Ultrafast Zn2+ Intercalation and Deintercalation in Vanadium Dioxide

Capacity-enhanced and kinetic-expedited zinc-ion storage ability in a Zn3V3O8/VO2 cathode enabled by heterostructural design

Heterostructured double-phase composites are promising electrode candidates for high-performance secondary metal batteries due to their superior capacity and ion transfer kinetics compared with the pristine phase. Herein, a Zn₃V₃O₈/VO₂ (ZVO/VO) heterostructure with abundant phase boundaries was designed as the cathode for aqueous zinc-ion batteries (ZIBs). The preparation method is based on a solid pre-intercalation approach, and the Zn content in the ZVO/VO heterostructure can be precisely controlled. The electrochemical performance of ZVO/VO containing different amounts of Zn, pristine ZVO, and VO phases was compared. ZVO/VO showed superior capacity and cycling stability compared to pristine ZVO and VO. The ZVO/VO heterostructure showed a capacity of 328.4 mA h g^-1 at 0.3 A g^-1 after 200 cycles. The long-term cycling performance of ZVO/VO was evaluated at 3 A g^-1, and it delivered a capacity retention of 90.5% after 1000 cycles. The ion storage mechanism of the ZVO/VO electrode was analyzed by ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). This work provides a simple strategy for designing vanadium-based heterostructure composites as advanced cathodes for ZIBs.

Unlocking Layered Double Hydroxide as a High-Performance Cathode Material for Aqueous Zinc-Ion Batteries

Advanced cathode materials play an important role in promoting aqueous battery technology for safe energy storage. Transition metal double hydroxides are usually elusive as a stable cathode for aqueous zinc-ion batteries (AZIBs) due to their unstable crystal structure, sluggish ion transportation, and insufficient active sites for zinc-ion storage. Here, a trinary layered double hydroxide (LDH) with hydrogen vacancies (Ni₃ Mn_0.7 Fe_0.3 -LDH) is reported as a new cathode material for AZIBs. A reversible high capacity up to 328 mAh g^-1 can be obtained and cycle stably over 500 cycles with a capacity retention of 85%. Experimental and theoretical studies reveal that the hydrogen vacancies in LDH can expose lattice oxygen atoms as active sites for zinc-ion storage and accelerate ion diffusion by reducing the electrostatic interactions between zinc ions and the host structure. In addition, the synergy of the trinary transitional metal cations can suppress the Jahn-Teller distortion of manganese (III) oxide octahedron and enable long cycle stability. This work provides not only a series of high-performance cathode materials for AZIBs but also a novel materials design strategy that can be extended to other multi-valence metal-ion batteries.

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.

Enhancing the kinetics of vanadium oxides via conducting polymer and metal ions co-intercalation for high-performance aqueous zinc-ions batteries

Aqueous zinc-ions batteries with low cost, reliable safety, high theoretical specific capacity and eco-friendliness have captured conspicuous attention in large-scale energy storage. However, the developed cathodes often suffer from low electrical conductivity and sluggish Zn²⁺ diffusion kinetics, which severely hampers the development of aqueous zinc-ions batteries. Herein, we successfully prepare Mg/PANI/V₂O₅•nH₂O (MPVO) nanosheets through conducting polymers (polyaniline) and metal ions (Mg²⁺) co-intercalated strategy and systematically explore its electrochemical performance as cathode materials for aqueous zinc-ion batteries. Benefitting from the synergistic effect of polyaniline and Mg²⁺ co-intercalated, the MPVO exhibits larger interlayer spacing and higher electrical conductivity than the single guest intercalation, which significantly enhances the electrochemical kinetics. As a consequence, the MPVO cathodes deliver superior specific capacity, rate capability and long-term cycling performance. Moreover, multiple characterizations and theoretical calculations are executed to expound the relevant mechanism.Therefore, this work provides a novel thought for the design of high-performance cathode materials for aqueous ZIBs.

Sodium Pre-Intercalated Carbon/V2 O5 Constructed by Sustainable Sodium Lignosulfonate for Stable Cathodes in Zinc-Ion Batteries: A Comprehensive Study

The aqueous zinc-ion battery (AZIB) has been widely investigated in recent years because it has the advantages of being green, safe, and made from abundant raw materials. It is necessary to continue to study how to prepare cathode materials with excellent performance and high cycling stability for future commercialization. In this work, a strategy was proposed that uses sustainable sodium lignosulfonate as both carbon and sodium sources to obtain a sodium pre-intercalated vanadium oxide/carbon (VO/LSC) composite as the cathode of AZIB. The carbon matrix could improve the electronic conductivity of vanadium oxide, while the sodium lignosulfonate could provide sodium ions pre-intercalated into the layered vanadium oxide simultaneously. Through this strategy, vanadium-based cathode materials with high stability and excellent rate capability were obtained. The VO/LSC cathode delivered high capacities of 350 and 112.8 mAh g^-1 at 0.1 and 4.0 A g^-1 , respectively. Zinc sulfate and zinc trifluoromethyl sulfonate were selected as electrolytes, and the influence of electrolytes on the performance of VO/LSC was analyzed. The oxygen in the environment was used to oxidize the low-priced vanadium oxide to achieve a self-charging AZIB. This paper provides a valuable strategy for the design of vanadium-based cathode material for AZIB, which can broaden the research and application of AZIB.

