Synergistic Cooperation of Zn(002) Texture and Amorphous Zinc Phosphate for Dendrite-Free Zn Anodes

Dipole Moment Dictates the Preferential Immobilization in Gel Electrolytes for Ah-level Aqueous Zinc-Metal Batteries

Aqueous Zn-metal batteries are of great interest due to their high material abundance, low production cost, and excellent safety. However, they suffer from severe side reactions and notorious dendrite growth closely related to electrolytes. Here, in situ generated zwitterionic polymers are used as gel electrolytes to overcome these problems. It is shown that anions and H2O, but not anions and cations, are preferentially immobilized at different sites of zwitterionic polymers, facilitating the free migration of Zn2+ and reducing the side reactions. This immobilization can be associated with the dipole moment of zwitterionic polymers. As a result, poly[3-dimethyl(methacryloyloxy ethyl) ammonium propane sulfonate] (PDMAPS) stands out from a series of zwitterionic polymers and outperforms the other candidates in electrochemical performance. The symmetric cells using PDMAPS smoothly operate ~9000 h at 0.5 mA cm-2 for 0.5 mAh cm-2, much better than the controls. Moreover, PDMAPS enables an Ah-level pouch cell for continuous cycling. These results not only benefit the rational molecular design of advanced electrolytes, but also demonstrate the promising potential of zwitterionic polymers in aqueous Zn-metal batteries.

Engineering of Charge Density at the Anode/Electrolyte Interface for Long-Life Zn Anode in Aqueous Zinc Ion Battery

The aqueous zinc ion battery emerges as the promising candidate applied in large-scale energy storage system. However, Zn anode suffers from the issues including Zn dendrite, Hydrogen evolution reaction and corrosion. These challenges are primarily derived from the instability of anode/electrolyte interface, which is associated with the interfacial charge density distribution. In this context, the recent advancements concentrating on the strategies and mechanisms to regulate charge density at the Zn anode/electrolyte interface are summarized. Different characterization techniques for charge density distribution have been analysed, which can be applied to assess the interfacial zinc ion transport. Additionally, the charge density regulations at the Zn anode/electrolyte interface are discussed, elucidating their roles in modulating electrostatic interactions, electric field, structure of solvated zinc ion and electric double layer, respectively. Finally, the perspectives and challenges on the further research are provided to establish the stable anode/electrolyte interface by focusing on charge density modifications, which is expected to facilitate the development of aqueous zinc ion battery.

Enhanced electro-catalysis for methanol oxidation reaction performance by edge defects of ordered mesoporous carbon

Heteroatom-doped carbon materials are widely used to improve the electrocatalytic oxidation of methanol; however, the underlying mechanisms driving this enhancement remain poorly understood. A major challenge lies in developing non-doped carbon supports with tunable intrinsic defect types tailored for metal-based catalysts. In this study, we synthesize a series of ordered mesoporous carbon (OMC) supports with adjustable edge defect densities by varying roasting temperatures and employing a zinc (Zn) evaporation strategy to systematically investigate the impact of edge defects on methanol oxidation reaction (MOR) performance. Theoretical calculations and structural characterizations confirm that the electron metal-support interaction (EMSI) between OMC edge defects and palladium nanoparticles (Pd NPs) effectively modulates the electronic structure of Pd NPs. This modulation not only enhances overall reaction activity and selectivity for the non-CO pathway but also strengthens the anchoring of Pd NPs, leading to superior activity and stability of the Pd/OMC-Zn0.55 catalyst in methanol electrocatalytic oxidation. Notably, after rigorously excluding the influence of various physicochemical properties of the carbon supports, the crucial role of edge defects in improving MOR performance is established. This work provides essential insights into the controlled synthesis of carbon-based catalysts with edge defects and introduces promising strategies for the development of high-performance anode catalysts for direct methanol fuel cells.

