Study On The Preparation Of Nickel Sulfide Composites And Their Properties Of Supercapacitors

As a new green energy storage device,supercapacitor has a good development potential and market value in many fields.After several decades of development,supercapacitors have many advantages such as higher power density,extremely long cycle charge/discharge performance,and no pollution.They have always been a hot spot in energy storage research.The rapid development depends largely on the design and research of electrode materials.In recent years,the better physical and electrochemical properties of metal sulfur compounds have attracted wide attention in the energy industry,and have appeared as electrode materials on the stage of researches on supercapacitors.Compared with traditional carbon materials,metal sulfur compounds have much higher specific capacitance.Compared with metal oxides,sulfides not only have high theoretical specific capacitance,but also have low cost and simple synthesis.It is considered to be a supercapacitor electrode material with greater development potential,but a single component of sulfides cannot meet the needs of high performance energy storage.A large number of studies have shown that electrochemical properties can be greatly improved by recombination.In this paper,nickel sulfide（mainly including Ni₃S₂ and NiS）is compounded with other materials.The synergistic effect of the special core-shell structure of the composite material greatly improves the electrochemical performance of the electrode materials.At the same time,the paper also explores the correlation between the influence of process parameters on the microstructure and electrochemical properties of the composites.The main research contents of this paper are as follows:1.Three-dimensional reticular Ni₃S₂ was prepared on nickel foam by an one-step hydrothermal method.On the one hand,MnO₂ was prepared on the three-dimensional Ni₃S₂ by hydrothermal method,and the synthesized Ni₃S₂@MnO₂ composite exhibited good electrochemical performance:the specific capacitance was 1.465 F·cm^-2 at current density of 2 mA·cm^-2,which was higher than that of 0.786 F·cm^-2 at the same current density for Ni₃S₂.On the other hand,it investigated the effect of activation for the prepared Ni₃S₂,by charging/discharging various cycles in the three-electrode test system.Due to this special activation characteristic,the specific capacitance at a current density of 2 mA·cm^-2 is 6.244 F·cm^-2 after 5000 cycles of charge and discharge,which is 956.1%higher than that of the uncirculated Ni₃S₂ sample.The specific capacitance remains 89.75%at 5000 cycles after 10000 charge/discharge cycles.2.A layered NiCo₂S₄@Ni₃S₂ core/shell nanorod array was prepared on carbon cloth by two-step hydrothermal method and cyclic voltammetry electrochemical deposition.The synergistic effect of the rod-like core-shell structure greatly improves the electrochemical properties of the monomer.The specific capacitance is 5.714 F·cm^-2 at a current density of 2 mA·cm^-2.After 2000 cycles of charging and discharging,the specific capacitance remains 76%of the original value.At the same time,the effect of electrochemical deposition numbers of Ni₃S₂ on the microstructure and electrochemical properties of NiCo₂S₄ was studied.When the number of electrochemical deposition circles was 5,the thickness of Ni₃S₂ was moderate and showed good electrochemical performance.The composite was used as the positive electrode,and Fe₂O₃-rGO as the negative electrode to assemble a flexible asymmetric supercapacitor.The energy density can reach 0.59 mWh·cm^-3 at a current density of 2 mA·cm^-2,and the corresponding power density is 117 mW·cm^-3.3.A layered sheet of NiS was prepared by hydrothermal method via carbon cloth as the substrate.Its specific capacitance was 1080 F·g^-1 at a current density of 1 A·g^-1,but its cycle performance was relatively poor.After 2000 cycles of charge and discharge,the specific capacitance was maintained 46.9%of the original value.Therefore,this paper uses a cyclic voltammetric electrochemical deposition method to load a layer of CoS on its surface to form a special NiS@CoS core-shell structure.By controlling the number of cycles of electrochemical deposition,it is possible to achieve the designed composite materials,which have different properties,and fully exert the value of the two materials.Due to the synergistic effect of the prepared composite material,the specific capacitance is as high as 1210 F·g^-1 at a current density of 1 A·g^-1,and the specific capacitance is maintained 87.2%after 2000 cycles.The assembled NiS@CoS//AC（activated carbon）all-solid-state asymmetric supercapacitor exhibits excellent performance with an energy density of 24.1 Wh·kg^-1 and a power density of752.15 W·kg^-1 at a current density of 1 A·g^-1.