| Covalent organic frameworks（COFs）have received wide attention in the fields of gas adsorption and separation,catalysis,and energy storage due to their stable framework structure,high surface area,well-defined and tunable molecular pores and structures,and excellent physical and chemical stability.In the field of lithium-ion batteries,COFs,composed of light elements such as carbon,nitrogen,hydrogen,and oxygen,have advantages such as good renewability,a rich library of monomers,and abundant lithium storage sites,and have also overcome the shortcomings of small organic molecule electrode materials in terms of cycling stability.Therefore,COFs are considered to be a promising electrode material for the next generation of lithium-ion batteries.However,COF materials still face challenges such as poor conductivity and low practical capacity,which limit their further development and application in electrochemical energy storage.To address these issues,this study attempts to design and synthesize several pure COF materials that can be directly used in lithium-ion batteries by changing the molecular components,and investigates the effects of molecular component changes on COF morphology,porosity,stability,and electrochemical performance.The details are as follows:（1）Three covalent organic frameworks（COFs）were synthesized using solvent-assistedencapsulationandimidazole-assistedmethods,with1,4,5,8-naphthalenetetracarboxylic dianhydride,terephthalic-3,4,9,10-tetracarboxylic dianhydride,and pyromellitic dianhydride as bridging ligands,and tri（4-aminophenyl）amine as the central ligand,named TA-PM-1,TA-NT-2,and TA-PT-3,respectively.The characterization and test results indicate that the different numbers of benzene rings in the bridging ligands have a certain influence on the microscopic morphology and thermal stability of the materials.When used as a negative electrode material for lithium-ion batteries,the TA-PT-3 electrode material exhibits stable specific capacity of 740 m Ah g-1after 200 cycles at a current density of 0.2 A g-1,and reversible specific capacity of 485.2m Ah g-1is maintained after 900 cycles at a high current density of 1 A g-1,with excellent rate performance.（2）A novel sheet-like imine-based COF,TA-BP-ICOF,was synthesized via the Schiff base reaction between three（4-aminophenyl）amine and 4,4’-biphenyldicarbaldehyde using a sealed-tube solvent thermal method.Characterization techniques such as XRD and FT-IR confirmed the successful preparation of TA-BP-ICOF,while solubility tests demonstrated its excellent stability in common polar solvents and electrolytes.Theπ-conjugated system of TA-BP-ICOF can enhance intrinsic electronic conductivity and facilitate electron transfer,while the induced ordered layer structure can provide abundant ion transport channels and expose more active sites.In cycling tests of lithium-ion batteries,after sufficient activation,TA-BP-ICOF exhibited stable capacity of 953 m Ah g-1at 0.1 A g-1current density for 500cycles,and also showed excellent cycling stability and high reversible capacity at 1 A g-1current density.Its capacity remained at 494.2 m Ah g-1after 1400 cycles.（3）The organic porous polymer TAPP-POPs was obtained by connecting the tetra（4-aminophenyl）porphyrin and terephthalic anhydride.The prepared TAPP-POPs were characterized and electrochemically tested,demonstrating excellent chemical stability and good electrochemical performance.After 200 cycles at a current density of 0.2 A g-1,the specific capacity of TAPP-POPs remained stable at 823.6 m Ah g-1.Especially at a higher current density of 1 A g-1,the reversible capacity could still maintain at 575.9 m Ah g-1after900 cycles.The conjugated structure of porphyrin and the microscopic lattice network of COFs are beneficial for exposing the available electrochemical active sites in the material,and also enhance the electronic transport capacity and reaction kinetics. |
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