Preparation Of Electrode Materials Based On Metal Oxides/Sulfides With Its Application Of Hybrid Capacitor

In recent years,supercapacitors have become a potential energy storage device,which can be used in various energy fields,including electric vehicles,large lifting equipment and small electronic equipment.Battery-capacitor hybrid supercapacitor is a new type of capacitor with battery type as the positive electrode and capacitor type as the negative electrode.Then,due to its poor electrical conductivity and structural stability,battery-type active materials have limited electrochemical reaction power,resulting in poor cyclic stability and rate performance.An effective method to solve this problem is to prepare binder-free electrodes by in-situ growing or depositing the battery-type active materials directly on the conductive substrates.In this thesis,binder-free electrodes prepared by different methods and materials are presented,and their energy storage properties are studied in detail.1.Hierarchical core-shell nanorods array was grown on carbon cloth(CC/Zn O@C@Ni O)conductive substrate by hydrothermal and chemical bath method.Zn O nanoarrays with good electrical conductivity can be directly grown on flexible carbon fibers.This structure can provide high-speed electrons and ions transport path and expand the specific surface area of active material.A about 20 nm carbon layer with high electrical conductivity,converted from glucose on the surface of Zn O nanorods,not only improves the transfer ability of electrons and charges in the rapid redox reaction,but also effectively prevents erosion of Zn O in alkaline electrolytes.Compared with Zn O@Ni O core-shell nanorods arrays without carbon layer,the cyclic stability of Zn O@C@Ni O core-shell nanorods arrays increase from 21%to 71%.In alkaline electrolytes,ultra-thin Ni O nanosheets coated on Zn O@C provide abundant Faradic redox active centers.The as-prepared electrode shows high specific capacitance(1346.3 F g^-1at 1.43 A g^-1).This new hierarchical nanostructure CC/Zn O@C@Ni O takes Zn O@C nanorods as the framework to improve the surface area and electronic conductivity of Ni O nanorods,which can be widely used in flexible,portable energy storage devices.The all-solid-state hybrid supercapacitors assembled with CC/Zn O@C@Ni O as positive electrode and commercial graphene as negative electrode showed highest energy density of 35.7 Wh kg^-1at 380.9 W kg^-1and highest power density of 2704.2 W kg^-1at 16.0 Wh kg^-1,and 87.5%retention after 10000 cycles.2.Metal sulfides have higher theoretical capacity and conductivity than oxides.The Co₃O₄nanoneedle arrays are grown on the nickel foam(NF),then Co₃O₄@precursor core-shell structure are prepared by solvothermal method.Finally,Co₃O₄nanoneedles doped with sulfur and Ni Co₂S₄nanosheets were prepared based on precursor by one-step sulfurization method and a bind-free electrode with improved electrochemical performance was obtained.Material characterization showed that the phenomenon of S element doping was happened to the“core”Co₃O₄during the preparation of Ni Co₂S₄nanosheets.S doped Co₃O₄,as the“core”of hierarchical electrode,can effectively improve the conductivity and capacitance performance of the electrode.When the current density is 8 m A cm^-2,the hierarchical electrode has a high area capacity(10.86 m Ah cm^-2),good rate performance(72.5%retention after the current density increases from 8 m A cm^-2to 30 m A cm^-2),and good cyclic stability(97.31%retention after 5000 cycles).The assembled hybrid supercapacitor NF/S-Co₃O₄@Ni Co₂S₄//AC has a high energy density of 50.5 Wh kg^-1at a power density of 375 W kg^-1and power density of 22080 W kg^-1at a power density of22.7 Wh kg^-1,and can maintain 90.6%of the original specific capacity after 10,000 cycles.3.It is an important method to construct three dimensional nanostructures of metal oxide heterojunction on conductive substrate to improve the activity and structural stability of active materials.In this chapter,needle-like and slice-like