V2O5 Layer Research Articles

Development of a Li-Ion Electrochemical Platform for in-Situ TEM of Solid State Electrode/Electrolyte Interfaces

The interface of electrode materials in contact with solid-state electrolytes is of current interest for the development of devices with high energy density and good safety. In-situ transmission electron microscopy (TEM) of energy storage materials allows for the detailed study of structure-property relationships near solid interfaces during electrochemical charge and discharge. Here, we will describe the design of an in-situ TEM platform to investigate the structure-property relationship of a model energy storage oxide, V2O5, in contact with a state-of-the-art solid-state electrolyte Li7La3Zr2O12 (LLZO). The cell was fabricated by the atomic layer deposition (ALD) of V2O5 (~ 50 nm thick) onto the electrolyte and subsequent focused ion beam (FIB) milling and lift-out of a micron-long electrode/electrolyte architecture. The lithium metal anode was electrochemically deposited directly onto the gold electrode of an in-situ TEM chip. Assembly of the electrochemical cell was performed in a scanning electron microscope using a micromanipulator. Bright-field TEM and electron energy loss spectroscopy (EELS) showed that the deposited V2O5 layer formed a well-defined interface with LLZO and this allowed for the determination of the vanadium oxidation state. This work demonstrates the fabrication of a platform for the in-situ TEM study of materials at electrode/solid-state electrolyte interfaces that can readily be adapted to other types of solid state battery chemistries.

Mechanisms of enhanced lithium intercalation into thin film V2O5 in ionic liquids investigated by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry

Room temperature ionic liquids (RTILs) attract much attention as a new type of environmentally benign electrolytes for Li-ion batteries due to their numerous interesting physicochemical properties. Here, in this paper, Li intercalation/deintercalation in presence of the N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR14TFSI) and N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI) containing 0.3 M LiTFSI, was evaluated in a thin 100 nm layer of V2O5 deposited on Al substrate by atomic layer deposition. Potentiodynamic tests performed in LiTFSI/Pyr14TFSI show a quasi-reversible Li intercalation during 10 cycles (between 2.4 and 5 V) with an average coulombic efficiency of 99%. The capacity, calculated from the 1st cycle, is found to be 182 mAh g−1, about 19% (±2%) higher than the theoretical capacity reported for V2O5 (147 mAh g−1). X-ray photoelectron spectroscopy analysis confirms that the intercalation of more than 1 mol of Li+ per V2O5 is achieved as also the possible presence of a solid permeable interface (SPI) layer on the V2O5 surface. Likewise, the Li+ in-depth distribution on the V2O5 layer after intercalation in RTILs measured by time-of-flight secondary ion mass spectrometry ion depth profiles, show small irreversible electrode modifications with the presence of lithium through the entire V2O5 layer with significant lithium trapping at the V2O5 layer/Al substrate interface.

Durability-reinforced electrochromic device based on surface-confined Ti-doped V2O5 and solution-phase viologen

A novel durability-reinforced electrochromic device (ECD) is described, in which the electrochromic materials remain in different physical form. Solution-phase ethyl viologen is used as the working electrochromic material, and modified Ti-doped V2O5 is utilized as counter electrochromic material. Electrochromic and spectral performances of the device are recorded here. The ECD shows good electrochromic performances in the visible and utraviolet region. Particularly, it’s worth mentioning that the ECD could work for 250,000 cycles at 60°C, with transmittance of 70% and 8% between bleached and colored states at the wavelength of 600nm, which shows remarkable long term stability. The excellent durability are mainly attributed to the reasonable choice of matching states and durability reinforced Ti-V2O5 film: the color change, charge capacity and switching speed of the viologen solution could be controlled through adjusting the concentration, and the addition of Ti provides excellent stability due to the distorted V2O5 layer structure.

