Coordinately Unsaturated Manganese-Based Metal-Organic Frameworks as a High-Performance Cathode for Aqueous Zinc-Ion Batteries

Achieving Non-Interfacial Blocking Zinc Ion Transport Based on MOF Derived Manganese Oxides and Amorphous Carbon Hybrid Materials

How to coordinate electron and ion transport behavior across scales and interfaces within ion battery electrodes? The exponential increase in surface area observed in nanoscale electrode materials results in an incomprehensibly vast spatial interval. Herein, to address the problems of volume expansion, dissolution of cathode material, and the charge accumulation problem existing in manganiferous materials for zinc ion batteries, metal organic framework is utilized to form the architecture of non-interfacial blocking ~10 nm Mn2O3 nanoparticles and amorphous carbon hybrid electrode materials, demonstrating a high specific capacity of 361 mAh g-1 (0.1 A g-1), and excellent cycle stability of 105 mAh g-1 after 2000 cycles under 1 A g-1. The uniform and non-separated disposition of Mn and C atoms constitutes an interconnected network with high electronic and ionic conductivity, minimizing issues like structural collapse and volume expansion of the electrode material during cycling. The cooperative insert mechanism of H+ and Zn2+ are analyzed via ex-situ XRD and in-situ Raman tests. The model battery is assembled to present practical possibilities. The results indicate that MOF-derived carbonization provides an effective strategy for exploring Mn-based electrode materials with high ion and electron transport capacity.

Metal-organic frameworks for high-performance cathodes in batteries

Metal-organic frameworks (MOFs) are functional materials that are proving to be indispensable for the development of next-generation batteries. The porosity, crystallinity, and abundance of active sites in MOFs, which can be tuned by selecting the appropriate transition metal/organic linker combination, enable MOFs to meet the performance requirements for cathode materials in batteries. Recent studies on the use of MOFs in cathodes have verified their high durability, cyclability, and capacity thus demonstrating the huge potential of MOFs as high-performance cathode materials. However, to keep pace with the rapid growth of the battery industry, several challenges hindering the development of MOF-based cathode materials need to be overcome. This review analyzes current applications of MOFs to commercially available lithium-ion batteries as well as advanced batteries still in the research stage. This review provides a comprehensive outlook on the progress and potential of MOF cathodes in meeting the performance requirements of the future battery industry.

Unlocking Double Redox Reaction of Metal-Organic Framework for Aqueous Zinc-Ion Battery

Metal-organic frameworks (MOFs) show wide application as the cathode of aqueous zinc-ion batteries (AZIBs) in the future owning to their high porosity, diverse structures, abundant species, and controllable morphology. However, the low energy density and poor cycling stability hinder the feasibility in practical application. Herein, an innovative strategy of organic/inorganic double electroactive sites is proposed and demonstrated to obtain extra capacity and enhance the energy density in a manganese-based metal-organic framework (Mn-MOF-74). Simultaneously, its energy storage mechanism is systematically investigated. Moreover, profiting from the coordination effect, the Mn-MOF-74 features with stable structure in ZnSO4 electrolyte. Therefore, the Zn/Mn-MOF-74 batteries exhibit a high energy density and superior cycling stability. This work aids in the future development of MOFs in AZIBs.

Utilization of 2D materials in aqueous zinc ion batteries for safe energy storage devices

Aqueous rechargeable battery has been an intense topic of research recently due to the significant safety issues of conventional Li-ion batteries (LIBs). Amongst the various candidates of aqueous batteries, aqueous zinc ion batteries (AZIBs) hold great promise as a next generation safe energy storage device due to its low cost, abundance in nature, low toxicity, environmental friendliness, low redox potential, and high theoretical capacity. Yet, the promise has not been realized due to their limitations, such as lower capacity compared to traditional LIB, dendrite growth, detrimental degradation of electrode materials structure as ions intercalate/de-intercalate, and gas evolution/corrosion at the electrodes, which remains a significant challenge. To address the challenges, various 2D materials with different physiochemical characteristics have been utilized. This review explores fundamental physiochemical characteristics of widely used 2D materials in AZIBs, including graphene, MoS2, MXenes, 2D metal organic framework, 2D covalent organic framework, and 2D transition metal oxides, and how their characteristics have been utilized or modified to address the challenges in AZIBs. The review also provides insights and perspectives on how 2D materials can help to realize the full potential of AZIBs for next-generation safe and reliable energy storage devices.

