Preparation Of Cobalt-Ni Based Sulfide Electrode Materials And Study On Properties Of Pseudo Capacitance

With the development of science and technology and the progress of human society,the traditional fossil energy will cause serious environmental pollution.Therefore,the development and utilization of green pollution-free energy storage device has become the main way to solve the problem of energy at present.The super capacitor and the birth of lithium ion battery greatly solved this difficult problem,but due to the defects in the field of power and energy,lithium ion secondary battery and traditional capacitor has fulfilled the development of science and technology,and the birth of the super capacitor to compensate for the disadvantages.Good electrode materials can greatly improve the electrochemical performance of supercapacitors.In many electrode materials,the multi-transition metal compounds have many advantages,such as excellent electrochemical stability,wide potential range,high conductivity,etc.,which have become the first choice for research.In this paper,cobalt-nickel-based bimetallic compounds were prepared by hydrothermal method,and they were compounded with graphene and g-C₃N₄,respectively.Their physical structures were characterized by XRD,SEM and XPS.Then the electrode was prepared with nickel foam as the substrate,polyvinylidene fluoride as the binder and N-methylpyrrolidone as the auxiliary agent.The electrochemical performance of the electrode was tested in the three-electrode body with KOH as the electrolyte.The specific work is as follows:(1)NiO,NiS and NiCo₂S₄ nanomaterials were prepared by two-step hydrothermal method and high-temperature pyrolysis method respectively,which were used as electrode materials for supercapacitors.Tests under different current density than the capacitor size,capacity retention are 42.4%,32.7%and 52.8%respectively,when the current density for 5 A/g cycle stability test of 2000 times,three kinds of electrode material capacity retention are 57.85%,43.93%and 78.96%respectively.Bimetallic element to further improve the synergies between the electrochemical performance of electrode materials.With the increase of electrolyte concentration,the capacity retention rates are 51%,52.73%,53.35%and 53.7%,respectively,when different electrolyte concentration is used to measure specific capacitance under different current density.In the AC impedance test,the charge transfer resistance in the electrode material decreases with the increase of electrolytic concentration,indicating that the charge transfer rate increases with the increase of electrolyte concentration.(2)Firstly,GO was prepared by Hummers method,and then NiCo₂S₄ and NiCo₂S₄/rGO nanomaterials were prepared by two-step hydrothermal method as electrode materials,respectively.The specific capacitance was measured at different current densities and the capacity retention rate was 71.03%.The capacity retention of NiCo₂S₄ electrode material is 51.01%.In the long cycle stability test,the capacity retention rate of NiCo₂S₄/rGO electrode material is 88.5%after 2000 cycles,and that of NiCo₂S₄ electrode material is 59.6%after 2000 cycles,indicating that the synergistic effect of graphene composite greatly improves the electrochemical performance of the electrode material.Finally,the NiCo₂S₄/rGO electrode material is used as the positive electrode,the activated carbon is used as the negative electrode,and the C2025 button battery shell is used to assemble the supercapacitor.The test data show that the supercapacitor has excellent cycling stability.(2)Taking melamine as raw material,g-C₃N₄ was prepared,and then NiCl₂·6H₂O,CoCl₂·6H₂O and thiourea as raw materials,NiCo₂S₄ was prepared by one-step hydrothermal method.Finally,NiCo₂S₄ and g-C₃N₄ with different molar ratio were compounded to make electrode materials.The specific capacitance of NiCo₂S₄ electrode material was measured at different current densities.The capacity retention rate of electrode material increased with the increase of g-C₃N₄ composite proportion,but the contribution to the electrode material was not significant when it increased from 30%to 40%,mainly because g-C₃N₄ occupied a small part of the contribution of the relative capacitance of NiCo₂S₄ electrode material.After 2000 cycles,the capacity retention rates of the four electrode materials are 53.83%,60.77%,62.68%and 66.24%,respectively.With the increase of the composite proportion of g-C₃N₄,the capacity retention rate increases,and the charge transfer resistance in the electrode material decreases,indicating that the charge transfer rate increases with the increase of the composite content of g-C₃N₄ in the electrode material.