Design and development of graphene intercalated V2O5 nanosheets based electrochemical sensors for effective determination of potentially hazardous 3,5–Dichlorophenol

In the present work, we present the facial synthesis of reduced graphene oxide (Gr) intercalated–vanadium pentoxide (Gr–V2O5) nanosheets with varying wt % of graphene oxide (GO) (1 wt% – 5 wt%) into V2O5 layers. Physio–chemical properties of as prepared V2O5 and Gr–V2O5 nanosheets were characterized by XRD, XPS, Raman, FTIR, FESEM and HRTEM techniques. Results reveals that the Gr was effectively intercalated into V2O5 nanostructures and morphology of V2O5 was tuned from nanorods to nanosheets. Further, the Gr–V2O5 nanosheets on modified glassy carbon electrode (Gr–V2O5/GCE) was fabricated and utilized for electrochemical characterization. Under the optimized conditions, the modified electrodes is a simple and versatile tool for electrochemical detection of potentially hazardous 3,5–Dichlorophenol (DCp) with the wide concentration range between 1.9 × 10−8 M to 2.2 × 10−4 M. The modified electrode possesses highly selective and it can able to detect DCp at nanomolar concentration (5 nM) with a high sensitivity of 0.3577 μAμM−1. The modified electrode exhibits good reproducibility, high stability and also has promising electrochemical oxidation behavior of DCp in environmental samples even in presence of common interfering electroactive species. In view of analytical application, our proposed sensor could be directly employed for the electrochemical detection of DCp in industrial wastes, river water and sediment soil dispersion, without any pre–treatment.

V2O5-decorated Mn-Fe/attapulgite catalyst with high SO2 tolerance for SCR of NOx with NH3 at low temperature

Fe-based catalysts were widely reported with high N2 selectivity in the NH3-SCR reaction in recent years. Unfortunately, the Fe-based catalysts usually exhibit poor NOx conversion at low temperature. In order to solve this problem, MnO2 was chosen to enhance the low temperature activity of the catalyst. In this work, V2O5-decorated Mn-Fe/attapulgite (V@Mn-Fe/ATP) with high SO2 tolerance were prepared by impregnation and sol-gel methods and used for selective catalytic reduction of NO by NH3 (NH3-SCR). In addition, γ-Fe2O3/ATP and Mn-Fe/ATP were also prepared for comparison with the V@Mn-Fe/ATP. The as-prepared catalysts were characterized by XRD, TEM, BET, H2-TPR, NH3-TPD, and XPS. It could be deduced from TEM, XRD, and BET, the specific surface area was improved due to a uniform V2O5 layer formed on the Mn-Fe/ATP surface. The results of XPS and NH3-TPD illustrated that the coating of V2O5 could also enhance the amount of surface chemisorbed oxygen and acidic sites, which play significant influence on oxidation of NO and NH3 absorption during NH3-SCR and are also beneficial to increase SCR reaction rates. Moreover, the test of SO2 tolerance and stability demonstrated that the V2O5 layer could effectively inhibit SO2 poisoning and improve the stability of catalysts. Therefore, the V@ Mn-Fe/ATP was proved to be an excellent catalyst for NH3-SCR.

Naturally formed ultrathin V2O5 heteroepitaxial layer on VO2/sapphire(001) film

Vanadium dioxide (VO2) and vanadium pentoxide (V2O5) thin films change their properties in response to external stimuli such as photons, temperature, electric field and magnetic field and have applications in electronics, optical devices, and sensors. Due to the multiple valence states of V and non-stoichiometry in thin films, it is challenging to grow epitaxial, single-phase V-oxide on a substrate, or a heterostructure of two epitaxial V-oxides. We report the formation of a heterostructure consisting of a few nm thick ultrathin V2O5 epitaxial layer on pulsed laser deposited tens of nm thick epitaxial VO2 thin films grown on single crystal Al2O3(001) substrates without post annealing of the VO2 film. The simultaneous observation of the ultrathin epitaxial V2O5 layer and VO2 epitaxial film is only possible by our unique reflection high energy electron diffraction pole figure analysis. The out-of-plane and in-plane epitaxial relationships are V2O5[100]||VO2[010]||Al2O3[001] and V2O5[032¯]||VO2[100]||Al2O3[11¯0], respectively. The existence of the V2O5 layer on the surface of the VO2 film is also supported by X-ray photoelectron spectroscopy and Raman spectroscopy.

