A Covalent Organic Framework as a Long-life and High-Rate Anode Suitable for Both Aqueous Acidic and Alkaline Batteries

Self-Charging Aqueous Zn//COF Battery with UltraHigh Self-Charging Efficiency and Rate

Self-charging zinc batteries that combine energy harvesting technology with batteries are candidates for reliable self-charging power systems. However, the lack of rational materials design results in unsatisfactory self-charging performance. Here, a covalent organic framework containing pyrene-4,5,9,10-tetraone groups (COF-PTO) is reported as a cathode material for aqueous self-charging zinc batteries. The ordered channel structure of the COF-PTO provides excellent capacity retention of 98% after 18 000 cycles at 10 A g-1 and ultra-fast ion transfer. To visually assess the self-charging performance, two parameters, namely self-charging efficiency (self-charging discharge capacity/galvanostatic discharge capacity, η) and average self-charging rate (total discharge capacity after cyclic self-charging/total cyclic self-charging time, ν), are proposed for performance evaluation. COF-PTO achieves an impressive η of 96.9% and an ν of 30 mAh g-1 self-charge capacity per hour in 100 self-charging cycles, surpassing the previous reports. Mechanism studies reveal the co-insertion of Zn2+ and H+ double ions in COF-PTO of self-charging zinc batteries. In addition, the C═N and C═O (on the benzene) in COF-PTO are ortho structures to each other, which can easily form metal heterocycles with Zn ions, thereby driving the forward progress of the self-charging reaction and enhancing the self-charging performance.

Covalent organic frameworks and their composites for rechargeable batteries

Covalent organic frameworks (COFs), characterized by well-ordered pores, large specific surface area, good stability, high precision, and flexible design, are a promising material for batteries and have received extensive attention from researchers in recent years. Compared with inorganic materials, COFs can construct elastic frameworks with better structural stability, and their chemical compositions and structures can be precisely adjusted and functionalized at the molecular level, providing an open pathway for the convenient transfer of ions. In this review, the energy storage mechanism and unique superiority of COFs and COF composites as electrodes, separators and electrolytes for rechargeable batteries are discussed in detail. Special emphasis is placed on the relationship between the establishment of COF structures and their electrochemical performance in different batteries. Finally, this review summarizes the challenges and prospects of COFs and COF composites in battery equipment.

Heterointerface regulation of covalent organic framework-anchored graphene via a solvent-free strategy for high-performance supercapacitor and hybrid capacitive deionization electrodes

Covalent organic frameworks (COFs) with customizable geometry and redox centers are an ideal candidate for supercapacitors and hybrid capacitive deionization (HCDI). However, their poor intrinsic conductivity and micropore-dominated pore structures severely impair their electrochemical performance, and the synthesis process using organic solvents brings serious environmental and cost issues. Herein, a 2D redox-active pyrazine-based COF (BAHC-COF) was anchored on the surface of graphene in a solvent-free strategy for heterointerface regulation. The as-prepared BAHC-COF/graphene (BAHCGO) nanohybrid materials possess high-speed charge transport offered by the graphene carrier and accelerated electrolyte ion migration within the BAHC-COF, allowing ions to effectively occupy ion storage sites inside BAHC. As a result, the BAHCGO//activated carbon asymmetric supercapacitor achieves a high energy output of 61.2 W h kg-1 and a satisfactory long-term cycling life. More importantly, BAHCGO-based HCDI possesses a high salt adsorption capacity (SAC) of 67.5 mg g-1 and excellent long-term desalination/regeneration stability. This work accelerates the application of COF-based materials in the fields of energy storage and water treatment.

Recent Advances in Aqueous Non-Metallic Ion Batteries with Organic Electrodes

Aqueous non-metallic ion batteries have attracted much attention in recent years owing to their fast kinetics, long cycle life, and low manufacture cost. Organic compounds with flexible structural designability are promising electrode materials for aqueous non-metallic ion batteries. In this review, the recent progress of organic electrode materials is systematically summarized for aqueous non-metallic ion batteries with the focus on the interaction between non-metallic ion charge carriers and organic electrode host materials. Both the cations (proton, ammonium ion, and methyl viologen ions) and anions (chloridion, sulfate ion, perchlorate ion, trifluoromethanesulfonate and trifluoromethanesulfonimide ion) storage are discussed. Moreover, the design strategies toward improving the comprehensive performance of organic electrode materials in aqueous non-metallic ion batteries will be summarized. More organic electrode materials with new reaction mechanisms need to be explored to meet the diverse demands of aqueous non-metallic ion batteries with different charge carriers in the future. This review provides insights into developing high-performance organic electrodes for aqueous non-metallic ion batteries.

