MoO3-doped V2O5 thin films electrode exhibit much enhanced
electrochemical performances than the pure V2O5 counterpart. 1M nonaqueous solution of
LiClO4 in propylene carbonate (PC) was the electrolyte solution about cyclic voltammetry
(CV) of V2O5/MoO3/ITO glass electrodes at room temperature. With the increasing
proportion of MoO3 doped in V2O5, all the redox peak currents of the five samples increased,
suggesting that their electrochemical activity increased with the initial CV cycles.
Disappearing of some phase transition peaks also show that the MoO3-doped V2O5 film
makes cyclic stability declining. Compared with the switching speed of films, the coloring
and the bleaching times of the MoO3-doped V2O5 thin films are shorter

Costa, Manuel F. M.

Cui, Haining

Sun, Shengnan

Teixeira, Vasco M. P.

Wang, He

Universidade do Minho: RepositoriUM

7th ECCOMAS Thematic Conference on Smart Structures and MaterialsSMART 2015A.L. Araújo, C.A. Mota Soares, et al. (Editors)© IDMEC 2015ELECTROCHEMICAL PERFORMANCES OF Li+ INTERCALATION ANDDEINTERCALATION PROCESSES FOR ELECTROCHROMISM of MoO3-DOPED V2O5 FILMS PREPARED BY THE SOL-GEL METHODHeWang1, Manuel F. Costa2, Shengnan Sun1, Vasco Teixeira2, Haining Cui1,*1Department of Optical and Electronic Information Science and Technology, College of Physics,College of Zhaoqing (526061) , Jilin University(130021), P. R. China.2Physics Department, University of Minho, Campus de Gualtar, 4720-057 Braga, Portugal.*cuihaining2009@126.comKey words: Electrochromism, MoO3-doped V2O5 films, Cyclic voltammetry.Summary: The MoO3-doped V2O5 thin films electrode exhibit much enhancedelectrochemical performances than the pure V2O5 counterpart. 1M nonaqueous solution ofLiClO4 in propylene carbonate (PC) was the electrolyte solution about cyclic voltammetry(CV) of V2O5/MoO3/ITO glass electrodes at room temperature. With the increasingproportion of MoO3 doped in V2O5, all the redox peak currents of the five samples increased,suggesting that their electrochemical activity increased with the initial CV cycles.Disappearing of some phase transition peaks also show that the MoO3-doped V2O5 filmmakes cyclic stability declining. Compared with the switching speed of films, the coloringand the bleaching times of the MoO3-doped V2O5 thin films are shorter.1 INTRODUCTIONElectrochromism, the reversible change in optical properties when a material iselectrochemically oxidized or reduced, has a long history of fundamental and practicalinterest.[1,2] Various types of materials and structures, can be used to construct electrochromicdevices, according to the specific applications.Vanadium-based oxides such as V2O5, LiV3O8 and V6O13 have aroused great interest dueto their high energy density, low price, abundant sources, and good safety performance whenused as cathode materials for rechargeable lithium-ion batteries. Moreover, vanadium astransition metal oxides used for electrochemical supercapacitor electrodes possessessignificantly higher special capacitances.[3]As a electrochromic material ,vanadium pentoxide(V2O5) has its low operating potential, -1 V,and very small amounts of energy to change itscoloration state.[4]V2O5(s)+xLi++xe- → LixV2O5(s) （1）First A. Author, Second B. Author, Third C. Author2Just like above expression, the electrochromic color of vanadium oxide changes fromyellow to green/gray.[5] What’s more, the compound easily undergoes various phasetransitions, such as α, ε, δ, γ, and ω phases, depending on the degree of Li intercalation (x)[6]The α-phase LixV2O5 (x < 0.01) and ε-phase LixV2O5 (0.35 < x < 0.7) which the structure ofunintercalated V2O5 have similar with, but result in weak puckering of V2O5 layers. The δ-phase LixV2O5 (0.7 < x < 1) has more puckered V2O5 layers. When the Li intercalation ismore than one, an irreversible structural change to γ-phase LixV2O5 (1 < x < 2) occurs. In γ-phase LixV2O5, the layer puckering becomes more pronounced than that in δ-phase LixV2O5.Further intercalation of the third Li into V2O5 results in the irreversible formation of ω-phaseLixV2O5 (2 < x < 3) with a rock salt type structure, where the Li+ diffusion will be very slow.In addition, this ω-phase rapidly loses the ability to cycle due to a large fraction of lithiumions that cannot be removed.