Lithium Diffusion Mechanism through Solid–Electrolyte Interphase in Rechargeable Lithium Batteries

The composition, structure, and the formation mechanism of the solid–electrolyte interphase (SEI) in lithium-based (e.g., Li-ion and Li metal) batteries have been widely explored in the literature. However, very little is known about the ion transport through the SEI. Understanding the underlying ion diffusion processes across the SEI could lead to a significant progress, enabling the performance increase and improving safety aspects of batteries. Herein, we report the results of first-principles density functional theory calculations on the dominant diffusion pathways, energetics, and the corresponding diffusion coefficients associated with Li diffusion through the polycrystalline SEI. This paper is particularly concerned with the Li diffusion through the grain boundary (GB) formed between the three major inorganic components of the SEI, such as Li2O, LiF, and Li2CO3. It is found that Li diffusion occurs through the numerous open channels formed by the GB. The energetics and potential barriers vary significantly depending upon the structure of these channels, with the general trend being that Li diffusion in the GB is generally faster than in the neighboring crystalline regions within the grain interiors. In addition, the elastic properties of the GB are calculated allowing for more profound understanding of the SEI stability and formation.