An Ultrafast, Durable, and High-Loading Polymer Anode for Aqueous Zinc-Ion Batteries and Supercapacitors

Zn metal has shown promise as an anode material for grid-level energy storage, yet is challenged by dendritic growth and low Coulombic efficiency. Herein, an ultrafast, stable, and high-loading polymer anode for aqueous Zn-ion batteries and capacitors (ZIBs and ZICs) is developed by engineering both the electrode and electrolyte. The anode polymer is rationally prepared to have a suitable electronic structure and a large π-conjugated structure, whereas the electrolyte is manufactured based on the superiority of triflate anions over sulfate anions, as analyzed and confirmed via experiments and simulations. This dual engineering results in an optimal polymer anode with a low discharge potential, near-theoretical capacity, ultrahigh-loading capability (≈50 mg cm^-2 ), ultrafast rate (100 A g^-1 ), and ultralong lifespan (one million cycles). Its mechanism involves reversible Zn²⁺ /proton co-storage at the carbonyl site. When the polymer anode is coupled with cathodes for both ZIB and ZIC applications, the devices demonstrate ultrahigh power densities and ultralong lifespans, far surpassing those of corresponding Zn-metal-based devices.

Achieving high-rate and durable aqueous rechargeable Zn-Ion batteries by enhancing the successive electrochemical conversion reactions

The mild electrolyte working environment of rechargeable aqueous Zn-ion batteries (AZIBs) features its promising characteristic and potential application for large-scale energy storage system. However, the poor cycling stability significantly hinders the broad application of AZIBs due to the complex electrochemical conversion reactions during charge-discharge process. Herein, we propose a strategy to improve the electrochemical performance of AZIB by enhancing the successive electrochemical conversion reactions. With a rational design of electrode, an even homogeneous electric field can be achieved in the cathode side, resulting to significantly enhanced efficiency of successive electrochemical conversion reactions. Charge storage mechanism studies reveal that the reversibility behaviors of byproducts alkaline zinc sulfate (ZHS) can dramatically determine the H⁺/Zn²⁺ de/intercalation process, and a high reversibility characteristic ensures the facilitated electrochemical kinetics. As expected, the resultant AZIB possesses outstanding electrochemical performance with a high specific capacity of 425.08 mAh⋅g^-1 at 0.1 A⋅g^-1, an excellent rate capacity of about 60% (246.6 mAh⋅g^-1 at 1 A⋅g^-1) and superior cycling stability of 93.7% after 3000 cycles (at 3 A⋅g^-1). This effective strategy and thinking proposed here may open a new avenue for the development of high-performing AZIBs.

Molten Salt Thermal Treatment Synthesis of S-Doped V2CTx and Its Performance as a Cathode in Aqueous Zn-Ion Batteries

The lack of suitable cathode materials with a high capacity and good stability is a crucial problem affecting the development of aqueous Zn-ion batteries. Herein, a novel strategy for the modification of V₂CT_x through molten salt thermal treatment is proposed. In the novel route, S heteroatoms were introduced into V₂CT_x through a substitution reaction during the dissolution of Li₂S in LiCl-KCl molten salts. Then, surface V₂O₅ was obtained through the in situ electrochemical charging/discharging of the S-doped V₂CT_x (MS-S-V₂CT_x) cathode. The assembled Zn/MS-S-V₂CT_x battery showed a high reversible discharge capacity of 411.3 mAh g^-1 at a current density of 0.5 A g^-1, an 80% capacitance retention after long cycle stability tests at 10 A g^-1 for 3000 cycles, and a high energy density of 375.5 Wh kg^-1 in 2M ZnSO₄. Density functional theory calculations demonstrate that the improved electrochemical performance of the cathode can be attributed to the introduced S heteroatoms, which considerably reduced the ion diffusion energy barrier for Zn²⁺ ions and improved the stability of V₂O₅. This work provides a novel method to produce highly active and stable vanadium-based cathodes for aqueous Zn-ion batteries.

