Reconstructing interfacial manganese deposition for durable aqueous zinc-manganese batteries

A Deep Eutectic Solvent Electrolyte Enables Planar Cu Deposition and High-Temperature Cu-MnO2 Battery

Cu anodes exhibit a higher theoretical specific capacity (843 mAh g-1 or 7558 mAh cm-3) than Zn anodes (820 mAh g-1 or 5855 mAh cm-3), and have garnered widespread attention. However, aqueous Cu-ion batteries suffer from severe Cu dendrite growth, limited cycle life, and poor high-temperature performance. To the best of our knowledge, this is the first time that a deep eutectic solvent (DES) electrolyte is proposed to address these issues. Fourier transform infrared spectroscopy and molecular dynamics simulations confirm that the DES electrolyte coordinates with Cu2+, thereby modulating the Cu deposition behavior. Consequently, planar deposition and extended cycle life (6000 h versus 730 h) are achieved. Furthermore, the DES electrolyte exhibits the promising application potential under harsh conditions. A high-temperature Cu─MnO2 full cell retains a capacity of 174.8 mAh g-1 after 300 cycles at 2 A g-1 under 50 °C.

Electrochemical engineering in aqueous metal-ion batteries

Aqueous metal ion batteries (AMIBs), with merits of safety, ambient assembly, and eco-friendliness, demonstrate great potential in various energy storage scenarios. Despite the laboratory-scale progress in battery components and mechanisms featured by large specific capacities and long lifespans, AMIBs' practical use meets challenges with electrodes and electrolytes. It is crucial to prepare a review discussing the problems and solutions for the battery performance degradation during the electrode/battery scaleup from the perspectives of ion mass transfer and electrode reaction, which is proposed as the electrochemical engineering in AMIBs. We first introduce the anodic reactions and their effective reinforcement by molecule chemistry and electrodeposition. Then, we discuss the ion diffusion in electrolytes by learning from the Nernst-Planck theory, followed by the interphase ion diffusion at the electrolyte-cathode interface. After that, we highlight the lattice-void and particle-gap ion diffusion in cathodes and the cathodic reactions reinforced by catalysis and micro-reactor construction. Finally, we present the challenge and perspective of this blooming field toward the lab-to-market transition of AMIBs.

Electrolyte Regulation toward Cathodes with Enhanced-Performance in Aqueous Zinc Ion Batteries

Enhancing cathodic performance is crucial for aqueous zinc-ion batteries, with the primary focus of research efforts being the regulation of the intrinsic material structure. Electrolyte regulation is also widely used to improve full-cell performance, whose main optimization mechanisms have been extensively discussed only in regard to the metallic anode. Considering that ionic transport begins in the electrolyte, the modulation of the electrolyte must influence the cathodic performance or even the reaction mechanism. Despite its importance, the discussion of the optimization effects of electrolyte regulation on the cathode has not garnered the attention it deserves. To fill this gap and raise awareness of the importance of electrolyte regulation on cathodic reaction mechanisms, this review comprehensively combs the underlying mechanisms of the electrolyte regulation strategies and classifies the regulation mechanisms into three main categories according to their commonalities for the first time, which are ion effect, solvating effect, and interfacial modulation effect, revealing the missing puzzle piece of the mechanisms of electrolyte regulation in optimizing the cathode.

A Comprehensive Strategy Enables High-Loading BiOBr@BiOIO3 Cathodes for Quasi Ah-Level Aqueous Zn-Ion Batteries

Aqueous Zn-ion batteries (AZIBs) recently have attracted broad attention. To achieve high energy density of AZIBs, constructing high-loading cathodes is the prerequisite. However, the cycling stability of high-loading cathodes still faces great challenges. Herein, a comprehensive strategy is proposed to improve the structural stability of the cathode material and mechanical stability of the high-loading cathode. The BiOBr@BiOIO3 heterostructure are successfully constructed via sharing the interfacial oxygen atoms, in which the interfacial effect can effectively enhance the reaction dynamics and structural stability. Meanwhile, a biomimetic binder is skillfully designed via in situ dual cross-linking between guar gum and cation ions to achieve the application of water-based and sustainable polymer binder in AZIBs. Density functional theory calculations demonstrate the guar gum possesses strong affinity toward BiOBr@BiOIO3 to firmly adhere the active materials. Quantitative nanomechanic technology visually demonstrates the robust mechanical properties of the as-obtained BiOBr@BiOIO3 cathode. As a result, when the active material loading increases to as high as 100.71 mg cm-2, an ultrahigh areal capacity of 20.02 mAh cm-2 can be achieved. Specially, a quasi-Ah-level (0.244 Ah) pouch-type cell with a loading of 1.17 g can be constructed, showing the practical application potential.

