Preparation Of Porous Carbon Electrode Materials Derived From Small Molecular Cyclic Compounds For EDLCs With High Withstanding Voltage

Electric double-layer capacitors(EDLCs)have the advantages of high power density and long cycle life,but low energy density is their fatal disadvantage.Increasing the withstanding voltage of EDLC can increase its energy density at a square rate.This thesis starts from reducing the oxygen content of EDLC electrode material-porous carbon,focuses on improving the withstanding voltage characteristics of porous carbon electrode materials,and thus increases the energy density of EDLCs.In the study,low-boiling small molecular cyclic compounds containing no oxygen elements were selected as precursors,and the strategy of“alkali metal-assisted promotion of high-temperature pyrolysis of precursors”was used for the research.With pyrrole as the precursor and assisted by metal Li,Na and K,respectively,the feasibility of preparing porous carbon through solvothermal reaction and high-temperature carbonization was investigated and confirmed,and three kinds of porous carbon materials were prepared.It is clear that the mechanism that alkali metals promote this process is that the products of Na and K reacting with pyrrole are thermally unstable,and the solvothermal products pyrolyze at high temperature,producing chemically active substances with double bonds(C₄H₈,C₃H₆ and C₄H₅N of double bond isomers).These structures contribute to the subsequent generation of condensed ring structures and even large?bond conjugated structures of carbon materials.The influence mechanism of alkali metal species on the chemical composition,morphology,microdomain structure and pore structure of porous carbon was studied.It is found that as the activity of alkali metals increases,the carbonaceous crystallite structure becomes more ordered,and the sp²C content of porous carbon gradually increases.The minimum oxygen content of the sample is6.87 wt%,which is still relatively high,mainly caused by the instability of the reaction intermediate of the five-membered ring pyrrole.In order to obtain a stable reaction intermediate(MCI),18 kinds of nanoporous carbon were obtained using three alkali metals-assisted carbonization of six kinds of halogenated aromatic hydrocarbons.Studies have shown that the alkali metal M attacks the C-X bond to form the salt MX and benzene radical.And the benzene radical further evolves into MCI with a six-membered ring as the basic unit through radical polymerization.Subsequently,the MCI undergoes high-temperature thermal polymerization to form nanoporous carbon.The salt MX plays the role of“in situ template”,undergoes a phase change(solid?liquid?solid or solid?liquid?gas)in the pyrolysis process,and finally detaches leaving holes.The preparation method has good universality.As the pyrolysis temperature increases,the crystallinity of carbonaceous crystallites firstly increases and then decreases,and the oxygen content of porous carbon gradually decreases.At 1000?,the oxygen content of the sample is 5.96 wt%.Pyrolysis in the Ar/H₂ mixed gas reduced some oxygen atoms on the nanoporous carbon,further reducding the oxygen content in the porous carbon,and successfully improved the withstanding voltage characteristics of the carbon electrode.Taking potassium-assisted carbonization of chlorobenzene in hydrogen-argon mixed gas to prepare a high withstanding voltage porous carbon(PC-KC)as an example,when the pyrolysis temperature is 1000?,the oxygen content of the PC-KC-1000 sample is only 4.09 wt%.When the PC-KC-1000 sample is used as the electrode material of EDLCs,the operating voltage in TEABF₄/PC and EMIMBF₄ electrolytes can be increased to 3.3 and 3.5 V,respectively,and the maximum energy density is 53.5 and64.4 Wh kg^-1,respectively.