Received: July 25, 2007

In Final Form: October 29, 2007

Abstract:

In this work, an investigation of the electrical and electrochemical properties responsible for the energy storage capability of nanocomposites has been carried out. We demonstrate that, in the case of the V₂O₅ xerogel and the nanocomposites polypyrrole (Ppy)/V₂O₅ and polyaniline (PANI)/V₂O₅, the quadratic logistic equation (QLE) can be used to fit the inverse of the resistance values as a function of the injected charge in non-steady-state conditions. This contributes to a phenomenological understanding of the lithium ion and electron transport. The departure of the experimental curve from the fitting observed for the V₂O₅ xerogel can be attributed to the trapping sites formed during the lithium electroinsertion, which was observed by electrochemical impedance spectroscopy. The amount of trapping sites was obtained on the basis of the QLE. Similar values used to fit the inverse of the resistance were also used to fit the absorbance changes, which is also associated with the small polaron hopping from the V(IV) to the V(V) sites. On the other hand, there was good agreement between the experimental and the theoretical data when the profile of the inverse of the resistance as a function of the amount of inserted lithium ions of the nanocomposites Ppy/V₂O₅ and PANI/V₂O₅ was concerned. We suggest that the presence of the conducting polymers is responsible for the different electrical profile of the V₂O₅ xerogel compared with those of the nanocomposites. In the latter case, interactions between the lithium ions and oxygen atoms from V₂O₅ are shielded, thus decreasing the trapping effect of lithium ions in the V₂O₅ sites. The different values of the lithium ion diffusion coefficient into these intercalation materials are in agreement with this hypothesis.

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