The Preparation And Supercapacitor Performances Of Transition Metal Ni-V Based Composite Electrodes

The excessive consumption of fossil fuels and serious environmental pollution have prompted people to seek a convenient and efficient non-polluting energy storage device,such as solar cells,supercapacitors,lithium-ion batteries and fuel cells.Supercapacitors have become popular storage devices because of their advantages such as fast charging and discharging speed,high power density,long cycle life,safety and environment-friendly,which are widely recognized and studied.The electrode materials are the key part of supercapacitors,and its properties is crucial to the properties of supercapacitors.In this paper,we have successfully prepared electrode materials with good electrical conductivity,high specific capacitance and excellent energy density by different methods using transition metal nickel-vanadium elemental compounds as the research object.The morphology,valence,and constituents of the electrode materials were analyzed by various characterization methods such as XRD,XPS,TEM,SEM,and EDS.The electrochemical performance of the composites were researched using cyclic voltammetry（CV）,constant current charge-discharge（GCD）and electrochemical impedance（ZK）testing methods.The details are as follows:（1）NiVSe/rGO/NF nanocomposites were prepared on reduced graphene oxide/nickel foam（rGO/NF）collectors by hydrothermal method,and the effects of selenization time on the morphology and electrochemical performance of the electrodes were researched.Their composition and morphology were tested and analyzed via different characterization means,and the related electrochemical properties were tested.The results reveals that the NiVSe-6h/rGO/NF composite has a specific capacity of 1197.6 C g^-1 at the current density of1 A g^-1 and an excellent cycling performance（89.4%capacity retention after 8000 tests）when the selenization time is 6 h.The constructed asymmetric supercapacitor accomplishes an energy density of 53.1 Wh kg^-1 at the power density of 878.5 W kg^-1 and retains 94.4%of the initial specific capacity after 6000 cycles.（2）Ni₃S₂/NiV-LDH/rGO/NF nanocomposites were synthesized by a two-step hydrothermal method to study the effects of different sulfidation times on the morphology and electrochemical properties of the materials.The results show that when the sulfidation time is3 h,NiV-LDH reaction is incomplete,and Ni₃S₂ and NiV-LDH exist simultaneously in the complex.The microscopic morphology exhibits interconnected nanosheet structure,which provides more open space and active sites for the enhancement of electrochemical properties.The synergistic effect between Ni₃S₂ and NiV-LDH and the introduction of rGO make the composite structure exhibit excellent specific capacitance(3004.3 F g^-1 at 1 A g^-1).The assembled supercapacitors exhibit superb electrochemical performance.The energy density is59.4 Wh kg^-1 at the power density of 852.3 W kg^-1,and the cycle life is 98.3%after 8000cycling tests.（3）The NiVO/rGO/NF nanocomposites were prepared by one-step solution combustion method.The results showed that nickel-vanadium solution with different ratios produced a significant effect on the morphology and electrochemical properties of the composites.The best performance was achieved When the ratio of nickel nitrate to ammonium metavanadate was 3:1.The NiVS/rGO/NF composites were further synthesized by annealing and sulfiding.Their composition,microstructure and morphology were explored via diverse characterization methods.The results revealed that the specific capacitance of NiVS/rGO/NF composite was1994.7 F g^-1 and the electrode cycle life was 92.4%after 5000 cycles.In addition,the energy density of the fabricated asymmetric supercapacitor with NiVS/rGO/NF as the positive electrode and AC as the negative electrode was 57.2 Wh kg^-1 and the power density was 850.2W kg^-1.The device exhibited outstanding cycle life of 99.6%after 8000 cycles,indicating its ultra-high cycling performance.