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

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

Ultrasmall, Amorphous V2O3 Intimately Anchored on a Carbon Nanofiber Aerogel Toward High-Rate Zinc-Ion Batteries

When considered as a cathode candidate for aqueous Zn-ion batteries, V2O3 faces several problems, such as inherently unsuitable structure, fast structural degradation, and sluggish charge transport kinetics. In this paper, we report the synthesis of a V2O3 intimately coupled carbon aerogel by a controllable ion impregnation and solid-state reaction strategy using bacterial cellulose and ammonium metavanadate as raw materials. In this newly designed structure, the carbonized carbon fiber network provides fast ion and electron transport channels. More importantly, the cellulose aerogel functions as a dispersing and supporting skeleton to realize the particle size reduction, uniform distribution, and amorphous features of V2O3. These advantages work together to realize adequate electrochemical activation during the initial charging process and shorter transport distance and faster transport kinetics of Zn2+. The batteries based on the V2O3/CNF aerogel exhibit a high-rate performance and an excellent cycling stability. At a current density of 20 A g-1, the V2O3/CNF aerogel delivers a specific capacity of 159.8 mAh g-1, and it demonstrates an exceptionally long life span over 2000 cycles at 12 A g-1. Furthermore, the electrodes with active material loadings as high as 10 mg cm-2 still deliver appreciable specific capacities of 257 mAh g-1 at 0.1 A g-1.

Nanofiber-Reinforced Composite Gel Enabling High Ionic Conductivity and Ultralong Cycle Life for Zn Ion Batteries

Despite the impressive merits of gel electrolytes for aqueous Zn-ion batteries, it remains a significant challenge to design and develop the gel electrolyte with high ionic conductivity, excellent dimensional stability, and long cycle life. Herein, a composite electrolyte (PTP) with thermolastic polyurethane -poly(m-phenylene isophthalamide)  nanofiber-reinforced polyvinyl alcohol gel strategy is proposed for highly reversible Zn plating/stripping. Mechanically robust and ultrathin PTP contains functional groups for building ion migration channels and immobilizing water molecules, which accelerates Zn2+ migration and mitigates water-related side reactions. Thus, the Zn anodes exhibit excellent electrochemical performance involving high cycling stability (6500 h at 5 mA cm-2 , 5 mA h cm-2 ) and achieving an exceptional cumulative capacity of more than 16 000 mA h cm-2 . This enhancement is well maintained when combined with MnO2 cathode. This work provides a reasonable solution for stabilizing Zn anodes and also provides new ideas for the modification of nanofiber-reinforced gel electrolytes.

Acetamide-Caprolactam Deep Eutectic Solvent-Based Electrolyte for Stable Zn-Metal Batteries

Aqueous Zn-ion batteries (AZIBs) are promising for grid-scale energy storage. However, conventional AZIBs face challenges including hydrogen evolution reaction (HER), leading to high local pH, and by-product formation on the anode. Hereby the hydrogen bonds in the aqueous electrolyte are reconstructed by using a deep eutectic co-solvent (DES) made of acetamide (H-bond donor) and caprolactam (H-bond acceptor), which effectively suppresses the reactivity of water and broadens the electrochemical voltage stability window. The coordination between Zn2+ and acetamide-caprolactam in DES-based electrolytes produces a unique solvation structure that promotes the preferential growth of Zn crystals along the (002) plane. This will inhibit the formation of Zn dendrites and ensure the uniform deposition of Zn-ions on the anode surface. In addition, it is found that this DES-based electrolyte can form a protective membrane on the anode surface, reducing the risks of Zn corrosion. Compared to conventional electrolytes, the DES-based electrolyte shows a long-term stable plating/stripping performance with a significantly improved Coulombic efficiency from 78.18% to 98.37%. It is further demonstrated that a Zn||VS2 full-cell with the DES-based electrolyte exhibits enhanced stability after 500 cycles with 85.4% capacity retention at 0.5 A g-1 .

Anti-Freezing Electrolytes in Aqueous Multivalent Metal-Ion Batteries: Progress, Challenges, and Optimization Strategies

Aqueous rechargeable multivalent metal-ion batteries (ARMMBs) have attracted considerable attention due to their high capacity, high energy density, and low cost. However, their performance is often limited by low temperature operation, which requires the development of anti-freezing electrolytes. In this review, we summarize the anti-freezing mechanisms and optimization strategies of anti-freezing electrolytes for aqueous batteries (especially for Zn-ion batteries). Besides, we investigate the possible interactions and side reactions between electrolytes and electrodes. We also analyze the problems between electrolytes and electrodes at low temperature, and propose possible solutions. The research progress in the field of low temperature energy storage for aqueous Mg-ion, Ca-ion, and Al-ion batteries, and the challenges faced in their anti-freezing electrolytes are investigated in detail. Last but not least, the outlook on the energy storage applications of ARMMBs is provided to guide the future research.

Construction of amorphous V2O5@Ti3C2Tx synergistic heterostructure on 3D carbon cloth substrate by a self-assembled strategy towards high-performance aqueous Zn-ion batteries

The emerging aqueous Zn-ion batteries (ZIBs) with their low price and inherent safety are showing strong competitiveness in the energy storage field. In this work, layer-by-layer stacked amorphous V2O5@Ti3C2Tx heterostructures anchored on three-dimensional carbon cloth (3D CC), synthesized by annealing process and subsequent in-situ electrochemical induction, are reported as high capacity and stable cathode for ZIBs. In this composite cathode, amorphous V2O5@Ti3C2Tx synergistic heterostructure provides isotropic Zn2+ migration channels and rapid electron transfer kinetics, while the 3D CC substrate can ensure that the bulk phase in the electrode material is also utilized to maximize the synergistic effect. As a result, the CC/a-V2O5@Ti3C2Tix cathode achieves a high specific capacity of 567 mAh/g at 0.1 A/g, a satisfactory rate performance of 213 mAh/g at 10 A/g, together with a long cycle life of 96.2 % capacity retention after 2000 cycles. Ex-situ characterizations show that the CC/a-V2O5@Ti3C2Tx cathode undergoes a highly reversible Zn2+/H+ co-intercalation/deintercalation mechanism during the discharge/charging process. In addition, based on the CC/a-V2O5@Ti3C2Tx cathode, the assembled flexible ZIB can operate properly under different bending degrees, showing its practicality in flexible devices. This work provides insight into the rational design of cathode materials with high Zn-storage performance.

Hydrated Eutectic Electrolyte Induced Bilayer Interphase for High-Performance Aqueous Zn-Ion Batteries with 100 °C Wide-Temperature Range

The practical implementation of aqueous zinc-ion batteries (AZIBs) encounters challenges such as dendrite growth, parasitic reactions, and severe decay in battery performance under harsh environments. Here, a novel hydrated eutectic electrolyte (HEE) composed of Zn(ClO4 )2 ·6H2 O, ethylene glycol (EG), and InCl3 solution is introduced to effectively extend the lifespan of AZIBs over a wide temperature range from -50 to 50 °C. Molecular dynamics simulations and spectroscopy analysis demonstrate that the H2 O molecules are confined within the liquid eutectic network through dual-interaction, involving coordination with Zn2+ and hydrogen bonding with EG, thus weakening the activity of free water and extending the electrochemical window. Importantly, cryo-transmission electron microscopy and spectroscopy techniques reveal that HEE in situ forms a zincophobic/zincophilic bilayer interphase by the dissociation-reduction of eutectic molecules. Specifically, the zincophilic interphase reduces the energy barrier for Zn nucleation, promoting uniform Zn deposition, while the zincophobic interphase prevents active water from contacting the Zn surface, thus inhibiting the side reactions. Furthermore, the relationships between the structural evolution of the liquid eutectic network and interfacial chemistry at electrode/electrolyte interphase are further discussed in this work. The scalability of this design strategy can bring benefits to AZIBs operating over a wide temperature range.

