VO2 nanowires assembled into hollow microspheres for high-rate and long-life lithium batteries

Reversible Deposition/Dissolution of Double Hydroxides to Modulate Electrolyte pH Enabling High-Performance Aqueous Zinc-Ion Batteries

Vanadium oxide has been extensively studied as a host of zinc ion intercalation but still suffers from low conductivity, dissolution, and byproduct accumulation during cycling. Here, we hydrothermally synthesize the VO2@MXene Ti3C2 (MV) composite and find that in the MV//3 M Zn(CF3SO3)2//Zn system, the double hydroxide Zn12(CF3SO3)9(OH)15·nH2O (ZCOH) uniformly covers VO2 during the charging process and dissolves reversibly during the discharge process. In situ X-ray diffraction of the MV combined with in situ pH measurements reveals that ZCOH acts as a pH buffer during cycling, which is beneficial to the cycling stability of batteries. And the theoretical calculation indicates that the decomposition energy required by ZCOH on the MV surface is lower than that on pure VO2, which is more conducive to ZCOH dissolution. The coin battery exhibits high-rate performance of 65.1% capacity retention at a current density of 15 A g-1 (compared to 0.6 A g-1) and a long cycling life of 20,000 cycles with a capacity retention of 80.7%. For a 22.4 mA h soft-packaged battery, its capacity remains at 72.1% after 2000 cycles. This work demonstrates the active role of ZCOH in the electrochemical process of VO2 and provides a new perspective for exploiting this mechanism to develop high-performance aqueous zinc-ion battery vanadium oxide cathode materials.

Re-evaluating the Magnesium-ion Storage Capability of Vanadium Dioxide, VO2 (B): Uncovering the Influence of Water Content on the Previously Overestimated High Capacity

Magnesium batteries have emerged as a promising alternative to lithium-ion batteries due to their theoretical high energy density and abundant magnesium resources. Vanadium dioxide, VO2 (B), has been reported as a high-capacity cathode material for magnesium batteries. However, the electrochemical intercalation mechanism requires further elucidation due to a limited understanding of the structure-property relationship. In this study, we re-evaluated the magnesium storage capability of the material, with a particular focus on the influence of water content in nonaqueous electrolytes. The higher discharge capacity of 250 mAh g-1 is achieved exclusively in the wet electrolyte with 650 ppm water content. A significantly lower capacity of 51 mAh g-1 was observed in the dry electrolyte solution containing 40 ppm water content. Through X-ray structural and elemental analyses, as well as magnesium-ion diffusion pathway analysis using bond-valence-energy-landscape calculations, the restricted capacity was clarified by examining the reaction mechanism. According to this study, the impressive capacity of magnesium-ion battery cathodes may be exaggerated due to the involvement of non-magnesium-ion insertion unless the electrolytes' water content is appropriately regulated.

Regulating Zinc Storage Behaviors of Tunnel Structure Cathodes Via Tungsten Induction

Aqueous zinc-ion batteries have received continuous interests because of applying low-cost and eco-friendly aqueous electrolytes and having high safety. Beyond energetically to explore new-type cathode materials, it is of great significance to regulate the zinc storage behavior of the existing cathodes in order to understand the underlying working mechanism. Therefore, as a proof of concept, this work achieves the regulation of zinc storage behaviors of the tunnel structure tunnel structure B-phase vanadium dioxide (VO2 (B)) and vanadium oxide (V6 O13 ) cathodes via a simple chemical tungsten-doping induction approach. Under low-concentration tungsten-doping induction of 1, 2 and 3 at.%, the tunnel sizes of VO2 (B) can be controlled readily. Moreover, the V6 O13 with large size tunnels can be achieved by medium-concentration tungsten induction of 6 and 9 at.%. It is demonstrated that tungsten induced VO2 (B) can achieve zinc storage without lattice structure change via operando X-ray diffraction analyses. Remarkably, via operando and non-operando analyses, tungsten induced V6 O13 with lager size tunnels can realize the oriented 1D zinc ion intercalation/deintercalation. The further kinetics analysis shows that the zinc storage is mainly diffusion control, which is different from most of vanadium-based cathodes with capacitance control. This viable tungsten-doping induction strategy provides a new insight into achieving the controllable regulation of zinc storage behaviors.

Proton/Mg2+ Co-Insertion Chemistry in Aqueous Mg-Ion Batteries: From the Interface to the Inner

Co-insertion of protons happens widely and enables divalent-ion aqueous batteries to achieve high performances. However, detailed investigations and comprehensive understandings of proton co-insertion are scarce. Herein, we demonstrate that proton co-insertion into tunnel materials is determined jointly by interface derivation and inner diffusion: at the interface, hdrated Mg2+ has poor insertion kinetics, and therefore accumulates and hydrolyzes to produce protons; in the tunnels, co-inserted/lattice H2 O molecules block the Mg2+ diffusion while facilitate the proton diffusion. When monoclinic vanadium dioxide (VO2 (B)) anode is tested in Mg(CH3 COO)2 aqueous solution, the formation of Mg-rich solid electrolyte interphase on the VO2 (B) electrode and co-insertion of derived protons are probed; in the tunnels, the diffusion energy barrier of Mg2+ +H2 O is 2.7 eV, while that of the protons is 0.37 eV. Thus, protons dominate the subsequent insertion and inner diffusion. As a consequence, the VO2 (B) achieves a high capacity of 257.0 mAh g-1 at 1 A g-1 , a high rate retention of 59.1 % from 1 to 8 A g-1 , and stable cyclability of 3000 times with a capacity retention of 81.5 %. This work provides an in-depth understanding of the proton co-insertion and may promote the development of rechargeable aqueous batteries.

