Reversible Zn Metal Anodes Enabled by Trace Amounts of Underpotential Deposition Initiators

Modulating solvated structure of Zn2+ and inducing surface crystallography by a simple organic molecule with abundant polar functional groups to synergistically stabilize zinc metal anodes for long-life aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have attracted significant attention owing to their inherent security, low cost, abundant zinc (Zn) resources and high energy density. Nevertheless, the growth of zinc dendrites and side reactions on the surface of Zn anodes during repeatedly plating/stripping shorten the cycle life of AZIBs. Herein, a simple organic molecule with abundant polar functional groups, 2,2,2-trifluoroether formate (TF), has been proposed as a high-efficient additive in the ZnSO4 electrolyte to suppress the growth of Zn dendrites and side reaction during cycling. It is found that TF molecules can infiltrate the solvated sheath layer of the hydrated Zn2+ to reduce the number of highly chemically active H2O molecules owing to their strong binding energy with Zn2+. Simultaneously, TF molecules can preferentially adsorb onto the Zn surface, guiding the uniform deposition of Zn2+ along the crystalline surface of Zn(002). This dual action significantly inhibits the formation of Zn dendrites and side reactions, thus greatly extending the cycling life of the batteries. Accordingly, the Zn//Cu asymmetric cell with 2 % TF exhibits stable cycling for more than 3,800 cycles, achieving an excellent average Columbic efficiency (CE) of 99.81 % at 2 mA cm-2/1 mAh cm-2. Meanwhile, the Zn||Zn symmetric cell with 2 % TF demonstrates a superlong cycle life exceeding 3,800 h and 2,400 h at 2 mA cm-2/1 mAh cm-2 and 5 mA cm-2/2.5 mAh cm-2, respectively. Simultaneously, the Zn//VO2 full cell with 2 % TF possesses high initial capacity (276.8 mAh/g) and capacity retention (72.5 %) at 5 A/g after 500 cycles. This investigation provides new insights into stabilizing Zn metal anodes for AZIBs through the co-regulation of Zn2+ solvated structure and surface crystallography.

3D Leaf-Like Copper-Zinc Alloy Enables Dendrite-Free Zinc Anode for Ultra-Long Life Aqueous Zinc Batteries

Metallic zinc exhibits immense potential as an anode material for aqueous rechargeable zinc batteries due to its high theoretical capacity, low redox potential, and inherent safety. However, practical applications are hindered by dendrite formation and poor cycling stability. Herein, a facile substitution reaction method is presented to fabricate a 3D leaf-like Cu@Zn composite anode. This unique architecture, featuring a 3D network of leaf-like Cu on a Zn foil surface, significantly reduces nucleation overpotential and facilitates uniform Zn plating/stripping, effectively suppressing dendrite growth. Notably, an alloy layer of CuZn5 forms in situ on the 3D Cu layer during cycling. DFT calculations reveal that this CuZn5 alloy possesses a lower Zn binding energy compared to both Cu and Zn metal, further promoting Zn plating/stripping and enhancing electrochemical kinetics. Consequently, the symmetric Cu@Zn electrode exhibits remarkable cycling stability, surpassing 1300 h at 0.5 mA cm-2 with negligible dendrite formation. Furthermore, full cells comprising Cu@Zn||VO2 exhibit superior capacity and rate performance compared to bare Zn anodes. This work provides a promising strategy for constructing highly stable and efficient Zn anodes for next-generation aqueous zinc batteries.

Sodium compensation: a critical technology for transforming batteries from sodium-starved to sodium-rich systems

Sodium-ion batteries (SIBs) have attracted wide attention from academia and industry due to the low cost and abundant sodium resources. Despite the rapid industrialization development of SIBs, it still faces problems such as a low initial coulombic efficiency (ICE) leading to a significant decrease in battery energy density (e.g., 20%). Sodium compensation technology (SCT) has emerged as a promising strategy to effectively increase the ICE to 100% and drastically boost battery cycling performance. In this review, we emphasize the importance of SCT in high-performance SIBs and introduce its working principle. The up-to-date advances in different SCTs are underlined in this review. In addition, we elaborate the current merits and demerits of different SCTs. This review also provides insights into possible future research directions in SCT for high-energy SIBs.

A dual-functional electrolyte additive displaying hydrogen bond fusion enables highly reversible aqueous zinc ion batteries

In recent years, aqueous zinc-ion batteries (AZIBs) have attracted significant attention in energy storage due to their notable advantages, including high safety, low cost, high capacity, and environmental friendliness. However, side reactions like hydrogen evolution and zinc (Zn) dendrites can significantly impact their Coulombic efficiency (CE) and lifespan. Effectively addressing these issues has become a focus of research in this field. In our study, dimethyl sulfoxide (DMSO) and nanodiamonds (NDs) were used to optimize the electrolyte of AZIBs. Benefiting from the hydrogen bond fusion of DMSO and NDs, which regulates the Zn deposition behavior, effectively inhibiting the growth of Zn dendrites, hydrogen evolution, and corrosion. The Zn | |Zn symmetric cells using NDs-DMSO-ZS demonstrate exceptional cycling stability for over 1500 h at 1 mA cm-2, while the Zn//Cu asymmetric cells achieve up to 99.8% CE at 2 mA cm-2. This study not only shows the application prospects of electrolyte optimization in enhancing AZIBs performance, but also provides a reference for the advancement of electrolyte technology in advanced AZIBs technology.