Enhanced Magnesium-Ion Charge Transport and Storage within Layered Vanadium Pentoxide-Poly(ethylene oxide) Nanocomposites

Cathode materials that have high reversible magnesium-ion capacities and reasonable operating voltages are needed for rechargeable magnesium batteries. Layered materials are a particularly promising class of materials for electrochemical Mg-ion charge storage, however additional research is needed to increase Mg-ion capacities, improve capacity retension upon cycling, and understand the nature of interlayer interactions. Our work has investigated hydrated vanadium pentoxide (V2O5) xerogels that incorporate poly(ethylene oxide) (PEO) between the layers as an approach to improve Mg-ion charge storage and control interlayer structure and dynamics. V2O5 nanosheets were grown in the presence of PEO to allow inimate interaction with the V2O5 layers and allow control of the PEO content in V2O5-PEO nanocomposites. X-ray diffraction and high resolution transmission electron microscopy demonstrate that the interlayer spacing between V2O5 layers was increased by incorporating PEO within the layers. The Mg-ion diffusion coefficient was shown to be strongly dependent on not only interlayer spacing, but also interlayer composition. With specific polymer compositions, Mg-ion diffusion within V2O5-PEO nanocomposites was significantly increased compared with V2O5 xerogels. Raman spectroscopy supports that the polymer interacts with the V2O5 lattice resulting in interlayer water that is less strongly bound to the V2O5 lattice. The V2O5-PEO nanocomposite with specific PEO compositions exhibited significantly improved Mg-ion specific capacity compared with V2O5 xerogels and showed improved capacity retension upon cycling. Our work supports that in addition to interlayer spacing, controlling interlayer interactions between V2O5 layers, PEO, H2O, and Mg-ions allows significant improvements in Mg-ion charge transport and storage. The design of layered materials with controlled interlayer compositions provides a novel route to significantly improve charge storage and transport in layered materials.

Air Dependence of Electrical Performance Parameters in Polymeric Organic Solar Cell

The manufacture under air environment of organic solar cells (OSC) has been the main attention of many research groups in the last years due to analyze and study the stability and degradation process of the photovoltaic devices. Recent advances in polymer-based organic solar cells have been possible due to different approaches such as design of new devices and synthesis of new materials such as small molecule and polymers with low band-gaps, control of the nanoscale morphology with additives, variation of the ratio of the donor/acceptor in the bulk heterojunction, application of thermal or solvent annealing process, among others [1-3]. For large area fabrication, most reports agree that the roll-to-roll process seems to be the most promising in the last years. However, the fabrication process is difficult to realize completely under N2 environment and it is well known that OSC under air environment degrade due to low-stability of some organic semiconductors when exposed under H2O and O2 environment. Tandem structures in combination with organic materials have been manufactured employing roll-to-roll process [4-7] which some of them are manufactured under air environment. The effects of exposing the samples to air environment during the fabrication process are not well studied, being necessary a more detailed analysis to indicate which the main effects that degraded the device. Results regarding the performance parameters of polymer OSCs under these conditions are not well known yet. In this scenario, we present the manufacture of OSCs partially under air environment and under N2 environment. The polymer used of low band-gap was poly[[4,8-bis[(2-ethylhexyl)-oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) in combination with [6,6]-phenyl-C71-butyric acid methyl (PC70BM) to get the blend layer. The device inverted structure was manufactured with the stack: indium tin oxide (ITO) / poly[(9,9-bis(3-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9–dioctylfluorene)] (PFN) / PTB7:PC70BM / vanadium oxide (V2O5) / silver (Ag) as is shown in Figure 1a. The PFN and the PTB7:PC70BM layers were prepared and deposited under N2 environment. Afterwards, two groups of solar cells were formed. The first group of samples was taken out of the glove box and exposed under air environment (60% relative humidity at 24 oC) for 10 min before depositing by thermal evaporation the V2O5 and Ag layers. While that the second group of samples were finished the fabrication completely under N2 environment. The last group was made to compare with the first group of samples. Electrical characterizations like current density–voltage were measured for both groups of inverted OSC samples under light conditions, which are shown in figure 1b. The basic parameters were extracted from J-V curves such as open circuit voltage, short-circuit current density, fill factor and power conversion efficiency. Results from the first group of cells was observed that the JSC was increased and Rs reduced due to the increment on conductivity of the active blend layer when the samples were exposed for 10 min under air environment before the metal contact deposition. Other electrical test were made such as incident photon-to-current efficiency and absorbance coefficient were obtained from the photovoltaic devices to understand the differences between the two groups of cells, as well as factors that limit the power conversion efficiency. The knowledge of this behavior is important for the fabrication, design and optimization of the OSC and to reduce the effects of manufacturing under air conditions during industrial process development in the transition from the laboratory to the large scale fabrication conditions.

