Synthesis and characterization of polypyrrole/vanadium pentoxide nanocomposite aerogels

Abstract

Vanadium pentoxide/polypyrrole aerogel (ARG) composites have been synthesized by sol–gel routes, and investigated as cathode materials in Li batteries. The primary method utilized simultaneous polymerisation of pyrrole and vanadium alkoxide precursors. Hydrolysis of VO(OC₃H₇)₃ using pyrrole–water–acetone mixtures yielded monolithic green–black gels with polypyrrole/V ratios ranging from 0.15 to 1.0. Supercritical drying yielded high surface (150–257 m² g^–1) aerogels with densities between 0.1 and 0.2 g cm^–3 , that were of sufficient mechanical integrity to allow them to be cut without fracturing. TEM studies of the ARGs show that they are comprised of fibers similar to that of V₂O₅ ARGs, but with a significantly shorter chain length. The interaction between the polypyrrole (PPy) and V₂O₅ aerogel in the nanocomposites was probed using IR spectroscopy. Our results suggest that the inorganic and organic components strongly interact during the initial stages, thus perhaps impeding the vanadium condensation process. Hence, the PPy/V₂O₅ nanocomposites exhibited lower electrical conductivity with increased polypyrrole content. The addition of (NH₄)₂S₂O₈ as an oxidizing agent improved the conductivity of the nanocomposites. The deleterious effect of the conductive polymer on the bulk conductivity does not necessarily affect the electrochemical properties of these materials. Nanocomposite materials that were subjected to post-oxidative treatment show enhanced Li insertion capacity compared to the pristine ARG. The physical properties of these ‘nanocomposite aerogels’ are different from ‘microcomposites’ prepared by an alternate route, in which the oxide gel is formed in the presence of a dispersion of preformed micrometer-sized polypyrrole particles.