Design Strategies for High-Performance Aqueous Zn/Organic Batteries

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.

Electrolytes in Organic Batteries

Organic batteries using redox-active polymers and small organic compounds have become promising candidates for next-generation energy storage devices due to the abundance, environmental benignity, and diverse nature of organic resources. To date, tremendous research efforts have been devoted to developing advanced organic electrode materials and understanding the material structure-performance correlation in organic batteries. In contrast, less attention was paid to the correlation between electrolyte structure and battery performance, despite the critical roles of electrolytes for the dissolution of organic electrode materials, the formation of the electrode-electrolyte interphase, and the solvation/desolvation of charge carriers. In this review, we discuss the prospects and challenges of organic batteries with an emphasis on electrolytes. The differences between organic and inorganic batteries in terms of electrolyte property requirements and charge storage mechanisms are elucidated. To provide a comprehensive and thorough overview of the electrolyte development in organic batteries, the electrolytes are divided into four categories including organic liquid electrolytes, aqueous electrolytes, inorganic solid electrolytes, and polymer-based electrolytes, to introduce different components, concentrations, additives, and applications in various organic batteries with different charge carriers, interphases, and separators. The perspectives and outlook for the future development of advanced electrolytes are also discussed to provide a guidance for the electrolyte design and optimization in organic batteries. We believe that this review will stimulate an in-depth study of electrolytes and accelerate the commercialization of organic batteries.

COF-Based Electrodes with Vertically Supported Tentacle Array for Ultrahigh Stability Flexible Energy Storage

As an emerging porous crystal polymer, covalent organic frameworks (COFs) possess unique characteristics, such as high porosity, excellent stability, diverse topologies, designable open channels, and functional tunability. However, limited by the solid powder form, most COFs display low active site utilization and weak binding force with the current collector. In this pioneering research, we integrate redox-active COFs onto carbon fiber surfaces (AC-COFs) via strong covalent bridging. The 2,6-diaminoanthraquinone (DAAQ) pillars embedded on the carbon fiber surface are the key to precisely controlling the growth direction of COFs. The obtained tentacle-like array vertically supported on the surface of the carbon fiber can effectively induce charge transfer and prevent COFs from aggregating/collapsing. The strong covalent coupling and increase of accessible active sites contributed to the high specific capacitance of AC-COFs electrode (1034 mF cm^-2). In addition, the COF-based flexible electrode retains an initial capacitance of 98% after 20000 charge-discharge cycles. The flexible all-solid-state symmetric supercapacitor is assembled by PVA/H₂SO₄ gel electrolyte with an areal capacitance of 715 mF cm^-2. Besides, a red LED can be easily powered by three-bending AC-COFs//AC-COFs devices. The innovative synthesis strategy opens up new opportunities to develop high-performance flexible energy storage devices based on COFs.

Three-dimensional Zn-based alloys for dendrite-free aqueous Zn battery in dual-cation electrolytes

Aqueous zinc-ion batteries, in terms of integration with high safety, environmental benignity, and low cost, have attracted much attention for powering electronic devices and storage systems. However, the interface instability issues at the Zn anode caused by detrimental side reactions such as dendrite growth, hydrogen evolution, and metal corrosion at the solid (anode)/liquid (electrolyte) interface impede their practical applications in the fields requiring long-term performance persistence. Despite the rapid progress in suppressing the side reactions at the materials interface, the mechanism of ion storage and dendrite formation in practical aqueous zinc-ion batteries with dual-cation aqueous electrolytes is still unclear. Herein, we design an interface material consisting of forest-like three-dimensional zinc-copper alloy with engineered surfaces to explore the Zn plating/stripping mode in dual-cation electrolytes. The three-dimensional nanostructured surface of zinc-copper alloy is demonstrated to be in favor of effectively regulating the reaction kinetics of Zn plating/stripping processes. The developed interface materials suppress the dendrite growth on the anode surface towards high-performance persistent aqueous zinc-ion batteries in the aqueous electrolytes containing single and dual cations. This work remarkably enhances the fundamental understanding of dual-cation intercalation chemistry in aqueous electrochemical systems and provides a guide for exploring high-performance aqueous zinc-ion batteries and beyond.

