| Recently,with the fast progress of flexible portable and wearable electronic equipment,the aqueous zinc-ion hybrid supercapacitors（ZHSCs）have drawn widespread attention as flexible energy storage systems.The focuses of research and development are the rational designs of flexible electrode materials and their structures.Graphene,as a two-dimensional（2D）material,has the advantages of high electrical conductivity,better chemical and thermal stability,large specific surface area and excellent mechanical flexibility,etc,make it possible to be an attractive flexible electrode material for the ZHSCs.However,graphene is easy to the self-agglomeration,the easy lamellar defects in the synthesis process and the poor dispersion in water etc,which result in its specific surface area and electrical conductivity to decrease.To solve these problems,the composite film electrodes of ZHSCs with high electrochemical performance and flexibility were synthesized by the method of graphene oxide（GO）,MXene or VS2 composited and reduced to films in this paper,which made full use of the high conductivities of MXene and VS2,the excellent hydrophilicity of MXene,and the synergistic effect between reduced graphene oxide（rGO）and MXene or VS2.The specific contents and results are as follows:1.A free-standing 2D layered rGO-MXene composite film with flexibility was prepared by the self-assembly method of reducing GO and MXene mixed solution using a zinc plate.The effects of the time of growing films,electrolyte concentrations,the embedding amounts of MXene in the composite films,etc on the compositions and structures of rGO-MXene composite electrodes were investigated.The best time of growing films was 60 min,the best Zn SO4 electrolyte concentration was 2 M and the best intercalation mass percentage of MXene was 30%of rGO-MXene composite electrodes were obtained.MXene is embedded between the layers of rGO,which effectively inhibits the restacking of rGO and MXene nanosheets.This more fully utilizes the specific surface areas of rGO and MXene nanosheets.Thereby accelerating ions migration in the composite electrodes and improving the conductivities and hydrophilicity of the composite films.Next,rGO-30%MXene composite cathode and zinc foil anode were used to assemble the aqueous and quasi-solid ZHSCs,respectively.Subsequently,the relationships between the specific capacities,energy densities,cycling stability and working conditions were studied.The results show that the aqueous ZHSC based on rGO-30%MXene composite film displays a large specific capacity of 367.86F g-1 at a scan rate of 2 m V s-1,a large energy density of 100.14 Wh kg-1 with a power density of 516.34 W kg-1 and the capacity retention ratio still attains 90%after 10000 cycles at a current density of 0.8 A g-1,which testifies that the aqueous ZHSC has remarkable cycling stability.As well as the quasi-solid ZHSC based on this composite film exhibits a specific capacity of 86.71 F g-1 at a scan rate of 50 m V s-1,and displays great electrochemical stabilities under different bending angles.2.In order to obtain a flexible ZHSC with higher energy density and cycling stability,the method in the first part of the work is used for reference.First,to prepare the VS2/Super-P/PVDF-Ti composite cathode materials,polyvinylidene fluoride（PVDF）,conductive carbon black（Super-P）and VS2 were added to N-methyl-2-pyrrolidone（NMP）in order and stirred until uniform.The mixed slurries were scraped onto the current collector titanium foils.Using Super-P as the conductive substrate,which alleviates the significant volume change of VS2 itself and improves its utilization rate through the synergistic effect of VS2 and Super-P.Thereby the problems of short cycling lifetime and poor rate performance are solved.Then,VS2/Super-P/PVDF-Ti composite cathode and zinc foil anode were used to assemble the aqueous ZHSCs.The influence of the composite mass ratios of VS2,Super-P and PVDF on the compositions and structures of the cathode materials was investigated.The optimal the composite mass ratio of VS2,Super-P and PVDF was 6:3:1 was obtained.Next,VS2/Super-P/PVDF-Ti composite cathode and rGO-30%MXene composite anode were used to assemble the aqueous ZHSCs.The capacity matching of the cathode and anode was investigated.When the mass of anode of rGO-30%MXene composite film was 1.2 mg,the best mass ratio of the capacity matching of the anode and cathode was 1.5:1 was obtained.Finally,based on the optimal content of VS2 in the VS2/Super-P/PVDF-Ti composite cathode,the optimal composite mass ratio of VS2 to rGO was 4:6 was obtained.Subsequently,the relationships between the specific capacities,energy densities,cycling stability and working conditions were studied.The results show that the aqueous ZHSC based on VS2/Super-P/PVDF-Ti/rGO-30%MXene exhibits a large specific capacity of 171.43 F g-1 at a scan rate of 0.5 m V s-1,a large energy density of 136.11 Wh kg-1 with a power density of 69.7W kg-1 and the capacity retention ratio still attains 97.47%after 10000 cycles at a current density of 0.2 A g-1,which proves that the aqueous ZHSC has outstanding cycling stability.As well as the quasi-solid ZHSC based on rGO-40%VS2/rGO-30%MXene shows a large specific capacity of 112.86 F g-1 at a scan rate of 1 m V s-1,and displays great electrochemical stabilities under different bending angles. |
