Three-Phase 3D Reconstruction of Li-Ion Batteries Electrodes Via FIB-SEM Tomography

Three-dimensional (3D) reconstructions of lithium-ion battery electrodes provide quantitative microstructural characteristics and input for 3D computational modeling of electrode lithiation and de-lithiation (1-3). In much of the work reported to date, it was not possible to identify all three electrode phases – oxide particles, carbon, and electrolyte – because there was little or no image contrast between the carbon-based epoxy used to fill the pore regions of the electrode (after electrolyte removal) and the carbon phase (4). Recently, it was shown that filling with a silicone resin allows good electrolyte/carbon contrast, although the high viscosity of the resins may make effective pore filling difficult (5). In this work, three-phase 3D reconstructions of a commercial LiCoO 2 cathode and lab-made LiFePO 4 cathodes (6) are demonstrated using a low viscosity silicone resin as a filling material. As illustrated in Figure 1, contrast among oxide, carbonaceous materials (conducting carbon and binders, CB) and resin-filled porosity (electrolyte space) is obtained using focused ion beam-scanning electron microscopy tomography. Structural parameters including, phase volume fraction, surface area, particle size distribution, pore connectivity and tortuosity are extracted for electrode microstructure-performance correlation analyses. For the commercial LiCoO 2 cathode, the electrolyte tortuosity within the electrode is found to be inhomogeneous. For LiFePO ­4 cathodes, the microstructure characteristics are compared with conventional electrodes and those with additional large-scale pores added using a sacrificial templating technique. The improved high rate performance found in the templated LiFePO 4 electrode can be explained by 3D microstructural characteristics created by the sacrificial template. The present study demonstrates the importance of obtaining all three phases for accurate analysis of microstructure-performance correlations. 1. Z. Liu, J. Scott Cronin, Y.-c. K. Chen-Wiegart, J. R. Wilson, K. J. Yakal-Kremski, J. Wang, K. T. Faber and S. A. Barnett, Journal of Power Sources , 227 , 267 (2013). 2. Andreas H. Wiedemann, Graham M. Goldin, Scott A. Barnett, Huayang Zhu and R. J. Kee, Electrochemica Acta , 88 , 580 (2013) 3. T. Hutzenlaub, S. Thiele, N. Paust, R. Spotnitz, R. Zengerle and C. Walchshofer, Electrochimica Acta , 115 , 131 (2014). 4. J. R. Wilson, J. S. Cronin, S. A. Barnett and S. J. Harris, Journal of Power Sources , 196 , 3443 (2011). 5. M. Ender, J. Joos, T. Carraro and E. Ivers-Tiffee, Journal of the Electrochemical Society , 159 , A972 (2012). 6. D. P. Singh, F. M. Mulder, A. M. Abdelkader and M. Wagemaker, Advanced Energy Materials , 3 , 572 (2013). Figure 1