Organic Electrode Materials for Energy Storage and Conversion: Mechanism, Characteristics, and Applications

ConspectusLithium ion batteries (LIBs) with inorganic intercalation compounds as electrode active materials have become an indispensable part of human life. However, the rapid increase in their annual production raises concerns about limited mineral reserves and related environmental issues. Therefore, organic electrode materials (OEMs) for rechargeable batteries have once again come into the focus of researchers because of their design flexibility, sustainability, and environmental compatibility. Compared with conventional inorganic cathode materials for Li ion batteries, OEMs possess some unique characteristics including flexible molecular structure, weak intermolecular interaction, being highly soluble in electrolytes, and moderate electrochemical potentials. These unique characteristics make OEMs suitable for applications in multivalent ion batteries, low-temperature batteries, redox flow batteries, and decoupled water electrolysis. Specifically, the flexible molecular structure and weak intermolecular interaction of OEMs make multivalent ions easily accessible to the redox sites of OEMs and facilitate the desolvation process on the redox site, thus improving the low-temperature performance, while the highly soluble nature enables OEMs as redox couples for aqueous redox flow batteries. Finally, the moderate electrochemical potential and reversible proton storage and release of OEMs make them suitable as redox mediators for water electrolysis. Over the past ten years, although various new OEMs have been developed for Li-organic batteries, Na-organic batteries, Zn-organic batteries, and other battery systems, batteries with OEMs still face many challenges, such as poor cycle stability, inferior energy density, and limited rate capability. Therefore, previous reviews of OEMs mainly focused on organic molecular design for organic batteries or strategies to improve the electrochemical performance of OEMs. A comprehensive review to explore the characteristics of OEMs and establish the correlation between these characteristics and their specific application in energy storage and conversion is still lacking.In this Account, we initially provide an overview of the sustainability and environmental friendliness of OEMs for energy storage and conversion. Subsequently, we summarize the charge storage mechanisms of the different types of OEMs. Thereafter, we explore the characteristics of OEMs in comparison with conventional inorganic intercalation compounds including their structural flexibility, high solubility in the electrolyte, and appropriate electrochemical potential in order to establish the correlations between their characteristics and potential applications. Unlike previous reviews that mainly introduce the electrochemical performance progress of different organic batteries, this Account specifically focuses on some exceptional applications of OEMs corresponding to the characteristics of organic electrode materials in energy storage and conversion, as previously published by our groups. These applications include monovalent ion batteries, multivalent ion batteries, low-temperature batteries, redox flow batteries with soluble OEMs, and decoupled water electrolysis employing organic electrodes as redox mediators. We hope that this Account will make an invaluable contribution to the development of organic electrode materials for next-generation batteries and help to unlock a world of potential energy storage applications.

Non-Metal Ion Storage in Zinc-Organic Batteries

Zinc-organic batteries (ZOBs) are receiving widespread attention as up-and-coming energy-storage systems due to their sustainability, operational safety and low cost. Charge carrier is one of the critical factors affecting the redox kinetics and electrochemical performances of ZOBs. Compared with conventional large-sized and sluggish Zn2+ storage, non-metallic charge carriers with small hydrated size and light weight show accelerated interfacial dehydration and fast reaction kinetics, enabling superior electrochemical metrics for ZOBs. Thus, it is valuable and ongoing works to build better ZOBs with non-metallic ion storage. In this review, versatile non-metallic cationic (H+, NH4 +) and anionic (Cl-, OH-, CF3SO3 -, SO4 2-) charge carriers of ZOBs are first categorized with a brief comparison of their respective physicochemical properties and chemical interactions with redox-active organic materials. Furthermore, this work highlights the implementation effectiveness of non-metallic ions in ZOBs, giving insights into the impact of ion types on the metrics (capacity, rate capability, operation voltage, and cycle life) of organic cathodes. Finally, the challenges and perspectives of non-metal-ion-based ZOBs are outlined to guild the future development of next-generation energy communities.

