Water molecules and oxygen-vacancy modulation of vanadium pentoxide with fast kinetics toward ultrahigh power density and durable flexible all-solid-state zinc ion battery

Aqueous zinc ion battery(ZIB)with many virtues such as high safety,cost-effective,and good environmental compatibility is a large-scale energy storage technology with great application potential.Nevertheless,its application is severely hindered by the slow diffusion of zinc ions in desirable cathode materials.Herein,a technique of water-incorporation coupled with oxygen-vacancy modulation is exploited to improve the zinc ions diffusion kinetics in vanadium pentoxide(V_(2)O_5)cathode for ZIB.The incorporated water molecules replace lattice oxygen in V_(2)O_5,and function as pillars to expand interlayer distance.So the structural stability can be enhanced,and the zinc ions diffusion kinetics might also be promoted during the repeated intercalation/deintercalation.Meanwhile,the lattice water molecules can effectively enhance conductivity due to the electronic density modulation effect.Consequently,the modulated V_(2)O_5(H-V_(2)O_5)cathode behaves with superior rate capacity and stable durability,achieving 234 mA h g^(-1)over 9000 cycles even at 20 A g^(-1).Furthermore,a flexible all-solid-state(ASS)ZIB has been constructed,exhibiting an admirable energy density of 196.6 Wh kg^(-1)and impressive power density of 20.4 kW kg^(-1)as well as excellent long-term lifespan.Importantly,the assembled flexible ASS ZIB would be able to work in a large temperature span(from-20 to 70℃).Additionally,we also uncover the energy storage mechanism of the H-V_(2)O_5 electrode,offering a novel approach for creating high-kinetics cathodes for multivalent ion storage.

Electrochemical properties of vanadium pentoxide xerogel films

Vanadium pentoxide xerogel（VXG） films were prepared by rapid quenching, then corn type 2016 size lithium rechargeable batteries were assembled and tested with the VXG film electrodes and lithium anodes. Electrochemical impedance spectroscopy（EIS） analysis result reveals the expected response for intercalation, except that there is almost no Warburg （diffusion） component. Analyses results of cyclic voltammetry（CV）, constant discharge （CD） and discharge-charge（DC） indicate that the sample achieves a high initial discharge specific capacity of approximate 400 mA·h/g and a corresponding efficiency of 97 % in the voltage diapason of 1.5 - 4.0 V with a draining current of 60 mA/g. Its preservation ratio of capacity still keeps as high as 85 % even after 100 cycles. The good electrochemical performance indicates that VXG film material is a promising cathode for lithium rechargeable batteries.

Free-standing vanadium pentoxide nanoribbon film as a high-performance cathode for rechargeable sodium batteries

Vanadium pentoxide （V2O5.nH2O） nanoribbons are synthesized via a hydrothermal process. These ribbons are 20nm thick, 200nm to 1 μm wide and several tens of micrometers long. Free-standing binder-free films are prepared by using these nanoribbons with multi-walled carbon nanotubes （MWCNTs） and used as the cathode for rechargeable sodium batteries. The large interlayer space between the V20s5 bilayers can enhance the kinetics of sodium ion intercalation/deintercalation. In addition, the intertwining network of the V2O5. 0.34H2O film provides efficient electron conduction pathways and shortens diffusion distances of sodium ion. The electrochemical tests prove that the free- standing V2O5. 0.34H2O film cathode delivers high reversible specific capacities （190 mAh/g） and good cycling stabilities （170 mAh/g after 150 cycles） in the voltage range between 1.5V and 3.5V.

Facile Synthesis,Characterization of Flower-Like Vanadium Pentoxide Powders and Their Photocatalytic Behavior

In this paper, V2O5 sol was firstly prepared using vanadyl sulfate as a vanadium source by modified sol-gel method at room temperature. Then flower-like V2O5 powders were prepared by coagulating as-prepared sol with anhydrous ethanol and subsequent annealing crystallization. The X-ray diffraction analysis indicated that V2O5 powders exhibited orthorhombic crystal structure after annealing at 450 ℃. The experimental data obtained from both field emission scanning electron microscopy and high-resolution transmission electron microscopy identified that V2O5 powders were approximately flower-like in shape and about 5 μm in size. Besides, the Brunauer-Emmett-Teller specific surface area of flowerlike V2O5 powders was 24.25 m^2/g. According to Uv-Vis spectroscopy, the degradation rate of toluidine blue O（TBO） on as-prepared flower-like V2O5 powders during 10 h of visible light irradiation with an intensity of 15.4 mW/m^2 was 88%,which was faster than those over P25（46%） as a comparison. In addition, the mineralization process of TBO was investigated, which primarily consisted of demethylation and ring-opening oxidation processes, and confirmed by liquid chromatograph-mass spectrometry. The precipitation-oxidation-peptization, coagulation, and crystallization processes were proposed as the formation mechanism for the preparation of flower-like V2O5.

