Unraveling the Structure–Raman Spectra Relationships in V2O5 Polymorphs via a Comprehensive Experimental and DFT Study

High-Energy-Density All-V2O5 Battery

Symmetrical batteries hold great promise as cost-effective and safe candidates for future battery technology. However, they realistically suffer low energy density due to the challenge in integrating high specific capacity with high voltage plateau from the limited choice of bipolar electrodes. Herein, a high-voltage all-V2O5 symmetrical battery with clear voltage plateau is conceptualized by decoupling the cathodic/anodic redox reactions based upon the episteme of V2O5 intercalation chemistry. As the proof-of-concept, a hierarchical V2O5-carboncomposite (VO-C) bipolar electrode with boosted electron/ion transport kinetics is fabricated, which shows high performance as both cathode and anode in their precisely clamped working potential windows. Accordingly, the symmetrical full-battery exhibits a high capacity of 174 mAh g-1 along with peak voltage output of above 2.9 V at 0.5C, remarkable capacity retention of 81% from 0.5C to 10C, and good cycling stability of 70% capacity retention after 300 cycles at 5C. Notably, its energy density reaches 429 Wh kg-1 at 0.5C estimated by the cathode mass, which outperforms most of the existing Li/Na/K-based symmetrical batteries. This study leaps forward the performance of symmetrical battery and provides guidance to extend the scope of future battery designs.

Laser-Scribed Battery Electrodes for Ultrafast Zinc-Ion Energy Storage

Aqueous Zn batteries are promising for large-scale energy storage but are plagued by the lack of high-performance cathode materials that enable high specific capacity, ultrafast charging, and outstanding cycling stability. Here, a laser-scribed nano-vanadium oxide (LNVO) cathode is designed that can simultaneously achieve these properties. The material stores charge through Faradaic redox reactions on/near the surface at fast rates owing to the small grain size of vanadium oxide and interpenetrating 3D graphene network, displaying a surface-controlled capacity contribution (90%-98%). Multiple characterization techniques unambiguously reveal that zinc and hydronium ions co-insert with minimal lattice change upon cycling. It is demonstrated that a high specific capacity of 553 mAh g-1 is achieved at 0.1 A g-1, and an impressive 264 mAh g-1 capacity is retained at 100 A g-1 within 10 s, showing excellent rate capability. The LNVO/Zn can also reach >90% capacity retention after 3000 cycles at a high rate of 30 A g-1, as well as achieving both high energy (369 Wh kg-1) and power densities (56306 W kg-1). Moreover, the LNVO cathode retains its excellent cycling performance when integrated into quasi-solid-state pouch cells, further demonstrating mechanical stability and its potential for practical application in wearable and grid-scale applications.

A nanoengineered vanadium oxide composite as a high-performance anode for aqueous Li-ion hybrid batteries

Aqueous lithium-ion batteries (LIBs) have received increasing attention as a promising solution for stationary energy storage systems due to their low environmental impact, non-flammability and low cost. Despite recent progress in electrolyte development and cathode manufacturing, the lack of anode materials with high specific capacity presents difficult challenges for a wide range of applications. In this study, we propose a novel synthetic strategy to fabricate a pseudocapacitive V2O5/graphene composite as a highly functional anode material for aqueous LIBs. The designed synthesis combines a fast laser-scribing step with controlled calcination to tune the morphology and oxidation state of the electrochemically active vanadium oxide species while obtaining a highly conductive graphene scaffold. The optimized V2O5/graphene anode shows an outstanding specific capacity of 158 mA h g-1 in three-electrode measurements. When the V2O5/graphene anode is paired with an LiMn2O4 cathode, the charge storage mechanism of the full cell is revealed to be dominantly surface-controlled, resulting in remarkable rate performance. Specifically, the full cell can reach a specific capacity of 151 and 107 mA h (g anode)-1 at C/6 and 3C, respectively. Moreover, this hybrid battery can achieve a high power density and an energy density of 650 W kg-1 at 15.6 W h kg-1 and 81.5 W h kg-1 at 13.6 W kg-1, respectively, outperforming most aqueous LIBs reported in the literature. This innovative strategy provides a pathway to incorporate pseudocapacitive electrodes for improving aqueous lithium-ion storage systems, enabling safe operation of large-scale energy storage without compromising their electrochemical performance.