Completely Activated and Phase-Transformed KFeMnHCF for Zn/K Hybrid Batteries with 14 500 Cycles by an OH-Rich Hydrogel Electrolyte

Metal hexacyanoferrates are recognized as superior cathode materials for zinc and zinc hybrid batteries, particularly the Prussian blue analog (PBA). However, PBA development is hindered by several limitations, including small capacities (<70 mAh g-1) and short lifespans (<1000 cycles). These limitations generally arise due to incomplete activation of redox sites and structure collapse during intercalation/deintercalation of metal ions in PBAs. According to this study, the adoption of a hydroxyl-rich (OH-rich) hydrogel electrolyte with extended electrochemical stability windows (ESWs) can effectively activate the redox site of low-spin Fe of the KxFeyMn1-y[Fe(CN)6]w·zH2O (KFeMnHCF) cathode while tuning its structure. Additionally, the strong adhesion of the hydrogel electrolyte inhibits KFeMnHCF particles from falling off the cathode and dissolving. The easy desolvation of metal ions in the developed OH-rich hydrogel electrolytes can lead to a fast and reversible intercalation/deintercalation of metal ions in the PBA cathode. As a result, the Zn||KFeMnHCF hybrid batteries achieve the unprecedented characteristics of 14 500 cycles, a 1.7 V discharge plateau, and a 100 mAh g-1 discharge capacity. The results of this study provide a new understanding of the development of zinc hybrid batteries with PBA cathode materials and present a promising new electrolyte material for this application.

A covalent organic framework as a dual-active-center cathode for a high-performance aqueous zinc-ion battery

Organic electrode materials have shown significant potential for aqueous Zn ion batteries (AZIBs) due to their flexible structure designability and cost advantage. However, sluggish ionic diffusion, high solubility, and low capacities limit their practical application. Here, we designed a covalent organic framework (TA-PTO-COF) generated by covalently bonding tris(4-formylbiphenyl)amine (TA) and 2,7-diaminopyrene-4,5,9,10-tetraone (PTO-NH2). The highly conjugated skeleton inside enhances its electron delocalization and intermolecular interaction, leading to high electronic conductivity and limited solubility. The open channel within the TA-PTO-COF provides ionic diffusion pathways for fast reaction kinetics. In addition, the abundant active sites (C[double bond, length as m-dash]N and C[double bond, length as m-dash]O) endow the TA-PTO-COF with a large reversible capacity. As a result, the well-designed TA-PTO-COF cathode delivers exceptional capacity (255 mA h g-1 at 0.1 A g-1), excellent cycling stability, and a superior rate capacity of 186 mA h g-1 at 10 A g-1. Additionally, the co-insertion mechanism of Zn2+/H+ within the TA-PTO-COF cathode is revealed in depth by ex situ spectroscopy. This study presents an effective strategy for developing high-performance organic cathodes for advanced AZIBs.

Robust links in photoactive covalent organic frameworks enable effective photocatalytic reactions under harsh conditions

Developing heterogeneous photocatalysts for the applications in harsh conditions is of high importance but challenging. Herein, by converting the imine linkages into quinoline groups of triphenylamine incorporated covalent organic frameworks (COFs), two photosensitive COFs, namely TFPA-TAPT-COF-Q and TFPA-TPB-COF-Q, are successfully constructed. The obtained quinoline-linked COFs display improved stability and photocatalytic activity, making them suitable photocatalysts for photocatalytic reactions under harsh conditions, as verified by the recyclable photocatalytic reactions of organic acid involving oxidative decarboxylation and organic base involving benzylamine coupling. Under strong oxidative condition, the quinoline-linked COFs show a high efficiency up to 11831.6 μmol·g-1·h-1 and a long-term recyclable usability for photocatalytic production of H2O2, while the pristine imine-linked COFs are less catalytically active and easily decomposed in these harsh conditions. The results demonstrate that enhancing the linkage robustness of photoactive COFs is a promising strategy to construct heterogeneous catalysts for photocatalytic reactions under harsh conditions.

