Lithium/V6O13 cells using silica nanoparticle-based composite electrolyte

The electrochemical behavior of Li/V₆O₁₃ cells is investigated at room temperature (22 °C) both in liquid electrolyte consisting of oligomeric poly(ethyleneglycol)dimethylether+lithium bis(trifluoromethylsulfonylimide) and composite electrolytes formed by blending the liquid electrolyte with silica nanoparticles (fumed silica). The addition of fumed silica yields a gel-like electrolyte that demonstrates the desirable property of suppressing lithium dendrite growth due to the rigidity and immobility of the electrolyte structure. The lithium/electrolyte interfacial resistance for composite gel electrolytes is less than that for the corresponding base-liquid electrolyte, and the charge-discharge cycle performance and electrochemical efficiency for the Li/V₆O₁₃ cell is significantly improved. The effect of fumed silica surface group on the electrochemical performance is discussed; the native hydrophilic silanol surface group appears better than fumed silica that is modified with a hydrophobic octyl surface moiety.     

Densification and properties of lime with V2O5 additions

Sintering of lime was carried out in the presence of V₂O₅ by a single firing process. A pure limestone was crushed, mixed with 1, 2 and 4 wt.% V₂O₅, pelletised and fired between 1550 and 1650 °C. The sintered lime was evaluated by bulk density, apparent porosity, microstructure, hydration resistance and hot modulus of rupture (HMOR) at 1300 °C. Incorporation of V₂O₅ forms liquid phase with lime at elevated temperature and influences the densification process by liquid phase sintering. As a result bulk density of sinters improved and they become more hydration resistant due to the larger grain size of the lime phase. The hot strength increased up to a certain temperature followed by deterioration because of the pressure of higher amount of liquid phase.     

Thermopower of Semiconducting Glasses in the V2O5-P2O5 and V2O5-CdS-P2O5 Systems

Vanadium phosphate and cadmium sulfide-doped vanadium phosphate glasses containing up to 50–80 mol % V₂O₅ are prepared. The thermopower of these glasses is measured in the temperature range 303–473 K. The activation energies are determined from the linear dependences of the thermopower S and the logarithm of the conductivity logσ on the reciprocal of the temperature 1/T. It is demonstrated that the activation energies obtained by two methods differ from each other. The difference between the activation energies is referred to as the hopping energy Δ. The possibility of an Anderson metal-insulator transition occurring is examined. It is revealed that similar transitions are not observed in the glasses under investigation. The data obtained are analyzed within the small-polaron hopping model describing the electron conduction. It is established that hopping conduction proceeds over localized states in the tail of the density of states. All the glasses are characterized by electron conduction. Original Russian Text Copyright ? 2005 by Fizika i Khimiya Stekla, Khairnar, Yawale, Pakade.     

Electrochemical and morphological stabilization of V2O5 nanofibers by the addition of polyaniline

In this work, the relationship between the nanoscale morphology and electrochemical performance of vanadium oxide and vanadium oxide/polyaniline nanofibers is analyzed. The nanofibers were prepared by reverse micelle method and their electrochemical performances were evaluated as potential cathode materials for secondary Li-ion batteries. Both types of samples were examined by electroacoustic impedance, ex situ X-ray diffraction, Raman and infrared spectroscopies, transmission and scanning electron microscopies to characterize their structure and morphology. It was found that vanadium oxide/polyaniline nanofibers show improved cycling behavior compared to the vanadium oxide ones. Nanofibers of vanadium oxide exhibit the largest capacity fading during cycling; on the other hand, the nanohybrid containing 30 mol% polyaniline exhibits a stable capacity of ∼300 mAh g⁻¹. Scanning electron microscopy analyses indicated that the vanadium oxide nanofibers change the morphology after 10 charge/discharge cycles while hybrid nanofibers retain the defined morphology after electrochemical cycling. The role of the polymeric component of the hybrid material seems to be the stabilization of the capacity due to a probable homogeneous distribution of the induced stress during cycling.     

