Metal-Organic Frameworks Functionalized Separators for Robust Aqueous Zinc-Ion Batteries

Ti2O3(H2PO4)2·2H2O as a Novel Intercalated Anode for Ultralong Lifespan "Rocking-Chair" Aqueous Zinc-Ion Batteries

The application of aqueous zinc-ion batteries (AZIBs) with Zn metal anode is hindered by severe dendritic growth, corrosion, and inefficient Zn utilization. "Rocking-chair" type AZIBs are considered a viable approach toward practical applications due to the success of commercial lithium-ion batteries employing intercalated graphite anodes. Herein, a new type of layered titanium phosphate Ti2O3(H2PO4)2·2H2O is proposed for the first time as the intercalated anodes for AZIBs, exhibiting a capacity of 108 mAh g-1 at 50 mA g-1, with a low discharge potential of 0.17 V (vs. Zn2+/Zn). The ion insertion process is thoroughly investigated, and a micro-dendrite growth-corrosion mode is proposed to explain the capacity degradation mechanism. Corresponding countermeasures are designed, resulting in a significant improvement in cycle life. When coupled with a zinc hexacyanoferrate (KZnHCF) cathode, the "rocking-chair" full battery exhibits an ultralong lifespan of 50000 cycles (111 days) at 2000 mA g-1 with 94% capacity retention. This work presents a novel perspective for the development of practical AZIBs.

Breaking Performance Limits of Zn Anodes in Aqueous Batteries by Tailoring Anion and Cation Additives

Crystallographic engineering of Zn anodes to favor the exposure of (002) planes is an effective approach for improving stability in aqueous electrolytes. However, achieving non-epitaxial electrodeposition with a pronounced (002) texture and maintaining this orientation during extended cycling remains challenging. This study questions the prevailing notion that a single (002)-textured Zn anode inherently ensures superior stability, showing that such anodes cannot sustain their texture in ZnSO4 electrolytes. We then introduced a novel electrolyte additive, benzyltriethylammonium chloride (TEBAC), which preserves the (002) texture over prolonged cycling. Furthermore, we successfully converted commercial Zn foils into highly crystalline (002)-textured Zn without any pretreatment. Experiments and theoretical calculations revealed that the cationic TEBA+ selectively adsorbs onto the anode surface, promoting the exposure of the Zn(002) plane and suppressing dendrite formation. A critical discovery was the pitting corrosion caused by chloride ions from TEBAC, which we mitigated by anion substitution. This modification leads to a remarkable lifespan of 375 days for the Zn||Zn symmetric cells at 1 mA cm-2 and 1 mAh cm-2. Furthermore, a TEBA+-modified Zn||VO2 full cell demonstrates high specific capacity and robust cycle stability at 10.0 A g-1. These results provide valuable insights and strategies for developing long-life Zn ion batteries.

Hydrazide chemistry for durable, dendrite-free zinc anodes: Insights into solvation structures and electrolyte interfaces

The practical application of aqueous Zn-ion batteries (AZIBs) is impeded by intrinsic limitations of Zn metal anode. Herein, benzoyl hydrazine (BH), incorporating multiple functional groups, serves as an electrolyte additive to mitigate interfacial side reactions and thereby enhancing its cycling durability. Experimental characterizations incorporating with theoretical simulations reveal that the BH molecule can not only reconstruct the solvation configuration by replacing the coordinated water of hydrated Zn2+, but strengthen hydrogen-bond network by forming strong hydrogen bonds, thus suppressing proton transport and active water decomposition. Additionally, BH molecules adsorb onto the Zn anode surface, establishing a versatile protective interfacial layer: hydrophobic benzene ring ligand can impede the direct desolvation of [Zn(H2O)6]2+ on the anode surface; nucleophilic sites coordinate desolvated Zn2+, modulating its flux to promote uniform Zn deposition and stripping. Consequently, Zn//Zn cells with low dosage of BH display a extended cycle life of 1200 h, and Zn//Cu cells run stably for 600 h with maintaining a high coulombic efficiency of 99.55 %. Moreover, Zn//MnO2 full cells with 10 mM BH exhibited superior capacity retention after 1400 cycles. This work proposes a practical strategy by harnessing hydrazide chemistry to facilitate the development of AZIBs.

Robust zincophilic-hydrophobic protection layer induces preferential growth of (0 0 2) crystal plane towards ultra-stable Zn anode

The practical deployment of aqueous zinc-ion batteries (AZIBs) in large-scale energy storage applications is hampered by short cycle lifespans and limited zinc utilization due to uncontrollable dendrite growth and water-induced side reactions. Herein, we propose an environmentally friendly electrolyte additive, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), which features dual zincophilic sites and a hydrophobic group, to enhance Zn stability. Theoretical calculations and experimental characterizations demonstrate that AMPS can firmly adsorb onto the Zn (0 0 2) plane through its dual zincophilic sites (SO3H and NHCO), while the CC hydrophobic group orients toward the electrolyte, ultimately forming a stable zincophilic/hydrophobic interface on the Zn electrode in situ. This unique structure not only inhibits water-induced side hydrogen evolution reactions but also induces preferential deposit propagation along the (0 0 2) crystal plane. Benefiting from this synergetic effect, the Zn//Cu asymmetric cell with AMPS electrolyte maintains an ultrahigh average coulombic efficiency of 99.8 % for over 2500 cycles at 2 mA cm-2, achieving 1 mAh cm-2. Furthermore, the Zn//MnO2 full cell shows a high-capacity retention of 67.7 % at 1.8 A g-1 after 1000 cycles, confirming the effectiveness of the AMPS additive in improving the cyclability and performance of AZIBs.

Self-adsorbing electrolyte additive promoting Zn(002) deposition on Zn anode for aqueous zinc-ion battery

The poor cycling stability of aqueous zinc-ion batteries (AZIBs), caused by zinc dendrite growth and surface corrosion-induced passivation at the zinc anode, significantly hinders their practical development. In this work, 7-(2,3-dihydroxypropyl)theophylline (DHTP) is introduced as a functional additive into Zn(CF3SO3)2 (ZOT) electrolyte to regulate the anode-electrolyte interface and mitigate side reactions. Theoretical calculations and experimental characterizations reveal that DHTP preferentially adsorbs on the zinc anode, reducing direct water contact and thereby suppressing hydrogen evolution and corrosion reactions. Notably, DHTP exhibits the lowest adsorption energy on the Zn(002) crystal plane, which optimizes Zn2+ diffusion and deposition behavior, guiding the preferential growth of the Zn(002) plane. Benefiting from this, the Zn||Zn symmetric cell with DHTP achieves stable cycling for over 800 h at 1 mA cm-2 and 1 mAh cm-2, outperforming the bare electrolyte. Furthermore, the Zn||NaV3O8·1.5H2O full cell demonstrates exceptional durability of 9,000 cycles with a remarkable capacity retention of 89 % under a high current density of 10 A g-1. This molecular adsorption strategy based on DHTP provides a novel approach to constructing highly reversible zinc anodes for advanced AZIBs.

