Self-Assembling Films of Covalent Organic Frameworks Enable Long-Term, Efficient Cycling of Zinc-Ion Batteries

Inorganic-metal hybrid coating for stabilizing and regulating aqueous zinc anodes

Aqueous zinc ion batteries (ZIBs) are expected to be the next generation of energy storage devices. However, the unwanted dendrites growth on zinc anodes, hydrogen evolution and other side reactions hinder the practical application of ZIBs. Here, we designed a novel inorganic-metal hybrid coating with an optimised electric double layer structure at the zinc anode/electrolyte interface. The hybrid coating effectively promotes ionic desolvation, reduces the nucleation overpotential, and suppresses the 2D diffusion process. Furthermore, the coating has good stability and inhibits the dendrites growth, hydrogen precipitation corrosion, and by-products generation. Consequently, the hybrid coating-modified Zn anode exhibited excellent electrochemical performance. Among them, the symmetric cell was able to cycle for 1480 h at 1 mA cm-2, 1 mAh cm-2 with an overpotential of ∼34 mV. The symmetric cell achieved a cycle life of ∼1000 h even at a high current of 3 mA cm-2. The cycling performance and multiplication rate performance in full cells were also demonstrated. This work shows the effectiveness and feasibility of hybrid coating to modulate zinc anode/electrolyte interface.

Shielding CO2-Philic Sites in Trimmed Covalent Organic Framework Pores by Atomic Layer Deposition

Strong adsorptive sites toward unwanted gas molecules in porous framework materials often lead to reversed sorption selectivity, creating tremendous challenges for enhancing the diffusion-driven membrane separations targeted at the weakly adsorbed species in the gas pair. While post-synthetic modification methods have been reported to downsize the pores in covalent organic frameworks (COFs), effective approaches to shield the highly adsorptive sites within the pores are rarely explored. Here, a solvent-less pore modification strategy is developed using atomic layer deposition (ALD). it is shown that controlled amounts of ZnO can be uniformly deposited into the COF pores, offering the ability to fine-tune the pore dimensions. Moreover, the Zn─O moieties grown into the COF pore are found to interact with the CO2-philic ketoenamine groups, and substantially reduce the CO2 solubility by 72.4% in the COF membrane. Accordingly, the simultaneously increased diffusion selectivity and sorption selectivity for H2/CO2 lead to a 330% improvement of the permselectivity in membrane separation, demonstrating the efficacy of the strategy for pore engineering in COFs.

Practical issues toward high-voltage aqueous rechargeable batteries

This review offers a critical and exhaustive examination of the current state and innovative advances in high-voltage Li, Na, K, and Zn aqueous rechargeable batteries, an area poised for significant technological breakthroughs in energy storage systems. The practical issues that have traditionally hampered the development of aqueous batteries, such as limited operating potential windows, challenges in stable solid-electrolyte interphase (SEI) formation, the need for active materials optimized for aqueous environments, the misunderstood intercalation chemistry, the unreliable assessment techniques, and the overestimated performance and underestimated physicochemical and electrochemical drawbacks, are highlighted. We believe that this review not only brings together existing knowledge but also pushes the boundaries by providing a roadmap for future research and development efforts aimed at overcoming the longstanding challenges faced by the promising aqueous rechargeable batteries.

Quaternary Alloy Interfaces for Stable Zinc Anodes for High-Performance Aqueous Zinc-Ion Batteries With Long-Term Cycling Stability

Aqueous zinc-ion batteries (AZIBs) have emerged as a promising energy storage solution owing to their intrinsic safety, low cost, environmental friendliness, and high theoretical specific capacity. However, their practical application is hindered by uncontrollable dendrite growth and side reactions at the zinc metal anode. To address these challenges, a simple and cost-effective electrodeposition strategy is proposed to construct a quaternary Zn-Cu-Sn-Bi alloy artificial interface layer on zinc foil (ZCSB@Zn) as the anode of AZIBs. Density functional theory (DFT) calculations and in situ optical dendrite observation confirm that this dense alloy interface layer reduces the migration barrier and weakens hydrogen adsorption, facilitating uniform zinc deposition while effectively suppressing side reactions and dendrite formation. The symmetric ZCSB@Zn cell exhibits extraordinary cycle stability exceeding 8000 h. Furthermore, the assembled ZCSB@Zn//CSB-MnO2 full cell demonstrates a high specific capacity of 199 mAh g-1 at 1 A g-1, maintaining stability even under high loading of 10 mg cm-2 and high temperature conditions (50 °C). This study presents a scalable and cost-effective strategy for constructing quaternary artificial interface layers in zinc metal anodes, highlighting their potential for practical AZIB applications.

Nano-Scale ZrN Film Modified Zn Anode with Ultra-Long Cycle Life Over 5000 H

Dendrite growth, corrosion, and hydrogen evolution are major issues for Zn anodes, which seriously hinder the further practical application of aqueous zinc-ion batteries. To address these issues, Zirconium Nitride (ZrN) layer with a thickness of 110 nm is uniformly deposited on the surface of Zn anode using plasma-enhanced atomic layer deposition (PE-ALD). In/ex situ characterizations verify that the as-introduced ZrN layer has excellent anticorrosive and zincophilic ability, which can suppress corrosion and hydrogen evolution, lower the nucleation energy barrier for Zn2+ deposition, and effectively inhibit dendrite growth. Theoretical calculations also reveal that ZrN exhibits significantly higher adsorption capacity for Zn2+ compared to bare Zn, which is conducive to regulating the Zn deposition behavior. This innovative interface significantly extends battery cycle life and enhances coulombic efficiency. Encouragingly, under a current density of 5 mA cm-2 and areal capacity of 1 mAh cm-2, the Zn@ZrN symmetrical cells demonstrate an extraordinary cycling life of up to 5000 h, significantly surpassing other reported Zn anodes modified by films/coatings. In addition, it also exhibits an impressive cycling life of 1200 h at 1 mA cm-2 and 1 mAh cm-2. The full cells of Zn@ZrN||MnO2 retain high capacity after 1000 cycles, markedly outperforming conventional Zn||MnO2 batteries.

Mechanistic Insights into the Formation of Nanofibrous Covalent Organic Frameworks (COFs) and their Promotion to the Catalysis of Hydrodechlorination

The nanoscale morphologies of COFs deeply affect their performance in practical applications. However, it still lacks studies to well understand their formation mechanism for guiding and controlling the synthesis for desired nanomorphology. To achieve more mechanistic insights into the formation of nanofibrous COFs, herein a series of nanofibrous and non-fibrous COFs are synthesized and the intrinsic relationships among the morphology, chemical constituent, structure planarity, and the DFT calculated interlayer stacking energy are investigated comprehensively. The study reveals the planarity of building monomers is not decisive for forming the nanofibrous COFs. The presence of electron-withdrawing triazine group in amine monomers and the electron-donating ─OH group in aldehyde monomers are essential for suppressing the growth of COF crystallites in x-y plane and promoting the stacking in z-direction to form nanofibrous COFs. The COF morphology can be modulated by the functional groups in monomers by regulating the competition between lateral reaction activity and interlayer stacking energy. The prepared nanofibrous COFs exhibited two-fold increased catalytic activity and better stability than the non-fibrous counterpart in hydrodechlorination. The new insights and proposed mechanism here can help open up a domain for precise designing and modulating the COF nanomorphology from molecular level for specific application.

