A fully coupled diffusional-mechanical finite element modeling for tin oxide-coated copper anode system in lithium-ion batteries

Abstract

Finite element (FE) modeling is a powerful method to investigate the volume change induced by lithium diffusion and the corresponding mechanical degradation for a deeper understanding of (dis)charging process in lithium-ion batteries. However, FE studies on the diffusion-stress interaction taking into consideration the effect of hydrostatic stress gradient in three-dimensional complex structures of electrodes are insufficient and limited. Higher charging rate can cause the high gradient of hydrostatic pressure which affects the diffusion flux in the electrode. Here, we present a fully coupled diffusional-mechanical FE model, which simultaneously solves the equations relevant to the diffusion and the mechanical behavior, by considering the mechanical contact between a tin oxide active layer and the hollow struts of a copper scaffold, as well as the pressure gradient. The numerically computed strains in the copper struts are in good agreement with the experimental strain data, previously measured in operando using X-ray diffraction. Calculations also show that large stresses are induced in the active layer during lithiation, causing elastic tensile strains in the scaffold which displays some residual strains after full discharging. The active layer is predicted to undergo plastic deformation during cyclic (dis)charging, and the amount of which grows significantly with increasing charging rate.