Ultra-High Proportion of Grain Boundaries in Zinc Metal Anode Spontaneously Inhibiting Dendrites Growth

Aqueous Zn-ion batteries are an attractive electrochemical energy storage solution for their budget and safe properties. However, dendrites and uncontrolled side reactions in anodes detract the cycle life and energy density of the batteries. Grain boundaries in metals are generally considered as the source of the above problems but we present a diverse result. This study introduces an ultra-high proportion of grain boundaries on zinc electrodes through femtosecond laser bombardment to enhance stability of zinc metal/electrolyte interface. The ultra-high proportion of grain boundaries promotes the homogenization of zinc growth potential, to achieve uniform nucleation and growth, thereby suppressing dendrite formation. Additionally, the abundant active sites mitigate the side reactions during the electrochemical process. Consequently, the 15 μm Fs-Zn||MnO2 pouch cell achieves an energy density of 249.4 Wh kg-1 and operates for over 60 cycles at a depth-of-discharge of 23 %. The recognition of the favorable influence exerted by UP-GBs paves a new way for other metal batteries.

Easy-to-Lay Poly-N Heterocyclic Additives Enable Long-Term Stabilization of Zinc-Ion Capacitor Anodes under Deep Plating/Stripping

Addition of organic compounds containing O/N heteroatoms to aqueous electrolytes such as ZnSO4 (ZS) solutions is one of the effective strategies to inhibit Zn anode dendrites and side reactions. However, addressing the stability of Zn plating/stripping at high current densities and areal capacities by this method is still a challenge, especially in capacitors known for high power and long life. Herein, an organic heterocyclic compound of 1, 4, 7, 10-tetraazacyclododecane (TC) containing four symmetrically distributed N atoms is employed as ZS additive, expanding the life of Zn anodes from ≈ 30 h to 1000 and 240 h at deep plating/stripping conditions of 10 and 20 mA cm-2/mAh cm-2, respectively; the cumulative capacity is as high as 5.0 Ah cm-2 with 99% Coulombic efficiency, far exceeding reported additives. TC with higher binding energies than H2O for Zn species tends to adsorb to Zn (002) in a lying manner and participate in the solvation shell of Zn2+, thus avoiding Zn dendrites and side-reaction damage, especially at high current densities. The TC-endowed Zn anode's stability under such extreme conditions is verified in Zn-ion capacitors (i.e., > 94.6% capacity retention after 28 000 cycles), providing new insights into the development of high-power Zn-based energy storage devices.

Universal Strike-Plating Strategy to Suppress Hydrogen Evolution for Improving Zinc Metal Reversibility

The development of highly reversible zinc (Zn) metal anodes is pivotal for determining the feasibility of rechargeable aqueous Zn batteries. Our research quantitively evalulates how the hydrogen evolution reaction (HER) adversely affects Zn reversibility in batteries and emphasizes the importance of substrate design in modulating HER and its associated side reactions. When the cathodic reaction is dominated by HER, the Zn electrode exhibits low plating/stripping efficiency, characterized by extensive coverage of a passivation layer that encompasses the electrochemical inactive Zn. Therefore, we propose a strike-plating strategy that modifies the pristine substrate by initiating Zn plating at a high current density for a short time. This straightforward and effective approach has been proven to suppress hydrogen evolution and transform the electrodeposition mode into one dominated by Zn reduction. Notably, Zn metal exhibits exceptionally high average reversibility of 98.80% over 200 h on a stainless steel substrate, which was typically precluded in aqueous electrolytes because of their favorable HER capability. Additionally, our strike-plating strategy demonstrates an appliable pathway to achieve high Zn reversibility on Cu substrate, showing an average efficiency of 99.83% over 540 h at a high areal capacity of 10 mAh cm-2 and high-performance Zn full cells with low N/P ratios. This research provides a foundation for future investigations into the underlying mechanisms of HER and strategies to optimize Zn-based battery performance.

Stabilizing Zn/electrolyte Interphasial Chemistry by a Sustained-Release Drug Inspired Indium-Chelated Resin Protective Layer for High-Areal-Capacity Zn//V2O5 Batteries

For zinc-metal batteries, the instable chemistry at Zn/electrolyte interphasial region results in severe hydrogen evolution reaction (HER) and dendrite growth, significantly impairing Zn anode reversibility. Moreover, an often-overlooked aspect is this instability can be further exacerbated by the interaction with dissolved cathode species in full batteries. Here, inspired by sustained-release drug technology, an indium-chelated resin protective layer (Chelex-In), incorporating a sustained-release mechanism for indium, is developed on Zn surface, stabilizing the anode/electrolyte interphase to ensure reversible Zn plating/stripping performance throughout the entire lifespan of Zn//V2O5 batteries. The sustained-release indium onto Zn electrode promotes a persistent anticatalytic effect against HER and fosters uniform heterogeneous Zn nucleation. Meanwhile, on the electrolyte side, the residual resin matrix with immobilized iminodiacetates anions can also repel detrimental anions (SO4 2- and polyoxovanadate ions dissolved from V2O5 cathode) outside the electric double layer. This dual synergetic regulation on both electrode and electrolyte sides culminates a more stable interphasial environment, effectively enhancing Zn anode reversibility in practical high-areal-capacity full battery systems. Consequently, the bio-inspired Chelex-In protective layer enables an ultralong lifespan of Zn anode over 2800 h, which is also successfully demonstrated in ultrahigh areal capacity Zn//V2O5 full batteries (4.79 mAh cm-2).

