Research On Preparation And Electrochemical Performance Of Nickel-Cobalt-Based Oxide Electrode Material

With the vigorous development of electronic technology,the demand for energy and energy storage equipment are increasing.As the main energy storage device,supercapacitors have the advantages of high power density,long life and low production cost,and have a wide range of applications.Electrode materials occupies a key position in the electrochemical performance of supercapacitors,and they have attracted more and more attention in recent years.Spinel-type nickel cobalt ore（NiCo₂O₄）has the advantages of low cost,environmental safety and low toxicity,and is considered to be a more promising and flexible alternative.The performance of the electrode material is affected by its morphology.Different morphologies lead to different specific surface areas.As the specific surface area increases,the material will react more fully and the electrochemical performance will be more excellent.Therefore,in this paper,the changes in the morphology and electrochemical performance of NiCo₂O₄electrode materials are studied by changing the types and concentrations of alkaline substances and acid-base treatment of NiCo₂O₄electrode materials.The materials are analyzed by XRD,SEM and other test methods.Structure and microscopic morphology;using a three-electrode system to analyze the electrochemical performance of the material through cyclic voltammetry,constant current charge and discharge tests.The main research contents are as follows:1.The best alkaline substance for preparing NiCo₂O₄by changing the types of alkaline substances was found.Using urea,sodium hydroxide,and ammonia as alkaline substances,sea urchin-shaped,flake-shaped,and spherical NiCo₂O₄were prepared respectively.According to electrochemical tests,at a current density of 1 A/g,the specific capacitance of sea urchin-like NiCo₂O₄is the highest at 744 F/g,followed by sheet NiCo₂O₄with a specific capacitance of 543 F/g,the spherical NiCo₂O₄only has a specific capacitance of 256 F/g.This is attributed to the largest specific surface area of the sea urchin-like structure,which allows the electrode material and the electrolyte to fully react.The sea urchin-like NiCo₂O₄electrode material has the best cycle stability.At a current density of 10 A/g,after 1000 cycles of charge and discharge,the sea urchin-like NiCo₂O₄retains 93%of the specific capacitance,the sheet-like NiCo₂O₄retains 87%of the specific capacitance,and the spherical NiCo₂O₄retains75%of the specific capacitance.2.Exploring the influence of the best alkaline substance concentration on the morphology and electrochemical performance of NiCo₂O₄materials,by adding 10 mmol,15 mmol,and 20mmol of urea with different contents to obtain three kinds of NiCo₂O₄.The results show that the sample presents a granular structure of uniform,and its electrochemical performance is also the best when the urea content is 15 mmol.At a current density of 1 A/g,it has a specific capacitance of 731.6 F/g.Due to the fact that the appropriate urea content form more nucleation sites without agglomeration,making the material structure have a larger specific surface area（55.50 m²/g）.In addition,at a current density of 10 A/g,after 1000charge-discharge cycles,the specific capacitance can still retain 94%,which shows that it has excellent cycle stability.3.The sea urchin-like NiCo₂O₄sample was subjected to acid-base treatment.The results showed that the morphology of the sample changed greatly,and the surface showed a slit and porous structure after the acid-base treatment.The specific surface area of this special structure was increased to that of the sea urchin-like NiCo₂O₄sample 3 times as much as165.0660 cm²/g.Through electrochemical test and analysis,at a current density of 1 A/g,the specific capacitance of the acid-base treated sample is as high as 1700 F/g,which is 3 times that of the sea urchin-like NiCo₂O₄sample.In addition,the acid-base treated samples have good rate performance.When the current density increases from 1 A/g to 10 A/g,about 75%of the specific capacitance can still be retained.4.By adding graphene in the alkali treatment process,NiCo₂O₄/rGO composite material is obtained.Due to the addition of graphene,the composite material shows a fluffy and porous structure.Through the analysis of electrochemical performance,when the current density is1 A/g,the composite material has a high specific capacitance of 2332.4 F/g.Because the addition of graphene can effectively increase the specific surface area of the material,and graphene has better conductivity,the synergy between the two greatly increases the specific capacitance.But when the current density increases to 10 A/g,the specific capacitance of the NiCo₂O₄/rGO composite is only 1127 F/g,only about 50%of the specific capacitance is retained,and after 1000 cycles,the specific capacitance is only 45.3%.Poor rate performance and poor cycle stability are caused by the instability of the fluffy porous structure.