Orthoquinone-Based Covalent Organic Frameworks with Ordered Channel Structures for Ultrahigh Performance Aqueous Zinc-Organic Batteries

Elaborate molecular design on cathodes is of great importance for rechargeable aqueous zinc-organic batteries' performance elevation. Herein, we design a novel orthoquinone-based covalent organic framework with an ordered channel structures (BT-PTO COF) cathode for an ultrahigh performance aqueous zinc-organic battery. The ordered channel structure facilitates ions transfer and makes the COF follow a redox pseudocapacitance mechanism. Thus, it delivers a high reversible capacity of 225 mAh g^-1 at 0.1 A g^-1 and an exceptional long-term cyclability (retention rate 98.0 % at 5 A g^-1 (≈18 C) after 10 000 cycles). Moreover, a co-insertion mechanism with Zn²⁺ first followed by two H⁺ is uncovered for the first time. Significantly, this co-insertion behaviour evolves to more H⁺ insertion routes at high current density and gives the COF ultra-fast kinetics thus it achieves unprecedented specific power of 184 kW kg^-1 _(COF) and a high energy density of 92.4 Wh kg^-1 _(COF) . Our work reports a superior organic material for zinc batteries and provides a design idea for future high-performance organic cathodes.

Enhanced Electrochemical Performance of Zn/VOx Batteries by a Carbon-Encapsulation Strategy

Aqueous zinc ion batteries show tremendous potential in emerging energy storage devices. However, it is challenging to explore the desired cathode materials that match well with the Zn anode. In this work, we report two kinds of carbon-encapsulated VO_x microspheres grown by controlling the calcination temperature. The assembled Zn/VO₂@C-0.5 batteries deliver a high specific capacity and reversible rate performance. They can still maintain 260 mA h g^-1 at 5 A g^-1 after 1000 cycles. In addition, the cells possess an energy density of 280 W h kg^-1 at a power density of 140 W kg^-1. The soft pack devices also show favorable mechanical stability and durable cycle ability. The excellent zinc ion storage capacity can be attributed to the large tunnel structure of VO₂ materials and the high conductivity of amorphous carbon.

Open-Framework Metal Oxides for Fast and Reversible Hydrated Zinc-Ion Intercalation

The development of high capacity and stable cathodes is the key to the successful commercialization of aqueous zinc-ion batteries. However, significant solvation penalties limit the choice of available positive electrodes. Herein, hydrated intercalation is proposed to promote reversible (de)intercalation within host materials by rationally designing a matching electrode. In contrast to previously reported works, the as-prepared electrode (NHVO@CC) can achieve fast and reversible intercalation of hydrated zinc ions in the interlayer gap, leading to a high capacity of 517 mAh g^-1 at 0.1 A g^-1 and excellent electrode stability for long-term cycling. Besides, as a consequence of the flexibility of the NHVO@CC electrode, a quasi-solid-state battery was achieved with equally advantageous electrochemical behavior under various bending states. The proposed hydrated cation direct insertion/extraction sets up an efficient way of developing high-performance positive electrodes for aqueous batteries.

Water-Processable and Multiscale-Designed Vanadium Oxide Cathodes with Predominant Zn2+ Intercalation Pseudocapacitance toward High Gravimetric/Areal/Volumetric Capacity

Layered vanadium oxides have great potential as cathode materials for recently surged aqueous zinc-ion batteries (AZIBs). However, achieving high energy/power densities simultaneously is challenging, and side reactions related to more frequently than disclosed Zn²⁺ /proton co-insertion mechanism aggravate stability concerns. Herein, an engineered binder-free cathode configuration based on water-processable and high packing-density sheet-shaped composites of carbon nanotubes network, surface poly(3,4-ethylenedioxythiophene) (PEDOT) bridging coating, and ultrasmall PEDOT-intercalated V₂ O₅ nanoflakes is developed, and therein, large pseudocapacitance via predominant (≈91%) Zn²⁺ intercalation is revealed. Besides competitive gravimetric/areal capacity, the binder-free cathodes exhibit high volumetric capacity of 1106.1 mAh cm^-3 and high-rate capability of 180.0 mA g^-1 at 30 A g^-1 as well as long-cycling stability. Such combined level of performance and unwanted reaction mechanism are attributed to the contained multiscale material/electrode design formula from crystal structure modification to 3D architecture construction of whole electrode, which endows the binder-free cathodes with abundant accessible sites for Zn²⁺ storage, but the least hydroxyl terminated surface for H⁺ insertion, as well as highly conductive network for electron transfer and fast Zn²⁺ diffusion kinetics throughout the electrode. Combined with scalable fabrication protocols, this study opens up great opportunities for high-performance vanadium oxide cathodes practically applicable to AZIBs.

