Graphene-Boosted, High-Performance Aqueous Zn-Ion Battery

Resilient and Reversible Phosphotungstic Acid Passivated Zinc Anode

Aqueous zinc ion batteries (ZIBs) present a compelling solution for grid-scale energy storage, which is crucial for integrating renewable energy resources into the electric infrastructure. The cycling stability of ZIBs hinges on the electrochemical reversibility of the zinc anode, which is often compromised by corrosion and dendritic zinc deposition. Here, we present a straightforward surface passivation strategy that significantly enhances the cycling stability of zinc anodes. By immersing zinc in a solution of phosphotungstic acid, we promoted the dominance of the 002 plane of zinc's hexagonal structure. This process facilitates the creation of a uniform nucleation and protective layer on the native zinc surface, resulting in a more uniform plating-stripping process and increased corrosion resistance. In symmetric cells, the passivated zinc exhibits a capacity retention of 68.7% after 1000 cycles at a current density of 1.0 Ag1-, whereas untreated zinc anodes retain only 7.4% of capacity under identical conditions. In full cell zinc iodine batteries employing the passivated zinc anode, over 1000 stable charge-discharge cycles were achieved at a current density of 20 mA cm-2, with approximately 96% Coulombic efficiency (CE), 86% voltage efficiency (VE), and 82% energy efficiency (EE). This study demonstrates a promising pathway for the construction and upscaling of flow batteries with high capacity and low cost.

Carbonized Ganoderma Lucidum/V2O3 Composites as a Superior Cathode for High-Performance Aqueous Zinc-Ion Batteries

In response to the suboptimal electrochemical performance of low-valence vanadium oxides, Ganoderma lucidum biomass-derived carbon@V2O3 (V2O3@CGL) composites were prepared by evaporative self-assembly technology and high-temperature calcination. In the prepared composites, V2O3 effectively encapsulates CGL, serving as a support for V2O3 and enhancing electrical conductivity and structural stability. This results in improved overall performance for the composites. They revealed satisfactory electrochemical properties when assembled in aqueous zinc-ion batteries (AZIBs). The preliminary discharge specific capacity of the V2O3@CGL-2 (VOCG-2) composite electrode reached 407.87 mAh g-1 at 0.05 A g-1. After 1000 cycles, the capacity retention is 93.69% at 3 A g-1. This research underscores the feasibility of employing V2O3 and abundantly available biomass for high-performance AZIB cathodes.

Hydrous Molybdenum Oxide Coating of Zinc Metal Anode via the Facile Electrodeposition Strategy and Its Performance Improvement Mechanisms for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) are widely recognized as highly promising energy storage devices because of their inherent characteristics, including superior safety, affordability, eco-friendliness, and various other benefits. However, the significant corrosion of the zinc metal anode, side reactions occurring between the anode and electrolyte, and the formation of zinc dendrites significantly hinder the practical utilization of ZIBs. Herein, we utilized an electrodeposition method to apply a unique hydrous molybdenum oxide (HMoOx) layer onto the surface of the zinc metal anode, aiming to mitigate its corrosion and side reactions during the process of zinc deposition and stripping. In addition, the HMoOx layer not only improved the hydrophilicity of the zinc anode, but also adjusted the migration of Zn2+, thus facilitating the uniform deposition of Zn2+ to reduce dendrite formation. A symmetrical cell with the HMoOx-Zn anode displayed reduced-voltage hysteresis (80 mV at 2.5 mA/cm2) and outstanding cycle stability after 3000 cycles, surpassing the performance of the uncoated Zn anode. Moreover, the HMoOx-Zn anode coupled with a γ-MnO2 cathode created a considerably more stable rechargeable full battery compared to the bare Zn anode. The HMoOx-Zn||γ-MnO2 full cell also displayed excellent cycling stability with a charge/discharge-specific capacity of 129/133 mAh g-1 after 300 cycles. In summary, this research offers a straightforward and advantageous approach that can significantly contribute to the future advancements in rechargeable ZIBs.

A Protective Layer of UIO-66/Reduced Graphene Oxide to Stabilize Zinc-Metal Anodes toward High-Performance Aqueous Zinc-Ion Batteries

Rechargeable aqueous Zn-ion batteries with a Zn anode hold great promise as promising candidates for advanced energy storage systems. The construction of protective layer coatings on Zn anode is an effective way to suppress the growth of Zn dendrites and water-induced side reactions. Herein, we reported a series of UIO-66 materials with different concentrations of reduced graphene oxide (rG) coated onto the surface of Zn foil (Zn@UIO-66/rGx; x = 0.05, 0.1, and 0.2). Benefiting from the synergistic effect of UIO-66 and rG, symmetric cells with Zn@UIO-66/rGx (x = 0.1) electrodes exhibit excellent reversibility (e.g., long cycling life over 1100 h at 1 mA cm-2/1 mAh cm-2) and superior rate capability (e.g., over 1100 and 400 h at 5 mA cm-2/2.5 mAh cm-2 and 10 mA cm-2/5 mAh cm-2, respectively). When the Zn@UIO-66/rG0.1 anode was paired with the NaV3O8·1.5H2O (NVO) cathode, the Zn@UIO-66/rG0.1||NVO cell also delivered a high reversible capacity of 189.9 mAh g-1 with an initial capacity retention of 61.3% after 500 cycles at 1 A g-1, compared to the bare Zn||NVO cell with only 92 cycles.

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.

Structure regulation and synchrotron radiation investigation of cathode materials for aqueous Zn-ion batteries

In view of the advantages of low cost, environmental sustainability, and high safety, aqueous Zn-ion batteries (AZIBs) are widely expected to hold significant promise and increasingly infiltrate various applications in the near future. The development of AZIBs closely relates to the properties of cathode materials, which depend on their structures and corresponding dynamic evolution processes. Synchrotron radiation light sources, with their rich advanced experimental methods, serve as a comprehensive characterization platform capable of elucidating the intricate microstructure of cathode materials for AZIBs. In this review, we initially examine available cathode materials and discuss effective strategies for structural regulation to boost the storage capability of Zn2+. We then explore the synchrotron radiation techniques for investigating the microstructure of the designed materials, particularly through in situ synchrotron radiation techniques that can track the dynamic evolution process of the structures. Finally, the summary and future prospects for the further development of cathode materials of AZIBs and advanced synchrotron radiation techniques are discussed.

