Hierarchical Porous Metallic V2O3@C for Advanced Aqueous Zinc-Ion Batteries

Carbon Superstructure-Supported Half-Metallic V2O3 Nanospheres for High-Efficiency Photorechargeable Zinc Ion Batteries

Photorechargeable zinc ion batteries (PZIBs), which can directly harvest and store solar energy, are promising technologies for the development of a renewable energy society. However, the incompatibility requirement between narrow band gap and wide coverage has raised severe challenges for high-efficiency dual-functional photocathodes. Herein, half-metallic vanadium (III) oxide (V2O3) was first reported as a dual-functional photocathode for PZIBs. Theoretical and experimental results revealed its unique photoelectrical and zinc ion storage properties for capturing and storing solar energy. To this end, a synergistic protective etching strategy was developed to construct carbon superstructure-supported V2O3 nanospheres (V2O3@CSs). The half-metallic characteristics of V2O3, combined with the three-dimensional superstructure assembled by ultrathin carbon nanosheets, established rapid charge transfer networks and robust framework for efficient and stable solar-energy storage. Consequently, the V2O3@CSs photocathode delivered record zinc ion storage properties, including a photo-assisted discharge capacities of 463 mA ⋅ h ⋅ g-1 at 2.0 A ⋅ g-1 and long-term cycling stability over 3000 cycles. Notably, the PZIBs assembled using V2O3@CSs photocathodes could be photorecharged without an external circuit, exhibiting a high photo conversion efficiency (0.354 %) and photorecharge voltage (1.0 V). This study offered a promising direction for the direct capture and storage of solar energy.

Recent Progress on Rechargeable Zn-X (X=S, Se, Te, I2, Br2) Batteries

Recently, aqueous Zn-X (X=S, Se, Te, I2, Br2) batteries (ZXBs) have attracted extensive attention in large-scale energy storage techniques due to their ultrahigh theoretical capacity and environmental friendliness. To date, despite tremendous research efforts, achieving high energy density in ZXBs remains challenging and requires a synergy of multiple factors including cathode materials, reaction mechanisms, electrodes and electrolytes. In this review, we comprehensively summarize the various reaction conversion mechanism of zinc-sulfur (Zn-S) batteries, zinc-selenium (Zn-Se) batteries, zinc-tellurium (Zn-Te) batteries, zinc-iodine (Zn-I2) batteries, and zinc-bromine (Zn-Br2) batteries, along with recent important progress in the design and electrolyte of advanced cathode (S, Se, Te, I2, Br2) materials. Additionally, we investigate the fundamental questions of ZXBs and highlight the correlation between electrolyte design and battery performance. This review will stimulate an in-deep understanding of ZXBs and guide the design of conversion batteries.

High-Performance Aqueous Zinc-Ion Batteries Based on Multidimensional V2O3 Nanosheets@Single-Walled Carbon Nanohorns@Reduced Graphene Oxide Composite and Optimized Electrolyte

The drawbacks of poor electronic conductivity and structural instability during the cycling process limit the electrochemical property of vanadium-based cathode materials for aqueous zinc-ion batteries. In addition, continuous growth and accumulation of zinc dendrites can puncture the separator and cause an internal short circuit in the battery. In this work, a unique multidimensional nanocomposite is designed by a facile freeze-drying method with subsequent calcination, consisting of V2O3 nanosheets and single-walled carbon nanohorns (SWCNHs) crosslinked together and wrapped by reduced graphene oxide (rGO). The multidimensional structure can largely enhance the structural stability and electronic conductivity of the electrode material. Besides, additive Na2SO4 in the ZnSO4 aqueous electrolyte not only prevents the dissolution of cathode materials but also suppresses the Zn dendrite growth. After considering the influence of additive concentration on ionic conductivity and electrostatic force for electrolyte, V2O3@SWCNHs@rGO electrode delivers a high initial discharge capacity of 422 mAh g-1 at 0.2 A g-1 and a high discharge capacity of 283 mAh g-1 after 1000 cycles at 5 A g-1 in 2 m ZnSO4 + 2 m Na2SO4 electrolyte. Experimental techniques reveal that the electrochemical reaction mechanism can be expressed as the reversible phase transformation between V2O5 and V2O3 with Zn3(VO4)2.

In situ electrochemically activated V2O3@MXene cathode for a super high-rate and long-life Zn-ion battery

The development of a high specific capacity and stable vanadium-based cathode material is very attractive for aqueous zinc-ion batteries (ZIBs). Herein, an in situ electrochemically oxidized cathode is fabricated based on a V2O3@MXene cathode for Zn-ion storage. V2O3@MXene undergoes a phase transition to Zn3(OH)2V2O7·2H2O and ZnyVOz on the first charge, thus allowing for the subsequent insertion/de-insertion of zinc ions, which can be regulated by the amount of H2O in the electrolyte. The MXene in the composite was also beneficial to electron transfer and cycling stability. V2O3@MXene delivered a high capacity of 450 mA h g-1 at 0.2 A g-1, ultra-high-rate performance and cycling stability as well as high energy density.