An Organic Coordination Manganese Complex as Cathode for High-Voltage Aqueous Zinc-metal Battery

Aqueous Zn-Mn battery has been considered as the most promising scalable energy-storage system due to its intrinsic safety and especially ultralow cost. However, the traditional Zn-Mn battery mainly using manganese oxides as cathode shows low voltage and suffers from dissolution/disproportionation of the cathode during cycling. Herein, for the first time, a high-voltage and long-cycle Zn-Mn battery based on a highly reversible organic coordination manganese complex cathode (Manganese polyacrylate, PAL-Mn) was constructed. Benefiting from the insoluble carboxylate ligand of PAL-Mn that can suppress shuttle effect and disproportionationation reaction of Mn3+ in a mild electrolyte, Mn3+ /Mn2+ reaction in coordination state is realized, which not only offers a high discharge voltage of 1.67 V but also exhibits excellent cyclability (100 % capacity retention, after 4000 cycles). High voltage reaction endows the Zn-Mn battery high specific energy (600 Wh kg-1 at 0.2 A g-1 ), indicating a bright application prospect. The strategy of introducing carboxylate ligands in Zn-Mn battery to harness high-voltage reaction of Mn3+ /Mn2+ well broadens the research of high-voltage Zn-Mn batteries under mild electrolyte conditions.

Application of Conductive MOF in Zinc-Based Batteries

The use of conductive MOFs (c-MOFs) in zinc-based batteries has been a popular research direction. Zinc-based batteries are widely used with the advantages of high specific capacity and safety and stability, but they also face many problems. c-MOFs have excellent conductivity compared with other primitive MOFs, and therefore have better applications in zinc-based batteries. In this paper, the transfer mechanisms of the unique charges of c-MOFs: hop transport and band transport, respectively, are discussed and the way of electron transport is further addressed. Then, the various ways to prepare c-MOFs are introduced, among which solvothermal, interfacial synthesis, and postprocessing methods are widely used. In addition, the applications of c-MOFs are discussed in terms of their role and performance in different types of zinc-based batteries. Finally, the current problems of c-MOFs and the prospects for their future development are presented.

Electrochemical Performance and Mechanism of Bimetallic Organic Framework for Advanced Aqueous Zn Ion Batteries

Widespread interest has been generated by aqueous zinc batteries (AZIBs), which have excellent theoretical capacities (820 mA h g-1), a low redox potential (-0.76 V vs SHE of Zn metal), and high security. Suitable cathodes for constructing high performance AZIBs are of great signification. Metal-organic frameworks (MOFs) with adjustable structure via metals and organic units show great potential in AZIBs. In this work, ZnMn-Squaric acid (ZnMn-SQ) was synthesized using squaric acid through coprecipitation and served as the cathode for AZIBs. The ZnMn-SQ electrode demonstrated a high capacity of 489.1 mA h g-1 at 0.2 A g-1. Meanwhile, ZnMn-SQ can obtain 80.7 mA h g-1 after 1300 cycles, showing an outstanding long cycle life. More importantly, ex situ characterizations of XRD, XPS, and FT-IR revealed that ZnMn-SQ undergoes a structural transformation from the initial ZnMn-SQ framework to manganese oxide accompanied by Zn-SQ and then reduced to MnOOH, ZnMn2O4, and Zn4SO4(OH)6·5H2O (ZHS) in subsequent cycles. In addition, a modified zinc anode using cubic porous Zn-SQ-3d was used to construct ZnMn-SQ // Zn-SQ-3d@Zn(Zn-SQ-3d-coated Zn) high performance AZIBs, the capacity of which reaches 171.3 mA h g-1 at 1 A g-1 after 660 cycles. This work provided chances for constructing high-performance zinc ion batteries using MOF compounds.

