Synthesis And Electrochemical Properties Of Ni,Co,Mn,Bi Oxide/Hydroxide Nanomaterials

As the core part of supercapacitors,electrode materials are the main factors determining their overall performance.The high-performance supercapacitor electrode is constructed by rational structural design of the electrode active material and optimization of the synthesis process.The fundamental purpose is to increase the conductivity,specific surface area and structural stability of the electrode material by a simple method to further achieve high energy density,high power density and excellent cycle stability.Compared to conventional carbon-based materials,Ni,Co,Mn,Bi oxide/hydroxide nanomaterials and their composites have high theoretical specific capacitance and low electrical resistance,so they can be used as promising high-performance super Capacitor electrode material.Based on the structural design,synthesis method and electrochemical performance of nanomaterials-electrode,a series of Ni,Co,Mn,Bi based on oxide/hydroxide and composites were synthesized by hydrothermal,solvothermal and chemical etching methods.The nanomaterial-electrodes have the characteristics of unique structure and excellent electrochemical performance.The main research contents of this thesis are as follows1.Bi7.53Co0.47O11.92 nanoflowers uniformly grown directly on the 3D foamed nickel skeleton were synthesized by one step of simple solvothermal and subsequent heat treatment without using any binder.The nanoflower consists of secondary thin nanosheets that grow on the core and form an integrated flower shape with large specific surface area,low electrical resistance and good structural stability.NF/Bi7.53Co0.47O11.92 electrode material has high specific capacitance(1046.1 F g-1,1 A g-1),excellent rate performance(capacitance retention rate 81.7%,from 1 to 10 A g-1)and good cycle stability(80.5%of initial capacity after 3000 cycles).The assembled NF/Bi7.53Co0.47O11.92//AC asymmetric supercapacitor has a maximum energy density of 41.2 Wh kg-1 and a maximum power density of 7500 W kg-1.After 8000 cycles,it still achieves 83%of the initial specific capacitance.In practical applications,the series and parallel connection of devices also have good performance.2.We designed and developed a new one-dimensional hierarchical hollow nickel-cobalt layered double hydroxide nanocages assembled on MnO2 nanotubel with uniformly dispersed CoS2 nanoparticles,MnO2@NiCo-LDH/CoS2,using zeolitic imidazolate skeleton(ZIF-67)as template via multiple hydrothermal and sulfuration processes.This unique one-dimensional hierarchical nanostructure is characterized by high specific area,high structural stability,and the presence of CoS2 nanoparticles with the nanocage increases the electrical conductivity and enhances the stability of the structure.Electrochemical studies show that MnO2@NiCo-LDH/CoS2 electrode materials have a high specific capacitance of 1547 F g-1 at a current density of 1 A g-1 and 1189 F g-1 at 10 A g-1,exhibiting high rate performance(76.9%)and high stability(82.3%),substantially better than most recently reported performance of similar systems.The asymmetric energy supercapacitor assembled with MnO2@NiCo-LDH/CoS2 and activated carbon has a maximum energy density of 49.5 Wh kg-1 and a maximum power density of 9657.6 W kg-13.We designed and synthesized a Co-Co LDH/C/Ni(OH)2 system with Ni(OH)2 nanodots with a particle size ranging from 4-8 nm on a hollow Co-Co LDH/C nanocage derived from MOFs.Make full use of the large specific area of Co-Co LDH/C nanocage,multi-aperture,excellent conductivity and high specific capacitance potential of Ni(OH)2,so as to achieve excellent electrochemical performance through the synergy between the two.By investigating the Ni(OH)2 nanodots loading,the obtained Co-Co LDH/C/Ni(OH)2-50 has a specific capacitance of up to 1426 F g-1(1 A g-1),excellent rate performance(90.2%,10 A g-1 vs.1 A g-1)and excellent cycle stability(81.1%capacity retention after 3000 cycles).The assembled Co-Co LDH/C/Ni(OH)2-50//AC hybrid supercapacitor has a maximum energy density of 42.9 Wh kg-1 and a maximum power density of 7500 W kg-1.Electrochemical kinetic analysis shows that the Co-Co LDH/C/Ni(OH)2-50 electrode is dominated by surface capacitance control,which provides a basis for the simultaneous realization of high specific capacitance and high rate performance.