Enhancing Interplanar Spacing in V2O3/V3O7 Heterostructures to Optimize Cathode Efficiency for Zn-Ion Batteries

The improvement of sophisticated cathode materials plays a major role in boosting the efficiency of Zn-ion batteries. These batteries have garnered considerable interest as a result of their excellent energy density and the promise of cost-effective solutions for energy storage. In this work, we present a novel approach to progress the electrochemical investigation of Zn-ion batteries by expanding the interplanar distance of layered hydrated V2O3/V3O7 heterostructure nanosheets. Electrochemical investigations were conducted to assess the effectiveness of the stacked hydrated V2O3/V3O7 heterostructure as a cathode component for Zn-ion batteries. The expanded interplanar space as a result of the introduction of water molecules facilitates the insertion/extraction of Zn ions, leading to significantly enhanced electrochemical characteristics. The layered hydrated V2O3/V3O7 heterostructure exhibited an impressive specific capacity of 330 mAh g-1 at a current density of 0.1 A g-1, maintaining a capacity retention of approximately 92.3% and a coulombic efficiency of 95.8% even after 2000 cycles.

Versatile MXenes for Aqueous Zinc Batteries

Aqueous zinc-ion batteries (AZIBs) are gaining popularity for their cost-effectiveness, safety, and utilization of abundant resources. MXenes, which possess outstanding conductivity, controllable surface chemistry, and structural adaptability, are widely recognized as a highly versatile platform for AZIBs. MXenes offer a unique set of functions for AZIBs, yet their significance has not been systematically recognized and summarized. This review article provides an up-to-date overview of MXenes-based electrode materials for AZIBs, with a focus on the unique functions of MXenes in these materials. The discussion starts with MXenes and their derivatives on the cathode side, where they serve as a 2D conductive substrate, 3D framework, flexible support, and coating layer. MXenes can act as both the active material and a precursor to the active material in the cathode. On the anode side, the functions of MXenes include active material host, zinc metal surface protection, electrolyte additive, and separator modification. The review also highlights technical challenges and key hurdles that MXenes currently face in AZIBs.

Ice crystal sublimation for easily producing MnO2 cathodes with hierarchically porous structure and enhanced cyclic reversibility

The charge/discharge performance of rechargeable aqueous zinc ion batteries (RAZIBs) at high currents is often unsatisfactory due to the cathode preparation process and the use of hydrophobic binders. By adding freeze-drying treatment to the preparation process of the cathodes, MnO2 cathodes with hierarchically porous structures are obtained, which provide additional channels for ion transfer, thus greatly enhancing the charge/discharge performance in aqueous Zn-MnO2 batteries.

A Comprehensive Evaluation of Battery Technologies for High-Energy Aqueous Batteries

Aqueous batteries have garnered significant attention in recent years as a viable alternative to lithium-ion batteries for energy storage, owing to their inherent safety, cost-effectiveness, and environmental sustainability. This study offers a comprehensive review of recent advancements, persistent challenges, and the prospects of aqueous batteries, with a primary focus on energy density compensation of various battery engineering technologies. Additionally, cutting-edge high-energy aqueous battery designs are emphasized as a reference for future endeavors in the pursuit of high-energy storage solutions. Finally, a dual-compatibility battery configuration perspective aimed at concurrently optimizing cycle stability, redox potential, capacity utilization for both anode and cathode materials, as well as the selection of potential electrode candidates, is proposed with the ultimate goal of achieving cell-level energy densities exceeding 400 Wh kg-1 .

Boosting Material Utilization via Direct Growth of Zn2 (V3 O8 )2 on the Carbon Cloth as a Cathode to Achieve a High-Capacity Aqueous Zinc-Ion Battery

Aqueous zinc-ion batteries (AZIBs) have attracted the attention of researchers because of their high theoretical capacity and safety. Among the many vanadium-based AZIB cathode materials, zinc vanadate is of great interest as a typical phase in the dis-/charge process. Here, a remarkable method to improve the utilization rate of zinc vanadate cathode materials is reported. In situ growth of Zn2 (V3 O8 )2 on carbon cloth (CC) as the cathode material (ZVO@CC) of AZIBs. Compared with the Zn2 (V3 O8 )2 cathode material bonded on titanium foil (ZVO@Ti), the specific capacity increases from 300 to 420 mAh g-1 , and the utilization rate of the material increases from 69.60% to 99.2%. After the flexible device is prepared, it shows the appropriate specific capacity (268.4 mAh g-1 at 0.1 A g-1 ) and high safety. The method proposed in this work improves the material utilization rate and enhances the energy density of AZIB and also has a certain reference for the other electrochemical energy storage devices.

How About Vanadium-Based Compounds as Cathode Materials for Aqueous Zinc Ion Batteries?

