Quanyao Zhu

Cost-saving synthesis of vanadium oxide nanotubes

Abstract The synthesis of vanadium oxide nanotubes has been achieved by using V 2 O 5 as vanadium oxide precursor. Due to its low cost, high yield and ease of handling, the synthesis starting from V 2 O 5 provides an advantageous access to large quantity of the tubular vanadium oxide nanotubes.

Raman spectroscopic study of vanadium oxide nanotubes

Abstract Raman-scattering measurements have been used to study the microstructure of vanadium oxide nanotubes (VO x -NTs). The Raman spectra of VO x -NTs reflect the various (group) vibrations of V–O type and lattice vibration of the layered structure as well as organic group vibration of the residual organic template. Moreover, it is confirmed that the residual organic template can be removed by irradiation of laser under the preservation of the tubular morphology, which provides the possibility for favoring the scaling-up of removing the residual organic template in the structure of VO x -NTs.

Effect of modification by poly(ethylene-oxide) on the reversibility of Li insertion/extraction in MoO 3 nanocomposite films

MoO3 xerogel films modified by poly(ethylene-oxide) (PEO) were obtained by combining ion-exchange method with sol-gel technique. Investigations were conducted by X-ray diffractometry (XRD), Fourier transformation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry. The results show that when MoO3 xerogel is modified by the intercalation of PEO, the H atoms in PEO are H-bonded with the O atoms in the Mo=O bonds of MoO3 xerogel, which effectively shields the electrostatic interaction between MoO3 interlayer and Li+ ions. The reversibility of the insertion/extraction of Li+ ions is greatly improved by the modification with PEO of MoO3 nanocomposite films.

Interpenetrating network V2O5 nanosheets/carbon nanotubes nanocomposite for fast lithium storage

Rapid charge and discharge cathode materials for lithium-ion batteries have been commonly researched for the development of electrical mobility applications. Here, an interpenetrating network vanadium pentoxide (V2O5) nanosheets/carbon nanotubes (CNTs) nanocomposite was fabricated by a freeze-drying process. Field emission scanning electron microscopy and transmission electron microscopy tests indicated that the CNTs and V2O5 nanosheets form an interpenetrating network structure. X-ray diffraction and X-ray photoelectron spectroscopy analyses confirmed that the V2O5 nanosheets exhibit orthorhombic crystal structure and mixed element states in the nanocomposite. The electrochemical properties of the V2O5 nanosheets/CNTs nanocomposite were studied by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements. The results indicated that the V2O5 nanosheets/CNTs nanocomposite exhibits high specific capacity and good cycling stability. The initial specific capacity of the V2O5 nanosheets/CNTs nanocomposite is 130.7 mA h g−1 for a current density up to 5.0 A g−1 and remains at 100.1 mA h g−1 after 100 cycles.

LOW-COST SYNTHESIS OF NOVEL VANADIUM DIOXIDE NANORODS

The synthesis of novel vanadium dioxide nanorods has been achieved by using V2O5 and cetyltrimethyl ammonium bromide (CTAB) in a sol–gel reaction followed by hydrothermal treatment. Morphology and structure of the sample as well as vanadium oxidation state were characterized by XRD, SEM, HRTEM, ESR, XPS and redox titration. The results show that the products are monoclinic (C/2m) B phase VO2 nanorods and they are 1~2 μm in length. HRTEM micrographs reveal that they indeed form bundles of agglomerated smaller filaments with diameters ranging from 20 to 40 nm besides single nanorod. This filament-like shape in the nanoscale dimension leads to the exposure of a large fraction of the atoms to the surface. Thus, these materials are promising candidates for the development of new functionalized materials. CTAB not only generates a reducing atmosphere, but also plays a key role in the growth of the nanorods. The simplicity of hydrothermal process, as well as cheapness and availability of raw materials are advantages of this method.

INFLUENCE OF SURFACE MODIFICATION ON STRUCTURE AND ELECTROCHEMICAL PERFORMANCE OF LINI0.5CO0.5VO4

The electrochemical stability of LiNi0.5Co0.5VO4 is improved by sol–gel coating with an amorphous SiO2 film. This limits direct contact between LiNi0.5Co0.5VO4 and electrolyte, and thus, effectively provides the structural stability for the electrochemically active intercalation compound LiNi0.5Co0.5VO4, resulting in improved specific capacity and cycling performance.

Understanding the Electrochemical Formation and Decomposition of Li2O2 and LiOH with Operando X-ray Diffraction

The lithium air, or Li–O2, battery system is a promising electrochemical energy storage system because of its very high theoretical specific energy, as required by automotive applications. Fundamental research has resulted in much progress in mitigating detrimental (electro)chemical processes; however, the detailed structural evolution of the crystalline Li2O2 and LiOH discharge products, held at least partially responsible for the limited reversibility and poor rate performance, is hard to measure operando under realistic electrochemical conditions. This study uses Rietveld refinement of operando X-ray diffraction data during a complete discharge–charge cycle to reveal the detailed structural evolution of Li2O2 and LiOH crystallites in 1,2-dimethoxyethane (DME) and DME/LiI electrolytes, respectively. The anisotropic broadened reflections confirm and quantify the platelet crystallite shape of Li2O2 and LiOH and show how the average crystallite shape evolves during discharge and charge. Li2O2 is shown to form via a nucleation and growth mechanism, whereas the decomposition appears to start at the smallest Li2O2 crystallite sizes because of their larger exposed surface. In the presence of LiI, platelet LiOH crystallites are formed by a particle-by-particle nucleation and growth process, and at the end of discharge, H2O depletion is suggested to result in substoichiometric Li(OH)1–x, which appears to be preferentially decomposed during charging. Operando X-ray diffraction proves the cyclic formation and decomposition of the LiOH crystallites in the presence of LiI over multiple cycles, and the structural evolution provides key information for understanding and improving these highly relevant electrochemical systems.

Synthesis and ion-selective properties of NH4V3O8 microcrystals

Microcrystals of ammonium trivanadate with belt-like morphology of particles have been synthesized by hydrothermal treatment of NH4VO3 (T = 140°C, 48 h) in the presence of acetic acid (pH 4). The average particle length is 7.4 ± 21.3 μm, the average width is 2–15 μm, and the average thickness is 600–900 nm. The IR spectra and thermal stability of NH4V3O8 have been studied. A solid film electrode with an ion-sensitive membrane based on NH4V3O8 exhibits ammonium function in the range

Nanocomposites of V1.67M0.33O5±δ·nH2O (M = Ti or Mo) xerogels intercalated with hydroquinone and poly(vinyl alcohol)

1 \leqslant pC_{NH_4^ + } \leqslant 4