title: Epitaxial LiCoO2 films as a model system for fundamental electrochemical studies of positive electrodes.
abstract: Epitaxial LiCoO2 (LCO) thin films of different orientations were fabricated by pulsed laser deposition (PLD) in order to model single-crystal behavior during electrochemical reaction. This paper demonstrates that deposition of conductive SrRuO3 between a SrTiO3 (STO) substrate and an LCO film allows (1) epitaxial growth of LCO with orientation determined by STO and (2) electrochemical measurements, such as cyclic voltammetry and impedance spectroscopy. Scanning transmission electron microscopy (S/TEM and SEM) has demonstrated an orientation relationship between LCO and STO of three orientations, (111), (110) and (100), and identified a LCO/electrolyte surface as consisting of two crystallographic facets of LCO, (001) and {104}. The difference in the orientation of LCO accounts for the difference in the exposed area of {104} planes to the electrolyte, where lithium ions have easy access to fast diffusion planes. The resistance for lithium ion transfer measured by electrochemical impedance spectroscopy had inverse correlation with exposed area of {104} plane measured by TEM. Chemical diffusivity of lithium ions in LCO was measured by fitting electrochemical impedance spectroscopy data to a modified Randles equivalent circuit and allowed us to determine its dependence on film orientation.
authors: †Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.
authors: Saya
authors: S
authors: Takeuchi
authors: †Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.|‡Theiss Research, La Jolla, California 92037, United States.
authors: Haiyan
authors: H
authors: Tan
authors: †Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.
authors: K Kamala
authors: KK
authors: Bharathi
authors: †Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.
authors: Gery R
authors: GR
authors: Stafford
authors: §Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States.
authors: Jongmoon
authors: J
authors: Shin
authors: †Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.|§Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States.|∥Materials and Structures Laboratory, Tokyo Institute of Technology 4259-J2-19, Nagatsuta, Midori, Yokohama, 226-8503 Japan.
authors: Shintaro
authors: S
authors: Yasui
authors: §Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States.
authors: Ichiro
authors: I
authors: Takeuchi
authors: †Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.
authors: Leonid A
authors: LA
authors: Bendersky
keywords: LiCoO2; epitaxial thin films; interface; orientation; transmission electron microscopy