Zn-In Alloying Powder Solvent Free Electrode Toward High-Load Ampere-Hour Aqueous Zn-Mn Secondary Batteries

Aqueous Zn-ion batteries (ZIBs) are promising candidates for large-scale energy storage due to high safety, abundant reserves, low-cost, and high energy density. However, the reversibility of the metallic Zn anode in the mild electrolyte is still unsatisfactory, due to the Zn dendrite growth, hydrogen evolution, and corrosion passivation. Herein, a Zn-In alloying powder solvent free electrode is proposed to replace the Zn foil in ZIBs. The novel Zn anodes are constructed by a solvent-free manufacturing process with carbons, forming a 3D Zn deposition network and providing uniformly electric field distribution. The In on the Zn powder surface can increase the overpotential for hydrogen evolution and further improve the morphology of Zn deposition against dendrite growth. The Zn solvent-free electrodes enable the Zn-MnO2 batteries with high cathode loading mass of 10-20 mg cm-2 to achieve >380 stable cycles. Furthermore, the assembled soft package batteries of 2.4 Ah (52 Wh kg-2 ) is evaluated and the capacity retention is maintained at 80% after 200 cycles at a high areal capacity of 5 mAh cm-2 without gas evolution. This work offers a workable strategy to develop a durable Zn anode for the eventually commercial applications of aqueous Zn-Mn secondary batteries.

Synergistically Stabilizing Zinc Anodes by Molybdenum Dioxide Coating and Tween 80 Electrolyte Additive for High-Performance Aqueous Zinc-Ion Batteries

Recently, aqueous zinc-ion batteries (ZIBs) have become increasingly attractive as grid-scale energy storage solutions due to their safety, low cost, and environmental friendliness. However, severe dendrite growth, self-corrosion, hydrogen evolution, and irreversible side reactions occurring at Zn anodes often cause poor cyclability of ZIBs. This work develops a synergistic strategy to stabilize the Zn anode by introducing a molybdenum dioxide coating layer on Zn (MoO2@Zn) and Tween 80 as an electrolyte additive. Due to the redox capability and high electrical conductivity of MoO2, the coating layer can not only homogenize the surface electric field but also accommodate the Zn2+ concentration field in the vicinity of the Zn anode, thereby regulating Zn2+ ion distribution and inhibiting side reactions. MoO2 coating can also significantly enhance surface hydrophilicity to improve the wetting of electrolyte on the Zn electrode. Meanwhile, Tween 80, a surfactant additive, acts as a corrosion inhibitor, preventing Zn corrosion and regulating Zn2+ ion migration. Their combination can synergistically work to reduce the desolvation energy of hydrated Zn ions and stabilize the Zn anodes. Therefore, the symmetric cells of MoO2@Zn∥MoO2@Zn with optimal 1 mM Tween 80 additive in 1 M ZnSO4 achieve exceptional cyclability over 6000 h at 1 mA cm-2 and stability (>700 h) even at a high current density (5 mA cm-2). When coupling with the VO2 cathode, the full cell of MoO2@Zn∥VO2 shows a higher capacity retention (82.4%) compared to Zn∥VO2 (57.3%) after 1000 cycles at 5 A g-1. This study suggests a synergistic strategy of combining surface modification and electrolyte engineering to design high-performance ZIBs.

Understanding the Role of Titanium Metal-Organic Framework Nanosheets in Modulating Anode Chemistry for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries have attracted a continually increasing level of interest for large-scale energy storage because they are highly safe and have high energy density and abundant reserves. However, Zn anodes face significant challenges such as severe dendrite growth and hydrogen evolution reaction (HER). We here propose an efficient Zn2+ sieve strategy for modulating the anode chemistry using two-dimensional NH2-MIL-125 (Ti) metal-organic framework (MOF) nanosheets. Theoretical investigations reveal the crucial role of the Ti MOF in regulating Zn2+ solvation structures for fast diffusion and uniform deposition and decreasing HER reactivity. The structure of the nanosheets enables abundant accessible desolvation sites and shortened ionic pathways. As a result, the MOF nanosheet-protected Zn anode exhibited greatly improved cycling stability in both symmetric cells and full cells. Operando optical monitoring and postmortem analysis revealed effective suppression of dendrite growth and HER by Ti MOF nanosheets. This anti-HER MOF-enabled Zn2+ sieve strategy provides a viable Zn anode and provides new insights for optimizing aqueous batteries.

Unlocking the Capacity of Bismuth Oxide by a Redox Mediator Strategy for High-Performance Aqueous Zn-Ion Batteries

Many cathode materials store zinc ions based on the intercalation reaction mechanism in neutral aqueous Zn-ion batteries, and the structural design of the cathodes has been stuck in the curing mode by extending the ion diffusion channel. Here, we first develop halide ions to unlock the electrochemical activity of conversion-type Bi2O3 in aqueous Zn-ion batteries. Notably, the iodide ion shows the best performance compatibility with the Bi2O3 cathode. The electrochemical reaction mechanism studies show that iodide ions can be regarded as a redox medium to reduce the charge-transfer activation energy and motivate the conversion of Bi2O3 from Bi3+ to Bi0 during the cycle. Unsurprising, the discharge-specific capacity can reach 436.8 mAh g-1 at 0.5 A g-1 and achieve a cyclic lifespan of 6000 cycles at a current density of 3 A g-1. The activation of the Bi2O3 conversion reaction by iodide ions is of great significance for broadening the research range of ZIB cathode materials.

Interfacial Modification of a Zn Anode by Amorphous Se toward Long-Life and Hydrogen Evolution-Free Aqueous Rechargeable Batteries

The Zn anode in rechargeable aqueous Zn-ion batteries suffers from hydrogen gas evolution and dendrite growth, which are critical issues that make the battery impractical. Here, the Zn anode performance is greatly improved by coating an amorphous selenium overlayer with a simple chemical bath reaction process. The reduction of SeO32- ions by the Zn metal leads to the formation of an amorphous Se layer, and the optimal reaction time that determines the thickness of the Se coating as well as the Zn anode performance is found to be 2 h. The symmetric cell using Zn@Se exhibits improved rate performance and an ultralong cycle life of 4500 h after being tested at 1 mA cm-2 and 1 mAh cm-2, respectively. Compared to the bare Zn anode, the Zn@Se anode leads to a larger Zn2+ transference number and reduced charge transfer resistance. The button-type MnO2∥Zn@Se full cell exhibits higher capacity and a much longer cycle life compared to the counterpart using a bare Zn anode. Also, pouch-type MnO2∥Zn@Se full cells with a high capacity of 9.7 mAh cm-2 are made to demonstrate the inhibition of hydrogen evolution and practical applications. It is found that the in situ formation of an amorphous ZnO nanosheet network induced by the amorphous Se overlayer plays a key role in enhancing the Zn anode performance.

