Ex situ and in situ infrared spectroelectrochemical investigations of V2O5crystalline films

Vanadium oxide (V2O5) films were prepared by dip-coating from V-oxoisopropo xide sols and heating at 300 degrees C for 1 h. Transmission electron micro scopy combined with small area electron and X-ray diffraction revealed that the films consist of disordered V2O5 grains with an orthorombic structure (P-mmm). Electromotor force (emf), cyclic voltammetric (CV), and chronocoul ometric measurements, combined with in situ ultraviolet-visible (UV-vis) sp ectroelectrochemical measurements, revealed similar electrochromic and elec trochemical properties with other sputtered and sol-gel derived V2O5 films. IR absorbance and reflection-absorption spectra, performed at near-grazing incidence angle (NGIA) conditions (80 degrees, P-polarized), allowed us to compare the observed transverse optical (TO) and longitudinal optical (LO) frequencies of films with the TO and LO mode frequencies obtained from the dispersion analyses of V2O5 crystalline reflection IR spectra. TO and LO s pectra of charged films show that Li+...O interactions modify the terminal V-OA (vanadyl), bridging V-O-B-V, and edge-sharing V-O-C stretching frequen cies, suggesting that these interactions take place between the oxygens bor dering the cavities in which Li+ ions are accommodated during charging. The red-frequency shift of the V-O-A stretchings [1016 cm(-1) (TO), 1035 cm(-1 ) (LO)] and the disappearance of the bridging V-OB-V stretching mode [795 c m(-1) (TO), 895 cm(-1) (LO)] can be used as a diagnostic tool to differenti ate between films cycled in the safe and unsafe potential regions. A polaro n absorption was observed above 2000 cm(-1) in the ex situ TO and in situ N GIA reflection-absorption (LO) spectra of films charged in the safe potenti al region. (C) 1999 The Electrochemical Society. S0013-4651(98)05-028-9. Al l rights reserved.