Boosting Zinc-Ion Storage Capability by Effectively Suppressing Vanadium Dissolution Based on Robust Layered Barium Vanadate

Multi-metal ions co-regulated vanadium oxide cathode toward long-life aqueous zinc-ion batteries

Interlayer intercalation engineering shows great feasibility to improve the structure stability of the layered oxides. Although high Zn-storage capability has been attained based on the pillar effect of multifarious intercalants, an in-depth understanding the synergistic effect of intercalated multiple metal ions is still in deficiency. Herein, alkali metal ion K+, alkaline earth metal ion Mg2+ and trivalent metal ion Al3+ are introduced into the VO interlayer of V2O5. Due to the different electronegativity and hydrated ion radius of K+, Mg2+ and Al3+, adjusting the relative proportions of these metal ions can achieve an appropriate interlayer spacing, stable layer structure and regular morphology, which facilitates the transport kinetics of Zn2+. Under the synergistic effect of pre-intercalated multi-metal ion, the optimal tri-metal ion intercalated hydrated V2O5 cathode exhibits a high specific capacity of 382.4 mAh g-1 at 0.5 A g-1, and long-term cycling stability with capacity retention of 86 % after 2000 cycles at the high current density of 10 A g-1. Ex-situ and kinetic characterizations reveal the fast charge transfer and reversible Zn2+ intercalation mechanism. The multi-ion engineering strategy provides an effective way to design desirable layered cathode materials for aqueous zinc-ion batteries.

Hydrogen Peroxide Tuned Morphology and Crystal Structure of Barium Vanadate-Based Nanostructures for Aqueous Zinc-Ion Storage Properties

Improving the layered-structure stability and suppressing vanadium (V) dissolution during repeated Zn2+ insertion/extraction processes are key to promoting the electrochemical stability of V-based cathodes for aqueous zinc (Zn)-ion batteries (AZIBs). In this study, barium vanadate (Ba2V2O7, BVO) nanostructures (NSs) are synthesized using a facile hydrothermal method. The formation process of the BVO NSs is controlled by adjusting the concentration of hydrogen peroxide (H2O2), and these NSs are employed as potential cathode materials for AZIBs. As the H2O2 content increases, the corresponding electrochemical properties demonstrate a discernible parabolic trend, with an initial increase, followed by a subsequent decrease. Benefiting from the effect of H2O2 concentration, the optimized BVO electrode with 20 mL H2O2 delivers a specific capacity of 180.15 mA h g-1 at 1 A g-1 with good rate capability and a long-term cyclability of 158.34 mA h g-1 at 3 A g-1 over 2000 cycles. Thus, this study provides a method for designing cathode materials with robust structures to boost the electrochemical performance of AZIBs.

Trigger a multi-electron reaction by tailoring electronic structure of VO2 toward more efficient aqueous zinc metal batteries

VO2 (B) is recognized as a promising cathode material for aqueous zinc metal batteries (AZMBs) owing to its remarkable specific capacity and its unique, expansive tunnel structure, which facilitates the reversible insertion and extraction of Zn2+. Nonetheless, challenges such as the inherent instability of the VO2 structure, poor ion/electron transport and a limited capacity due to the low redox potential of the V3+/V4+ couple have hindered its wider application. In this study, we present a strategy to replace vanadium ions by doping Al3+ in VO2. This approach activates the multi-electron reaction (V4+/V5+), to increase the specific capacity and improve the structural stability by forming robust V5+O and Al3+O bonds. It also induces a local electric field by altering the local electron arrangement, which significantly accelerates the ion/electron transport process. As a result, Al-doped VO2 exhibits superior specific capacity, improved cycling stability, and accelerated electronic transport kinetics compared to undoped VO2. The beneficial effects of heterogeneous atomic doping observed here may provide valuable insights into the improvement electrode materials in metal-ion battery systems other than those based on Zn.

An artificial aluminum-tin alloy layer on aluminum metal anodes for ultra-stable rechargeable aluminum-ion batteries

Rechargeable aluminum ion batteries (RAIBs) exhibit great potential for next-generation energy storage systems owing to the abundant resources, high theoretical volumetric capacity and light weight of the Al metal anode. However, the development of RAIBs based on Al metal anodes faces challenges such as dendrite formation, self-corrosion, and volume expansion at the anode/electrolyte interface, which needs the rational design of an aluminum anode for high-performance RAIBs. This work proposes a novel and low-cost strategy by utilizing an alloy electrodeposition method in a low-temperature molten salt system to fabricate an aluminum-tin (AlSn) alloy coating layer on copper foil as the anode for RAIBs, which successfully addresses the issues of dendrite formation and corrosion at the anode/electrolyte interface. The artificial AlSn alloy layer could enhance the active sites for metal Al homogeneous deposition and effectively retard the dendrite formation, which was verified by an in situ optical microscopy study. The symmetric AlSn@Cu cell demonstrates a low average overpotential of ∼38 mV at a current density of 0.5 mA cm-2 and a long-term lifespan of over 1100 h. Moreover, the AlSn@Cu//Mo6S8 full cells deliver a high capacity of 114.9 mA h g-1 at a current density of 100 mA g-1 and maintain ultra-stable cycling stability even over 1400 cycles with a ∼100% coulombic efficiency (CE) during the long-term charge/discharge processes. This facile alloy electrodeposition approach for designing high-performance Al-based anodes provides insights into the understanding of artificial interface chemistry on Al-based anodes and potentially accelerates the design of high-performance RAIBs.

