Computational Investigation of LiF Formation at Graphite-Electrolyte Interfaces

The performance of rechargeable batteries is strongly influenced by the solid-electrolyte interphase (SEI), and a comprehensive understanding of SEI formation from the atomic level is crucial for effective battery design. The dynamics of the electrode-electrolyte interface is important and needs to be considered when evaluating the mechanism of the SEI formation. Here, we employed ab initio molecular dynamics (AIMD) and density functional theory (DFT) calculations to examine interfacial behaviors and LiF formation. Through molecular dynamics and structure sampling, we successfully constructed an electrochemical stability diagram correlating the thermodynamic free energy with the potential, which is determined by the work function of electrode surfaces. DFT calculations revealed that LiF formation at the graphite-electrolyte interfaces occurs easily via the intermediate LiHF complex. Interestingly, LiF tends to be solvated by solvents rather than directly deposited onto electrode surfaces (e.g., the Au electrode), a phenomenon we identify as a critical determinant of the porous and uneven nature of the LiF layer observed on graphite electrodes. Our finding offers new mechanistic insights into LiF formation at graphite-electrolyte interfaces.