Study On Microstructure Regulation Of Functional Carbon Composites Based On Coal-tar Pitch And Its Capacitor Performance

Supercapacitors,one important energy storage devices,has many outstanding advantages.such as high power density,good cycle stability and the safety in use,which is widely used in energy storage.Electrode materials are carriers for charge storage and electron transport,playing one crucial role for determining the performance of capacitors.Porous carbon has many advantages,such as low cost,high specific surface area and adjustable pore structure.which is most widely used for commercial electrode materials.However.due to the energy storage mechanism and its low energy density,porous carbon is limited in the advanced supercapacitors and improving energy density has become a major thrust of research.Because of complex graphite microcrystalline unit and high carbon content,coal tar pitch has been used as main carbon precursor for functional carbon materials and task-specific coal pitch has been a hot area of research in coal chemical industry.Based on the above.this paper focuses on the study of the functionalized coal tar pitch,and lot of other work,such as the porous structure design and controllable carbonization for porous carbon,have also been intensively studied.Some typical porous carbons with various microstructures and morphology are compared and analyzed,that specific surface area along with pore size distribution play important roles,and functional components are also important.This paper provides insights on the modified coal tar pitch and functional carbon that the main contents are as follows:(1)Based on Friedel-Crafts acetoxylation and Baeyer-Villiger oxidation,carboxyl coal tar pitch is successfully prepared and the three-dimensional cross-linked diketone improves amphiphilic properties of coal tar pitch.Because of the change of molecular structure,the ?-?interaction between aromatics is reduced that the micro/mesoporous structure of functional carbons are effectively regulated after carbonization.Experimental results show that mesoporous ratio of carbon left behind pyrolysis reaches nearly 73.4%and the specific surface area is 1394.6m²g^-1 with 1.54cm³g^-1 pore volume.The specific capacity of the obtained micro/mesoporous carbon is 317Fg^-1 when the current density is limited in 1Ag^-1.After activation by KOH,the functional carbons has high surface area(2098.2m²g^-1,1.63cm³g^-1 pore volume)attended by improved mesoporous ratio(80.1%)and the specific capacity is 320Fg^-1 as the current density limits in 1Ag^-1.(2)Based on in-situ polymerization,functional carboxyl pitch hydrogels have successfully prepared improved by intermolecular valence bond from polyacrylic acid and polyacrylamide.Mingle with carboxyl pitch,improved surface area and pore structure of functional carbons have been obtained after carbonization with help of polyacrylic acid and polyacrylamide.Experimental results show that specific surface area of carbon left behind after dopling pyrolysis carboxyl pitch or polyacrylamide reach nearly 1294.6m²g^-1 and 1210.1m²g^-1 with higher pore volume(1.34cm³g^-1 and 1.32cm³g^-1)respectively.The specific capacity of the obtained micro/mesoporous carbons are 279Fg^-1 and 273Fg^-1 with the higher capacity retention rate(88.3%and 73%)respectively when the current density is limited in 1 Ag^-1.In comparison,functional carboxyl pitch hydrogels show better capacitive performance after carbonizing,which is clearly attributable to polyacrylic acid and polyacrylamide components.(3)Based on mental carbon composites,Mn²⁺ doping functional carbons are successfully prepared that the matrix is proved to be homogeneously disperse structure.Experimental results show that functional carbons carbonized with help of polyacrylamide play excellent electronic transport and charge-discharge performance doping with Mn2+.When the current density is 0.25 Ag^-1,the specific capacitance of Mn²⁺-doping carbon as electrode material is 483.7Fg^-1,and it still maintain a high retention(97.9%)after circulating for 3000 times.The synergistic effect of manganese oxide nanocrystals,pore size distribution and specific surface area,attribute to its excellent electrochemical performance.(4)Based on nitrogen-doped carbon composite,a blend with carboxyl coal tar pitch could be obtained by adding aniline and pyrrole,and nitrogen-doped carbon composite materials are obtained after carbonization.When the nitrogen content of carboxyl coal tar pitch blending polyaniline is holding at around 4.99%after carbonization,the chemical bonding state of nitrogen maintains as graphite nitrogen(N-Q)and pyridine nitrogen(N-6)accounting for 72.9%.When the nitrogen content of carboxyl coal tar pitch blending polypyrrole is holding at around 3.13%after carbonization,the chemical bonding state of nitrogen maintains as graphite nitrogen(N-Q)and pyridine nitrogen(N-6)accounting for 81.8%.As the current density is 1Ag^-1,the specific capacitance of N-doping carbon as electrode material are 371.6Fg^-1 and 287.2Fg^-1 respectively.The introduction of nitrogen atom significantly improves the electrochemical performance of carbon composite.