Ultrastable Zinc Anodes Enabled by Anti-Dehydration Ionic Liquid Polymer Electrolyte for Aqueous Zn Batteries

Recent progress in critical electrode and electrolyte materials for flexible zinc-ion batteries

With the increasing popularity of flexible and wearable electronic devices, the demand for power supplies that can be easily bent or worn is also rapidly growing. However, traditional lithium ion batteries are difficult to adapt to complex wearable devices because of their unsatisfactory flexibility and thickness as well as safety issues. Zinc-ion batteries have several advantages, including low redox potential, high theoretical capacity, high safety, and abundant reserves. These features make flexible zinc-ion batteries (FZIBs) an ideal wearable energy storage device candidate. The electrochemical performance and mechanical deformability of FZIBs were pivotally determined based on the properties of their electrode and electrolyte. Herein, we summarize some recent advances from 2015 to 2023 in the design and preparation of various electrode and electrolyte materials for FZIBs with controllable morphology and structure, excellent mechanical property, and enhanced electrochemical performance. Moreover, efforts to explore the potential practical applications of FZIBs have also been considered. Finally, we present and discuss current challenges and opportunities for the development of high-performance FZIBs.

Theoretical investigation of electronic, energetic, and mechanical properties of polyvinyl alcohol/cellulose composite hydrogel electrolyte

Hydrogels are a new class of electrolytic materials employed in zinc-air batteries due to their significant on the battery's performance. However, the effectiveness of electrolytic hydrogel is affected by factors such as water content, temperature, additives, etc. Using DMol3 and molecular dynamics modeling techniques, this research aimed at investigating the electronic properties, effect of water content, and temperature on the binding energy, cohesive energy, and the mechanical properties of polyvinyl alcohol/cellulose-based composite hydrogel at the molecular level. The electronic optimized structures of the polymeric materials and parameters such as frontier molecular orbitals, band gap and electron density were analyzed. The results revealed that the binding energies of hydrogel polymer composite increased as the number of water molecules in the composite increased up to 60 % after which the binding energy decreased. In addition, the temperature increase led to a decrease in the binding energy of the composite. The cohesive energy density of the composite was highest at 40 % water content while higher temperatures decreased the cohesive energy density of the hydrogel. As the number of water molecules increased from 29 to 256, the tensile modulus increased from 0.707 × 10-3 to 2.821 × 10-3 Gpa; while the bulk modulus (K) increased in the order of K 40 > 50 > 30 > 20 > 10 respectively. These results serve as a theoretical enlightenment and a guide for experimental works in the field of energy conversion and storage devices.

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.

A Minireview of the Solid-State Electrolytes for Zinc Batteries

Aqueous zinc-ion batteries (ZIBs) have gained significant recognition as highly promising rechargeable batteries for the future due to their exceptional safety, low operating costs, and environmental advantages. Nevertheless, the widespread utilization of ZIBs for energy storage has been hindered by inherent challenges associated with aqueous electrolytes, including water decomposition reactions, evaporation, and liquid leakage. Fortunately, recent advances in solid-state electrolyte research have demonstrated great potential in resolving these challenges. Moreover, the flexibility and new chemistry of solid-state electrolytes offer further opportunities for their applications in wearable electronic devices and multifunctional settings. Nonetheless, despite the growing popularity of solid-state electrolyte-based-ZIBs in recent years, the development of solid-state electrolytes is still in its early stages. Bridging the substantial gap that exists is crucial before solid-state ZIBs become a practical reality. This review presents the advancements in various types of solid-state electrolytes for ZIBs, including film separators, inorganic additives, and organic polymers. Furthermore, it discusses the performance and impact of solid-state electrolytes. Finally, it outlines future directions for the development of solid-state ZIBs.

Solid State Zinc and Aluminum ion batteries: Challenges and Opportunities

Solid-state zinc ion batteries (ZIBs) and aluminum-ion batteries (AIBs) are deemed as promising candidates for supplying power in wearable devices due to merits of low cost, high safety, and tunable flexibility. However, their wide-scale practical application is limited by various challenges, down to the material level. This Review begins with elaboration of the root causes and their detrimental effect for four main limitations: electrode-electrolyte interface contact, electrolyte ionic conductivity, mechanical strength, and electrochemical stability window of the electrolyte. Thereafter, various strategies to mitigate each of the described limitation are discussed along with future research direction perspectives. Finally, to estimate the viability of these technologies for wearable applications, economic-performance metrics are compared against Li-ion batteries.

