Synthesis Of Transition Metal Sulfide Nanomaterials And Their Electrochemical Energy Storage Performances

As a new type of electrochemical energy storage element,the super capacitor has the characteristics of rapid charge and discharge,ultra high power density,extremely long cycle life,safer operation and environmental friendliness,thus becoming a response to the energy crisis One of the important members.The electrode material is the core component of the supercapacitor,which directly determines the energy storage principle and performance of the supercapacitor.Therefore,the preparation of electrode materials with excellent properties is the key to improving the overall performance of supercapacitors.Transition metal sulfides have attracted much attention due to their high theoretical specific capacitance and good electrical conductivity.In this paper,three kinds of metal sulfides nanomaterials were prepared by a fast and facile method,and X-ray diffractometer（XRD）,Raman spectroscopy（Raman）,field emission scanning electron microscope（FE-SEM）,X-ray energy spectroscopy（EDS）,X-ray photoelectron spectroscopy（XPS）and transmission electron microscopy（TEM）were used to characterize them.Cyclic voltammetry（CV）,constant current charge and discharge（GCD）and AC impedance were used to investigate the electrochemical energy storage performance,and the relationship between electrochemical performance and the structure of the electrode materials was studied.The main research findings and contents are as follows:（1）The solution impregnation method was used to quickly and efficiently prepare Cu₂S nanosheet films on any substrate.By characterizing their morphology and electrochemical tests,the feasibility of preparing Cu₂S nanosheet films on any substrate and their use as energy storage electrode materials was studied.The size of these nanosheets can be adjusted by parameters such as reaction time and sodium polysulfide concentration.Electrochemical test results show that the internal resistance and electronic charge transfer resistance of Cu₂S nanosheet film/arbitrary substrate electrode are low.The low internal resistance indicates that the nanosheet film has grown firmly on the substrate.The low electronic charge transfer resistance was very low,indicating that the nanosheet array structure of the Cu₂S nanosheet film was beneficial to the rapid electron transport and good interface transport of the aqueous solution in the electrolyte.The Cu₂S nanosheet film/any substrate can be directly used as a device electrode,without the need to add any binder and conductive agent,which can meet the needs of practical electrochemical energy storage applications.（2）NiS₂·xH₂O nanoparticles were prepared by a simple chemical precipitation method using nickel chloride,and Ni S₂ ultrafine nanoparticles were obtained by annealing,and their electrochemical energy storage properties were tested.The effect of bound water on its electrochemical energy storage properties was studied.Electrochemical tests have found that the presence of water can improve the rate performance of the electrode material,and the capacity of Ni S₂·x H₂O could retain 62.36%at 20 A/g comparing that at 1 A/g.The pure phase Ni S₂ obtained after annealing shows good electrochemical performance.Being charged and discharged at a current density of1 A/g,the specific capacitance can reach 900 C/g.After being charged and discharged for 5000 cycles at a current density of 20 A/g,the specific capacitance still retain71.11%.It shows that the prepared nanomaterials have the potential as excellent materials for electrochemical energy storage devices.（3）Co_xS_y nanomaterials were synthesized by a fast and green two-step method,and their electrochemical energy storage properties as supercapacitor electrode materials were tested.The effects of different concentrations of cobalt nitrate solution and sodium polysulfide solution on the microstructure and size of Co_xS_y were studied.It was found that Co_xS_y nanoparticles prepared using 0.8 M cobalt nitrate solution and 2 M sodium polysulfide solution exhibited the best electrochemical properties.Being charged and discharged at a current density of 1 A/g,the specific capacitance can reach 378 C/g.After being charged and discharged for 1000 cycles at a current density of 40 A/g,the specific capacitance still retain 65%.Not only micro-nano materials with excellent morphology and size were obtained,but also Co_xS_y as a rubidium capacitor material can be applied to electrochemical energy storage.