A viscoplastic approach to the chemomechanical behavior of Sn microstructure

Due to the high theoretical capacity and environmental benignity, the tin (Sn) anode is one of the most promising candidates for applications as an electrode. Using an image-based finite element approach, we rebuilt the Sn active phase and evaluated the distribution of Li-ion concentration and evolution of stress. To account for the large deformation of the Sn electrode during the charge/discharge process, we proposed a theoretical framework based on viscoplasticity theory to study the chemomechanical coupling behavior of the Sn anode. First, we applied finite deformation theory to investigate the proposal that viscoplasticity induced the reduction in von Mises stress. Then, considering the stress-dependent diffusion in Li-Sn systems, the effects of microstructure on the stress evolution, local electric potential, and cycle performance were elucidated. Our results revealed that the microstructure significantly influenced the stress field and distribution of electric potential. Additionally, our results showed that concentration distributions result in a sharp gradient and that the von Mises stress varied significantly at the chosen concave or convex sites of the surface. Then, we proposed the effects of the number of cycles on the plastic stress and the stress-biased voltage. As a result, the predicted behavior of real microstructure has the potential to be utilized in the design of electrodes with tunable microstructure.