(Invited) Solution Processing and Structural Control of 2D Materials of Bi2Te3, MoS2 and V2O5 and Their Applications

Embedding 2D layered materials into polymers can form a paint with many useful applications. In bulk form the thermoelectric material bismuth telluride (Bi2Te3) has a high figure of merit (ZT) at room temperature. When bulk Bi2Te3 is exfoliated to smaller dimensions, such as its 2D form (nanosheets), its thermoelectric effects are improved by reduction in thermal conductivity due to phonon confinement and scattering, thus increasing the ZT. The difficulty involved in incorporating nanosheets into energy harvesting systems motivated the search for a form of Bi2Te3 that retains the high ZT apparent at the nanoscale with the capability of being deposited or painted onto device infrastructures. This work highlights a method whereby solvent exfoliation of Bi2Te3 into solution-dispersible 2D nanosheets can form a practical thin film that can be distributed across a surface. Optical transmission measurements quantify the relationship between efficient and stable exfoliation and the reduction in optical density. Optimized exfoliated suspension are also shown to form smooth, uniform blends when mixed with poly ethylene glycol and other polymers to produce a paintable Bi2Te3film that can be applied to surfaces using an innovative painting technique. Atomic force microscopy, transmission electron spectroscopy, Raman spectroscopy and scanning electron spectroscopy are used to examine the structure of the 2D nanosheets and the highly reproducible Bi2Te3thin films. Electrical transport studies show that the films have conductive pathways over a range of surfaces and various structural formations, linking the conductivity to the percolating conduction through the nanosheet ensemble. The combination of the facile preparation method and the scope for diverse surface coating as a cohesive and conductive thin film offers methods for integration with heat producing devices for energy harvesting applications. Direct Seebeck coefficient and thermal diffusivity measurements examine the role of the pain conductivity on its thermoelectric response. Separately, MoS2 nanosheets are also demonstrated by solvent exfoliation of uniquely formed hexagonal single crystals. These crystals are formed under high pressure from layered MoS2 and this talk demonstrates how multi-micron scale dimension flakes of 2D and few-layer hexagonal MoS2can be formed from compressed soluble solutions of the 2D and layered material. Finally, we demonstrate a method whereby 2D layers of V2O5 can be turbostratically assembled using organic-inorganic interactions with alkylamines under hydrothermal conditions, to scroll into very high quality V2O5 nanotubes. V2O5 layered materials intercalated with 1D Pt-Pt metal complexes exhibit high directional conductivity. We also show that the method can be used to make nanotubes of 2D and layered materials, and how MoS2 sheets can also be rolled into nanotubular form.