Organic Zinc-Ion Battery: Planar, π-Conjugated Quinone-Based Polymer Endows Ultrafast Ion Diffusion Kinetics

A novel poly(phenazine-alt-pyromellitic anhydride) (PPPA) has been successfully designed and synthesized via a condensation polymerization strategy as promising cathode material in organic zinc-ion batteries. Electrochemical quartz crystal microbalance (EQCM), FTIR and XPS characterizations verify a reversible Zn²⁺ -coordination mechanism in our PPPA cathode. Intriguingly, an ultrahigh Zn²⁺ diffusion coefficient of 1.2×10^-7  cm²  s^-1 was found in this large π-conjugated system, which is the highest one among all organic cathode materials for zinc-ion batteries. Theoretical calculations reveal the extended π-conjugated plane in our PPPA sample results in a significant reduction on energy gap, effectively accelerating intramolecular electron transfer during charge/discharge process. Our finding provides insights to achieve high zinc-ion transport kinetics by a design strategy on planar polymer system.

Challenges and Perspectives of Organic Multivalent Metal-Ion Batteries

Rechargeable organic multivalent metal-ion batteries (MMIBs) have attracted a surge of interest as promising alternatives for large-scale energy storage applications because they can combine the advantages of both organic electrodes and multivalent metal-ion batteries. However, the development of organic MMIBs is hampered by many factors, which mean they lag far behind organic alkali-metal- (e.g., Li-, Na-, and K-) ion batteries. Herein, the challenges that are specifically faced by organic MMIBs are analyzed and the strategies that can probably solve such challenges are then discussed. As a special challenge that organic MMIBs are facing, the charge-storage mechanism is particularly underlined to deeply understand the structure-property relationships for guiding the future design of high-performance organic electrodes for MMIBs. The perspectives are thereby elaborated in this review with the outlook of practical applications of organic MMIBs.

Organic Small-Molecule Electrodes: Emerging Organic Composite Materials in Supercapacitors for Efficient Energy Storage

Organic small molecules with electrochemically active and reversible redox groups are excellent candidates for energy storage systems due to their abundant natural origin and design flexibility. However, their practical application is generally limited by inherent electrical insulating properties and high solubility. To achieve both high energy density and power density, organic small molecules are usually immobilized on the surface of a carbon substrate with a high specific surface area and excellent electrical conductivity through non-covalent interactions or chemical bonds. The resulting composite materials are called organic small-molecule electrodes (OMEs). The redox reaction of OMEs occurs near the surface with fast kinetic and higher utilization compared to storing charge through diffusion-limited Faraday reactions. In the past decade, our research group has developed a large number of novel OMEs with different connections or molecular skeletons. This paper introduces the latest development of OMEs for efficient energy storage. Furthermore, we focus on the design motivation, structural advantages, charge storage mechanism, and various electrode parameters of OMEs. With small organic molecules as the active center, OMEs can significantly improve the energy density at low molecular weight through proton-coupled electron transfer, which is not limited by lattice size. Finally, we outline possible trends in the rational design of OMEs toward high-performance supercapacitors.

Molecular and Morphological Engineering of Organic Electrode Materials for Electrochemical Energy Storage

Organic electrode materials (OEMs) can deliver remarkable battery performance for metal-ion batteries (MIBs) due to their unique molecular versatility, high flexibility, versatile structures, sustainable organic resources, and low environmental costs. Therefore, OEMs are promising, green alternatives to the traditional inorganic electrode materials used in state-of-the-art lithium-ion batteries. Before OEMs can be widely applied, some inherent issues, such as their low intrinsic electronic conductivity, significant solubility in electrolytes, and large volume change, must be addressed. In this review, the potential roles, energy storage mechanisms, existing challenges, and possible solutions to address these challenges by using molecular and morphological engineering are thoroughly summarized and discussed. Molecular engineering, such as grafting electron-withdrawing or electron-donating functional groups, increasing various redox-active sites, extending conductive networks, and increasing the degree of polymerization, can enhance the electrochemical performance, including its specific capacity (such as the voltage output and the charge transfer number), rate capability, and cycling stability. Morphological engineering facilitates the preparation of different dimensional OEMs (including 0D, 1D, 2D, and 3D OEMs) via bottom-up and top-down methods to enhance their electron/ion diffusion kinetics and stabilize their electrode structure. In summary, molecular and morphological engineering can offer practical paths for developing advanced OEMs that can be applied in next-generation rechargeable MIBs.

