Fabrication Of Metal Hydroxide Hierarchical Structure And Investigation Of Supercapacitor Performances

With the rapid consumption of non-renewable resources such as oil and coal,energy problems have become increasingly prominent.Therefore,the development of efficient and convenient energy storage technology has become a research hotspot worldwide.Electrochemical energy storage,a kind of clean energy,has become a research hotspot in recent years due to its characteristics of high conversion efficiency,flexible configuration and fast response.Supercapacitors have attracted wide attention because of their excellent power density,high charging-discharge rate and long cycle stability.However,compared with alkali metal batteries,there is still a problem of low energy density,so it is the key of current research to develop new electrode materials for supercapacitors with both high energy density and high power density.As a new pseudocapacitor material,transition metal hydroxide has become a popular electrode material for supercapacitors due to its high redox activity,adjustable composition,low cost and environmental friendliness.However,transition metal hydroxides have poor conductivity and are easy to stack,resulting in low specific capacitance of actual energy storage devices.This work starts from the point of view of regulating the microstructure of electrode materials.The multi-stage structure of two LDH-coated nanowires is constructed in situ on nickel foam to obtain excellent supercapacitor performance.The specific work is as follows:(1)The multistage structure of ZnCoNi-LDH coated ZnCo hydroxide nano wires is constructed by hydrothermal method,solution immersion method and solution etching method.The research shows that the construction of multistage structure can improve the electrochemical performance significantly.By optimizing the solvothermal etching time,the optimal energy storage performance is obtained under the condition of 4 h solution etching(the specific capacitance of 10.216 F cm-2 can be shown under the current density of 20 mA cm-2).Using this electrode as a positive electrode,the asymmetric supercapacitor constructed with active carbon anode has an energy density of 0.45 Wh cm-2 when the power density is 15 mW cm-2.The capacitance retention rate is 90.1%after 2500 cycles at the current density of 60 mA cm-2.In this work,the mechanism of electrochemical performance improvement caused by the construction of multistage structure is further explored by electrochemical dynamics,electrochemical impedance spectroscopy and other methods.The results show that the construction of multistage structure can significantly increase the electrochemical specific surface area,reduce the impedance,and increase the contribution ratio of pseudocapacitance,thus improving the electrochemical energy storage performance.(2)The multistage structure of NiCoMn-LDH coated Co(OH)F hydroxide nanorods is constructed by Through a simple wet chemical process.The effects of multistage structure on the microstructure,electronic structure and electrochemical performance of the electrode is systematically studied.By optimizing the ratio of metal ions in the etching agent,it is found that NiCoMn-LDH/Co(OH)F-NR shows the best electrochemical energy storage perforamance when the molar ratio of Ni/Mn in the etching agent was 2:1,and the specific capacitance of 23.01 F cm-2 was obtained at the current density of 1 mA cm-2.When the power density is 3.75 mW cm-2,the energy density is 0.845 mWh cm-2.The capacitance retention rate is 70.0%after 5000 cycles at the current density of 60 mA cm-2.In this work,we explore the influence mechanism of the metal ratio in the etching agent on the electrochemical performance.The research shows that the electrode material with the molar ratio of 2:1 Ni/Mn has the smallest impedance and the highest contribution ratio of pseudocapacitance,thus improving the electrochemical energy storage performance.