Lotus Effect Inspired Hydrophobic Strategy for Stable Zn Metal Anodes

Zn-ion batteries (ZIBs) have long suffered from the unstable Zn metal anode, which faces numerous challenges concerning dendrite growth, corrosion, and hydrogen evolution reaction. The absence of H2 O adsorption control techniques has become a bottleneck for the further development of ZIBs. Using the stearic acid (SA)-modified Cu@Zn (SA-Cu@Zn) anode as an example, this work illustrates how the lotus effect controls the H2 O adsorption energy on the Zn metal anode. In situ integrated Cu nanorods arrays and hydrophobic long-chain alkyl groups are constructed, which provide zincophilic ordered channels and hydrophobic property. Consequently, the SA-Cu@Zn anode exhibits long-term cycling stability over 2000 h and high average Coulombic efficiency (CE) of 99.83% at 1 mA cm-2 for 1 mAh cm-2 , which improves the electrochemical performance of the Zn||V2 O5 full cell. Density functional theory (DFT) calculations combined with water contact angle (CA) measurements demonstrate that the SA-Cu@Zn exhibits larger water CA and weaker H2 O adsorption than Zn. Moreover, the presence of Cu ensures the selective adsorption of Zn on the SA-Cu@Zn anode, well explaining how the excellent reversibility is achieved. This work demonstrates the effectiveness of the lotus effect on controllable H2 O adsorption and Zn deposition mechanism, offering a universal strategy for achieving stable ZIB anodes.

Phase Engineering of Nonstoichiometric Cu2-xSe as Anode for Aqueous Zn-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are receiving widespread attention due to their abundant resources, low material cost, and high safety. However, the susceptibility of Zn metal anodes to corrosion and hydrogen evolution limits their further practical applications. Replacing Zn metal with intercalation-type anode material and constructing rocking-chair-type batteries could be an effective way to significantly prolong the cycle life of AZIBs. Herein, we present copper selenide with different crystal phase structures through a facile redox reaction as an anode for AZIBs. By comparing and analyzing different copper selenide phases, it is found that the cubic Cu2-xSe shows superior structural stability and highly reversible Zn2+ storage. Theoretical calculation results further demonstrate that the cubic Cu2-xSe possesses an increased electrical conductivity, higher Zn2+ adsorption energy, and reduced diffusion barrier, thereby promoting the storage reversibility and (de)intercalation kinetics of the Zn2+ ion. Thus, the Cu2-xSe anode delivers a long-term service life of over 15 000 cycles and impressive cumulative capacity. Furthermore, the full-cells assembled with the MnO2/CNT cathode operate stably for over 1500 cycles at 6 mA cm-2 at a negative/positive (N/P) capacity ratio of ∼1.53. This work provides a more ideal Zn-metal-free anode, which helps to push the practical applications of AZIBs.

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.

Ultraviolet-Assisted Printing of Flexible Solid-State Zn-Ion Battery with a Heterostructure Electrolyte

Flexible solid-state Zn-ion batteries (ZIBs) have garnered considerable attention for next-generation power sources, but the corrosion, dendrite growth, and interfacial problems severely hinder their practical applications. Herein, a high-performance flexible solid-state ZIB with a unique heterostructure electrolyte is facilely fabricated through ultraviolet-assisted printing strategy. The solid polymer/hydrogel heterostructure matrix not only isolates water molecules and optimizes electric field distribution for dendrite-free anode, but also facilitates fast and in-depth Zn2+ transport in the cathode. The in situ ultraviolet-assisted printing creates cross-linked and well-bonded interfaces between the electrodes and the electrolyte, enabling low ionic transfer resistance and high mechanical stability. As a result, the heterostructure electrolyte based ZIB outperforms single-electrolyte based cells. It not only delivers a high capacity of 442.2 mAh g-1 with long cycling life of 900 cycles at 2 A g-1 , but also maintains stable operation under mechanical bending and high-pressure compression in a wide temperature range (-20 °C to 100 °C).

Combined operando and ex-situ monitoring of the Zn/electrolyte interface in Zn-ion battery systems

Operando optical microscopy enables imaging at the interface between the Zn electrode and the electrolyte of 1 M ZnSO4(aq) in the symmetrical Zn/Zn cells assembled as the pouch cells with the mechanical load of 0.8 MPa. The imaging was executed during cycling of Zn plating and stripping at the different current densities of 0.5, 1.0, 2.0, and 4.0 mA cm-2, and the areal capacity of 2 mAh·cm-2. When the current densities are below 4.0 mA cm-2, no intense Zn dendrites are observed. However, at 4.0 mA cm-2, the severe Zn dendrites can penetrate through the separator and cause short-circuiting. From the electrochemical perspective, the voltage profile of such system drops to almost zero volt. Both operando optical and ex-situ synchrotron X-ray imaging further prove the appearance of the Zn dendrites. By Raman spectroscopy and X-ray diffraction, the cycled Zn electrode surface contains passivation species of Zn4(OH)6SO4, ZnO, and Zn(OH)2 that could limit the active surface area for the Zn plating/stripping, accelerating the localized current density and favoring the growth of Zn dendrites. With the SiO2 additive of 0.5% w/v in 1 M ZnSO4(aq), the severe Zn dendrites disappear, as well as the cycled Zn/electrolyte interface becomes close to the pristine state; low degree of the Zn electrode roughness and the Zn surface passivation is noticed. The appearance of the claimed Zn surface morphology was also confirmed by Scanning Electron Microscopy (SEM). In turn, too low or too high SiO2 content in the electrolyte does not generate desirable effects. A high level of Zn dendrites and short circuiting are still recognized. Hence, both the operando and ex-situ characterizations can mutually validate the phenomena at the Zn/electrolyte interface.

Interfacial Designs of MXenes for Mild Aqueous Zinc-Ion Storage

Limited Li resources, high cost, and safety risks of using organic electrolytes have stimulated a strong motivation to develop non-Li aqueous batteries. Aqueous Zn-ion storage (ZIS) devices offer low-cost and high-safety solutions. However, their practical applications are at the moment restricted by their short cycle life arising mainly from irreversible electrochemical side reactions and processes at the interfaces. This review sums up the capability of using 2D MXenes to increase the reversibility at the interface, assist the charge transfer process, and thereby improve the performance of ZIS. First, they discuss the ZIS mechanism and irreversibility of typical electrode materials in mild aqueous electrolytes. Then, applications of MXenes in different ZIS components are highlighted, including as electrodes for Zn2+ intercalation, protective layers of Zn anode, hosts for Zn deposition, substrates, and separators. Finally, perspectives are put forward on further optimizing MXenes to improve the ZIS performance.

Tackling the Challenges of Aqueous Zn-Ion Batteries via Polymer-Derived Strategies

Zn-ion batteries (ZIBs) have gathered unprecedented interest recently benefiting from their intrinsic safety, affordability, and environmental benignity. Nevertheless, their practical implementation is hampered by low rate performance, inferior Zn²⁺ diffusion kinetics, and undesired parasitic reactions. Innovative solutions are put forth to address these issues by optimizing the electrodes, separators, electrolytes, and interfaces. Remarkably, polymers with inherent properties of low-density, high processability, structural flexibility, and superior stability show great promising in tackling the challenges. Herein, the recent progress in the synthesis and customization of functional polymers in aqueous ZIBs is outlined. The recent implementations of polymers into each component are summarized, with a focus on the inherent mechanisms underlying their unique functions. The challenges of incorporating polymers into practical ZIBs are also discussed and possible solutions to circumvent them are proposed. It is hoped that such a deep analysis could accelerate the design of polymer-derived approaches to boost the performance of ZIBs and other aqueous battery systems as they share similarities in many aspects.