Advances of Electroactive Metal-Organic Frameworks

The preparation of electroactive metal-organic frameworks (MOFs) for applications of supercapacitors and batteries has received much attention and remarkable progress during the past few years. MOF-based materials including pristine MOFs, hybrid MOFs or MOF composites, and MOF derivatives are well designed by a combination of organic linkers (e.g., carboxylic acids, conjugated aromatic phenols/thiols, conjugated aromatic amines, and N-heterocyclic donors) and metal salts to construct predictable structures with appropriate properties. This review will focus on construction strategies of pristine MOFs and hybrid MOFs as anodes, cathodes, separators, and electrolytes in supercapacitors and batteries. Descriptions and discussions follow categories of electrochemical double-layer capacitors (EDLCs), pseudocapacitors (PSCs), and hybrid supercapacitors (HSCs) for supercapacitors. In contrast, Li-ion batteries (LIBs), Lithium-sulfur batteries (LSBs), Lithium-oxygen batteries (LOBs), Sodium-ion batteries (SIBs), Sodium-sulfur batteries (SSBs), Zinc-ion batteries (ZIBs), Zinc-air batteries (ZABs), Aluminum-sulfur batteries (ASBs), and others (e.g., LiSe, NiZn, H⁺ , alkaline, organic, and redox flow batteries) are categorized for batteries.

Metal-Organic Framework-Based Materials in Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are promising for large-scale energy storage systems due to their high safety, large capacity, cost-effectiveness, and environmental friendliness. However, their commercialization is currently hindered by several challenging issues, including cathode degradation and zinc dendrite growth. Recently, metal-organic frameworks (MOFs) and their derivatives have gained significant attention and are widely used in AZIBs due to their highly porous structures, large specific surface area, and ability to design frameworks for Zn²⁺ shuttle. Based on preceding contributions, this review aims to generalize two design principles for MOF-based materials in AZIBs: cathode preparation and anode protection. For cathode preparation, we mainly introduce novel MOF-based electrode materials such as pure MOFs, porous carbon materials, metal oxides, and their compounds, focusing on the analysis of the specific capacity of AZIBs. For anode protection, we systematically analyze MOF-based materials used as 3D Zn architecture, solid electrolyte interfaces, novel separators, and solid-state electrolytes, highlighting the improvement in the cyclic stability of Zn anodes. Finally, we propose the future development of MOF-based materials in AZIBs. Our work can give some clues for raising the practical application level of aqueous ZIBs.

A hexagon based Mn(II) rod metal-organic framework - structure, SF6 gas sorption, magnetism and electrochemistry

A manganese(II) metal-organic framework based on the hexatopic hexakis(4-carboxyphenyl)benzene, cpb^6-: [Mn₃(cpb)(dmf)₃], was solvothermally prepared showing a Langmuir area of 438 m² g^-1, rapid uptake OF sulfur hexafluoride (SF₆) as well as electrochemical and magnetic properties, while single crystal diffraction reveals an unusual rod-MOF topology.

One-Dimensional π-d Conjugated Conductive Metal-Organic Framework with Dual Redox-Active Sites for High-Capacity and Durable Cathodes for Aqueous Zinc Batteries

Aqueous Zn-based batteries (ZIBs) possess huge advantages in terms of high safety, low cost, and environmental friendliness. However, the lack of suitable cathodes with high-capacity, long-cycling, and high-rate capability limits their practical application. Herein, we present a highly crystalline one-dimensional π-d conjugated conductive metal-organic framework by coordinating ultrasmall 1,2,4,5-benzenetetramine (BTA) linkers with copper ions (Cu-BTA-H), as a cathode for ZIBs. The large ratio of active sites and dual redox mechanism of Cu-BTA-H, including the one-electron-redox reaction over copper ions (via Cu²⁺/Cu⁺) and the two-electron-redox reaction over organic ligands (via C═N/C-N), effectively enhance its reversible capacity. Meanwhile, the abundant porosity, small band gap, high crystallinity, and stable coordination structure of Cu-BTA-H endow it with fast ion/electron transport and effectively hinder the dissolution of organic ligands during cycling, respectively. Consequently, Cu-BTA-H possesses a high reversible capacity of 330 mAh g^-1 at 200 mA g^-1 and excellent rate performance and long-cycle stability, with a high capacity of 106.1 mAh g^-1 at 2.0 A g^-1 after 500 cycles and a high Coulombic efficiency of ∼100%. The proposed conductive MOFs with dual redox-active sites provide an efficient approach for constructing fast, stable, and high-capacity energy storage devices.

