Nonepitaxial Electrodeposition of (002)-Textured Zn Anode on Textureless Substrates for Dendrite-Free and Hydrogen Evolution-Suppressed Zn Batteries

Establishing Ohmic contact with ultra-thin semiconductor layer through magnetron sputtering for dendrite-free Zn metal batteries

The improvement in reversibility and kinetics for Zn metal anodes is crucial to facilitate the further application of aqueous zinc ion batteries. However, the abnormal surface-caused dendrites and parasitic reactions significantly impede the commercial application. Herein, we established Ohmic contact by fabricating an ultrathin semiconductor ZnTe (∼150 nm) layer on the Zn surface via magnetron sputtering to form an electron enrichment region for zinc ions attraction. Particularly, the ZnTe with a higher work function than that of Zn could render a spontaneous electron transfer from Zn to ZnTe, accelerating the zinc ions diffusion, and repelling water and negative sulfate radicals. As a result, the ultrathin ZnTe layer decreases the nucleation and deposition barrier of Zn leading to homogeneous deposition, and restrains the Zn from corrosion and hydrogen evolution reaction. The ZnTe-modified symmetric cells can stably cycle for over 2,400 h and 1,100 h at current density 1 mA cm-2 with area capacity of 1 mAh cm-2 and 5 mAh cm-2, respectively. The full cell matched with CaV8O20·nH2O shows a 63 % capacity retention after 3,000 cycles at 3 A/g. Our work demonstrates that the construction of Ohmic contact could be an effective way to obtain highly reversible Zn anodes and promote the development of aqueous zinc ions batteries.

Low Strain Mediated Zn (0002) Plane Epitaxial Plating for Highly Stable Zinc Metal Batteries

Optimizing the crystalline orientation to achieve stable Zn (0002) plane growth is pursued for highly reversible zinc metal batteries (ZMBs). However, the lattice strain of Zn substrate hinders stable Zn2+ plating/stripping and sustainable epitaxial growth of Zn (0002) texture. Herein, we present a low-strain strategy to mediate nucleated-Zn grains for stabilizing Zn2+ electrodeposition/stripping process and guiding sustainable Zn2+ growth along (0002) surfaces. Fluorinated anthracene triptycene polymer (FATP) photopolymerized on Zn exhibits nanocrystalline structure with highly ordered nanochannels (1.5 nm), enabling oriented nucleation and sustainable epitaxial stacking of Zn (0002) plane due to low nucleation energy (0.2 vs. 1.1 e- Å-3 of pure Zn) and low grain strain (-0.2 to 0.4 vs. -0.9 to 0.9 MPa). Besides, the ordered porous FATP nanofilm refines electroplating Zn grains (9.4 vs. 26.7 µm), alleviating strain accumulation (3.7 vs. 28.2 MPa) and lattice distortion. Consequently, FATP-Zn||Cu cell achieves a high average Coulombic efficiency of 99.6% over 6000 cycles, while FATP-Zn||FATP-Zn cell shows stable plating/stripping after 5000 h. Notably, FATP-Zn||MnO2 pouch cell (2.77 Ah) demonstrates stable operation over 1000 cycles. This work presents a new approach to designing Zn anodes with refined nucleated-Zn grains and sustainable Zn (0002) plane stacking for advanced ZMBs.

Boron-Fluoride Dual-atom Synergistic Regulated Interface Coating Enables Stable Zn-Metal Anodes

Aqueous zinc-based batteries provide promising opportunities for next-generation rechargeable batteries. Nevertheless, Zn anode encounters severe challenges, such as Zn dendrite formation, surface corrosion, and hydrogen evolution reaction (HER). Here, we report a strategy to spontaneously construct a boron-fluoride dual-atom regulated SEI (ZnBOF), which involves the formation of a B-compound coating through an etching process followed by an in situ F substitution during the initial electrochemical cycling. The ZnBOF/Zn anode benefits preferential deposition of Zn2+ along the (002) plane without Zn dendrite, and the side reactions including by-product and HER are dramatically suppressed. A combination of characterization methods, such as X-ray absorption spectroscopy, shows that the B-containing passivation layer facilitates the transport of Zn2+ and mitigates water-related side reactions, and the F atoms serve as zincophilic sites that enhance the transfer kinetics of Zn2+. As expected, the well-designed ZnBOF/Zn anode exhibits ultra-stable Zn plating/stripping for 5000 h at 2 mA cm-2. The assembled ZnBOF/Zn||MnO2 batteries show impressive cycling stability, remaining 96.2% of the initial capacity (234.3 mAh g-1) after 1700 cycles at 1.0 A g-1. Therefore, this work reveals a dual-atom synergistic regulated strategy to fabricate a robust SEI for Zn anode, which contributes to the development of aqueous zinc-based batteries.

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.

Overcoming the Challenges in Aqueous Zinc Metal Batteries: Underlying Issues and Mitigation Strategies

The increasing demand for green and clean energy harvesting and their judicious storage call for pursuing new energy storage technologies. Building better batteries has drawn significant attention to fulfilling the energy demand by delivering the stored electrical energy at the anticipated time and minimal cost. Li-ion batteries play a crucial role in transitioning to a sustainable energy landscape. However, their safety and environmental issues are of concern. Zn-based batteries provide more sustainable solutions due to their low cost, enhanced safety, and environmental benignity. Still, poor thermodynamic reversibility and stability of Zn anode in the aqueous electrolytes prevent its practical application. Significant efforts such as Zn anode surface engineering and electrolyte and/or interface modification alleviate these issues. However, in-depth studies of the root causes associated with the reversibility and stability issues of Zn electrodes are still deficient. Hence, this review focuses on the underlying causes of the major issues (dendrite, hydrogen evolution, corrosion, and passivation) associated with Zn anodes. Furthermore, we have summarized the technological advances that have been made to address these issues. Finally, some promising future directions and perspectives are provided for a further in-depth understanding of thermodynamic irreversibility and to improve the overall performance of the Zn anode.

α-Methyl Group Reinforced Amphiphilic Poly(Ionic Liquid) Additive for High-Performance Zinc-Iodine Batteries

Aqueous zinc-iodine (Zn-I2) batteries are prospective on energy storage, yet the practical application is severely hindered by side reactions of Zn metal and the shuttle effects for polyiodide. Herein, a polymer additive was copolymerized by 1-vinyl-3-ethylimidazolium trifluoromethanesulfonate (VEImOTf) and methacrylamide (MAAm) (PVEMA) to alleviate the above issues. The polymer chain of PVEMA endows amphipathic properties for Zn2+ diffusion and solvation structure regulation, and the α-methyl of MAAm enhances the hydrophobic properties to avoid side reactions on Zn metal. In addition, the imidazole groups adsorb onto Zn metal with electrostatic shielding effect for further side reaction alleviation and mitigate shuttle effects by electrostatic interactions with polyiodides. Consequently, the PVEMA confers the symmetrical Zn battery with great cycling stability for over 400 h at 20 mA cm-2 and high depth of discharge (DOD) of 77.7%. The Zn-I2 batteries with PVEMA also demonstrate stable cycling performance under various current densities and temperatures.

