The Preparation Of Composite Electrode Materials With Mico-nano Multi-level Structure And Their Application In Supercapacitors

With the global energy shortages and environmental degradation, all kinds of recycledelectrochemical energy storage devices are increasingly brought lots of attention, and thesupercapacitor as a new energy storage has been widely applied because of its advantages oflarge power density, long cycle life and pollution-free. Electrode materials are the key to theperformances of supercapacitor. Considering the advantages and disadvantages of carbonmaterials and metal oxide electrode materials as electrode materials, the preparing ofcomposite electrode materials with good electrochemical performances by loading the metaloxides with carbon materials and nickel foam has become the primary goal of researchscholars.In this paper microwave hydrothermal method was used to research the related issuesaround the preparation of nano-nickel oxide and composite materials which have themicro-nano structure by nickel foam or carbon fiber cloth for the carrier loading nickel oxide,the structure and morphology of the material were characterized and observed by X-raydiffraction(XRD), thermal analysis and scanning electron microscope(SEM), theelectrochemical performances of electrode materials were tested and analyzed by cyclicvoltammetry and AC impedance method. The main work includes the following aspects:Nano NiO powders were synthesized by microwave hydrothermal method using NiSO4as source of nickel, urea as the precipitant, polyethylene glycol4000(PEG-4000) or polyetherimide (PEI) as a surfactant, by changing the holding time and the type and amount ofsurfactant. The results showed that: nano lamellar NiO precursor was synthesized at amicrowave heating temperature of160℃, the thickness of the single slice is approximately10nm, the NiO with flower flake microspheres was obtained after calcination at400℃for2h,the diameter of microspheres is approximately2μm, and the thickness of single flake isapproximately10nm. The agglomerate phenomena of NiO microspheres decreasedsignificantly, and microspheres shape and uniform size were obtained with surfactantadditives. Electrochemical tests show the specific capacitance of NiO prepared by adding3.7%PEG-4000, holding time for30min is about85.4F/g, the specific capacitance onlydecays13.3%of the original value after500cycles, reflecting stabilized electrochemical performances.With nickel foam as the carrier, NiO/nickel foam composite electrode materials withmicro-nano multi-level structure were prepared by microwave solventhermal method usingNi(NO3)2·6H2O and NiSO4as source of nickel ion, respectively, with changing theconcentration of nickel ion, surfactant type and amount and holding time. The results showedthat: nano NiO using NiSO4as nickel source with formation of flower flake microspheresuniformly grew in-situ on the surface of nickel foam. PEG-4000inhibits the growth ofnano-NiO on nickel foam. The capacitance of NiO/nickel foam electrode with no additive and30-min thermal insulation is about234.8F/g. Granular nano NiO was synthesized anduniformly grew on the surface of nickel foam with Ni(NO3)2·6H2O as source of nickel ion,60min thermal insulation, nano NiO stickedto the surface of nickel foam because ofPEG-4000, against the transfer of ions and electrons. Thf e capacitance NiO/nickel foamelectrode with no surfactant and60min thermal insulationis about224.4F/g.With activated carbon fiber cloth (ACFC) as the carrier, NiO/ACFC composite electrodematerials were synthesized by microwave hydrothermal method under the condition ofchanging the reaction solvent, concentration and reaction time. Electrochemical properties ofthese electrodes were studied. Results showed that: nano-NiO with flower flake microspheresstructure grewin situon the surface of activated carbon fiber cloth, and lamellar thickness isabout10nm. In the same situation of microwave synthesis, the amount of PEI and urea has agreater impact on the structure and morphology of the samples. Witha molar ratio CNi2+:C(NH2)2COof1:4,1ml PEI,60min thermal insulation, the specific capacitance of190.4F/g wasobtained, with excellent electrochemical performances and stability.