[7] Vanadium pentoxide prepared by sol-gel method has theadvantage of large area production, however, weak physical adhesion strength which itattaches themselves to a transparent current collector (e.g., ITO, FTO) among individualelectrochromic nanomaterials may cause the release of active materials, resulting in opticalcontrast loss in long-term testing.[8] In this study, we researched the effect of Mo doping onthe microstructure and Li+ intercalations/extractions properties of V2O5 films. The pure andMo-doped V2O5 films were prepared by using the sol-gel method, followed by annealing400℃ for 4h in the air. The Mo-doped V2O5 thin films electrode exhibit much enhancedelectrochemical performances than the pure V2O5 counterpart.2 PREPARATION SECTIONAnalytical reagent grade MoO3 and V2O5 powder of various molar concentrations havebeen taken in an agate mortar and ground well to get a fine powder of the mixed oxide, whichis then pelletized. After that the mixed oxide powder which is in the air, was heated to 800℃that rised up 10℃ per minute. And then the system was put into 800℃ surrounding for30min. We took it out quickly into the 500mL of cold pure water, at the same time, stired andheated the material rapidly and uniformly for 1h. To obtain the sol precursor, the precipitatewas filtered. Then we got sol-gel mixed vanadium oxide which was sealed to avoid lightpreservation for 7 days. The sol-gel vanadium oxide is stable that no deposition occurs.Indium-doped tin oxide substrates (ITO, 10~15R/sq, 2cm*3cm) were cleanedultrasonically in acetone, in absolute alcohol, and then in distilled water, for 20 min each.The cleaned ITO glass substrates were placed into cylindrical vessels.After finishing all the preparations, the thin films were obtained by sol-gel method on thesurface of ITO. The films of 5% MoO3, 95%V2O5; 3% MoO3, 97% V2O5; 2% MoO3, 98%V2O5; 1% MoO3, 99% V2O5 and 100% V2O5 have been used for optical and electricalinvestigations which ensured that the quality of MoO3 would be not cover the quality of V2O5.Then they were kept at a temperature of 40°C for drying that the films were notcrystallization.3 RESULTS AND DISCUSSIONThe phase structure, surface morphology, and the oxidation state of the thin Mo-dopedV2O5 films and pure V2O5 films was analyzed with the help of X-ray diffractometer (RigakuD/max-2550). For XRD tests, in order to eliminate the interference of ITO layer, both the Sn-doped V2O5 film and pure V2O5 film were prepared on bare glass substrate. The XRD withCu-Ka source, was performed a scan of θ-2θ in the range between 10° and 70° . Figure.1shows the XRD test curve of each different concentration of the film. The pure V2O5 filmFirst A. Author, Second B. Author, Third C. Author3shows a single orthorhombic V2O5 phase.[4] For the pure V2O5, there are three peaks locatedat 20.3°, 21.4° and 41.3°, which correspond to the (001), (101) and (002) directions. In thecase of 1% MoO3-doped V2O5 film, there are no peaks other than those observed for pureV2O5 film, indicating that Molybdenum oxide is either amorphous or crystalline with verysmall crystallites. However, 2-5% MoO3-doped V2O5 films have different and more peaks.These peaks position is neither MoO3[9] nor V2O5 . At the same time, these are not same withthe peaks in other XRD of some doping experiments. The reason for this phenomenon is thatthe MoO3 in doped thin films as the solute donor forms solid-solution phases[10] with V2O5.There are the same location of peaks in this curve between pure V2O5 