Anion-endowed high-dielectric water-deficient interface towards ultrastable Zn metal batteries

To achieve reversible metallic Zn anodes for aqueous rechargeable zinc batteries, regulating the electrolyte-Zn interface is the key to addressing the side reactions on Zn. Beyond water-deficiency, design rules for constructing the highly efficient electrochemical interface are still vague. Anions, as primary electrolyte constituents, not only play a role in solvation structure, but also influence the electrolyte-Zn interface. Here, the characteristics of representative anions in current aqueous zinc electrolytes are surveyed. A candidate combining polarizability, H-bond tuning ability and high solubility is proposed to construct a high-dielectric water-deficient electrolyte-Zn interface to regulate the interfacial chemistry on Zn. The anion-dominated electrochemical interface promotes the Zn deposition kinetics and achieves uniform Zn deposition with high stability, which further enables the in situ formation of an SEI for highly stable Zn stripping/plating, e.g., at 20 mA cm-2 and 20 mA h cm-2. Furthermore, this built-in interface exhibits an effect in stabilizing the V2O5 cathode, endowing the V2O5/Zn cell with ultra-stable long-term cycling, e.g., 10 000 cycles at 10 A g-1 with a high retention rate of 89.7%. Our design offers insight into guidelines for the development of novel electrolytes towards rationally designed electrochemical interfaces.

Single (002)-Textured Zinc Anode via Nonepitaxial Electrodeposition with In Situ Texture Maintenance for Stable Aqueous Zinc Batteries

Crystallography regulation of a zinc (Zn) metal substrate to expose more (002) textures holds great promise for stabilizing Zn anodes. However, significant challenges remain in directly constructing a single (002)-plane-textured Zn metal anode (S-(002)-Zn) and realizing a sustainable (002)-texture exposure in working batteries. Herein, we report an anion and cation coregulated nonepitaxial electrodeposition to fabricate S-(002)-Zn by introducing 1-ethyl-3-methylimidazolium iodide (EmimI) additives in low-cost ZnSO4 aqueous electrolyte (ZS). Mechanistic studies reveal that the cooperation of Emim+ and I- with oriented adsorption behaviors on Zn can synergistically boost the (100) plane growth, depress the (002) plane growth, and suppress H2 evolution, thus enabling compact S-(002)-Zn electrodeposition. Moreover, other similar organic iodides (e.g., dimethyl-imidazolium iodide and 1-propyl-3-methylimidazolium iodide) are applicable to this scalable electrodeposition. On the other hand, the as-designed ZS-EmimI electrolyte can be directly applied in working Zn batteries, thus effectively sustaining the smooth (002) texture of S-(002)-Zn and inhibiting HER during cycling. Consequently, the combination of single-(002)-texture and ZS-EmimI electrolyte endows the S-(002)-Zn anode with an ultralong lifespan over 10,100 h (>14 months) at 1 mAh cm-2 and superior deep-cycling stability under 88.0% utilization (25 mAh cm-2) over 500 h and assures the stable operation of full Zn batteries.

Step-Edge Guided Homoepitaxy Enables Highly Reversible Zn Plating/Stripping

Metal anodes are of profound impact towards the realization of energy-dense rechargeable batteries. However, the "hostless" metal redox always presents the disordered plating/stripping, aggravated by the side reactions and local anisotropy that cause the formation of excessive dendrites/voids and quickly lead to battery failure. Here we report step-edge guided homoepitaxy enabling ordered layer-by-layer Zn plating/stripping regardless of the (dis)charging conditions. Through engineering the atomic terrace height on the mono-oriented Zn(0002) foil anodes, both in-plane and out-of-plane epitaxy aligned to the underlying Zn lattice are demonstrated via the favored edge nucleation and strong interfacial interaction driven by the surface/interface energy minimization, achieving the electrochemical homoepitaxy of continuous, submillimeter-scale Zn(0002) crystal with nearly 100 % theoretical density. Accordingly, we achieve a high Coulombic efficiency of 99.8 %, high depths of discharge exceeding 51 % and 82 % along with record-high lifetimes of over a thousand and hundreds of hours, respectively, in zinc metal batteries. The breakthrough results provide new insights on the intrinsic metal plating/stripping from the view of reversible homoepitaxy for rechargeable energy-dense metal batteries.

Tailoring Crystalline States of Alloy Coating for High Current Density and Large Areal Capacity of Zn

Due to issues of hydrogen evolution, corrosion, and uncontrolled deposition behaviors at the Zn anode, the practical implementation of Zn-ion batteries has faced significant obstacles. Very limited attention is directed toward various alloy crystalline states for the Zn anode protection primarily due to the challenge of synthesizing high-quality alloy coatings with diverse crystalline states. In this study, the crystalline state of NiCr alloy coating is precisely manipulated using magnetron sputtering, revealing distinct thermodynamic and kinetic changes induced by variation in the crystalline state. This research emphasizes the fundamental understanding of microstructure dynamics and achieves a highly reversible Zn anode at harsh conditions of high current density (80 mA cm-2) and large areal capacity (40 mAh cm-2), thus enabling high-capacity and longevous pouch battery.

Sn Penetrated Zincophilic Interface Design in Porous Zn Substrate for High Performance Zn-Ion Battery

Rechargeable zinc-ion batteries are considered an ideal energy storage system due to their low cost and nonflammable aqueous electrolyte. However, dendrite growth, hydrogen evolution reaction, and self-corrosion of zinc anode brought about serious safety risks including short circuits and electrode expansion. Therefore, a modified host-design strategy with a 3D porous structure and bulk-phase penetrated zincophilic interface is proposed to boost the stability and lifetime of the Zn anode. The porous Zn substrate is constructed by universal HCl etching and the uniform and tight Sn-penetrated zincophilic interface is formed by effective electron beam evaporation (EBE). The porous substrate can uniform zinc ion flux and the Sn coating could effectively improve zinc ion deposition behavior, thus inhibiting the risk of dendrites growth and side reaction. As a result, the 3D Zn substrate with Sn interface (3D Zn@Sn) exhibits prolonged galvanostatic cycling performance up to 4500 h with a low polarization of ≈25 mV (1 mA cm-2, 1 mAh cm-2) in the symmetric cell. The full cell assembled with KVOH@Ti could maintain a high specific capacity of 148.6 mAh g-1 after 500 galvanostatic cycles (10 A g-1). This work proposed an improved electrode design to realize the high performance of zinc ion batteries.

Synergistic interface regulation for achieving fast kinetics and highly reversible zinc metal anodes

Uncontrolled zinc dendrite growth and adverse side reactions at the Zn anode interface severely limit its practical application. Based on theoretical calculations, this study in situ constructs a functional interface (ICFI Zn) on the Zn anode surface, consisting of a surface-textured structure and a zinc-philic protective layer. Benefiting from the synergistic effect of ion regulation and atomic anchoring of this functional interface, the ICFI Zn anode achieves homogenised regulation of ion fluxes, facilitates ion transport kinetics, effectively suppresses side reactions and guides the deposition of dendrite-free Zn. Consequently, this functional interface endows the zinc anode with significantly enhanced cycling stability, lower nucleation barriers, and reduced voltage polarization. Surprisingly, the ICFI Zn anode exhibits over 3000 h of stable cycling performance at a high current density of 2 mA cm-2. Even at high current densities of 5, 10, and 20 mA cm-2, it still maintains high reversibility. Furthermore, in practical applications with the ICFI Zn||MnO2 battery, it also demonstrates ultra-long cycling stability. The one-step in situ construction of this functional interface provides a novel strategy for developing zinc metal anodes with rapid kinetics and high reversibility.

Greatly Enhancing the Stability and Reversibility of Zn Electrode in the Alkaline Electrolyte by Introducing Lauryl Phosphate Potassium

Alkaline Zn batteries are currently among the most important energy storage technologies due to their low cost, safety, and high energy density. However, the storage lifespan and reversibility of these batteries are severely restricted by the side reactions of the Zn electrode in the alkaline electrolytes, such as hydrogen evolution, self-corrosion, and uneven Zn deposition. This work addresses these issues by introducing lauryl phosphate potassium (PLP) into the alkaline electrolyte and forming a protective layer adsorbed onto the Zn surface. This approach significantly inhibits the hydrogen evolution reaction, thereby reducing the self-corrosion of Zn, as well as effectively preventing shape changes and Zn dendrites, resulting from uneven Zn deposition. Specially, the introduction of 100 ppm of PLP can reduce the hydrogen evolution rate of the Zn electrode by over 90% and extend the cyclic life by about 10 times. The incorporation of 500 ppm of PLP not only enhances the discharge performances of alkaline Zn-MnO2 battery but also significantly improves their storage lifespan. Furthermore, introducing 100 ppm of PLP into aqueous and solid-state Zn-air batteries can greatly enhance their discharge capacities and cycling stabilities. This research provides a facile approach to enhance the storage performance and reversibility of alkaline Zn batteries.

