An efficient electrolyte additive of tetramethylammonium sulfate hydrate for Dendritic-Free zinc anode for aqueous Zinc-ion batteries

A self-assembled 2-hydroxyphosphonoacetic acid protective layer enables dendrite-free Zn anodes

A stable self-assembled 2-hydroxyphosphonoacetic acid (HPAA) layer was constructed on the Zn surface via chelation. This HPAA protective layer significantly inhibits the water-related side reactions and suppresses Zn dendrite growth. Consequently, the Zn-HPAA-1h anode shows a long cycling lifetime of 650 h in a symmetric cell at 30.0 mA cm-2. Also, the Zn-HPAA-1h//V2O5 full cell demonstrates a high capacity of 154.1 mA h g-1 after 1000 cycles at 2 A g-1. This study provides a new strategy for developing dendrite-free Zn anodes.

Screening Ammonium-Based Cationic Additives to Regulate Interfacial Chemistry for Aqueous Ultra-Stable Zn Metal Anode

The interfacial dynamics and chemistry at the electrolyte/metal interface, particularly the formation of an adsorption interphase, is paramount in dictating the reversibility of Zn metal deposition and dissolution processes in battery systems. Herein, a series of different cationic ammonium-based electrolyte additives are screened that effectively modulate the interfacial chemistry of zinc anodes in aqueous electrolytes, significantly improving the reversibility of Zn metal plating/stripping processes. As initially comprehensive investigation by combining theoretical calculation and molecular dynamic simulation, the tetramethylammonium cation, with its specific molecular structure and charge distribution, is identified as pivotal in mediating the Zn(H2O)6 2+ solvation shell structure at the electrode/electrolyte interface and shows the strong resistance against electrolyte corrosion as revealed by X-ray and optical measurements. As a result, the Zn||Zn symmetric cell with optimal electrolyte lasts for over 4400 h of stable plating/stripping behaviors, and the Zn||Cu asymmetric cell stabilizes for 2100 cycles with an average Coulombic efficiency of 99.8%, which is much better than the-state-of-art progress. Consequently, full-cells coupled with various cathodes showcase improved electrochemical performance, displaying high capacity-retention and low self-discharge behaviors. These findings offer essential insights of cationic additives in ameliorating zinc anode performance.

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.

Highly reversible Zn anodes enabled by in-situ construction of zincophilic zinc polyacrylate interphase for aqueous Zn-ion batteries

The irreversibility and low utilization of Zn anode stemming from the corrosion and dendrite growth have largely limited the commercialization of aqueous zinc batteries. Here, a carbonyl-rich polymer interphase of zinc polyacrylate (ZPAA) is spontaneously in-situ constructed on Zn anode to address the above-mentioned dilemmas. The ZPAA interlayer enables fast transport kinetics of Zn2+ and tailors the interfacial electric field for realizing the uniform Zn deposition due to superior zincophilicity, high Zn2+ transference number and inherent ion-diffusion channel. Importantly, acting as a buffer interphase with strong adhesion and isolation of electrolytes, this functional layer effectively protects the Zn electrode against the water-induced erosion and passivation. Remarkably, the ZPAA@Zn electrode realizes an enhanced Coulombic efficiency of 99.71 % within 2200 cycles, delivers an ultra-long cycling stability over 7660 h (>319 days, 1 mA cm-2) and 2460 h (5 mA cm-2) with lower voltage hysteresis. Also, the ZPAA@Zn/MnO2 full cell maintains a high capacity of 114 mAh/g after 2000 cycles, much better that of untreated Zn/MnO2 cell (25 mAh/g). This concept of in-situ fabricating ion-sieve-like polymer interphase provides a facile approach to stabilize Zn anode and further paves a way for high-performance aqueous batteries.