Ion Diffusion-Directed Assembly of an Artificial Electronic-Ionic Conductor Layer with Zn-Ion Selective Channels for Highly Reversible Zinc Anodes

Although aqueous zinc-ion batteries have attracted much attention due to their high safety, low cost, and relatively high energy density, their practical applications are severely limited by the uncontrollable dendrite growth and side reactions at the zinc anode. Herein, we design an electronic-ionic conductor artificial layer with Zn-ion selective channels on the Zn surface to regulate the Zn plating/stripping behavior through a one-step ion diffusion-directed assembly strategy using the commercially available conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). Significantly, the functional PEDOT:PSS-Zn²⁺ (PPZ) layer with abundant selective Zn-ion channels works as both an electron regulator and an ion regulator that could not only simultaneously uniformize the electrical and Zn²⁺ concentration field on the Zn surface and accelerate the Zn²⁺ transport kinetics but also block the access of SO₄^2- and H₂O. With such a synergy effect, the PEDOT:PSS-Zn²⁺-modified Zn anode (2PPZ@Zn) achieves a long lifespan of 2400 h of the symmetrical cell at a current density of 3 mA cm^-2 (1 mA h cm^-2). Additionally, a long-term lifespan of 500 h is harvested even at a high current of 5 mA cm^-2 with a high capacity of 3 mA h cm^-2. Furthermore, combined with a manganese dioxide cathode, a full cell similarly provides a cycling stability of over 1500 cycles with 75% capacity retention at a high rate of 10 C (1 C = 308 mA h g^-1).

A Sulfur Heterocyclic Quinone Cathode Towards High-Rate and Long-Cycle Aqueous Zn-Organic Batteries

Organic materials have attracted much attention in aqueous zinc-ion batteries (AZIBs) due to their sustainability and structure-designable, but their further development is hindered by the high solubility, poor conductivity, and low utilization of active groups, resulting in poor cycling stability, terrible rate capability, and low capacity. In order to solve these three major obstacles, a novel organic host, benzo[b]naphtho[2',3':5,6][1,4]dithiino[2,3-i]thianthrene-5,7,9,14,16,18-hexone (BNDTH), with abundant electroactive groups and stable extended π-conjugated structure is synthesized and composited with reduced graphene oxide (RGO) through a solvent exchange composition method to act as the cathode material for AZIBs. The well-designed BNDTH/RGO composite exhibits a high capacity of 296 mAh g^-1 (nearly a full utilization of the active groups), superior rate capability of 120 mAh g^-1 , and a long lifetime of 58 000 cycles with a capacity retention of 65% at 10 A g^-1 . Such excellent performance can be attributed to the ingenious structural design of the active molecule, as well as the unique solvent exchange composition strategy that enables effective dispersion of excess charge on the active molecule during discharge/charge process. This work provides important insights for the rational design of organic cathode materials and has significant guidance for realizing ideal high performance in AZIBs.

Unlocking the Interfacial Adsorption-Intercalation Pseudocapacitive Storage Limit to Enabling All-Climate, High Energy/Power Density and Durable Zn-Ion Batteries

Sluggish storage kinetics and insufficient performance are the major challenges that restrict the transition metal dichalcogenides (TMDs) applied for zinc ion storage, especially at the extreme temperature conditions. Herein, a multiscale interface structure-integrated modulation concept was presented, to unlock the omnidirectional storage kinetics-enhanced porous VSe2-x·nH2O host. Theory research indicated that the co-modulation of H2O intercalation and selenium vacancy enables enhancing the interfacial zinc ion capture ability and decreasing the zinc ion diffusion barrier. Moreover, an interfacial adsorption-intercalation pseudocapacitive storage mechanism was uncovered. Such cathode displayed remarkable storage performance at the wide temperature range (-40~60oC) in aqueous and solid electrolytes. In particular, it can retain a high specific capacity of 173 mAh g-1 after 5000 cycles at 10 A g-1, as well as a high energy density of 290 Wh kg-1 and a power density of 15.8 kW kg-1 at room temperature. Unexpectedly, a remarkably energy density of 465 Wh kg-1 and power density of 21.26 kW kg-1 at 60oC also can be achieved, as well as 258 Wh kg-1 and 10.8 kW kg-1 at -20oC. This work realizes a conceptual breakthrough for extending the interfacial storage limit of layered TMDs to construct all-climate high-performance Zn-ion batteries.

Polycation-Regulated Electrolyte and Interfacial Electric Fields for Stable Zinc Metal Batteries

Zn metal as one of promising anode materials for aqueous batteries but suffers from disreputable dendrite growth, grievous hydrogen evolution and corrosion. Here, a polycation additive, polydiallyl dimethylammonium chloride (PDD), is introduced to achieve long-term and highly reversible Zn plating/stripping. Specifically, the PDD can simultaneously regulate the electric fields of electrolyte and Zn/electrolyte interface to improve Zn2+ migration behaviors and guide dominant Zn (002) deposition, which is veritably detected by Zeta potential, Kelvin probe force microscopy and scanning electrochemical microscopy. Moreover, PDD also creates a positive charge-rich protective outer layer and a N-rich hybrid inner layer, which accelerates the Zn2+ desolvation during plating process and blocks the direct contact between water molecules and Zn anode. Thereby, the reversibility and long-term stability of Zn anodes are substantially improved, as certified by a higher average coulombic efficiency of 99.7% for Zn//Cu cells and 22 times longer life for Zn//Zn cells compared with that of PDD-free electrolyte.

Carbon Nitride Pillared Vanadate Via Chemical Pre-Intercalation Towards High-PerformanceAqueous Zinc-Ion Batteries

Vanadium compounds are promising cathode materials for aqueous zinc-ion batteries (AZIBs) due to their high specific capacity. However, the narrow interlayer spacing, low intrinsic conductivity and the vanadium dissolution still restrict their further application. Herein, we present an oxygen-deficient vanadate pillared by carbon nitrides (C3N4) as the cathode for AZIBs through a facile self-engaged hydrothermal strategy. Of note, C3N4 nanosheets can act as both the nitrogen source and pre-intercalation species to transform the orthorhombic V2O5 into layered NH4V4O10 with expanded interlayer spacing. Owing to the pillared structure and abundant oxygen vacancies, both the Zn2+ ion (de)intercalation kinetics and the ionic conductivity in the NH4V4O10 cathode are promoted. As a result, the NH4V4O10 cathode delivers exceptional Zn-ion storage ability with a high specific capacity of 398.7 mAh g-1 at 0.5 A g-1, a high-rate capability of 194.7 mAh g-1 at 20 A g-1 and a stable cycling performance of 10000 cycles.

Coupling Zn2+ doping and rich oxygen vacancies in MnO2 nanowire toward advanced aqueous zinc-ion batteries

Easy collapse of structure and sluggish reaction kinetics restrict the practical application of MnO₂ in the field of aqueous Zn-ion batteries (ZIBs). To circumvent these obstacles, Zn²⁺ doping MnO₂ nanowire electrode material with rich oxygen vacancies is prepared by one-step hydrothermal method combined with plasma technology. The experimental results indicate that Zn²⁺ doping MnO₂ nanowire not only stabilizes the interlayer structure of MnO₂, but also provide additional specific capacity as electrolyte ions. Meanwhile, plasma treatment technology induces the oxygen-deficient Zn-MnO₂ electrode optimizing the electronic structure to improve the electrochemical behavior of the cathode materials. Especially, the optimized Zn/Zn-MnO₂ batteries obtain outstanding specific capacity (546 mAh g^-1 at 1 A g^-1) and superior cycling durability (94% over 1000 continuous discharge/charge tests at 3 A g^-1). Greatly, the H⁺ and Zn²⁺ reversible co-insertion/extraction energy storage system of Zn//Zn-MnO₂-4 battery is further revealed by the various characterization analyses during the cycling test process. Further, from the perspective of reaction kinetics, plasma treatment also optimizes the diffusion control behavior of electrode materials. This research proposes a synergistic strategy of element doping and plasma technology, which has enhanced the electrochemical behaviors of MnO₂ cathode and shed light on the design of the high-performance manganese oxide-based cathodes for ZIBs.