films and 1% MoO3-doped V2O5 films because in the 1% MoO3-doped V2O5 films, MoO3 does not insert into theV2O5 crystal and it's rare to check out. Furthermore, about the location of the peaks of 2-5%MoO3-doped V2O5 films there are not same peaks with the existing literature or XRDalignment card. And the intensity of those peaks rise up following with the increase of dopantconcentration.）Figure.2 is compared the crystallization temperature of different doping concentration ofthe films. From Figure.2(a) which curve has peaks in XRD spectra of the film was annealedat 65℃,and the other one was annealed at 60℃. We can see that crystallization temperatureof the pure V2O5 thin film is between 60℃and 65℃. The same can be seen in Figure.2(b),the crystal temperature of 1% MoO3-doped is between 55℃ and 60 ℃ ; Figure.2(c), thecrystal temperature of 2% MoO3-doped is between 50℃ and 55 ℃; Figure.2(d), the crystaltemperature of 3% MoO3-doped is between 50℃ and 55 ℃ ; Figure.2(f), the crystaltemperature of 5% MoO3-doped is between 45℃and 50℃. The conclusion can be obtained,that different mixed ratio has the effects of crystallization temperature about the films. TheV2O5 films doped with more MoO3 have the lower the crystallization temperature. Thereason for this phenomenon is that the band gap of the films becomes smaller along with theMoO3-doped which MoO3 was inserted into the V2O5 crystal. So the crystallizationtemperature decreased with the amount of doped films increasing. The crystallizationtemperature of 1% MoO3-doped and pure V2O5 film declined, but in the 1% MoO3-dopedV2O5 film, MoO3 did not insert into V2O5 crystal because of the pure physical mixing.Lithium insertion in sol-gel deposited V2O5 films was accomplished using cyclicvoltammetry (CV). The CV was performed on V2O5/MoO3/ITO glass electrodes in anelectrolyte of 1 M LiClO4 with PC at room temperature. Several cycles were required toachieve a steady-state voltammogram in each case. Figure. 3 shows typical cyclicvoltammograms (CV) of V2O5/MoO3 in the potential range of -1.2 ~1.5 V (vs Li/Li+) at thescan rate of 10mV/s. Over this potential range, the shape of the curves is a typical diffusion-controlled CV of a highly reversible lithium intercalation / deintercalation process. With theincreasing proportion of MoO3 doped in V2O5, all the redox peak currents of the five samplesincreased, suggesting that their electrochemical activity increased with the initial CV cycles.For the pure V2O5 films, two couples of the redox peaks can be observed at Figure. 3. Thetwo well-defined reduction peaks at about −0.202V and −0.520V correspond to therespective α/ε and ε/δ phase transitions, and the two well-defined oxidation peaks at about−0.227V and −0.072 V correspond to the respective δ/ε, and ε/α phase transitions.[10]However, for the MoO3-doped V2O5 films, two more couples of the redox peaks can beobserved at Figure. 3. Their positions are about -0.75V/0.42V and 0.76V/-0.95V respectively.The two well-defined reduction peaks at about −0.219V and −0.513V correspond to therespective α/ε and ε/δ phase transitions, and oxidation peaks about δ/ε, and ε/α phasetransitions move to right with the proportion of MoO3 in V2O5.First A. Author, Second B. Author, Third C. Author4The comparison of oxidation peaks about ε/α phase transitions in the pure V2O5 film andMoO3-doped V2O5 film was summarized as Table.1. At the same scan rate, the peaks of ε/αphase transitions shifted to right and became higher as the more amount MoO3 doped in V2O5.With the incorporation of MoO3, and the number of phase transitions changed. The numberof peaks increasing, the properties of the films are becoming more and more lively with theincreasing of mixed concentration. This conclusion of Fig.3 is same with the test results ofpure V2O5 films and thin MoO3-doped V2O5 films about cyclic voltammograms. During moreelectrochemical cycling, all