AmV2O5 with Binary Phases as High-Performance Cathode Materials for Zinc-Ion Batteries: Effect of the Pre-Intercalated Cations A and Reversible Transformation of Coordination Polyhedra

In this work, five vanadium oxide materials with a series of pre-intercalated cations A (A_mV₂O₅), including Zn²⁺, Mg²⁺, NH₄⁺, Li⁺, and Ag⁺, have been successfully prepared by a two-step method. All of them possess binary monoclinic and orthorhombic V₂O₅ phases with an open layered structure that allows the ionic storage and diffusion of hydrated cations. The interlayer space for the monoclinic V₂O₅ phase is strongly dependent on the radii of hydrated cations A, while the one for the orthorhombic V₂O₅ phase remains the same regardless of the radii of cations A. Among them, A_mV₂O₅ with pre-intercalated Zn²⁺ (ZVO) has the best storage ability of Zn²⁺ with a reversible capacity close to 400 mAh g^-1, and A_mV₂O₅ with pre-intercalated Ag⁺ shows the highest rate capacity with a nearly 40% capacity retention at a current of 20 A g^-1 (≈25 C). Kinetic studies have clearly shown that pseudocapacitive behavior dominates the electrochemical reaction on ZVO. During the Zn²⁺ (de)intercalation reaction, a highly reversible transformation of binary monoclinic or orthorhombic V₂O₅ phases into a single triclinic Zn_xV₂O₅·nH₂O phase is demonstrated on ZVO. Vanadium atoms are identified as the redox centers that undergo the mutual transition among the chemical states of V³⁺, V⁴⁺, and V⁵⁺. They together with oxygen atoms constitute reasonable V-O coordination polyhedra to generate a layered structure with a suitable interlayer space for the insertion or removal of zinc ions. Actually, the intrinsic coordination chemistry changes between VO₅ square pyramids and VO₆ octahedra account for the phase transformation during the Zn²⁺-(de)intercalation reaction.

Construction of Schottky contact by modification with Pt particles to enhance the performance of ultra-long V2O5 nanobelt photodetectors

Schottky-contacted nanosensors have attracted extensive attention due to their high sensitivity and fast response time. In this article, we proved that the construction of Schottky contact by Pt nanoparticles (NPs) decoration can effectively improve the performance of V₂O₅ nanobelts photodetectors. After modified by Pt NPs, the photocurrent of V₂O₅ nanobelts is increased by more than two orders of magnitude, and the photoresponse speed is improved by at least three orders of magnitude. Detailed studies have shown that the performance enhancement is attributed to the formation of the Schottky contact at the electrode-semiconductor interface due to the decrease of surface gas adsorption and the increase of V₂O₅ work function after Pt NPs modification. The strong built-in field in the Schottky barrier region will quickly separate photogenerated carriers, thereby reducing the electron-hole recombination rate, resulting in the fast response time and an increase in the free carrier density. Moreover, it is found that this enhancement effect can be regulated by controlling the pressure to modulating the Schottky barrier height at the interface. Overall, the Pt NPs-modified V₂O₅ nanobelts photodetector exhibits a broad response spectrum (visible to near infrared), fast rise/fall response time (less than 6.12/6.15 ms), high responsivity (5.6 A/W), and high specific detectivity (6.9 × 10⁸ Jones). This study demonstrates the feasibility of building a Schottky barrier to enhance the photodetection performance, which provides a general and effective strategy towards the construction and its practical application of supersensitive and fast-response nanosensors.

Electronic and Vibrational Decoupling in Chemically Exfoliated Bilayer Thin Two-Dimensional V2O5

The synthesis of high-quality two-dimensional (2D) transition metal oxides is challenging compared to 2D transition metal dichalcogenides as a result of the exotic surface changes that can appear during formation. Herein, we report the synthesis of bilayer 2D V₂O₅ nanosheets with a thickness of ∼1 nm using the chemical exfoliation method and a comprehensive study on the vibrational and optical properties of bilayer 2D V₂O₅. We report, for the first time, a thickness-dependent blue shift of 1.33 eV in the optical bandgap, which signifies the emergence of electronic decoupling in bilayer 2D V₂O₅. In addition, a thickness-dependent vibrational decoupling of phonon modes observed via Raman spectroscopy fingerprinting was verified by computing the lattice vibrational modes using the density functional perturbation theory. We demonstrate that the manifestation of the electronic and vibrational decoupling can be used as a benchmark to confirm the successful formation of bilayer 2D V₂O₅ from its bulk counterpart.

