Enhancement of intercalation properties of V2O5 film by TiO2 addition

Although it is well-known that TiO2 incorporation can greatly improve the cyclic stability of V2O5, the influences of TiO2 addition on the Li+ intercalation properties of V2O5 remain an issue of debate in literature. In this paper, we report on a systematic investigation of the preparation and intercalation properties of V2O5-TiO2 mixture films. The present work demonstrates that high Li+ intercalation rates and capacity in V2O5 films are achievable with TiO2 addition. For example, the addition of 20 mol % Ti into V2O5 polycrystalline demonstrated an approximated 100% improvement in Li+ intercalation performance as compared to single V2O5 electrodes. Such enhancement in intercalation properties of V2O5 films with TiO2 addition was attributed to changes in microstructure, crystallinity, and also a possible lattice structure and interaction force between adjacent layers in V2O5.     

电泳沉积法制备V2O5薄膜的结构和性能

V2O5 thin films were successfully prepared on ITO substrate with electrophoresis deposition (EDP) through V2O5 sol. X-ray diffraction and scanning electron microscopy were used for studying the structure of the films. The optical and electrochemical properties were measured by the transmittance spectra and cyclic voltammetry measurements, respectively. It is found that V2O5 thin films deposited by EDP are a compact microstructure with finer adhesive force with ITO substrate and the thickness is uniform. During the cycle experiment, the films exhibited reversible two-color (yellow at oxidation and green at reduction) with a maximum transmittance change of around 30%. Moreover, the films had an excellent cycle for lithium intercalation/deintercalation and good cycle stability, the cycle efficiency for the 50th cycle was 88.02% and the films still had fine adhesive force with ITO substrate with no dissolving over more than 50 cycles. The Li+ diffusion coefficient in V2O5 thin film was 5.10×10-12 cm2/s by the electrochemical impedance spectra method. All results indicate that V2O5 thin films by the electrophoresis deposition may be suitable for the use in the electrochromic devices.     

Effects of thermal annealing on the Li(+) intercalation properties of V(2)O(5) x nH(2)O xerogel films

V(2)O(5) x nH(2)O xerogel films with n = 1.6, 0.6, and 0.3 have been prepared from the sol-gel route by reacting V(2)O(5) with H(2)O(2) followed by drying under ambient conditions and thermal annealing at 110 and 250 degrees C, respectively. After dehydration, V(2)O(5) crystallizes at 300-330 degrees C, as revealed by thermal gravimetric analysis and X-ray diffraction. Electrochemical characterization demonstrated that V(2)O(5) x 0.3H(2)O film exhibits the best Li(+) intercalation performance, with an initial capacity of 275 mAh/g and a stabilized capacity of 185 mAh/g under a high current density of 100 microA/cm(2) after 50 cycles. Under a low current density of 10 microA/cm(2), the capacity of this film can reach 390 mAh/g. Such an enhanced electrochemical property by thermal treatment is ascribed to the reduced water content, the retained interlayer spacing, and the dominant amorphous phase in the film.     

Ni-V2O5.nH2O core-shell nanocable arrays for enhanced electrochemical intercalation

We have prepared Ni-V(2)O(5).nH(2)O core-shell nanocable arrays for Li(+) intercalation applications. Ni-V(2)O(5).nH(2)O nanocables were prepared via formation of Ni nanorod arrays through the template based electrochemical deposition, followed by coating of V(2)O(5).nH(2)O on Ni nanorods through electrophoretic deposition. Transmission electron microscopy (TEM) micrograph clearly shows the Ni core was covered completely by a V(2)O(5).nH(2)O shell. Electrochemical analysis demonstrates that in a current density of 1.6 A/g, the Li(+) intercalation capacity of Ni-V(2)O(5).nH(2)O nanocable array is approximately 10 times higher than that of single-crystal V(2)O(5) nanorod array and 20 times higher than that of sol-gel-derived V(2)O(5) film. Both energy density and power density of such nanocable-array electrodes are higher than the V(2)O(5) film electrode by at least 1 order of magnitude. Such significant improvement in electrochemical performance is due to the large surface area and short diffusion path offered by the nanostructured V(2)O(5).nH(2)O.     