Novel Zn0.079V2O5·0.53H2O/Graphene aerogel as high-rate and long-life cathode materials of aqueous zinc-ion batteries

Aqueous zinc-ion batteries (ZIBs) have attracted more and more attention due to their advantages of low cost, high safety and environmental protection. Unfortunately, the unsatisfactory capacity at high current density and long-term cycling performance of cathode materials hinder the development of ZIBs. Here, a novel Zn0.079V2O5·0.53H2O/graphene (ZVOH@rGO) hybrid aerogel composed of ultrathin Zn0.079V2O5·0.53H2O (ZVOH) nanoribbons and 3D continuous graphene conductive network was successfully prepared and used as cathode of ZIBs. Taking advantage of the synergistic effects associated with ion doping, morphology control and unique aerogel structure, the ZVOH@rGO electrode demonstrated ultrafast charge/discharge capability and remarkable cycling stability: A high reversible capacity of 286.7 mAh g-1 was achieved at a current density as large as 30 A g-1, and an impressive capacity retention ratio of 75.6 % was realized over 9800 ultra-long cycles at 12 A g-1. This work is of great significance for the synthesis modification of vanadium oxides and the development of high performance ultrafast charge-discharge ZIBs.

Layered BaV6O16·3H2O@GO as a high performance cathode material for calcium ion batteries

The lack of suitable cathode materials has hampered the further development of calcium-ion batteries (CIBs). A novel composite cathode material, namely BaV6O16·3H2O@GO, was fabricated, which delivers a high specific capacity of 285.72 mA h g-1 at 50 mA g-1 after 50 cycles and a long cycle life, benefiting from a large layer spacing and robust structure. This study provides guidance for the development of vanadium-based cathode materials for CIBs.

One-Step Hydrothermal Synthesis of NVO Cathodes with Varied Lattice NH4 + Content: Effect on Structural Evolution and Electrochemical Performance

Aqueous zinc ion batteries have been extensively researched due to their distinctive advantages such as low cost and high safety. Vanadium oxides are important cathode materials, however, poor cycle life caused by vanadium dissolution limits their application. Recent studies show that the lattice NH4 + in vanadium oxides can act as a pillar to enhance structural stability and play a crucial role in improving its cycling stability. Nevertheless, there is still a lack of research on the effect of the lattice NH4 + content on structural evolution and electrochemical performance. Herein, we synthesize vanadium oxides with different contents of lattice NH4 + by a one-step hydrothermal reaction. The vanadium oxides with lattice NH4 + exhibit high initial capacity, as well as good cycling stability and rate performance compared to bare vanadium oxide. Combined with electrochemical analyses, ex-situ structural characterizations, and in-situ X-ray diffraction tests, we reveal that the lattice NH4 + content plays a positive role in vanadium oxides' structural stability and cation diffusion kinetics. This work presents a direction for designing high-performance vanadium cathodes for aqueous zinc ion batteries.

Inhibition of Vanadium Cathodes Dissolution in Aqueous Zn-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have experienced a rapid surge in popularity, as evident from the extensive research with over 30 000 articles published in the past 5 years. Previous studies on AZIBs have showcased impressive long-cycle stability at high current densities, achieving thousands or tens of thousands of cycles. However, the practical stability of AZIBs at low current densities (<1C) is restricted to merely 50-100 cycles due to intensified cathode dissolution. This genuine limitation poses a considerable challenge to their transition from the laboratory to the industry. In this study, leveraging density functional theory (DFT) calculations, an artificial interphase that achieves both hydrophobicity and restriction of the outward penetration of dissolved vanadium cations, thereby shifting the reaction equilibrium and suppressing the vanadium dissolution following Le Chatelier's principle, is described. The approach has resulted in one of the best cycling stabilities to date, with no noticeable capacity fading after more than 200 cycles (≈720 h) at 200 mA g-1 (0.47C). These findings represent a significant advance in the design of ultrastable cathodes for aqueous batteries and accelerate the industrialization of aqueous zinc-ion batteries.

Unraveling the "Gap-Filling" Mechanism of Multiple Charge Carriers in Aqueous Zn-MoS2 Batteries

The utilization rate of active sites in cathode materials for Zn-based batteries is a key factor determining the reversible capacities. However, a long-neglected issue of the strong electrostatic repulsions among divalent Zn2+ in hosts inevitably causes the squander of some active sites (i.e., gap sites). Herein, we address this conundrum by unraveling the "gap-filling" mechanism of multiple charge carriers in aqueous Zn-MoS2 batteries. The tailored MoS2 /(reduced graphene quantum dots) hybrid features an ultra-large interlayer spacing (2.34 nm), superior electrical conductivity/hydrophilicity, and robust layered structure, demonstrating highly reversible NH4 + /Zn2+ /H+ co-insertion/extraction chemistry in the 1 M ZnSO4 +0.5 M (NH4 )2 SO4 aqueous electrolyte. The NH4 + and H+ ions can act as gap fillers to fully utilize the active sites and screen electrostatic interactions to accelerate the Zn2+ diffusion. Thus, unprecedentedly high rate capability (439.5 and 104.3 mAh g-1 at 0.1 and 30 A g-1 , respectively) and ultra-long cycling life (8000 cycles) are achieved.

