Amorphous V2O5 Research Articles

Enhanced pseudocapacitive Li+ charge storage on lithium-rich disordered rock salt vanadium oxide nanocrystalline

Cation disordered rock-salt (DRS) metal compounds, featuring a three-dimensional percolation network for Li+ transportation, have attracted extensive attention as novel anode candidates for high-power lithium-ion batteries (LIBs) and capacitors (LICs). However, their low capacity and poor conductivity remain bottlenecks for their wide-scale usage, especially for high-energy applications. Here, we report a nanocrystal DRS Li3V2O5 (a-DRS-LVO) achieved by an electrochemically induced transformation on amorphous V2O5. The nanocrystalline phase of a-DRS-LVO can provide large active sites for Li+, leading to a surface-controlled solid-state Li+ diffusion behavior. In particular, the specific capacity for a-DRS-LVO reaches 716.8mAh g−1 at 0.1 A/g, exceeding that of DRS-LVO achieved by electrochemically induced transformation on well-crystallized V2O5. Further, a-DRS-LVO can work stably over 1,200 charge–discharge cycles with negligible capacity decay, due to the highly structural integrity stability, no phase change and limited volume change (∼8.2 %). A LIC with this a-DRS-LVO anode yields both high energy density (183 Wh kg−1) and power density (50,000 W kg−1), which are much higher than that of the state-of-art LICs based on graphite and other pseudocapacitive anodes, such as niobium and titanium oxides.

Advancing zinc-ion batteries: Amorphous V2O5 as a protective layer on Zn anode surface

Recently, Zn-ion batteries (ZIBs) have emerged as prominent solutions for next-generation rechargeable batteries due to abundant Zn resources and the reduced explosion risk associated with aqueous electrolytes. Nonetheless, the low charge–discharge performance of ZIBs due to the corrosive interactions between mildly acidic aqueous electrolytes and Zn anodes, as well as dendrite growth, limit their further application. To mitigate these degradation effects, this study incorporates an amorphous phase V2O5-coated Zn (AVO-Zn) anode into ZIBs. The amorphous phase V2O5 enhances the wettability of the Zn anode and mitigates hydrogen evolution and corrosion, enabling high stability of the anode over 500 h with a low overpotential of 42 mV during symmetric cell analysis. Furthermore, by providing flat Zn plating by increasing the number of nucleation sites to inhibit dendrite formation, the AVO-Zn anode achieves a high energy density of 236 Wh kg−1 at a power density of 270 W kg−1 and good long-term cyclability with a high specific capacity of 136 mAh g−1 after 200 cycles.

Phase transformation concurrent to charge storage governing electrochemical thermopower in amorphous and crystalline V2O5

Under urgent threat of global climate change, pressing need for efficient energy harvesting solutions exists. Electrochemical waste heat harvesting using solid electrodes offers a promising potential due to its high energy density. Yet, strategies for enhancing electrochemical thermopower in solid electrodes remain unidentified. Here, we investigate the LixV2O5 material system with controllably differentiated charge storage mechanisms and phase change behaviors. We show that concurrent phase transitions during lithiation significantly enhance the electrochemical thermopower to 1.04 mV/K, compared to 0.14 mV/K without phase transition. This discovery provides valuable insights into enhancing electrochemical thermopower for improved efficiency, underscoring the importance of mechanisms that facilitate entropy exchange, as demonstrated by the phase transformations.

Structural Properties of Amorphous Vanadium Pentoxide Under Compression

Structural properties of amorphous vanadium pentoxide (V2O­5) under compression investigated by molecular dynamics simulation. The simulated amorphous V2O5 is composed of basic structural units of type VO5, VO6 at low-pressure and VO6, VO7 at high-pressure. These basic structural units connected by vertex-, edge- and face- shared links to form a structural network. The random distribution of atom and void clusters leading to a high degree of disorder in the V2O5 structure. Under compression, the fraction of average vertex-, edge- and face- shared links increased strongly. The number of VCs and VTs also increases as the large voids are divided into smaller voids. Our results also elucidated the decreasing of cross-section and increasing of length in VTs are main causes for increasing ion conductivity of the amorphous V2O5.

