title: Lithiation of Crystalline Silicon As Analyzed by Operando Neutron Reflectivity.
abstract: We present an operando neutron reflectometry study on the electrochemical incorporation of lithium into crystalline silicon for battery applications. Neutron reflectivity is measured from the ⟨100⟩ surface of a silicon single crystal which is used as a negative electrode in an electrochemical cell. The strong scattering contrast between Si and Li due to the negative scattering length of Li leads to a precise depth profile of Li within the Si anode as a function of time. The operando cell can be used to study the uptake and the release of Li over several cycles. Lithiation starts with the formation of a lithium enrichment zone during the first charge step. The uptake of Li can be divided into a highly lithiated zone at the surface (skin region) (x ∼ 2.5 in LixSi) and a much less lithiated zone deep into the crystal (growth region) (x ∼ 0.1 in LixSi). The total depth of penetration was less than 100 nm in all experiments. The thickness of the highly lithiated zone is the same for the first and second cycle, whereas the thickness of the less lithiated zone is larger for the second lithiation. A surface layer of lithium (x ∼ 1.1) remains in the silicon electrode after delithiation. Moreover, a solid electrolyte interface is formed and dissolved during the entire cycling. The operando analysis presented here demonstrates that neutron reflectivity allows the tracking of the kinetics of lithiation and delithiation of silicon with high spatial and temporal resolution.
authors.affiliation: Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner-Platz 1, 14109 Berlin, Germany.
authors.forename: Beatrix-Kamelia
authors.initials: BK
authors.lastname: Seidlhofer
authors.affiliation: Institut für Metallurgie, Technische Universität Clausthal , AG Mikrokinetik, Robert-Koch-Str. 42, 38678 Clausthal-Zellerfeld, Germany.
authors.forename: Bujar
authors.initials: B
authors.lastname: Jerliu
authors.affiliation: Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner-Platz 1, 14109 Berlin, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Trapp
authors.affiliation: Institut für Metallurgie, Technische Universität Clausthal , AG Mikrokinetik, Robert-Koch-Str. 42, 38678 Clausthal-Zellerfeld, Germany.
authors.forename: Erwin
authors.initials: E
authors.lastname: Hüger
authors.affiliation: Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner-Platz 1, 14109 Berlin, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Risse
authors.affiliation: Institute Laue-Langevin , 71 avenue des Martyrs - CS 20156, 38042 Cedex 9 Grenoble, France.
authors.forename: Robert
authors.initials: R
authors.lastname: Cubitt
authors.affiliation: Institut für Metallurgie, Technische Universität Clausthal , AG Mikrokinetik, Robert-Koch-Str. 42, 38678 Clausthal-Zellerfeld, Germany.|Clausthaler Zentrum für Materialtechnik , Leibnizstraße 9, 38678 Clausthal-Zellerfeld, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Schmidt
authors.affiliation: Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner-Platz 1, 14109 Berlin, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Steitz
authors.affiliation: Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner-Platz 1, 14109 Berlin, Germany.|Institute of Physics, Humboldt-University Berlin , 10099 Berlin, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Ballauff
keywords: energy storage; lithiation; lithium-ion batteries; neutron reflectivity; operando; silicon anode; time-resolved