Binding Sulfur‐Doped Nb2O5 Hollow Nanospheres on Sulfur‐Doped Graphene Networks for Highly Reversible Sodium Storage

Orthorhombic Nb₂O₅ (T‐Nb₂O₅) has recently attracted great attention for its application as an anode for sodium ion batteries (NIBs) owing to its patulous framework and larger interplanar lattice spacing. Sulfur‐doped T‐Nb₂O₅ hollow nanospheres (diameter:180 nm) uniformly encapsulate into sulfur‐doped graphene networks (denoted: S‐Nb₂O₅ HNS@S‐rGO) using hard template method. The 3D ordered porous structure not only provides good electronic transportation path but also offers outstanding ionic conductive channels, leading to an improved sodium storage performance. In addition, the introduction of sulfur to graphene and Nb₂O₅ leads to oxygen vacancy and enhanced electronic conductivity. The sodium storage performance of S‐Nb₂O₅ HNS@S‐rGO is unprecedented. It delivers a reversible capacity 215 mAh g^?1 at 0.5 C over 100 cycles. In addition, it also possesses a great high‐rate capability, retaining a stable capacity of 100 mAh g^?1 at 20 C after 3000 cycles. This design demonstrates the potential applications of Nb₂O₅ as anode for high performance NIBs.     

High Pseudocapacitance from Ultrathin V2O5 Films Electrodeposited on Self‐Standing Carbon‐Nanofiber Paper

An ultrathin V₂O₅ layer was electrodeposited by cyclic voltammetry on a self‐standing carbon‐nanofiber paper, which was obtained by stabilization and heat‐treatment of an electrospun polyacrylonitrile (PAN)‐based nanofiber paper. A very‐high capacitance of 1308 F g^?1 was obtained in a 2 M KCl electrolyte when the contribution from the 3 nm thick vanadium oxide was considered alone, contributing to over 90% of the total capacitance (214 F g^?1) despite the low weight percentage of the V₂O₅ (15 wt%). The high capacitance of the V₂O₅ is attributed to the large external surface area of the carbon nanofibers and the maximum number of active sites for the redox reaction of the ultrathin V₂O₅ layer. This ultrathin layer is almost completely accessible to the electrolyte and thus results in maximum utilization of the oxide (i.e., minimization of dead volume). This hypothesis was experimentally evaluated by testing V₂O₅ layers of different thicknesses.     

A Lyotropic Liquid‐Crystal‐Based Assembly Avenue toward Highly Oriented Vanadium Pentoxide/Graphene Films for Flexible Energy Storage

A novel lyotropic liquid‐crystal (LC) based assembly strategy is developed for the first time, to fabricate composite films of vanadium pentoxide (V₂O₅) nanobelts and graphene oxide (GO) sheets, with highly oriented layered structures. It is found that similar lamellar LC phases can be simply established by V₂O₅ nanobelts alone or by a mixture of V₂O₅ nanobelts and GO nanosheets in their aqueous dispersions. More importantly, the LC phases can be retained with any proportion of V₂O₅ nanobelts and GO, which allows facile optimization of the ratio of each component in the resulting films. Named VrGO, composite films manifest high electrical conductivity, good mechanical stability, and excellent flexibility, which allow them to be utilized as high performance electrodes in flexible energy storage devices. As demonstrated in this work, the VrGO films containing 67 wt% V₂O₅ exhibit excellent capacitance of 166 F g^?1 at 10 A g^?1; superior to those of the previously reported composites of V₂O₅ and nanocarbon. Moreover, the VrGO film in flexible lithium ion batteries delivers a high capacity of 215 mAh g^?1 at 0.1 A g^?1; comparable to the best V₂O₅ based cathode materials.     