Multifunctional Interface Layer Constructed by Trace Zwitterions for Highly Reversible Zinc Anodes

The inhomogeneous plating/stripping of Zn anode, attributed to dendrite growth and parasitic reactions at the electrode/electrolyte interface, severely restricts its cycling life-span. Here, trace zwitterions (trifluoroacetate pyridine, TFAPD) are introduced into the aqueous electrolyte to construct a multifunctional interface that enhances the reversibility of Zn anode. The TFA- anions with strong specific adsorption adhere onto the Zn surface to reconstruct the inner Helmholtz plane (IHP), preventing the hydrogen evolution and corrosion side reactions caused by free H2O. The Py+ cations accumulate on the outer Helmholtz plane (OHP) of Zn anode with the force of electric field during Zn2+ plating, forming a shielding layer to uniformize the deposition of Zn2+. Besides, the adsorbed TFA- and Py+ promote the desolvation process of Zn2+ resulting in fast reaction kinetics. Thus, the Zn||Zn cells present an outstanding cycling performance of more than 10000 hours. And even at 85 % utilization rate of Zn, it can stably cycle for over 200 hours at 10 mA cm-2 and 10 mAh cm-2. The Zn||I2 full cell exhibits a capacity retention of over 95 % even after 30000 cycles. Remarkably, the Zn||I2 pouch cells (95 mAh) deliver a high-capacity retention of 99 % after 750 cycles.

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.

Innovative Zinc Anodes: Advancing Metallurgy Methods to Battery Applications

Aqueous zinc metal batteries (AZMBs) are emerging as a powerful contender in the realm of large-scale intermittent energy storage systems, presenting a compelling alternative to existing ion battery technologies. They harness the benefits of metal zinc's high safety, natural abundance, and favorable electrochemical potential (-0.762 V vs Standard hydrogen electrode, SHE), alongside an impressive theoretical capacity (820 mAh g-1 and 5655 mAh cm-3). However, the electrochemical performance of ZMBs is impeded by several challenges, including poor compatibility with high-loading cathodes and persistent side reactions. These issues are intricately linked to the inherent physicochemical properties of the zinc metal anodes (ZMAs). Here, this review delves into the traditional methods of ZMAs production, encompassing extraction, electrodeposition, and rolling processes. The discussion then progresses to an exploration of cutting-edge methodologies designed to enhance the electrochemical performance of ZMAs. These methods are categorized into alloying, pre-treatment of substrate, advanced electrodeposition techniques, and the development of composite anodes utilizing zinc powder. The review offers a comparative analysis of the merits and drawbacks of various optimization strategies, highlighting the beneficial outcomes achieved. It aspires to inspire novel concepts for the advancement and innovation of next-generation zinc-based energy storage solutions.

A Versatile Redox-Active Electrolyte for Solid Fixation of Polyiodide and Dendrite-Free Operation in Sustainable Aqueous Zinc-Iodine Batteries

Practical utilization of zinc-iodine (Zn-I2) batteries is hindered by significant challenges, primarily stemming from the polyiodide shuttle effect on the cathode and dendrite growth on the anode. Herein, a feasible redox-active electrolyte has been introduced with tetraethylammonium iodide as an additive that simultaneously addresses the above mentioned challenges via polyiodide solidification on the cathode and the electrostatic shielding effect on the anode. The tetraethylammonium (TEA+) captures water-soluble polyiodide intermediates (I3 -, I5 -), forming a solid complex at the cathode, thereby suppressing capacity loss during charge/discharge. Furthermore, the TEA+ mitigates dendrite growth on the Zn anode via the electrostatic shielding effect, promoting uniform and compact Zn deposition at the anode. Consequently, the Zn||Zn symmetric cell demonstrates superior cycling stability during Zn plating/stripping over 4,200 h at 1 mA cm-2 and 1 mAh cm-2. The Zn||NiNC full-cell exhibits a stable capacity retention of 98.4% after 20 000 cycles (>5 months) with near-unity Coulombic efficiency at 1 A g-1. The study provides novel insights for establishing a new direction for low-cost, sustainable, and long-lifespan Zn-I2 batteries.

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.

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.

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.

Planar Deposition via In Situ Conversion Engineering for Dendrite-Free Zinc Batteries

Owing to the considerable capacity, high safety, and abundant zinc resources, zinc-ion batteries (ZIBs) have been garnering much attention. Nonetheless, the unsatisfactory cyclic lifespan and poor reversibility originate from side reactions and dendrite obstacles to their practical applications. In addition to inhibiting the corrosion of aqueous electrolytes, regulating planar deposition is a key strategy to enhance their long-term stability. Herein, an in situ conversion strategy is reported to construct a protective "dual-layer" structure (VZSe/V@Zn) on zinc metal, consisting of the VSe2-ZnSe outer layer with low lattice mismatch to Zn (002) plane, and corrosion-resistant nanometallic V inner layer. Such design integrates superior interfacial ionic/electronic transfer, corrosion resistance, and unique planar deposition regulation capability. The as-prepared VZSe/V@Zn demonstrates remarkable durability of 238 h at 50 mA cm-2 with a high depth of discharge (68.3% DOD) in the Zn||Zn symmetric cell. Even in the anode-free system, the as-prepared protective layer can extend the cycle life up to 2000 cycles, with an outstanding capacity retention of 93.1% and ultra-high average coulombic efficiency of 99.998%. This work delineates an effective strategy for fabricating lattice-matching protective layers, with profound implications for elucidating zinc deposition mechanisms and paving the way for the development of high-performance zinc 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.

