Surface-Alloyed Nanoporous Zinc as Reversible and Stable Anodes for High-Performance Aqueous Zinc-Ion Battery

Designing an Anionic Layer in Low-Concentration Electrolytes to Promote In-Plane Ion Diffusion for Dendrite-Free Zinc-Ion Batteries

In contrast to high-concentration electrolyte systems, low-concentration electrolytes provide a cost-effective strategy to advance the commercialization of aqueous zinc-ion batteries (AZIBs). However, such electrolytes frequently exhibit severe dendrite formation caused by localized Zn2+ concentration gradients, which critically compromise the cycling stability and operational safety of AZIBs. In this work, an innovative approach is proposed that involves the in situ construction of a fluoride-ion (F-) enriched interfacial layer on zinc anodes. This method facilitates in-plane diffusion of zinc ions at the anode interface, resulting in accelerated lateral growth of zinc deposits rather than dendritic formation. The results indicate that this orientated growth is closely associated with an anionic layer that effectively reduces random and irregular deposition as well as undesirable side reactions. The proposed system exhibits exceptional electrochemical performance within a low-concentration electrolyte framework, achieving a battery lifespan exceeding 1500 h at a current density of 2 mA cm-2. Furthermore, it maintains Coulombic efficiency above 99% after 800 h of cycling. Additionally, the Na2V6O16·3H2O (NVO)//Zn full battery incorporating this additive showcases enhanced long-term cycling performance and improved capacity retention, further confirming the excellent reversibility of the plating/stripping processes for zinc anode.

A solid solution alloy current collector to stabilize zinc metal anodes

Dendrite growth limits the performance of aqueous zinc-metal batteries. Here, we present a Cu-In solid solution alloy current collector, where indium enhances zinc affinity and lowers nucleation overpotential, enabling dendrite-free zinc deposition. The Zn@Cu-In anode demonstrates stable cycling at high current densities.

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.

Synergistic Effects of CuZn Nanoparticles and Graphene for Advanced Zinc Anodes in Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have garnered significant attention as promising next-generation energy storage devices due to their advantages of low cost, operational safety, and high theoretical specific capacity. Nevertheless, interface instability issues including dendrite growth, hydrogen evolution, and corrosion severely compromise zinc anode reversiblity. This study presents a novel strategy employing CuZn alloy nanoparticles anchored on graphene sheets (CZPG) as a multifuctional protective coating. The CZPG architecture establishes a dual-functional interface: graphene provides high-conductivity pathways and abundant nucleation sites, while CuZn nanoparticles demonstrate expecetional zincophilicity and hydrogen evolution suppression. The alloy's elevated dezincification potential synergizes with graphene's conductive network to regulate Zn2+ flux distribution and deposition kinetics. Systematic characterization reveals that the CZPG coating enable homogeneous zinc nucleation while suppressing parasitic reactions. Consequently, CZPG@Zn symmetric cells achieve remarkable cycling stability exceeding 1300 h at a 5.0 mA·cm-2 and 2.5 mAh·cm-2, providing a 24-fold increase in cycle life compared to bare Zn. When paired with KVO cathodes, full cells maintain 81.9% capacity retention after 1000 cycles, demonstrating 10-fold improvement over conventional Zn anodes. This interfacial engineering approach through alloy-graphene hybrid coatings provides new insights for developing high-preformance AZIBs, showing significant potential for grid-scale enegy storage applications.

Pre-Established Ion Transport Pathways Through Electrolyte Initiator for High-Efficiency Polymer Interface Enabling Ultra-Stable Aqueous Zinc-Metal Anodes

Achieving stable zinc-metal anodes is pivotal to realizing high-performance aqueous zinc-metal batteries (AZMBs). The construction of a functional polymer interface layer on the zinc-metal anode surface is confirmed as an effective strategy for mitigating dendrite growth and side reactions, thereby significantly enhancing the stability of zinc-metal anode. However, polymers capable of withstanding electrolyte environments over the long term typically suffer from elevated interfacial impedance, which hinders Zn2+ transport. Here, a pioneering zinc-metal anode enabled by a functional polymer interface layer with high-efficiency ion transport is introduced. This polymer layer is polymerized in situ on the zinc-metal anode surface through an innovative redox initiation system, where zinc trifluoromethanesulfonate (Zn(OTf)2) salts function as both reductant and ion transport pre-pathways, ensuring high-efficiency ion transport. The resultant interface layer achieves an ideal balance of ionic conductivity, water resistance, adhesion, and mechanical properties, effectively suppressing dendrite growth and side reactions. Symmetric cells assembled with this interface layer deliver an impressive lifespan of 8800 and 1600 h under 1 and 5 mA cm-2, respectively. This interface layer further demonstrates exceptional feasibility and versatility in Zn-NVO and Zn-PANI batteries. This work provides groundbreaking insights into the strategic design of high-performance polymer interface layers for AZMBs.

Spatial Confinement and Induced Deposition of ZnHCF in 3D Structure for Ultrahigh-Rate and Dendrite-Free Zn Anodes

Aqueous Zn-metal batteries (AZBs) are thought as highly prospective candidates for large-scale energy-storage systems because of their abundant natural resources, low cost, high safety, and environmentally friendly. Nevertheless, the key problems of AZBs are the uncontrollable zinc dendrites growth and water-induced erosion faced by zinc anodes. Therefore, reducing the hydrophilicity of zinc anode and introducing the zincophilic sites are the availably strategy. Herein, 3D highly-conductive host is developed to inhibit Zn dendrites growth, which have a porous structure consisting of graphene and carbon nanotubes embedded with a zincophilic nucleation sites of Zn Prussian blue analogs (ZnHCF@3D-GC). The inner ZnHCF possess minimized nucleation barriers, which can serve as favorable nucleation sites, and 3D host provide a buffer interspace to allow for even more high-capacity Zn plating. Additionally, density functional theory results show that ZnHCF exhibits a strong Zn binding energy and high adsorption energy of Zn (002) plane, which can guide Zn horizontal deposition in the 3D host. As a result, the assembled symmetrical cell is able to stabilize 900 cycles at an ultrahigh current density of 100 mA cm-2. Zn-ZnHCF@3D-GC//MnO2 and Zn-ZnHCF@3D-GC//ZnHCF full cells can be stably cycled 1000 cycles at 2.0 A g-1.

