Synthesis And Properties Of Ni_3xCo_3-3xS₄@Carbon Coated From Different Organic Sources Electrode Materials For Supercapacitors

Supercapacitors,also known as electrochemical capacitors,have attracted wide attention due to their superior power density than conventional capacitors and higher power density than batteries.The advantages of supercapacitors make it practical in the fields of backup energy system,hybrid electric vehicle and portable electronic equipment.It is well known that the capacitance performance of supercapacitors depends largely on the morphology and structure of the electrically active material.Because the electronegativity of sulfur is lower than that of oxygen,transition metal sulfides have more flexible structure and higher electrical conductivity than transition metal oxides.Among many transition metal sulfides,Ni and Co sulfides are expected to meet the energy storage demand of electrode materials for supercapacitors because of their advantages such as high theoretical capacitance,rich raw materials and safety.In this paper,transition metal sulfide composite nanomaterials were prepared and their capacitive properties were studied,using ZIF-67 as precursor,by hydrothermal sulfide double metal sulfide hollow nickel cobalt?NCS?preparation method,then through different organic compounds as carbon source coating,double metal sulfide carbon composites were successfully prepared,and to be used as supercapacitor electrode material.The XRD,SEM,TEM and XPS were used to characterize the prepared materials analysis of element composition and microstructure,and cyclic voltammetry?CV?,constant current charge and discharge and electrochemical impedance spectroscopy?EIS?to test the electrochemical performance of technology.The main contents and results are as follows:?1?Using nickel cobalt ZIF-67 as template,nickel cobalt sulfide Ni_3xCo_3-3xS₄@carbon composites were successfully synthesized?NCSC-x,x=0.2?.NCSC-0.2 composites were prepared by solvothermal method and carbon coating by glucose as carbon source through using ZIF-67 as precursor.The above material were used as supercapacitor electrode to evaluate the electrochemical performance.In the KOH electrolyte?6 M?and at the current density of 1 A·g^-1 and 20 A·g^-1,the specific capacitance of NCSC-0.2can reach 696 F·g^-1 and 480 F·g^-1,which are obviously higher than those without carbon composite under the same measurement conditions?NCS-0.2,x=0.2?(305 F·g^-1 and 116.7F·g^-1).In addition,the NCSC-0.2 electrode has good cycling stability,73%capacitance is maintained after 2000 charging and discharging cycles at 10 A·g^-1 current density.?2?According to the previous work,we replaced the carbon source as polydopamine?PDA?and synthesized NCS@0.5PDA-800 composites.The NCS@0.5PDA-800 composite was synthesized by the method of carbon coating hollow nickel cobalt sulfide,through polymerization of dopamine on the surface of sulfide into polydopamine and carbonization at high temperature.Taking the above material as supercapacitor electrode,we conducted a series of experimental studies to explore the method of using PDA as carbon source to coat transition metal sulfide.The experimental results show that the best electrochemical performance is obtained when the ratio of dopamine to nickel cobalt sulfide is 0.5,and the carbonization temperature is 800 ^oC.The NCS@0.5PDA-800electrode material shows a best electrochemical performance when the current density is 1A·g^-1 and the specific capacitance is 292 F·g^-1.In this paper,the electrochemical properties of the transition metal sulfide were improved by using the special structure of the bimetallic component,and the synthesis of Ni_3xCo_3-3xS₄@carbon composite coated by different organic compounds as carbon source.The two kinds of materials all show good electrochemical performance,and provide ideas and significance for method of other functionalized nanomaterials as precursors and advanced high-performance supercapacitors.