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.

Interfacial Engineering of Zn Metal via a Localized Conjugated Layer for Highly Reversible Aqueous Zinc Ion Battery

Aqueous zinc-ion batteries are regarded as promising and efficient energy storage systems owing to remarkable safety and satisfactory capacity. Nevertheless, the instability of zinc metal anodes, characterized by issues such as dendrite growth and parasitic side reactions, poses a significant barrier to widespread applications. Herein, we address this challenge by designing a localized conjugated structure comprising a cyclic polyacrylonitrile polymer (CPANZ), induced by a Zn2+-based Lewis acid (zinc trifluoromethylsulfonate) at a temperature of 120 °C. The CPANZ layer on the Zn anode, enriched with appropriate pyridine nitrogen-rich groups (conjugated cyclic -C=N-), exhibits a notable affinity for Zn2+ with ample deposition sites. This zincophilic skeleton not only serves as a protective layer to guide the deposition of Zn2+ but also functions as proton channel blocker, regulating the proton flux to mitigate the hydrogen evolution. Additionally, the strong adhesion strength of the CPANZ layer guarantees its sustained protection to the Zn metal during long-term cycling. As a result, the modified zinc electrode demonstrates long cycle life and high durability in both half-cell and pouch cells. These findings present a feasible approach to designing high performance aqueous anodes by introducing a localized conjugated layer.

Recent Advances in Graphene-Based Materials for Zinc-Ion Batteries

Zinc-ion batteries (ZIBs) are a promising alternative for large-scale energy storage due to their advantages of environmental protection, low cost, and intrinsic safety. However, the utilization of their full potential is still hindered by the sluggish electrode reaction kinetics, poor structural stability, severe Zn dendrite growth, and narrow electrochemical stability window of the whole battery. Graphene-based materials with excellent physicochemical properties hold great promise for addressing the above challenges foe ZIBs. In this review, the energy storage mechanisms and challenges faced by ZIBs are first discussed. Key issues and recent progress in design strategies for graphene-based materials in optimizing the electrochemical performance of ZIBs (anode, cathode, electrolyte, separator and current collector) are then discussed. Finally, some potential challenges and future research directions of graphene-based materials in high-performance ZIBs are proposed for practical applications.

Separator designs for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are attracting worldwide attention due to their multiple merits such as extreme safety, low cost, feasible assembly, and environmentally friendly enabled by water-based electrolytes. At present, AZIBs have experienced systematic advances in battery components including cathode, anode, and electrolyte, whereas research involving separators is insufficient. The separator is the crucial component of AZIBs through providing ion transport, forming contact with electrodes, serving as a container for electrolyte, and ensuring the efficient battery operation. Considering this great yet ignored significance, it is timely to present the latest advances in design strategies, the systematic classification and summary of separators. We summarize the separator optimization strategies mainly along two approaches including the modification of the frequently used glass fiber and the exploitation of new separators. The advantages and disadvantages of the two strategies are analyzed from the material types and the characteristics of different strategies. The effects and mechanisms of various materials on regulating the uniform migration and deposition of Zn2+, balancing the excessively concentrated nucleation points, inhibiting the growth of dendrites, and the occurrence of side reactions were discussed using confinement, electric field regulation, ion interaction force, desolvation, etc. Finally, potential directions for further improvement and development of AZIBs separators are proposed, aiming at providing helpful guidance for this booming field.

Achieving stable Zn metal anode via a hydrophobic and Zn2+-conductive amorphous carbon interface

High security and low cost enable aqueous zinc ion batteries (AZIBs) with huge application potential in large-scale energy storage. Nevertheless, the loathsome dendrite and side reactions of Zn anode are harmful to the cycling lifespan of AZIBs. Here, a new type of thin amorphous carbon (AC) interface layer (∼100 nm in thickness) is in-situ constructed on the Zn foil (Zn@AC) via a facile low-temperature chemical vapor deposition (LTCVD) method, which owns a hydrophobic peculiarity and a high Zn2+ transference rate. Moreover, this AC coating can homogenize the surface electric field and Zn2+ flux to realize the uniform deposition of Zn. Consequently, dendrite growth and side reactions are concurrently mitigated. Symmetrical cell achieves a dendrite-free Zn plating/stripping over 500 h with a low overpotential of 31 mV at 1 mA cm-2/1 mAh cm-2. Of note, the full cell with a MnO2/CNT cathode harvests a capacity retention of 70.0 % after 550 cycles at 1 A/g. In addition, the assembled flexible quasi-solid-state AZIBs display a stable electrochemical performance under deformation conditions and maintain a capacity of 76.5 mAh/g at 5 A/g after 300 cycles. This innovative amorphous carbon layer is expected to provide a new insight into stabilizing Zn anode.

Engineering Interfacial Fast Ion Channels toward Highly Stable Zn Metal Batteries

The development of aqueous zinc-ion batteries (AZIBs) is hindered by dendrites and side reactions, such as interfacial byproducts, corrosion, and hydrogen evolution. The construction of an artificial interface protective layer on the surface of the zinc anode has been extensively researched due to its strong operability and potential for large-scale application. In this study, we have designed an organic hydrophobic hybrid inorganic intercalation composite coating to achieve stable Zn2+ plating/stripping. The hydrophobic poly(vinylidene fluoride) (PVDF) effectively prevents direct contact between free water and the zinc anode, thereby mitigating the risk of dendrite formation. Simultaneously, the inorganic layer of vanadium phosphate (VOPO4·2H2O) after the insertion of polyaniline (PA) establishes a robust ion channel for facilitating rapid transport of Zn2+, thus promoting uniform electric field distribution and reducing concentration polarization. As a result, the performance of the modified composite PVDF/PA-VOP@Zn anode exhibited significant enhancement compared with that of the bare zinc anode. The assembled symmetric cell exhibits an exceptionally prolonged lifespan of 3070 h at a current density of 1 mA cm-2, while the full battery employing KVO as the cathode demonstrates a remarkable capability to undergo 2000 cycles at 5 A g-1 with a capacity retention rate of 78.2%. This study offers valuable insights into the anodic modification strategy for AZIBs.