Ordered planar plating/stripping enables deep cycling zinc metal batteries

Metal anodes are emerging as culminating solutions for the development of energy-dense batteries in either aprotic, aqueous, or solid battery configurations. However, unlike traditional intercalation electrodes, the low utilization of "hostless" metal anodes due to the intrinsically disordered plating/stripping impedes their practical applications. Herein, we report ordered planar plating/stripping in a bulk zinc (Zn) anode to achieve an extremely high depth of discharge exceeding 90% with negligible thickness fluctuation and long-term stable cycling. The Zn can be plated/stripped with (0001)Zn preferential orientation throughout the consecutive charge/discharge process, assisted by a self-assembled supramolecular bilayer at the Zn anode-electrolyte interface. Through real-time tracking of the Zn atoms migration, we reveal that the ordered planar plating/stripping is driven by the construction of in-plane Zn─N bindings and the gradient energy landscape at the reaction fronts. The breakthrough results provide alternative insights into the ordered plating/stripping of metal anodes toward rechargeable energy-dense batteries.

Mixed-Dimensional (2D/3D/3D) Heterostructured Vanadium Oxide with Rich Oxygen Vacancies for Aqueous Zinc Ion Batteries with High Capacity and Long Cycling Life

Heterostructure engineering and oxygen vacancy engineering are the most promising modification strategies to reinforce the Zn2+ ion storage of vanadium oxides. Herein, a rare mixed-dimensional material (VOx), composed of V2O5 (2D), V3O7 (3D), and V6O13 (3D) heterostructures, rich in oxygen vacancies, was synthesized via thermal decomposition of layered ammonium vanadate. The VOx cathode provides an exceptional discharge capacity (411 mA h g-1 at 0.1 A g-1) and superior cycling stability (the capacity retention remains close to 100% after 800 cycles at 2 A g-1) for aqueous zinc-ion batteries (AZIBs). Ex situ characterizations confirm that the byproduct Zn3V2O7(OH)2·nH2O is generated/decomposed during discharge/charge processes. Furthermore, VOx demonstrates reversible intercalation/deintercalation of H+/Zn2+ ions, enabling efficient energy storage. Remarkably, a reversible crystal-to-amorphous transformation in the V2O5 phase of VOx during charge-discharge was observed. This investigation reveals that mixed-dimensional heterostructured vanadium oxide, with abundant oxygen vacancies, serves as a highly promising electrode material for AZIBs, further advancing the comprehension of the storage mechanism within vanadium-based cathode materials.

Vanadium-Based Cathodic Materials of Aqueous Zn-Ion Battery for Superior-Performance with Prolonged-Life Cycle

Aqueous Zn-ion battery systems (AZIBs) have emerged as the most dependable solution, as demonstrated by successful systematic growth over the past few years. Cost effectivity, high performance and power density with prolonged life cycle are some major reason of the recent progress in AZIBs. Development of vanadium-based cathodic materials for AZIBs has appeared widely. This review contains a brief display of the basic facts and history of AZIBs. An insight section on zinc storage mechanism ramifications is given. A detailed discussion is conducted on features of high-performance and long life-time cathodes. Such features include design, modifications, electrochemical and cyclic performance, along with stability and zinc storage pathway of vanadium based cathodes from 2018 to 2022. Finally, this review outlines obstacles and opportunities with encouragement for gathering a strong conviction for future advancement in vanadium-based cathodes for AZIBs.

Boosting zinc-ion storage performance by interlayer chemistry modulation on an organic-inorganic hybrid cathode

Aqueous zinc-ion batteries (AZIBs) have triggered a surge of scientific research due to the unique merits of high safety, volumetric specific capacity, and environmental benignity. However, the implementation of this technology is still plagued by the lack of high-performance cathodes that can output high energy density and exceptional cycle life and inadequate Zn reversibility. Here, an organic-inorganic hybrid cathode based on a poly(3,4-ethylenedioxythiophene) (PEDOT) intercalated hydrated vanadium oxide (denoted PVO), which delivers an ultrahigh discharge capacity of 513.1 mAh g-1 (0.5 A g-1) and an ultra-stable cycle with 95.3 % capacity retention and approximately 100 % Coulombic efficiency over 2000 cycles (20 A g-1), is developed. Combining substantive measurements and theoretical calculations, it is demonstrated that favorable structural features with expanded interlayer galleries and robust architecture are believed to be responsible for the enhanced electrochemical performance, which can be further boosted by the improved Zn reversibility because of the introduction of maltitol electrolyte additive. This work provides a new attempt to achieve organic-inorganic composites for high-performance cathode materials of AZIBs and new insights into the charge storage behavior under the synergistic regulation of bilateral interfaces.

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.