Anti-Fatigue Hydrogel Electrolyte for All-Flexible Zn-Ion Batteries

Hydrogel electrolytes are widely explored in Zn metal batteries for application in wearable electronics. While extensive studies have been conducted on optimizing the chemical structure and boosting the tensile elasticity, the mechanical stability of the hydrogel under repeated deformation is largely overlooked, leading to unsatisfactory performance at large cycling capacity. This work systematically analyzes the compressive fatigue-resistance properties of the hydrogel electrolyte, revealing the critical roles of the salt and copolymer matrix on crack initiation and propagation. It shows that, on the premise of homogeneous Zn deposition, an improved anti-fatigue property is essential to achieve high-capacity Zn metal anodes. The optimal Zn(ClO4 )2 -polyacrylamide/chitosan hydrogel electrolyte (C-PAMCS) exhibits an unprecedented lifespan of 1500 h for Zn//Zn cells at a current density of 10 mA cm-2 and a high areal capacity of 10 mAh cm-2 . The potential application of C-PAMCS is exemplified in all-flexible Zn-ion batteries enabled by a flexible current collector consisting of a Ag nanowires embedded elastomer. This study provides the rationale under hydrogel electrolyte engineering toward advanced Zn-ion battereis and the application in flexible devices.

Recent progress in structural modification of polymer gel electrolytes for use in solid-state zinc-ion batteries

Zinc-ion batteries are one of the promising energy storage devices, which have the advantages of environmental friendliness, high safety and low price and are expected to be used in large-scale battery application fields. However, four prominent water-induced adverse reactions, including zinc dendrite formation, zinc corrosion, passivation and the hydrogen evolution reaction in aqueous systems, seriously shorten the cycling life of zinc-ion batteries and greatly hinder their development. Based on this, polymer gel electrolytes have been developed to alleviate these issues due to their unique network structure, which can reduce water activity and suppress water-induced side reactions. Based on the challenges of polymer gel electrolytes, this review systematically summarizes the latest research progress in the use of additives in them and explores new perspectives in response to the existing problems with polymer electrolytes. In order to expand the performance of polymer gel electrolytes in zinc-ion batteries, a range of different types of additives are added via physical/chemical crosslinking, such as organic or inorganic substances, natural plants, etc. In addition, different types of additives and polymerization crosslinking from different angles essentially improve the ionic conductivity of the gel electrolyte, inhibit the growth of zinc dendrites, and reduce hydrogen evolution and oxygen-absorbed corrosion. After these modifications of polymer gel electrolytes, a more stable and superior electrochemical performance of zinc-ion batteries can be obtained, which provides some strategies for solid-state zinc-ion batteries.

Activating Gel Polymer Electrolyte Based Zinc-Ion Conduction with Filler-Integration for Advanced Zinc Batteries

Quasi solid zinc batteries (QSZBs) based on gel electrolyte have performed as a significant application prospect as advanced high energy density electrochemical storage devices with safety, low cost, eco-friendliness, and flexibility. While, the practical application of QSZBs was enormously restricted by low ionic conductivity and poor strength of pure gel electrolyte. Here, in order to activate the zinc ion conduction in gel electrolyte, the kinds of inorganic fillers constituting the composite electrolyte was investigated. The theoretical study was also revealed by density functional theory to have deep insight into the mechanism. In particular, appropriate filler amount (ZnO#20) can make a noteworthy ion conductivity elevation (1.3 × 10-3 S cm-1) which is much better than the control sample (2.0 × 10-4 S cm-1) at -20 °C. As a result, the symmetric cell with ZnO#20 can achieve a long-term cycling life of over 1500 h. Moreover, the pouch cell coupled with vanadium pentoxide is assembled, and corresponding versatility is also identified with twisting, refrigeration (-20 °C) and cutting.

Challenges and Strategies in the Development of Zinc-Ion Batteries

Although promising, the practical use of zinc-ion batteries (ZIBs) remains plagued with uncontrollable dendrite growth, parasitic side reactions, and the high intercalation energy of divalent Zn²⁺ ions. Hence, much work has been conducted to alleviate these issues to maximize the energy density and cyclic life of the cell. In this holistic review, the mechanisms and rationale for the stated challenges shall be summarized, followed by the corresponding strategies employed to mitigate them. Thereafter, a perspective on present research and the outlook of ZIBs would be put forth in hopes to enhance their electrochemical properties in a multipronged approach.