Gold-Nanolayer-Derived Zincophilicity Suppressing Metallic Zinc Dendrites and Its Efficacy in Improving Electrochemical Stability of Aqueous Zinc-Ion Batteries

Herein, an Au-coating layer adjusted on the surface of a Zn metal electrode that effectively suppresses the dendrite growth as well as the mechanisms underlying the dendrite suppression as a result of the zincophilic character of Au is introduced. For the Au-coated Zn metal symmetric cell, uniform deposition of Zn-derived compounds was revealed by operando synchrotron tomography. Microscopic studies demonstrate that the Au-coating layer is induced to form a new Zn-Au alloy during the initial Zn deposition, resulting in stabilized long-term stripping/plating of Zn via the 'embracing effect' that intimately accommodates Zn deposition for further cycles. This property supports the successful operation of symmetrical cells up to 50 mA cm-2 . According to Zn electrodeposition simulation, it is verified that the suppression of dendrite growth is responsible for the electro-conducting Au nanolayer that uniformly distributes the electric field and protects the Zn electrode from corrosion, ultimately promoting uniform Zn growth. The compatibility of the Au-coating layer for full cell configuration is verified using NaV3 O8 as a cathode material over 1 000 cycles. This finding provides a new pathway for the enhancement of the electrochemical performance of ZIBs by suppressing the dendritic growth of Zn by means of a zincophilic Au nanolayer.

Understanding the Electrical Mechanisms in Aqueous Zinc Metal Batteries: From Electrostatic Interactions to Electric Field Regulation

Aqueous Zn metal batteries are considered as competitive candidates for next-generation energy storage systems due to their excellent safety, low cost, and environmental friendliness. However, the inevitable dendrite growth, severe hydrogen evolution, surface passivation, and sluggish reaction kinetics of Zn metal anodes hinder the practical application of Zn metal batteries. Detailed summaries and prospects have been reported focusing on the research progress and challenges of Zn metal anodes, including electrolyte engineering, electrode structure design, and surface modification. However, the essential electrical mechanisms that significantly influence Zn2+ ions migration and deposition behaviors have not been reviewed yet. Herein, in this review, the regulation mechanisms of electrical-related electrostatic repulsive/attractive interactions on Zn2+ ions migration, desolvation, and deposition behaviors are systematically discussed. Meanwhile, electric field regulation strategies to promote the Zn2+ ions diffusion and uniform Zn deposition are comprehensively reviewed, including enhancing and homogenizing electric field intensity inside the batteries and adding external magnetic/pressure/thermal field to couple with the electric field. Finally, future perspectives on the research directions of the electrical-related strategies for building better Zn metal batteries in practical applications are offered.

Recent Advances and Strategies in MXene-Based Electrodes for Supercapacitors: Applications, Challenges and Future Prospects

With the growing demand for technologies to sustain high energy consumption, supercapacitors are gaining prominence as efficient energy storage solutions beyond conventional batteries. MXene-based electrodes have gained recognition as a promising material for supercapacitor applications because of their superior electrical conductivity, extensive surface area, and chemical stability. This review provides a comprehensive analysis of the recent progress and strategies in the development of MXene-based electrodes for supercapacitors. It covers various synthesis methods, characterization techniques, and performance parameters of these electrodes. The review also highlights the current challenges and limitations, including scalability and stability issues, and suggests potential solutions. The future outlooks and directions for further research in this field are also discussed, including the creation of new synthesis methods and the exploration of novel applications. The aim of the review is to offer a current and up-to-date understanding of the state-of-the-art in MXene-based electrodes for supercapacitors and to stimulate further research in the field.

Utilization of 2D materials in aqueous zinc ion batteries for safe energy storage devices

Aqueous rechargeable battery has been an intense topic of research recently due to the significant safety issues of conventional Li-ion batteries (LIBs). Amongst the various candidates of aqueous batteries, aqueous zinc ion batteries (AZIBs) hold great promise as a next generation safe energy storage device due to its low cost, abundance in nature, low toxicity, environmental friendliness, low redox potential, and high theoretical capacity. Yet, the promise has not been realized due to their limitations, such as lower capacity compared to traditional LIB, dendrite growth, detrimental degradation of electrode materials structure as ions intercalate/de-intercalate, and gas evolution/corrosion at the electrodes, which remains a significant challenge. To address the challenges, various 2D materials with different physiochemical characteristics have been utilized. This review explores fundamental physiochemical characteristics of widely used 2D materials in AZIBs, including graphene, MoS2, MXenes, 2D metal organic framework, 2D covalent organic framework, and 2D transition metal oxides, and how their characteristics have been utilized or modified to address the challenges in AZIBs. The review also provides insights and perspectives on how 2D materials can help to realize the full potential of AZIBs for next-generation safe and reliable energy storage devices.

Solvation Modulation Enhances Anion-Derived Solid Electrolyte Interphase for Deep Cycling of Aqueous Zinc Metal Batteries

Stable Zn anodes with a high utilization efficiency pose a challenge due to notorious dendrite growth and severe side reactions. Therefore, electrolyte additives are developed to address these issues. However, the additives are always consumed by the electrochemical reactions over cycling, affecting the cycling stability. Here, hexamethylphosphoric triamide (HMPA) is reported as an electrolyte additive for achieving stable cycling of Zn anodes. HMPA reshapes the solvation structures and promotes anion decomposition, leading to the in situ formation of inorganic-rich solid-electrolyte-interphase. More interestingly, this anion decomposition does not involve HMPA, preserving its long-term impact on the electrolyte. Thus, the symmetric cells with HMPA in the electrolyte survive ≈500 h at 10 mA cm-2 for 10 mAh cm-2 or ≈200 h at 40 mA cm-2 for 10 mAh cm-2 with a Zn utilization rate of 85.6 %. The full cells of Zn||V2 O5 exhibit a record-high cumulative capacity even under a lean electrolyte condition (E/C ratio=12 μL mAh-1 ), a limited Zn supply (N/P ratio=1.8) and a high areal capacity (6.6 mAh cm-2 ).