Non-Metallic NH4 + /H+ Co-Storage in Organic Superstructures for Ultra-Fast and Long-Life Zinc-Organic Batteries

Compared with Zn2+ storage, non-metallic charge carrier with small hydrated size and light weight shows fast dehydration and diffusion kinetics for Zn-organic batteries. Here we first report NH4 + /H+ co-storage in self-assembled organic superstructures (OSs) by intermolecular interactions of p-benzoquinone (BQ) and 2, 6-diaminoanthraquinone (DQ) polymer through H-bonding and π-π stacking. BQ-DQ OSs exhibit exposed quadruple-active carbonyl motifs and super electron delocalization routes, which are redox-exclusively coupled with high-kinetics NH4 + /H+ but exclude sluggish and rigid Zn2+ ions. A unique 4e- NH4 + /H+ co-coordination mechanism is unravelled, giving BQ-DQ cathode high capacity (299 mAh g-1 at 1 A g-1 ), large-current tolerance (100 A g-1 ) and ultralong life (50,000 cycles). This strategy further boosts the capacity to 358 mAh g-1 by modulating redox-active building units, giving new insights into ultra-fast and stable NH4 + /H+ storage in organic materials for better Zn batteries.

Covalent Organic Framework-based Solid-State Electrolytes, Electrode Materials, and Separators for Lithium-ion Batteries

The increasing global energy consumption has led to the rapid development of renewable energy storage technologies. Lithium-ion batteries (LIBs) have been extensively studied and utilized for reliable, efficient, and sustainable energy storage. Nevertheless, designing new materials for LIB applications with high capacity and long-term stability is highly desired but remains a challenging task. Recently, covalent organic frameworks (COFs) have emerged as superior candidates for LIB applications due to their high porosity, well-defined pores, highly customizable structure, and tunable functionalities. These merits enable the preparation of tailored COFs with predesigned redox-active moieties and suitable porous channels that can improve the lithium-ion storage and transportation. This review summarizes the recent progress in the development of COFs and their composites for a variety of LIB applications, including (quasi) solid-state electrolytes, electrode materials, and separators. Finally, the challenges and potential future directions of employing COFs for LIBs are also briefly discussed, further promoting the foundation of this class of exciting materials for future advances in energy-related applications.

Two-Dimensional Conjugated Polymers: a New Choice For Organic Thin-Film Transistors

Organic thin-film transistors (OTFTs) as a vital component among transistors have shown great potential in smart sensing, flexible displays, and bionics due to their flexibility, biocompatibility and customizable chemical structures. Even though linear conjugated polymer semiconductors are common for constructing channel materials of OTFTs, advanced materials with high charge carrier mobility, tunable band structure, robust stability, and clear structure-property relationship are indispensable for propelling the evolution of OTFTs. Two-dimensional conjugated polymers (2DCPs), featured with conjugated lattice, tailorable skeletons, and functional porous structures, match aforementioned criteria closely. In this review, we firstly introduce the synthesis of 2DCP thin films, focusing on their characteristics compatible with the channels of OTFTs. Subsequently, the physics and operating mechanisms of OTFTs and the applications of 2DCPs in OTFTs are summarized in detail. Finally, the outlook and perspective in the field of OTFTs using 2DCPs are provided as well.

Synergetic Coupling of Redox-Active Sites on Organic Electrode Material for Robust and High-Performance Sodium-Ion Storage