Demystifying the Semiconductor‐to‐Metal Transition in Amorphous Vanadium Pentoxide: The Role of Substrate/Thin Film Interfaces

AbstractThe precise mechanism governing the reversible semiconductor‐to‐metal transition (SMT) in V2O5 remains elusive, yet its investigation is of paramount importance due to the remarkable potential of V2O5 as a versatile “smart” material in advancing optoelectronics, plasmonics, and photonics. In this study, distinctive experimental insights into the SMT occurring in amorphous V2O5 through the application of highly sensitive, temperature‐dependent, in situ analyses on a V2O5 thin film deposited on soda‐lime glass are presented. The ellipsometry measurements reveal that the complete SMT occurs at ≈340 °C. Remarkably, the refractive index and extinction coefficients exhibit reversible characteristics across visible and near‐infrared wavelengths, underscoring the switch‐like behavior inherent to V2O5. The findings obtained from ellipsometry are substantiated by calorimetry and in situ secondary ion mass spectrometry analyses. In situ electron microscopy observations unveil a separation of oxidation states within V2O5 at 320 °C, despite the thin film retaining its amorphous state. The comprehensive experimental investigations effectively demonstrate that alterations in electronic state can trigger the SMT in amorphous V2O5. It is revealed for the first time that the SMT in V2O5 is solely contingent upon electronic state changes, independent of structural transitions, and importantly, it is a reversible transformation within the amorphous state itself.

Emerging Amorphous to Crystalline Conversion Chemistry in Ca-Doped VO2 Cathodes for High-Capacity and Long-Term Wearable Aqueous Zinc-Ion Batteries.

Amorphous transition metal oxides have attracted significant attention in energy storage devices owing to their potentially desirable electrochemical properties caused by abundant unsaturated dangling bonds. However, the amorphization further amplifies the shortcoming of the poor intrinsic electronic conductivity of the metal oxides, resulting in unsatisfying rate capability and power density. Herein, freestanding amorphous Ca-doped V2 O5 (a-Ca-V2 O5 ) cathodes are successfully prepared via in situ electrochemical oxidation of Ca-doped VO2 nanoarrays for wearable aqueous zinc-ion batteries. The doping of Ca and construction of freestanding structure effectively uncover the potential of amorphous V2 O5 , which can make full use of the abundant active sites for high volumetric capacity and simultaneously achieve fast reaction kinetics for excellent rate performance. More importantly, the introduction of Ca can notably reduce the formation energy of VO2 according to theoretical calculation results and realizes amorphous to crystalline reversible conversion chemistry in the charge/discharge procedure, thereby facilitating the reversible capacity of the newly developed a-Ca-V2 O5 . This work provides an innovative design strategy to construct high-rate capacity amorphous metal oxides as freestanding electrodes for low-cost and high-safe wearable energy-storage technology.

In situ XRD and Raman study of the phase transition in V2O5 xerogels

Vanadium oxide xerogel samples (V2O5∙nH2O) were successfully synthesized using a liquid phase reaction between α-V2O5 and H2O2, as well as through the interaction of amorphous V2O5 films with atmospheric water. The samples were systematically investigated by X-ray diffraction and Raman spectroscopy. Temperature-dependent studies confirmed the existence of two distinct phases. Depending on synthesis and processing protocols, either phase can be stabilized in ambient conditions. It was proved that the formation of a high-temperature phase from amorphous vanadium oxide previously led to some misinterpretations associated with the high-pressure δ-V2O5 polymorph. While current structural models of vanadium oxide xerogel provide some insights, our findings underscore the exciting potential for refining and expanding these models in future research endeavors.

Stabilization of the VO2(M2) Phase and Change in Lattice Parameters at the Phase Transition Temperature of WXV1-XO2 Thin Films.

