Identifying the Structural Basis for the Increased Stability of the Solid Electrolyte Interphase Formed on Silicon with the Additive Fluoroethylene Carbonate.
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To elucidate the role of fluoroethylene carbonate (FEC) as an additive in the standard carbonate-based electrolyte for Li-ion batteries, the solid electrolyte interphase (SEI) formed during electrochemical cycling on silicon anodes was analyzed with a combination of solution and solid-state NMR techniques, including dynamic nuclear polarization. To facilitate characterization via 1D and 2D NMR, we synthesized 13C-enriched FEC, ultimately allowing a detailed structural assignment of the organic SEI. We find that the soluble poly(ethylene oxide)-like linear oligomeric electrolyte breakdown products that are observed after cycling in the standard ethylene carbonate-based electrolyte are suppressed in the presence of 10 vol% FEC additive. FEC is first defluorinated to form soluble vinylene carbonate and vinoxyl species, which react to form both soluble and insoluble branched ethylene-oxide-based polymers. No evidence for branched polymers is observed in the absence of FEC.
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1520-5126
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European Research Council (247411)
United States Department of Energy (DOE) (via University of California) (7057154)
Engineering and Physical Sciences Research Council (EP/L019469/1)
Technology Strategy Board (132220)
Engineering and Physical Sciences Research Council (EP/M009521/1)
Engineering and Physical Sciences Research Council (EP/N001583/1)
European Commission Horizon 2020 (H2020) Future and Emerging Technologies (FET) (696656)