A defect-based viscoplastic model for large-deformed thin film electrode of lithium-ion battery

The interaction among solute atoms, local deformation velocity and viscoplasticity of host material plays a significant role in determining the stress evolution and concentration distribution in host material, especially in large-deformed electrode materials made from silicon and tin. In this work, a new viscoplastic model that describes diffusion-induced deformation is developed from the framework of the generation of defects due to the migration of solute atoms. The total flux in the diffusion equation is separated into two parts; one is the diffusion part due to the migration of solute atoms, and the other is the convection part due to the local deformation velocity in host material. Using the diffusion-convection equation, the theory of nonlinear continuum mechanics and the developed constitutive relationship, we analyze the Cauchy stress and viscoplastic deformation in a thin film Si-electrode on a "rigid" substrate numerically. The average Cauchy stress during lithiation and de-lithiation with the boundary fluxes of j(0), 2j(0) and 0.33j(0) is calculated, and the numerical results reveal that the magnitude of compressive Cauchy stress in the thin film Si-electrode increases with the increase of the boundary flux. The numerical results are in good accord with the results from experimental study and the first principle simulation for the entire charging/discharging process.