Various methods have been used to fabricate vanadium dioxide (VO2) thin films exhibiting polymorph phases and an identical chemical formula suited to different applications. Most fabrication techniques require post-annealing to convert the amorphous VO2 thin film into the VO2 (M1) phase. In this study, we provide a temperature-dependent XRD analysis that confirms the change in lattice parameters responsible for the metal-to-insulator transition as the structure undergoes a monoclinic to the tetragonal phase transition. In our study, we deposited VO2 and W-doped VO2 thin films onto silica substrates using a high repetition rate (10 kHz) fs-PLD deposition without post-annealing. The XRD patterns measured at room temperature revealed stabilization of the monoclinic M2 phase by W6+ doping VO2. We developed an alternative approach to determine the phase transition temperatures using temperature-dependent X-ray diffraction measurements to evaluate the a and b lattice parameters for the monoclinic and rutile phases. The a and b lattice parameters versus temperature revealed phase transition temperature reduction from ∼66 to 38 °C when the W6+ concentration increases. This study provides a novel unorthodox technique to characterize and evaluate the structural phase transitions seen on VO2 thin films.

Operando crystal-amorphous transformation cathode for enhanced zinc storage

Aqueous zinc-ion batteries have obtained broad attention due to their high safety, eco-friendliness, and low cost. However, they are still in the developing stage considering the limited candidate of high-performance cathode materials. Furthermore, the intrinsic storage zinc mechanism is also needed to uncover. Here, we propose an operando crystal-amorphous transformation of tunnel-type VOOH and the obtained amorphous V2O5 serves as a high-performance zinc-ion battery cathode. In-situ X-ray diffraction corroborates the unique operando crystal-amorphous transformation of VOOH during the initial charging process. X-ray photoelectron spectroscopy and transmission electron microscopy further demonstrate the element valence evolution and the lattice structure change, respectively. The operando electrochemical crystal-amorphous transformation allows the obtained amorphous V2O5 to achieve the high capacity of ∼ 350.7 mAh g−1, rate performance (151.2 mAh g−1 at 6.4 A g−1), energy and power densities (137 Wh kg−1 at 6831 W kg−1), unveiling a promising approach of cathode materials via operando crystal-amorphous transformation to achieve the enhanced zinc storage.

Electrochemical investigation of ZnO effect of amorphous V2O5–P2O5 glassy electrodes

Electrochemical investigation of ZnO effect of amorphous V2O5–P2O5 glassy electrodes

In Situ Electrochemical Tuning of MIL‐88B(V)@rGO into Amorphous V2O5@rGO as Cathode for High‐Performance Aqueous Zinc‐Ion Battery

AbstractThe design and fabrication of advanced cathode materials with excellent electrochemical properties to match the Zn anode is crucial for the development of aqueous zinc‐ion batteries (ZIBs). Herein the synthesis of MIL‐88B(V)@rGO composites is reported, in which MIL‐88B(V) nanorods are anchored on reduced graphene oxide (rGO) sheets, as cathode for ZIBs, where the graphene oxide induces the formation of small‐size nanorods instead of typical prism morphology. During the initial charge/discharge process, the cathode undergoes an in situ irreversible transformation from MIL‐88B(V) to amorphous V2O5 that acts as active site for the subsequent Zn2+ insertion/extraction. The hierarchical structure of the composites and the amorphous V2O5 provide abundant channels and active sites for Zn2+ diffusion and adsorption. The density functional theory calculation reveals that the rGO sheets have two functions, i.e., to improve the conductivity and to reduce the Zn2+ migration energy barrier. Consequently, the MIL‐88B(V)@rGO cathode exhibits an ultrahigh reversible capacity of 479.6 mAh g−1 at 50 mA g−1 and good rate performance of 263.6 mAh g−1 at 5000 mA g−1, which are superior to metal–organic frameworks (MOFs) cathodes reported in literature. This work may shed a new light to the design and fabrication of MOFs‐based cathodes for aqueous ZIBs.

