Highly Reversible Zinc Metal Anode in a Dilute Aqueous Electrolyte Enabled by a pH Buffer Additive

Aqueous zinc-ion batteries have drawn increasing attention due to the intrinsic safety, cost-effectiveness and high energy density. However, parasitic reactions and non-uniform dendrite growth on the Zn anode side impede their application. Herein, a multifunctional additive, ammonium dihydrogen phosphate (NHP), is introduced to regulate uniform zinc deposition and to suppress side reactions. The results show that the NH₄⁺ tends to be preferably absorbed on the Zn surface to form a “shielding effect” and blocks the direct contact of water with Zn. Moreover, NH₄⁺ and (H₂PO₄)⁻ jointly maintain pH values of the electrode-electrolyte interface. Consequently, the NHP additive enables highly reversible Zn plating/stripping behaviors in Zn//Zn and Zn//Cu cells. Furthermore, the electrochemical performances of Zn//MnO₂ full cells and Zn//active carbon (AC) capacitors are improved. This work provides an efficient and general strategy for modifying Zn plating/stripping behaviors and suppressing side reactions in mild aqueous electrolyte.     

A Bio-Inspired Trehalose Additive for Reversible Zinc Anodes with Improved Stability and Kinetics

The moderate reversibility of Zn anodes, as a long-standing challenge in aqueous zinc-ion batteries, promotes the exploration of suitable electrolyte additives continuously. It is crucial to establish the absolute predominance of smooth deposition within multiple interfacial reactions for stable zinc anodes, including suppressing side parasitic reactions and facilitating Zn plating process. Trehalose catches our attention due to the reported mechanisms in sustaining biological stabilization. In this work, the inter-disciplinary application of trehalose is reported in the electrolyte modification for the first time. The pivotal roles of trehalose in suppressed hydrogen evolution and accelerated Zn deposition have been investigated based on the principles of thermodynamics as well as reaction kinetics. The electrodeposit changes from random accumulation of flakes to dense bulk with (002)-plane exposure due to the unlocked crystal-face oriented deposition with trehalose addition. As a result, the highly reversible Zn anode is obtained, exhibiting a high average CE of 99.8 % in the Zn/Cu cell and stable cycling over 1500 h under 9.0 % depth of discharge in the Zn symmetric cell. The designing principles and mechanism analysis in this study could serve as a source of inspiration in exploring novel additives for advanced Zn anodes.     

Guiding Zn Uniform Deposition with Polymer Additives for Long-lasting and Highly Utilized Zn Metal Anodes

The parasitic side reaction on Zn anode is the key issue which hinders the development of aqueous Zn-based energy storage systems on power-grid applications. Here, a polymer additive (PMCNA) engineered by copolymerizing 2-methacryloyloxyethyl phosphorylcholine (MPC) and N-acryloyl glycinamide (NAGA) was employed to regulate the Zn deposition environment for satisfying side reaction inhibition performance during long-term cycling with high Zn utilization. The PMCNA can preferentially adsorb on Zn metal surface to form a uniform protective layer for effective water molecule repelling and side reaction resistance. In addition, the PMCNA can guide Zn nucleation and deposition along 002 plane for further side reaction and dendrite suppression. Consequently, the PMCNA additive can enable the Zn//Zn battery with an ultrahigh depth of discharge (DOD) of 90.0 % for over 420 h, the Zn//active carbon (AC) capacitor with long cycling lifespan, and the Zn//PANI battery with Zn utilization of 51.3 % at low N/P ratio of 2.6.     