Fluorinated inverse opal carbon nitride combined with vanadium pentoxide as a Z-scheme photocatalyst with enhanced photocatalytic activity

In this work,Z-scheme V_(2)O_(5) loaded fluorinated inverse opal carbon nitride(IO F-CN/V_(2)O_(5)) was synthesized as a product of ternary collaborative modification with heterostructure construction,element doping and inverse opal structure.The catalyst presented the highest photocatalytic activity and rate constant for degradation of typical organic pollutants Rhodamine B(RhB)and was also used for the efficient removal of antibiotics,represented by norfloxacin(NOR),sulfadiazine(SD)and levofloxacin(LVX).Characterizations confirmed its increased specific surface area,narrowed bandgap,and enhanced visible light utilization capacity.Further mechanism study including band structure study and electron paramagnetic resonance(EPR)proved the successful construction of Z-scheme heterojunction,which improved photogenerated charge carrier migration and provide sufficient free radicals for the degradation process.The combination of different modifications contributed to the synergetic improvement of removal efficiency towards different organic pollutants.

Vanadium recovery from clay vanadium mineral using an acid leaching method

A technique including direct acid leaching, vanadium precipitation with alkaline, sodium hydroxide releaching, impurity removing by adjusting pH value, precipitation vanadium with ammonium chloride, and vanadium pentoxide by roasting steps was proposed according to the characteristic of Xichuan clay vanadium mineral. The factors influencing leaching vanadium such as temperature and the concentration of sulfuric acid were investigated and optimized. The experimental results indicate that the extract ratios of V205 can reach 94% and 92% at a sodium chlorate ratio of 3% and a manganese dioxide ratio of 3%, respectivdy. A completely chemical precipitation method was adopted to decontaminate and enrich the vanadium in the acid leaching solution. The X-ray diffraction （XRD） pattern and the purity analysis of vanadium pentoxide indicate that the purity of final vanadium pentoxide can reach 99% and meet the standard specifications. The total recovery can reach about 75%. The technique has the characteristics of simplicity, less investment, and more environment safety as compared with the traditional salt roasting method.

Direct electrochemical reduction of solid vanadium oxide to metal vanadium at low temperature in molten CaCl_2-NaCl

V205 sintered pellets and graphite rods were employed as the cathode and the anode, respectively; a molten CaC12-NaCI salt was used as the electrolyte. Then, V205 was directly reduced to metal vanadium by the Fray-Farthing-Chen （FFC） method at 873 K to realize low-temperature electrolysis. Two typical experimental conditions, electrolysis time and voltage, were taken into account to investigate the current efficiency and remaining oxygen content in electrolyzed products. The composition and microstmcture of the products were charac- terized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. SEM observations show that a higher voltage （1.8-3.4 V） and a longer electrolysis time （2-5 h） can improve the product quality separately, that is, a lower remaining oxygen content and a more uniform microstructure. The products with an oxygen content of 0.205wt% are successfully obtained below 3.4 V for 10 h. However, the current effi- ciency is low, and further work is required.

Optimization of preparing V_2O_5 by calcination from ammonium metavanadate using response surface methodology

Parameters of technique to prepare vanadium pentoxide by calcination from ammonium metavanadate were optimized using central composite design of response surface methodology. A quadratic equation model for decomposition rate was built and effects of main factors and their corresponding relationships were obtained. The results of the statistical analysis show that the decomposition rate of ammonium metavanadate is significantly affected by calcination temperature and calcination time. The optimized calcination conditions are as follows： calcination temperature 669.71 K, calcination time 35.9 min and sample mass 4.25 g. The decomposition rate of ammonium metavanadate is 99.71%,which coincides well with experimental value of 99.27% under the optimized conditions, suggesting that regressive equation fits the decomposition rates perfectly. XRD reveals that it is feasible to prepare the V2O5 by calcination from ammonium metavanadate using response surface methodology.