Graphene functionalised by laser-ablated V2O5 for a highly sensitive NH3 sensor.

Graphene has been recognized as a promising gas sensing material. The response of graphene-based sensors can be radically improved by introducing defects in graphene using, for example, metal or metal oxide nanoparticles. We have functionalised CVD grown, single-layer graphene by applying pulsed laser deposition (PLD) of V2O5 which resulted in a thin V2O5 layer on graphene with average thickness of ≈0.6 nm. From Raman spectroscopy, it was concluded that the PLD process also induced defects in graphene. Compared to unmodified graphene, the obtained chemiresistive sensor showed considerable improvement of sensing ammonia at room temperature. In addition, the response time, sensitivity and reversibility were essentially enhanced due to graphene functionalisation by laser deposited V2O5. This can be explained by an increased surface density of gas adsorption sites introduced by high energy atoms in laser ablation plasma and formation of nanophase boundaries between deposited V2O5 and graphene.

Controlling interlayer interactions in vanadium pentoxide-poly(ethylene oxide) nanocomposites for enhanced magnesium-ion charge transport and storage

Abstract Rechargeable magnesium batteries provide the potential for lower cost and improved safety compared with lithium-ion batteries, however obtaining cathode materials with highly reversible Mg-ion capacities is hindered by the high polarizability of divalent Mg-ions and slow solid-state Mg-ion diffusion. We report that incorporating poly(ethylene oxide) (PEO) between the layers of hydrated vanadium pentoxide (V2O5) xerogels results in significantly improved reversible Mg-ion capacities. X-ray diffraction and high resolution transmission electron microscopy show that the interlayer spacing between V2O5 layers was increased by PEO incorporation. Vibrational spectroscopy supports that the polymer interacts with the V2O5 lattice. The V2O5-PEO nanocomposite exhibited a 5-fold enhancement in Mg-ion capacity, improved stability, and improved rate capabilities compared with V2O5 xerogels. The Mg-ion diffusion coefficient of the nanocomposite was increased compared with that of V2O5 xerogels which is attributed to enhanced Mg-ion mobility due to the shielding interaction of PEO with the V2O5 lattice. This study shows that beyond only interlayer spacing, the nature of interlayer interactions of Mg-ions with V2O5, PEO, and H2O are key factors that affect Mg-ion charge transport and storage in layered materials. The design of layered materials with controlled interlayer interactions provides a new approach to develop improved cathodes for magnesium batteries.

Effects of V2O5/Au bi-layer electrodes on the top contact Pentacene-based organic thin film transistors

Top-contact Pentacene-based organic thin film transistors (OTFTs) with a thin layer of Vanadium Pent-oxide between Pentacene and Au layer are fabricated. Here we have found that the devices with V2O5/Au bi-layer source–drain electrode exhibit better field-effect mobility, high on–off ratio, low threshold voltage and low sub-threshold slope than the devices with Au only. The field-effect mobility, current on–off ratio, threshold voltage and sub-threshold slope of V2O5/Au bi-layer OTFT estimated from the device with 15 nm thick V2O5 layer is .77 cm2 v−1 s−1, 7.5×105, −2.9 V and .36 V/decade respectively.

Improved electrochemical performance of LiNi0.5Co0.2Mn0.3O2 cathode material by double-layer coating with graphene oxide and V2O5 for lithium-ion batteries