Effectively Modulating Oxygen Vacancies in Flower-Like δ-MnO2 Nanostructures for Large Capacity and High-Rate Zinc-Ion Storage

In recent years, manganese-based oxides as an advanced class of cathode materials for zinc-ion batteries (ZIBs) have attracted a great deal of attentions from numerous researchers. However, their slow reaction kinetics, limited active sites and poor electrical conductivity inevitably give rise to the severe performance degradation. To solve these problems, herein, we introduce abundant oxygen vacancies into the flower-like δ-MnO2 nanostructure and effectively modulate the vacancy defects to reach the optimal level (δ-MnO2-x-2.0). The smart design intrinsically tunes the electronic structure, guarantees ion chemisorption-desorption equilibrium and increases the electroactive sites, which not only effectively accelerates charge transfer rate during reaction processes, but also endows more redox reactions, as verified by first-principle calculations. These merits can help the fabricated δ-MnO2-x-2.0 cathode to present a large specific capacity of 551.8 mAh g-1 at 0.5 A g-1, high-rate capability of 262.2 mAh g-1 at 10 A g-1 and an excellent cycle lifespan (83% of capacity retention after 1500 cycles), which is far superior to those of the other metal compound cathodes. In addition, the charge/discharge mechanism of the δ-MnO2-x-2.0 cathode has also been elaborated through ex situ techniques. This work opens up a new pathway for constructing the next-generation high-performance ZIBs cathode materials.

Polyvinylpyrrolidone-Intercalated Mn0.07 VOx toward High Rate and Long-Life Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are expected to be an attractive alternative in advanced energy storage devices due to large abundance and dependable security. Nevertheless, the undesirable energy density and operating voltage still hinder the development of AZIBs, which is intimately associated with the fundamental properties of the cathode. In this work, polyvinylpyrrolidone (PVP) intercalated Mn0.07 VOx (PVP-MnVO) with a large interlayer spacing of 13.5 Å (against 12.5 Å for MnVO) synthesized by a facile hydrothermal method is adopted for the cathode in AZIBs. The experimental results demonstrate that PVP-MnVO with expanded interlayer spacing provides beneficial channels for the rapid diffusion of Zn2+ , resulting in a high discharge capacity of 402 mAh g-1 at 0.1 A g-1 , superior to that of MnVO (275 mAh g-1 at 0.1 A g-1 ). Meanwhile, the PVP molecule remains in the layer structure as a binder/pillar, which can maintain its structural integrity well during the charging/discharging process. Consequently, PVP-MnVO cathode exhibits superior rate capability and cycling stability (89% retention after 4300 cycles at 10 A g-1 ) compared to that of MnVO (≈51% retention over 500 cycles at 2 A g-1 ). This work proposes a new approach to optimize the performance of vanadium-based electrode materials in AZIBs.

Oxygen vacancy enriched Na1.19V8O20·4.42H2O nanosheets for fast and stable Zn-ion batteries

Here, a facile hydrothermal method is employed to prepare an oxygen vacancy enriched sodium-ion intercalation Na1.19V8O20·4.42H2O nanosheet cathode with large interlayer spacing, fast reaction kinetics, and stable structure for superior zinc-ion batteries (ZIBs). The assembled ZIB exhibits a high specific capacity and excellent structural stability without capacity decay over 2000 cycles. Moreover, the multiple ion co-intercalation mechanism and partial phase transition mechanism are elucidated based on ex situ characterization techniques.

All-Round Enhancement in Zn-Ion Storage Enabled by Solvent-Guided Lewis Acid-Base Self-Assembly of Heterodiatomic Carbon Nanotubes

Designing zincophilic and stable carbon nanostructures is critical for Zn-ion storage with superior capacitive activity and durability. Here, we report solvent-guided Lewis acid-base self-assembly to customize heterodiatomic carbon nanotubes, triggered by the reaction between iron chloride and α,α'-dichloro-p-xylene. In this strategy, modulating the solvent-precursor interaction through the optimization of solvent formula stimulates differential thermodynamic solubilization, growth kinetics, and self-assembly behaviors of Lewis polymeric chains, thereby accurately tailoring carbon nanoarchitectures to evoke superior Zn-ion storage. Featured with open hollow interiors and porous tubular topologies, the solvent-optimized carbon nanotubes allow low ion-migration barriers to deeply access the built-in zincophilic sites by high-kinetics physical Zn²⁺/CF₃SO₃^- adsorption and robust chemical Zn²⁺ redox with pyridine/carbonyl motifs, which maximizes the spatial capacitive charge storage density. Thus, as-designed heterodiatomic carbon nanotube cathodes provide all-round improvement in Zn-ion storage, including a high energy density (140 W h kg^-1), a large current activity (100 A g^-1), and an exceptional long-term cyclability (100,000 cycles at 50 A g^-1). This study provides appealing insights into the solvent-mediated Lewis pair self-assembly design of nanostructured carbons toward advanced Zn-ion energy storage.

De-Ammonium Ba0.18V2O4.95/NH4V4O10 Film Electrodes as High-Performance Cathode Materials for Magnesium-Ion Batteries

Magnesium-ion batteries (MIBs) have been pushed into the research boom in the post-lithium-ion batteries era due to their low cost, no dendrite hazard, and high capacity. However, finding suitable cathode materials to improve the slow kinetics of Mg2+ is an ongoing challenge. In this work, Ba0.18V2O4.95/NH4V4O10 film electrodes were grown in one step on indium tin oxide (ITO) conductive glass using a low-temperature liquid-phase deposition method. Temperature was used as the probe condition, and it was concluded that the films annealed at 400 °C had suitable crystallinity and de-ammonium lattice space. At lower current density, with 0.5 M Mg(ClO4)2/PC as the electrolyte, it exhibited an initial discharge capacity of 130.99 mA h m-2 at 210 mA m-2 and 106.52% capacity retention after 100 cycles. In addition, it exhibited excellent electrochemical performance in long-term cycling (92.98% capacity retention after 300 cycles at 600 mA m-2). According to the results of ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM), the removal of NH4+ created more lattice space, assisting Ba0.18V2O4.95 to increase the transfer channels of Mg2+, providing more active sites to promote diffusion kinetics (the average DMg2+ was 2.07 × 10-12 cm2 s-1) and specific capacity. Therefore, these film electrodes for scalable Mg2+ storage are promising MIB cathode candidates that exhibit good performance advantages in storage applications.

