electrode level. The particles in the vicinity of the separator undergo more severe fracturing than those close to the current collector. We also report the lateral reaction heterogeneity at the electrode level, suggesting that the degree of local electrode utilization develops as a function of position and time. Our results offer insights into designing chemomechanically robust battery particles and formulating fast charge capable electrodes.