Redox Electrolytes-Assisting Aqueous Zn-Based Batteries by Pseudocapacitive Multiple Perovskite Fluorides Cathode and Charge Storage Mechanisms

Aqueous Zn-based batteries (AZBs) have attracted intensive attention. However, to explore advanced cathode materials with in-depth elucidation of their charge storage mechanisms, improve energy storage capacity, and construct novel cell systems remain a great challenge. Herein, a new pseudocapacitive multiple perovskite fluorides (ABF3 ) cathode is designed, represented by KMF-(IV, V, and VI; M = NiCoMnZn/-Mg/-MgFe), and constructed Zn//KMF-(IV, V, and VI) AZBs and their flexible devices. Ex situ tests have revealed a typical bulk phase conversion mechanism of KMF-VI electrode for charge storage in alkaline media dominated by redox-active Ni/Co/Mn species, with transformation of ABF3 nanocrystals into amorphous metal oxide/(oxy)hydroxide nanosheets. By employing single or bipolar redox electrolyte strategies of 20 mm [Fe(CN)6 ]3- or/and 10 mm SO3 2- /Cu[(NH3 )4 ]2+ acting on KMF-(IV, V, and VI) cathode and Zn anode, the AZBs show an improved energy storage owing to additional capacity contribution of redox electrolytes. The as-designed Zn//polyvinyl alcohol (PVA)-KOH-K3 [Fe(CN)6 ]//KMF-(IV, V, and VI) redox gel electrolytes-assisting flexible AZBs (RGE-FAZBs) exhibit remarkable performance under different bending angles because of slight dissolution corrosion of zinc anode compared with liquid electrolytes. Overall, the work demonstrates the novel idea of conversion-type multiple ABF3 cathode for redox electrolytes-assisting AZBs (RE-AZBs) and their flexible systems, showing great significance on electrochemical energy storage.

3D hierarchical graphene matrices enable stable Zn anodes for aqueous Zn batteries

Metallic zinc anodes of aqueous zinc ion batteries suffer from severe dendrite and side reaction issues, resulting in poor cycling stability, especially at high rates and capacities. Herein, we develop two three-dimensional hierarchical graphene matrices consisting of nitrogen-doped graphene nanofibers clusters anchored on vertical graphene arrays of modified multichannel carbon. The graphene matrix with radial direction carbon channels possesses high surface area and porosity, which effectively minimizes the surface local current density, manipulates the Zn²⁺ ions concentration gradient, and homogenizes the electric field distribution to regulate Zn deposition. As a result, the engineered matrices achieve a superior coulombic efficiency of 99.67% over 3000 cycles at 120 mA cm^-2, the symmetric cells with the composite zinc anode demonstrates 2600 h dendrite-free cycles at 80 mA cm^-2 and 80 mAh cm^-2. The as-designed full cell exhibits an inspiring capacity of 16.91 mAh cm^-2. The Zn capacitor matched with activated carbon shows a superior long-term cycle performance of 20000 cycles at 40 mA cm^-2. This strategy of constructing a 3D hierarchical structure for Zn anodes may open up a new avenue for metal anodes operating under high rates and capacities.

Interface engineering strategy construction of covalent organic framework for promoting highly reversible zinc metal

Zn-ion energy storage devices will play important roles in the future energy storage field. However, Zn-ion device development suffers significantly from adverse chemical reactions (dendrite formation, corrosion, and deformation) on the Zn anode surface. Zn dendrite formation, hydrogen evolution corrosion, and deformation combine to degrade Zn-ion devices. Zincophile modulation and protection using covalent organic frameworks (COF) inhibited dendritic growth by induced uniform Zn ion deposition, which also prevented chemical corrosion. The Zn@COF anode circulated stably for more than 1800 cycles even at high current density in symmetric cells and maintained a low and stable voltage hysteresis. This work explains the surface state of the Zn anode and provides information for further research.

A Heteroanionic Zinc Ion Conductor for Dendrite-Free Zn Metal Anodes

Although zinc-based batteries are promising candidates for eco-friendly and cost-effective energy storage devices, their performance is severely retarded by dendrite formation. As the simplest zinc compounds, zinc chalcogenides, and halides are individually applied as a Zn protection layer due to high zinc ion conductivity. However, the mixed-anion compounds are not studied, which constrains the Zn²⁺ diffusion in single-anion lattices to their own limits. A heteroanionic zinc ion conductor (Zn_y O_{1- x} F_x ) coating layer is designed by in situ growth method with tunable F content and thickness. Strengthened by F aliovalent doping, the Zn²⁺ conductivity is enhanced within the wurtzite motif for rapid lattice Zn migration. Zn_y O_{1- x} F_x also affords zincophilic sites for oriented superficial Zn plating to suppress dendrite growth. Therefore, Zn_y O_{1- x} F_x -coated anode exhibits a low overpotential of 20.4 mV for 1000 h cycle life at a plating capacity of 1.0 mA h cm^-2 during symmetrical cell test. The MnO₂ //Zn full battery further proves high stability of 169.7 mA h g^-1 for 1000 cycles. This work may enlighten the mixed-anion tuning for high-performance Zn-based energy storage devices.

