Li-ion distribution and diffusion-induced stress calculations of particles using an image-based finite element method

Abstract

The realistic particles in lithium batteries have unique microstructures, which should be determined in the analysis of chemo-mechanical behaviors during charge/discharge cycles. In this paper, an image-based finite element method (IBFEM) is developed to investigate the volume expansion, Li-ion distribution, and diffusion-induced stress (DIS) of a realistic particle. A threshold-based segmentation method is proposed to improve the segmentation accuracy based on the improved threshold of each phase. Based on the IBFEM, the active material phase, conductive additive and binder phase, and pore space are segmented and reconstructed using microstructural images. The volume expansion, Li-ion distribution, and DIS of an image-based SnO2 nanoparticle are simulated under galvanostatic/potentiostatic charging process. The predicted lithiation that induced the volume expansion of the SnO2 nanoparticle is approximately coincided with the experiment result observed by TEM. The realistic particle shape and size have a significant impact on the Li-ion distribution and DIS. The concentration profile is analogous to the boundary of the realistic particle at the early stage of lithiation and gradually disappears with further lithiation. The von Mises stress near a concave region is higher than that near a convex region. The maximum von Mises stress in the realistic particle with a larger equivalent radius is higher than that in the smaller particle with the same state of charge. By considering the comprehensive effect of particle shape and size, the size can be increased appropriately while guaranteeing the particle mechanical integrity. These results will contribute to understanding DIS evolution in a realistic particle and can be used to guide the selection of active particles for electrode preparation.