An Artificial MnWO4 Cathode Electrolyte Interphase Enabling Enhanced Electrochemical Performance of δ-MnO2 Cathode for Aqueous Zinc Ion Battery

The dissolution of active material in aqueous batteries can lead to a rapid deterioration in capacity, and the presence of free water can also accelerate the dissolution and trigger some side reactions that affect the service life of aqueous batteries. In this study, a MnWO₄ cathode electrolyte interphase (CEI) layer is constructed on a δ-MnO₂ cathode by cyclic voltammetry, which is effective in inhibiting the dissolution of Mn and improving the reaction kinetics. As a result, the CEI layer enables the δ-MnO₂ cathode to produce a better cycling performance, with the capacity maintained at 98.2% (vs. activated capacity at 500 cycles) after 2000 cycles at 10 A g^-1. In comparison, the capacity retention rate is merely 33.4% for pristine samples in the same state, indicating that this MnWO₄ CEI layer constructed by using a simple and general electrochemical method can promote the development of MnO₂ cathodes for aqueous zinc ion batteries.

Coupling Engineering of NH4 + Pre-Intercalation and Rich Oxygen Vacancies in Tunnel WO3 Toward Fast and Stable Rocking Chair Zinc-Ion Battery

Herein, for the first time, a pre-intercalated non-metal ion (NH₄ ⁺ ) with rich oxygen vacancies stabilized tunnel WO₃ is proposed as a new intercalation anode to construct Zn-metal-free rocking-chair ZIBs. With the ethylene glycol additive in the aqueous electrolyte, the Zn²⁺ solvation structure can be regulated and the side reaction of hydrogen evolution can also be suppressed. Owing to the integrated synergetic modification, a high-rate and ultra-stable aqueous Zn-(NH₄ )_x WO₃ battery can be constructed, which exhibits an improved specific capacity (153 mAh g^-1 at 0.1 A g^-1 ), excellent rate performance (when the current density increases to 3 A g^-1 , the specific capacitance is still 86 mAh g^-1 ), and a high cycle stability with 100% capacity retention after 2,200 cycles under 5 A g^-1 . Ex situ X-ray diffraction and XPS reveal the reversible insertion/extraction of Zn²⁺ in (NH₄ )_x WO₃ . The assembled (NH₄ )_x WO₃ //MnO₂ rocking-chair ZIBs delivers excellent capacity of 82 mAh g^-1 at 0.1 A g^-1 , impressive cyclic stability. Additionally, the flexible (NH₄ )_x WO₃ //MnO₂ ZIBs can power the electrochromic device-based PANI/WO₃ with high color contrast and fast response time. This study provides new insight for developing high-performance rechargeable aqueous ZIBs.

Prioritizing Hetero-Metallic Interfaces via Thermodynamics Inertia and Kinetics Zincophilia Metrics for Tough Zn-Based Aqueous Batteries

Poor thermodynamic stability and sluggish electrochemical kinetics of metallic Zn anode in aqueous solution greatly hamper its practical application. To solve such problems, to date, various zincophilic surface modification strategies are developed, which can facilitate reversible Zn plating/stripping behavior. However, there is still a lack of systematic and fundamental understanding regarding the metrics of thermodynamics inertia and kinetics zincophilia in selecting zincophilic sites. Herein, hetero-metallic interfaces are prioritized for the first time via optimizing different hetero metals (Fe, Co, Ni, Sn, Bi, Cu, Zn, etc.) and synthetic solvents (ethanol, ethylene glycol, n-propanol, etc.). Specifically, both theoretical simulations and experimental results suggest that this Bi@Zn interface can exhibit high efficiency owing to the thermodynamics inertia and kinetics zincophilia. A best practice for prioritizing zincophilic sites in a more practical metric is also proposed. As a proof of concept, the Bi@Zn anode delivers ultralow overpotential of ≈55 mV at a high rate of 10 mA cm^-2 and stable cycle life over 4700 cycles. The elaborated "thermodynamics inertia and kinetics metalphilia" metrics for hetero-metallic interfaces can benchmark the success of other metal-based batteries.

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.

Enhanced H+ Storage of a MnO2 Cathode via a MnO2 Nanolayer Interphase Transformed from Manganese Phosphate

The MnO₂ cathode has attracted extensive attention in aqueous zinc ion battery research due to its environmental benignity, low cost, and high capacity. However, sluggish kinetics of hydrated zinc ion and manganese dissolution lead to insufficient rate and cycle performances. In this study, a manganese phosphate nanolayer synthesized in situ on a MnO₂ cathode can be transformed into a δ-MnO₂ nanolayer interphase after activation upon cycling, endowing the interphase with abundant interlayer water. As a result, the δ-MnO₂ nanolayer interphase with the function of H⁺ topochemistry significantly enhances H⁺ (de)insertion in the MnO₂ cathode, which leads to a kinetics conversion from Zn²⁺-dominated (de)insertion to H⁺-dominated (de)insertion, thus endowing the MnO₂ cathode with superior rate and cycle performances (85.9% capacity retention after 1000 cycles at 10 A g^-1). This strategy can be highly scalable for other manganese-based cathodes and provides an insight for developing high-performance aqueous zinc ion batteries.