Carboxyl-CNTs Act as "Defensive Shield" to Boost Proton Insertion for Stable and Fast-Charging Aqueous Zn-Mn Batteries

Proton insertion mechanism with fast reaction kinetics is attracting more and more attention for high-rate and durable aqueous Zn─MnO2 batteries. However, hydrated Zn2+ insertion reaction accompanied with Jahn-Teller effect and Mn3+ disproportionation generally leads to sluggish rate capability and irreversible structure transformation. Here, carboxyl-carbon nanotubes supported α-MnO2 nanoarrays (C─MnO2) cathode is successfully fabricated by a convent grinding process for high-performance Zn batteries. Specifically, the carboxyl-carbon nanotubes (CNTs) skeleton endows α-MnO2 with a shorter ion diffusion route and more active sites for proton adsorption, benefiting to the fast electron transport and reversible structure evolution of MnO2. More importantly, electronegative carboxyl groups and Mn─O─C interfacial bonds can effectively restrain Mn2+ dissolution and shuttle for improved structural integrity and redox reactivity. Consequently, the C─MnO2 cathode exhibits high capacity, superior rate capability, and outstanding cycling stability over 10 000 cycles. Even at ultra-high mass loading (20 mg cm-2), the Zn//C─MnO2 punch cell displays excellent capacity (202 mAh) and 94.5% capacity retention after 114 cycles, providing new insights for the practical application of advanced Zn-Mn batteries.

Fundamentals, Advances and Perspectives in Designing Eutectic Electrolytes for Zinc-Ion Secondary Batteries

Zinc-ion secondary batteries have been competitive candidates since the "post-lithium-ion" era for grid-scale energy storage, owing to their plausible security, high theoretical capacity, plentiful resources, and environment friendliness. However, many encumbrances like notorious parasitic reactions and Zn dendrite growth hinder the development of zinc-ion secondary batteries remarkably. Faced with these challenges, eutectic electrolytes have aroused notable attention by virtue of feasible synthesis and high tunability. This review discusses the definition and advanced functionalities of eutectic electrolytes in detail and divides them into nonaqueous, aqueous, and solid-state eutectic electrolytes with regard to the state and component of electrolytes. In particular, the corresponding chemistry concerning solvation structure regulation, electric double layer (EDL) structure, solid-electrolyte interface (SEI) and charge/ion transport mechanism is systematically elucidated for a deeper understanding of eutectic electrolytes. Moreover, the remaining limitations and further development of eutectic electrolytes are discussed for advanced electrolyte design and extended applications.

Electrolyte Decoupling Strategy for Metal Oxide-Based Zinc-Ion Batteries Free of Crosstalk Effect

The crosstalk of transition metal ions between the metal oxide cathode and Zn anode restricts the practical applications of aqueous zinc-ion batteries (ZIBs). Herein, we propose a decoupled electrolyte (DCE) consisting of a nonaqueous-phase (N-phase) anolyte and an aqueous-phase (A-phase) catholyte to prevent the crosstalk of Mn2+, thus extending the lifespan of MnO2-based ZIBs. Experimental measurements and theoretical modelling verify that trimethyl phosphate (TMP) not only synergistically works with NH4Cl in the N-phase anolyte to enable fast Zn2+ conduction while blocking Mn2+ diffusion toward anode, but also modifies the Zn2+ solvation structure to suppress the dendrite formation and corrosion on Zn anode. Meanwhile, the A-phase catholyte effectively accelerates the cathode reaction kinetics. The as-developed Zn|DCE|MnO2 cell delivers 80.13 % capacity retention after 900 cycles at 0.5 A g-1. This approach is applicable for other metal oxide cathode-based ZIBs, thereby opening a new avenue for developing ultrastable ZIBs.

In situ synthetic C encapsulated δ-MnO2 with O vacancies: a versatile programming in bio-engineering

In this study, we successfully synthesized a δ-MnO2 cathode with O vacancies, encapsulated by C derived from pyromellitic acid, using a facile hydrothermal method followed by annealing in an Ar atmosphere. The cathode's structural stability and charge transfer kinetics are enhanced by inhibiting the formation of the by-product Zn4SO4(OH)6·4H2O, regulating the Mn valence state, and suppressing the Jahn-Teller effect through the synergy of C encapsulation and O vacancies. This results in remarkable electrochemical performance, including a large capacity of 421.2 mAh g-1 at 0.1 A g-1, a high specific energy density of 595.53 Wh kg-1, and exceptional long-cycle life stability with 90.88% over 4000 cycles at 10 A g-1, together with superior coulombic efficiency (∼100%) in pure ZnSO4 electrolyte. Moreover, the cathode materials demonstrate specific antitumor efficacy. In brief, this work introduces an in situ synthetic C encapsulated δ-MnO2 with O vacancies expected to be applied in both large-scale energy storage and biomedicine.

Effective Proton Conduction in Quasi-Solid Zinc-Manganese Batteries via Constructing Highly Connected Transfer Pathways

Elusive ion behaviors in aqueous electrolyte remain a challenge to break through the practicality of aqueous zinc-manganese batteries (AZMBs), a promising candidate for safe grid-scale energy storage systems. The proposed electrolyte strategies for this issue most ignore the prominent role of proton conduction, which greatly affects the operation stability of AZMBs. Here we report a water-poor quasi-solid electrolyte with efficient proton transfer pathways based on the large-space interlayer of montmorillonite and strong-hydration Pr3+ additive in AZMBs. Proton conduction is deeply understood in this quasi-solid electrolyte. Pr3+ additive not only dominates the proton conduction kinetics, but also regulates the reversible manganese interfacial deposition. As a result, the Cu@Zn||α-MnO2 cell could achieve a high specific capacity of 433 mAh g-1 at 0.4 mA cm-2 and an excellent stability up to 800 cycles with a capacity retention of 92.2 % at 0.8 mA cm-2 in such water-poor quasi-solid electrolyte for the first time. Ah-scale pouch cell with mass loading of 15.19 mg cm-2 sustains 100 cycles after initial activation, which is much better than its counterparts. Our work provides a new path for the development of zinc metal batteries with good sustainability and practicality.

