Lithium ion diffusion mechanism on the inorganic components of the solid–electrolyte interphase

Abstract

The diffusion behavior of lithium (Li) ions on the solid–electrolyte interphase (SEI) is fundamentally essential to Li metal batteries, whereas the underlying microscopic mechanism is still indistinct. Answers for what could be the main inorganic components of SEI and how Li ions migrate through inorganic parts remain controversial. Herein, based on cryogenic electron microscopy, we identified four nanocrystalline inorganic components, namely LiOH, Li₂O, Li₂CO₃, and LiF, which were embedded in the amorphous organic part. Accordingly, we simulated the Li ion diffusion process and demonstrated that the LiF surface presented the fastest diffusion rate for Li ions, owing to its considerably lower migration energy barrier. In addition, a relatively large diffusion coefficient for Li ions on the LiF surface accounts for a high ionic conductivity in SEI layers. These results contribute to clarifying the Li ion diffusion mechanism, and help design new lithium battery systems with high efficiency and safety.