Article pubs.acs.org/JACS
Cite This: J. Am. Chem. Soc. 2017, 139, 14992-15004
Identifying the Structural Basis for the Increased Stability of the Solid Electrolyte Interphase Formed on Silicon with the Additive Fluoroethylene Carbonate Yanting Jin,† Nis-Julian H. Kneusels,† Pieter C. M. M. Magusin,† Gunwoo Kim,†,‡ Elizabeth Castillo-Martínez,† Lauren E. Marbella,† Rachel N. Kerber,† Duncan J. Howe,† Subhradip Paul,§ Tao Liu,† and Clare P. Grey*,† †
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom Cambridge Graphene Centre, University of Cambridge, Cambridge CB3 0FA, United Kingdom § DNP MAS NMR Facility, Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham NG7 2RD, United Kingdom ‡
S Supporting Information *
ABSTRACT: 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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INTRODUCTION The formation of a solid electrolyte interphase (SEI) on the electrode surface is critical for the cycle life of lithium ion batteries (LIBs). Stable SEI formation on the anode is particularly important, because current LIBs operate outside the stable voltage window of the organic carbonate-based liquid electrolyte (
