Prepartion And Lithium Storage Performance Research Of KOH Activated Conjugated Microporous Polymer Hard Carbon

Conjugated microporous polymer(CMP)has high carbon content and low mass loss after high temperature pyrolysis,and the carbides obtained can maintain the original morphology and structure of CMP.In addition,the structure of CMP is adjustable,which facilitates the introduction of heteroatoms into its structure through monomers,so it is an ideal precursor for hard carbon materials.In this paper,CMP,nitrogen-containing CMP and sulfur-containing CMP,were synthesized from different monomers and carbonized by KOH activation to prepare KOH-activated porous hard carbon,nitrogen-containing hard carbon and sulfur-containing hard carbon.The effects of KOH activated carbonization on the structure and electrochemical properties of porous hard carbon,nitrogen-containing hard carbon and sulfur-containing hard carbon materials were investigated.The main research contents are as follows:(1)Conjugated microporous polymer(CMP)was synthesized by self-polymerization reaction using 1,3,5-triethynylbenzene as monomer,cuprous iodide and bis(triphenylphosphine)palladium dichloride(II)as catalyst.Then porous hard carbon(PHC)and porous hard carbon activated by KOH(PHC-K)were prepared by high temperature treatment with CMP as precursor,and their properties were studied.The results of SEM show that PHC and PHC-K are formed by the accumulation of many nanoparticles,which can still maintain the original morphology and structure of CMP.Nitrogen adsorption desorption test shows that the specific surface area of PHC-K increased obviously after activated carbonization.The electrochemical test results show that PHC-K has good electrochemical performance.The initial charging specific capacity of PHC-K is up to 972.1 m Ah·g^-1 at the current density of 0.1 A·g^-1,and the charging specific capacity of PHC-K is up to 621.7 m Ah·g^-1 after 300 cycles at the current density of 0.6A·g^-1.(2)The network structure nitrogen-containing conjugated microporous polymers(N2CMP)and spherical nitrogen-containing conjugated microporous polymers(N1CMP)were synthesized by reaction of 1,3,5-triethynylbenzene with 2,5-dibromopyrazine and 2,5-dibromopyridine,respectively,using cuprous iodide(Cu I)and tetra(triphenylphosphine)palladium(0)as catalysts.Then nitrogen-containing hard carbon N2HC,N1HC and KOH activated nitrogen-containing hard carbon N2HC-K were prepared by high temperature pyrolysis and KOH activated carbonization using N2CMP and N1CMP as precursors,and their properties were studied.SEM characterization shows that N2HC-K,N2HC and N1HC all retain the morphology and structure of their precursors;Nitrogen adsorption and desorption tests show that KOH activated carbonization increases the specific surface area of N2HC-K;Elemental analysis shows that the nitrogen contents of N1HC,N2HC and N2HC-K were 3.75%,5.08%and 5.34%,respectively.The electrochemical test results show that the electrochemical performance of N2HC-K is good.At the current density of 0.1A·g^-1,the first charge specific capacity of N2HC-K is as high as 604.8 m Ah·g^-1.The specific capacity is as high as 488.2 m Ah·g^-1 after cycling for 500 times at 0.6 A·g^-1 current density.(3)Sulfur-containing conjugated microporous polymer(SCMP),was synthesized from sulfur-containing monomers 2-dibromothiophene and 1-3-triethynylbenzene,and then sulfur-containing hard carbon SHC was prepared by carbonization at high temperature.In order to further improve its electrochemical performance,KOH was used as activator to activate and modify SCMP,and then pyrolyzed at high temperature to obtain KOH activated sulfur-containing hard carbon SHC-K.SEM characterization shows that the morphology and structure of SCMP,SHC and SHC-K are similar,indicating that SCMP can maintain the original morphology and structure after high temperature pyrolysis.Nitrogen adsorption-desorption tests show that SCMP,SHC and SHC-K are porous materials with specific surface areas of 697.2,741.4 and 1624.2 m2·g^-1,respectively.The specific surface area of SHC-K is greatly increased by KOH activation;Elemental analysis shows that the sulfur content of SHC and SHC-K is 3.657%and 4.438%,respectively;The electrochemical test results show that the electrochemical performance of SHC-K material is obviously improved after KOH activated carbonization treatment.At the current density of 0.1A·g^-1,the first charge specific capacity of SHC-K is as high as 842.2 m Ah·g^-1,which is much higher than that of SHC material(614.4 m Ah·g^-1).The specific capacity of SHC-K is as high as 565.9 m Ah·g^-1after charging and discharging for 500 times at current density of 0.6 A·g^-1.