Micelle-induced Assembly Of Graphene Quantum Dots Into Conductive Porous Carbon For High Rate Supercapacitor Electrodes At High Mass Loadings

Supercapacitors have been widely used as high-power devices in portable electronics,power backups,and electric vehicles owing to their fast charge-discharge ability and long lifespan.In most of the practical cases,supercapacitors should be installed in a limited space.To meet this requirement,the active mass loading on electrodes should be increased as high as possible to improve the total energy density of the devices.Porous carbon materials with a robust electric double-layer behavior show great potential in this field.Unfortunately,most of the carbon materials still confront with the rapidly reduced rate performance due to the decreased conductivity and blocked ion migration channels with the rising of mass loadings,which severely hinders their practical applications.Porous structure can be easily constructed through template-assisted methods.However,well-developed pores will break the large-area conjugated networks,resulting in the products with low electric conductivity.To solve this problem,a highly conductive porous carbon was prepared through a simple micelle-induced assembly method using crystallized graphene quantum dots as precursors and block copolymer F127 as soft template.The influence of the block polymer F127 and KOH the dosage on the morphology and electrochemical energy storage performance of porous carbons were detailedly investigated.This thesis mainly contains the following content:1.The porous carbons were prepared with different block polymer F127 and KOH dosages.The morphology of the samples gradually transformed from denesly blocks to ant nest structure with the increasing of block polymer F127.By increasing of KOH dosage,the dense structure of the sample gradually becomes porous structure and the specific surface gradually increases.The unique sp² hybridized graphene quantum dots as precursors ensure the product with a two times higher electric conductivity than the commercial activated carbon.Under the optimal condition,the specific surface area of porous carbon is 1323 m² g^-1,the total pore volume is 0.858 cm³ g^-1.The mesoporous volume is 0.176 cm³g^-1and the pore dimater is mainly distributed at 20-50 nm.The interconnected mesoporous structure promotes robust ion transport kinetics.2.By increasing the block polymers F127 and KOH dosage,the specific capacitance and rate performance of the samples first increased and then decreased,which was mainly attributed to the high conductivity of the samples and the complete interconnected mesoporous structure.Using 6 mol L^-1 KOH as electrolyte,in three-electrode system,it shows high specific capacitances of 315 F g^-1 at 1 A g^-1 under the optimal condition.The capacitance retention is up to 54%at 100 A g^-1.In two-electrode system,it also performs superior specific capacitance of 270 F g^-1 at 1 A g^-1 as well as excellent rate performance with 56%capacitance retention at 100 A g^-1.3.The supercapacitor performance of the optimized sample was measured at high mass loadings.It was found that the sample still had excellent electrochemical performance at high mass loadings.In three-electrode system,the thick CPC-0.3 electrode at a high mass loading of 20 mg cm^-2still maintains a remarkable capacitance of 142 F g^-1at 10 A g^-1,leading to an ultrahigh electrode areal capacitance of 2.8 F cm^-2 at 10 A g^-1.In the symmetric supercapacitor,the areal specific capacitance is two times higher than commercial activated carbon at 1 A g^-1 under 20 mg cm^-2 high mass loading.The areal specific capacance is2.49 F cm^-2 at 10 mg cm^-2 mass loading.The CPC-0.3//CPC-0.3 supercapacitor with 2 mg cm^-2mass loading on each electrode exhibits a maximum energy density of 9.21 Wh kg^-1at the power density of 247.75 W kg^-1.Noticeably,even at a very high mass loading of 20 mg cm^-2,the energy density is still as high as6.45 Wh kg^-1.Moreover,the device at 10 mg cm^-2shows excellent cycle stability with no obvious capacitance fading after 10,000 cycles at 10 A g^-1.The results suggest that the conductive porous carbon prepared by highly crystalline graphene quantum dots as the precursor has great potential for practical applications.