NH4 + Deprotonation at Interfaces Induced Reversible H3 O+ /NH4 + Co-insertion/Extraction

Ion insertions always involve electrode-electrolyte interface process, desolvation for instance, which determines the electrochemical kinetics. However, it's still a challenge to achieve fast ion insertion and investigate ion transformation at interface. Herein, the interface deprotonation of NH₄ ⁺ and the introduced dissociation of H₂ O molecules to provide sufficient H₃ O⁺ to insert into materials' structure for fast energy storages are revealed. Lewis acidic ion-NH₄ ⁺ can, on one hand provide H₃ O⁺ itself via deprotonation, and on the other hand hydrolyze with H₂ O molecules to produce H₃ O⁺ . In situ attenuated total reflection-Fourier transform infrared ray method probed the interface accumulation and deprotonation of NH₄ ⁺ , and density functional theory calculations manifested that NH₄ ⁺ tend to thermodynamically adsorb on the surface of monoclinic VO₂ , and deprotonate to provide H₃ O⁺ . In addition, the inserted NH₄ ⁺ has a positive effect for stabilizing the VO₂ (B) structure. Therefore, high specific capacity (>300 mAh g^-1 ) and fast ionic insertion/extraction (<20 s) can be realized in VO₂ (B) anode. This interface derivation proposes a new path for designing proton ion insertion/extraction in mild electrolyte.

Vanadium Oxide: Phase Diagrams, Structures, Synthesis, and Applications

Vanadium oxides with multioxidation states and various crystalline structures offer unique electrical, optical, optoelectronic and magnetic properties, which could be manipulated for various applications. For the past 30 years, significant efforts have been made to study the fundamental science and explore the potential for vanadium oxide materials in ion batteries, water splitting, smart windows, supercapacitors, sensors, and so on. This review focuses on the most recent progress in synthesis methods and applications of some thermodynamically stable and metastable vanadium oxides, including but not limited to V₂O₃, V₃O₅, VO₂, V₃O₇, V₂O₅, V₂O₂, V₆O₁₃, and V₄O₉. We begin with a tutorial on the phase diagram of the V-O system. The second part is a detailed review covering the crystal structure, the synthesis protocols, and the applications of each vanadium oxide, especially in batteries, catalysts, smart windows, and supercapacitors. We conclude with a brief perspective on how material and device improvements can address current deficiencies. This comprehensive review could accelerate the development of novel vanadium oxide structures in related applications.

Synthesis and Physical Characteristics of Undoped and Potassium-Doped Cubic Tungsten Trioxide Nanowires through Thermal Evaporation

We report an efficient method to synthesize undoped and K-doped rare cubic tungsten trioxide nanowires through the thermal evaporation of WO₃ powder without a catalyst. The WO₃ nanowires are reproducible and stable with a low-cost growth process. The thermal evaporation processing was conducted in a three-zone horizontal tube furnace over a temperature range of 550-850 °C, where multiple substrates were placed at different temperature zones. The processing parameters, including pressure, temperature, type of gas, and flow rate, were varied and studied in terms of their influence on the morphology, aspect ratio and density of the nanowires. The morphologies of the products were observed with scanning electron microscopy. High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction studies were conducted to further identify the chemical composition, crystal structure and growth direction of the nanostructures. Additionally, the growth mechanism has been proposed. Furthermore, we investigated the potassium doping effect on the physical properties of the nanostructures. Photoluminescence measurements show that there were shorter emission bands at 360 nm and 410 nm. Field emission measurements show that the doping effect significantly reduced the turn-on electric field and increased the enhancement factor. Furthermore, as compared with related previous research, the K-doped WO₃ nanowires synthesized in this study exhibited excellent field emission properties, including a superior field enhancement factor and turn-on electric field. The study reveals the potential of WO₃ nanowires in promising applications for sensors, field emitters and light-emitting diodes.