"Pumping" Trace Cu Impurity out of Zn Foil for Sustainable Aqueous Battery Interface

Dendritic zinc (Zn) electrodeposition presents a significant obstacle to the large-scale development of rechargeable zinc-ion batteries. To mitigate this challenge, various interfacial strategies have been employed. However, these approaches often involve the incorporation of foreign materials onto Zn anode surface, resulting in increased material costs and processing complexities, not to mention the compromised interface endurability due to structural and compositional heterogeneity. Realizing that Cu atoms typically exist as trace impurities in commercial Zn, a novel approach is demonstrated that leverages these Cu impurities to create a Cu-rich surface for effective modulation of Zn electrodeposition. By simply heating commercially available Zn foil with a naturally oxidized surface, not only the internal Cu atoms are thermally activated to become diffusible, their diffusion is also navigated toward the surface via oxygen attraction. The resulting Cu-rich surface effectively regulates Zn electrodeposition, comparable to conventional interfacial strategies, yet exhibits superior cycling durability. 3D in situ microscopy confirms that this Cu-rich surface enables dendrite-free, compact, and (101)-oriented Zn electrodeposition, contrasting with the traditional (002)-oriented dendrite-suppression mechanism. By transforming trace Cu impurity within Zn foil into a Cu-rich surface, this work demonstrates a straightforward, cost-effective and efficient method for controlling Zn electrodeposition.

Pulse Current-Induced Homogeneous Phase Nucleation for High-Performance Conversion-Type Cathodes

Conversion-type transition metal-based materials (MZx) are considered promising cathodes for lithium metal batteries due to their low cost, abundant availability, and high theoretical energy density. However, they suffer from rapid capacity decay caused by the transformation into two inhomogeneous phases during discharge. Herein, we use a pulse current discharge activation method (under 3C) to induce homogeneous phase nucleations. As a result, the microsized FeS2 cathode transforms into a homogeneous mixture of nanosized Fe and Li2S, effectively mitigating volume expansion. It exhibits exceptional cycling performance, delivering a specific capacity of 572.8 mAh g-1 after 800 cycles at 0.33C. Even at a high areal capacity of 5.4 mAh cm-2, it undergoes 180 cycles with a capacity retention of 89.3% at 0.33C. This work highlights the crucial role of homogeneous nucleation in achieving long cycling life for conversion-type cathodes.

Polyoxotungstate Featuring Zinc-Ion-Triggered Structural Transformation as An Efficient Electrolyte Additive for Aqueous Zinc-Ion Batteries

It is promising but still challenging for the widespread application of aqueous zinc batteries due to the poor reversibility of the zinc anode caused by prevalent dendrite growth and pronounced interfacial side reactions. Herein, we report a rare soluble and water-stable high-nuclearity {Nd9Si4W39} polyoxotungstate. Interestingly, upon encountering Zn2+ ions, the discrete {Nd9Si4W39} nanocluster undergoes a structural transformation to form an infinitely extended cluster-based {[Zn(H2O)4]3[Nd9Si4W39]2} two-dimensional honeycomb layer, with which atomic-level Zn2+ ion effects in reconstructing the layer are determined. More interestingly, we demonstrate that the structural transformation property renders the {Nd9Si4W39} cluster an efficient electrolyte additive for aqueous zinc batteries, enabling the formation of the 2D layer as a protective layer on the zinc anode, significantly enhancing the reversibility of the zinc anode. Compared to the pristine Zn//Zn symmetric battery, the Zn//Zn symmetric battery with the {Nd9Si4W39} additive exhibits an extended lifespan of over 2000 hours at a current density of 1 mA cm-2. In situ optical microscopy, Raman spectroscopy, and molecular dynamics simulations reveal that the formation of the protective layer effectively promotes uniform zinc deposition, and inhibits zinc agglomeration, dendrite growth, and side reactions, thereby enabling the zinc anode to exhibit high reversibility and long-term service life.

Popularizing Holistic High-Index Crystal Plane via Nonepitaxial Electrodeposition Toward Hydrogen-Embrittlement-Relieved Zn Anode

Electrodeposition is promising to fabricate Zn electrodes affording nonepitaxial single-crystal textures. Previous research endeavors focus on achieving Zn(002) faceted deposition, nevertheless, the popularization of a high-index Zn plane with favorable electrochemical activity remains poorly explored. There also exists a deficiency in the assessment of the electrodeposited quality of Zn. Here, a straightforward strategy to address such concerns by cultivating predominant Zn(112) texture via a potentiostatic electrodeposition mode is reported. By precisely identifying the "limiting" conditions for electrodeposition, a striking balance between improved deposition quality, tailored deposition kinetics, and suppressed hydrogen evolution is found. (002) Faceted Zn electrode is shown that be indeed produced, yet the rampant hydrodynamic convection and hydrogen embrittlement issue under such "over-limiting" preparation conditions pose challenges in the electrode lifespan. In contrast, an optimized deposition minimizes hydrodynamic disturbances and mitigates the hydrogen embrittlement effect, where the thus-generated high-index (112)-textured Zn electrode manifests impressive deposition quality and demonstrates holistic cycling stability. The pouch cell by pairing a ZnxV2O5 (ZnVO) cathode manages a reversible capacity of ≈130 mAh and a capacity retention of 98.42%. This study offers guidance for the development of dendrite-free and hydrogen-embrittlement-relieved Zn anodes, unleashing the potential of high-index plane textures for advanced Zn batteries.

Dissolution, solvation and diffusion in low-temperature zinc electrolyte design

Aqueous zinc-based batteries have garnered the attention of the electrochemical energy storage community, but they suffer from electrolytes freezing and sluggish kinetics in cold environments. In this Review, we discuss the key parameters necessary for designing anti-freezing aqueous zinc electrolytes. We start with the fundamentals related to different zinc salts and their dissolution and solvation behaviours, by highlighting the effects of anions and additives on salt solubility, ion diffusion and freezing points. We then focus on the complex structures and energetics of cation-anion-solvent interaction. We also evaluate the prevailing strategies to improve the performance of electrolytes at low temperatures, with a discussion on the kinetics of plating and stripping of zinc anodes and charge storage in various cathode materials. Furthermore, we consider the current challenges and envisage future research directions in cold-resistant aqueous electrolyte formulations for zinc batteries.

Single Exposed Zn (0002) Plane and Sustainable Zn-Oriented Growth Achieving Highly Reversible Zinc Metal Batteries

To prevent dendrite growth and hydrogen evolution reaction, directional epitaxial growth of Zn2+ ions on Zn anode, especially along the lowest-surface-energy Zn (0002) plane, is pursued for highly reversible zinc metal batteries (ZMBs). However, designing single Zn (0002) exposed anodes for sustained uniaxial crystalline orientation of Zn electroplating faces challenges. Herein, we propose an anode engineering that utilizes a low lattice mismatch substrate and ordered Zn2+ migration channels to modify Zn anodes with single (0002) surface exposure and sustainable Zn-oriented growth, yielding highly reversible ZMBs. A vapor-deposited metal-organic framework Cu3(C6O6)2 film on brass foil shows low lattice mismatch (4.24 %) with electrodeposited Zn anodes, enabling the exposure of a single (0002) plane. Furthermore, the low desolvation energy (-1.36 eV) between solvated Zn2+ ions and the ordered porous Cu3(C6O6)2 film guides sustainable Zn-oriented nucleation along the Zn (0002) surface. Consequently, the Zn||Zn cells with brass-Cu3(C6O6)2 substrate shows a high average Coulombic efficiency of 99.55 % after 4,000 cycles at 10 mA cm-2. This work provides a new window to design highly reversible Zn metal anode with a single-exposed Zn (0002) plane and sustainable oriented growth for emerging ZMBs.