Design Strategies toward High-Performance Zn Metal Anode

Rechargeable aqueous Zn-ion batteries (AZIBs) are one of the most promising alternatives for traditional energy-storage devices because of their low cost, abundant resources, environmental friendliness, and inherent safety. However, several detrimental issues with Zn metal anodes including Zn dendrite formation, hydrogen evolution, corrosion and passivation, should be considered when designing advanced AZIBs. Moreover, these thorny issues are not independent but mutually reinforcing, covering many technical and processing parameters. Therefore, it is necessary to comprehensively summarize the issues facing Zn anodes and the corresponding strategies to develop roadmaps for the development of high-performance Zn anodes. Herein, the failure mechanisms of Zn anodes and their corresponding impacts are outlined. Recent progress on improving the stability of Zn anode is summarized, including structurally designed Zn anodes, Zn alloy anodes, surface modification, electrolyte optimization, and separator design. Finally, this review provides brilliant and insightful perspectives for stable Zn metal anodes and promotes the large-scale application of AZIBs in power grid systems.

Rational Design of Flexible Zn-Based Batteries for Wearable Electronic Devices

The advent of 5G and the Internet of Things has spawned a demand for wearable electronic devices. However, the lack of a suitable flexible energy storage system has become the "Achilles' Heel" of wearable electronic devices. Additional problems during the transformation of the battery structure from conventional to flexible also present a severe challenge to the battery design. Flexible Zn-based batteries, including Zn-ion batteries and Zn-air batteries, have long been considered promising candidates due to their high safety, eco-efficiency, substantial reserve, and low cost. In the past decade, researchers have come up with elaborate designs for each portion of flexible Zn-based batteries to improve the ionic conductivities, mechanical properties, environment adaptabilities, and scalable productions. It would be helpful to summarize the reported strategies and compare their pros and cons to facilitate further research toward the commercialization of flexible Zn-based batteries. In this review, the current progress in developing flexible Zn-based batteries is comprehensively reviewed, including their electrolytes, cathodes, and anodes, and discussed in terms of their synthesis, characterization, and performance validation. By clarifying the challenges in flexible Zn-based battery design, we summarize the methodology from previous investigations and propose challenges for future development. In the end, a research paradigm of Zn-based batteries is summarized to fit the burgeoning requirement of wearable electronic devices in an iterative process, which will benefit the future development of Zn-based batteries.

Molecular-Crowding Effect Mimicking Cold-Resistant Plants to Stabilize the Zinc Anode with Wider Service Temperature Range

Growth of dendrites, the low plating/stripping efficiency of Zn anodes, and the high freezing point of aqueous electrolytes hinder the practical application of aqueous Zn-ion batteries. Here, a zwitterionic osmolyte-based molecular crowding electrolyte is presented, by adding betaine (Bet, a by-product from beet plant) to the aqueous electrolyte, to solve the abovementioned problems. Substantive verification tests, density functional theory calculations, and ab initio molecular dynamics simulations consistently reveal that side reactions and growth of Zn dendrites are restrained because Bet can break Zn²⁺ solvation and regulate oriented 2D Zn²⁺ deposition. The Bet/ZnSO₄ electrolyte enables superior reversibility in a Zn-Cu half-cell to achieve a high Coulombic efficiency >99.9% for 900 cycles (≈1800 h), and dendrite-free Zn plating/stripping in Zn-Zn cells for 4235 h at 0.5 mA cm^-2 and 0.5 mAh cm^-2 . Furthermore, a high concentration of Bet lowers the freezing point of the electrolyte to -92 °C via the molecular-crowding effect, which ensures the stable operation of the aqueous batteries at -30 °C. This innovative concept of such a molecular crowding electrolyte will inject new vitality into the development of multifunctional aqueous electrolytes.