A Liquid Metal Microdroplets Initialized Hemicellulose Composite for 3D Printing Anode Host in Zn-Ion Battery

Maintaining a steady affinity between gallium-based liquid metals (LM) and polymer binders, particularly under continuous mechanical deformation, such as extrusion-based 3D printing or plating/stripping of Zinc ion (Zn²⁺ ), is very challenging. Here, an LM-initialized polyacrylamide-hemicellulose/EGaIn microdroplets hydrogel is used as a multifunctional ink to 3D-print self-standing scaffolds and anode hosts for Zn-ion batteries. The LM microdroplets initiate acrylamide polymerization without additional initiators and cross-linkers, forming a double-covalent hydrogen-bonded network. The hydrogel acts as a framework for stress dissipation, enabling recovery from structural damage due to the cyclic plating/stripping of Zn²⁺ . The LM-microdroplet-initialized polymerization with hemicelluloses can facilitate the production of 3D printable inks for energy storage devices.

Bi-MOF Modulating MnO2 Deposition Enables Ultra-Stable Cathode-Free Aqueous Zinc-Ion Batteries

The Mn-based materials are considered as the most promising cathodes for zinc-ion batteries (ZIBs) due to their inherent advantages of safety, sustainability and high energy density, however suffer from poor cyclability caused by gradual Mn²⁺ dissolution and irreversible structural transformation. The mainstream solution is pre-adding Mn²⁺ into the electrolyte, nevertheless faces the challenge of irreversible Mn²⁺ consumption results from the MnO₂ electrodeposition reaction (Mn²⁺  → MnO₂ ). This work proposes a "MOFs as the electrodeposition surface" strategy, rather than blocking it. The bismuth (III) pyridine-3,5-dicarboxylate (Bi-PYDC) is selected as the typical electrodeposition surface to regulate the deposition reaction from Mn²⁺ to MnO₂ . Because of the unique less hydrophilic and manganophilic nature of Bi-PYDC for Mn²⁺ , a moderate MnO₂ deposition rate is achieved, preventing the electrolyte from rapidly exhausting Mn²⁺ . Simultaneously, the intrinsic stability of deposited R-MnO₂ is enhanced by the slowly released Bi³⁺ from Bi-PYDC reservoir. Furthermore, Bi-PYDC shows the ability to accommodate H⁺ insertion/extraction. Benefiting from these merits, the cathode-free ZIB using Bi-PYDC as the electrodeposition surface for MnO₂ shows an outstanding cycle lifespan of more than 10 000 cycles at 1 mA cm^-2 . This electrode design may stimulate a new pathway for developing cathode free long-life rechargeable ZIBs.

Reducing the Surface Tension of Zn Anodes by an Abietic Acid Layer for High Redox Kinetics and Reversibility

Aqueous zinc batteries are appealing devices for cost-effective and environmentally sustainable energy storage. However, the critical issues of uncontrolled dendrite propagation and side reactions with Zn anodes have hindered their practical applications. Inspired by the functions of the rosin flux in soldering, an abietic acid (ABA) layer is fabricated on the surface of Zn anodes (ABA@Zn). The ABA layer protects the Zn anode from corrosion and the concomitant hydrogen evolution reaction. It also facilitates fast interfacial charge transfer and horizontal growth of the deposited Zn by reducing the surface tension of the Zn anode. Consequently, promoted redox kinetics and reversibility are simultaneously achieved by the ABA@Zn. It demonstrates stable Zn plating/stripping cycling over 5100 h and a high critical current of 8.0 mA cm^-2. Moreover, the assembled ABA@Zn|(NH₄)₂V₆O₁₆ full cell delivers outstanding long-term cycling stability with an 89% capacity retention after 3000 cycles. This work provides a straightforward yet effective solution to the key issues of aqueous zinc batteries.

3D Cold-Trap Environment Printing for Long-Cycle Aqueous Zn-Ion Batteries

Zn powder (Zn-P)-based anodes are always regarded as ideal anode candidates for zinc ion batteries owing to their low cost and ease of processing. However, the intrinsic negative properties of Zn-P-based anodes such as easy corrosion and uncontrolled dendrite growth have limited their further applications. Herein, a novel 3D cold-trap environment printing (3DCEP) technology is proposed to achieve the MXene and Zn-P (3DCEP-MXene/Zn-P) anode with highly ordered arrangement. Benefitting from the unique inhibition mechanism of high lattice matching and physical confinement effects within the 3DCEP-MXene/Zn-P anode, it can effectively homogenize the Zn²⁺ flux and alleviate the Zn deposition rate of the 3DCEP-MXene/Zn-P anode during Zn plating-stripping. Consequently, the 3DCEP-MXene/Zn-P anode exhibits a superior cycling lifespan of 1400 h with high coulombic efficiency of ≈9.2% in symmetric batteries. More encouragingly, paired with MXene and Co doped MnHCF cathode via 3D cold-trap environment printing (3 DCEP-MXene/Co-MnHCF), the 3DCEP-MXene/Zn-P//3DCEP-MXene/Co-MnHCF full battery delivers high cyclic durability with the capacity retention of 95.7% after 1600 cycles. This study brings an inspired universal pathway to rapidly fabricate a reversible Zn anode with highly ordered arrangement in a cold environment for micro-zinc storage 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.

Stable Zn Anodes with Triple Gradients

Aqueous zinc-ion batteries are highly desirable for sustainable energy storage, but the undesired Zn dendrites growth severely shortens the cycle life. Herein, a triple-gradient electrode that simultaneously integrates gradient conductivity, zincophilicity, and porosity is facilely constructed for a dendrite-free Zn anode. The simple mechanical rolling-induced triple-gradient design effectively optimizes the electric field distribution, Zn²⁺ ion flux, and Zn deposition paths in the Zn anode, thus synergistically achieving a bottom-up deposition behavior for Zn metals and preventing the short circuit from top dendrite growth. As a result, the electrode with triple gradients delivers a low overpotential of 35 mV and operates steadily over 400 h at 5 mA cm^-2 /2.5 mAh cm^-2 and 250 h at 10 mA cm^-2 /1 mAh cm^-2 , far surpassing the non-gradient, single-gradient and dual-gradient counterparts. The well-tunable materials and structures with the facile fabrication method of the triple-gradient strategy will bring inspiration for high-performance energy storage devices.

