Preparation And Properties Study Of PEO/Tungsten-doped Vanadium Oxide Films

The synthesis, structure, properties and interface behavior of nanocomposite materials based on layered V₂O₅ and MoO₃, which can be topotactically reacted with alkali-medal ions (Li⁺, Na⁺, etc.) have attracted more attention in recent years. The intercalation of polymer into the interlayer is expected to improve the interface and interlayer structure of these materials, resulting in desirable novel characteristics. In this dissertation, W was doped to vanadium pentoxide sols by the sol-gel and hydrothermal route for host material, and then PEO was intercalated by polymer solution direct intercalation. Meanwhile, the structure and properties of these films were investigated by XRD, TG-DSC, IR, XPS, SEM, AFM, TEM, AC, EIS, CV and UV-vis method.V/W-oxide sols were successfully prepared by sol-gel route combined with hydrothermal method. It is found that the prepared V/W-oxide sols with a high viscosity were uniform and could be stable for several months. The V/W-oxide xerogel exhibits excellent performance. The films have a layered structure, the WO3 has been highly dispersed into V₂O₅·nH₂O framework and forms a solid solution phase, and the present of tungsten can increase the order degree of the layered structure. IR spectral shown that two peaks of v_as(V-O-V) and v_as(V-O-V) move remarkably toward lower frequencies. It is probably due to the fact that the V sites are partially substituted by heavier atoms (W) and form a new bond as V-O-W after hydrothermal synthesis. XPS results indicated that a redox reaction was probably occurred in the mixed precursor sol before hydrothermal synthesis, then the V sites were partially substituted by the reduced W⁵⁺ and W⁴⁺ ions during the hydrothermal synthesis. The proper amount of W can remarkably increase the ion storage capacity and improve the transmission modulation of the films. The charge densities of the V_1.8W_0.5O₅·nH₂O film can reach the maximum value of 45.5 mC/cm² and the film exhibit good reversibility. And the transmission modulation (AT) was improved as large as 52 % at 730 nm, while it's only 12 % for V₂O₅·nH₂O film.By the means of polymer solution direct intercalation method, PEO was successfully intercalated into the layer of V/W-oxide and forms the V=O…O bonding interaction, which can be supported by the results of XRD, TG-DSC and IR. The intercalation of PEO effectively shields the electrostatic interaction between Li⁺ ions and V/W-oxide layers, resulting in the improvement of the cycling reversibility, stability of Li⁺ ions insertion / extraction in the interlayer. The charge densities of the PEO_0.08V_1.8W_0.2O₅·nH₂O film can reach the maximum value of 55.4mC/cm², which is higher than that of V_1.8W_0.2O₅·nH₂O xerogel film. And the transmission modulation (AT) was 46.7% at 730 nm, which is as well as V_1.8W_0.2O₅·nH₂O xerogel film. It is indicated that the proper amount of PEO can remarkably increase the Li⁺ intercalation properties and improve the cycle stability without the decrease in transmission modulations.