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

Wednesday, 27 May 2015
Salon C (Hilton Chicago)
Z. Liu (Northwestern Univerisity), H. Wang (Northwestern University), D. P. Singh, M. Wagemaker (Delft University of Technology), K. T. Faber, and S. A. Barnett (Northwestern University)
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 LiCoO2 cathode and lab-made LiFePO4 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 LiCoO2 cathode, the electrolyte tortuosity within the electrode is found to be inhomogeneous. For LiFePO­4 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 LiFePO4 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.

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