Preparation and Electrochemical Performance of V2O3-C Dual-Layer Coated LiFePO4 by Carbothermic Reduction of V2O5

The V₂O₃-C dual-layer coated LiFePO₄ cathode materials with excellent rate capability and cycling stability were prepared by carbothermic reduction of V₂O₅. X-ray powder diffraction, elemental analyzer, high resolution transmission electron microscopy and Raman spectra revealed that the V₂O₃ phase co-existed with carbon in the coating layer of LiFePO₄ particles and the carbon content reduced without graphitization degree changing after the carbothermic reduction of V₂O₅. The electrochemical measurement results indicated that small amounts of V₂O₃ improved rate capability and cycling stability at elevated temperature of LiFePO₄/C cathode materials. The V₂O₃-C dual-layer coated LiFePO₄ composite with 1wt% vanadium oxide delivered an initial specific capacity of 167 mAh/g at 0.2 C and 129 mAh/g at 5 C as well as excellent cycling stability. Even at elevated temperature of 55 oC, the specific capacity of 151 mAh/g was achieved at 1 C without capacity fading after 100 cycles.     

Lithium-ion intercalation and electrochromism in ordered V2O5 nanoporous layers

Highly ordered V₂O₅ porous layers were fabricated from vanadium metal foils by self-organizing anodization. The defined porous structure of this material provides excellent lithium-ion transportation and intercalation/extraction properties. As a result the highly ordered porous structure shows a very good electrochromic performance with long term switching stability.     

Electrodeposition of mesoporous V2O5 with enhanced lithium-ion intercalation property

Mesoporous vanadium oxide (V₂O₅) thin films were deposited electrochemically onto indium tin oxide-coated glass substrates from an aqueous solution of vanadyl sulfate using CTAB (hexadecyltrimethylammonium bromide) as a templating agent. For comparison, a control sample was electrodeposited without CTAB templating. Transmission electron microscopy and small angle X-ray diffraction indicated the presence of mesoporosity with a well-ordered lamellar phase in the electrodeposited films. The crystallinity of the V₂O₅ thin films was confirmed by X-ray diffraction. Cyclicvoltammetry and chronoamperometry were used to measure electrochemical properties of synthesized films. The mesoporous films prepared with CTAB templating had a much higher capacity and lithium-ion diffusion rate than the non-porous electrode prepared without CTAB templating.     

Acidic properties of V2O5-WO3/ZrO2 catalysts

The adsorption of pyridine on V₂O₅−WO₃/ZrO₂ has been studied by FTIR. In V₂O₅/ZrO₂ (2 wt.%), the number of both Br?nsted and Lewis acidic sites increased with the addition of WO₃, while in V₂O₅/ZrO₂ (5 wt.%), Br?nsted sites increased and Lewis sites did not change.     

Zn/V2O5水相二次电池的交流阻抗研究

The dependence of charge transfer resistances of electrodes in the aqueous Zn/V 2O 5 secondary battery on the Zn 2+ amount intercalated was studied by means of AC impedance experiments. The results showed that the electrode reaction on cathode was controlled by the diffusion of Zn 2+ at the beginning of the discharge process. With the increase of Zn 2+ amount intercalated into the cathode, the reaction became a kinetic controlled process, i.e.a process controlled by intercalation of Zn 2+ in V 2O 5.     

Topotactic insertion of lithium in the layered structure Li4VO(PO4)2: The tunnel structure Li5VO(PO4)2

A new V(III) lithium phosphate Li₅VO(PO₄)₂ has been synthesized by electrochemical insertion of lithium into Li₄VO(PO₄)₂. This phase, which crystallizes in the space group I4/mcm, exhibits a tunnel structure closely related to the layered structure of Li₄VO(PO₄)₂ and to the tunnel structure of VO(H₂PO₄)₂. The topotactic reactions that take place during lithium exchange and intercalation, starting from VO(H₂PO₄)₂ and going to the final phase Li₅VO(PO₄)₂ are explained on the basis of the flexible coordinations of V⁴⁺ and V³⁺ species. The electrochemical and magnetic properties of this new phase are also presented and explained on the basis of the structure dimensionality.     

