Study On Electrochemical Performance Of Nickel Cobalt Sulfide And Carbon Composite Electrode Material

Fossil energy exhaustion and environmental degradation have prompted mankind to seek green and efficient new energy technologies.As an important green and sustainable energy storage device,supercapacitors exhibit high power density,long cycle life,and fast charge and discharge.To design high performance electrode materials is an effective strategy to build green and high performance supercapacitors.Nickel cobalt sulfide has become a research hotspot of electrode materials because of its rich chemical valence and high theoretical specific capacity.In this article,solvothermal and electrochemical deposition methods were used to prepare nickel cobalt sulfide and carbon composite materials with different morphologies,and the electrochemical performance of the composite electrode materials were studied.The main research contents of the article are as follows:1)Electron microscopic analysis shows that the yolk-shell structured nickel cobalt sulfide material was prepared by a two-step solvothermal method,and the optimal sulfurization time for constructing the yolk-shell structure is 8 h.The analysis of the specific surface area and X-ray photoelectron spectroscopy shows that there are mesopores on the surface of the yolk-shell structure and the nickel cobalt sulfide material is rich in chemical valence states,which is conducive to the rapid electron/ion transport during the energy storage process and exhibits good electrochemical performance.The electrode exhibits a maximum specific capacity of 428.4 C g-1 at 1 A g-1,and the rate performance is 53%.After 5000 cycles of charge/discharge,the capacity retention rate is 73.49%.However,the active material is very easy to agglomerate,resulting in a reduction in surface active sites,a reduction in its utilization rate,and a lower rate performance.2)To solve the above problems,a two-step solvothermal method was further proposed to prepare the yolk-shell structured nickel cobalt sulfide and carbon nanotube composite using carboxyl carbon nanotubes as a carrier.And the effect of carbon content on the electrochemical performance of the composite material was explored.The results show that when the mass of the precursor and carbon nanotubes is 3:1,the best composite material is obtained.Moreover,the composite electrode shows a maximum specific capacity value of 603 C g-1,and the rate performance is 67.4%.After 5000 cycles of charge/discharge,the capacity retention rate is 88.08%.Compared with the above-mentioned yolk-shell structured nickel cobalt sulfide,the carbon nanotubes in this composite facilitate rapid electron/ion transport.At the same time,they serve as support for nickel cobalt sulfide,effectively alleviating the agglomeration of nickel cobalt sulfide,and revealing more active sites.Therefore,the utilization rate of the active material itself is improved,and it shows the superior specific capacity and rate performance.3)Wood-derived carbon bulk material with porous structure has many advantages in energy storage applications,without conductive agents and binders,and directly loads active materials to build self-supporting electrodes.One-step cyclic voltammetric electrodeposition was used to grow nickel cobalt sulfide nanosheets directly on wood-derived carbon electrode,and the electrochemical performance of the prepared nickel cobalt sulfide electrode materials was investigated at different scanning cycles.The results show that the nickel cobalt sulfide electrode material prepared at 120 scanning cycles has a maximum specific capacity value of 599.1 C g-1 and a specific capacity retention rate of 76.59%at 30 mA cm-2 with 3000 charge/discharge cycles.However,the nickel cobalt sulfide nanosheets are easy to overlap,which leads to the reduction of active sites and stability of the active material surface.Based on the above problems,carbon nanotubes were introduced inside the wood-derived carbon electrode by chemical vapor deposition,and on this basis,nickel cobalt sulfide and carbon nanotube composites were prepared by cyclic voltammetric electrodeposition.Electron microscopic analysis shows that the composites have an acacia-like structure.And the prepared composites have excellent electrochemical performance at 100 cycles of cyclic voltammetric scanning.The electrode has a maximum specific capacity of 1379.2 C g-1 at 5 mA cm-2,and the rate performance is 62.9%.After 3000 cycles of charge/discharge,the capacity retention rate is 88.8%.Compared with the single nickel cobalt sulfide nanosheet electrode material,the cycling performance is improved.The stacked nanosheets are dispersed with carbon nanotubes as the supporting skeleton,and the nanosheets are tightly wrapped around the surface of carbon nanotubes,which improves the stability of the material.In this paper,a composite electrode of acacia-like nickel cobalt sulfide and carbon nanotubes based on wood-derived carbon was prepared.Compared with the yolk-shell structured nickel cobalt sulfide and carbon nanotubes composite electrode、nickel cobalt sulfide electrode,this electrode has a low cost and simple preparation process,and it achieves the full combination of active material and collector and enhances the stability of active material.The design of this electrode provides a new idea for the application of biomass-derived carbon materials in the field of energy storage.