Recent Functionalized Strategies of Metal-Organic Frameworks for Anode Protection of Aqueous Zinc-Ion Battery

The inherent benefits of aqueous Zn-ion batteries (ZIBs), such as environmental friendliness, affordability, and high theoretical capacity, render them promising candidates for energy storage systems. Nevertheless, the Zn anodes of ZIBs encounter severe challenges, including dendrite formation, hydrogen evolution reaction, corrosion, and surface passivation. These would result in the infeasibility of ZIBs in practical situations. To this end, artificial interfaces with functionalized materials are crafted to protect the Zn anode. They have the capability to modulate the zinc ion flux in proximity to the electrode surface and shield it from aqueous electrolytes by leveraging either size effects or charge effects. Considering metal-organic frameworks (MOFs) with tunable pore size, chemical composition, and stable framework structures, they have emerged as effective materials for building artificial interfaces, prolonging the lifespan, and improving the unitization of Zn anode. In this review, the contributions of MOFs for protecting Zn anode, which mainly involves facilitating homogeneous nucleation, manipulating selective deposition, regulating ion and charge flux, accelerating Zn desolvation, and shielding against free water and anions are comprehensively summarized. Importantly, the future research trajectories of MOFs for the protection of the Zn anode are underscored, which may propose new perspectives on the practical Zn anode and endow the MOFs with high-value applications.

An artificial aluminum-tin alloy layer on aluminum metal anodes for ultra-stable rechargeable aluminum-ion batteries

Rechargeable aluminum ion batteries (RAIBs) exhibit great potential for next-generation energy storage systems owing to the abundant resources, high theoretical volumetric capacity and light weight of the Al metal anode. However, the development of RAIBs based on Al metal anodes faces challenges such as dendrite formation, self-corrosion, and volume expansion at the anode/electrolyte interface, which needs the rational design of an aluminum anode for high-performance RAIBs. This work proposes a novel and low-cost strategy by utilizing an alloy electrodeposition method in a low-temperature molten salt system to fabricate an aluminum-tin (AlSn) alloy coating layer on copper foil as the anode for RAIBs, which successfully addresses the issues of dendrite formation and corrosion at the anode/electrolyte interface. The artificial AlSn alloy layer could enhance the active sites for metal Al homogeneous deposition and effectively retard the dendrite formation, which was verified by an in situ optical microscopy study. The symmetric AlSn@Cu cell demonstrates a low average overpotential of ∼38 mV at a current density of 0.5 mA cm-2 and a long-term lifespan of over 1100 h. Moreover, the AlSn@Cu//Mo6S8 full cells deliver a high capacity of 114.9 mA h g-1 at a current density of 100 mA g-1 and maintain ultra-stable cycling stability even over 1400 cycles with a ∼100% coulombic efficiency (CE) during the long-term charge/discharge processes. This facile alloy electrodeposition approach for designing high-performance Al-based anodes provides insights into the understanding of artificial interface chemistry on Al-based anodes and potentially accelerates the design of high-performance RAIBs.

Dual-Function Electrolyte Additive Design for Long Life Alkaline Zinc Flow Batteries

Alkaline zinc-based flow batteries (AZFBs) have emerged as a promising electrochemical energy storage technology owing to Zn abundance, high safety, and low cost. However, zinc dendrite growth and the formation of dead zinc greatly impede the development of AZFBs. Herein, a dual-function electrolyte additive strategy is proposed to regulate zinc nucleation and mitigate the hydroxide corrosion of zinc depositions for stable AZFBs. This strategy, as exemplified by urea, introduces an electrolyte additive to coordinate with Zn2+/Zn with proper strength, slowing zinc deposition kinetics to induce uniform nucleation and protecting the deposited zinc surface from attack by hydroxide ions through preferable adsorption. The zincate complexes with urea are identified to be Zn(OH)2(urea)(H2O)2 and Zn2(OH)4(H2O)4(urea), which exhibit slow zinc deposition kinetics, allowing instantaneous nucleation. Calculation results reveal an additional energy barrier of 1.29 eV for the subsequent adsorption of an OH- group when a urea molecule absorbs on the zinc cluster, significantly mitigating the formation of dead zinc. Consequently, prolonged cell cycling of the prototype alkaline zinc-iron flow battery demonstrates stable operation for over 130 h and an average coulombic efficiency of 98.5%. It is anticipated that this electrolyte additive strategy will pave the way for developing highly stable AZFBs.