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Long-Life Aqueous Zinc-Ion Batteries of Organic Iminodianthraquinone/rGO Cathode Assisted by Zn2+ Binding with Adjacent Molecules

Organic compounds have been extensively used as zinc-ion battery (ZIB) cathodes due to their high capacities and outstanding properties. Nevertheless, poor electrical conductivity limits their developments. RGO (reduced graphene oxide) can well interact with organic compounds through π-π stacking for furnishing capacious ion diffusion paths and active sites to enhance conductivity and capacity. Herein, a 1,1'-iminodianthraquinone (IDAQ)/rGO composite is utilized as cathode of ZIBs, demonstrating ultrahigh stability with 96% capacity retention after 5000 cycles. Zn2+ and H+ synergetic mechanism in IDAQ/rGO has been deeply discussed by ex situ analysis and theoretical calculation. Consequently, the structure of IDAQ2(H+)6(Zn2+) is the most probable product after discharging progress. Prospectively, the IDAQ/rGO material with excellent stability and good performance would provide new insights into designing advanced ZIBs.

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.

Multifunctional Carbon Modification Enhancement for Vanadium-Based Phosphates as an Advanced Cathode of Zinc-Ion Batteries

In recent years, rechargeable aqueous zinc-ion batteries (ZIBs) have shown extraordinary potential due to their safety, nontoxicity, sustainable zinc resources, and low price. However, the lack of suitable cathode materials hinders the development of ZIBs. Recently, layered phosphates have been widely used as cathode materials. As one typical phosphate cathode, vanadium oxyphosphate (VOPO₄) has inherently low electronic conductivity and structural dissolution in electrochemical reactions, limiting its development. To solve these problems, VOPO₄/C is prepared by combining multifunctional carbon material with a VOPO₄ interlayer and an external surface, which not only improves the electronic conductivity of the composite material but also effectively inhibits the dissolution of VOPO₄ in the electrolyte. As a result, the prepared VOPO₄/C could deliver a reversible capacity of 140 mA h g^-1 at a current density of 100 mA g^-1. Furthermore, the rate performance of the VOPO₄/C composite has also been improved significantly. In the process of charging and discharging, zinc ions in the composite show perfect intercalate and deintercalate performance.

Design and Synthesis of a π-Conjugated N-Heteroaromatic Material for Aqueous Zinc-Organic Batteries with Ultrahigh Rate and Extremely Long Life

Electroactive organic materials with tailored functional groups are of great importance for aqueous Zn-organic batteries due to their green and renewable nature. Herein, a completely new N-heteroaromatic material, hexaazatrinaphthalene-phenazine (HATN-PNZ) is designed and synthesized, by an acid-catalyzed condensation reaction, and its use as an ultrahigh performance cathode for Zn-ion batteries demonstrated. Compared with phenazine monomer, it is revealed that the π-conjugated structure of N-heteroaromatics can effectively increase electron delocalization, thereby improving its electrical conductivity. Furthermore, the enlarged aromatic structure noticeably suppresses its dissolution in aqueous electrolytes, thus enabling high structural stability. As expected, the HATN-PNZ cathode delivers a large reversible capacity of 257 mAh g^-1 at 5 A g^-1 , ultrahigh rate capability of 144 mAh g^-1 at 100 A g^-1 , and an extremely long cycle life of 45 000 cycles at 50 A g^-1 . Investigation of the charge-storage mechanism demonstrates the synergistic coordination of both Zn²⁺ and H⁺ cations with the phenanthroline groups, with Zn²⁺ first followed by H⁺ , accompanying the reversible formation of zinc hydroxide sulfate hydrate. This work provides a molecular-engineering strategy for superior organic materials and adds new insights to understand the charge-storage behavior of aqueous Zn-organic batteries.

Two-Dimensional Organic Supramolecule via Hydrogen Bonding and π-π Stacking for Ultrahigh Capacity and Long-Life Aqueous Zinc-Organic Batteries

Aqueous zinc-ion batteries (ZIBs) are promising for next-generation energy storage. However, the reported electrode materials for ZIBs are facing shortcomings including low capacity and unsatisfactory cycling stability etc. Herein, hexaazatrinaphthalene-quione (HATNQ) is reported for aqueous ZIBs. The HATNQ electrodes delivered an ultrahigh capacity (482.5 mAh g-1 at 0.2 A g-1 ) and outstanding cyclability of >10 000 cycles at 5 A g-1 . The capacity sets a new record for organic cathodes in aqueous ZIBs. The high performances are ascribed to the rich C=O and C=N groups that endowed HATNQ with a 2D layered supramolecular structure by multiple hydrogen bonds in plane with π-π interactions out-of-plane, leading to enhanced charge transfer, insolubility, and rapid ion transport for fast-charge and -discharge batteries. Moreover, the 2D supramolecular structure boosted the storage of Zn2+ /H+ , particularly the storage of Zn2+ , due to the more favorable O⋅⋅⋅Zn⋅⋅⋅N coordination in HATNQ.