Charge Storage Capability in Nanoarchitectures of V2O5/Chitosan/Poly(ethylene oxide) Produced Using the Layer‐by‐Layer Technique

The electrochemical and electrochromic properties of layer‐by‐layer nanoarchitectures of V₂O₅/chitosan and V₂O₅ alternated with a blend of poly(ethylene oxide) (PEO) and chitosan have been examined. Using a blend was important, since multilayers of PEO/V₂O₅ could not be built. The number of electrochemically active V₂O₅ sites was estimated to be around 3.4 × 10^–8 mol cm^–2 and 4.4 × 10^–8 mol cm^–2 for V₂O₅/chitosan and V₂O₅/blend, respectively, based on the UV‐vis absorbance attributed to the intervalence V⁴⁺→V⁵⁺ transfer. A pronounced effect from PEO was observed in the migration/diffusion process, according to cyclic voltammetry and impedance spectroscopy data. The charges injected were 3.29 mC cm^–2 and 8.02 mC cm^–2 for V₂O₅/chitosan and V₂O₅/blend, respectively, at 20 mV s^–1. For V₂O₅/blend, the chronopotentiometric curves show that x in Li_xV₂O₅ is about 1.77. Evidence of enhanced ionic transport was provided by the Fourier transform infrared (FTIR) spectrum, which indicated lithium complexation by PEO and formation of a larger amorphous phase of PEO within the V₂O₅ matrix. The importance of these results for the production of Li secondary microbatteries and electrochromic devices is discussed.     

Nanostructured Vanadium Oxide Electrodes for Enhanced Lithium‐Ion Intercalation

This article summarizes our most recent studies on improved Li⁺‐intercalation properties in vanadium oxides by engineering the nanostructure and interlayer structure. The intercalation capacity and rate are enhanced by almost two orders of magnitude with appropriately fabricated nanostructures. Processing methods for single‐crystal V₂O₅ nanorod arrays, V₂O₅·n H₂O nanotube arrays, and Ni/V₂O₅·n H₂O core/shell nanocable arrays are presented; the morphologies, structures, and growth mechanisms of these nanostructures are discussed. Electrochemical analysis demonstrates that the intercalation properties of all three types of nanostructure exhibit significantly enhanced storage capacity and rate performance compared to the film electrode of vanadium pentoxide. Addition of TiO₂ to orthorhombic V₂O₅ is found to affect the crystallinity, microstructure, and possible interaction force between adjacent layers in V₂O₅, and subsequently leads to enhanced Li⁺‐intercalation properties in V₂O₅. The amount of water intercalated in V₂O₅ is found to have a significant influence on the interlayer spacing and electrochemical performance of V₂O₅·n H₂O. A systematic electrochemical study has demonstrated that the V₂O₅·0.3 H₂O film has the optimal water content and exhibits the best Li⁺‐intercalation performance.     

Inverted Organic Solar Cells with Sol–Gel Processed High Work‐Function Vanadium Oxide Hole‐Extraction Layers

For large‐scale and high‐throughput production of organic solar cells (OSCs), liquid processing of the functional layers is desired. We demonstrate inverted bulk‐heterojunction organic solar cells (OSCs) with a sol–gel derived V₂O₅ hole‐extraction‐layer on top of the active organic layer. The V₂O₅ layers are prepared in ambient air using Vanadium(V)‐oxitriisopropoxide as precursor. Without any post‐annealing or plasma treatment, a high work function of the V₂O₅ layers is confirmed by both Kelvin probe analysis and ultraviolet photoelectron spectroscopy (UPS). Using UPS and inverse photoelectron spectroscopy (IPES), we show that the electronic structure of the solution processed V₂O₅ layers is similar to that of thermally evaporated V₂O₅ layers which have been exposed to ambient air. Optimization of the sol gel process leads to inverted OSCs with solution based V₂O₅ layers that show power conversion efficiencies similar to that of control devices with V₂O₅ layers prepared in high‐vacuum.     

Hydrogenated V2O5 Nanosheets for Superior Lithium Storage Properties

V₂O₅ is a promising cathode material for lithium ion batteries boasting a large energy density due to its high capacity as well as abundant source and low cost. However, the poor chemical diffusion of Li⁺, low conductivity, and poor cycling stability limit its practical application. Herein, oxygen‐deficient V₂O₅ nanosheets prepared by hydrogenation at 200 °C with superior lithium storage properties are described. The hydrogenated V₂O₅ (H‐V₂O₅) nanosheets deliver an initial discharge capacity as high as 259 mAh g^?1 and it remains 55% when the current density is increased 20 times from 0.1 to 2 A g^?1. The H‐V₂O₅ electrode has excellent cycling stability with only 0.05% capacity decay per cycle after stabilization. The effects of oxygen defects mainly at bridging O(II) sites on Li⁺ diffusion and overall electrochemical lithium storage performance are revealed. The results reveal here a simple and effective strategy to improve the capacity, rate capability, and cycling stability of V₂O₅ materials which have large potential in energy storage and conversion applications.     