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.

Improving the Oxygen Evolution Reaction Kinetics in Zn-Air Battery by Iodide Oxidation Reaction

Zinc-air batteries (ZABs) have garnered considerable attention as a highly promising contender in the field of energy storage and conversion. Nevertheless, their performance is considerably impeded by the proliferation of dendrites on the Zinc anode and the slow kinetics of the redox reaction on the air cathode. Herein, taking Ag30%@LaCoO3 (Ag30%@LCO) heterojunction catalyst as the cathode, it is demonstrated that adding KI additives to the alkaline electrolyte can not only enhance the oxygen electrocatalytic reaction but also inhibit the formation of zinc anode dendrites, thereby achieving a comprehensive improvement in the performance of ZABs. Under the action of the KI additive, the optimized Ag30%@LCO catalyst shows a decreased overpotential from 460 to 220 mV at j = 10 mA cm-2, while the assembled ZAB shows reduced charging potential (1.8 V), and long cycle stability (180 h). Furthermore, the morphology characterization results indicate a reduction in dendrites on the Zn anode. Both experimental and calculated results indicate that the presence of I- as a reaction modifier alters the trajectory of the conventional oxygen evolution reaction, resulting in a more thermodynamically favorable pathway. The introduction of KI additives as electrolytes provides a straightforward approach to developing comprehensively improved ZABs.

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.

Multi-metal ions co-regulated vanadium oxide cathode toward long-life aqueous zinc-ion batteries

Interlayer intercalation engineering shows great feasibility to improve the structure stability of the layered oxides. Although high Zn-storage capability has been attained based on the pillar effect of multifarious intercalants, an in-depth understanding the synergistic effect of intercalated multiple metal ions is still in deficiency. Herein, alkali metal ion K+, alkaline earth metal ion Mg2+ and trivalent metal ion Al3+ are introduced into the VO interlayer of V2O5. Due to the different electronegativity and hydrated ion radius of K+, Mg2+ and Al3+, adjusting the relative proportions of these metal ions can achieve an appropriate interlayer spacing, stable layer structure and regular morphology, which facilitates the transport kinetics of Zn2+. Under the synergistic effect of pre-intercalated multi-metal ion, the optimal tri-metal ion intercalated hydrated V2O5 cathode exhibits a high specific capacity of 382.4 mAh g-1 at 0.5 A g-1, and long-term cycling stability with capacity retention of 86 % after 2000 cycles at the high current density of 10 A g-1. Ex-situ and kinetic characterizations reveal the fast charge transfer and reversible Zn2+ intercalation mechanism. The multi-ion engineering strategy provides an effective way to design desirable layered cathode materials for aqueous zinc-ion batteries.

Promoting Electrocatalytic Oxygen Reactions Using Advanced Heterostructures for Rechargeable Zinc-Air Battery Applications

In order to facilitate electrochemical oxygen reactions in electrically rechargeable zinc-air batteries (ZABs), there is a need to develop innovative approaches for efficient oxygen electrocatalysts. Due to their reliability, high energy density, material abundance, and ecofriendliness, rechargeable ZABs hold promise as next-generation energy storage and conversion devices. However, the large-scale application of ZABs is currently hindered by the slow kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). However, the development of heterostructure-based electrocatalysts has the potential to surpass the limitations imposed by the intrinsic properties of a single material. This Account begins with an explanation of the configurations of ZABs and the fundamentals of the oxygen electrochemistry of the air electrode. Then, we summarize recent progress with respect to the variety of heterostructures that exploit bifunctional electrocatalytic reactions and overview their impact on ZAB performance. The range of heterointerfacial engineering strategies for improving the ORR/OER and ZAB performance includes tailoring the surface chemistry, dimensionality of catalysts, interfacial charge transfer, mass and charge transport, and morphology. We highlight the multicomponent design approaches that take these features into account to create advanced highly active bifunctional catalysts. Finally, we discuss the challenges and future perspectives on this important topic that aim to enhance the bifunctional activity and performance of zinc-air batteries.

