Solid electrolyte interphase (SEI) is an important key of the stability and durability of the lithium ion batteries (LIB). It is generally accepted that molecules in the electrolyte solution reductively decompose to form various SEI film components (SFCs), such as organic oligomers and inorganic moieties, and that the SFCs precipitate on the electrode surface to form a stable SEI film with a thickness of several tens of nanometers. The formation processes of SEI have been typically assumed to involve “surface growth mechanism”. Decomposed products of the electrolyte molecules immediately precipitate to the electrode surface. At a certain thickness of the SFC aggregate, electron tunneling from the electrode to the electrolyte is suppressed. Growth of the SFC aggregate then stops and the formation of the SEI film are completed. However, there is a question as to how the reductive decompositions of the electrolyte are repeated until the thickness reaches several tens of nanometers. In this talk, we investigated the solubility properties of SFCs into the EC solution, a measure of aggregation tendency, and the adhesion to the edges of possible reduced graphite by first principles molecular dynamics (DFT-MD) simulations. From these results, we discuss how SEI films grow and when the growth stops in the present modeling of the SFCs. We also discuss about the glue effect of LiF in the SEI film.

First-principles molecular dynamics study for SEI film formation mechanism of lithium ion batteries

2019 Spring National Meeting

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