3D printing flexible zinc-ion microbatteries with ultrahigh areal capacity and energy density for wearable electronics

A flexible zinc ion micro-battery with ultra-high surface capacity (10.1 mA h cm^-2) and energy density (8.1 mW h cm^-2), as well as good flexibility, is fabricated based on the co-doping effect of V₂O₅ through an improved 3D printing technology, and is further integrated with flexible solar cells for self-powered wearable electronics.

Intercalation-induced amorphous hydrated vanadium oxide for boosted aqueous Zn2+ storage

An amorphous hydrated vanadium oxide induced by Zn²⁺ intercalation in Mg-ion inserted V₂O₅·nH₂O (MgVOH) is developed as a high-performance cathode for ZIBs. In particular, zinc pyrovanadate as the product of the second phase transition is found to suppress the dissolution issue of the vanadium species for the cathode to facilitate long lifespan.

MXene-Boosted Imine Cathodes with Extended Conjugated Structure for Aqueous Zinc-Ion Batteries

Organic molecules have been considered promising energy-storage materials in aqueous zinc-ion batteries (ZIBs), but are plagued by poor conductivity and structural instability because of the short-range conjugated structure and low molecular weight. Herein, an imine-based tris(aza)pentacene (TAP) with extended conjugated effects along the CN backbones is proposed, which is in situ injected into layered MXene to form a TAP/Ti₃ C₂ T_x cathode. Theoretical and electrochemical analyses reveal a selective H⁺ /Zn²⁺ co-insertion/extraction mechanism in TAP, which is ascribed to the steric effect on the availability of active CN sites. Moreover, Ti₃ C₂ T_x , as a conductive scaffold, favors fast Zn²⁺ diffusion to boost the electrode kinetics of TAP. Close electronic interactions between TAP and Ti₃ C₂ T_x preserve the structural integrity of TAP/Ti₃ C₂ T_x during the repeated charge/discharge. Accordingly, the TAP/Ti₃ C₂ T_x cathode delivers a high reversible capacity of 303 mAh g^-1 at 0.04 A g^-1 in aqueous ZIBs, which also realizes an ultralong lifetime over 10 000 cycles with a capacity retention of 81.6%. Furthermore, flexible Zn||TAP/Ti₃ C₂ T_x batteries with a quasi-solid-state electrolyte demonstrate potential application in wearable electronic devices. This work offers pivotal guidance to create highly stable organic electrodes for advanced ZIBs.

Interspace and Vacancy Modulation: Promoting the Zinc Storage of an Alcohol-Based Organic-Inorganic Cathode in a Water-Organic Electrolyte

Expanding interspace and introducing vacancies are desired to promote the mobility of Zn ions and unlock the inactive sites of layered cathodes. However, this two-point modulation has not yet been achieved simultaneously in vanadium phosphate. Here, a strategy is proposed for fabricating an alcohol-based organic-inorganic hybrid material, VO_{1- x} PO₄ ·0.56C₆ H₁₄ O₄ , to realize the conjoint modulation of the d-interspace and oxygen vacancies. Peculiar triglycol molecules with an inclined orientation in the interlayer also boost the improvement in the conversion rate of V⁵⁺ to V⁴⁺ and the intensity of the PO bond. Their synergism can ensure steerable adjustment for intercalation kinetics and electron transport, as well as realize high chemical reactivity and redox-center optimization, leading to at least 200% increase in capacity. Using a water-organic electrolyte, the designed Zn-ion batteries with an ultrahigh-rate profile deliver a long-term durability (fivefold greater than pristine material) and an excellent energy density of ≈142 Wh kg^-1 (including masses of cathode and anode), thereby substantially outstripping most of the recently reported state-of-the-art zinc-ion batteries. This work proves the feasibility to realize the two-point modulation by using organic intercalants for exploiting high-performance new 2D materials.

Synthesis of Zn2+-Pre-Intercalated V2O5·nH2O/rGO Composite with Boosted Electrochemical Properties for Aqueous Zn-Ion Batteries

Layered vanadium-based materials are considered to be great potential electrode materials for aqueous Zn-ion batteries (AZIBs). The improvement of the electrochemical properties of vanadium-based materials is a hot research topic but still a challenge. Herein, a composite of Zn-ion pre-intercalated V₂O₅·nH₂O combined with reduced graphene oxide (ZnVOH/rGO) is synthesized by a facile hydrothermal method and it shows improved Zn-ion storage. ZnVOH/rGO delivers a capacity of 325 mAh·g⁻¹ at 0.1 A·g⁻¹, and this value can still reach 210 mAh·g⁻¹ after 100 cycles. Additionally, it exhibits 196 mAh·g⁻¹ and keeps 161 mAh·g⁻¹ after 1200 cycles at 4 A·g⁻¹. The achieved performances are much higher than that of ZnVOH and VOH. All results reveal that Zn²⁺ as “pillars” expands the interlayer distance of VOH and facilitates the fast kinetics, and rGO improves the electron flow. They both stabilize the structure and enhance efficient Zn²⁺ migration. All findings demonstrate ZnVOH/rGO’s potential as a perspective cathode material for AZIBs.