Electrolyte and Additive Engineering for Zn Anode Interfacial Regulation in Aqueous Zinc Batteries

Aqueous Zn-metal batteries (AZMBs) have gained great interest due to their low cost, eco-friendliness, and inherent safety, which serve as a promising complement to the existing metal-based batteries, e.g., lithium-metal batteries and sodium-metal batteries. Although the utilization of aqueous electrolytes and Zn metal anode in AZMBs ensures their improved safety over other metal batteries meanwhile guaranteeing their decent energy density at the cell level, plenty of challenges involved with metallic Zn anode still await to be addressed, including dendrite growth, hydrogen evolution reaction, and zinc corrosion and passivation. In the past years, several attempts have been adopted to address these problems, among which engineering the aqueous electrolytes and additives is regarded as a facile and promising approach. In this review, a comprehensive summary of aqueous electrolytes and electrolyte additives will be given based on the recent literature, aiming at providing a fundamental understanding of the challenges associated with the metallic Zn anode in aqueous electrolytes, meanwhile offering a guideline for the electrolytes and additives engineering strategies toward stable AZMBs in the future.

Improvement of surface stability of Zn anode by a cost-effective ErCl3 additive for realizing high-performance aqueous zinc-ion batteries

Rechargeable aqueous-zinc ion batteries (AZIB) have notable benefits in terms of high safety and low cost. Nevertheless, the challenges, such as dendrite growth, zinc anode corrosion, and hydrogen evolution reaction, impede its practical implementation. Hence, this study proposes the introduction of an economical ErCl3 electrolyte additive to stabilize the Zn anode surface and address the aforementioned issues. The introduced Er3+ will cover the raised zinc dendrite surface and weaken the "tip effect" on the surface of the zinc anode via the "electrostatic shielding" effect. Simultaneously, the introduced Cl- can reduce the polarization of the zinc anode. Due to the synergistic effect of Er3+ and Cl-, the zinc anode corrosion, dendrite growth and hydrogen evolution have been efficiently inhibited. As a result, the Zn||Zn-symmetric battery using ErCl3 additive can stably cycle for 1100 h at 1 mA cm-2, 1 mAh cm-2, and exhibit a high average coulomb efficiency (99.2 %). Meanwhile, Zn||MnO2 full battery based on ErCl3-added electrolyte also demonstrates a high reversible capacity of 157.1 mAh/g after 500 cycles. Obviously, the capacity decay rate of the full battery is also improved, only 0.113 % per cycle. This study offers a straightforward and economically efficient method for stabilizing the zinc anode and realizing high-performance AZIBs.

Restraining the shuttle effect of polyiodides and modulating the deposition of zinc ions to enhance the cycle lifespan of aqueous Zn-I2 batteries

The boom of aqueous Zn-based energy storage devices, such as zinc-iodine (Zn-I2) batteries, is quite suitable for safe and sustainable energy storage technologies. However, in rechargeable aqueous Zn-I2 batteries, the shuttle phenomenon of polyiodide ions usually leads to irreversible capacity loss resulting from both the iodine cathode and the zinc anode, and thus impinges on the cycle lifespan of the battery. Herein, a nontoxic, biocompatible, and economical polymer of polyvinyl alcohol (PVA) is exploited as an electrolyte additive. Based on comprehensive analysis and computational results, it is evident that the PVA additive, owing to its specific interaction with polyiodide ions and lower binding energy, can effectively suppress the migration of polyiodide ions towards the zinc anode surface, thereby mitigating adverse reactions between polyiodide ions and zinc. Simultaneously, the hydrogen bond network of water molecules is disrupted due to the abundant hydroxyl groups within the PVA additive, leading to a decrease in water activity and mitigating zinc corrosion. Further, because of the preferential adsorption of PVA on the zinc anode surface, the deposition environment for zinc ions is adjusted and its nucleation overpotential increases, which is favorable for the dense and uniform deposition of zinc ions, thus ensuring the improvement of the performance of the Zn-I2 battery. This investigation has inspired the development of a user-friendly and high-performance Zn-I2 battery.

