Energy Storage Properties Of Thienyl-modified Porphyrin Complexes

With the advent of intercalated inorganic materials such as Li Co O₂ and graphite,rechargeable secondary lithium-ion batteries have entered a new era in the field of energy storage.The cathode materials have always been the bottleneck restricting the development of batteries.Current commercial applications are mainly transition metal oxide or phosphate cathodes,but these materials are mainly produced from non-renewable ores.In this case,we have to develop renewable and environmentally friendly electrode materials.Organic electrode materials can obtain a wide range of raw materials from nature,and used organic electrode waste can be decomposed by microorganisms without causing pollution.At the same time,organic electrode materials can be synthesized at normal temperature and pressure,which greatly reduces the cost in the production process.However,organic electrodes have poor electrochemical performance due to their high solubility and low intrinsic conductivity.So,we designed the structure of the porphyrin molecule to suppress its dissolution and improve its electrical conductivity.In this paper,we reported the thiophene-functionalized porphyrin MDETP（[5,15-bis-（ethynyl）-10,20-dithienylporphinato]M（II））,（M=Cu,Zn,Co and 2H）,Cu TTP（[5,10,15,20-tetrathiophenporphyrinato]copper（II））and polymerized Cu T₂TP（[5,10,15,20-tetra（2,2′-bithiophen-5-yl）porphyrinato]copper（II））（COP-Cu T₂TP）for energy storage applications.Here we had studied the effects of different functional groups and different coordination metal centers on the properties of porphyrins and the effect of polymerization on the properties of porphyrins.The main research contents of this paper are as follows:1)MDETP（[5,15-bis-（ethynyl）-10,20-dithienylporphinato]M（II）,（M=Cu,Zn,Co and 2H））and Cu TTP（[5,10,15,20-tetrathiophenporphyrinato]copper（II））in energy storage.Among them,the more thiophene active functional groups were introduced,the poorer the performance of Cu TTP was.This is related to the dissolution of Cu TTP in the electrolyte.In order to inhibit the dissolution,a self-polymerizing alkynyl group was introduced.In MDETP,Thiophene groups and nitrogen atoms act as active sites affording 8 electrons transfer during redox reaction.When Cu DETP was used in organic lithium batteries,it delivered a reversible capacity of 350 m Ah g^-1 at 100 m A g^-1 and a high specific energy density of 773.6 Wh kg^-1（based on the cathode material）.Meanwhile,extremely stable cyclability up to 9000 cycles was achieved owing to the self-polymerziation during initial charging process.This investigation has great enlightenment for the molecular design and application of organic electrodes in terms of both high energy densities and long cycling life.2)COP-Cu T₂TP（[5,10,15,20-tetra（2,2′-bithiophen-5-yl）porphyrinato]copper（II））in energy storage.Polymerization to form conjugated macromolecules can not only inhibit the dissolution of organic electrodes in the electrolyte,but also enhance the conductivity of organic molecules.Therefore,we synthesized the conjugated organic polymers（COPs）COP-Cu T₂TP with porphyrin macromolecule Cu T₂TP（[5,10,15,20-tetra（2,2′-bithiophen-5-yl）porphyrinato]copper（II））as the structural unit by electrochemical method.In the lithium-ion half-cell,it exhibited the reversible discharge specific capacity of 420 m Ah g^-1 and the high specific energy of 900 Wh Kg^-1 at 100 m A g^-1 and the voltage range of 1.3 V to 4.5 V.Besides,the reversible discharge specific capacity of 150 m Ah g^-1 were maintained at 5 A g^-1 after 8000 cycles.Due to the bipolar property of porphyrins,it can be used as both cathode and anode.Here,we assembled a fully symmetric cell（COP500-Cu T₂TP//1 M Li PF₆ in PC//COP500-Cu T₂TP）,it megnifested a reversible capacity of 104 m Ah g^-1 at 2 A g^-1 after 500 cycles.