Research On Supercapacitor Electrode Materials Based On Transition Metal Composites

With the shortage of fossil fuels and the intensification of environmental pollution,the development of clean and sustainable energy has become one of the most important issues in today's society.As a new energy storage device,supercapacitor has attracted widespread attention because of it's high power density,fast charge/discharge speed,long cycle life and wide operating temperature range.Electrode material is one of the key factors to determin the performance of supercapacitors.Transition metal compounds have low cost and low toxicity,and because of xcellent electrical conductivity,multiple oxidation states and higher theoretical capacity than commercial carbon materials,they showed greater advantages in improving the electrochemical performance of supercapacitor.In this thesis,a series of transition metal-based nanocomposites were prepared by hydrothermal method,chemical precipitation method,high temperature annealing and subsequent vulcanization.The morphology,composition and structural properties of composites were analyzed and discussed through various detection instruments.The main contents are as follows:?1?A two-step hydrothermal method and subsequent annealing were used to synthesize the NiO/NiCo₂O₄ nano-electrode materials on hydrochloric acid-activated nickel foam.In the first step,NiO nanospheres were grown on a foamed nickel substrate.In the second step,NiCo₂O₄ nanoneedles were grown in situ on the surface of NiO to obtain a novel structural characteristics of NiO/NiCo₂O₄ needle/sphere composites.The nitrogen adsorption result shows that the synthesized NiO/NiCo₂O₄ three-dimensional composite structure has a high specific surface area of 57.244 m²·g^-1,which can provide more active sites for charge transfer and obtain a higher specific capacitance.When the current density is 2A/g,the specific capacitances of NiO/NiCo₂O₄ nanoelectrodes are 2447 F/g.After 3000 cycles at a current density of 12A/g,the retention rate of capacitance was 85.2%,which indicates that the prepared NiO/NiCo₂O₄ needle/sphere nanomaterial has good rate performance and cycle stability.?2?A two-step hydrothermal method and subsequent heating vulcanization were used to prepare the MOF-modified NiCo₂S₄@Ni₃S₂ nanocomposites with terephthalic acid as a ligand,and the Influence of micromorphology and electrical properties of materials with different amounts of modifiers were further studied.The results show that when the used amount of terephthalic acid is 0.045g,the prepared NiCo₂S₄@Ni₃S₂ porous nanomaterials have good morphological structure and electrochemical performance.When the current density is 2A/g,the specific capacitance of electrode material is 2866.5F/g;when the current density is 10A/g,the specific capacitance is 1360F/g.After 3000 cycles at a current density of 12A/g,the maintain specific capacitance can still be 81.4%.The results show that the MOF-modified NiCo₂S₄@Ni₃S₂ porous nanomaterials have excellent specific capacitance and good cycle stability.?3?MnCo₂O₄ nanowires were grown on nickel foam by a simple hydrothermal method and calcination process.Following immersion of the MnCo₂O₄ precursor in Na₂S aqueous solution,sulfur replaces the oxygen to form MnCo₂S₄ to obtain MnCo₂O₄@MnCo₂S₄supercapacitor composite electrode material.According to SEM and TEM analysis,the shell of MnCo₂S₄ is evenly coated on the surface of MnCo₂O₄,forming an obvious core-shell structure.The results of XRD,XPS and electron diffraction show that the composition of the obtained composite material is MnCo₂O₄@MnCo₂S₄,and the as-prepared core-shell nanostructure revealed its component ad-vantages and a synergistic effect for electrode materials of supercapacitors.The material can provide a high specific capacitance of2212.5F/g at the current density of 1A/g,while the specific capacitance of single-component MnCo₂O₄ nanowire is 1280.6F/g,which indicates that the MnCo₂S₄ shell formed by sulfuration is effective to improve the specific capacitance of composite material.in the three-electrode system,the material shows a good rate performance,and After 5000 cycles at a current density of 10A/g,the capacitance retention is 89%,which proves that it has excellent cycle stability.The influence of the composition and morphology of nanomaterials on their electro chemical performance was explored by changing the synthesis conditions and composite methods,and transition metal-based supercapacitor electrode materials with novel structure and excellent performance have been obtained.The results show that the prepared NiO/NiCo₂O₄needle/sphere nanomaterials,NiCo₂S₄@Ni₃S₂ porous materials and MnCo₂O₄@MnCo₂S₄core/shell nanomaterials all have good electrochemical performance,which indicated that the design principles and preparation methods adopted in this paper are correct and effective,which can provide an idea for the design,preparation and performance research of transition metal-based nano-electrode materials in the future.