Aspartame Endowed ZnO-Based Self-Healing Solid Electrolyte Interface Film for Long-Cycling and Wide-Temperature Aqueous Zn-Ion Batteries

Metallic Zn anodes suffer from hydrogen evolution and dendritic deposition in aqueous electrolytes, resulting in low Coulombic efficiency and poor cyclic stability for aqueous Zn-ion batteries (AZIBs). Constructing stable solid electrolyte interphase (SEI) with strong affinity for Zn and exclusion of water corrosion of Zn metal anodes is a promising strategy to tackle these challenges. In this study, we develop a self-healing ZnO-based SEI film on the Zn electrode surface by employing an aspartame (APM) as a versatile electrolyte additive. The hydrophobic nature and strong Zn affinity of APM can facilitate the dynamic self-healing of ZnO-based SEI film during cyclic Zn plating/stripping process. Benefiting from the superior protection effect of self-healing ZnO-based SEI, the Zn║Cu cells possess an average coulombic efficiency more than 99.59% over 1,000 cycles even at a low current density of 1 mA cm-2 - 1 mAh cm-2. Furthermore, the Zn║NH4+-V2O5 full cells display a large specific capacity of 150 mAh g-1 and high cyclic stability with a capacity retention of 77.8% after 1,750 cycles. In addition, the Zn║Zn cell delivers high temperature adaptability at a wide-temperature range from - 5 to 40 °C even under a high DOD of 85.2%. The enhanced capability and durability originate from the self-healing SEI formation enabled by multifunctional APM additives mediating both corrosion suppression and interfacial stabilization. This work presents an inspired and straightforward approach to promote a dendrite-free and wide-temperature rechargeable AZIBs energy storage system.

Advanced Alkali Metal Batteries Based on MOFs and Their Composites

The integration of metal-organic frameworks (MOFs) with functional materials has established a versatile platform for a wide range of energy storage applications. Due to their large specific surface area, high porosity, and tunable structural properties, MOFs hold significant promise as components in energy storage systems, including electrodes, electrolytes, and separators for alkali metal-ion batteries (AIBs). Although lithium-ion batteries (LIBs) are widely used, their commercial graphite anode materials are nearing their theoretical capacity limits, and the scarcity of lithium and cobalt resources increases costs. Although zinc-ion batteries (ZIBs) suffer from limited cycling stability, they are attractive for their low cost, high capacity, and excellent safety. Meanwhile, potassium-ion (PIBs) and sodium-ion batteries (SIBs) show promise due to their affordability and abundant resources, but they encounter issues such as short cycle life and low energy density. This review outlines the applications of MOF composites in LIBs, SIBs, and ZIBs, introduces common synthesis methods, and forecasts future development directions and challenges in energy storage applications. We emphasize how the understanding can lay the foundation for developing MOF composites with enhanced functionalities.

Recent advances in cellulose-based separators for zinc ion batteries: A review

Aqueous zinc ion batteries (AZIBs) have attracted increasing attention because of their high energy density, excellent safety features, and environmentally friendly properties. The separator plays a crucial role in the battery, greatly influencing its performance and stability. Therefore, the separator for AZIBs has attracted increasing interest in recent years. Glass fiber (GF) is the predominant separator material, and exhibits favorable hydrophilicity and remarkable ionic conductivity. Nevertheless, its internal inhomogeneous pore structure makes it difficult to achieve uniform deposition of zinc ions, while the GF separator is easy to pierce due to its inadequate mechanical properties. In response to these issues, cellulose materials have garnered significant interest owing to their exceptional hydrophilicity, cost-effectiveness, and widespread availability. This review summarizes the potential of cellulose separators to substitute GF separators for AZIBs because of their high porosity, ion mobility number, electrolyte wetting rate, and liquid absorption rate. Different methods for preparing cellulose separators for AZIBs and various strategies to enhance their performance are summarized. The future outlook of cellulose-based separators for ZIBs is also prospected.

Dual-functional cellulose separator regulating Zn deposition for long lifespan zinc-based energy storage

Aqueous zinc-ion batteries (ZIBs) hold significant promise for next-generation energy storage due to their low cost and inherent safety, but their lifespan is limited by zinc dendrites and hydrogen evolution during the cycling. Herein, long lifespan ZIBs are achieved using a dual-functional separator with ultrathin (18 μm) and high mechanical strength (91 MPa). The abundant polar hydroxyl groups in the separator's structure repel free SO42- anions, accelerate the Zn2+ ion transport, and modify the solvation structure of Zn(H2O)62+, ensuring uniform Zn2+ ion flux and inhibiting zinc dendrite formation. Consequently, the Zn//Zn symmetrical cells with dual-functional separators exhibit superior electrochemical performance, with a cycle life exceeding 1100 h at 1 mA cm-2 and 440 h at 10 mA cm-2, 5-9 times longer than cells using glass-fiber separators. The zinc-ion hybrid supercapacitor with the functional separator achieves a high capacity retention ratio (93.1 %) after 1000 cycles at 1.0 A g-1. This work offers new insights into the development of multifunctional separator for high-performance zinc-based energy storage.

Towards Ultra-Stable Wide-Temperature Zinc-Ion Batteries by Using Ion-Sieving Organic Framework Membrane

Aqueous zinc-ion batteries (AZIBs) offer notable advantages in safety and cost-efficiency, but Zn dendrite growth and unstable interfacial reactions hinder their commercial viability. A crucial factor in addressing these challenges lies in optimizing the separator to regulate ion transport and stabilize electrode interfaces. Herein, we propose a covalent organic framework (COF)-based separator with quasi-single-ion conduction, specifically a Zn2+-substituted sulfonate COF (COF-Zn) membrane, designed to tackle these issues. Featuring a high Zn transference number (0.87) and a thin 25 μm profile, the COF-Zn separator allows for reduced electrolyte usage (20 μL mg-1) while effectively minimizing cathode dissolution. Its quasi-single-ion conductivity and electronegative properties improve Zn anode's stability by lowering water activity. This separator enables ultra-stable AZIBs, as demonstrated in various full cells including Zn//4,5,9,10-pyrenetetrone (PTO), Zn//I2 and Zn//V2O5. Remarkably, the Zn//PTO cell achieves an energy density of 260 Wh kg-1, 100 % capacity retention under reduced electrolyte conditions, and stable all-weather cycling from -40 to +100 °C with a customized electrolyte.

Regulating Extra-Layer Ion Channels in the Conductive V2O5 Hydrogel Cathode

High-power energy storage devices rely on the synergistic coordination of ion and electron transport. Here, an extra-layer channels engineering strategy is presented for developing high power and energy density cathode materials for aqueous zinc batteries (AZIBs). This approach utilizes a cation-induced self-assembly process to form conductive hydrogels with extra-layer channels by adding diverse cations (Li+, Na+, K+, Mg2+, Zn2+, Al3+, and NH4 +) into the carbon nanotubes (CNTs) ink dispersed hydrated V2O5 (h-V2O5) nanowires. The cations bridge h-V2O5 nanowires and create self-assembly network on the CNT surfaces, providing extra-layer ion channels beyond the intrinsic interlayer of h-V2O5. These external channels exhibit distinct properties depending on the cations, significantly influencing the performance of V2O5 hydrogel cathode for AZIBs. Larger cations reduce Zn2+ migration resistance enhancing diffusion kinetics; smaller cations strengthen the M─O bond, improving structural stability. For instance, K-V2O5/CNT demonstrates an initial specific capacity of up to 618 mAh g-1 at 0.2 A g-1 and retains a capacity of 248 mAh g-1 even at 20 A g-1. In contrast, the Zn-V2O5/CNT maintains excellent cycling stability, with 230 mAh g-1 after 700 cycles at 1 A g-1. This offers a versatile platform for tailoring ion transport channels in hydrogel cathodes for ZIBs.