Electrochromic properties of anodically grown mixed V2O5–TiO2 nanotubes

Mixed V₂O₅–TiO₂ nanotube arrays were fabricated by self-organizing anodization of different Ti–V alloys. The mixed oxide nanotubes show switchable V-oxidation states and strong cathodic coloration. Already a low V content of ≈ 0.2 at.% significantly increases the electrochromic switching properties. Using a sample with 3 at.% V, very high electrochromic contrast can be established and a significantly lower switching onset voltage than for pure TiO₂ nanotubes is observed. At high V contents, although charge storage is increased, the improvement of contrast is diminished due to the strong background color of the sample.     

Properties of passivation film on carbon electrode in LiPF6/EC+DEC electrolytes

The co-solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was used to investigate the decomposition of electrolyte in Li-ion batteries. The electrolyte solutions were prepared by mixing in various volume ratios from pure DEC to 7:3 (EC:DEC). The potentials at which they are decomposed on the anodic electrode were examined using cyclic voltammetry. It was found that some kinds of reduction reactions proceeded and a film on the surface of the anode was formed. The film showed different properties, which were dependent on the mixing ratio of the solvents. From our results, we concluded that the best composition ratio of EC:DEC in 1 M LiPF₆/(EC+DEC) system was approximately 4:6 (EC:DEC, volume ratio).     

锂离子电池正极材料LiMn2O4的合成与晶体结构（英）

Spinel LiMn₂O₄ powders were prepared using two-step synthesis method consisting of solid-state reaction method and citrate modified sol-gel method. The effects of the calcination temperature and the Li/Mn ratio of raw materials were studied on the physicochemical and electrochemical properties of the spinel LiMn₂O₄ powders, such as crystallinity, lattice constant and density. The title compound was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Polycrystalline LiMn₂O₄ powers calcined at 750 ℃ were found to be composed of very uniformly-sized microcrystal with an average particle size of 300 nm. The improvement in electrochemical properties was mainly attributed to the process of re-grinding by absolute alcohol.     

Li ion diffusion in Li4Ti5O12 thin film electrode prepared by PVP sol-gel method

Li₄Ti₅O₁₂ thin films for rechargeable lithium batteries were prepared by a sol-gel method with poly(vinylpyrrolidone). Interfacial properties of lithium insertion into Li₄Ti₅O₁₂ thin film were examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and potentiostatic intermittent titration technique (PITT). Redox peaks in CV were very sharp even at a fast scan rate of 50 mV s⁻¹, indicating that Li₄Ti₅O₁₂ thin film had a fast electrochemical response, and that an apparent chemical diffusion coefficient of Li⁺ ion was estimated to be 6.8×10⁻¹¹ cm² s⁻¹ from a dependence of peak current on sweep rates. From EIS, it can be seen that Li⁺ ions become more mobile at 1.55 V vs. Li/Li⁺, corresponding to a two-phase region, and the chemical diffusion coefficients of Li⁺ ion ranged from 10⁻¹⁰ to 10⁻¹² cm² s⁻¹ at various potentials. The chemical diffusion coefficients of Li⁺ ion in Li₄Ti₅O₁₂ were also estimated from PITT. They were in a range of 10⁻¹¹-10⁻¹² cm² s⁻¹.     

Li2O-TiO2-SiO2-P2O5和Li2O-TiO2-Al2O3-P2O5体系锂离子固体电解质的制备及性能研究

一些具有NASICON型网格结构的固体电解质具有高的电导率和好的稳定性,NASICON的意思是Na Super Ionic Conductor[1]。当NaZr2(PO4)3中P5 被Si4 部分取代时便可以得到具有NASICON结构的Na1 xZr2SixP3-xO12体系,其具有高的钠离子电导率。然而有相同结构的Li1 xZr2SixP3-xO12体系的离子电导率却很低,这是因为Li 半径太小,而NASICON三维网格结构的离子通道太大,两者不匹配而使电导率下降[2]。但当LiZr2(PO4)3中Zr4 被离子半径小些的Ti4 取代,所得LiTi2(PO4)3的通道就与Li 半径相匹配,适合于锂离子的迁移,从而使其电导率…     

Bromolactonization of alkenoic acids mediated by V2O5 via bromide to bromenium in situ oxidation

An efficient protocol for the bromolactonization of alkenoic acids is presented that obviates the use of molecular bromine or exogenous bromenium sources. Vanadium (V) oxide catalyzes the in situ oxidation of bromide salts to bromenium (Br⁺) in a process mediated by urea–hydrogen peroxide complex. Initial mechanistic investigations indicate that the presence of urea does not accelerate the halolactonization reaction.     