Organic electrode materials (OEMs), valued for their sustainability and structural tunability, have been attracting increasing attention for wide application in sodium-ion batteries (SIBs) and other rechargeable batteries. However, most OEMs are plagued with insufficient specific capacity or poor cycling stability. Therefore, it's imperative to enhance their specific capacity and cycling stability through molecular design. Herein, we designed and synthesized a heteroaromatic molecule 2,3,8,9,14,15-hexanol hexaazatrinaphthalene (HATN-6OH) by the synergetic coupling of catechol (the precursor of ortho-quinone)/ortho-quinone functional groups and HATN conjugated core structures. The abundance of catechol/ortho-quinone and imine redox-active moieties delivers a high specific capacity of nine-electron transfer for SIBs. Most notably, the π-π interactions and intermolecular hydrogen bond forces among HATN-6OH molecules secure the stable long-term cycling performance of SIBs. Consequently, the as-prepared HATN-6OH electrode exhibited a high specific capacity (554 mAh g-1 at 0.1 A g-1 ), excellent rate capability (202 mAh g-1 at 10 A g-1 ), and stable long-term cycling performance (73 % after 3000 cycles at 10 A g-1 ) in SIBs. Additionally, the nine-electron transfer mechanism is confirmed by systematic density functional theory (DFT) calculation, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and Raman analysis. The achievement of the synergetic coupling of the redox-active sites on OEMs could be an important key to the enhancement of SIBs and other metal-ion batteries.

Refreshing the Legacy of Rudolf Nietzki: Benzene-1,2,4,5-tetramine and Related Compounds

Like hydroquinones and quinones, aromatic compounds with multiple NH2 groups and the corresponding quinonediimines have the potential to serve as components of useful redox-active organic materials. Benzene-1,2,4,5-tetramine (BTA) and its oxidized form BTA-H2 offer a promising redox pair of this type, and the compounds have proven to be useful in many areas of chemistry. However, key aspects of their behavior have remained poorly studied, such as the nature of their protonated forms, their preferred molecular structures, their reactivity, and their organization in condensed phases. In the present work, we have used a combination of improved methods of synthesis, computation, spectroscopic studies, and structural analyses to develop a deeper understanding of BTA, BTA-H2, their salts, and related compounds. The new knowledge is expected to accelerate exploitation of the compounds in areas of materials science where desirable properties can only be attained by properly controlling the organization of molecular components.

Proton Intercalation/De-intercalation Chemistry in Phenazine-based Anode for Hydronium-ion Batteries

Hydronium-ion batteries have received significant attention owing to the merits of extraordinary sustainability and excellent rate abilities. However, achieving high-performance hydronium-ion batteries remains a challenge due to the inferior properties of anode materials in strong acid electrolyte. Herein, a hydronium-ion battery is constructed which is based on a diquinoxalino [2,3-a:2',3'-c] phenazine (HATN) anode and a MnO2 @graphite felt cathode in a hybrid acidic electrolyte. The fast kinetics of hydronium-ion insertion/extraction into HATN electrode endows the HATN//MnO2 @GF battery with enhanced electrochemical performance. This battery exhibits an excellent rate performance (266 mAh g-1 at 0.5 A g-1 , 97 mAh g-1 at 50 A g-1 ), attractive energy density (182.1 Wh kg-1 ) and power density (31.2 kW kg-1 ), along with long-term cycle stability. These results shed light on the development of advanced hydronium-ion batteries.

Aqueous Organic Batteries Using the Proton as a Charge Carrier

Benefiting from the merits of low cost, nonflammability, and high operational safety, aqueous rechargeable batteries have emerged as promising candidates for large-scale energy-storage applications. Among various metal-ion/non-metallic charge carriers, the proton (H+ ) as a charge carrier possesses numerous unique properties such as fast proton diffusion dynamics, a low molar mass, and a small hydrated ion radius, which endow aqueous proton batteries (APBs) with a salient rate capability, a long-term life span, and an excellent low-temperature electrochemical performance. In addition, redox-active organic molecules, with the advantages of structural diversity, rich proton-storage sites, and abundant resources, are considered attractive electrode materials for APBs. However, the charge-storage and transport mechanisms of organic electrodes in APBs are still in their infancy. Therefore, finding suitable electrode materials and uncovering the H+ -storage mechanisms are significant for the application of organic materials in APBs. Herein, the latest research progress on organic materials, such as small molecules and polymers for APBs, is reviewed. Furthermore, a comprehensive summary and evaluation of APBs employing organic electrodes as anode and/or cathode is provided, especially regarding their low-temperature and high-power performances, along with systematic discussions for guiding the rational design and the construction of APBs based on organic electrodes.