In-Situ Integration of a Hydrophobic and Fast-Zn2+-Conductive Inorganic Interphase to Stabilize Zn Metal Anodes

The irreversible issues of Zn anode stemming from dendrite growth and water-induced erosion have severely hindered the commercialization of rechargeable aqueous Zn batteries. Herein, a hydrophobic and fast-Zn²⁺-conductive zinc hexacyanoferrate (HB-ZnHCF) interphase layer is in situ integrated on Zn by a rapid room-temperature wet-chemistry method to address these dilemmas. Different from currently proposed hydrophilic inorganic cases, the hydrophobic and compact HB-ZnHCF interphase effectively prevents the access of water molecules to Zn surface, thus avoiding H₂ evolution and Zn corrosion. Moreover, the HB-ZnHCF with large internal ion channels, strong zincophilicity, and high Zn²⁺ transference number (0.86) permits fast Zn²⁺ transport and enables smooth Zn deposition. Remarkably, the resultant HB-ZnHCF@Zn electrode delivers unprecedented reversibility with 99.88 % Coulombic efficiency over 3000 cycles, realizes long-term cycling over 5800 h (>8 months, 1 mA cm⁻²) and 1000 h (10 mA cm⁻²), and assures the stable operation of full Zn battery with both coin- and pouch-type configurations.     

Boosting Zn Anode Utilization by Trace Iodine Ions in Organic-Water Hybrid Electrolytes through Formation of Anion-rich Adsorbing Layers

Aqueous Zn batteries are attracting extensive attentions, but their application is still hindered by H₂O-induced Zn-corrosion and hydrogen evolution reactions. Addition of organic solvents into aqueous electrolytes to limit the H₂O activity is a promising solution, but at the cost of greatly reduced Zn anode kinetics. Here we propose a simple strategy for this challenge by adding 50 mM iodine ions into an organic-water (1,2-dimethoxyethane (DME)+water) hybrid electrolyte, which enables the electrolyte simultaneously owns the advantages of low H₂O activity and accelerated Zn kinetics. We demonstrate that the DME breaks the H₂O hydrogen-bond network and exclude H₂O from Zn²⁺ solvation shell. And the I⁻ is firmly adsorbed on the Zn anode, reducing the Zn²⁺ de-solvation barrier from 74.33 kJ mol⁻¹ to 32.26 kJ mol⁻¹ and inducing homogeneous nucleation behavior. With such electrolyte, the Zn//Zn symmetric cell exhibits a record high cycling lifetime (14.5 months) and achieves high Zn anode utilization (75.5 %). In particular, the Zn//VS₂@SS full cell with the optimized electrolyte stably cycles for 170 cycles at a low N : P ratio (3.64). Even with the cathode mass-loading of 16.7 mg cm⁻², the full cell maintains the areal capacity of 0.96 mAh cm⁻² after 1600 cycles.     

Electrocrystallization Regulation Enabled Stacked Hexagonal Platelet Growth toward Highly Reversible Zinc Anodes

Realizing durative flattened and dendrite-free zinc (Zn) metal configuration is the key to resolving premature battery failure caused by the internal short circuit, which is highly determined by the crystal growth in the electrocrystallization process. Herein, we report that regulating the molecular structure of the inner Helmholtz plane (HIP) can effectively convert the deposition into activation control by weakening the solvated ion adsorption at the interface. The moderated electrochemical reaction kinetics lower than the adatom self-diffusion rate steers conformal stratiform Zn growth and dominant Zn (0001) texture, achieving crystallographic optimization. Through in situ mediation of electrolyte engineering, orientational plating and stripping behaviors at edge-sites and tailored solvation structure immensely improve the utilization efficiency and total charge passed of Zn metal, even under extreme conditions, including high areal capacity (3 mAh cm⁻²) and wide temperature range (−40–60 °C).     

Zincophilic Electrode Interphase with Appended Proton Reservoir Ability Stabilizes Zn Metal Anodes

The rampant dendrites and hydrogen evolution reaction (HER) resulting from the turbulent interfacial evolution at the anode/electrolyte are the main culprits of short lifespan and low Coulombic efficiency of Zn metal batteries. In this work, a versatile protective coating with excellent zincophilic and amphoteric features is constructed on the surface of Zn metal (ZP@Zn) as dendrite-free anodes. This kind of protective coating possesses the advantages of reversible proton storage and rapid desolvation kinetics, thereby mitigating the HER and facilitating homogeneous nucleation concomitantly. Furthermore, the space charge polarization effect promotes charge redistribution to achieve uniform Zn deposition. Accordingly, the ZP@Zn symmetric cell manifests excellent reversibility at an ultrahigh cumulative plating capacity of 4700 mAh cm⁻² and stable cycling at 80 % depth of discharge (DOD). The ZP@Zn//V₆O₁₃ pouch cell also reveals superior cycling stability with a high capacity of 326.6 mAh g⁻¹.     