Erythritol as a Saccharide Multifunctional Electrolyte Additive for Highly Reversible Zinc Anode

Dendrite formation and water-triggered side reactions on the surface of Zn metal anodes severely restrict the commercial viability of aqueous zinc-ion batteries (AZIBs). In this work, we introduce erythritol (Et) as an electrolyte additive to enhance the reversibility of zinc anodes, given its cost-effectiveness, mature technology, and extensive utilization in various domains such as food, medicine, and other industries. By combining multiscale theoretical simulation and experimental characterization, it was demonstrated that Et molecules can partially replace the coordination H2O molecules to reshape the Zn2+ solvation sheath and destroy the hydrogen bond network of the aqueous electrolyte. More importantly, Et molecules tend to adsorb on the zinc anode surface, simultaneously inhibit water-triggered side reactions by isolating water and promote uniform and dense deposition by accelerating the Zn2+ diffusion and regulating the nucleation size of the Zn grain. Thanks to this synergistic mechanism, the Zn anode can achieve a cycle life of more than 3900 h at 1 mA cm-2 and an average Coulombic efficiency of 99.77%. Coupling with δ-MnO2 cathodes, the full battery delivers a high specific capacity of 228.1 mAh g-1 with a capacity retention of 76% over 1000 cycles at 1 A g-1.

Constructing amphipathic molecular layer to assists de-solvation process for dendrite-free Zn anode

Due to the excellent safety feature, substantial theoretical capacity and abundant zinc reserves in the earth's crust, Aqueous Zn-ion batteries (AZIBs) are promising as the next generation energy storage system. However, the problem of dendrite growth and the related side reactions in Zn surface limit their further development and application. Herein, an amphipathic molecular layer (Polyacrylic Acid, named as PAA) is constructed on Zn surface to hinder the side reactions and zinc dendrites by intervening the de-solvation process. It is found that the rich hydroxyl group in polyacrylic acid is very hydrophilic. On the contrary, hydrocarbon group on the other side is nearly hydrophobic. The amphiphilic PAA molecular layer on Zn surface results in lower de-solvation energy barrier, thus inhibits the decomposition of water and related side reactions. Additionally, the accumulate abundant negative charge at the interface of polyacrylic acid and Zn surface can attract homogeneous deposition of Zn atoms. Using only 0.01 M PAA as additive in 2.0 M ZnSO4 electrolyte. Zn||Zn symmetric cells expresses a superior cycling stability of 4643 h (5 mA cm-2, 1 mAh cm-2). This study provides new insights into the long-life AZIBs modulated by amphipathic molecular layer.

Efficient Suppression of Dendrites and Side Reactions by Strong Electrostatic Shielding Effect via the Additive of Rb2 SO4 for Anodes in Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have attracted considerable attention due to their low cost and environmental friendliness. However, the rampant dendrite growth and severe side reactions during plating/stripping on the surface of zinc (Zn) anode hinder the practicability of AZIBs. Herein, an effective and non-toxic cationic electrolyte additive of Rb2 SO4 is proposed to address the issues. The large cation of Rb+ is preferentially adsorbed on the surface of Zn metal to induce a strong shielding effect for realizing the lateral deposition of Zn2+ ions along the Zn surface and isolating water from Zn metal to effectively inhibit side reactions. Consequently, the Zn||Zn symmetric cell with the addition of 1.5 mm Rb2 SO4 can cycle more than 6000 h at 0.5 mA cm-2 /0.25 mAh cm-2 , which is 20 times longer than that without Rb2 SO4 . Besides, the Zn||Cu asymmetric cell with Rb2 SO4 achieves a very high average Coulombic efficiency of 99.16% up to 500 cycles. Moreover, the electrolyte with Rb2 SO4 well matches with the VO2 cathode, achieving high initial capacity of 412.7 mAh g-1 at 5 A g-1 and excellent cycling stability with a capacity retention of 71.6% at 5 A g-1 after 500 cycles for the Zn//VO2 full cell.