Aqueous zinc-ion batteries (AZIBs) stand out among many monovalent/multivalent metal-ion batteries as promising new energy storage devices because of their good safety, low cost, and environmental friendliness. Nevertheless, there are still many great challenges to exploring new-type cathode materials that are suitable for Zn2+ intercalation. Vanadium-based compounds with various structures, large layer spacing, and different oxidation states are considered suitable cathode candidates for AZIBs. Herein, the research advances in vanadium-based compounds in recent years are systematically reviewed. The preparation methods, crystal structures, electrochemical performances, and energy storage mechanisms of vanadium-based compounds (e.g., vanadium phosphates, vanadium oxides, vanadates, vanadium sulfides, and vanadium nitrides) are mainly introduced. Finally, the limitations and development prospects of vanadium-based compounds are pointed out. Vanadium-based compounds as cathode materials for AZIBs are hoped to flourish in the coming years and attract more and more researchers' attention.

Rational design of pyrrolic-N dominated carbon material derived from aminated lignin for Zn-ion supercapacitors

Developing highly efficient, sustainable carbon cathodes is essential for emerging Zn-ion hybrid supercapacitors (ZICs). Herein, lignin's novel chemical modification (amination) has been developed to produce high quantity pyrrolic-N moieties as active sites. Furthermore, chemically modified amine moieties in lignin are vital as a natural self-activating template to generate hierarchical porosity in the 2D (graphene-like) architecture with exceedingly high surface area (2926.4 m²g^-1). The rationally introduced dominated pyrrolic-N moieties boost the Zn-ion storage capacity and reaction kinetics due to the dual energy storage mechanism and efficient charge transfer between pyrrolic-N and Zn⁺² ions. Furthermore, the pyrrolic-N species are energetically favorable for the adsorption of Zn⁺² ions by the formation of N-Zn⁺² chemical bonds. Besides, the nitrogen oxides reduce the intrinsic resistance and induce a more polarized surface, resulting in high wettability and efficient transfer of electrolytes into the pores of hydrophobic carbon materials. Subsequently, the chemically modified lignin-derived activated carbon material (Chem-ACM) as a cathode in ZICs delivers a high capacity of 161.2 mA h g^-1 at 1 A g^-1 with the admirable energy density of 106.7 W h kg^-1 at 897 W kg^-1 and excellent retention capacity (94%) after 10,000 cycles. Mainly, the assembled quasi solid-state ZICs using Chem-ACM retains the remarkable storage capacity (202 mA h g^-1 at 0.2 Ag^-1) even at a high bending angle. Notably, the Chem-ACM has been further employed in symmetric supercapacitors as an electrode, and it displays exceptional specific capacitance of 354 Fg^-1 at 0.5 Ag^-1 with tremendous energy (43.5 W h kg^-1) and the power density (0.53 kW kg^-1). Additionally, the charge storage capability of Chem-ACM is positively dependent on high nitrogen contents, and it is extrapolated that pyrrolic-N moieties are dominant active sites. Hence, the designed amination-assisted biocarbon synthesis provides a new way to prepare high nitrogen-containing biocarbon for ZICs and further understand pyrrolic-N species' impact on Zn-ion storage.

Bio-Template Synthesis of V2O3@Carbonized Dictyophora Composites for Advanced Aqueous Zinc-Ion Batteries

In terms of new-generation energy-storing devices, aqueous zinc-ion batteries (AZIBs) are becoming the prime candidates because of their inexpensive nature, inherent safety, environmental benignity and abundant resources. Nevertheless, due to a restrained selection of cathodes, AZIBs often perform unsatisfactorily under long-life cycling and high-rate conditions. Consequently, we propose a facile evaporation-induced self-assembly technique for preparing V₂O₃@carbonized dictyophora (V₂O₃@CD) composites, utilizing economical and easily available biomass dictyophora as carbon sources and NH₄VO₃ as metal sources. When assembled in AZIBs, the V₂O₃@CD exhibits a high initial discharge capacity of 281.9 mAh g^-1 at 50 mA g^-1. The discharge capacity is still up to 151.9 mAh g^-1 after 1000 cycles at 1 A g^-1, showing excellent long-cycle durability. The extraordinary high electrochemical effectiveness of V₂O₃@CD could be mainly attributed to the formation of porous carbonized dictyophora frame. The formed porous carbon skeleton can ensure efficient electron transport and prevent V₂O₃ from losing electrical contact due to volume changes caused by Zn²⁺ intercalation/deintercalation. The strategy of metal-oxide-filled carbonized biomass material may provide insights into developing high-performance AZIBs and other potential energy storage devices, with a wide application range.

Defect engineering of molybdenum disulfide nanosheets boosting super Zn2+ storage from polyaniline intercalation

In this work, peony-like structured MoS₂ with intercalation of polyaniline and crystal defects was prepared by a simple hydrothermal method. The defect-rich structure and broad interlayer distance can effectively provide vast ion transport paths to enhance the ion diffusion rate. PA-MoS₂ can maintain 157.7 mA h g^-1 at 0.1 A g^-1 after 80 cycles and 77.8 mA h g^-1 at 1 A g^-1 after 750 cycles.

