Research On Supercapacitor Electrode Materials And Devices Of Transition Metal Sulfide/Carbon

Supercapacitors,as a kind of promising energy storage device,have attracted much attention owing to their excellent characteristics,such as fast charge and discharge speed,long cycle life,wide temperature range,high power density and environmental friendliness.At present,electronic products are mainly developing in the direction of thinner,lighter,portable and wearable.The development of electronic products can not be separated from the improvement of requirements of energy storage devices.Therefore,balancing the relationship between the volume and electrochemical performance of energy storage devices has become the focus of current research.Excellent electrode materials are the key to achieving excellent electrochemical performance of supercapacitors.At present,the electrode materials of supercapacitors that are widely used in the market are mainly carbon materials.However,the carbon materials exist many problems,such as low specific capacity,low energy density,large volume and short cycle life,which limits its application range.Therefore,it is the focus of current research to find electrode materials that are affordable,superior in performance and environmentally friendly to replace traditional carbon materials.In this thesis,transition metal sulfides and transition metal sulfide/carbon composites with different microstructures were prepared as supercapacitor electrode materials to obtain excellent electrochemical performance.It was also assembled into an asymmetric supercapacitor to research its application in the devices.The specific research on electrode materials of this paper are as follows:（1）Based on the simple solvothermal method,a composite with Ni Co₂S₄ nanoparticles in situ grown on graphene sheets（GS-NCS）was prepared and used as electrode materials.At the same time,the effects of different concentrations of graphene on the properties of composite electrode materials were explored.GS-NCS exhibited excellent electrochemical activity due to abundance of active sites and had a higher capacitance than other unitary metal oxides or sulfides.The electrode of GS-NCS-0.5 achieved a specific capacitance of2418 F/g at a current density of 1 A/g.In the asymmetric supercapacitor,Ni Co₂S₄@r GO and N-doped graphene are used as the cathode and anode,respectively,and an extended potential working window of 1.6 V can be obtained.A combination of pseudocapacitance and double layer capacitance resulted in GS-NCS achieving good rate performance and excellent cyclic stability.The device delivered a maximum energy density of 34.1 Wh/kg at a power density of 411 W/kg.In addition,the device possessed acceptable cyclic stability,with 86.4%capacitance retention after 5000 cycles.The proposed method provides a general route for assembling supercapacitors with high capacitance and wide voltage window.（2）We prepared a three-dimensional porous bowl-shaped cobalt disulfide/carbon（Co S₂/C）composite electrode material through carbonization and sulfidation processes,and explored the effect of the mass ratio of carbon and Co（CH₃COO）₂·4H₂O on the electrode material performance.The results show that when the mass ratio of carbon and Co（CH₃COO）₂·4H₂O is 1:2,a perfect 3D bowl-like structure can be obtained,and an excellent electrochemical performance was also obtained.Co S₂/C-2 can reach 588.8 F/g at a current density of 1 A/g and has good rate performance.In the asymmetric supercapacitor,Co S₂/C-2 and N-r GO as the cathode and anode respectively,and the electrochemical characteristics of the device were explored.The device has an operating voltage window of 1.6 V in an aqueous electrolyte.And possessed a specific capacitance of 43.5 F/g at a current density of 0.5 A/g.The device can retain a capacitance of more than 90.1%after 5000 cycles.In addition,the device has a power density of 374.5 W/kg at an energy density of 13.6 Wh/kg.（3）We prepared a unique urchin-like structure of cobalt tetrasulfide（Co₃S₄）composed of many nano-needles.And explored the influence of sulfur concentration on electrode material morphology,microstructure and electrochemical performance.The results show that when the sulfidation concentration is 0.1 M,perfect urchin-like Co₃S₄-1 was obtained,and it has good electrochemical performance.The specific capacity is as high as 1620.6 F/g at a current density of 1 A/g.When the current density is increased by 10 times,the capacitance remained at 87%,showing good capacitance characteristics and rate performance.The also exhibit excellent stability,specific capacitance decreased by only 14.1%after 5000 cycles,at current density of 5 A/g.