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Open AccessCCS ChemistryMINI REVIEW30 May 2023

Recent Advances in Covalent Organic Framework Electrode Materials for Alkali Metal-Ion Batteries

    CCS Chemistry. 2023, 5, 1259–1276
    https://doi.org/10.31635/ccschem.023.202302808

    Owing to the shortcomings of traditional electrode materials in alkali metal-ion batteries (AIBs), such as limited reversible specific capacity, low power density, and poor cycling performance, it is particularly important to develop new electrode materials. Covalent organic frameworks (COFs) are crystalline porous polymers that incorporate organic building blocks into their periodic structures through dynamic covalent bonds. COFs are superior to organic materials because of their high designability, regular channels, and stable topology. Since the first report of DTP-ANDI-COF as a cathode material for lithium-ion batteries in 2015, research on COF electrode materials has made continuous progress and breakthroughs. This review briefly introduces the characteristics and current challenges associated with COF electrode materials. Furthermore, we summarize the basic reaction types and active sites according to the categories of covalent bonds, including B–O, C=N, C–N, and C=C. Finally, we emphasize the perspectives on basic structure and morphology design, dimension and size design, and conductivity improvement of COFs based on the latest progress in AIBs. We believe that this review provides important guidelines for the development of high-efficiency COF electrode materials and devices for AIBs.

    Introduction

    With the increasing demand for electronics and electric vehicles, electrochemical energy storage technology is expected to play a pivotal role in our daily lives.1–5 Since the first commercialization of lithium-ion batteries (LIBs) in 1990, alkali metal-ion batteries (AIBs), including LIBs, sodium-ion batteries (NIBs), and potassium-ion batteries (KIBs), have been extensively studied because of their advantages of high energy density, rechargeability, and environmental benignity.6–8 Nevertheless, the challenges of capacity fading and fast charging and discharging under high current densities remain.9–11 Electrode materials with high capacity, high rate capability, long cyclic stability, and low cost still must be explored.12–14 In comparison with conventional inorganic materials, such as transition metal oxides and alloy-based materials, organic materials possess a designable molecular architecture and are composed of lightweight elements that can be used as both positive and negative electrodes.15–17 Although organic electrode materials are very attractive, several issues, such as easy solubility in organic electrolytes based on the principle of compatibility, poor electronic conductivity, and low discharge voltage, hinder their commercial application.18,19

    As a new class of crystalline porous polymers, covalent organic frameworks (COFs) were first synthesized in 2005.20,21 Their regular network structures with strong covalent bonds effectively alleviated the issue of rapid dissolution of electrode materials and provided a new opportunity for the development of organic electrode materials.22 Subsequently, as illustrated in Figure 1a, the COF electrode material was first utilized as a cathode for LIBs in 2015, showing that they can undergo reversible redox reactions. Since then, various COF electrode materials have been investigated and reported for use in AIBs. Research on COF-based electrode materials has shown an upward trend from January 2019 to February 2023 (Figure 1b). COF electrode materials have been most studied in LIBs, based on the extensive research on LIBs (Figure 1c). Both COF cathode and anode materials have been reported (Figure 1d); however, due to their low discharge voltage, novel electrode materials with high performance are still highly desirable.

    Figure 1

    Figure 1 | (a) Timeline of COF electrode material in AIBs. Reprinted with permission from refs 23–28. Copyright 2015–2022 Springer Nature, Royal Society of Chemistry, Wiley-VCH, American Chemical Society. (b) The growing trend of COF electrode material in AIBs. (c) The research article number of the application of COF electrode material in AIBs. (d) The proportion of research papers published on LIBs, NIBs, and KIBs.

    In this mini review, we first summarize the main characteristics of COF electrode materials. We then list the reaction types and electrochemically active sites of COF electrode materials in AIBs developed in recent years. Subsequently, the latest developments in multifunctional COF electrode materials for AIBs are discussed in detail. Finally, the opportunities and challenges of basic and applied research on COF electrode materials are briefly analyzed. We believe that this review will bridge the gap between experimental research and future practical applications and provide valuable guidance for exploring efficient COF electrode materials in the field of energy storage.

    Merits and Issues of COFs as Electrode Materials

    Currently, COF synthesis is mainly achieved using solvothermal methods. By selecting appropriate building units, COFs can be successfully constructed into two-dimensional (2D) or three-dimensional (3D) structures.29–31 For AIBs, 2D COFs have been widely investigated. The main properties of 2D COFs as electrode materials are summarized in Figure 2.

    Figure 2

    Figure 2 | The inherent characteristics of COFs in rechargeable AIBs and major considerations as electrode materials.

    Periodically open channels

    COFs are usually prepared through the condensation of monomers to form stable ring structures with periodic open channels.32,33 These open channels facilitate ion transport and lower the energy barrier for ion diffusion, as well as endowing COFs with a high porosity and specific surface area,34,35 where the latter is beneficial to the exposure of the active sites of electrode materials.36 In addition, the covalently bonded structure can be finely tuned by virtue of monomer size selectivity, which is conducive to the transmission of alkali metal-ions with different sizes and the construction of multiple active sites in the framework, thereby achieving a large reversible specific capacity of the battery.

    However, a majority of the currently reported COF electrode materials have a 2D architecture similar to the layered structure of graphite. Excessive π–π interactions between COF layers cause the formation of bulky solids with long channels and poor conductivity, resulting in slow transport of electrolyte ions and electrons, making it difficult for ions and electrons to reach deeply buried active sites.22 Due to the particularity of organic reactions, COFs often possess some defects that also hinder electron conduction, leading to low utilization of active sites.37 Additionally, the excessive construction of active sites can easily lead to structural damage of electrode materials during charging and discharging and reduce the reversibility of the redox reaction, resulting in a rapid decline in battery capacity.38 Therefore, designing more active sites in COF electrode materials with stable structures is necessary. Considering long-term cycling stability, the existence of inactive linking groups is necessary.

    Designable covalent backbone

    Designable covalent skeletons are another advantage of COFs. During preparation, diverse frameworks can be designed at the molecular level by utilizing different monomers or different types of organic reactions.39,40 This is favorable for us anchoring different functional groups at preselected positions on the framework and provides COF electrode materials with preferentially designed redox sites.32,41,42 However, in the synthesis of COF materials, there are challenges that cannot be ignored, such as difficult monomer preparation, low crystallinity, long synthesis time, and complicated purification.

    As with most of the 2D COFs reported so far, the design and synthesis of some building units with 3D configurations can lead to the emergence of 3D COF materials with larger specific surface areas.43,44 Nonetheless, owing to the instability of the 3D architecture, there are few reports on these materials as electrodes in batteries.45,46 Constructing larger conjugated structures or weakening 2D overlapping layers can allow the adjustment of the overall electron distribution and thus the plateau voltage and conductivity of the battery.47 Furthermore, the structural design at the molecular level enables the material to have a special chemical structure, which is beneficial for analyzing the structural changes of the materials during the charging/discharging process of the battery, thereby assisting with in-depth analysis of the reaction mechanism. Clearly, the exploration and elucidation of the reaction mechanism can provide the possibility of designing more ideal electrode materials.

    Lightweight elements and insolubility

    Unlike ordinary electrode materials, COF electrode materials usually do not contain metal elements but are composed of lightweight elements such as C, N, H, O, and B.32,48 Lightweight elements reduce the density of the material, which is beneficial for increasing the energy density of the battery. Moreover, such elements are abundant in nature and are not influenced by metal resources, which would theoretically decrease the comparative cost of COF electrode materials.49 However, due to the requirement for long-range ordered covalent structures, to ensure excellent thermal and chemical stability, complex preparation and tedious purification processes are currently adopted, making the cost relatively high.50

    Unlike other small-molecule organic electrodes, COFs are insoluble, reducing their dissolution in organic electrolytes.49,51 However, their insolubility also leads to adverse effects on the commonly used binders for AIBs, which affects the electronic transportation between electrode materials and current collectors. When the mass loading of a COF electrode is increased, it becomes easy to peel off, resulting in the poor cycle stability of the battery. Moreover, the nature of insoluble powder crystals makes it difficult to determine the actual structure of COFs and the true content of the active groups. Consequently, it is difficult to analyze the utilization rate and mechanism of the active groups.

