Study On Preparation And Supercapacitor Performance Of NiCo-LDH Nanocomposite

With the rapid development of society and economy,it has been eager to find and develop the sustainable,environmentally friendly and efficient energy storage materials to solve the growing energy crisis.Due to their superior performance in high power density,operational safety and long cycle life,supercapacitors are widely studied.In the area of energy storage research,electrode materials play a key role in the high-performance of supercapacitors.Layered double hydroxides,which have a unique layered structure,large specific surface area and flexible ion-exchange ability,are potential electrochemical capacitor electrode materials.Therefore,it is important to develop the low-cost nickel-based LDH at the application of supercapacitors.It is negative for the supercapacitor performance of the poor conductivity of LDH.Graphene?Gr?and ZnO have been respectively grown on the conductive substrates,and subsequently deposit the NiCo-LDH to form nanocomposites.Moreover,NiCo-LDH grown on the cloth was used as the substrate to prepare nanocomposites with MnO₂.The morphology,structure,composition and electrochemical properties of the three kinds of nanocomposites were studied.A supercapacitor was fabricated to illuminate the LED light.The main research contents are as follows:?1?Different morphology of graphene?Graphene films?GF?and graphene nanowalls?GW??were grown on nickel foam?NF?substrates by chemical vapor deposition.Subsequently,NiCo-LDH nanosheets were grown on GF/NF and GW/NF substrates by hydrothermal method to form 3D self-supporting NiCo-LDH/GF/NF and NiCo-LDH/GW/NF composite electrodes.The morphology,structure,chemical composition and electrochemical performance of the composite electrode have been studied.It was found that the conductivity,pore size and specific surface area of the NiCo-LDH composites were improved due to the introduction of graphene.NiCo-LDH/GF/NF electrode exhibits optimal electrochemical performance with a maximum specific capacitance 2690 F g^-1 at a current density of 5 A g^-1,approximately1.2 times that of NiCo-LDH/GW/NF.It also significantly improved the rate characteristics and cycle stability of the electrode material.In addition,NiCo-LDH/GF//AC asymmetric capacitor,which is made of NiCo-LDH/GF/NF as the positive electrode and commercial activated carbon as the negative electrode,with a high-power density,energy density and good electrochemical stability.?2?In order to increase the application range of the capacitor device,a flexible carbon cloth?CC?is used as the substrate.Different morphologies of ZnO(ZnO nanosheets?ZnO NF?and ZnO nanorods?ZnO NR?were prepared on carbon cloth by a hydrothermal method.NiCo-LDH nanosheets were deposited on ZnO NF/CC and ZnO NR/CC substrates by hydrothermal method to form NiCo-LDH/ZnO NF/CC and NiCo-LDH/ZnO NR/CC electrodes.It was found that the NiCo-LDH nanosheet grown on the ZnO NF/CC substrate is denser and more uniform than on the ZnO NR/CC substrate,which is beneficial to the generation of more redox active sites and storage charges.NiCo-LDH/ZnO NF/CC electrode exhibits a high capacitance of 1748 F g^-1 at a current density of 1 A g^-1,which is 2.6 times that of the NiCo-LDH/ZnO NR/CC electrode(664 F g^-1).Moreover,the current density has been increased to 8 A g^-1,the specific capacitance retained 648 F g^-1,which indicates that the electrode has a remarkable rate performance.?3?Three kinds of MnO₂/NiCo-LDH/CC flexible electrodes?MnO₂-1/NiCo-LDH/CC,MnO₂-2/NiCo-LDH/CC and MnO₂-3/NiCo-LDH/CC?with different loadings of MnO₂ were synthesized on the NiCo-LDH/CC electrodes by hydrothermal method in different concentrations of KMnO₄ solution?0.01M,0.02M,0.03M?.By studying the structure,morphology and electrochemical properties of different composite electrodes,we have founded that MnO₂-2/NiCo-LDH/CC electrodes have a suitable pore,providing more transport channels for electrolyte ions and electrons.The specific capacitance of the MnO₂-2/NiCo-LDH/CC electrode is 312F g^-1 at a current density of 0.2 A g^-1.Moreover,after 5,000 cycles of charge-discharge tests,the MnO₂ nanosheets still maintain a vertical sheet structure,97%specific capacitance have been retained,indicating that the material has good mechanical stability and excellent cycle performance.