peaks of pure V2O5 film doesn’t have began to graduallydisappear. However, the disappearing of some phase transition peaks about the MoO3-dopedV2O5 films also show that the MoO3-doped makes electrochromic cyclical declining.Fig. 4 shows the chronoamperometric response curves of the pure V2O5 films and the thinMoO3-doped V2O5 films in the potential region of -1.0V to 1.3V. The amplificatory curve onthe left of Fig. 4 was current density changing with time under the condition of -1.0V. Andthe other potential was 1.3V on the right of Fig. 4. Consistent with the switching responseresults, the films doped with high concentration have faster response, and the differentresponse time of intercalation processes is clearer than deintercalation processes. Theincorporation of MoO3 has changed the structure of V2O5 crystal. The atomic radius of Mo islarger than the atomic radius of V. With the increase in MoO3 , structure of thin films becomemore and more loose, blocking effect of lithium ion becomes smaller, the channel of lithiumion intercalation /deintercalation becomes much smoother and the resistance of ion migrationchanges less, then, the films doped with high concentration have faster response.[10]We took cyclic voltammetric tests of different concentration MoO3-doped V2O5 films ,and the test results obtained: the higher doping concentration is, the lower the cycleperformance of thin film. It's same with the former result. So to improve the performance offilms effectively, we took the lowest cycle performance of 5% MoO3-doped V2O5 films toconduct experiments. In order to improve the cycle performance of the thin film, we put themin acetone horizontally at room temperature where the films were put right side up, and theexperimental variable was just time. Treatment time were 10min, 30min, 60min, 2h, 4h, 8h,16h, 24h, 30h, 36h, 42h, 48h. Figure.5 shows the cyclic voltammetric of the original film,acetone treatment confirmed by 10min, 4h, and 16h about 5% MoO3-doped V2O5 films at20mV/s. As we can see from the curve, the cyclicity of film which 10min acetone treatmentdidn't any enhance, while the difference of tenth circle and fiftieth circle CV cycle reductionpeak current density of the film that 4h processed is only 5*10-4A/cm-2. The film that 16hacetone treated has changed the crystal characteristics of the thin film, so CV curve haschanged. Analysis in combination with the patterns of any other treatment time, we can drawthe conclusion: the cyclical films treated below 1h are not significantly increased, and thecyclical films whose treatment time is from 2h to 8h rised considerably, it leads to theposition change of cyclic peak by 16h or more acetone treatment. Fig.6 show the colored andbleached states of 5% MoO3-doped V2O5 films which is treated by acetone treatment for 4hin the range from 300nm to 1000nm at different voltages in 1M LiClO4/PC electrolyte. Asshown in Fig.6, the film which is added with different voltage does show the sametransmittance spectra.First A. Author, Second B. Author, Third C. Author54 TITLE, AUTHORS, AFFILIATION, KEYWORDS4.1 TitleELECTROCHEMICAL PERFORMANCES OF Li+ INTERCALATION ANDDEINTERCALATION PROCESSES FOR ELECTROCHROMISM of MoO3-DOPED V2O5 FILMS PREPARED BY THE SOL-GEL METHOD4.2 AuthorHe Wang, Manuel F. Costa, Shengnan Sun, Vasco Teixeira, Haining Cui4.3 Key wordsElectrochromism, MoO3-doped V2O5 films, Cyclic voltammetry.5 FIGURES20 40 60（101）（002）  Intensity(a.u.)2θ (degree) Pure 1% 2% 3% 5%（001）Figure 1: XRD patterns of different concentration of the filmFirst A. Author, Second B. Author, Third C. Author6Figure 2: The crystallization temperature of different doping concentration of the filmsFirst A. Author, Second B. Author, Third C. Author7Figure 3: Cyclic voltammograms of V2O5 -MoO3 films0 100 200 300 400 500 600 700-0.020-0.015-0.010-0.0050.0000.0050.0100.015370 380 390 4000.0000.0020.0040.0060.0080.0100.012 