    Low conductivity

    COF electrodes usually suffer from low electronic conductivity, preventing batteries from achieving advanced rate performance.52 Since the π–π stacking interaction can significantly improve the conductivity of 2D COFs, constructing larger conjugated structures has become another common method besides the recombination with conductive substrates.53,54 Nonetheless, excessive stacking is not conducive to the exposure of active sites.55 In contrast, some nonplanar architectures, such as the random conformation of amine structures and the nonplanar orientation of sp3 C, can affect the extension of the conjugated structure and hinder charge transfer. Therefore, they are usually limited to a few delocalized aromatic structures.49

    Overview of COFs as Electrode Materials in AIBs

    As mentioned above, COFs have attracted the attention of researchers because of their inherent channelability, designability, insolubility, and use of lightweight elements. In particular, their diversity at the molecular level has been extensively studied, and various COF electrodes have been reported successively.39,56 To further design electrode materials suitable for AIBs with high specific capacity, advanced rate performance, and long-term cyclic stability, in-depth studies on their electrochemically active sites have become the focus.50,57,58 In this section, we systematically summarize the recently reported active organic groups for COF electrodes and their design principles, as well as synthesis strategies for AIBs.

    Electrochemically active sites in COFs

    COF electrodes enable charge storage through the combination of positive/negative charges and active groups for redox reactions during the charging/discharging process.59 According to the redox-active groups, the currently reported COFs can generally be classified into borates, borazines, triazines, imines and enamines, imides, ketoenamines, and hexazines.37,60–62 Figure 3 shows the COF electrodes in the research of AIBs in recent years.

    Figure 3

    Figure 3 | The structures of COF electrodes employed in the research on AIBs during past years.

    The bonding structures of COFs have been widely studied and can be roughly divided into boron-based63–65 (boroxine and boronate), amine-based66–68 (Schiff bases, imides, and ketoenamides), triazine-based,69 and sp2 (C=C) linkages.70,71 The formation of B–O involves the dehydration and condensation of phenylboronic acid; however, this is easily hydrolyzed, leading to structural instability.72 Therefore, it has been the subject of relatively few recent studies in the field of energy storage. The formation of C=N is most commonly achieved through condensation of aldehydes and amines. It follows a dynamic reversible reaction for continuous repair to increase crystallinity.73–75 Due to their excellent stability, imine-based COFs have been the most investigated. C–N often exists in the imide structure obtained through the condensation of aromatic amine and phthalic anhydride.76 Such COFs are stable but difficult to prepare.77 In addition to C–N units, covalent triazine frameworks (CTFs) obtained by cyanide polymerization contain C=N units.78 The formation of C=C bonds is generally through the Knoevenagel reaction, which helps to further expand the conjugated structure, thereby improving the conductivity.79 C=O groups mainly exist in organic compounds such as quinones, acid anhydrides, and ketones, which can be introduced into COFs as building blocks. Through research on the mechanism of charging and discharging in batteries, it was found that C=N and C=O are typical active sites (Table 1), formed through the interaction of O and N with alkali metal-ions (Li+, Na+, and K+). Although the benzene skeleton can be used as the active site in a specific structure, in most cases, it is considered as an inactive component to connect the active group to ensure the stability of the architecture.50 It is worth noting that hexaazatrinaphthalene (HATN) structures have been widely studied because their conjugated structures and high-density C=N groups are beneficial for improving the specific capacity of the battery.

    Table 1 | Electrochemically Active Sites Involved in AIBs
    Type Sample Active Site Battery References
    Boron-based linkage PPTODB COFCOF-10 C=OBenzene LIBs 80
    KIBs 28
    Amine-based linkage COF TPDA-PMDAUSTB-6PGF COFHAB-COFHATN-HHTPPICOF-1MPc-2D-cCOFAza COFP-COFTAEB-COF C=O & benzeneC=N & C=OC=NC=NC=NC=OC=NC=NC=O & benzeneC=N & alkynyl LIBsLIBsLIBsLIBsLIBsNIBsNIBsNIBsKIBsKIBs 81
    82838485868788
    89
    90
    Triazine-based linkage DCB-COF-450CTF-2 triazinetriazine & benzene LIBsLIBs 9192
    Sp2 (C=C) linkage TFPPy-ICTO-COF C=O LIBs 93

    Current design principles and synthesis strategies

    To improve the specific capacity, cycle stability, and rate capability of batteries, diverse strategies for synthesizing and modifying COFs have been proposed, such as chemical structure and morphology design, dimensionality and size design, and conductivity enhancement.94 The following is a systematic overview of the recent exploratory work done.

    Chemical structure and morphology design

    To develop multiple active sites or improve the utilization of active sites, innovation in monomer design and synthesis methods becomes the primary goal. The excellent stability of the rigid triazine linker unit and its benzene ring can provide rich active sites for high-capacity lithium storage, making CTFs an attractive electrode material for LIBs.95 In 2022, in order to solve the problems of poor structural stability and low capacity, Jiang et al.92 synthesized biphenyl-based CTFs (CTF-2) for the first time as a LIB anode (Figure 4a,b). In the study, CTF-2 showed a superlithiation of 13.2 Li+ insertions per repeat unit, which is different from the Li+ insertions into benzene rings previously shown by Fourier transform infrared (FTIR) spectroscopy, thus demonstrating high lithium storage capacity. To obtain an anode for LIBs with excellent rate performance, Wu et al.97 designed a piperazine-terephthalaldehyde (PA-TA) COF with superlayer spacing. Owing to the tetrahedral piperazine unit, the PA-TA COF exhibited fast ion/electron transport and delivered a specific capacity of 207 mAh g−1 even at a high current density of 5.0 A g−1 (Figure 4c,d).

    Figure 4

    Figure 4 | (a) Schematic illustration of CTF-2 and (b) the color-mapped profiles of in situ FTIR spectra. Reprinted with permission from ref 92. Copyright 2022 Elsevier. (c) Schematic and (d) rate performance of PA-TA COF. (e) Simulated packing structure of MPc-2D-cCOFs. (f) Representation of the interaction between Na-ions and CuPc-2D-cCOF. (g, h) Electrochemical performance of as-synthetized MPc-2D-cCOFs and reference electrode. Reprinted with permission from ref 87. Copyright 2022 Springer Nature. (i) Schematic illustration of the construction of FAC-Pc-COFs. (j) Structural evolution during the potassiation process and (k) long cycling stability of QPP-FAC-Pc-COF//PTCDA@450 potassium-ion full battery at 2 A g−1. Reprinted with permission from ref 96. Copyright 2022 Wiley-VCH.

    N-rich phthalocyanine (Pc) units partially fused with benzene can be used to synthesize complete π-conjugated COF electrode materials with good rate capabilities and excellent cycle stabilities. For example, Yang et al.23,96 successfully designed a series of COF electrode materials by preenrichment of N and conjugated pyrrole, such as MPc-2D-cCOF (M = Cu, Fe, Co, and Ni; Figure 4e) as the anode for NIBs, and BB-FAC-Pc-COF and QPP-FAC-Pc-COF (Figure 4i) as the anode for KIBs. The results show that Na+ can be stored through the interaction of N···Na and Na–π, and all MPc-2D-cCOF samples showed excellent sodium storage performance (Figure 4f–h). Similarly, in KIBs, K+ gradually interacts with C=N and benzene rings to produce K···N and K–π (Figure 4j). In addition, a QPP-FAC-Pc COF//PTCDA@450 organic potassium-ion full battery was constructed to further explore K+ storage performance. Even at a high current density of 2 A g−1, the assembled full cell maintained a reversible capacity of 125 mAh g−1 after 1000 cycles (Figure 4k).

    In recent years, some polyimide-based COFs have been repeatedly synthesized; however, it is often difficult to obtain COFs with high crystallinity due to the rapid reaction between monomers and the poor reversibility of the reaction. To improve the crystallinity, the reaction-solvent ratio and temperature are often modulated for optimization.98 Based on the discovery that the addition of water promotes the reversibility of the polyimidization reaction, Yao et al.81 designed a water-assisted fabrication strategy to regulate the reaction rate of polyimidization. Their work reported the successful synthesis of COFTPDA-PMDA through N,N,N',N'-tetra (4-aminophenyl)-1,4-phenylenediamine (TPDA) and pyromellitic dianhydride (PMDA) ligands. The COF has an ordered layered porosity, including triangular micropores (1.2 nm) and hexagonal mesopores (2.7 nm) (Figure 5a). This unique architecture helps Li+ and TFSI– to fully interact with the active sites on the COF backbone (Figure 5b). COFTPDA-PMDA is a carbonyl compound that balances the negative charge of the COF electrode by the movement of Li+. A typical n-type working principle is shown based on the charged state in the redox process. Furthermore, the synergistic effect of the C=N and C=O redox groups expands the operating voltage of COFTPDA-PMDA and increases the specific capacity of the cathode materials for LIBs.

    Figure 5

    Figure 5 | (a) Synthesis and (b) mechanism during the reversible electrochemical process of COFTPDA-PMDA. Reprinted with permission from ref 81. Copyright 2022 American Chemical Society. (c) Redox mechanism of PICOF-1 with sodium and (d) charge-discharge profiles of potential versus capacity at 23 mA g−1. Reprinted with permission from ref 86. Copyright 2023 Wiley-VCH. (e) Schematic illustration of the preparation and charge-discharge mechanism of S@TAPA-COFs and (f) cycling performance comparison. Reprinted with permission from ref 99. Copyright 2023 Elsevier.

