Synthesis And Electrochemical Property Of Cu,Ni-based Integrated Electrode For Supercapacitors

With the increasing environmental pollution and energy crisis,efficient energy storage and conversion technologies have become a major demand at present.In particular,in order to meet the needs of high-power power supplies,electric vehicles and smart grids,hybrid electric vehicles and smart grids,it is urgent to develop supercapacitors with high power density,high energy density,high rate performance and long cycle life.The electrochemical performance of supercapacitors mainly depends on electrode materials,and most electrode materials have problems such as low charge transfer efficiency and structural instability during the electrochemical reaction process,which severely limits the application and development of supercapacitors.In response to the above problems,we select some copper（Cu）and nickel（Ni）-based transition metal nitride and hydroxide supercapacitor electrode materials as the research object,and use the phase transformation and morphology controlling,along with the integrated electrode design to optimize the performance of these electrode materials.By systematically study of the influence of phase transition,microstructure,and morphology on the electrochemical performance,we got a much comprehensive understanding on the energy storage mechanism of thses active materials,which will bring a foundation for the efficient usage of these materials in the field of electrochemical energy storage.The specific research content of the thesis is as follows:（1）.An integrated Cu₃N nanorod arrays directly grown on Cu foam substrate by oxidation etching process,following by a post-nitridation treatment.The morphology characterization results showed that a one-dimensional（1D）porous Cu₃N nanorod array was grown on the 3D Cu foam.This unique structure makes the material have a large specific surface area and much stronger structural stability.Therefore,the integrated Cu₃N/CF electrode exhibits excellent electrochemical properties for supercapacitors,such as high area specific capacitance（1.77 F cm-1）,excellent rate performance and long cycle stability.When Cu₃N/CF and VN/NF are assembled into an asymmetric supercapacitor,its energy density can reach 111 μWh cm^-2.（2）.Ultrathin Ni（OH）₂ nanosheets are grown on the surface of Cu₃N nanorods by solvothermal method to prepare three-dimensional porous Cu₃N@Ni（OH）₂ core-shell heterogeneous nanoarrays.As an integrated electrode,the Cu₃N nanorod core in Cu₃N@Ni（OH）₂/CF accelerates the transmission of electrons and the diffusion of ions,while the Ni（OH）₂ nanosheet shell can provide abundant active sites.Under the synergistic effect between the Cu₃N nanorods and Ni（OH）₂ nanosheets,the Cu₃N@Ni（OH）₂/CF electrode exhibits excellent electrochemical performance.At 1 mA cm^-2,its area specific capacitance is as high as 3.74 C cm^-2,which is about 3.5 times higher than Cu₃N/CF electrode(1.06 C cm^-2)and shows high cycling stability.In addition,the AAS device of Cu₃N@Ni（OH）₂/CF//AC also delivers a high energy density of 0.26 mWh cm^-2 at the power density of 1.6 mW cm^-2.（3）.A novel integrated P-Ni（OH）₂@Co（OH）₂/NF with hierarchical core-shell heterostructure was grown in situ on a Ni foam by hydrothermal method.The morphological characterization results show that the blade-shaped Co（OH）₂ nanosheets are uniformly grown on the surface of the hexagonal prism-shaped P-Ni（OH）₂ micro/nanorods,and they are interconnected to form a three-dimensional network structure.P-Ni（OH）₂@Co（OH）₂/NF shows excellent performance when used as a supercapacitor integrated electrode.It has an ultrahigh area capacitance of 4.4 C cm^-2 at 1 mA cm^-2 and extralong cycle life due to the unique core-shell nanostructure and the synergistic effects of the P-Ni（OH）₂ rods and Co（OH）₂ nanoflakes.When assembling AHS with Fe2O3/CC anode,it delivers an impressive energy density of 0.21 mWh cm^-2,an attractive power density of 16 mW cm^-2 and an extended operating voltage window of 1.6 V.Moreover,the AHS also shows an excellent cycling stability with capacitance retention of 81%after 5000 cycles at 20 mA cm^-2,showing high cycle stability.（4）.CoN-Ni3N/N-C nanosheets with honeycomb-like texture were successfully in-situ grown on flexible carbon cloth by solvothermal method and post-nitridation treatment,and its superelectric properties were studied.Benefiting from the unique structural design of the material and the synergistic effect between multiple components,the CoN-Ni3N/NC/CC integrated electrode exhibits excellent supercapacitor performance,and its area specific capacitance is as high as 1.48 F cm^-2 at 0.5 mA cm^-2,the capacitance retention rate is 93.3%after 10,000 cycles,showing high cycle life and electrochemical reversibility.Beside,a flexible quasi-solid-state asymmetric supercapacitor was assembled with CoN-Ni3N/N-C//CC cathode and VN/CC anode,which delivers an excellent energy density of 106μWh cm^-2,maximum power density of 40 mW cm^-2,and an outstanding cycle stability with 82%capacitance retention after 6000 cycles.