Effect of the Electrolyte Composition on SEI Reactions at Si Anodes of Li-Ion Batteries
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2015 American Chemical Society. Solid electrolyte interphase (SEI) layers formed at the surface of silicon anodes due to reductive decomposition of the electrolyte components are partially responsible of the irreversible capacity loss that negatively affects battery performance. We use ab initio molecular dynamics simulations to investigate how the electrolyte composition including organic carbonates and LiPF6 affects such reactions. Solvent polarity defines salt dissociation, and there is a competition between salt and solvent/additive dissociation. The salt anion decomposes, yielding a PF3 group and three F anions. The PF3 group is relatively stable, but after some time, it decomposes nucleating on the anode surface as LiF. During anion decomposition the P atom progressively reduces finally becoming coupled to a surface atom or to fragments of the solvent/additive decomposition that takes place prior or simultaneously with the salt decomposition. New pathways are found for formation of CO2 from vinylene carbonate reaction with the surface and for nucleation of Li oxide precursors.