XPS study of the Li intercalation process in sol–gel‐produced V2O5 thin film: influence of substrate and film synthesis modification

We report on the process of lithium intercalation in V₂O₅ thin films deposited onto standard ITO‐coated glass substrates. The films were deposited via a well‐established sol–gel route, and the samples were examined as working electrodes in a range of potentials versus lithium reference electrode. This paper follows up issues arising from parallel spectroscopic characterizations of the films by X‐ray photoelectron spectroscopy (XPS). Specifically, the XPS examination showed that not all of the Li‐ion charge inserted was accounted for by the V(5) to V(4) reduction, but the stoichiometric balance could be maintained only by considering additional oxygens arising from the intercalation procedure, leading to Li₂O formation. In this work, we have examined the possibility that the source of oxygen is the ITO substrate. To this purpose, films of V₂O₅ deposited on silicon substrates have been prepared using the sol–gel process and examined by XPS after electrochemical intercalation/de‐intercalation cycles. We show that in this case a perfect balance between electrochemical charge, inserted Li and reduced vanadium is obtained. A further indication of ITO‐substrate effects was obtained from examination, by the same methods, of some unconventional V₂O₅ films that had been co‐precipitated with a siloxane, designed to provide a template structure. The results obtained from this material imply that a barrier layer is formed at the ITO interface and, therefore, the formation of Li₂O is avoided. The results are discussed in terms of the possible degradation of conventional V₂O₅ on ITO as a result of electrochemically induced interface reactions. Copyright © 2005 John Wiley & Sons, Ltd.     

尖晶石型LiMn2O4薄膜电极的制备及电化学性质研究──电化学石英晶体微天平(EQCM)技术研究

石英晶体微天平(QCM)作为纳克级的质量传感器,可通过测定石英晶体振动频率的变化来测定石英晶体表面微小的质量变化.近年来,电化学石英晶体微天平(EQCM)技术已广泛应用于电化学研究领域[1].在锂嵌入型电极充放电过程中,锂离子在嵌基材料中嵌入脱出会引起电极质量的微小变化,因而利用EQCM技术研究Li+的嵌入脱出过程有其独到之处.     

Synchrotron light scattering on nanostructured V/Ce oxide films intercalated with Li+ ions

Vanadium oxide and new V/Ce oxide films on a glass substrate were obtained by the sol-gel process. The morphology of these nanostructured and porous films was studied by grazing-incidence small-angle X-ray scattering (GISAXS) at the ELETTRA synchrotron (Italy, Trieste). The aim of performing GISAXS was to study changes, which might occur in the grain sizes and the porosity of vanadium oxide and V/Ce oxide at 38 and 55 atom % of V, upon the intercalation of Li+ ions. The average grain radius obtained by GISAXS varied with the layer thickness and upon the intercalation of Li+ ions. The layer structure in V/Ce oxides was revealed by the grazing-incidence X-ray reflectivity (GIXR) method. The average grain radius , obtained by GISAXS, was correlated with the intercalation of Li+ ions. The specific surface area of these films was also determined and generally varied from 0.5 nm(-1) to 0.03 nm(-1).     

V2O5电致变色薄膜的Raman光谱

The amorphous V 2O 5 films prepared by vacuum evaporation are unstable and easily dissolved by electrolyte during the electrochromic process, so unfit to make electrochromic materials. We found that the annealed films have enhanced stability and electrochromic properties. We studied the microstructural changes during the electrochromic process by Raman spectra and discussed the mechanism for the enhancement. The results indicated that the amorphous films annealed by 400-500℃became polycrystalline and the films contained (V 2O 5)n ordered chains which prevented the films from solution effectively and enhanced the electrochromic characteristics. When colored and decolored, the microstructure of the polycrystalline V 2O 5 films changed inversely. During the cathodic polarization process, Li+ inserted into the V 2O 5 crystal cell , formed V-O-Li band, disordered the films and UV absorption of the films blue shifted. On the contrary , during the anodic polarization process, Li +escaped from the crystal cell. The films largely restored .     