Regulating Interfacial Molecular Configuration to Drive Facet-Selective Zn Metal Deposition

The direct use of metal anode emerges as a key strategy in advancing high-energy-density batteries, applicable across non-protonic, aqueous, and solid-state battery systems. To enhance battery durability, one effective approach involves employing interfacial molecular modification to modulate metal's facet orientation, reducing the tendency of metals to form random and loose morphologies during deposition. Herein, we propose a model to elucidate how dicarboxylic acid molecules with varying alkyl chain lengths modulate their adsorption behavior and deposition rate on zinc (Zn) surfaces, achieving facet-selective Zn deposition. Taking glutaric acid (GA) as an example, its medium alkyl chain length allows for a "flat-lying" adsorption configuration on Zn(002) surface, resulting in strong adsorption and Zn-GA metal-molecule bridging interface. This regulates Zn2+ diffusion process and restricts its accessibility to Zn(002) facet, facilitating the selective exposure of Zn(002) facet. Due to this design, the Zn||Zn symmetric cell stably operates at a high current density of 20 mA cm-2 and a high depth of discharge of 85%. The Zn||MnO2 pouch cell achieves a high capacity of 1.1 Ah with 90% capacity retention. This metal-molecule interface design can be extended to other metal anodes, with the potential for tailored molecular selections to regulate the selective growth of crystal facets.

Dissecting ionic favorable hydrogen bond chemistry in hybrid separators for aqueous zinc-ion batteries

Separators, regulating the ion transport channels between electrodes, are crucial for maintaining the properties of electrochemical batteries. However, sluggish ion transport and desolvation kinetics in aqueous zinc-ion batteries (AZIBs) cause uneven ion flux at the separator-electrode interface, accelerating Zn dendrite growth. Herein, we systematically dissect ionic favorable hydrogen bond chemistry in a hybrid separator engineered through rational boron nitride (BN) doping into polyacrylonitrile (PAN) separators. Notably, in situ Fourier transform infrared spectroscopy (FTIR) analyses reveal that the hydrogen bond network in a BN-PAN separator improved the desolvation of Zn2+ by immobilizing water molecules through hydrogen bond interactions, thus effectively increasing the transference number of zinc ions. Capitalizing on the ionic favorable properties, uniform electric field distribution and zinc plating/stripping behavior are achieved at the separator-electrode interface, efficiently suppressing the formation of zinc dendrites and by-products. As a result, the BN-PAN separator demonstrates extended cycling stability, exceeding 1100 h at a current density of 1.0 mA cm-2 and 700 h at a current density of 5.0 mA cm-2, while exhibiting enhanced rate capability and stability in full cells. This work offers valuable insights into leveraging hydrogen bond chemistry for the design of fast ion-transport separators in aqueous batteries.

Construction of amino functional metal-organic framework modified aramid composite separators with high Li+ transport channels for dendrite-free lithium-ion batteries

The formation and growth of lithium dendrites is an ever-present and urgent problem in lithium-ion batteries (LIBs). At the same time, the low melting point of commercial polyolefin separators may lead to safety issues during application. On this basis, in this work, poly (m-phenylene isophthalamide) (PMIA)/Zr-based metal-organic framework (NH2-UiO-66) composite separator was prepared by non-solvent induced phase separation (NIPS). Firstly, the substantial quantity of Lewis acid sites and channels present in NH2-UiO-66 plays a great role in obstructing anions in electrolytes while improving the transport of lithium-ion (Li+). Besides, simultaneously, because of the incorporation of -NH2 within NH2-UiO-66, electrolyte uptake and retention were further enhanced, while the resistance to Li+ migration is reduced, resulting in a lower interfacial impedance (the interface resistance is 2.3 Ω). And the ion conductivity of the PMIA/NH2-UiO-66 composite separator is measured at 0.79 mS/cm, with a Li+ migration number also at 0.79, indicating superior performance. Furthermore, when MOF nanoparticles are incorporated into PMIA, the exposed Zr sites significantly increase the lithium affinity. It also regulates the Li+ transport path at the electrolyte-anode interface, resulting in a uniform and smooth Li metal surface topography after cycling, achieving excellent electrochemical performance, and ensuring long-term electrochemical stability over a wide range. The results show that the battery constructed using PMIA/NH2-UiO-66 composite separator demonstrated outstanding rate performance and cycling stability. In a word, the designed PMIA/NH2-UiO-66 composite separator provides an innovative way to develop high-performance separators in LIBs.

Comprehensive Experimental Insights into Ultra-Long Cycle Life of Zinc-Ion Batteries Inspired by Super Low Concentrations of a Derivative of Urea in the Zinc Sulfate Electrolyte

In this study, a low-cost and friendly compound diazolidinylurea carrying a number of heteroatoms and inter/intra hydrogen bonding, a derivative of urea (DU), efficiently strengthened aqueous zinc ions batteries (AZIBs) in ZnSO4 electrolyte. The influence of DU on the zinc anode in the 2 M ZnSO4 electrolyte was fully studied by various surface chemistry and electrochemistry means. It is demonstrated that the super low concentration of DU (2 mM, 0.00556 wt %) could inhibit the formation of zinc dendrites, zinc corrosion, and the hydrogen evolution reaction during the constant current cycling of water system ZIBs, which thus enabled symmetric zinc-zinc batteries to reach a cycle life of 7336 h (nearly 306 days) under 1 mA·cm-2, 1 mA h·cm-2 at 25 °C and 426 h (nearly 18 days) at 55 °C, and inspired zinc-manganese full battery to maintain a capacity retention rate of more than 52% after cycling for 1000 cycles under a current of 2 A·g-1. These results are much superior over zinc ion cells based on the blank ZnSO4 batteries. Even if the Zn-Cu half cells including the DU/2 M ZnSO4 electrolyte were also more pronounced than those with the bare ZnSO4 electrolyte. The maximum corrosion inhibition efficiency of the DU for the zinc electrode in ZnSO4 solution exceeded 82%. Hence, the suppression of zinc corrosion and parasitic side reactions, as well as the formation and growth of zinc dendritic crystals by the addition of DU in zinc sulfate electrolyte, played a central role in intensifying aqueous zinc ion batteries.

Uniform single-crystal mesoporous metal-organic frameworks

The synthesis of mesoporous metal-organic frameworks (meso-MOFs) is desirable as these materials can be used in various applications. However, owing to the imbalance in structural tension at the micro-scale (MOF crystallization) and the meso-scales (assembly of micelles with MOF subunits), the formation of single-crystal meso-MOFs is challenging. Here we report the preparation of uniform single-crystal meso-MOF nanoparticles with ordered mesopore channels in microporous frameworks with definite arrangements, through a cooperative assembly method co-mediated by strong and weak acids. These nanoparticles feature a truncated octahedron shape with variable size and well-defined two-dimensional hexagonally structured (p6mm) columnar mesopores. Notably, the match between the crystallization kinetics of MOFs and the assembly kinetics of micelles is critical for forming the single-crystal meso-MOFs. On the basis of this strategy, we have constructed a library of meso-MOFs with tunable large pore sizes, controllable mesophases, various morphologies and multivariate components.

