Preparation Of Graphene-based Electrode Materials And Their Electrochemical Energy Storage Properties

In this paper,Graphene quantum dots?GQDs?were directly used as a novel nano-sized conductive additive instead of the common carbon black?CB?,to prepare activated carbon?AC?-based electrodes with effective conductive network and investigate the influence of surface properties of graphene on the electrochemical characteristics of the electrodes.At the same time,graphene oxide was used as a precursor and composited with surfactant to prepare reduced graphene oxide micro-flower?rGOF?by spray granulation-thermal reduction method.The"structure-effect" relationship between the crystal structure,oxygen-containing functional groups and defects of the materials and the electrochemical performance were studied to determine the best structure for electrolyte in supercapacitors and lithium ion to intercalate and transfer.The specific research contents are as follows:First,GQDs were directly used as a novel conductive additive with different amounts.Composite electrodes of GQDs and AC with effective conductive network were prepared by liquid-phase mixing?AC-G?and thermal reduction recombination?AC-HG?respectively.The effects of the two composite methods on the structural characteristics of AC electrode and the performance for the electrical double-layer capacitors were investigated.It was found that???the specific capacitance?SC?and rate performance were enhanced for the electrodes with 1 wt%GQDs as conductive additive,comparied with 10 wt%CB.The corresponding SC values declined from 110 F g^-1 to 85 F g^-1,100 F g^-1 to 65 F g^-1,respectively,when the current density varied from 0.1 A g^-1 to 10 A g^-1;???the oxygen functional groups from GQDs were removed by the thermal reduction,which enhanced the electronic conductivity at the expense of decline of the ionic conductivity for the AC-HG electrode.As a result,its rate performance slightly decreased,but a substantial increase in cycle stability.After 3600 cycles at 65?,the SC values of AC-G1 and AC-HG1 electrodes were 46.5 F g^-1 and 71.7 F g^-1,respectively,and the capacity retention rates were 62.2%and 81.7%,respectively.rGOF with three-dimensional corrugated structure was prepared by the spray drying-thermal reduction method using graphene oxide as precursor and composited with surfactant.By changing the reduction temperature to adjust morphology,layer spacing,oxygen content and defects,respectively,rGOF was acted as the electrode material in supercapacitors and lithium ion battery.The results showed that:???The supercapacitor assembled with rGOF could still work under high voltage of 4.0 V.The discharge capacity for the electrodes treated with 400 ? can reach 141.84 F g^-1,and the energy density reaches 126.6 Wh kg^-1 which is greatly higher than the energy density of AC-based supercapacitors.It was closely related to the electrochemical activation caused by the special interlayer structure,oxygen content and defects of the materials.???rGOF as a negative electrode material of lithium ion,the sample with thermal reduction at 400? exhibited the highest initial charge capacity(691.3 mAh g^-1).The samples treated at 700? showed the best rate and cycling performance,with specific capacity of 196.2 mAh g^-1 at a current density of 1 A g^-1 and 288.9 mAh g^-1 after 100 cycles.