Hewettite ZnV6 O16 ⋅ 8H2 O with Remarkably Stable Layers and Ultralarge Interlayer Spacing for High-Performance Aqueous Zn-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) are promising candidates for grid-scale energy storage because of their intrinsic safety, low-cost and high energy-intensity. Vanadium-based materials are widely used as the cathode of ZIBs, especially A₂ V₆ O₁₆  ⋅ nH₂ O (AVO, A=NH₄ ⁺ , Na, K). However, AVO suffers from serious dissolution, phase transformation and narrow gallery spacing (∼3 Å), leading to poor cycling stability and rate capability. Herein, we unveiled the root cause of the performance degradation in the AVO cathode and therefore developed a new high-performance cathode of ZnV₆ O₁₆  ⋅ 8H₂ O (ZVO) for ZIB. Through a method of ion exchange induced phase transformation, AVO was converted to hewettite ZVO with larger gallery spacing (∼6 Å) and more stable V₆ O₁₆ layers. ZVO cathode thus constructed delivers a high capacity of 365 and 170 mAh g^-1 at 0.5 and 15 A g^-1 , while 86 % and 70 % of its capacity are retained at 0.5 A g^-1 after 300 cycles and at 15 A g^-1 after 10000 cycles, substantially better than conventional AVO.

Aging-Responsive Phase Transition of VOOH to V10O24·nH2O vs Zn2+ Storage Performance as a Rechargeable Aqueous Zn-Ion Battery Cathode

Vanadium oxyhydroxide has been recently investigated as a starting material to synthesize different phases of vanadium oxides by electrochemical or thermal conversion and has been used as an aqueous zinc-ion battery (AZIB) cathode. However, the low-valent vanadium oxides have poor phase stability under ambient conditions. So far, there is no study on understanding the phase evolution of such low-valent vanadium oxides and their effect on the electrochemical performance toward hosting the Zn²⁺ ions. The primary goal of the work is to develop a high-performance AZIB cathode, and the highlight of the current work is the insight into the auto-oxidation-induced phase transition of VOOH to V₁₀O₂₄·nH₂O under ambient conditions and Zn²⁺ intercalation behavior thereon as an aqueous zinc-ion battery cathode. Herein, we demonstrate that hydrothermally synthesized VOOH undergoes a phase transition to V₁₀O₂₄·nH₂O during both the electrochemical cycling and aerial aging over 38-45 days. However, continued aging till 150 days at room temperature in an open atmosphere exhibited an increased interlayer water content in the V₁₀O₂₄·nH₂O, which was associated with a morphological change with different surface area/porosity characteristics and notably reduced charge transfer/diffusion resistance as an aqueous zinc-ion battery cathode. Although the fresh VOOH cathode had impressive specific capacity at rate performance, (326 mAh/g capacity at 0.1 A/g current and 104 mAh/g capacity at 4 A/g current) the cathode suffered from a continuous capacity decay. Interestingly, the aged VOOH electrodes showed gradually decreasing specific capacity with aging at low current and however followed the reverse order at high current. At a comparable specific power of ∼64-66 W/kg, the fresh VOOH and aged VOOH after 60, 120, and 150 days of aging showed the respective energy densities of 208.3, 281.2, 269.2, and 240.6 Wh/kg. Among all the VOOH materials, the 150 day-aged VOOH cathode exhibited the highest energy density at a power density beyond 1000 W/kg. Thanks to the improved kinetics, the 150 day-aged VOOH cathode delivered a considerable energy density of 39.7 Wh/kg with a high specific power of 4466 W/kg. Also, it showed excellent cycling performance with only 0.002% capacity loss per cycle over 20 300 cycles at 10 A/g.

Carbon-encapsulated V2O3 nanorods for high-performance aqueous Zn-ion batteries

Searching for stable cathodes is of paramount importance to the commercial development of low-cost and safe aqueous Zn-ion batteries (AZIBs). V₂O₃ is a good candidate for AZIB cathodes but has unsatisfied cycling stability. Herein, we solve the stability issue of a V₂O₃ cathode by coating a robust carbon shell. Strong evidence was provided that V₂O₃ was oxidized to favorable V₂O₅·nH₂O during charging and the carbon shell could promote the oxidation of V₂O₃ to V₂O₅·nH₂O. The discharge capacity was increased from ∼45 mA h g⁻¹ to 336 mA h g⁻¹ after V₂O₃ was oxidized to V₂O₅·nH₂O, indicating a higher Zn²⁺-storage capability of V₂O₅·nH₂O than V₂O₃. In addition, the rate-capability and long-term cycling performance are greatly enhanced after coating carbon shells on the surface of V₂O₃ nanorods. Therefore, the presented strategy of introducing carbon shells and fundamental insights into the favorable role of carbon shells in this study contribute to the advancement of highly stable AZIBs.

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.

Methods for Rational Design of Advanced Zn-Based Batteries

Rechargeable aqueous zinc-based batteries (AZBs) have received massive attention as promising contenders for the future large-scale energy storage due to their low cost, inherent safety, and abundant resources. However, the insufficient energy density and poor stability have become the key to hinder their further application. As is well known, the energy densities (E, Wh kg^-1 ) of AZBs are determined by the specific capacity (mAh g^-1 ) and output voltage (V). Given the fixed redox potential and capacity of the Zn metal anode, the energy density of AZBs is mainly determined by the cathode material, and the rich material systems of the cathode provide more possibilities to this field. Meanwhile, the methods to improve the stability and performance of the Zn anodes have gained more and more attention due to the severe Zn dendrite growth that can pierce the separator and lead to short-circuiting of the cell. Therefore, in this review, we comprehensively summarize the rational design methods in optimizing the cathode, anode, and device architecture, and classic examples of each catalogue are discussed in details as well. Last, the issues and outlook for further development of high performance AZBs are also presented.