Critical triple roles of sodium iodide in tailoring the solventized structure, anode-electrolyte interface and crystal plane growth to achieve highly reversible zinc anodes for aqueous zinc-ion batteries

Aqueous rechargeable Zn-ion batteries (ARZIBs) are promising for energy storage. However, the Zn dendrite and corrosive reactions on the surface of Zn anode limit the practical uses of ARZIBs. Herein, we present a valid electrolyte additive of NaI, in which I- can modulate the morphology of Zn crystal growth by adsorbing on specific crystal surfaces (002), and guide Zn deposition by inducing a negative charge on the Zn anode. Simultaneously, it enhances the reduction stability of water molecules by participating in the solvation structure of Zn(H2O)62+ by forming ZnI(H2O)5+. At 10 mA cm-2, the assembled Zn symmetrical batteries can run stably over 1,100 h, and the depth of discharge (DOD) can reach 51.3 %. At 1 A g-1, the VO2||Zn full-cell in 2 M ZnCl2 electrolyte with 0.4 M NaI (2 M ZnCl2-0.4 M NaI) maintains of the capacity retention of 75.7 % over 300 cycles. This work offers an insight into inorganic anions as electrolyte additives for achieving stable zinc anodes of ARZIBs.

Printing 3D mesh-like grooves on zinc surface to enhance the stability of aqueous zinc ion batteries

Aqueous zinc ion batteries (AZIBs) are receiving broad attention owing to their high safety and low cost. However, the high mechanical strength and irreversible growth of zinc dendrites limit the practical application of AZIBs. Herein, regular mesh-like gullies are built on the surface of zinc foil (M150 Zn) by using simple model pressing method and stainless steel mesh as a mold. Due to the charge-enrichment effect, zinc ion deposition and stripping will be preferentially carried out in the grooves to keep the outer surface flat. In addition, zinc is exposed to 002 crystal surface in the gully after being pressed, and the deposited zinc is more inclined to grow at a small angle, so that it has a sedimentary morphology parallel to the basement. Consequently, at a current density of 0.5 mA cm^-2, the M150 zinc anode has a voltage hysteresis of only 35 mV and a cycle life of up to 400 h (relative to a zinc foil of 96 mV and 160 h). Even more imposing is that the full cell has a capacity retention of approximately 100% after 1000 cycles at 2 A g^-1 and a specific capacity of almost 60 mAh g^-1 when activated carbon is used as the cathode. It is a promising method to improve the stable cycle performance of AZIBs by using a simple method to realize the non-prominent dendrites on the surface of zinc electrode.

Surfactant Additives Containing Hydrophobic Fluorocarbon Chains and Hydrophilic Sulfonate Anion for Highly Reversible Zn Anode

Aqueous zinc-ion batteries (AZIBs) show enormous potential as a large-scale energy storage technique. However, the growth of Zn dendrites and serious side reactions occurring at the Zn anode hinder the practical application of AZIBs. For the first time, we reported a fluorine-containing surfactant, i.e., potassium perfluoro-1-butanesulfonate (PPFBS), as an additive to the 2 M ZnSO₄ electrolyte. Benefitting from its hydrophilic sulfonate anion and hydrophobic long fluorocarbon chain, PPFBS can promote the uniform distribution of Zn²⁺ flux at the anode/electrolyte interface, allowing the Zn/Zn cell to cycle for 2200 h. Furthermore, PPFBS could inhibit side reactions due to the existence of the perfluorobutyl sulfonate (C₄F₉SO₃^-) adsorption layer and the presence of C₄F₉SO₃^- in the solvation structure of Zn²⁺. The former can reduce the amount of H₂O molecules and SO₄^2- in contact with the Zn anode and C₄F₉SO₃^- entering the Zn²⁺-solvation structure by replacing SO₄^2-. The Zn/Cu cell exhibits a superior average CE of 99.47% over 500 cycles. When coupled with the V₂O₅ cathode, the full cell shows impressive cycle stability. This work provides a simple, effective, and economical solution to the common issues of the Zn anode.

