| With the advantages of rapid charge/discharge,high power density,long cycle life,safety and environmental protection and wide operating temperature range,supercapacitors have been favored by people.As the core of supercapacitors,the electrochemical performance of electrode materials has a decisive impact on the energy storage performance of supercapacitors.Metal-based sulfide electrode materials have become potential supercapacitor electrode materials due to their abundant material sources,low cost,high theoretical specific capacity and high electrical conductivity.However,due to the slow reaction kinetics process and limited active sites,the electrochemical performance of the actual specific capacitance,cycle stability and rate performance is poor.In order to solve the above problems,In this paper,high-performance electrode materials were prepared by rational design of nickel sulfide electrode materials?such as core-shell structure and composite structure?.The thesis consists of three parts as following:In the first part of the works,A facile method for general synthesis of core-shell structured Ni3S2@NiMoO4 nanowires as a binder-free electrode for asymmetric supercapacitors is described in this study.One-dimensional Ni3S2 nanowires directly grown on Ni foam are prepared by a facile solvothermal method,followed by synthesizing thin NiMoO4 sheets on the surface of nanowires to form core-shell structured Ni3S2@NiMoO4 nanowires.The as-prepared binder-free Ni3S2@NiMoO4electrode can significantly improve the conductivity between Ni3S2 and NiMoO4 and effectively avoid the aggregation of NiMoO4 nanosheets,which provide more active space for storing the charges.The Ni3S2@NiMoO4 electrode presents a high specific capacity of 1327.3?Ah cm-2 and 67.8%retention of its initial capacitance when current density increases from 2 mA cm-2 to 40 mA cm-2.In a two electrode Ni3S2@NiMoO4//active carbon cell,the active materials deliver a high energy density of 121.5 Wh kg-11 at a power density of 2.285 kW kg-1 with excellent cycling stability.In the second part of the works,,a low-cost and facile method was developed to directly synthesize core-shell structured CoNi2S4/Ni3S2@Ni?OH?2 nanosheet arrays on Ni foam,which was then used as binder-free electrode in electrochemical capacitors.Due to such unique structure,the obtained CoNi2S4/Ni3S2@Ni?OH?2 showed a high specific capacity of 772.2?Ah cm-2 at a current density of 1 mA cm-2,and a superior cyclic stability.Moreover,electrochemical properties of CoNi2S4/Ni3S2@Ni?OH?2 for energy storage were also evaluated in“real-world”conditions,i.e.asymmetric supercapacitor cells?ASC?were assembled with CoNi2S4/Ni3S2@Ni?OH?2 used as the cathode and activated carbon?AC?as the anode.As expected,the CoNi2S4/Ni3S2@Ni?OH?2//AC cell delivered an excellent areal energy density of0.432 mWh cm-2 at a power density of 1.646 mW cm-2,and an outstanding cycling performance??97%of capacity retention after 6,000 cycles?.In the third part of the works,NiS/Ni3S2 hybrid nanosheets with good crystallinity as binder-free cathodes for asymmetric supercapacitors were fabricated via a low-cost single step solvothermal method.Physical characteristics of the obtained NiS/Ni3S2 hybrids reveal open and sponge-like structure consisting of interconnected thin sheets.During electrochemical study in a three-electrode cell NiS/Ni3S2 exhibited a high capacity of 315?mA cm-2 at a current density of 1 mA cm-2 and retained 87.6%of the capacity when the current density increased 10 folds.A two electrode asymmetric supercapacitor containing NiS/Ni3S2 as a cathode and activated carbon as an anode demonstrated a high energy density of 0.289 mWh cm-2at a power density of 1.794 mW cm-2,which remained at 0.242 mWh cm-2 when the power density increased to 12.825 mW cm-2.New electrode material developed in this study has good potential for practical applications in asymmetric supercapacitors. |
PDF Full Text Request