    Moreover, Shehab et al.86 improved the crystal stability of polyimide COFs through a typical condensation reaction based on joint exchange. A porous polyimide COF (PICOF-1) was synthesized by linker exchange using imine-linked COF as a template. The abundant carbonyl groups in this COF backbone demonstrate the n-type working principle and are used as redox active sites for charge storage (Figure 5c). As a result, the reversible capacity was approximately 230 mAh g−1, which is the same as the theoretical specific capacity of PICOF-1 (Figure 5d). Postsynthetic modification is a technique that can introduce desired functionalities into COFs to improve their performance. Because sulfur has a larger atomic radius than oxygen, it can significantly alter electron mobility, thus improving battery performance.100 In 2023, Shi et al.99 achieved the conversion of C=O to C=S bonds through a synthetic modification strategy (Figure 5e), which further alleviated the solubility problem of electrode materials and enhanced the activity of COFs based on the more active C=S bonding with sodium. Therefore, in terms of cycle capacity (Figure 5f), the postvulcanized TAPT-COF (TAPT = 2,4,6-tris(4-aminophenyl)-1,3,5-triazine) hybrid showed the highest capacity among the NIBs.99

    The imine group (C=N) is one of the typical active sites of COFs for alkali metal-ion storage. The design of high-density imine groups can effectively improve the theoretical specific capacities of the batteries. For the first time, Zhao et al.84 synthesized a COF (HAB-COF) via the condensation reaction of hexaaminobenzene trihydrochloride (HAB·3HCl) and terephthalaldehyde (Td). Notably, benefiting from the synergistic effect of the conjugated structure of HAB-COF and the high density of the C=N group, the HAB-COF electrode exhibited a high reversible capacity and excellent cycle life (1255 mAh g−1 at 1 A g−1 after 1100 cycles) (Figure 6a,b). The HATN unit, a typical component of high-density imine groups, is also a common cathode material with a high theoretical capacity. Given the solubility problem of HATN, Li et al.85 first designed ether bonds to combine with HATN units to improve the structural stability of the positive electrode HATN-hexahydroxytriphenylene (HHTP) (Figure 6c). Subsequently, carbon nanotubes (CNTs) were doped to guide the growth to obtain a few layers of COFs, which can improve the conductivity of COFs while exposing more active sites. The cathode material, HATN-HHTP@CNT, showed a reversible capacity close to its theoretical value (231 mAh g−1) in AIBs (Figure 6d,e). At a current density of 2 A g−1, HATN-HHTP@CNT retained a capacity of 130 mAh g−1, which was 60% of the value at 50 mA g−1 (Figure 6d).

    Figure 6

    Figure 6 | (a) Structure and (b) the cycling performance at 1 A g−1 of HAB-COF. Reprinted with permission from ref 84. Copyright 2022 Springer Nature. (c) Architecture and electrochemical redox mechanism of HATN-HHTP. (d) Rate performance of HATN-HHTP and HATN-HHTP@CNT in LIBs. (e) Galvanostatic discharge-charge curves of HATN-HHTP@CNT in KIBs. Reprinted with permission from ref 85. Copyright 2022 Elsevier. (f) Schematic illumination, (g) TEM image, and (h) cycling performance at 100 mA g−1 of Sn@COF-hollow composite. Reprinted with permission from ref 101. Copyright 2022 Elsevier.

    Controlling the morphology of COF materials to achieve the exposure of internal active sites is another effective strategy to optimize the performance of AIBs. Based on the tin–nitrogen (Sn–N) coordination interaction and amino-modified SiO2 template strategy (Figure 6f), Tang et al.101 synthesized a Sn@COF hollow electrode for LIB anodes. Sn@COF displayed a hollow microsphere structure with a shell thickness of ∼20 nm, as confirmed by transmission electron microscopy (TEM) (Figure 6g); this promoted ion/electron transport and offered more sites for lithium reactions involving activated aromatic C=C groups and Sn ions. The Sn@COF electrode achieved a high capacity of 1080 mAh g−1 after 100 cycles at 100 mA g−1 (Figure 6h).

    In summary, by controlling the synthetic conditions and selection of monomers, the structure and morphology of COFs can be effectively manipulated, thereby regulating the number and utilization of active sites, which is conducive to obtaining excellent AIB performance.

    Dimension and size design

    In general, apart from designing a structure with multiple active sites, boosting the utilization of active sites can considerably increase the specific capacity of the battery. Therefore, researchers enhanced the specific surface area and accelerated ion diffusion by changing the dimension and size of the material to help improve the utilization of the active sites.43,50 Chen et al.102 first constructed all-π-conjugated 3D PYTRI-COFs (PYTRI-COF = imine-based “[3 + 4]” 3D COF) containing triazine and pyrazine (Figure 7a) and then introduced vinyl units into the framework structure to provide multiple active sites for ion adsorption, demonstrating excellent lithium storage performance. The specific surface areas of PYTRI-COF-1 and PYTRI-COF-2, determined by N2 adsorption–desorption analysis, were 894 and 317 m2 g–1, respectively (Figure 7b,c). Owing to the exposure of the active sites and the improved conductivity of the fully conjugated architecture, PYTRI-COF-2 exhibited an excellent cycle stability of 227.3 mAh g–1 after 450 cycles (Figure 7d). In striking contrast, PYTRI-COF-1, with relatively low chemical stability and π-coupling, displayed very fast capacity decay.

    Figure 7

    Figure 7 | (a) Structures and (b, c) N2 adsorption–desorption isotherms of PYTRI-COF-1 and PYTRI-COF-2. (d) Cycling performance of PYTRI-COF-1 and PYTRI-COF-2. Reprinted with permission from ref 102. Copyright 2022 American Chemical Society. (e) Schematic illustration of CON-UV-1. (f) The comparison of COF-935, CON-UV-0.5, CON-UV-1, CON-UV-2, and CON-UV-33. (g) Mechanistic study of CON-UV-1. Reprinted with permission from ref 103. Copyright 2022 Elsevier.

    The efficient exfoliation of COFs to expose their buried active sites has been the focus of much research on electrode materials. Various exfoliation techniques have been reported, such as self-exfoliation, liquid-assisted exfoliation, mechanical exfoliation, and chemical exfoliation.22,104 Among these approaches, chemical exfoliation is prominent because it can introduce new functional units and has a higher degree of structural retention than mechanical exfoliation. In 2023, Wang et al.103 designed and synthesized a new 2D COF (COF-935). In oligo(phenylene vinylidene) (OPV)-based 2D COF, thiols can be added to the vinylene units of OPV under ultraviolet irradiation, known as thiol-alkene reactions, enabling COF-935 to be successfully exfoliated into a covalent organic nanosheet (CON) (Figure 7e). By exploring the feed ratios (repeating unit:monothioglycerol = 1:0.5, 1:1, 1:2, and 1:33), it was found that CON-UV-1 had a reasonable π-conjugated layer and exhibited fast charge transfer and rich reaction sites for optimal lithium storage performance (Figure 7f,g).

    Recently, exfoliation strategies have been reported in the study of COF electrode materials for NIBs and KIBs. In 2019, Zhang et al.105 introduced fluorine atoms into CTF to obtain 2D-layered fluorinated CTF (FCTF) and its stripped few-layer product (E-FCTF) and studied its electrochemical performance as an NIB anode (Figure 8a). The introduction of highly electronegative fluorine atoms can effectively adjust the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels, enhance the chemical stability of CTF, and provide the possibility for ball-milling exfoliation. According to the results of atomic force microscopy (AFM), the average thickness of the obtained E-FCTF layer structure was 4.2 nm (Figure 8b,c). The E-FCTF anode exhibited a charge capacity of 220 mAh g–1 after 200 cycles (Figure 8d).

    Figure 8

    Figure 8 | (a) Synthesis of FCTF and E-FCTF. (b, c) Thickness profile of AFM image of E-FCTF. (d) Cycling performance of E-FCTF and FCTF at 0.1 A g–1. Reprinted with permission from ref 105. Copyright 2019 American Chemical Society. (e) Schematic structure of COF-Co. (f) Cycling performance of COF and COF-Co at 100 mA g–1. Reprinted with permission from ref 106. Copyright 2021 American Chemical Society.

    In 2021, Zhao et al.106 designed a few-layer COF material (COF-Co) as the anode material for KIBs based on the characteristic that cyanide groups can bond with Co (Figure 8e). The introduction of Co produces abundant defects, changes the π-electron architecture of the benzene ring, and promotes the π–K+ effect. Consequently, COF-Co exhibited an improved cycle capacity (371 mAh g–1 after 400 cycles at 100 mA g–1), which benefited from the utilization of interlayer active sites after stripping (Figure 8f). These exfoliation-related studies provide feasible strategies for the effective utilization of the active sites of COFs and promote their application in energy storage.