Dual-function additive enables a self-regulatory mechanism to balance cathode-anode interface demands in Zn‖MnO2 batteries

The poor reversibility of the zinc (Zn) anodes and the irreversible deposition/dissolution of Mn2+/MnO2 significantly impede the commercialization of Zn-Mn aqueous batteries (ZMABs). In reducing the difference between the desired interfacial reaction environments of the cathode and anode, we found that they face the same problem of interference-the generation of irreversible corrosion products. Herein, we have introduced a novel self-regulatory mechanism. This mechanism involves the addition of sodium dihydrogen phosphate, which shifts from passive protection to active regulation. It effectively captures OH- ions, prevents corrosion product formation, and facilitates the in situ generation of a solid electrolyte interface (SEI) film. This modification also homogenizes Zn ion flow and improves the reversibility of Zn plating and stripping. Furthermore, a stable and slightly acidic environment has been established to stabilize the pH at the cathodic interface, mitigate corrosion product formation, and enhance the reversible deposition and dissolution of Mn2+/MnO2. With the optimal electrolyte, Zn‖Zn symmetric cells demonstrate stable operation for over 3000 hours at 1 mA cm-2, 1 mA h cm-2. Additionally, the Zn‖Cu cells maintain high reversibility after 1000 cycles, achieving an average coulombic efficiency (CE) of 99.76%. The assembled Zn‖MnO2 full cells exhibit exceptional cycling stability and rate performance. This work adopts the approach of seeking common ground and emphasizing the balance of cathode and anode interfacial requirements, which represents a new and significant insight for design of ZMABs with high reversibility and high cyclability.

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.

Unveiling the Failure Mechanism of Zn Anodes in Zinc Trifluorosulfonate Electrolyte: The Role of Micelle-like Structures

Zinc trifluorosulfonate [Zn(OTf)2] is considered as the most suitable zinc salt for aqueous Zn-ion batteries (AZIBs) but cannot support the long-term cycling of the Zn anode. Here, we reveal the micelle-like structure of the Zn(OTf)2 electrolyte and reunderstand the failing mechanism of the Zn anode. Since the solvated Zn2+ possesses a positive charge, it can spontaneously attract OTf- with the hydrophilic group of -SO3 and the hydrophobic group of -CF3 via electrostatic interaction and form a "micelle-like" structure, which is responsible for the poor desolvation kinetics and dendrite growth. To address these issues, an antimicelle-like structure is designed by using ethylene glycol monomethyl ether (EGME) as a cosolvent for highly reversible AZIBs. The modified electrolyte shows lower dissociation ability to Zn(OTf)2 and higher coordination tendency with Zn2+ compared to the Zn(OTf)2 electrolyte, resulting in the unique solvation structure of Zn2+(H2O)1.2(OTf-)2(EGME)2.8, which significantly reduces the charge of micelle, damages the micelle-like structure, and boosts the desolvation kinetics. Moreover, the reduction of EGME and OTf- can form a robust dual-layered SEI with high Zn2+ ion conductivity. Consequently, the Zn/Cu asymmetric coin cell using ZT-EGME can work at a high rate and a capacity of 50 mA cm-2 and 5 mA h cm-2 for more than 120 cycles, while its counterparts using ZT can barely work. Moreover, a 505.1 mA h pouch cell with practical parameters including a lean electrolyte supply of 15 mL A h-1 and an N/P ratio of ∼3.5 can work for 50 cycles.

Surface Engineering on Zinc Anode for Aqueous Zinc Metal Batteries

Rechargeable aqueous zinc metal batteries (AZMBs) are considered as a potential alternative to lithium-ion batteries due to their low cost, high safety, and environmental friendliness. However, the Zn anodes in AZMBs face severe challenges, such as dendrite growth, metal corrosion, and hydrogen evolution, all of which are closely related to the Zn/electrolyte interface. This article offers a short review on surface passivation to alleviate the issues on the Zn anodes. The composition and structure of the surface layers significantly influence their functions and then the performance of the Zn anodes. The recent progresses are introduced, according to the chemical components of the passivation layers on the Zn anodes. Moreover, the challenges and prospects of surface passivation in stabilizing Zn anodes are discussed, providing valuable guidance for the development of AZMBs.