Horizontally Arranged Zn Platelet Deposition Regulated by Bi2O3/Bi toward High-Rate and Dendrite-Free 3D Zn Composite Anode

Aqueous Zn-metal battery is considered as a promising energy-storage system. However, uncontrolled zinc dendrite growth is the main cause of short-circuit failure in aqueous Zn-based batteries. One of the most efficient and convenient strategies to alleviate this issue is to introduce appropriate zincophilic nucleation sites to guide zinc metal deposition and regulate crystal growth. Herein, this work proposes Bi2O3/Bi nanosheets anchored on the cell wall surface of the 3D porous conductive host as the Zn deposition sites to modulate Zn deposition behavior and hence inhibit the zinc dendrite growth. Density functional theory and experimental results demonstrate that Bi2O3 has a super zinc binding energy and strong adsorption energy with zinc (002) plane, as a super-zincophilic nucleation site, which results in the deposition of zinc preferentially along the horizontal direction of (002) crystal plane, fundamentally avoids the formation of Zn dendrites. Benefiting from the synergistic effect Bi2O3/Bi zincophilic sites and 3D porous structure in the B-BOGC host, the electrochemical performance of the constructed Zn-based battery is significantly improved. As a result, the Zn anode cycles for 1500 cycles at 50 mA cm-2 and 1.0 mAh cm-2. Meanwhile, the Zn@B-BOGC//MnO2 full cell can operate stably for 2000 cycles at 2.0 A g-1.

Zigzag Hopping Site Embedded Covalent Organic Frameworks Coating for Zn Anode

Precise design and tuning of Zn hopping/transfer sites with deeper understanding of the dendrite-formation mechanism is vital in artificial anode protective coating for aqueous Zn-ion batteries (AZIBs). Here, we probe into the role of anode-coating interfaces by designing a series of anhydride-based covalent organic frameworks (i.e., PI-DP-COF and PI-DT-COF) with specifically designed zigzag hopping sites and zincophilic anhydride groups that can serve as desired platforms to investigate the related Zn2+ hopping/transfer behaviours as well as the interfacial interaction. Combining theoretical calculations with experiments, the ABC stacking models of these COFs endow the structures with specific zigzag sites along the 1D channel that can accelerate Zn2+ transfer kinetics, lower surface-energy, homogenize ion-distribution or electric-filed. Attributed to these superiorities, thus-obtained optimal PI-DT-COF cells offer excellent cycling lifespan in both symmetric-cell (2000 cycles at 60 mA cm-2) and full-cell (1600 cycles at 2 A g-1), outperforming almost all the reported porous crystalline materials.

Understanding the Role of Zinc Hydroxide Sulfate and its Analogues in Mildly Acidic Aqueous Zinc Batteries: A Review

Mildly acidic aqueous zinc batteries (AZBs) have attracted tremendous attention for grid storage applications with the expectation to tackle the issues of Li-ion batteries on high cost and poor safety. However, the performance, particularly energy density and cycle stability of AZBs are still unsatisfactory when compared with LIBs. To help the development of AZBs, a lot of effort have been made to understand the battery reaction mechanisms and precedent microscopic and spectroscopic analyses have shown flake-like large particles of zinc hydroxide sulfate (ZHS) and its analogues formed on the surfaces of cathodes and anodes in sulfate and other electrolyte systems during cycling. However, because of the complexity of the thermodynamics and kinetics of aqueous reactions to understand different battery conditions, controversies still exist. This article will review the roles of ZHS discussed in recent representative references aiming to shine light on the fundamental mechanisms of AZBs and pave ways to further improve the battery performance.

Customization of Manganese Oxide Cathodes via Precise Electrochemical Lithium-Ion Intercalation for Diverse Zinc-Ion Batteries

Manganese oxide-based aqueous zinc-ion batteries (ZIBs) are attractive energy storage devices, owing to their good safety, low cost, and ecofriendly features. However, various critical issues, including poor conductivity, sluggish reaction kinetics, and unstable structure still restrict their further development. Oxygen defect engineering is an effective strategy to improve the electrochemical performance of manganese oxides, but challenging in the accurate regulation of oxygen defects. In this work, an effective and controllable defect engineering strategy-controllable electrochemical lithium-ion intercalation - is proposed to tackle this issue. The incorporation of lithium ions and oxygen defects can promote the conductivity, lattice spacing, and structural stability of Mn2O3 (MO), thus improving its capacity (232.7 mAh g-1), rate performance, and long-term cycling stability (99.0% capacity retention after 3000 cycles). Interestingly, the optimal ratio of intercalated lithium-ion varies at different temperature or mass-loading of MO, which provides the possibility to customize diverse ZIBs to meet different application conditions. In addition, the fabricated ZIBs present good flexibility, superior safety, and admirable adaptability under extreme temperatures (-20-100 °C). This work provides an inspiration on the structural customization of metal oxide nanomaterials for diverse ZIBs, and sheds light on the construction of future portable electronics.

