Elucidating Oligomer-Surface and Oligomer-Oligomer Interactions at a Lithiated Silicon Surface
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2016 Elsevier Ltd Solid-electrolyte interphase (SEI) layers are multicomponent films formed at the surface of electrodes in Li-ion batteries due to electrochemical instability of the electrolyte components. The properties of this film significantly affect the lifetime of the battery. Here we study the interaction of some electrolyte reduction products (oligomers) with a bare Li13Si4 (010) surface and a Li13Si4 (010) surface partially covered with lithium fluoride (LiF) using classical Monte Carlo and density functional theory-based methods The adsorption, charge transfer, and association of oligomers on the surface are reported. Overall, the oligomers attach firmly to the surface. Our findings indicate that the surface-oligomer interaction dominates the stabilization of the system up to a coverage of approximately 1oligomer/nm2 and once this coverage is reached, oligomer-oligomer interactions dominate the stabilization of the porous block. Regarding association, lithium ethylene dicarbonate (Li2EDC) tends to associate with the bare and partially covered surface through O.Li.O bridges. However, the association mechanism varies depending on the existing nucleating products at the surface. In contrast, lithium vinylene dicarbonate (Li2VDC)s backbone is closer to the surface and exhibits a more flexible structure than the Li2EDC oligomer. This difference may further affect the compactness of the SEI layer. Aligned with our previous studies, we also found oligomer decomposition on the surface. Our calculations offer critical information regarding the structure of electrolyte decomposition products over silicon electrodes.
