Solid-state NMR study of ion-exchange processes in V₂O₅ xerogel, polyaniline/V₂O₅, and sulfonated polyaniline/V₂O₅ nanocomposites

The local lithium environment in electrochemically lithiated V₂O₅ xerogel, polyaniline/V₂O₅, and sulfonated polyaniline/V₂O₅ nanocomposites is probed with solid-state ⁷Li static and magic angle spinning (MAS) nuclear magnetic resonance (NMR). The line width from the static NMR spectra reveals differences between the lithium environments in the three materials. The MAS NMR spectrum of the V₂O₅ parent material in its unreduced (as-prepared) state shows the presence of an intrinsic ion-exchange site that can be populated with Li⁺ by simple exposure to LiCiO₄ in propylene carbonate (PC). Following electrochemical lithiation, both ion-exchange and intercalated lithium sites are observed. After lithiation, Li⁺ ions at the ion-exchange site can be displaced by exposure to NaClO₄ in PC via a simple ion-exchange process. Both the ion-exchange and intercalated sites are observed for a sulfonated polyaniline/V₂O₅ nanocomposite while the polyaniline/V₂O₅ nanocomposite response is dominated by the intercalated lithium site. The results show that charge compensation of the intrinsic negatively charged ion-exchange sites in the V₂O₅ xerogel by conducting polymers used to form the nanocomposites is important in determining the number and type of Li⁺ sites available.