Design And Electrochemical Properties Of Cobalt-based Ultrathin Nanosheets

Energy storage is a very important link in the energy system and the market demand is increasing under a series of policies issued by the government Among which,electrochemical energy storage,also known as secondary battery energy storage,is the most rapidly developed energy storage technology and is being developed and popularized.Compared with traditional electrochemical energy storage devices such as lithium battery and lead battery,supercapacitor is a new kind of environmental protection energy storage device.Because of the different storage principles,it has higher power density and better cycle performance than batteries,but its energy density is relatively low compared with other energy storage devices,which also limits its application.In order to improve energy density,people need to find suitable electrode materials.Among them,oxide semiconductor materials of transition metals have attracted extensive attention because of their advantages such as simple preparation process,relatively low price,stable material structure and higher ratio of capacitance.Among these transition metals,cobalt-base metal oxide has a very high theoretical capacity,which is very suitable for electrode materials,but the multiplier performance of capacitors is also limited due to the poor conductivity of cobalt-base oxide semiconductor materials.Research was conducted through experiments on how to optimize its performance.?.Synthesis and conversion of cobalt-based MOF nanosheet materials.The transformation of metal organic framework(MOF)as template is a common method to synthesize metal oxide nanoporous materials.In this part we base on foam nickel,titanium sheet,etc.2-methyl(2-MI)imidazole and cobaltous nitrate hexahydrate were used for coordination in aqueous solution to form the triangle-shaped MOF(Co-MOF)material based on cobalt under normal temperature and pressure.The Co-MOF material directly grew in the basal surface growth,no coating required,which avoids the adhesive to block active sites.Then the Co-MOF precursor is transformed by ion exchange method.By changing the reaction conditions,nanomaterials that can not only maintain the nano-wall structure of the Co-MOF precursor,but also convert the triangular nano-wall into the two-level hollow nano-sheet structure composed of ultra-thin nano-sheet are obtained.The two-level hollow Co3O4 nano sheets grown on the substrate are obtained by annealing.The electrochemical properties of the nanomaterials are tested and the specific capacity is 797.5 Fg-1 at lAg-1.When the current density increases to 16Ag-1,the specific capacity can still reach 716.8 Fg-1,almost 90%of 1Ag-1.After 5,000 cycles of 8ag-1 current,the specific capacity can still reach about 80%of the initial level.?.Synthesis and conversion of zinc-cobalt bimetallic nanosheets.A new Zn-Co precursors with ultrathin nano flake array structure was designed by hydrothermal method with nickel foam as the base without surfactant and template,and porous cobalt zinc bimetallic oxide nano flake was obtained by annealing.In this process,on the one hand,the conductivity of the material was significantly improved,and that of the utilization rate of cobalt,and the multiplier performance and cycle performance of the supercapacitor were further optimized.On the other hand,this new porous nano-structure had a great specific surface area,so it had more active sites,which is conducive to more rapid charging and discharging.The porous structure could ensure the effective transmission of electrolyte so that the electrode could more fully contact with the electrolyte.At the same time,the effect of direct sulfidation on Zn-Co precursors was studied.Experiments show that during the vulcanization process,while the precursor sheet structure was maintained,a new ultrathin nanometer was formed on the original nanometer flake,and the specific surface area was further increased.And the conductivity was further improved after vulcanization.Electrochemical test showed that after curing,the material was 70%higher than that of direct annealing,reaching 1900Fg-1 at lAg-1,and maintaining about 90%after 5000 cycles,with super capacity and good cycle stability.Finally,the vulcanized material and activated carbon material as the two electrodes of the supercapacitor respectively and assembled them into the all-capacitor.After testing,the capacity reached 191.7 Fg-1,and the capacity still reached about 82%after 5,000 cycles.