Opportunities of Flexible and Portable Electrochemical Devices for Energy Storage: Expanding the Spotlight onto Semi-solid/Solid Electrolytes

The ever-increasing demand for flexible and portable electronics has stimulated research and development in building advanced electrochemical energy devices which are lightweight, ultrathin, small in size, bendable, foldable, knittable, wearable, and/or stretchable. In such flexible and portable devices, semi-solid/solid electrolytes besides anodes and cathodes are the necessary components determining the energy/power performances. By serving as the ion transport channels, such semi-solid/solid electrolytes may be beneficial to resolving the issues of leakage, electrode corrosion, and metal electrode dendrite growth. In this paper, the fundamentals of semi-solid/solid electrolytes (e.g., chemical composition, ionic conductivity, electrochemical window, mechanical strength, thermal stability, and other attractive features), the electrode-electrolyte interfacial properties, and their relationships with the performance of various energy devices (e.g., supercapacitors, secondary ion batteries, metal-sulfur batteries, and metal-air batteries) are comprehensively reviewed in terms of materials synthesis and/or characterization, functional mechanisms, and device assembling for performance validation. The most recent advancements in improving the performance of electrochemical energy devices are summarized with focuses on analyzing the existing technical challenges (e.g., solid electrolyte interphase formation, metal electrode dendrite growth, polysulfide shuttle issue, electrolyte instability in half-open battery structure) and the strategies for overcoming these challenges through modification of semi-solid/solid electrolyte materials. Several possible directions for future research and development are proposed for going beyond existing technological bottlenecks and achieving desirable flexible and portable electrochemical energy devices to fulfill their practical applications. It is expected that this review may provide the readers with a comprehensive cross-technology understanding of the semi-solid/solid electrolytes for facilitating their current and future researches on the flexible and portable electrochemical energy devices.

Electrolyte Engineering Enables High Performance Zinc-Ion Batteries

Zinc-ion batteries (ZIBs) feature high safety, low cost, environmental-friendliness, and promising electrochemical performance, and are therefore regarded as a potential technology to be applied in large-scale energy storage devices. However, ZIBs still face some critical challenges and bottlenecks. The electrolyte is an essential component of batteries and its properties affect the mass transport, energy storage mechanisms, reaction kinetics, and side reactions of ZIBs. The adjustment of electrolyte formulas usually has direct and obvious impacts on the overall output and performance. In this review, advanced electrolyte strategies are overviewed for optimizing the compatibility between cathode materials and electrolytes, inhibiting anode corrosion and dendrite growth, extending electrochemical stability windows, enabling wearable applications, and enhancing temperature tolerance. The underlying scientific mechanisms, electrolyte design principles, and recent progress are presented to provide a better understanding and inspiration to readers. In addition, a comprehensive perspective about electrolyte design and engineering for ZIBs is included.

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

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

From room temperature to harsh temperature applications: Fundamentals and perspectives on electrolytes in zinc metal batteries

As one of the most competitive candidates for the next-generation energy storage systems, the emerging rechargeable zinc metal battery (ZMB) is inevitably influenced by beyond-room-temperature conditions, resulting in inferior performances. Although much attention has been paid to evaluating the performance of ZMBs under extreme temperatures in recent years, most academic electrolyte research has not provided adequate information about physical properties or practical testing protocols of their electrolytes, making it difficult to assess their true performance. The growing interest in ZMBs is calling for in-depth research on electrolyte behavior under harsh practical conditions, which has not been systematically reviewed yet. Hence, in this review, we first showcase the fundamentals behind the failure of ZMBs in terms of temperature influence and then present a comprehensive understanding of the current electrolyte strategies to improve battery performance at harsh temperatures. Last, we offer perspectives on the advance of ZMB electrolytes toward industrial application.

Initiating a high-temperature zinc ion battery through a triazolium-based ionic liquid

Triazolium-based ionic liquids (T1, T2 and T3) with or without terminal hydroxyl groups were prepared via Cu(i) catalysed azide–alkyne click chemistry and their properties were investigated using various technologies. The hydroxyl groups obviously affected their physicochemical properties, where with a decrease in the number of hydroxyl groups, their stability and conductivity were enhanced. T1, T2 and T3 showed relatively high thermal stability, and their electrochemical stability windows (ESWs) were 4.76, 4.11 and 3.52 V, respectively. T1S-20 was obtained via the addition of zinc trifluoromethanesulfonic acid (Zn(CF₃SO₃)₂) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to T1, displaying conductivity and ESW values of 1.55 × 10⁻³ S cm⁻¹ and 6.36 V at 30 °C, respectively. Subsequently, a Zn/Li₃V₂(PO₄)₃ battery was assembled using T1S-20 as the electrolyte and its performances at 30 °C and 80 °C were investigated. The battery showed a capacity of 81 mA h g⁻¹ at 30 °C, and its capacity retention rate was 89% after 50 cycles. After increasing the temperature to 80 °C, its initial capacity increased to 111 mA h g⁻¹ with a capacity retention rate of 93.6% after 100 cycles, which was much higher than that of the aqueous electrolyte (WS-20)-based zinc ion battery (71.8%). Simultaneously, the T1S-20 electrolyte-based battery exhibited a good charge/discharge efficiency, and its Coulomb efficiency was 99%. Consequently, the T1S-20 electrolyte displayed a better performance in the Zn/Li₃V₂(PO₄)₃ battery than that with the aqueous electrolyte, especially at high temperature.