Ni Co₂O₄(denoted as CC/Ni Co₂O₄-N and CC/Ni Co₂O₄-S)were grown on CC by two-step hydrothermal method,respectively,as the three-dimensional well-conductive skeleton(“core”)and slice-like Ni O as the shell.The unique three-dimensional structure has excellent charge transfer,ion dispersion and large specific surface area.Due to the heterogeneous structure of Ni O and Ni Co₂O₄,electron mobility is significantly improved,and rapid redox reactions occur on the surface of active materials,so as to jointly exert the electrochemical properties of Ni O and Ni Co₂O₄.The specific capacitance of CC/Ni Co₂O₄-N@Ni O and CC/Ni Co₂O₄-S@Ni O is higher than that of single Ni Co₂O₄electrode on carbon cloth.Since needle-like and slice-like structure of Ni Co₂O₄promotes ion diffusion,charge transfer and reduces volume expansion during redox process,both types of electrodes exhibit good rate performance and excellent cycling capacity(capacitance remains 100%after 10000 cycles).Hybrid supercapacitors assembled with CC/Ni Co₂O₄@Ni O as positive electrode and commercial graphene as negative electrode have excellent energy storage performance.CC/Ni Co₂O₄-N@Ni O//graphene has the highest energy density of 33.8 Wh kg^-1at power density of 75 W kg^-1and the highest power density of 5692 at the energy density of 28 Wh kg^-1,while CC/Ni Co₂O₄-S@Ni O//graphene has the highest energy density of 27.9 Wh kg^-1at the power density of 375 W kg^-1and the highest power density of 5692 W kg^-1at the energy density of 20.1 Wh kg^-1.The capacity of two hybrid devices can keep 95.2%and92.3%retention after 10000 cycles under 4 A g^-1.4.The composite of metal oxide and conductive carbon material is an effective strategy to prepare high performance hybrid electrode.In this chapter,a nanometer to nanometer electrochemical preparation method is used to assemble highly active Ni Co₂O₄(NCO)nanoparticles and highly conductive Ketjenblack composite nanomaterial electrode on a conductive substrate of nickel foam.Highly active Ni Co₂O₄nanoparticles and highly conductive Ketjenblack have similar Zeta positive potential in isopropanol solution after charging charge.Under the action of negative electric field,the nanoparticles and Ketjenblack can be uniformly deposited on the conductive nickel foam substrate at the same time.Long chains of Ketjenblack interpenetrate to Ni Co₂O₄nanoparticles,which provides good charge transfer and reduce volume change during redox during long cycles.The binder-free electrode has high specific capacity(460 C g^-1at 1 A g^-1),excellent rate capacity(68.9%capacity retention from 1 A g^-1to 32 A g^-1)and excellent cycling performance(82.5%capacity retention after 15000 cycles).The optimized electrode was assembled into a NF/NCO-KB(6:4)//NF/KB hybrid supercapacitor,which had the highest energy density(53.0 Wh kg^-1)at the power density(746 W kg^-1)and the highest energy density(10928 W kg^-1)at the energy density(34.6 Wh kg^-1)and maintained a capacity of88.6%after 10,000 cycles.5.Metal Organic Frameworks(MOFs)material derivatives,such as metal oxides and sulfides,are widely used in the field of energy storage.A porous Ni Co₂S₄nanoarray based on nickel foam was prepared after annealing and sulfurizing the Ni Co₂O₄derived from the new bimetallic MOFs(isostructural 2,6-naphthalenedicarboxylate tetrahydrate salts of nickel(II)/cobalt(II)).The porous nanoarray provides abundant electrochemical active sites,fast ion diffusion and transfer,high specific capacity,good rate performance,and stable cycling performance.The NF/Ni Co₂S₄delivers excellent specific capacity of 1354.4 C g^-1at 1 A g^-1,good rate performance of 72.3%retention from 1 A g^-1to 16 A g^-1,and outstanding cycling stability of 82.6%retention after 10000 cycles at 8 A g^-1.The hybrid supercapacitor constructed by using porous Ni Co₂S₄nanosheet arrays as positive electrode and activated carbon as negative electrode,can providehigh energy density of 49.1 Wh kg^-1at power density of 375 W kg^-1,and has an excellent cycling stability of 94.5%after10000 cycles.