Insights into the cycling stability of manganese-based zinc-ion batteries: from energy storage mechanisms to capacity fluctuation and optimization strategies

Manganese-based materials are considered as one of the most promising cathodes in zinc-ion batteries (ZIBs) for large-scale energy storage applications owing to their cost-effectiveness, natural availability, low toxicity, multivalent states, high operation voltage, and satisfactory capacity. However, their intricate energy storage mechanisms coupled with unsatisfactory cycling stability hinder their commercial applications. Previous reviews have primarily focused on optimization strategies for achieving high capacity and fast reaction kinetics, while overlooking capacity fluctuation and lacking a systematic discussion on strategies to enhance the cycling stability of these materials. Thus, in this review, the energy storage mechanisms of manganese-based ZIBs with different structures are systematically elucidated and summarized. Next, the capacity fluctuation in manganese-based ZIBs, including capacity activation, degradation, and dynamic evolution in the whole cycle calendar are comprehensively analyzed. Finally, the constructive optimization strategies based on the reaction chemistry of one-electron and two-electron transfers for achieving durable cycling performance in manganese-based ZIBs are proposed.

Rescuing zinc anode-electrolyte interface: mechanisms, theoretical simulations and in situ characterizations

The research interest in aqueous zinc-ion batteries (AZIBs) has been surging due to the advantages of safety, abundance, and high electrochemical performance. However, some technique issues, such as dendrites, hydrogen evolution reaction, and corrosion, severely prohibit the development of AZIBs in practical utilizations. The underlying mechanisms regarding electrochemical performance deterioration and structure degradation are too complex to understand, especially when it comes to zinc metal anode-electrolyte interface. Recently, theoretical simulations and in situ characterizations have played a crucial role in AZIBs and are exploited to guide the research on electrolyte engineering and solid electrolyte interphase. Herein, we present a comprehensive review of the current state of the fundamental mechanisms involved in the zinc plating/stripping process and underscore the importance of theoretical simulations and in situ characterizations in mechanism research. Finally, we summarize the challenges and opportunities for AZIBs in practical applications, especially as a stationary energy storage and conversion device in a smart grid.

Stable Zinc Electrode Reaction Enabled by Combined Cationic and Anionic Electrolyte Additives for Non-Flow Aqueous Zn─Br2 Batteries

Aqueous zinc-bromine batteries hold immense promise for large-scale energy storage systems due to their inherent safety and high energy density. However, achieving a reliable zinc metal electrode reaction is challenging because zinc metal in the aqueous electrolyte inevitably leads to dendrite growth and related side reactions, resulting in rapid capacity fading. Here, it is reported that combined cationic and anionic additives in the electrolytes using CeCl3 can simultaneously address the multiple chronic issues of the zinc metal electrode. Trivalent Ce3+ forms an electrostatic shielding layer to prevent Zn2+ from concentrating at zinc metal protrusions, while the high electron-donating nature of Cl- mitigates H2O decomposition on the zinc metal surface by reducing the interaction between Zn2+ and H2O. These combined cationic and anionic effects significantly enhance the reversibility of the zinc metal reaction, allowing the non-flow aqueous Zn─Br2 full-cell to reliably cycle with exceptionally high capacity (>400 mAh after 5000 cycles) even in a large-scale battery configuration of 15 × 15 cm2.

Inhibition of Vanadium Cathodes Dissolution in Aqueous Zn-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have experienced a rapid surge in popularity, as evident from the extensive research with over 30 000 articles published in the past 5 years. Previous studies on AZIBs have showcased impressive long-cycle stability at high current densities, achieving thousands or tens of thousands of cycles. However, the practical stability of AZIBs at low current densities (<1C) is restricted to merely 50-100 cycles due to intensified cathode dissolution. This genuine limitation poses a considerable challenge to their transition from the laboratory to the industry. In this study, leveraging density functional theory (DFT) calculations, an artificial interphase that achieves both hydrophobicity and restriction of the outward penetration of dissolved vanadium cations, thereby shifting the reaction equilibrium and suppressing the vanadium dissolution following Le Chatelier's principle, is described. The approach has resulted in one of the best cycling stabilities to date, with no noticeable capacity fading after more than 200 cycles (≈720 h) at 200 mA g-1 (0.47C). These findings represent a significant advance in the design of ultrastable cathodes for aqueous batteries and accelerate the industrialization of aqueous zinc-ion batteries.

Advancements in aqueous zinc-iodine batteries: a review

Aqueous zinc-iodine batteries stand out as highly promising energy storage systems owing to the abundance of resources and non-combustible nature of water coupled with their high theoretical capacity. Nevertheless, the development of aqueous zinc-iodine batteries has been impeded by persistent challenges associated with iodine cathodes and Zn anodes. Key obstacles include the shuttle effect of polyiodine and the sluggish kinetics of cathodes, dendrite formation, the hydrogen evolution reaction (HER), and the corrosion and passivation of anodes. Numerous strategies aimed at addressing these issues have been developed, including compositing with carbon materials, using additives, and surface modification. This review provides a recent update on various strategies and perspectives for the development of aqueous zinc-iodine batteries, with a particular emphasis on the regulation of I2 cathodes and Zn anodes, electrolyte formulation, and separator modification. Expanding upon current achievements, future initiatives for the development of aqueous zinc-iodine batteries are proposed, with the aim of advancing their commercial viability.

