Phase-Field Simulation of Li-Ion Diffusion and Stress Evolution in Cathode Materials in NCA-Type Li-Ion Batteries

Abstract

The crack propagation in a positive electrode of lithium (Li)-ion batteries degrades the performance of Li-ion batteries. The crack propagation is driven by the Li intercalation- and deintercalation-induced stress-field in the electrode. In order to prevent the degradation of Li-ion battery performance, it is essential to understand the Li-ion diffusion and stress evolution in the positive electrode during the charging and discharging processes. Phase-field (PF) method has been widely used as a powerful numerical simulation methodology for analyzing micro- and meso-scale phenomena including electrochemical reactions. In this study, we develop a PF model for simulating the Li-ion diffusion and stress evolution in a positive electrode in a LiNi1-x-y Co x Al y O2 (NCA)-type Li-ion battery, which attracts attentions as a high-capacity cathode material. In the PF model, the Li-ion diffusion in the NCA electrode is treated by the Cahn-Hilliard equation which incorporates the Butler-Volmer equation. The stress evolution is analyzed based on the PF microelasticity theory. The elastic constants and lattice misfit strains of NCA electrode used in the PF model were obtained from first-principles calculation. Using the developed PF model, we investigate the Li-ion diffusion and stress evolution in a NCA second-particle, which strongly depends on the distribution and crystal orientation of primary NCA particles in the second-particle.