    Conductivity enhancement

    Conductivity has always been an important consideration for electrode materials, and the development of COF electrode materials has been hindered by their poor conductivity. Conjugated structure design and the introduction of conductive media, such as graphene, reduced graphene oxide, polyethylene dioxythiophene, and CNTs, are common methods of improving COF electrode materials.32,107 Recently, Xu et al.93 found that olefin-connected COFs have excellent photoelectric properties because of their excellent stability and complete conjugated architecture. Conductive olefin-connected COFs have never been attempted in the field of electrode materials. Therefore, new Janus dione-based COFs (TFPPy-ICTO-COF and TFPPer-ICTO-COF) were designed and synthesized (Figure 9a). COFs linked by olefin bonds have abundant accessible carbonyl groups, which are the most common active groups in cathode material research. Owing to their fully conjugated structures, their conductivity reached the order of 10−3 S cm−1, as measured by a four-point probe (Figure 9b), exceeding those of most reported COFs. Furthermore, the polarity of the field-dependent Hall resistance plots indicates that both the COFs were p-type semiconductors (Figure 9c). Intriguingly, the experimental capacity of TFPPer-ICTO-COF was 303 mAh g–1 at 0.1 A g–1 (Figure 9d). According to the computed theoretical capacity, the redox active site utilization rate of TFPPer-ICTO-COF was as high as 89%, and the comprehensive performance outperformed that of the typical COF electrodes previously reported (Figure 9e).

    Figure 9

    Figure 9 | (a) Design and synthesis of Janus dione-based COFs. (b) Temperature-dependent current plots of pressed pellets, (c) field-dependent Hall resistance plots, and (d) rate performances. (Note that black circle is TFPPy-ICTO-COF, and red circle is TFPPer-ICTO-COF.) (e) Overall performance comparison of TFPPy-ICTO-COF (red curve), TFPPer-ICTO-COF (blue curve), HATN-AQ-COF (yellow curve), PIBN-G (purple curve), and PT-COF50 (green curve). Reprinted with permission from ref 93. Copyright 2023 American Chemical Society. SEM images of (f) USTB-6 and (g) USTB-6@G. (h) Nyquist plots and (i) cycling performance at 2 C (1 C = 272 mA g−1) of USTB-6@G, USTB-6/G, and USTB-6. Reprinted with permission from ref 82. Copyright 2022 Wiley-VCH. (j) The Fourier-filtered HRTEM image of PGF-1. Inset is a modeled partial structure of PGF-1. (k) Schematic diagram of the structure of PGF-1. (l) Voltage-capacity plot of the PGF-1 cathode at different current densities. Reprinted with permission from ref 83. Copyright 2020 Elsevier.

    Conductive graphene and CNTs are widely employed as conductive media, especially in COF materials, because they improve the conductivity and guide the growth of COFs to form lamellar and tubular morphologies. For example, Liu et al.82 reported a COF (USTB-6) grown on graphene (USTB-6@G) applied to the cathode of LIBs. As revealed by scanning electron microscopy (SEM) (Figure 9f,g), agglomerated nanoparticles were observed in USTB-6, whereas USTB-6@G presented nanoslices. As expected, electrochemical impedance spectroscopy (EIS) demonstrated the lower resistance and better diffusion property of USTB-6@G (Figure 9h). After the in situ growth of USTB-6 on the graphene surface, USTB-6@G exhibited a higher lithium storage capacity (198 mAh g–1) than pristine USTB-6 (Figure 9i). Based on the discovery of the dynamic reversibility of the C=N bonds in the pyrazine ring, Li et al.83 successfully adjusted the energy band structure and synthesized a porous graphite framework (PGF) with ∼1.2 nm ordered hexagonal micropores (Figure 9j,k). Benefiting from its high conductivity and HATN structure with abundant active sites, PGF-1 showed 480 and 189 mAh g−1 at high current densities of 500 and 5000 mA g−1, respectively, when used as a LIB cathode (Figure 9l).

    Due to the slow ion diffusion kinetics resulting from the 2D dense layer architecture, CNTs have been used to grow COFs and improve the conductivity and utilization of active sites. In 2022, Yang et al.108 controlled the growth of COF layers with different thicknesses on CNTs to accelerate Li+ diffusion kinetics and obtain corresponding large capacities (Figure 10a). According to EIS, the charge transfer resistance of TPDA-COF was determined to be 423 Ω by fitting, whereas those of COF@CNT-1 and COF@CNT-2 decreased to 301 and 118 Ω, respectively (Figure 10b). In the same year, Duan et al.24 constructed several layers of DAAQ-COF (DAAQ = 2,6-diaminoanthraquinone) on CNTs (DAAQ-COF@CNT) as the cathode in KIBs (Figure 10c). TEM images at different magnifications showed that DAAQ-COF with a thickness of 3–8 nm grows uniformly on CNTs (Figure 10d). According to galvanostatic intermittent titration technique calculations, the diffusion coefficient of K+ in the composite material increased after the introduction of CNTs (Figure 10e). The discharge capacity of the DAAQ-COF@CNT was 111.2 mAh g−1 at 1 A g−1. When the current density returned to 0.1 A g−1, the capacity of DAAQ-COF@CNT also recovered to 99.4%, indicating an advanced rate performance after the introduction of CNTs (Figure 10f). Moreover, Luo et al.89 prepared polyimide COF (P-COF) by in situ condensation on single-walled CNTs and then peeled it off by ball milling it to obtain a composite material (P-COF@SWCNT) as the anode for KIBs. It is shown that K+ can be reversibly inserted in and extracted from the C=O and benzene ring structures, as demonstrated in Figure 10g. The enhanced conductivity of P-COF@SWCNT promoted electron/ion migration, leading to greater capacitance (Figure 10h,i). At 0.7 A g−1, the capacity retention rate of the P-COF@SWCNT after 1400 cycles was 55.9% (Figure 10j).

    Figure 10

    Figure 10 | (a) Preparation scheme of the COF@CNT composite and (b) AC-impedance measurements of the TPDA-COF (blue), COF@CNT-1 (yellow), and COF@CNT-2 (cyan) anode materials. Reprinted with permission from ref 108. Copyright 2022 Royal Society of Chemistry. (c) Schematic illustration and (d) TEM images of DAAQ-COF@CNT. (e) Calculated DK+ and (f) rate performance of DAAQ-COF and DAAQ-COF@CNT. Reprinted with permission from ref 24. Copyright 2022 American Chemical Society. (g) Schematic diagram of the proposed K+ storage mechanism (grey for carbon, red for oxygen, white for hydrogen, and purple for potassium). (h) EIS spectra of P-COF and P-COF@SWCNT. (i) Capacitive-controlled contribution ratios and (j) cycle performance of P-COF@SWCNT at 0.7 A g−1. Reprinted with permission from ref 89. Copyright 2022 Wiley-VCH.

    Conclusions and Perspectives

    In summary, we reviewed the history and latest progress of COFs as anode and cathode materials for AIBs (LIBs, NIBs, and KIBs). Through the analysis of the characteristics of COFs, it was found that their open channels, high porosity and specific surface area, designable covalent structure, lightweight elements, and insolubility show their unique advantages as electrode materials. Nevertheless, the impact of these properties on the electrode materials is complicated. Low electronic conductivity, low discharge voltage, and low utilization of active sites are disadvantages that cannot be ignored for energy storage materials. Thus far, a variety of active organic groups have been confirmed, such as C=N, C=O, and benzene rings. In particular, C=O, which is commonly found in imides, quinones, and anhydrides, has attracted extensive attention from cathode material researchers, owing to its high working voltage (∼2.5 V vs Li/Li+). In most cases, the existence of some inactive groups that connect active groups in organic matter ensures structural stability, but this is not always the case. For example, the benzene skeleton can play an active role under special conditions, and its storage mechanism is still being explored.

    At present, to improve the electrochemical performance of batteries, various structural design strategies, such as monomer design and dimension regulation, as well as material modification strategies, such as conductive medium compounding, are constantly being explored.48 The synthesis of novel COF structures is the most direct means of solving the problems of battery capacity and rate performance. Among the reported studies, HATN enriched with a high density of C=N is highly attractive. Notably, the rational design of C=O-rich structures may create novel and effective cathode materials.

    Compared with the widely studied 2D COF materials, 3D COF materials are rarely used as electrode materials due to the lack of proper building units and crystallization problems.109,110 However, their richer network structure may expose more active sites. By designing monomers with multiple active sites or introducing functional groups after synthesis, more high-efficiency 3D COF-based AIB electrode materials can be prepared.