Electrochemically and chemically in-situ interfacial protection layers towards stable and reversible Zn anodes

Aqueous zinc metal batteries (AZMBs) have received widespread attention for large-scale sustainable energy storage due to their low toxicity, safety, cost-effectiveness. However, the technology and industrialization of AZMBs are greatly plagued by issues of Zn anode such as persistent dendrites and parasitic side reactions, resulting in rapid capacity degradation or battery failure. Electrochemically or chemically in-situ interfacial protection layers have very good self-adaption features for stability and reversibility of Zn anodes, which can also be well matched to current battery manufacturing. However, the in-situ interfacial strategies are far from the practical design for effective Zn anodes. Therefore, a targeted academic discussion that serves the development of this field is very urgent. Herein, the comprehensive insights on electrochemically and chemically in-situ interfacial protection layers for Zn anode were proposed in this review. It showcased a systematic summary of research advances, followed by detailed discussions on electrochemically and chemically in-situ interfacial protection strategies. More importantly, several crucial issues facing in-situ interfacial protection strategies have been further put forward. The final section particularly highlighted a systematic and rigorous scheme for precise designing highly stable and reversible in-situ interface for practical zinc anodes.

Nano-Metal-Organic Frameworks and Nano-Covalent-Organic Frameworks: Controllable Synthesis and Applications

Nanoscale framework materials have attracted extensive attention due to their diverse morphology and good properties, and synthesis methods of different size structures have been reported. Therefore, the relationship between different sizes and performance has become a research hotspot. This paper reviews the controllable synthesis strategies of nano-metal-organic frameworks (nano-MOFs) and nano-covalent-organic frameworks (nano-COFs). Firstly, the synthetic evolution of nano-frame materials is summarized. Due to their special surface area, regular pores and adjustable structural functions, nano-frame materials have attracted much attention. Then the preparation methods of nanostructures with different dimensions are introduced. These synthetic strategies provide the basis for the design of novel energy storage and catalytic materials. In addition, the latest advances in the field of energy storage and catalysis are reviewed, with emphasis on the application of nano-MOFs/COFs in zinc-, lithium-, and sodium-based batteries, as well as supercapacitors.

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

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

Organic-Inorganic Coupling Strategy: Clamp Effect to Capture Mg2+ for Aqueous Magnesium Ion Capacitor

The rapid transport kinetics of divalent magnesium ions are crucial for achieving distinguished performance in aqueous magnesium-ion battery-based energy storage capacitors. However, the strong electrostatic interaction between Mg2+ with double charges and the host material significantly restricts Mg2+ diffusivity. In this study, a new composite material, EDA-Mn2O3, with double-energy storage mechanisms comprising an organic phase (ethylenediamine, EDA) and an inorganic phase (manganese sesquioxide) was successfully synthesized via an organic-inorganic coupling strategy. Inorganic-phase Mn2O3 serves as a scaffold structure, enabling the stable and reversible intercalation/deintercalation of magnesium ions. The organic phase EDA adsorbed onto the surface of Mn2O3 as an elastic matrix, works synergistically with Mn2O3, and utilizes bidentate chelating ligands to capture Mg2+. The robust coordination effect of terminal biprotonic amine in EDA enhances the structural diversity and specific capacity characteristics of the composite material, as further corroborated by density functional theory (DFT) calculations, ex situ XRD, XPS, and Raman spectroscopy. As expected, the EDA-Mn2O3 composite achieved an outstanding specific discharge capacity of 188.97 mAh/g at 0.1 A/g. Additionally, an aqueous magnesium ion capacitor with EDA-Mn2O3 serving as the cathode can reach 110.17 Wh/kg, which stands out among the aqueous magnesium ion capacitors that have been reported thus far. The abundant reversible redox sites are ensured by the strategic design concept based on the synergistic structure and composition advantages of organic and inorganic phases. This study aimed to explore the practical application value of organic-inorganic composite electrodes with double-energy storage mechanisms.

Two-Dimensional (2D) Conductive Metal-Organic Framework Thin Films: The Preparation and Applications in Electrochemistry

Two-dimensional conductive MOF thin films have attracted attention due to their rich pore structure and unique electrical properties, and their applications in many fields, including batteries, sensing, supercapacitors, electrocatalysis, etc. This paper discusses several preparation methods for 2D conductive MOF thin films. And the applications of 2D conductive MOF thin films are summarized. In addition, the current challenges in the preparation of 2D conductive MOF thin films and the great potential in practical applications are discussed.