Eco-friendly and strong lignin-containing microfibrillated cellulose films for high-performance separators of aqueous zinc batteries

Aqueous zinc-ion batteries have gained significant interest, offering several distinct advantages over conventional lithium-ion batteries owing to their compelling low cost, enhanced battery safety, and excellent environmental friendliness. Nevertheless, the unfortunate growth of zinc dendrites during cycling leads to poor electrochemical performance of zinc batteries, primarily attributed to the diminished wet mechanical properties and limited electrolyte uptake of existing commercial separators. Herein, a bio-based separator was developed from sustainable resources using natural polymers derived from wood pulp to replace fossil-based polyolefin separators. The inherent hydrophilicity and swelling ability of cellulose fibers provide separators with superior electrolyte wettability and uptake. Notably, the structural reinforcement provided by lignin, especially after hot pressing, enhances the separator's wet mechanical integrity and performance during battery cycling. These improvements contribute to the separator's more stable electrochemical performance and improved ion transport properties. Separators composed of lignin-rich microfibrillated cellulose fibers showed superior dimensional stability under heat compared to Celgard, ensuring higher thermal safety and enhanced performance of aqueous zinc-ion batteries. Our results reveal the great potential of lignin-rich cellulose-based separators for future zinc-ion batteries.

Biomimetic and biodegradable separator with high modulus and large ionic conductivity enables dendrite-free zinc-ion batteries

The advancement of aqueous zinc-based batteries is greatly restricted by zinc dendrites. One potential solution to this challenge lies in the employment of high-modulus separators. However, achieving both high modulus and large ionic conductivity in a single separator remains a formidable task. Inspired by the wood architecture, this study breaks this trade-off by designing an anisotropic and biodegradable separator. This design significantly improves the modulus along the oriented direction while simultaneously facilitating fast Zn2+ ion transport through aligned vertical channels. Additionally, this configuration resolves the contradiction between low separator thickness and good dendrite-inhibition capability. These benefits are supported by finite element simulations and comprehensive experimental validation, which also underscore the critical role of modulus enhancement for separators. By employing the anisotropic separator, a prolonged life span is realized for Zn||Zn cells, along with improved cyclability in full batteries. This work presents a strategy for separator modification towards dendrite-free metal batteries.

Long-Life Zinc Anodes via Molecular-Layer-Deposited Inorganic-Organic Hybrid Titanicone Thin Films

Zinc-ion batteries (ZIBs) have consistently faced challenges related to the instability of the zinc anode. Uncontrolled dendrite growth, hydrogen evolution reaction (HER), and byproduct accumulation on the zinc anode severely affect the cycling life of ZIBs. Herein, inorganic-organic hybrid thin films of titanicones (Ti-based hydroquinone, TiHQ) were fabricated by molecular layer deposition (MLD) technology to modify the zinc metal anode. The MLD-based Zn@TiHQ anode suppresses the dendrite growth on the anode surface, reduces side reactions, and facilitates the desolvation and rapid transport of Zn2+ ions. As a result, it maintains an average Coulombic efficiency (CE) as high as 99.1% over 300 cycles at 0.5 mA cm-2 and 1 mAh cm-2, exhibiting excellent cycling stability for over 2800 h and enhancing the reversible capacity of the Zn@TiHQ||MnO2 full cell. This work demonstrates that the MLD-derived inorganic-organic hybrid TiHQ coating provides a more stable interfacial environment for the zinc anode, opening an avenue for designing high-performance zinc anodes.

Magnetic field-assisted vertically aligned NiFe2O4 nanosheets in composite solid polymer electrolytes for advanced all solid-state lithium metal batteries

Two-dimensional materials (2D Ms) as fillers have been applied in polyethylene oxide (PEO)-based electrolyte to enhance the low ionic conductivity and poor interface compatibility. However, the randomly dispersed fillers in PEO matrix result in anisotropy of Li+ transportation and insufficent ionic conductivity. Herein, NiFe2O4 (NFO) nanosheets are firstly introduced in polymer matrix to form vertically aligned NFO-PEO (ANFO-PEO) composite solid-state electrolytes (CSEs) through magnetic field-assisted alignment strategy. The vertically aligned NFO/PEO interface in CSEs can construct oriented Li+ transport channels and maximize the utilization of high in-plane conductivity. Meanwhile, the NFO nanosheets with abundant oxygen vacancies could effectively anchor TFSI- to promote the dissociation of Li salts. Furthermore, the optimized Li+ transport flux in CSEs enables homogeneous Li deposition and effectively mitigates the growth of dendrites. Owing to the synergistic effects, the ANFO-PEO CSEs exhibit high ionic conductivity (9.16 × 10-4 S cm-1 at 60 °C) and stable potential window up to 5.0 V vs Li/Li+. Therefore, LiFePO4 in the full cell and pouch cell with ANFO-PEO CSEs could deliver excellent cycling performance (92.78 % capacity retention after 1000 cycles at 0.5C; 96.88 % capacity retention after 105 cycles at 0.1C).

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

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

Advancing Anode Performance in Aqueous Zinc-Ion Batteries: A Review of Metal-Organic Framework-Based Strategies

Aqueous zinc-ion batteries (AZIBs) are garnering substantial research interest in electric vehicles, energy storage systems, and portable electronics, primarily for the reason that the inexpensive cost, high theoretical specific capacity, and environmental sustainability of zinc metal anodes, which are an essential component to their design. Nonetheless, the progress of AZIBs is hindered by significant obstacles, such as the occurrence of anodic side reactions (SR) and the formation of zinc dendrites. Metal-organic framework (MOF)-based materials are being explored as promising alternatives owing to homogeneous porous structure and large specific surface areas. There has been a rare overview and discussion on strategies for protecting anodes using MOF-based materials. This review specifically aims to investigate cutting-edge strategies for the design of highly stable MOF-based anodes in AZIBs. Firstly, the mechanisms of dendrites and SR are summarized. Secondly, the recent advances in MOF-based anodic protection including those of pristine MOFs, MOF composites, and MOF derivatives are reviewed. Furthermore, the strategies involving MOF-based materials for zinc anode stabilization are presented, including the engineering of surface coatings, three-dimensional zinc structures, artificial solid electrolyte interfaces, separators, and electrolytes. Finally, the ongoing challenges and prospective directions for further enhancement of MOF-based anodic protection technologies in AZIBs are highlighted.

Anti-dendrite separator interlayer enabling staged zinc deposition for enhanced cycling stability of aqueous zinc batteries

Aqueous zinc ion batteries exhibit great prospects due to their low cost and high safety, while their lifespan is limited by severe dendritic growth problems. Herein, we develop an anti-dendrite hot-pressing separator interlayer through a mass-producible hot-pressing strategy, by spreading metal-organic framework (MOF) precursor on nonwoven matrix followed by a simple hot-pressing process. The in situ modification of MOF crystals on fiber surface processes abundant nitrogenous functional groups and high specific surface area (190.8 m2 g-1) with a strong attraction to Zn2+. These features contribute to a staged deposition behavior to promote uniform nucleation at high concentrations and two-dimensional grain growth at low concentrations. Consequently, Zn | |Zn symmetrical cells with hot-pressing separator interlayer demonstrate cycle lives of 3000 hours at 2 mA cm-2, 2 mAh cm-2. Moreover, Zn | |I2 pouch batteries with hot-pressing separator interlayer realizes 840 cycles lifespan with a capacity retention of 90.9% and a final discharge capacity of 110.6 mAh at 25 °C.