    In addition, the enhancement of the conductivity of COFs usually depends on the conjugated structure and the composition of the conducting medium.111 The newly reported olefin- and carbonyl-rich COFs (TFPPer-ICTO-COF) broaden the category of organic framework compounds and provide new expectations for electron conduction.93 The olefin-rich and high-density imide-based architectures may also have satisfactory rate performance and long-term cycle stability. Therefore, it is expected to create new building blocks and synthetic routes to realize COF electrode materials with improved electronic conductivity and excellent AIB performance.

    In situ and operando techniques are crucial for monitoring the alkali metal-ion storage reaction process of COF electrode materials. Specifically, the change in the reaction potential, expansion/contraction of the bond length, detailed reaction process, and relevant electrochemical environment (temperature, crystallinity, etc.) are the main concerns in the research. Equally important, the combination of theoretical simulation techniques and experimental investigations will help determine appropriate COF building units and framework structures, which will accelerate the research progress of COFs for AIBs.

    COF electrode materials are becoming increasingly important for the study of large-scale energy storage systems. The conductivity and operating voltage range are pivotal issues that require further research for the development of high-efficiency COF-based AIBs. We hope that this review can inspire researchers to rationally design and fabricate COF electrode materials with superior AIB performance. Undoubtedly, there will be rapid development in this field, and further optimization will endow COF electrode materials with the potential for commercial application.

    Conflict of Interest

    There is no conflict of interest to report.

    Acknowledgments

    This work was supported by the National Natural Science Foundation of China (grant no. 22179063). Q.Z. gratefully acknowledges the funding support from the City University of Hong Kong (grant nos. 9380117, 7005620, and 7020040) and Hong Kong Institute for Advanced Study, City University of Hong Kong, Hong Kong, China.