Electric Double Layer Oriented Eutectic Additive Design toward Stable Zn Anodes with a High Depth of Discharge

ZnSO4-based electrolytes for aqueous zinc ion batteries fail to meet practical application metrics due to hydrogen evolution reaction (HER) and dendrite growth. In this work, a highly polarized eutectic additive, glycerophosphorylcholine (GPC) is rationally designed, to regulate the electric double layer (EDL) structure for stable Zn anodes with a high depth of discharge (DOD). On one hand, GPC molecules with abundant hydroxyl groups can precisely regulate the hydrogen bond network in EDL to suppress HER. On the other hand, the enrichment of GPC at the interface is positively responsible for the negative charge density on the Zn surface, which leads to the formation of a robust ZnxPyOz-rich solid-electrolyte interphase and terminates dendrite growth in the charge-rich sites. This EDL-oriented eutectic additive engineering enables highly reversible and selectively (002)-textured Zn anodes to operate for over 1450 h at a high DOD of 45.3%. Meanwhile, a high-capacity (185.7 mAh g-1) aqueous Zn||VS2 full cell shows remarkable cycling stability over 220 cycles with an excellent capacity retention of 90.4% even at a low current density of 0.1 A g-1 (0.5 C). This work sheds light on electrolyte design and interface engineering for high-performance aqueous batteries.

In Situ Spontaneous Construction of Zinc Phosphate Coating Layer Toward Highly Reversible Zinc Metal Anodes

Aqueous zinc ion batteries have received widespread attention due to their merits of high safety, high theoretical specific capacity, low cost, and environmental benignity. Nevertheless, the irreversible issues of Zn anode deriving from side reactions and dendrite growth have hindered its commercialization in large-scale energy storage systems. Herein, a zinc phosphate tetrahydrate (Zn3(PO4)2·4H2O, ZnPO) coating layer is in situ formed on the bare Zn by spontaneous redox reactions at room temperature to tackle the above issues. Particularly, the dense and brick-like ZnPO layer can effectively separate the anode surface from the aqueous electrolyte, thus suppressing the serious side reactions. Moreover, the ZnPO layer with high ionic conductivity, high Zn2+ transference number, and low nucleation barrier permits rapid Zn2+ transport and enables uniform Zn deposition, ensuring dendrite-free Zn deposition. As a result, the ZnPO@Zn symmetric battery achieves a high Coulombic efficiency of 99.8% and displays ultrahigh cycle stability over 6000 h (> 8 months), far surpassing its counterparts. Furthermore, the ZnPO@Zn||MnO2 full battery exhibits excellent electrochemical performances. Therefore, this work provides a new reference for simple and large-scale preparation of highly reversible Zn metal anodes, and has great potential for practical applications.

Backside Coating for Stable Zn Anode with High Utilization Rate

Stable Zn anodes with high utilization rate are urgently required to promote the specific and volumetric energy densities of Zn-ion batteries for practical applications. Herein, contrary to the widely utilized surface coating on Zn anodes, this work shows that a zinc foil with a backside coated layer delivers much enhanced cycling stability even under high depth of discharge. The backside coating significantly reduces stress concentration, accelerates heat diffusion, and facilitates electron transfer, thus effectively preventing dendrite growth and structural damage at high Zn utilization. As a result, the developed anode can be stably cycled for 334 h at 85.5% Zn utilization, which outperforms bare Zn and previously reported results on surface-coated Zn foils. An NVO-based full cell also shows stable performance with high Zn utilization rate (69.4%), low negative-positive electrodes ratio (1.44), and high specific/volumetric energy densities (155.8 Wh kg-1/178 Wh L-1), which accelerates the progress toward practical zinc-ion batteries.

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

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

In-Situ Spontaneous Electropolymerization Enables Robust Hydrogel Electrolyte Interfaces in Aqueous Batteries

Hydrogels hold great promise as electrolytes for emerging aqueous batteries, for which establishing a robust electrode-hydrogel interface is crucial for mitigating side reactions. Conventional hydrogel electrolytes fabricated by ex situ polymerization through either thermal stimulation or photo exposure cannot ensure complete interfacial contact with electrodes. Herein, we introduce an in situ electropolymerization approach for constructing hydrogel electrolytes. The hydrogel is spontaneously generated during the initial cycling of the battery, eliminating the need of additional initiators for polymerization. The involvement of electrodes during the hydrogel synthesis yields well-bonded and deep infiltrated electrode-electrolyte interfaces. As a case study, we attest that, the in situ-formed polyanionic hydrogel in Zn-MnO2 battery substantially improves the stability and kinetics of both Zn anode and porous MnO2 cathode owing to the robust interfaces. This research provides insight to the function of hydrogel electrolyte interfaces and constitutes a critical advancement in designing highly durable aqueous batteries.

