Synthesis And Electrochemical Performance Of Transition Metal (iron, Cobalt, Nickel) Sulfide Nanomaterials

Supercapacitors?SCs?,as a unique class of energy storage devices,are famous for excellent properties:the high power density,the short charging time,the superior cycling stability and environmental friendliness.However,their energy density is always lower than batteries,this limits the application and development of supercapacitors.As a class of SCs,asymmetric supercapacitors?ASCs?have both larger energy density and higher power density.As the electrode materials for ASCs,the transition metal sulfides have become a new research hot topic because of theirs excellent electrochemical properties.In this paper,we synthesize the unique nano-structure with high energy density of transition metal?iron,cobalt,nickel?sulfides supercapacitor electrode materials.The assembly asymmetric supercapacitors can achieve high energy density,outstanding cycling stability and high rate performance.Firstly,the Ni-Co precursor pseudo-cubic particles were synthesized by using nickel nitrate,cobalt nitrate,polyvinylpyrrolidone?PVP-K30?and ammonium oxalate as precipitant.Then,the Ni-Co precursor was converted to Ni Co₂O₄ by a calcination process in air.Subsequently,the mesoporous Ni Co₂S₄ microaggregates were synthesized by sulfuration process.We studied the effect of different curing processes on the structure and properties of Ni Co₂S_4,the experimental results show that the prepared Ni Co₂S₄ can produce rich mesoporous?a suitable pore size distribution?due to the proper curing process.The Ni Co₂S₄ microaggregates have abundant mesoporous structure with high surface area of 63.79 m² g^-1.The Ni Co₂S₄ microaggregates show the high specific capacity of 249 m Ah g^-1(at 1 A g^-1).In addition,the assembled Ni Co₂S₄//AC ACS reveals the high energy density of 47.9 Wh kg^-1(at a power density of 783 W kg^-1)and excellent cycling stability?98.8%retention of the initial capacitance after 4000 cycles?.Furthermore,we design a novel synthetic method to construct 3D Co_1.29Ni_1.71O₄@Co Ni₂S₄ heterogeneous nanosheet networks with 0D nanoparticles?the size of 10?20 nm?shell and 2D sheets?about 1.5 nm?core nanostructure on nickel foam?NF?by Fast-Repeated-Charging/Discharging?FRCD?electro-oxidation combined with ion-exchange methods for the first time.We studied the structural composition and electrochemical properties of Co_1.29Ni_1.71O₄@Co Ni₂S₄.This multi-dimensional nanostructure can endow the electrode material with rich active sites,fast ion transport path,high conductivity and excellent structural stability.Benefiting from the excellent multi-dimensional nanostructure,the assembled Co_1.29Ni_1.71O₄@Co Ni₂S₄/NF//AC ACS shows the high energy density of 47 Wh kg^-1 at527 W kg^-1 and topping cycling stability of 85.3%retention after 8000 cycles.Finally,self-supporting petal-like Ni Fe Co-S?Sulfides?@Ni Fe Co-TH?Ternary Hydroxides?heterogeneous ultrathin nanosheets were synthesized easily on NIF by fast-repeated-charging/discharging,sulfuration and controllable Co²⁺exchange process.We have studied the effect of reaction temperature on the structure and electrochemical properties of the Ni Fe Co-S@Ni Fe Co-TH heterogeneous nanosheets in the process of cobalt ion exchange.The Ni Fe Co-S@Ni Fe Co-TH nanosheets?only 1.8 nm?consist of Ni₂S₃,Fe S,Co Ni₂S₄,Fe Co S₂ and Ni Fe Co hydroxides,this structure provides the rich electrochemical reactivity interface.The fabricated Ni Fe Co-S@Ni Fe Co-TH/NIF//AC all-solid-state ASC shows the high energy density of 56.3 Wh kg^-1(at the power density of 543 W kg^-1)and remarkable cycling stability?90.1%capacity retention after 4000cycles?.This synthesis strategy shows the good application prospect for energy storage and conversion.