Study On 3-Dimentional Carbon Nanocomposites As Novel Electrode Materials For Supercapacitors

Starting from the investigation of conventional activated carbon(AC)electrodes,this thesis combines carbon nanomaterials,namely carbon nanotube(CNT)and graphene,with activated carbon to develop novel nanocomposite electrodes for supercapacitors.Combining single-component(CNT or graphene)or multi-component(CNT and graphene)carbon nanomaterials as conductive additives with AC,the resultant nanocomposite electrodes showed superior rate capability and cycling stability over conventional AC electrodes.The microstructure,pore size distribution,and specific surface area of the nanocomposite electrodes were studied by scanning electron microscopy(SEM)and nitrogen adsorption desorption(BET)and the electrochemical behavior by electrochemical techniques(including constant current charge and discharge,cyclic voltammetry,and electrochemical impedance spectroscopy).Furthermore,by comprehensively analyzing the electrochemical performances of these electrode materials against their physicochemical properties,we were able to optimize the compositions(specifically the contents of CNT and/or graphene)and the electrode preparation process towards the achievement of high-performance nanocomposite electrodes for supercapacitors:1.When incorporated as a single-component conductive additive into the conventional energy-type AC electrode,either CNT or graphene can significantly improve the conductivity and rate performance for the resultant ternary nanocomposite electrodes.Moreover,the combination of CNT and graphene as a multi-component conductive additive resulted in quaternary nanocomposite electrodes showing farther enhanced rate performance;2.With the introduction of CNT or graphene,the obtained ternary nanocomposite electrodes showed modified pore structures and pore size distributions with decreased microporosity and increased mesoporosity and macroporosity.These provided the electrodes with an easy-accessible channel for the rapid migration and transport of electrolyte ions,thereby reducing the internal impedance and enhancing the rate performance for the electrodes;3.With the introduction of CNT and graphene.,the obtained quaternary nanocomposite electrodes showed further enhanced rate performance over their ternary counterparts,which has been demonstrated to be due to the further improvement in pore structures and pore size distributions along with the synergistic effects from SP,CNT,and graphene in the electrodes;4.At 80 A g-1,the capacitance retention,maximum specific power,and specific energy at the maximum specific power of the optimized ternary nanocomposite electrodes AC/SP/CNT(90/3/2)and AC/SP/Graphene(90/4/1)were 80.13%and 79.84%.,81.53 kW kg-1 and 79.2 kW kg-1,and 11 Wh kg-1 and 10.01 Wh kg-1,respectively,which were significantly better than those the conventional AC electrodes of 28.51%,46.72 kW kg-1,and 1.71 Wh kg-1.This clearly demonstrated the excellent energy-power characteristics of the ternary nanocomposite electrodes;5.By introducing CNT and graphene together as a multi-component conductive additive and further optimizing the electrode preparation process,the resultant quaternary nanocomposite electrodes displayed farther enhanced rate performances and energy-power characteristics over their ternary counterparts.Specifically,the AC/SP/CNT/Graphene(90/1.25/2.75/1)quaternary nanocomposite electrode showed a higher capacitance retention of 87.29%and a higher maximum specific power of 85.81 kW kg-1 accompanying with a higher specific energy of 12.65 Wh kg-1.6.Upon cycled at 10 A g-1 for 30000 cycles,the AC/SP/CNT/Graphene(90/1.25/2.75/1)quaternary nanocomposite electrode retained its capacitance at 79.44%versus that of 65.94%for the conventional AC electrodes,clearly demonstrating the significance of introducing carbon nanomaterials in enhancing the cycling stability for the proposed nanocomposite electrodes in the present work.