    References

    • 1. Hosaka T.; Kubota K.; Hameed A. S.; Komaba S.Research Development on K-Ion Batteries.Chem. Rev.2020, 120, 6358–6466. Google Scholar
    • 2. Manthiram A.An Outlook on Lithium Ion Battery Technology.ACS Cent. Sci.2017, 3, 1063–1069. Google Scholar
    • 3. Li M.; Lu J.; Chen Z.; Amine K.30 Years of Lithium-Ion Batteries.Adv. Mater.2018, 30, 1800561. Google Scholar
    • 4. Xie C.; Guo Y.; Zheng Z.Pushing the Limit of Flexible Batteries.CCS Chem.2023, 5, 531–543. Link, Google Scholar
    • 5. Zhan X.; Chen Z.; Zhang Q.Recent Progress in Two-Dimensional COFs for Energy-Related Applications.J. Mater. Chem. A2017, 5, 14463–14479. Google Scholar
    • 6. Liu H.; Cheng X.-B.; Huang J.-Q.; Kaskel S.; Chou S.; Park H. S.; Zhang Q.Alloy Anodes for Rechargeable Alkali-Metal Batteries: Progress and Challenge.ACS Materials Lett.2019, 1, 217–229. Google Scholar
    • 7. Zhang W.; Xie Z.; Zheng M.; Hu H.; Xiao Y.; Liu Y.; Liang Y.A General Strategy for Metal Compound Encapsulated into Network-Structured Carbon as Fast-Charging Alkali-Metal Ion Battery Anode.Energy Storage Mater.2020, 29, 300–309. Google Scholar
    • 8. Tong Y.; Sun Z.; Wang J.; Huang W.; Zhang Q.Covalent Organic Framework Containing Dual Redox Centers as an Efficient Anode in Li-Ion Batteries.SmartMat2022, 3, 685–694. Google Scholar
    • 9. Porzio J.; Scown C. D.Life-Cycle Assessment Considerations for Batteries and Battery Materials.Adv. Energy Mater.2021, 11, 2100771. Google Scholar
    • 10. Zhang T.; Chen Q.; Li X.; Liu J.; Zhou W.; Wang B.; Zhao Z.; Li W.; Chao D.; Zhao D.Redox Mediator Chemistry Regulated Aqueous Batteries: Insights into Mechanisms and Prospects.CCS Chem.2022, 4, 2874–2887. Link, Google Scholar
    • 11. Zhang Z.; Hu Q.; Liao J.; Xu Y.; Duan L.; Tian R.; Du Y.; Shen J.; Zhou X.Uniform P2-K0.6CoO2 Microcubes as a High-Energy Cathode Material for Potassium-Ion Batteries.Nano Lett.2023, 23, 694–700. Google Scholar
    • 12. Xu J.; Dou Y.; Wei Z.; Ma J.; Deng Y.; Li Y.; Liu H.; Dou S.Recent Progress in Graphite Intercalation Compounds for Rechargeable Metal (Li, Na, K, Al)-Ion Batteries.Adv. Sci.2017, 4, 1700146. Google Scholar
    • 13. Lin Z.-Q.; Xie J.; Zhang B.-W.; Li J.-W.; Weng J.; Song R.-B.; Huang X.; Zhang H.; Li H.; Liu Y.; Xu Z. J.; Huang W.; Zhang Q.Solution-Processed Nitrogen-Rich Graphene-like Holey Conjugated Polymer for Efficient Lithium Ion Storage.Nano Energy2017, 41, 117–127. Google Scholar
    • 14. Ji B.; Yao W.; Zheng Y.; Kidkhunthod P.; Zhou X.; Tunmee S.; Sattayaporn S.; Cheng H.-M.; He H.; Tang Y.A Fluoroxalate Cathode Material for Potassium-Ion Batteries with Ultra-Long Cyclability.Nat. Commun.2020, 11, 1225. Google Scholar
    • 15. Zhao-Karger Z.; Gao P.; Ebert T.; Klyatskaya S.; Chen Z.; Ruben M.; Fichtner M.New Organic Electrode Materials for Ultrafast Electrochemical Energy Storage.Adv. Mater.2019, 31, 1806599. Google Scholar
    • 16. Yang Y.; Chu X.; Zhang H.-Y.; Zhang R.; Liu Y.-H.; Zhang F.-M.; Lu M.; Yang Z.-D.; Lan Y.-Q.Engineering β-Ketoamine Covalent Organic Frameworks for Photocatalytic Overall Water Splitting.Nat. Commun.2023, 14, 593. Google Scholar
    • 17. Zhang W.; Huang W.; Zhang Q.Organic Materials as Electrodes in Potassium-Ion Batteries.Chem. Eur. J.2021, 27, 6131–6144. Google Scholar
    • 18. Chang J.-N.; Li Q.; Shi J.-W.; Zhang M.; Zhang L.; Li S.; Chen Y.; Li S.-L.; Lan Y.-Q.Oxidation-Reduction Molecular Junction Covalent Organic Frameworks for Full Reaction Photosynthesis of H2O2.Angew. Chem. Int. Ed.2023, 62, e202218868. Google Scholar
    • 19. Lu Y.; Zhang Q.; Li L.; Niu Z. Q.; Chen J.Design Strategies Toward Enhancing the Performance of Organic Electrode Materials in Metal-Ion Batteries.Chem2018, 4, 2786–2813. Google Scholar
    • 20. Wang H.; Zeng Z.; Xu P.; Li L.; Zeng G.; Xiao R.; Tang Z.; Huang D.; Tang L.; Lai C.; Jiang D.; Liu Y.; Yi H.; Qin L.; Ye S.; Ren X.; Tang W.Recent Progress in Covalent Organic Framework Thin Films: Fabrications, Applications and Perspectives.Chem. Soc. Rev.2019, 48, 488–516. Google Scholar
    • 21. Tao S.; Jiang D.Covalent Organic Frameworks for Energy Conversions: Current Status, Challenges, and Perspectives.CCS Chem.2020, 3, 2003–2024. Google Scholar
    • 22. Li J.; Jing X.; Li Q.; Li S.; Gao X.; Feng X.; Wang B.Bulk COFs and COF Nanosheets for Electrochemical Energy Storage and Conversion.Chem. Soc. Rev.2020, 49, 3565–3604. Google Scholar
    • 23. Shi R. J.; Liu L. J.; Lu Y.; Wang C. C.; Li Y. X.; Li L.; Yan Z. H.; Chen J.Nitrogen-Rich Covalent Organic Frameworks with Multiple Carbonyls for High-Performance Sodium Batteries.Nat. Commun.2020, 11, 178. Google Scholar
    • 24. Duan J.; Wang W.; Zou D.; Liu J.; Li N.; Weng J.; Xu L. P.; Guan Y.; Zhang Y.; Zhou P.Construction of a Few-Layered COF@CNT Composite as an Ultrahigh Rate Cathode for Low-Cost K-Ion Batteries.ACS Appl. Mater. Interfaces2022, 14, 31234–31244. Google Scholar
    • 25. Xu F.; Jin S.; Zhong H.; Wu D.; Yang X.; Chen X.; Wei H.; Fu R.; Jiang D.Electrochemically Active, Crystalline, Mesoporous Covalent Organic Frameworks on Carbon Nanotubes for Synergistic Lithium-Ion Battery Energy Storage.Sci. Rep.2015, 5, 8225. Google Scholar
    • 26. Bai L. Y.; Gao Q.; Zhao Y. L.Two Fully Conjugated Covalent Organic Frameworks as Anode Materials for Lithium Ion Batteries.J. Mater. Chem. A2016, 4, 14106–14110. Google Scholar
    • 27. Liu J. J.; Lyu P.; Zhang Y.; Nachtigall P.; Xu Y. X.New Layered Triazine Framework/Exfoliated 2D Polymer with Superior Sodium-Storage Properties.Adv. Mater.2018, 30, 1705401. Google Scholar
    • 28. Chen X.; Zhang H.; Ci C.; Sun W.; Wang Y.Few-Layered Boronic Ester Based Covalent Organic Frameworks/Carbon Nanotube Composites for High-Performance K-Organic Batteries.ACS Nano2019, 13, 3600–3607. Google Scholar
    • 29. Wei C.; Tan L.; Zhang Y.; Zhang K.; Xi B.; Xiong S.; Feng J.; Qian Y.Covalent Organic Frameworks and Their Derivatives for Better Metal Anodes in Rechargeable Batteries.ACS Nano2021, 15, 12741–12767. Google Scholar
    • 30. El-Kaderi H. M.; Hunt J. R.; Mendoza-Cortés J. L.; Côté A. P.; Taylor R. E.; O’Keeffe M.; Yaghi O. M.Designed Synthesis of 3D Covalent Organic Frameworks.Science2007, 316, 268–272. Google Scholar
    • 31. Shi Y.; Yang J.; Zhang Q.Covalent Organic Frameworks: Recent Progress in Biomedical Applications.ACS Nano2023, 17, 1879–1905. Google Scholar
    • 32. Cao Y.; Wang M.; Wang H.; Han C.; Pan F.; Sun J.Covalent Organic Framework for Rechargeable Batteries: Mechanisms and Properties of Ionic Conduction.Adv. Energy Mater.2022, 12, 2200057. Google Scholar
    • 33. Luan T.-X.; Du L.; Wang J.-R.; Li K.; Zhang Q.; Li P.-Z.; Zhao Y.Highly Effective Generation of Singlet Oxygen by an Imidazole-Linked Robust Photosensitizing Covalent Organic Framework.ACS Nano2022, 16, 21565–21575. Google Scholar
    • 34. Davis M. E.Ordered Porous Materials for Emerging Applications.Nature2002, 417, 813–821. Google Scholar
    • 35. Di J.; Li L.; Wang Q.; Yu J.Porous Membranes with Special Wettabilities: Designed Fabrication and Emerging Application.CCS Chem.2021, 3, 2280–2297. Link, Google Scholar
    • 36. Liao J.; Hu Q.; Du Y.; Li J.; Duan L.; Bao J.; Zhou X.Robust Carbon Nanotube-Interwoven KFeSO4F Microspheres as Reliable Potassium Cathodes.Sci. Bull.2022, 67, 2208–2215. Google Scholar
    • 37. Kandambeth S.; Kale V. S.; Shekhah O.; Alshareef H. N.; Eddaoudi M.2D Covalent-Organic Framework Electrodes for Supercapacitors and Rechargeable Metal-Ion Batteries.Adv. Energy Mater.2021, 12, 2100177. Google Scholar
    • 38. Xu Y.; Ding T.; Sun D.; Ji X.; Zhou X.Recent Advances in Electrolytes for Potassium-Ion Batteries.Adv. Funct. Mater.2022, 33, 2211290. Google Scholar
    • 39. Huang N.; Zhai L.; Coupry D. E.; Addicoat M. A.; Okushita K.; Nishimura K.; Heine T.; Jiang D.Multiple-Component Covalent Organic Frameworks.Nat. Commun.2016, 7, 12325. Google Scholar
