Preparation And Performance Of Carbon-based Flexible Electrode Materials

Benefiting from its high power density,fast charging and discharging capability,high circulation stability and instantaneous large current supplying,supercapacitor has been widely used in many fields.With the increasing demanding for flexible and wearable portable devices,the developments of flexible supercapacitors are attracting more and more attentions,among which the preparation of flexible electrode materials with high electrochemical activity is the most critical issue.In this thesis,flexible electrode materials possessing high specific capacity and good cycling stability were prepared based on the synergistic effect of multiwalled carbon nanotube?MWNT?,reduced graphene oxide?rGO?and polyaniline?PANI?.Firstly,environment-friendly and flexible film of PANI/rGO with high toughness was prepared by doping with organic proton acid of PA-550 which had long hydrophilic chains.Furthermore,using graphene quantum dots?GQD?that possessed plenty of hydrophilic groups as linkers,GQD,MWNT,rGO and PANI were deposited on the carbon cloth by in-situ polymerization and layer-by-layer spraying self-assembly method respectively.Thus flexible electrodes of supercapacitors were prepared.The main contents of this thesis are as follows:?1?The polyaniline/graphene?PANI/rGO?nanocomposites with different rGO content?0wt%,0.5wt%,1wt%,2wt%?were prepared by interfacial polymerization method.Then the composite was doped twice by organic proton acid PA-550 which had long hydrophilic chains tointroducehydrophilicitytoPANI/r GO,thusstableaqueousdispersionof environment-friendly PANI/rGO could be easily obtained.Furthermore,the flexibility film of PANI/rGO with high toughness was prepared by solution casting of the aqueous dispersion of PANI/rGO.Due to the presence of rGO,the conductivity,specific capacitance and cycle life of PANI/rGO composites were significantly improved compared with pure PANI.When rGO mass content is 1%,the specific capacitance reaches the highest of 343.3 F/g.?2?The PANI/carbon cloth flexible electrode was prepared by in-situ polymerization method.Meanwhile,to increase the loading amount of the active material,MWNT/GQD,consisting by the GQD assembling on the surface of MWNT,was initially absorbed to the surface of carbon cloth with the help of?-?and hydrogen bond interactions forming MWNT/GQD/carbon cloth.Further,flexible electrode material of MWNT/GQD/PANI/carbon cloth with good electrochemical performance was prepared by in situ polymerization of PANI onto the surface of MWNT/GQD/carbon cloth under the cooperating of electrostatic force,hydrogen bonding and?-?interactions.Due to the presence of MWNT/GQD,the hydrophilicity of the electrode material was significantly improved,and the loading amount of the electrochemical active material on the carbon cloth was obviously increased.The high specific capacitance of 361.5 mF/cm² was reached by the prepared MWNT/GQD/PANI/carbon cloth electrode at a scan rate of 30 m V/s,which was nearly three times higher than that obtained by the PANI/carbon cloth electrode having no MWNT/GQD.When assembling into a solid flexible supercapacitor,the area ratio capacitance of MWNT/GQD/PANI/carbon cloth electrode was obviously improved compared with that of PANI/carbon cloth electrode.More importantly,with the presence of MWNT/GQD the capacitance retention of the MWNT/GQD/PANI/carbon cloth electrode was also increased from 25.5%of the PANI/carbon cloth to 85%.?3?In order to solve the puzzles of rGO and PANI such as surface inertness,poor water solubility,and inclined to to agglomerate,which were also the serious problems affecting the performance of the electrode materials,water-soluble GQD with abundant functional groups was modified onto the surface of rGO to form uniformly aqueous dispersed of rGO/GQD with the aids of the?-?interaction.Driven by the electrostatic interaction between-COO^-on rGO/GQD and–NH⁺-on PANI,as well as the?-?interaction between them and the carbon cloth,the uniform and stable dispersions of rGO/GQD and PANI were alternately deposited on the surface of carbon cloth substrate,forming?rGO/GQD/PANI?_n/carbon cloth.When the number of assembled layers was 20,rGO/GQD and PANI particles were evenly and densely packed on the surface of the carbon fiber to form a porous structure.Furthermore,an all-solid flexible supercapacitor was assembled by using?rGO/GQD/PANI?₂₀/carbon cloth as the electrode and PVA/H₃PO₄ gel as solid electrolyte.The constant current charge/discharge test shows that the area specific capacitance of?rGO/GQD/PANI?₂₀/carbon cloth in the all-solid flexible supercapacitor can reach 28.86 mF/cm² with good cycling stability and high capacitance retention rate of 84%.