Crafting amorphous VO2–crystalline NiS2 heterostructures as bifunctional electrocatalysts for efficient water splitting: The different cocatalytic function of VO2

The rational design of bifunctional electrocatalysts is essential to achieve efficient hydrogen production from water splitting. Here, inspired by cocatalysts widely utilized in photocatalysis, we designed a heterostructure comprising amorphous VO2 and crystalline NiS2, aiming at using VO2 cocatalyst to boost activity of NiS2 for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Intriguingly, we found that VO2 displayed different co-catalytic function in boosting the OER and HER. Specifically, the VO2 optimized the binding energy of hydrogen intermediate on NiS2 and thus improved the HER activity. As for the OER, the amorphous VO2 was easily dissolved in the KOH electrolyte, resulting in the generation of abundant oxygen vacancies in the in-situ generated active phase of NiOOH from NiS2, thereby drastically enhancing the OER activity. Consequently, the obtained VO2–NiS2@CC displayed excellent performance for overall water splitting, with a low voltage of 1.53 V at 10 mA cm−2.

In-situ preparation of amorphous VO2@rGO cathode for ultra-high capacity and ultra-long cycle life aqueous zinc ion batteries

Aqueous zinc-ion batteries (AZIBs) are considered as a promising alternative to lithium-ion batteries for stationary energy storage due to their environmental benignity and cost-effectiveness. However, the development of AZIBs continues to be plagued by a lack of cathode materials with high specific capacity and superior lifetime. Herein, we in-situ synthesize amorphous VO2@rGO assisted by controlling the charging cut-off voltage. Experimental results and theoretical calculations confirm that the amorphous VO2(A)@rGO can effectively reduce the migration energy barrier of Zn2+, improve the conductivity of the electrode, and promote the insertion/extraction of Zn2+. Consequently, the Zn//VO2(A)@rGO battery exhibits an ultra-high specific capacity of 527.0 mAh·g−1 at 1 A·g−1 after 100 cycles, an ultra-long cycle stability of 183.4 mAh·g−1 at 20 A·g−1 after 30,000 cycles, and an energy of 316.1 Wh·Kg−1 at a power density of 6082.9 W·Kg−1 power density. Meanwhile, we reveal that the amorphous VO2@rGO electrode follows a hybrid mechanism of classical Zn2+ insertion/de-insertion and the reversible phase transition from amorphous VO2 to V2O3. This study highlights that in-situ preparation of amorphous VO2@rGO cathode materials by controlling the charging voltage interval, opening up further possibilities for the development of high-performance AZIB cathodes.

Rationally designed hierarchical three-dimensional amorphous V2O5@Ti3C2Tx microsphere for high performance aqueous zinc-ion batteries

As candidates of the next generation batteries, aqueous zinc-ion batteries (ZIBs) have drawn widespread attention owing to the advantages of environmental friendliness, low cost and ultrahigh theoretical capacity. In order to obtain superior zinc ions (Zn2+) storage ability, the cathode materials with eminent electrochemical property are placed great expectations. Herein, the hierarchical 3D a-V2O5@Ti3C2Tx microsphere is prepared by a simple spray drying process. In the heterostructure, the amorphous V2O5 not only endows abundant active sites for Zn2+ storage but also effectively alleviates Ti3C2Tx MXene nanosheets restacking. Meanwhile, the presence of conductive Ti3C2Tx MXene framework significantly enhances the conductivity and reaction kinetics of the electrode material. As a result, the 3D a-V2O5@Ti3C2Tx exhibits an impressive Zn2+ storage ability, including the high reversible capacity (604 mAh g−1 at 0.5 A g−1), the superior rate performance and the splendid cycling stability. Furthermore, the relevant mechanism is illustrated via various characterizations. Moreover, the as-fabricated pouch ZIBs based on the 3D a-V2O5@Ti3C2Tx displays a potential practical application prospect as flexible energy storage devices. Hence, this work may provide an inspiration for the rational design of high performance ZIBs cathode materials.

