The Synthesis Of Nickel Sulfide Composite And Its Application In Supercapacitor

In the context of energy shortage and environmental pollution today, developing a new type of green energy storage device has become an important solution.Supercapacitor serves as a novel energy storage device which performs between batteries and traditonal capacitors. It has characteristics of high power density, high charge-discharge efficiency, good cycling stability, environmentally friendly,etc.Therefore, it is widely used in many areas. However, low energy density becomes an important restricted factor for its development. According to the calculation equation of energy density: E=1/2CV2, we can achieve the improvement of the energy density by improving the capacitance（C） of electrode material and broadening the working voltage（V）. Assembling an asymmetric supercapacitor by designing and matching with two kind of electrode with different way of energy storage to improve energy density has become a hot topic of research in recent years. Nickel sulfides with a variety of stoichiometric compositions have low prices, widely sources and high specific cpacitance, which have good prospect in high-performance supercapacitor application. In this paper, porous nickel foam was served as a substrate, and nickel sulfides and their composite nanomaterials with high specific capacitance, high energy density and good cycling stability were successfully prepared, and then assembled with active carbon（AC） to fabricate an asymmetric supercapcitor. The morphologies and structures of composite materials and their electrochemical properties were characterized and investigated through relevant tests. The main research contents are listed as follows:A simple and convenient successive ionic layers adsorption and reaction（SILAR）route was developed, high purity NiS nanosheets were directly synthesized on the nickel foam current collector at room temperature. Three-dimensional lamella structure can increased specific surface area and the utilization rate of active material.In the testing condition of three electrodes system, the NiS naosheets showed an excellent characteristic of faradaic pseudocapacitance. The specific capacitance was1678 F g-1at a current density of 1 A g-1. After an asymmetric supercapacitor was assembled, a high energy density of 42.3 Wh kg-1 was achieved, retaining 83.0%capacity after 5000 charging-discharging cycles. It shows that the composite has good electrochemical properties and cycling stability. Compared with the normal SILAR method which obtains amorphous thin film, it is innovative that metal sulphide layers were prepared by one-step route.The fabrication of Co₃O₄@Ni₃S₂ three-demensional nanowire arrays with core/shell structure was achieved through two-step method. On the substrate of porous nickel foam, an orderly hierarchical structure nanocomposite was made up by hydrothermal synthesize Co₃O₄ nanowires and electrodeposited Ni₃S₂ ultrathin nanosheets. Compared with the pristine Co₃O₄ nanowire arrays and Ni₃S₂ nanosheets,the composite showed much more excellent capacitive behaviors. In the testing condition of three electrodes system, the specific capacitance achieved 1710 F g-1 at a current density of 1 A g-1 and retained 88.5 % capacity after 1000 cycles. Afer an asymmetric supercapacitor was assembled, it exhibited an ultrahigh specific capacitance of 126.6 F g-1 and a high energy density of 44.9 Wh kg-1 at a current density of 1 A g-1. The design of core/shell nanowire arrays in this issue can shorten the ion diffusion and electronic transmission and offer synergy of composite materials,so the performance was significantly improved.CoAl-LDH@Ni₃S₂ nanosheets arrays with three-demensional hierarchical structures were prepared by two-step route. Cobalt aluminum layered double hydroxide（CoAl-LDH） nanosheets arrays were directly grown on the porous nickel foam via a facile hydrothermal method. Ni₃S₂ ultrathin nanosheets were uniformly coated on the surface of CoAl-LDH naosheets by controlling the electrodeposition conditions. The novel design of morphology in this paper attributed to the excellent electrochemical performance of the synthetic composite materials. In the testing condition of three electrodes system, the specific capacitance was 1904 F g-1at a current density of 1 A g-1. An asymmetric supercapacitor was assembled based on CoAl-LDH nanosheets as the positive electrode and activated carbon as the negative electrode, the working voltage was broadened to 1.6 V. It retained 84.2% capacity after 5000 charging-discharging cycles. The study shows that the formative special structure of “sheet-net” can significantly increase the contact probability betweenelectrode materials and electrolyte ions, maintainiing the mechanical stability, so as to achieve the enhancement of performance for energy storage.