V2O5 xerogel-poly(ethylene oxide) hybrid material: Synthesis, characterization, and electrochemical properties

In this work, we report the synthesis, characterization, and electrochemical properties of vanadium pentoxide xerogel-poly(ethylene oxide) (PEO) hybrid materials obtained by varying the average molecular weight of the organic component as well as the components’ ratios. The materials were characterized by X-ray diffraction, ultraviolet/visible and infrared spectroscopies, thermogravimetric analysis, scanning electron microscopy, electron paramagnetic resonance, and cyclic voltammetry. Despite the presence of broad and low intensity peaks, the X-ray diffractograms indicate that the lamellar structure of the vanadium pentoxide xerogel is preserved, with increase in the interplanar spacing, giving evidence of a low-crystalline structure. We found that the electrochemical behaviour of the hybrid materials is quite similar to that found for the V₂O₅ xerogel alone, and we verified that PEO leads to stabilization and reproducibility of the Li⁺ electrochemical insertion/de-insertion into the V₂O₅ xerogel structure, which makes these materials potential components of lithium ion batteries.     

V2.38Nb10.7O32.7: A V2O5-Nb2O5 mixed oxide tunnel structure related to the tetragonal tungsten bronzes

A crystal structural model for the orthorhombic compound V_2.38Nb_10.7O_32.7, which is known as “V₂Nb₉O_27.5”, was developed by means of selected area electron diffraction (SAED), Rietveld refinement and high resolution electron microscopy (HREM). The metastable compound is obtained by thermal decomposition of freeze-dried precursors as chain-like agglomerated nanoparticles or by reaction of V₂O₅ with fresh-precipitated Nb₂O₅ as more compact micro-scaled crystals. With the latter, it was possible to identify its structure for the first time (space group Cmmm). The tetragonal tungsten bronze (TTB)-type structure shows high potential for ionic intercalation, since easily reducible [V⁵⁺₂O²⁻] units are implemented in the tunnels of a rigid niobium oxide framework.     

层状Li(Ni1-xCox)O2结构研究

0引言层状钴酸锂是目前锂离子电池主要正极材料,但是,随着锂离子电池的广泛使用,急需比钴酸锂价格低和来源广泛的正极材料,层状锰酸锂和层状镍酸锂受到重视。由于锰氧化物存在有J-T效应,因此,严格意义上的层状锰酸锂的制备极其困难。制备层状镍酸锂也非常困难,高温反应极易生成Li1-xNi1 xO2,具有此种结构的镍酸锂存在严重首次能量衰减和循环性能下降的缺点。采用其他元素掺杂镍酸锂克服其缺点的研究已经很多,其中钴掺杂镍酸锂由于显示了良好的效果而被认为是最有希望替代钴酸锂的锂离子电池正极材料。有关层状镍钴酸锂的研究很多,但不少的…     

Influence of the crystallinity on the Li+ intercalation process in Nb2O5 films

Nb₂O₅ thin films were prepared by the Pechini method. The effect of the film crystallinity on the electrochemical and electrochromic properties was investigated. A relationship between the crystalline structure and the Li⁺ intercalation/extraction process, stability and kinetics was observed. A significant decrease in the electrochemical response was observed as a function of the number of cycles for films treated at 400 and 450 °C. However, as the calcination temperature increases this effect disappears. XRD studies shown that at 400 °C, the material is amorphous, evolving to orthorhombic phase. The transmittance variation as well as the coloration efficiency increases as the temperature is increased. In the initial cycles the intercalation charge is higher for the amorphous oxide than for the orthorhombic phase. However, the variation in the optical density is small. On the other hand, the charge of the orthorhombic phase oxide does not change. These results suggest that there are two different processes associated with Li⁺ intercalation, but only one of them leads to the coloration process.     

