Microstructural characterization and grain scale modeling of lithium-ion electrodes

Tomography is a widely used tool for analyzing microstructures in three dimensions (3D). The analysis, however, faces difficulty because the constituent materials produce similar greyscale values. Sometimes, this prompts the image segmentation process to assign a pixel/voxel to the wrong phase (active material or pore). Consequently, errors are introduced in the microstructure characteristics calculation. In this work, we develop a filtering algorithm called PerSplat based on topological persistence (a technique used in topological data analysis) to improve segmentation quality. One problem faced when evaluating filtering algorithms is that real image data in general are not equipped with the ‘ground truth’ for the microstructure characteristics. For this study, we construct synthetic images for which the ground-truth values are known. On the synthetic images, we compare the pore tortuosity and Minkowski functionals (volume and surface area) computed with our PerSplat filter and other methods such as total variation (TV) and non-local means (NL-means). Moreover, on a real 3D image, we visually compare the segmentation results provided by our filter against TV and NL-means. The experimental results indicate that PerSplat provides a significant improvement in segmentation quality. Microstructure engineering of lithium-ion battery (LIB) electrodes is an important approach for optimizing the design and thereby enhancing the batteries' performance especially at high rate. There are diversified approaches going into the engineering of LIB electrode microstructures by creating less tortuous diffusion pathways, for example. Here, we have tested these hierarchical strategies using a microstructurally controlled electrode with a gradient porosity while keeping the three key features of the electrode constant: amount of active material, overall porosity, and surface area. With this modeling, we have determined the effect of the porosity gradient on the battery discharge performance for NMC111 electrodes. It was observed that having a gradient in porosity with higher porosity towards the separator side benefits the better utilization of the electrode active material, which enables a more uniform high-rate discharge process for deep cycle charge/discharge. The reverse gradient packing arrangement on the other hand provides advantages for shorter pulse operation since the weighted average location of cathode mass is closer to the separator.