Fast Ionic Storage in Aqueous Rechargeable Batteries: From Fundamentals to Applications

The highly dynamic nature of grid-scale energy systems necessitates fast kinetics in energy storage and conversion systems. Rechargeable aqueous batteries are a promising energy-storage solution for renewable-energy grids as the ionic diffusivity in aqueous electrolytes can be up to 1-2 orders of magnitude higher than in organic systems, in addition to being highly safe and low cost. Recent research in this regard has focussed on developing suitable electrode materials for fast ionic storage in aqueous electrolytes. In this review, breakthroughs in the field of fast ionic storage in aqueous battery materials, and 1D/2D/3D and over-3D-tunnel materials are summarized, and tunnels in over-3D materials are not oriented in any direction in particular. Various materials with different tunnel sizes are developed to be suitable for the different ionic radii of Li⁺ , Na⁺ , K⁺ , H⁺ , NH₄ ⁺ , and Zn²⁺ , which show significant differences in the reaction kinetics of ionic storage. New topochemical paths for ion insertion/extraction, which provide superfast ionic storage, are also discussed.

In Situ Electrochemical Transformation toward Structure Optimized VEG@MXene Cathode for Enhanced Zinc-Ion Storage

Vanadium-based derivatives, featuring affordable cost and high theoretical capacity, have gathered widespread interest in the context of aqueous zinc-ion batteries (ZIBs). However, the further application of vanadium-based materials is hindered by the limited electrical conductivity and cycling lifespan. Herein, 1D chain-like structure vanadyl ethylene glycolate (VEG, (VO(CH₂ O)₂ )), growing on the Ti₃ C₂ T_x MXene nanosheets, is synthesized via a one-step oil-bath heating process as cathode materials for ZIBs. Benefiting from the hybrid structure with high conductivity and abundant reactive sites, the VEG@MXene cathode exhibits a remarkable specific capacity (360.3 mAh g^-1 at 0.5 A g^-1 ), and impressive capacity retention (up to 85.2% after 3000 cycles at 10 A g^-1 ). Mechanism analysis reveals a gradual phase transition from the original VEG on MXene to the stable Zn₃ V₂ O₇ (OH)₂ ·2H₂ O nanoflakes accompanied by continuous zinc ion intercalation/deintercalation, offering more pathways for zinc ion transport. This work suggests that engineering conductivity-enhanced vanadium-based materials is a rational approach for developing promising cathode materials of ZIBs.

Organic-Inorganic Hybrid Cathode with Dual Energy-Storage Mechanism for Ultrahigh-Rate and Ultralong-Life Aqueous Zinc-Ion Batteries

The exploitation of cathode materials with high capacity as well as high operating voltage is extremely important for the development of aqueous zinc-ion batteries (ZIBs). Yet, the classical high-capacity materials (e.g., vanadium-based materials) provide a low discharge voltage, while organic cathodes with high operating voltage generally suffer from a low capacity. In this work, organic (ethylenediamine)-inorganic (vanadium oxide) hybrid cathodes, that is, EDA-VO, with a dual energy-storage mechanism, are designed for ultrahigh-rate and ultralong-life ZIBs. The embedded ethylenediamine (EDA) can not only increase the layer spacing of the vanadium oxide, with improved mobility of Zn ions in the V-O layered structure, but also act as a bidentate chelating ligand participating in the storage of Zn ions. This hybrid provides a high specific capacity (382.6 mA h g^-1 at 0.5 A g^-1 ), elevated voltage (0.82 V) and excellent long-term cycle stability (over 10 000 cycles at 5 A g^-1 ). Assistant density functional theory (DFT) calculations indicate the cathode has remarkable electronic conductivity, with an ultralow diffusion barrier of 0.78 eV for an optimal Zn-ion diffusion path in the EDA-VO. This interesting idea of building organic-inorganic hybrid cathode materials with a dual energy-storage mechanism opens a new research direction toward high-energy secondary batteries.

Highly Sensitive and Ultra-Broadband VO2(B) Photodetector Dominated by Bolometric Effect

In this study, Wadsley B phase vanadium oxide (VO₂(B)) with broad-band photoabsorption ability, a large temperature coefficient of resistance (TCR), and low noise was developed for uncooled broad-band detection. By using a freestanding structure and reducing the size of active area, the VO₂(B) photodetector shows stable and excellent performances in the visible to the terahertz region (405 nm to 0.88 mm), with a peak TCR of -4.77% K^-1 at 40 °C, a peak specific detectivity of 6.02 × 10⁹ Jones, and a photoresponse time of 83 ms. A terahertz imaging ability with 30 × 30 pixels was demonstrated. Scanning photocurrent imaging and real-time temperature-photocurrent measurements confirm that a photothermal-type bolometric effect is the dominating mechanism. The study shows the potential of VO₂(B) in applications as a new type of uncooled broad-band photodetection material and the potential to further raise the performance of broad-band photodetectors by structural design.