The structuring of porous reticular materials for energy applications at industrial scales

Reticular synthesis constructs crystalline architectures by linking molecular building blocks with robust bonds. This process gave rise to reticular chemistry and permanently porous solids. Such precise control over pore shape, size and surface chemistry makes reticular materials versatile for gas storage, separation, catalysis, sensing, and healthcare applications. Despite their potential, the transition from laboratory to industrial applications remains largely limited. Among various factors contributing to this translational gap, the challenges associated with their formulation through structuring and densification for industrial compatibility are significant yet underexplored areas. Here, we focus on the shaping strategies for porous reticular materials, particularly metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), to facilitate their industrial application. We explore techniques that preserve functionality and ensure durability under rigorous industrial conditions. The discussion highlights various configurations - granules, monoliths, pellets, thin films, gels, foams, and glasses - structured to maintain the materials' intrinsic microscopic properties at a macroscopic level. We examine the foundational theory and principles behind these shapes and structures, employing both in situ and post-synthetic methods. Through case studies, we demonstrate the performance of these materials in real-world settings, offering a structuring blueprint to inform the selection of techniques and shapes for diverse applications. Ultimately, we argue that advancing structuring strategies for porous reticular materials is key to closing the gap between laboratory research and industrial utilization.

Regulating Water Molecules via Bioinspired Covalent Organic Framework Membranes for Zn Metal Anodes

The Zn metal anode in aqueous zinc-ion batteries (AZIBs) faces daunting challenges including undesired water-induced parasitic reactions and sluggish ion migration kinetics. Herein, we develop three-dimensional covalent organic framework (COF) membranes with bioinspired ion channels toward stabilized Zn anodes. These COFs, featured by zincophilic pyridine-N sites, enable effective regulation of water molecules at the anode-electrolyte interphase. Systematic experimental analysis and theoretical simulations reveal the optimized COF-320N membrane functions as ion pumps, accordingly facilitating Zn2+ transport and inhibiting direct contact between Zn anode and free water molecules. Consequently, the bio-inspired strategy achieves improved Zn2+ transference number (0.61), rapid de-solvation kinetics, and suppressed hydrogen evolution. The assembled Zn||MnO2 pouch cell integrated with COF-320N membrane exhibits favorable electrochemical performances. Such a bioinspired concept for optimizing Zn anodes opens new pathways in developing advanced energy storage devices.

Pioneering the Future: Principles, Advances, and Challenges in Organic Electrodes for Aqueous Ammonium-Ion Batteries

Aqueous ammonium-ion (NH4 +) batteries (AAIBs) have recently been considered as attractive alternatives for next-generation large-scale energy storage systems, on account of their cost-effectiveness, nonflammability, less corrosive, small hydrated ionic radius, and rapid NH4 + diffusion kinetics. In addition, the tetrahedral structure of NH4 + exhibits preferential orientation characteristics, resulting in a different electrochemical storage mechanism from spherical charge carriers such as Li+, Na+, and K+. Therefore, unlocking the NH4 +-ion storage mechanisms in host electrode materials is pivotal to advancing the design of high-performance AAIBs. Organic materials, with their customizable, flexible, and stable molecular structures, along with their ease of recycling and disposal, offer tremendous potential. However, the development of cutting-edge organic electrode materials specifically for ammonium-ion storage in AAIBs remains an exciting, yet largely untapped, frontier. This review systematically explores the interaction mechanisms between NH4 + ions and organic electrode materials, such as electrostatic interactions including hydrogen bonding. It also highlights the application of diverse organic electrode materials, such as small molecules, conducting polymers, covalent organic frameworks (COFs), and organic-inorganic hybrids in AAIBs. Lastly, the review addresses the key challenges and future perspectives of organic-material-based AAIBs, aiming to push the boundaries of cutting-edge aqueous energy storage systems.

Suppressing Hydrogen Evolution and Dendrite Formation on a Zn Anode by Coating In2O3 with Tailored Affinity to H* and Zn

To suppress the hydrogen evolution reaction (HER) and dendrite formation on the Zn anode in aqueous Zn-ion batteries, a submicrometer In2O3 coating on the Zn anode (referred to as Zn@In2O3) was constructed via magnetron sputtering. Density functional theory (DFT) and experimental data show that the In2O3 coating suppresses the HER because of its weaker interactions with H* compared with Zn, inhibiting the Volmer step. At the same time, the In2O3 coating exhibits a moderate affinity for Zn*, higher than that on Zn but lower than that at the In2O3-Zn interface, thus facilitating the desolvation of the hydrated Zn2+ ions while promoting its deposition on the Zn substrate beneath the In2O3 coating. The resultant suppression of side reactions and dendrite growth significantly enhance the reversible plating/stripping of Zn. The optimized Zn@In2O3 stably cycles over 6400 h with a low voltage hysteresis of 9.5 mV at 1 mA cm-2 and 1 mAh cm-2 in symmetric cells. The average Coulombic efficiency of Zn plating/stripping is increased from 95.8 to 99.6% owing to the In2O3 coating. Moreover, when coupled with the Mn0.15V2O5·nH2O cathode, the Zn@In2O3 battery maintains a capacity retention of 78.6% after 2000 cycles at 5 A g-1. This facile and economical modification of Zn anodes provides an idea for realizing the practical application of AZIBs.

Advancing Zinc Anodes: Strategies for Enhanced Performance in Aqueous Zinc-Ion Batteries

The promising features of aqueous zinc ion batteries (AZIBs), including their inherent safety, environmental friendliness, abundant raw materials, cost-effectiveness, and simple manufacturing process, position them as strong candidates for large-scale energy storage. However, their practical application faces significant challenges, such as uncontrolled dendritic growth, undesirable side reactions, and hydrogen evolution reactions (HER), which undermine the efficiency and longevity of the system. To address these issues, extensive research has been conducted to improve these batteries' energy density and lifespan. This comprehensive review explores the fundamental mechanisms of zinc dendrite formation, its properties, and the interfacial chemistry between the electrode and electrolyte. It also delves into strategies for protecting the zinc anode, with a focus on the modulation of zinc ion deposition dynamics at the electrolyte interface. The discussion concludes with an evaluation of the current challenges and future prospects of AZIB, aiming to enhance their viability for grid-scale energy storage solutions.

Electrochemically and chemically in-situ interfacial protection layers towards stable and reversible Zn anodes

Aqueous zinc metal batteries (AZMBs) have received widespread attention for large-scale sustainable energy storage due to their low toxicity, safety, cost-effectiveness. However, the technology and industrialization of AZMBs are greatly plagued by issues of Zn anode such as persistent dendrites and parasitic side reactions, resulting in rapid capacity degradation or battery failure. Electrochemically or chemically in-situ interfacial protection layers have very good self-adaption features for stability and reversibility of Zn anodes, which can also be well matched to current battery manufacturing. However, the in-situ interfacial strategies are far from the practical design for effective Zn anodes. Therefore, a targeted academic discussion that serves the development of this field is very urgent. Herein, the comprehensive insights on electrochemically and chemically in-situ interfacial protection layers for Zn anode were proposed in this review. It showcased a systematic summary of research advances, followed by detailed discussions on electrochemically and chemically in-situ interfacial protection strategies. More importantly, several crucial issues facing in-situ interfacial protection strategies have been further put forward. The final section particularly highlighted a systematic and rigorous scheme for precise designing highly stable and reversible in-situ interface for practical zinc anodes.