Molecular-Level Zn-Ion Transfer Pump Specifically Functioning on (002) Facets Enables Durable Zn Anodes

The modification of metallic Zn anode contributes to solving the cycling issue of Zn-ion batteries (ZIBs) by restraining the dendrite growth and side reactions. In this regard, modulating (002) Zn is an effective way to prolong the lifespan of ZIBs with a parallel arrangement of Zn deposition. Herein, the authors propose to add trace amounts of Zn(BF₄ )₂ additive in 3 M ZnSO₄ to promote in-plane Zn deposition by forming a BF₄ ^- -[Zn(H₂ O)₆ ]²⁺ -[Zn(BF₄ )₃ ]^- transfer process and specifically functioning on (002) facets. In this way, the optimized electrolyte highly boosts the cycling stability of Zn anodes with a long lifespan at 34.2% Zn utilization (500 h/10 mA cm^-2 ) and 51.3% Zn utilization (360 h/10 mA cm^-2 ; 834 h/1 mA cm^-2 ). Moreover, the electroplated Zn on Cu substrate exhibits a competitive cumulative plating capacity (CPC) of 2.87 Ah cm^-2 under harsh conditions. The assembled Zn|(NH₄ )₂ V₆ O₁₆ ·3H₂ O full cells with a high cathode loading of 29.12 mg cm^-2 also realizes almost no capacity degradation even after 2000 cycles at 2 A g^-1 . With this cost-effective strategy, it is promising to push the development of aqueous ZIBs as well as provide inspiration for metal anode optimization in other energy storage systems.

Heterostructures Stimulate Electric-Field to Facilitate Optimal Zn2+ Intercalation in MoS2 Cathode

The electric-field effect is an important factor to enhance the charge diffusion and transfer kinetics of interfacial electrode materials. Herein, by designing a heterojunction, the influence of the electric-field effect on the kinetics of the MoS₂ as cathode materials for aqueous Zn-ion batteries (AZIBs) is deeply investigated. The hybrid heterojunction is developed by hydrothermal growth of MoS₂ nanosheets on robust titanium-based transition metal compound ([titanium nitride, TiN] and [titanium oxide, TiO₂ ]) nanowires, denoted TNC@MoS₂ and TOC@MoS₂ NWS, respectively. Benefiting from the heterostructure architecture and electric-field effect, the TNC@MoS₂ electrodes exhibit an impressive rate performance of 200 mAh g^-1 at 50 mA g^-1 and cycling stability over 3000 cycles. Theoretical studies reveal that the hybrid architecture exhibits a large-scale electric-field effect at the interface between TiN and MoS₂ , enhances the adsorption energy of Zn-ions, and increases their charge transfer, which leads to accelerated diffusion kinetics. In addition, the electric-field effect can also be effectively applied to TiO₂ and MoS₂ , confirming that the concept of heterostructures stimulating electric-field can provide a relevant understanding for the architecture of other cathode materials for AZIBs and beyond.

Interspace and Vacancy Modulation: Promoting the Zinc Storage of an Alcohol-Based Organic-Inorganic Cathode in a Water-Organic Electrolyte

Expanding interspace and introducing vacancies are desired to promote the mobility of Zn ions and unlock the inactive sites of layered cathodes. However, this two-point modulation has not yet been achieved simultaneously in vanadium phosphate. Here, a strategy is proposed for fabricating an alcohol-based organic-inorganic hybrid material, VO_{1- x} PO₄ ·0.56C₆ H₁₄ O₄ , to realize the conjoint modulation of the d-interspace and oxygen vacancies. Peculiar triglycol molecules with an inclined orientation in the interlayer also boost the improvement in the conversion rate of V⁵⁺ to V⁴⁺ and the intensity of the PO bond. Their synergism can ensure steerable adjustment for intercalation kinetics and electron transport, as well as realize high chemical reactivity and redox-center optimization, leading to at least 200% increase in capacity. Using a water-organic electrolyte, the designed Zn-ion batteries with an ultrahigh-rate profile deliver a long-term durability (fivefold greater than pristine material) and an excellent energy density of ≈142 Wh kg^-1 (including masses of cathode and anode), thereby substantially outstripping most of the recently reported state-of-the-art zinc-ion batteries. This work proves the feasibility to realize the two-point modulation by using organic intercalants for exploiting high-performance new 2D materials.

Electrolyte Salts and Additives Regulation Enables High Performance Aqueous Zinc Ion Batteries: A Mini Review

Aqueous zinc ion batteries (ZIBs) are regarded as one of the most ideally suited candidates for large-scale energy storage applications owning to their obvious advantages, that is, low cost, high safety, high ionic conductivity, abundant raw material resources, and eco-friendliness. Much effort has been devoted to the exploration of cathode materials design, cathode storage mechanisms, anode protection as well as failure mechanisms, while inadequate attentions are paid on the performance enhancement through modifying the electrolyte salts and additives. Herein, to fulfill a comprehensive aqueous ZIBs research database, a range of recently published electrolyte salts and additives research is reviewed and discussed. Furthermore, the remaining challenges and future directions of electrolytes in aqueous ZIBs are also suggested, which can provide insights to push ZIBs' commercialization.

Design and Synthesis of a π-Conjugated N-Heteroaromatic Material for Aqueous Zinc-Organic Batteries with Ultrahigh Rate and Extremely Long Life

Electroactive organic materials with tailored functional groups are of great importance for aqueous Zn-organic batteries due to their green and renewable nature. Herein, a completely new N-heteroaromatic material, hexaazatrinaphthalene-phenazine (HATN-PNZ) is designed and synthesized, by an acid-catalyzed condensation reaction, and its use as an ultrahigh performance cathode for Zn-ion batteries demonstrated. Compared with phenazine monomer, it is revealed that the π-conjugated structure of N-heteroaromatics can effectively increase electron delocalization, thereby improving its electrical conductivity. Furthermore, the enlarged aromatic structure noticeably suppresses its dissolution in aqueous electrolytes, thus enabling high structural stability. As expected, the HATN-PNZ cathode delivers a large reversible capacity of 257 mAh g^-1 at 5 A g^-1 , ultrahigh rate capability of 144 mAh g^-1 at 100 A g^-1 , and an extremely long cycle life of 45 000 cycles at 50 A g^-1 . Investigation of the charge-storage mechanism demonstrates the synergistic coordination of both Zn²⁺ and H⁺ cations with the phenanthroline groups, with Zn²⁺ first followed by H⁺ , accompanying the reversible formation of zinc hydroxide sulfate hydrate. This work provides a molecular-engineering strategy for superior organic materials and adds new insights to understand the charge-storage behavior of aqueous Zn-organic batteries.

Manipulating Hierarchical Orientation of Wet-Spun Hybrid Fibers via Rheological Engineering for Zn-Ion Fiber Batteries

Wet-spinning is a promising strategy to fabricate fiber electrodes for real commercial fiber battery applications, according to its great compatibility with large-scale fiber production. However, engineering the rheological properties of the electrochemical active materials to accommodate the viscoelasticity or liquid crystalline requirements for continuous wet-spinning remains a daunting challenge. Here, with entropy-driven volume-exclusion effects, the rheological behavior of vanadium pentoxide (V₂ O₅ ) nanowire dispersions is regulated through introducing 2D graphene oxide (GO) flakes in an optimal ratio. By optimizing the viscoelasticity and liquid-crystalline behavior of the spinning dope, the wet-spun hybrid fibers display controlled hierarchical orientation. The wet-spun V₂ O₅ /rGO hybrid fiber with the optimal 10:1 mass fraction (V₂ O₅ /rGO_10:1 ) exhibits a highly oriented nanoblock arrangement, enabling efficient Zn-ion migration and an excellent Zn-ion storage capacity of 486.03 mAh g^-1 at 0.1 A g^-1 . A half-meter long quasi-solid-state fiber Zn-ion battery is assembled with a polyacrylamide gel electrolyte and biocompatible Ecoflex encapsulation. The thus-derived fiber Zn-ion battery is integrated into a wearable self-powered system, incorporating a highly efficient GaAs solar cell, which delivers a record-high overall efficiency (9.80%) for flexible solar charging systems.