Zinc ion thermal charging cell for low-grade heat conversion and energy storage

Converting low-grade heat from environment into electricity shows great sustainability for mitigating the energy crisis and adjusting energy configurations. However, thermally rechargeable devices typically suffer from poor conversion efficiency when a semiconductor is employed. Breaking the convention of thermoelectric systems, we propose and demonstrate a new zinc ion thermal charging cell to generate electricity from low-grade heat via the thermo-extraction/insertion and thermodiffusion processes of insertion-type cathode (VO2-PC) and stripping/plating behaviour of Zn anode. Based on this strategy, an impressively high thermopower of ~12.5 mV K-1 and an excellent output power of 1.2 mW can be obtained. In addition, a high heat-to-current conversion efficiency of 0.95% (7.25% of Carnot efficiency) is achieved with a temperature difference of 45 K. This work, which demonstrates extraordinary energy conversion efficiency and adequate energy storage, will pave the way towards the construction of thermoelectric setups with attractive properties for high value-added utilization of low-grade heat.

Hierarchical Atomic Layer Deposited V2 O5 on 3D Printed Nanocarbon Electrodes for High-Performance Aqueous Zinc-Ion Batteries

Aqueous rechargeable zinc-ion batteries (ARZIBs) are promising energy storage systems owing to their ecofriendliness, safety, and cost-efficiency. However, the sluggish Zn²⁺ diffusion kinetics originated from its inherent large atomic mass and high polarization remains an ongoing challenge. To this end, electrodes with 3D architectures and high porosity are highly desired. This work reports a rational design and fabrication of hierarchical core-shell structured cathodes (3D@V₂ O₅ ) for ARZIBs by integrating fused deposition modeling (FDM) 3D-printing with atomic layer deposition (ALD). The 3D-printed porous carbon network provides an entangled electron conductive core and interconnected ion diffusion channels, whereas ALD-coated V₂ O₅ serves as an active shell without sacrificing the porosity for facilitated Zn²⁺ diffusion. This endows the 3D@V₂ O₅ cathode with high specific capacity (425 mAh g^-1 at 0.3 A g^-1 ), competitive energy and power densities (316 Wh Kg^-1 at 213 W kg^-1 and 163 Wh Kg^-1 at 3400 W kg^-1 ), and good rate performance (221 mAh g^-1 at 4.8 A g^-1 ). The developed 3D@V₂ O₅ cathode provides a promising model for customized and scalable battery electrode engineering technology. As the ALD-coated layer determines the functional properties, the proposed strategy shows a promising prospect of FDM 3D printing using 1D carbon materials for future energy storage.

Phase B vanadium dioxide: characteristics, synthesis and applications

Starting from the numerous and unique characteristics of VO2(B), we will introduce to readers the research progress of VO2(B) in recent years, including the detailed mainstream methods for its preparation and popular fields of application.

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.

A high-capacity polyaniline-intercalated layered vanadium oxide for aqueous ammonium-ion batteries

A 1.55 nm-interlayer spacing-expanded polyaniline-intercalated vanadium oxide, as a new electrode material for NH₄⁺-ion batteries, exhibits the highest ever reported capacity of ∼307 mA h g^-1 at a current density of 0.5 A g^-1. In situ FT-IR and XPS studies confirm the reversible NH₄⁺ storage is accompanied by H bond formation/breaking within the functional group of -VO···H.

Flexible Electron-Rich Ion Channels Enable Ultrafast and Stable Aqueous Zinc-Ion Storage

Aqueous zinc-ion batteries (ZIBs) are regarded as a promising candidate for ultrafast charge storage owing to the high ionic conductivity of aqueous electrolytes and high theoretical capacity of zinc metal anodes. However, the strong electrostatic interaction between high-charge-density zinc ions and host materials generally leads to sluggish ion-transport kinetics and structural collapse of rigid cathode materials during the charge/discharge process, so searching for suitable cathode materials for ultrafast and long-term stable ZIBs remains a great challenge. Herein, flexible electron-rich ion channels enabling fast-charging and stable aqueous ZIBs have been demonstrated. Because of the nitrogen-rich conjugated structure of organic phenazine (PNZ) molecules, electron-rich ion channels are formed with the C═N redox centers situated on the channel surface, where zinc ions can transport rapidly and react with active moieties directly. Meanwhile, the π-conjugated systems and inherent flexibility of PNZ molecules can accommodate rapid strain changes and maintain their structural stability during zinc-ion intercalation/deintercalation. Consequently, they exhibit a high capacity of 94.2 mAh g^-1 at an ultrahigh rate of 700C (208.6 A g^-1) and an ultralong life over 100,000 cycles at 100C, which are superior to those of previously reported aqueous ZIBs. Our work presents a new way for developing ultrafast and ultrastable aqueous ZIBs.