Fast Polysulfide Conversion Catalysis and Reversible Anode Operation by A Single Cathode Modifier in Li-Metal Anode-Free Lithium-Sulfur Batteries

The two major issues confronting the commercialization of rechargeable lithium-sulfur (Li−S) batteries are the sluggish kinetics of the sulfur electrochemical reactions on the cathode and inadequate lithium deposition/stripping reversibility on the anode. They are commonly mitigated with additives designed specifically for the anode and the cathode individually. Here, we report the use of a single cathode modifier, In₂Se₃, which can effectively catalyse the polysulfide reactions on the cathode, and also improve the reversibility of Li deposition and removal on the anode through a LiInS₂/LiInSe₂ containing solid electrolyte interface formed in situ by the Se and In ions dissolved in the electrolyte. The amounts of dissolved Se and In are small relative to the amount of In₂Se₃ administered. The benefits of using this single modification approach were verified in Li-metal anode-free Li−S batteries with a Li₂S loading of 4 mg cm⁻² and a low electrolyte/Li₂S ratio of 7.5 μL mg⁻¹. The resulting battery showed 60 % capacity retention after 160 cycles at the 0.2 C rate and an average Coulombic efficiency of 98.27 %, comparing very well with recent studies using separate electrode modifiers.     

Solid-Electrolyte Interphase Chemistries Towards High-Performance Aqueous Zinc Metal Batteries

Aqueous zinc metal batteries (AZMBs) are deemed a promising technology for electrochemical energy storage due to their high safety, low cost, and high energy density. However, AZMBs still suffer from severe side reactions, including Zn dendrite formation and intrinsic hydrogen evolution reaction. In contrast to the solid-electrolyte interphase (SEI) layer that stabilizes Li/Na/K metal anodes in organic electrolytes, it is difficult to form an SEI layer on the Zn surface because of the difficulty in decomposing the salt anions within the narrow electrochemical potential window of water. A team from the University of Adelaide reports a novel pure or hybrid electrolyte with H₂O by using dimethyl methylphosphonate (DMMP) as solvent or co-solvent to construct a uniform and stable phosphate-based SEI layer (ZnP₂O₆ and Zn₃(PO₄)₂). As a result, high Coulombic efficiencies and improved capacity retentions are obtained.     

Tetraphenylporphyrin-based Chelating Ligand Additive as a Molecular Sieving Interfacial Barrier toward Durable Aqueous Zinc Metal Batteries

The sustained water consumption and uncontrollable dendrite growth strongly hamper the practical applications of rechargeable zinc (Zn) metal batteries (ZMBs). Herein, for the first time, we demonstrate that trace amount of chelate ligand additive can serve as a “molecular sieve-like” interfacial barrier and achieve highly efficient Zn plating/stripping. As verified by theoretical modeling and experimental investigations, the benzenesulfonic acid groups on the additive molecular not only facilitates its water solubility and selective adsorption on the Zn anode, but also effectively accelerates the de-solvation kinetics of Zn²⁺. Meanwhile, the central porphyrin ring on the chelate ligand effectively expels free water molecules from Zn²⁺ via chemical binding against hydrogen evolution, and reversibly releases the captured Zn²⁺ to endow a dendrite-free Zn deposition. By virtue of this non-consumable additive, high average Zn plating/stripping efficiency of 99.7 % over 2100 cycles together with extended lifespan and suppressed water decomposition in the Zn||MnO₂ full battery were achieved, thus opening a new avenue for developing highly durable ZMBs.     

