Controllable Synthesis And Investigation Of Performance In Supercapacitor Of Heterogeneous Transition Metal Sulfides

Supercapacitors(SCs)based on the environmentally benign aqueous electrolyte are entering the spotlight due to their high power density,long cycling life,and high security.However,the relatively lower energy density of SCs greatly limits their practical application.In order to make up for its low energy density,we assembled a hybrid supercapacitor.The equilibrium of energy and power density in HSC devices is attributed to the different charge storage types of the positive and negative electrodes.Typically,battery-type electrode materials serve as the positive electrode to provide a high energy density,while the double-electric-layer capacitive electrode with a high power density serves as the negative electrode.The performance of the electrode material determines the energy storage capacity of the device.Therefore,many recent works focus on designing novel battery-type electrode materials with outstanding electrochemical performances.As a typical battery-type material,transition metal sulfide has the advantages of high theoretical specific capacity,low electronegativity,and good conductivity.However,a single transition metal sulfide has poor rate performance and is prone to volume expansion,which makes their application is restricted.Therefore,the preparation of two-component or multi-component composites with easy-to-control morphology is particularly important for improving the electrochemical performance of electrode materials.The main research contents are as follows:(1)In the third chapter,the construction of multi-dimensional structured battery-type electrode materials is a promising strategy to develop high-performance electrodes for supercapacitors.Herein,a series of battery-type Ni₃S₂@Co₃S₄electrodes with different morphologies are synthesized by controlling the hydrothermal reaction time.When the reaction time is 60 minutes,Ni₃S₂@Co₃S₄(NCS-60)has a unique structure with independent but interconnected 2D nanosheets and 3D cubic frameworks,NCS-60 displays high conductivity,numerous active sites,and good wettability behavior.It can deliver a high specific capacity of 388.9 m Ah g^-1(3500 F g^-1)at 1 A g^-1,an outstanding rate capacity of maintaining 88.6%at 10 A g^-1and long cycle stability.The battery-type supercapacitor hybrid(BSH)device with active carbon(AC)as the negative electrode delivers an energy density of 41.8 W h kg^-1at the power density of 800 W kg^-1.This study provides a feasible route for regulating the morphologies of in situ growth materials that improve the electrochemical performance of supercapacitors.(2)In the fourth chapter,we prepared the high mass loading and high-performance electrode.Generally,in-situ growth of the active electrode material with low mass loading has prevented its wide applications.Herein,core-shell Ni₃S₂/Mo S₂nanoneedle arrays are grown on nickel foam by a facile one-step hydrothermal synthesis method.Such Ni₃S₂nanowire core-Ni₃S₂/Mo S₂nanosheet shell structure provides appropriate geometries and electronic structures,helping suppress stack tendency at high mass loading and improve the specific capacitance of electrode.Consequently,the optimized Ni₃S₂/Mo S₂(NM-24)electrode achieves a very high areal capacitance of 8.04 F cm^-2at 2 m A cm^-2,good rate capability(87.1%of capacitance retention at 15 m A cm^-2),and outstanding cycle life in a three-electrode system with high mass loading of 6.3 mg cm^-2.Besides,the hybrid supercapacitors device of Ni₃S₂/Mo S₂//AC shows a high energy density of 718.88?W h cm^-2at the power density of 8.5 m W cm^-2and retains 76%after 3000 cycles.(3)In the fifth chapter,the rational design of a multi-component electrode material with hollow structures grown on the conductive substrate is an effective approach to boost the electrochemical performance of supercapacitors(SCs).However,there is still a challenge in the in-situ construction of such unique structures on the conductive substrate.Herein,a heterostructured multi-component electrode material,a Zn-Mo-Ni-O-S hollow micro-flower(Zn-Mo-Ni-O-S HMF)in situ grown on a Ni foam(NF),is fabricated by a simple top-down strategy.Based on the ion exchange and Kirkendall effect,the microflowers are composed of numerous hollow nanosheets,which are covered by uniform Zn S nanoparticles with robust adherence.Profiting from the structural merits and the synergistic effect of multiple components,the Zn-Mo-Ni-O-S HMF electrode exhibits a high areal capacitance of 4.39 C cm^-2(6.27 F cm^-2)at 1 m A cm^-2.The Zn-Mo-Ni-O-S HMF displays an excellent cycling performance(maintaining 87.9%after 3000 cycles).The hybrid supercapacitor device is assembled by the Zn-Mo-Ni-O-S HMF as the positive electrode and active carbon(AC)as the negative electrode.The device delivers a high energy density of 60.8 Wh kg^-1at a power density of 750.2 W kg^-1.The synthetic route provides a reference to the in-situ construction of a heterostructured multi-component electrode material for high-energy SCs.