Surface Laser Texturing and Alloying: Front-End Design Optimization of Zinc Metal Anode for Dendrite-Free Deposition

A critical barrier to commercializing aqueous Zn-metal batteries lies in the dual challenges of dendritic Zn growth and parasitic side reactions at the anode/electrolyte interface. Here, this study presents a front-end design optimization strategy for Zn metal anodes (ZMAs), combining surface laser texturing with alloying treatment to stabilize the interfacial chemistry. Specifically, laser texturing creates a geometrically ordered microstructure on the Zn surface, while subsequent chemical permeation induces the in situ transformation of this microstructured layer into a CuZn5 alloy, forming the LT-Zn@CuZn5 anode. The geometrically ordered alloy coating homogenizes the electronic filed distribution across the zinc surface and enhances corrosion resistance. Thereby, the LT-Zn@CuZn5 anode demonstrated optimized electrochemical reversibility, sustaining over 3000 cycles at 3 mA cm-2/1 mAh cm-2. This performance translates into a high improvement in the cycling behavior of the assembled Zn||I2 soft pack battery, which acquired an initial capacity of 225.8 mAh g-1 and retained 79.1% after 4000 cycles. In contrast, the counterpart employing untreated Zn foil started with a lower initial capacity of 180.7 mAh g-1 and failed after less than 478 cycles. The demonstrated effective approach improves the front-end design strategy of ZMAs and contributes to the development of dendrite-free ZMAs.

MXene-Reinforced Organic-Inorganic Hybrid Protective Layer Enables Dendrite-Free and Ultra-Durable Zinc Metal Anodes

Zn metal is considered a promising anode for aqueous zinc ion batteries (AZIBs) owing to its high capacity and cost-effectiveness. However, dendrite growth, corrosion, and hydrogen evolution occurring on the Zn surface pose significant challenges to achieving stable and reliable AZIBs. Herein, a robust organic-inorganic protective layer, comprising organic zinc alginate (ZA) and inorganic Ti3C2Tx MXene, is fabricated on the Zn anode surface via a simple blade-coating approach. The organic ZA and inorganic MXene synergistically complement each other, with ZA playing a crucial role in inhibiting hydrogen evolution and enhancing electrolyte affinity, while the MXene mitigates severe side reactions, enables uniform Zn2+ deposition, and accelerates electron/ion transfer. Consequently, the ZA/MXene layer (MXZA) facilitates the Zn anode to exhibit remarkable reversibility and stability during continuous Zn plating/stripping, achieving a long-term lifespan of 2500 h at 2 mA cm-2 and 2 mAh cm-2, and 360 h even at 50 mA cm-2 and 50 mAh cm-2 in symmetric cells. When configurated with a sodium vanadate (NVO) cathode, the MXZA@Zn||NVO full cell operates stably with a high-capacity retention of 98.4% over 1000 cycles. This work provides a new perspective on developing efficient surface/interface modifications with synergistic effects toward high-performance zinc metal anodes.

Advanced electrolyte strategies for dendrite-free aqueous Zn-metal batteries

Aqueous Zn-metal batteries have attracted wide attention due to the abundant Zn reserves and the safety and non-toxicity of aqueous electrolytes, and have become a research hotspot in the field of electrochemical energy. However, the dendrite defects of metal Zn anodes and the resulting interfacial instability limit the large-scale development. Despite comprehensive studies and in-depth understanding, this issue still affects the electrochemical performance of Zn-metal batteries dramatically. In light of the great progress and recent focus, this review analyzes the origin of critical Zn dendrite related problems, and recapitulates the development of electrolyte strategies. In the end, various outlooks are summarized from different angles to improve the performance of Zn metal anodes. This study is expected to provide new inspiration for innovation in aqueous Zn battery electrolytes in the future.

Gradient Nanoporous Copper-Zinc Alloy Regulating Dendrite-Free Zinc Electrodeposition for High-Performance Aqueous Zinc-Ion Batteries

Zinc metal is an attractive anode material of aqueous batteries, but its practical use is persistently hampered by irregular zinc electrodeposition/dissolution and parasitic side reactions. Here we report engineering copper-zinc alloy with a composition- and structure-gradient nanoporous architecture as an effective strategy to regulate high-efficiency and dendrite-free zinc electrodeposition/dissolution for high-performance aqueous zinc-ion batteries. The dual-gradient nanoporous copper-zinc alloy electrodes not only guarantee electron and ion transport pathways but work as host materials with abundant zincophilic sites to guide zinc nucleation and deposition, enabling highly reversible zinc plating/stripping behaviors with low and stable voltage polarizations at various current densities and an ultralong lifespan of >6700 h. When assembled with carbon cloth-supported ZnxV2O5 cathode material, these outstanding electrochemical properties allow zinc-metal battery full cells to show exceptional rate capability and excellent stability. The capacity is retained at ∼95% after 5000 cycles at 5 A g-1, along with a Coulombic efficiency of ∼99.5%.

Electrochemical and chemical dealloying of nanoporous anode materials for energy storage applications

Traditionally employed in alloy corrosion studies, dealloying has evolved into a versatile technique for fabricating advanced porous materials. The unique architecture of interconnected pore channels and continuous metal ligaments endows dealloyed materials with high surface-to-volume ratio, excellent electron conductivity, efficient mass transport and remarkable catalytic activity, positioning them at the forefront of nanomaterial applications with significant potential. However, reproducible synthesis of these structures remains challenging due to limitations in conventional dealloying techniques. Herein, this review attempts to consolidate recent progress in electrochemical and chemical dealloying methods for nanoporous anodes in energy storage and conversion applications. We begin by elucidating the fundamental mechanisms driving dealloying and evaluate key factors influencing dealloying conditions. Through a review of current research, we identify critical properties of dealloyed nanoporous anodes that warrant further investigation. Applications of these materials as anodes in metal-ion batteries, supercapacitors, water splitting and photocatalyst are discussed. Lastly, we address ongoing challenges in this field and propose perspectives on promising research directions. This review aims to inspire new pathways and foster the development of efficient dealloyed porous anodes for sustainable energy technologies.

Current status and advances in zinc anodes for rechargeable aqueous zinc-air batteries

To promote sustainable development and reduce fossil fuel consumption, there is a growing demand for high-performance, cost-effective, safe and environmentally friendly batteries for large-scale energy storage systems. Among the emerging technologies, zinc-air batteries (ZABs) have attracted significant interest. By integrating the principles of traditional zinc-ion batteries and fuel cells, ZABs offer remarkably high theoretical energy density at lower production cost compared to the current state-of-the-art lithium-ion batteries (LIBs). However, the critical challenge remains in developing high-performance zinc anode. Herein, this review provides a comprehensive analysis of the current status and advancements in zinc anodes for rechargeable aqueous ZABs. We begin by highlighting the major challenges and underlying mechanisms associated with zinc anodes including issues such as uneven zinc deposition, dendrite growth and hydrogen evolution reaction. Then, this review discusses the recent advancements in zinc anode modifications, focusing on strategies such as alloying, surface porosity and zincophilicity. By reviewing the latest research, we also identify existing gaps and pose critical questions that need further exploration to push the field forward. The goal of this review is to inspire new research directions and promote the development of more efficient zinc anodes.