V2O5/TiO2催化剂表面结构FT-IR发射光谱研究(II)

用傅里哀变换红外发射光谱原位考察了V_2O_5/TiO_2催化剂在制备焙烧过程中担载偏钒酸铵的热分解步骤及其形成的表面活性相结构。偏钒酸铵在200 ℃左右分解, 在300 ℃之前完全转化为晶相V_2O_5。担载于TiO_2上的偏钒酸铵在100 ℃左右与TiO_2已产生强的化学作用, 在200 ℃之前已完全分解。对于10%(质量分数)V_2O_5/TiO_2催化剂其担载偏钒酸分解后在1020 cm~(-1)附近出现晶相V_2O_5的特征峰。但在500 ℃进一步焙烧后晶相V_5O_5的峰减弱并在1025—900 cm~(-1)区出现宽峰, 表明部分晶相V_2O_5可能转化为二维高分散的VO_x物种。2%(质量分数)V_2O_5/TiO_2催化剂在焙烧过程中也显示晶相V_2O_5的弱峰, 但同时也观察到属于VO_x物种的宽峰。进一步降低钒担载量, V_2O_5晶相特征峰逐渐消失, 而在1025—900 cm~(-1)区出现二维VO_x物种的宽峰。结果还表明傅里哀变换红外发射光谱是表征氧化物催化剂表面相结构的一种有力的方法。     

SnO_2改性TiO_2对V_2O_5-WO_3/TiO_2催化剂结构和SCR性能影响

采用共沉淀法将SnO_2组分掺入到V_2O_5-WO_3/TiO_2催化剂载体TiO_2中,并通过多种物理化学手段,考察了不同SnO_2掺入量时对催化剂结构,表面分散物种和SCR性能影响.结果表明,SnO_2掺入到TiO_2中,元素Sn与Ti以Sn—O—Ti键形式相互作用,促进锐钛矿型TiO_2向金红石型TiO_2转变.在特定条件下,VO_x与WO_x物种和SnTi氧化物之间以V—O—Ti(Sn)和W—O—Ti(Sn)键形式相互作用,提高了VO_x物种可还原能力、促进了具有更多B酸酸量四面体WOx物种和V~(5+)物种生成.VW/SnTi催化剂表面VO_x物种与WO_x物种之间的相互作用更强.因此,VW/SnTi催化剂具有更好的SCR活性.     

A combined X-ray and neutron Rietveld study of the chemically lithiated electrode materials Li2.7V3O8 and Li4.8V3O8

The lithium insertion in the positive electrode material Li_1+αV₃O₈ (α close to 0.1-0.2) includes a phenomenon near 2.6 V (voltage vs. the Li metal electrode), the mechanism being a two-phase process with the transformation from ca. Li_2.9V₃O₈ to ca. Li₄V₃O₈. Near 2.4 V down to 2 V, Li is inserted in a single phase up to ca. Li₅V₃O₈. Chemical Li insertions have been performed in a Li_1.1V₃O₈ precursor prepared at 350 °C and the structures of the products Li_2.7V₃O₈ (before the 2.6 V phenomenon) and Li_4.8V₃O₈ (near the expected maximum) have been studied by a combined Rietveld refinement of X-ray and neutron diffraction data. The structure of Li_4.8V₃O₈ is an ordered derivative of the rock-salt type, with all the Li and V ions in slightly distorted octahedral sites. Li_2.7V₃O₈ has a poor crystallization state and, although the expected V₃O₈ layers are obtained, only a part of the Li sites have been reliably determined. Between adjacent V₃O₈ layers, several unidentified sites are likely weakly occupied, thus giving a markedly disordered character for the structure of the compound formed just before the transition at 2.6 V. The atomic shifts at the transition are briefly discussed.     

Effect of the extent of reduction of V2O5 on the adsorption of propylene and the oxidative dehydrogenation of propane to give propylene on V2O5 and V2O5/TiO2-SiO2

An increase in the propylene output in the oxidative dehydration of propane on V₂O₅/TiO₂-SiO₂ was observed after prior reduction of V₂O₅ in the reaction mixture to V₂O₄, which reduces the destructive chemisorption of propylene. A low titanium dioxide content in TiO₂-SiO₂ hinders the deep reduction of V₂O₅ to V₂O₃, which reduces the conversion of propane. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 6, pp. 373–378, November–December, 2007.