Fluorinated interphase enables reversible aqueous zinc battery chemistries

Dual-functional ionic liquids additive enables dendrite-free Zn anode with ultra-long cycle life over one year

Zn anodes suffer from the formation of uncontrolled dendrites aggravated by the uneven electric field and the insulating by-product accumulation in aqueous zinc-ion batteries (AZIBs). Here, an effective strategy implemented by 1-butyl-3-methylimidazolium hydrogen sulfate (BMIHSO4) additive is proposed to synergistically tune the crystallographic orientation of zinc deposition and suppress the formation of zinc hydroxide sulfate for enhancing the reversibility on Zn anode surface. As a competing cation, BMI+ is proved to preferably adsorb on Zn-electrode compared with H2O molecules, which shields the "tip effect" and inhibits the Zn-deposition agglomerations to inducing the horizontal growth along Zn (002) crystallographic texture. Simultaneously, the protonated BMIHSO4 additives could remove the detrimental OH- in real-time to fundamentally eliminate the accumulation of 6Zn(OH)2·ZnSO4·4H2O and Zn4SO4(OH)6·H2O on Zn anode surface. Consequently, Zn anode exhibits an ultra-long cycling stability of one year (8762 h) at 0.2 mA cm-2/0.2 mAh cm-2, 3600 h at 2 mA cm-2/2 mAh cm-2 with a high plating cumulative capacity of 3.6 Ah cm-2, and a high average Coulombic efficiency of 99.6 % throughout 1000 cycles. This work of regulating Zn deposition texture combined with eliminating notorious by-products could offer a desirable way for stabilizing the Zn-anode/electrolyte interface in AZIBs.

A Multifunctional Additive Based on the Cation-Anion Synergistic Effect for Highly Stable Zinc Metal Anodes

The Zn dendrite and hydrogen evolution reaction have been a "stubborn illness" for the life span of zinc anodes, which significantly hinders the development of aqueous zinc batteries (AZBs). Herein, considering the ingenious molecular structure, a multifunctional additive based on the synergistic regulation of cations and anions at the interface is designed to promote a dendrite-free and stable Zn anode. Theoretical calculations and characterization results verified that the electrostatic shield effect of the cation, the solvation sheath structure, and the bilayer structural solid electrolyte film (SEI) jointly account for the uniform Zn deposition and side reaction suppression. Ultimately, a remarkably high average Coulombic efficiency (CE) of 99.4% is achieved in the Zn||Cu cell for 300 cycles, and a steady charge/discharge cycling over 3000 and 300 h at 1.0 mA cm-2/1.0 mAh cm-2 and 10 mA cm-2/10 mAh cm-2 is obtained in the Zn||Zn cell. Furthermore, the assembled full battery demonstrates a prolonged cycle life of 2000 cycles.

Tuning Proton Insertion Chemistry for Sustainable Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) have emerged as an alternative to lithium-ion batteries due to their affordability and high level of safety. However, their commercialization is hindered by the low mass loading and irreversible structural changes of the cathode materials during cycling. Here, a disordered phase of a manganese nickel cobalt dioxide cathode material derived from wastewater via a coprecipitation process is reported. When used as the cathode for aqueous ZIBs , the developed electrode delivers 98% capacity retention at a current density of 0.1 A g-1 and 72% capacity retention at 1 A g-1 while maintaining high mass loading (15 mg cm-2). The high performance is attributed to the structural stability of the Co and Ni codoped phase; the dopants effectively suppress Jahn-Teller distortion of the manganese dioxide during cycling, as revealed by operando X-ray absorption spectroscopy. Also, it is found that the Co and Ni co-doped phase effectively inhibits the dissolution of Mn2+, resulting in enhanced durability without capacity decay at first 20 cycles. Further, it is found that the performance of the electrode is sensitive to the ratio of Ni to Co, providing important insight into rational design of more efficient cathode materials for low-cost, sustainable, rechargeable aqueous ZIBs.

Chemical vapor deposition growth of graphene and other nanomaterials with 3D architectures towards electrocatalysis and secondary battery-related applications

Recently, two-dimensional (2D) layered materials, such as graphene and transition metal dichalcogenides (TMDCs), have garnered a lot of attention in energy storage/conversion-related fields due to their novel physical and chemical properties. Constructing flat graphene and TMDCs nanosheets into 3D architectures can significantly increase their exposed surface area and prevent the restacking of adjacent 2D layers, thus dramatically promoting their applications in various energy-related fields. Chemical Vapor Deposition (CVD) is a low-cost, facile, and scalable method, which has been widely employed to produce high-quality graphene and TMDCs nanosheets with 3D architectures. During the CVD process, the morphologies and properties of the 3D architectures of such 2D materials can be designed by selecting substrates with different compositions, stacking geometries, and micro-structures. In this review, we focus on the recent advances in the CVD synthesis of graphene, TMDCs, and their hybrids with 3D architectures on different 3D-structured substrates, as well as their applications in the electrocatalytic hydrogen evolution reaction (HER) and various secondary batteries. In addition, the challenges and future prospects for the CVD synthesis and energy-related applications of these unique layered materials will also be discussed.

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.

Tailoring Localized Electrolyte via a Dual-Functional Protein Membrane toward Stable Zn Anodes

Considerable attention has been by far paid to stabilizing metallic Zn anodes, where side reactions and dendrite formation still remain detrimental to their practical advancement. Electrolyte modification or protected layer design is widely reported; nonetheless, an effective maneuver to synergize both tactics has been rarely explored. Herein, we propose a localized electrolyte optimization via the introduction of a dual-functional biomass modificator over the Zn anode. Instrumental characterization in conjunction with molecular dynamics simulation indicates local solvation structure transformation owing to the limitation of bound water with intermolecular hydrogen bonds, effectively suppressing hydrogen evolutions. Meanwhile, the optimized nucleation throughout the protein membrane allows uniform Zn deposition. Accordingly, the symmetric cell exhibits an elongated lifespan of 3280 h at 1.0 mA cm-2/1.0 mAh cm-2, while the capacity retention of the full cell sustains 91.1% after 2000 cycles at 5.0 A g-1. The localized electrolyte tailoring via protein membrane introduction might offer insights into operational metal anode protection.

In Situ Formed Robust Solid Electrolyte Interphase with Organic-Inorganic Hybrid Layer for Stable Zn Metal Anode

Stabilizing the Zn anode/electrolyte interface is critical for advancing aqueous zinc ion storage technologies. Addressing this challenge helps minimize parasitic reactions and controls the formation of Zn dendrites, which is fundamental to achieving highly reversible Zn electrochemistry. In this study, 2% by volume of dimethyl sulfoxide (DMSO) is introduced into the baseline zinc sulfate (ZS) electrolyte, which acts as an efficient regulator to form a robust solid-electrolyte interphase (SEI) on the Zn anode. This innovative approach enables uniform Zn deposition and does not substantially modify the Zn2+ solvation structure. The Zn||Zn symmetric cell exhibits an extended cycle life of nearly one calendar year (>8500 h) at a current density of 0.5 mA cm-2 and an areal capacity of 0.5 mAh cm-2. Impressive full cell performance can be achieved. Specifically, the Zn||VS2 full cell achieves an areal capacity of 1.7 mAh cm-2, with a superior negative-to-positive capacity ratio of 2.5, and an electrolyte-to-capacity ratio of 101.4 µL mAh-1, displaying remarkable stability over 1000 cycles under a high mass loading of 11.0 mg cm-2 without significant degradation. This innovative approach in electrolyte engineering provides a new perspective on in situ SEI design and furthers the understanding of Zn anode stabilization.