Controllable Phase Transition Properties in VO2 Films via Metal-Ion Intercalation

VO₂ has shown great promise for sensors, smart windows, and energy storage devices, because of its drastic semiconductor-to-metal transition (SMT) near 340 K coupled with a structural transition. To push its application toward room-temperature, effective transition temperature (T_c) tuning in VO₂ is desired. In this study, tailorable SMT characteristics in VO₂ films have been achieved by the electrochemical intercalation of foreign ions (e.g., Li ions). By controlling the relative potential with respect to Li/Li⁺ during the intercalation process, T_c of VO₂ can be effectively and systematically tuned in the window from 326.7 to 340.8 K. The effective T_c tuning could be attributed to the observed strain and lattice distortion and the change of the charge carrier density in VO₂ introduced by the intercalation process. This demonstration opens up a new approach in tuning the VO₂ phase transition toward room-temperature device applications and enables future real-time phase change property tuning.

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.

Vanadium Dioxide Nanosheets Supported on Carbonized Cotton Fabric as Bifunctional Textiles for Flexible Pressure Sensors and Zinc-Ion Batteries

Flexible pressure sensors and aqueous batteries have been widely used in the rapid development of wearable electronics. The synergistic functionalities of versatile materials with multidimensional architectures are recognized to have a significant impact on the performance of flexible electronics. Herein, a facile hydrothermal strategy was demonstrated to conformally grow vanadium dioxide nanosheets on carbonized cotton fabrics (VO₂/CCotton), which is a candidate material used in flexible piezoresistive sensors. As a result, the VO₂/CCotton-based pressure sensor behaved with high sensitivity (S = 7.12 kPa^-1 in the pressure range of 0-2.0 kPa) and a stable sensing ability in a wide pressure scale of 0-120 kPa. Further practical applications were performed in monitoring delicate physiological signals as well, such as twisting, blowing, and voice vibration recognitions. In addition, another application for energy storage was investigated as well. A quasi-solid-state aqueous zinc-ion battery was assembled with VO₂/CCotton as the cathode and a film of Zn nanosheets/carbon nanotube as the anode. A capacity as high as 301.5 mAh g^-1 and remarkable durability of 88.7% capacity retention after 5000 cycles at 10 A g^-1 were found. These exceptional outcomes are attributed to the unique three-dimensional architecture and the prominent synergetic effects of CCotton and VO₂ and allow for the proposal of novel guidelines for next-generation multifunctional flexible electronics.

Monodispersed flower-like MXene@VO2 clusters for aqueous zinc ion batteries with superior rate performance

Monoclinic B phase VO₂ with a distinctive tunnel structure is regarded as a viable cathode material for use in aqueous zinc ion batteries (AZIBs). However, the low electron conductivity and poor rate performance prevent it from being used further. Herein, we report 3D flower-like MXene nanosheets loaded with the VO₂ cluster (MXene@VO₂) synthesized via a one-step hydrothermal process, where MXene nanosheets were spontaneously stacked as a skeleton for the growth of VO₂ nanobelts. The synergistic effect between MXene nanosheets with high electronic conductivity and VO₂ nanobelts with a unique tunnel structure benefitted the electron and Zn²⁺ transport; the 3D hybrid structure with a high specific surface area provided an increased contact area with the electrolyte and a shortened distance of the Zn²⁺ transfer path. As a result, this material exhibits a promising Zn²⁺ storage behavior with a superior rate capability (363.2 mA h g^-1 at 0.2C and 169.1 mA h g^-1 at 50C) and outstanding long-cycling performance (206.6 mA h g^-1 and 76% capacity retention over 5000 cycles at 20C). In addition, a self-charging battery could be prepared by using oxygen in air to oxidize vanadium oxide with lower valence states. Our prepared MXene@VO₂ composite with a synergistic effect has been proved to be a promising cathode for AZIBs, offering a progressive paradigm for the development of AZIBs.

V2O5/NaV6O15nanocomposites synthesized by molten salt method as a high-performances cathode material for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (ZIBs) is a potential energy storage system due to its advantages of low cost, good safety, and high theoretical capacity (820 mAh g^-1). However, the lack of cathode materials with long cycle stability severely restricts the development of ZIBs. In this paper, V₂O₅/ NaV₆O₁₅nanocomposites are synthesized by molten salt method in one step and used as cathode material for ZIBs, which have good electrochemical performances. The specific capacity of the materials remain 160 mAh g^-1when the current density is 0.5 A g^-1after 1000 cycles, and the capacity retention rate is 102.03% when the current density is 5 A g^-1for 1000 cycles. This is mainly due to the large number of active sites generated by crystal defects and the synergistic interaction between the dual-phase materials, which reduces the stress of ions inserted/extracted during the Zn²⁺storage process and improves the electrochemical performance.