In Situ Growth of Covalent Organic Framework Nanosheets on Graphene as the Cathode for Long-Life High-Capacity Lithium-Ion Batteries

The poor electronic and ionic conductivities of covalent organic frameworks (COFs) severely restrict the development of COF-based electrodes for practical rechargeable batteries, therefore inspiring more research interest from the direction of both material synthesis and technology. Herein, a dual-porous COF, USTB-6, with good crystallinity and rich redox-active sites is conceived and fabricated by the polymerization of 2,3,8,9,14,15-hexa(4-formylphenyl)diquinoxalino [2,3-a:2',3'-c]phenazine and 2,7-diaminopyrene-4,5,9,10-tetraone. In particular, the heterogeneous polymerization of the same starting materials in the presence of graphene affords uniformly dispersed COF nanosheets with a thickness of 8.3 nm on a conductive carbon substrate, effectively enhancing the electronic conductivity of the COF-based electrode. Such a graphene-supported USTB-6 nanosheets cathode when used in a lithium-ion battery exhibits a specific capacity of 285 mA h g^-1 at a current density of 0.2 C and excellent rate performance with a prominent capacity of 188 mA h g^-1 at 10 C. More importantly, a capacity of 170 mA h g^-1 is retained by using the USTB-6 nanosheets cathode after 6000 cycles charge and discharge measurement at 5 C.

Synthesis of Zn2+-Pre-Intercalated V2O5·nH2O/rGO Composite with Boosted Electrochemical Properties for Aqueous Zn-Ion Batteries

Layered vanadium-based materials are considered to be great potential electrode materials for aqueous Zn-ion batteries (AZIBs). The improvement of the electrochemical properties of vanadium-based materials is a hot research topic but still a challenge. Herein, a composite of Zn-ion pre-intercalated V₂O₅·nH₂O combined with reduced graphene oxide (ZnVOH/rGO) is synthesized by a facile hydrothermal method and it shows improved Zn-ion storage. ZnVOH/rGO delivers a capacity of 325 mAh·g⁻¹ at 0.1 A·g⁻¹, and this value can still reach 210 mAh·g⁻¹ after 100 cycles. Additionally, it exhibits 196 mAh·g⁻¹ and keeps 161 mAh·g⁻¹ after 1200 cycles at 4 A·g⁻¹. The achieved performances are much higher than that of ZnVOH and VOH. All results reveal that Zn²⁺ as “pillars” expands the interlayer distance of VOH and facilitates the fast kinetics, and rGO improves the electron flow. They both stabilize the structure and enhance efficient Zn²⁺ migration. All findings demonstrate ZnVOH/rGO’s potential as a perspective cathode material for AZIBs.

Insight on Cathodes Chemistry for Aqueous Zinc-Ion Batteries: From Reaction Mechanisms, Structural Engineering, and Modification Strategies

By virtue of low cost, eco-friendliness, competitive gravimetric energy density, and intrinsic safety, more and more attention has increasingly focused on aqueous zinc ion batteries (AZIBs) as a promising alternative for scalable energy storage. However, plagued by a complex interfacial process, sluggish dynamics, lability of electrodes and electrolytes, insufficient energy density, and poor cycle life heavily restrict practical applications of AZIBs, indicating that profound understandings on cathode storage chemistry are necessarily needed. Hence, this paper comprehensively summarizes recent advance in cathodes with critical insight on the energy storage mechanism. Furthermore, the issues and challenges for high-performance cathodes are meticulously explored, presenting inspiring structural engineering and modification strategies. Finally, rational evaluations on representative cathodes are rendered, suggesting the potential development direction of AZIBs.