A simple solution method to prepare VO2:Co2+ precursors for thin film deposition by solution-processing method

Solution-processing is a low-cost solution method to preparea variety of organic or inorganic thin films. For metal oxide compounds, a solution-processing solution of an organometallic compound is frequently used as a precursor to be spin coated, followed by a thermal annealing to form metal oxide. In this work, vanadium oxide powders are obtained from a simple acid-base reaction, and then they are dispersed in isopropyl alcohol to form a solution for spin-coating. Different amount of cobalt salt are also added together with VOx into isopropyl alcohol to form VOx:Co2+ solutions. After thermal annealing at 200 °C, continuous transparent thin films are obtained. Optical, structural, morphological and chemical binding energies of those films are analyzed. It is found that amorphous VO2:Co2+ compound is formed in those films with V:Co atomic ratios between 6.6:1 and 1.6:1. Optical absorption onsets of those films are around 2.3 eV. An interesting interconnected porous morphology is observed when the atomic ratio of V:Co is around 4.9:1. It is concluded that porous amorphous cobalt doped vanadium oxide thin films can be obtained from a spin-coating process at low annealing temperature from a simple solution without any complex agent.

Electrochemical oxidation endows VN/V3S4 heterostructure with high performance in aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZBs) draw significant attention owing to their unique advantages such as high safety, facile assembly, and low cost, profiting from the intrinsic properties of water-based electrolytes and the zinc metal anode. However, cathode materials suffer from slow zinc ion diffusion and low electronic conductivity, thereby limiting the improvement of electrochemical performance. Herein, we proposed an advanced heterostructure composite consisting of vanadium nitride and V3S4 (VN/V3S4). Compared with pure V3S4, the VN/V3S4 composite can achieve preferable rate capability and cyclic durability. These improvements are attributed to the collaborative effect between V3S4 and VN, which could effectively reduce the diffusion energy barrier and enhance conductivity, as demonstrated by density functional theory (DFT) calculations. Moreover, to achieve high charge-storage performance, the VN/V3S4 heterostructure was activated using an in-situ electrochemical oxidational process. After electrochemical oxidation process, the formed O-VN/V3S4 is endowed with abundant active sites originating from the amorphous V2O5, while holds the advantages of VN/V3S4 heterostructure. As demonstrated by electrochemical tests, the O-VN/V3S4 cathode displayed outstanding rate capability and exceptional cyclic stability, in which a reversible capacity of 115.4 mA h g−1 can be sustained after 4000 cycles at 10 A g−1.

Phase-engineered cathode for super-stable potassium storage

The crystal phase structure of cathode material plays an important role in the cell performance. During cycling, the cathode material experiences immense stress due to phase transformation, resulting in capacity degradation. Here, we show phase-engineered VO2 as an improved potassium-ion battery cathode; specifically, the amorphous VO2 exhibits superior K storage ability, while the crystalline M phase VO2 cannot even store K+ ions stably. In contrast to other crystal phases, amorphous VO2 exhibits alleviated volume variation and improved electrochemical performance, leading to a maximum capacity of 111 mAh g−1 delivered at 20 mA g−1 and over 8 months of operation with good coulombic efficiency at 100 mA g−1. The capacity retention reaches 80% after 8500 cycles at 500 mA g−1. This work illustrates the effectiveness and superiority of phase engineering and provides meaningful insights into material optimization for rechargeable batteries.

In situ constructing amorphous V2O5@Ti3C2Tx heterostructure for high-performance aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries are emerged as fascinating “beyond Li-ion” battery technologies for large-scale energy storage due to low cost, high theoretical capacity, high safety and environmental friendliness. However, developing cathode materials with outstanding electrochemical performance are prerequisites. Herein, the a-V2O5@Ti3C2Tx heterostructure is prepared by in situ incorporating amorphous V2O5 with Ti3C2Tx MXene to enhance the rechargeable aqueous Zn-ion batteries performance. Benefitting from the distinctive amorphous structure of a-V2O5, outstanding conductivity of Ti3C2Tx MXene and the strong synergistic effect between two components, the a-V2O5@Ti3C2Tx heterostructure presents isotropic ion diffusion paths, plentiful ion storage sites and splendid conductivity. As a consequence, the a-V2O5@Ti3C2Tx heterostructure displays excellent specific capacity of 544 mAh g−1 at 0.5 A g−1 and outstanding rate performance. Particularly, even at a fairly high current density of 30 A g−1, the a-V2O5@Ti3C2Tx heterostructure shows an impressive specific capacity of 135 mAh g−1 along with about 100% coulombic efficiency after 1000 cycles. Furthermore, the mechanism related is expounded via comprehensive characterizations. Therefore, this work offers a way for developing high-performance vanadium-based cathode materials for aqueous zinc-ion batteries.