Characterization of V_2O_5/MoO_3 composite photocatalysts prepared via electrospinning and their photodegradation activity for dimethyl phthalate

Vanadium pentoxide（V2O5）/molybdenum trioxide（MoO 3） composites with different molar ratios of vanadium（V） to molybdenum（Mo） were synthesized via a simple electrospinning technique. The photocatalytic activity of the composites were evaluated by their ability to photodegrade methylene blue and dimethyl phthalate（DMP） under visible-light irradiation. Compared with pure V2O5 and MoO 3,the V2O5/MoO 3 composites showed enhanced visible-light photocatalytic activity because of a V 3d impurity energy level and the formation of heterostructures at the interface between V2O5 and MoO 3. The optimal molar ratio of V to Mo in the V2O5/MoO 3 composites was found to be around 1/2. Furthermore,high-performance liquid chromatographic monitoring revealed that phthalic acid was the main intermediate in the photocatalytic degradation process of DMP.

Structure of V_2O_5-P_2O_5-Sb_2O_3-Bi_2O_3 glass

The structure ofV2O5-P2O5-Sb2O3-Bi2O3glass and its state of crystallization were studied by means of infrared spectroscopy and X-ray diffraction analysis. The results indicate that, in this glass, V and P exist mainly in the form of a single-stranded linear （VO3）n and an isolated （PO4） tetrahedral with no double bond. Partial V and P are connected through O, forming an amorphous structure of layered vana- dium phosphate. Trivalent Sb3＋ and Bi3＋ open the V=O bond and appear in interlayers, so a weak three-dimensional structure is connected successfully. Along with the substitution of Sb203 for partial V205 or that of P205 for partial V205, the network structure of the glass is rein- forced, and the crystallization is reduced.

Preparation of narrow band gap V_2O_5/TiO_2 composite films by micro-arc oxidation

V2Os/TiO2 composite films were prepared on pure titanium substmtes via micro-arc oxidation （MAO） in electrolytes consisting of NaVO3. Their morphology and dements were characterized by scanning electron microscopy （SEM） and energy-dispersive X-ray （EDX） analysis. Phase composition and valence states of species in the films were characterized by X-ray diffraction （XRD） and X-ray photoelec- tron spectroscopy （XPS）. Ultraviolet-visible diffuse reflectance spectra （UV-Vis DRS） were also employed to evaluate the photophysical property of the films. The VEOs/TiO2 composite films show a sheet-like morphology. Not only V205 phase appears in the films when the NaVO3 concentration of the electrolyte is higher than 6,10 g/L and is loaded at the surface of anatase, but also V4＋ is incorporated into the crystal lattice of anatase. In comparison with pure TiO2 films the V2Os/TiO2 composite films exhibit significantly narrow band gap energy. The film prepared in an electrolyte consisting of NaVO3 with a concentration of 8.54 g/L exhibits the narrowest band gap energy, which is approximately 1.89 eV. The V2Os/TiO2 composite films also have the significantly enhanced visible light photocatalytic activity. The film prepared in an electrolyte consisting of NaVO3 with a concentration of 8.54 g/L exhibits the best photocatalytic activity and about 93% of rhodamine is degraded after 14 h visible light radiation.

A porous puckered V_(2)O_(5) polymorph as new high performance cathode material for aqueous rechargeable zinc batteries

Aqueous rechargeable zinc batteries are getting increasing attention for large-scale energy storage owing to their advantages in terms of cost,environmental friendliness and safety.Here,the layered puckeredγ’-V_(2)O_(5) polymorph with a porous morphology is firstly introduced as cathode for an aqueous zinc battery system in a binary Zn^(2+)/Li^(+)electrolyte.The Zn‖γ’-V_(2)O_(5) cell delivers high capacities of 240 and190 mAh g^(-1) at current densities of 29 and 147 mA g^(-1),respectively,and remarkable cycling stability in the 1.6 V-0.7 V voltage window(97%retention after 100 cycles at 0.15 A g^(-1)).The detailed structural evolution during first discharge-charge and subsequent cycling is investigated using X-ray diffraction and Raman spectroscopy.We demonstrate a reaction mechanism based on a selective Li insertion in the1.6 V-1.0 V voltage range.It involves a reversible exchange of 0.8 Li^(+)in γ’-V_(2)O_(5) and the same structural response as the one reported in lithiated organic electrolyte.However,in the extended 1.6 V-0.7 V voltage range,this work puts forward a concomitant and gradual phase transformation from γ’-V_(2)O_(5) to zinc pyrovanadate Zn_(3)V_(2)O_(7)(OH)2.2 H_(2)O(ZVO)during cycling.Such mechanism involving the in-situ formation of ZVO,known as an efficient Zn and Li intercalation material,explains the high electrochemical performance here reported for the Zn‖γ’-V_(2)O_(5) cell.This work highlights the peculiar layered-puckeredγ’-V_(2)O_(5) polymorph outperforms the conventionalα-V_(2)O_(5) with a huge improvement of capacity of 240 mAh g^(-1)vs 80 mAh g^(-1) in the same electrolyte and voltage window.