Improving the Performance of Aqueous Zinc-ion Batteries by Inhibiting Zinc Dendrite Growth: Recent Progress

Aqueous zinc-ion batteries (ZIBs) are promising candidates for the next-generation high-energy storage devices, owing to their resource availability, low cost, eco-friendliness, and high safety. The zinc (Zn) metal anode in a suitable battery system, including an electrolyte and a high-performance cathode electrode, can deliver an excellent electrochemical performance. However, several obstacles must be overcome to utilize aqueous ZIBs. Among these, Zn dendrite growth, corrosion, and side reactions severely impair the performance of rechargeable ZIBs. To deal with these issues, a profound understanding of the mechanism of the matter occurring in electrochemical cycles is essential to thoroughly solve the challenges. Instead of focusing solely on techniques for improving the performance of Zn metal anodes, this review delves into and summarizes the causes of side reactions and dendrite formation, thereby establishing a logical system of methodologies for improving the electrochemical performance of mild aqueous ZIBs. The correlation between the Zn metal anode, aqueous electrolyte, separators and the performance of ZIBs is also discussed in detail. There is also a brief perspective on the future development of Zn metal anodes in aqueous solutions. This study sheds a light on the challenges associated with the construction of high-performance ZIBs, which will significantly aid in their practical implementation.

A Binary Hydrate-Melt Electrolyte with Acetate-Oriented Cross-Linking Solvation Shells for Stable Zinc Anodes

Aqueous zinc-ion batteries (ZIBs) with low cost and high safety are promising energy-storage devices. However, ZIBs with metal Zn anodes usually suffer from low coulombic efficiency and poor cycling performance due to the occurrence of side reactions on the Zn anodes. Here, a binary hydrate-melt ZnCl₂ /Zn(OAc)₂ electrolyte is designed to suppress the hydrogen evolution reaction and by-product formation on Zn anodes by adjusting the Zn²⁺ solvation structure. In the solvation structure of the hydrate-melt ZnCl₂ /Zn(OAc)₂ electrolyte, the carboxylate group in OAc^- will coordinate with the Zn²⁺ , which will weaken the interaction between Zn²⁺ and H₂ O molecules to achieve higher ionization energy of H₂ O molecules. Simultaneously, these carboxylate groups of OAc^- can serve as H-bond acceptors to construct H-bonds with H₂ O molecules in their neighboring solvation structures, forming a cross-linking H-bond network. Such a cross-linking H-bond network further suppresses the water activity in ZnCl₂ /Zn(OAc)₂ electrolyte. As a result, in such an electrolyte, the side reactions are effectively restricted on Zn anodes and thus Zn anodes can achieve a high coulombic efficiency of 99.59% even after cycling. To illustrate the feasibility of the ZnCl₂ /Zn(OAc)₂ electrolyte in aqueous ZIBs, Zn||p-chloranil cells are assembled based on the ZnCl₂ /Zn(OAc)₂ electrolyte. The resultant Zn||p-chloranil cells exhibit enhanced cycling performance compared with the cases with a conventional ZnSO₄ electrolyte.

Storing Mg Ions in Polymers: A Perspective

The electrochemical performance of rechargeable Mg batteries (RMBs) is primarily determined by the cathodes. However, the strong interaction between highly polarized Mg²⁺ and the host lattice is a big challenge for inorganic cathode materials. While endowed with weak interaction with Mg²⁺ , organic polymers are capable of fast reaction kinetics. Besides, with the advantages of light weight, abundance, low cost, and recyclability, polymers are deemed as ideal cathode materials for RMBs. Although polymer cathodes have remarkably progressed in recent years, there are still significant challenges to overcome before reaching practical application. In this perspective, the challenges faced by polymer cathodes are critically focused, followed by the retrospection of efforts devoted to design polymers. Some feasible strategies are proposed to explore new structures and chemistries for the practical application of polymer cathodes in RMBs.

Design Strategies for High-Energy-Density Aqueous Zinc Batteries

In recent years, the increasing demand for high-capacity and safe energy storage has focused attention on zinc batteries featuring high voltage, high capacity, or both. Despite extensive research progress, achieving high-energy-density zinc batteries remains challenging and requires the synergistic regulation of multiple factors including reaction mechanisms, electrodes, and electrolytes. In this Review, we comprehensively summarize the rational design strategies of high-energy-density zinc batteries and critically analyze the positive effects and potential issues of these strategies in optimizing the electrochemistry, cathode materials, electrolytes, and device architecture. Finally, the challenges and perspectives for the further development of high-energy-density zinc batteries are outlined to guide research towards new-generation batteries for household appliances, low-speed electric vehicles, and large-scale energy storage systems.