Converting Commercial Zn Foils into Single (002)-Textured Zn with Millimeter-Sized Grains for Highly Reversible Aqueous Zinc Batteries

Rechargeable aqueous zinc batteries are promising but hindered by unfavorable dendrite growth and side reactions on zinc anodes. In this study, we demonstrate a fast melting-solidification approach for effectively converting commercial Zn foils into single (002)-textured Zn featuring millimeter-sized grains. The melting process eliminates initial texture, residual stress, and grain size variations in diverse commercial Zn foils, guaranteeing the uniformity of commercial Zn foils into single (002)-textured Zn. The single (002)-texture ensures large-scale epitaxial and dense Zn deposition, while the reduction in grain boundaries significantly minimizes intergranular reactions. These features enable large grain single (002)-textured Zn shows planar and dense Zn deposition under harsh conditions (100 mA cm-2, 100 mAh cm-2), impressive reversibility in Zn||Zn symmetric cell (3280 h under 1 mA cm-2, 830 h under 10 mAh cm-2), and long cycling stability over 180 h with a high depth of discharge value of 75 %. This study successfully addresses the issue of uncontrollable texture formation in Zn foils following routine annealing treatments with temperatures below the Zn melting point. The findings of this study establish a highly efficient strategy for fabricating highly reversible single (002)-textured Zn anodes.

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

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

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

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

Manipulating Zn Metal Texture with Guided Zincophilic Sites via Electrochemical Stripping for Dendrite-Free Zn Anodes

Constructing a three-dimensional (3D) structure along with Zn (002) texture selective exposure is a promising strategy to tackle the issues faced by Zn metal anodes. Herein, for the first time, we proposed an electrochemical stripping strategy to achieve controlled modification of the texture and microstructure of zinc foils in one step, building a hierarchical structure with (002) texture preferred exposed Zn (SZ). The SZ with favorable zincophilic properties not only can reduce the concentration polarization at the interface but also allow Zn to grow horizontally on the edge of the (002) texture by guiding the adsorption sites for Zn2+. Moreover, the honeycomb-like structure is beneficial to rearrange the distribution of the Zn2+ flux as well as alleviating stress changes during cycling. Thus, the SZ||Cu cell exhibits excellent stability with a Coulombic efficiency of 99.76% over 1800 cycles. The SZ||NaV3O8·xH2O cell with inconspicuous self-discharge effect maintains a high areal capacity of 3.67 mA h cm-2 even after 700 cycles with a low N/P ratio of 3.6. This work achieves texture architecture and structure designing on Zn foils simultaneously by metallurgical electrochemical methods and opens up a potential strategy to implement the practicality of zinc metal anodes.

Fundamental Understanding of Hydrogen Evolution Reaction on Zinc Anode Surface: A First-Principles Study

Hydrogen evolution reaction (HER) has become a key factor affecting the cycling stability of aqueous Zn-ion batteries, while the corresponding fundamental issues involving HER are still unclear. Herein, the reaction mechanisms of HER on various crystalline surfaces have been investigated by first-principle calculations based on density functional theory. It is found that the Volmer step is the rate-limiting step of HER on the Zn (002) and (100) surfaces, while, the reaction rates of HER on the Zn (101), (102) and (103) surfaces are determined by the Tafel step. Moreover, the correlation between HER activity and the generalized coordination number ([Formula: see text]) of Zn at the surfaces has been revealed. The relatively weaker HER activity on Zn (002) surface can be attributed to the higher [Formula: see text] of surface Zn atom. The atomically uneven Zn (002) surface shows significantly higher HER activity than the flat Zn (002) surface as the [Formula: see text] of the surface Zn atom is lowered. The [Formula: see text] of surface Zn atom is proposed as a key descriptor of HER activity. Tuning the [Formula: see text] of surface Zn atom would be a vital strategy to inhibit HER on the Zn anode surface based on the presented theoretical studies. Furthermore, this work provides a theoretical basis for the in-depth understanding of HER on the Zn surface.

