Design, Synthesis And Electrochemical Performance Of Conjugated Microporous Polymers Containing Heteroatoms

Since the concept of rechargeable lithium-ion batteries(LIBs)was first proposed in the 1970s,LIBs have received widespread attention as an important energy storage system in the past few decades,and achieved great success in portable electronic products and electric vehicles.Electrode materials play a vital role in LIBs that achieve high energy density and long cycle life.At present,commercial LIBs are mainly based on lithium-rich metal compounds as positive electrodes and graphite as negative electrode electrochemical energy storage technology.With the increasing demand for clean and efficient energy,it is extremely urgent to develop a new generation of environmentally friendly electrode materials.In recent years,the development of organic electrode materials has attracted wide attention of many researchers.Among them,conjugated polymers are prone to redox doping due to their unique conjugated framework structure,thus showing good electrochemical performance.In addition to the conjugated skeletal structure,the organic conjugated microporous polymer has a rich pore structure and a high specific surface area,which can shorten the ion migration distance and increase the utilization rate of the active site.At the same time,the highly crosslinked polymer structure imparts excellent physicochemical stability and insolubility to the material,which is beneficial to improve the cycle stability.A series of novel functionalized organic conjugated polymer electrode materials rich in hetero-atoms(N,O,S)were designed and synthesized.The electrochemical properties of polymers as anode materials for LIBs were studied.The effects of the chemical structure,active unit and electronic structure of the polymer on its electrochemical performance were also investigated.The main work of this thesis is as follows:(1)Two kinds of thiophenyl conjugated microporous polymers with different degree of crosslinking were designed and synthesized by polymerization of tetrafunctional thiophene derivatives with dibromobenzene and tribromobenzene by Suzuki polymerization.Their electrochemical properties as LIBs and SIBs anode materials were also studied.The results show that the polymers with higher crosslinking degree,higher thiophene content and lower LUMO energy level exhibit better electrochemical performance.The assembled LIBs display a specific capacity of up to 939 mAh/g at current density of 50 mA/g.The specific capacity remains at 595 mAh/g after 300 cycles at 100 mA/g.At the same time,the assembled SIBs exhibited a specific capacity of 350 mAh/g at 50 mA/g.These results indicate that increasing the degree of cross-linking and the content of active units in conjugated microporous polymers is an effective way to improve their electrochemical performance.(2)Four kinds of biheterocyclic organic conjugated polymer containing benzodithiazole(BT)and thiazolyl thiazole(TZTZ)were designed and synthesized by Schiff base condensation reaction.Their electrochemical properties as anode materials for LIBs were studied.Among them,the prepared polymer BT-CP has relatively low LUMO energy level and band gap,showing more excellent electrochemical performance.After 200 cycles at 100 mA/g,the assembled battery still has a specific capacity of 903 mAh/g,and the coulomb efficiency is close to 99%.At a high current density of 2000 mA/g,it is shown to be 263 mAh/g.It's suggesting that the prepared material has excellent cycle stability and double rate performance.(3)Three kinds of conjugated microporous polymers containing different hetero-atoms(N,O,S)were designed and synthesized by Schiff base condensation reaction.Their electrochemical properties as anode materials for LIBs were studied.Among them,the polymer TABI containing benzobisole unit has the lowest LUMO level(-3.69 eV)and band gap(1.85 eV).At the same time,the LUMO orbital distribution of the polymer has a higher degree of delocalization,so the polymer exhibits excellent electrochemical performance.The LIBs assembled by TABI has a specific capacity of 645 mAh/g at current density of 100 mA/g after 100 cycles.The results show that the electronic structures such as polymer energy levels and band gaps can be regulated by introducing different kinds of elements,thus improving their electrochemical performance,which is of great significance for the development of organic electrode materials with high performance.