    • 40. Dalapati S.; Jin S.; Gao J.; Xu Y.; Nagai A.; Jiang D.An Azine-Linked Covalent Organic Framework.J. Am. Chem. Soc.2013, 135, 17310–17313. Google Scholar
    • 41. Fang Y. J.; Luan D. Y.; Gao S. Y.; Lou X. W.Rational Design and Engineering of One-Dimensional Hollow Nanostructures for Efficient Electrochemical Energy Storage.Angew. Chem. Int. Ed.2021, 60, 20102–20118. Google Scholar
    • 42. Zhang C.; Ma W.; Han C.; Luo L.-W.; Daniyar A.; Xiang S.; Wu X.; Ji X.; Jiang J.-X.Tailoring the Linking Patterns of Polypyrene Cathodes for High-Performance Aqueous Zn Dual-Ion Batteries.Energy Environ. Sci.2021, 14, 462–472. Google Scholar
    • 43. Guan X.; Chen F.; Qiu S.; Fang Q.Three-Dimensional Covalent Organic Frameworks: From Synthesis to Applications.Angew. Chem. Int. Ed.2022, 61, e202213203. Google Scholar
    • 44. Zang Y.; Lu D.-Q.; Lan Y.-Q.Covalent Organic Frameworks: A New Platform for Next-Generation Batteries of Na-, K- and Zn-Ions.Sci. Bull.2022, 67, 1621–1624. Google Scholar
    • 45. Gui B.; Lin G.; Ding H.; Gao C.; Mal A.; Wang C.Three-Dimensional Covalent Organic Frameworks: From Topology Design to Applications.Acc. Chem. Res.2020, 53, 2225–2234. Google Scholar
    • 46. Liu W.; Gong L.; Liu Z.; Jin Y.; Pan H.; Yang X.; Yu B.; Li N.; Qi D.; Wang K.; Wang H.; Jiang J.Conjugated Three-Dimensional High-Connected Covalent Organic Frameworks for Lithium–Sulfur Batteries.J. Am. Chem. Soc.2022, 144, 17209–17218. Google Scholar
    • 47. Zhao X.; Pachfule P.; Thomas A.Covalent Organic Frameworks (COFs) for Electrochemical Applications.Chem. Soc. Rev.2021, 50, 6871–6913. Google Scholar
    • 48. Li Y.; Karimi M.; Gong Y.-N.; Dai N.; Safarifard V.; Jiang H.-L.Integration of Metal-Organic Frameworks and Covalent Organic Frameworks: Design, Synthesis, and Applications.Matter2021, 4, 2230–2265. Google Scholar
    • 49. Sun T.; Xie J.; Guo W.; Li D. S.; Zhang Q.Covalent–Organic Frameworks: Advanced Organic Electrode Materials for Rechargeable Batteries.Adv. Energy Mater.2020, 10, 1904199. Google Scholar
    • 50. Kong L.; Liu M.; Huang H.; Xu Y.; Bu X. H.Metal/Covalent-Organic Framework Based Cathodes for Metal-Ion Batteries.Adv. Energy Mater.2021, 12, 2100172. Google Scholar
    • 51. Holst J. R.; Trewin A.; Cooper A. I.Porous Organic Molecules.Nat. Chem.2010, 2, 915–920. Google Scholar
    • 52. Xu J.; Xu Y.; Lai C.; Xia T.; Zhang B.; Zhou X.Challenges and Perspectives of Covalent Organic Frameworks for Advanced Alkali-Metal Ion Batteries.Sci. China Chem.2021, 64, 1267–1282. Google Scholar
    • 53. Kang X.; Han X.; Yuan C.; Cheng C.; Liu Y.; Cui Y.Reticular Synthesis of tbo Topology Covalent Organic Frameworks.J. Am. Chem. Soc.2020, 142, 16346–16356. Google Scholar
    • 54. Li M.; Liu J.; Zhang T.; Song X.; Chen W.; Chen L.2D Redox-Active Covalent Organic Frameworks for Supercapacitors: Design, Synthesis, and Challenges.Small2021, 17, 2005073. Google Scholar
    • 55. Yusran Y.; Fang Q.; Valtchev V.Electroactive Covalent Organic Frameworks: Design, Synthesis, and Applications.Adv. Mater.2020, 32, 2002038. Google Scholar
    • 56. Ji D.; Li T.; Fuchs H.Patterning and Applications of Nanoporous Structures in Organic Electronics.Nano Today2020, 31, 100843. Google Scholar
    • 57. Li C.; Yang Q.; Shen M.; Ma J. Y.; Hu B. W.The Electrochemical Na Intercalation/Extraction Mechanism of Ultrathin Cobalt(II) Terephthalate-Based MOF Nanosheets Revealed by Synchrotron X-ray Absorption Spectroscopy.Energy Storage Mater.2018, 14, 82–89. Google Scholar
    • 58. Xu Y.; Wu X.; Sandstrom S. K.; Hong J.; Jiang H.; Chen X.; Ji X.Fe-Ion Bolted VOPO4·2H2O as an Aqueous Fe-Ion Battery Electrode.Adv. Mater.2021, 33, 2105234. Google Scholar
    • 59. Zeng S.-M.; Huang X.-X.; Ma Y.-J.; Zhi L.-J.A Review of Covalent Organic Framework Electrode Materials for Rechargeable Metal-Ion Batteries.New Carbon Mater.2021, 36, 1–18. Google Scholar
    • 60. Chen M.; Li H.; Liu C.; Liu J.; Feng Y.; Wee A. G. H.; Zhang B.Porphyrin- and Porphyrinoid-Based Covalent Organic Frameworks (COFs): From Design, Synthesis to Applications.Coord. Chem. Rev.2021, 435, 213778. Google Scholar
    • 61. Gropp C.; Ma T.; Hanikel N.; Yaghi O. M.Design of Higher Valency in Covalent Organic Frameworks.Science2020, 370, eabd6406. Google Scholar
    • 62. Guan Q.; Zhou L.-L.; Dong Y.-B.Construction of Covalent Organic Frameworks via Multicomponent Reactions.J. Am. Chem. Soc.2023, 145, 1475–1496. Crossref, Google Scholar
    • 63. Cao S.; Li B.; Zhu R.; Pang H.Design and Synthesis of Covalent Organic Frameworks Towards Energy and Environment Fields.Chem. Eng. J.2019, 355, 602–623. Google Scholar
    • 64. Hunt J. R.; Doonan C. J.; LeVangie J. D.; Côté A. P.; Yaghi O. M.Reticular Synthesis of Covalent Organic Borosilicate Frameworks.J. Am. Chem. Soc.2008, 130, 11872–11873. Google Scholar
    • 65. Tilford R. W.; Gemmill W. R.; zur Loye H.-C.; Lavigne J. J.Facile Synthesis of a Highly Crystalline, Covalently Linked Porous Boronate Network.Chem. Mater.2006, 18, 5296–5301. Google Scholar
    • 66. Uribe-Romo F. J.; Doonan C. J.; Furukawa H.; Oisaki K.; Yaghi O. M.Crystalline Covalent Organic Frameworks with Hydrazone Linkages.J. Am. Chem. Soc.2011, 133, 11478–11481. Google Scholar
    • 67. Yang S.; Yang C.; Dun C.; Mao H.; Khoo R. S. H.; Klivansky L. M.; Reimer J. A.; Urban J. J.; Zhang J.; Liu Y.Covalent Organic Frameworks with Irreversible Linkages via Reductive Cyclization of Imines.J. Am. Chem. Soc.2022, 144, 9827–9835. Google Scholar
    • 68. Qian C.; Feng L.; Teo W. L.; Liu J.; Zhou W.; Wang D.; Zhao Y.Imine and Imine-Derived Linkages in Two-Dimensional Covalent Organic Frameworks.Nat. Rev. Chem.2022, 6, 881–898. Google Scholar
    • 69. Liu X.; Qi R.; Li S.; Liu W.; Yu Y.; Wang J.; Wu S.; Ding K.; Yu Y.Triazine–Porphyrin-Based Hyperconjugated Covalent Organic Framework for High-Performance Photocatalysis.J. Am. Chem. Soc.2022, 144, 23396–23404. Google Scholar
    • 70. Ding S.-Y.; Wang W.Covalent Organic Frameworks (COFs): From Design to Applications.Chem. Soc. Rev.2013, 42, 548–568. Google Scholar
    • 71. Geng K.; He T.; Liu R.; Dalapati S.; Tan K. T.; Li Z.; Tao S.; Gong Y.; Jiang Q.; Jiang D.Covalent Organic Frameworks: Design, Synthesis, and Functions.Chem. Rev.2020, 120, 8814–8933. Google Scholar
    • 72. Côté A. P.; Benin A. I.; Ockwig N. W.; O’Keeffe M.; Matzger A. J.; Yaghi O. M.Porous, Crystalline, Covalent Organic Frameworks.Science2005, 310, 1166–1170. Google Scholar
    • 73. Belowich M. E.; Stoddart J. F.Dynamic Imine Chemistry.Chem. Soc. Rev.2012, 41, 2003–2024. Google Scholar
    • 74. Jin Y.; Yu C.; Denman R. J.; Zhang W.Recent Advances in Dynamic Covalent Chemistry.Chem. Soc. Rev.2013, 42, 6634–6654. Google Scholar
    • 75. Sasmal H. S.; Kumar Mahato A.; Majumder P.; Banerjee R.Landscaping Covalent Organic Framework Nanomorphologies.J. Am. Chem. Soc.2022, 144, 11482–11498. Google Scholar
    • 76. Fang Q.; Zhuang Z.; Gu S.; Kaspar R. B.; Zheng J.; Wang J.; Qiu S.; Yan Y.Designed Synthesis of Large-Pore Crystalline Polyimide Covalent Organic Frameworks.Nat. Commun.2014, 5, 4503. Google Scholar
    • 77. Qian C.; Zhou W.; Qiao J.; Wang D.; Li X.; Teo W. L.; Shi X.; Wu H.; Di J.; Wang H.; Liu G.; Gu L.; Liu J.; Feng L.; Liu Y.; Quek S. Y.; Loh K. P.; Zhao Y.Linkage Engineering by Harnessing Supramolecular Interactions to Fabricate 2D Hydrazone-Linked Covalent Organic Framework Platforms Toward Advanced Catalysis.J. Am. Chem. Soc.2020, 142, 18138–18149. Google Scholar
    • 78. Kuhn P.; Antonietti M.; Thomas A.Porous, Covalent Triazine-Based Frameworks Prepared by Ionothermal Synthesis.Angew. Chem. Int. Ed.2008, 47, 3450–3453. Google Scholar
    • 79. Jin E.; Li J.; Geng K.; Jiang Q.; Xu H.; Xu Q.; Jiang D.Designed Synthesis of Stable Light-Emitting Two-Dimensional sp2 Carbon-Conjugated Covalent Organic Frameworks.Nat. Commun.2018, 9, 4143. Google Scholar
    • 80. Yao C.-J.; Wu Z.; Xie J.; Yu F.; Guo W.; Xu Z. J.; Li D.-S.; Zhang S.; Zhang Q.Two-Dimensional (2D) Covalent Organic Framework as Efficient Cathode for Binder-Free Lithium-Ion Battery.ChemSusChem2020, 13, 2457–2463. Google Scholar