Theoretical and experimental determination of the electronic structure of V(2)O(5), reduced V(2)O(5-x) and sodium intercalated NaV(2)O(5)

In this work the electronic structure of V(2)O(5), reduced V(2)O(5-x) (V(16)O(39)) and sodium intercalated NaV(2)O(5) has been studied by both theoretical and experimental methods. Theoretical band structure calculations have been performed using density functional methods (DFT). We have investigated the electron density distribution of the valence states, the total density of states (total DOS) and the partial valence band density of states (PVBDOS). Experimentally, amorphous V(2)O(5) thin films have been prepared by physical vapour deposition (PVD) on freshly cleaved highly oriented pyrolytic graphite (HOPG) substrates at room temperature with an initial oxygen understoichiometry of about 4%, resulting in a net stoichiometry of V(2)O(4.8). These films have been intercalated by sodium using vacuum deposition with subsequent spontaneous intercalation (NaV(2)O(5)) at room temperature. Resonant V3p-V3d photoelectron spectroscopy (ResPES) experiments have been performed to determine the PVBDOS focusing on the calculation of occupation numbers and the determination of effective oxidation state, reflecting ionicity and covalency of the V-O bonds. Using X-ray absorption near edge spectra (XANES) an attempt is made to visualize the changes in the unoccupied DOS due to sodium intercalation. For comparison measurements on nearly stoichiometric V(2)O(5) single crystals have been performed. The experimental data for the freshly cleaved and only marginally reduced V(2)O(5) single crystals and the NaV(2)O(5) results are in good agreement with the calculated values. The ResPES results for V(2)O(4.8) agree in principle with the calculations, but the trends in the change of the ionicity differ between experiment and theory. Experimentally we find partly occupied V 3d states above the oxygen 2p-like states and a band gap between these and the unoccupied states. In theory one finds this occupation scheme assuming oxygen vacancies in V(2)O(5) and by performing a spin-polarized calculation of an antiferromagnetic ordered NaV(2)O(5.).     

锂-氧化铜电池反应机理(Ⅰ)——光电化学方法研究阴极嵌入反应

采用光电化学方法现场研究了锂-氧化铜电池的嵌入反应,氧化铜电极光电流的变化直观地反映了该电化学嵌入过程.发现锂离子嵌入氧化铜电极的反应始于2.5V(vs.Li/Li⁺),锂以施主杂质状态存在于氧化铜晶格中,改变了阴极的半导体性质.在较低电位下,可能有产生氧化亚铜的后续反应.     

MoO_3电致变色薄膜的XPS研究

近年来 ,随着人们提倡节能和使用洁净能源 ,无机电致变色材料在建筑物采光控制系统和反射率可调表面的应用研究 ,已成为材料领域的一个新热点 .WO3、 MoO3等过渡金属氧化物薄膜具有良好的电致变色效应 ,是人们研究的重点 .其中 MoO3的电致变色效果要好于 IrO2、 TiOx、 CoO及 NiOx等电致变色材料 [1],而且它在可见光区有比 WO3更柔和的色彩 ,使人眼更易于适应其颜色变化 .着色态的 MoO3称为钼青铜 ,其开路记忆也好于钨青铜 [2].故 MoO3电致变色薄膜是极有潜力用于实用化的电致变色器件 .MoO3薄膜常用的制备方法有真空蒸 发、化学气…     

实用电极材料体系的共焦显微拉曼光谱研究(英文)

本文简要介绍了实验室内有关利用共焦显微拉曼光谱于某些实用电极材料 (表面 )性能研究的结果 .具体的研究实例包括 :尖晶石锂锰氧化物中Li+ 的嵌入 脱出过程 ,AB5 型金属氢化物电极表面氧化物的性能和钢筋电极表面钝化膜及其孔蚀过程 .     