Will Vanadium-Based Electrode Materials Become the Future Choice for Metal-Ion Batteries?

Metal-ion batteries have emerged as promising candidates for energy storage system due to their unlimited resources and competitive price/performance ratio. Vanadium-based compounds have diverse oxidation states rendering various open-frameworks for ions storage. To date, some vanadium-based polyanionic compounds have shown great potential as high-performance electrode materials. However, there has been a growing concern regarding the cost and environmental risk of vanadium. In this Review, all links in the industry chain of vanadium-based electrodes were comprehensively summarized, starting with an analysis of the resources, applications, and price fluctuation of vanadium. The manufacturing processes of the vanadium extraction and recovery technologies were discussed. Moreover, the commercial potentials of some typical electrode materials were critically appraised. Finally, the environmental impact and sustainability of the industry chain were evaluated. This critical Review will provide a clear vision of the prospects and challenges of developing vanadium-based electrode materials.

Rapid Electrochemical Activation of V2 O3 @C Cathode for High-Performance Zinc-Ion Batteries in Water-in-Salt Electrolyte

Aqueous Zn-ion batteries (ZIBs), with the advantages of low cost, high safety, and high capacity, have great potential for application in grid energy storage and wearable flexible devices. However, their commercial application is still restricted by their inferior long-term cycling stability, Zn dendrite formation, and the decomposition of aqueous electrolyte. In this study, a Zn|Zn(CF₃ SO₃ )₂ +LiTFSI|V₂ O₃ @C cell is constructed to address the above issues. The V₂ O₃ @C electrode can be fully oxidized into amorphous V₂ O₅ @C simultaneously with Zn²⁺ and H₂ O co-insertion. The cell delivers a high specific capacity of more than 240 mAh g^-1 at 3 A g^-1 , with extraordinary coulombic efficiency and capacity retention. The excellent electrochemical performances are attributed to synergistic effects between the V₂ O₃ @C electrode and the water-in-salt electrolyte with enhanced stability and improved interface reaction kinetics. Systematic improvements of this architecture indicate much promise for application.

Fabrication of TiN/CNTs on carbon cloth substrates via a CVD–ALD method as free-standing electrodes for zinc ion hybrid capacitors

A novel fabrication of TiN/CNTs@CC was presented and can be used as electrodes with good flexibility and conductivity in ZIHCs.

A distinctive conversion mechanism for reversible zinc ion storage

V2O3@C exhibits a different energy storage mechanism at high voltage from intercalation chemistry (in the low voltage range) with the decomposition and deposition of Zn3V2O7(OH)2·2H2O.

Binder-free three-dimensional interconnected CuV2O5•nH2O nest as cathodes for high-loading aqueous zinc-ion batteries

In large-scale energy storage applications, aqueous zinc ion batteries (ZIBs) with low cost, safety, high theoretical capacity, and environmentally friendly have wide application prospects. In the reported cathode materials, the...

Recent Developments and Challenges of Vanadium Oxides (Vx Oy ) Cathodes for Aqueous Zinc-Ion Batteries

The rapid depletion of lithium resources and the increasing demand for electrical energy storage have stimulated the pursuit of emerging electrochemical energy storage. Aqueous zinc ion batteries (ZIBs) are highly sought after for their low cost, high safety, and increased environmental compatibility. However, the search for suitable cathode materials is still tricky for a wide range of researchers. Vanadium oxides (V_x O_y ), with their abundant vanadium valence, easily deformable V-O polyhedrons, and tunable chemical compositions, are of significant advantage in developing emerging materials. This work provides a detailed review of different V_x O_y for the application in aqueous ZIBs. The current problems and optimization strategies of V_x O_y cathode materials are systematically discussed. Finally, the current challenges and possible directions for future research of V_x O_y cathode materials in aqueous ZIBs are presented.

Oxygen Defect Hydrated Vanadium Dioxide/Graphene as a Superior Cathode for Aqueous Zn Batteries

Zinc ion batteries have become a new type of energy storage device because of the low cost and high safety. Among the various cathode materials, vanadium-oxygen compounds stand out due to their high theoretical capacity and variable chemistry valence state. Here, we construct a 3D spongy hydrated vanadium dioxide composite (O_d-HVO/rG) with abundant oxygen vacancy defects and graphene modifications. Thanks to the stable structure and abundant active sites, O_d-HVO/rG exhibits superior electrochemical properties. In aqueous electrolyte, the O_d-HVO/rG cathode provides high initial charging capacity (428.6 mAh/g at 0.1 A/g), impressive rate performance (186 mAh/g even at 20 A/g), and cycling stability, which can still maintain 197.5 mAh/g after 2000 cycles at 10 A/g. Also, the superior specific energy of 245.3 Wh/kg and specific power of 14142.7 W/kg are achieved. In addition, MXene/O_d-HVO/rG cathode materials are prepared and PAM/ZnSO₄ hydrogel electrolytes are applied to assemble flexible soft pack quasi-solid-state zinc ion batteries, which also exhibit excellent flexibility and cycling stability (206.6 mAh/g after 2000 cycles). This work lays the foundation for advances in rechargeable aqueous zinc ion batteries, while revealing the potential for practical applications of flexible energy storage devices.