Regulating Zn deposition via an ion-sieving, nanoporous cellulose separator for high performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs), one of the most promising renewable energy storage devices, are largely impeded by the disreputable cycling stability in its large-scale application as a result of the undesirable Zn dendrites growth and the side reactions. In this context, a carboxylate (-COO-) anionic group functionalized cellulose nanofibrils separator (A-CNF) with nanoporous structure and ion-sieving effect is developed to realize a stable Zn anode without dendrites and by-products. An increased Zn2+ transference number and uniform Zn deposition can be achieved through the electrostatic adsorption between -COO- and Zn2+. More importantly, the synergistic effect between -COO- and hydroxyl group (-OH) in the cellulose nanofibrils separator inhibits the occurrence of side reactions caused by SO42- and free water molecules. As a result, the nanoporous separator consisting of carboxylated cellulose nanofibrils enables Zn anode with high stability and utilization, exhibiting a stable cycling life for 950 h in Zn//Zn cell and an admirable coulombic efficiency of 98.9 % after 300 cycles in Zn//Cu cell. The assembled Zn//MnO2 full cell with the nanoporous cellulose nanofibrils-based separator shows exceptional cyclability and capacity retention after 1000 cycles. This work provides a valuable and practical separator for high performance AZIBs, which might spur its practical application.

Stable Zinc Metal Battery Development: Using Fibrous Zirconia for Rapid Surface Conduction of Zinc Ions With Modified Water Solvation Structure

The two most critical technical issues in Zn-based batteries, dendrite formation, and hydrogen evolution reaction, can be simultaneously addressed by introducing negatively charged fibrous ZrO2 as a separator. Electron redistribution between ZrO2 and Zn2+ ions renders the ZrO2 surface a preferred adsorption site for Zn2+ ions, making surface conduction the primary ion-transport mode. Surface conduction enables fibrous ZrO2 to exhibit a 6.54 times higher single-Zn-ion conductivity than that of conventional glass fiber, minimizing the concentration gradient of Zn2+ and suppressing dendrite formation. Additionally, strong Zr─O─Zn bonding stabilizes the Zn2+ ions with fewer solvated H2O molecules (≈2), preventing water molecules from approaching the electrode surface, as evidenced by a 58.8% decrease in the hydrogen evolution rate. Consequently, the cycling stability of a fibrous-ZrO2-based Zn/Zn symmetric cell (3000 h at 1 mAh cm-2 and 5 mA cm-2) is approximately ten times greater than that of the conventional variant. Furthermore, a fibrous-ZrO2-based Zn-I2 full cell exhibits a notably high energy density (271.4 Wh kg-1) as well as a long lifespan (≈5000 cycles) at an ultrahigh current density (4 A g-1).

Superabsorbent starch protective layer modulates zinc anode interface for long-life aqueous zinc ion batteries

Aqueous zinc ion batteries (AZIBs) have attracted much attention for their safety, low cost and high theoretical capacity. Nevertheless, Zn dendrites and the adverse reactions such as corrosion, hydrogen evolution and passivation on the anode affect the cycle life and stability of AZIBs. Herein, superabsorbent starch (SS) was employed on Zn foil to form an artificial interface protection layer, which inhibited the formation of dendrites by guiding the uniform deposition of Zn2+. SS with a large amount of oxygen-containing functional group is superabsorbent, which can attract the active water around the hydrated Zn2+, promoting the desolvation process of the hydrated Zn2+ and significantly inhibiting the occurrence of hydrogen evolution reaction. In addition, the inherent pore structure of the SS artificial interfacial layer can induce uniform nucleation of Zn2+ and inhibit the dendrites growth. Moreover, compared to bare Zn//MnO2 cell (44.1 %), the capacity retention of Zn@SS//MnO2 cell remained as high as 87.8 % after 1000 cycles at 1.5 A g-1. The simple method provided a new method for the rapid development of AZIBs.

Modulating Ion Behavior by Functional Nanodiamond Modified Separator for High-Rate Durable Aqueous Zinc-Ion Battery

Aqueous zinc-ion batteries (AZIBs) have garnered widespread attention due to their promising development and application prospects. However, progress of AZIBs has been hindered by zinc (Zn) dendrites and side reactions at the electrode-electrolyte interface (EEI). In particular, the large and uneven pores of commercial glass fiber (GF) separators lead to nonuniform Zn2+ transport, which causes side reactions. In this study, we employed nanodiamonds (NDs) to regulate the separator pore structure and utilized its surface oxygen-containing functional groups to control the Zn2+ transport properties. Due to their excellent chemical inertness, superhardness, ultrahigh thermal conductivity, and abundant surface functional groups, NDs modified GF separators for dendrite-free and high-performance AZIBs. Experimental outcomes demonstrate that Zn||Zn symmetric cells using NDs-GF separators exhibit regular charge-discharge profiles, minimal fluctuations, and an ultralong cycling lifespan of nearly 1800 h under a current density of 5 mA cm-2 with a capacity density of 1 mAh cm-2 and 240 h under a high current density of 10 mA cm-2 with a capacity density of 10 mAh cm-2. The Zn||MnO2 full cells using NDs-GF separators showcase a high retention after 1000 cycles at 1 A g-1. This research proposes a modification method for developing advanced separators in AZIBs technology.

Maltodextrin as a Commercial-Grade Electrolyte Additive Against Dendrite Formation and Side Reactions for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) directly using zinc metal anodes are promising candidates for grid-scale energy storage systems due to their intrinsic high theoretical capacity, high safety, and environmental friendliness. However, the uncontrolled dendrite growth and water-triggered side reactions seriously plague its practical application. Herein, a cost-effective and green additive, maltodextrin (MD) is presented, to simultaneously guide the smooth Zn deposition and inhibit the occurrence of water-related side reactions. Combing experimental characterizations and theoretical calculations shows that the MD molecules could reconstruct the Helmholtz plane, induces a preferential growth of zinc along the (002) plane, and the optimized regulation of the Zn2+ diffusion path and deposition location also results in the formation of fine-grained Zn deposition layers, thereby inhibiting dendrite growth. In addition, MD molecules readily adsorb to the zinc anode surface, which isolates water molecules from direct contact with the zinc metal, reducing hydrogen precipitation reactions and inhibiting the formation of by-products. Consequently, the Zn||Zn symmetric cell with MD achieves ultra-long stable cycles of up to 5430 h at 1 mA cm-2 and 1 mA h cm-2, and the Cu||Zn asymmetric cell can stable cycle 1000 cycles with an average coulomb efficiency of 99.78%.

Realizing the Electrode Engineering Significance Through Porous Organic Framework Materials for High-Capacity Aqueous Zn-Alkaline Battery

Energy storage technologies are eminently developed to address renewable energy utilization efficiently. Porous framework materials possess high surface area and pore volume, allowing for efficient ion transportation and storage. Their unique structure facilitates fast electron transfer, leading to improved battery kinetics. Porous organic framework materials like metal-organic (MOF) and covalent organic (COF) frameworks have immense potential in enhancing the charge/discharge performances of aqueous Zn-alkaline batteries. Organic frameworks and their derivatives can be modified feasibly to exhibit significant chemical stability, enabling them to tolerate the harsh battery environment. Zn-alkaline batteries can achieve enhanced energy density, longer lifespan, and improved rechargeability by incorporating MOFs and COFs, such as electrodes, separators, or electrolyte additives, into the battery architecture. The present review highlights the significant electrode design strategies based on porous framework materials for aqueous Zn-alkaline batteries, such as Zn-Ni, Zn-Mn, Zn-air, and Zn-N2/NO3 batteries. Besides, the discussion on the issues faced by the Zn anode and the essential anode design strategies to solve the issues are also included.