Biomolecular Regulation of Zinc Deposition to Achieve Ultra-Long Life and High-Rate Zn Metal Anodes

Aqueous zinc-ion batteries (ZIBs) have been extensively studied due to their inherent safety and high energy density for large-scale energy storage. However, the practical application is significantly limited by the growing Zn dendrites on metallic Zn anode during cycling. Herein, an environmental biomolecular electrolyte additive, fibroin (FI), is proposed to guide the homogeneous Zn deposition and stabilize Zn anode. This work demonstrates that the FI molecules with abundant electron-rich groups (NH, OH, and CO) can anchor on Zn anode surface to provide more nucleation sites and suppress the side reactions, and the strong interaction with water molecules can simultaneously regulate the Zn²⁺ coordination environment facilitating the uniform deposition of Zn. As a consequence, only 0.5 wt% FI additive enables a highly reversible Zn plating/stripping over 4000 h at 1 mA cm^-2 , indicating a sufficient advance in performance over state-of-the-art Zn anodes. Furthermore, when applied to a full battery (NaVO/Zn), the cell exhibits excellent capacity retention of 98.4% after 1000 cycles as well as high Coulombic efficiency of 99%, whereas the cell only operates for 68 cycles without FI additive. This work offers a non-toxic, low-cost, effective additive strategy to solve dendrites problems and achieve long-life and high-performance rechargeable aqueous ZIBs.

The Dopamine Assisted Synthesis of MoO3/Carbon Electrodes With Enhanced Capacitance in Aqueous Electrolyte

A capacitance increase phenomenon is observed for MoO₃ electrodes synthesized via a sol-gel process in the presence of dopamine hydrochloride (Dopa HCl) as compared to α-MoO₃ electrodes in 5M ZnCl₂ aqueous electrolyte. The synthesis approach is based on a hydrogen peroxide-initiated sol-gel reaction to which the Dopa HCl is added. The powder precursor (Dopa)_xMoO_y, is isolated from the metastable gel using freeze-drying. Hydrothermal treatment (HT) of the precursor results in the formation of MoO₃ accompanied by carbonization of the organic molecules; designated as HT-MoO₃/C. HT of the precipitate formed in the absence of dopamine in the reaction produced α-MoO₃, which was used as a reference material in this study (α-MoO₃-ref). Scanning electron microscopy (SEM) images show a nanobelt morphology for both HT-MoO₃/C and α-MoO₃-ref powders, but with distinct differences in the shape of the nanobelts. The presence of carbonaceous content in the structure of HT-MoO₃/C is confirmed by FTIR and Raman spectroscopy measurements. X-ray diffraction (XRD) and Rietveld refinement analysis demonstrate the presence of α-MoO₃ and h-MoO₃ phases in the structure of HT-MoO₃/C. The increased specific capacitance delivered by the HT-MoO₃/C electrode as compared to the α-MoO₃-ref electrode in 5M ZnCl₂ electrolyte in a −0.25–0.70 V vs. Ag/AgCl potential window triggered a more detailed study in an expanded potential window. In the 5M ZnCl₂ electrolyte at a scan rate of 2 mV s⁻¹, the HT-MoO₃/C electrode shows a second cycle capacitance of 347.6 F g⁻¹. The higher electrochemical performance of the HT-MoO₃/C electrode can be attributed to the presence of carbon in its structure, which can facilitate electron transport. Our study provides a new route for further development of metal oxides for energy storage applications.

Highly Reversible Zinc Anode Enabled by a Cation-Exchange Coating with Zn-Ion Selective Channels

Rechargeable aqueous zinc-ion batteries (ZIBs) have attracted extensive attention due to their low cost and high safety. However, the critical issues of dendrite growth and side reactions on the Zn metal anode hinder the commercialization of ZIBs. Herein, we demonstrated that the formation of Zn₄SO₄(OH)₆·5H₂O byproducts is closely relevant to the direct contact between the Zn electrode and SO₄^2-/H₂O. On the basis of this finding, we developed a cation-exchange membrane of perfluorosulfonic acid (PFSA) coated on the Zn surface to regulate the Zn plating/stripping behavior. Importantly, the PFSA film with abundant sulfonic acid groups could simultaneously block the access of SO₄^2- and H₂O, accelerate the Zn²⁺ ion transport kinetics, and uniformize the electrical and Zn²⁺ ion concentration field on the Zn surface, thus achieving a highly reversible Zn plating/stripping process with corrosion-free and dendrite-free behavior. Consequently, the PFSA-modified Zn anode exhibits high reversibility with 99.5% Coulombic efficiency and excellent plating/stripping stability (over 1500 h), subsequently enabling a highly rechargeable Zn-MnO₂ full cell. The strategy of the cation-exchange membrane proposed in this work provides a simple but efficient method for suppression of side reactions.

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

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

Reunderstanding the Reaction Mechanism of Aqueous Zn-Mn Batteries with Sulfate Electrolytes: Role of the Zinc Sulfate Hydroxide

Rechargeable aqueous Zn-Mn batteries have garnered extensive attention for next-generation high-safety energy storage. However, the charge-storage chemistry of Zn-Mn batteries remains controversial. Prevailing mechanisms include conversion reaction and cation (de)intercalation in mild acid or neutral electrolytes, and a MnO₂ /Mn²⁺ dissolution-deposition reaction in strong acidic electrolytes. Herein, a Zn₄ SO₄ ·(OH)₆ ·xH₂ O (ZSH)-assisted deposition-dissolution model is proposed to elucidate the reaction mechanism and capacity origin in Zn-Mn batteries based on mild acidic sulfate electrolytes. In this new model, the reversible capacity originates from a reversible conversion reaction between ZSH and Zn_x MnO(OH)₂ nanosheets in which the MnO₂ initiates the formation of ZSH but contributes negligibly to the apparent capacity. The role of ZSH in this new model is confirmed by a series of operando characterizations and by constructing Zn batteries using other cathode materials (including ZSH, ZnO, MgO, and CaO). This research may refresh the understanding of the most promising Zn-Mn batteries and guide the design of high-capacity aqueous Zn batteries.

A Biomimetic Polymer-Based Composite Coating Inhibits Zinc Dendrite Growth for High-Performance Zinc-Ion Batteries

Because of their low cost, safety, and green nature, aqueous Zn-ion batteries are promising candidates for energy storage. However, the appearance of Zn dendrites, hydrogen evolution reaction (HER), and corrosion limit the development of the aqueous Zn-ion batteries. Here, inspired by fibrous cartilage, a biomimetic poly(vinylidene fluoride) (PVDF)-based composite polymer coating layer, including aramid nanofiber (ANF) and zinc trifluoromethanesulfonate [Zn(CF₃SO₃)₂], called ANFZ, was designed and fabricated. The high ionic conductivity (3.84 mS cm^-1) of the flexible PVDF matrix, optimized by Zn(CF₃SO₃)₂, combined with the highly mechanical ANF network can effectively guide the rate of Zn stripping/plating, homogenize the Zn²⁺ distribution, and suppress the dendrites. In addition, the high Coulombic efficiency is obtained due to the suppression of HER and corrosion by the biomimetic coating layer. Symmetric ANFZ@Zn//ANFZ@Zn can steadily work over 1000 h at 1 mA cm^-2 with a high degree of reversibility, which is greater than that of bare Zn//bare Zn. Furthermore, the ANFZ@Zn//MVO batteries show a high specific capacity (400.2 mAh g^-1, 0.1 A g^-1) and a long cycle life. This work presents a novel method combined with bionics for designing and assembling Zn anodes without dendrites for zinc-ion batteries.