Regulating Zn Deposition via Honeycomb-like Covalent Organic Frameworks for Stable Zn Metal Anodes

The irreversible chemistry of the Zn anode, attributed to parasitic reactions and the growth of zinc dendrites, is the bottleneck in the commercialization of aqueous zinc-ion batteries. Herein, an efficient strategy via constructing an organic protective layer configured with a honeycomb-like globular-covalent organic framework (G-COF) was constructed to enhance the interfacial stability of Zn anodes. Theoretical analyses disclose that the methoxy and imine groups in G-COF have more negative adsorption energy and electrostatic potential distribution, favorable Zn2+ adsorption, and diffusion. Experimental results demonstrate that G-COF effectively protects the Zn anode from dendrite formation and surface corrosion, leading to a stable and homogeneous Zn2+ deposition. Notably, the G-COF@Zn||G-COF@Zn symmetric cell obtained high stability for over 1650 h under 3 mA cm-2 for 1 mA h cm-2. Full cells assembled with the δ-MnO2 cathode and G-COF@Zn anode demonstrates exceptional rate capability and consistent cycling over 1000 cycles at a current density of 1 A g-1, achieving a specific capacity of 217 mA h g-1. Our work provides novel insight into interfacial regulation of Zn anodes for the implementation of practical aqueous zinc-ion batteries with long-term cycling characteristics.

Nano-Metal-Organic Frameworks and Nano-Covalent-Organic Frameworks: Controllable Synthesis and Applications

Nanoscale framework materials have attracted extensive attention due to their diverse morphology and good properties, and synthesis methods of different size structures have been reported. Therefore, the relationship between different sizes and performance has become a research hotspot. This paper reviews the controllable synthesis strategies of nano-metal-organic frameworks (nano-MOFs) and nano-covalent-organic frameworks (nano-COFs). Firstly, the synthetic evolution of nano-frame materials is summarized. Due to their special surface area, regular pores and adjustable structural functions, nano-frame materials have attracted much attention. Then the preparation methods of nanostructures with different dimensions are introduced. These synthetic strategies provide the basis for the design of novel energy storage and catalytic materials. In addition, the latest advances in the field of energy storage and catalysis are reviewed, with emphasis on the application of nano-MOFs/COFs in zinc-, lithium-, and sodium-based batteries, as well as supercapacitors.

Designing Cooperative Ion Transport Pathway in Ultra-Thin Solid-State Electrolytes toward Practical Lithium Metal Batteries

Solid polymer electrolytes (SPEs) are promising for high-energy-density solid-state Li metal batteries due to their decent flexibility, safety, and interfacial stability. However, their development was seriously hindered by the interfacial instability and limited conductivity, leading to inferior electrochemical performance. Herein, we proposed to design ultra-thin solid-state electrolyte with long-range cooperative ion transport pathway to effectively increase the ionic conductivity and stability. The impregnation of PVDF-HFP inside pores of fluorinated covalent organic framework (CF3-COF) can disrupt its symmetry, rendering rapid ion transportation and inhibited anion immigration. The functional groups of CF3-COF can interact with PVDF-HFP to form fast Li+ transport channels, which enables the uniform and confined Li+ conduction within the electrolyte. The introduction of CF3-COF also enhances the mechanical strength and flexibility of SPEs, as well as ensures homogeneous Li deposition and inhibited dendrite growth. Hence, a remarkably high conductivity of 1.21×10-3 S cm-1 can be achieved. Finally, the ultra-thin SPEs with an extremely long cycle life exceed 9000 h can be obtained while the NCM523/Li pouch cell demonstrates a high capacity of 760 mAh and 96 % capacity retention after cycling, holding great promises to be utilized for practical solid-state Li metal batteries.

Towards Superior Aqueous Zinc-Ion Batteries: The Insights of Artificial Protective Interfaces

Aqueous zinc ion batteries (AZIBs) with metallic Zn anode have the potential for large-scale energy storage application due to their cost-effectiveness, safety, environmental-friendliness, and ease of preparation. However, the concerns regarding dendrite growth and side reactions on Zn anode surface hamper the commercialization of AZIBs. This review aims to give a comprehensive evaluation of the protective interphase construction and provide guidance to further improve the electrochemical performance of AZIBs. The failure behaviors of the Zn metal anode including dendrite growth, corrosion, and hydrogen evolution are analyzed. Then, the applications and mechanisms of the constructed interphases are introduced, which are classified by the material species. The fabrication methods of the artificial interfaces are summarized and evaluated, including the in-situ strategy and ex-situ strategy. Finally, the characterization means are discussed to give a full view for the study of Zn anode protection. Based on the analysis of this review, a stable and high-performance Zn anode could be designed by carefully choosing applied material, corresponding protective mechanism, and appropriate construction technique. Additionally, this review for Zn anode modification and construction techniques for anode protection in AZIBs may be helpful in other aqueous metal batteries with similar problems.

Mechanism-Guided Rational Design of Anode Coatings for Aqueous Zinc Ion Batteries

Aqueous zinc ion batteries (ZIBs) hold promises as a safer, more cost-effective, and environmental-friendly alternative to lithium-ion batteries, especially for stationary energy storage. Recent advancements in protective anode coatings, which fine-tune zinc ion solvation structure, have yielded significant improvements in the aqueous ZIB performance, addressing dendrite formation and side reactions, thereby prolonging cycle lifetime. Understanding the underlying mechanisms of these coatings as ions sieves is crucial for further optimization and achieving long-term stability, which is a key requirement for practical applications. This concept explores recent developments in ZIB anode coatings from the view of molecular mechanisms and points out future research directions.

Advances of Nanomaterials for High-Efficiency Zn Metal Anodes in Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have emerged as one of the most promising candidates for next-generation energy storage devices due to their outstanding safety, cost-effectiveness, and environmental friendliness. However, the practical application of zinc metal anodes (ZMAs) faces significant challenges, such as dendrite growth, hydrogen evolution reaction, corrosion, and passivation. Fortunately, the rapid rise of nanomaterials has inspired solutions for addressing these issues associated with ZMAs. Nanomaterials with unique structural features and multifunctionality can be employed to modify ZMAs, effectively enhancing their interfacial stability and cycling reversibility. Herein, an overview of the failure mechanisms of ZMAs is presented, and the latest research progress of nanomaterials in protecting ZMAs is comprehensively summarized, including electrode structures, interfacial layers, electrolytes, and separators. Finally, a brief summary and optimistic perspective are given on the development of nanomaterials for ZMAs. This review provides a valuable reference for the rational design of efficient ZMAs and the promotion of large-scale application of AZIBs.