LiNi0.5Co0.2Mn0.3O2 cathode material synthesized by a sol-gel method was surface-modified by double-layer coating. The results of X-ray diffraction (XRD) confirm that the intrinsic structure was no change after surface modification. A double-layer structure consisting of an inner V2O5 (VO) layer and an outer conductive graphene oxide (GO) layer was coated on the surface of active material, as confirmed by transmission electron microscopy (TEM). The results of field emission scanning electron microscope (FE-SEM) equipped with an energy dispersive spectroscope (EDS) show that both graphene oxide and V2O5 uniformly covered LiNi0.5Co0.2Mn0.3O2 cathode material. The double-layer-coated LiNi0.5Co0.2Mn0.3O2 cathode material shows improved electrochemical performance with a capacity retention of 74.2% after 50 cycles in a range of 2.5–4.5V at 55°C, compared with only 67.8% capacity retention for the pristine material. In addition, the double-layer-coated LiNi0.5Co0.2Mn0.3O2 releases 116.6mAhg−1 under a high current rate, while the pristine material only remains at 105.7mAhg−1. The results can be ascribed to the double coating layer not only avoids the side reaction between electrolyte and active material but also promotes Li+ and electronic conductivity. Differential capacity (dQ/dV) and electrochemical impedance spectroscopy (EIS) measurements reveal that the double coating layer effectively suppresses the increase of the electrode polarization during cycling.

Surface texture of single-crystal silicon oxidized under a thin V2O5 layer

The process of surface texturing of single-crystal silicon oxidized under a V2O5 layer is studied. Intense silicon oxidation at the Si–V2O5 interface begins at a temperature of 903 K which is 200 K below than upon silicon thermal oxidation in an oxygen atmosphere. A silicon dioxide layer 30–50 nm thick with SiO2 inclusions in silicon depth up to 400 nm is formed at the V2O5–Si interface. The diffusion coefficient of atomic oxygen through the silicon-dioxide layer at 903 K is determined (D ≥ 2 × 10–15 cm2 s–1). A model of low-temperature silicon oxidation, based on atomic oxygen diffusion from V2O5 through the SiO2 layer to silicon, and SiOx precipitate formation in silicon is proposed. After removing the V2O5 and silicon-dioxide layers, texture is formed on the silicon surface, which intensely scatters light in the wavelength range of 300–550 nm and is important in the texturing of the front and rear surfaces of solar cells.

V2O5/C3H6N6: A Hybrid Material with Reversible Lithium Intercalation/Deintercalation in a Wide Potential Range

The (C3H6N6)0.67V2O5 hybrid nanorods are synthesized through the self-assembly of melamine organic molecules confined by V2O5 layers and used as cathode material in the lithium-ion battery. The prepared hybrid overcomes the irreversible structure puckering problem of LixV2O5 when excess Li+, x > 1, is intercalated. It demonstrates that layered oxides combined with selective organic moieties forming an ordered structure can significantly reduce the lattice stress and structure puckering problems during lithium intercalation/deintercalation process thereby extending their cycle reversibility in the wide potential range from 1.9 to 3.5 V and reaching to x = 2 of Lix(C3H6N6)0.67V2O5. The hybrid material developed in this work tackles the structure puckering problem of V2O5 layers and opens the door for studying new battery system with greater ionic radii, such as Na+, Mg2+ and Al3+.

Volatile Organic Compounds and Dimethyl Methyl Phosphonate (DMMP) Sensing Properties of the Metal Oxide Functionalized QCM Transducers at Room Temperature

ZnO nanorods were synthesized directly on the mass sensitive transducer elements, namely the quartz crystal microbalance (QCM), by electrochemical deposition techniques. Besides, vanadium pentaoxide (V2O5) thin films were evaporated on the ZnO nanorods using a thermal evaporation system. The fabricated chemical gas sensors were exposed to different levels of various volatile organic compounds (VOCs). The VOCs sensing measurements were realized at room temperature. The application of an additional V2O5 layer on the ZnO nanorods was found to improve the sensing performance of the nanorods. The highest responses were obtained for the analyte DMMP and the DMMP sensitivities of the sensors are at least three times higher than the sensitivities for the other tested VOCs. ZnO nanorods are considered excellent sensing materials on the QCM allowing selective detection of DMMP and other analytes at room temperature.