Bimetallic Antimony-Vanadium Oxide Nanoparticles Embedded in Graphene for Stable Lithium and Sodium Storage

Bimetallic oxides have received considerable attention as anodes for lithium/sodium-ion batteries (LIBs/SIBs) due to their high electrochemical activity and theoretical specific capacity. However, their cycling performance is limited by large volume variation, severe aggregation, and pulverization of bimetallic oxide nanoparticles during repeated metal ion insertion/extraction processes. Herein, bimetallic antimony-vanadium oxide nanoparticles embedded in graphene (SbVO₄/G) composites are prepared by a one-step hydrothermal method. Bimetallic SbVO₄ with abundant redox reaction sites can provide high specific capacity by a multi-electron reaction. A robust graphene substrate can not only alleviate volume expansion but also prevent aggregation and collapse of highly active bimetallic SbVO₄. Due to the excellent synergy between the two building components, SbVO₄/G hybrids exhibit excellent electrochemical activity, structural stability, and electrochemical performance. When employed as anodes for LIBs and SIBs, SbVO₄/G composites display excellent cycling performance (1079.5 mAh g^-1 at 0.1 A g^-1 after 150 cycles for LIBs and 401.6 mAh g^-1 at 0.1 A g^-1 after 450 cycles for SIBs) and impressive rate capability. This work demonstrates that SbVO₄/G composites are promising anodes for both LIBs and SIBs.

Stabilizing Hybrid Electrochromic Devices through Pairing Electrochromic Polymers with Minimally Color-Changing Ion-Storage Materials Having Closely Matched Electroactive Voltage Windows

Conjugated electrochromic polymers hold great promises for next-generation color-changing windows and displays. One of the major roadblocks in their solid-state electrochromic devices is the relatively poor cycling stability. Finding ion-storage materials as a charge-balancing component is critical in improving their electrochemical cycling stability. A key criterion for the selection of ion-storage materials is to match their electroactive voltage windows with the paired electrochromic polymers. Thus, we developed a nanostructured, amorphous vanadium oxide (VO_x) ion-storage material that exhibits high transmissivity, minimal color interference, and excellent charge-balancing capability in a closely matched electroactive window with the paired electrochromic polymers. High-performance magenta-to-transmissive hybrid electrochromic devices constructed from pairing the polymer with the VO_x can be reversibly switched for 50 000 cycles with an optical loss less than 5%.

Strategy of Enhancing the Volumetric Energy Density for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries hold the promise of the next generation energy storage system beyond state-of-the-art lithium-ion batteries. Despite the attractive gravimetric energy density (W_G ), the volumetric energy density (W_V ) still remains a great challenge for the practical application, based on the primary requirement of Small and Light for Li-S batteries. This review highlights the importance of cathode density, sulfur content, electroactivity in achieving high energy densities. In the first part, key factors are analyzed in a model on negative/positive ratio, cathode design, and electrolyte/sulfur ratio, orientated toward energy densities of 700 Wh L^-1 /500 Wh kg^-1 . Subsequently, recent progresses on enhancing W_V for coin/pouch cells are reviewed primarily on cathode. Especially, the "Three High One Low" (THOL) (high sulfur fraction, high sulfur loading, high density host, and low electrolyte quantity) is proposed as a feasible strategy for achieving high W_V , taking high W_G into consideration simultaneously. Meanwhile, host materials with desired catalytic activity should be paid more attention for fabricating high performance cathode. In the last part, key engineering technologies on manipulating the cathode porosity/density are discussed, including calendering and dry electrode coating. Finally, a future outlook is provided for enhancing both W_V and W_G of the Li-S batteries.

Recent Progress and Challenges in the Optimization of Electrode Materials for Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (RMBs) have been regarded as one of the promising electrochemical energy storage systems to complement Li-ion batteries owing to the low-cost and high safety characteristics. However, the various challenges including the sluggish solid-state diffusion of highly polarizing Mg²⁺ ions in hosts, and the formation of blocking layers on Mg metal surface have seriously impeded the development of high-performance RMBs. In order to solve these problems toward practical applications of RMBs, a tremendous amount of work on electrodes and electrolytes has been conducted in the last few decades. Creative optimization strategies including the modification of cathodes and anodes such as shielding the charges of divalent Mg²⁺ , expanding the layers of host materials, and optimizing the interface of electrode-electrolyte are raised to promote the technology. In this review, the detailed description of innovative approaches, representative examples, and facing challenges for developing high-performance electrodes are presented. Based on the review of these strategies, guidelines are provided for future research directions on improving the overall battery performance, especially on the electrodes.

VO2 Nanostructures for Batteries and Supercapacitors: A Review

Vanadium dioxide (VO₂ ) received tremendous interest lately due to its unique structural, electronic, and optoelectronic properties. VO₂ has been extensively used in electrochromic displays and memristors and its VO₂ (B) polymorph is extensively utilized as electrode material in energy storage applications. More studies are focused on VO₂ (B) nanostructures which displayed different energy storage behavior than the bulk VO₂ . The present review provides a systematic overview of the progress in VO₂ nanostructures syntheses and its application in energy storage devices. Herein, a general introduction, discussion about crystal structure, and syntheses of a variety of nanostructures such as nanowires, nanorods, nanobelts, nanotubes, carambola shaped, etc. are summarized. The energy storage application of VO₂ nanostructure and its composites are also described in detail and categorically, e.g. Li-ion battery, Na-ion battery, and supercapacitors. The current status and challenges associated with VO₂ nanostructures are reported. Finally, light has been shed for the overall performance improvement of VO₂ nanostructure as potential electrode material for future application.