Synchronous Redox Reactions in Copper Oxalate Enable High-Capacity Anode for Proton Battery

Proton batteries are competitive due to their merits such as high safety, low cost, and fast kinetics. However, it is generally difficult for current studies of proton batteries to combine high capacity and high stability, while the research on proton storage mechanism and redox behavior is still in its infancy. Herein, the polyanionic layered copper oxalate is proposed as the anode for a high-capacity proton battery for the first time. The copper oxalate allows for reversible proton insertion/extraction through the layered space but also achieves high capacity through synchronous redox reactions of Cu2+ and C2O42-. During the discharge process, the bivalent Cu-ion is reduced, whereas the C═O of the oxalate group is partially converted to C-O. This synchronous behavior presents two units of charge transfer, enabling the embedding of two units of protons in the (110) crystal face. As a result, the copper oxalate anode demonstrates a high specific capacity of 226 mAh g-1 and maintains stable operation over 1000 cycles with a retention of 98%. This work offers new insights into the development of dual-redox electrode materials for high-capacity proton batteries.

Layered Topological Insulator MnBi2Te4 as a Cathode for a High Rate Performance Aqueous Zinc-Ion Battery

Recently, the topological insulator MnBi2Te4 has aroused great attention owing to its exotic quantum phenomena and intriguing device applications, but the superior performances of MnBi2Te4 have not been researched in the field of electrochemistry. By theoretical calculations, it is found that MnBi2Te4 exhibits excellent Zn2+ storage and transport properties. Therefore, it is speculated that MnBi2Te4 has excellent electrochemical performance in zinc-ion batteries (ZIBs). In this research, MnBi2Te4 as a pioneer has been explored in ZIBs, showing surprising electrochemical properties. The MnBi2Te4 electrode displays a high average discharge specific capacity (264.8 mA h g-1 at 0.40 A g-1), a competitive cycle life (88.6% of initial capacity after 400 cycles at 4.00 A g-1), and an excellent rate performance (average capacity retention rate of 95.1% from 0.40 to 8.00 A g-1) owing to the fast ion transport of the conductive topological surface state and dissipationless channel of the edge state. Surprisingly, the quasi-solid-state (QSS) MnBi2Te4/Zn battery delivers excellent Zn2+ storage capability and possesses a capacity retention of 79.9% after 1000 cycles at 4.00 A g-1. In addition, the QSS MnBi2Te4/Zn battery can exhibit excellent performance and the GCD curves maintain stability without distortion deformation even at temperatures of 0 and 75 °C.

Ion Sieve Interface Assisted Zinc Anode with High Zinc Utilization and Ultralong Cycle Life for 61 Wh/kg Mild Aqueous Pouch Battery

The cycling stability of a thin zinc anode under high zinc utilization has a critical impact on the overall energy density and practical lifetime of zinc ion batteries. In this study, an ion sieve protection layer (ZnSnF@Zn) was constructed in situ on the surface of a zinc anode by chemical replacement. The ion sieve facilitated the transport and desolvation of zinc ions at the anode/electrolyte interface, reduced the zinc deposition overpotential, and inhibited side reactions. Under a 50% zinc utilization, the symmetrical battery with this protection layer maintained stable cycling for 250 h at 30 mA cm-2. Matched with high-load self-supported vanadium-based cathodes (18-20 mg cm-2), the coin battery with 50% zinc utilization possessed an energy density retention of 94.3% after 1000 cycles at 20 mA cm-2. Furthermore, the assembled pouch battery delivered a whole energy density of 61.3 Wh kg-1, surpassing the highest mass energy density among reported mild zinc batteries, and retained 76.7% of the energy density and 85.3% (0.53 Ah) of the capacity after 300 cycles.

Molecularly modulating solvation structure and electrode interface enables dendrite-free zinc-ion batteries

The performance of aqueous Zn ion batteries (AZIBs) is hindered by the uncontrollable growth of Zn dendrites and side reactions at the Zn anode/electrolyte interface. Here, we introduce low-cost glucosamine hydrochloride (GLA) into the ZnSO4 electrolyte system to modulate the Zn anode/electrolyte interface and the solvation structure of Zn2+, which leads to improved reversibility of Zn plating/striping. Through experimental and theoretical analyses, we demonstrate that GLA molecules could adsorp on the Zn metal surface to form a new interface with reduced active water, effectively suppressing water-induced side reactions. Moreover, after adding GLA, the flux of Zn2+ ions is regulated, the desolvation of the primary [Zn(H2O)6]2+ ions is promoted, and the Zn dendrite growth is significantly inhibited. Consequently, superior cyclic stability with a lower voltage hysteresis is simultaneously achieved in a Zn//Zn symmetric cell. When coupled with the Mn3O4 cathode, the fabricated Zn-Mn batteries with the modified ZnSO4 + GLA electrolyte system deliver boosted capacity, improved long-term cycling stability, and better self-discharge performance. This work provides insight into the development of high-efficient and low-cost electrolytes for high-performance Zn-based energy storage devices.

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.

