Baisc Studies On Application Of Carbonyl Compound Organic Electrode Materials In New Battery System

Increasing attention has been gained to the sustainable development of energy and environment.It is imperative to accelerate the transformation of energy structure and to develop advanced technologies of energy conversion and storage.Benefiting from the abundant resource and low cost of sodium and potassium,sodium-ion batteries（SIBs）and potassium-ion batteries（KIBs）are promising battery systems for large-scale energy storage applications.Unfortunately,the larger radius of sodium（potassium）ion hinder the development of Na（K）-storage materials.The organic electrode materials have been considered as one of the most promising electrode materials for SIBs and KIBs due to their less restrictions on the cation size,structural diversity,low cost and environmental friendliness.In recent years,carbonyl organic electrode materials have attracted great interest owing to their high theoretical specific capacity and redox reactions reversibility.However,the dissolution of small carbonyl compounds in the electrolyte limits their further applications.Based on the above issues,we investigated the electrochemical performance of carbonyl compounds materials in SIBs and KIBs,and successfully improved the specific capacity,cycle stability and operating voltage of the carbonyl-based organic electrode materials by the methods of polymerization and introducing electron-withdrawing functional groups.1.The electrochemical properties of a small carbonyl compound 3,4,9,10-perylene tetracarboxylic dianhydride（PTCDA）in SIBs is investigated in this work.In the voltage range of 0.01-3.5V（vs.Na/Na⁺）,the discharge capacity of PTCDA reached up to 637.9mAh g-1 at the first cycle,which rapidly decayed in following steps.The superb specific capacity is partly contributed by the enolization reaction of C=O at 0.6-3.5V and the other from Na⁺embedding in the conjugated benzene ring at 0.01-0.6V.Shortening the voltage range to 1.5-3.5 V,PTCDA showed considerable cycling performance and rate capability as the capacity retained 107.7 mAh g^-11 after 200 cycles.PTCDA also delivered reversible specific capacity(123.7 mAh g^-1)as a cathode material for KIBs.However,the dissolution of PTCDA is inevitable in the electrolyte,which leading to poor cycling stabilty.2.In order to improve the dissolution problem of PTCDA in the electrolyte,polyimide material（PI）with multi-active redox-center was synthesized through the condensation polymerization of PTCDA and 26DAAQ,and investigated as a cathode material for SIBs.PI demonstrated high reversible capacity(146.7 mAh g^-1)and excellent cycle performance,which maintained 128 mAh g^-11 after 300 cycles.However,due to the poor conductivity,the rate capability of PI is poor.The Na⁺storage mechanism of PI can be described as redox reaction of four C=O in molecular structure.3.Although the cycling stability of carbonyl compounds has been improved by polymerization,the electrical conductivity of PI remains a problem.To improve the electronic conductivity of PI,poly（1,5-diaminoanthraquinone）（P15DAAQ）,with redox-active anthraquinone segments linked by polyaniline skeleton,was synthesized and investigated as cathode materials for KIBs.P15DAAQ is a kind of multi-active center material with electrolyte anion TSFI^-doping/dedoping reaction on the polyaniline backbone and the enolization reaction of carbonyl groups.In the voltage range of 1.2³.2V（vs.K/K⁺）,P15DAAQ delivered considerable rate performances of 121 mAh g^-11 at 250 mA g^-1and outstanding cycling-stability with capacity retention of 80%over 200 cycles.4.For most of the quinone-based cathode,the low redox potential limit the energy density of the battery system.To further increase the working voltage of the PI,poly（1,4-diamino-2,3-dicyanoquinone）（PDDAQ）was synthesized by introducing the electron-withdrawing functional group（cyano-CN）to the polymer backbone and investigated as a novel cathode material of KIBs for the first time.Compared to poly（1,4-diaminoanthraquinone）（P14DAAQ）,the redox voltage of PDDAQ was significantly increased by⁰.3V due to the introduction of the electron-withdrawing group.PDDAQ demonstrated a high reversible capacity of 188 mAh g^-1 at 25 mA g^-1 with a capacity retention rate of 81.9%after 50 cycles,possibly serving as flexible and high performance cathode for non-aqueous K-ion batteries.