Studying the Conversion Mechanism to Broaden Cathode Options in Aqueous Zinc-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) are regarded as alternatives to Li-ion batteries benefiting from both improved safety and environmental impact. The widespread application of ZIBs, however, is compromised by the lack of high-performance cathodes. Currently, only the intercalation mechanism is widely reported in aqueous ZIBs, which significantly limits cathode options. Beyond Zn-ion intercalation, we comprehensively study the conversion mechanism for Zn²⁺ storage and its diffusion pathway in a CuI cathode, indicating that CuI occurs a direct conversion reaction without Zn²⁺ intercalation due to the high energy barrier for Zn²⁺ intercalation and migration. Importantly, this direct conversion reaction mechanism can be readily generalized to other high-capacity cathodes, such as Cu₂ S (336.7 mA h g^-1 ) and Cu₂ O (374.5 mA h g^-1 ), indicating its practical universality. Our work enriches the Zn-ion storage mechanism and significantly broadens the cathode horizons towards next-generation ZIBs.

Tailoring double-layer aromatic polymers with multi-active sites towards high performance aqueous Zn-organic batteries

Unlike most reported organic-inorganic cathodes, the organic-organic zinc hosts can fully exploit the flexible structures and various redox chemistries of the organics. Herein, nanoporous carbon electrodeposited with a wrapped poly(meta-aminophenol, 3-AP) sandwich layer and a good conductive poly(para-aminophenol, 4-AP) skin, designated as a C@poly(3-AP)/poly(4-AP) cathode, has been synthesized for the first time via a novel two-step electrodeposition method. The synergistic effect of the double-layer polymers endows the C@poly(3-AP)/poly(4-AP) cathode with an ultrahigh specific capacity, excellent rate performance and long-term lifespan that are superior to those of the pristine C@poly(3-AP) and C@poly(4-AP) electrodes. Also, the strong electron donor capabilities of the multiple active sites (CO and CN) in the hetero-structural organic cathode can exhibit symmetrical bending to host inserted Zn ions during the discharge process, which opens up new opportunities to construct advanced Zn-organic batteries.

Suppressing vanadium dissolution of V2O5via in situ polyethylene glycol intercalation towards ultralong lifetime room/low-temperature zinc-ion batteries

Zinc-ion batteries (ZIBs) are a main focus worldwide for their potential use in large-scale energy storage due to their abundant resources, environmental friendliness, and high safety. However, the cathode materials of ZIBs are limited, requiring a stable host structure and fast Zn²⁺ channel diffusion. Here, we develop a strategy for the intercalation of polyethylene glycol (PEG) to facilitate Zn²⁺ intercalation and to suppress the dissolution of vanadium in V₂O₅. In particular, PEG-V₂O₅ shows a high capacity of 430 mA h g^-1 at a current density of 0.1 A g^-1 as well as excellent 100 mA h g^-1 specific capacity after 5000 cycles, with a high current density of 10.0 A g^-1. A reversible capacity of 81 mA h g^-1 can even be achieved with a low temperature of -20 °C at a current density of 2.0 A g^-1 after 3500 cycles. The superior electrochemical performance comes from the intercalation of PEG molecules, which can improve kinetic transport and structural stability during the cycling process. The Zn²⁺ storage mechanism, which provides essential guidelines for the development of high-performance ZIBs, can be found through various ex situ characterization technologies and density functional density calculations.

Vanadium dioxide-zinc oxide stacked photocathodes for photo-rechargeable zinc-ion batteries

The development of batteries that can be recharged directly by light, without the need for external solar cells or external power supplies, has recently gained interest for powering off-grid devices. Vanadium dioxide (VO₂) has been studied as a promising photocathode for zinc-ion batteries because it can both store energy and harvest light. However, the efficiency of the photocharging process depends on electrode structure and charge transport layers. In this work, we report photocathodes using zinc oxide as an electron transport and hole blocking layer on top of which we synthesise VO₂. The improved interface and charge separation in these photocathodes offer an improvement in photo-conversion efficiency from ∼0.18 to ∼0.51% compared to previous work on mixed VO₂ photocathodes. In addition, a good capacity retention of ∼73% was observed after 500 cycles. The proposed stacked photocathodes reduce the battery light charging time by 3-fold and are therefore an important step towards making this technology more viable.

2,3-diaminophenazine as a high-rate rechargeable aqueous zinc-ion batteries cathode

Organic materials are attracting extensive attention as promising cathodes for rechargeable aqueous zinc-ion batteries (ZIBs). However, most of them fail to implement the requirement of batteries with combined high-rate and long-cycle performance. Herein, we report a flexible organic molecule 2,3-diaminophenazine (DAP) which exhibits ultrahigh rate performance up to 500C and high capacity retention of 80% after 10,000 cycles at 100C (25.5 A g^-1). Moreover, the Zn²⁺ storage mechanism in the DAP electrode is revealed by ex-situ characterization technologies and theoretical calculation, and the redox active centers CN participate in the reversible electrochemical reaction process. Furthermore, electrochemical analyses show that surface-controlled electrochemical behavior contributes to the high-rate performance of DAP cathodes. Besides, its excellent long-cycle performance can be ascribed to the suppressed DAP dissolubility by using a modified glass fiber separator with carbon nanotubes (CNT) film. Our work provides useful insight into the design of high-rate and long-life ZIBs.