Trace alcohol ether electrolytes with dual-site hydrogen bonds and modulated solvation structures for ultralong-life zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are highly regarded for their affordability, stability, safety, and eco-friendliness. Nevertheless, their practical application is hindered by severe side reactions and the formation of zinc (Zn) dendrites on the Zn metal anode surface. In this study, we employ tetrahydrofuran alcohol (THFA), an efficient and cost-effective alcohol ether electrolyte, to mitigate these issues and achieve ultralong-life AZIBs. Theoretical calculations and experimental findings demonstrate that THFA acts as both a hydrogen bonding donor and acceptor, effectively anchoring H2O molecules through dual-site hydrogen bonding. This mechanism restricts the activity of free water molecules. Moreover, the two oxygen (O) atoms in THFA serve as dual solvation sites, enhancing the desolvation kinetics of [Zn(H2O)6]2+ and improving the deposition dynamics of Zn2+ ions. As a result, even trace amounts of THFA significantly suppress adverse reactions and the formation of Zn dendrites, enabling highly reversible Zn metal anodes for ultralong-life AZIBs. Specifically, a Zn-based symmetric cell containing 2 % THFA achieves an ultralong cycle life of 8,800 h at 0.5 mA cm-2/0.5 mAh cm-2, while a Zn//VO2 full cell containing 2 % THFA maintains a remarkable 80.03 % capacity retention rate at 5 A g-1 over 2,000 cycles. This study presents a practical strategy to develop dendrite-free, cost-effective, and highly efficient aqueous energy storage systems by leveraging alcohol ether compounds with dual-site hydrogen bonding capabilities.

Synergistic Regulation of Anode and Cathode Interphases via an Alum Electrolyte Additive for High-Performance Aqueous Zinc-Vanadium Batteries

A zinc (Zn) metal anode paired with a vanadium oxide (VOx) cathode is a promising system for aqueous Zn-ion batteries (AZIBs); however, side reactions proliferating on the Zn anode surface and the infinite dissolution of the VOx cathode destabilise the battery system. Here, we introduce a multi-functional additive into the ZnSO4 (ZS) electrolyte, KAl(SO4)2 (KASO), to synchronise the in situ construction of the protective layer on the surface of the Zn anode and the VOx cathode. Theoretical calculations and synchrotron radiation have verified that the high-valence Al3+ plays dual roles of competing with Zn2+ for solvation and forming a Zn-Al alloy layer with a homogeneous electric field on the anode surface to mitigate the side reactions and dendrite generation. The Al-containing cathode-electrolyte interface (CEI) considerably alleviates the irreversible dissolution of the VOx cathode and the accumulation of byproducts. Consequently, the Zn||Zn cell with KASO exhibits an ultra-long cycle of 6000 h at 2 mA cm-2. Importantly, the VOx cathodes (VO2, V2O5 and NH4V4O10) in the ZS-KASO electrolyte showed excellent cycling stability, including Zn powder||VO2 cells and Zn||VO2 pouch cells. Even better, the full cell exhibits excellent cycling stability at low negative/positive (N/P) ratio of 2.83 and high mass loading (~16 mg cm-2). This study offers a straightforward and practical reference for concurrently addressing challenges at the anode and cathode of AZIBs.

A Dynamically Ion-Sieved Electrolyte towards Ultralong-Lifespan Zn-Ion Batteries

The practical deployment of Zn-ion batteries faces challenges such as dendrite growth, side reactions and cathode dissolution in traditional electrolytes. Here, we develop a highly conductive and dynamically ion-sieved electrolyte to simultaneously enhance the Zn metal reversibility and suppress the cathode dissolution. The dynamic ion screen at the electrode/electrolyte interface is achieved by numerous pyrane rings with a radius of 3.69 Å, which can selectively facilitate the plating/stripping and insertion/extraction process of [Zn(H2O)6]2+ and Zn2+ on the anode and cathode surfaces. As a proof of concept, Zn//Zn symmetric cells deliver exceptional cyclic stability for over 6,800 h and ultrahigh cumulative plated capacity of 1.95 Ah cm-2. Zn//Na2Mn3O7 cells exhibit satisfactory cycling performance with capacity retention of 82.7 % after 4,000 cycles, and the assembled pouch cells achieve excellent stability and durability. This work provides valuable insights into the development of electrolytes aimed at enhancing the interface stability of aqueous batteries.

Innovative Zinc Anodes: Advancing Metallurgy Methods to Battery Applications

Aqueous zinc metal batteries (AZMBs) are emerging as a powerful contender in the realm of large-scale intermittent energy storage systems, presenting a compelling alternative to existing ion battery technologies. They harness the benefits of metal zinc's high safety, natural abundance, and favorable electrochemical potential (-0.762 V vs Standard hydrogen electrode, SHE), alongside an impressive theoretical capacity (820 mAh g-1 and 5655 mAh cm-3). However, the electrochemical performance of ZMBs is impeded by several challenges, including poor compatibility with high-loading cathodes and persistent side reactions. These issues are intricately linked to the inherent physicochemical properties of the zinc metal anodes (ZMAs). Here, this review delves into the traditional methods of ZMAs production, encompassing extraction, electrodeposition, and rolling processes. The discussion then progresses to an exploration of cutting-edge methodologies designed to enhance the electrochemical performance of ZMAs. These methods are categorized into alloying, pre-treatment of substrate, advanced electrodeposition techniques, and the development of composite anodes utilizing zinc powder. The review offers a comparative analysis of the merits and drawbacks of various optimization strategies, highlighting the beneficial outcomes achieved. It aspires to inspire novel concepts for the advancement and innovation of next-generation zinc-based energy storage solutions.

Insights into the design of zincophilic artificial protective layers enabling uniform nucleation and deposition for stable dendrite-free Zn anodes

Aqueous zinc-ion batteries (AZIBs) are highly attractive as energy-storage systems owing to their inherent safety, low cost, and simple assembly processes. However, the growth of Zn dendrites and side reactions at the Zn metal anode significantly degrade their electrochemical performance. To address these challenges, this study introduces a surface modification that increases the lifespan and cycling stability of AZIBs by constructing an artificial zinc sulfide (ZnS) protective layer on the Zn anode. For the first time, the fundamental mechanism of uniform Zn plating underneath the ZnS protective layer is demonstrated through experiments and density functional theory simulations. In addition, the artificial ZnS protective layer of optimized thickness is formed using a simple, thickness-controllable coating method. Notably, the ZnS protective layer favors Zn atom adsorption while suppressing clustering, enabling uniform Zn deposition. In addition, defects within the thin ZnS coating modulate Zn2+ adsorption and diffusion, which facilitates Zn plating underneath the protective layer. This mechanism promotes uniform Zn nucleation and enhances the kinetics of Zn2+, preventing dendrite formation and side reactions and thereby improving the stability and electrochemical performance of the battery. The resulting Zn@ZnS||Zn@ZnS symmetric cell exhibits a cycle life of over 1600 h and excellent rate performance. Moreover, it maintains a high coulombic efficiency of 99.5 % and capacity retention of 80.1 % after 1500 cycles at a current density of 0.5 A g-1, demonstrating exceptional long-term cycling stability. These insights into developing effective artificial protective layers that enable uniform nucleation will promote durable, dendrite-free Zn anodes for advanced AZIBs.