Design Strategies toward High-Utilization Zinc Anodes for Practical Zinc-Metal Batteries

Aqueous Zn-metal batteries (AZMBs) hold a promise as the next-generation energy storage devices due to their low cost and high specific energy. However, the actual energy density falls far below the requirements of commercial AZMBs due to the use of excessive Zn as anode and the associated issues including dendritic growth and side reactions. Reducing the N/P ratio (negative capacity/positive capacity) is an effective approach to achieve high energy density. A significant amount of research has been devoted to increasing the cathode loading and specific capacity or tuning the Zn anode utilization to achieve low N/P ratio batteries. Nevertheless, there is currently a lack of comprehensive overview regarding how to enhance the utilization of the Zn anode to balance the cycle life and energy density of AZMBs. In this review, we summarize the challenges faced in achieving high-utilization Zn anodes and elaborate on the modifying strategies for the Zn anode to lower the N/P ratio. The current research status and future prospects for the practical application of high-performance AZMBs are proposed at the end of the review.

Stable Zinc Anode Facilitated by Regenerated Silk Fibroin-modified Hydrogel Protective Layer

Inherent dendrite growth and side reactions of zinc anode caused by its unstable interface in aqueous electrolytes severely limit the practical applications of zinc-ion batteries (ZIBs). To overcome these challenges, a protective layer for Zn anode inspired by cytomembrane structure is developed with PVA as framework and silk fibroin gel suspension (SFs) as modifier. This PVA/SFs gel-like layer exerts similar to the solid electrolyte interphase, optimizing the anode-electrolyte interface and Zn2+ solvation structure. Through interface improvement, controlled Zn2+ migration/diffusion, and desolvation, this buffer layer effectively inhibits dendrite growth and side reactions. The additional SFs provide functional improvement and better interaction with PVA by abundant functional groups, achieving a robust and durable Zn anode with high reversibility. Thus, the PVA/SFs@Zn symmetric cell exhibits an ultra-long lifespan of 3150 h compared to bare Zn (182 h) at 1.0 mAh cm-2-1.0 mAh cm-2, and excellent reversibility with an average Coulombic efficiency of 99.04% under a large plating capacity for 800 cycles. Moreover, the PVA/SFs@Zn||PANI/CC full cells maintain over 20 000 cycles with over 80% capacity retention under harsh conditions at 5 and 10 A g-1. This SF-modified protective layer for Zn anode suggests a promising strategy for reliable and high-performance ZIBs.

Multifunctionalized Supramolecular Cyclodextrin Additives Boosting the Durability of Aqueous Zinc-Ion Batteries

The poor cycling stability of aqueous zinc-ion batteries hinders their application in large-scale energy storage due to uncontrollable dendrite growth and harmful hydrogen evolution reactions. Here, we designed and synthesized an electrolyte additive, N-methylimidazolium-β-cyclodextrin p-toluenesulfonate (NMI-CDOTS). The cations of NMI-CD+ are more easily adsorbed on the abrupt Zn surface to regulate the deposition of Zn2+ and reduce dendrite generation under the combined action of the unique cavity structure with abundant hydroxyl groups and the electrostatic force. Meanwhile, p-toluenesulfonate (OTS-) is able to change the Zn2+ solvation structure and suppress the hydrogen evolution reaction by the strong interaction of Zn2+ and OTS-. Benefiting from the synergistic role of NMI-CD+ and OTS-, the Zn||Zn symmetric cell exhibits superior cycling performance as high as 3800 h under 1 mA cm-2 and 1 mA h cm-2. The Zn||V2O5 full battery also shows a high specific capacity (198.3 mA h g-1) under 2.0 A g-1 even after 1500 cycles, and its Coulomb efficiency is nearly 100% during the charging and discharging procedure. These multifunctional composite strategies open up possibilities for the commercial application of aqueous zinc-ion batteries.

Advanced cathodes for aqueous Zn batteries beyond Zn2+ intercalation

Aqueous zinc (Zn) batteries have attracted global attention for energy storage. Despite significant progress in advancing Zn anode materials, there has been little progress in cathodes. The predominant cathodes working with Zn2+/H+ intercalation, however, exhibit drawbacks, including a high Zn2+ diffusion energy barrier, pH fluctuation(s) and limited reproducibility. Beyond Zn2+ intercalation, alternative working principles have been reported that broaden cathode options, including conversion, hybrid, anion insertion and deposition/dissolution. In this review, we report a critical assessment of non-intercalation-type cathode materials in aqueous Zn batteries, and identify strengths and weaknesses of these cathodes in small-scale batteries, together with current strategies to boost material performance. We assess the technical gap(s) in transitioning these cathodes from laboratory-scale research to industrial-scale battery applications. We conclude that S, I2 and Br2 electrodes exhibit practically promising commercial prospects, and future research is directed to optimizing cathodes. Findings will be useful for researchers and manufacturers in advancing cathodes for aqueous Zn batteries beyond Zn2+ intercalation.

Zn-based batteries for sustainable energy storage: strategies and mechanisms

Batteries play a pivotal role in various electrochemical energy storage systems, functioning as essential components to enhance energy utilization efficiency and expedite the realization of energy and environmental sustainability. Zn-based batteries have attracted increasing attention as a promising alternative to lithium-ion batteries owing to their cost effectiveness, enhanced intrinsic safety, and favorable electrochemical performance. In this context, substantial endeavors have been dedicated to crafting and advancing high-performance Zn-based batteries. However, some challenges, including limited discharging capacity, low operating voltage, low energy density, short cycle life, and complicated energy storage mechanism, need to be addressed in order to render large-scale practical applications. In this review, we comprehensively present recent advances in designing high-performance Zn-based batteries and in elucidating energy storage mechanisms. First, various redox mechanisms in Zn-based batteries are systematically summarized, including insertion-type, conversion-type, coordination-type, and catalysis-type mechanisms. Subsequently, the design strategies aiming at enhancing the electrochemical performance of Zn-based batteries are underscored, focusing on several aspects, including output voltage, capacity, energy density, and cycle life. Finally, challenges and future prospects of Zn-based batteries are discussed.

Enabling High Reversibility of Zn anode via Interfacial Engineering Induced by Amino acid Electrolyte Additive

Despite possessing substantial benefits of enhanced safety and cost-effectiveness, the aqueous zinc ion batteries (AZIBs) still suffers with the critical challenges induced by inherent instability of Zn metal in aqueous electrolytes. Zn dendrites, surface passivation, and corrosion are some of the key challenges governed by water-driven side reactions in Zn anodes. Herein, a highly reversible Zn anode is demonstrated via interfacial engineering of Zn/electrolyte driven by amino acid D-Phenylalanine (DPA) additions. The preferential adsorption of DPA and the development of compact SEI on the Zn anode suppressed the side reactions, leading to controlled and uniform Zn deposition. As a result, DPA added aqueous electrolyte stabilized Zn anode under severe test environments of 20.0 mA cm-2 and 10.0 mAh cm-2 along with an average plating/stripping Coulombic efficiency of 99.37%. Under multiple testing conditions, the DPA-incorporated electrolyte outperforms the control group electrolyte, revealing the critical additive impact on Zn anode stability. This study advances interfacial engineering through versatile electrolyte additive(s) toward development of stable Zn anode, which may lead to its practical implementation in aqueous rechargeable zinc batteries.