Design and Conformation of Separators for High-performance Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are considered promising candidates for large-scale energy storage due to their high safety, low cost, and environmental friendliness. As a core component, separator plays a unique yet oftentimes overlooked role in providing electrochemical stability in AZIBs. This concept focuses on the exquisite structure-property relationship of separators, highlighting three forms of these components and their structural design requirements, i. e., traditional membranes, solid-state electrolytes, and electrode coatings. The mechanism by which separators influence the zinc anode and the cathode is discussed. The article also identifies the challenges and potential future directions for functional separators in the development of high-performance AZIBs.

Tailoring Zn2+ Flux by an Ion Acceleration Layer Modified Separator for High-Rate Long-Lasting Zn Metal Anodes

A large concentration gradient originating from sluggish ion transport on the surface of Zn metal anodes will result in uneven Zn2+ flux, giving rise to severe dendrite growth, especially at high current density. Herein, an ion acceleration layer is introduced by a facile separator engineering strategy to realize modulated Zn2+ flux and dendrite-free deposition. Zinc hexacyanoferrate as the modifying agent featuring strong zincophilicity and rapid diffusion tunnel can enable fast trap for Zn2+ near the electrode surface and immediate transport onto deposition sites, respectively. The ion acceleration effect is substantiated by improved ion conductivity, decreased activated energy, and promoted Zn2+ transference number, which can moderate concentration gradient to guide homogenous Zn2+ flux distribution. As a result, the separator engineering guarantees Zn||Zn symmetrical cells with long-term stability of 2700 h at 2 mA cm-2, and 1770 h at a large current density of 10 mA cm-2. Moreover, cycling stability and rate capability for full cells with different cathodes can be substantially promoted by the modified separator, validating its superior practical feasibility. This study supplies a new scalable approach to tailoring ion flux near the electrode surface to enable robust Zn metal anodes at a high current density.

Recent Functionalized Strategies of Metal-Organic Frameworks for Anode Protection of Aqueous Zinc-Ion Battery

The inherent benefits of aqueous Zn-ion batteries (ZIBs), such as environmental friendliness, affordability, and high theoretical capacity, render them promising candidates for energy storage systems. Nevertheless, the Zn anodes of ZIBs encounter severe challenges, including dendrite formation, hydrogen evolution reaction, corrosion, and surface passivation. These would result in the infeasibility of ZIBs in practical situations. To this end, artificial interfaces with functionalized materials are crafted to protect the Zn anode. They have the capability to modulate the zinc ion flux in proximity to the electrode surface and shield it from aqueous electrolytes by leveraging either size effects or charge effects. Considering metal-organic frameworks (MOFs) with tunable pore size, chemical composition, and stable framework structures, they have emerged as effective materials for building artificial interfaces, prolonging the lifespan, and improving the unitization of Zn anode. In this review, the contributions of MOFs for protecting Zn anode, which mainly involves facilitating homogeneous nucleation, manipulating selective deposition, regulating ion and charge flux, accelerating Zn desolvation, and shielding against free water and anions are comprehensively summarized. Importantly, the future research trajectories of MOFs for the protection of the Zn anode are underscored, which may propose new perspectives on the practical Zn anode and endow the MOFs with high-value applications.

Ion-Sieving Separator Functionalized by Natural Mineral Coating toward Ultrastable Zn Metal Anodes

Aqueous zinc-ion batteries (AZIBs) exhibit promising prospects in becoming large-scale energy storage systems due to environmental friendliness, high security, and low cost. However, the growth of Zn dendrites and side reactions remain heady obstacles for the practical application of AZIBs. To solve these challenges, a functionalized Janus separator is successfully constructed by coating halloysite nanotubes (HNTs) on glass fiber (GF). Impressively, the different electronegativity on the inner and outer surfaces of HNTs endows the HNT-GF separator with ion-sieving property, leading to a significantly high transference number of Zn2+ (tZn2+ = 0.71). Meanwhile, the HNT-GF separator works as an interfacial ion comb to regular Zn2+ flux and realizes multisite progressive nucleation, bringing decreased nucleation overpotential and uniform Zn2+ deposition. Consequently, the HNT-GF separator enables the Zn anode to display an ultralong plating/stripping life of 3000 h and high rate tolerance with a stable long cycle life even under a density of 50 mA cm-2. Moreover, the Z n ∥ H N T - G F ∥ M n O 2 full cell represents an ultrastable cycling stability with a high capacity retention of 93.4% even after 1000 cycles at a current density of 2 A g-1. This work provides a convenient method for the separator modification of AZIBs.

Stable Interlayer Zinc Plating/Stripping in the Maxwell-Wagner Effect-Enhanced Interface

Zinc metal batteries have recently emerged as a promising stable and reversible anode aqueous battery. However, due to the serious dendrite problem and hydrogen evolution problem of the zinc metal anode, the practical application of the zinc metal battery is limited. Here, we propose Y2O3 as an effective coating, which inhibits hydrogen evolution and side reactions by physical isolation and simultaneously prevents dendrite growth by ensuring a uniform Zn-ion flux and fast transport channels generated by Maxwell-Wagner polarization, thus improving the stability of batteries. Meanwhile, in situ/ex situ characterizations and different simulations are conducted to investigate in detail the effect of Maxwell-Wagner polarization on the performance of Zn metal batteries. The symmetric Y2O3@Zn anode system exhibits a stable electroplating/stripping performance over 780 h and enables the Zn battery to achieve a Coulombic efficiency of up to 99.81% over 1000 cycles by reducing side reactions. The Y2O3@Zn||MnO2 full cell delivers a high energy density of 301.42 Wh kg-1 at a power density of 205.04 W kg-1. The work provides insights into the reversibility and stability of zinc anodes and provides a promising way to promote the practical application of Zn metal batteries.

Recent Progress of Low-Dimensional Metal-Organic Frameworks for Aqueous Zinc-Based Batteries

Aqueous zinc-based batteries (AZBs) are promising energy storage solutions with remarkable safety, abundant Zn reserve, cost-effectiveness, and relatively high energy density. However, AZBs still face challenges such as anode dendrite formation that reduces cycling stability and limited cathode capacity. Recently, low-dimensional metal-organic frameworks (LD MOFs) and their derivatives have emerged as promising candidates for improving the electrochemical performance of AZBs owing to their unique morphologies, high structure tunability, high surface areas, and high porosity. However, clear guidelines for developing LD MOF-based materials for high-performance AZBs are scarce. In this review, the recent progress of LD MOF-based materials for AZBs is critically examined. The typical synthesis methods and structural design strategies for improving the electrochemical performance of LD MOF-based materials for AZBs are first introduced. The recent noteworthy research achievements are systematically discussed and categorized based on their applications in different AZB components, including cathodes, anodes, separators, and electrolytes. Finally, the limitations are addressed and the future perspectives are outlined for LD MOFs and their derivatives in AZB applications. This review provides clear guidance for designing high-performance LD MOF-based materials for advanced AZBs.

π-π Stacking Induces Fast Zinc Ion Flux for High Power Zinc Ion Devices

Metallic zinc has been regarded as an ideal anode material for aqueous batteries due to its high capacity, abundance, and low toxicity. Numerous strategies have been proposed for anode protection to address its intrinsic deficiencies. However, existing methods can only suppress dendrite growth at limited current densities, and achieving stable cycling at high rates remains a great challenge. Herein, density functional theory (DFT) reveals that Mn-MOF, with a distinctive π-π stacking structure (π-MOF), can induce accelerated ion transfer dynamics, providing high-speed pathways for Zn2+ flux, which can enable stable deposition even at high rates. As anticipated, the π-MOF@Zn anode exhibits remarkable stability for over 1900 h with the lowest voltage hysteresis (71 mV) at a current density of 10 mA cm-2. This study presents a viable approach to enhance the interface stability of high-rate metal anodes by modulating charge or ion behavior at the interface.