Electrochemical preparation and characterization of V2O5/polyaniline composite film cathodes for Li battery

Vanadium pentoxide/polyaniline (V₂O₅/PANi) composite films were prepared by a two-step electrochemical method and evaluated for their application in lithium batteries. As a first step the PANi film was potentiodynamically grown in an acid solution containing aniline monomer, and secondly vanadium oxide was oxidatively deposited on the polyaniline film in a temperature controlled VOSO₄ solution. The increased current efficiency obtained with the larger anodic current in the high temperature solutions results in high contents of V₂O₅ in the composites, even if the oxidative dissolution of PANi also occurs. The large value of the diffusion coefficient estimated from the cyclic voltammograms for the composite film provides evidence for the synergistic effect of the conducting polymer and the inorganic composite. The cell exhibited excellent cycle stability with a high charge storage capacity. The large increase in the specific capacity for the composite film prepared in this work demonstrates that the conducting polymer in the composite acts as a binding and conducting element by contributing its electroactivity. The V₂O₅/PANi composite film cathodes show a large specific capacity (ca. 270 mAh/g) and improved cyclability with an extremely small amount of capacity fading (ca. 3.4%) during repeated charge/discharge cycles.     

Limonene oxidation over V2O5/TiO2 catalysts

Vanadia-titania catalysts prepared by different sol–gel procedures were studied as heterogeneous catalysts for the liquid phase oxidation of limonene. The catalysts were characterized by XRD, XPS, ICP and nitrogen adsorption. According to the XRD results the catalyst samples can be divided in two different groups: anatase samples and anatase + rutile samples. XRD signals of vanadia are not found in the diffractograms.

The main reaction products are polymers. Limonene oxide, limonene glycol, carveol and carvone are obtained in small amounts. A number of autoxidation products, alcohols, aldehydes and ketones, are also obtained.

The effects of titania composition on the reaction orientation are discussed.     

Electrochemical properties of bare and Ta-substituted Nb2O5 nanostructures

In this work, bare and Ta-substituted Nb₂O₅ nanofibers are prepared by electrospinning followed by sintering at temperatures in the 800–1100 °C range for 1 h in air. Obtained bare and Ta-substituted Nb₂O₅ polymorphs are characterized by X-ray diffraction, scanning electron microscopy, density measurement, and Brunauer, Emmett and Teller surface area. Electrochemical properties are evaluated by cyclic voltammetry and galvanostatic techniques. Cycling performance of Nb₂O₅ structures prepared at temperature 800 °C, 900 °C, and 1100 °C shows following discharge capacity at the end of 10th cycle: 123, 140, and 164 (±3) mAh g⁻¹, respectively, in the voltage range 1.2–3.0 V and at current rate of 150 mA g⁻¹ (1.5 C rate). Heat treated composite electrode based on M-Nb₂O₅ (1100 °C) in argon atmosphere at 220 °C, shows an improved discharge capacity of 192 (±3) mAh g⁻¹ at the end of 10th cycle. The discharge capacity of Ta-substituted Nb₂O₅ prepared at 900 °C and 1100 °C showed a reversible capacity of 150, 202 (±3) mAh g⁻¹, respectively, in the voltage range 1.2–3.0 V and at current rate of 150 mA g⁻¹. Anodic electrochemical properties of M-Nb₂O₅ deliver a reversible capacity of 382 (±5) mAh g⁻¹ at the end of 25th cycle and Ta-substituted Nb₂O₅ prepared at 900 °C, 1000 °C and 1100 °C shows a reversible capacity of 205, 130 and 200 (±3) mAh g⁻¹ (at 25th cycle) in the range, 0.005–2.6 V, at current rate of 100 mA g⁻¹.     

Corrosion mechanisms of Al2O3/MgAl2O4 by V2O5, NiO, Fe2O3 and vanadium slag

The effects of V₂O₅, NiO, Fe₂O₃ and vanadium slag on the corrosion of Al₂O₃ and MgAl₂O₄ have been investigated. The specimens of Al₂O₃ and MgAl₂O₄ with the respective oxides above mentioned were heated at 10 °C/min from room temperature up to three different temperatures: 1400, 1450 and 1500 °C. The corrosion mechanisms of each system were followed by XRD and SEM analyses. The results obtained showed that Al₂O₃ was less affected by the studied oxides than MgAl₂O₄. Alumina was only attacked by NiO forming NiAl₂O₄ spinel, while the MgAl₂O₄ spinel was attacked by V₂O₅ forming MgV₂O₆. It was also observed that Fe₂O₃ and Mg, Ni, V and Fe present in the vanadium slag diffused into Al₂O₃. On the other hand, the Fe₂O₃ and Ca, S, Si, Na, Mg, V and Fe diffused into the MgAl₂O₄ structure. Finally, the results obtained were compared with those predicted by the FactSage software.     

