Synthesis Of Salen-based Porous Organic Frameworks And Their Application In Lithium-ion Batteries

Salen based porous organic frameworks integrate Salen motifs into the porous polymers,effectively improving the stability of Salen motifs.At the same time,Salen based porous organic frameworks have the structural characteristics and properties of them.The porous structures and open channels promote the penetration of electrolyte and facilitate the migration of electrons and metal ions.They are insoluble in the electrolyte due to the stable skeleton structures,which may enhance the cycling stability when served as electrode materials.In addition,the C=N bond can react with lithium to enhance the lithium storage capacity.Based on the above advantages,Salen-based porous organic frameworks are used as anode for lithium-ion batteries（LIBs）.For the sake of optimizing the performance of Salen-based porous organic frameworks as anode material,we have designed the structure appropriately.The Salen-based porous organic frameworks with conjugated structures are successfully prepared by coordination with transition metal ions,which effectively enhances the conductivity and capacity of the materials.Besides,in the cause of further improving the electrochemical performance of the materials,Salen-based covalent organic framework（Salen-COF）is composited successfully with amino modified multi-walled carbon nanotube（NH₂-f-MWCNT）.The specific research contents are as follows:（1）A novel Salen-based porous aromatic framework（Zn/Salen-PAF）with multiple redox sites is synthesized with 1,3,5-tri[（3-formyl-4-hydroxy-phenyl）ethyl]benzene and ethylenediamine through a metal-guided method.When used as anode material for LIBs,Zn/Salen-PAF shows better electrochemical performance,relative to the metal-free Salen-PAF.At 50 m A·g^-1,the discharge capacity of Zn/Salen-PAF is 846 m Ah·g^-1,while the discharge capacity of Salen-PAF is only 601 m Ah·g^-1.Subsequently,we use X-ray photoelectron spectroscopy（XPS）and theoretical calculation to explore the lithium storage mechanism of Zn/Salen-PAF.The results show that Zn/Salen-PAF has double active sites of C=N and C=O,and higher electrical conductivity.（2）The copper-coordinated Salen-based porous aromatic framework（Cu/Salen-T-PAF）is successfully synthesized using Cu/Salen-Br and 1,3,6,8-tetraacetyneyl pyrene as monomers by Sonogashira-Hagihara cross-coupling reaction.When used as the anode material for LIBs,it exhibits stable cycling performance and a high discharge capacity of 559m Ah·g^-1 at 1.0 A·g^-1.The coulombic efficiency remains more than 99%after 800 cycles.Compared with Salen-T-PAF,the electrochemical performance of Cu/Salen-T-PAF improves.（3）Due to the inherent electrical conductivity of the aminated carbon nanotubes（NH₂-f-MWCNT）,we synthesized Salen-COF@NH₂-f-MWCNT with Salen-based covalent organic framework（Salen-COF）and NH₂-f-MWCNT.In addition,the Salen-COF displays layered structures on the NH₂-f-MWCNT,so that the active sites of it are fully exposed and a shorter path for the diffusion of Li⁺/electrons is provided.The advantages above effectively enhance the dynamics of Li⁺embedding/removal.Therefore,Salen-COF@NH₂-f-MWCNT shows better electrochemical performance as anode material of LIBs than Salen-COF.