磁控溅射制备的铜钒氧化物薄膜及其电化学性能

采用射频磁控溅射技术在硅基底上分别制备了无掺杂和掺杂Cu的氧化钒薄膜. X射线衍射(XRD)分析和扫描电子显微镜(SEM)观察表明, 无掺杂的薄膜为多晶V2O5, 掺杂Cu的薄膜为非晶态. X射线光电子能谱(XPS)分析结果表明, 掺杂Cu的薄膜为铜钒氧化物膜, 其中Cu离子表现为+2价, V离子为+4与+5价的混合价态. 随着Cu掺杂量的增大, +4价V的含量增加. 电化学测试结果表明, V2O5薄膜在掺杂Cu以后其放电容量有显著的提高, 其中Cu2.1VO4.4薄膜在100次循环后容量还保持为83.4 μA·h·cm-2·μm-1, 表现出较高的放电容量和较好的循环性能.     

锂嵌入对α-V2O5中O2p和V3d轨道电子结构的影响

运用第一性原理计算了锂嵌入对α-V2O5中O2p和V3d轨道电了结构的影响．计算结果表明，不同的锂嵌入位置对O2p和V3d轨道的电了结构有着不同的影响．但锂的嵌入会减弱了V2O5中V=O1键，同时导致V3d导带的劈裂变窄或消失和HO2p价带变宽．最后计算出从每个Li2s轨道到V3d轨道的电子传递数为0．52．     

锌镀层P—Mo—V三元杂多酸盐配合物膜的性能和结构

在锌镀层材料表面,磷钼矾(P-Mo-V)三元杂多酸盐具有较好的配位能力,获得了多种具有金属光泽的不溶性彩色配合物膜,有良好的耐蚀性能和装饰效果。加速化学和电化学腐蚀实验(LSV)研究结果表明,Na6(PMo9V3O40).xH2O与锌镀层材料表面反应时,形成的一种新型金黄色杂多酸盐配合物膜(P-Mo-V金黄色配合物膜)的耐蚀性最佳。XPS和AES分析表明,P-Mo-V金黄色配合物膜层中Mo在膜表面的价态为 6,而在膜内层则以 6、 4价共存,其它元素的价态分别为Zn( 2),P( 5),V( 5),从其AES深度剥蚀曲线的组成恒定区求得膜的组成分别为Zn 19.7%,Mo 29.3%,V 21.2%,P 16.1%,O 13.5%;膜层的厚度约为160 nm。     

V2O5-anchored carbon nanotubes for enhanced electrochemical energy storage

Functionalized multiwalled carbon nanotubes (CNTs) are coated with a 4-5 nm thin layer of V(2)O(5) by controlled hydrolysis of vanadium alkoxide. The resulting V(2)O(5)/CNT composite has been investigated for electrochemical activity with lithium ion, and the capacity value shows both faradaic and capacitive (nonfaradaic) contributions. At high rate (1 C), the capacitive behavior dominates the intercalation as 2/3 of the overall capacity value out of 2700 C/g is capacitive, while the remaining is due to Li-ion intercalation. These numbers are in agreement with the Trasatti plots and are corroborated by X-ray photoelectron spectroscopy (XPS) studies on the V(2)O(5)/CNTs electrode, which show 85% of vanadium in the +4 oxidation state after the discharge at 1 C rate. The cumulative high-capacity value is attributed to the unique property of the nano V(2)O(5)/CNTs composite, which provides a short diffusion path for Li(+)-ions and an easy access to vanadium redox centers besides the high conductivity of CNTs. The composite architecture exhibits both high power density and high energy density, stressing the benefits of using carbon substrates to design high performance supercapacitor electrodes.     