Insight into Anionic Discrepancies in Bipolar Poly(Thionine) Organic Cathodes for Aqueous Zinc Ion Batteries

Electroactive organic electrode materials exhibit remarkable potential in aqueous zinc ion batteries (AZIBs) due to their abundant availability, customizable structures, sustainability, and high reversibility. However, the research on AZIBs has predominantly concentrated on unraveling the storage mechanism of zinc cations, often neglecting the significance of anions in this regard. Herein, bipolar poly(thionine) is synthesized by a simple and efficient polymerization reaction, and the kinetics of different anions are investigated using poly(thionine) as the cathode of AZIBs. Notably, poly(thionine) is a bipolar organic polymer electrode material and exhibits enhanced stability in aqueous solutions compared to thionine monomers. Kinetic analysis reveals that ClO4 - exhibits the fastest kinetics among SO4 2-, Cl-, and OTF-, demonstrating excellent rate performance (109 mAh g-1 @ 0.5 A g-1 and 92 mAh g-1 @ 20 A g-1). Mechanism studies reveal that the poly(thionine) cathode facilitates the co-storage of both anions and cations in Zn(ClO4)2. Furthermore, the lower electrostatic potential of ClO4 - influences the strength of hydrogen bonding with water molecules, thereby enhancing the overall kinetics in aqueous electrolytes. This work provides an effective strategy for synthesizing high-quality organic materials and offers new insights into the kinetic behavior of anions in AZIBs.

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.

Lithiation Induced Hetero-Superlattice Zn/ZnLi as Stable Anode for Aqueous Zinc-Ion Batteries

Three dimensional (3D) framework structure is one of the most effective ways to achieve uniform zinc deposition and thus inhibit the Zn dendrites growth in working Zn metallic anode. A major challenge facing for the most commonly used 3D zincophilic hosts is that the zincophilic layer tends to peel off during repeatedly cycling, making it less stable. Herein, for the first time, a hetero-superlattice Zn/ZnLi (HS-Zn/ZnLi) anode containing periodic arrangements of metallic Zn phase and zincophilic ZnLi phase at the nanoscale, is well designed and fabricated via electrochemical lithiation method. Based on binding energy and stripping energy calculation, and the operando optical observation of plating/stripping behaviors, the zincophilic ZnLi sites with a strong Zn adsorption ability in the interior of the 3D ZnLi framework structure can effectively guide uniform Zn nucleation and dendrite-free zinc deposition, which significantly improves the cycling stability of the HS-Zn/ZnLi alloy (over 2800 h without a short-circuit at 2 mA cm-2). More importantly, this strategy can be extended to HS-Zn/ZnNa and HS-Zn/ZnK anodes that are similar to the HS-Zn/ZnLi microstructure, also displaying significantly enhanced cycling performances in AZIBs. This study can provide a novel strategy to develop the dendrite-free metal anodes with stable cycling performance.

Activating the Intrinsic Zincophilicity of PAM Hydrogel to Stabilize the Metal-Electrolyte Dynamic Interface for Stable and Long-Life Zinc Metal Batteries

As a potential material to solve rampant dendrites and hydrogen evolution reaction (HER) problem of aqueous zinc metal batteries (AZMB), hydrogel electrolytes usually require additional additives or multi-molecular network strategies to solve existing problems of ionic conductivity, mechanical properties and interface stability. However, the intrinsic zincophilic properties of the gel itself are widely neglected leading to the addition of additional molecules and the complexity of the preparation process. In this work, we innovatively utilize the characteristics of acrylamide's high zincophilic group density, activating the intrinsic zincophilic properties of PAM gel through a simple concentration control strategy which reconstructs a novel zinc-electrolyte interface different from conventional PAM electrolyte. The activated novel gel electrolyte with intrinsic zincophilic properties has high ionic conductivity and effectively suppresses water activity, thereby inhibiting HER corrosion. Meanwhile, it induces uniform deposition of (002) crystal planes, leading to excellent deposition kinetics and long cycle life, thereby ensuring high interfacial stability. Compared with conventional PAM gel electrolytes, the activated zincophilic group-rich hydrogel maintained excellent cycling stability (1 mA/cm2, 1 mAh/cm2) over 2250 hours; The Zn//MnO₂ coin cell using novel zincophilic group -rich hydrogel still retains a high specific capacity of more than 170 mAh/g at 0.5 A/g after 1000 cycles.

Host-design strategies of zinc anodes for aqueous zinc-ion batteries

Aqueous zinc ion batteries (AZIBs) have garnered considerable interest as an eco-friendly, safe, and cost-effective energy storage solution. Although significant strides have been made in recent years, there remain technical hurdles to overcome. Herein, this review summarizes in detail the primary challenges confronting aqueous zinc ion batteries, including the rampant dendrite growth, and water-induced parasitic reactions, and proposes host-engineering modification strategies focusing on optimizing the structure design of the zinc anode substrates, involving three-dimensional structure design, zincophilicity regulation, and epitaxial-oriented modification, and comprehensively analyzes the structure-activity relationship between different modification strategies and battery performance. In addition, we highlight the research trends and prospects in future anode modification for aqueous zinc-ion batteries. This work offers valuable insights into advanced Zn anode constructions for further applications in high-performance AZIBs.

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.

Lamellar Nanoporous Metal/Intermetallic Compound Heterostructure Regulating Dendrite-Free Zinc Electrodeposition for Wide-Temperature Aqueous Zinc-Ion Battery

Aqueous zinc-ion batteries are attractive post-lithium battery technologies for grid-scale energy storage because of their inherent safety, low cost and high theoretical capacity. However, their practical implementation in wide-temperature surroundings persistently confronts irregular zinc electrodeposits and parasitic side reactions on metal anode, which leads to poor rechargeability, low Coulombic efficiency and short lifespan. Here, this work reports lamellar nanoporous Cu/Al2Cu heterostructure electrode as a promising anode host material to regulate high-efficiency and dendrite-free zinc electrodeposition and stripping for wide-temperatures aqueous zinc-ion batteries. In this unique electrode, the interconnective Cu/Al2Cu heterostructure ligaments not only facilitate fast electron transfer but work as highly zincophilic sites for zinc nucleation and deposition by virtue of local galvanic couples while the interpenetrative lamellar channels serving as mass transport pathways. As a result, it exhibits exceptional zinc plating/stripping behaviors in aqueous hybrid electrolyte of diethylene glycol dimethyl ether and zinc trifluoromethanesulfonate at wide temperatures ranging from 25 to -30 °C, with ultralow voltage polarizations at various current densities and ultralong lifespan of >4000 h. The outstanding electrochemical properties enlist full cell of zinc-ion batteries constructed with nanoporous Cu/Al2Cu and ZnxV2O5/C to maintain high capacity and excellent stability for >5000 cycles at 25 and -30 °C.