NH4 + Charge Carrier Coordinated H-Bonded Organic Small Molecule for Fast and Superstable Rechargeable Zinc Batteries

Organic small molecules as high-capacity cathodes for Zn-organic batteries have inspired numerous interests, but are trapped by their easy-dissolution in electrolytes. Here we knit ultrastable lock-and-key hydrogen-bonding networks between 2, 7-dinitropyrene-4, 5, 9, 10-tetraone (DNPT) and NH4 + charge carrier. DNPT with octuple-active carbonyl/nitro centers (H-bond acceptor) are redox-exclusively accessible for flexible tetrahedral NH4 + ions (H-bond donator) but exclude larger and rigid Zn2+ , due to a lower activation energy (0.14 vs. 0.31 eV). NH4 + coordinated H-bonding chemistry conquers the stability barrier of DNPT in electrolyte, and gives fast diffusion kinetics of non-metallic charge carrier. A stable two-step 4e- NH4 + coordination with DNPT cathode harvests a high capacity (320 mAh g-1 ), a high-rate capability (50 A g-1 ) and an ultralong life (60,000 cycles). This finding points to a new paradigm for H-bond stabilized organic small molecules to design advanced zinc batteries.

Covalent Organic Framework with Multiple Redox Active Sites for High-Performance Aqueous Calcium Ion Batteries

Organic materials are promising for cation storage in calcium ion batteries (CIBs). However, the high solubility of organic materials in an electrolyte and low electronic conductivity remain the key challenges for high-performance CIBs. Herein, a nitrogen-rich covalent organic framework with multiple carbonyls (TB-COF) is designed as an aqueous anode to address those obstacles. TB-COF demonstrates a high reversible capacity of 253 mAh g-1 at 1.0 A g-1 and long cycle life (0.01% capacity decay per cycle at 5 A g-1 after 3000 cycles). The redox mechanism of Ca2+/H+ co-intercalated in COF and chelating with C═O and C═N active sites is validated. In addition, a novel C═C active site was identified for Ca2+ ion storage. Both computational and empirical results reveal that per TB-COF repetitive unit, up to nine Ca2+ ions are stored after three staggered intercalation steps, involving three distinct Ca2+ ion storage sites. Finally, the evolution process of radical intermediates further elucidates the C═C reaction mechanism.

Application of New COF Materials in Secondary Battery Anode Materials

Covalent organic framework materials (COFs), as a new type of organic porous material, not only have the characteristics of flexible structure, abundant resources, environmental friendliness, etc., but also have the characteristics of a regular structure and uniform pore channels, so they have broad application prospects in secondary batteries. Their functional group structure, type, and number of active sites play a crucial role in the performance of different kinds of batteries. Therefore, this article starts from these aspects, summarizes the application and research progress of the COF anode materials used in lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries in recent years, discusses the energy storage mechanism of COF materials, and expounds the application prospects of COF electrodes in the field of energy storage.

Immobilizing Quinone-Fused Aza-Phenazine into π-d Conjugated Coordination Polymers with Multiple-Active Sites for Sodium-Ion Batteries

The development of coordination polymers with π-d conjugation (CCPs) provides ide prospects for exploring the next generation of environmental-friendliness energy storage systems. Herein, the synthesis, experimental characterizations, and Na-ion storage mechanism of π-d CCPs with multiple-active sites are reported, which use quinone-fused aza-phenazine (AP) and aza-phenazin (AP) as the organic ligands coordinated with the metal center (Ni2+ ). Among them, NiQAP as the cathode material exhibits impressive electrochemical properties applied in sodium-ion batteries (SIBs), including the high initial/stable discharge specific capacities (180.0/225.6 mAh g-1 ) at 0.05 A g-1 , a long-term cycle stability up to 10,000 cycles at 1.0 A g-1 with a high reversible capacity of 100.1 mAh g-1 , and good rate capability of 99.6 mAh g-1 even at 5.0 A g-1 . Moreover, the Na-ion storage mechanism of NiQAP is also performed by the density functional theory (DFT) calculation, showing multiple-active sites of C≐O and C≐N (in the quinone and phenazine structure) and NiO4 (in the coordination unit) for Na-ion storage. These results highlight the importance of organic electrode material with the coordination units and provide a foundation for further studying the CCPs with multiple active sites for energy storage systems.