Solid-Adsorbed Polymer-Electrolyte Interphases for Stabilizing Metal Anodes in Aqueous Zn and Non-Aqueous Li Batteries

Polymers are known to adsorb spontaneously from liquid solutions in contact with high-energy substrates to form configurationally complex, but robust phases that often exhibit higher durability than might be expected from the individual physical bonds formed with the substrate. Rational control of the physical, chemical, and transport properties of such interphases has emerged as a fundamental opportunity for scientific and technological advances in energy storage technology but requires in-depth understanding of the conformation states and electrochemical effect of the adsorbed polymers. Here, we analyze the interfacial adsorption of oligomeric polyethylene glycol (PEG) chains of moderate sizes dissolved in protic and aprotic liquid electrolytes and find that there is an optimum polymer molecular weight of approximately 400 Da at which the highest columbic efficiency is achieved for both Zn and Li deposition. These findings point to a simple, versatile approach for extending the lifetime of batteries.     

Monolithic Phosphate Interphase for Highly Reversible and Stable Zn Metal Anode

Zinc metal battery (ZMB) is promising as the next generation of energy storage system, but challenges relating to dendrites and corrosion of the zinc anode are restricting its practical application. Here, to stabilize Zn anode, we report a controlled electrolytic method for a monolithic solid-electrolyte interphase (SEI) via a high dipole moment solvent dimethyl methylphosphonate (DMMP). The DMMP-based electrolytes can generate a homogeneous and robust phosphate SEI (Zn₃(PO₄)₂ and ZnP₂O₆). Benefiting from the protecting impact of this in situ monolithic SEI, the zinc electrode exhibits long-term cycling of 4700 h and a high Coulombic efficiency 99.89 % in Zn|Zn and Zn|Cu cell, respectively. The full V₂O₅|Zn battery with DMMP-H₂O hybrid electrolyte exhibits a high capacity retention of 82.2 % following 4000 cycles under 5 A g⁻¹. The first success in constructing the monolithic phosphate SEI will open a new avenue in electrolyte design for highly reversible and stable Zn metal anodes.     

Realizing Textured Zinc Metal Anodes through Regulating Electrodeposition Current for Aqueous Zinc Batteries

Crystallography modulation of zinc (Zn) metal anode is promising to promote Zn reversibility in aqueous electrolytes, but efficiently constructing Zn with specific crystallographic texture remains challenging. Herein, we report a current-controlled electrodeposition strategy to texture the Zn electrodeposits in conventional aqueous electrolytes. Using the electrolytic cell with low-cost Zn(CH₃COO)₂ electrolyte and Cu substrate as a model system, the texture of as-deposited Zn gradually transforms from (101) to (002) crystal plane as increasing the current density from 20 to 80 mA cm⁻². Moreover, the high current accelerates the Zn nucleation rate with abundant nuclei, enabling uniform deposition. The (002) texture permits stronger resistance to dendrite growth and interfacial side reactions than the (101) texture. The resultant (002)-textured Zn electrode achieves deep cycling stability and supports the stable operation of full batteries with conventional V/Mn-based oxide cathodes.     

Amphoteric Cellulose-Based Double-Network Hydrogel Electrolyte Toward Ultra-Stable Zn Anode

Zinc (Zn) metal anode suffers from uncontrollable Zn dendrites and parasitic side reactions at the interface, which restrict the practical application of aqueous rechargeable zinc batteries (ARZBs). Herein, an amphoteric cellulose-based double-network is introduced as hydrogel electrolyte to overcome these obstacles. On one hand, the amphoteric groups build anion/cation transport channels to regulate electro-deposition behavior on Zn (002) crystal plane enabled by homogenizing Zn²⁺ ions flux. On the other hand, the strong bonding between negatively charged carboxyl groups and Zn²⁺ ions promote the desolvation process of [Zn(H₂O)₆]²⁺ to eliminate side reactions. Based on the above two functions, the hydrogel electrolyte enables an ultra-stable cycling with a cumulative capacity of 7 Ah cm⁻² at 20 mA cm⁻²/20 mAh cm⁻² for Zn||Zn cell. This work provides significant concepts for developing hydrogel electrolytes to realize stable anode for high-performance ARZBs.     

