Three-Dimensional Phase-Field Simulation of Li Diffusion and Stress Evolution in a Polycrystalline LiCoO2 Cathode

Abstract

The evolutions of stress and strain caused by Li-extraction and -insertion in a LiCoO2 (LCO) is one of the most important phenomena which affect performance of a Li-ion battery (LIB) with the LCO cathode. However, because experimental measurement of the stress and strain evolutions in the LCO is very difficult, numerical simulation models that enable us to investigate mechanical behaviors and electrochemical reactions in LIBs have been actively studied. Recently, the phase-field method, which has been originally developed for simulating microstructure evolutions during solidification and phase transformation in various materials, is used for investigating electrochemical reactions in various electrode materials used in LIBs. In this study, three-dimensional (3D) phase-field simulations of the Li diffusion and the stress evolution in a polycrystalline LCO cathode were performed. In order to perform the 3D simulations efficiently, the stress evolution in the LCO was calculated on the basis of the phase-field microelasticity theory that employes the fast Fourier transform algorithm to solve the mechanical equilibrium equation. As an example of the simulation results, the calculated distributions of Li concentration and the von Mises stress in a polycrystalline LCO cathode are shown in Fig. 1. Through the 3D simulations, the effects of microstructural factor of the LCO cathode, such as crystal orientation and grain size, and external mechanical boundary conditions on the Li diffusion and the stress evolution in the cathode were investigated. Figure 1