A Highly Reversible Zinc Anode for Rechargeable Aqueous Batteries

Induced Anionic Functional Group Orientation-Assisted Stable Electrode-Electrolyte Interphases for Highly Reversible Zinc Anodes

Dendrite growth and other side-reaction problems of zinc anodes in aqueous zinc-ion batteries heavily affect their cycling lifespan and Coulombic efficiency, which can be effectively alleviated by the application of polymer-based functional protection layer on the anode. However, the utilization rate of functional groups is difficult to improve without destroying the polymer chain. Here, a simple and well-established strategy is proposed by controlling the orientation of functional groups (─SO3H) to assist the optimization of zinc anodes. Depending on the electrostatic effect, the surface-enriched ─SO3H groups increase the ionic conductivity and homogenize the Zn2+ flux while inhibiting anionic permeation. This approach avoids the destruction of the polymer backbone by over-sulfonation and amplifies the effect of functional groups. Therefore, the modified sulfonated polyether ether ketone (H-SPEEK) coating-optimized zinc anode is capable of longtime stable zinc plating/stripping, and moreover an enhanced cycling steadiness under high current densities is also detected in a series of Zn batteries with different cathode materials, which achieved by the inclusion of H-SPEEK coating without causing any harmful effects on the electrolyte and cathode. This work provides an easy and efficient approach to further optimize the plating/stripping of cations on metal electrodes, and sheds lights on the scale-up of high-performance aqueous zinc-ion battery technology.

Towards Superior Aqueous Zinc-Ion Batteries: The Insights of Artificial Protective Interfaces

Aqueous zinc ion batteries (AZIBs) with metallic Zn anode have the potential for large-scale energy storage application due to their cost-effectiveness, safety, environmental-friendliness, and ease of preparation. However, the concerns regarding dendrite growth and side reactions on Zn anode surface hamper the commercialization of AZIBs. This review aims to give a comprehensive evaluation of the protective interphase construction and provide guidance to further improve the electrochemical performance of AZIBs. The failure behaviors of the Zn metal anode including dendrite growth, corrosion, and hydrogen evolution are analyzed. Then, the applications and mechanisms of the constructed interphases are introduced, which are classified by the material species. The fabrication methods of the artificial interfaces are summarized and evaluated, including the in-situ strategy and ex-situ strategy. Finally, the characterization means are discussed to give a full view for the study of Zn anode protection. Based on the analysis of this review, a stable and high-performance Zn anode could be designed by carefully choosing applied material, corresponding protective mechanism, and appropriate construction technique. Additionally, this review for Zn anode modification and construction techniques for anode protection in AZIBs may be helpful in other aqueous metal batteries with similar problems.

A trinity strategy enabled by iodine-loaded nitrogen-boron-doped carbon protective layer for dendrite-free zinc-ion batteries

Although aqueous zinc ion batteries (AZIBs) have the merits of environmental friendliness, high safety and theoretical capacity, the slow kinetics associated with zinc deposition and unavoidable interfacial corrosion have seriously affected the commercialization of aqueous zinc ion batteries. In this work, an ingenious "trinity" design is proposed by applying a porous hydrophilic carbon-loaded iodine coating to the zinc metal surface (INBC@Zn), which simultaneously acts as an artificial protective layer, electrolyte additive and anode curvature regulator, so as to reduce the nucleation overpotential of Zn and promote the preferential deposition of (002) planes to some extent. With this synergistic effect, INBC@Zn exhibits high reversibility and strong side reaction inhibition. As a result, INBC@Zn shows high symmetric cycling stability up to 4500 h at 1 mA cm-2. An ultra-long cycle stability of 1500 cycles with high Coulombic efficiency (99.8 %) is achieved in the asymmetric cell. In addition, the INBC@Zn//NVO full cells exhibit impressive capacity retention (96 % after 1000 cycles at 3 A/g). Importantly, the designed pouch cell demonstrates stable performance and shows certain prospects for application. This work provides a facile and instructive approach toward the development of high-performance AZIBs.

Enhancing the Performance of Reversible Zn Deposition by Ultrathin Polyelectrolyte Coatings

Modifying the surfaces of zinc and other metallic substrates is considered an effective strategy to enhance the reversibility of the zinc deposition and stripping processes. While a variety of surface modification strategies have been explored, their ability to be practically implemented is not always trivial due to the associated high costs and complexity of the proposed techniques. In this study, we showcase a straightforward method for preparing ultrathin polyelectrolyte coatings using polydiallyldimethylammonium chloride (PDDA) and polyethylenimine (PEI). The coatings, characterized by their electrostatic charge and hydrophobicity, suppress side reactions and even out the electrodeposition process across the substrate surface. The PDDA-coated anodes demonstrate significantly reduced voltage hysteresis, uniform zinc morphology, improved self-discharge rates, and an impressive Coulombic efficiency exceeding 99% over prolonged cycling. Our findings highlight the potential that such cost-effective and straightforward surface treatments could be widely applied in Zn metal-based batteries.