Dual-Parasitic Effect Enables Highly Reversible Zn Metal Anode for Ultralong 25,000 Cycles Aqueous Zinc-Ion Batteries

The use of electrolyte additives is an efficient approach to mitigating undesirable side reactions and dendrites. However, the existing electrolyte additives do not effectively regulate both the chaotic diffusion of Zn2+ and the decomposition of H2O simultaneously. Herein, a dual-parasitic method is introduced to address the aforementioned issues by incorporating 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIm]OTf) as cosolvent into the Zn(OTf)2 electrolyte. Specifically, the OTf- anion is parasitic in the solvent sheath of Zn2+ to decrease the number of active H2O. Additionally, the EMIm+ cation can construct an electrostatic shield layer and a hybrid organic/inorganic solid electrolyte interface layer to optimize the deposition behavior of Zn2+. This results in a Zn anode with a reversible cycle life of 3000 h, the longest cycle life of full cells (25,000 cycles), and an extremely high initial capacity (4.5 mA h cm-2), providing a promising electrolyte solution for practical applications of rechargeable aqueous zinc-ion batteries.

Carbonate Ester-Based Electrolyte Enabling Rechargeable Zn Battery to Achieve High Voltage and High Zn Utilization

Owing to the high H2O activity, the aqueous electrolyte in the Zn battery exhibits a narrow electrochemical window and inevitable hydrogen evolution reaction, limiting the anode utilization ratio and performance at high voltage. Carbonate ester, the well-developed electrolyte solvent in Li-ion batteries, exhibits aprotic properties and high anodic stability. However, its use in Zn metal batteries is limited due to the low solubility of Zn salts in carbonate esters. Herein, we propose a carbonate ester-based electrolyte (EC:DMC:EMC = 1:1:1 wt %), which contains a new Zn salt (Zn(BHFip)2) characterized by low cost, easy synthesis, and excellent aprotic solvent solubility. The BHFip- anion assists in forming Zn2+ conductive SEI on the anode and decomposes at high voltage to generate a protective CEI layer on the cathode. The Zn//Zn symmetric cell using such electrolyte achieves a remarkable Zn utilization ratio of 91% for 125 h, which has rarely been reported before. Furthermore, the Zn//LiMn2O4 full cell with an average operation voltage of 1.7 V demonstrates reliable cycling for 135 cycles with an N/P ratio of 1:1. In addition, the Zn//LiNi0.5Mn1.5O4 full cell exhibits a high discharge median voltage exceeding 2.2 V for 280 cycles, with the high voltage plateau (above 2 V) constituting 82% of the total capacity.

Inhibition of Vanadium Cathodes Dissolution in Aqueous Zn-Ion Batteries

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

Electrolyte and Interphase Engineering of Aqueous Batteries Beyond "Water-in-Salt" Strategy

Aqueous batteries are promising alternatives to non-aqueous lithium-ion batteries due to their safety, environmental impact, and cost-effectiveness. However, their energy density is limited by the narrow electrochemical stability window (ESW) of water. The "Water-in-salts" (WIS) strategy is an effective method to broaden the ESW by reducing the "free water" in the electrolyte, but the drawbacks (high cost, high viscosity, poor low-temperature performance, etc.) also compromise these inherent superiorities. In this review, electrolyte and interphase engineering of aqueous batteries to overcome the drawbacks of the WIS strategy are summarized, including the developments of electrolytes, electrode-electrolyte interphases, and electrodes. First, the main challenges of aqueous batteries and the problems of the WIS strategy are comprehensively introduced. Second, the electrochemical functions of various electrolyte components (e.g., additives and solvents) are summarized and compared. Gel electrolytes are also investigated as a special form of electrolyte. Third, the formation and modification of the electrolyte-induced interphase on the electrode are discussed. Specifically, the modification and contribution of electrode materials toward improving the WIS strategy are also introduced. Finally, the challenges of aqueous batteries and the prospects of electrolyte and interphase engineering beyond the WIS strategy are outlined for the practical applications of aqueous batteries.

A Photolithographable Electrolyte for Deeply Rechargeable Zn Microbatteries in On-Chip Devices

Zn batteries show promise for microscale applications due to their compatibility with air fabrication but face challenges like dendrite growth and chemical corrosion, especially at the microscale. Despite previous attempts in electrolyte engineering, achieving successful patterning of electrolyte microscale devices has remained challenging. Here, successful patterning using photolithography is enabled by incorporating caffeine into a UV-crosslinked polyacrylamide hydrogel electrolyte. Caffeine passivates the Zn anode, preventing chemical corrosion, while its coordination with Zn2+ ions forms a Zn2+-conducting complex that transforms into ZnCO3 and 2ZnCO3·3Zn(OH)2 over cycling. The resulting Zn-rich interphase product significantly enhances Zn reversibility. In on-chip microbatteries, the resulting solid-electrolyte interphase allows the Zn||MnO2 full cell to cycle for over 700 cycles with an 80% depth of discharge. Integrating the photolithographable electrolyte into multilayer microfabrication creates a microbattery with a 3D Swiss-roll structure that occupies a footprint of 0.136 mm2. This tiny microbattery retains 75% of its capacity (350 µAh cm-2) for 200 cycles at a remarkable 90% depth of discharge. The findings offer a promising solution for enhancing the performance of Zn microbatteries, particularly for on-chip microscale devices, and have significant implications for the advancement of autonomous microscale devices.

Amphipathic Phenylalanine-Induced Nucleophilic-Hydrophobic Interface Toward Highly Reversible Zn Anode

Aqueous Zn2+-ion batteries (AZIBs), recognized for their high security, reliability, and cost efficiency, have garnered considerable attention. However, the prevalent issues of dendrite growth and parasitic reactions at the Zn electrode interface significantly impede their practical application. In this study, we introduced a ubiquitous biomolecule of phenylalanine (Phe) into the electrolyte as a multifunctional additive to improve the reversibility of the Zn anode. Leveraging its exceptional nucleophilic characteristics, Phe molecules tend to coordinate with Zn2+ ions for optimizing the solvation environment. Simultaneously, the distinctive lipophilicity of aromatic amino acids empowers Phe with a higher adsorption energy, enabling the construction of a multifunctional protective interphase. The hydrophobic benzene ring ligands act as cleaners for repelling H2O molecules, while the hydrophilic hydroxyl and carboxyl groups attract Zn2+ ions for homogenizing Zn2+ flux. Moreover, the preferential reduction of Phe molecules prior to H2O facilitates the in situ formation of an organic-inorganic hybrid solid electrolyte interphase, enhancing the interfacial stability of the Zn anode. Consequently, Zn||Zn cells display improved reversibility, achieving an extended cycle life of 5250 h. Additionally, Zn||LMO full cells exhibit enhanced cyclability of retaining 77.3% capacity after 300 cycles, demonstrating substantial potential in advancing the commercialization of AZIBs.

