The behavior of vanadium oxide gels as potential battery materials and liquid crystals: NMR, electrochemical, and X-ray absorption analysis

Lithium ions were electrochemically inserted into V₂O ₅·0.5H₂O xerogel, polyaniline/V₂O ₅, and sulfonated polyaniline/V₂O₅ nanocomposites and studied with 7Li magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Two distinct lithium environments were resolved and assigned to lithium ions occupying either interfacial or intercalated sites in the V₂O₅·0.5H₂O xerogel matrix. Lithium chemical shifts, relaxation measurements and variable-temperature (VT) MAS NMR are used to determine the mobility of both interfacial and intercalated lithium ions and the associated coupling to paramagnetic sites on the V ₂O₅ xerogel lattice. From spin-lattice relaxation (T ₁) data, a minimum is observed, yielding an average polaron correlation time in excellent agreement with a value based independently on conductivity measurements. Thus, revealing that the dominant relaxation mechanism is associated with the nuclear dipole coupling to polaron motion.; X-ray absorption near edge spectroscopy (XANES), BET surface area, FTIR and thermogravimetric analysis were used to characterize two xerogels of V ₂O₅ prepared using the vanadate hydrolysis (i.e. the ν-V ₂O₅ material) or the vanadyl tris(isopropoxide) hydrolysis (i.e. the a-V₂O₅ material) synthetic routes. XANES spectra were obtained and analyzed for samples at varying degrees of lithiation that were either bathed in 0.5 M LiClO₄/propylene carbonate (PC) supporting electrolyte (i.e. in situ) or from which the solvent had been removed by treatment under high vacuum (i.e. ex situ), as judged by FTIR. The pre-edge, main edge and edge resonance peak intensities were examined to track the symmetry around the vanadium center.; The magnetic alignment of V₂O₅ nematic gels is monitored with 2H and 1H pulsed field gradient spin echo (PFGSE) NMR. Comparisons are made between the native nematic gel which has 1% V4+ sites and a reduced form with 4% V 4+. The 2H quadrupole splitting and directional dependent 1H self-diffusion coefficient are representative of a nematic phase with its principal axis aligned along the external magnetic field (B _z) in both forms. However, a larger quadrupole splitting, shift anisotropy and more rapid 1H self-diffusion coefficient is observed for the reduced form indicating a greater degree of alignment. NaCl is added to the reduced gel to observe variations in alignment as a function of salt concentration. The salt causes both a decrease in the observed shift anisotropy, quadrupole splitting and 1H self-diffusion coefficient along z due to disruption of the nematic phase and eventual collapse at high salt concentrations. These results indicate that the alignment properties of V₂O₅ gels can be tuned by changing the oxidation state of the vanadium metal center.