The zinc ion concentration dynamically regulated by an ionophore in the outer Helmholtz layer for stable Zn anode

The Zn dendrite limits the practical application of aqueous zinc-ion batteries in the large-scale energy storage systems. To suppress the growth of Zn dendrites, a zinc ionophore of hydroxychloroquine (defined as HCQ) applied in vivo treatment is investigated as the electrolyte additive. HCQ dynamically regulates zinc ion concentration in the outer Helmholtz layer, promoting even Zn plating at the anode/electrolyte interface. This is evidenced by the scanning electron microscopy, which delivers planar Zn plating after cycling. It is further supported by the X-ray diffraction spectroscopy, which reveals the growth of Zn (002) plane. Additionally, the reduced production of H2 during Zn plating/stripping is detected by the in-situ differential electrochemical mass spectrometry (DEMS), which shows the resistance of Zn (002) to hydrogen evolution reaction. The mechanism of dynamic regulation for zinc ion concentration is demonstrated by the in-situ optical microscopy. The hydrated zinc ion can be further plated more rapidly to the uneven location than the case in other regions, which is resulted from the dynamic regulation for zinc ion concentration. Therefore, the uniform Zn plating is formed. A cycling life of 1100 h is exhibited in the Zn||Zn symmetric cell at 1.6 mA cm-2 with the capacity of 1.6 mAh cm-2. The Zn||Cu battery exhibits a cycling life of 200 cycles at 4 mA cm-2 with a capacity of 4 mAh cm-2 and the average Coulombic efficiency is larger than 99 %. The Zn||VO2 battery with HCQ modified electrolyte can operate for 1500 cycles at 4 A g-1 with a capacity retention of 90 %. This strategy in the present work is wished to advance the development of zinc-ion batteries for practical application.

Transforming Zinc-Ion Batteries with DTPA-Na: A Synergistic SEI and CEI Engineering Approach for Exceptional Cycling Stability and Self-Discharge Inhibition

Aqueous zinc-ion batteries (ZIBs) hold immense potential for large-scale energy storage, but their practical implementation faces significant challenges related to the zinc anode, including dendrite formation, corrosion, and hydrogen evolution. This study addresses these challenges by introducing diethylenetriamine pentaacetate sodium salt (DTPA-Na) as a novel electrolyte additive. DTPA-Na exhibits a unique dual functionality, enabling the formation of a robust, multi-layered solid electrolyte interphase (SEI) on the zinc anode and a stable cathode electrolyte interphase (CEI) on the MnOOH cathode. The engineered SEI effectively suppresses interfacial side reactions, facilitates uniform zinc deposition, and mitigates dendrite growth, while the CEI inhibits MnOOH dissolution and detrimental cathode side reactions. This synergistic SEI/CEI engineering approach significantly enhances ZIB performance, achieving remarkable cycling stability and self-discharge inhibition, as evidenced by the extended lifespan of Zn||Zn symmetrical cells (4400 hours at 0.5 mA/cm2) and the exceptional capacity retention of Zn||MnOOH full cells after prolonged rest (98.61 % after 720 hours).

Unraveling the Anionic Redox Chemistry in Aqueous Zinc-MnO2 Batteries

Activating anionic redox reaction (ARR) has attracted a great interest in Li/Na-ion batteries owing to the fascinating extra-capacity at high operating voltages. However, ARR has rarely been reported in aqueous zinc-ion batteries (AZIBs) and its possibility in the popular MnO2-based cathodes has not been explored. Herein, the novel manganese deficient MnO2 micro-nano spheres with interlayer "Ca2+-pillars" (CaMnO-140) are prepared via a low-temperature (140 °C) hydrothermal method, where the Mn vacancies can trigger ARR by creating non-bonding O 2p states, the pre-intercalated Ca2+ can reinforce the layered structure and suppress the lattice oxygen release by forming Ca-O configurations. The tailored CaMnO-140 cathode demonstrates an unprecedentedly high rate capability (485.4 mAh g-1 at 0.1 A g-1 with 154.5 mAh g-1 at 10 A g-1) and a marvelous long-term cycling durability (90.6 % capacity retention over 5000 cycles) in AZIBs. The reversible oxygen redox chemistry accompanied by CF3SO3 - (from the electrolyte) uptake/release, and the manganese redox accompanied by H+/Zn2+ co-insertion/extraction, are elucidated by advanced synchrotron characterizations and theoretical computations. Finally, pouch-type CaMnO-140//Zn batteries manifest bright application prospects with high energy, long life, wide-temperature adaptability, and high operating safety. This study provides new perspectives for developing high-energy cathodes for AZIBs by initiating anionic redox chemistry.

Regulation of Zn2+ Solvation Configuration in Aqueous Batteries via Selenium-Substituted Crown Ether Engineering

The efficient utilization of the metallic Zn in rechargeable aqueous Zn-ion batteries (RAZBs) struggle to suffer from parasitic Zn dendrite formation, hydrogen evolution reactions as well as severe interfacial degradation at high areal capacity loadings. This study thus proposes to employ the modified crown ether as an aqueous electrolyte additive to regulate the Zn2+ desolvation kinetic and facilitates the horizontally oriented (002) deposition of Zn, extending the lifespan of both the symmetric cell and full cell models. Specifically, zincophilic cyano and hydrophobic selenium atoms are incorporated into the crown ether supramolecule to enhance Zn2+ coordination and desolvation capability. The addition of 4-cyanobenzo-21-crown-7-selenium at a low concentration of 0.5 wt.% effectively mitigates hydrogen evolution and Zn corrosion caused by water, promoting the oriented deposition of Zn2+. The Zn||V2O5 full cell prototype, assembled with the areal capacity loadings of 2 mAh cm-2 and N/P ratio of 2.95, exhibits negligible capacity fading at 2.0A g-1 for 300 cycles, highlighting the commercial feasibility of supramolecular macrocycles additive for practical RAZBs applications.