Fluorine Chemistry in Rechargeable Batteries: Challenges, Progress, and Perspectives

The renewable energy industry demands rechargeable batteries that can be manufactured at low cost using abundant resources while offering high energy density, good safety, wide operating temperature windows, and long lifespans. Utilizing fluorine chemistry to redesign battery configurations/components is considered a critical strategy to fulfill these requirements due to the natural abundance, robust bond strength, and extraordinary electronegativity of fluorine and the high free energy of fluoride formation, which enables the fluorinated components with cost effectiveness, nonflammability, and intrinsic stability. In particular, fluorinated materials and electrode|electrolyte interphases have been demonstrated to significantly affect reaction reversibility/kinetics, safety, and temperature tolerance of rechargeable batteries. However, the underlining principles governing material design and the mechanistic insights of interphases at the atomic level have been largely overlooked. This review covers a wide range of topics from the exploration of fluorine-containing electrodes, fluorinated electrolyte constituents, and other fluorinated battery components for metal-ion shuttle batteries to constructing fluoride-ion batteries, dual-ion batteries, and other new chemistries. In doing so, this review aims to provide a comprehensive understanding of the structure-property interactions, the features of fluorinated interphases, and cutting-edge techniques for elucidating the role of fluorine chemistry in rechargeable batteries. Further, we present current challenges and promising strategies for employing fluorine chemistry, aiming to advance the electrochemical performance, wide temperature operation, and safety attributes of rechargeable batteries.

Spontaneous Molecule Aggregation for Nearly Single-Ion Conducting Sol Electrolyte to Advance Aqueous Zinc Metal Batteries: The Case of Tetraphenylporphyrin

Zn metal as a promising anode of aqueous batteries faces severe challenges from dendrite growth and side reactions. Here, tetraphenylporphyrin tetrasulfonic acid (TPPS) is explored as an electrolyte additive for advanced Zn anodes. It is interesting to note that TPPS spontaneously assembles into unique aggregates. As they adsorb on the Zn anode, the aggregates enhance the resistance to electrolyte percolation and dendrite growth compared to single molecules. Meanwhile, TPPS facilitates anion association in the solvation sheath of Zn2+, and boosts the transference number of Zn2+ up to 0.95. Therefore, anion-related side reactions and anion-induced electrode overpotentials are reduced accordingly. In this context, the electrolyte containing TPPS exhibits excellent electrochemical performance. Even under a high loading of MnO2 (25 mg cm-2), a limited Zn supply (N/P ratio=1.7), and a lean electrolyte (15 μL mAh-1), the full cells still represent a higher cumulative capacity compared to the reported data. The advantages of this electrolyte are also adapted to other cathode materials. The pouch cells of Zn||NaV3O8 ⋅ 1.5H2O realize a capacity of ~0.35 Ah at 0.4 C under harsh conditions.

Dilute Aqueous-Aprotic Electrolyte Towards Robust Zn-Ion Hybrid Supercapacitor with High Operation Voltage and Long Lifespan

With the merits of the high energy density of batteries and power density of supercapacitors, the aqueous Zn-ion hybrid supercapacitors emerge as a promising candidate for applications where both rapid energy delivery and moderate energy storage are required. However, the narrow electrochemical window of aqueous electrolytes induces severe side reactions on the Zn metal anode and shortens its lifespan. It also limits the operation voltage and energy density of the Zn-ion hybrid supercapacitors. Using 'water in salt' electrolytes can effectively broaden their electrochemical windows, but this is at the expense of high cost, low ionic conductivity, and narrow temperature compatibility, compromising the electrochemical performance of the Zn-ion hybrid supercapacitors. Thus, designing a new electrolyte to balance these factors towards high-performance Zn-ion hybrid supercapacitors is urgent and necessary. We developed a dilute water/acetonitrile electrolyte (0.5 m Zn(CF3SO3)2 + 1 m LiTFSI-H2O/AN) for Zn-ion hybrid supercapacitors, which simultaneously exhibited expanded electrochemical window, decent ionic conductivity, and broad temperature compatibility. In this electrolyte, the hydration shells and hydrogen bonds are significantly modulated by the acetonitrile and TFSI- anions. As a result, a Zn-ion hybrid supercapacitor with such an electrolyte demonstrates a high operating voltage up to 2.2 V and long lifespan beyond 120,000 cycles.

Towards More Sustainable Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are considered as the promising candidates for large-scale energy storage because of their high safety, low cost and environmental benignity. The large-scale applications of AZIBs will inevitably result in a large amount of spent AZIBs, which not only induce the waste of resources, but also pose environmental risks. Therefore, sustainable AZIBs have to be considered to minimize the risk of environmental pollution and maximize the utilization of spent compounds. Herein, this minireview focuses on the sustainability of AZIBs from material design and recycling techniques. The structure and degradation mechanism of AZIBs are discussed to guide the recycling design of the materials. Subsequently, the sustainability of component materials in AZIBs is further analysed to pre-evaluate their recycling behaviors and mentor the selection of more sustainable component materials, including active materials in cathodes, Zn anodes, and aqueous electrolytes, respectively. According to the features of component materials, corresponding green and economic approaches are further proposed to realize the recycling of active materials in cathodes, Zn anodes and electrolytes, respectively. These advanced technologies endow the recycling of component materials with high efficiency and a closed-loop control, ensuring that AZIBs will be the promising candidates of sustainable energy storage devices. This review will offer insight into potential future directions in the design of sustainable AZIBs.

In situ Nafion-nanofilm oriented (002) Zn electrodeposition for long-term zinc-ion batteries

Dendrite growth and parasitic reactions of a Zn metal anode in aqueous media hinder the development of up-and-coming Zn-ion batteries. Optimizing the crystal growth after Zn nucleation is promising to enable stable cyclic performance of the anode, but directly regulating specific crystal plane growth for homogenized Zn electrodeposition remains highly challenging. Herein, a perfluoropolymer (Nafion) is introduced into an aqueous electrolyte to activate a thermodynamically ultrastable Zn/electrolyte interface for long-term Zn-ion batteries. The low adsorption energy (-2.09 eV) of Nafion molecules on Zn metal ensures the in situ formation of a Nafion-nanofilm during the first charge process. This ultrathin artificial solid electrolyte interface with zincophilic -SO3- groups guides the directional Zn2+ electrodeposition along the (002) crystal surface even at high current density, yielding a dendrite-free Zn anode. The synergic Zn/electrolyte interphase electrochemistry contributes an average coulombic efficiency of 99.71% after 4500 cycles for Zn‖Cu cells, and Zn‖Zn cells achieve an ultralong lifespan of over 7000 h at 5 mA cm-2. Besides, Zn‖MnO2 cells operate well over 3000 cycles. Even at -40 °C, Zn‖Zn cells achieve stable Zn2+ plating/stripping for 1200 h.

