Design,Synthesis,and Alkali Metal Ion Storage Performance Of Covalent Organic Frameworks

Alkali metal ion(Li+,Na+ and K+)batteries(AMIBs)have attracted much attention in recent years owing to their high energy density.However,conventional metal-ion batteries are often based on inorganic electrode materials such as carbon material and transition-metal oxides,which usually show low practical capacity or depend on scarce natural resources.Therefore,it is urgent to develop alternative electrode materials with high capacity,low cost,and sustainability.In this regard,organic materials have huge application potential in the field of electronic equipment,electric vehicles,and large-scale energy storage due to their tunable structures,renewable resources,and environmental friendliness and so on.However,most organic electrodes suffer from the dissolution in the electrolyte during the cycling process,resulting in capacity degradation.In addition,organic molecular aggregate solids are usually nonporous materials,limiting the exposure of active sites and the rapid carrier transports.Introducing redox-active groups into crystalline covalent organic frameworks(COFs)is an effective strategy to solve these problems.This helps to gain a deeper understanding of the structure property correlations at the atomic level,as they have clear ordered structures and further optimize performance.However,most COFs can only be manufactured in milligrams by solvothermal methods,hinder the wide application of COFs electrode materials.Therefore,the development of the simple,green,and industrial-grade preparation strategy of COFs electrode materialsis critical to achieve their industrialization.This paper aims to introduce redox-active groups into COFs skeleton to obtain COFs which are able to intrinsically undergo alkali metal ion insertion/removal,and in turn achieve efficient energy storage.Besides,we have developed the new strategy for the large-scale,low-cost and non-toxic synthesis of COFs-based electrode materials.The main research content are as follows:(1)Ligand Melting Synthesis of Conjugated Phthalocyanine COFs for Anodic Sodium StorageA series of 2D phthalocyanine conjugated COFs(MPc-2D-cCOFs)was selfpolymerized from tetracyanobenzene using a simple and fast ligand melt synthesis method under the template of different metal ions(Cu,Fe,Co,and Ni).The successful polymerization of phthalocyanine was confirmed by solid ultraviolet and FR-IR spectroscopy.These COFs materials with AA stacked structures were confirmed by Powder X-ray diffraction(PXRD)and high-resolution transmission electron microscopy(HR-TEM).Due to its nitrogen rich,highly conjugated,and ordered pore structure characteristics,MPc-2D-cCOFs as anode electrode materials for sodium ion batteries exhibit significantly enhanced specific capacity and better rate performance compared to phthalocyanine monomers.Taking CuPc-2D-cCOF as an example,it provides a specific capacity of 538 mA h g-1 at a current density of 50 mA g-1,and has a capacity of 325 mA h g-1 after 2500 cycles at a current density of 1000 mA g-1,with a capacity retention of nearly 100%.It is worth noting that the comprehensive performance of CuPc-2D-cCOF electrode exceeds that of most organic framework materials.Moreover,ex situ X-ray photoelectron(XPS)and Fourier transform infrared(FT-IR)spectra together with theoretical calculations disclose the N atoms at the pore channels and pyrrole moieties of MPc2D-cCOFs provide abundant Na-ion storage sites.The research in this chapter not only develops a series of phthalocyanine based COFs by ligand self-melting strategy,but also reveals the potential application of N-rich COFs in Na+ ion storage.(2)Ionothermal Synthesis of Conjugated Phthalocyanine COFs for Anodic Potassium StorageTwo aromatic conjugated monomers with four cyano groups were designed and synthesized,benzo[1,2-b:4,5-b’]bis[1,4]benzodioxin-2,3,9,10-tetracarbonitrile(BBTC)and quinoxalino[2’,3’:9,10]phenanthro[4,5-abc]phenazine-6,7,15,16tetracarbonitrile(QPPTC).Self-polymerize of BBTC or QPPTC in ZnCl2 leads to the formation and isolation of BB-FAC-Pc-COF and QPP-FAC-Pc-COF,respectively.Fused ZnCl2 at high temperatures not only serves as a solvent but also as a metal ion template.These two COFs materials with AA stacked structures were confirmed by PXRD and HR-TEM.In addition,a series of physical and chemical characterization shows that two COFs possess ordered one-dimensional tunnels and excellent