    • 81. Yao L.; Ma C.; Sun L.; Zhang D.; Chen Y.; Jin E.; Song X.; Liang Z.; Wang K.-X.Highly Crystalline Polyimide Covalent Organic Framework as Dual-Active-Center Cathode for High-Performance Lithium-Ion Batteries.J. Am. Chem. Soc.2022, 144, 23534–23542. Google Scholar
    • 82. Liu X.; Jin Y.; Wang H.; Yang X.; Zhang P.; Wang K.; Jiang J.In Situ Growth of Covalent Organic Framework Nanosheets on Graphene as the Cathode for Long-Life High-Capacity Lithium-Ion Batteries.Adv. Mater.2022, 34, e2203605. Google Scholar
    • 83. Li X.; Wang H.; Chen H.; Zheng Q.; Zhang Q.; Mao H.; Liu Y.; Cai S.; Sun B.; Dun C.; Gordon M. P; Zheng H.; Reimer J. A.; Urban J. J.; Ciston J.; Tan T.; Chan E. M.; Zhang J.; Liu Y.Dynamic Covalent Synthesis of Crystalline Porous Graphitic Frameworks.Chem2020, 6, 933–944. Google Scholar
    • 84. Zhao H.; Luo D.; Xu H.; He W.; Ding B.; Dou H.; Zhang X.A Novel Covalent Organic Framework with High-Density Imine Groups for Lithium Storage as Anode Material in Lithium-Ion Batteries.J. Mater. Sci.2022, 57, 9980–9991. Google Scholar
    • 85. Li S.; Liu Y.; Dai L.; Li S.; Wang B.; Xie J.; Li P.A Stable Covalent Organic Framework Cathode Enables Ultra-Long Cycle Life for Alkali and Multivalent Metal Rechargeable Batteries.Energy Storage Mater.2022, 48, 439–446. Google Scholar
    • 86. Shehab M. K.; Weeraratne K. S.; El-Kadri O. M.; Yadavalli V. K.; El-Kaderi H. M.Templated Synthesis of 2D Polyimide Covalent Organic Framework for Rechargeable Sodium-Ion Batteries.Macromol. Rapid Commun.2023. doi: https://doi.org/10.1002/marc.202200782 Google Scholar
    • 87. Yang X.; Jin Y.; Yu B.; Gong L.; Liu W.; Liu X.; Chen X.; Wang K.; Jiang J.Two-Dimensional Conjugated N-Rich Covalent Organic Frameworks for Superior Sodium Storage.Sci. China Chem.2022, 65, 1291–1298. Google Scholar
    • 88. Shehab M. K.; Weeraratne K. S.; Huang T.; Lao K. U.; El-Kaderi H. M.Exceptional Sodium-Ion Storage by an Aza-Covalent Organic Framework for High Energy and Power Density Sodium-Ion Batteries.ACS Appl. Mater. Interfaces2021, 13, 15083–15091. Google Scholar
    • 89. Luo X. X.; Li W. H.; Liang H. J.; Zhang H. X.; Du K. D.; Wang X. T.; Liu X. F.; Zhang J. P.; Wu X. L.Covalent Organic Framework with Highly Accessible Carbonyls and π-Cation Effect for Advanced Potassium-Ion Batteries.Angew. Chem. Int. Ed.2022, 61, e202117661. Google Scholar
    • 90. Wolfson E. R.; Schkeryantz L.; Moscarello E. M.; Fernandez J. P.; Paszek J.; Wu Y.; Hadad C. M.; McGrier P. L.Alkynyl-Based Covalent Organic Frameworks as High-Performance Anode Materials for Potassium-Ion Batteries.ACS Appl. Mater. Interfaces2021, 13, 41628–41636. Google Scholar
    • 91. Cai Y.-Q.; Gong Z.-T.; Rong Q.; Liu J.-M.; Yao L.-F.; Cheng F.-X.; Liu J.-J.; Xia S.-B.; Guo H.Improved and Stable Triazine-Based Covalent Organic Framework for Lithium Storage.Appl. Surface Sci.2022, 594, 153481. Google Scholar
    • 92. Jiang F.; Wang Y.; Qiu T.; Yang G.; Yang C.; Huang J.; Fang Z.; Li J.Synthesis of Biphenyl-Linked Covalent Triazine Frameworks with Excellent Lithium Storage Performance as Anode in Lithium Ion Battery.J. Power Sources2022, 523, 231041. Google Scholar
    • 93. Xu X.; Zhang S.; Xu K.; Chen H.; Fan X.; Huang N.Janus Dione-Based Conjugated Covalent Organic Frameworks with High Conductivity as Superior Cathode Materials.J. Am. Chem. Soc.2023, 145, 1022–1030. Google Scholar
    • 94. Li Y.; Chen W.; Xing G.; Jiang D.; Chen L.New Synthetic Strategies Toward Covalent Organic Frameworks.Chem. Soc. Rev.2020, 49, 2852–2868. Google Scholar
    • 95. Buyukcakir O.; Ryu J.; Joo S. H.; Kang J.; Yuksel R.; Lee J.; Jiang Y.; Choi S.; Lee S. H.; Kwak S. K.; Park S.; Ruoff R. S.Lithium Accommodation in a Redox-Active Covalent Triazine Framework for High Areal Capacity and Fast-Charging Lithium-Ion Batteries.Adv. Funct. Mater.2020, 30, 2003761. Google Scholar
    • 96. Yang X.; Gong L.; Wang K.; Ma S.; Liu W.; Li B.; Li N.; Pan H.; Chen X.; Wang H.; Liu J.; Jiang J.Ionothermal Synthesis of Fully Conjugated Covalent Organic Frameworks for High-Capacity and Ultrastable Potassium-Ion Batteries.Adv. Mater.2022, 34, e2207245. Google Scholar
    • 97. Wu M.; Zhao Y.; Zhang H.; Zhu J.; Ma Y.; Li C.; Zhang Y.; Chen Y.A 2D Covalent Organic Framework with Ultra-Large Interlayer Distance as High-Rate Anode Material for Lithium-Ion Batteries.Nano Res.2022, 15, 9779–9784. Google Scholar
    • 98. Xiong Z.; Sun B.; Zou H.; Wang R.; Fang Q.; Zhang Z.; Qiu S.Amorphous-to-Crystalline Transformation: General Synthesis of Hollow Structured Covalent Organic Frameworks with High Crystallinity.J. Am. Chem. Soc.2022, 144, 6583–6593. Google Scholar
    • 99. Shi J.; Tang W.; Xiong B.; Gao F.; Lu Q.Molecular Design and Post-Synthetic Vulcanization on Two-Dimensional Covalent Organic Framework@rGO Hybrids Towards High-Performance Sodium-Ion Battery Cathode.Chem. Eng. J.2023, 453, 139607. Google Scholar
    • 100. Omachi H.; Inoue T.; Hatao S.; Shinohara H.; Criado A.; Yoshikawa H.; Syrgiannis Z.; Prato M.Concise, Single-Step Synthesis of Sulfur-Enriched Graphene: Immobilization of Molecular Clusters and Battery Applications.Angew. Chem. Int. Ed.2020, 59, 7836–7841. Google Scholar
    • 101. Tang X. X.; Lv L. P.; Chen S. Q.; Sun W. W.; Wang Y.Tin-Nitrogen Coordination Boosted Lithium-Storage Sites and Electrochemical Properties in Covalent-Organic Framework with Layer-Assembled Hollow Structure.J. Colloid Interface Sci.2022, 622, 591–601. Google Scholar
    • 102. Chen R.; Zhao J.; Yu Z.; Cong M.; Wang Y.; Wang M.; Li G.; Li Z.; Zhao Y.Post-Synthetic Fully π-Conjugated Three-Dimensional Covalent Organic Frameworks for High-Performance Lithium Storage.ACS Appl. Mater. Interfaces2023, 15, 830–837. Google Scholar
    • 103. Wang K.; Zhang H.; Xiao Y.; Ren S.; Wang Y.; Li L.Efficient Exfoliation of Covalent Organic Frameworks by a Facile Thiol-ene Reaction.Chem. Eng. J.2023, 454, 140283. Google Scholar
    • 104. Wang L.; Xu C.; Zhang W.; Zhang Q.; Zhao M.; Zeng C.; Jiang Q.; Gu C.; Ma Y.Electrocleavage Synthesis of Solution-Processed, Imine-Linked, and Crystalline Covalent Organic Framework Thin Films.J. Am. Chem. Soc.2022, 144, 8961–8968. Crossref, Google Scholar
    • 105. Zhang H.; Sun W.; Chen X.; Wang Y.Few-Layered Fluorinated Triazine-Based Covalent Organic Nanosheets for High-Performance Alkali Organic Batteries.ACS Nano2019, 13, 14252–14261. Google Scholar
    • 106. Zhao L.; Zheng L.; Li X.; Wang H.; Lv L.-P.; Chen S.; Sun W.; Wang Y.Cobalt Coordinated Cyano Covalent-Organic Framework for High-Performance Potassium-Organic Batteries.ACS Appl. Mater. Interfaces2021, 13, 48913–48922. Google Scholar
    • 107. He F.; Li Y.Advances on Theory and Experiments of the Energy Applications in Graphdiyne.CCS Chem.2023, 5, 72–94. Link, Google Scholar
    • 108. Yang X. B.; Lin C.; Han D. D.; Li G. J.; Huang C.; Liu J.; Wu X. L.; Zhai L. P.; Mi L. W.In Situ Construction of Redox-Active Covalent Organic Frameworks/Carbon Nanotube Composites as Anodes for Lithium-Ion Batteries.J. Mater. Chem. A2022, 10, 3989–3995. Google Scholar
    • 109. Xu X.; Cai P.; Chen H.; Zhou H.-C.; Huang N.Three-Dimensional Covalent Organic Frameworks with she Topology.J. Am. Chem. Soc.2022, 144, 18511–18517. Google Scholar
    • 110. Slater A. G.; Little M. A.; Pulido A.; Chong S. Y.; Holden D.; Chen L.; Morgan C.; Wu X.; Cheng G.; Clowes R.; Briggs M. E.; Hasell T.; Jelfs K. E.; Day G. M.; Copper A. I.Reticular Synthesis of Porous Molecular 1D Nanotubes and 3D Networks.Nat. Chem.2017, 9, 17–25. Google Scholar
    • 111. Veber G.; Diercks C. S.; Rogers C.; Perkins W. S.; Ciston J.; Lee K.; Llinas J. P.; Liebman-Peláez A.; Zhu C.; Bokor J.; Fischer F. R.Reticular Growth of Graphene Nanoribbon 2D Covalent Organic Frameworks.Chem2020, 6, 1125–1133. Google Scholar
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