Construction And Properties Study Of Graphene-Based Composite Electrode Material For Supercapacitor

Supercapacitor,one of new types of energy storage equipment,is energy-saving and environmentally friendly.As an electrochemical capacitor,supercapacitors have higher powerd ensity and energy density than conventional batteries and capacitors,respectively.In addition to excellent electrochemical performance,supercapacitors have many other advantages,such as mature preparation process,wide material source,low environmental requirements,environmental friendliness.Also,supercapacitors have excellent potential in experimental research and practical applications.According to the energy storage in different working principles,supercapacitors can be divided into pseudocapacitors?PC?and electric double layer capacitors?EDLC?.In the scientific research and application process,metal oxides?PC?have poor electrical conductivity,carbon-based materials?EDLC?also have low capacity.As a consequence,supercapacitor material rate performance and cycle life are reduced.In order to solve the shortcomings of single supercapacitor materials,this paper combines two kinds of capacitor materials to form a synergistic way to prepare high performance supercapacitor electrodes with higher specific capacitance,power density,energy density and cycle performance.The main research results are as follows:?1?Carbon/Co₃O₄ composite mesoporous hollow spheres?C/Co₃O₄ MHSs?and graphene oxide were successfully synthesized to fabricate hybrid films.Unique sandwich and mesoporous structures can provide more pathways for electrolyte transmission and obtain excellent electrochemical performance.After combinding with C/Co₃O₄ MHSs,the hybrid films can achieve a specific capacity of 1266.0 F g^-1(at 1 A g^-1),which is much higher than that of the C/Co₃O₄ MHSs(153.9 F g^-1)and reduced graphene oxide?RGO?films(213.5 F g^-1).Moreover,the C/Co₃O₄/RGO//RGO asymmetric supercapacitor?ASC?device was fabricated.The ASC exhibits a high energy density of 32.7 Wh kg^-1(power density of 800 W kg^-1)and an excellent cycling stability?85.9%capacitance retention,5000 cycles?.Besides,white LED bulbs?3.2 V?can be lit by two ASCs in series.?2?Mixed metal oxide hollow spheres?NiCo₂O₄?/reduced graphene oxide?RGO?hybrid lamellar films are fabricated via a vacuum filtration process.After a simple assembling process,the mixed metal oxide hollow spheres are inserted in-between the RGO nanosheets.The self-restacking of RGO nanosheets will be prevented effectively and the interlayer spacing will be increased,which is benefit for electrolyte ions penetration and fast electron diffusion.The as-prepared NiCo₂O₄/2RGO,hybrid lamellar films exhibit superior electrochemical performances(1414.7 F g^-1)and remarkable cycling retention?90.2%,5000 cycles?.Meanwhile,the asymmetric supercapacitor?ASC?is successfully constructed utilizing the activated carbon?AC?and NiCo₂O₄/2RGO hybrid lamellar films as the negative electrode and positive electrode,which deliver maximal specific capacitance of 97.4 F g^-1(1 A g^-1)and a high energy density of 34.6 Wh k g^-1(799.0 W kg^-1 for power density)and power density of8007.4 W kg^-1(19.1 Wh kg^-1 for energy density).After charging,two ASCs devices connected in series can light a white light-emitting diode?LED?.?3?Flexible yolk-shelled NiCo₂S₄ hollow spheres/reduced graphene oxide?RGO?hybrid lamellar films were successfully fabricated by developing a facile strategy of vacuum filtration.After constructing the sandwich-like structures,the NiCo₂S₄ hollow spheres were inserted in-between the RGO nanosheets.The special structure can effectively prevent the self-restacking of RGO nanosheets.Besides,the increased interlayer spacing,leading to fast ions penetration and diffusion.The as prepared NiCo₂S₄/2RGO hybrid lamellar films with excellent conductivity delivered appreciable capacitance of 1000.5 F g^-1 at 1 A g^-1.Moreover,the asymmetric supercapacitor?ASC?was successfully synthesized utilizing the activated carbon?AC?and NiCo₂S₄/2RGO lamellar films as the negative electrode and positive electrode,which manifested a high energy density(15.4 Wh kg^-1),power density(2227.3 W kg^-1)coupled with remarkable cycling stability?80.5%retention over 5000 cycles?.After charging,two ASCs devices connected in series were capable of lighting two red LEDs connected in parallel for at least 2.0 minute.