context: In this work, we carry out classical reactive molecular dynamics (MD) simulations for studying the initial formation of SEI films occurring by Li oxidation and simultaneous decomposition of electrolyte (salt and solvent) molecules in the liquid phase in contact with the Li-metal electrode. We use lithium hexafluorophosphate (LiPF6) as a salt because its reductive decomposition has been pointed as critical on the SEI formation and lithium trifluoromethanesulfonate (lithium triflate or LiTF) that has shown interesting performance in various systems. We study the behavior of the various system components (i.e. Li-metal anode slab, and salt and solvent molecules) when the electrolyte solution is put in contact with the Li metal surface. We follow the evolution of various events including the lithium metal expansion/dissolution, salt and solvent decomposition, and initial nucleation of the SEI intermediates and products as well as the electron exchange among the species. We aim to identify the effects of electrolyte composition on the Li-metal anode behavior and the SEI formation and growth at open circuit conditions. We focus only on the initial stages of SEI formation, concentrated in a specific part of the battery system, and do not examine the Li deposition events occurring when an ionic flux arrives at the anode during charge, and the effects of an applied field. To gain further understanding of the structures and mechanisms of the initial stages of SEI formation, density functional theory (DFT) calculations on initial Li–F were used to evaluate SEI fragments observed in MD simulations. Once optimized structures of such fragments are obtained, we investigated the fragment clustering processes found at initial stages of SEI nucleation. These simulations provide preliminary estimations for the energies of formation and clustering of LiF fragments.
answer: Li-metal