Morphological Evolution of (NH4)0.5V2O5·mH2O Fibers into Belts, Triangles, and Rings

Valid design and evaluation of cathode and anode materials of aqueous zinc ion batteries with high-rate capability and cycle stability

Although non-aqueous lithium-ion batteries have a high gravimetric density, aqueous zinc-ion batteries (ZIBs) have recently been in the spotlight as an alternative, because ZIBs have characteristics such as high volumetric density, high ionic conductivity, eco-friendliness, low cost, and high safety. However, the improvement in electrochemical performance is limited due to insufficient rate capability and severe cycle fading of the vanadium-oxide-based cathode and zinc-metal-based anode material, which are frequently used as active materials for ZIBs. In addition, complex methods are required to prepare high-performance cathode and anode materials. Therefore, a simple yet effective strategy is needed to obtain high-performance anodes and cathodes. Herein, an ammonium vanadate nanofiber (AVNF) intercalated with NH₄⁺ and H₂O as a cathode material for ZIBs was synthesized within 30 minutes through a facile sonochemical method. In addition, an effective Al₂O₃ layer of 9.9 nm was coated on the surface of zinc foil through an atomic layer deposition technique. As a result, AVNF//60Al₂O₃@Zn batteries showed a high rate capability of 108 mA h g^-1 even at 20 A g^-1, and exhibited ultra-high cycle stability with a capacity retention of 94% even after 5000 cycles at a current density of 10 A g^-1.

Single-Crystal Inorganic Helical Architectures Induced by Asymmetrical Defects in Sub-Nanometric Wires

Constructing single-crystal inorganic helical structures is a fascinating subject for a large variety of research fields. However, the driving force of self-coiling, particularly in helical architectures, still remains a major challenge. Here, using MoO_3-x sub-nanometric wires (SNWs) as an example, we identified that spontaneous helical architecture with different dimensional features is closely related with their surface asymmetrical defects. Specifically, the surface defects of SNWs are critical to produce the self-coiling process, thereby achieving the ordered helical conformations. Theoretical calculations further suggest that the formation of in-plane and out-of-plane coiling structures is determined by the asymmetrical distribution of the surface defects, and the inhomogeneous charge separation with strong Coulomb attraction dominates the different structural configurations. The resulting MoO_3-x SNW exhibits excellent photothermal behaviors in both aqueous solutions and hydrogel matrixes. Our study provides a novel protocol to achieve helical structure design for their future applications.

Exploring new hydrated delta type vanadium oxides for lithium intercalation

Three hydrated double layered vanadium oxides, namely Na_0.35V₂O₅·0.8(H₂O), K_0.36(H₃O)_0.15V₂O₅ and (NH₄)_0.37V₂O₅·0.15(H₂O), were obtained by using mild hydrothermal conditions. Their delta type structural frameworks were solved by high-resolution synchrotron X-ray powder diffraction and the interlayer spacings were interpreted from difference Fourier maps. The inter-slab distances are modulated by the water content and the special arrangements of the alkali and ammonium cations. The XPS measurements denote mixed valence systems with high contents of V⁴⁺ ions up to 40%. The monitoring of the V⁴⁺ EPR signal over time suggests a reduction of the electronic delocalization on account of the partial oxidation to V⁵⁺. The electrochemical performance of the active phases is strongly conditioned by the vacuum-drying process of the electrodes, showing better capacity retention when vacuum is not applied. In situ X-ray diffraction shows a structural mechanism of contraction/expansion of the bilayers upon lithium insertion/extraction where the alkali ions behave as structural stabilizers. Galvanostatic cycling at very low current density implies migration of the alkali "pillars" triggering the collapse of the structure.

Impact of Cu doping on the structural, morphological and optical activity of V2O5 nanorods for photodiode fabrication and their characteristics

In this paper, we report a wet chemical precipitation method used to synthesize pure and Cu-doped V2O5 nanorods with different doping concentrations (Cu x V2O5 where x = 3, 5 or 7 at%), followed by annealing at 600 °C and characterizations using several techniques. Indeed, a growth mechanism explaining the morphological evolution under the experimental conditions is also proposed. The XRD patterns revealed that all of the studied samples consist of a single V2O5 phase and are well crystallized with a preferential orientation towards the (200) direction. The presence of intrinsic defects and internal stresses in the lattice structure of the Cu x V2O5 samples has been substantiated by detailed analysis of the XRD. Apart from the doping level, there was an assessment of identical tiny peaks attributed to the formation of a secondary phase of CuO. SEM images confirmed the presence of agglomerated particles on the surface; the coverage increased with Cu doping level. XPS spectral analysis showed that Cu in the V5+ matrix exists mainly in the Cu2+ state on the surface. The appearance of satellite peaks in the Cu 2p spectra, however, provided definitive evidence for the presence of Cu2+ ions in these studied samples as well. Doping-induced PL quenching was observed due to the absorption of energy from defect emission in the V5+ lattice by Cu2+ ions. We have proposed a cost-effective, less complicated but effective way of synthesizing pure and doped samples in colloidal form, deposited by the nebulizer spray technique on p-Si to establish junction diodes with enhanced optoelectronic properties.