Emulating "Curvature-Enhanced Adsorbate Coverage" for Superconformal and Orientated Zn Electrodeposition in Zinc-ion-Batteries

Uneven Zn deposition and unfavorable side reactions have prevented the reversibility of the Zn anode. Herein, we design a rearranged (002) textured Zn anode inspired by a traditional curvature-enhanced adsorbate coverage (CEAC) process to realize the highly reversible Zn anode. The rearranged (002) textured structure directs superconformal Zn deposition by controlling the spatial deposition rate of the rearranged crystal planes, thereby promoting bottom-up "superfilling" of the 3D Zn skeletons. Meanwhile, our designed anode also induces the epitaxial Zn deposition, alleviating the parasitic reactions owing to the lowest surface energy of the (002) plane. Attributed to these superiorities, uniform and oriented Zn deposition can be obtained, exhibiting an ultra-long lifespan over 479 hrs at an ultrahigh depth of discharge (DOD) of 82.12 %. The Zn|Na2V6O16 ⋅ 3H2O battery delivers an improved cycling performance, even at a high area capacity of 5.15 mAh/cm2 with a low negative/positive (N/P) capacity ratio of 1.63. The superconformal deposition approach for Zn anodes paves the way for the practical application of high-performance zinc-ion batteries.

Untangling the Role of Capping Agents in Manipulating Electrochemical Behaviors Toward Practical Aqueous Zinc-Ion Batteries

Long-standing challenges including notorious side reactions at the Zn anode, low Zn anode utilization, and rapid cathode degradation at low current densities hinder the advancement of aqueous zinc-ion batteries (AZIBs). Inspired by the critical role of capping agents in nanomaterials synthesis and bulk crystal growth, a series of capping agents are employed to demonstrate their applicability in AZIBs. Here, it is shown that the preferential adsorption of capping agents on different Zn crystal planes, coordination between capping agents and Zn2+ ions, and interactions with metal oxide cathodes enable preferred Zn (002) deposition, water-deficient Zn2+ ion solvation structure, and a dynamic cathode-electrolyte interface. Benefiting from the multi-functional role of capping agents, dendrite-free Zn plating and stripping with an improved Coulombic efficiency of 99.2% and enhanced long-term cycling stability are realized. Remarkable capacity retention of 91% is achieved for cathodes after more than 500 cycles under a low current density of 200 mA g-1, marking one of the best cycling stabilities to date. This work provides a proof-of-concept of capping agents in manipulating electrochemical behaviors, which should inspire and pave a new avenue of research to address the challenges in practical energy storage beyond AZIBs.

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.

Breaking Mass Transport Limit for Hydrogen Evolution-Inhibited and Dendrite-Free Aqueous Zn Batteries

It is commonly accepted that batteries perform better at low current densities below the mass-transport limit, which restricts their current rate and capacity. Here, it is demonstrated that the performance of Zn metal electrodes can be dramatically enhanced at current densities and cut-off capacities exceeding the mass-transport limit by using pulsed-current protocols. These protocols achieve cumulative plating/stripping capacities of 11.0 Ah cm-2 and 3.8 Ah cm-2 at record-high current densities of 80 and 160 mA cm-2, respectively. The study identifies and understands the promoted (002)-textured Zn growth and suppressed hydrogen evolution based on the thermodynamics and kinetics of competing reactions. Furthermore, the over-limiting pulsed-current protocol enables long-life Zn batteries with high mass loading (29 mgcathode cm-2) and high areal capacity (7.9 mAh cm-2), outperforming cells using constant-current protocols at equivalent energy and time costs. The work provides a comprehensive understanding of the current-capacity-performance relationship in Zn plating/stripping and offers an effective strategy for dendrite-free metal batteries that meet practical requirements for high capacity and high current rates.

The ZnO-SiO2 Composite Phase with Dual Regulation Function Enables Uniform Zn2+ Flux and Fast Zinc Deposition Kinetics Toward Zinc Metal Batteries

As an important candidate for rechargeable energy storage devices, the large-scale development of aqueous zinc ion batteries has been hindered by hydrogen evolution and uncontrollable dendrites of metal anodes. A novel ZnO-SiO2 composite interface phase (Zn@ZSCP) with a double protective effect based on in situ synthesis by hydrothermal method is used to improve these difficulties. The hydrophilic SiO2 layer is beneficial to the dissolution of hydrated zinc ions and reduces the nucleation barrier during zinc deposition, while the stable ZnO layer helps to adjust the electric field distribution on the surface of the metal anode to further induce uniform zinc nucleation. The cycle life of the Zn@ZSCP||Zn@ZSCP symmetric battery based on this innovative interface phase modification is up to 2500 h. Even at a high current density of 8 mA cm-2, the symmetric battery still has a stable cycle life of more than 2000 h. The zinc-iodine full battery based on Zn@ZSCP anode and low-cost biomass-derived porous carbon exhibits an excellent specific capacity and outstanding cycle stability. This simple and reasonable battery structure design not only improves the practicability of aqueous zinc ion batteries to a certain extent but also helps to develop more efficient and environmentally friendly zinc metal batteries.

Microscopic Insights into Zn (002) Epitaxial Electrodeposition in Aqueous Zinc Metal Batteries

Dendrite growth, corrosion, passivation, and other side reactions during Zn plating and stripping have consistently hindered the capacity and lifespan of Zn metal batteries. In this study, we employ first-principles calculations to unravel the epitaxial electroplating mechanism of Zn (002) planes on various substrate surfaces. We identify six critical factors, including interfacial stability, zincophilicity, surface atomic arrangement, lattice mismatch, responsiveness, and adaptability, that profoundly influence the electrochemical behavior of zinc deposition. Our findings reveal that substrates with hexagonal surface atomic arrangements and strong metallic bonding with zinc, such as (002)-Zn, (111)-Cu, and Ti3C2 MXenes, facilitate uniform and dendrite-free zinc deposition. Notably, lattice contraction induced by substrate lattice mismatch exerts a greater impact on the deposition stability than lattice expansion. Kinetic analyses demonstrate that substrates exhibiting high responsiveness and adaptability can tolerate higher current densities and larger areal capacities, which are crucial for practical applications.

Can NiFe-Layered-Double-Hydroxide Catalysts Suppress Carbon Corrosion in Electrochemical Oxygen Evolution?