Covalent organic frameworks and their composites for rechargeable batteries

Covalent organic frameworks (COFs), characterized by well-ordered pores, large specific surface area, good stability, high precision, and flexible design, are a promising material for batteries and have received extensive attention from researchers in recent years. Compared with inorganic materials, COFs can construct elastic frameworks with better structural stability, and their chemical compositions and structures can be precisely adjusted and functionalized at the molecular level, providing an open pathway for the convenient transfer of ions. In this review, the energy storage mechanism and unique superiority of COFs and COF composites as electrodes, separators and electrolytes for rechargeable batteries are discussed in detail. Special emphasis is placed on the relationship between the establishment of COF structures and their electrochemical performance in different batteries. Finally, this review summarizes the challenges and prospects of COFs and COF composites in battery equipment.

Biomimetic Superstructured Interphase for Aqueous Zinc-Ion Batteries

The practical application of aqueous zinc-ion batteries (AZIBs) is greatly challenged by rampant dendrites and pestilent side reactions resulting from an unstable Zn-electrolyte interphase. Herein, we report the construction of a reliable superstructured solid electrolyte interphase for stable Zn anodes by using mesoporous polydopamine (2D-mPDA) platelets as building blocks. The interphase shows a biomimetic nacre's "brick-and-mortar" structure and artificial transmembrane channels of hexagonally ordered mesopores in the plane, overcoming the mechanical robustness and ionic conductivity trade-off. Experimental results and simulations reveal that the -OH and -NH groups on the surface of artificial ion channels can promote rapid desolvation kinetics and serve as an ion sieve to homogenize the Zn2+ flux, thus inhibiting side reactions and ensuring uniform Zn deposition without dendrites. The 2D-mPDA@Zn electrode achieves an ultralow nucleation potential of 35 mV and maintains a Coulombic efficiency of 99.8% over 1500 cycles at 5 mA cm-2. Moreover, the symmetric battery exhibits a prolonged lifespan of over 580 h at a high current density of 20 mA cm-2. This biomimetic superstructured interphase also demonstrates the high feasibility in Zn//VO2 full cells and paves a new route for rechargeable aqueous metal-ion batteries.

Zigzag Hopping Site Embedded Covalent Organic Frameworks Coating for Zn Anode

Precise design and tuning of Zn hopping/transfer sites with deeper understanding of the dendrite-formation mechanism is vital in artificial anode protective coating for aqueous Zn-ion batteries (AZIBs). Here, we probe into the role of anode-coating interfaces by designing a series of anhydride-based covalent organic frameworks (i.e., PI-DP-COF and PI-DT-COF) with specifically designed zigzag hopping sites and zincophilic anhydride groups that can serve as desired platforms to investigate the related Zn2+ hopping/transfer behaviours as well as the interfacial interaction. Combining theoretical calculations with experiments, the ABC stacking models of these COFs endow the structures with specific zigzag sites along the 1D channel that can accelerate Zn2+ transfer kinetics, lower surface-energy, homogenize ion-distribution or electric-filed. Attributed to these superiorities, thus-obtained optimal PI-DT-COF cells offer excellent cycling lifespan in both symmetric-cell (2000 cycles at 60 mA cm-2) and full-cell (1600 cycles at 2 A g-1), outperforming almost all the reported porous crystalline materials.

Engineering Covalent Organic Frameworks Toward Advanced Zinc-Based Batteries

Zinc-based batteries (ZBBs) have demonstrated considerable potential among secondary batteries, attributing to their advantages including good safety, environmental friendliness, and high energy density. However, ZBBs still suffer from issues such as the formation of zinc dendrites, occurrence of side reactions, retardation of reaction kinetics, and shuttle effects, posing a great challenge for practical applications. As promising porous materials, covalent organic frameworks (COFs) and their derivatives have rigid skeletons, ordered structures, and permanent porosity, which endow them with great potential for application in ZBBs. This review, therefore, provides a systematic overview detailing on COFs structure pertaining to electrochemical performance of ZBBs, following an in depth discussion of the challenges faced by ZBBs, which includes dendrites and side reactions at the anode, as well as dissolution, structural change, slow kinetics, and shuttle effect at the cathode. Then, the structural advantages of COF-correlated materials and their roles in various ZBBs are highlighted. Finally, the challenges of COF-correlated materials in ZBBs are outlined and an outlook on the future development of COF-correlated materials for ZBBs is provided. The review would serve as a valuable reference for further research into the utilization of COF-correlated materials in ZBBs.

Tackling the Challenges of Aqueous Zn-Ion Batteries via Polymer-Derived Strategies

Zn-ion batteries (ZIBs) have gathered unprecedented interest recently benefiting from their intrinsic safety, affordability, and environmental benignity. Nevertheless, their practical implementation is hampered by low rate performance, inferior Zn2+ diffusion kinetics, and undesired parasitic reactions. Innovative solutions are put forth to address these issues by optimizing the electrodes, separators, electrolytes, and interfaces. Remarkably, polymers with inherent properties of low-density, high processability, structural flexibility, and superior stability show great promising in tackling the challenges. Herein, the recent progress in the synthesis and customization of functional polymers in aqueous ZIBs is outlined. The recent implementations of polymers into each component are summarized, with a focus on the inherent mechanisms underlying their unique functions. The challenges of incorporating polymers into practical ZIBs are also discussed and possible solutions to circumvent them are proposed. It is hoped that such a deep analysis could accelerate the design of polymer-derived approaches to boost the performance of ZIBs and other aqueous battery systems as they share similarities in many aspects.

Constructing Ionic Self-Concentrated Electrolyte via Introducing Montmorillonite Toward High-Performance Aqueous Zn-MnO2 Batteries

Aqueous zinc metal batteries are regarded as one of the most promising alternatives to lithium-ion batteries for large-scale energy storage due to the abundant zinc resources, high safety, and low cost. Herein, an ionic self-concentrated electrolyte (ISCE) is proposed to enable uniform Zn deposition and reversible reaction of MnO2 cathode. Benefitting from the compatibility of ISCE with electrodes and its adsorption on the electrode surface for guidance, the Zn/Zn symmetrical batteries exhibit the long-life cycle stability with more than 5000 and 1500 h at 0.2 and 5 mA cm-2, respectively. The Zn/MnO2 battery also exhibits a high capacity of 351 mA h g-1 at 0.1 A g-1 and can enable a stability over 2000 cycles at 1 A g-1. This work provides a new insight into electrolyte design for stable aqueous Zn-MnO2 battery.

In Situ Grown Coordination-Supramolecular Layer Holding 3D Charged Channels for Highly Reversible Zn Anodes

Dynamic reversible noncovalent interactions make supramolecular framework (SF) structures flexible and designable. A three-dimensional (3D) growth of such frameworks is beneficial to improve the structure stability while maintaining unique properties. Here, through the ionic interaction of the polyoxometalate cluster, coordination of zinc ions with cationic terpyridine, and hydrogen bonding of grafted carboxyl groups, the construction of a 3D SF at a well-crystallized state is realized. The framework can grow in situ on the Zn surface, further extending laterally into a full covering without defects. Relying on the dissolution and the postcoordination effects, the 3D SF layer is used as an artificial solid electrolyte interphase to improve the Zn-anode performance. The uniformly distributed clusters within nanosized pores create a negatively charged nanochannel, accelerating zinc ion transfer and homogenizing zinc deposition. The 3D SF/Zn symmetric cells demonstrate high stability for over 3000 h at a current density of 5 mA cm-2.