Anchoring Polar Organic Molecules in Defective Ammonium Vanadate for High-Performance Flexible Aqueous Zinc-Ion Battery

Ammonium vanadate (NVO) often has unsatisfactory electrochemical performance due to the irreversible removal of NH4 + during the reaction. Herein, layered DMF-NVO nanoflake arrays (NFAs) grown on highly conductive carbon cloth (CC) are employed as the binder-free cathode (DMF-NVO NFAs/CC), which produces an enlarged interlayer spacing of 12.6 Å (against 9.5 Å for NH4 V4 O10 ) by effective N, N-dimethylformamide (DMF) intercalation. Furthermore, the strong attraction of highly polar carbonyl and ammonium ions in DMF can stabilize the lattice structure, and low-polar alkyl groups can interact with the weak electrostatic generated by Zn2+ , which allows Zn2+ to be freely intercalated. The DMF-NVO NFAs/CC//Zn battery exhibits an impressive high capacity of 536 mAh g-1 at 0.5 A g-1 , excellent rate capability, and cycling performance. The results of density functional theory simulation demonstrate that the intercalation of DMF can significantly reduce the band gap and the diffusion barrier of Zn2+ , and can also accommodate more Zn2+ . The assembled flexible aqueous rechargeable zinc ion batteries (FARZIBs) exhibit outstanding energy density and power density, up to 436 Wh kg-1 at 400 W kg-1 , and still remains 180 Wh kg-1 at 4000 W kg-1 . This work can provide a reference for the design of cathode materials for high-performance FARZIBs.

Atomic Pinning of Trace Additives Induces Interfacial Solvation for Highly Reversible Zn Metal Anodes

Aqueous Zn metal batteries are considered promising energy storage devices due to their high energy density and low cost. Unfortunately, such great potential is at present obscured by two clouds called dendrite growth and parasitic reactions. Herein, trace amounts of sodium cyclamate (CYC-Na) are introduced as an electrolyte additive, and accordingly, an atomic-pinning-induced interfacial solvation mechanism is proposed to summarize the effect of trace addition. Specifically, coadsorption of -NH- and -SO3 groups overcomes the ring-flipping effect and pins the CYC anion near the Zn anode surface in parallel, which significantly modifies the Zn2+ solvation sheath at the interface. This process homogenizes the surface Zn2+ flux and reduces the H2O and SO42- content on the surface, thus eliminating byproducts and leveling Zn deposition. Cells with trace CYC-Na cycle stably for 3650 h and still cycle for 330 h at high depths of discharge of 56.9%. This work dispels the clouds for efficient trace additives for AZMBs.

Ammonium fluoride additive-modified interphase chemistry stabilizes zinc anodes in aqueous electrolytes

Herein, ammonium fluoride is reported as an additive within 1 M ZnSO4 aqueous electrolyte to improve zinc anodes. The as-formed electrostatic shielding layer and ZnF2-rich solid-state interphase layer can jointly inhibit side reactions and dendrite growth. Consequently, symmetric Zn‖Zn cells, asymmetric Zn‖Cu cells and Zn‖MnO2 cells with the additives present dramatically enhanced performance in comparison to the ones with pure ZnSO4 electrolyte counterparts. This work proposes a facile but effective method to achieve highly reversible zinc anodes.

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.

Amino-Functionalized Interfacial Layer Enables an Ultra-Uniform Amorphous Solid Electrolyte Interphase for High-Performance Aqueous Zinc-Based Batteries

Aqueous rechargeable zinc-based batteries (ZBBs) are emerging as desirable energy storage systems because of their high capacity, low cost, and inherent safety. However, the further application of ZBBs still faces many challenges, such as the issues of uncontrolled dendrite growth and severe parasitic reactions occurring at the Zn anode. Herein, an amino-grafted bacterial cellulose (NBC) film is prepared as artificial solid electrolyte interphase (SEI) for the Zn metal anodes, which can significantly reduce zinc nucleation overpotential and lead to the dendrite-free deposition of Zn metal along the (002) crystal plane more easily without any external stimulus. More importantly, the chelation between the modified amino groups and zinc ions can promote the formation of an ultra-even amorphous SEI upon cycling, reducing the activity of hydrate ions, and inhibiting the water-induced side reactions. As a result, the Zn||Zn symmetric cell with NBC film exhibits lower overpotential and higher cyclic stability. When coupled with the V2 O5 cathode, the practical pouch cell achieves superior electrochemical performance over 1000 cycles.

Fine-Tuning Electrolyte Concentration and Metal-Organic Framework Surface toward Actuating Fast Zn2+ Dehydration for Aqueous Zn-Ion Batteries

Functional porous coating on zinc electrode is emerging as a powerful ionic sieve to suppress dendrite growth and side reactions, thereby improving highly reversible aqueous zinc ion batteries. However, the ultrafast charge rate is limited by the substantial cation transmission strongly associated with dehydration efficiency. Here, we unveil the entire dynamic process of solvated Zn2+ ions' continuous dehydration from electrolyte across the MOF-electrolyte interface into channels with the aid of molecular simulations, taking zeolitic imidazolate framework ZIF-7 as proof-of-concept. The moderate concentration of 2 M ZnSO4 electrolyte being advantageous over other concentrations possesses the homogeneous water-mediated ion pairing distribution, resulting in the lowest dehydration energy, which elucidates the molecular mechanism underlying such concentration adopted by numerous experimental studies. Furthermore, we show that modifying linkers on the ZIF-7 surface with hydrophilic groups such as -OH or -NH2 can weaken the solvation shell of Zn2+ ions to lower the dehydration free energy by approximately 1 eV, and may improve the electrical conductivity of MOF. These results shed light on the ions delivery mechanism and pave way to achieve long-term stable zinc anodes at high capacities through atomic-scale modification of functional porous materials.