Structural and optical properties of MoO3 and V2O5 thin films prepared by Spray Pyrolysis

MoO₃ and V₂O₅ thin films were prepared on glass substrates by Spray Pyrolysis technique at a substrate temperature of 423 K. The precursor solutions were obtained by varying the concentrations of MoCl₅ and VCl₃ in bi-distilled water. The structural investigation conducted by X-ray diffraction showed that MoO₃ and V₂O₅ thin films were polycrystalline with orthorhombic structure. The optical properties studied in the 300–2500 nm range suggest that the thin film behaviours are related to bound electronic states. The optical band gaps have been estimated from slopes of ln(hν) versus hν plots of MoO₃ and V₂O₅ films were 3.35 and 2.44 eV, respectively. The electrical conductivity was measured using four probes method.     

SO2 and NO removal from flue gas over V2O5/AC at lower temperatures — role of V2O5 on SO2 removal

Supporting V₂O₅ onto an activated coke (AC) has been reported to significantly increase the AC's activity in simultaneous SO₂ and NO removal from flue gas. To understand the role of V₂O₅ on SO₂ removal, V₂O₅/AC is studied through SO₂ removal reaction, surface analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) techniques. It is found that the main role of V₂O₅ in SO₂ removal over V₂O₅/AC is to catalyze SO₂ oxidation through a VOSO₄-like intermediate species, which reacts with O₂ to form SO₃ and V₂O₅. The SO₃ formed transfers from the V sites to AC sites and then reacts with H₂O to form H₂SO₄. At low V₂O₅ loadings, a V atom is able to catalyze as many as 8 SO₂ molecules to SO₃. At high V₂O₅ loadings, however, the number of SO₂ molecules catalyzed by a V atom is much less, due possibly to excessive amounts of V₂O₅ sites in comparison to the pores available for SO₃ and H₂SO₄ storage.     

Structural changes of Nb2O5 and V2O5 as rechargeable cathodes for lithium battery

The structural changes of T-Nb₂O₅ and V₂O₅ cathodes with discharge and recharge were investigated by X-ray photoelectron spectroscopy (ESCA) and X-ray diffractometory etc.ESCA spectra of the discharge products shows that M⁵⁺ is reduced to a lower valence state such as M⁴⁺ on the discharge, and the chemical bond between Li⁺ inserted into the oxide and O^2? of the oxide exhibits a higher ionic character than that of Li₂O. X-ray diffraction measurement shows that T-Nb₂O₅ gives the reversible structural change accompanying the disorder and order of the atomic arrangement on the charge-discharge cycling. On the other hand, V₂O₅ takes two discharge steps, within the 1st step of which it gives the reversible lattice change along b-axis caused by the intercalation of Li⁺ into the oxide layer, whereas within the 2nd step it is considered that the reaction in the charge-discharge takes place in the vicinity of the surface of the oxide particle. In both oxides, ternary phases such as Li_xM₂O₅ are produced as discharge products, where x is at least 2 for Nb₂O₅ and x is at least 3 for V₂O₅.     

反相微乳法制备纳米V2O5

采用十六烷基三甲基溴化铵(CTAB)/正丁醇/正辛烷/水溶液微乳体系成功制备了纳米V2O5。先采用反相微乳法分别制备碱性偏钒酸铵微乳液和稀硫酸单相微乳液,再将两种微乳液混合得到V2O5前驱物,经陈化、洗涤、干燥、焙烧得到纳米V2O5。通过测定电导率分析了微乳体系的稳定性,采用FTIR、XRD、TEM对纳米V2O5的结构、成分、晶形、粒径等进行了表征。结果表明,采用反相微乳法制备的纳米V2O5为球形、分散性较好、颗粒粒径为6～20nm。     

Preparation of V2O3 nanopowders by supercritical fluid reduction

V₂O₃ nanoparticles, with diameters of 30-60 nm, have been synthesized by supercritical ethanol fluid reduction of VOC₂O₄. It was found that the reaction time has little influence on the purity and morphology of as-prepared products. And carbon oxides decomposed from C₂O₄²⁻ were conducive to the formation of the uniform sphere-like nanoparticles. The reaction mechanism of synthesizing uniform V₂O₃ nanoparticles is believed to be the redox reaction between VOC₂O₄ and ethanol in the supercritical condition. The crystal growth mechanism was proposed on the basis of the discussion about the formation process of the uniform sphere-like nanoparticles.     