Mesoporous VCN Nanobelts for High-Performance Flexible Zn-Ion Batteries

Vanadium nitride (VN) with a wide working window has been identified as a promising electrode material candidate for batteries due to the high specific capacitance and the excellent electrical conductivity. Here, we have successfully prepared VCN nanobelts, which display mesoporous structure with high specific surface area (54.4 m2 g−1) and the total pore volume was 0.266 cm3 g−1. Furthermore, the prepared flexible Zn-ion battery (FZIB) with VCN-5 not only exhibited high specific capacitance (81 μAh cm−2), excellent rate capability, and long cyclic durability (77% after 1000 cycles at 0.6 mA cm−2) but also had the characteristics of flexibility. This FZIB is important to reduce the difficulty in thermal management and can be used in a series of applications, including wearable electric devices.

The Emergence of 2D MXenes Based Zn-Ion Batteries: Recent Development and Prospects

Rechargeable zinc-ion batteries (ZIBs) with exceptional theoretical capacity have garnered significant interest in large-scale electrochemical energy storage devices due to their low cost, abundant material, inherent safety, high specific energy, and ecofriendly nature. Metal carbides/nitrides, known as MXenes, have emerged as a large family of 2D transition metal carbides or carbonitrides with excellent properties, e.g., high electrical conductivity, large surface functional groups (e.g., F, O, and OH), low energy barriers for the diffusion of electrolyte ions with wide interlayer spaces. After a decade of effort, significant development has been achieved in the synthesis, properties, and applications of MXenes. Thus, it has opened up various exciting opportunities to construct advanced MXene-based nanostructures for ZIBs with excellent specific energy and power. Herein, this review summarizes the advances across multiple synthesis routes, related properties, morphological and structural characteristics, and chemistries of MXenes for ZIBs. The recent development of MXene-based electrodes is introduced, and electrolytes for ZIBs are elucidated in detail. MXene-based rocking chair ZIBs, strategies to enhance the performance of MXene-based cathodes, suppress the dendrites in MXene-based anodes, and MXene-based flexible ZIBs are pointed out. A rational design and modification of the MXenes as well as the production of composites with metal oxides exhibits promise in solving issues and enhancing the electrochemical performance of ZIBs. Finally, the present challenges and future prospects for MXene-based ZIBs are discussed.

Dual intercalation of inorganics-organics for synergistically tuning the layer spacing of V2O5·nH2O to boost Zn2+ storage for aqueous zinc-ion batteries

Possessing a 2D zinc-ion transport channel, layered vanadium oxides have become good candidates as cathode materials for aqueous rechargeable zinc-ion batteries (ARZIBs). Tuning the lamellar structure of vanadium oxides to enhance their zinc-ion storage is a great challenge. In the present study, we proposed and investigated a "co-intercalation mechanism" in which Mg²⁺ and polyaniline (PANI) were simultaneously intercalated into the layers of hydrated V₂O₅ (MgVOH/PANI) by a one-step hydrothermal method. Inorganic-organic co-intercalation could tune the layer spacing of VOH, and this combination played a synergistic role in enhancing the zinc-ion storage in MgVOH/PANI. It showed an extremely large layer spacing of 14.2 Å, specific capacity of up to 412 mA h g^-1 at 0.1 A g^-1, and the capacity retention rate could reach 98% after 1000 cycles. PANI itself has a zinc-storage capacity, and Mg²⁺ intercalated with PANI can improve the conductivity of the material and enhance its stability. Further first-principles calculations clearly revealed the structural changes and improved electrochemical performance of vanadium oxides. This method of inorganic and organic co-regulation of the VOH structure opens a new strategy for tuning the lamellar structure of layered materials to boost their electrochemical performances.

Boosted H+ Intercalation Enables Ultrahigh Rate Performance of the δ-MnO2 Cathode for Aqueous Zinc Batteries

H+ intercalation, as a critical battery chemistry, enables electrodes' high rate performance due to the fast diffusion kinetics of H+. In this work, more water molecules are introduced into δ-MnO2 by the protonation of δ-MnO2 with abundant oxygen vacancies. Benefiting from the structure with a close arrangement of water molecules in interlayers, the Grotthuss transport of proton is achieved in the energy storage of the δ-MnO2 cathode. As a result, the δ-MnO2 cathode exhibits an ultrahigh rate performance with a capacity of 368.1 mAh g-1 at 0.5 A g-1 and 83.4 mAh g-1 at 50 A g-1, which has a capacity retention of 73% after 1100 cycles at 10 A g-1. The study of the storage mechanism reveals that the Grotthuss intercalation of proton predominates the storage process, which empowers the cathode with high rate performance.

