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Due to the nature of how porous battery electrodes are fabricated, their microstructure is not uniform. For instance, there are variations in composition, effective electronic transport, and effective ionic transport. Such heterogeneity has been associated with several battery application issues. For example, variability in transport of ions can lead to a tendency for localized plating of lithium on anodes during fast charging [1-2]. Studying the heterogeneity of electrodes is a growing research topic. Our research group has previously developed a micro-four-line probe that successfully measured the variation of electronic conductivity of electrodes [3]. Another method to study the microstructure of electrodes is by means of SEM and X-ray tomography, and the variation of tortuosity (effective ionic resistance) in electrodes was computed by analyzing the tomographic data of microstructure [4]. We report here on a new technique to measure the local ionic resistance on a sub-mm length scale. A probe was made to detect the local transport of ions through a small aperture. The probe is scanned across the surface of a porous thin-film electrode in order to create maps of tortuosity or MacMullin number. The measurement was performed using electrochemical impedance spectroscopy, and an associated model is needed to invert the experimental results. [1] Harris et al., The Journal of Physical Chemistry C 117, 6481 (2013). [2] Vogel et al., Electrochimica Acta 297, 820 (2019). [3] Lanterman et al., Journal of the Electrochemical Society 162, A2145 (2015). [4] Kehrwald et al. Journal of The Electrochemical Society 158, A1393 (2011). Figure 1 |
