Study On Simple Preparation And Electrochemical Energy Storage Performance Of Transition Metal Sulfide Composite Materials

Supercapacitors are electrochemical energy storage devices with high power density.The performance of electrode materials largely determines the performance of supercapacitors.Transition metal sulfides are widely used as electrode materials for supercapacitors due to their rich redox valence and high conductivity.By combining with carbon nanotubes and graphene and other one-dimensional and two-dimensional nanomaterials,it can effectively improve the charge storage capacity,rate and cycle energy of transition metal sulfides.Therefore,transition metal sulfide-based composite materials have attracted much attention in recent years.attention.However,the current methods for preparing transition metal sulfides and their composite materials are mainly liquid-phase synthesis methods such as hydrothermal methods,which have disadvantages such as cumbersome preparation process,long time-consuming,poor environmental protection and economic efficiency,and are not suitable for industrial production.The solid-phase synthesis method has the advantages of high yield,high selectivity,simple process,green and pollution-free,etc.,and is very suitable for industrialized large-scale production.In view of this,in this paper,sulfide-based composite materials of transition metals(Fe,Co,and Ni)were prepared by solid-phase synthesis,and their preparation conditions were systematically optimized,and the phase and morphology of the preparation conditions were investigated.It is used as the electrode material of supercapacitor,and the electrochemical performance of the system is studied.(1)Co₉S₈/GO composites were successfully prepared by solid phase method in a closed high pressure reactor with cobalt acetate as raw material and sublimated sulfur as sulfur source.Co₉S₈ nanoparticles were wrapped by graphene or dispersed on the surface of graphene.The addition of graphene effectively solved the serious problem of agglomeration of Co₉S₈ nanoparticles synthesized by solid-phase synthesis.By investigating the influence of the amount of graphene on the electrochemical properties of the composites,it is found that when the amount of graphene is cobalt acetate:graphene=5:1,the obtained Co₉S₈/GO composites have the best electrochemical properties.In 6 M KOH electrolyte,the typical material Co₉S₈/GO-5 can provide A high specific capacity of 111.39 m Ah g^-1 at the current density of 1 A g^-1.The capacity retention rate is up to 90%when the current density is increased by 20 times.After1000 charge-discharge cycles,91.9%of the initial capacity can still be maintained.The specific capacity of Co₉S₈/GO-5 assembled with fraction-porous carbon derived from sycamore is 48 m Ah g^-1.The capacity retention rate is still close to 100%after 16,000charge-discharge cycles,and the energy density can reach 36 Wh kg^-1 at a power density of 871 W kg^-1.(2)In order to explore high performance anode materials for supercapacitors,Fe S₂/GO composites were successfully prepared in a closed high pressure reactor by solid phase method using iron acetate as raw material and sublimated sulfur as sulfur source.By adjusting the ratio of graphene,it is found that when the content of graphene is iron acetate:graphene=5:1,the electrochemical performance of the composite is the best.In 1 M KOH,the Fe S₂/GO-5 electrode material prepared can provide A high specific capacity of 111.33 m Ah g^-1 at the current density of 1 A g^-1,but when the current density increases to 20 A g^-1,the capacity still reaches 64%,which is nearly one times higher than that of pure Fe S₂.The capacity retention rate of the composite reached 89.9%after 1000 cycles in the three-electrode test system.The addition of graphene can effectively improve the poor rate performance caused by poor conductivity of iron sulfide,and alleviate the poor cycle performance caused by volume change and structural collapse in redox reaction of iron sulfide.A battery-type asymmetric supercapacitor was assembled with Co₉S₈/GO-5 composite material.The energy density reached 51.1 Wh kg^-1 at the power density of 946 W kg^-1,and the capacity retention rate reached 52%after 10,000 charge-discharge cycles.(3)Ni₃S₂/NF composite material was synthesized by autogrowth in a closed high-pressure reactor with nickel foil(NF)as substrate,using diacetyldioxime nickel and sublimated sulfur,and then the Ni₃S₂/NF/PTFE composite electrode with excellent performance was obtained by further compacting with PTFE.The addition of PTFE can effectively reduce the shedding of active substances in the process of charge and discharge of Ni₃S₂/NF composite material,and greatly improve the cycle life of the composite electrode.The results show that the specific capacity of the active substance of the Ni₃S₂/NF/PTFE composite electrode can reach 179.3 m Ah g^-1at the current density of 1 A g^-1,which is due to the direct growth of Ni₃S₂ micron particles on the highly conductive nickel foil,which ensures the excellent rate performance of the composite electrode.The capacity retention is as high as 86%when the current density is increased by 20 times.The specific capacity of the supercapacitor was 87.83 m Ah g^-1 at the current density of 1 A g^-1,the capacity retention rate was up to 192%after40,000 cycles of charge and discharge,and the energy density was up to 75 Wh kg^-1 at the power density of 1.0 k W kg^-1.