Abstract
A mechanically coupled diffusion model combined with finite element formulation is developed to study the influence of dislocations on ion diffusion in lithium-ion batteries. The dislocation is modeled by the regularized eigenstrain based on a non-singular continuum dislocation theory. The model is validated with the analytical solution of the stress field of edge dislocations and the solution for the stress-dependent equilibrium concentration around the dislocation. Simulation results on LiMn2O4 demonstrate strong ion enrichment and depletion on the tensile and compressive sides of an edge dislocation, respectively. A stronger influence of the edge dislocation on diffusion is found at a lower state-of-charge, which verifies the experimental observation reported in the literature. The diffusion-induced stress compensates partially the stress field of the edge dislocation and is ascertained to have a state-of-charge dependency. The existence of dislocation does not introduce obvious mobility anisotropy in the bulk material but it results in local mobility heterogeneity around the dislocation. A three-dimensional simulation of the diffusion along the edge dislocation line reveals that the pipe diffusion can be initiated or accelerated on the tensile side of the edge dislocation.
Highlights
Lithium-ion batteries (LIBs) represent the subject of rapidly growing research efforts due to their outstanding physical properties, such as high energy density, superior rate capability, and excellent cycling performance
The existence of dislocation does not introduce obvious mobility anisotropy in the bulk material but it results in local mobility heterogeneity around the dislocation
The dislocation is introduced in the model using an eigenstrain distribution derived from a non-singular continuum dislocation model
Summary
Lithium-ion batteries (LIBs) represent the subject of rapidly growing research efforts due to their outstanding physical properties, such as high energy density, superior rate capability, and excellent cycling performance. How material heterogeneity and structural defects influence the ion diffusion process is one of the major research topics toward improving the performance of LIBs.[1,2] Generally, defects as dislocations can be generated and accumulated and lead to failure of the material. There is an increasing interest in the study of “defect engineering,” aiming to achieve desired functionalities through defect manipulation.[3] Dislocations, which introduce large local stress and strain fields, are one of the most prevalent defects in experimental studies in LIBs.[1,4,5,6] an in-depth understanding of how dislocations influence the ion diffusion process is key to understand the experimental observations and further guide the dislocation-based defect engineering
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