Structure-Activity Relationship Of Conjugated Thiophene Polymers As Lithium Ion Storage Materials

Lithium-ion batteries(LIBs)have been successfully used in electric vehicles,smart grids and portable electronic products because of their high capacity and high energy density.As a key component of lithium-ion batteries,negative electrode materials are one of the important factors to improve the performance of lithium-ion batteries.At this stage,these inorganic anode materials are often accompanied by huge volume changes during the charge and discharge process,which leads to rapid capacity degradation and short cycle life.Compared with inorganic materials,organic electrode materials have become a research hotspot in this field due to their low cost,low environmental pollution,and designable molecular structure.Therefore,it is necessary for us to study negative electrode materials with high capacity,good stability and high safety.In this paper,we designed and synthesized several donor-acceptor conjugated polymers containing thiophene compounds,and combined them with carbon materials in situ as anode materials for lithium-ion batteries,and characterized and studied their performance.The main research contents are as follows:1.We designed and synthesized two new types of donor-acceptor(D-A)conjugated polymers,poly[(thiophene-2,5-yl)-((benzo[1,2-b:6,5-b']Dithiophene-4,5-dione)-2,7-yl)](PTDT)andpoly[(3,4-ethylenedioxythiophene-yl)-((benzo[1,2-b:6,5-b']Dithiophene-4,5-dione)-2,7-yl)](PTDO),through the in-situ composite strategy with supercapacitor carbon powder,two composites were successfully synthesized as lithium-ion batteries Anode material,and electrochemical test on it.The experimental results show that the specific capacities of PTDT@C and PTDO@C after 350 cycles at a current density of 0.1A g^-1 are 246.9 m Ah g^-1 and 322.3 m Ah g^-1,respectively.PTDO@C has carried out a 1000-lap cycle test and a rate performance test,showing good stability and excellent rate performance.In addition,we deduct the capacity of pure carbon from the total capacity to obtain the capacity of the polymer.PTDO has a good cycle life and high capacity mainly due to a stable conjugated molecular structure and a low LUMO value.2.On the basis of our research on D-A conjugated polymers in the previous chapter,we used the same method to prepare a series of 7a,11a-dihydro-3,4-dithia-7,12-diaza heterocycles Pentano[a,c]anthracene and benzo[1,2-b:6,5-b']dithiophene-4,5-dione are the acceptor units,and thiophene is the donor unit.The in-situ composite synthesis of supercapacitor carbon powder is used as the negative electrode material of lithium-ion batteries.Through physical characterization and electrochemical characterization,it is found that PTPTD@C has excellent capacity,excellent rate performance,and good stability.In addition,the Eg and LUMO energy levels of PTPTD are less than PTPP.When the donor is the same,the acceptor is different,which affects the electrochemical performance of the polymer.3.We have prepared three composite materials PMT@CNT,PMOP@CNT and PMOT@CNT by in-situ polymerization strategy by coating the polymer on carbon nanotubes as anode materials for lithium-ion batteries.Experimental data shows that compared with other composites,PMOT@CNT composite has good stability and higher capacity at 0.1 A g^-1.At the same time,we also found that the EDOT unit has stronger electronic capabilities,which helps stabilize the inserted lithium ions.Electron microscopy tests show that CNTs has better conductivity and flexibility.We also explored and revealed the underlying mechanism of different electrochemical properties of polymers through theoretical calculations.4.We use the calcination method to prepare anode material for lithium-ion batteries.In this work,we obtained the TPAO@600 composite material.When the TPAO@600electrode is used as a negative electrode material for lithium ion batteries(LIBs),it exhibits a high reversible specific capacity of 645.7 m Ah g^-1 at 0.1 A g^-1,and excellent performance at a current density of 2 A g^-1 The rate capacity is 275 m Ah g^-1.1000charge-discharge cycles show that the material has good cycle performance,and the capacity remains at 490.9 m Ah g^-1.Such excellent lithium storage performance can be attributed to the larger specific surface area and pore size.In addition,the lithium storage mechanism of TPAO@600 is mainly based on pseudo-capacitors.