Orthoquinone-Based Covalent Organic Frameworks with Ordered Channel Structures for Ultrahigh Performance Aqueous Zinc-Organic Batteries

Elaborate molecular design on cathodes is of great importance for rechargeable aqueous zinc-organic batteries' performance elevation. Herein, we design a novel orthoquinone-based covalent organic framework with an ordered channel structures (BT-PTO COF) cathode for an ultrahigh performance aqueous zinc-organic battery. The ordered channel structure facilitates ions transfer and makes the COF follow a redox pseudocapacitance mechanism. Thus, it delivers a high reversible capacity of 225 mAh g^-1 at 0.1 A g^-1 and an exceptional long-term cyclability (retention rate 98.0 % at 5 A g^-1 (≈18 C) after 10 000 cycles). Moreover, a co-insertion mechanism with Zn²⁺ first followed by two H⁺ is uncovered for the first time. Significantly, this co-insertion behaviour evolves to more H⁺ insertion routes at high current density and gives the COF ultra-fast kinetics thus it achieves unprecedented specific power of 184 kW kg^-1 _(COF) and a high energy density of 92.4 Wh kg^-1 _(COF) . Our work reports a superior organic material for zinc batteries and provides a design idea for future high-performance organic cathodes.

A π-Conjugated Polyimide-Based High-Performance Aqueous Potassium-Ion Asymmetric Supercapacitor

Aqueous asymmetric supercapacitor has captured widespread attention as a sustainable high-power energy resource. Organic electrode materials are appealing owing to their sustainability and high redox reactivity, but suffer from structural instability and low power density. Here the π-conjugated polyimide-based organic electrodes with different lengths of alkyl chains are explored to achieve high rate capability and long lifespan in an aqueous K⁺ -ion electrolyte. The fabricated asymmetric supercapacitor exhibits high capacities of 107 mAh g^-1 at 2 A g^-1 and 67 mAh g^-1 at 90 A g^-1 . A specific capacity of 65 mAh g^-1 which is over 70% of the initial performance is obtained after 65,000 cycles. Molecular engineering of long alkyl chains in polyimide could reduce the degree of π-conjugation and spatially block the π-conjugated imide bond with limited redox activity but improved stability against chemical degradation. Further electrochemical quartz crystal microbalance (EQCM) and ex situ FTIR and XPS characterizations reveal the pseudocapacitance behavior originated from the π-conjugated polyimide-based redox reaction with potassium ions and hydrated potassium ions. We showcase a promising polyimide-based polymer with extended π-conjugated system for high-performance asymmetric supercapacitor. This article is protected by copyright. All rights reserved.

A carbonyl-rich covalent organic framework as a high-performance cathode material for aqueous rechargeable zinc-ion batteries

Aqueous rechargeable zinc-ion batteries (ZIBs) provide high theoretical capacity, operational safety, low-cost and environmental friendliness for large-scale energy storage and wearable electronic devices, but their future development is plagued by low capacity and poor cycle life due to the lack of suitable cathode materials. In this work, a covalent organic framework (Tp-PTO-COF) with multiple carbonyl active sites is synthesized and successfully introduced in aqueous rechargeable ZIBs for the first time. Tp-PTO-COF delivers high specific capacities of 301.4 and 192.8 mA h g-1 at current densities of 0.2 and 5 A g-1, respectively, along with long-term durability and flat charge-discharge plateaus. The remarkable electrochemical performance is attributed to the abundance of nucleophilic carbonyl active sites, well defined porous structure and inherent chemical stability of Tp-PTO-COF. Moreover, the structural evolution and Zn2+ ion intercalation mechanism are discussed and revealed by the experimental analysis and density functional theory calculations. These results highlight a new avenue to develop organic cathode materials for high performance and sustainable aqueous rechargeable ZIBs.

Organic-Inorganic Hybrid Cathode with Dual Energy-Storage Mechanism for Ultrahigh-Rate and Ultralong-Life Aqueous Zinc-Ion Batteries

The exploitation of cathode materials with high capacity as well as high operating voltage is extremely important for the development of aqueous zinc-ion batteries (ZIBs). Yet, the classical high-capacity materials (e.g., vanadium-based materials) provide a low discharge voltage, while organic cathodes with high operating voltage generally suffer from a low capacity. In this work, organic (ethylenediamine)-inorganic (vanadium oxide) hybrid cathodes, that is, EDA-VO, with a dual energy-storage mechanism, are designed for ultrahigh-rate and ultralong-life ZIBs. The embedded ethylenediamine (EDA) can not only increase the layer spacing of the vanadium oxide, with improved mobility of Zn ions in the V-O layered structure, but also act as a bidentate chelating ligand participating in the storage of Zn ions. This hybrid provides a high specific capacity (382.6 mA h g^-1 at 0.5 A g^-1 ), elevated voltage (0.82 V) and excellent long-term cycle stability (over 10 000 cycles at 5 A g^-1 ). Assistant density functional theory (DFT) calculations indicate the cathode has remarkable electronic conductivity, with an ultralow diffusion barrier of 0.78 eV for an optimal Zn-ion diffusion path in the EDA-VO. This interesting idea of building organic-inorganic hybrid cathode materials with a dual energy-storage mechanism opens a new research direction toward high-energy secondary batteries.