Thermal annealing induced multiple phase in V/V2O5 alternating multilayer structure

In this paper, we report on microstructural, optical and electrical properties of alternating multilayer of vanadium pentoxide (V2O5), 25 nm, and vanadium (V), 5 nm, thin films deposited at room temperature by radio frequency (RF) and DC magnetron sputtering, respectively. Raman and photoluminescence (PL) spectroscopy have been employed to investigate the effects of thermal annealing for 20, 30 and 40 min at 400[Formula: see text]C in Nitrogen (N2) atmosphere on the multiple phase formation and its impact on the film resistance and temperature coefficient of resistance (TCR). We demonstrate that the oxygen free annealing environment allows the formation of multiple phases including V2O5, V6O[Formula: see text] and VO2 through oxygen diffusion and consequent deficiency in V2O5 layer.

Mg Secondary Batteries Using Nano-Crystalline V2O5

Vanadium oxide (V2O5) is available as an active material for secondary batteries. Intercalation of cations to the layer of V2O5 crystal occurs with a reduction of vanadium receiving electrons up to 3 (theoretical capacity: 442 mAh g−1). Fabrications of V2O5 crystal directly affect the battery property. Nano-sizing, thinly supporting on carbon materials with large specific surface area, and solvent-insertion were studied to shorten a diffusion resistance of ions in layers. When carrier cation is Mg2+, V2O5 can be applied for a positive material of Mg battery. In this study, nano-crystalline V2O5 was synthesized by ball-mill and calcination. Ball-mill in toluene as a solvent with φ0.2 mm zirconia balls, removal of toluene, and burning in air at 400°C during 4 h were conducted. SEM and particle size distribution measurement show V2O5 was spherical in shape with an average diameter of 200 nm. XPS analysis shows this ball-mill process partially caused a chemical reaction including reduction of V2O5 and oxidation of toluene. Chemical etching and physical ball-milling gave the uniform nano-particles. Burning in air removed carbon species derived from toluene, re-oxidizes vanadium species to V2O5, and raises crystallinity. Obtained V2O5 was mixed with AB and PVdF (80 : 10 : 10, wt%) in NMP and the slurry was pasted/dried on Al foil to make a working electrode. The effect of nano-sizing on the electrochemical performance as an active material was tested in a system of Li secondary battery. Compared to unprocessed V2O5, nano-crystalline V2O5 has better electrochemical properties of cyclability and capacity. As to Mg secondary battery test, different electrolytes were utilized: 5 mol% Mg[TFSA]2 / 95 mol% acetonitrile (AN), diglyme (G2), triglyme (G3), tetraglyme (G4), 12-crown-4ether (12C4), and diethylmethylmethoxyethylammonium TFSA (DEMETFSA); 5 mol% Mg[TFSA]2 / 5 mol% 18C6 and 90 mol% THF; 3 mol% Mg[TFSA]2 and MgCl2 / 94 mol% G3; 5 mol% Mg[TFSA]2 and MgBr2 / 90 mol% G3. Battery tests were performed in a three electrode cell: counter electrode, magnesium metal; reference electrode, Ag wire immersing in 0.05 M AgBF4/EMImBF4. In many cases of these electrolytes, only Mg[TFSA]2/G3 shows electrochemically active against Mg intercalation to V2O5. The discharge and charge capacities at the 10th cycle were 180.3 and 176.5 mAh g−1, and cycle efficiency is over 95 %. The electrolytes with only different carbon number to G3, Mg[TFSA]2/G2 or G4, gave little capacity. In the case of 12C4 with the same carbon number to G3, lower capacity and overpotential were shown. In the case of ionic liquid, only 6 mAh g−1 appeared at room temperature, whereas 100 mAh g−1 appeared at 100°C. These results indicate that intercalation and decalation of Mg2+ to V2O5 are mainly influenced by solvents which are desolvated and solvated to Mg2+. The SEM images of charged and discharged electrodes show little morphology change of V2O5 particle. The XPS analyses show that the peaks of V2p1/2 and V2p3/2 in the discharged electrode appeared at a lower energy compared to the charged electrode, indicating reduction of vanadium from +5 to a lower valence. The XRD pattern of discharged electrode has a small difference to charged one, where the peaks derived from (020) and (040) shift to a lower angle (b axis means the vertical direction to V2O5 layer). This result shows an extension of interlayer distance from 5.76 Å to 6.15 Å, indicating intercalation of Mg2+, not co-intercalation of Mg2+ and organic solvent.