Adsorption and oxidation of NH3 over V2O5/AC surface

V₂O₅/AC has been reported to be active for selective catalytic reduction (SCR) of NO with NH₃ at around 200 °C and resistant to SO₂ deactivation. To elucidate its SCR mechanism, adsorption and oxidation of NH₃ over V₂O₅/AC are studied in this paper using TG, MS and DRIFTS techniques. It is found that the adsorption and oxidation of NH₃ take place mainly at VO bond of V₂O₅. A higher V₂O₅ loading results in more NH₃ adsorption on the catalyst. V₂O₅ contains both Brnsted and Lewis acid sites; NH₄⁺ on Brnsted acid sites is less stable and easier to be oxidized than NH₃ on Lewis acid sites. Gaseous O₂ promotes interaction of NH₃ with AC and oxidation of NH₃ over V₂O₅/AC. NH₃ is oxidized into NH₂ and acylamide structures and then to isocyanate species, which is an intermediate for N₂ formation.     

Promoting effect of calcium on reduction of NO by C3H6 over V2O5/ZrO2 catalysts

The reduction of nitrogen monoxide by propene on V₂O₅/ZrO₂ doped with or without calcium has been studied by FTIR spectroscopy as well as by analysis of the reaction products. Considerable promoting effect of calcium doping on the reduction of nitrogen monoxide by propene was observed on the V₂O₅/ZrO₂ catalysts. For the reaction of a mixture of NO+C₃H₆, carbonyl and carboxylate species were observed above 373 K, although nitrate species formed at room temperature on V₂O₅/ZrO₂ doped with calcium. No bands due to a compound including both carbon and nitrogen atoms were observed. Thus, the redox mechanism, i.e. propene reduces the catalyst and nitrogen monoxide oxidizes the catalyst, is confirmed on V₂O₅/ZrO₂ catalysts doped with or without calcium. The analysis of the V=O band in the region of 1100–900 cm⁻¹ indicates that this promotion is mainly due to new V=O species formed by the addition of calcium onto the catalyst. This species is easily reproduced in comparison with the other V=O species on the surface in the reoxidation process of the catalyst.     

Electrochemical properties of nanostructured Li1.2V3O8 in aqueous LiNO3 solution

The amorphous hydrated precursor of Li_1.2V₃O₈ was synthesized by soft chemistry method, and then heat-treated in air at several temperatures within the range 200–400 °C. The heat-treatment changed its morphological, structural and charging/discharging performance. The product obtained upon the treatment at 300 °C, consisting of uniform, rod-shaped particles, 100–150 nm in diameter and 300–800 nm in length, displayed the best electrochemical performance in aqueous LiNO₃ solution. Its initial discharge capacity amounted to 136.8 mAh g⁻¹ at a rate of C/5, which upon 50 charging/discharging cycles decreased for only 12%.     

Selective photo-oxidation of various hydrocarbons in the liquid phase over V2O5/Al2O3

More than 0.22 mmol of isolated VO₄ species of V₂O₅/Al₂O₃ exhibited the highest evolution of the partial oxidation products (alcohol and ketone) in the oxidation of cyclohexane and cyclopentane. The conversion of cyclohexane and the selectivity of the partial oxidation products were achieved to be 0.49% and 85% over 0.8 g of 3.5 wt.% V₂O₅/Al₂O₃, respectively, where the K/A ratio was 6.2. In addition, V₂O₅/Al₂O₃ can selectively oxidize various hydrocarbons in the liquid phase by the one-step oxygen atom insertion to CH bond. The order of priority was tertiary carbon > secondary carbon > primary carbon > benzene ring.     

Electrochemical properties of microwave irradiated synthesis of poly(3,4-ethylenedioxythiophene)/V2O5 nanocomposites as cathode materials for rechargeable lithium batteries

A series of poly(3,4-ethylenedioxythiophene) (PEDOT)/V₂O₅ nanocomposites are prepared via the redox intercalative polymerization reaction of 3,4-ethylenedioxythiophene (EDOT) monomer and crystalline V₂O₅ within 10 min by using rapid 2.45 GHz microwave irradiation with full power (800 W). The unique properties of the resultant nanocomposites are investigated by various characterization techniques using powder XRD, TGA/DTA and four-point probe conductivity analysis supports the intercalation of polymer nanosheet between V₂O₅ layers leading to enhanced bi-dimensionality. X-ray photoelectron spectroscopy analysis clearly shows the presence of mixed valent V⁴⁺/V⁵⁺ in the V₂O₅ framework after the redox intercalative polymerization which also confirms charge transfer from the polymer to the V₂O₅ framework. The application potential of these composites as cathode materials in rechargeable lithium batteries is also demonstrated by the electrochemical intercalation of lithium into the PEDOT/V₂O₅ nanocomposites, where an enhancement in the discharge capacity (370 mAh/g) is observed compared to that of crystalline V₂O₅.