Tandem Chemistry with Janus Mesopores Accelerator for Efficient Aqueous Batteries

A reliable solid electrolyte interphase (SEI) on the metallic Zn anode is imperative for stable Zn-based aqueous batteries. However, the incompatible Zn-ion reduction processes, scilicet simultaneous adsorption (capture) and desolvation (repulsion) of Zn2+(H2O)6, raise kinetics and stability challenges for the design of SEI. Here, we demonstrate a tandem chemistry strategy to decouple and accelerate the concurrent adsorption and desolvation processes of the Zn2+ cluster at the inner Helmholtz layer. An electrochemically assembled perforative mesopore SiO2 interphase with tandem hydrophilic -OH and hydrophobic -F groups serves as a Janus mesopores accelerator to boost a fast and stable Zn2+ reduction reaction. Combining in situ electrochemical digital holography, molecular dynamics simulations, and spectroscopic characterizations reveals that -OH groups capture Zn2+ clusters from the bulk electrolyte and then -F groups repulse coordinated H2O molecules in the solvation shell to achieve the tandem ion reduction process. The resultant symmetric batteries exhibit reversible cycles over 8000 and 2000 h under high current densities of 4 and 10 mA cm-2, respectively. The feasibility of the tandem chemistry is further evidenced in both Zn//VO2 and Zn//I2 batteries, and it might be universal to other aqueous metal-ion batteries.

All-Round Ionic Liquids for Shuttle-Free Zinc-Iodine Battery

The practical implementation of aqueous zinc-iodine batteries (ZIBs) is hindered by the rampant Zn dendrites growth, parasite corrosion, and polyiodide shuttling. In this work, ionic liquid EMIM[OAc] is employed as an all-round solution to mitigate challenges on both the Zn anode and the iodine cathode side. First, the EMIM+ embedded lean-water inner Helmholtz plane (IHP) and inert solvation sheath modulated by OAc- effectively repels H2 O molecules away from the Zn anode surface. The preferential adsorption of EMIM+ on Zn metal facilitates uniform Zn nucleation via a steric hindrance effect. Second, EMIM+ can reduce the polyiodide shuttling by hindering the iodine dissolution and forming an EMIM+ -I3 - dominated phase. These effects holistically enhance the cycle life, which is manifested by both Zn || Zn symmetric cells and Zn-I2 full cells. ZIBs with EAc deliver a capacity decay rate of merely 0.01 ‰ per cycle after over 18,000 cycles at 4 A g-1 , and lower self-discharge and better calendar life than the ZIBs without ionic liquid EAc additive.

Robust Zinc Anode Enabled by Sulfonate-Rich MOF-Modified Separator

Aqueous zinc ion batteries (ZIBs) hold great promise for large-scale energy storage; however, severe zinc dendritic growth and side reactions on the anode dramatically impede their commercial application. Herein, a Zr-based MOF (UiO-66) functionalized with a high density of sulfonic acid (─SO3 H) groups is used to modify the glass fiber (GF) separator of ZIBs, providing a unique solution for stabilizing Zn anode. Benefiting from the strong interaction between zincophilic -SO3 H and Zn2+ , this sulfonate-rich UiO-66 modified GF (GF@UiO-S2) separator not only guarantees the homogeneous distribution of ion flux, but also accelerates the ion migration kinetics. Hence, the GF@UiO-S2 separator promotes uniform Zn plating/stripping on the Zn anode and facilitates the desolvation of hydrated Zn2+ ions at the interface, which helps guide dendrite-free Zn deposition and inhibit undesired side reactions. Accordingly, the Zn||Zn symmetric cell with this separator achieves excellent cycling stability with a long cycle life exceeding 3450 h at 3 mA cm-2 . Besides, the Zn||MnO2 full cell paired with this separator delivers remarkable cyclability with 90% capacity retention after 1200 cycles. This design of metal-organic frameworks functionalized separators provides a new insight for constructing highly robust ZIBs.

A Review on Covalent Organic Frameworks as Artificial Interface Layers for Li and Zn Metal Anodes in Rechargeable Batteries

Li and Zn metals are considered promising negative electrode materials for the next generation of rechargeable metal batteries because of their non-toxicity and high theoretical capacity. However, the uneven deposition of metal ions (Li+ , Zn2+ ) and the uncontrolled growth of dendrites result in poor electrochemical stability, unsatisfactory cycle life, and rapid capacity decay of batteries assembled with Li and Zn electrodes. Owing to the unique internal directional channels and abundant redox active sites of covalent organic frameworks (COFs), they can be used to promote uniform deposition of metal ions during stripping/electroplating through interface modification strategies, thereby inhibiting dendrite growth. COFs provide a new perspective in addressing the challenges faced by the anodes of Li metal batteries and Zn ion batteries. This article discusses the stability and types of COFs, and summarizes some novel COF synthesis methods. Additionally, it reviews the latest progress and optimization methods of using COFs for metal anodes to improve battery performance. Finally, the main challenges faced in these areas are discussed. This review will inspire future research on metal anodes in rechargeable batteries.

Membranes based on Covalent Organic Frameworks through Green and Scalable Interfacial Polymerization using Ionic Liquids for Antibiotic Desalination

Covalent organic framework (COF) membranes featuring uniform topological structures and devisable functions, show huge potential in water purification and molecular separation. Nevertheless, the inability of uniform COF membranes to be produced on an industrial scale and their nonenvironmentally friendly fabrication method are the bottleneck preventing their industrial applications. Herein, we report a new green and industrially adaptable scraping-assisted interfacial polymerization (SAIP) technique to fabricate scalable and uniform TpPa COF membranes. The process used non-toxic and low-volatility ionic liquids (ILs) as organic phase instead of conventional organic solvents for interfacial synthesis of TpPa COF layer on a support membrane, which can simultaneously achieve the purposes of (i) improving the greenness of membrane-forming process and (ii) fabricating a robust membrane that can function beyond the conventional membranes. This approach yields a large-area, continuous COF membrane (19×25 cm2 ) with a thickness of 78 nm within a brief period of 2 minutes. The resulting membrane exhibited an unprecedented combination of high permeance (48.09 L m-2 h-1 bar-1 ) and antibiotic desalination efficiency (e.g., NaCl/adriamycin separation factor of 41.8), which is superior to the commercial benchmarking membranes.

