Quantitative Characterization of LiFePO₄Cathodes Reconstructed by FIB/SEM Tomography

The three-dimensional microstructures of a lab-scale and a high-power LiFePO 4 cathode for lithium-ion cells are analyzed by combined focused ion beam (FIB) / scanning electron microscopy (SEM) tomography. The spatial distributions of (a) carbon black as electronic conductor (b) LiFePO 4 as active material and (c) pore volume are reconstructed by appropriate image processing methods. The global threshold segmentation procedure is replaced by a refined local threshold method, which accounts for gradients in luminosity even within very large imaged volumes. The precise analysis of the high-power cathode demands for reconstructing a very large volume of 18.15 × 17.75 × 27.8 μm 3 , caused by the dual length-scale design of LiFePO 4 , carbon black and pore phase. The microstructure features, (a) electrochemically active surface area and particle size distribution of LiFePO 4 , (b) shape and particle size distribution of carbon black and (c) porosity and tortuosity of the pore phase are compared between lab-scale and high-power cathode.