Sustainable energy societies demand rechargeable batteries using ubiquitous-material electrodes of geopolitical-risk-free elements. We aim to develop low-overpotential oxygen-evolution-reaction (OER) catalysts that suppress carbon corrosion of gas-diffusion electrodes (GDEs) to realize two-electrode rechargeable Zn-air batteries (r-ZABs). Herein, single-walled-carbon-nanotube (SWNT) thin films are used as a scaffold for a benchmark OER catalyst, doping-free NiFe-layered double hydroxide (NiFeLDHs), operating in r-ZABs using alkali aqueous electrolytes. Metal compositions of NiFeLDHs are controlled with an atomic-level quality using Prussian-blue-analog nanoparticles of NixFe1-x[Fe(CN)6]0.67 (x = 0-1). The nanoparticles with dimensions of ∼8 nm adhere to SWNTs on carbon paper as a GDE model by a drop-casting method using their aqueous dispersion solutions. Ni0.6Fe0.4[Fe(CN)6]0.67 shows OER activity by hydrolysis for generating NiFeLDH nanodots of metal compositions between Ni0.5Fe0.5 and Ni0.6Fe0.4 with a size distribution of 1.75 ± 0.26 nm and exposing OER-active (018) and (015) planes on SWNTs. The activity is investigated by regulating the loading amounts of the NPs to avoid aggregating the nanodots. An optimal low-loading amount of 270 nmol cm-2 minimizes iR-corrected overpotential to 156 mV at 10 mA cm-2. The iR-uncorrected overpotential is 260 mV and suppresses carbon corrosion of SWNTs and carbon black. Using an r-ZAB half-cell with a Zn foil, OER-driven charging stably proceeds at 10 mA cm-2 over 3 h with an average voltage of 1.99 V vs Zn/Zn2+. Limited metal electrodes have further improved OER overpotentials by third-element doping, while carbon electrodes still offer room for discovering intrinsically high OER activities of NiFeLDHs without doping.

Synergistic Gradient Anodes for Long-Term Stability in Aqueous Zinc-Ion Batteries

The stability of aqueous zinc metal anodes is still constrained by their severe dendrite growth. Optimizing electric field distribution and crystallography to modulate the diffusion and deposition behavior of zinc ions can effectively suppress dendrite growth. However, the fabrication strategy to directly endow specific textured zinc anodes with gradient electric field distribution is still lacking. Herein, a strategy combining crystal reconstruction of commercial zinc foil with graphene oxide (GO) protective layer is proposed to construct an in situ gradient electric field-enhanced strong (002) textured GO@ZnO/Zn(002) anode. Based on the experimental and theoretical results, the GO protective layer can regulate a wide-range homogeneous Zn2+ ions flow, while the dense and uniform ZnO/Zn(002) nanoneedles /nanoparticles can enhance localized polarized electric field to accelerate rapid localized transfer of Zn2+ ions and guide them toward directional deposition along (002) plane. Therefore, the hierarchical GO@ZnO/Zn(002) anode enables the symmetric cell to operate continuously and stably for 5700 and 4200 h at 2 and 4 mA cm-2, respectively, which is comparable to or better than most high-end Zn anodes. This work presents new insights into the zinc foil reconstruction and gradient electric field fabrication strategy, offering a scalable approach for the development of long-term stable metal anodes.

Biomineralization Inspired the Construction of Dense Spherical Stacks for Dendrite-Free Zinc Anodes

Aqueous zinc-ion batteries (AZIBs) are considered to be one of the most promising energy storage systems due to their high degree of safety and low cost. However, the deposition of the uncontrolled zinc dendritic morphology on the surface of the Zn anode seriously reduces the cycle life of AZIBs. Herein, inspired by natural biomineralization, a uniform spherical zinc deposition is achieved via the addition of a biological macromolecule to the electrolyte. The proposed biological macromolecule makes Zn2+ undergo dense spherical deposition by regulating the relative growth rate of high-index planes of metal zinc, effectively avoiding the destruction from irregular zinc dendrites. The symmetric cell with the addition of such a biological macromolecule can be stably cycled for >3200 h at 1 mA cm-2 for 1 mAh cm-2. This work sheds light on expanding morphological regulation of metal deposition to spherical shapes for stable metal anodes in addition to a single-crystal plane control strategy.

Grain Boundary Filling Empowers (002)-Textured Zn Metal Anodes with Superior Stability

Aqueous Zn battery is promising for grid-level energy storage due to its high safety and low cost, but dendrite growth and side reactions at the Zn metal anode hinder its development. Designing Zn with (002) orientation improves the stability of the Zn anode, yet grain boundaries remain susceptible to corrosion and dendrite growth. Addressing these intergranular issues is crucial for enhancing the electrochemical performance of (002)-textured Zn. Here, a strategy based on grain boundary wetting to fill intergranular regions and mitigate these issues is reported. By systematically investigating boundary fillers and filling conditions, In metal is chosen as the filler, and one-step annealing is used to synergistically convert commercial Zn foils into single (002)-textured Zn while filling In into the boundaries. The inter-crystalline-modified (002)-textured Zn (IM(002) Zn) effectively inhibits corrosion and dendrite growth, resulting in excellent stability in batteries. This work offers new insights into Zn anode protection and the development of high-energy Zn batteries.

Regulating the solvation structure of Zn2+ via glycine enables a long-cycling neutral zinc-ferricyanide flow battery

Zinc-based flow batteries hold potential promise for extensive energy storage on a large scale owing to their high energy density and low cost. However, their widespread implementation is impeded by challenges associated with zinc (Zn) dendrites and side reactions like the hydrogen evolution reaction on the anode. Theoretical calculations have confirmed that glycine (Gly) has the ability to coordinate with Zn2+, displacing H2O molecules in the solvation shell, thereby restoring the solvation structure of Zn2+ and promoting the release of reactive Zn2+ during plating/stripping processes. As a result, the incorporation of Gly into the anolyte of a neutral zinc-ferricyanide (Zn/Fe) flow battery (ZIFB) effectively inhibits the formation of Zn dendrites and impedes side reactions, leading to highly reversible and stable Zn plating/stripping reactions. A Zn||Zn symmetric flow battery utilizing Gly in the anolyte demonstrated extended cycling durability, lasting over 550 h at a current density of 30 mA cm-2, in contrast to the failure of a Gly-free anolyte system after 150 h. Notably, this approach facilitates a neutral ZIFB achieving an impressive energy efficiency exceeding 70 %, even at a high current density of 70 mA cm-2, with a cycle lifespan exceeding 800 h (33 days) at a current density of 30 mA cm-2. Conversely, the neutral ZIFB lacking Gly showed a significantly shorter cycle life of only 260 h under identical operational conditions (30 mA cm-2). Due to the economic benefits of Gly and the proposed user-friendly route, this strategy demonstrates great potential for promoting the widespread adoption of zinc-based flow batteries with improved performance for practical use.

Synergetic bifunctional Cu-In alloy interface enables Ah-level Zn metal pouch cells

Rechargeable aqueous zinc-metal batteries, considered as the possible post-lithium-ion battery technology for large-scale energy storage, face severe challenges such as dendrite growth and hydrogen evolution side reaction (HER) on Zn negative electrode. Herein, a three-dimensional Cu-In alloy interface is developed through a facile potential co-replacement route to realize uniform Zn nucleation and HER anticatalytic effect simultaneously. Both theoretical calculations and experimental results demonstrate that this bifunctional Cu-In alloy interface inherits the merits of low Zn-nucleation overpotential and high HER overpotential from individual copper and indium constituents, respectively. Moreover, the dynamical self-reconstruction during cycling leads to an HER-anticatalytic and zincophilic gradient hierarchical structure, enabling highly reversible Zn chemistry with dendrite-free Zn (002) deposition and inhibited HER. Moreover, the improved interface stability featured by negligible pH fluctuations in the diffusion layer and suppressed by-product formation is evidenced by in-situ scanning probe technology, Raman spectroscopy, and electrochemical gas chromatography. Consequently, the lifespan of the CuIn@Zn symmetric cell is extended to more than one year with a voltage hysteresis of 6 mV. Importantly, the CuIn@Zn negative electrode is also successfully coupled with high-loading iodine positive electrode to fabricate Ah-level (1.1 Ah) laminated pouch cell, which exhibits a capacity retention of 67.9% after 1700 cycles.