Construction of reduced graphene oxide wrapped yolk-shell vanadium dioxide sphere hybrid host for high-performance lithium-sulfur batteries

Owing to the considerable theoretical energy density, lithium-sulfur batteries have been deemed as a competitive candidate for the next-generation energy storage devices. However, its commercialization still depends on the moderation of the shuttle effect and the conductivity improvement of the sulfur cathode. Herein, a novel reduced graphene oxide (rGO) wrapped yolk-shell vanadium dioxide (VO2) sphere hybrid host (rGO/VO2) is reported to simultaneously tackle these barriers. In particular, the polar VO2 sphere can chemically anchor and catalyze the conversion of polysulfides effectively both on the yolk and the shell surfaces. Meanwhile, the highly conductive 3D porous rGO network not only allows sufficient penetration of electrolyte and provides efficient transport pathways for lithium ions and electrons, but also buffers the volume variation during the lithiation process. Besides, the dissolution of the polysulfides can also be alleviated by physical confinement via the interconnected carbon network. Benefiting from these synergistic features, such designed rGO/VO2/S cathode delivers outstanding cycle stability (718.6 mA h g-1 initially, and 516.1 mA h g-1 over 400 cycles at 1C) with a fading rate of 0.07% per cycle. Even at 3C, a capacity of 639.7 mA h g-1 is reached. This proposed unique structure could provide novel insights into high-energy batteries.

Spiky-shaped niobium pentoxide nano-architecture: highly stable and recoverable Lewis acid catalyst

Niobium pentoxide particles with a complex three-dimensional (3D) nanostructure consisting of a spiky structure have been developed as recyclable and recoverable Lewis acid catalysts. The morphology of the niobium pentoxide was successfully controlled from 1D to 3D via a bridging-ligand-assisted hydrothermal treatment, without changing the crystal structure. Compared with dispersed one-dimensional (1D) niobium pentoxide nanorods with a major-axis length and minor-axis length of 20 nm and 5-8 nm, respectively, the spiky-shaped niobium pentoxide composed of 300 nm spherical cores and nanorods with a minor-axis length of 5 nm maintained its surface nanostructure even after calcination at 400 °C in air. The 400 °C-calcined spiky particles exhibited the highest production rate of 2-((4-methoxyphenyl)amino)-2-phenylacetonitrile (0.115 mmol m^-2) in a Strecker reaction, resulting in a nanoscale and ordered surface structure of spiky particles that simultaneously exhibit high specific reactivity and high structural stability. Acid site analysis and Raman spectroscopy revealed that stable nanorods that grew in the (001) orientation functioned as Lewis acid catalysts and that the origin of the acidity was a flexible Nb-O polyhedral structure in the single-nanoscale (<10 nm) niobium oxide rods. This study proposes that the spiky-shaped niobium pentoxide exhibits sintering resistivity and high activity and has potential applications as a recoverable and recyclable solid acid catalyst.

Uniform β-Na0.33V2O5 nanorod cathode providing superior rate capability for lithium ion batteries

A vanadium bronze nanomaterial, β-Na_0.33V₂O₅, was synthesized using a facile sol-gel method followed by annealing at high temperature. The morphology of the sample was observed using a scanning electron microscope (SEM) and a transmission electron microscope (TEM), and the crystal phase was determined by x-ray diffraction (XRD) spectroscopy. The as-prepared sample displays a morphology of nanorods, and has a pure phase with a high crystallinity. When used as the cathode material for rechargeable lithium batteries, the β-Na_0.33V₂O₅ nanorods fired at 400 °C exhibit better electrochemical properties at a 2.0 V cutoff voltage than those at a 1.5 V cutoff voltage. Over the voltage range of 2.0-4.0 V, they can deliver an initial capacity of 221 mAh g^-1 at a 0.5 C rate, and retain 212 mAh g^-1 after 200 cycles, accounting for a capacity fading of only 0.02% per cycle. At a 5 C rate, the discharge capacity still reaches 146 mAh g^-1, displaying an outstanding rate capability. Control of the electrochemical window is proved to be an effective strategy in boosting the cycling stability of the β-Na_0.33V₂O₅ cathode in this work in spite of a discounted capacity. Results suggest the as-prepared β-Na_0.33V₂O₅ nanorods are promising for use as high-performance cathode materials for rechargeable lithium batteries.

The ultralong cycle life of solid flexible asymmetric supercapacitors based on nickel vanadium sulfide nanospheres

The nickel vanadium sulfide electrodes shows an capacitance of 697.4 C g⁻¹ at current density of 1A g⁻¹. The flexible ACS Ni–V–S–2//rGO gives rise to a remarkable cyclic stability with 100% capacitance retention over 7000 charge–discharge cycles.