ZnF2-Riched Inorganic/Organic Hybrid SEI: in situ-Chemical Construction and Performance-Improving Mechanism for Aqueous Zinc-ion Batteries

Uncontrolled dendrites growth and serious parasitic reactions in aqueous electrolytes, greatly hinder the practical application of aqueous zinc-ion battery. On the basis of in situ-chemical construction and performance-improving mechanism, multifunctional fluoroethylene carbonate (FEC) is introduced into aqueous electrolyte to construct a high-quality and ZnF₂-riched inorganic/organic hybrid SEI (ZHS) layer on Zn metal anode (ZMA) surface. Notably, FEC additive can regulate the solvated structure of Zn²⁺ to reduce H₂O molecules reactivity. Additionally, the ZHS layer with strong Zn²⁺ affinity can avoid dendrites formation and hinder the direct contact between the electrolyte and anode. Therefore, the dendrites growth, Zn corrosion, and H₂ evolution reaction on ZMA in FEC-included ZnSO₄ electrolyte are highly suppressed. Thus, ZMA in such electrolyte realize a long cycle life over 1000 h and deliver a stable coulombic efficiency of 99.1 % after 500 cycles.     

In situ Implanting 3D Carbon Network Reinforced Zinc Composite by Powder Metallurgy for Highly Reversible Zn-based Battery Anodes

Aqueous Zn-based batteries have emerged as compelling candidates for grid-scale energy storage, owing to their intrinsic safety, remarkable theoretical energy density and cost-effectiveness. Nonetheless, the dendrite formation, side reactions, and corrosion on anode have overshadowed their practical applications. Herein, we present an in situ grown carbon network reinforcing Zn matrix anode prepared by powder metallurgy. This carbon network provides an uninterrupted internal electron transport pathway and optimize the surface electric field distribution, thereby enabling highly reversible Zn deposition. Consequently, symmetrical cells demonstrate impressive stability, running for over 880 h with a low voltage hysteresis (≈32 mV). Furthermore, this Zn matrix composite anode exhibits enhanced performance in both the aqueous Zn-ion and the Zn-air batteries. Notably, Zn//MnO₂ cells display superior rate capabilities, while Zn-air batteries deliver high power density and impressive Zn utilization rate (84.9 %). This work provides a new idea of powder metallurgy method for modified Zn anodes, showcasing potential for large-scale production.     

An Ultrathin Inorganic Molecular Crystal Interfacial Layer for Stable Zn Anode

Zn metal anode suffers from dendrite growth and side reactions during cycling, significantly deteriorating the lifespan of aqueous Zn metal batteries. Herein, we introduced an ultrathin and ultra-flat Sb₂O₃ molecular crystal layer to stabilize Zn anode. The in situ optical and atomic force microscopes observations show that such a 10 nm Sb₂O₃ thin layer could ensure uniform under-layer Zn deposition with suppressed tip growth effect, while the traditional WO₃ layer undergoes an uncontrolled up-layer Zn deposition. The superior regulation capability is attributed to the good electronic-blocking ability and low Zn affinity of the molecular crystal layer, free of dangling bonds. Electrochemical tests exhibit Sb₂O₃ layer can significantly improve the cycle life of Zn anode from 72 h to 2800 h, in contrast to the 900 h of much thicker WO₃ even in 100 nm. This research opens up the application of inorganic molecular crystals as the interfacial layer of Zn anode.     