Trade-Off between Rough and Smooth Electrode Surfaces toward Stable Zn Stripping/Plating in Aqueous Electrolytes

The effects of surface roughness on the performance of the Zn metal anode in aqueous electrolytes are investigated by experiments and computational simulations. Smooth surfaces can homogenize the nucleation and growth of Zn, which helps to form a flat Zn anode under high current density. In spite of these advantages, the whole surface of the smooth electrode serves as the reactive contact area for parasitic reactions, generating severe hydrogen evolution, corrosion, and byproduct formation, which seriously hinder the long-term cycle stability of the Zn anode. To trade off this double-sided effect, we identify a medium degree of surface roughness that could stabilize the Zn anode for 1000 h cycling at 1.0 mAh cm-2. The electrode also enabled stable cycling for 800 h at a high current density of 5.0 mAh cm-2. This naked Zn metal anode with optimized surface roughness holds great promise for direct use in aqueous zinc ion batteries.

Zn(002)-preferred and pH-buffering triethanolamine as electrolyte additive for dendrite-free Zn anodes

Zn anodes of aqueous batteries face severe challenges from side reactions and dendrite growth. Here, triethanolamine (TEOA) is developed as an electrolyte additive to address these challenges. It enhances the exposure of Zn(002) and diminishes the change in pH. Therefore, the electrolyte containing TEOA shows improved electrochemical performance.

Covalent Organic Framework with 3D Ordered Channel and Multi-Functional Groups Endows Zn Anode with Superior Stability

Achieving a highly robust zinc (Zn) metal anode is extremely important for improving the performance of aqueous Zn-ion batteries (AZIBs) for advancing "carbon neutrality" society, which is hampered by the uncontrollable growth of Zn dendrite and severe side reactions including hydrogen evolution reaction, corrosion, and passivation, etc. Herein, an interlayer containing fluorinated zincophilic covalent organic framework with sulfonic acid groups (COF-S-F) is developed on Zn metal (Zn@COF-S-F) as the artificial solid electrolyte interface (SEI). Sulfonic acid group (- SO3H) in COF-S-F can effectively ameliorate the desolvation process of hydrated Zn ions, and the three-dimensional channel with fluoride group (-F) can provide interconnected channels for the favorable transport of Zn ions with ion-confinement effects, endowing Zn@COF-S-F with dendrite-free morphology and suppressed side reactions. Consequently, Zn@COF-S-F symmetric cell can stably cycle for 1,000 h with low average hysteresis voltage (50.5 mV) at the current density of 1.5 mA cm-2. Zn@COF-S-F|MnO2 cell delivers the discharge specific capacity of 206.8 mAh g-1 at the current density of 1.2 A g-1 after 800 cycles with high-capacity retention (87.9%). Enlightening, building artificial SEI on metallic Zn surface with targeted design has been proved as the effective strategy to foster the practical application of high-performance AZIBs.

Orientational Electrodeposition of Highly (002)-Textured Zinc Metal Anodes Enabled by Iodide Ions for Stable Aqueous Zinc Batteries

Regulating the crystallographic texture of the zinc (Zn) metal anode is promising to promote Zn reversibility in aqueous electrolytes, but the direct fabrication of specific textured Zn still remains challenging. Herein, we report a facile iodide ion (I-)-assisted electrodeposition strategy that can scalably fabricate highly (002) crystal plane-textured Zn metal anode (H-(002)-Zn). Theoretical and experimental characterizations demonstrate that the presence of I- additives can significantly elevate the growth rate of the Zn (100) plane, homogenize the Zn nucleation, and promote the plating kinetics, thus enabling the uniform H-(002)-Zn electrodeposition. Taking the electrolytic cell with the conventional ZnSO4-based electrolyte and commercial Cu substrate as a model system, the Zn texture gradually transforms from (101) to (002) as the increase of NaI additive concentration. In the optimized 1 M ZnSO4 + 0.8 M NaI electrolyte, the as-prepared H-(002)-Zn features a compact structure and an ultrahigh intensity ratio of (002) to (101) signal without containing the (100) signal. The free-standing H-(002)-Zn electrode manifests stronger resistance to interfacial side reactions than the conventional (101)-textured Zn electrode, thus delivering a high efficiency of 99.88% over 400 cycles and ultralong cycling lifespan over 6700 h (>9 months at 1 mA cm-2) and assuring the stable operation of full Zn batteries. This work will enlighten the efficient electrosynthesis of high-performance Zn anodes for practical aqueous Zn batteries.