Enhanced Kinetics over VS4 Microspheres with Multidimensional Na+ Transfer Channels for High-Rate Na-Ion Battery Anodes

Developing 3 D self-assembled nanoarchitectures with well-defined crystal structures is an effective strategy to enhance the electrochemical performances of electrode materials. (1 1 0)-oriented and bridged-nanoblocks self-assembled VS₄ microspheres are controllably synthesized by a facile one-step hydrothermal method. The (1 1 0)-bridged structure sets up open pathways for Na⁺ diffusion among nanoblocks, and the (1 1 0)-oriented structure provides unobstructed pathways for Na⁺ diffusion in the nanoblocks, which collectively constructs multidimensional Na⁺ transfer channels in the VS₄ microspheres, promoting the electrochemical kinetics. As an anode for Na-ion batteries (SIBs), this material exhibits pseudocapacitive Na⁺ storage and excellent rate capability, delivering high capacities of 339 and 270 mAh g^-1 at rates of 0.1 and 2.0 A g^-1 , respectively, with a capacity retention of 79 % in the voltage window of 0.5-3.0 V. In particular, the reversible capacity reaches 575 mAh g^-1 after 300 cycles even at 1.0 A g^-1 in the voltage window of 0.05-3.0 V, outperforming those of the ever-reported VS₄ -based anode materials. This work presents an effective strategy to the exploration and design of high-performance anodes for SIBs.

Fast-Charging High-Energy Battery-Supercapacitor Hybrid: Anodic Reduced Graphene Oxide-Vanadium(IV) Oxide Sheet-on-Sheet Heterostructure

The battery-supercapacitor hybrid (BSH) device has potential applications in energy storage and can be a remedy for low-power batteries and low-energy supercapacitors. Although several studies have investigated electrode materials (particularly for a battery-type anode material) and design for BSHs, the energy density and power density are insufficient (far from the levels required for practical applications). Herein, a hierarchical vanadium(IV) oxide on reduced graphene oxide (rGO@VO₂) heterostructure as an anode and activated carbon on carbon cloth (AC@CC) as a cathode are proposed for fabricating an advanced BSH. The mixed valency of V ions inside the as-prepared VO₂ matrix (V³⁺ and V⁴⁺) facilitates redox reactions at a low potential, giving rise to rGO@VO₂ as a typical anode with a working potential of 0.01-3 V (vs Li/Li⁺). The sheet-on-sheet heterostructured rGO@VO₂ yields a high specific capacity of 1214 mAh g^-1 at 0.1 A g^-1 after 120 cycles, with a high rate capability and stability. The rGO@VO₂//AC@CC BSH device exhibits a maximum gravimetric energy density of 126.7 Wh kg^-1 and a maximum gravimetric power density of ∼10 000 W kg^-1 within a working voltage range of 1-4 V. Moreover, it exhibits fast charging times of 5 and 834 s with energy densities of 15.6 and 82 Wh kg ^-1, respectively.

Synthesis and Electrochemical Performance of Ni-Doped VO2(B) as a Cathode Material for Lithium Ion Batteries

Ni-doped VO2(B) samples (NixVO2(B)) were fabricated by a facile one-step hydrothermal method. When evaluated as a cathode material for lithium ion batteries (LIBs), these Ni-doped VO2(B) exhibited improved lithium storage performance as compared to the pure VO2(B). In particular, when the doping amount is 3%, NixVO2(B) showed the highest lithium storage capacity, best cycling stability, smallest electrochemical reaction resistance, and largest lithium diffusion coefficient. For example, after 100 cycles at a current density of 32.4 mA/g, NixVO2(B) delivered a high specific discharge capacity of 163.0 mAh/g, much higher than that of the pure VO2(B) sample (95.5 mAh/g). Therefore, Ni doping is an effective strategy for enhancing the lithium storage performance of VO2(B).

Eco-friendly synthesis of VO2 with stripped pentavalent vanadium solution extracted from vanadium-bearing shale by hydrothermal process in high conversion rate

VO₂(B) has shown excellent cathode performance in lithium batteries and become a hot research topic in recent years. A stripped vanadium solution extracted from vanadium-bearing shale containing a high concentration of vanadium and certain amounts of impurities was used as a vanadium source to synthesize VO₂(B) by hydrothermal process. The VO₂ conversion rate can reach as high as 99.47% in a reaction time of 8 h, and this is the highest result reported. The crystalline structure and morphology of the synthesized products were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Furthermore, the electrochemical properties of VO₂(B) in lithium-ion batteries were investigated. The results indicated that the VO₂(B) has the initial specific discharge capacity of 192.0 mAh g^-1. Stripped vanadium solution is a raw material for producing V₂O₅ and NH₄VO₃, which are indispensable vanadium sources in VO₂ synthesis. Therefore, synthesis of VO₂ via hydrothermal reduction by oxalic acid using stripped vanadium solution extracted from vanadium-bearing shale as a direct vanadium source is an eco-friendly, innovative and efficient method, and will have a great impact on VO₂ synthesis.

Superior electrochemical sodium storage of V4P7 nanoparticles as an anode for rechargeable sodium-ion batteries

V₄P₇ nanoparticles as an insertion type anode were synthesized via high-energy milling and introduced as an anode for sodium-ion batteries for the first time.