Advanced Multifunctional Aqueous Rechargeable Batteries Design: From Materials and Devices to Systems

Multifunctional aqueous rechargeable batteries (MARBs) are regarded as safe, cost-effective, and scalable electrochemical energy storage devices, which offer additional functionalities that conventional batteries cannot achieve, which ideally leads to unprecedented applications. Although MARBs are among the most exciting and rapidly growing topics in scientific research and industrial development nowadays, a systematic summary of the evolution and advances in the field of MARBs is still not available. Therefore, the review presented comprehensively and systematically summarizes the design principles and the recent advances of MARBs by categories of smart ARBs and integrated systems, together with an analysis of their device design and configuration, electrochemical performance, and diverse smart functions. The two most promising strategies to construct novel MARBs may be A) the introduction of functional materials into ARB components, and B) integration of ARBs with other functional devices. The ongoing challenges and future perspectives in this research and development field are outlined to foster the future development of MARBs. Finally, the most important upcoming research directions in this rapidly developing field are highlighted that may be most promising to lead to the commercialization of MARBs and to a further broadening of their range of applications.

MXene/Organics Heterostructures Enable Ultrastable and High-Rate Lithium/Sodium Batteries

Organic electrode materials have shown potential for rechargeable batteries because they are environmentally friendly, earth-abundant sources, recyclable, high sustainable, designable, flexible, and lightweight. However, low electrical conductivity and dissolution in organic liquid electrolytes hinder their further development. Herein, MXene/organics heterostructures are designed to address the problems of organic electrodes via a scalable and simple electrostatic self-assembly strategy. Under the effect of the electrostatic interaction, organic cathode material, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), is tightly attached to MXene nanosheets. Owing to the high electronic conductivity and special two-dimensional (2D) structure of MXene nanosheets, the issues of PTCDA cathode are effectively relieved. When applied in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), the MXene@PTCDA heterostructure exhibits significantly enhanced rate capability and cycling performance than bare PTCDA. The heterostructures proposed here can be applied to other (K, Zn, Al, Mg, Ca, etc.) battery systems. In addition to energy storage and conversion, the heterostructures can be also extended to many fields such as catalysis, sensors, electronics, optics, membranes, semiconductors, biomedicines, etc.

Activating the Stepwise Intercalation-Conversion Reaction of Layered Copper Sulfide toward Extremely High Capacity Zinc-Metal-Free Anodes for Rocking-Chair Zinc-Ion Batteries

Conventional zinc-ion batteries (ZIBs) are severely hindered by the inherent drawbacks of Zn metal anodes including dendrite growth, side reactions, and interface passivation. Developing intercalation-type anodes to fabricate rocking-chair ZIBs is a promising approach to overcome the above issues. However, the low capacity resulting from the limited transfer electron number of intercalation reactions impedes their practical applications. Herein, we report an effective strategy to break the capacity limit of layered CuS materials as a Zn-metal-free anode through activating its intrinsic conversion reaction. It is found that the preintercalation of cetyltrimethylammonium bromide in CuS (CuS@CTMAB) significantly lowers the energy barrier of the conversion reaction, thus realizing a record-breaking capacity (367.4 mAh g^-1 at 0.1 A g^-1) as a Zn-metal-free anode based on the reversible conversion of Cu²⁺/Cu⁰. Theoretical calculation, ex situ microscopy, and spectroscopy results verify that the characteristic stepwise intercalation-conversion reaction route occurred in CuS@CTMAB. Moreover, the moderate structure transformation and good electronic conduction during the phase evolution process led to excellent cycling stability and high rate performance. Consequently, the rocking-chair ZIB full battery system utilizing CuS@CTMAB and Zn²⁺-preintercalated MnO₂ as the anode and cathode, respectively, exhibits exceptional capacity retention of 93.9% up to 8000 cycles at 2 A g^-1. Besides, the CuS@CTMAB anode is also compatible with high-voltage Prussian blue cathodes, demonstrating its outstanding practicality.

