XPS study of the Li intercalation process in sol-gel-produced V2O5 thin film: influence of substrate and film synthesis modification

Abstract

We report on the process of lithium intercalation in V 2 O 5 thin films deposited onto standard ITO-coated glass substrates. The films were deposited via a well-established sol-gel route, and the samples were examined as working electrodes in a range of potentials versus lithium reference electrode. This paper follows up issues arising from parallel spectroscopic characterizations of the films by X-ray photoelectron spectroscopy (XPS). Specifically, the XPS examination showed that not all of the Li-ion charge inserted was accounted for by the V(5) to V(4) reduction, but the stoichiometric balance could be maintained only by considering additional oxygens arising from the intercalation procedure, leading to Li 2 O formation. In this work, we have examined the possibility that the source of oxygen is the ITO substrate. To this purpose, films of V 2 O 5 deposited on silicon substrates have been prepared using the sol-gel process and examined by XPS after electrochemical intercalation/de-intercalation cycles. We show that in this case a perfect balance between electrochemical charge, inserted Li and reduced vanadium is obtained. A further indication of ITO-substrate effects was obtained from examination, by the same methods, of some unconventional V 2 O 5 films that had been co-precipitated with a siloxane, designed to provide a template structure. The results obtained from this material imply that a barrier layer is formed at the ITO interface and, therefore, the formation of Li 2 O is avoided. The results are discussed in terms of the possible degradation of conventional V 2 O 5 on ITO as a result of electrochemically induced interface reactions.

Synthesis and Functional Properties of Vanadium Oxides: V2O3, VO2, and V2O5 Deposited on Glass by Aerosol‐Assisted CVD

“…[9][10][11][12][13][14] We have shown previously that VO 2 , VO x , and V 2 O 5 phases can be fabricated by using APCVD from reactions of VCl 4 , VOCl 3 , and water. The ratio of water to vanadium precursor and the substrate temperatures were the determining factors in which the oxide formed.…”

Li+ distribution into V2O5 films resulting from electrochemical intercalation reactions

“…This change in the oxidation state of V has been already studied by us in the past using XPS. 5 In order to calculate the rate of the solid-state diffusion process of the inserted ion inside the oxide host matrix we have performed PITT experiments in the two different electrode configurations already shown above, and we have analyzed the current transients according to the treatment given by Levi et , and this is the results we indeed obtained when inserting the Li ions from the electrode front surface (see data points in Figure 4a). When the edge of the electrode has been exposed to the solution, on the other hand, the diffusion coefficient , a value considerably higher than that expected for a solid-state diffusion process (Figure 4b).…”

“…3 nm) of the surface, possibly associated with trapped lithium ions. 4,5 Recent SIMS analysis have shown some accumulation of Li + at both interfaces, the one exposed to the electrolyte and the buried one between V 2 O 5 and ITO. 6 This accumulation of Li + is a severe source of error for the computation of the thin film average stoichiometry from the inserted cation charge, and may have a deleterious influence on device performance due to problems associated with lithium trapping and charge transport across any one of the two interfaces.…”

Characterisation of sol–gel crystalline V2O5 thin films after Li intercalation cycling

“…The spectrum shows In and Sn signals at low intensity and the presence of an adsorbed layer of lithium carbonate component derived from the electrolyte. 4 There is a Ba 3d signal, probably from Ba as an impurity in the electrolyte, precipitated as the carbonate after multicycling. Sample 3 is very different: peaks for V almost disappear, while In becomes prevalent and Sn more visible.…”

“…4 The samples described here were all taken from the same batch and are Sample 1, the 'as-received' V 2 O 5 film; Sample 2, a film after 662 CV cycles and Sample 3, a film after 745 cycles with many intermediate washes and x-ray photoelectron spectroscopy (XPS) analyses.…”