Research On Preparation And Performances Of Transition Metal Compound Based Electrode Materials For Supercapacitors

As a new energy storage device between battery and conventional capacitor,supercapacitor exhibits higher power density than that of battery and higher energy density than that of traditional capacitor,respectively.Therefore,the rapid development of supercapacitor has brought the hope for the widespread applications of high-power or high-energy electrical devices.As one of key factors determing the performances of supercapacitor,properties of electrode materials have great influence on its' performances.Transition metal compound and the corresponding composites possess some advantages,such as simple preparation,low cost;high capacity and environmental friendliness,etc,which have attracted widespread concerns of researchers.In this thesis.a serial of transition metal compound and the corresponding composites materials are prepared by simple hydrothermal method and chemical precipitation method.In addition,the component.morphology,structure and electrochemical performances of as-prepared materials have been tested and further analyzed.The main contents are as follows:(1)K-birnessite type MnO2 nanosheets are prepared by simple hydrothermal method.where KMnO4 uses as oxidant and nano-network structured bacterial cellulose acts as reducing agent and support skeleton.The results of X-ray diffraction spectroscopy(XRD),Fourier transform infrared spectroscopy(FTIR)and energy dispersive spectroscopy(EDS)show that crystal structure of as-prepared MnO2 is K-bismaneite type.By analyzing the results of field emission scanning electron microscopy(FE-SEM)and transmission electron microscopy(TEM),it is indicated that as-prepared K-bismaneite type MnO2 nanosheet is an ultrathin layered nanosheet.When the current densities are 0.2 A g-1 and 2.0 A g-1,the corresponding specific capacitances of as-prepared K-bismaneite type MnO2 nanosheets materials based electrode are 328.2 F g-1 and 200.4 F g-1,respectively,showing that as-prepared K-bismaneite type MnO2 nanosheets materials exhibit high rate performance.After continuous charge/discharge of 2000 cycles at current density of 3.0 A g-1,the retention rate of specific capacitance reaches up to 91.60%,manifesting that as-prepared K-bismaneite type MnO2 nanosheets materials have excellent cycle stability.(2)Sm2O3 modified layered CuO nanoflowers materials are prepared by simple hydrothermal method and we further investigate the effects of different amounts of modifiers on the microstructure and electrochemical performances of CuO matrix materials.The results show that,when the concentration of Sm(NO3)3 is 0.0090 M(0.30 mmol)in the reaction system,as-prepared Sm2O3 modified layered CuO nanoflowers materials exhibit the optimal electeochemical poperties in all as-prepared modified materials.The specific capacitance is 393.2 F g-1 when the current density is 0.3 g-1,while when the current density is increased by 10 times(3.0 A g-1),the specific capacitance still reaches up to 246.3 F g-1.In addition,after continuous charge/discharge of 2000 cycles at current density of 1.0 A g-1,the retention rate of specific capacitance is up to 84.6%.These results demonstrate that as-prepared Sm2O3 modified layered CuO nanoflowers materials present high capacitance,excellent rate capability and benign cycle stability.(3)The specific capacitance of as-prepared electrode materials is improved by combining the advantages of two materials without sacrificing the power density and cycling stability performances.Cobalt hex acyanoferrate/multi-walled carbon nanotubes(CoHCF/MWCNTs)nanocomposites are successfully prepared by simple chemical precipitation method and we further discuss the electrochemical performances of as-prepared CoHCF/MWCNTs nanocomposites composited with different mass fractions of MWCNTs.By analyzing the results of FE-SEM,it is concluded that the presence of MWCNTs alleviate the surface agglomeration of CoHCF.The analysis results of XRD,FTIR and Raman show that as-prepared nanocomposites contain CoHCF and MWCNTs.When the composite amount of MWCNTs is 25.0 wt%,specific capacitance of as-prepared CoHCF/MWCNTs nanocomposite based electrode is 648.5 F g-1 at current density of 1.4 A g-1,whereas specific capacitances of single-component CoHCF and MWCNTs materials based electrodes are 318.0 F g-1 and 45.7 F g-1,respectively,showing that specific capacitance of as-prepared CoHCF/MWCNTs nanocomposite is greatly improved compared with these of single-component CoHCF and MWCNTs.After continuous charge/discharge of 3000 cycles at current density of 2.0 A g-1,the retention rate of specific capacitance reaches up to 94.3%,indicating that as-prepared CoHCF/MWCNTs nanocomposites possess excellent cycle stability.(4)Manganese hexacyanoferrate/graphene oxide(CoHCF/GO)nanocomposites are synthesized on the substrate surface of GO by chemical precipitation method and we further investigate the electrochemical properties of as-prepared nanocomposites with different mass fraction of GO.By analyzing the results of FE-SEM,it is concluded that GO of high specific surface area can make MnHCF uniformly disperse on its surface and reduce the particle size of MnHCF.The results of XRD and FTIR demonstrate that the components of as-prepared nanocomposites contain MnHCF and GO.When the composite amount of GO is 20.3 wt%,the specific capacitance of as-prepared MnHCF/GO nanocomposite based electrode is 279.3 F g-1 at current density of 0.3 A g-1,while the specific capacitance of single-component MnHCF is only 91.1 F g-1,showing that specific capacitance of MnHCF/GO nanocomposite is increased by 3 times compared with that of single-component MnHCF.After continuous charge/discharge of 2000 cycles at current density of 0.8 A g-1,the retention rate of specific capacitance is 65.3%,indicating that nanocomposite exhibits favourable cycle stability.The electrode materials are designed by modification and compounding methods and we further investigate the effects of the corresponding composition,structure and morphology on the electrochemical properties,According to the acquired experimental result,as-prepared four materials,such as K-birnessite type MnO2 nanosheets,Sm2O3 modified layered CuO nanoflowers materials,CoHCF/MWCNTs and MnHCF/GO nanocomposites,exhibit excellent electrochemical properties,further illustrating that the design principles,the preparation method and research ideas can provide a reference for the design,preparation and performance research of supercapacitor electrode materials in the future.