Porosity‐ and Graphitization‐Controlled Fabrication of Nanoporous Silicon@Carbon for Lithium Storage and Its Conjugation with MXene for Lithium‐Metal Anode

Silicon (Si) and lithium metal are the most favorable anodes for high‐energy‐density lithium‐based batteries. However, large volume expansion and low electrical conductivity restrict commercialization of Si anodes, while dendrite formation prohibits the applications of lithium‐metal anodes. Here, uniform nanoporous Si@carbon (NPSi@C) from commercial alloy and CO₂ is fabricated and tested as a stable anode for lithium‐ion batteries (LIBs). The porosity of Si as well as graphitization degree and thickness of the carbon layer can be controlled by adjusting reaction conditions. The rationally designed porosity and carbon layer of NPSi@C can improve electronic conductivity and buffer volume change of Si without destroying the carbon layer or disrupting the solid electrolyte interface layer. The optimized NPSi@C anode shows a stable cyclability with 0.00685% capacity decay per cycle at 5 A g^?1 over 2000 cycles for LIBs. The energy storage mechanism is explored by quantitative kinetics analysis and proven to be a capacitance‐battery dual model. Moreover, a novel 2D/3D structure is designed by combining MXene and NPSi@C. As lithiophilic nucleation seeds, NPSi@C can induce uniform Li deposition with buffered volume expansion, which is proven by exploring Li‐metal deposition morphology on Cu foil and MXene@NPSi@C. The practical potential application of NPSi@C and MXene@NPSi@C is evaluated by full cell tests with a Li(Ni_0.8Co_0.1Mn_0.1)O₂ cathode.     

Template‐Assisted Formation of Rattle‐type V2O5 Hollow Microspheres with Enhanced Lithium Storage Properties

In this work, rattle‐type ball‐in‐ball V₂O₅ hollow microspheres are controllably synthesized with the assistance of carbon colloidal spheres as hard templates. Carbon spheres@vanadium‐precursor (CS@V) core–shell composite microspheres are first prepared through a one‐step solvothermal method. The composition of solvent for the solvothermal synthesis has great influence on the morphology and structure of the vanadium‐precursor shells. V₂O₅ hollow microspheres with various shell architectures can be obtained after removing the carbon microspheres by calcination in air. Moreover, the interior hollow shell can be tailored by varying the temperature ramping rate and calcination temperature. The rattle‐type V₂O₅ hollow microspheres are evaluated as a cathode material for lithium‐ion batteries, which manifest high specific discharge capacity, good cycling stability and rate capability.     

B‐doped Carbon Coating Improves the Electrochemical Performance of Electrode Materials for Li‐ion Batteries

An evolutionary modification approach, boron doped carbon coating, is initially used to improve the electrochemical properties of electrode materials of lithium‐ion batteries, such as Li₃V₂(PO₄)₃, and demonstrates apparent and significant modification effects. Based on the precise analysis of X‐ray photoemission spectroscopy results, Raman spectra, and electrochemical impedance spectroscopy results for various B‐doped carbon coated Li₃V₂(PO₄)₃ samples, it is found that, among various B‐doping types (B₄C, BC₃, BC₂O and BCO₂), the graphite‐like BC₃ dopant species plays a huge role on improving the electronic conductivity and electrochemical activity of the carbon coated layer on Li₃V₂(PO₄)₃ surface. As a result, when compared with the bare carbon coated Li₃V₂(PO₄)₃, the electrochemical performances of the B‐doped carbon coated Li₃V₂(PO₄)₃ electrode with a moderate doping amount are greatly improved. For example, when cycled under 1 C and 20 C in the potential range of 3.0–4.3 V, this sample shows an initial capacity of 122.5 and 118.4 mAh g^?1, respectively; after 200 cycles, nearly 100% of the initial capacity is retained. Moreover, the modification effects of B‐doped carbon coating approach are further validated on Li₄Ti₅O₁₂ anode material.     