3D self-assembled VS4 microspheres with high pseudocapacitance as highly efficient anodes for Na-ion batteries

Surface structure plays a decisive role in the surface capacity and electrochemical kinetics of rechargeable batteries. Tuning the surface structure of building blocks has been considered to be a new effective strategy to promote the electrochemical performance of 3D self-assembled nanoarchitectures. Herein, VS4 microspheres assembled from the nano-units with different crystallinities are synthesized via a facile template-free hydrothermal method. The results show that the electrochemical performance of VS4 microspheres as anode materials for sodium-ion batteries (SIBs) largely depends on their crystallinity, and a VS4 electrode with the lowest crystallinity delivers a high reversible capacity of 412 mA h g-1 at 0.2 A g-1 after 230 cycles and that of 345 and 293 mA h g-1 even at 1.0 and 2.0 A g-1, respectively. The insertion mechanism is revealed within the selected voltage window of 0.50-3.00 V. Further analysis suggests that decreasing the crystallinity of the nano-units can dramatically enhance the pseudocapacitive behavior of VS4 microspheres, which takes the main responsibility for the improvement of sodium storage properties. This work can provide a new insight for the exploration and design of high-performance anodes for SIBs.

Inheritance of spherical morphology and optimization of assembled structures during preparation of LiMnPO4 cathodes for high electrochemical properties

Microspherical structures of cathodes facilitate high tap densities and good cycling stabilities, but their inferior rate capabilities due to low surface permeability for the electrolyte, remains a hurdle. An effective strategy to address this issue would be the optimization of the assembled microspheres structure. In this work, LiMnPO4 hollow microspheres assembled by radially aligned nanoprisms with fully exposed (010) facets are prepared by the solvothermal method using Li3PO4 as the self-sacrificed templates to improve the rate capability. By simply varying ammonium based salts during the solvothermal reaction, the nanoprisms-randomly assembled and the wedges-radially assembled microspheres are also fabricated. A plausible formation mechanism is carefully proposed. When the three kinds of microspheres are evaluated by charge/discharge measurements, their electrochemical properties are highly dependent on the variation of the assembled structures. In particular, microspheres with radially aligned nanoprisms exhibit high rate capabilities, delivering discharge capacities of 125 mA h g-1 at 1C and 113 mA h g-1 at 2C. These results originate from the unique structure of the microspheres, which not only ensures rapid electrolyte penetration to the interior of the shells due to the radial pore channels, but also guarantees fast Li+ insertion into the nanoprisms owing to their fully exposed (010) facets.

Tailoring hollow microflower-shaped CoSe2 anodes in sodium ion batteries with high cycling stability

Hollow microflower-shaped CoSe2 particles were successfully constructed and further evaluated as an anode material for sodium-ion batteries. It yielded a large discharge capacity of 220 mA h g-1 and ultralong cycle life of 1690 cycles at 1 A g-1. This ultralong cycle life can be attributed to a surface-controlled pseudocapacitive behavior and resulting rapid electron/sodium ion transport.

Large Intercalation Pseudocapacitance in 2D VO2 (B): Breaking through the Kinetic Barrier

VO2 (B) features two lithiation/delithiation processes, one of which is kinetically facile and has been commonly observed at 2.5 V versus Li/Li+ in various VO2 (B) structures. In contrast, the other process, which occurs at 2.1 V versus Li/Li+ , has only been observed at elevated temperatures due to large interaction energy barrier and extremely sluggish kinetics. Here, it is demonstrated that a rational design of atomically thin, 2D nanostructures of VO2 (B) greatly lowers the interaction energy and Li+ -diffusion barrier. Consequently, the kinetically sluggish step is successfully enabled to proceed at room temperature for the first time ever. The atomically thin 2D VO2 (B) exhibits fast charge storage kinetics and enables fully reversible uptake and removal of Li ions from VO2 (B) lattice without a phase change, resulting in exceptionally high performance. This work presents an effective strategy to speed up intrinsically sluggish processes in non-van der Waals layered materials.

Complex Three-Dimensional Co₃O₄ Nano-Raspberry: Highly Stable and Active Low-temperature CO Oxidation Catalyst

Highly stable and active low-temperature CO oxidation catalysts without noble metals are desirable to achieve a sustainable society. While zero-dimensional to three-dimensional Co₃O₄ nanoparticles show high catalytic activity, simple-structured nanocrystals easily self-aggregate and become sintered during catalytic reaction. Thus, complex three-dimensional nanostructures with high stability are of considerable interest. However, the controlled synthesis of complex nanoscale shapes remains a great challenge as no synthesis theory has been established. In this study, 100 nm raspberry-shaped nanoparticles composed of 7–8 nm Co₃O₄ nanoparticles were synthesized by hydrothermally treating cobalt glycolate solution with sodium sulfate. Surface single nanometer-scale structures with large surface areas of 89 m²·g⁻¹ and abundant oxygen vacancies were produced. The sulfate ions functioned as bridging ligands to promote self-assembly and suppress particle growth. The Co₃O₄ nano-raspberry was highly stable under catalytic tests at 350 °C and achieved nearly 100% CO conversion at room temperature. The addition of bridging ligands is an effective method to control the formation of complex but ordered three-dimensional nanostructures that possessed extreme thermal and chemical stability and exhibited high performance.