Guiding uniform Zn deposition with a multifunctional additive for highly utilized Zn anodes

The practical applications of aqueous zinc-ion batteries (AZIBs) have been restricted by the fast growth of Zn dendrites and severe side reactions at the Zn/electrolyte interface. Herein, a multifunctional additive, L-leucine (Leu), is incorporated into a mild acidic electrolyte to stabilize the Zn anode. The Leu molecule, featuring both carboxyl and amino groups, exhibits strong interactions with Zn2+, which can reshape the solvation structure of Zn2+ and facilitate the uniform electrodeposition of Zn. Simultaneously, the Leu molecule exhibits preferential adsorption onto the Zn surface, effectively isolating it from direct contact with water, thus suppressing unwanted side reactions. Consequently, the Zn∥Cu asymmetric cell exhibits a high and stable coulombic efficiency of 99.5% at a current density of 5 mA cm-2 for 1100 h. Importantly, the capacity retention of the Zn∥NH4V4O10 full cell based on the Leu electrolyte reaches 80% after 1200 cycles at a current density of 2 A g-1. The successful application of the low-cost Leu effectively enhances the cycling stability of the AZIBs and accelerates their applications.

Multifunctional Self-Assembled Bio-Interfacial Layers for High-Performance Zinc Metal Anodes

Rechargeable aqueous zinc-ion (Zn-ion) batteries are widely regarded as important candidates for next-generation energy storage systems for low-cost renewable energy storage. However, the development of Zn-ion batteries is currently facing significant challenges due to uncontrollable Zn dendrite growth and severe parasitic reactions on Zn metal anodes. Herein, we report an effective strategy to improve the performance of aqueous Zn-ion batteries by leveraging the self-assembly of bovine serum albumin (BSA) into a bilayer configuration on Zn metal anodes. BSA's hydrophilic and hydrophobic fragments form unique and intelligent ion channels, which regulate the migration of Zn ions and facilitate their desolvation process, significantly diminishing parasitic reactions on Zn anodes and leading to a uniform Zn deposition along the Zn (002) plane. Notably, the Zn||Zn symmetric cell with BSA as the electrolyte additive demonstrated a stable cycling performance for up to 2400 hours at a high current density of 10 mA cm-2. This work demonstrates the pivotal role of self-assembled protein bilayer structures in improving the durability of Zn anodes in aqueous Zn-ion batteries.

Non-Epitaxial Electrodeposition of Overall 99 % (002) Plane Achieves Extreme and Direct Utilization of 95 % Zn Anode and By-Product as Cathode

Zn anode protection in Zn-ion batteries (ZIBs) face great challenges of high Zn utilization rate (i.e., depth of discharge, DOD) and high current density due to the large difficulty in obtaining an extreme overall RTC (relative texture coefficient) of Zn (002) plane. Through the potent interaction of Mn(III)aq and H+ with distinct Zn crystal planes under an electric field, large-size Zn foils with a breakthrough (002) plane RTC of 99 % (i.e., close to Zn single crystal) are electrodeposited on texture-less substrates, which is also applicable from recycled Zn. The ultra-high (002) plane RTC remarkably enhances cyclic performance of the Zn anode (70 % DOD @ 45.5 mA cm-2), and the DOD is even up to 95 % (@ 28.1 mA cm-2) with an electrolyte additive of polyaniline. Furthermore, MnO2, the by-product of electrodeposition, is directly used as cathode of both coin cell and pouch battery, surpassing the cyclic performance exhibited by the majority of Zn||MnO2 batteries in previous instances. These results demonstrate the great potential of our strategy for high-performance, low-cost and large-scale ZIBs.

Formulating Self-Repairing Solid Electrolyte Interface via Dynamic Electric Double Layer for Practical Zinc Ion Batteries

Zinc ion batteries (ZIBs) encounter interface issues stemming from the water-rich electrical double layer (EDL) and unstable solid-electrolyte interphase (SEI). Herein, we propose the dynamic EDL and self-repairing hybrid SEI for practical ZIBs via incorporating the horizontally-oriented dual-site additive. The rearrangement of distribution and molecular configuration of additive constructs the robust dynamic EDL under different interface charges. And, a self-repairing organic-inorganic hybrid SEI is constructed via the electrochemical decomposition of additive. The dynamic EDL and self-repairing SEI accelerate interfacial kinetics, regulate deposition and suppress side reactions in the both stripping and plating during long-term cycles, which affords high reversibility for 500 h at 42.7 % depth of discharge or 50 mA ⋅ cm-1. Remarkably, Zn//NVO full cells deliver the impressive cycling stability for 10000 cycles with 100 % capacity retention at 3 A ⋅ g-1 and for over 3000 cycles even at lean electrolyte (7.5 μL ⋅ mAh-1) and high loading (15.26 mg ⋅ cm-2). Moreover, effectiveness of this strategy is further demonstrated in the low-temperature full cell (-30 °C).

In-Situ Solid Electrolyte Interface via Dual Reaction Strategy for Highly Reversible Zinc Anode

In situ construction of solid electrolyte interfaces (SEI) is an effective strategy to enhance the reversibility of zinc (Zn) anodes. However, in situ SEI to afford high reversibility under high current density conditions (≥20 mA cm-2) is highly desired yet extremely challenging. Herein, we propose a dual reaction strategy of spontaneous electrostatic reaction and electrochemical decomposition for the in situ construction of SEI, which is composed of organic-rich upper layer and inorganic-rich inner layer. Particularly, in situ SEI performs as "growth binder" at small current density and "orientation regulator" at high current density, which significantly suppresses side reactions and dendrite growth. The in situ SEI affords the record-breaking reversibility of Zn anode under practical conditions, Zn//Zn symmetric cells can stably cycle for over 1300 h and 400 h at current densities of 50 mA cm-2 and 100 mA cm-2, respectively, showcasing an exceptional cumulative capacity of 67.5 Ah cm-2. Furthermore, the practicality of this in situ SEI is verified in Zn//PANI pouch cells with high mass loading of 25.48 mg cm-2. This work provides a universal strategy to design advanced SEI for practical Zn-ion batteries.

Hydrophobic Ion Barrier-Enabled Ultradurable Zn (002) Plane Orientation towards Long-Life Anode-Less Zn Batteries

Gradual disability of Zn anode and high negative/positive electrode (N/P) ratio usually depreciate calendar life and energy density of aqueous Zn batteries (AZBs). Herein, within original Zn2+-free hydrated electrolytes, a steric hindrance/electric field shielding-driven "hydrophobic ion barrier" is engineered towards ultradurable (002) plane-exposed Zn stripping/plating to solve this issue. Guided by theoretical simulations, hydrophobic adiponitrile (ADN) is employed as a steric hindrance agent to ally with inert electric field shielding additive (Mn2+) for plane adsorption priority manipulation, thereby constructing the "hydrophobic ion barrier". This design robustly suppresses the (002) plane/dendrite growth, enabling ultradurable (002) plane-exposed dendrite-free Zn stripping/plating. Even being cycled in Zn‖Zn symmetric cell over 2150 h at 0.5 mA cm-2, the efficacy remains well-kept. Additionally, Zn‖Zn symmetric cells can be also stably cycled over 918 h at 1 mA cm-2, verifying uncompromised Zn stripping/plating kinetics. As-assembled anode-less Zn‖VOPO4 ⋅ 2H2O full cells with a low N/P ratio (2 : 1) show a high energy density of 75.2 Wh kg-1 full electrode after 842 cycles at 1 A g-1, far surpassing counterparts with thick Zn anode and low cathode loading mass, featuring excellent practicality. This study opens a new avenue by robust "hydrophobic ion barrier" design to develop long-life anode-less Zn batteries.