Integrated Interfacial Modulation Strategy: Trace Sodium Hydroxyethyl Sulfonate Additive for Extended-Life Zn Anode Based on Anion Adsorption and Electrostatic Shield

Aqueous zinc-ion batteries (AZIBs) are poised to play a pivotal part in meeting the growing demands for energy storage and powering portable electronics for their superior security, affordability, and environmentally friendly characteristics. However, the detrimental side reactions occurring at the zinc anode and the dendrite caused by uneven zinc plating/stripping have greatly compromised the cycling life of AZIBs, thereby impeding their practical prospects. In this study, the interfacial comodulation strategy was employed by combining the "electrostatic shielding" effect of cations with the characteristic adsorption of anions. Two molar ZnSO4 served as the matrix, and sodium hydroxyethyl sulfonate (SHES) was selected as a low-cost, nontoxic additive. Experimental results confirm that SHES and zinc anode exhibit robust interactions that lead to the formation of an electrostatic shield and a dynamic adsorption layer at the interface, thereby suppressing hydrogen evolution and corrosion. The combined "electrostatic shielding" effect of sodium ions and the robust characteristic adsorption of hydroxyethyl sulfonate anions serve to guide the directed three-dimensional (3D) diffusion of Zn2+, facilitating rapid, stable, and uniform deposition of zinc. Due to these effects, incorporating 0.2 M SHES as an additive extends the cycle life beyond 3600 h and enables a highly reversible process of deposition and stripping in symmetric cells. Additionally, the Zn-Cu half-cell exhibits reliable cycling for over 1400 cycles, achieving an average Coulombic efficiency of 99.6%. Moreover, the introduction of this additive substantially enhances the performance of Zn-MnO2 and Zn-NH4V4O10 full cells. This study demonstrates the practical feasibility of achieving anodes with high reversibility in AZIBs through the implementation of a strategy that involves anion adsorption at the interface, which holds paramount significance for the practical application of AZIBs.

Stabilizing Zinc Anode through Ion Selection Sieving for Aqueous Zn-Ion Batteries

Uncontrollable dendrite growth and corrosion induced by reactive water molecules and sulfate ions (SO42-) seriously hindered the practical application of aqueous zinc ion batteries (AZIBs). Here we construct artificial solid electrolyte interfaces (SEIs) realized by sodium and calcium bentonite with a layered structure anchored to anodes (NB@Zn and CB@Zn). This artificial SEI layer functioning as a protective coating to isolate activated water molecules, provides high-speed transport channels for Zn2+, and serves as an ionic sieve to repel negatively charged anions while attracting positively charged cations. The theoretical results show that the bentonite electrodes exhibit a higher binding energy for Zn2+. This demonstrates that the bentonite protective layer enhances the Zn-ion deposition kinetics. Consequently, the NB@Zn//MnO2 and CB@Zn//MnO2 full-battery capacities are 96.7 and 70.4 mAh g-1 at 2.0 A g-1 after 1000 cycles, respectively. This study aims to stabilize Zn anodes and improve the electrochemical performance of AZIBs by ion-selection sieving.

Stabilizing Zn/electrolyte Interphasial Chemistry by a Sustained-Release Drug Inspired Indium-Chelated Resin Protective Layer for High-Areal-Capacity Zn//V2O5 Batteries

For zinc-metal batteries, the instable chemistry at Zn/electrolyte interphasial region results in severe hydrogen evolution reaction (HER) and dendrite growth, significantly impairing Zn anode reversibility. Moreover, an often-overlooked aspect is this instability can be further exacerbated by the interaction with dissolved cathode species in full batteries. Here, inspired by sustained-release drug technology, an indium-chelated resin protective layer (Chelex-In), incorporating a sustained-release mechanism for indium, is developed on Zn surface, stabilizing the anode/electrolyte interphase to ensure reversible Zn plating/stripping performance throughout the entire lifespan of Zn//V2O5 batteries. The sustained-release indium onto Zn electrode promotes a persistent anticatalytic effect against HER and fosters uniform heterogeneous Zn nucleation. Meanwhile, on the electrolyte side, the residual resin matrix with immobilized iminodiacetates anions can also repel detrimental anions (SO4 2- and polyoxovanadate ions dissolved from V2O5 cathode) outside the electric double layer. This dual synergetic regulation on both electrode and electrolyte sides culminates a more stable interphasial environment, effectively enhancing Zn anode reversibility in practical high-areal-capacity full battery systems. Consequently, the bio-inspired Chelex-In protective layer enables an ultralong lifespan of Zn anode over 2800 h, which is also successfully demonstrated in ultrahigh areal capacity Zn//V2O5 full batteries (4.79 mAh cm-2).

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

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

Less is More: Underlying Mechanism of Zn Electrode Long-Term Stability using Sodium L-Ascorbate as Electrolyte Additive

Structured passivation layers and hydrated Zn2+ solvation structure strongly influence Zn depositions on Zn electrodes and then the cycle life and electrochemical performance of aqueous zinc ion batteries. To achieve these, the electrolyte additive of sodium L-ascorbate (Ass) is introduced into aqueous zinc sulfate (ZnSO4, ZS) electrolyte solutions. Combined experimental characterizations with theoretical calculations, the unique passivation layers with vertical arrayed micro-nano structure are clearly observed, as well as the hydrated Zn2+ solvation structure is changed by replacing two ligand water molecules with As-, thus regulating the wettability and interfacial electric field intensity of Zn surfaces, facilitating rapid ionic diffusions within electrolytes and electrodes together with the inhibited side reactions and uniform depositions of Zn2+. When tested in Zn||Zn symmetric cell, the electrolyte containing Ass is extraordinarily stably operated for the long time ≈3700 h at both 1 mA cm-2 and 1 mAh cm-2. In Zn||MnO2 full coin cells, the energy density can still maintain as high as ≈184 Wh kg-1 at the power density high up to 2 kW kg-1, as well as the capacity retention can reach up to 80.5% even after 1000 cycles at 2 A g-1, which are substantially superior to the control cells.

Correlating Buffering Agents' Premier pH with Interface Stability Toward Long-Term Zn Metal Anodes

Aqueous solvents in Zn metal batteries inevitably induces hydrogen evolution reactions (HER) due to fluctuating pH levels in electrolytes, leading to severe side reactions and dendrite growth. To address these challenges, buffering agents have been recently proposed as a solution to maintain constant electrolyte pH values upon cycling. Nonetheless, the critical role of buffering additives' premier pH in determining interface stability is largely overlooked. Herein, two types of buffering agents, single amphoteric and conjugate acid-base pairs, are employed to correlate their initial pHs with the interface stability. Based on the observations, the lifetime of Zn metal anodes initially increases and then decreases as the initial pH level goes up from 2.0 to 5.0, with an optimal lifetime at pH 3.3 for both buffering agent categories. This phenomenon lies in ample H+ in low pH and rich OH- in high pH, leading to either severe HER or by-products passivation layer. The optimized pH allows cells to deliver a high average Coulombic efficiency of 99.61% over 1500 cycles at a large current density of 5 mA cm-2, which is significantly superior to 345 cycles achieved in the pristine electrolyte. Furthermore, this enhanced interface enables stable Zn/activated carbon full batteries over 15 000 cycles.