A rationally designed self-standing V2O5 electrode for high voltage non-aqueous all-solid-state symmetric (2.0 V) and asymmetric (2.8 V) supercapacitors

The maximum capacitive potential window of certain pseudocapacitive materials cannot be accessed in aqueous electrolytes owing to the low dissociation potential of 1.2 V possessed by water molecules. However, the inferior pseudocapacitance exhibited by the commonly used electrode materials when integrated with non-aqueous electrolytes still remains a challenge in the development of supercapacitors (SC). Proper selection of materials for the electrode and a rational design process are indeed important to overcome these practical intricacies so that such systems can perform well with non-aqueous electrolytes. We address this challenge by fabricating a prototype all-solid-state device designed with high-capacitive V2O5 as the electrode material along with a Li-ion conducting organic electrolyte. V2O5 is synthesized on a pre-treated carbon-fibre paper by adopting an electrochemical deposition technique that effects an improved contact resistance. A judicious electrode preparation strategy makes it possible to overcome the constraints of the low ionic and electrical conductivities imposed by the electrolyte and electrode material, respectively. The device, assembled in a symmetrical fashion, achieves a high specific capacitance of 406 F g-1 (at 1 A g-1). The profitable aspect of using an organic electrolyte is also demonstrated with an asymmetric configuration by using activated carbon as the positive and V2O5 as the negative electrode materials, respectively. The asymmetric device displays a wide working-voltage window of 2.8 V and delivers a high energy density of 102.68 W h kg-1 at a power density of 1.49 kW kg-1. Moreover, the low equivalent series resistance of 9.9 Ω and negligible charge transfer resistance are observed in the impedance spectra, which is a key factor that accounts for such an exemplary performance.

In situ soft-chemistry synthesis of β-Na0.33V2O5 nanorods as high-performance cathode for lithium-ion batteries

β-Na_0.33V₂O₅ nanorods were prepared via a facile soft-chemistry strategy using Na⁺ intercalated (NH₄)_0.5V₂O₅ nanosheets as precursor.

Surfactant Effects on the Morphology and Pseudocapacitive Behavior of V2 O5 ⋅H2 O

To overcome the drawback of low electrical conductivity within supercapacitor applications, several surfactants are used for nanoscale V2 O5 to enhance the specific surface area. Polyethylene glycol 6000 (PEG-6000), sodium dodecylbenzene sulfonate (SDBS), and Pluronic P-123 (P123) controllers, if used as soft templates, easily form large specific surface area crystals. However, the specific mechanism through which this occurs and the influence of these surfactants is not clear for V2 O5 ⋅H2 O. In the present study, we aimed to investigate the mechanism of crystal growth through hydrothermal processes and the pseudocapacitive behavior of these crystals formed by using diverse surfactants, including PEG-6000, SDBS, and P123. Our results show that different surfactants can dramatically influence the morphology and capacitive behavior of V2 O5 ⋅H2 O powders. Linear nanowires, flower-like flakes, and curly bundled nanowires can be obtained because of electrostatic interactions in the presence of PEG-6000, SDBS, and P123, respectively. Furthermore, the electrochemical performance of these powders shows that the nanowires, which are electrodes mediated by PEG-6000, exhibit the highest capacitance of 349 F g(-1) at a scan rate of 5 mV s(-1) of all the surfactants studied. However, a symmetric P123 electrode comprising curly bundled nanowires with numerous nanopores showed an excellent and stable specific capacitance of 127 F g(-1) after 200 cycles. This work is beneficial to understanding the fundamental role of the surfactant in the assisted growth of V2 O5 ⋅H2 O and the resulting electrochemical properties of the pseudocapacitors, which could be useful for the future design of appropriate materials.

Rational design of one-dimensional vanadium(v) oxide nanocrystals: an insight into the physico-chemical parameters controlling the crystal structure, morphology and size of particles

This highlight deals with the recent advances on the synthesis in aqueous solution of one-dimensional vanadium(v) oxide nanocrystals.