Study On The Synthesis And Energy Storage Properties Of TCNQ-based Metal-organic Frameworks And Their Derivatives

Metal organic frameworks(MOFs)are a novel class of porous materials which can be synthesized via the self-assemble reaction between organic ligands and metal ions.MOFs and their derivatives have attracted considerable attention in the fields of lithium-ion batteries(LIBs)and supercapacitors.The electrochemical properties of7,7,8,8-tetracyanoquinodimethane(TCNQ)-based MOFs and their derivatives were studied in this paper,and the results are as follows:(1)TCNQ was selected as ligand to react with Cu2+ salt to prepare the Cu(TCNQ)material with nanorod structure via a facile spontaneous electrolysis technique.The results indicated that Cu(TCNQ)nanorods have a diameter of-500 nm and a room-temperature conductivity of 1.98 × 10-1 S cm-1.As the anode material for recharge lithium-ion batteries,the Cu(TCNQ)electrode exhibited a high capacity of445.8 mA h g-1 after 100 cycles at current density of 100 mA g-1.The high performance can be attributed to the excellent skeleton structure of Cu(TCNQ),which provides channels for Li+intercalation/extraction,as well as the intrinsically good conductivity of Cu(TCNQ)contributing fast electronic transport.(2)Co3O4 and Co3O4-PVP nanospheres with different sizes were fabricated by carbonizing [Co(TCNQ)bpy]·8MeOH precursors in the air.As anode materials for recharge lithium-ion batteries,the Co3O4-PVP-based anode material exhibited excellent cycling stability at the current density of 100 mA g-1 after 100 cycles.The smaller particle size of Co3O4-PVP nanospheres relative to pure Co3O4 and larger specific surface area are beneficial to the effective contact between the active materials and electrolyte during the charge/discharge process,and consequently improve the utilization of the electrode material.Furthermore,the[Co(TCNQ)bpy]·8MeOH precursors with various morphologies and sizes have also been successfully synthesized via changing the amount of polyvinyl pyrrolidone(PVP).This method can be extended to prepare other functional nanostructure materials.(3)Nitrogen-doped carbon composites were synthesized by directly carbonizing TCNQ-based MOFs under N2 atmosphere.The presence of TCNQ ligand and effect of the pyrolysis temperature were two key factors for the preparation of N-doped carbon composites with different nitrogen contents and species,which can effectively adjust electrochemical properties of electrode materials.The results showed that theN-C-650 material exhibited a good capacitance of 223.7 F g-1 at a rate of 1 A g-1 and the cycle stability.The specific capacitance declined to 78.3% of the first cycle capacitance after 2000 cycles,however,the capacity decay was only 4.86%(170.1 F g-1 after 3000 cycles)between 2000 to 3000 cycles.More importantly,the N-C-550 material was used as the anode for lithium-ion batteries,which exhibited a good reversible capacity of 675 mA h g-1 at a current density of 100 mA g-1 and excellent cycling stability(736.8 mA h g-1 after 50 cycles).The good electrochemical performances of electrode materials were attributed to the high nitrogen contents and controllable nitrogen species in nitrogen doped carbon composites.