Porous Graphene/Nickel And Iron-based Composite Electrode Materials For Flexible Supercapacitors

With the advancement of science and the popularization of intelligence,the relectronic equipment was developing for miniaturization,thinness and softness.However,traditional energy storage device is rigid and easy to cause electrode material separated from the current collector once bent or folded,even causing a sharp drop in electrochemical performance.So,it is imperative to develop flexible energy storage equipment.In flexible electrode materials,graphene has attracted much attention because of its large theoretical specific surface area and excellent conductivity.Nevertheless,during the film assembling and electrochemical testing,the strong van der Waals force and?-?attraction drive graphene sheets to restack themselves,resulting in a decrease in its surface area.The specific capacitance(especially the volume specific capacity)of traditional graphene-based materials is not very ideal.The introduction of pseudocapacitance materials between graphene nanosheets solves the problem of graphene nanosheet agglomeration,and chemical etching is used to create cavities of different sizes on the graphene surface,thereby improving the electrolyte ions perpendicular to the graphite.The radial transmission in the ene direction,through the combination of graphene and the pseudocapacitance material,improves the cycle life of the composite material and obtains a larger specific capacity.The research is as followed:Firstly,we demonstrate free-standing PGNs/Ni(OH)₂ films can be easily fabricated through a simple and efficient vacuum filtration self-assembly technique.For the PGNs/Ni(OH)₂ film,the Ni(OH)₂ nanosheets in between the graphene sheets can serve as“spacers”to prevent the restacking of the graphene sheets,and efficiently improve the ion transport through the film in-plane direction.Further,the pores in graphene sheets are beneficial for electrolyte ion transport through the graphene sheets in the cross-plane direction.As a result,the as obtained PGNs/Ni(OH)₂ film exhibits high specific capacitance(1407 F g^–1 and 2701 F cm^-3 at 5 mV s^–1),excellent rate capability and cycle stability.Moreover,the assembled ASC device,based on PGNs/Ni(OH)₂ and PGNs/CNT as positive electrode and negative electrode,respectively,delivers both ultrahigh gravimetric and volumetric energy densities of 51.9 Wh kg^–1 and 73.0 Wh L^–1(based on the total mass and volume of two electrodes).Therefore,the PGNs/Ni(OH)₂film electrodes possess great application prospects for promoting the development of energy storage and conversion.Secondly,pseudocapacitance material were growth on CNT as one of the positive/negative material with high conductivity.(CNT@Ni(OH)₂,CNT@Fe₂O₃).Compositing them with PGNs to prepare composite film(PGNs/CNT@Ni(OH)₂,PGNs/CNT@Fe₂O₃).The pores in graphene sheets are beneficial for electrolyte ion transport through the graphene sheets in the cross-plane direction.Further,The addition of CNT can greatly improve the conductivity of the material;the CNT@pseudocapacitance between the graphene sheets could prevent the restacking of the graphene sheets,and efficiently improve the ion transport through the film in-plane direction.As a result,the as obtained PGNs/CNT@Fe₂O₃film exhibits high specific capacitance(1396 F g^–1 and 1845 F cm^-3 at 2 mV s^–1),PGNs/CNT@Ni(OH)₂ film exhibits high specific capacitance(1034 F g^–1 and 1396 F cm^-3 at 2 mV s^–1),excellent rate capability and cycle stability.Moreover,the assembled ASC device,based on PGNs/CNT@Ni(OH)₂ and PGNs/CNT@Fe₂O₃ as positive electrode and negative electrode,respectively,delivers both ultrahigh gravimetric and volumetric energy densities of 84 Wh kg^–1 and 116.0 Wh L^–1(based on the total mass and volume of two electrodes).