Benzoquinone-Lubricated Intercalation in Manganese Oxide for High-Capacity and High-Rate Aqueous Aluminum-Ion Battery

Aqueous aluminum-ion batteries are attractive post-lithium battery technologies for large-scale energy storage in virtue of abundant and low-cost Al metal anode offering ultrahigh capacity via a three-electron redox reaction. However, state-of-the-art cathode materials are of low practical capacity, poor rate capability, and inadequate cycle life, substantially impeding their practical use. Here layered manganese oxide that is pre-intercalated with benzoquinone-coordinated aluminum ions (BQ-AlxMnO2) as a high-performance cathode material of rechargeable aqueous aluminum-ion batteries is reported. The coordination of benzoquinone with aluminum ions not only extends interlayer spacing of layered MnO2 framework but reduces the effective charge of trivalent aluminum ions to diminish their electrostatic interactions, substantially boosting intercalation/deintercalation kinetics of guest aluminum ions and improving structural reversibility and stability. When coupled with Zn50Al50 alloy anode in 2 m Al(OTf)3 aqueous electrolyte, the BQ-AlxMnO2 exhibits superior rate capability and cycling stability. At 1 A g-1, the specific capacity of BQ-AlxMnO2 reaches ≈300 mAh g-1 and retains ≈90% of the initial value for more than 800 cycles, along with the Coulombic efficiency of as high as ≈99%, outperforming the AlxMnO2 without BQ co-incorporation.

Dynamic Molecular Interphases Regulated by Trace Dual Electrolyte Additives for Ultralong-Lifespan and Dendrite-Free Zinc Metal Anode

Metallic zinc is a promising anode material for rechargeable aqueous multivalent metal-ion batteries due to its high capacity and low cost. However, the practical use is always beset by severe dendrite growth and parasitic side reactions occurring at anode/electrolyte interface. Here we demonstrate dynamic molecular interphases caused by trace dual electrolyte additives of D-mannose and sodium lignosulfonate for ultralong-lifespan and dendrite-free zinc anode. Triggered by plating and stripping electric fields, the D-mannose and lignosulfonate species are alternately and reversibly (de-)adsorbed on Zn metal, respectively, to accelerate Zn2+ transportation for uniform Zn nucleation and deposition and inhibit side reactions for high Coulombic efficiency. As a result, Zn anode in such dual-additive electrolyte exhibits highly reversible and dendrite-free Zn stripping/plating behaviors for >6400 hours at 1 mA cm-2, which enables long-term cycling stability of Zn||ZnxMnO2 full cell for more than 2000 cycles.

A Multifunctional Zwitterion Electrolyte Additive for Highly Reversible Zinc Metal Anode

Although zinc metal anode is promising for zinc-ion batteries (ZIBs) owing to high energy density, its reversibility is significantly obstructed by uncontrolled dendrite growth and parasitic reactions. Optimizing electrolytes is a facile yet effective method to simultaneously address these issues. Herein, 2-(N-morpholino)ethanesulfonic acid (MES), a pH buffer as novel additive, is initially introduced into conventional ZnSO4 electrolyte to ensure a dendrite-free zinc anode surface, enabling a stable Zn/electrolyte interface, which is achieved by controlling the solvated sheath through H2O poor electric double layer (EDL) derived from zwitterionic groups. Moreover, this zwitterionic additive can balance localized H+ concentration of the electrolyte system, thus preventing parasitic reactions in damaging electrodes. DFT calculation proves that the MES additive has a strong affinity with Zn2+ and induces uniform deposition along (002) orientation. As a result, the Zn anode in MES-based electrolyte exhibits exceptional plating/stripping lifespan with 1600 h at 0.5 mA cm-2 (0.5 mAh cm-2) and 430 h at 5.0 mA cm-2 (5.0 mAh cm-2) while it maintains high coulombic efficiency of 99.8%. This work proposes an effective and facile approach for designing dendrite-free anode for future aqueous Zn-based storage devices.

Layered Topological Insulator MnBi2Te4 as a Cathode for a High Rate Performance Aqueous Zinc-Ion Battery

Recently, the topological insulator MnBi2Te4 has aroused great attention owing to its exotic quantum phenomena and intriguing device applications, but the superior performances of MnBi2Te4 have not been researched in the field of electrochemistry. By theoretical calculations, it is found that MnBi2Te4 exhibits excellent Zn2+ storage and transport properties. Therefore, it is speculated that MnBi2Te4 has excellent electrochemical performance in zinc-ion batteries (ZIBs). In this research, MnBi2Te4 as a pioneer has been explored in ZIBs, showing surprising electrochemical properties. The MnBi2Te4 electrode displays a high average discharge specific capacity (264.8 mA h g-1 at 0.40 A g-1), a competitive cycle life (88.6% of initial capacity after 400 cycles at 4.00 A g-1), and an excellent rate performance (average capacity retention rate of 95.1% from 0.40 to 8.00 A g-1) owing to the fast ion transport of the conductive topological surface state and dissipationless channel of the edge state. Surprisingly, the quasi-solid-state (QSS) MnBi2Te4/Zn battery delivers excellent Zn2+ storage capability and possesses a capacity retention of 79.9% after 1000 cycles at 4.00 A g-1. In addition, the QSS MnBi2Te4/Zn battery can exhibit excellent performance and the GCD curves maintain stability without distortion deformation even at temperatures of 0 and 75 °C.

Fundamental Understanding of Hydrogen Evolution Reaction on Zinc Anode Surface: A First-Principles Study

Hydrogen evolution reaction (HER) has become a key factor affecting the cycling stability of aqueous Zn-ion batteries, while the corresponding fundamental issues involving HER are still unclear. Herein, the reaction mechanisms of HER on various crystalline surfaces have been investigated by first-principle calculations based on density functional theory. It is found that the Volmer step is the rate-limiting step of HER on the Zn (002) and (100) surfaces, while, the reaction rates of HER on the Zn (101), (102) and (103) surfaces are determined by the Tafel step. Moreover, the correlation between HER activity and the generalized coordination number ([Formula: see text]) of Zn at the surfaces has been revealed. The relatively weaker HER activity on Zn (002) surface can be attributed to the higher [Formula: see text] of surface Zn atom. The atomically uneven Zn (002) surface shows significantly higher HER activity than the flat Zn (002) surface as the [Formula: see text] of the surface Zn atom is lowered. The [Formula: see text] of surface Zn atom is proposed as a key descriptor of HER activity. Tuning the [Formula: see text] of surface Zn atom would be a vital strategy to inhibit HER on the Zn anode surface based on the presented theoretical studies. Furthermore, this work provides a theoretical basis for the in-depth understanding of HER on the Zn surface.