Inorganic Electrolyte Additive Promoting the Interfacial Stability for Durable Zn-Ion Batteries

The development of Zn-ion batteries (ZIBs) is always hindered by the ruleless interface reactions between the solid electrode and liquid electrolyte, and seeking appropriate electrolyte additives is considered as a valid approach to stabilize the electrode/electrolyte interphases for high-performance ZIBs. Benefiting from the unique solubility of TiOSO4 in acidic solution, the composite electrolyte of 2 m ZnSO4+30 mm TiOSO4 (ZSO/TSO) is configured and its positive contribution to Zn//Zn cells, Zn//Cu cells, and Zn//NH4V4O10 batteries are comprehensively investigated by electrochemical tests and theoretical calculations. Based on the theoretical calculations, the introduction of TiOSO4 contributes to facilitating the desolvation kinetics of Zn2+ ions and guarantees the stable interface reactions of both zinc anode and NH4V4O10 cathode. As expected, Zn//Zn cells keep long-term cycling behavior for 3750 h under the test condition of 1 mA cm-2-1 mAh cm-2, Zn//Cu cells deliver high Coulombic efficiency of 99.9% for 1000 cycles under the test condition of 5 mA cm-2-1 mAh cm-2, and Zn//NH4V4O10 batteries maintain reversible specific capacity of 193.8 mAh g-1 after 1700 cycles at 5 A g-1 in ZSO/TSO electrolyte. These satisfactory results manifest that TiOSO4 additive holds great potential to improve the performances of ZIBs.

Se-dopant Modulated Selective Co-Insertion of H+ and Zn2+ in MnO2 for High-Capacity and Durable Aqueous Zn-Ion Batteries

MnO2 is commonly used as the cathode material for aqueous zinc-ion batteries (AZIBs). The strong Coulombic interaction between Zn ions and the MnO2 lattice causes significant lattice distortion and, combined with the Jahn-Teller effect, results in Mn2+ dissolution and structural collapse. While proton intercalation can reduce lattice distortion, it changes the electrolyte pH, producing chemically inert byproducts. These issues greatly affect the reversibility of Zn2+ intercalation/extraction, leading to significant capacity degradation of MnO2. Herein, we propose a novel method to enhance the cycling stability of δ-MnO2 through selenium doping (Se-MnO2). Our work indicates that varying the selenium doping content can regulate the intercalation ratio of H+ in MnO2, thereby suppressing the formation of ZnMn2O4 by-products. Se doping mitigates the lattice strain of MnO2 during Zn2+ intercalation/deintercalation by reducing Mn-O octahedral distortion, modifying Mn-O bond length upon Zn2+ insertion, and alleviating Mn dissolution caused by the Jahn-Teller effect. The optimized Se-MnO2 (Se concentration of 0.8 at.%) deposited on carbon nanotube demonstrates a notable capacity of 386 mAh g-1 at 0.1 A g-1, with exceptional long-term cycle stability, retaining 102 mAh g-1 capacity after 5000 cycles at 3.0 A g-1.

"Anions-in-Colloid" Hydrated Deep Eutectic Electrolyte for High Reversible Zinc Metal Anodes

Zn metal as a promising anode for aqueous batteries suffers from severe zinc dendrites, anion-related side reactions, hydrogen evolution reaction (HER) and narrow electrochemical stable window (ESW). Herein, an "anions-in-colloid" hydrated deep eutectic electrolyte consisting of Zn(ClO4)2 ⋅ 6H2O, β-cyclodextrin (β-CD), and H2O with mass ratio of 7 : 4.5 : 3 (ACDE-3) is designed to improve the stability of zinc anode. The ACDE-3 reconfigures the hydrogen-bond (HB) network and regulates the solvation shell. More importantly, the hydroxyl-rich β-cyclodextrins (β-CDs) in ACDE-3 self-assemble into micelles, in which the steric effect between adjacent β-CDs in micelles restricts the movement of anions. This unique "anions-in-colloid" structure enables the eutectic system with a high Zn2+ transference number (tZn 2+) of 0.84. Thus, ACDE-3 inhibits the formation of dendrite, prevents the anion-involved side reactions, suppresses the HER, and enlarges the ESW to 2.32 V. The Zn//Zn symmetric cell delivers a long lifespan of 900 hours at 0.5 mA cm-2, and the Zn//Cu half cells have a high average columbic efficiency (ACE) of 97.9 % at 0.5 mA cm-2 from cycle 15 to 200 with a uniform and compact zinc deposition. When matched with a poly(1,5-naphthalenediamine) (poly(1, 5-NAPD)) cathode, the full battery with a low negative/positive capacity (N/P) ratio of 2 can still cycle steadily for 200 cycles at a current density of 1.0 A g-1. Additionally, this electrolyte has been proven to be operative over a wide temperature range from -40 °C to 40 °C.

Strategically Modulating Proton Activity and Electric Double Layer Adsorption for Innovative All-Vanadium Aqueous Mn2+/Proton Hybrid Batteries

Aqueous Mn-ion batteries (MIBs) exhibit a promising development potential due to their cost-effectiveness, high safety, and potential for high energy density. However, the development of MIBs is hindered by the lack of electrode materials capable of storing Mn2+ ions due to acidic manganese salt electrolytes and large ion radius. Herein, the tunnel-type structure of monoclinic VO2 nanorods to effectively store Mn2+ ions via a reversible (de)insertion chemistry for the first time is reported. Utilizing exhaustive in situ/ex situ multi-scale characterization techniques and theoretical calculations, the co-insertion process of Mn2+/proton is revealed, elucidating the capacity decay mechanism wherein high proton activity leads to irreversible dissolution loss of vanadium species. Further, the Grotthuss transfer mechanism of protons is broken via a hydrogen bond reconstruction strategy while achieving the modulation of the electric double-layer structure, which effectively suppresses the electrode interface proton activity. Consequently, the VO2 demonstrates excellent electrochemical performance at both ambient temperatures and -20 °C, especially maintaining a high capacity of 162 mAh g-1 at 5 A g-1 after a record-breaking 20 000 cycles. Notably, the all-vanadium symmetric pouch cells are successfully assembled for the first time based on the "rocking-chair" Mn2+/proton hybrid mechanism, demonstrating the practical application potential.