Boosting the Electrochemical Performance of V2 O3 by Anchoring on Carbon Nanotube Microspheres with Macrovoids for Ultrafast and Long-Life Aqueous Zinc-Ion Batteries

Zinc-ion batteries (ZIBs) are next-generation energy storage systems with high safety and environmental friendliness because they can be operated in aqueous systems. However, the search for electrode materials with ideal nanostructures and compositions for aqueous ZIBs is in progress. Herein, the synthesis of porous microspheres, consisting of V₂ O₃ anchored on entangled carbon nanotubes (p-V₂ O₃ -CNT) and their application as cathode for ZIBs is reported. From various analyses, it is revealed that V₂ O₃ phase disappears after the initial charge process, and Zn_{3+ x} (OH)_{2+3 x} V_{2- x} O_{7-3 x} ∙2H₂ O and zinc vanadate (Zn_y VO_z ) phases undergo zinc-ion intercalation/deintercalation processes from the second cycle. Additionally, the electrochemical performances of p-V₂ O₃ -CNT, V₂ O₃ -CNT (without macrovoids), and porous V₂ O₃ (without CNTs) microspheres are compared to determine the effects of nanostructures and conductive carbonaceous matrix on the zinc-ion storage performance. p-V₂ O₃ -CNT exhibits a high reversible capacity of 237 mA h g^-1 after 5000 cycles at 10 A g^-1 . Furthermore, a reversible capacity of 211 mA h g^-1 is obtained at an extremely high current density of 50 A g^-1 . The macrovoids in V₂ O₃ nanostructure effectively alleviate the volume changes during cycling, and the entangled CNTs with high electrical conductivity assist in achieving fast electrochemical kinetics.

Robust VS4@rGO nanocomposite as a high-capacity and long-life cathode material for aqueous zinc-ion batteries

Although vanadium (V)-based sulfides have been investigated as cathodes for aqueous zinc-ion batteries (ZIBs), the performance improvement and the intrinsic zinc-ion (Zn²⁺) storage mechanism revelation is still challenging. Here, VS₄@rGO composite with optimized morphology is designed and exhibits ultrahigh specific capacity (450 mA h g^-1 at 0.5 A g^-1) and high-rate capability (313.8 mA h g^-1 at 10 A g^-1) when applied as cathode material for aqueous ZIBs. Furthermore, the VS₄@rGO cathode presents long-life cycling stability with capacity retention of ∼82% after 3500 cycles at 10 A g^-1. The structural evolution, redox, and degradation mechanisms of VS₄ during (dis)charge processes are further probed by in situ XRD/Raman techniques and TEM analysis. Our results indicate that the main energy storage mechanism is derived from the intercalation/deintercalation reactions in the open channels of VS₄. Notably, an irreversible phase transition of VS₄ into Zn₃(OH)₂V₂O₇·2H₂O (ZVO) during the charging process and the further transition from ZVO to ZnV₃O₈ during long-term cycles are also observed, which might be the main reason leading to the capacity degradation of VS₄@rGO. Our study further improves the electrochemical performance of VS₄ in aqueous ZIBs through morphology design and provides new insights into the energy storage and performance degradation mechanisms of Zn²⁺ storage in VS₄, and thus may endow the large-scale application of V-based sulfides for energy storage systems.

Selenium Defect Boosted Electrochemical Performance of Binder-Free VSe2 Nanosheets for Aqueous Zinc-Ion Batteries

As a typical transition-metal dichalcogenides, vanadium diselenide (VSe₂) is a promising electrode material for aqueous zinc-ion batteries due to its metallic characteristics and excellent electronic conductivity. In this work, we propose a strategy of hydrothermal reduction synthesis of stainless-steel (SS)-supported VSe₂ nanosheets with defect (VSe_2-x-SS), thereby further improving the conductivity and activity of VSe_2-x-SS. Density functional theory calculations confirmed that Se defect can adjust the adsorption energy of Zn²⁺ ions. This means that the adsorption/desorption process of Zn²⁺ ions on VSe_2-x-SS is more reversible than that on pure SS-supported VSe₂ (VSe₂-SS). As a result, the Zn//VSe_2-x-SS battery showed more excellent electrochemical performance than Zn//VSe₂-SS. The VSe_2-x-SS electrode shows a good specific capacity of 265.2 mA h g^-1 (0.2 A g^-1 after 150 cycles), satisfactory rate performance, and impressive cyclic stability. In addition, we also have explored the energy-storage mechanism of Zn²⁺ ions in this VSe_2-x-SS electrode material. This study provides an effective strategy for the rational design of electrode materials for electrochemical energy-storage devices.

