Study On Preparation And Electrochemical Properties Of Three-dimensional Transition Metal Oxide/sulphide Electrode Materials

With the increasing consumption of energy and the deterioration of the environment,the development and utilization of high-performance energy storage and conversion devices have attracted more and more attention.As a kind of energy storage device with high power density and long cycle life,supercapacitors have attracted more and more attention from researchers.There are some problems,such as low energy density and low working voltage,in the practical use of supercapacitors.Electrode materials restrict the performance of supercapacitors.Therefore,the design of electrode materials is an important direction to improve the performance of supercapacitors.Whether carbon-based materials or pseudocapacitive materials,shortcomings always exist in the single material.The application of composite materials can overcome the shortcomings of a single material and improve the electrochemical performance of supercapacitors.Based on the idea of binder-free electrode,the pseudocapacitive materials?transition metal compounds,conducting polymers?are directly grown on three dimensional conductive substrates such as carbon cloth and nickel foam.Well-designed components of of transition metal oxide/sulphide and micro/nano structure make the electrodes have excellent electrochemical performance.?1?Nickel cobalt oxide nanosheet arrays and PPy nanoparticles were grown on carbon cloth by electrodeposition to formate CC/NiCo₂O₄/PPy composite electrodes.The effect of the deposition time of PPy on the electrochemical properties of the composites was also investigated and found out the best deposition time of PPy was 20 minutes.CC/NiCo₂O₄/PPy20min electrode exhibits a capacity of 306.3 F/g at the current density of 0.5A/g and 81.8%of the initial capacitance value after 10000 cycling tests.Large specific surface area of NiCo₂O₄ nanosheet arrays,uniformly coated PPy nanoparticles,and the synergistic effect between NiCo₂O₄ and PPy enable CC/NiCo₂O₄/PPy20min electrode good electrochemical performance.?2?Manganese doped Co₃O₄ mesoporous nanoneedles were synthesized via one-step hydrothermal reaction followed by annealing grown on nickel foam?noted as Mn_xCo_yO/NF,x+y=2.25?for supercapacitors.The effects of different Manganese-Cobalt ratios on the properties of materials were also explored.Mn_1.5Co_0.75O/NF demonstrated the superior electrochemical performance,with an excellent cycling stability of 104%capacitance retention after 10000 charge–discharge cycles at 6 A/g,as well as a good capability?668.4F/g at 1 A/g compared to that of undoped Co₃O₄ is 201.3 F/g?.Moreover,the assembled asymmetric supercapacitor based on Mn_1.5Co_0.75O/NF//graphene performs a high energy density of 25.88 Wh kg^-1 at the power density of 359.5 W kg^-1.The improved electrochemical properties are mainly owing to the enhanced intrinsic conductivity and electrochemical activity of Co₃O₄ after doped with appropriate Mn.The three-dimensional nanostructure of mesoporous nanoneedle array grown on NF also provides short ion diffusion path and large active surface areas,contributing to the high rate performance and high energy density.?3?Zn_0.76Co_0.24S nano arrays were grown on the foam nickel substrate by the hydrothermal method.The amount of ammonium fluoride was regulated to get different morphologies?nanoneedles and nanosheets,noted as ZnCoS-N and ZnCoS-S?of Zn_0.76Co_0.24S.Then MnO₂ ultrathin nanosheets were grown on the surface of Zn_0.76Co_0.24S nanomaterials by hydrothermal method.finally,two kinds of electrodes,ZnCoS-N@MnO₂and ZnCoS-S@MnO₂ were obtained.The electrochemical tests showed that the ZnCoS-N@MnO₂ electrode exhibit better electrochemical properties than ZnCoS-S@MnO₂.Hollow nanoneedle-like Zn_0.76Co_0.24S and ultra-thin nanosheet MnO₂ can provide a large amount of active sites,and make electrolyte reach the inner part of the material.Thus,the specific capacitance of ZnCoS-N@MnO₂ material can reach 1759.8 F/g?1 A/g?and maintain 68.1%capacitance retention rate?1²0 A/g?.In addition,Zn_0.76Co_0.24S with excellent conductivity as the core can support and provide a conductive bridge for MnO₂.As a shell material,MnO₂can protect Zn_0.76Co_0.24S during charging and discharging process.Therefore,ZnCoS-N@MnO₂ material has good capacitance retention of 110% after 6000 cycles test.