Comparative Review on the Aqueous Zinc-Ion Batteries (AZIBs) and Flexible Zinc-Ion Batteries (FZIBs)

Lithium-ion batteries (LIBs) have been considered an easily accessible battery technology because of their low weight, cheapness, etc. Unfortunately, they have significant drawbacks, such as flammability and scarcity of lithium. Since the components of zinc-ion batteries are nonflammable, nontoxic, and cheap, AZIBs could be a suitable replacement for LIBs. In this article, the advantages and drawbacks of AZIBs over other energy storage devices are briefly discussed. This review focused on the cathode materials and electrolytes for AZIBs. In addition, we discussed the approaches to improve the electrochemical performance of zinc batteries. Here, we also discussed the polymer gel electrolytes and the electrodes for flexible zinc-ion batteries (FZIBs). Moreover, we have outlined the importance of temperature and additives in a flexible zinc-ion battery. Finally, we have discussed anode materials for both AZIBs and FZIBs. This review has summarized the advantages and disadvantages of AZIBs and FZIBs for future applications in commercial battery technology.

Anchoring I3- via Charge-Transfer Interaction by a Coordination Supramolecular Network Cathode for a High-Performance Aqueous Dual-Ion Battery

Iodine is considered to have broad application prospects in the field of electrochemical energy storage. However, the high solubility of I₃^- severely hampers its practical application, and the lack of research on the anchoring mechanism of I₃^- has seriously hindered the development of advanced cathode materials for iodine batteries. Herein, based on the molecular orbital theory, we studied the charge-transfer interaction between the acceptor of I₃^- with a σ* empty antibonding orbital and the donor of pyrimidine nitrogen with lone-pair electrons, which is proved by the results of UV-vis absorption spectroscopy, Raman spectroscopy, and density functional theory (DFT) calculations. The prepared dual-ion battery (DIB) exhibits a high voltage platform of 1.2 V, a remarkable discharge-specific capacity of up to 207 mAh g^-1, and an energy density of 233 Wh kg^-1 at a current density of 5 A g^-1, as well as outstanding cycle stability (operating stably for 5000 cycles) with a high Coulombic efficiency of 97%, demonstrating excellent electrochemical performance and a promising prospect in stationary energy storage.

An Anti-Aromatic Covalent Organic Framework Cathode with Dual-Redox Centers for Rechargeable Aqueous Zinc Batteries

Covalent organic frameworks (COFs) are promising cathode candidates with high structural stability. However, they contain redox inactive linkages and experience low redox potential. Herein, a full anti-aromatic microporous COF cathode material of TAQ-BQ is designed for aqueous zinc batteries. The anti-aromatic conjugation effectively lowers the energy level of the lowest unoccupied molecular orbital as revealed by theoretical calculations, which corresponds to an elevated redox potential. Besides, the structure contains imino active sites at the linkages, in addition to carbonyl at the active parts. As a result, the TAQ-BQ cathode exhibits a voltage of 1.53 V/1.54 V and between 1.35 and 0.45 V in zinc cells. It delivers 208 mAh g^-1 capacity at 0.1 A g^-1 and maintains 136 mAh g^-1 at 2 A g^-1. Stable cycling is realized for 1000 cycles with 87% capacity retention. The co-de/insertion of Zn²⁺ and protons is identified for energy storage. Our work reveals the promises of COF cathode materials for aqueous zinc batteries.

Metal-Organic Framework-Based Materials for Aqueous Zinc-Ion Batteries: Energy Storage Mechanism and Function

Aqueous rechargeable zinc-ion batteries (ZIBs) featuring competitive performance, low cost and high safety hold great promise for applications in grid-scale energy storage and portable electronic devices. Metal-organic frameworks (MOFs), relying on their large framework structure and abundant active sites, have been identified as promising materials in ZIBs. This review comprehensively presents the current development of MOF-based materials including MOFs and their derivatives in ZIBs, which begins with Zn storage mechanism of MOFs, followed by introduction of various types of MOF-based cathode materials (PB and PBA, Mn-based MOF, V-based MOF, conductive MOF and their derivatives), and the regulation approaches for Zn deposition behavior. The key factors and optimization strategies of MOF-based materials that affect ZIBs performance are emphasized and discussed. Finally, the challenges and further research directions of MOF-based materials for advanced zinc-ion batteries are provided.