A Targeted Functional Design for Highly Efficient and Stable Cathodes for Rechargeable Li‐Ion Batteries

Despite the great success of Li‐ion batteries (LIBs) up to now, higher demand has been raised with the emergence of the new generation electrics, such as portable devices and electrical vehicles. Even with the improvement on anodes, the cathodes with high capacity and long‐lastingness still remain a challenge. New 3D NiCo₂O₄@V₂O₅ core–shell arrays (CSAs) on carbon cloth as cathodes in LIBs have been reported in this work. The nanodesigned materials realize the theoretical specific capacity of V₂O₅ with high power rate based on the total mass of the framework and amount of active materials. The electrodes achieve superb cycling stability, among the most stable cathodes for LIBs ever reported. From both in situ transmission electron microscopy and quantum level calculations, the 3D NiCo₂O₄ nanosheet frameworks provide high electron conductivity and the skeleton of the robust CSAs without participating in the lithiation/delithiation; the thickness of the layered V₂O₅ plays a key role for Li diffusivity and the capacity contribution of electrodes. The structures herein point to new design concepts for high‐performance nanoarchitectures for LIB cathodes.     

ZnCl2 “Water‐in‐Salt” Electrolyte Transforms the Performance of Vanadium Oxide as a Zn Battery Cathode

Zn batteries potentially offer the highest energy density among aqueous batteries that are inherently safe, inexpensive, and sustainable. However, most cathode materials in Zn batteries suffer from capacity fading, particularly at a low current rate. Herein, it is shown that the ZnCl₂ “water‐in‐salt” electrolyte (WiSE) addresses this capacity fading problem to a large extent by facilitating unprecedented performance of a Zn battery cathode of Ca_0.20V₂O₅?0.80H₂O. Upon increasing the concentration of aqueous ZnCl₂ electrolytes from 1 m to 30 m, the capacity of Ca_0.20V₂O₅?0.80H₂O rises from 296 mAh g^?1 to 496 mAh g^?1; its absolute working potential increases by 0.4 V, and most importantly, at a low current rate of 50 mA g^?1, that is, C/10; its capacity retention increases from 8.4% to 51.1% over 100 cycles. Ex situ characterization results point to the formation of a new ready‐to‐dissolve phase on the electrode in the dilute electrolyte. The results demonstrate that the Zn‐based WiSE may provide the underpinning platform for the applications of Zn batteries for stationary grid‐level storage.     

A Scalable Free‐Standing V2O5/CNT Film Electrode for Supercapacitors with a Wide Operation Voltage (1.6 V) in an Aqueous Electrolyte

While vanadium oxides have many attractive pseudocapacitive features for energy storage, their applications are severely limited by the poor electronic conductivity and low specific surface area. To overcome these limitations, a scalable, free‐standing film electrode composed of intertwined V₂O₅ nanowires and carbon nanotubes (CNTs) using a blade coating process has been prepared. The unique architecture of this hybrid electrode greatly facilitates electronic transport along CNTs while maintaining rapid ion diffusion within V₂O₅ nanowires and fast electron transfer across the V₂O₅/CNTs interfaces. When tested in a neutral aqueous electrolyte, this hybrid film electrode demonstrates a volumetric capacitance of ≈460 F cm^?3. Moreover, a symmetric capacitor based on two identical film electrodes displays a wide operation voltage window of 1.6 V, delivering a volumetric energy density as high as 41 Wh L^?1.     

