Local Variation in Microstructure Causes Heterogeneity in the Conductivity of Commercial Lithium-Ion Cathode Films

Abstract

Lithium-Ion battery success can be defined by a series of measureable characteristics. Two important characteristics that have been difficult to fully explore are the ionic [1] and electronic tortuosity. Micro-N-line probes were previously developed [2][3] in order to accurately measure electronic thin-film conductivity on a micro-scale. Multiple iterations of the probe have been produced, tested and verified. In order to meet the final goal of a probe that could be implemented in any laboratory or production line, changes to the substrate, probe, and sizing were necessary. The final design also required substantial changes to methodology as well as the conductivity inversion calculations. The new probe is produced on a flexible substrate for a fraction of the original production cost and a fraction of the original production time. Here we show that the new probe has been used to test battery films and measure battery film heterogeneity on a mm scale (See Figure 1). COMSOL modeling of the battery under testing conditions shows minimal influence by the battery current collector on measurements; this allows for non-destructive measurements of standard battery films. The probe shows key advances in robustness and flexibility which allows for implementation on a rolling production line. New affordable stages have been developed to produce reliable measurements. High and low conductivity locations are still able to be found which is consistent with previous results. Acknowledgements This research is supported by the US Department of Energy through the Advanced Battery Material Research (BMR) Program. References [1] S.W. Peterson and D.R. Wheeler, "Direct Measurements of effective electronic transport in porous li-ion electrodes", Journal of the Electrochemical Society, vol. 161, no. 14, A2175-A2181, 2014 [2] B.J. Lanterman, A.A. Riet, N.S. Gates, J.D. Flygare, A.D. Cutler, J.E. Vogel, D.R. Wheeler, and B.A. Mazzeo, "Micro-four-line probe to measure electronic conductivity and contact resistance of thin-film battery electrodes", Journal of the Electrochemical Society, vol. 162, no. 10, A2145-A2151, 2015 [3] M.M. Forouzan, C.-W. Chao, D. Bustamante, B.A. Mazzeo, and D.R. Wheeler, "Experiment and simulation of the fabrication process of lithium-ion battery cathodes for determining microstructure and mechanical properties", Journal of Power Sources, vol. 312, pp. 172-183, 2016 Figure 1: Figure (a) showing the new probe, (b) the COMSOL model of the new probe, and (c) the results of a simple electrode conductivity mapping experiment run on a standard NMC TODA523 electrode. Figure 1

Micro-Flexible-Surface Probe for Determining Spatially Heterogeneous Electronic Conductivity of Lithium-Ion Battery Electrode Films

“…Probes with a new geometry and produced on a flexible substrate were explored to overcome limitations inherent to a rigid cleanroom-produced probe. 33,34 Due to the change in probe design a new inversion procedure is introduced to correctly estimate conductivity and contact resistance values.…”