Design, Synthesis And Performance Of Redox-active Conjugated Microporous Polymers For Lithium-ion Batteries

Energy shortage and environmental pollution have become two major challenges at the currently society.To solve these problems,the development of clean renewable energy system and the establishment of efficient energy storage systems are important.Among various energy storage methods,lithium-ion secondary batteries have attracted much attention owing to excellent cycling performance,low self-discharge and high energy density.Commercial lithium-ion batteries are leading electrochemical energy storage devices that mainly use metal oxides or metal phosphates as the cathodes and graphite as the anodes.However,the current technology of commercial LIBs has realized the theoretical capacity of graphite(372 mAh/g),which is far from meeting the ever-increasing energy-storage requirements.Moreover,the preparation of inorganic electrodes results in growing concerns upon resource-and environment-related problems.Hence,there is an urgent demand to explore next-generation organic electrode materials with green,environment-friendliness and high performance to promote the reform and innovation of lithium ion batteries.The extended ?-conjugation backbone offers conjugated microporous polymers good electrical conductivity and electrochemical doping/dedoping abilities.Meanwhile,the large surface area and permanent porous structure of conjugated microporous polymers could increase the utilization of active site and shorten the immigration distance of charge carriers,leading to the high redox activity and fast kinetics.Furthermore,the highly crosslinked polymer network structure with insoluble nature in organic electrolytes,improving the cycling stability.Considering these advantages,conjugated microporous polymers anodes offers a great prospect for the next-generation Li-organic batteries.Herein,we designed and synthesized a class of redox-active conjugated microporous polymers and systematically investigated the influence of chemical composition and structure,active units and electronic structure on the storage performance of Li+ions.This research project is mainly divided into three parts:(1)The preparation and Li+ions storage performance of triazine-thiophene based (2)conjugated microporous polymersA series of triazine-thiophene based conjugated microporous polymers were designed and synthesized,in which the electronic structure was effectively regulated by using the same triazine ring as the core unit and adjusting the length of chain(thiophene,bithiophene,and trithiophene).The structure-performances relationship of CMPs demonstrates that thiophene content,low LUMO energy leve and narrow band gap endows the CMPs high redox activity.The LIBs assembled by CTF3T with high thiophene content(83%)and optimized electronic structure exhibits a specific capacity of 1236 mAh/g at 50 mA/g.(2)The preparation and Li+ions storage performance of CMP containing plentiful redox-active unitsA conjugated microporous polymer with plentiful redox-active units was designed and synthesized by introducing triazine ring,thiophene and benzothiadiazole active units into a polymer backbone simultaneously.The layered porous structure and plentiful redox-active units improve the Li+ions storage performance of polymer-based electrodes,including ultra-high Li+ions storage capacity(1599 mAh/g,50 mA/g),superior rate behavior(363 mAh/g,5 A/g)and outstanding cyclability(1500 cycles,5000 mA/g).(3)The preparation and Li+ions storage performance of azo-based conjugated microporous polymers.A series of azo-based conjugated microporous polymers with different electronic structure were designed and synthesized by fixing same azo units as the core building blocks and selecting different cross linkers of benzene,pyrene and benzothiadiazole.The influence of their chemical and electronic structure on the electrochemical performances was investigated.The comparative study announces that the low LUMO level and narrow band gap of polymer-based electrodes can promote the n-type doping reaction of polymer chains,which improving the storage performance of Li+ions.The polymer AzoBT combining redox-active azo and BT units delivers a Li+ions storage capacity of 1543 mAh/g at 50 mA/g.