Optimizing Porous Metal-Organic Layers for Stable Zinc Anodes

Aqueous zinc-ion batteries (ZIBs) have been considered as alternative stationary energy storage systems, but the dendrite and corrosion issues of Zn anodes hinder their practical applications. Here we report a series of two-dimensional (2D) metal-organic frameworks (MOFs) with Zr12 clusters, which act as artificial solid electrolyte interphase (SEI) layers to prevent dendrites and corrosion of Zn anodes. The Zr12-based 2D MOF layers were formed by incubating 3D layer-pillared Zr-MOFs in ZnSO4 aqueous electrolytes, which replaced the pillar ligands with terminal SO42-. Furthermore, the pore sizes of Zr12-based 2D MOF layers were systematically tuned, leading to optimized Zn2+ conduction properties and protective performance for Zn anodes. In contrast to the traditional 2D-MOFs with Zr6 clusters, Zr12-based 2D MOF layers as artificial SEI significantly reduced the polarization and increased the stability of Zn anodes in MOF@Zn||MOF@Zn symmetric cells and MOF@Zn||MnO2 full cells. In situ experiments and DFT computations reveal that the enhanced cell performance is attributed to the unique Zr12-based layered structure with intrinsic pores to allow fast Zn2+ diffusion, surface Zr-SO4 zincophilic sites to induce uniform Zn deposition, and inhibited hydrogen evolution by 2D MOF Zr12 layers.

Covalent Organic Frameworks: Their Composites and Derivatives for Rechargeable Metal-Ion Batteries

Covalent organic frameworks (COFs) have attracted considerable interest in the field of rechargeable batteries owing to their three-dimensional (3D) varied pore sizes, inerratic porous structures, abundant redox-active sites, and customizable structure-adjustable frameworks. In the context of metal-ion batteries, these materials play a vital role in electrode materials, effectively addressing critical issues such as low ionic conductivity, limited specific capacity, and unstable structural integrity. However, the electrochemical characteristics of the developed COFs still fall short of practical battery requirements due to inherent issues such as low electronic conductivity, the tradeoff between capacity and redox potential, and unfavorable micromorphology. This review provides a comprehensive overview of the recent advancements in the application of COFs, COF-based composites, and their derivatives in rechargeable metal-ion batteries, including lithium-ion, lithium-sulfur, sodium-ion, sodium-sulfur, potassium-ion, zinc-ion, and other multivalent metal-ion batteries. The operational mechanisms of COFs, COF-based composites, and their derivatives in rechargeable batteries are elucidated, along with the strategies implemented to enhance the electrochemical properties and broaden the range of their applications.

Covalent Organic Frameworks in Aqueous Zinc-Ion Batteries

The development and utilization of green renewable energy are imperative with the aggravation of environmental pollution and energy crisis. In recent years, the exploration of electrochemical energy storage systems has gradually become a research hotspot in energy. Among them, aqueous zinc-ion batteries (ZIBs) have progressively developed into highly competitive and efficient energy storage devices owing to their inherent safety, natural abundance, and higher theoretical capacity. However, the practical application of ZIBs suffers from the limitation of challenges such as the absence of proper cathode materials and the unavoidable zinc dendrites and side reactions of Zn anode. Covalent organic frameworks (COFs) are an attractive class of electrode materials due to their inherent advantages, like structural designability, high stability, and ordered-open channels, bestowing them with great potential to overcome the problems of ZIBs. In this review, we concentrate on the discussion of designed strategies of COFs applied to ZIBs. Furthermore, the methods of using COFs to solve the challenging problems of cathode development, anode modification, and electrolyte optimization for ZIBs are summarized. Finally, the existing difficulties, solution measures, and prospects of COFs for ZIBs applications are discussed. Our commentary hopes to serve as a valuable reference for developing COFs-based ZIBs.

Three-Dimensional Zinc-Seeded Carbon Nanofiber Architectures as Lightweight and Flexible Hosts for a Highly Reversible Zinc Metal Anode

Uneven zinc (Zn) deposition typically leads to uncontrollable dendrite growth, which renders an unsatisfactory cycling stability and Coulombic efficiency (CE) of aqueous zinc ion batteries (ZIBs), restricting their practical application. In this work, a lightweight and flexible three-dimensional (3D) carbon nanofiber architecture with uniform Zn seeds (CNF-Zn) is prepared from bacterial cellulose (BC), a kind of biomass with low cost, environmental friendliness, and abundance, as a host for highly reversible Zn plating/stripping and construction of high-performance aqueous ZIBs. The as-prepared 3D CNF-Zn with a porous interconnected network significantly decreases the local current density, and the functional Zn seeds provide uniform nuclei to guide the uniform Zn deposition. Benefiting from the synergistic effect of Zn seeds and the 3D porous framework in the flexible CNF-Zn host, the electrochemical performance of the as-constructed ZIBs is significantly improved. This flexible 3D CNF-Zn host delivers a high and stable CE of 99.5% over 450 cycles, ensuring outstanding rate performance and a long cycle life of over 500 cycles at 4 A g-1 in the CNF-Zn@Zn//NaV3O8·1.5H2O full battery. More importantly, owing to the flexibility of the 3D CNF-Zn host, the as-assembled pouch cell shows outstanding mechanical flexibility and excellent energy storage performance. This strategy of producing readily accessible carbon from biomass can be employed to develop advanced functional nanomaterials for next-generation flexible energy storage devices.

Balancing Interfacial Reactions through Regulating p-Band Centers by an Indium Tin Oxide Protective Layer for Stable Zn Metal Anodes

Metallic zinc (Zn) is considered as one of the most attractive anode materials for the post-lithium metal battery systems owing to the high theoretical capacity, low cost, and intrinsic safety. However, the Zn dendrites and parasitic side reaction impede its application. Herein, we propose a new principle of regulating p-band center of metal oxide protective coating to balance Zn adsorption energy and migration energy barrier for effective Zn deposition and stripping. Experimental results and theoretical calculations indicate that benefiting from the uniform zincophilic nucleation sites and fast Zn transport on indium tin oxide (ITO), highly stable and reversible Zn anode can be achieved. As a result, the I-Zn symmetrical cell achieves highly reversible Zn deposition/stripping with an extremely low overpotential of 9 mV and a superior lifespan over 4000 h. The Cu/I-Zn asymmetrical cell exhibits a long lifetime of over 4000 cycles with high average coulombic efficiency of 99.9 %. Furthermore, the assembled I-Zn/AC full cell exhibits an excellent lifetime for 70000 cycles with nearly 100 % capacity retention. This work provides a general strategy and new insight for the construction of efficient Zn anode protection layer.

Tuning the Electrode/Electrolyte Interface Enabled by a Trifunctional Inorganic Oligomer Electrolyte Additive for Highly Stable and High-Rate Zn Anodes

The practical application of aqueous Zn-ion batteries is still greatly hindered by the unstable Zn anode with severe Zn dendrites growth and side reactions. As it is accessible and economical, the exploitation of electrolyte additives is one of the most promising strategies to stabilize the Zn electrode/electrolyte interface. Herein, the penta-potassium triphosphate (KTPP) as a novel trifunctional electrolyte additive is introduced to tune the electrode/electrolyte interface. First, the KTPP additive can induce an ion-conducting and mechanically robust solid electrolyte interphase film to stabilize the Zn anode. Second, the KTPP can complex with Zn2+ ions to reconstitute the dissolution sheath structure of the Zn2+ ion. Finally, the K+ cations in KTPP adsorb on the tips of the Zn anode surface as a shielding film to regulate Zn2+ ion flux. As a result, Zn//Zn symmetric cells can achieve significantly prolonged cycling stability (e.g., from 1077 to 3800 h at 1 mA cm-2 /1 mAh cm-2 , from 256 to 2500 h at 2 mA cm-2 /2 mAh cm-2 ), and ultrahigh cumulative capacity of 6400/7200 mAh cm-2 at high current density (40/20 mA cm-2 ). A four-layer Zn-MnO2 pouch full cell with a high capacity of 9 mAh can be constructed, showing impressive practical application potential.