Inhibited Passivation by Bioinspired Cell Membrane Zn Interface for Zn-Air Batteries with Extended Temperature Adaptability

Due to the slow dynamics of mass and charge transfer at Zn|electrolyte interface, the stable operation of Zn-air batteries (ZABs) is challenging, especially at low temperature. Herein, inspired by cell membrane, a hydrophilic-hydrophobic dual modulated Zn|electrolyte interface is constructed. This amphiphilic design enables the quasi-solid-state (QSS) ZABs to display a long-term cyclability of 180 h@50 mA cm-2 at 25 °C. Moreover, a record-long time of 173 h@4 mA cm-2 at -60 °C is also achieved, which is almost threefolds of untreated QSS ZABs. Control experiments and (in situ) characterization reveal that the growth of insulating ZnO passivation layers is largely inhibited by tuned hydrophilic-hydrophobic behavior. Thus, the enhanced transfer dynamic of Zn2+ at Zn|electrolyte interface from 25 to -60 °C is attained. As an extension, the QSS Al-air batteries (AABs) with bioinspired interface also show unprecedented discharge stability of 420 h@1 mA cm-2 at -40 °C, which is about two times of untreated QSS AABs. This bioinspired-hydrophilic-hydrophobic dual modulation strategy may provide a reference for energy transform and storage devices with broad temperature adaptability.

Promoting Preferential Zn (002) Deposition with a Low-Concentration Electrolyte Additive for Highly Reversible Zn-Ion Batteries

Aqueous zinc-ion batteries have promising potential as energy storage devices due to their low cost and environmental friendliness. However, their development has been hindered by zinc dendrite formation and parasitic side reactions. Herein, we introduce a low-concentration sodium benzoate (NaBZ) electrolyte additive to stabilize the electrode-electrolyte interface and promote deposition on the Zn (002) crystal plane. From experimental characterization and computational analyses, NaBZ was found to adsorb on the Zn surface and inhibit side reactions while guiding homogeneous Zn deposition on the (002) plane. Consequently, Zn|Zn symmetric cells with the NaBZ additive cycled stably for over 1000 h at a current density of 0.5 mA cm-2 and an areal capacity of 0.5 mAh cm-2, while Zn|Cu cells showed excellent reversibility with a Coulombic efficiency of 99.05%. Moreover, Zn|Na0.33V2O5 full cells achieve a high specific capacity of 124 mAh g-1 while cycling for 600 h at 2 A g-1. These findings present a low-cost electrolyte modification strategy for reversible zinc-ion batteries.

Noncovalent Interactions-Driven Self-Assembly of Polyanionic Additive for Long Anti-Calendar Aging and High-Rate Zinc Metal Batteries

Zinc anodes of zinc metal batteries suffer from unsatisfactory plating/striping reversibility due to interfacial parasitic reactions and poor Zn2+ mass transfer kinetics. Herein, methoxy polyethylene glycol-phosphate (mPEG-P) is introduced as an electrolyte additive to achieve long anti-calendar aging and high-rate capabilities. The polyanionic of mPEG-P self-assembles via noncovalent-interactions on electrode surface to form polyether-based cation channels and in situ organic-inorganic hybrid solid electrolyte interface layer, which ensure rapid Zn2+ mass transfer and suppresses interfacial parasitic reactions, realizing outstanding cycling/calendar aging stability. As a result, the Zn//Zn symmetric cells with mPEG-P present long lifespans over 9000 and 2500 cycles at ultrahigh current densities of 120 and 200 mA cm-2, respectively. Besides, the coulombic efficiency (CE) of the Zn//Cu cell with mPEG-P additive (88.21%) is much higher than that of the cell (36.4%) at the initial cycle after the 15-day calendar aging treatment, presenting excellent anti-static corrosion performance. Furthermore, after 20-day aging, the Zn//MnO2 cell exhibits a superior capacity retention of 89% compared with that of the cell without mPEG-P (28%) after 150 cycles. This study provides a promising avenue for boosting the development of high efficiency and durable metallic zinc based stationary energy storage system.