Hygroscopic Solutes Enable Non-van der Waals Electrolytes for Fire-Tolerant Dual-Air Batteries

Thermal safety issues of batteries have hindered their large-scale applications. Nonflammable electrolytes improved safety but solvent evaporation above 100 °C limited thermal tolerance, lacking reliability. Herein, fire-tolerant metal-air batteries were realized by introducing solute-in-air electrolytes whose hygroscopic solutes could spontaneously reabsorb the evaporated water solvent. Using Zn/CaCl2 -in-air/carbon batteries as a proof-of-concept, they failed upon burning at 631.8 °C but self-recovered then by reabsorbing water from the air at room temperature. Different from conventional aqueous electrolytes whose irreversible thermal transformation is determined by the boiling points of solvents, solute-in-air electrolytes make this transformation determined by the much higher decomposition temperature of solutes. It was found that stronger intramolecular bonds instead of intermolecular (van der Waals) interactions were strongly correlated to ultra-high tolerance temperatures of our solute-in-air electrolytes, inspiring a concept of non-van der Waals electrolytes. Our study would improve the understanding of the thermal properties of electrolytes, guide the design of solute-in-air electrolytes, and enhance battery safety.

Direct Growth of a Polymer Film to Induce Horizontal Orientation of Zn4(OH)6SO4·xH2O for Stable Zn Metal Batteries

The loose and randomly oriented byproduct (i.e., Zn4(OH)6SO4·xH2O, ZHS) in situ formed on the zinc (Zn) surface is recognized to be the primary cause for dendritic Zn growth and side reactions. Switching the detrimental passivation film into a dense and kinetically favorable solid electrolyte interphase (SEI) is a straightforward strategy to tackle these issues faced by Zn metal anodes but remains largely unexplored. Herein, a new polymer film directly grown on Zn metal through room-temperature plasma-enhanced chemical vapor deposition is proposed to induce the lateral growth of ZHS nanosheets and decrease the Zn2+ desolvation barrier, thereby forming a beneficial composite SEI for suppressing Zn dendrite growth and surface corrosion. As a result of the joint effect, we realize an impressively stable cycling behavior in symmetric cell over 3400 h at 2 mA cm-2. Moreover, full cells also demonstrate prolonged lifespans. This work opens a new avenue for stabilizing Zn metal batteries by turning detrimental ZHS into a favorable interlayer.

Steric-hindrance Effect Tuned Ion Solvation Enabling High Performance Aqueous Zinc Ion Batteries

Despite many additives have been reported for aqueous zinc ion batteries, steric-hindrance effect of additives and its correlation with Zn2+ solvation structure have been rarely reported. Herein, large-sized sucrose biomolecule is selected as a paradigm additive, and steric-hindrance electrolytes (STEs) are developed to investigate the steric-hindrance effect for solvation structure regulation. Sucrose molecules do not participate in Zn2+ solvation shell, but significantly homogenize the distribution of solvated Zn2+ and enlarge Zn2+ solvation shell with weakened Zn2+-H2O interaction due to the steric-hindrance effect. More importantly, STEs afford the water-shielding electric double layer and in situ construct the organic and inorganic hybrid solid electrolyte interface, which effectively boost Zn anode reversibility. Remarkably, Zn//NVO battery presents high capacity of 3.9 mAh ⋅ cm-2 with long cycling stability for over 650 cycles at lean electrolyte of 4.5 μL ⋅ mg-1 and low N/P ratio of 1.5, and the stable operation at wide temperature (-20 °C~+40 °C).

Asymmetric Anion Zinc Salt Derived Solid Electrolyte Interphase Enabled Long-Lifespan Aqueous Zinc Bromine Batteries

Organic additives with high-reduction potentials are generally applied in aqueous electrolytes to stabilize the Zn anode, while compromise safety and environmental compatibility. Highly concentrated water-in-salt electrolytes have been proposed to realize the high reversibility of Zn plating/stripping; however, their high cost and viscosity hinder their practical applications. Therefore, exploring low-concentration Zn salts, that can be used directly to stabilize Zn anodes, is of primary importance. Herein, we developed an asymmetric anion group, bi(difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide (DFTFSI- )-based novel zinc salt, Zn(DFTFSI)2 , to obtain a high ionic conductivity and a highly stable dendrite-free Zn anode. Experimental tests and theoretical calculations verified that DFTFSI- in the Zn2+ solvation sheath and inner Helmholtz plane would be preferentially reduced to construct layer-structured SEI films, inhibiting hydrogen evolution and side reactions. Consequently, the Zn| | ${||}$ Zn symmetric cell with 1M Zn(DFTFSI)2 aqueous electrolyte delivers an ultralong cycle life for >2500 h outperforming many other conventional Zn salt electrolytes. The Zn| | ${||}$ Br2 battery also exhibits a long lifespan over 1200 cycles at ~99.8 % Coulombic efficiency with a high capacity retention of 92.5 %. Furthermore, this outstanding performance translates well to a high-areal-capacity Zn| | ${||}$ Br2 battery (~5.6 mAh ⋅ cm-2 ), cycling over 320 cycles with 95.3 % initial capacity retained.

Proton-selective coating enables fast-kinetics high-mass-loading cathodes for sustainable zinc batteries

The pressing demand for sustainable energy storage solutions has spurred the burgeoning development of aqueous zinc batteries. However, kinetics-sluggish Zn2+ as the dominant charge carriers in cathodes leads to suboptimal charge-storage capacity and durability of aqueous zinc batteries. Here, we discover that an ultrathin two-dimensional polyimine membrane, featured by dual ion-transport nanochannels and rich proton-conduction groups, facilitates rapid and selective proton passing. Subsequently, a distinctive electrochemistry transition shifting from sluggish Zn2+-dominated to fast-kinetics H+-dominated Faradic reactions is achieved for high-mass-loading cathodes by using the polyimine membrane as an interfacial coating. Notably, the NaV3O8·1.5H2O cathode (10 mg cm-2) with this interfacial coating exhibits an ultrahigh areal capacity of 4.5 mAh cm-2 and a state-of-the-art energy density of 33.8 Wh m-2, along with apparently enhanced cycling stability. Additionally, we showcase the applicability of the interfacial proton-selective coating to different cathodes and aqueous electrolytes, validating its universality for developing reliable aqueous batteries.

Ordered planar plating/stripping enables deep cycling zinc metal batteries

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

Critical Solvation Structures Arrested Active Molecules for Reversible Zn Electrochemistry

Aqueous Zn-ion batteries (AZIBs) have attracted increasing attention in next-generation energy storage systems due to their high safety and economic. Unfortunately, the side reactions, dendrites and hydrogen evolution effects at the zinc anode interface in aqueous electrolytes seriously hinder the application of aqueous zinc-ion batteries. Here, we report a critical solvation strategy to achieve reversible zinc electrochemistry by introducing a small polar molecule acetonitrile to form a "catcher" to arrest active molecules (bound water molecules). The stable solvation structure of [Zn(H2O)6]2+ is capable of maintaining and completely inhibiting free water molecules. When [Zn(H2O)6]2+ is partially desolvated in the Helmholtz outer layer, the separated active molecules will be arrested by the "catcher" formed by the strong hydrogen bond N-H bond, ensuring the stable desolvation of Zn2+. The Zn||Zn symmetric battery can stably cycle for 2250 h at 1 mAh cm-2, Zn||V6O13 full battery achieved a capacity retention rate of 99.2% after 10,000 cycles at 10 A g-1. This paper proposes a novel critical solvation strategy that paves the route for the construction of high-performance AZIBs.

