Effects of concentration-dependent modulus and external loads on Li-ion diffusion and stress distribution in a bilayer electrode

Structural batteries offer a new way to reduce device mass and increase the overall energy density of devices. An important feature of structural batteries is that they are designed to be subjected to external loads, which generally have a significant impact on electrochemical reactions in normal batteries. In the present work, a multi-field coupled model for a bilayer electrode was developed by considering the effects of external loads and concentration-dependent modulus. It was found that a positive external load, which bent the unlithiated electrode toward the active electrode side, accelerated the Li-ion diffusion process, whereas a negative external load, which was applied in the opposite direction to the positive external load, hindered the diffusion of Li ions. The curvature variation of the bilayer electrode was a result of the coupling effect of external loading, Li-ion concentration distribution, and the concentration-dependent modulus. The convex curvature of the bilayer electrode (bending toward the active electrode side) increased the Li-ion binding capacity of the active electrode, and an opposite effect was found for the concave curvature. During the lithiation process, positive external load exerts a greater influence on the stress distribution across the bilayer electrode compared to negative external load. The results of this work can provide theoretical guidance to design structural batteries under external loading.