ZIB with T1S-20 electrolyte displays good charge/discharge performances and dendrite-free structure at high temperature, which is better than that with aqueous electrolyte (WS-20).

New Phosphate Zn2Fe(PO4)2 Cathode Material for Nonaqueous Zinc Ion Batteries with Long Life Span

Phosphate-based cathode materials attract much more attention and are widely used as energy storage materials based on their high economic efficiency and eco-friendly property, their stable potential plateau, and their high thermodynamic stability. A new phosphate family member, Zn₂Fe(PO₄)₂ (ZFP), was successfully explored and synthesized by the scalable high-temperature annealing method, followed by coating a thin carbon layer to optimize the electrotonic conductivity. This obtained ZFP featuring with a tunnel structure can be utilized as a cathode material for Zn²⁺ ion extraction and insertion, in which Zn²⁺ ion diffusion behaviors primarily contribute the specific capacity. Based on the actual reversible capacity of ZFP@C of 73 mA h g^-1, the application for zinc ion batteries (ZIBs) has potential due to its long life span. The electrochemical performance is primarily contributed from the high Zn²⁺ ion diffusion rate and low apparent activation energy. This new explored ZFP can accelerate the development of realizing ZIBs with long life span.

Potassium Polyacrylate-Based Gel Polymer Electrolyte for Practical Zn-Ni Batteries

Because of their high theoretical value of volumetric energy density, excellent rate performance, and high level of safety, zinc-nickel batteries (ZNBs) show potential applications for uninterrupted power supply (UPS) systems. However, despite all the advantages of ZNBs, the commercial application of ZNBs has been prevented by their short lifetime caused by the shape change, the corrosion, and the dendrite formation of the Zn anode. In this work, we proposed a flexible and durable potassium polyacrylate (PAAK)-KOH gel polymer electrolyte (GPE) prepared in a very simple way to solve the above problems of the Zn anode. The obtained highly porous gel electrolyte showed higher water retention, satisfying ionic conductivity (0.918 S cm-1), and a broad electrochemical stable voltage window. By providing a stable and homogeneous electrode/electrolyte interface for the Zn anode, the gel electrolyte can inhibit the uneven deposition and dendrite formation. As a result, the gel electrolyte greatly prolonged the cycling life to 776 h. In addition, because of the considerably batter corrosion resistance of the Zn anode in the PAAK-KOH GPE, the ZNB with gel electrolyte also exhibited a superior shelf life of more than 431 h and a superior cycling performance under float charge for more than 400 h at 60 °C. This work demonstrates that the gel electrolyte with a simple preparation method is suitable for large-scale practical production and can be successfully used in Zn-Ni batteries as an electrolyte exhibiting excellent performance.

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

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

Ultra-High-Capacity and Dendrite-Free Zinc-Sulfur Conversion Batteries Based on a Low-Cost Deep Eutectic Solvent

Traditional cathodes for aqueous Zn-ion batteries are afflicted by a limited specific capacity and fearful Zn dendrites. Herein, these troubles are disposed of with a conversion-type Zn-S battery and low-cost deep eutectic solvent (DES). By utilizing the optimized electrolyte, the symmetrical Zn battery can stably cycle over 3920 h, which also confers on the Zn-S battery an ultrahigh specific capacity of ∼846 mA h g_S^-1 and energy density of 259 W h kg^-1 at 0.5 A g^-1. Importantly, the conversion chemistry of S and ZnS is responsible for the superior anti-self-discharge behavior (capacity retention: 94.58 and 68.58% after standing for 72 and 288 h versus Zn//VO₂ battery: 76.82 and 47.80% after resting for 24 and 72 h versus Zn//MnO₂ battery: 95.96 and 91.57% after resting for 24 and 72 h, respectively). This work is the first authentication of Zn-S batteries based on a newly developed low-cost DES-based electrolyte, which meanwhile settles the deep-rooted low specific capacity and infamous Zn dendrite issues in conventional (de)intercalation Zn-ion batteries.

