Correlating CT Of Real-World Batteries with Computational Models—Methods to Overcome Manufacturing Imperfections

High-resolution X-ray computed tomography (CT) is an indispensable tool for its ability to probe material phase distributions from within sealed batteries. By correlating battery CT with a computational battery model, kinetic parameters can be refined, and transport effects can be better understood. However, for batteries with cylindrical symmetry like bobbin-type batteries, the typical Cartesian coordinates used to describe the CT image stack are not ideal. The most prominent bobbin-type battery is the alkaline Zn−MnO₂ AA cell. In this work we demonstrate recent mechanistic findings on the alkaline Zn anode, as well as methods used to cast the CT image stack into pseudo-cylindrical coordinates.¹ The pseudo-cylindrical method corrects for asymmetries observed in bobbin-type batteries because the pin is often off-center, and the separator often has a noncircular shape. This reconciles the ideal geometry of a battery model with the reality of battery manufacturing.<br/><br/>For the pseudo-cylindrical method, the pseudo-radius is defined as the relative distance in the anode between the central current collecting pin and the separator. This allows the radial volume fractions of Zn and ZnO in the anode to be converted to dimensionless 1D profiles that vary only in radius. Such a method allows direct comparison to a battery module, which also outputs material fractions as 1D radial profiles. Ten anodes from Zn−MnO₂ AA batteries with a range of discharge histories are used to validate that this method results in averaged 1D material profiles that, when compared to other methods, show a better quantitative match to individual local slices of the anodes in the polar θ-direction. The other methods tested are methods that average to an absolute center point based on either the pin or the separator, both of which are shown to be inferior.<br/><br/>Using this method, we analyze Zn−MnO₂ batteries discharged with both continuous and pulsed profiles.² ZnO is found to have a wide range of densities within discharged cells, and pulsed operation provokes lower-density ZnO to form. This sparsely-dense ZnO has significant microporosity and takes up a larger volume within the cell. These effects are shown to have a significant impact on ion transport across the cell.<br/><br/><b>References</b><br/><br/>1. Guida, D.P.; Stavola, A.M.; Chuang, A.C.; Okasinski, J.S.; Wendling, M.T.; Chadderdon, X.H.; and Gallaway, J.W. "Methods for Tomographic Segmentation in Pseudo-Cylindrical Coordinates for Bobbin-Type Batteries," ACS Measurement Science Au, 2023, 3, 344-354.<br/><br/>2. Guida, D.P.; Chuang, A.C.; Okasinski, J.S.; Wendling, M.T.; Chadderdon, X.H.; and Gallaway, J.W. "Discharge intermittency considerably changes ZnO spatial distribution in porous Zn anodes," J Power Sources, 2023, 556, 232460.