Geometric Characteristics of Lithium Ion Battery electrodes with Different Packing Densities
To investigate geometric characteristics of porous microstructures, cathode electrodes were fabricated from a 94:3:3 (weight %) mixture of LiCoO2 (average particle radius = 5 µm), PVDF, and super-P carbon black. To change the packing density, initial thickness of the electrodes was set in a range of 40 ~ 80 µm. Then all electrodes were pressed down to 40 µm by using a rolling press machine. A synchrotron X-ray nano-computed tomography instrument (nano-CT) at the Advanced Phothon Source of Argonne National Lab was employed to obtain morphological data of the electrodes, with a spatial resolution of 60 nm. The morphology data sets were quantitatively analyzed to characterize their geometric properties. Fig. 1 shows the porosity (ε), specific surface area (As, µm-1), tortuosity (τ), and pore size distribution of 4 different electrode microstructures. The pore size distribution of the un-pressed electrode (ε = 0.56, black color) demonstrates nonuniformly dispersed active material. The highest packing density electrode (ε = 0.36, red color) shows the highest tortuosity. The charge/discharge experiments were also conducted for these 4 different electrodes. The geometric properties and cell testing results will be analyzed and reported.
Acknowledgments: This work was supported by US National Science Foundation under Grant No. 1335850.
1. R. E. Garcia and Y. M. Chiang, Journal of the Electrochemical Society, 154, A856 (2007).
2. I. V. Thorat, D. E. Stephenson, N. A. Zacharias, K. Zaghib, J. N. Harb and D. R. Wheeler, J. Power Sources, 188, 592 (2009).
3. R. Thiedmann, O. Stenzel, A. Spettl, P. R. Shearing, S. J. Harris, N. P. Brandon and V. Schmidt, Computational Materials Science, 50, 3365 (2011).
4. B. Hellweg, Microstructural Modeling of Lithium Battery Electrodes, in Materials Science and Engineering, Massachusetts Institute of Technology (2000).