Aqueous Rechargeable Zn-ion Batteries: Strategies for Improving the Energy Storage Performance

The growing demand for the renewable energy storage technologies stimulated the quest for efficient energy storage devices. In recent years, the rechargeable aqueous zinc-based battery technologies are emerging as a compelling alternative to the lithium-based batteries owing to safety, eco-friendliness, and cost-effectiveness. Among the zinc-based energy devices, rechargeable zinc-ion batteries (ZIBs) are drawing considerable attention. However, they are plagued with several issues, including cathode dissolution, dendrite formation, etc.. Despite several efforts in the recent past, ZIBs are still in their infant stages and have yet to reach the stage of large-scale production. Finding stable Zn²⁺ intercalation cathode material with high operating voltage and long cycling stability as well as dendrite-free Zn anode is the main challenge in the development of efficient zinc-ion storage devices. This Review discusses the various strategies, in terms of the engineering of cathode, anode and electrolyte, adopted for improving the charge storage performance of ZIBs and highlights the recent ZIB technological innovations. A brief account on the history of zinc-based devices and various cathode materials tested for ZIB fabrication in the last five years are also included. The main focus of this Review is to provide a detailed account on the rational engineering of the electrodes, electrolytes, and separators for improving the charge storage performance with a future perspective to achieving high energy density and long cycling stability and large-scale production for practical application.

Chemically assembling chromium vanadate into an urchin-like porous rich matrix with ultrathin nanosheets for rapid Zn2+ storage

Aqueous zinc ion battery (AZIB) is a promising battery system developed in recent years, which has the advantages of safety, environmental protection and low price. However, it is still a puzzle to develop and improve cathode materials with satisfactory performance. In this paper, the chromium vanadate (CrVO₃) electrode material was reported for the first time. The obtained CrVO₃ have mesoporous structure (the mesopore sizes: 2-50 nm), excellent conductivity, high surface area (129.3 m² g^-1) and uniform thickness of 2 nm, which provides a short path for rapid transfer of zinc ions, a large surface area for high pseudocapacitance, and sufficient voids to mitigate volume expansion. Given these structural advantages, the CrVO₃ cathode delivers high capacities of 188.8 and 112.8 mAh g^-1 at 0.5 and 4 A g^-1 and excellent long cycle stability, respectively. More importantly, the Zn//CrVO₃ battery provided an energy density of 231.9 Wh kg^-1 at a power density of 100.4 W kg^-1. Meanwhile, insight into the formation mechanism and Zn²⁺ storage mechanism by ex situ methods. The results show that the porous CrVO₃ is a promising cathode material for AZIBs, which provide a valuable idea for the design of porous vanadate with significantly enhanced performances in electrochemical energy storage.

High-performance reversible aqueous zinc-ion battery based on iron-doped alpha-manganese dioxide coated by polypyrrole

The development of zinc-ion storage cathode materials for aqueous zinc-ion batteries (AZIBs) is a necessary step for the construction of large-scale electrochemical energy conversion and storage devices. Iron-doped alpha-manganese dioxide (α-MnO₂) nanocomposites were achieved in this study via pre-intercalation of Fe³⁺ during the formation of α-MnO₂ crystals. A polypyrrole (PPy) granular layer was fabricated on the surface of α-MnO₂ using acid-catalyzed polymerization of pyrroles. The pre-intercalation of Fe³⁺ effectively enlarges the lattice spacing of α-MnO₂ and consequently decreases the hindrance for Zn²⁺ insertion/extraction in the iron-doped α-MnO₂ coated by PPy (Fe/α-MnO₂@PPy) composite. Meanwhile, the PPy buffer layer can ameliorate electron and ion conductivity and prevent dissolution of α-MnO₂during the charge/discharge process. This unique structure makes the Fe/α-MnO₂@PPy composite an efficient zinc-ion storage cathode for AZIBs. The targeted Fe/α-MnO₂@PPy cathode achieves superior performance with reversible specific capacity (270 mA h g^-1 at 100 mA g^-1) and exhibits highdiffusioncoefficientof 10^-10-10^-14 cm^-2 s^-1. Therefore, a feasible approach is implemented on advanced electrode materials using in AZIBs for practical applications.

Melamine-assisted synthesis of porous V2O3/N-doped carbon hollow nanospheres for efficient sodium-ion storage

Vanadium-based oxides with relatively high theoretical capacity have been regarded as promising electrode materials for boosting energy conversion and storage. However, their poor electrical conductivity usually leads to unsatisfied performance and poor cycling stability. Herein, uniform V₂O₃/N-doped carbon hollow nanospheres (V₂O₃/NC HSs) with mesoporous structures were successfully synthesized through a melamine-assisted simple hydrothermal reaction and carbonization treatment. We demonstrated that the introduction of melamine played an essential role in the construction of V₂O₃/NC HSs. Benefitting from the special mesoporous structure and large specific surface area, the as-obtained sample exhibited enhanced conductivity and structural stability. As a proof of concept, well-defined V₂O₃/NC HSs exhibited excellent cycling stability and rate performance for sodium-ion batteries, and achieved a discharge capacity of 263.8 mA h g^-1 at a current density of 1.0 A g^-1 after 1000 cycles, one of the best performances of V-based compounds. The enhanced performance could be attributed to the synergistic effect of the hollow structure and surface carbon coating. The present work describes the design of the morphology and structure of vanadium-based oxides for energy storage devices.