Wearable Two-Dimensional Nanomaterial-Based Flexible Sensors for Blood Pressure Monitoring: A Review

Flexible sensors have been extensively employed in wearable technologies for physiological monitoring given the technological advancement in recent years. Conventional sensors made of silicon or glass substrates may be limited by their rigid structures, bulkiness, and incapability for continuous monitoring of vital signs, such as blood pressure (BP). Two-dimensional (2D) nanomaterials have received considerable attention in the fabrication of flexible sensors due to their large surface-area-to-volume ratio, high electrical conductivity, cost effectiveness, flexibility, and light weight. This review discusses the transduction mechanisms, namely, piezoelectric, capacitive, piezoresistive, and triboelectric, of flexible sensors. Several 2D nanomaterials used as sensing elements for flexible BP sensors are reviewed in terms of their mechanisms, materials, and sensing performance. Previous works on wearable BP sensors are presented, including epidermal patches, electronic tattoos, and commercialized BP patches. Finally, the challenges and future outlook of this emerging technology are addressed for non-invasive and continuous BP monitoring.

Valid design and evaluation of cathode and anode materials of aqueous zinc ion batteries with high-rate capability and cycle stability

Although non-aqueous lithium-ion batteries have a high gravimetric density, aqueous zinc-ion batteries (ZIBs) have recently been in the spotlight as an alternative, because ZIBs have characteristics such as high volumetric density, high ionic conductivity, eco-friendliness, low cost, and high safety. However, the improvement in electrochemical performance is limited due to insufficient rate capability and severe cycle fading of the vanadium-oxide-based cathode and zinc-metal-based anode material, which are frequently used as active materials for ZIBs. In addition, complex methods are required to prepare high-performance cathode and anode materials. Therefore, a simple yet effective strategy is needed to obtain high-performance anodes and cathodes. Herein, an ammonium vanadate nanofiber (AVNF) intercalated with NH₄⁺ and H₂O as a cathode material for ZIBs was synthesized within 30 minutes through a facile sonochemical method. In addition, an effective Al₂O₃ layer of 9.9 nm was coated on the surface of zinc foil through an atomic layer deposition technique. As a result, AVNF//60Al₂O₃@Zn batteries showed a high rate capability of 108 mA h g^-1 even at 20 A g^-1, and exhibited ultra-high cycle stability with a capacity retention of 94% even after 5000 cycles at a current density of 10 A g^-1.

Melamine Foam-Derived Carbon Scaffold for Dendrite-Free and Stable Zinc Metal Anode

Aqueous Zn-ion batteries (AZIBs) are one of the most promising large-scale energy storage devices due to the excellent characteristics of zinc metal anode, including high theoretical capacity, high safety and low cost. Nevertheless, the large-scale applications of AZIBs are mainly limited by uncontrollable Zn deposition and notorious Zn dendritic growth, resulting in low plating/stripping coulombic efficiency and unsatisfactory cyclic stability. To address these issues, herein, a carbon foam (CF) was fabricated via melamine-foam carbonization as a scaffold for a dendrite-free and stable Zn anode. Results showed that the abundant zincophilicity functional groups and conductive three-dimensional network of this carbon foam could effectively regulate Zn deposition and alleviate the Zn anode's volume expansion during cycling. Consequently, the symmetric cell with CF@Zn electrode exhibited lower voltage hysteresis (32.4 mV) and longer cycling performance (750 h) than the pure Zn symmetric cell at 1 mA cm^-2 and 1 mAh cm^-2. Furthermore, the full battery coupling CF@Zn anode with MnO₂ cathode can exhibit a higher initial capacity and better cyclic performance than the one with the bare Zn anode. This work brings a new idea for the design of three-dimensional (3D) current collectors for stable zinc metal anode toward high-performance AZIBs.

2D Materials Boost Advanced Zn Anodes: Principles, Advances, and Challenges

Aqueous zinc-ion battery (ZIB) featuring with high safety, low cost, environmentally friendly, and high energy density is one of the most promising systems for large-scale energy storage application. Despite extensive research progress made in developing high-performance cathodes, the Zn anode issues, such as Zn dendrites, corrosion, and hydrogen evolution, have been observed to shorten ZIB's lifespan seriously, thus restricting their practical application. Engineering advanced Zn anodes based on two-dimensional (2D) materials are widely investigated to address these issues. With atomic thickness, 2D materials possess ultrahigh specific surface area, much exposed active sites, superior mechanical strength and flexibility, and unique electrical properties, which confirm to be a promising alternative anode material for ZIBs. This review aims to boost rational design strategies of 2D materials for practical application of ZIB by combining the fundamental principle and research progress. Firstly, the fundamental principles of 2D materials against the drawbacks of Zn anode are introduced. Then, the designed strategies of several typical 2D materials for stable Zn anodes are comprehensively summarized. Finally, perspectives on the future development of advanced Zn anodes by taking advantage of these unique properties of 2D materials are proposed.

In Situ Electrochemically Oxidative Activation Inducing Ultrahigh Rate Capability of Vanadium Oxynitride/Carbon Cathode for Zinc-Ion Batteries

As a promising candidate for large-scale energy storage, aqueous zinc-ion batteries (ZIBs) still lack cathode materials with large capacity and high rate capability. Herein, a spherical carbon-confined nanovanadium oxynitride with a polycrystalline feature (VN_xO_y/C) was synthesized by the solvothermal reaction and following nitridation treatment. As a cathode material for ZIBs, it is interesting that the electrochemical performance of the VN_xO_y/C cathode is greatly improved after the first charging process viain situ electrochemically oxidative activation. The oxidized VN_xO_y/C delivers a greatly enhanced reversible capacity of 556 mAh g^-1 at 0.2 A g^-1 compared to the first discharge capacity of 130 mAh g^-1 and a high capacity of 168 mAh g^-1 even at 80 A g^-1. The ex situ characterizations verify that the insertion/extraction of Zn²⁺ does not affect the crystal structure of oxidized VN_xO_y/C to promise a stable cycle life (retain 420 mAh g^-1 after 1000 cycles at 10 A g^-1). The experimental analysis further elucidates that charging voltage and H₂O in the electrolyte are curial factors to activate VN_xO_y/C in that the oxygen replaces the partial nitrogen and creates abundant vacancies, inducing a conversion from VN_xO_y/C to VN_x-mO_y+2m/C and then resulting in considerably strengthened rate performance and improved Zn²⁺ storage capability. The study broadens the horizons of fast ion transport and is exceptionally desirable to expedite the application of high-rate ZIBs.

