Coupling interconnected MoO3/WO3 nanosheets with a graphene framework as a highly efficient anode for lithium-ion batteries

Localized nitride strategy to construct interfacial and electronic modulated WO3/WN nanoparticles for superior lithium-ion storage

The interfacial effect is important for the tungsten trioxide (WO3)-based anode to achieve superior lithium-ion storage performance. Herein, the interfacial effect was constructed by in-situ surface direct nitridation reaction at 600 ℃ for 30 min of the as-synthesis WO3 nanoparticles (WO3/WN). X-ray photoelectron spectroscopy (XPS) analysis confirms evident chemical interaction between WO3 and WN via the interfacial covalent bond (WON). This WO3/WN anode shows a distinct interfacial effect for an efficient interatomic electron migration. Electrochemical kinetic analysis shows enhanced pseudocapacitance contribution. The galvanostatic intermittent titration technique (GITT) result demonstrates improved charge transfer kinetics. Ex-situ X-ray diffraction (XRD) analysis reveals the reversible oxidation and reduction reaction of the WO3/WN anode. The density functional theory (DFT) result shows that the evident interfacial bonding effect can enhance the electrochemical reaction kinetics of the WO3/WN anode. The discharge capacity can reach up to 546.9 mA h g-1 at 0.1 A g-1 after 200 cycles. After 2000 cycles, the capacity retention is approximately 85.97 % at 1.0 A g-1. In addition, the WO3/WN full cell (LiFePO4/C//WO3/WN) demonstrates excellent rate capability and capacity retention ratio. This in-situ surface nitridation strategy is an effective solution for designing an oxide-based anode with good electrochemical performance and beyond.

The valance state of vanadium-key factor in the flexibility of potassium vanadates structure as cathode materials in Li-ion batteries

Potassium hexavanadate (K₂V₆O₁₆·nH₂O) nanobelts have been synthesized by the LPE-IonEx method, which is dedicated to synthesis of transition metal oxide bronzes with controlled morphology and structure. The electrochemical performance of K₂V₆O₁₆·nH₂O as a cathode material for lithium-ion batteries has been evaluated. The KVO nanobelts demonstrated a high discharge capacity of 260 mAh g⁻¹, and long-term cyclic stability up to 100 cycles at 1 A g⁻¹. The effect of the vanadium valence state and unusual construction of the nanobelts, composed of crystalline and amorphous domains arranged alternately were also discussed in this work. The ex-situ measurements of discharged electrode materials by XRD, MP-AES, XAS and XPS show that during the subsequent charge/discharge cycle the potassium in the K₂V₆O₁₆·nH₂O structure are replacing by lithium. The structural stability of the potassium hexavandate during cycling depends on the initial vanadium valence state on the sample surface and the presence of the “fringe free” domains in the K₂V₆O₁₆·nH₂O nanobelts.

An Easy and Ecological Method of Obtaining Hydrated and Non-Crystalline WO3-x for Application in Supercapacitors

In this work, we report the synthesis of hydrated and non-crystalline WO₃ flakes (WO_3−x) via an environmentally friendly and facile water-based strategy. This method is described, in the literature, as exfoliation, however, based on the results obtained, we cannot say unequivocally that we have obtained an exfoliated material. Nevertheless, the proposed modification procedure clearly affects the morphology of WO₃ and leads to loss of crystallinity of the material. TEM techniques confirmed that the process leads to the formation of WO₃ flakes of a few nanometers in thickness. X-ray diffractograms affirmed the poor crystallinity of the flakes, while spectroscopic methods showed that the materials after exfoliation were abundant with the surface groups. The thin film of hydrated and non-crystalline WO₃ exhibits a seven times higher specific capacitance (C_s) in an aqueous electrolyte than bulk WO₃ and shows an outstanding long-term cycling stability with a capacitance retention of 92% after 1000 chronopotentiometric cycles in the three-electrode system. In the two-electrode system, hydrated WO_3−x shows a C_s of 122 F g⁻¹ at a current density of 0.5 A g⁻¹. The developed supercapacitor shows an energy density of 60 Whkg⁻¹ and power density of 803 Wkg⁻¹ with a decrease of 16% in C_sp after 10,000 cycles. On the other hand, WO_3−x is characterized by inferior properties as an anode material in lithium-ion batteries compared to bulk WO₃. Lithium ions intercalate into a WO₃ crystal framework and occupy trigonal cavity sites during the electrochemical polarization. If there is no regular layer structure, as in the case of the hydrated and non-crystalline WO₃, the insertion of lithium ions between WO₃ layers is not possible. Thus, in the case of a non-aqueous electrolyte, the specific capacity of the hydrated and non-crystalline WO₃ electrode material is much lower in comparison with the specific capacity of the bulk WO₃-based anode material.

Review on Recent Progress in the Development of Tungsten Oxide Based Electrodes for Electrochemical Energy Storage

Current progress in the advancement of energy-storage devices is the most important factor that will allow the scientific community to develop resources to meet the global energy demands of the 21st century. Nanostructured materials can be used as effective electrodes for energy-storage devices because they offer various promising features, including high surface-to-volume ratios, exceptional charge-transport features, and good physicochemical properties. Until now, the successful research frontrunners have focused on the preparation of positive electrode materials for energy-storage applications; nevertheless, the electrochemical performance of negative electrodes is less frequently reported. This review mainly focuses on the current progress in the development of tungsten oxide-based electrodes for energy-storage applications, primarily supercapacitors (SCs) and batteries. Tungsten is found in various stoichiometric and nonstoichiometric oxides. Among the different tungsten oxide materials, tungsten trioxide (WO₃ ) has been intensively investigated as an electrode material for different applications because of its excellent charge-transport features, unique physicochemical properties, and good resistance to corrosion. Various WO₃ composites, such as WO₃ /carbon, WO₃ /polymers, WO₃ /metal oxides, and tungsten-based binary metal oxides, have been used for application in SCs and batteries. However, pristine WO₃ suffers from a relatively low specific surface area and low energy density. Therefore, it is crucial to thoroughly summarize recent progress in utilizing WO₃ -based materials from various perspectives to enhance their performance. Herein, the potential- and pH-dependent behavior of tungsten in aqueous media is discussed. Recent progress in the advancement of nanostructured WO₃ and tungsten oxide-based composites, along with related charge-storage mechanisms and their electrochemical performances in SCs and batteries, is systematically summarized. Finally, remarks are made on future research challenges and the prospect of using tungsten oxide-based materials to further upgrade energy-storage devices.