Surface phosphation of 3D mesoporous NiCo2O4 nanowire arrays as bifunctional anodes for lithium and sodium ion batteries

A novel surface phosphate strategy was adopted to dramatically improve the charge transport, ion diffusion, electroactive sites, and cycle stability of mesoporous NiCo2O4 nanowire arrays (NWAs), drastically boosting their electrochemical properties. Consequently, the as-prepared phosphated NiCo2O4 NWA (P-NiCo2O4 NWA) electrode achieved excellent energy storage performance as a bifunctional anode material for both lithium ion batteries (LIBs) and sodium ion batteries (SIBs). When evaluated as an anode for LIBs, this P-NiCo2O4 NWA electrode showed a high reversible capacity up to 1156 mA h g-1 for 1500 cycles at 200 mA g-1 without appreciable capacity attenuation, while in SIBs, the electrode could also deliver an admirable initial capacity as high as 687 mA h g-1 and maintained 83.5% of this after 500 cycles at the same current density. Most important, when the current density increased from 100 to 1000 mA g-1, the capacity retention was about 63% in LIBs and 54% in SIBs. This work may shed light on the engineering of efficient electrodes for multifunctional flexible energy storage device applications.

Ultrafast Zn2+ Intercalation and Deintercalation in Vanadium Dioxide

Although rechargeable aqueous zinc-ion batteries have attracted extensive interest due to their environmental friendliness and low cost, they still lack suitable cathodes with high rate capabilities, which are hampered by the intense charge repulsion of bivalent Zn²⁺ . Here, a novel intercalation pseudocapacitance behavior and ultrafast kinetics of Zn²⁺ into the unique tunnels of VO₂ (B) nanofibers in aqueous electrolyte are demonstrated via in situ X-ray diffraction and various electrochemical measurements. Because VO₂ (B) nanofibers possess unique tunnel transport pathways with big sizes (0.82 and 0.5 nm² along the b- and c-axes) and little structural change on Zn²⁺ intercalation, the limitation from solid-state diffusion in the vanadium dioxide electrode is eliminated. Thus, VO₂ (B) nanofibers exhibit a high reversible capacity of 357 mAh g^-1 , excellent rate capability (171 mAh g^-1 at 300 C), and high energy and power densities as applied for zinc-ion storage.

Two-Dimensional VO2 Mesoporous Microarrays for High-Performance Supercapacitor

Two-dimensional (2D) mesoporous VO₂ microarrays have been prepared using an organic-inorganic liquid interface. The units of microarrays consist of needle-like VO₂ particles with a mesoporous structure, in which crack-like pores with a pore size of about 2 nm and depth of 20-100 nm are distributed on the particle surface. The liquid interface acts as a template for the formation of the 2D microarrays, as identified from the kinetic observation. Due to the mesoporous structure of the units and high conductivity of the microarray, such 2D VO₂ microarrays exhibit a high specific capacitance of 265 F/g at 1 A/g and excellent rate capability (182 F/g at 10 A/g) and cycling stability, suggesting the effect of unique microstructure for improving the electrochemical performance.

Template-Free Synthesis of Sb2S3 Hollow Microspheres as Anode Materials for Lithium-Ion and Sodium-Ion Batteries

Hierarchical Sb₂S₃ hollow microspheres assembled by nanowires have been successfully synthesized by a simple and practical hydrothermal reaction. The possible formation process of this architecture was investigated by X-ray diffraction, focused-ion beam-scanning electron microscopy dual-beam system, and transmission electron microscopy. When used as the anode material for lithium-ion batteries, Sb₂S₃ hollow microspheres manifest excellent rate property and enhanced lithium-storage capability and can deliver a discharge capacity of 674 mAh g^-1 at a current density of 200 mA g^-1 after 50 cycles. Even at a high current density of 5000 mA g^-1, a discharge capacity of 541 mAh g^-1 is achieved. Sb₂S₃ hollow microspheres also display a prominent sodium-storage capacity and maintain a reversible discharge capacity of 384 mAh g^-1 at a current density of 200 mA g^-1 after 50 cycles. The remarkable lithium/sodium-storage property may be attributed to the synergetic effect of its nanometer size and three-dimensional hierarchical architecture, and the outstanding stability property is attributed to the sufficient interior void space, which can buffer the volume expansion.

A one-step synthesis of porous V2O3@C hollow spheres as a high-performance anode for lithium-ion batteries

V₂O₃@C hollow spheres with a large specific surface area exhibited high reversible capacity for LIBs.

Controlled synthesis of 3D porous VO2(B) hierarchical spheres with different interiors for energy storage

3D VO₂(B) hollow spheres exhibit better electrochemical properties, including specific capacitance, areal energy density and cycling stability, than VO₂(B) solid spheres.