Working mechanism of MXene as the anode protection layer of aqueous zinc-ion batteries

In recent years, the research on intrinsically safe aqueous zinc-ion batteries (AZIBs) has gained significant attention. However, the commercialization of AZIBs is hindered because of the formation of dendrites in them and undesired hydrogen evolution reaction (HER) at their anode. MXene is a promising two-dimensional material that can inhibit dendrite growth and undesired HER at the anode when used as a protective layer for the anode in AZIBs. MXene's surface functional groups play a crucial role in this protective function. However, the working mechanisms of these surface functional groups have not been thoroughly understood. Based on first-principles calculations and molecular dynamics simulation, we investigated the mechanisms of MXene with nine surface functional groups, including oxygen and halogen elements, as an anode protection layer. We checked their structural stability, electronic structure, adsorption energy, HER reaction free energy, Zn2+ diffusion energy barriers, coordination number of Zn2+- H2O and diffusion coefficients of Zn2+. The MXene species with -S and -O functional groups exhibit good electrical conductivity and greatly adsorb Zn2+. Conversely, MXene species with halogen-functional groups significantly inhibit HER reactions. MXene materials with -Se functional group have the best desolvation effect (ΔCN = 0.31), while those with -I end group have the fastest ability to diffuse zinc ion. This research provides a theoretical guidance for the design of MXene based anode protection layers, which can help to develop dendrite-free and low side-reaction AZIBs.

Covalent Organic Framework with 3D Ordered Channel and Multi-Functional Groups Endows Zn Anode with Superior Stability

Achieving a highly robust zinc (Zn) metal anode is extremely important for improving the performance of aqueous Zn-ion batteries (AZIBs) for advancing "carbon neutrality" society, which is hampered by the uncontrollable growth of Zn dendrite and severe side reactions including hydrogen evolution reaction, corrosion, and passivation, etc. Herein, an interlayer containing fluorinated zincophilic covalent organic framework with sulfonic acid groups (COF-S-F) is developed on Zn metal (Zn@COF-S-F) as the artificial solid electrolyte interface (SEI). Sulfonic acid group (- SO3H) in COF-S-F can effectively ameliorate the desolvation process of hydrated Zn ions, and the three-dimensional channel with fluoride group (-F) can provide interconnected channels for the favorable transport of Zn ions with ion-confinement effects, endowing Zn@COF-S-F with dendrite-free morphology and suppressed side reactions. Consequently, Zn@COF-S-F symmetric cell can stably cycle for 1,000 h with low average hysteresis voltage (50.5 mV) at the current density of 1.5 mA cm-2. Zn@COF-S-F|MnO2 cell delivers the discharge specific capacity of 206.8 mAh g-1 at the current density of 1.2 A g-1 after 800 cycles with high-capacity retention (87.9%). Enlightening, building artificial SEI on metallic Zn surface with targeted design has been proved as the effective strategy to foster the practical application of high-performance AZIBs.

Converting commercial Bi2O3 particles into Bi2O2Se@Bi4O8Se nanosheets for "rocking chair" zinc-ion batteries

The development of a low-cost, high-capacity, and insertion-type anode is key for promoting "rocking chair" zinc-ion batteries. Herein, commercial Bi2O3 (BiO) particles are transformed into Bi2O2Se@Bi4O8Se (BiOSe) nanosheets through a simple selenylation process. The change in morphology from commercial BiO particle to BiOSe nanosheet leads to an increased specific surface area of the material. The enhanced electronic/ionic conductivity results in its excellent electrochemical kinetics. Ex situ XRD and XPS tests prove the intercalation-type mechanism of BiO and BiOSe as well as the superior electrochemical reversibility of BiOSe compared to BiO. Furthermore, the H+/Zn2+ co-insertion mechanism of BiOSe is revealed. This makes BiOSe to have low discharge plateaus of 0.38/0.68 V, a high reversible capacity of 182 mA h g-1 at 0.1 A g-1, and a long cyclic life of 500 cycles at 1 A g-1. Besides, the BiOSe//MnO2 "rocking chair" zinc-ion battery offers a high capacity of ≈90 mA h g-1 at 0.2 A g-1. This work provides a reference for turning commercial material into high-performance anode for "rocking chair" zinc-ion batteries.

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.

Zinc-Bromine Rechargeable Batteries: From Device Configuration, Electrochemistry, Material to Performance Evaluation

Zinc-bromine rechargeable batteries (ZBRBs) are one of the most powerful candidates for next-generation energy storage due to their potentially lower material cost, deep discharge capability, non-flammable electrolytes, relatively long lifetime and good reversibility. However, many opportunities remain to improve the efficiency and stability of these batteries for long-life operation. Here, we discuss the device configurations, working mechanisms and performance evaluation of ZBRBs. Both non-flow (static) and flow-type cells are highlighted in detail in this review. The fundamental electrochemical aspects, including the key challenges and promising solutions, are discussed, with particular attention paid to zinc and bromine half-cells, as their performance plays a critical role in determining the electrochemical performance of the battery system. The following sections examine the key performance metrics of ZBRBs and assessment methods using various ex situ and in situ/operando techniques. The review concludes with insights into future developments and prospects for high-performance ZBRBs.

Recent Advances in Structural Optimization and Surface Modification on Current Collectors for High-Performance Zinc Anode: Principles, Strategies, and Challenges

The last several years have witnessed the prosperous development of zinc-ion batteries (ZIBs), which are considered as a promising competitor of energy storage systems thanks to their low cost and high safety. However, the reversibility and availability of this system are blighted by problems such as uncontrollable dendritic growth, hydrogen evolution, and corrosion passivation on anode side. A functionally and structurally well-designed anode current collectors (CCs) is believed as a viable solution for those problems, with a lack of summarization according to its working mechanisms. Herein, this review focuses on the challenges of zinc anode and the mechanisms of modified anode CCs, which can be divided into zincophilic modification, structural design, and steering the preferred crystal facet orientation. The possible prospects and directions on zinc anode research and design are proposed at the end to hopefully promote the practical application of ZIBs.