stability.Compared to traditional solvothermal synthesis methods for preparing FAC-Pc-COFs,the newly developed route avoids the use of toxic organic solvents and catalysts,and is easy to large-scale production.In particular,due to its highly ordered structure,excellent thermal and chemical stability,and N/O rich skeleton properties,the prepared FAC-Pc COF exhibits high performance K+ion storage in PIBs.The QPP-FAC-Pc-COF electrode exhibits a large reversible capacity of 424 mA h g-1 at a current of 50 mA g-1,and the capacity retention rate for 10000 cycles at 2000 mA g-1 is close to 100%,superior to most organic PIBs battery electrodes.Moreover,ex situ XPS together with theoretical calculations reveal that the N atoms,conjugated pyrrole,and conjugated pyrene groups at the pores of QPP-FAC-Pc-COF provide storage sites for K+ions.The research in this chapter expands the synthesis strategy of phthalocyanine based COFs using ionthermal strategy,and demonstrates the potential application of nitrogen rich conjugated COFs in K+ion storage.(3)Synthesis of Multiple Redox-active Polyimide-linked COF for Cathodic lithium StorageA novel redox hexaazatrinaphthalene-based building block,hexacarboxylic anhydride hexaazatrinaphthalene,(HATN-AP),was designed and synthesized.And a 2D imide based COF,HATN-AQ-COF,was fabricated from of HATN-AP with 2,6-diaminoanthraquinone linker by solvothermal reaction.The HATN-AQ-COF with AA stacked structures were confirmed by PXRD and HR-TEM.A series of physical and chemical tests have demonstrated that the COF has good chemical and thermal stability,with permanent porosity and ordered mesoporous channels(3.8 nm).Benefited from the high loading density of redox-active sites for storing Li+ions including six pyrazine C=N,three imide C=O,and three quinone C=O active centers per asymmetric unit,the HATN-AQ-COF possess a high theoretical capacity of 358 mA h g-1.These structure merits of HATN-AQ-COF,in combination with its mesoporous tunnel for rapid carrier transport,result in the high reversible capacities of 319 mA h g-1 at 0.5 C and 226 mA h g-1 at 10 C(1 C=358 mA g-1)as cathode material in LIBs.In addition,the HATN-AQ-COF electrodes also have good long-term cycling performance,with a capacity retention of 80%after 3000 cycles at a current density of 10 C.Moreover,ex situ XPS and FT-IR spectra together with theoretical calculations disclose the reaction pathway and mechanism of Li+ion storage.The research in this chapter not only designed and prepared novel building blocks for redox active COFs materials,but also provided a design strategy for preparing high-performance organic cathode materials for LIBs based on two building blocks with rich redox active sites.(4)Hydrothermal synthesis of Redox-active polyimide COFs for Cathodic Sodium StorageTwo polyimide-linked covalent organic frameworks(COFs),namely HATNPD-COF and HATN-TAB-COF,were fabricated from hydrothermal synthesis with redox-active triphenylene-2,3,6,7,10,11-hexacarboxylic acid and aromatic amines as starting materials.In addition,compared to traditional solvothermal methods for the preparation of PI-COFs,the hydrothermal method avoids the use of toxic organic solvents and catalysts,and does not require the low-pressure environment,which is beneficial for large-scale production.These two COFs with A A stacked structures were confirmed by PXRD and HR-TEM.A series of physical and chemical tests have demonstrated that the COFs has good chemical and thermal stability,with permanent porosity and ordered mesoporous channels(2.1-3.0 nm).In particular,the prepared COFs cathode exhibits ultra-fast and stable Na+ion storage in SIBs,where HATN-PD-COF exhibits a high reversible capacity of 210 mA h g-1 at 200 mA g-1,a record 195 mA h g-1 in organic electrode materials at a high current density of 10000 mA g-1,and the capacity retention of nearly 91%after 7000 cycles.Galvanostatic intermittent titration technique and density functional theory calculations reveal the facile Na+ ion diffusion along the mesoporous tunnel of these COFs with a small energy barrier of 0.13-0.40 eV.Moreover,ex situ XPS and FT-IR spectra together with theoretical calculations disclose the reaction pathway and mechanism of Na+ion storage.The present investigation not only provides the new strategy for the preparation of HATN-based PI-COFs using green hydrothermal synthesis strategy,but also helps to design mesoporous COFs based electrode materials for high-rate Na+ ion storage.