Electrode microstructure influences ionic transport and electronic transport and is a key factor that affects lithium-ion battery performance. Non-uniform microstructure or heterogeneity in battery electrodes has long been observed and leads to non-uniform transport properties. This work provides a better understanding of in-plane heterogeneity at millimeter length scale and through-plane heterogeneity at micrometer length scale, through a combination of experiment and modeling. The first part of this work develops the aperture probe technique, which is an experimental method and associated model to locally estimate ionic transport, represented by MacMullin number, in the electrode. By generating contour maps of MacMullin number, the in-plane variation of ionic transport is visualized in the electrodes. The local ionic transport measurement technique is validated by comparing with another measurement technique and showing an agreement between the results obtained from the two techniques. The second part of this work focuses on characterizing dual-layer anodes that consist of two layers of coating with distinctly different microstructures. The aperture probe technique was adapted to determine the MacMullin numbers in the two layers separately. The method was validated by a series of virtual experiments and by comparing in one case to an electrode film that was delaminated from the current collector and experimentally sampled from both sides. Because both the electronic transport and the ionic transport are found to be related with the electrode microstructure, it is of interest to understand how these two transport properties relate to each other. The local electronic conductivity and MacMullin number of several commercial-grade electrodes were mapped. The correlation between the two transport properties is distinct for each electrode and significant at length scales larger than about 6 mm. The last part of this work investigates how heterogeneity of ionic transport affects the cycling performance of a lithium-ion cell. A localized MacMullin number measurement is made to characterize the ionic transport heterogeneity of electrodes prior to cycling. Then synchrotron-based X-ray diffraction is applied to analyze the heterogeneity in state of lithiation after high-rate cycling. When comparing the ionic transport map and the state-of-charge map, no strong correlation is observed. While this experiment was inconclusive, it suggests that other factors are more responsible for spatial variations in state of lithiation.
College and Department
BYU ScholarsArchive Citation
Liu, Baichuan, "Understanding Microstructure Heterogeneity in Li-Ion Battery Electrodes Through Localized Measurement of Ionic Transport" (2022). Theses and Dissertations. 9514.
Li-ion battery, tortuosity, heterogeneity, ionic transport, EIS