Study On Preparation And Electrochemical Performance Of Transition Metal Sulfide Electrode Materials

With the rapid development of science and technology,people's demand for energy is increasing day by day.At present,the energy we rely on is mainly fossil fuels,but fossil fuels are non-renewable energy sources,and as consumption increases,the world's reserves become less and less.Therefore,the development of clean energy is one of the important research topics.Ultracapacitors are widely concerned because of their unique characteristics.The core of the supercapacitor is electrode material,which determines the specific capacity.Therefore,the preparation of high-performance electrode material is one of the most important factors.Biomass carbon material has the advantages of good cyclic stability and low price,but its low energy density limits its application in the market.Due to its unique physicochemical properties,metal sulfides are several times higher than the specific capacitance of carbon materials,which show a broad prospect in the field of fabrication of pseudo-capacitor electrode materials.However,it still has the defects of multiplicity and poor cyclic stability,which will limit its practical application.Therefore,the composite preparation of carbon material and metal sulfide into electrode material can not only solve the problem of insufficient energy density of carbon material but also alleviate the problem of volume expansion of metal sulfide during electrochemical reaction.The electrode materials were prepared and improved by direct carbonization,electrostatic spinning,hydrothermal synthesis and low temperature annealing.Scanning electron microscope?SEM?,Raman,X-ray photoelectron diffraction?XPS?,X-ray diffraction?XRD?were used to characterize the prepared electrode materials.The main contents are as follows:?1?The porous carbon was prepared by means of high temperature carbonization by using the fruit of Fujimoto bean as raw material and KOH as activator.Electrochemical tests showed that the porous carbon prepared with a carbonization time of 1.5 h,a carbonization temperature of 900?and an activator ratio of 1:1 had the best electrochemical performance.The specific capacitance performance under this condition:the specific capacitance at a current density of 1 A g^-11 is 232.5 F g^-1,the energy density is 32.292 Wh kg^-1,and the power density is 500 W kg^-1;from 1 A g^-11 increased to 10 A g^-1,the capacitance retention rate is 84.73%;5,000 cycles under a current density of 2 A g^-1,the capacitance retention rate is 96.0%.?2?Using cobalt acetate as the source,thioacetamide as the sulfur source,the prepared carbon material and polymer polyacrylonitrile?PAN?as carbon source,CoS₂-CNFs composite materials were prepared by electrostatic spinning,muffle furnace pre-oxidation,tube furnace carbonization and hydrothermal reaction.By means of microscopic characterization,it was found that CoS₂ was uniformly dispersed on the surface of carbon nanofibers without agglomeration.Electrochemical tests showed that the CoS₂-CNFs composites prepared with the addition of cobalt acetate at 3 mmol,hydrothermal temperature of 150?,and hydrothermal time of 12 h had the best electrochemical performance.The specific capacitance at a current density of 1 A g^-11 is 488.0 F g^-1,and the specific capacitance at a current density of 10A g^-11 is 360 F g^-1.When the current density increases from 1 A g^-11 to 10 A g^-1,the capacitance retention rate is 74%;at a current density of 5 A g^-1,the capacitance retention rate is 91%after 1,000 cycles.?3?Using iron acetylacetonate as the iron source,thioacetamide as the sulfur source,the prepared carbon material and polymer polyacrylonitrile?PAN?as carbon source,FeS-CNFs composite materials were prepared by electrostatic spinning,muffle furnace pre-oxidation,tube furnace carbonization hydrothermal reaction and low temperature annealing.By means of microscopic characterization,it was found that FeS was uniformly dispersed on the surface of carbon nanofibers without agglomeration.That shows that carbon nanofibers effectively prevent metal sulfide from agglomerating.The low temperature annealing can remove the amorphous carbon on the surface of the carbon nanofibers and improve the crystallinity of the metal compound.Electrochemical tests showed that the FeS-CNFs composites had the best electrochemical performance when the ratio of metal addition to sulfur source was 1:10,hydrothermal temperature was 120?,hydrothermal time was 12 h,and low temperature annealing.The specific capacitance at a current density of 2 A g^-11 is 502 F g^-1,and the specific capacitance at a current density of 10 A g^-11 is 401 F g^-1.When the current density increases from 2 A g^-11 to 10 A g^-1,the capacitance retention rate is80%;at a current density of 2 A g^-1,the capacitance retention rate is 90%after 1,000cycles.