Highly Potent and Low-Volume Concentration Additives for Durable Aqueous Zinc Batteries: Machine Learning-Enabled Performance Rationalization

The essential virtues of aqueous zinc battery chemistry stem from the energy-dense zinc metal anode and mild aqueous electrolytes. Yet, their incompatibility - as exposed by zinc's corrosion and associated dendrite problem - poses a challenge to achieving improved cycle life under practically relevant parameters. While electrolyte additives are a scalable strategy, additives that can function at low volume concentrations remain elusive. Here, through screening alkanol and alkanediol chemistries, 1,2-butanediol and pentanediol are unveiled as highly potent additives, which operate at a practical 1 volume% concentration owing to their ability to furnish dynamic solid-electrolyte interphase through pronounced interfacial filming. This unique mechanistic action renders effective corrosion and dendrite mitigation, resulting in up to five to twenty-fold zinc cyclability enhancement with a high Coulombic efficiency (up to 99.9%) and improved full-cell performance under demanding conditions, including at elevated temperatures. A machine learning-based analysis is presented to rationalize the additive performance relative to critical physicochemical descriptors, which can pave the way for a rational approach to efficient additive discoveries.

Electrochemical Hydrophobic Tri-layer Interface Rendered Mechanically Graded Solid Electrolyte Interface for Stable Zinc Metal Anode

The aqueous zinc-ion battery is promising as grid scale energy storage device, but hindered by the instable electrode/electrolyte interface. Herein, we report the lean-water ionic liquid electrolyte for aqueous zinc metal batteries. The lean-water ionic liquid electrolyte creates the hydrophobic tri-layer interface assembled by first two layers of hydrophobic OTF- and EMIM+ and third layer of loosely attached water, beyond the classical Gouy-Chapman-Stern theory based electrochemical double layer. By taking advantage of the hydrophobic tri-layer interface, the lean-water ionic liquid electrolyte enables a wide electrochemical working window (2.93 V) with relatively high zinc ion conductivity (17.3 mS/cm). Furthermore, the anion crowding interface facilitates the OTF- decomposition chemistry to create the mechanically graded solid electrolyte interface layer to simultaneously suppress the dendrite formation and maintain the mechanical stability. In this way, the lean-water based ionic liquid electrolyte realizes the ultralong cyclability of over 10000 cycles at 20 A/g and at practical condition of N/P ratio of 1.5, the cumulated areal capacity reach 1.8 Ah/cm2 , which outperforms the state-of-the-art zinc metal battery performance. Our work highlights the importance of the stable electrode/electrolyte interface stability, which would be practical for building high energy grid scale zinc-ion battery.

Bio-Inspired Trace Hydroxyl-Rich Electrolyte Additives for High-Rate and Stable Zn-Ion Batteries at Low Temperatures

High-rate and stable Zn-ion batteries working at low temperatures are highly desirable for practical applications, but are challenged by sluggish kinetics and severe corrosion. Herein, inspired by frost-resistant plants, we report trace hydroxyl-rich electrolyte additives that implement a dual remodeling effect for high-performance low-temperature Zn-ion batteries. The additive with high Zn absorbability not only remodels Zn2+ primary solvent shell by alternating H2 O molecules, but also forms a shielding layer thus remodeling the Zn surface, which effectively enhances fast Zn2+ de-solvation reaction kinetics and prohibits Zn anode corrosion. Taking trace α-D-glucose (αDG) as a demonstration, the electrolyte obtains a low freezing point of -55.3 °C, and the Zn//Zn cell can stably cycle for 2000 h at 5 mA cm-2 under -25 °C, with a high cumulative capacity of 5000 mAh cm-2 . A full battery that stably operates for 10000 cycles at -50 °C is also demonstrated.

Suppressing Zn pulverization with three-dimensional inert-cation diversion dam for long-life Zn metal batteries

Tremendous attention has been paid to the water-associated side reactions and zinc (Zn) dendrite growth on the electrode-electrolyte interface. However, the Zn pulverization that can cause continuous depletion of active Zn metal and exacerbate hydrogen evolution is severely neglected. Here, we disclose that the excessive Zn feeding that causes incomplete crystallization is responsible for Zn pulverization formation through analyzing the thermodynamic and kinetics process of Zn deposition. On the basis, we introduce 1-ethyl-3-methylimidazolium cations (EMIm+) into the electrolyte to form a Galton-board-like three-dimensional inert-cation (3DIC) region. Modeling test shows that the 3DIC EMIm+ can induce the Zn2+ flux to follow in a Gauss distribution, thus acting as elastic sites to buffer the perpendicular diffusion of Zn2+ and direct the lateral diffusion, thus effectively avoiding the local Zn2+ accumulation and irreversible crystal formation. Consequently, anti-pulverized Zn metal deposition behavior is achieved with an average Coulombic efficiency of 99.6% at 5 mA cm-2 over 2,000 cycles and superb stability in symmetric cell over 1,200 h at -30 °C. Furthermore, the Zn||KVOH pouch cell can stably cycle over 1,200 cycles at 2 A g-1 and maintain a capacity of up to 12 mAh.

Surface Patterning of Metal Zinc Electrode with an In-Region Zincophilic Interface for High-Rate and Long-Cycle-Life Zinc Metal Anode

The undesirable dendrite growth induced by non-planar zinc (Zn) deposition and low Coulombic efficiency resulting from severe side reactions have been long-standing challenges for metallic Zn anodes and substantially impede the practical application of rechargeable aqueous Zn metal batteries (ZMBs). Herein, we present a strategy for achieving a high-rate and long-cycle-life Zn metal anode by patterning Zn foil surfaces and endowing a Zn-Indium (Zn-In) interface in the microchannels. The accumulation of electrons in the microchannel and the zincophilicity of the Zn-In interface promote preferential heteroepitaxial Zn deposition in the microchannel region and enhance the tolerance of the electrode at high current densities. Meanwhile, electron aggregation accelerates the dissolution of non-(002) plane Zn atoms on the array surface, thereby directing the subsequent homoepitaxial Zn deposition on the array surface. Consequently, the planar dendrite-free Zn deposition and long-term cycling stability are achieved (5,050 h at 10.0 mA cm-2 and 27,000 cycles at 20.0 mA cm-2). Furthermore, a Zn/I2 full cell assembled by pairing with such an anode can maintain good stability for 3,500 cycles at 5.0 C, demonstrating the application potential of the as-prepared ZnIn anode for high-performance aqueous ZMBs.

Adaptive Ion Channels Formed in Ultrathin and Semicrystalline Polymer Interphases for Stable Aqueous Batteries

Aqueous Zn batteries have recently emerged as promising candidates for large-scale energy storage, driven by the need for a safe and cost-effective technology with sufficient energy density and readily accessible electrode materials. However, the energy density and cycle life of Zn batteries have been limited by inherent chemical, morphological, and mechanical instabilities at the electrode-electrolyte interface where uncontrolled reactions occur. To suppress the uncontrolled reactions, we designed a crystalline polymer interphase for both electrodes, which simultaneously promotes electrode reversibility via fast and selective Zn transport through the adaptive formation of ion channels. The interphase comprises an ultrathin layer of crystalline poly(1H,1H,2H,2H-perfluorodecyl acrylate), synthesized and applied as a conformal coating in a single step using initiated chemical vapor deposition (iCVD). Crystallinity is optimized to improve interphase stability and Zn-ion transport. The optimized interphase enables a cycle life of 9500 for Zn symmetric cells and over 11,000 for Zn-MnO2 full-cell batteries. We further demonstrate the generalizability of this interphase design using Cu and Li as examples, improving their stability and achieving reversible cycling in both. The iCVD method and molecular design unlock the potential of highly reversible and cost-effective aqueous batteries using earth-abundant Zn anode materials, pointing to grid-scale energy storage.