Na superionic conductor-type compounds as protective layers for dendrites-free aqueous Zn-ion batteries

Aqueous rechargeable Zn-ion batteries (ARZIBs) have attracted much attention owing to their safety, high energy density and environmental friendliness. However, dendrite formation and corrosive reactions on Zn anode surface limit the development of ARZIBs. Here, Ga3+-doped NaV2(PO4)3 with Na superionic conductor (NASICON) structure [NVP-Ga(x), x = 0, 0.25, 0.5, 0.75] have been exploited as the high-efficiency artificial layer to stabilize Zn anode. The optimal NVP-Ga(0.5) layer can homogenize ion flux and promote uniform deposition of zinc, the dendrite growth and the parasitic reactions can be greatly inhibited. The symmetric cell based on this unique protection layer can stably operate over 1,300 h at 0.5 mA cm-2 with 0.5 mAh cm-2. Benefitting from the high-performance Zn metal anode, the full batteries paired with MnO2 cathode deliver a high discharge capacity of 106 mAh/g with the capacity retention rate of 85 % after 8,000 cycles. This work provides an advanced strategy to stabilize Zn anode for the industrialization of ARZIBs in the near future.

Isotropic Amorphous Protective Layer with Uniform Interfacial Zincophobicity for Stable Zinc Anode

Aqueous zinc-ion batteries (AZIBs) have drawn the attention of numerous researchers owing to their high safety and cost-effectiveness. However, the dendrite growth and side reactions of the zinc (Zn) anodes limit their further practical applications. Herein, a porous amorphous silicon nitride protective layer with high zincophobicity is constructed on the Zn anode surface, which can guide the uniform stripping/plating of Zn²⁺ underneath the protective layer through its isotropic Zn affinity to alleviate the growth of dendrites and by-products. As a result, the amorphous silicon nitride-protected Zn anode can maintain a stable Coulombic efficiency (CE) of 98.8% and low voltage hysteresis for 710 cycles in the half cell. The full cell with the as-prepared Zn anode can deliver excellent electrochemical performances (89.0% capacity retention and 144.4 mAh g^-1 discharge capacity after 1000 cycles at 4 A g^-1 ). This work reveals the key role of uniform metal affinity induced by the amorphous materials in the interface modification of metal anodes, which is instructive for the design of stable metal anodes.

Artificial Interphase Layer for Stabilized Zn Anodes: Progress and Prospects

The burgeoning Li-ion battery is regarded as a powerful energy storage system by virtue of its high energy density. However, inescapable issues concerning safety and cost aspects retard its prospect in certain application scenarios. Accordingly, strenuous efforts have been devoted to the development of the emerging aqueous Zn-ion battery (AZIB) as an alternative to inflammable organic batteries. In particular, the instability from the anode side severely impedes the commercialization of AZIB. Constructing an artificial interphase layer (AIL) has been widely employed as an effective strategy to stabilize the Zn anode. This review specializes in the state-of-the-art of AIL design for Zn anode protection, encompassing the preparation methods, mechanism investigations, and device performances based on the classification of functional materials. To begin with, the origins of Zn instability are interpreted from the perspective of electrical field, mass transfer, and nucleation process, followed by a comprehensive summary with respect to functions of AIL and its designing criteria. In the end, current challenges and future outlooks based upon theoretical and experimental considerations are included.

Freestanding and Flexible Interfacial Layer Enables Bottom-Up Zn Deposition Toward Dendrite-Free Aqueous Zn-Ion Batteries

Aqueous rechargeable zinc ion batteries are regarded as a competitive alternative to lithium-ion batteries because of their distinct advantages of high security, high energy density, low cost, and environmental friendliness. However, deep-seated problems including Zn dendrite and adverse side reactions severely impede the practical application. In this work, we proposed a freestanding Zn-electrolyte interfacial layer composed of multicapsular carbon fibers (MCFs) to regulate the plating/stripping behavior of Zn anodes. The versatile MCFs protective layer can uniformize the electric field and Zn²⁺ flux, meanwhile, reduce the deposition overpotentials, leading to high-quality and rapid Zn deposition kinetics. Furthermore, the bottom-up and uniform deposition of Zn on the Zn-MCFs interface endows long-term and high-capacity plating. Accordingly, the Zn@MCFs symmetric batteries can keep working up to 1500 h with 5 mAh cm^-2. The feasibility of the MCFs interfacial layer is also convinced in Zn@MCFs||MnO₂ batteries. Remarkably, the Zn@MCFs||α-MnO₂ batteries deliver a high specific capacity of 236.1 mAh g^-1 at 1 A g^-1 with excellent stability, and maintain an exhilarating energy density of 154.3 Wh kg^-1 at 33% depth of discharge in pouch batteries.

Construction of Mixed Ionic-Electronic Conducting Scaffolds in Zn Powder: A Scalable Route to Dendrite-Free and Flexible Zn Anodes

Zn powder (Zn-P)-based anodes are considered ideal candidates for Zn-based batteries because they enable a positive synergistic integration of safety and energy density. However, Zn-P-based anodes still experience easy corrosion, uncontrolled dendrite growth, and poor mechanical strength, which restrict their further application. Herein, a mixed ionic-electronic conducting scaffold is introduced into Zn-P to successfully fabricate anti-corrosive, flexible, and dendrite-free Zn anodes using a scalable tape-casting strategy. The as-established scaffold is characterized by robust flexibility, facile scale-up synthesis methodology, and exceptional anti-corrosive characteristics, and it can effectively homogenize the Zn²⁺ flux during Zn plating/stripping, thus allowing stable Zn cycling. Benefiting from these comprehensive attributes, the as-prepared Zn-P-based anode provides superior electrochemical performance, including long-life cycling stability and high rate capability in practical coin and flexible pouch cells; thus, it holds great potential for developing advanced Zn-ion batteries. The findings of this study provide insights for a promising scalable pathway to fabricate highly efficient and reliable Zn-based anodes and will aid in the realization of advanced flexible energy-storage devices.