Electrochemical impedance spectra of V_2O_5 xerogel films with intercalation of lithium ion

Vanadium pentoxide xerogel films used for lithium rechargeable batteries were prepared from crystalline c-V2O5 by melt quenching method,then the electrochemical process of lithium intercalation into vanadium pentoxide xerogel films was simulated with an equivalent circuit model, which was derived from the mechanism of electrode reactions. Measured electrochemical impedance spectra at various electrode potentials were analyzed by using the complex non-linear least-squares fitting method. The results show that impedance spectra consist of 2 high-to- medium frequency depressed arcs and a low frequency straight line. The high frequency arc is attributed to the absorption reaction of lithium ions into the oxide film, the medium frequency arc is attributed to the charge transfer reaction at the vanadium oxide/electrolyte interface and the low frequency is characterized by a straight line with a phase angle of 45° corresponding to the diffusion of lithium ion through vanadium oxide phase. The experimental and calculated results are compared and discussed focusing on the electrochemical performance and the state of charge of the electrode. Moreover, the high consistence of the fitted values of the model to the experimental data indicates that this mathematical model does give a satisfying description of the intercalation process of vanadium pentoxide xerogel films.

Electrochemical and structural evolution of structured V_(2)O_(5) microspheres during Li-ion intercalation

With the development of stable alkali metal anodes,V_(2)O_(5) is gaining traction as a cathode material due to its high theoretical capacity and the ability to intercalate Li,Na and K ions.Herein,we report a method for synthesizing structured orthorhombic V_(2)O_(5) microspheres and investigate Li intercalation/deintercalation into this material.For industry adoption,the electrochemical behavior of V_(2)O_(5) as well as structural and phase transformation attributing to Li intercalation reaction must be further investigated.Our synthesized V_(2)O_(5) microspheres consisted of small primary particles that were strongly joined together and exhibited good cycle stability and rate capability,triggered by reversible volume change and rapid Li ion diffusion.In addition,the reversibility of phase transformation(a,e,d,c and xLixV_(2)O_(5))and valence state evolution(5+,4+,and 3.5+)during intercalation/de-intercalation were studied via in-situ X-ray powder diffraction and X-ray absorption near edge structure analyses.

Formation of Na_(1+x)V_3O_8 Nanoribbon Thin Film from V_2O_5 Xerogel on Sodium Silicate Glass Substrate

Na1＋xV3O8 nanoribbon thin film was successfully fabricated by annealing the V2O5 xerogel film on sodium sili-cate glass substrate at 450℃. It has been identified that the amount of sodium ions diffused into the V2O5 xerogel film increases with the high temperature of annealing treatment. The sodium glass substrate serves as a limited sodium source to induce the transformation from V2O5 to Na1＋xV3O8.

Synthesis and Characterization of Self-Assembled V_2O_5 Mesostructures Intercalated by Polyaniline

A new nanocomposite of vanadium pentoxide (V_2O_5) and polyaniline (PANI)were synthesized by in situ oxidative polymerization/intercalation on V_2O_5 powder at roomtemperature. The reaction was facile and topotactic, forming polyaniline as the emeraldine salt. Itwas indicated that V_2O_5 itself can catalyze the oxidative polymerization of aniline and thatlayered structure could make aniline intercalate into the V_2O_5 framework. It makes the in situpolymerization feasible to occur in the layer of V_2O_5 structure. XRD results showed PANI/V_2O_5nanocomposite possessed lamellar mesostructure, which was determined by an X-ray diffraction peak at6.5° and SEM photograph. And FT-IR spectrum suggested that there was interaction between PANI andV_2O_5. The hybrid had better thermal stability in N_2 and air ambience.

