Synthesis And Electrochemical Performance Of Hexaazatriphenylene-Based Organic Framework Cathode Materials

Organic electrode materials（OEMs）have attracted broad attention from researchers because of their high theoretical capacity,environmental friendliness,resource sustainability,and low cost.In particular,the designability of the structure can effectively modulate the electrochemical performance,which is also significant for alleviating the current increasing energy demand.Hexaazatriphenylene（HAT）and its derivatives have shown great potential as OEMs in the field of energy storage owing to their simple synthesis,easy modification and high theoretical capacity.However,they also suffer from the drawbacks of easy solubility,poor electrical conductivity,and slow ion transport rate,which easily lead to poor electrochemical cycling performance and multiplicative performance,and thereby severely limit the commercialization of HAT-based OEMs.Therefore,to address the above problems of HAT-like OEMs,several organic framework-based materials were designed and synthesized in this thesis,and their performance and energy storage mechanisms as rechargeable battery cathode materials were investigated.The details of the study are as follows:（1）Cobalt-based metal-organic frameworks as organic cathodes for lithium-ion batteriesHAT small molecules containing carboxyl functional groups（1,4,5,8,9,12-hexaazabenzophenanthrene-2,3,6,7,10,11-hexanecarboxylic acid,HAT-COOH）were designed and synthesized,and then coordinated with cobalt ions Co²⁺to obtain a kind of nano-flower-like MOFs.as the Co²⁺acted as a connecting node to form MOFs effectively inhibited the HAT-COOH units during charge and discharge,which endows the material with excellent cycling stability.When used as an organic cathode for Li-ion batteries,it exhibits a reversible capacity of 215.6 m Ah g^-1 at a current density of0.5 A g^-1 and still retains a reversible capacity of 209.7 m Ah g^-1 after 200 cycles,with a capacity retention rate of 97.3%.（2）Cerium-based metal-organic frameworks as organic cathodes for lithium-ion batteriesBased on the previous chapter,in order to further improve the stability of the materials,this chapter further forms metal-organic frameworks（MOFs）by introducing Ce⁴⁺ligated with HAT-COOH.The MOFs with the better conductivity and higher specific surface area（Ce-HAT-COOH-2）were obtained by modulating the morphology and size of MOFs by introducing the amount of commercial nonionic surfactant F127.Therefore,when used as lithium-ion battery cathodes,they exhibit excellent long-cycle stability and rate performance with almost no capacity decay after 2000 and 10000cycles at 1 A g^-1 and 4 A g^-1 current densities,respectively.（3）Copper-based metal-organic frameworks as organic cathodes for aqueous zinc ion batteriesTo further improve the electrical conductivity,this chapter designs MOFs formed by coordination of metal Cu²⁺ions with 5,6,11,12,17,18-hexaazanonaphthalene-2,8,17-tricarboxylic acid（HATN-COOH）.The copper-based MOFs exhibit a typical two-dimensional layered stacking structure,which enhances the electron transfer and ion transport within the material and promotes the electrode redox reaction Kinetics.When used as a cathode material for aqueous Zn-ion batteries,it provides a high discharge capacity of 380.7 m Ah A g^-1 at a current density of 0.1 A g^-1,and even at a high current density of 6 A g^-1,the material still retains a reversible capacity of 126.4 m Ah g^-1.（4）Two-dimensional hydrogen-bonded organic supramolecular lithium-ion battery cathode based on cyanoTo obtain higher capacity cathode materials,this chapter integrates a conjugated electron-absorbing cyano（-CN）with redox activity into hexaazanonaphthalene（HATN）and designs a two-dimensional planar supramolecule 5,6,11,12,17,18-hexaazanonaphthalene-2,3,8,9,14,15-hexacrylonitrile（HATN-6CN）based on hydrogen bonding interactions.The hydrogen bonding andπ-πintermolecular interactions allow HATN-6CN to display good stability during the cycling process.In addition,both the-C=N and-CN groups in HATN-6CN can act as redox active centers,thus endowing the material with a high specific capacity.As a result,HATN-6CN can provide a reversible capacity of up to 297.6 m Ah g^-1 at a current density of 0.5 A g^-1and retains 211.8 m Ah g^-1 after 200 cycles when used as a lithium-ion battery cathode.The reversible capacity of HATN-6CN with 80%mass loading was 193.6 m Ah g^-1 after100 cycles at a current density of 0.5 A g^-1,with a capacity retention rate of 80.4%.