Infrared optical properties modulation of VO2 thin film fabricated by ultrafast pulsed laser deposition for thermochromic smart window applications

Over the years, vanadium dioxide, (VO2(M1)), has been extensively utilised to fabricate thermochromic thin films with the focus on using external stimuli, such as heat, to modulate the visible through near-infrared transmittance for energy efficiency of buildings and indoor comfort. It is thus valuable to extend the study of thermochromic materials into the mid-infrared (MIR) wavelengths for applications such as smart radiative devices. On top of this, there are numerous challenges with synthesising pure VO2 (M1) thin films, as most fabrication techniques require the post-annealing of a deposited thin film to convert amorphous VO2 into a crystalline phase. Here, we present a direct method to fabricate thicker VO2(M1) thin films onto hot silica substrates (at substrate temperatures of 400 °C and 700 °C) from vanadium pentoxide (V2O5) precursor material. A high repetition rate (10 kHz) femtosecond laser is used to deposit the V2O5 leading to the formation of VO2 (M1) without any post-annealing steps. Surface morphology, structural properties, and UV–visible optical properties, including optical band gap and complex refractive index, as a function of the substrate temperature, were studied and reported below. The transmission electron microscopic (TEM) and X-ray diffraction studies confirm that VO2 (M1) thin films deposited at 700 °C are dominated by a highly texturized polycrystalline monoclinic crystalline structure. The thermochromic characteristics in the mid-infrared (MIR) at a wavelength range of 2.5–5.0 μm are presented using temperature-dependent transmittance measurements. The first-order phase transition from metal-to-semiconductor and the hysteresis bandwidth of the transition were confirmed to be 64.4 °C and 12.6 °C respectively, for a sample fabricated at 700 °C. Thermo-optical emissivity properties indicate that these VO2 (M1) thin films fabricated with femtosecond laser deposition have strong potential for both radiative thermal management or control via active energy-saving windows for buildings, and satellites and spacecraft.

Boosting fast and stable symmetric sodium-ion storage by synergistic engineering and amorphous structure

Tuning the microstructure and crystallinity of electrode materials is a great challenge and crucial for the development of high-performance sodium-ion batteries (SIBs). Herein, we develop a series of rationally designed carbon-coated V2O5 core-shell nanostructures (S-V2O5-HS, S-V2O5-HCS, P-V2O5/C-SCS, A-V2O5/C-SCS, and A-V2O5/C-WCS) in which the phase (single/polycrystalline, amorphous), microstructure (hollow, solid, porous) for the V2O5 core, and the thickness of the carbon shell are controlled via a one-pot solvothermal method followed by a single calcination process, and the performance differences between them are systematically studied. In this composite of amorphous carbon-coated V2O5 well-defined porous core-shell heterostructure (A-V2O5/C-WCS), synergistically the amorphous V2O5 core accelerates ions diffusion, carbon shell boosts the electronic conductivity, and the defect-rich porous structure lowers the binding energy compared to its counterparts as confirmed by DFT calculations and electrochemical results. Out of the ordinary, the A-V2O5/C-WCS used as a symmetric electrode for SIBs exhibits an excellent rate capability of 148 mAh g−1 at 5.0 A g−1 and outstanding ultralong cyclic stability (95% capacity retentions over 3000 cycles at 2.0 A g−1), when applied as a cathode (1.5–4.0 V) and anode (0.01–3.0 V) for SIBs. The A-V2O5/C-WCS displays a fully pseudocapacitive manner over the whole voltage thus the electrochemical performance of cathode and anode are well-matched. Impressively, the symmetric full-cell possesses a superior energy density of 219 Wh kg−1 at a high specific density of 6.0 KW kg−1 and superior cycling stability (95% capacity retained over 1200 cycles at 1.0 A g−1), demonstrating the great potential for practical application.