Boosting the Cycling Stability of Aqueous Zinc-Ion Batteries through Nanofibrous Coating of a Bead-like MnOx Cathode

Rechargeable aqueous zinc-ion batteries (AZIBs) are close complements to lithium-ion batteries for next-generation grid-scale applications owing to their high specific capacity, low cost, and intrinsic safety. Nevertheless, the viable cathode materials (especially manganese oxides) of AZIBs suffer from poor conductivity and inferior structural stability upon cycling, thereby impeding their practical applications. Herein, a facile synthetic strategy of bead-like manganese oxide coated with carbon nanofibers (MnO_x-CNFs) based on electrospinning is reported, which can effectively improve the electron/ion diffusion kinetics and provide robust structural stability. These benefits of MnO_x-CNFs are evident in the electrochemical performance metrics, with a long cycling durability (i.e., a capacity retention of 90.6% after 2000 cycles and 71% after 5000 cycles) and an excellent rate capability. Furthermore, the simultaneous insertion of H⁺/Zn²⁺ and the Mn redox process at the surface and in the bulk of MnO_x-CNFs are clarified in detail. Our present study not only provides a simple avenue for synthesizing high-performance Mn-based cathode materials but also offers unique knowledge on understanding the corresponding electrochemical reaction mechanism for AZIBs.

Hexagonal WO3/3D Porous Graphene as a Novel Zinc Intercalation Anode for Aqueous Zinc-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) have acquired great attention because of their high safety and environmentally friendly properties. However, the uncontrollable Zn dendrites and the irreversibility of electrodes seriously affect their practical application. Herein, hexagonal WO₃/three-dimensional porous graphene (h-WO₃/3DG) is investigated as an intercalation anode for ZIBs. As a result, the h-WO₃/3DG//Zn half-battery shows excellent electrochemical performance with a high capacity of 115.6 mAh g^-1 at 0.1 A g^-1 and 89% capacity retention at 2.0 A g^-1 after 10 000 cycles. The reason could be that the crystalline structure of WO₃, which has hexagonal channels, with a diameter of 5.36 Å, much higher than the diameter of Zn²⁺ (0.73 Å), accelerating the insertion/extraction of Zn ions. A zinc metal-free full battery using h-WO₃/3DG as the anode and ZnMn₂O₄/carbon black (ZnMn₂O₄/CB) as the cathode is constructed, exhibiting an initial capacity of 66.8 mAh g^-1 at 0.1 A g^-1 corresponding to an energy density of 73.5 W h kg^-1 (based on the total mass of anode and cathode-active materials) and a capacity retention of 76.6% after 1000 cycles at 0.5 A g^-1. This work demonstrates the high potential of hexagonal WO₃ as an advanced intercalation anode material for Zn metal-free batteries and may inspire new ideas for the development of other intercalation anode hosts for ZIBs.

Metal organic framework-based nanostructure materials: applications for non-lithium ion battery electrodes

Non-lithium ion (e.g., Al3+, Ca2+, K+, Mg2+, Na+, and Zn2+) batteries have emerged as a promising platform for next-generation energy storage systems.

High-Performance Aqueous Zn Battery Based on MoS2-Loaded MnO2-x@Carbon Aerogel

The MnO₂-based aqueous Zn cell can meet the requirements of safety, flexibility, and low cost for portable/wearable electronics; however, its low intrinsic conductivity, weak kinetics, and poor high-loading capacity restrict its practical performance. In this study, the synergistic architecture of MoS₂-loaded, oxygen-defect-rich MnO_2-x nanocrystals with a carbon coating (M-PM_2-x-H₂ aerogel) was prepared. As corevealed by various characterizations, this synergistic design not only improves the electronic/ionic conductivity but also motivates the conversion kinetics of the surficial electrochemical reaction. As a result, the M-PM_2-x-H₂ cathode delivers a much improved capacity of 567 mA h·g^-1 at 0.1 A·g^-1 and shows a high capacity retention of 176% after 150 cycles at 0.5 A·g^-1. More impressively, the high areal loading (3.97 mg·cm^-1) of the M-PM_2-x-H₂ electrode also displays a high capacity of 367 mA h·g^-1 at 0.1 A·g^-1. In addition, the derived all-solid-state cell exhibits excellent flexibility and safety under the conditions of weight loading, cutting, and bending.