1.3 V  0 20 40 60 80 100-0.020-0.015-0.010-0.0050.000  -1.0 V  i(A/cm2)i(A/cm2) pure 1% 2% 3% 5%Figure 4: Chronoamperometric response curves different doping concentration of the films. The amplificatorycurve on the left is current density changing with time under the condition of -1.0V. And the right one is 1.3V.First A. Author, Second B. Author, Third C. Author8-1.0 -0.5 0.0 0.5 1.0 1.5-4-20246-1.0 -0.5 0.0 0.5 1.0 1.5-4-20246-1.0 -0.5 0.0 0.5 1.0 1.5-4-20246-1.0 -0.5 0.0 0.5 1.0 1.5-15-10-5051015   Original   10min   4hVOLTAGE (V)   CURRENT DENSITY (mA/cm^2) 16hFigure 5: Cyclic voltammetric of the original film, acetone treatment confirmed by 10min, 4h, and 16h about5% MoO3-doped V2O5 filmsFirst A. Author, Second B. Author, Third C. Author9300 450 600 700 800 900 1000020406080100  Transmittance/%Wavelength /nm  1.5V -1.5VFigure 6 : Transmittance spectra of 5% MoO3-doped V2O5 films at different voltages6 TABLESThe doping concentration of MoO3 Oxidation peaks(V)0% -0.0721% -0.0342% -0.0093% 0.0485% 0.080Table 1: Comparison of oxidation peaks about ε/α phase transitions in the Pure V2O5 Film and MoO3-Doped V2O5 Film7 CONCLUSIONSComparing the cyclic voltammetric of the pure V2O5 films and the thin Mo-doped V2O5films, the number of oxidation ε/α phase transitions changed with the incorporation of MoO3.The incorporation of MoO3 has changed the structure of V2O5 crystal. With the increase inMoO3, the properties of the films are becoming more and more lively, and the films dopedwith high concentration have faster response. Treated by acetone horizontally at roomtemperature with different time, the cyclical films obviously increased, and the position ofFirst A. Author, Second B. Author, Third C. Author10cyclic peak could change by much acetone treatment.REFERENCES[1] D. R. Rosseinsky , R. J. Mortimer, Electrochromic systems and the prospects for devices .ADVANCED MATERIALS , 13, 783, 2001.[2] P.M.S. Monk, R. J. Mortimer, D. R. Rosseinsky, Electrochromism and ElectrochromicDevices. Paddyfield ShopInHK, 2007[3] I. Shakir, Z. Ali, J. Bae, J.J. Park and D. J. Kang, Layer by layer assembly of ultrathinV2O5 anchored MWCNTs and graphene on textile fabrics for fabrication of high energydensity flexible supercapacitor electrodes. Nanoscale, 6, 4125, 2014[4] Y. W. Li, J.H. Yao, E. Uchaker, M. Zhang, J. J. Tian, X.Y. Liu, G.Z Cao, Sn-DopedV2O5 Film with Enhanced Lithium-Ion Storage Performance. J. Phys. Chem. C, 117,23507−23514, 2013[5] D. Wei, M. R. J. Scherer, C. Bower, P. Andrew, T. Ryhänen, U. Steiner, ANanostructured Electrochromic Supercapacitor. Nano Lett. 12, 1857−1862, 2012[6] C. Delmas, H. C. Auradou, J. M. Cocciantelli, M. Menetrier, J. P. Doumerc, The LixV2O5System: An Overview of the Structure Modifications Induced by the LithiumIntercalation. Solid State Ionics. 69, 257−264, 1994.[7] M. S. Whittingham, Lithium Batteries and Cathode Materials. Chem. Rev. 104, 4271−4301, 2004.[8] Z. Q. Tong, J. Hao, K. Zhang, J. P. Zhao, B. L. Su, Y. Li, Improved electrochromicperformance and lithium diffusion coefficient in three-dimensionally orderedmacroporous V2O5 films . JOURNAL OF MATERIALS CHEMISTRY C . 2, 3651-3658,2014[9] N. L. Shi, Y. Nicholas, S. Jason, A. Rose, H. N. Yun, Influence of MoO3(110) CrystallinePlane on Its Self-Charging Photoelectrochemical Properties. Scientific Reports. 4, 7428,2014[10] S. Q. Xu, H. P. Ma, S. X. Dai, Z. H. Jiang, Switching Properties and Phase TransitionMechanism of Mo6+-Doped Vanadium Dioxide Thin Films. CHIN.PHYS.LETT. 20, 148-150, 2003

Electrochemical Performances of Li+ Intercalation and Deintercalation Processes for Electrochromism of MoO3-Doped V2o5 Films Prepared By The Sol-Gel Method

Electrochemical Performances of Li+ Intercalation and Deintercalation Processes for Electrochromism of MoO3-Doped V2o5 Films Prepared By The Sol-Gel Method

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