Studies on Kinetic Properties of Active Oxygen on the Surfaces of V_2O_5/SiO_2, V_2O_5-MoO_3/SiO_2 and V_2O5-P_2O5/SiO_2 Catalysts

Applying the TPD-MS with a high sensitivity of determination, the TPD spectrum of surface oxygen of V2O5/SiO2, V2O5-MoO3/SiO2 and V2O6-P2O5/SiO2 catalysts was obtained. The surface oxygen of these catalysts can be divided into three groups according to the desorption temperature. O2- desorbs mainly from 373K. to 423K, O- from 673K to 873K and O2- at above 873K. The activation energy and frequency factor of all the three kinds of oxygen species were calculated. Based on these results, the mechanism of oxygen desorption and the influence of P2O5 and MoO3 on the properties of oxygen supply of V2O5/SiO2 catalst were investigated. MoO3 and a small amount of P2Os increase the number of supplying oxygen and increase the activity of O- species. A large amount of P2O5 increases the number of supplying oxygen and restrains the activity of O- species.

Calcium ion pinned vanadium oxide cathode for high-capacity and long-life aqueous rechargeable zinc-ion batteries

Rechargeable aqueous zinc ion batteries (ZIBs),with the easy operation,cost effectiveness,and high safety,are emerging candidates for high-energy wearable/portable energy storage systems.Unfortunately,the unsatisfactory energy density and undesired long-term cycling performance of the cathode hinder the development of ZIBs.Here,we report the chemical preintercalation of a small amount of calcium ions into V2O5 as the cathode material.The cathode of Ca0.04V2O5·1.74H2O (CVO)was demonstrated to have a high specific capacity of 400 mA h g^-1at the current density of 0.05 A g^-1and 187 mA h g^-1at 10 A g^-1,along with impressive capacity retention (100%capacity retention at 10 A g^-1 for 3,000 cycles).Meanwhile,the CVO//Zn battery exhibits a high energy density of 308 Wh kg^-1and a power density of 467 W kg^-1at 0.5 A g^-1.The superior performance originates from the pinning effect of the calcium ions and the lubricating effect of the structural water.The energy storage mechanism of the CVO cathode was also investigated in detail.The new phase (Zn3(OH)2V2O7·2H2O) generated upon cycling participates in the electrochemical reaction and thus contributes to the excellent electrochemical performance.The small amount of Ca^2+ pre-inserted into the interlayer of V2O5 sheds light on constructing cathodes with high energy density for ZIBs.

Vanadium-Doped Magnesium Oxide Nanoparticles Formation in Presence of Ionic Liquids and Their Use in Photocatalytic Degradation of Methylene Blue

Magnesium oxide（MgO） is one of the metal oxides having unique properties with numerous potential industrial applications.In this study,MgO and vanadium-doped MgO nanoparticles were synthesized by sol–gel method in 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF_4] and 1-octyl-3-methylimidazolium tetrafluoroborate [OMIM][BF_4] ionic liquids.Vanadium-doped MgO nanoparticles exhibited nanosphere and nanorod morphologies with 40–80 nm in particle size,primarily due to the influence of ionic liquids as demonstrated by high-resolution scanning electron microscopy and transmission electron microscopy.Characteristics of nanoparticles were also studied by thermal gravimetric analysis,X-ray diffraction and energy-dispersive X-ray spectroscopy.Photodegradation ability of synthesized nanoparticles was evaluated for methylene blue（MB） in specially designed UV reactor.Photodegradation is found to be dependent on doping,and particle characteristics change due to the influence of ionic liquid.The ionic liquid-assisted vanadium-doped MgO nanoparticles showed good reusability under UV irradiation and MB degradation ability under visible light.

Compact self-standing layered film assembled by V2O5·nH2O/CNTs 2D/1D composites for high volumetric capacitance flexible supercapacitors

Flexible supercapacitors (SCs) are attractive energy storage devices for wearable electronics, but their applications are hindered by their low volumetric energy densities. Two dimensional (2D) non-carbon nanomaterials are the most promising pseudocapacitive materials for high volumetric capacitance electrodes. However, they are poorly conductive and prone to self-stacking, which results in unsatisfactory electrochemical performance. In this work, large-scale V2O5·nH2O ultrathin nanosheets are synthesized by a facile and scalable method and transformed into layered and compact composite films with one-dimensional carbon nanotubes (CNTs). The self-standing films show an optimized volumetric capacitance of 521.0Fcm^-3 with only 10 wt% of CNTs, which is attributed to dramatically enhanced electrical conductivity beyond the electrical percolation threshold, high dispersion of pseudocapacitive V2O5·nH2O nanosheets, and high mass density of the films. All-solid-state flexible SCs made of V2O5·nH2O/CNTs films show a maximum energy density of 17.4WhL^-1.