An All‐Ceramic Solid‐State Rechargeable Na+‐Battery Operated at Intermediate Temperatures

A major challenge to the development of the next‐generation all‐solid‐state rechargeable battery technology is the inferior performance caused by insufficient ionic conductivity in the electrolyte and poor mixed ionic‐electronic conductivity in the electrodes. Here we demonstrate the utility of elevated temperature as an advantageous means of enhancing the conductivity in the electrolyte and promoting the catalytic activity at electrodes in an all‐ceramic rechargeable Na⁺‐battery. The new Na⁺‐battery consists of a 154‐μm thick Na‐β′′‐Al₂O₃ electrolyte membrane, a 22‐μm thick P₂‐Na_2/3[Fe_1/2Mn_1/2]O₂ cathode and 52‐μm thick Na₂Ti₃O₇‐La_0.8Sr_0.2MnO₃ composite anode. The battery is shown to be capable of producing a reversible and stable capacity of 152 mAhg^?1 at 350 °C. While the battery's achievable capacity is limited by the electrode materials employed, it does exhibit unique low self‐discharge rate, high tolerance to thermal cycling and an outstanding safety feature.     

Associating and Tuning Sodium and Oxygen Mixed‐Ion Conduction in Niobium‐Based Perovskites

Pure ionic conductors as solid‐state electrolytes are of high interest in electrochemical energy storage and conversion devices. They systematically involve only one ion as the charge carrier. The association of two mobile ionic species, one positively and the other negatively charged, in a specific network should strongly influence the total ion conduction. Nb⁵⁺‐ (4d⁰) and Ti⁴⁺‐based (3d⁰) derived‐perovskite frameworks containing Na⁺ and O^2? as mobile species are investigated as mixed ion conductors by electrochemical impedance spectroscopy. The design of Na⁺ blocking layers via sandwiched pellet sintered by spark plasma sintering at high temperatures leads to quantified transport number of both ionic charge carriers t_Na+ and t_O2?. In the 350–700 °C temperature range, ionic conductivity can be tuned from major Na⁺ contribution (t_Na+ = 88%) for NaNbO₃ to pure O^2? transport in NaNb_0.9Ti_0.1O_2.95 phase. Such a Ti‐substitution is accompanied with a ≈100‐fold increase in the oxygen conductivity, approaching the best values for pure oxygen conductors in this temperature range. Besides the demonstration of tunable mixed ion conduction with quantifiable cationic and anionic contributions in a single solid‐state structure, a strategy is established from structural analysis to develop other architectures with improved mixed ionic conductivity.     

Graphene Oxide Gel‐Derived,Free‐Standing,Hierarchically Porous Carbon for High‐Capacity and High‐Rate Rechargeable Li‐O2 Batteries

Lithium‐oxygen (Li‐O₂) batteries are one of the most promising candidates for high‐energy‐density storage systems. However, the low utilization of porous carbon and the inefficient transport of reactants in the cathode limit terribly the practical capacity and, in particular, the rate capability of state‐of‐the‐art Li‐O₂ batteries. Here, free‐standing, hierarchically porous carbon (FHPC) derived from graphene oxide (GO) gel in nickel foam without any additional binder is synthesized by a facile and effective in situ sol‐gel method, wherein the GO not only acts as a special carbon source, but also provides the framework of a 3D gel; more importantly, the proper acidity via its intrinsic COOH groups guarantees the formation of the whole structure. Interestingly, when employed as a cathode for Li‐O₂ batteries, the capacity reaches 11 060 mA h g^?1 at a current density of 0.2 mA cm^?2 (280 mA g^?1); and, unexpectedly, a high capacity of 2020 mA h g^?1 can be obtained even the current density increases ten times, up to 2 mA cm^?2 (2.8 A g^?1), which is the best rate performance for Li‐O₂ batteries reported to date. This excellent performance is attributed to the synergistic effect of the loose packing of the carbon, the hierarchical porous structure, and the high electronic conductivity of the Ni foam.     