Dendrites-Free Zn Metal Anodes Enabled by an Artificial Protective Layer Filled with 2D Anionic Nanosheets

Metallic zinc (Zn) has been considered to be an ideal anode material for aqueous batteries, but is impeded by the growth of Zn dendrites and its side reactions with an aqueous electrolyte. Here, it is reported that an artificial protective layer filled with novel 2D Zn²⁺ adsorbed Sb₃ P₂ O₁₄ ^3- (denoted as Zn-Sb₃ P₂ O₁₄ ) nanosheets provide an effective route to mitigate the above challenging problems. The Zn-Sb₃ P₂ O₁₄ protection layer not only avoids the direct contact with the aqueous electrolyte to suppress the side reactions but also allows for Zn-ions to pass through the protection layer rapidly. Moreover, the 2D Sb₃ P₂ O₁₄ ^3- skeleton with negative charge also confines the 2D diffusion of Zn-ion along the lateral surface of Zn anode, resulting in a uniform electron-deposition. This unique protection layer not only enables dendrite-free Zn plating/stripping with an average Coulombic efficiency of 99.2% for 200 cycles, but also sustains the symmetric Zn||Zn cell over 1300 h at 1 mA cm^-2 and 1 mAh cm^-2 as well as for 450 h at 10 mA cm^-2 and 10 mAh cm^-2 . Such advantages bring high reversibility to full Zn batteries with MnO₂ cathodes, which deliver a discharge capacity of 111.7 mAh g^-1 after 1000 cycles.

Tremella-like Hydrated Vanadium Oxide Cathode with an Architectural Design Strategy toward Ultralong Lifespan Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising systems for energy storage due to their operational safety, low cost, and environmental friendliness. However, the development of suitable cathode materials is plagued by the sluggish dynamics of Zn²⁺ with strong electrostatic interaction. Herein, an Al³⁺-doped tremella-like layered Al_0.15V₂O₅·1.01H₂O (A-VOH) cathode material with a large pore diameter and high specific surface area is demonstrated to greatly boost electrochemical performance as ZIB cathodes. Resultant ZIBs with a 3 M Zn(CF₃SO₃)₂ electrolyte deliver a high specific discharge capacity of 510.5 mAh g^-1 (0.05 A g^-1), and an excellent energy storage performance is well maintained with a specific capacity of 144 mAh g^-1 (10 A g^-1) even after ultralong 10,000 cycles. The decent electrochemical performance roots in the novel tremella-like structure and the interlayer of Al³⁺ ions and water molecules, which could improve the electrochemical reaction kinetics and structural long cycle stability. Furthermore, the assembled coin-type cells could power a light-emitting diode (LED) lamp for 2 days. We believed that the design philosophy of unique morphology with abundant active sites for Zn²⁺ storage will boost the development of competitive cathodes for high-performance aqueous batteries.

Sodium Alginate Binders for Bivalency Aqueous Batteries

Environmental friendly sodium alginate (SA) cannot be used as a binder in aqueous batteries due to its high solubility in water. A water-insoluble polyvinylidene difluoride (PVDF) binder has been widely applied for an aqueous battery, in which the toxic and expensive organic solvent of N-methy-2-pyrrolidone (NMP) is required during the coating process. Herein, we report that the water-soluble SA can be utilized as a binder in aqueous Zn batteries because SA could cross-link with the Zn²⁺ ion to form a water-insoluble and mechanically super strong binder for electrodes. Aqueous Zn||LiFePO₄ cells are assembled to demonstrate the performance of the SA binder for LiFePO₄ cathodes. Due to the high adhesion strength of cross-linked Zn-SA, LiFePO₄ with the SA binder displays a high capacity retention of 93.7% with a high Coulombic efficiency of nearly 100% after 100 cycles at a 0.2 C rate, while the capacity of LiFePO₄ with the PVDF binder quickly decays to 84.7% after 100 cycles at 0.2 C. In addition, the LiFePO₄ cathode with the SA binder also has smaller redox polarization, faster ion diffusion rate, and more favorable electrochemical kinetics than that with the PVDF binder.