Tuning the Zn2+ solvation structure in dual-salts hybrid aqueous electrolyte to stabilize the Zn metal anode

Aqueous Zn-ion battery is expected to become a substitute for Li-ion battery due to its inherent safety, low cost, and environmental friendliness. Dendrite growth and side reaction problems during electroplating lead to its low Coulombic efficiency and unsatisfactory life, which greatly limits its practical application. Here, we propose a dual-salts hybrid electrolyte, which alleviates the above issues by mixing Zn(OTf)₂ to ZnSO₄ solution. Extensive tests and MD simulations have shown that the dual-salts hybrid electrolyte can regulate the solvation structure of Zn²⁺, facilitating uniform Zn deposition, and inhibiting side reactions and dendrite growth. Hence, the dual-salts hybrid electrolyte exhibits good reversibility in Zn//Zn batteries, which can provide a lifetime of more than 880 h at 1 mA cm^-2 and 1 mAh cm^-2. Moreover, the average Coulombic efficiency of Zn//Cu cells in hybrid system can reach 98.2% after 520 h, much better than that of 90.7% in pure ZnSO₄ electrolyte and 92.0% in pure Zn(OTf)₂ electrolyte. Benefiting from the fast ion exchange rate and high ion conductivity, Zn-ion hybrid capacitor in hybrid electrolyte also displays excellent stability and capacitive performance. This effective strategy for dual-salts hybrid electrolytes provides a promising direction for designing aqueous electrolytes for Zn-ion batteries.

Zn and N co-doped three-dimensional honeycomb-like carbon featured with interconnected nano-pools for dendrite-free zinc anode

The zinc-ion battery (ZIB) has been extensively researched as one of the promising electrochemical power sources. However, the problem of Zn-dendrite formation during repeated plating and stripping process seriously hinders the development of ZIBs. Herein, three-dimensional (3D) honeycomb-like porous carbon (HPC) with co-doping of zinc and nitrogen is prepared through confining growth of nanoscale zeolite imidazole framework-8 (ZIF-8) on the well-designed nano-pools walls of HPC followed by pyrolysis at 600 ℃ to obtain the final product ZnN/HPC-600, which exhibits large surface area and abundant zincophilic interfaces, ensuring homogeneous distribution of electronic field and low polarization during cycling process. Importantly, ZnN/HPC-600 facilitates the uniform distribution and migration of Zn²⁺ in this nano-pools structure, avoiding the growth of dendritic Zn crystal during charging stage. The symmetric and asymmetric cells with Zn/ZnN/HPC-600 anodes are assembled, demonstrating excellent cycling reversibility, good rate performance and long-term stability. Besides, a Zn||MnO₂ full cell with Zn/ZnN/HPC-600 anode also exhibits robust cycling stability, fast reaction kinetics and almost 100 % coulombic efficiency. This work offers a novel and efficient carbonaceous nano-pools strategy to realize dendrite-free zinc anode in ZIBs.

Polyaniline functionalized separator as synergistic medium for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have received increasing attention as a promising energy storage device. However, it was rarely reported that the separators as a synergistic medium stabilize the cathode and anode materials. Herein, a polyaniline functionalized glass fiber separator (PANI-GF) was synthesized in situ. The porous structure of PANI effectively regulated the flux of zinc ions inside the separator and its deposition behavior through ion confinement. The abundant N-containing functional groups can adsorb water molecules and effectively reduce harmful side reactions. Moreover, the PANI-GF separator adjusted pH to inhibit dissolution of the cathode by protonation. Importantly, based on the synergistic separator, the Zn-MnO₂ full cell exhibited more than twice discharge capacity compared to the conventional cell after 1000 cycles at 2 A g^-1. This study provided in-depth insight into the design of convenient, reliable, cost-effective, and synergistic separators for AZIBs.