Surface and Interface Engineering of Zn Anodes in Aqueous Rechargeable Zn-Ion Batteries

Rechargeable zinc-ion batteries (ZIBs) have shown great potential as an alternative to lithium-ion batteries. The ZIBs utilize Zn metal as the anode, which possesses many advantages such as low cost, high safety, eco-friendliness, and high capacity. However, on the other hand, the Zn anode also suffers from many issues, including dendritic growth, corrosion, and passivation. These issues are largely related to the surface and interface properties of the Zn anode. Many efforts have therefore been devoted to the modification of the Zn anode, aiming to eliminate the above-mentioned problems. This review gives a comprehensive summary on the mechanism behind these issues as well as the recent progress on Zn anode modification with focus on the strategies of surface and interface engineering, covering the design and application of both the Zn anode supports and surface protective layers, along with abundant examples. In addition, the promising research directions and perspective on these strategies are also presented.

Production of fast-charge Zn-based aqueous batteries via interfacial adsorption of ion-oligomer complexes

Aqueous zinc batteries are attracting interest because of their potential for cost-effective and safe electricity storage. However, metallic zinc exhibits only moderate reversibility in aqueous electrolytes. To circumvent this issue, we study aqueous Zn batteries able to form nanometric interphases at the Zn metal/liquid electrolyte interface, composed of an ion-oligomer complex. In Zn||Zn symmetric cell studies, we report highly reversible cycling at high current densities and capacities (e.g., 160 mA cm⁻²; 2.6 mAh cm⁻²). By means of quartz-crystal microbalance, nuclear magnetic resonance, and voltammetry measurements we show that the interphase film exists in a dynamic equilibrium with oligomers dissolved in the electrolyte. The interphase strategy is applied to aqueous Zn||I₂ and Zn||MnO₂ cells that are charged/discharged for 12,000 cycles and 1000 cycles, respectively, at a current density of 160 mA cm⁻² and capacity of approximately 0.85 mAh cm⁻². Finally, we demonstrate that Zn||I₂-carbon pouch cells (9 cm² area) cycle stably and deliver a specific energy of 151 Wh/kg (based on the total mass of active materials in the electrode) at a charge current density of 56 mA cm⁻².

Aqueous zinc batteries attract interest because of their potential for cost-effective and safe electricity storage. Here, the authors develop an in situ formed ion-oligomer nanometric interphase strategy to enable fast-charge aqueous Zn cells.

Synthesis, characterisation, and feasibility studies on the use of vanadium tellurate(vi) as a cathode material for aqueous rechargeable Zn-ion batteries

Aqueous rechargeable zinc-ion batteries (AZIBs) have drawn enormous attention in stationary applications due to their high safety and low cost. However, the search for new positive electrode materials with satisfactory electrochemical performance for practical applications remains a challenge. In this work, we report a comprehensive study on the use of the vanadium tellurate (NH4)4{(VO2)2[Te2O8(OH)2]}·2H2O, which is tested for the first time as a cathode material in AZIBs.

Highly Strengthened and Toughened Zn-Li-Mn Alloys as Long-Cycling Life and Dendrite-Free Zn Anode for Aqueous Zinc-Ion Batteries

Zn-ion batteries (ZIBs) using aqueous electrolyte, recently, have been a hot topic owing to the high safety, low cost, and high specific energy capacity. However, the formation of dendrite and side reactions on the Zn anode during cycling inhibit the application of ZIBs. An advanced Zn anode by alloying a small amount of Li and Mn with Zn is hereby reported. It is found that Li and Mn can form cationic ions which restrain lateral diffusion of Zn ions and regulate zinc electrodeposition through the electrostatic shield mechanism. As a result, the formation of Zn dendrite is greatly inhibited. This process also mitigates the formation of Zn-based byproduct and Zn passivation. Consequently, the symmetric ZnLiMn/ZnLiMn cell presents a small overpotential of 30 mV at 1 mA cm^-2 , greatly enhanced cycling durability (1000 h at a current density of 1 mA cm^-2 ), and a dendrite-free morphology after cycles. Moreover, the authors find that the ZnLiMn alloy has greatly enhanced mechanical properties. The assembled ZnLiMn/MnO₂ full cell can retain 96% capacity after 400 cycles at 1 C. Thus, the alloying low-cost Li/Mn strategy is very promising for large-scale production of dendrite-free Zn electrode in rechargeable ZIBs.

Efficient Zn Metal Anode Enabled by O,N-Codoped Carbon Microflowers

Zinc metal anodes show great promise for cheap and safe energy storage devices. However, it remains challenging to regulate highly efficient Zn plating/stripping under a high depth of discharge (DOD). Guided by density functional theory calculation, we here synthesized an oxygen- and nitrogen-codoped carbon superstructure as an efficient host for high-DOD Zn metal anodes through rational monomer selection, polymer self-assembly, and structure-preserved carbonization. With microscale 3D hierarchical structures, microcrystalline graphitic layers, and zincophilic heteroatom dopants, a flower-shaped carbon (C_flower) host could guide Zn nucleation and growth in a heteroepitaxial mode, affording horizontal plating with a high Coulombic efficiency (CE) and long life. As a demonstration, the C_flower-hosted Zn anode was paired with both battery and supercapacitor cathodes and delivered large capacity/capacitance, fast rates, long life, and ca. 100% CE even under a high DOD, outclassing hostless Zn-based devices. As they possess cheap, scalable, and efficient features, C_flower hosts hold the potential for practical zinc-metal-based energy devices.

