Synthesis and electrochemical lithium insertion in polyaniline/HMWO 6 (M = Ta, Nb) nanocomposites

Abstract

The relatively strong Brønsted acidity of the trirutile-like layered oxides HMWO 6 · nH 2 O (M = Ta, Nb) was used to intercalate aniline to form a bilayer of the guest species within the interlayer gap having the formulation [Aniline] 0.68HMWO 6. Thermal treatment in air resulted in expulsion of half of the aniline, together with polymerization of the remaining aniline within the layers and formation of the novel nanocomposite, PANI 0.34HMWO 6. FTIR studies showed that the emeraldine salt form of PANI was present. This was consistent with measurements which showed increased conductivity for the nanocomposite (1 × 10 −6 S/cm), compared to that of the insulator [Aniline] 0.68 HMWO 6 ( ⪡ 10 −13 S/cm ). The electrochemical properties of these materials for lithium insertion reactions were studied using the polymer nanocomposites as cathodes in conventional lithium cells. Electrochemical insertion of lithium was compared to lithium insertion in the oxide in the absence of the polymer. In the case of PANI y HMWO 6 (M = Ta, Nb), the Li diffusion coefficient was measured using the geometrical surface area, the BET surface area, and the SEM surface area. Irrespective of the method of surface area measurement, the chemical diffusion coefficient increases for both Ta and Nb oxides upon insertion of polyaniline into the host. In the case of HTaWO 6 the diffusion coefficient increases by more than an order of magnitude (factor of 20). We ascribe this increase in Li ion mobility to a decrease in the Li + ion interaction with the host lattice in the polymer nanocomposite.