An ionically cross-linked composite hydrogel electrolyte based on natural biomacromolecules for sustainable zinc-ion batteries

Zinc-ion batteries (ZIBs) are regarded as promising power sources for flexible and biocompatible devices due to their good sustainability and high intrinsic safety. However, their applications have been hindered by the issues of uncontrolled Zn dendrite growth and severe water-induced side reactions in conventional liquid electrolytes. Herein, an ionically cross-linked composite hydrogel electrolyte based on natural biomacromolecules, including iota-carrageenan and sodium alginate, is designed to promote highly efficient and reversible Zn plating/stripping. The abundant functional groups of macromolecules effectively suppress the reactivity of water molecules and facilitate uniform Zn deposition. Moreover, the composite hydrogel electrolyte exhibits a high ionic conductivity of 5.89 × 10-2 S cm-1 and a Zn2+ transference number of 0.58. Consequently, the Zn‖Zn symmetric cell with the composite hydrogel electrolyte shows a stable cycle life of more than 500 h. Meanwhile, the Zn‖NH4V4O10 coin cell with the composite hydrogel electrolyte retains a high specific capacity of approximately 200 mA h g-1 after 600 cycles at 2 A g-1. The Zn‖NVO pouch cell based on the composite hydrogel electrolyte also shows a high specific capacity of 246.1 mA h g-1 at 0.5 A g-1 and retains 70.7% of its initial capacity after 150 cycles. The pouch cell performs well at different bending angles and exhibits a capacity retention rate of 98% after returning to its initial state from 180° folding. This work aims to construct high-performance hydrogel electrolytes using low-cost natural materials, which may provide a solution for the application of ZIBs in flexible biocompatible devices.

Intrinsically Decoupled Coordination Chemistries Enable Quasi-Eutectic Electrolytes with Fast Kinetics toward Enhanced Zinc-Ion Capacitors

Eutectic electrolytes show potential beyond conventional low-concentration electrolytes (LCEs) in zinc (Zn)-ion capacitors (ZICs) yet suffer from high viscosity and sluggish kinetics. Herein, we originally propose a universal theory of intrinsically decoupling to address these issues, producing a novel electrolyte termed "quasi-eutectic" electrolyte (quasi-EE). Joint experimental and theoretical analyses confirm its unique solution coordination structure doped with near-LCE domains. This enables the quasi-EE well inherit the advanced properties at deep-eutectic states while provide facilitated kinetics as well as lower energy barriers via a vehicle/hopping-hybridized charge transfer mechanism. Consequently, a homogeneous electroplating pattern with much enhanced Sand's time is achieved on the Zn surface, followed by a twofold prolonged service-life with drastically reduced concentration polarization. More encouragingly, the quasi-EE also delivers increased capacitance output in ZICs, which is elevated by 12.4 %-144.6 % compared to that before decoupling. Furthermore, the pouch cell with a cathodic mass loading of 36.6 mg cm-2 maintains competitive cycling performances over 600 cycles, far exceeding other Zn-based counterparts. This work offers fresh insights into eutectic decoupling and beyond.

Rescue of dead MnO2 for stable electrolytic Zn-Mn redox-flow battery: a metric of mediated and catalytic kinetics

The virtues of electrolytic MnO2 aqueous batteries are high theoretical energy density, affordability and safety. However, the continuous dead MnO2 and unstable Mn2+/MnO2 electrolysis pose challenges to the practical output energy and lifespan. Herein, we demonstrate bifunctional cationic redox mediation and catalysis kinetics metrics to rescue dead MnO2 and construct a stable and fast electrolytic Zn-Mn redox-flow battery (eZMRFB). Spectroscopic characterizations and electrochemical evaluation reveal the superior mediation kinetics of a cationic Fe2+ redox mediator compared with the anionic ones (e.g. I- and Br-), thus eliminating dead MnO2 effectively. With intensified oxygen vacancies, density functional theory simulations of the reaction pathways further verify the concomitant Fe-catalysed Mn2+/MnO2 electrolysis kinetics via charge delocalization and activated O 2p electron states, boosting its rate capability. As a result, the elaborated eZMRFB achieves a coulombic efficiency of nearly 100%, ultra-high areal capacity of 80 mAh cm-2, rate capability of 20 C and a long lifespan of 2500 cycles. This work may advance high-energy aqueous batteries to next-generation scalable energy storage.

Improving Aqueous Zinc Ion Batteries with Alkali Metal Ions

Aqueous zinc (Zn) ion batteries have received broad attention recently. However, their practical application is limited by severe Zn dendrite growth and the hydrogen evolution reaction. In this study, three alkali metal ions (Li+, Na+, and K+) are added in ZnSO4 electrolytes, which are subjected to electrochemical measurements and molecular dynamics simulations. The studies show that since K+ has the highest mobility and self-diffusion coefficient among the four ions (Li+, Na+, K+, and Zn2+), it enables K+ to preferentially approach a zinc dendrite at an earlier time, driven by a negative electric field during a cathodic process. The electric double layer, with K+ around the negatively charged Zn dendrite, inhibits dendrite growth and mitigates the hydrogen evolution reaction on the Zn anode. Under this kinetic effect, the Zn-Zn symmetric cell with K+ exhibits a long cycling stability of 1000 h at 1 mA·cm-2 of 1 mAh·cm-2 and 190 h at 30 mA·cm-2 of 2 mAh·cm-2. Such a kinetic effect is also observed with additives Na+ and Li+, though less profound than that of K+.

