Simulation and Experiment on Solid Electrolyte Interphase (SEI) Morphology Evolution and Lithium-Ion Diffusion

In this study, a phase-field model is developed to simulate the microstructure morphology evolution that occurs during solid electrolyte interphase (SEI) growth. Compared with other simulation methodologies, the phase-field method has been widely applied in the solidification modeling that has great relevance to SEI formation. The developed model can simulate SEI structure and morphology evolution, and can predict SEI thickness growth rate. X-ray photoelectron spectroscopy (XPS) experiments are performed to confirm the major SEI species as LiF, Li2O, ROLi, and ROCO2Li. Transmission electron microscopy (TEM) experiment is performed to present the SEI layer structures. The experiments reduce the complexity of the model development and provide validation to some extent. Fick's law and mass balance are applied to investigate lithium-ion concentration distributions and diffusion coefficients in different types of SEI layers predicted by the phase-field simulations. Simulation results show that lithium-ion diffusion coefficients between 298 K and 318 K are 1.340–7.328(10−16) cm2/s, 1.734–3.405(10−12) cm2/s, and 2.611–2.389(10−15) cm2/s in the compact, porous, and multilayered structures of SEI layer, respectively. The resistances between 298 K and 318 K are 0.740–1.693 Ω⋅cm2, 2.827–5.517 Ω⋅cm2, and 3.726–5.839 Ω⋅cm2 in the compact, porous, and multilayered structures of SEI layer, respectively.