Weak Solvation Effect Induced Optimal Interfacial Chemistry Enables Highly Durable Zn Anodes for Aqueous Zn-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are emerging as one of the most reliable energy storage technologies for scale-up applications, but still suffer from the instability of Zn anode, which is mainly caused by the undesirable dendrite growth and side reactions. To tackle these issues, we formulate a new aqueous electrolyte with weak solvation effect by introducing low-dielectric-constant acetone to achieve H2 O-poor solvation structure of Zn2+ . Experimental and theoretical calculation studies concurrently reveal that such solvation structure can: i) relieve the solvated H2 O related side reactions, ii) suppress the dendrite growth by boosting the desolvation kinetics of Zn2+ and iii) in situ form solid electrolyte interface (SEI) to synergistically inhibit the side reaction and dendrite growth. The synergy of these three factors prolongs the cycling life of Cu/Zn asymmetric cell from 30 h to more than 800 h at 1 mA cm-2 /1 mAh cm-2 , and can work at more harsh condition of 5 mA cm-2 /5 mAh cm-2 . More encouragingly, Zn/V2 O5  ⋅ nH2 O full cell also shows enhanced cycling stability of 95.9 % capacity retention after 1000 cycles, much better than that with baseline electrolyte (failing at ≈700th  cycle).

A High-Energy Tellurium Redox-Amphoteric Conversion Cathode Chemistry for Aqueous Zinc Batteries

Rechargeable aqueous zinc batteries are potential candidates for sustainable energy storage systems at a grid scale, owing to their high safety and low cost. However, the existing cathode chemistries exhibit restricted energy density, which hinders their extensive applications. Here, a tellurium redox-amphoteric conversion cathode chemistry is presented for aqueous zinc batteries, which delivers a specific capacity of 1223.9 mAh gTe -1 and a high energy density of 1028.0 Wh kgTe -1 . A highly concentrated electrolyte (30 mol kg-1 ZnCl2 ) is revealed crucial for initiating the Te redox-amphoteric conversion as it suppresses the H2 O reactivity and inhibits undesirable hydrolysis of the Te4+ product. By carrying out multiple operando/ex situ characterizations, the reversible six-electron Te2- /Te0 /Te4+ conversion with TeCl4 is identified as the fully charged product and ZnTe as the fully discharged product. This finding not only enriches the conversion-type battery chemistries but also establishes a critical step in exploring redox-amphoteric materials for aqueous zinc batteries and beyond.

Synergistic Modulation of Mass Transfer and Parasitic Reactions of Zn Metal Anode via Bioinspired Artificial Protection Layer

Rechargeable aqueous zinc-ion batteries are regarded as promising energy storage devices due to their attractive economic benefits and extraordinary electrochemical performance. However, the sluggish Zn2+ mass transfer behavior and water-induced parasitic reactions that occurred on the anode-electrode interface inevitably restrain their applications. Herein, inspired by the selective permeability and superior stability of plasma membrane, a thin UiO-66 metal-organic framework layer with smart aperture size is ex-situ decorated onto the Zn anode. Experimental characterizations in conjunction with theoretical calculations demonstrate that this bio-inspired layer promotes the de-solvation process of hydrated Zn2+ and reduces the effective contact between the anode and H2 O molecules, thereby boosting Zn2+ deposition kinetics and restraining interfacial parasitic reactions. Hence, the Zn||Zn cells could sustain a long lifespan of 1680 h and the Zn||Cu cells yielded a stable coulombic efficiency of over 99.3% throughout 600 cycles under the assistance of the bio-inspired layer. Moreover, pairing with δ-MnO2 cathode, the full cells also demonstrate prominent cycling stability and rate performance. From the bio-inspired design philosophy, this work provides a novel insight into the development of aqueous batteries.

Rechargeable Aqueous Zinc-Halogen Batteries: Fundamental Mechanisms, Research Issues, and Future Perspectives

Aqueous zinc-halogen batteries (AZHBs) have emerged as promising candidates for energy storage applications due to their high security features and low cost. However, several challenges including natural subliming, sluggish reaction kinetics, and shuttle effect of halogens, as well as dendrite growth of the zinc (Zn) anode, have hindered their large-scale commercialization. In this review, first the fundamental mechanisms and scientific issues associated with AZHBs are summarized. Then the research issues and progresses related to the cathode, separator, anode, and electrolyte are discussed. Additionally, emerging research opportunities in this field is explored. Finally, ideas and prospects for the future development of AZHBs are presented. The objective of this review is to stimulate further exploration, foster the advancement of AZHBs, and contribute to the diversified development of electrochemical energy storage.

Ion Sieve Interface Assisted Zinc Anode with High Zinc Utilization and Ultralong Cycle Life for 61 Wh/kg Mild Aqueous Pouch Battery

The cycling stability of a thin zinc anode under high zinc utilization has a critical impact on the overall energy density and practical lifetime of zinc ion batteries. In this study, an ion sieve protection layer (ZnSnF@Zn) was constructed in situ on the surface of a zinc anode by chemical replacement. The ion sieve facilitated the transport and desolvation of zinc ions at the anode/electrolyte interface, reduced the zinc deposition overpotential, and inhibited side reactions. Under a 50% zinc utilization, the symmetrical battery with this protection layer maintained stable cycling for 250 h at 30 mA cm-2. Matched with high-load self-supported vanadium-based cathodes (18-20 mg cm-2), the coin battery with 50% zinc utilization possessed an energy density retention of 94.3% after 1000 cycles at 20 mA cm-2. Furthermore, the assembled pouch battery delivered a whole energy density of 61.3 Wh kg-1, surpassing the highest mass energy density among reported mild zinc batteries, and retained 76.7% of the energy density and 85.3% (0.53 Ah) of the capacity after 300 cycles.

Suppressing metal corrosion through identification of optimal crystallographic plane for Zn batteries

Direct use of metals as battery anodes could significantly boost the energy density, but suffers from limited cycling. To make the batteries more sustainable, one strategy is mitigating the propensity for metals to form random morphology during plating through orientation regulation, e.g., hexagonal Zn platelets locked horizontally by epitaxial electrodeposition or vertically aligned through Zn/electrolyte interface modulation. Current strategies center around obtaining (002) faceted deposition due to its minimum surface energy. Here, benefiting from the capability of preparing a library of faceted monocrystalline Zn anodes and controlling the orientation of Zn platelet deposits, we challenge this conventional belief. We show that while monocrystalline (002) faceted Zn electrode with horizontal epitaxy indeed promises the highest critical current density, the (100) faceted electrode with vertically aligned deposits is the most important one in suppressing Zn metal corrosion and promising the best reversibility. Such uniqueness results from the lowest electrochemical surface area of (100) faceted electrode, which intrinsically builds upon the surface atom diffusion barrier and the orientation of the pallets. These new findings based on monocrystalline anodes advance the fundamental understanding of electrodeposition process for sustainable metal batteries and provide a paradigm to explore the processing-structure-property relationships of metal electrodes.