A Stable Triazole-Based Covalent Gel for Long-Term Cycling Zn Anode in Zinc-Ion Batteries

In this work, a functional covalent gel material is developed to resolve the severe dendritic growth and hydrogen evolution reaction toward Zn/electrolyte interface in aqueous zinc-ion batteries (ZIBs). A covalent gel layer with superior durability forms homogeneously on the surface of Zn foil. The covalent gel with triazole functional groups can uniformize the transport of Zn2+ due to the interactions between Zn2+ ions and the triazole groups in the covalent gel. As a consequence, the symmetrical battery with triazole covalent gel maintains stable Zn plating/stripping for over 3000 h at 1 mA cm-2 and 1 mAh cm-2 , and the full cell combined with a V2 O5 cathode operates steadily and continuously for at least 1800 cycles at 5 A g-1 with a capacity retention rate of 67.0%. This work provides a train of thought to develop stable covalent gels for the protection of zinc anode toward high-performance ZIBs.

Ni-doped Bi2O2CO3 nanosheet with H+/Zn2+ co-insertion for "rocking chair" zinc-ion battery

Developing insertion-type anode is key to advancing "rocking chair" zinc-ion batteries, though there are few reported insertion-type anodes. Herein, the Bi₂O₂CO₃ is a high-potential anode, with a special layered structure. A one-step hydrothermal method was used to prepare Ni-doped Bi₂O₂CO₃ nanosheet, and also a free-standing electrode consisting of Ni-Bi₂O₂CO₃ and CNTs was designed. Both cross-linked CNTs conductive networks and Ni doping improve charge transfer. Ex situ tests (XRD, XPS, TEM, etc.) reveal the H⁺/Zn²⁺ co-insertion mechanism of Bi₂O₂CO₃ and that Ni doping improves its electrochemical reversibility and structural stability. Therefore, this optimized electrode offers a high specific capacity of 159 mAh g^-1 at 100 mA g^-1, a suitable average discharge voltage of ≈0.400 V, and a long-term cycling stability of 2200 cycles at 700 mA g^-1. Besides, the Ni-Bi₂O₂CO₃//MnO₂ "rocking chair" zinc-ion battery (based on the total mass of cathode and anode) delivers a high capacity of ≈100 mAh g^-1 at 50.0 mA g^-1. This work provides a reference for designing high-performance anode in zinc-ion batteries.

BiOIO3@Zn3(PO4)2·4H2O Heterojunction with Fast Ionic Diffusion Kinetics for Long-Life "Rocking-Chair" Zinc Ion Batteries

Increasing insertion host materials are developed as high-performance anodes of "rocking-chair" zinc ion batteries. However, most of them show unsatisfactory rate capabilities. Herein, layered BiOIO₃ is reported as an excellent insertion host and a zinc ion conductor, i.e., Zn₃(PO₄)₂·4H₂O (ZPO), is introduced to construct a BiOIO₃@ZPO heterojunction with a built-in electric field (BEF). Both ZPO and a BEF obviously enhance Zn²⁺ transfer and storage, which is proven by theoretical calculations and experimental studies. The conversion-type mechanism of BiOIO₃ is revealed through ex situ characterizations. The optimized electrode exhibits a high reversible capacity of 130 mAh g^-1 at 0.1 A g^-1, a low average discharge voltage of 0.58 V, an ultrahigh rate performance with 68 mAh g^-1 at 5 A g^-1 (52% of capacity at 0.1 A g^-1), and an ultralong cyclic life of 6000 cycles at 5 A g^-1. Significantly, the BiOIO₃@ZPO//Mn₃O₄ full cell shows a good cyclic life of 67 mAh g^-1 over 1000 cycles at 0.1 A g^-1. This work provides a new insight into the design of anodes with excellent rate capability.

3D Printing of Electron/Ion-Flux Dual-Gradient Anodes for Dendrite-Free Zinc Batteries

3D porous Zn-metal anodes have aroused widespread interest for Zn-ion batteries (ZIBs). Nevertheless, the notorious "top-growth" dendrites caused by the intrinsic top-concentrated ions and randomly distributed electrons may ultimately trigger a cell failure. Herein, an electron/ion-flux dual-gradient 3D porous Zn anode is reported for dendrite-free ZIBs by adopting 3D printing technology. The 3D-printed Zn anode with layer-by-layer bottom-up attenuating Ag nanoparticles (3DP-BU@Zn) establishes dual-gradient electron/ion fluxes, i.e., an internal bottom-up gradient electron flux created by bottom-rich conductive Ag nanoparticles, and a gradient ion flux resulting from zincophilic Ag nanoparticles which pump ions toward the bottom. Meanwhile, the 3D-printing-enabled hierarchical porous structure and continuously conducting network endow unimpeded electron transfer and ion diffusion among the electrode, dominating a bottom-preferential Zn deposition behavior. As a result, the 3DP-BU@Zn symmetrical cell affords highly reversible Zn plating/stripping with an extremely small voltage hysteresis of 17.7 mV and a superior lifespan over 630 h at 1 mA cm^-2 and 1 mAh cm^-2 . Meanwhile, the 3DP-BU@Zn//VO₂ full cell exhibits remarkable cyclic stability over 500 cycles. This unique dual-gradient strategy sheds light on the roadmap for the next-generation safe and durable Zn-metal batteries.

Progress and Prospect of Zn Anode Modification in Aqueous Zinc-Ion Batteries: Experimental and Theoretical Aspects

Aqueous zinc-ion batteries (AZIBs), the favorite of next-generation energy storage devices, are popular among researchers owing to their environmental friendliness, low cost, and safety. However, AZIBs still face problems of low cathode capacity, fast attenuation, slow ion migration rate, and irregular dendrite growth on anodes. In recent years, many researchers have focused on Zn anode modification to restrain dendrite growth. This review introduces the energy storage mechanism and current challenges of AZIBs, and then some modifying strategies for zinc anodes are elucidated from the perspectives of experiments and theoretical calculations. From the experimental point of view, the modification strategy is mainly to construct a dense artificial interface layer or porous framework on the anode surface, with some research teams directly using zinc alloys as anodes. On the other hand, theoretical research is mainly based on adsorption energy, differential charge density, and molecular dynamics. Finally, this paper summarizes the research progress on AZIBs and puts forward some prospects.

