Coupling effects of self-limiting lithiation, reaction front evolution and free volume evolution on chemical stress in amorphous wire-based electrodes

The lithiation of silicon (Si) involves the evolution of reaction front, self-limiting lithiation, and visco-plastic deformation. During the lithiation of crystalline Si, solid-state amorphization occurs to lower Gibbs free energy, and lithiated Si-electrode in lithium-ion battery is mainly present in amorphous phase. In this work, we develop a viscoplastic constitutive relationship for the lithiation-induced deformation of amorphous materials from the theory of free volume, and establish a chemo-mechanical model for the lithiation-induced deformation of a-Si electrode from the frameworks of phase-field theory, stress-assisted thermal activation process and the viscoplastic constitutive relationship. The chemo-mechanical model takes into account three important chemophysical phenomena of the self-limiting lithiation, evolution of reaction front/interphase zone and plastic flow. Using the newly developed chemo-mechanical model, we investigate the lithiation-induced deformation of an a-Si nanowire. The numerical results reveal that both the stress-assisted thermal activation process and plastic flow retard the motion of the reaction front from free surface to the center of the a-Si nanowire. The annihilation and creation of free volume significantly reduces the Cauchy stress.