Atomic-Level Customization of Zinc Crystallization Kinetics at the Interface for High-Utilization Zn Anodes

Understanding the crystallization occurring at the inner interfaces during electrochemical deposition is crucial for achieving a high reversibility in zinc anodes. However, design rules for crystallization kinetics still lack predictive power, particularly at the atomic scale, posing a significant challenge. Herein, we propose a crystal facet terminating agent, LaCl3, which modulates the preferential crystallization orientation of Zn by regulating its growth kinetics through the synergistic adsorption of dual ions. Interface molecular dynamics (MD) simulations and crucial experimental parameters reveal that the strong (002) facet texture of Zn deposits primarily depends on the adsorption of strong inhibitors. Specifically, the high adsorption free energy of Cl- on the Zn (002) facet and the concomitant aggregation of La3+ reduces the growth rate of the Zn (002) facet, thereby favoring its preservation as the final crystal facet. Consequently, this terminating agent enables the Zn anodes to deliver a high cumulative capacity of 12 Ah cm-2 at 40 mA cm-2, 20 mAh cm-2. The Zn||MnO2 full cell, when coupled with a high-mass-loading cathode and limited Zn supply, can maintain a practical areal capacity of 3.39 mAh cm-2. Furthermore, rigorous testing conditions and the successful scaling up to a 0.34 Ah pouch cell further confirm its promising prospects for practical applications.

An extended substrate screening strategy enabling a low lattice mismatch for highly reversible zinc anodes

Aqueous zinc batteries possess intrinsic safety and cost-effectiveness, but dendrite growth and side reactions of zinc anodes hinder their practical application. Here, we propose the extended substrate screening strategy for stabilizing zinc anodes and verify its availability (dsubstrate: dZn(002) = 1: 1→dsubstrate: dZn(002)=n:1, n = 1, 2). From a series of calculated phyllosilicates satisfying dsubstrate ≈ 2dZn(002), we select vermiculite, which has the lowest lattice mismatch (0.38%) reported so far, as the model to confirm the effectiveness of "2dZn(002)" substrates for zinc anodes protection. Then, we develop a monolayer porous vermiculite through a large-scale and green preparation as a functional coating for zinc electrodes. Unique "planting Zn(002) seeds" mechanism for "2dZn(002)" substrates is revealed to induce the oriented growth of zinc deposits. Additionally, the coating effectively inhibits side reactions and promotes zinc ion transport. Consequently, the modified symmetric cells operate stably for over 300 h at a high current density of 50 mA cm-2. This work extends the substrate screening strategy and advances the understanding of zinc nucleation mechanism, paving the way for realizing high-rate and stable zinc-metal batteries.

Molecularly modulating solvation structure and electrode interface enables dendrite-free zinc-ion batteries

The performance of aqueous Zn ion batteries (AZIBs) is hindered by the uncontrollable growth of Zn dendrites and side reactions at the Zn anode/electrolyte interface. Here, we introduce low-cost glucosamine hydrochloride (GLA) into the ZnSO4 electrolyte system to modulate the Zn anode/electrolyte interface and the solvation structure of Zn2+, which leads to improved reversibility of Zn plating/striping. Through experimental and theoretical analyses, we demonstrate that GLA molecules could adsorp on the Zn metal surface to form a new interface with reduced active water, effectively suppressing water-induced side reactions. Moreover, after adding GLA, the flux of Zn2+ ions is regulated, the desolvation of the primary [Zn(H2O)6]2+ ions is promoted, and the Zn dendrite growth is significantly inhibited. Consequently, superior cyclic stability with a lower voltage hysteresis is simultaneously achieved in a Zn//Zn symmetric cell. When coupled with the Mn3O4 cathode, the fabricated Zn-Mn batteries with the modified ZnSO4 + GLA electrolyte system deliver boosted capacity, improved long-term cycling stability, and better self-discharge performance. This work provides insight into the development of high-efficient and low-cost electrolytes for high-performance Zn-based energy storage devices.

Optimizing Porous Metal-Organic Layers for Stable Zinc Anodes

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

Preventing Dissolution of Cathode Active Materials by Ion-anchoring Zeolite-based Separators for Durable Aqueous Zinc Batteries

Aqueous zinc batteries have emerged as promising energy storage devices due to their safety and low cost. However, they face challenges such as anodic dendrite formation and cathodic compound dissolution. Here, we present the development of a polymer-matrixed zeolite separator (SZ) by synthesizing zeolite materials on a flexible polymeric membrane. This separator acts as an effective ionic barrier, preventing the leaching and shuttling of vanadium from the cathode, while significantly inhibiting the formation of by-products and zinc dendrites. The SZ cells demonstrate stable operation for more than 400 cycles at 0.5 A g-1 , with an initial capacity of 375.4 mAh g-1 , and over 10,000 cycles at 15 A g-1 . Notably, when pre-anchored with vanadium ions, the SZ-V cells exhibited excellent capacity retention of up to 94.6 % over 1000 cycles. The SZ separator featuring an ion barrier represents a crucial advancement towards the commercialization of zinc storage devices.

Design Strategies for Aqueous Zinc Metal Batteries with High Zinc Utilization: From Metal Anodes to Anode-Free Structures

Aqueous zinc metal batteries (AZMBs) are promising candidates for next-generation energy storage due to the excellent safety, environmental friendliness, natural abundance, high theoretical specific capacity, and low redox potential of zinc (Zn) metal. However, several issues such as dendrite formation, hydrogen evolution, corrosion, and passivation of Zn metal anodes cause irreversible loss of the active materials. To solve these issues, researchers often use large amounts of excess Zn to ensure a continuous supply of active materials for Zn anodes. This leads to the ultralow utilization of Zn anodes and squanders the high energy density of AZMBs. Herein, the design strategies for AZMBs with high Zn utilization are discussed in depth, from utilizing thinner Zn foils to constructing anode-free structures with theoretical Zn utilization of 100%, which provides comprehensive guidelines for further research. Representative methods for calculating the depth of discharge of Zn anodes with different structures are first summarized. The reasonable modification strategies of Zn foil anodes, current collectors with pre-deposited Zn, and anode-free aqueous Zn metal batteries (AF-AZMBs) to improve Zn utilization are then detailed. In particular, the working mechanism of AF-AZMBs is systematically introduced. Finally, the challenges and perspectives for constructing high-utilization Zn anodes are presented.

Electrolyte Additives for Stable Zn Anodes

Zn-ion batteries are regarded as the most promising batteries for next-generation, large-scale energy storage because of their low cost, high safety, and eco-friendly nature. The use of aqueous electrolytes results in poor reversibility and leads to many challenges related to the Zn anode. Electrolyte additives can effectively address many such challenges, including dendrite growth and corrosion. This review provides a comprehensive introduction to the major challenges in and current strategies used for Zn anode protection. In particular, an in-depth and fundamental understanding is provided of the various functions of electrolyte additives, including electrostatic shielding, adsorption, in situ solid electrolyte interphase formation, enhancing water stability, and surface texture regulation. Potential future research directions for electrolyte additives used in aqueous Zn-ion batteries are also discussed.