Coupled electrochemical-mechanical modeling with strain gradient plasticity for lithium-ion battery electrodes

Abstract We first present a model coupling the electrochemical reaction with strain gradient plasticity for a spherical electrode, which aims to analyze the evolutions and distributions of electrochemical-reaction dislocations and diffusion-induced stress during lithiation process. Several critical features viewed by in-situ TEM are incorporated into this model, such as the two-phase boundary and high-density dislocations at the reaction front. It is shown that the microstructure evolution can impact the mechanical properties and electrochemical performances of electrode materials. The results obtained by a finite difference method indicate that, as lithiation proceeds, the circumferential stress on the surface of the lithiated shell changes from compression to tensile stress, which may cause fracture of the active materials. Especially, the electrochemical-reaction dislocation zone results in fairly large stresses at the front of the interface. Furthermore, the lithiation reaction displays a strong size effect, and the movement rate of reaction front reduces as the size of the particles decreases. This work provides a framework for large-capacity, multi-scale research on high-capacity lithium-ion battery electrodes.