Coulombic Efficiency for Practical Zinc Metal Batteries: Critical Analysis and Perspectives

Climate change and energy depletion are common worries of this century. During the global clean energy transition, aqueous zinc metal batteries (AZMBs) are expected to meet societal needs due to their large-scale energy storage capability with earth-abundant, non-flammable, and economical chemistries. However, the poor reversibility of Zn poses a severe challenge to AZMB implementation. Coulombic efficiency (CE) is a quantitative index of electrode reversibility in rechargeable batteries but is not well understood in AZMBs. Thus, in this work,  the state-of-art CE to present the status quo of AZMB development is summarized.  A fictional 120 Wh kg-1 AZMB pouch cell is also proposed and evaluated revealing the improvement room and technical goal of AZMB chemistry. Despite some shared mechanisms between AZMBs and lithium metal batteries, misconceptions prevalent in AZMBs are clarified. Essentially, AZMB has its own niche in the market with unique merits and demerits. By incorporating academic and industrial insights, the development pathways of AZMB are suggested.

Trade-off between Zincophilicity and Zincophobicity: Toward Stable Zn-Based Aqueous Batteries

Zn-based aqueous batteries (ZABs) hold great promise for large-scale energy storage applications due to the merits of intrinsic safety and low cost. Nevertheless, the thorny issues of metallic Zn anodes, including dendrite growth and parasitic side reactions, have severely limited the application of ZABs. Despite the encouraging improvements for stabilizing Zn anodes through surface modification, electrolyte optimization, and structural design, fundamentally addressing the inherent thermodynamics and kinetics obstacles of Zn anodes remains crucial in realizing reliable ZABs with ultrahigh efficiency, capacity, and cyclability. The target of this perspective is to elucidate the prominent status of Zn metal anode electrochemistry first from the perspective of zincophilicity and zincophobicity. Recent progress in ZABs is critically appraised for addressing the key issues, with special emphasis on the trade-off between zincophilic and zincophobic electrochemistry. Challenges and prospects for further exploration of a reliable Zn anode are presented, which are expected to boost in-depth research and practical applications of advanced ZABs.

Dendrite-free zinc metal anodes enabled by electrolyte additive for high-performing aqueous zinc-ion batteries

Rechargeable aqueous zinc (Zn)-ion batteries are regarded as a suitable candidate for large-scale energy storage due to their high safety and the natural abundance of Zn. However, the Zn anode in the aqueous electrolyte faces the challenges of corrosion, passivation, hydrogen evolution reaction, and the growth of severe Zn dendrites. These problems severely affect the performance and service life of aqueous Zn ion batteries, making it difficult to achieve their large-scale commercial applications. In this work, the sodium bicarbonate (NaHCO₃) additive was introduced into the zinc sulfate (ZnSO₄) electrolyte to inhibit the growth of Zn dendrites by promoting uniform deposition of Zn ions on the (002) crystal surface. This treatment presented a significant increase in the intensity ratio of (002) to (100) from an initial value of 11.14 to 15.31 after 40 cycles of plating/stripping. The Zn//Zn symmetrical cell showed a longer cycle life (over 124 h at 1.0 mA cm^-2) than the symmetrical cell without NaHCO₃. Additionally, the high capacity retention rate was increased by 20% for Zn//MnO₂ full cells. This finding is expected to be beneficial for a range of research studies that use inorganic additives to inhibit Zn dendrites and parasitic reactions in electrochemical and energy storage applications.

Stabilizing a zinc anode via a tunable covalent organic framework-based solid electrolyte interphase

Zinc (Zn) is an excellent material for use as an anode for rechargeable batteries in water-based electrolytes. Nevertheless, the high activity of water leads to Zn corrosion and hydrogen evolution, along with the formation of dendrites on the Zn surface during repeated charge-discharge (CD) cycles. To protect the Zn anode and limit parasitic side reactions, an artificial solid electrolyte interphase (ASEI) protective layer is an effective strategy. Herein, an ASEI made of a covalent organic framework (COFs: HqTp and BpTp) was fabricated on the surface of a Zn anode via Schiff base reactions of aldehyde and amine linkers. It is seen that COFs can regulate the Zn-ion flux, resulting in dendritic-free Zn. COFs can also mitigate the formation of an irreversible passive layer and the hydrogen evolution reaction (HER). Zn plating/stripping tests using a symmetrical cell suggest that HqTpCOF@Zn shows superior stability and greater coulombic efficiency (CE) compared to bare Zn. The full cell having COFs@Zn also displays much improved cyclability. As a result, the COF proves to be a promising ASEI material to enhance the stability of the Zn anode in aqueous media.

Uniform Zinc Deposition Regulated by a Nitrogen-Doped MXene Artificial Solid Electrolyte Interlayer

The dendrite growth and side reactions of zinc metal anode in mildly acidic electrolytes seriously hinder the practical application of aqueous zinc-ion battery. To address these issues, an artificial protective layer of nitrogen-doped MXene (NMX) is used to protect the zinc anode. The NMX protective layer has high conductivity and uniformly distributed zincophilic sites, which can not only homogenize the local electric field on the electrode interface but also accelerate the kinetics for Zn deposition. As a result, the NMX protective layer induces uniform zinc deposition and reduces the overpotential of the electrode. Encouragingly, this NMX-protected Zn anode can cycle stably for 1900 h at 1 mA cm^-2 and 1 mAh cm^-2 . In asymmetric cells, it achieves high cycle reversibility with an average Coulomb efficiency of 99.79% for 4800 cycles at 5 mA cm^-2 .

A Seamless Metal-Organic Framework Interphase with Boosted Zn2+ Flux and Deposition Kinetics for Long-Living Rechargeable Zn Batteries

Zn metal has received immense interest as a promising anode of rechargeable aqueous batteries for grid-scale energy storage. Nevertheless, the uncontrollable dendrite growth and surface parasitic reactions greatly retard its practical implementation. Herein, we demonstrate a seamless and multifunctional metal-organic framework (MOF) interphase for building corrosion-free and dendrite-free Zn anodes. The on-site coordinated MOF interphase with 3D open framework structure could function as a highly zincophilic mediator and ion sifter that synergistically induces fast and uniform Zn nucleation/deposition. In addition, the surface corrosion and hydrogen evolution are significantly suppressed by the interface shielding of the seamless interphase. An ultrastable Zn plating/stripping is achieved with elevated Coulombic efficiency of 99.2% over 1000 cycles and prolonged lifetime of 1100 h at 10 mA cm^-2 with a high cumulative plated capacity of 5.5 Ah cm^-2. Moreover, the modified Zn anode assures the MnO₂-based full cells with superior rate and cycling performance.