V2O5 Nanowires with an Intrinsic Peroxidase‐Like Activity

V₂O₅ nanowires exhibit an intrinsic catalytic activity towards classical peroxidase substrates such as 2,2‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS) and 3,3,5,5,‐tetramethylbenzdine (TMB) in the presence of H₂O₂. These V₂O₅ nanowires show an optimum reactivity at a pH of 4.0 and the catalytic activity is dependent on the concentration. The Michaelis‐Menten kinetics of the ABTS oxidation over these nanowires reveals a behavior similar to that of their natural vanadium‐dependent haloperoxidase (V‐HPO) counterparts. The V₂O₅ nanowires mediate the oxidation of ABTS in the presence of H₂O₂ with a turnover frequency (k_cat) of 2.5 × 10³ s^?1. The K_M values of the V₂O₅ nanowires for ABTS oxidation (0.4 μM ) and for H₂O₂ (2.9 μM ) at a pH of 4.0 are significantly smaller than those reported for horseradish peroxidases (HRP) and V‐HPO indicating a higher affinity of the substrates for the V₂O₅ nanowire surface. Based on the kinetic parameters and similarity with vanadium‐based complexes a mechanism is proposed where an intermediate metastable peroxo complex is formed as the first catalytic step. The nanostructured vanadium‐based material can be re‐used up to 10 times and retains its catalytic activity in a wide range of organic solvents (up to 90%) making it a promising mimic of peroxidase catalysts.     

Electronic Structure Regulation of Layered Vanadium Oxide via Interlayer Doping Strategy toward Superior High‐Rate and Low‐Temperature Zinc‐Ion Batteries

Currently, development of suitable cathode materials for zinc‐ion batteries (ZIBs) is plagued by the sluggish kinetics of Zn²⁺ with multivalent charge in the host structure. Herein, it is demonstrated that interlayer Mn²⁺‐doped layered vanadium oxide (Mn_0.15V₂O₅·nH₂O) composites with narrowed direct bandgap manifest greatly boosted electrochemical performance as zinc‐ion battery cathodes. Specifically, the Mn_0.15V₂O₅·nH₂O electrode shows a high specific capacity of 367 mAh g^?1 at a current density of 0.1 A g^?1 as well as excellent retentive capacities of 153 and 122 mAh g^?1 after 8000 cycles at high current densities up to 10 and 20 A g^?1, respectively. Even at a low temperature of ?20 °C, a reversible specific capacity of 100 mAh g^?1 can be achieved at a current density of 2.0 A g^?1 after 3000 cycles. The superior electrochemical performance originates from the synergistic effects between the layered nanostructures and interlayer doping of Mn²⁺ ions and water molecules, which can enhance the electrons/ions transport kinetics and structural stability during cycling. With the aid of various ex situ characterization technologies and density functional theory calculations, the zinc‐ion storage mechanism can be revealed, which provides fundamental guidelines for developing high‐performance cathodes for ZIBs.     

Porous Ti4O7 Particles with Interconnected‐Pore Structure as a High‐Efficiency Polysulfide Mediator for Lithium–Sulfur Batteries

Multifunctional Ti₄O₇ particles with interconnected‐pore structure are designed and synthesized using porous poly(styrene‐b ‐2‐vinylpyridine) particles as a template. The particles can work efficiently as a sulfur‐host material for lithium–sulfur batteries. Specifically, the well‐defined porous Ti₄O₇ particles exhibit interconnected pores in the interior and have a high‐surface area of 592 m² g^?1; this shows the advantage of mesopores for encapsulating of sulfur and provides a polar surface for chemical binding with polysulfides to suppress their dissolution. Moreover, in order to improve the conductivity of the electrode, a thin layer of carbon is coated on the Ti₄O₇ surface without destroying its porous structure. The porous Ti₄O₇ and carbon‐coated Ti₄O₇ particles show significantly improved electrochemical performances as cathode materials for Li–S batteries as compared with those of TiO₂ particles.     

A Na3V2(PO4)2O1.6F1.4 Cathode of Zn‐Ion Battery Enabled by a Water‐in‐Bisalt Electrolyte

Aqueous zinc‐ion batteries are receiving increasing attention; however, the development of high‐voltage cathodes is limited by the narrow voltage window of conventional aqueous electrolytes. Herein, it is reported that Na₃V₂(PO₄)₂O_1.6F_1.4 exhibits the excellent performance, optimal to date, among polyanion cathode materials in a novel neutral water‐in‐bisalts electrolyte of 25 m ZnCl₂ + 5 m NH₄Cl. It delivers a reversible capacity of 155 mAh g^?1 at 50 mA g^?1, a high average operating potential of ≈1.46 V, and stable cyclability of 7000 cycles at 2 A g^?1.