Engineering Fluorine-rich Double Protective Layer on Zn Anode for Highly Reversible Aqueous Zinc-ion Batteries

The high thermodynamic instability and side reactions of Zn-metal anode (ZMA), especially at high current densities, greatly impede the commercialization of aqueous zinc-ion batteries (AZIBs). Herein, a fluorine-rich double protective layer strategy is proposed to obtain the high reversibility of AZIBs through the introduction of a versatile tetradecafluorononane-1,9-diol (TDFND) additive in aqueous electrolyte. TDFND molecule with large adsorption energy (−1.51 eV) preferentially absorbs on the Zn anode surface to form a Zn(OR)₂⁻ (R=−CH₂−(CF₂)₇−CH₂−) cross-linking complex network, which balances space electric field and controls the Zn²⁺ ion flux, thus enabling the uniform and compact deposition of Zn (002) crystal planes. Meanwhile, TDFND with low Lowest unoccupied molecular orbital (LUMO, 0.10 eV) energy level is priorly decomposed to regulate the interfacial chemistry of ZMA by building a ZnF₂-rich solid electrode/electrolyte interface (SEI) layer. It is found that a 14 nm-thick SEI layer delivers excellent structural integrity to suppress parasitic reactions by blocking the direct contact of active water and ZMA. Consequently, the Zn electrode exhibits a superior cycling life over 430 h at 10 mA cm⁻² and a high average Coulombic efficiency of 99.8 % at 5 mA cm⁻². Furthermore, a 68 mAh pouch cell delivers 80.3 % capacity retention for 1000 cycles.     

Improved Interfacial Ion Migration and Deposition through the Chain-Liquid Synergistic Effect by a Carboxylated Hydrogel Electrolyte for Stable Zinc Metal Anodes

The large-scale applicability of Zn-metal anodes is severely impeded by the issues such as the dendrite growth, complicated hydrogen evolution, and uncontrollable passivation reaction. Herein, a negatively charged carboxylated double-network hydrogel electrolyte (Gelatin/Sodium alginate-acetate, denoted as Gel/SA-acetate) has been developed to stabilize the interfacial electrochemistry, which restructures a type of Zn²⁺ ion solvent sheath optimized via a chain-liquid synergistic effect. New hydrogen bonds are reconstructed with water molecules by the zincophilic functional groups, and directional migration of hydrated Zn²⁺ ions is therefore induced. Concomitantly, the robust chemical bonding of such hydrogel layers to the Zn slab exhibits a desirable anti-catalytic effect, thereby greatly diminishing the water activity and eliminating side reactions. Subsequently, a symmetric cell using the Gel/SA-acetate electrolyte demonstrates a reversible plating/stripping performance for 1580 h, and an asymmetric cell reaches a state-of-the-art runtime of 5600 h with a high average Coulombic efficiency of 99.9 %. The resultant zinc ion hybrid capacitors deliver exceptional properties including the capacity retention of 98.5 % over 15000 cycles, energy density of 236.8 Wh kg⁻¹, and high mechanical adaptability. This work is expected to pave a new avenue for the development of novel hydrogel electrolytes towards safe and stable Zn anodes.     

甲醇在欠电位沉积Ru修饰Pt电极上的催化氧化

采用欠电位沉积(upd)方法在Pt 表面沉积亚单层的Ru制备出upd-Ru/Pt 电极. 通过欠电位沉积前后电极在0.5 mol·L-1 H2SO4溶液中循环伏安图-152 - 128 mV(vs Ag/AgCl)电位范围内对氢区的数值积分确定Pt表面Ru 的覆盖度. 用电化学方法测试了甲醇在upd-Ru/Pt电极上的催化氧化, 并讨论分析了欠电位沉积电位和Ru的表面覆盖度对甲醇氧化的影响. 结果表明, Ru能够欠电位沉积到Pt表面. Pt表面欠电位沉积少量的Ru 即能大大促进甲醇的氧化.只要控制upd-Ru的沉积量, upd-Ru原子就能大大促进甲醇氧化而与沉积电位无关. Ru原子对甲醇氧化的促进作用与Ru和Pt是否形成合金无关, 而取决于Ru 在Pt表面的百分含量.