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

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

Highly Reversible Zn Anodes Achieved by Enhancing Ion-Transport Kinetics and Modulating Zn (002) Deposition

Uncontrolled dendrite growth and water-related side reactions in mild electrolytes are the main causes of poor cycling stability of zinc anodes, resulting in the deterioration of aqueous zinc-based batteries. Herein, a multifunctional fluorapatite (Ca5(PO4)3F) aerogel (FAG) interface layer is proposed to realize highly stable zinc anodes via the integrated regulation of Zn2+ migration kinetics and Zn (002) orientation deposition. Owing to the well-defined aerogel nanochannels and the rich Zn2+ adsorption sites resulting from the ion exchange between Ca2+ and Zn2+, the FAG interface layer could significantly accelerate the Zn2+ migration and effectively homogenize the Zn2+ flux and nucleation sites, thus promoting rapid and uniform Zn2+ migration at the electrode/electrolyte interface. Additionally, during the cycling process, the F atoms from FAG promote the in situ generation of ZnF2, which facilitates the manipulation of the preferred Zn (002) orientation deposition, thus efficiently suppressing dendrite growth and side reactions by combining with the above synergistic effects. Consequently, the FAG-modified Zn anode displays a stable cycle life of over 4000 h at 1 mA cm-2 and exhibits highly reversible Zn plating/stripping behavior. Meanwhile, the Zn||MnO2 full cells exhibit improved cycle stability over 2000 cycles compared with that of the bare Zn, highlighting the virtues of the FAG protective layer for highly reversible Zn anodes. Our work brings the insight in to stabilize Zn anodes and power the commercial applications of aqueous zinc-based batteries.

Coulombic Efficiency for Practical Zinc Metal Batteries: Critical Analysis and Perspectives

Climate change and energy depletion are common worries of this century. During the global clean energy transition, aqueous zinc metal batteries (AZMBs) are expected to meet societal needs due to their large-scale energy storage capability with earth-abundant, non-flammable, and economical chemistries. However, the poor reversibility of Zn poses a severe challenge to AZMB implementation. Coulombic efficiency (CE) is a quantitative index of electrode reversibility in rechargeable batteries but is not well understood in AZMBs. Thus, in this work,  the state-of-art CE to present the status quo of AZMB development is summarized.  A fictional 120 Wh kg-1 AZMB pouch cell is also proposed and evaluated revealing the improvement room and technical goal of AZMB chemistry. Despite some shared mechanisms between AZMBs and lithium metal batteries, misconceptions prevalent in AZMBs are clarified. Essentially, AZMB has its own niche in the market with unique merits and demerits. By incorporating academic and industrial insights, the development pathways of AZMB are suggested.

Solid Electrolyte Interface in Zn-Based Battery Systems

Due to its high theoretical capacity (820 mAh g^-1), low standard electrode potential (- 0.76 V vs. SHE), excellent stability in aqueous solutions, low cost, environmental friendliness and intrinsically high safety, zinc (Zn)-based batteries have attracted much attention in developing new energy storage devices. In Zn battery system, the battery performance is significantly affected by the solid electrolyte interface (SEI), which is controlled by electrode and electrolyte, and attracts dendrite growth, electrochemical stability window range, metallic Zn anode corrosion and passivation, and electrolyte mutations. Therefore, the design of SEI is decisive for the overall performance of Zn battery systems. This paper summarizes the formation mechanism, the types and characteristics, and the characterization techniques associated with SEI. Meanwhile, we analyze the influence of SEI on battery performance, and put forward the design strategies of SEI. Finally, the future research of SEI in Zn battery system is prospected to seize the nature of SEI, improve the battery performance and promote the large-scale application.

Scientific Challenges and Improvement Strategies of Zn-Based Anodes for Aqueous Zn-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) have attracted widespread attention due to the intrinsic features of Zn-based anodes, mainly including high capacity, low cost, and low working potential together with high over-potential for hydrogen evolution reaction. Aqueous ZIBs are considered to be strong competitors and substitutes for lead-acid, nickel-metal hydrogen, nickel-cadmium, and even lithium-ion batteries. Great efforts have been made in the past few years towards the issues existed in aqueous ZIBs, mainly including alkaline and mild acidic systems. In this perspective, we illustrate the advantages, the main challenges, and the corresponding solution strategies of Zn-based anodes in various aqueous rechargeable ZIBs with alkaline and mild acidic electrolytes. Furthermore, feasible aqueous ZIBs for practical use are prospected.

Stable Zinc Anodes Enabled by a Zincophilic Polyanionic Hydrogel Layer

The practical application of the Zn-metal anode for aqueous batteries is greatly restricted by catastrophic dendrite growth, intricate hydrogen evolution, and parasitic surface passivation. Herein, a polyanionic hydrogel film is introduced as a protective layer on the Zn anode with the assistance of a silane coupling agent (denoted as Zn-SHn). The hydrogel framework with zincophilic -SO₃ ^- functional groups uniformizes the zinc ions flux and transport. Furthermore, such a hydrogel layer chemically bonded on the Zn surface possesses an anti-catalysis effect, which effectively suppresses both the hydrogen evolution reaction and formation of Zn dendrites. As a result, stable and reversible Zn stripping/plating at various currents and capacities is achieved. A full cell by pairing the Zn-SHn anode with a NaV₃ O₈ ·1.5 H₂ O cathode shows a capacity of around 176 mAh g^-1 with a retention around 67% over 4000 cycles at 10 A g^-1 . This polyanionic hydrogel film protection strategy paves a new way for future Zn-anode design and safe aqueous batteries construction.

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

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

Long-life zinc electrodes achieved by oxygen plasma functionalization

A facile oxygen plasma treatment strategy is proposed to promote zinc dendrite inhibition by modifying the surface oxygen functional groups. The plasma-treated zinc electrodes achieved an extended working lifespan of 3800 h with an average Coulombic efficiency of over 99% for 1000 cycles when applied in full batteries. This work provides great prospects for the fabrication of long-life zinc batteries for grid systems.