Epitaxial growth and electrochemical properties of Li4Ti5O12 thin-film lithium battery anodes

Epitaxial Li(4)Ti(5)O(12) thin-films were successfully synthesized on SrTiO(3) single-crystal substrates with (111), (110), and (100) lattice plane orientations using pulsed laser deposition (PLD). Thin-film X-ray diffraction (XRD) revealed that the Li(4)Ti(5)O(12) films had the same orientation as the SrTiO(3) substrates: Li(4)Ti(5)O(12) (111) on SrTiO(3) (111), Li(4)Ti(5)O(12) (110) on SrTiO(3) (110), and Li(4)Ti(5)O(12) (100) on SrTiO(3) (100). These epitaxial films contained island structures, and the morphology of the (111), (110), and (100) films, observed by field emission scanning electron microscopy (FE-SEM), exhibited angular, needle-like, and circular shapes, respectively. The electrochemical properties of 20 nm thick Li(4)Ti(5)O(12) (111) and (110) films were investigated by cyclic voltammetry. Reversible intercalation proceeded through both lattice planes due to the three-dimensional diffusion pathway of lithium in the spinel framework. Reduction peaks in the first cathodic scan appeared at different positions from those in subsequent scans, suggesting a surface reconstruction at the Li(4)Ti(5)O(12) surface due to interfacial reactions.     

Synthesis and electrochemical properties of vanadium pentoxide nanotube arrays

Nanotube arrays of amorphous vanadium pentoxide (V(2)O(5)) were synthesized via template-based electrodeposition, and its electrochemical properties were investigated for Li-ion intercalation applications. The nanotubes have a length of 10 microm, outer diameter of 200 nm and inner diameter of 100 nm. Electrochemical analyses demonstrate that the V(2)O(5) nanotube array delivers a high initial capacity of 300 mAh/g, about twice that of the electrochemically prepared V(2)O(5) film. Although the V(2)O(5) nanotube array shows a more drastic degradation than the film under electrochemical redox cycles, the nanotube array reaches a stabilized capacity of 160 mAh/g, which remains about 1.3 times the stabilized capacity of the film.     

脉冲激光沉积具有锂离子储存能力的CeO2薄膜

锂电池具有比能量高,循环性能好的优点,已成为二次电池研究的热点．锂离子电极材料的电致变色性能也引起了人们的广泛兴趣．最近一项日本专利报导了水热法合成的氧化铈粉末,属单斜晶系,作为锂离子电池阳极时,其体积比容量达５３０ｍＡｈ·ｃｍ－３,高于通常用的石墨阳极．该专利还指出,以ＣｅＯ２为阳极,ＬｉＣｏＯ２为阴极,与非水电解质组成的锂电池平均放电电压为３．５Ｖ左右［１］．近年来,全固态薄膜锂离子微电池为适应电子器件的微型化而受到重视,它可以采用不同的二维形状直接构织到集成电路上．例如,可作为动态随机存储…     

First-principles studies of vanadia-titania catalysts: beyond the monolayer

Periodic density functional calculations have been used to investigate the structure and stability of epitaxial vanadium oxide films grown on the TiO(2)(001) anatase surface. The formation energy of films of V(2)O(5) stoichiometry, initially low, is found to rapidly increase with the film thickness, at variance to what is obtained for reduced pseudomorphic VO(2) films. This is in tune with results of oxygen-assisted molecular beam epitaxy. The oxidation of thick, viz. >2 monolayers (ML), VO(2) films yields a c(2 x 2) reconstructed surface, in agreement with low energy electron diffraction. These films are composed by partially reduced inner V atoms in a distorted-octahedral environment, and by isolated surface dioxovanadium centers exhibiting a distorted trigonal-bipyramidal coordination. Single scattering simulations of X-ray photoelectron diffraction patterns have also been performed, taking both 2- and 3-ML surface surface-oxidized films as models. Results are in fair agreement with experiments referring to films grown in oxidizing conditions, which suggests that coherent vanadia ultrathin films could be formed in vanadia-titania catalysts. The electronic structure of the films has been finally studied, finding that the terminal oxygens carried by the surface dioxovanadium species have a strong nucleophilic character, which makes them potential active centers for selective oxidation catalysis.