Preparation Of Core-Shell Cobalt-based Composites Nanomaterials And Study On The Properties Of Supercapacitors

In the past few decades,with the continuous development of industrialization,the excessive consumption of fossil fuels by human society has resulted in a large amount of greenhouse gas emissions and environmental pollution,which has greatly stimulated people's pursuit of sustainable green electrochemical energy.In recent years,supercapacitors have become one of the most promising electric energy storage devices due to their advantages of high specific power,fast charging and discharging,long life,and no pollution.Among them,the cathode materials prepared by pseudocapacitive materials have attracted more and more attention due to their higher specific capacitance.Most of the pseudocapacitive materials mainly use transition metal oxides,sulfides,and phosphides as electrode materials.However,most transition metal electrode materials have some disadvantages such as poor cycle stability and low actual specific capacitance,which further limits their application in the field of electrical energy storage.Therefore,this research intends to improve the electrochemical performance of pseudocapacitive materials by constructing a reasonable structure and material composite method.And further application exploration is carried out by assembling the electrode materials with commercial Active carbon(AC)to assemble a hybrid asymmetric supercapacitor device.The main research contents are as follows:1.Cobalt hydroxide nanoneedles were grown vertically on the surface of carbon fibers by a simple hydrothermal reaction.Then,in order to further expand the specific surface area and increase the active sites,Ni2+ was added under stirring at room temperature,and ammonia water and potassium persulfate were used as initiators.NiOOH nanosheets were grown on the cobalt surface to form NiOOH@Co(OH)2@CF with a hierarchical core-shell structure,and finally,after high temperature annealing,NiO@CoO@CF nanocomposites material with nano-array structure was obtained.The product also had a hierarchical core-shell nanostructure and exhibited excellent cycling stability,with a capacitance retention rate as high as 75.91%after 5000 cycles at 40 mA cm-2.2.The sea urchin-like cobalt-nickel oxalate was obtained in a specific solvent by means of a constant temperature water bath.After high temperature calcination,a binary cobaltnickel-based oxide(CoNiO2)precursor that maintained a sea urchin-like structure was obtained.Then,through a simple ultrasonic deposition reaction,a layer of Co-LDH was modified on the surface of CoNiO2 to form a hierarchical core-shell material with CoNiO2 as the core and Co-LDH as the shell.Finally,sea urchin-like core-shell CoNiO2@Co3S4 nanocomposites were obtained by hydrothermal sulfide.The composite not only exhibited a maximum specific capacitance of 1300.2 F g-1 at 1 A g-1,but also has a capacitance retention rate of 86.17%after 5000 cycles at 10 A g-1.In addition,the hybrid device exhibited excellent electrochemical performance,with a high energy density of 64.28 Wh kg-1 at a power density of 865.81 W kg-1.3.NiCo-glycerol spheres(NCGS)were obtained by a simple hydrothermal reaction using glycerol as a solvent,and the synthesis of flower-like hierarchical core-shell NCGS@NiCo2S4/Ni3S2 nanocomposites was controlled by changing the amount of sulfide and the introduction of additional cations(Ni2+)under reflux conditions.Through the characterization of morphology and structure,it could be found that with the increase of sulfide content,the evolution process of its structure gradually changed from solid to hollow.At the same time,it could be observed that the addition of Ni2+ during the sulfuration process determined the flower-like outer layer.Finally,hierarchical core-shell CoNiO2@NiCo2S4/Ni3S2 nanocomposites were obtained after double high-temperature annealing process.The composite material exhibited a mass specific capacitance of 1334.7 F g-1 in electrochemical performance tests.In addition,the hybrid device CoNiO2@NiCo2S4/Ni3S2//AC could maintain capacitance up to 90.23%after 5000 cycles at a current density of 10 A g-1.And when the power density is 850 W kg-1,its energy density is as high as 55.20 Wh kg-1.