The Preparation And Application Of Asphalt-Based Heteroatom-Doped Porous Carbon For Electrochemical Energy Storage

Lithium-ion batteries（LIBs）and lithium-ion capacitors（LICs）are regarded as two novel energy storage devices because of the high-energy density and low self-discharge,however,there are still some issues with these energy storage devices,such as the low power density in LIBs,and the unbalance of reaction kinetics between anode and cathode in LICs.The electrochemical performance of energy storage devices depends on the performance of electrode materials.Carbon-based materials are widely studied in the present stage.As a by-product of the oil refining process,petroleum asphalt has a high carbon content and rich aromatic hydrocarbons.therefore it is a high-quality precursor for the preparation of carbon materials.Here in,petroleum asphalt as the carbon precursor,two kinds of carbon materials were fabricated by template method,and the effects of the composition and microstructure of carbon materials on the electrochemical performance was studied.The details are as follows.（1）Nitrogen-doped porous carbon nanosheets（NCN）were synthesized by a one-pot method using petroleum asphalt as a carbon source,urea as a nitrogen source,and hexagonal porous magnesium oxide nanosheets as a template.NCN with abundant hierarchically porous structure has a rich active site for lithium storage,showing excellent rate performance and cycling stability.The specific capacity can still maintain 600 m Ah g^-1after 1000 cycles at the current density of 2 A g^-1.Additionally,the specific capacity reached 360 m Ah g^-1even at a high current density of 10 A g^-1.（2）Thiosemicarbazide reacts easily with carboxylic acid.Sulphur-nitrogen co-doped carbon（H-SN-C）was prepared by using petroleum asphalt as a carbon source and magnesium oxide as a template in the presence of polymer formed by thiosemicarbazide and glycolic acid.H-SN-C with honeycomb structure can increase the contact area between electrolyte and electrode,and the sulfur and nitrogen doping can provide more active sites for Li⁺storage,when used as anode materials,the specific capacity can reach 740 m Ah g^-1after 1000 cycles at 2 A g^-1.（3）The LICs were assembled using NCN and H-SN-C.Firstly,the symmetric LICs were assembled with NCN as both anode and cathode,which displays a high energy density of 167Wh kg^-1and a high-power density of 12000 W kg^-1when the mass ratio of cathode to anode is1.5:1.Furthermore,the assymmetric LICs composed of the H-SN-C anode and NCN cathode were constructed.The optimized performance is obtained when the mass ratio of the cathode and anode is 2:1,and the high energy density reaches 150 Wh kg^-1when the high-power density is 225 W kg^-1.