Preparation And Supercapacitor Performance Of Flexible Bimetallic Sulfide/Graphene Film

The rapid development of future flexible electronic devices has called for ever-growing demands for flexible supercapacitors with high power density,fast charging-discharging rate and long cycle life.Two-dimensional reduced graphene oxide(rGO)film,as one of the most promising materials,can be combined with bimetallic sulfide to further improve capacity performance.However,the rGO nanosheets will self-stack in assembly process,leading to a compact layered structure,which affects the diffusion of electrolyte ions,further affects the electrochemical performance.In this paper,we designed and prepared a loose layered bimetallic sulfide/rGO film electrode by controlling the morphology of bimetallic sulfides and constructing three-dimensional framework structure,and studied the assembly process,morphology structure and electrochemical performance,as well as applied to flexible asymmetric supercapacitors.NiCo₂S₄with different morphology structure(i.e.,nanoparticle,nanosheet,nanotube)were prepared by hydrothermal process through changing the reaction conditions,and assembled to NiCo₂S₄/rGO films with rGO through vacuum filtration.NiCo₂S₄nanotubes with unique hollow structure become one of the most suitable materials to assemble rGO-based hybrid film.The morphology structure and electrochemical performance of NiCo₂S₄-NT@rGO film were studied.The hybrid film exhibits high specific capacitance of 771.4 F/g at the current density of 1 A/g.The good electrochemical performance come from the tube-like structure with large specific surface area,and the channels formed from the hollow structure of the tubes and the intercalation into rGO,which facilitate the ions/electrons transport.NiCo₂S₄@rGO/rGO film constructed by three-dimensional NiCo₂S₄@rGO frameworks was prepared through the hydrothermal process,freeze-drying and vacuum filtration.The hybrid film possesses a loose layered structure due to the steric effect and the support of rGO-based three-dimensional framework structure,which facilitate the free diffusion of electrolyte ions and provide the fast transmission channels for electrons,and exhibiting a high specific capacitance of 1100.0 F/g at 1 A/g,a good rate performance of 89.1%capacity retention at 10 A/g coupled with long cycling stability of 90.2%after 5000 cycles.Zn-Co-S@rGO/rGO and Mn-Co-S@rGO/rGO film were successfully prepared through the same idea of assembling a hybrid film from rGO-based three-dimensional framework structure.Our studies show that both films possess the loose layered structure and excellent electrochemical performance(1005.0 and 977.8 F/g at 1 A/g).A flexible asymmetric supercapacitor assembled using the NiCo₂S₄@rGO/rGO film as cathode and the rGO film as anode can light up a group of green LEDs,and shows a high energy density of 30.0 Wh/kg at a power density of 857.6 W/kg at an extended operating voltage of 1.8 V.