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

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

Coupling High Hardness and Zn Affinity in Amorphous-Crystalline Diamond for Stable Zn Metal Anodes

The highly reversible plating/stripping of Zn is plagued by dendrite growth and side reactions on metallic Zn anodes, retarding the commercial application of aqueous Zn-ion batteries. Herein, a distinctive nano dual-phase diamond (NDPD) comprised of an amorphous-crystalline heterostructure is developed to regulate Zn deposition and mechanically block dendrite growth. The rich amorphous-crystalline heterointerfaces in the NDPD endow modified Zn anodes with enhanced Zn affinity and result in homogeneous nucleation. In addition, the unparalleled hardness of the NDPD effectively overcomes the high growth stress of dendrites and mechanically impedes their proliferation. Moreover, the hydrophobic surfaces of the NDPD facilitate the desolvation of hydrate Zn2+ and prevent water-mediated side reactions. Consequently, the Zn@NDPD presents an ultrastable lifespan exceeding 3200 h at 5 mA cm-2 and 1 mAh cm-2. The practical application potential of Zn@NDPD is further demonstrated in full cells. This work exhibits the great significance of a chemical-mechanical synergistic anode modification strategy in constructing high-performance aqueous Zn-ion batteries.

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.

Massively Reconstructing Hydrogen Bonding Network and Coordination Structure Enabled by a Natural Multifunctional Co-Solvent for Practical Aqueous Zn-Ion Batteries

The practical application of aqueous Zn-ion batteries (AZIBs) is hindered by the crazy Zn dendrites growth and the H2O-induced side reactions, which rapidly consume the Zn anode and H2O molecules, especially under the lean electrolyte and Zn anode. Herein, a natural disaccharide, d-trehalose (DT), is exploited as a novel multifunctional co-solvent to address the above issues. Molecular dynamics simulations and spectral characterizations demonstrate that DT with abundant polar -OH groups can form strong interactions with Zn2+ ions and H2O molecules, and thus massively reconstruct the coordination structure of Zn2+ ions and the hydrogen bonding network of the electrolyte. Especially, the strong H-bonds between DT and H2O molecules can not only effectively suppress the H2O activity but also prevent the rearrangement of H2O molecules at low temperature. Consequently, the AZIBs using DT30 electrolyte can show high cycling stability even under lean electrolyte (E/C ratio = 2.95 µL mAh-1), low N/P ratio (3.4), and low temperature (-12 °C). As a proof-of-concept, a Zn||LiFePO4 pack with LiFePO4 loading as high as 506.49 mg can be achieved. Therefore, DT as an eco-friendly multifunctional co-solvent provides a sustainable and effective strategy for the practical application of AZIBs.

Electrolyte Strategies Facilitating Anion-Derived Solid-Electrolyte Interphases for Aqueous Zinc-Metal Batteries

Rechargeable aqueous zinc-metal batteries (AZBs) are a promising complimentary technology to the existing lithium-ion batteries and the re-emerging lithium-metal batteries to satisfy the increasing demands on energy storage. Despite considerable progress achieved in the past years, the fundamental understanding of the solid-electrolyte interphase (SEI) formation and how its composition influences the SEI properties are limited. This review highlights the functionalities of anion-tuned SEI on the reversibility of zinc-metal anode, with a specific emphasis on new structural insights obtained through advanced characterizations and computational techniques. Recent efforts in terms of key variables that govern the interfacial behaviors to improve the long-term stability of zinc anode, i.e., Coulombic efficiency, plating morphology, dendrite formation, and side-reactions, are comprehensively reviewed. Lastly, the remaining challenges and future perspectives are presented, providing insights into the rational design of practical high-performance AZBs.

Industrial Waste Derived Separators for Zn-Ion Batteries Achieve Homogeneous Zn(002) Deposition Through Low Chemical Affinity Effects

Designing a cost-effective and multifunctional separator that ensures dendrite-free and stable Zn metal anode remains a significant challenge. Herein, a multifunctional cellulose-based separator is presented consisting of industrial waste-fly ash particles and cellulose nanofiber using a facile solution-coating method. The resulting fly ash-cellulose (FACNF) separators enable a high ion conductivity (5.76 mS cm-1) and low desolvation energy barrier of hydrated Zn2+. These features facilitate fast ion transfer kinetics and inhibit water-induced side reactions. Furthermore, experimental results and theoretical simulations confirm that the presence of fly ash particles in FACNF separators effectively accommodate the preferential deposition of Zn(002) planes, due to the weak chemical affinity between Zn(002) plane and fly ash, to mitigate dendrite formation and growth. Consequently, the utilization of FACNF separators causes an impressive cycling performance in both Zn||Zn symmetric cells (1600 h at 2 mA cm-2/1 mAh cm-2) and Zn||(NH4)2V10O25 (NVO) full cells (4000 cycles with the capacity retention of 92.1% at 5 A g-1). Furthermore, the assembled pouch cells can steadily support digital thermometer over two months without generating gas and volume expansion. This work provides new insights for achieving crystallographic uniformity in Zn anodes and realizing cost-effective and long-lasting aqueous zinc-ion batteries (AZIBs).

Non-Metal Ion Storage in Zinc-Organic Batteries

Zinc-organic batteries (ZOBs) are receiving widespread attention as up-and-coming energy-storage systems due to their sustainability, operational safety and low cost. Charge carrier is one of the critical factors affecting the redox kinetics and electrochemical performances of ZOBs. Compared with conventional large-sized and sluggish Zn2+ storage, non-metallic charge carriers with small hydrated size and light weight show accelerated interfacial dehydration and fast reaction kinetics, enabling superior electrochemical metrics for ZOBs. Thus, it is valuable and ongoing works to build better ZOBs with non-metallic ion storage. In this review, versatile non-metallic cationic (H+, NH4 +) and anionic (Cl-, OH-, CF3SO3 -, SO4 2-) charge carriers of ZOBs are first categorized with a brief comparison of their respective physicochemical properties and chemical interactions with redox-active organic materials. Furthermore, this work highlights the implementation effectiveness of non-metallic ions in ZOBs, giving insights into the impact of ion types on the metrics (capacity, rate capability, operation voltage, and cycle life) of organic cathodes. Finally, the challenges and perspectives of non-metal-ion-based ZOBs are outlined to guild the future development of next-generation energy communities.

Outer Sphere Electron Transfer Enabling High-Voltage Aqueous Electrolytes

Aqueous electrolytes with a low voltage window (1.23 V) and prone side reactions, such as hydrogen evolution reaction and cathode dissolution, compromise the advantages of high safety and low cost of aqueous metal-ion batteries. Herein, introducing catechol (CAT) into the aqueous electrolyte, an outer sphere electron transfer mechanism is initiated to inhibit the water reactivity, achieving an electrochemical window of 3.24 V. In a typical Zn-ion battery, the outer sphere electrons jump from CAT to Zn2+-H2O at a geometrically favorable situation and between the solvation molecules without breaking or forming chemical bonds as that of the inner sphere electron transfers. The excited state π-π stacking further leads to the outer sphere electron transfer occurring at the electrolyte/electrode interface. This high-voltage electrolyte allows achieving an operating voltage two times higher than that of the usual aqueous electrolytes and provides almost the highest energy density and power density for the V2O5-based aqueous Zn-ion full batteries. The Zn//Zn symmetric battery delivers a 4000 h lifespan, and the Zn//V2O5 full battery achieves a ∼380 W h kg-1 energy density and a 92% capacity retention after 3000 cycles at 1 A g-1 and a 2.4 V output voltage. This outer sphere electron transfer strategy paves the way for designing high-voltage aqueous electrolytes.