Lithium-ion battery electrodes are known to have irregularities in their microstructure. When electrodes are not uniform in terms of conductivity, such inhomogeneities can lead to localized variability in current flow, potential, and species concentrations, which are associated with cell degradation [1]. Understanding and quantifying heterogeneity of battery electrodes is therefore an important step in engineering better batteries.

Our research group has previously succeeded in quantifying the variation of electronic conductivity of electrodes using a four-line microprobe [2]. Methods have also previously been developed for measuring the average ionic conductivity of battery electrodes [3], but there was no method for measuring localized ionic conductivity. Our research group recently developed a way to do such a measurement, allowing us to investigate the heterogeneity of effective ionic conductivity across an electrode.

We report the results of local MacMullin Number measurements (proportional to tortuosity or the inverse of conductivity) for various electrodes. We show the heterogeneity of both conventional Li-ion anodes and cathodes and the effect of cycling. In the future, we hope that this technology can be used as a diagnostic tool for improving design and manufacture of electrodes.

Fig. 1. Map of MacMullin Number for a Li-ion cathode

References:

[1] Vogel et al., Electrochimica Acta 297, 820 (2019).

[2] Lanterman et al., Journal of the Electrochemical Society 162, A2145 (2015).

[3] Pouraghajan et al., Journal of the Electrochemical Society 165, A2644 (2018).