The structure-Raman spectra relationships of Mg3(PO4)2 polymorphs: A comprehensive experimental and DFT study

Three Mg₃(PO₄)₂ polymorphs (Mg₃(PO₄)₂-I, II, III) were synthesized at high-pressure and high-temperature conditions. The structures and vibrational properties of Mg₃(PO₄)₂ polymorphs were studied by X-ray diffraction (XRD), Raman spectroscopy, and density functional theory (DFT) calculations. The obvious different PO stretching vibrational modes were experimentally observed for Mg₃(PO₄)₂-I, II, III. The calculated vibrational frequencies were in good agreement with measurements. All the observed vibrational modes for Mg₃(PO₄)₂-I, II, III were well assigned based on the calculations, which provided a support for investigating and comparing vibrational properties of three Mg₃(PO₄)₂ polymorphs.

Mechanistic Investigation of a Hybrid Zn/V2 O5 Rechargeable Battery with a Binary Li+ /Zn2+ Aqueous Electrolyte

Low-cost, easily processable, and environmentally friendly rechargeable aqueous zinc batteries have great potential for large-scale energy storage, which justifies their receiving extensive attention in recent years. An original concept based on the use of a binary Li⁺ /Zn²⁺ aqueous electrolyte is described herein for the case of the Zn/V₂ O₅ system. In this hybrid, the positive side involves mainly the Li⁺ insertion/deinsertion reaction of V₂ O₅ , whereas the negative electrode operates according to zinc dissolution-deposition cycles. The Zn//3 mol L^-1 Li₂ SO₄ -4 mol L^-1 ZnSO_4/ //V₂ O₅ cell worked in the narrow voltage range of 1.6-0.8 V with capacities of approximately 136-125 mA h g^-1 at rates of C/20-C/5, respectively. At 1 C, the capacity of 80 mA h g^-1 was outstandingly stable for more than 300 cycles with a capacity retention of 100 %. A detailed structural study by XRD and Raman spectroscopy allowed the peculiar response of the V₂ O₅ layered host lattice on discharge-charge and cycling to be unraveled. Strong similarities with the well-known structural changes reported in nonaqueous lithiated electrolytes were highlighted, although the emergence of the usual distorted δ-LiV₂ O₅ phase was not detected on discharge to 0.8 V. The pristine host structure was restored and maintained during cycling with mitigated structural changes leading to high capacity retention. The present electrochemical and structural findings reveal a reaction mechanism mainly based on Li⁺ intercalation, but co-intercalation of a few Zn²⁺ ions between the oxide layers cannot be completely dismissed. The presence of zinc cations between the oxide layers is thought to relieve the structural stress induced in V₂ O₅ under operation, and this resulted in a limited volume expansion of 4 %. This fundamental investigation of a reaction mechanism operating in an environmentally friendly aqueous medium has not been reported before.

Bilayered Potassium Vanadate K0.5 V2 O5 as Superior Cathode Material for Na-Ion Batteries

A bilayered potassium vanadate K_0.5 V₂ O₅ (KVO) is synthesized by a fast and facile synthesis route and evaluated as a positive electrode material for Na-ion batteries. Half the potassium ions can be topotactically extracted from KVO through the first charge, allowing 1.14 Na⁺ ions to be reversibly inserted. A good rate capability is also highlighted, with 160 mAh g^-1 at C/10, 94 mAh g^-1 at C/2, 73 mAh g^-1 at 2C and excellent cycling stability with 152 mAh g^-1 still available after 50 cycles at C/10. Ex situ X-ray diffraction reveals weak and reversible structural changes resulting in soft breathing of the KVO host lattice upon Na extraction-insertion cycles (ΔV/V≈3 %). A high structure stability upon cycling is also achieved, at both the long-range order and atomic scale probed by Raman spectroscopy. This remarkable behavior is ascribed to the large interlayer spacing of KVO (≈9.5 Å) stabilized by pillar K ions, which is able to accommodate Na ions without any critical change to the structure. Kinetics measurements reveal a good Na diffusivity that is hardly affected upon discharge. This study opens an avenue for further exploration of potassium vanadates and other bronzes in the field of Na-ion batteries.