Preparation Of ZnCo₂O₄-ZnO-Based Electrode Materials And Research On Their Supercapacitor Properties

Traditional energy sources,such as coal and oil,have been partially replaced by renewable energy due to the air pollution and the greenhouse effect.One of the commonly used sustainable energy storage devices is the supercapacitor.In fact,compared with other electrochemical devices such as conventional capacitors,lithium-ion batteries,fuel cells and solar cells,supercapacitors have a specific position in energy storage devices due to their longer cycle life,higher power and energy density,and greater cost effectiveness.Based on the energy storage mechanism,supercapacitors can be divided into two types:the first is a electrical double-layer capacitor which utilizes the charge separation of electrostatic storage;the second is a pseudocapacitor with excellent energy performance due to the reversible faradic reactions.The choice of electrode material is of great importance to the performance of supercapacitor.Good electrical conductivity of the electrode is beneficial to electron transport and ion diffusion in the charging and discharging process of the supercapacitor,and the morphology determines the available active specific surface area and structural stability.Therefore,ZnCo₂O₄-ZnO based core-shell structure composite electrode material was designed through morphology engineering,which was used as the positive electrode,and commercial activated carbon was selected as the negative electrode to construct an asymmetric supercapacitor.The experiment is divided into the following two parts:（1）ZnCo₂O₄-ZnO microspheres（ZCO-ZO）were prepared by hydrothermal method and annealing treatment.Through a series of characterization and electrochemical tests,the effect and capacitance contribution of ZnCo₂O₄ and ZnO microspheres were investigated by changing the mass ratio of ZnCo₂O₄ and ZnO.The ZCO-ZO microspheres with a mass ratio of about 1:1 had the best electrochemical performance.ZCO-ZO was used as the core and ZnCo₂O₄ porous nanosheets were coated on the surface to prepare hierarchical ZnCo₂O₄-ZnO/ZnCo₂O₄ core-shell microstructural composites（ZCO-ZO/ZCO）.The core-shell structure of the composite was proved by adjusting the amount of nanosheets for shell by changing the reaction time.Finally,the capacitance contribution,conductivity and cycling properties of single ZCO-ZO core,ZnCo₂O₄ shell and core-shell ZCO-ZO/ZCO composites were investigated respectively.It was proved that the core-shell ZCO-ZO/ZCO pseudocapacitive materials have the best capacitance and cycling properties.The energy storage capacity and practical application prospect of the pseudocapacitance material were studied in the two-electrode system.（2）Based on the above research content,in order to further improve the conductivity of ZCO-ZO,ZCO-ZO@C microspheres were prepared by coating the surface of ZCO-ZO with amorphous carbon.The ZCO-ZO@C@CoS-m（m=3,6,and 9）core-shell composites were prepared by changing the number of deposition cycles on the surface of ZCO-ZO@C core by galvanostatic electrodeposition technology,so as to explore the effect of the content of CoS nanosheets for shell on the electrochemical properties of core-shell composites.It is proved that ZCO-ZO@C@CoS-6 had the best electrochemical performance.Finally,ZCO-ZO@C@CoS-6//AC asymmetric supercapacitor was constructed to study the application potential of the composite electrode materials in energy storage equipment.