title: Solid Electrolyte Interphase (SEI) at TiO2Electrodes in Li-Ion Batteries: Defining Apparent and Effective SEI Based on Evidence from X-ray Photoemission Spectroscopy and Scanning Electrochemical Microscopy.
abstract: The high (de)lithiation potential of TiO2(ca. 1.7 V vs Li/Li+in 1 M Li+) decreases the voltage and, thus, the energy density of a corresponding Li-ion battery. On the other hand, it offers several advantages such as the (de)lithiation potential far from lithium deposition or absence of a solid electrolyte interphase (SEI). The latter is currently under controversial debate as several studies reported the presence of a SEI when operating TiO2electrodes at potentials above 1.0 V vs Li/Li+. We investigate the formation of a SEI at anatase TiO2electrodes by means of X-ray photoemission spectroscopy (XPS) and scanning electrochemical microscopy (SECM). The investigations were performed in different potential ranges, namely, during storage (without external polarization), between 3.0-2.0 V and 3.0-1.0 V vs Li/Li+, respectively. No SEI is formed when a completely dried and residues-free TiO2electrode is cycled between 3.0 and 2.0 V vs Li/Li+. A SEI is detected by XPS in the case of samples stored for 6 weeks or cycled between 3.0 and 1.0 V vs Li/Li+. With use of SECM, it is verified that this SEI does not possess the electrically insulating character as expected for a "classic" SEI. Therefore, we propose the term apparent SEI for TiO2electrodes to differentiate it from the protecting and effective SEI formed at graphite electrodes.
authors.forename: Edgar
authors.identifier: http://orcid.org/0000-0002-8993-4285
authors.initials: E
authors.lastname: Ventosa
authors.forename: Edyta
authors.initials: E
authors.lastname: Madej
authors.forename: Giorgia
authors.initials: G
authors.lastname: Zampardi
authors.affiliation: Photocatalytic Synthesis Group, MESA+ Institute for Nanotechnology, Faculty of Science and Technology, University of Twente , Meander 229, P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Bastian
authors.identifier: http://orcid.org/0000-0002-3973-9254
authors.initials: B
authors.lastname: Mei
authors.forename: Philipp
authors.initials: P
authors.lastname: Weide
authors.forename: Hendrik
authors.initials: H
authors.lastname: Antoni
authors.affiliation: Energiespeicher- und Energiewandlersysteme, Universität Bremen , Wiener Str. 12, D-28359 Bremen, Germany.
authors.forename: Fabio
authors.initials: F
authors.lastname: La Mantia
authors.forename: Martin
authors.identifier: http://orcid.org/0000-0001-5343-6922
authors.initials: M
authors.lastname: Muhler
authors.forename: Wolfgang
authors.identifier: http://orcid.org/0000-0003-2916-5223
authors.initials: W
authors.lastname: Schuhmann
keywords: Li-ion batteries; X-ray photoemission spectroscopy; scanning electrochemical microscopy; solid electrolyte interphase; titanium dioxide