Solvation Effect on the Improved Sodium Storage Performance of N-Heteropentacenequinone for Sodium-Ion Batteries

The performance of electrode material is correlated with the choice of electrolyte, however, how the solvation has significant impact on electrochemical behavior is underdeveloped. Herein, N-heteropentacenequinone (TAPQ) is investigated to reveal the solvation effect on the performance of sodium-ion batteries in different electrolyte environment. TAPQ cycled in diglyme-based electrolyte exhibits superior electrochemical performance, but experiences a rapid capacity fading in carbonate-based electrolyte. The function of solvation effect is mainly embodied in two aspects: one is the stabilization of anion intermediate via the compatibility of electrode and electrolyte, the other is the interfacial electrochemical characteristics influenced by solvation sheath structure. By revealing the failure mechanism, this work presents an avenue for better understanding electrochemical behavior and enhancing performance from the angle of solvation effect.

Interfacial Engineering Strategy for High-Performance Zn Metal Anodes

Due to their high safety and low cost, rechargeable aqueous Zn-ion batteries (RAZIBs) have been receiving increased attention and are expected to be the next generation of energy storage systems. However, metal Zn anodes exhibit a limited-service life and inferior reversibility owing to the issues of Zn dendrites and side reactions, which severely hinder the further development of RAZIBs. Researchers have attempted to design high-performance Zn anodes by interfacial engineering, including surface modification and the addition of electrolyte additives, to stabilize Zn anodes. The purpose is to achieve uniform Zn nucleation and flat Zn deposition by regulating the deposition behavior of Zn ions, which effectively improves the cycling stability of the Zn anode. This review comprehensively summarizes the reaction mechanisms of interfacial modification for inhibiting the growth of Zn dendrites and the occurrence of side reactions. In addition, the research progress of interfacial engineering strategies for RAZIBs is summarized and classified. Finally, prospects and suggestions are provided for the design of highly reversible Zn anodes.

High-Performance Aqueous Zinc Batteries Based on Organic/Organic Cathodes Integrating Multiredox Centers

Organic cathode materials with redox-active sites and flexible structure are promising for developing aqueous zinc ion batteries with high capacity and large output power. However, the energy storage of most organic hosts relies on the coordination/incoordination reaction between Zn²⁺ /H⁺ and a single functional group, which result in inferior capacity, low discharge platform, and structural instability. Here, the lead is taken in in situ electrodepositing stable poly(1,5-naphthalenediamine, 1,5-NAPD) as interlayer and excellent conductive poly(para-aminophenol, pAP) skin onto nanoporous carbon in sequence for the structural optimization of organic/organic cathodes, designated as C@multi-layer polymer. In situ analyses, electrochemical measurements, and theoretical calculation prove that both CO and CN active groups can act as a strong electron donor as well as Zn²⁺ host during the discharging process. Benefiting from the synergistic effect of the double organic layers, C@multi-layer polymer delivers high capacity, long lifespan, and excellent capacity reservation even at large discharge current and commercial mass loading (>10 mg cm^-2 ). Introducing multiredox centers into one organic composites will provide new insights into designing advanced Zn-organic batteries.

A rechargeable aqueous manganese-ion battery based on intercalation chemistry

Aqueous rechargeable metal batteries are intrinsically safe due to the utilization of low-cost and non-flammable water-based electrolyte solutions. However, the discharge voltages of these electrochemical energy storage systems are often limited, thus, resulting in unsatisfactory energy density. Therefore, it is of paramount importance to investigate alternative aqueous metal battery systems to improve the discharge voltage. Herein, we report reversible manganese-ion intercalation chemistry in an aqueous electrolyte solution, where inorganic and organic compounds act as positive electrode active materials for Mn2+ storage when coupled with a Mn/carbon composite negative electrode. In one case, the layered Mn0.18V2O5·nH2O inorganic cathode demonstrates fast and reversible Mn2+ insertion/extraction due to the large lattice spacing, thus, enabling adequate power performances and stable cycling behavior. In the other case, the tetrachloro-1,4-benzoquinone organic cathode molecules undergo enolization during charge/discharge processes, thus, contributing to achieving a stable cell discharge plateau at about 1.37 V. Interestingly, the low redox potential of the Mn/Mn2+ redox couple vs. standard hydrogen electrode (i.e., -1.19 V) enables the production of aqueous manganese metal cells with operational voltages higher than their zinc metal counterparts.