title: Solid Electrolyte Interphase Growth and Capacity Loss in Silicon Electrodes.
abstract: The solid electrolyte interphase (SEI) of the high capacity anode material Si is monitored over multiple electrochemical cycles by (7)Li, (19)F, and (13)C solid-state nuclear magnetic resonance spectroscopies, with the organics dominating the SEI. Homonuclear correlation experiments are used to identify the organic fragments -OCH2CH2O-, -OCH2CH2-, -OCH2CH3, and -CH2CH3 contained in both oligomeric species and lithium semicarbonates ROCO2Li, RCO2Li. The SEI growth is correlated with increasing electrode tortuosity by using focused ion beam and scanning electron microscopy. A two-stage model for lithiation capacity loss is developed: initially, the lithiation capacity steadily decreases, Li(+) is irreversibly consumed at a steady rate, and pronounced SEI growth is seen. Later, below 50% of the initial lithiation capacity, less Si is (de)lithiated resulting in less volume expansion and contraction; the rate of Li(+) being irreversibly consumed declines, and the Si SEI thickness stabilizes. The decreasing lithiation capacity is primarily attributed to kinetics, the increased electrode tortuousity severely limiting Li(+) ion diffusion through the bulk of the electrode. The resulting changes in the lithiation processes seen in the electrochemical capacity curves are ascribed to non-uniform lithiation, the reaction commencing near the separator/on the surface of the particles.
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, United Kingdom.
authors.forename: Alison L
authors.initials: AL
authors.lastname: Michan
authors.affiliation: Department of Material Science and Metallurgy, University of Cambridge , 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Divitini
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, United Kingdom.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Pell
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, United Kingdom.
authors.forename: Michal
authors.initials: M
authors.lastname: Leskes
authors.affiliation: Department of Material Science and Metallurgy, University of Cambridge , 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom.
authors.forename: Caterina
authors.initials: C
authors.lastname: Ducati
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, United Kingdom.
authors.forename: Clare P
authors.initials: CP
authors.lastname: Grey