Zinc Anode for Mild Aqueous Zinc-Ion Batteries: Challenges, Strategies, and Perspectives

The rapid advance of mild aqueous zinc-ion batteries (ZIBs) is driving the development of the energy storage system market. But the thorny issues of Zn anodes, mainly including dendrite growth, hydrogen evolution, and corrosion, severely reduce the performance of ZIBs. To commercialize ZIBs, researchers must overcome formidable challenges. Research about mild aqueous ZIBs is still developing. Various technical and scientific obstacles to designing Zn anodes with high stripping efficiency and long cycling life have not been resolved. Moreover, the performance of Zn anodes is a complex scientific issue determined by various parameters, most of which are often ignored, failing to achieve the maximum performance of the cell. This review proposes a comprehensive overview of existing Zn anode issues and the corresponding strategies, frontiers, and development trends to deeply comprehend the essence and inner connection of degradation mechanism and performance. First, the formation mechanism of dendrite growth, hydrogen evolution, corrosion, and their influence on the anode are analyzed. Furthermore, various strategies for constructing stable Zn anodes are summarized and discussed in detail from multiple perspectives. These strategies are mainly divided into interface modification, structural anode, alloying anode, intercalation anode, liquid electrolyte, non-liquid electrolyte, separator design, and other strategies. Finally, research directions and prospects are put forward for Zn anodes. This contribution highlights the latest developments and provides new insights into the advanced Zn anode for future research.

Fabrication of dual-functional electrodes using oxygen vacancy abundant NiCo2O4 nanosheets for advanced hybrid supercapacitors and Zn-ion batteries

V-ZnCo2O4/Ni composites with rich oxygen vacancies are designed through a hydrothermal method followed by post calcination and reduction. This strategy enhanced electrical conductivity, modulated electronic structure, and increased active sites.

Stable Zinc Anodes Enabled by Zincophilic Cu Nanowire Networks

Zn-based electrochemical energy storage (EES) systems have received tremendous attention in recent years, but their zinc anodes are seriously plagued by the issues of zinc dendrite and side reactions (e.g., corrosion and hydrogen evolution). Herein, we report a novel strategy of employing zincophilic Cu nanowire networks to stabilize zinc anodes from multiple aspects. According to experimental results, COMSOL simulation and density functional theory calculations, the Cu nanowire networks covering on zinc anode surface not only homogenize the surface electric field and Zn²⁺ concentration field, but also inhibit side reactions through their hydrophobic feature. Meanwhile, facets and edge sites of the Cu nanowires, especially the latter ones, are revealed to be highly zincophilic to induce uniform zinc nucleation/deposition. Consequently, the Cu nanowire networks-protected zinc anodes exhibit an ultralong cycle life of over 2800 h and also can continuously operate for hundreds of hours even at very large charge/discharge currents and areal capacities (e.g., 10 mA cm^-2 and 5 mAh cm^-2), remarkably superior to bare zinc anodes and most of currently reported zinc anodes, thereby enabling Zn-based EES devices to possess high capacity, 16,000-cycle lifespan and rapid charge/discharge ability. This work provides new thoughts to realize long-life and high-rate zinc anodes.

Separator Effect on Zinc Electrodeposition Behavior and Its Implication for Zinc Battery Lifetime

Uncontrolled zinc electrodeposition is an obstacle to long-cycling zinc batteries. Much has been researched on regulating zinc electrodeposition, but rarely are the studies performed in the presence of a separator, as in practical cells. Here, we show that the microstructure of separators determines the electrodeposition behavior of zinc. Porous separators direct zinc to deposit into their pores and leave "dead zinc" upon stripping. In contrast, a nonporous separator prevents zinc penetration. Such a difference between the two types of separators is distinguished only if caution is taken to preserve the attachment of the separator to the zinc-deposited substrate during the entire electrodeposition-morphological observation process. Failure to adopt such a practice could lead to misinformed conclusions. Our work reveals the mere use of porous separators as a universal yet overlooked challenge for metal anode-based rechargeable batteries. Countermeasures to prevent direct exposure of the metal growth front to a porous structure are suggested.

Dynamic interphase-mediated assembly for deep cycling metal batteries

Secondary batteries based on earth-abundant, multivalent metals provide a promising path for high energy density and potentially low-cost electricity storage. Poor anodic reversibility caused by disordered metal crystallization during battery charging remains a fundamental, century-old challenge for the practical use of deep cycling metal batteries. We report that dynamic interphases formed by anisotropic nanostructures dispersed in a battery electrolyte provide a general method for achieving ordered assembly of metal electrodeposits and high anode reversibility. Interphases formed by anisotropic graphitic carbon nitride nanostructures in colloidal electrolytes are shown to promote formation of vertically aligned and spatially compact (~100% compactness) zinc electrodeposits with unprecedented, high levels of reversibility (>99.8%), even at quite high areal capacity (6 to 20 milliampere hour per square centimeter). It is also reported that the same concept enables uniform growth of compact magnesium and aluminum electrodeposits, defining a general pathway toward energy-dense metal batteries based on earth-abundant anode chemistries.

Interfacial Engineering Strategy for High-Performance Zn Metal Anodes

Due to their high safety and low cost, rechargeable aqueous Zn-ion batteries (RAZIBs) have been receiving increased attention and are expected to be the next generation of energy storage systems. However, metal Zn anodes exhibit a limited-service life and inferior reversibility owing to the issues of Zn dendrites and side reactions, which severely hinder the further development of RAZIBs. Researchers have attempted to design high-performance Zn anodes by interfacial engineering, including surface modification and the addition of electrolyte additives, to stabilize Zn anodes. The purpose is to achieve uniform Zn nucleation and flat Zn deposition by regulating the deposition behavior of Zn ions, which effectively improves the cycling stability of the Zn anode. This review comprehensively summarizes the reaction mechanisms of interfacial modification for inhibiting the growth of Zn dendrites and the occurrence of side reactions. In addition, the research progress of interfacial engineering strategies for RAZIBs is summarized and classified. Finally, prospects and suggestions are provided for the design of highly reversible Zn anodes.