Quasi-Solid Electrolyte Interphase Boosting Charge and Mass Transfer for Dendrite-Free Zinc Battery

The practical applications of zinc metal batteries are plagued by the dendritic propagation of its metal anodes due to the limited transfer rate of charge and mass at the electrode/electrolyte interphase. To enhance the reversibility of Zn metal, a quasi-solid interphase composed by defective metal-organic framework (MOF) nanoparticles (D-UiO-66) and two kinds of zinc salts electrolytes is fabricated on the Zn surface served as a zinc ions reservoir. Particularly, anions in the aqueous electrolytes could be spontaneously anchored onto the Lewis acidic sites in defective MOF channels. With the synergistic effect between the MOF channels and the anchored anions, Zn2+ transport is prompted significantly. Simultaneously, such quasi-solid interphase boost charge and mass transfer of Zn2+, leading to a high zinc transference number, good ionic conductivity, and high Zn2+ concentration near the anode, which mitigates Zn dendrite growth obviously. Encouragingly, unprecedented average coulombic efficiency of 99.8% is achieved in the Zn||Cu cell with the proposed quasi-solid interphase. The cycling performance of D-UiO-66@Zn||MnO2 (~ 92.9% capacity retention after 2000 cycles) and D-UiO-66@Zn||NH4V4O10 (~ 84.0% capacity retention after 800 cycles) prove the feasibility of the quasi-solid interphase.

Interface Reversible Electric Field Regulated by Amphoteric Charged Protein-Based Coating Toward High-Rate and Robust Zn Anode

Metallic interface engineering is a promising strategy to stabilize Zn anode via promoting Zn²⁺ uniform deposition. However, strong interactions between the coating and Zn²⁺ and sluggish transport of Zn²⁺ lead to high anodic polarization. Here, we present a bio-inspired silk fibroin (SF) coating with amphoteric charges to construct an interface reversible electric field, which manipulates the transfer kinetics of Zn²⁺ and reduces anodic polarization. The alternating positively and negatively charged surface as a build-in driving force can expedite and homogenize Zn²⁺ flux via the interplay between the charged coating and adsorbed ions, endowing the Zn-SF anode with low polarization voltage and stable plating/stripping. Experimental analyses with theoretical calculations suggest that SF can facilitate the desolvation of [Zn(H₂O)₆]²⁺ and provide nucleation sites for uniform deposition. Consequently, the Zn-SF anode delivers a high-rate performance with low voltage polarization (83 mV at 20 mA cm^-2) and excellent stability (1500 h at 1 mA cm^-2; 500 h at 10 mA cm^-2), realizing exceptional cumulative capacity of 2.5 Ah cm^-2. The full cell coupled with Zn_xV₂O₅·nH₂O (ZnVO) cathode achieves specific energy of ~ 270.5/150.6 Wh kg^-1 (at 0.5/10 A g^-1) with ~ 99.8% Coulombic efficiency and retains ~ 80.3% (at 5.0 A g^-1) after 3000 cycles.

Few-Atomic-Layered Co-Doped BiOBr Nanosheet: Free-Standing Anode with Ultrahigh Mass Loading for "Rocking Chair" Zinc-Ion Battery

Insertion host materials are considered as a candidate to replace metallic Zn anode. However, the high mass loading anode with good electrochemical performances is reported rarely. Herein, a few-atomic-layered Co-doped BiOBr nanosheet (Co-UTBiOBr) is prepared via one-step hydrothermal method and a free-standing flexible electrode consisting of Co-UTBiOBr and CNTs is designed. Ultrathin nanosheet (3 atomic layers) and CNTs accelerate Zn²⁺ and electron transfer respectively. The Co-doping is conducive to the reduced Zn²⁺ diffusion barrier, the improved volume expansion after Zn²⁺ intercalation, and the enhanced electronic conductivity of BiOBr, verified by experimental and theoretical studies. An insertion-conversion mechanism is proposed according to ex situ characterizations. Benefiting from many advantages, Co-UTBiOBr displays a high capacity of 150 mAh g^-1 at 0.1 A g^-1 and a long-term cyclic life with ≈100% capacity attention over 3000 cycles at 1 A g^-1 . Remarkably, excellent electrochemical performances are maintained even at an ultrahigh mass loading of 15 mg cm^-2 . Co-UTBiOBr//MnO₂ "rocking chair" zinc-ion battery exhibits a stable capacity of ≈130 mAh g^-1 at 0.2 A g^-1 during cyclic test and its flexible quasi-solid-state battery shows outstanding stability under various bending states. This work provides a new idea for designing high mass loading anode.

Iodine Promoted Ultralow Zn Nucleation Overpotential and Zn-Rich Cathode for Low-Cost, Fast-Production and High-Energy Density Anode-Free Zn-Iodine Batteries

The anode-free design is a promising strategy to increase the energy density of aqueous Zn metal batteries (AZMBs). However, the scarcity of Zn-rich cathodes and the rapid loss of limited Zn greatly hinder their commercial applications. To address these issues, a novel anode-free Zn-iodine battery (AFZIB) was designed via a simple, low-cost and scalable approach. Iodine plays bifunctional roles in improving the AFZIB overall performance: enabling high-performance Zn-rich cathode and modulating Zn deposition behavior. On the cathode side, the ZnI₂ serves as Zn-rich cathode material. The graphene/polyvinyl pyrrolidone heterostructure was employed as an efficient host for ZnI₂ to enhance electron conductivity and suppress the shuttle effect of iodine species. On the anode side, trace I₃^- additive in the electrolyte creates surface reconstruction on the commercial Cu foil. The in situ formed zincophilic Cu nanocluster allows ultralow-overpotential and uniform Zn deposition and superior reversibility (average coulombic efficiency > 99.91% over 7,000 cycles). Based on such a configuration, AFZIB exhibits significantly increased energy density (162 Wh kg^-1) and durable cycle stability (63.8% capacity retention after 200 cycles) under practical application conditions. Considering the low cost and simple preparation methods of the electrode materials, this work paves the way for the practical application of AZMBs.

A smelting-rolling strategy for ZnIn bulk phase alloy anodes

Reversibility and stability are considered as the key indicators for Zn metal anodes in aqueous Zn-ion batteries, yet they are severely hindered by uncontrolled Zn stripping/plating and side reactions. Herein, we fabricate a bulk phase ZnIn alloy anode containing trace indium by a typical smelting-rolling process. A uniformly dispersed bulk phase of the whole Zn anode is constructed rather than only a protective layer on the surface. The Zn deposition can be regarded as instantaneous nucleation due to the adsorption of the evenly dispersed indium, and formation of the exclusion zone for further nucleation can be prevented at the same time. Owing to the bulk phase structure of ZnIn alloy, the indium not only plays a crucial role in Zn deposition, but also improves the Zn stripping. Consequently, the as-designed ZnIn alloy anode can sustain stable Zn stripping/plating for over 2500 h at 4.4 mA cm-2 with nearly 6 times smaller voltage hysteresis than that of pure Zn. Moreover, it enables a substantially stable ZnIn//NH4V4O10 battery with 96.44% capacity retention after 1000 cycles at 5 A g-1. This method of regulating the Zn nucleation by preparing a Zn-based alloy provides a potential solution to the critical problem of Zn dendrite growth and by-product generation fundamentally.