Comparison of V₂O₅ xerogels prepared by the vanadate and alkoxide routes using x-ray absorption and other methods

X-ray absorption near edge spectroscopy (XANES), Brunauer-Emmett-Teller surface area, Fourier transform infrared (FTIR), and thermogravimetric analysis were used to characterize two xerogels of V₂O₅ prepared using the vanadate hydrolysis (i.e., the v-V₂O₅ 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 analysis. The pre-edge, main edge, and edge resonance peak intensities were examined to track the symmetry around the vanadium center. The results for the in situ samples made by both synthetic routes showed that the local symmetry around vanadium did not change significantly for x values ranging from 0 to 0.98, where x represents the degree of reduction in the formulation Li_xV₂O₅. For the ex situ samples, substantial distortion was observed on going from either the hydrated or PC-swollen states to states in which solvent was absent. Further, the XANES spectrum for an unlithiated ex situ a-V₂O₅ material showed very substantial distortion around vanadium compared to the v-V₂O₅ material, presumably due to the rapidity of polymerization in the alkoxide synthetic procedure. The galvanostatic intermittent titration technique was used to obtain the apparent Li^- diffusion coefficient in both materials, revealing Li⁺ diffusion in the v-V₂O₅ material that appeared to be more than two orders of magnitude faster than in the a-V₂O₅ material. The origin of that observation is discussed.