Cathode|Electrolyte Interface Engineering by a Hydrogel Polymer Electrolyte for a 3D Porous High-Voltage Cathode Material in a Quasi-Solid-State Zinc Metal Battery by In Situ Polymerization

This work highlights the development of a superior cathode|electrolyte interface for the quasi solid-state rechargeable zinc metal battery (QSS-RZMB) by a novel hydrogel polymer electrolyte using an ultraviolet (UV) light-assisted in situ polymerization strategy. By integrating the cathode with a thin layer of the hydrogel polymer electrolyte, this technique produces an integrated interface that ensures quick Zn2+ ion conduction. The coexistence of nanowires for direct electron routes and the enhanced electrolyte ion infiltration and diffusion by the 3D porous flower structure with a wide open surface of the Zn-MnO electrode complements the interface formation during the in situ polymerization process. The QSS-RZMB configured with an integrated cathode (i-Zn-MnO) and the hydrogel polymer electrolyte (PHPZ-30) as the separator yields a comparable specific energy density of 214.14 Wh kg-1 with that of its liquid counterpart (240.38 Wh kg-1, 0.5 M Zn(CF3SO3)2 aqueous electrolyte). Other noteworthy features of the presented QSS-RZMB system include its superior cycle life of over 1000 charge-discharge cycles and 85% capacity retention with 99% coulombic efficiency at the current density of 1.0 A g-1, compared to only 60% capacity retention over 500 charge-discharge cycles displayed by the liquid-state system under the same operating conditions.

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.

Interfacial chemistry in multivalent aqueous batteries: fundamentals, challenges, and advances

As one of the most promising electrochemical energy storage systems, aqueous batteries are attracting great interest due to their advantages of high safety, high sustainability, and low costs when compared with commercial lithium-ion batteries, showing great promise for grid-scale energy storage. This invited tutorial review aims to provide universal design principles to address the critical challenges at the electrode-electrolyte interfaces faced by various multivalent aqueous battery systems. Specifically, deposition regulation, ion flux homogenization, and solvation chemistry modulation are proposed as the key principles to tune the inter-component interactions in aqueous batteries, with corresponding interfacial design strategies and their underlying working mechanisms illustrated. In the end, we present a critical analysis on the remaining obstacles necessitated to overcome for the use of aqueous batteries under different practical conditions and provide future prospects towards further advancement of sustainable aqueous energy storage systems with high energy and long durability.

Anion Chemistry towards On-Site Construction of Solid-Electrolyte Interface for Highly Stable Metallic Zn Anode

Reversibility of metallic Zn anode serves as the corner stone for the development of aqueous Zn metal battery, which motivates scrutinizing the electrolyte-Zn interface. As the representative organic zinc salt, zinc trifluorosulfonate (Zn(OTf)2) facilitates a broad class of aqueous electrolytes, however, the stability issue of Zn anode remains crucial. The great challenge lies in the lack of Zn anode protection by the pristinely formed surface structure in aqueous Zn(OTf)2 electrolytes. Accordingly, an electrochemical route was developed to grow a uniform zinc trifluorosulfonate hydroxide (ZTH) layer on Zn anode as an artificial SEI, via regulation on metal dissolution and strong coordination ability of zinc ions. Co-precipitation was proposed to be the formation mechanism for the artificial SEI, where the reduction stability of OTf- anion and the low-symmetry layer structure of ZTH was unmasked. This artificial SEI favors interfacial kinetics, depresses side reactions, and well maintains its integrity during cycling, leading to a prolonged lifespan of Zn stripping/plating with a high DOD of ~85 %, and an improved cycling stability of ~92 % retention rate for V2O5/Zn cell at 1 A g-1. The unveiled role of anion on Zn anode drives the contemplation on the surface chemistry for the blooming aqueous rechargeable battery.

Interface engineering enabled by sodium dodecyl sulfonate surfactant for stable Zn metal batteries

Aqueous zinc-ion batteries are emerging as powerful candidates for large-scale energy storage, due to their inherent high safety and high theoretical capacity. However, the inevitable hydrogen evolution and side effects of the deposition process limit their lifespan, which requires rational engineering of the interface between anode and aqueous electrolyte. In this paper, an anionic surfactant as electrolyte additive, sodium dodecyl sulfonate (SDS), is introduced to deliver highly reversible zinc metal batteries. Unlike traditional surfactants, the solvation structure is not affected by SDS, which tends to adsorb on the (002) crystal plane of Zn with the purpose of effectively limiting the water molecules adsorption. Attributed to the natural hydrophobic part of SDS, a dynamic electrostatic shielding layer and a unique hydrophobic interface are constructed on the anode. Assisted by the above merits, the adverse surface corrosion, hydrogen evolution and dendrite growth are significantly inhibited without the sacrifice in the deposition kinetics of Zn ions. As a result, the Zn||Zn symmetric batteries demonstrate an increased cycle life of 2000 h (1 mA cm-2, 1 mA h cm-2) with the presence of SDS additive. Such strategy provides a new avenue for the developing advanced electrolytes to be applied in aqueous energy storage systems.

Improvements and Challenges of Hydrogel Polymer Electrolytes for Advanced Zinc Anodes in Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are widely regarded as desirable energy storage devices due to their inherent safety and low cost. Hydrogel polymer electrolytes (HPEs) are cross-linked polymers filled with water and zinc salts. They are not only widely used in flexible batteries but also represent an ideal electrolyte candidate for addressing the issues associated with the Zn anode, including dendrite formation and side reactions. In HPEs, an abundance of hydrophilic groups can form strong hydrogen bonds with water molecules, reducing water activity and inhibiting water decomposition. At the same time, special Zn2+ transport channels can be constructed in HPEs to homogenize the Zn2+ flux and promote uniform Zn deposition. However, HPEs still face issues in practical applications, including poor ionic conductivity, low mechanical strength, poor interface stability, and narrow electrochemical stability windows. This Review discusses the issues associated with HPEs for advanced AZIBs, and the recent progresses are summarized. Finally, the Review outlines the opportunities and challenges for achieving high performance HPEs, facilitating the utilization of HPEs in AZIBs.

Highly Reversible and Dendrite-Free Zinc Anodes Enabled by PEDOT Nanowire Interfacial Layers for Aqueous Zinc-Ion Batteries

The aqueous zinc-ion batteries (ZIBs) have gained increasing attention because of their high specific capacity, low cost, and good safety. However, side reactions, hydrogen evolution reaction, and uncontrolled zinc dendrites accompanying the Zn metal anodes have impeded the applications of ZIBs in grid-scale energy storage. Herein, the poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires as an interfacial layer on the Zn anode (Zn-PEDOT) are reported to address the above issues. Our experimental results and density functional theory simulation reveal that the interactions between the Zn2+ and S atoms in thiophene rings of PEDOT not only facilitate the desolvation of hydrated Zn2+ but also can regulate the diffusion of Zn2+ along the thiophene molecular chains and induce the dendrite-free deposition of Zn along the (002) surface. Consequently, the Zn||Cu-PEDOT half-cell exhibits highly reversible plating/stripping behavior with an average Coulombic efficiency of 99.7% over 2500 cycles at 1 mA cm-2 and a capacity of 0.5 mAh cm-2. A symmetric Zn-PEDOT cell can steadily operate over 1100 h at 1 mA cm-2 (1 mAh cm-2) and 470 h at 10 mA cm-2 (2 mAh cm-2), outperforming the counterpart bare Zn anodes. Besides, a Zn-PEDOT||V2O5 full cell could deliver a specific capacity of 280 mAh g-1 at 1 A g-1 and exhibits a decent cycling stability, which are much superior to the bare Zn||V2O5 cell. Our results demonstrate that PEDOT nanowires are one of the promising interfacial layers for dendrite-free aqueous ZIBs.