Integrated Micro Space Electrostatic Field in Aqueous Zn-Ion Battery: Scalable Electrospray Fabrication of Porous Crystalline Anode Coating

The inhomogeneous consumption of anions and direct contact between electrolyte and anode during the Zn-deposition process generate Zn-dendrites and side reactions that can aggravate the space-charge effect to hinder the practical implementation of zinc-metal batteries (ZMBs). Herein, electrospray has been applied for the scalable fabrication (>10 000 cm² in a batch-experiment) of hetero-metallic cluster covalent-organic-frameworks (MCOF-Ti₆ Cu₃ ) nanosheet-coating (MNC) with integrated micro space electrostatic field for ZMBs anode protection. The MNC@Zn symmetric cell presents ultralow overpotential (≈72.8 mV) over 10 000 cycles at 1 mAh cm^-2 with 20 mA cm^-2 , which is superior to bare Zn and state-of-the-art porous crystalline materials. Theoretical calculations reveal that MNC with integrated micro space electrostatic field can facilitate the deposition-kinetic and homogenize the electric field of anode to significantly promote the lifespan of ZMBs.

Sustained-Compensated Interfacial Zincophilic Sites to Assist High-Capacity Aqueous Zn Metal Batteries

Aqueous Zn metal batteries have attracted extensive attention due to their intrinsic advantages. However, zinc ions tend to deposit irregularly, seriously depleting the capacity and stability of the battery. The construction of zincophilic sites can effectively regulate the nucleation and growth of Zn, but there is a defect that these sites will be covered with gradual failure after long-term cycling. Here, in combination with the sustained-compensated strategy, interfacial zincophilic sites are continuously constructed, thus effectively avoiding the threat of dendrites and improving the electrochemical performance. Impressively, at 10 mA cm^-2 and 5 mAh cm^-2, the protected Zn metal exhibits excellent cycling stability over 2000 cycles in the Zn//Zn battery. Moreover, even the cathode mass loading is considerably high (35 mg cm^-2), and the Zn//NVO full cell significantly outperforms with high areal capacity (up to 4 mAh cm^-2). This novel strategy provides a direction for the development of high-capacity aqueous batteries.

Step by Step Induced Growth of Zinc-Metal Interface on Graphdiyne for Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc ion batteries (AZIBs) promise high energy density, low redox potential, low cost and safety; however, their cycle performances are seriously insufficient to restrict the progress in this field. We propose a new concept of atomic electrode formed on the graphdiyne (GDY). This new idea electrode was synthesized by selectively, uniformly, and stably anchoring Zn atoms on GDY at the beginning of plating. The Zn atoms are induced to grow into larger size Zn clusters, which continue to grow into nanoflat. Finally, a new heterojunction interface is formed on GDY without any Zn dendrites and side reactions, even at high current densities. Such stepwise induction of growth greatly suppresses the formation of Zn dendrites, resulting in high electroplating/stripping reversibility and lifespan of AZIBs.

Decreasing Water Activity Using the Tetrahydrofuran Electrolyte Additive for Highly Reversible Aqueous Zinc Metal Batteries

Aqueous zinc metal batteries show great promise in large-scale energy storage. However, the decomposition of water molecules leads to severe side reactions, resulting in the limited lifespan of Zn batteries. Here, the tetrahydrofuran (THF) additive was introduced into the zinc sulfate (ZnSO₄) electrolyte to reduce water activity by modulating the solvation structure of the Zn hydration layer. The THF molecule can play as a proton acceptor to form hydrogen bonds with water molecules, which can prevent water-induced undesired reactions. Thus, in an optimal 2 M ZnSO₄/THF (5% by volume) electrolyte, the hydrogen evolution reaction and byproduct precipitation can be suppressed, which greatly improves the cycling stability and Coulombic efficiency of reversible Zn plating/stripping. The Zn symmetrical cells exhibit ultralong working cycles with a wide range of current density and capacity. The THF additive also enables a high Coulombic efficiency in the Zn||Cu cell with an average value of 99.59% over 400 cycles and a high reversible capacity with a capacity retention of 97.56% after 250 cycles in the Zn||MnO₂ full cells. This work offers an effective strategy with high scalability and low cost for the protection of the Zn metal electrodes in aqueous rechargeable batteries.

Highly Stretchable, Self-Healing, and Low Temperature Resistant Double Network Hydrogel Ionic Conductor as Flexible Sensor and Quasi-Solid Electrolyte

With the rapid development of flexible energy storage and wearable strain sensing, conductive hydrogels are attracting attention as electrolyte materials for flexible strain sensors and flexible supercapacitors due to their excellent flexibility and wetting properties. In this work, antifreezing hydrogels with high stretchability, adhesion, and conductivity are designed and prepared by introducing phosphoric acid solutions into polyacrylamide and chitosan systems. The multifunctional hydrogel samples prepared by this method can be used as both quasi-solid electrolytes and wearable strain sensors. The hydrogel-based supercapacitor shows a charge/discharge efficiency of 99.67% and a capacitance retention of 98.85% after 10 000 cycles charge/discharge tests at -30 °C. The tiny characteristic heartbeat wave forms are detected by the hydrogel as a flexible strain sensor. It is foreseeable that PCP multifunctional hydrogel can be a promising flexible material for a new generation of flexible sensors and flexible energy storage devices in a certain range of temperatures.

Advanced Covalent Organic Frameworks for Multi-Valent Metal Ion Batteries

Covalent organic frameworks (COFs) have received increased interest in recent years as an advanced class of materials. By virtue of the available monomers, multiple conformations and various linkages, COFs offer a wide range of opportunities for complex structural design and specific functional development of materials, which has facilitated the widespread application in many fields, including multi-valent metal ion batteries (MVMIBs), described as the attractive candidate replacing lithium-ion batteries (LIBs). With their robust skeletons, diverse pores, flexible structures and abundant functional groups, COFs are expected to help realize a high performance MVMIBs. In this review, we present an overview of COFs, describe advances in topology design and synthetic reactions, and study the application of COFs in MVMIBs, as well as discuss challenges and solutions in the preparation of COFs electrodes, in the hope of providing constructive insights into the future direction of COFs.

Two-Dimensional Organic-Inorganic Heterostructure as a Multifunctional Protective Layer for High Performance Zinc Metal Anode

Dendrite growth and side reactions of Zn metal anodes remain unresolved obstacles for practical application of aqueous Zn ion batteries. Herein, a two-dimensional (2D) organic-inorganic heterostructure with controlled thickness was constructed as a protective layer for a Zn metal anode. The reduction of uniformly distributed polyoxometalate in the layer causes a negative charge density gradient, which can accelerate zinc ion transfer, homogenize zinc deposition, and shield sulfates at the electrode interface, while the exposed hydrophobic alkyl chain of the layer can isolate the direct contact of water with the Zn anode. As a result of the synergetic effect, this 2D organic-inorganic heterostructure enables high Zn plating/stripping reversibility, with high average Coulombic efficiencies of 99.97% for 3700 cycles at 2 mA cm^-2. Under high Zn utilization conditions, a high areal-capacity full cell with hundreds of cycles was demonstrated.