The Synthesis Of Triazine-thiophene Based Polymers And Their Composites With Carbon Materials As The Electrode In Lithium-ion Battery

In the experiment,seven D-A(electron donor-acceptor)type polymers are synthesized through stille coupling reaction which are then named PTT-1,PTT-O,PTT-2,PTT.-3,PTT-4,PTT-5 and PTT-6.Among them,2,4,6-tris(5-bromothiophen-2-yl)-1,3,5-triazine(TBYT)is used as the building block of the polymers,toghther with 7 kinds of thiophene derivatives that differ in molecular length,connection mode and monomer structure,including thiophene,ethylenedioxythiophene,dithiophene,trithiophene,tetrathiophene,bidithiophene and bitrithiophene as the side chains of polymers.Subsequently,the composite materials with the polymers and conductive carbon Vulcan XC-72 are synthesized through in-situ polymerization and the synthesized composites are used as the active material in the electrode of lithium-ion battery.Galvanostatic charge-discharge,cyclic voltammetry,AC impedance testing and other methods are used to test their electrochemical performances.Scanning electron microscopy results show that when the thiophene derivative used in the polymerization process has long molecular length,it can effectively reduce the intramolecular steric hindrance and form a cross-linked network structure in the composite material.In addition,the experimental results have shown that the D-A type polymers could effectively reduce the band gaps of the polymers and the band gaps of the polymers could be further redued with the increase number of the thiophene structures within the molecules.The polymer PTT-4 with tetrathiophene as the side chains has the lowest band gap of 1.53 e V.Cyclic voltammetry test results show that the potentials of these composite materials are all around 1.0V vs.Li/Li~+,so that they are suitable for use as anode materials for lithium-ion batteries.At a current density of 100m A/g,the specific capacities of PTT-1@C,PTT-O@C,PTT-2@C,PTT-3@C,PTT-4@C,PTT-5@C and PTT-6@C are 515 m Ah/g,645 m Ah/g,671 m Ah/g,707 m Ah/g,772 m Ah/g,652 m Ah/g and 725 m Ah/g,respectively.The results show that by using thiophene derivatives with longer molecular lengths to synthesize polymers and then composite them with small-sized carbon particles,a clear cross-linked network structure can be formed in the material.And the long thiophene derivatives could also bring stronger conjugation effect for the polymers,which could further reduce their band gaps and it also increases the proportion of thiophene rings in the materials.The synergistic effect of these factors can effectively improve the electrochemical performances of the materials used as the electrode in the lithium-ion batteries.