A reaction-controlled diffusion model for the lithiation of silicon in lithium-ion batteries

Silicon is considered as a promising anode material for lithium ion batteries. Despite the great attention on Si anode materials, a consistent description of the diffusion and reaction mechanism at the reaction front of crystalline silicon, amorphous silicon, and delithiated amorphous silicon has not yet been proposed. To better understand those mechanisms, a new reaction-controlled diffusion formulation is proposed. The new formulation makes use of the bond-breaking energy barrier E0E0 as the key physical quantity. With the consideration of different values of E0E0, the two-phase diffusion during initial lithiation of both crystalline Si and amorphous Si can be well represented with an evident reaction front. In addition, by varying E0E0, the one phase lithiation of amorphous Si, obtained after the delithiation process, can be captured with the new formulation. The effect of deformation, hydrostatic pressure at the reaction front, and Li concentration level on the reaction front velocity is taken into account in the proposed model. Numerical simulations are provided to support the model.