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.

Two Birds with One Stone: Boosting Zinc-Ion Insertion/Extraction Kinetics and Suppressing Vanadium Dissolution of V2O5 via La3+ Incorporation Enable Advanced Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) with cost-effective and safe features are highly competitive in grid energy storage applications, but plagued by the sluggish Zn²⁺ diffusion kinetics and poor cyclability of cathodes. Herein, a one-stone-two-birds strategy of La³⁺ incorporation (La-V₂O₅) is developed to motivate Zn²⁺ insertion/extraction kinetics and stabilize vanadium species for V₂O₅. Theoretical and experimental studies reveal the incorporated La³⁺ ions in V₂O₅ can not only serve as pillars to expand the interlayer distance (11.77 Å) and lower the Zn²⁺ migration energy barrier (0.82 eV) but also offer intermediated level and narrower band gap (0.54 eV), thus accelerating the electron/ion diffusion kinetics. Importantly, the steadily doped La³⁺ ions effectively stabilize the V-O bonds by shortening the bond length, thereby inhibiting vanadium species dissolution. Therefore, the resulting La-V₂O₅-ZIBs deliver an exceptional rate capacity of 405 mA h g^-1 (0.1 A g^-1), long-term stability with 93.8% retention after 5000 cycles (10 A g^-1), and extraordinary energy density of 289.3 W h kg^-1, outperforming various metal-ions-doped V₂O₅ cathodes. Moreover, the La-V₂O₅ pouch cell presents excellent electrochemical performance and impressive flexibility and integration ability. The strategies of incorporating rare-earth-metal ions provide guidance to other well-established aqueous ZIBs cathodes and other advanced electrochemical devices.

Cathode materials for aqueous zinc-ion batteries: A mini review

Although lithium-ion batteries (LIBs) have many advantages, they cannot satisfy the demands of numerous large energy storage industries owing to their high cost, low security, and low resource richness. Aqueous zinc-ion batteries (ZIBs) with low cost, high safety, and high synergistic efficiency have attracted an increasing amount of attention and are considered a promising choice to replace LIBs. However, the existing cathode materials for ZIBs have many shortcomings, such as poor electron and zinc ion conductivity and complex energy storage mechanisms. Thus, it is crucial to identify a cathode material with a stable structure, substantial limit, and suitability for ZIBs. In this review, several typical cathode materials for ZIBs employed in recent years and their detailed energy storage mechanisms are summarized, and various methods to enhance the electrochemical properties of ZIBs are briefly introduced. Finally, the existing problems and expected development directions of ZIBs are discussed.

Atomic-scale unveiling of multiphase evolution during hydrated Zn-ion insertion in vanadium oxide

An initial crystalline phase can transform into another phases as cations are electrochemically inserted into its lattice. Precise identification of phase evolution at an atomic level during transformation is thus the very first step to comprehensively understand the cation insertion behavior and subsequently achieve much higher storage capacity in rechargeable cells, although it is sometimes challenging. By intensively using atomic-column-resolved scanning transmission electron microscopy, we directly visualize the simultaneous intercalation of both H₂O and Zn during discharge of Zn ions into a V₂O₅ cathode with an aqueous electrolyte. In particular, when further Zn insertion proceeds, multiple intermediate phases, which are not identified by a macroscopic powder diffraction method, are clearly imaged at an atomic scale, showing structurally topotactic correlation between the phases. The findings in this work suggest that smooth multiphase evolution with a low transition barrier is significantly related to the high capacity of oxide cathodes for aqueous rechargeable cells, where the crystal structure of cathode materials after discharge differs from the initial crystalline state in general.

The detailed understanding of the structural variations during cycling in cathodes for Zn-ion aqueous rechargeable batteries is still limited. Here, the authors utilize atomic-column-resolved scanning transmission electron microscopy to elucidate multiphase evolution during hydrated Zn-Ion insertion in vanadium oxide.

