Open AccessOptical Modulation and Phase Distribution in LiCoO2 upon Li-Ion De/Intercalation
Author(s) -
Sanaz Banifarsi,
Yug Joshi,
Robert Lawitzki,
Gábor Csiszár,
Guido Schmitz
Publication year - 2022
Publication title -
journal of the electrochemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.258
H-Index - 271
eISSN - 1945-7111
pISSN - 0013-4651
DOI - 10.1149/1945-7111/ac63f6
Subject(s) - electrochromism , lithium (medication) , intercalation (chemistry) , refractive index , analytical chemistry (journal) , absorption (acoustics) , electrochromic devices , materials science , sputtering , phase (matter) , absorption spectroscopy , chemistry , electron diffraction , thin film , diffraction , optics , optoelectronics , electrode , inorganic chemistry , nanotechnology , medicine , physics , organic chemistry , chromatography , composite material , endocrinology
Modulation of reflectance resulting from the change in optical constants in Li x CoO 2 during lithium de/intercalation is studied and quantified by in-operando and ex situ optical spectroscopy. To this aim, the LiCoO 2 (LCO) thin films are sputter deposited using radio-frequency ion-beam sputtering. The films are structurally characterized by X-ray diffraction and transmission electron microscopy. The reversible electrochemical and electrochromic performance is determined by in-operando optical reflectance. Ex-situ reflectance, at particular charge states, is used to determine the optical constants by modeling the optical spectrum using the Clausius-Mossotti relation. The model reveals a dominant resonant wavelength at 646 nm for the fully intercalated state of LCO. For the delithiated state or Li 0.5 CoO 2 , a much broader and significantly larger absorption peak is obtained by the model description. This significantly broad and intense absorption peak can be associated with the conducting nature of the films upon lithium removal. Furthermore, the observed complex refractive index (CRI), evolving with the lithium content, is justified by the prior reported density of states calculations. With the CRI, the corresponding variation of the real and imaginary part of the dielectric function reveals that the intercalation of lithium and the consequent phase propagation follows a layer-like reaction.