Conversion-type anode chemistry with interfacial compatibility toward Ah-level near-neutral high-voltage zinc ion batteries

High-voltage aqueous zinc ion batteries (AZIBs) with a high-safety near-neutral electrolyte is of great significance for practical sustainable application; however, they suffer from anode and electrode/electrolyte interfacial incompatibility. Herein, a conversion-type anode chemistry with a low anodic potential, which is guided by the Gibbs free energy change of conversion reaction, was designed for high-voltage near-neutral AZIBs. A reversible conversion reaction between ZnC2O4·2H2O particles and three-dimensional Zn metal networks well-matched in CH3COOLi-based electrolyte was revealed. This mechanism can be universally validated in the battery systems with sodium or iodine ions. More importantly, a cathodic crowded micellar electrolyte with a water confinement effect was proposed in which lies the core for the stability and reversibility of the cathode under an operating platform voltage beyond 2.0 V, obtaining a capacity retention of 95% after 100 cycles. Remarkably, the scientific and technological challenges from the coin cell to Ah-scale battery, sluggish kinetics of the solid-solid electrode reaction, capacity excitation under high loading of active material, and preparation complexities associated with large-area quasi-solid electrolytes, were explored, successfully achieving an 88% capacity retention under high loading of more than 20 mg cm-2 and particularly a practical 1.1 Ah-level pouch cell. This work provides a path for designing low-cost, eco-friendly and high-voltage aqueous batteries.

Water Catchers within Sub-Nano Channels Promote Step-by-Step Zinc-Ion Dehydration Enable Highly Efficient Aqueous Zinc-Metal Batteries

Zinc metal suffers from violent and long-lasting water-induced side reactions and uncontrollable dendritic Zn growth, which seriously reduce the coulombic efficiency (CE) and lifespan of aqueous zinc-metal batteries (AZMBs). To suppress the corresponding harmful effects of the highly active water, a stable zirconium-based metal-organic framework with water catchers decorated inside its sub-nano channels is used to protect Zn-metal. Water catchers within narrow channels can constantly trap water molecules from the solvated Zn-ions and facilitate step-by-step desolvation/dehydration, thereby promoting the formation of an aggregative electrolyte configuration, which consequently eliminates water-induced corrosion and side reactions. More importantly, the functionalized sub-nano channels also act as ion rectifiers and promote fast but even Zn-ions transport, thereby leading to a dendrite-free Zn metal. As a result, the protected Zn metal demonstrates an unprecedented cycling stability of more than 10 000 h and an ultra-high average CE of 99.92% during 4000 cycles. More inspiringly, a practical NH4V4O10//Zn pouch-cell is fabricated and delivers a capacity of 98 mAh (under high cathode mass loading of 25.7 mg cm-2) and preserves 86.2% capacity retention after 150 cycles. This new strategy in promoting highly reversible Zn metal anodes would spur the practical utilization of AZMBs.

Highly Solubilized Urea as Effective Proton Donor-Acceptors for Durable Zinc-Ion Storage Beyond Single-Anion Selection Criteria

Urea, as one of the most sustainable organic solutes, denies the high salt consumption in commercial electrolytes with its peculiar solubility in water. The bi-mixture of urea-H2O shows the eutectic feature for increased attention in aqueous Zn-ion electrochemical energy storage (AZEES) technologies. While the state-of-the-art aqueous electrolyte recipes are still pursuing the high-concentrated salt dosage with limited urea adoption and single-anion selection category. Here, a dual-anion urea-based (DAU) electrolyte composed of dual-Zn salts and urea-H2O-induced solutions is reported, contributing to a stable electric double-layer construction and in situ organic/inorganic SEI formation. The optimized ZT2S0.5-20U electrolytes show a high initial Coulombic efficiency of 93.2% and durable Zn-ion storage ≈4000 h regarding Zn//Cu and Zn//Zn stripping/plating procedures. The assembled Zn//activated carbon full cells maintain ≈100% capacitance over 50 000 cycles at 4 A g-1 in coin cell and ≈98% capacitance over 20 000 cycles at 1 A g-1 in pouch cell setups. A 12 × 12 cm2 pouch cell assembly illustrates the practicality of AZEES devices by designing the cheap, antifreezing, and nonflammable DAU electrolyte system coupling proton donor-acceptor molecule and multi-anion selection criteria, exterminating the critical technical barriers in commercialization.

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.

Chelating Additive Regulating Zn-Ion Solvation Chemistry for Highly Efficient Aqueous Zinc-Metal Battery

Aqueous zinc-metal batteries (AZMBs) usually suffered from poor reversibility and limited lifespan because of serious water induced side-reactions, hydrogen evolution reactions (HER) and rampant zinc (Zn) dendrite growth. Reducing the content of water molecules within Zn-ion solvation sheaths can effectively suppress those inherent defects of AZMBs. In this work, we originally discovered that the two carbonyl groups of N-Acetyl-ϵ-caprolactam (N-ac) chelating ligand can serve as dual solvation sites to coordinate with Zn2+, thereby minimizing water molecules within Zn-ion solvation sheaths, and greatly inhibit water-induced side-reactions and HER. Moreover, the N-ac chelating additive can form a unique physical barrier interface on Zn surface, preventing the harmful contacting with water. In addition, the preferential adsorption of N-ac on Zn (002) facets can promote highly reversible and dendrite-free Zn2+ deposition. As a result, Zn//Cu half-cell within N-ac added electrolyte delivered ultra-high 99.89 % Coulombic efficiency during 8000 cycles. Zn//Zn symmetric cells also demonstrated unprecedented long life of more than 9800 hours (over one year). Aqueous Zn//ZnV6O16 ⋅ 8H2O (Zn//ZVO) full-cell preserved 78 % capacity even after ultra-long 2000 cycles. A more practical pouch-cell was also obtained (90.2 % capacity after 100 cycles). This method offers a promising strategy for accelerating the development of highly efficient AZMBs.