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 CMM Magusin, Gunwoo Kim, Elizabeth Castillo-Martínez, Lauren E Marbella, Rachel N Kerber, Duncan J Howe, Subhradip Paul, Tao Liu, Clare P Grey

OAI: oai:www.repository.cam.ac.uk:1810/296460 • DOI: 10.17863/CAM.43509

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.

physics.chem-ph physics.chem-ph