Multidimensional Tracking and Clustering of Electrochemical Reactions in the Positive Electrode of Lithium-Ion Batteries via Operando X‑ray Nanoscale Chemical Imaging.

Understanding heterogeneous electrochemical reactions in the positive electrode of the Li-ion battery is essential for improving battery capacity and fast charging capabilities. Observing these reactions under operando conditions is essential to clarify the relationship between microstructure and chemical heterogeneity during the electrochemical processes. While X-ray nanoimaging is a valuable tool for operando measurements, mitigating X-ray radiation damage poses a significant challenge that requires optimized measurement protocols. In this study, we conducted a comprehensive analysis of the microstructure and chemical state distribution from the electrode to the particle scale using full-field transmission X-ray microscopy combined with X-ray absorption fine-structure spectroscopy (TXM-XAFS). We developed a dedicated operando cell to explore the relationship between microstructure, chemical state during the operando stepped charging process conditions. To mitigate X-ray-induced damage, the beam irradiation time has been optimized, and a coarse-to-fine approach combining quick 2-dimensional TXM-XAFS scans and 3-dimensional computed tomography-TXM-XAFS measurement has been adopted to reduce the overall dose while maintaining multidimensional and high-resolution information acquisition. Our results indicated that the distribution of charge varied among particles within the electrode and was significantly influenced by the proximity to the separator. By employing data clustering with the Gaussian mixture model, we identified factors of inactive domains that impede charge reaction. This analytical approach aids in understanding the factors contributing to reaction stagnation within a complex Li-ion battery, despite the challenges posed by X-ray radiation damage.