Deposition Of Nickel-cobalt Sulfide On Activated Carbon Fiber Network And Its Electrochemical Performance Study

Nowadays,developing clean and renewable energy to solve the problem of accelerated consumption of fossil fuels and the consequent environmental pollution problems becomes a global issue.It is particularly important to develop high-performance green energy storage devices to store and use energy more effectively.Supercapacitor is a new energy storage device.It is safe,environment friendly,maintenance-free and with high power density.Electrode materials are the key of an energy storage device.With the various demands for electronic devices characterized with flexibility,portability and high quality,development of high performance flexible electrode materials is vital important.A network-like conductive carbon material with a self-supporting structure has flexibility characteristic,which acts as both a collector material and an electrochemical active material.Therefore,it is possible to design high-performance flexible electrode material by surface modification of carbon network-like materials.In this thesis,a cotton fabric with a weft-woven yarn woven structure was used as a raw material.A carbon fiber network?CNW?was prepared by high-temperature carbonization activation.The cotton fabric activated by high-temperature carbonization retains the original weft-dyed woven structure,which can be continuously folded,bent and stretched,and has good electrical conductivity.The CNW with excellent conductivity and flexibility is selected as the substrate,and the one-step hydrothermal method is used to deposit the oriented nickel-cobalt bimetallic sulfide NiCo₂S₄on the surface of CNW.The parameters such as reaction time,reaction temperature and thiourea concentration during the preparation process affect the coating condition and coating morphology of NiCo₂S₄.Under the condition of optimal coating time of 24 h and reaction temperature of180°C,NiCo₂S₄ layer can be uniformly and densely coated on the surface of CNW.By controlling the concentration of thiourea to be 0.8 mol/L and 1.2 mol/L,nanorod NiCo₂S₄ and flake NiCo₂S₄ can be obtained respectively.The rod-shaped NiCo₂S₄ has a diameter of about 40nm and a length of about 2?m.The sheet-like NiCo₂S₄ has a width of about 500 nm and a thickness of about 20 nm.The single metal sulfides NiS₂ and CoS prepared under similar conditions have completely different morphological characteristics:NiS₂ has a triangular prism shape with a particle size of about 400 nm;CoS exhibits irregular granular shape with a particle size of about 800 nm.CNW/NiCo₂S₄ exhibits very excellent capacitance characteristics.Among them,CNW/NiCo₂S₄?rod?has a maximum specific capacitance of 1492.9 F/g?current density of 2mA/cm²?,and after a charge and discharge cycle of 1000 mA at a current density of 20 mA/cm²,the specific capacitance is attenuated by 19.3%.The CNW/NiCo₂S₄?sheet?performance is more prominent.When the current density is 2 mA/cm²,the maximum specific capacitance is 1648.6F/g.Under the current density of 20 mA/cm²,the charge and discharge cycle is 1000 times,and the specific capacitance is reduced by 17.4%.Compared with CNW/NiS₂?maximum specific capacitance 520.4 F/g,attenuation rate 18.1%?and CNW/CoS?maximum specific capacitance850.0 F/g,attenuation rate 18.7%?under the same test conditions,it exhibits higher charge storage capacity and More stable charge and discharge performance.CNW/NiCo₂S₄ composites can be stretched,bent and folded repeatedly.The elongation at break is 20.9%and the maximum tensile strength is 0.14 MPa.The CNW/NiCo₂S₄?sheet?was placed in a tensile state for electrochemical performance test,and the measured maximum capacitance value did not differ much from the natural state.After 100 times of repeated folding and bending,the electrochemical performance of CNW/NiCo₂S₄?sheet?was hardly affected.This paper explores a one-step hydrothermal synthesis of bimetallic nickel-cobalt sulfide deposited on the surface of a flexible substrate material CNW.The composite material combines the flexibility of CNW with the high specific capacitance of bimetallic nickel-cobalt sulfide,showing excellent performance.Electrochemical performance and good flexibility.It can be used in sensors,wearable electronics and medical devices,providing more possibilities for the development of flexible electrode materials.