Interfacial Biomacromolecular Engineering Toward Stable Ah-Level Aqueous Zinc Batteries

Interfacial instability within aqueous zinc batteries (AZBs) spurs technical obstacles including parasitic side reactions and dendrite failure to reach the practical application standards. Here, an interfacial engineering is showcased by employing a bio- derived zincophilic macromolecule as the electrolyte additive (0.037 wt%), which features a long-chain configuration with laterally distributed hydroxyl and sulfate anion groups, and has the propensity to remodel the electric double layer of Zn anodes. Tailored Zn2+-rich compact layer is the result of their adaptive adsorption that effectively homogenizes the interfacial concentration field, while enabling a hybrid nucleation and growth mode characterized as nuclei-rich and space-confined dense plating. Further resonated with curbed corrosion and by-products, a dendrite-free deposition morphology is achieved. Consequently, the macromolecule-modified zinc anode delivers over 1250 times of reversible plating/stripping at a practical area capacity of 5 mAh cm-2, as well as a high zinc utilization rate of 85%. The Zn//NH4V4O10 pouch cell with the maximum capacity of 1.02 Ah can be steadily operated at 71.4 mA g-1 (0.25 C) with 98.7% capacity retained after 50 cycles, which demonstrates the scale-up capability and highlights a "low input and high return" interfacial strategy toward practical AZBs.

Organic Cations Texture Zinc Metal Anodes for Deep Cycling Aqueous Zinc Batteries

Manipulating the crystallographic orientation of zinc (Zn) metal to expose more (002) planes is promising to stabilize Zn anodes in aqueous electrolytes. However, there remain challenges involving the non-epitaxial electrodeposition of highly (002) textured Zn metal and the maintenance of (002) texture under deep cycling conditions. Herein, a novel organic imidazolium cations-assisted non-epitaxial electrodeposition strategy to texture electrodeposited Zn metals is developed. Taking the 1-butyl-3-methylimidazolium cation (Bmim+) as a paradigm additive, the as-prepared Zn film ((002)-Zn) manifests a compact structure and a highly (002) texture without containing (100) signal. Mechanistic studies reveal that Bmim+ featuring oriented adsorption on the Zn-(002) plane can reduce the growth rate of (002) plane to render the final exposure of (002) texture, and homogenize Zn nucleation and suppress H2 evolution to enable the compact electrodeposition. In addition, the formulated Bmim+-containing ZnSO4 electrolyte effectively sustains the (002) texture even under deep cycling conditions. Consequently, the combination of (002) texture and Bmim+-containing electrolyte endows the (002)-Zn electrode with superior cycling stability over 350 h under 20 mAh cm-2 with 72.6% depth-of-discharge, and assures the stable operation of full Zn batteries with both coin-type and pouch-type configurations, significantly outperforming the (002)-Zn and commercial Zn-based batteries in Bmim+-free electrolytes.

Achieving Planar Zn Electroplating in Aqueous Zinc Batteries with Cathode-Compatible Current Densities by Cycling under Pressure

The value of aqueous zinc-ion rechargeable batteries is held back by the degradation of the Zn metal anode with repeated cycling. While raising the operating current density is shown to alleviate this anode degradation, such high cycling rates are not compatible with full cells, as they cause Zn-host cathodes to undergo capacity decay. A simple approach that improves anode performance while using more modest cathode-compatible current densities is required. This work reports reversible planar Zn deposition under cathode-compatible current densities can instead be achieved by applying external pressure to the cell. Employing multiscale characterization, this work illustrates how cycling under pressure results in denser and more uniform Zn deposition, analogous to that achieved under high cycling rates, even at low areal current densities of 1 to 10 mA cm-2. Microstructural mechanical measurements reveal that Zn structures plated under lower current densities are particularly susceptible to pressure-induced compression. The ability to achieve planar Zn plating at cathode-compatible current densities holds significant promise for enabling high-capacity Zn-ion battery full cells.

Laser-Scribed Battery Electrodes for Ultrafast Zinc-Ion Energy Storage

Aqueous Zn batteries are promising for large-scale energy storage but are plagued by the lack of high-performance cathode materials that enable high specific capacity, ultrafast charging, and outstanding cycling stability. Here, a laser-scribed nano-vanadium oxide (LNVO) cathode is designed that can simultaneously achieve these properties. The material stores charge through Faradaic redox reactions on/near the surface at fast rates owing to the small grain size of vanadium oxide and interpenetrating 3D graphene network, displaying a surface-controlled capacity contribution (90%-98%). Multiple characterization techniques unambiguously reveal that zinc and hydronium ions co-insert with minimal lattice change upon cycling. It is demonstrated that a high specific capacity of 553 mAh g-1 is achieved at 0.1 A g-1, and an impressive 264 mAh g-1 capacity is retained at 100 A g-1 within 10 s, showing excellent rate capability. The LNVO/Zn can also reach >90% capacity retention after 3000 cycles at a high rate of 30 A g-1, as well as achieving both high energy (369 Wh kg-1) and power densities (56306 W kg-1). Moreover, the LNVO cathode retains its excellent cycling performance when integrated into quasi-solid-state pouch cells, further demonstrating mechanical stability and its potential for practical application in wearable and grid-scale applications.

Electric Double Layer Regulator Design through a Functional Group Assembly Strategy towards Long-Lasting Zinc Metal Batteries

Regulating the electric double layer (EDL) structure of the zinc metal anode by using electrolyte additives is an efficient way to suppress interface side reactions and facilitate uniform zinc deposition. Nevertheless, there are no reports investigating the proactive design of EDL-regulating additives before the start of experiments. Herein, a functional group assembly strategy is proposed to design electrolyte additives for modulating the EDL, thereby realizing a long-lasting zinc metal anode. Specifically, by screening ten common functional groups, N, N-dimethyl-1H-imidazole-1-sulfonamide (IS) is designed by assembling an imidazole group, characterized by its high adsorption capability on the zinc anode, and a sulfone group, which exhibits strong binding with Zn2+ ions. Benefiting from the adsorption functionalization of the imidazole group, the IS molecules occupy the position of H2O in the inner Helmholtz layer of the EDL, forming a molecular protective layer to inhibit H2O-induced side reactions. Meanwhile, the sulfone group in IS, acting as a binding site to Zn2+, promotes the de-solvation of Zn2+ ions, facilitating compact zinc deposition. Consequently, the utilization of IS significantly extending the cycling stability of Zn||Zn and Zn||NaV3O8 ⋅ 1.5H2O full cell. This study offers an innovative approach to the design of EDL regulators for high-performance zinc metal batteries.

Self-Zincophilic Dual Protection Host of 3D ZnO/Zn⊂CF to Enhance Zn Anode Cyclability

Zn dendrite growth and side reactions restrict the practical use of Zn anode. Herein, the design of a novel 3D hierarchical structure is demonstrated with self-zincophilic dual-protection constructed by ZnO and Zn nanoparticles immobilized on carbon fibers (ZnO/Zn⊂CF) as a versatile host on the Zn surface. The unique 3D frameworks with abundant zinc nucleation storage sites can alleviate the structural stress during the plating/stripping process and overpower Zn dendrite growth by moderating Zn2+ flux. Moreover, given the dual protection design, it can reduce the contact area between active zinc and electrolyte, inhibiting hydrogen evolution reactions. Importantly, density functional theory calculations and experimental results confirm that the introduced O atoms in ZnO/Zn⊂CF enhance the interaction between Zn2+ and the host and reduce Zn nucleation overpotential. As expected, the ZnO/Zn⊂CF-Zn electrode exhibits stable Zn plating/stripping with low polarization for 4200 h at 0.2 mA cm-2 and 0.2 mAh cm-2. Furthermore, the symmetrical cell displays a significantly long cycling life of over 1800 h, even at 30 mA cm-2. The fabricated full cells also show impressive cycling performance when coupled with V2O3 cathodes.