"Mn-locking" effect by anionic coordination manipulation stabilizing Mn-rich phosphate cathodes

High-voltage cathodes with high power and stable cyclability are needed for high-performance sodium-ion batteries. However, the low kinetics and inferior capacity retention from structural instability impede the development of Mn-rich phosphate cathodes. Here, we propose light-weight fluorine (F) doping strategy to decrease the energy gap to 0.22 eV from 1.52 eV and trigger a "Mn-locking" effect-to strengthen the adjacent chemical bonding around Mn as confirmed by density functional theory calculations, which ensure the optimized Mn ligand framework, suppressed Mn dissolution, improved structural stability and enhanced electronic conductivity. The combination of in situ and ex situ techniques determine that the F dopant has no influence on the Na+ storage mechanisms. As a result, an outstanding rate performance up to 40C and an improved cycling stability (1000 cycles at 20C) are achieved. This work presents an effective and widely available light-weight anion doping strategy for high-performance polyanionic cathodes.

Separator-free Zn-ion Battery with Mn:V3O7·H2O Nanobelts and a Zn2+-Polyacrylamide Semisolid Electrolyte with Ultralong Cycle Life

Vanadium based oxides are immensely suitable for zinc-ion-batteries (ZIBs) due to their layered and stable crystal structures. In this study, Mn doped V₃O₇·H₂O nanobelts were synthesized and used as cathodes in ZIBs for the very first time and the doped oxide exhibited an enhanced capacity of 258 mAh g^-1 compared to its undoped counterpart (208 mAh g^-1) at the same current density of 40 mA g^-1. Mn:V₃O₇·H₂O outperforms the V₃O₇·H₂O due to the superior bulk electrical conductivity as well as higher nanoscale current carrying capability imparted by a high proportion of mixed valent states of Mn³⁺, Mn²⁺, V⁵⁺, and V⁴⁺ and the smaller crystallite size that affords short diffusion lengths for Zn²⁺ ions. The Mn:V₃O₇·H₂O cathode is coupled with a Zn²⁺ ion conducting polyacrylamide gel electrolyte and a Zn flakes/activated carbon (Zn Fs/C) composite anode to yield a unique separator free Mn:V₃O₇·H₂O/Zn²⁺-PAM gel/Zn-Fs/C battery. The cell exhibits a capacity of ∼205 mAh g^-1 (at 40 mA g^-1) and retains 99% of its original capacity after 3500 cycles. The Zn²⁺-PAM gel shows a high ionic conductivity in the range of 5.9 to 28.2 S cm^-1, over a wide temperature span of 0 to 70 °C, and a wide electrochemical potential stability window of -0.5 to +2.3 V, thus rendering it suitable for low temperature applications as well. The gel also inhibits dendritic growth of Zn over the Zn-Fs/C anode through regulated flow of Zn²⁺ ions during charging, prevents cathode dissolution, and improves cycle life via preservation of structural integrity of the Mn:V₃O₇·H₂O cathode after 200 charge-discharge cycles. This is a highly scalable cell configuration and opens up opportunities to produce long lasting batteries completely free of costly separators with a semisolid free-standing electrolyte and a robust doped oxide.

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.

Improving the Cycling Stability of Aqueous Zinc-Ion Batteries by Preintercalation of Polyaniline in Hydrated Vanadium Oxide

This paper reports the synthesis and characterization of hydrated vanadium oxide (VOH) and chemically preintercalated polyanilines in VOH, labeled as PAVO-H as the cathode material for aqueous zinc-ion batteries. Synthesized PAVO-H has a high surface area and rod-shaped morphology. PAVO-H has an increased interlayer distance of 13.36 Å. PAVO-H offers high specific capacities of 330 and 225 mAh g^-1 at 50 mA g^-1 and 4 A g^-1 of current densities, respectively, with a 92% capacity retention rate of over 3000 cycles. The preintercalation of polyaniline is likely to catalyze the redox reaction and facilitate and simplify transport kinetics. It is also possible that the preintercalation of polyaniline permits the insertion of large hydrated Zn ions and reduces the formation of zinc basic salts.

Reversible Zn Metal Anodes Enabled by Trace Amounts of Underpotential Deposition Initiators

Routine electrolyte additives are not effective enough for uniform zinc (Zn) deposition, because they are hard to proactively guide atomic-level Zn deposition. Here, based on underpotential deposition (UPD), we propose an "escort effect" of electrolyte additives for uniform Zn deposition at the atomic level. With nickel ion (Ni2+ ) additives, we found that metallic Ni deposits preferentially and triggers the UPD of Zn on Ni. This facilitates firm nucleation and uniform growth of Zn while suppressing side reactions. Besides, Ni dissolves back into the electrolyte after Zn stripping with no influence on interfacial charge transfer resistance. Consequently, the optimized cell operates for over 900 h at 1 mA cm-2 (more than 4 times longer than the blank one). Moreover, the universality of "escort effect" is identified by using Cr3+ and Co2+ additives. This work would inspire a wide range of atomic-level principles by controlling interfacial electrochemistry for various metal batteries.