Quicker and More Zn2+ Storage Predominantly from the Interface

Aqueous zinc-ion batteries are highly desirable for large-scale energy storage because of their low cost and high-level safety. However, achieving high energy and high power densities simultaneously is challenging. Herein, a VO_x sub-nanometer cluster/reduced graphene oxide (rGO) cathode material composed of interfacial VOC bonds is artificially constructed. Therein, a new mechanism is revealed, where Zn²⁺ ions are predominantly stored at the interface between VO_x and rGO, which causes anomalous valence changes compared to conventional mechanisms and exploits the storage ability of non-energy-storing active yet highly conductive rGO. Further, this interface-dominated storage triggers decoupled transport of electrons/Zn²⁺ ions, and the reversible destruction/reconstruction allows the interface to store more ions than the bulk. Finally, an ultrahigh rate capability (174.4 mAh g^-1 at 100 A g^-1 , i.e., capacity retention of 39.4% for a 1000-fold increase in current density) and a high capacity (443 mAh g^-1 at 100 mA g^-1 , exceeding the theoretical capacities of each interfacial component) are achieved. Such interface-dominated storage is an exciting way to build high-energy- and high-power-density devices.

High-Voltage and Super-Stable Aqueous Sodium-Zinc Hybrid Ion Batteries Enabled by Double Solvation Structures in Concentrated Electrolyte

Aqueous sodium-zinc hybrid ion batteries are attracting extensive attention due to high energy density, low cost, and environmental friendliness. Unfortunately, there are still some drawbacks associated with the low voltage and cycle performance degradation that limit their practical application. Here, a concentrated aqueous electrolyte with solvation-modulated Zn²⁺ is reported that reduces the hydrogen evolution reaction on the surface of Zn metal, avoiding the generation of ZnO and uneven deposition. Accordingly, the Zn anode exhibits 1600 h Zn plating/stripping and ≈99.96% Coulombic efficiency after 700 cycles. In addition, solvation-modulated Na⁺ promotes the excellent structural stability of zinc hexacyanoferrate (ZnHCF) due to the rhombohedral-rhombohedral rather than rhombohedral-cubic phase transition. A ZnHCF//Zn full cell delivers an average voltage of 1.76 V and 98% capacity retention after 2000 cycles at 5 C rates.

An Artificial Polyacrylonitrile Coating Layer Confining Zinc Dendrite Growth for Highly Reversible Aqueous Zinc-Based Batteries

Aqueous rechargeable zinc-metal-based batteries are an attractive alternative to lithium-ion batteries for grid-scale energy-storage systems because of their high specific capacity, low cost, eco-friendliness, and nonflammability. However, uncontrollable zinc dendrite growth limits the cycle life by piercing the separator, resulting in low zinc utilization in both alkaline and mild/neutral electrolytes. Herein, a polyacrylonitrile coating layer on a zinc anode produced by a simple drop coating approach to address the dendrite issue is reported. The coating layer not only improves the hydrophilicity of the zinc anode but also regulates zinc-ion transport, consequently facilitating the uniform deposition of zinc ions to avoid dendrite formation. A symmetrical cell with the polymer-coating-layer-modified Zn anode displays dendrite-free plating/stripping with a long cycle lifespan (>1100 h), much better than that of the bare Zn anode. The modified zinc anode coupled with a Mn-doped V2 O5 cathode forms a stable rechargeable full battery. This method is a facile and feasible way to solve the zinc dendrite problem for rechargeable aqueous zinc-metal batteries, providing a solid basis for application of aqueous rechargeable Zn batteries.

Electrochemically Induced Phase Transition in V3 O7 · H2 O Nanobelts/Reduced Graphene Oxide Composites for Aqueous Zinc-Ion Batteries

V₃ O₇ ·H₂ O nanobelts/reduced graphene oxide (rGO) composites (weight ratio: 86%/14%) are synthesized by a microwave approach with a high yield (85%) through controlling pH with acids. The growth mechanisms of the highly crystalline nanobelts (average diameter: 25 nm; length: ≈20 µm; oriented along the [101] direction) have been thoroughly investigated, with the governing role of the acid upon the morphology and oxidation state of vanadium disclosed. When used as the ZIB cathode, the composite can deliver a high specific capacity of 410.7 and 385.7 mAh g^-1 at the current density of 0.5 and 4 A g^-1 , respectively, with a high retention of the capacity of 93%. The capacity of the composite is greater than those of V₃ O₇  · H₂ O, V₂ O₅ nanobelts, and V₅ O₁₂  · 6H₂ O film. Zinc ion storage in V₃ O₇ ·H₂ O/rGO is mainly a pseudocapacitive behavior rather than ion diffusion. The presence of rGO enables outstanding cycling stability of up to 1000 cycles with a capacity retention of 99.6%. Extended cycling shows a gradual phase transition, that is, from the original orthorhombic V₃ O₇  · H₂ O to a stable hexagonal Zn₃ (VO₄ )₂ (H₂ O)_2.93 phase, which is a new electrochemical route found in V₃ O₇ materials. This phase transition process provides new insight into the reactions of aqueous ZIBs.