Regulating Interfacial Ion Migration via Wool Keratin Mediated Biogel Electrolyte toward Robust Flexible Zn-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) have emerged as a promising energy supply for next-generation wearable electronics, yet they are still impeded by the notorious growth of zinc dendrite and uncontrollable side reaction. While the rational design of electrolyte composition or separator decoration can effectively restrain zinc dendrite growth, synchronously regulating the interfacial electrochemical performance by tackling the physical delamination venture between electrode and electrolyte remains a major obstacle for high-performance wearable aqueous ZIB. Herein, a category of hybrid biogel electrolyte containing carrageenan and wool keratin (CWK) is put forward to regulate the interfacial electrochemistry in aqueous ZIB. Systematic electrochemical kinetics analyses and ex situ scanning electrochemical microscopy (SECM) characterizations achieve comprehensive understanding of the keratin enhanced interfacial Zn²⁺ redox reaction. Thanks to the keratin triggered selective ion permeability, the as-designed CWK hybrid biogel electrolyte manifests a promoted Zn²⁺ transference number and excellent reversibility of Zn plating/stripping and outstanding Zn utilization (average Coulombic efficiency ≈98%). More impressively, the CWK hybrid biogel electrolyte also demonstrates cathode side-reaction depression and strengthened interfacial adhesion while assembled into a quasi-solid-state flexible ZIB. This work offers a strategy to synchronously solve concurrent challenges for both of Zn anode and cathode toward realistic wearable aqueous ZIB.

Electrostatic Shielding Regulation of Magnetron Sputtered Al-Based Alloy Protective Coatings Enables Highly Reversible Zinc Anodes

The uncontrolled zinc dendrite growth during plating leads to quick battery failure, which hinders the widespread applications of aqueous zinc-ion batteries. The growth of Zn dendrites is often promoted by the "tip effect". In this work, we propose a generate strategy to eliminate the "tip effect" by utilizing the electrostatic shielding effect, which is achieved by coating Zn anodes with magnetron sputtered Al-based alloy protective layers. The Al can form a surface insulating Al₂O₃ layer and by manipulating the Al content of Zn-Al alloy films, we are able to control the strength of the electrostatic shield, therefore realizing a long lifespan of Zn anodes up to 3000 h at a practical operating condition of 1.0 mA cm^-2 and 1.0 mAh cm^-2. In addition, the concept can be extended to other Al-based systems such as Ti-Al alloy and achieve enhanced stability of Zn anodes, demonstrating the generality and efficacy of our strategy.

Hexagonal WO3/3D Porous Graphene as a Novel Zinc Intercalation Anode for Aqueous Zinc-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) have acquired great attention because of their high safety and environmentally friendly properties. However, the uncontrollable Zn dendrites and the irreversibility of electrodes seriously affect their practical application. Herein, hexagonal WO₃/three-dimensional porous graphene (h-WO₃/3DG) is investigated as an intercalation anode for ZIBs. As a result, the h-WO₃/3DG//Zn half-battery shows excellent electrochemical performance with a high capacity of 115.6 mAh g^-1 at 0.1 A g^-1 and 89% capacity retention at 2.0 A g^-1 after 10 000 cycles. The reason could be that the crystalline structure of WO₃, which has hexagonal channels, with a diameter of 5.36 Å, much higher than the diameter of Zn²⁺ (0.73 Å), accelerating the insertion/extraction of Zn ions. A zinc metal-free full battery using h-WO₃/3DG as the anode and ZnMn₂O₄/carbon black (ZnMn₂O₄/CB) as the cathode is constructed, exhibiting an initial capacity of 66.8 mAh g^-1 at 0.1 A g^-1 corresponding to an energy density of 73.5 W h kg^-1 (based on the total mass of anode and cathode-active materials) and a capacity retention of 76.6% after 1000 cycles at 0.5 A g^-1. This work demonstrates the high potential of hexagonal WO₃ as an advanced intercalation anode material for Zn metal-free batteries and may inspire new ideas for the development of other intercalation anode hosts for ZIBs.

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.

Advanced Zinc Anode with Nitrogen-Doping Interface Induced by Plasma Surface Treatment

Aqueous zinc-ion batteries (ZIBs) are one of the most ideal candidates for grid-scale energy storage applications due to their excellent price and safety advantages. However, formation of Zn dendrites and continuous side reactions during cycling result in serious instability problems for ZIBs. In this work, the authors develop a facile and versatile plasma-induced nitrogen-doped Zn (N-Zn) foil for dendrite-free Zn metal anode. Benefitting from the uniform nucleation sites and enhanced surface kinetics, the N-Zn anode exhibits exceptionally low overpotential (around 23 mV) at 1 mA cm-2 and can be cycled for over 3000 h under 1 mA cm-2 because of the enhanced interface behavior. The potential application of N-Zn anode is also confirmed by introducing a full Zn/MnO2 battery with outstanding capacity stability for 2000 cycles at 1 A g-1 . Overall, this work offers new fundamental insights into homogenizing Zn electrodeposition processes by pre-introduced active nucleation sites and provides a novel direction of interface design engineering for ultra-stable Zn metal anode.

Regulating Interfacial Desolvation and Deposition Kinetics Enables Durable Zn Anodes with Ultrahigh Utilization of 80

Rechargeable aqueous zinc ion batteries (ZIBs) represent a promising technology for large-scale energy storage due to their high capacity, intrinsic safety and low cost. However, Zn anodes suffer from poor reversibility and cycling stability caused by the side-reactions and dendrite issues, which limit the Zn utilization in the ZIBs. Herein, to improve the durability of Zn under high utilization, an aluminum-doped zinc oxide (AZO) interphase is presented. The AZO interphase inhibits side reactions by isolating active Zn from the bulk electrolyte, and enables facile and uniform Zn deposition kinetics by accelerating the desolvation of hydrated Zn²⁺ and homogenizing the electric field distribution. Accordingly, the AZO-coated Zn (AZO@Zn) anode exhibits a long lifespan of 600 h with Zn utilization of 34.1% at the current density of 10 mA cm^-2 . Notably, even under ultrahigh Zn utilization of 80%, the AZO@Zn remains stable cycling over 200 h. Meanwhile, the V₂ O₅ /AZO@Zn full cell with limited Zn excess displays high capacity retention of 86.8% over 500 cycles at 2 A g^-1 . This work provides a simple and efficient strategy to ensure the reversibility and durability of Zn anodes under high utilization conditions, holding a great promise for commercially available ZIBs with competitive energy density.

Rationally Designed Mn2 O3 -ZnMn2 O4 Hollow Heterostructures from Metal-Organic Frameworks for Stable Zn-Ion Storage

Mn-based oxides have sparked extensive scientific interest for aqueous Zn-ion batteries due to the rich abundance, plentiful oxidation states, and high output voltage. However, the further development of Mn-based oxides is severely hindered by the rapid capacity decay during cycling. Herein, a two-step metal-organic framework (MOF)-engaged templating strategy has been developed to rationally synthesize heterostructured Mn₂ O₃ -ZnMn₂ O₄ hollow octahedrons (MO-ZMO HOs) for stable zinc ion storage. The distinctive composition and hollow heterostructure endow MO-ZMO HOs with abundant active sites, enhanced electric conductivity, and superior structural stability. By virtue of these advantages, the MO-ZMO HOs electrode shows high reversible capacity, impressive rate performance, and outstanding electrochemical stability. Furthermore, ex situ characterizations reveal that the charge storage of MO-ZMO HOs mainly originates from the highly reversible Zn²⁺ insertion/extraction reactions.