A new tunnel-type V4O9 cathode for high power density aqueous zinc ion batteries

A mixed-valence vanadium oxide V4O9 with a tunnel structure was synthesized as a cathode material for aqueous zinc ion batteries. A Zn//V4O9 battery displays high specific capacity and excellent rate performance.

Synergistic Effects of Phosphorus and Boron Co-Incorporated Activated Carbon for Ultrafast Zinc-Ion Hybrid Supercapacitors

The rapid expansion of the development of the electrochemical capacitor appliance and its industry areas has created the need for long cycling stability of over 30 000 cycles along with an ultrafast performance (referred to as ultrafast longevity). In recent years, zinc-ion hybrid supercapacitors (ZICs) are considered to be emerging energy storage applications thanks to their high specific capacity and remarkable cycling stability. However, ZICs still face serious challenges in overcoming the ultrafast performance and lifetime limitations related to the cathode materials, activated carbon (AC), due to inadequate electrical properties and poor wettability between the electrolyte and the electrode, which cause reductions in specific capacity and lifetime rapidly at high current densities during cycling. To address these drawbacks, a novel phosphorus (P) and boron (B) codoped AC (designated P&B-AC) is presented herein with enhanced electrical properties due to B-doping along with improved wettability due to P-doping to provide an ultrafast longevity ZICs. The prepared ZICs display a superior electrochemical performance with an excellent specific capacity of 169.4 mAh g^-1 at 0.5 A g^-1, a remarkable ultrafast performance of 84.0 mAh g^-1 at 10 A g^-1, and outstanding ultrafast longevity indicated by an 88% capacity retention for up to 30 000 cycles at 10 A g^-1. The excellent energy storage ability is firmly ascribed to the P and B codoping synergistic effect, leading to a superior diffusion capability of Zn ion and charge-transfer process of the AC cathode.

Tuning the Kinetics of Zinc-Ion Insertion/Extraction in V2 O5 by In Situ Polyaniline Intercalation Enables Improved Aqueous Zinc-Ion Storage Performance

Rechargeable zinc-ion batteries (ZIBs) are emerging as a promising alternative for Li-ion batteries. However, the developed cathodes suffer from sluggish Zn²⁺ diffusion kinetics, leading to poor rate capability and inadequate cycle life. Herein, an in situ polyaniline (PANI) intercalation strategy is developed to facilitate the Zn²⁺ (de)intercalation kinetics in V₂ O₅ . In this way, a remarkably enlarged interlayer distance (13.90 Å) can be constructed alternatively between the VO layers, offering expediting channels for facile Zn²⁺ diffusion. Importantly, the electrostatic interactions between the Zn²⁺ and the host O^2- , which is another key factor in hindering the Zn²⁺ diffusion kinetics, can be effectively blocked by the unique π-conjugated structure of PANI. As a result, the PANI-intercalated V₂ O₅ exhibits a stable and highly reversible electrochemical reaction during repetitive Zn²⁺ insertion and extraction, as demonstrated by in situ synchrotron X-ray diffraction and Raman studies. Further first-principles calculations clearly reveal a remarkably lowered binding energy between Zn²⁺ and host O^2- , which explains the favorable kinetics in PANI-intercalated V₂ O₅ . Benefitting from the above, the overall electrochemical performance of PANI-intercalated V₂ O₅ electrode is remarkable improved, exhibiting excellent high rate capability of 197.1 mAh g^-1 at current density of 20 A g^-1 with capacity retention of 97.6% over 2000 cycles.

Anodic Oxidation Strategy toward Structure-Optimized V2O3 Cathode via Electrolyte Regulation for Zn-Ion Storage

The lack of suitable cathodes is one of the key reasons that impede the development of aqueous zinc-ion batteries. Because of the inherently unsuitable structure and inferior physicochemical properties, the low-valent V₂O₃ as Zn²⁺ host could not be effectively discharged. Herein, we demonstrate that V₂O₃ (theoretical capacity up to 715 mAh g^-1) can be utilized as a high-performance cathode material by an in situ anodic oxidation strategy. Through simultaneously regulating the concentration of the electrolyte and the morphology of the V₂O₃ sample, the ultraefficient anodic oxidation process of the V₂O₃ cathode was achieved within the first charging, and the mechanism was also schematically investigated. As expected, the V₂O₃ cathode with a hierarchical microcuboid structure achieved a nearly two-electron transfer process, enabling a high discharging capacity of 625 mAh g^-1 at 0.1 A g^-1 (corresponding to a high energy density of 406 Wh kg^-1) and cycling stability (100% capacity retention after 10 000 cycles). This work not only sheds light on the phase transition process of low-valent V₂O₃ but also exploits a method toward design of advanced cathode materials.