Hydrogen storage characteristics of Ti– and V–based thin films

Abstract Series of thin films of single-, bi- and tri-layered structure consisting of Ti, V, TiO2 and V2O5 layer and/or mixed Ti–V–Ni layer with different layer sequences and thicknesses were prepared by the sputtering technique on Si and SiO2 substrates. The layer chemical composition and thickness were determined by a combined analysis of X-ray diffraction, X-ray reflectometry, Rutherford backscattering and optical reflectivity spectra. The films were hydrogenated at 1 bar at 300 °C and/or at high pressures up to 100 bar at room temperature. The hydrogen concentration and hydrogen profile was determined by means of a secondary ion mass spectroscopy and N-15 Nuclear Reaction Analysis. The highest hydrogen storage with a concentration up to 50 at.% was found in the pure Ti layers, while it amounts to about 30 at.% in the metallic Ti–V–Ni layers. A large hydrogen storage (up to 20 at.%) was also found in the V2O5 layers, while no hydrogen accumulation was found in the TiO2 layers. Hydrogen could remove the preferential orientation of the Ti films and induce a complete transition of V2O5 to VO2.

Effects of amorphous V2O5 coating on the electrochemical properties of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 as cathode material for Li-ion batteries

Lithium-rich layered oxide Li[Li0.2Mn0.54Ni0.13Co0.13]O2 coated with V2O5 layers (labeled as LMNCO@V2O5) has been synthesized and its electrochemical properties as cathode material for lithium ion batteries have been measured and compared with pristine Li[Li0.2Mn0.54Ni0.13Co0.13]O2 (labeled as LMNCO) and LMNCO–V2O5 composite. As a lithium ions insertion host material, both the V2O5 in the LMNCO@V2O5 and the LMNCO–V2O5 can reduce the irreversible capacity losses and improve the Coulombic efficiencies of the cathode in the first charge-discharge cycle. However, for improving the cycling stabilities and the high-rate capabilities of the LMNCO, the effects of the V2O5 coating layers in the LMNCO@V2O5 are far beyond the effects of the V2O5 nanoparticles in the LMNCO–V2O5. When charge-discharged galvanostatically at 25 mA g−1 between 2.0 and 4.8 V (vs. Li+/Li), the LMNCO@V2O5 with 3 wt.% V2O5 exhibits a discharge capacity of 279.5 mAh g−1 in the first cycle and maintains a discharge capacity of 269.1 mAh g−1 after 50 cycles, with capacity retention of 96.3%. In contrast, the discharge capacity of the pristine LMNCO changes from 251.2 mAh g−1 in the initial cycle to 202.2 mAh g−1 in the 50th cycle, with capacity retention of 80.2%; and the LMNCO–V2O5 shows the same capacity fading trend as the pristine LMNCO, with no obvious improvement in the capacity retention. At high rate of 1250 mA g−1, the discharge capacity of the LMNCO@V2O5 can reach 113.6 mAh g−1, which is much higher than the capacities that the pristine LMNCO and the LMNCO–V2O5 can reach. Different effects of V2O5 are due to their different roles in the cathode materials. While the V2O5 coating layer in the LMNCO@V2O5 can reduce the charge transfer resistance at the electrode-electrolyte interfaces and improve the transportation of lithium ions among the LMNCO particles, the V2O5 nanoparticles in the LMNCO–V2O5 can only work as a Li+ ions insertion host material.