Co-intercalation strategy of constructing partial cation substitution of ammonium vanadate {(NH4)2V6O16} for stable zinc ion storage

Recently, aqueous zinc-ion batteries have become a hot research topic in the field of grid-scale application, which can be attributed to their low-cost, aqueous electrolyte and dominant theoretical reversible capacity. Nevertheless, the lack of suitable cathode materials greatly hinders the development of aqueous zinc-ion batteries. In this work, we adopt a simple one-step synthesis strategy to prepare (NH₄)₂V₆O₁₆ with an intercalation of Na⁺ and H₂O, which exhibits a novel crystal structure in which the ammonium ion, crystal water, and sodium ion co-locate in the V₃O₈ layers. The co-intercalation not only effectively enhances the binding energy between V-O layers to suppress vanadium dissolution but also successfully improves the structural stability to alleviate the structural collapse during the cyclic process. As result, (NH₄)₂V₆O₁₆ with the intercalation of crystal water and Na⁺ presents a remarkable reversible discharge capacity of 423.9 mA h g^-1 after 90 cycles at 0.1 A g^-1 with an excellent energy density of 350.3 W h kg^-1 and demonstrates an outstanding specific capacity of 182.5 mA h g^-1 at the high current density of 5 A g^-1 upon 1400 cycles during the ultra-wide voltage window of 0.1-2.0 V.

Corrosion as the origin of limited lifetime of vanadium oxide-based aqueous zinc ion batteries

Aqueous zinc ion batteries are receiving increasing attention for large-scale energy storage systems owing to their attractive features with respect to safety, cost, and scalability. Although vanadium oxides with various compositions have been demonstrated to store zinc ions reversibly, their limited cyclability especially at low current densities and their poor calendar life impede their widespread practical adoption. Herein, we reveal that the electrochemically inactive zinc pyrovanadate (ZVO) phase formed on the cathode surface is the main cause of the limited sustainability. Moreover, the formation of ZVO is closely related to the corrosion of the zinc metal counter electrode by perturbing the pH of the electrolyte. Thus, the dissolution of VO₂(OH)₂⁻, the source of the vanadium in the ZVO, is no longer prevented. The proposed amalgamated Zn anode improves the cyclability drastically by blocking the corrosion at the anode, verifying the importance of pH control and the interplay between both electrodes.

Aqueous zinc ion batteries are good systems for large-scale energy storage. Here, the authors report that the corrosion of zinc metal anode is the origin of limited lifetime of vanadium oxide-based aqueous zinc ion batteries, and supressing corrosion improves the calendar and cycle lifetime markedly.

Highly Reversible Zn Metal Anodes Enabled by Freestanding, Lightweight, and Zincophilic MXene/Nanoporous Oxide Heterostructure Engineered Separator for Flexible Zn-MnO2 Batteries

Aqueous zinc (Zn)-ion batteries are regarded as promising candidates for large-scale energy storage systems because of their high safety, low cost, and environmental benignity. However, the dendrite issue of Zn anode hinders their practical application. Herein, a freestanding, lightweight, and zincophilic MXene/nanoporous oxide heterostructure engineered separator is designed to stabilize a Zn metal anode. The nanoporous oxides prepared by a one-step vacuum distillation technique afford the advantages of large surface area, high porosity, and homogeneous porous structure. The zincophilic MXene@oxides layer can homogenize the electric field distribution, facilitate ion diffusion kinetics, reduce local current density, and promote even Zn ionic flux, which will regulate uniform Zn deposition and suppress side reactions. Accordingly, dendrite-free Zn anodes with stable cyclability are achieved for over 500 h at an ultrahigh area capacity of 10 mAh cm^-2. Besides, flexible, long-lifespan, and high-rate N/S-doped three-dimensional MXene@MnO₂||Zn full cells are constructed with the engineered separator. Moreover, this strategy can be successfully extended to lithium, sodium, potassium, and magnesium metal batteries, indicating that separator regulation is a universal approach to overcome the challenges of metal batteries.

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.

Novel Polymer/Barium Intercalated Vanadium Pentoxide with Expanded Interlayer Spacing as High-Rate and Durable Cathode for Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) exhibit great potential in large-scale energy storage systems. However, limited reaction kinetics and poor long-cycle stability restrict the application of vanadium oxide cathode materials. Herein, we designed and successfully synthesized a novel composite material with polyethylene glycol (PEG) and barium cation (Ba²⁺) preintercalated between the layers of vanadium pentoxide, denoted as PEG-Ba_0.38V₂O₅·nH₂O (PEG-BVO), as a cathode material of AZIBs. The optimized PEG-BVO material shows a uniform nanobelt-like structure with the expanded interlayer spacing of 1.07 nm, significantly promoting the transport kinetics of zinc ions. The theoretical calculation results unravel that an interlayer spacing of 1.07 nm may be at the most stable state for this layered composite structure, ensuring a robust architecture for rapid reversible (de)intercalation of zinc ions. As a result, the PEG-BVO electrode (with a large mass loading of 4 mg cm^-2) exhibits an outstanding electrochemical performance including a high specific capacity (345 mAh g^-1 at 0.1 A g^-1), decent rate capability (up to 175 mAh g^-1 at 10 A g^-1), and long-term cycling stability (98.8% capacity retention upon 4000 cycles at 6 A g^-1). Our discovery provides a new guest preinsertion strategy to construct a robust layered vanadium-based electrode with the expanded interlayer spacing, and the as-prepared PEG-Ba_0.38V₂O₅·nH₂O shows great potential as a high-rate positive electrode for AZIBs.