Preparation Of Transition Metal Sulfide/Phosphide Electrode Materials And Their Application In Supercapacitors

The development of energy storage devices that have an improved energy density and maintain the high power density and long cycle life of supercapacitors has remained a great challenge.Because the energy density of supercapacitor is related to its capacitance and operating voltage window,it can be increased by either enhancing the specific capacitance or expanding the voltage window of the device.Of these,the increase in specific capacitance is related to the electrode material,so the development of high-performance electrode materials is particularly important to optimize the energy density of supercapacitors;and the widening of the operating voltage window can be achieved by assembling asymmetric devices.To achieve the above purpose,this dissertation has studied the components,structure,and morphology of the positive and negative electrode materials,the electrochemical properties and mechanism of the positive and negative electrode materials in order to improve the energy density of supercapacitors,and has achieved the following results:1.Hierarchical CuCo₂S₄ nanobelt array electrodes were constructed for the first time by hydrothermal method on a 3D nickel foam skeleton,the formation mechanism of nanobelts and the important effects of sulfidation process on the morphology and electrochemical properties of electrode materials were investigated in detail.The specific surface area analysis showed that the prepared CuCo₂S₄ material has a specific surface area of 85.27 m² g^–1.The electrochemical test results revealed that it has a specific capacity of 1014 C g^–1 at a current density of 1 A g^–1 and a high specific capacity of 802 C g^–1 at 10 A g^–1 and retains 89.71%of the initial capacitance after 5000 cycles at a current density of 20 m A cm^–2,showing a good electrochemical performance.The aqueous asymmetric supercapacitors were assembled using the prepared CuCo₂S₄nanobelt arrays and nitrogen-doped double layer carbon hollow microspheres（N-DLCHs）as the positive and negative electrode materials,respectively,and 6 mol L^–1KOH as the electrolyte,which possessed a stable output voltage of 1.6 V and a maximum energy density of 40.20 W h kg^–1 at a power density of 799.10 W kg^–1.2.On the basis of the advantages of the morphology and structure of the CuCo₂S₄nanobelt array electrode materials,the CuCo₂S₄@NiFe-LDH nanoarrays electrode materials with core-shell structure were further constructed by introducing Ni-Fe layered double hydroxide（NiFe-LDH）ultrathin nanosheets through hydrothermal method.The specific surface area analysis showed that it has a large specific surface area of 70.38 m² g^–1.The electrochemical test results indicated that the electrode material possessed a specific capacity of 917 C g^–1 at a current density of 3 A g^–1 and a high rate performance of 71.2%at 20 A g^–1,and 92.66%initial capacitance retention after 10,000 cycles at a current density of 10 A g^–1.In addition,three-dimensional hollow nitrogen-doped carbons（NHCs）derived from the metal-organic frameworks ZIF-67 were modified using the metal oxide Fe₂O₃ to obtain NHCs@Fe₂O₃ negative electrode materials with a core-shell structure,which exhibited a wide potential window of–1.0-0.0 V and favorable electrochemical properties.The pouch-type asymmetric supercapacitors were assembled with the prepared CuCo₂S₄@NiFe-LDH and NHCs@Fe₂O₃ as positive and negative electrode materials,respectively,and the energy density of the devices was as high as 68.60 W h kg^–1 at a power density of 828.90 W kg^–1.3.The unique Ni₂P coated polyaniline（PANI）hollow nanotube composites（Ni₂P@PANI）were successfully prepared by a"two-in-one template-assisted method"and used as the positive electrode material for supercapacitors.Electrochemical test results exhibited that the Ni₂P@PANI nanotube electrode has a high specific capacity of 892 C g^–1 at a current density of 2 A g^–1 and a capacitance retention of 83.70%after10,000 cycles at a current density of 10 A g^–1.Furthermore,the origin of the electrochemical properties of Ni₂P@PANI was investigated in detail,and a potentially applicable electrochemical storage mechanism was proposed.Meanwhile,Fe₂O₃modified polyaniline derived nitrogen doped carbon nanotubes（Fe₂O₃@PNCT）were synthesized using the same"two-in-one template-assisted method"and used as the negative electrode of supercapacitors.The prepared Ni₂P@PANI and Fe₂O₃@PNCT were used as positive and negative electrode materials,respectively,and PVA/KOH gel as the electrolyte,to assemble the quasi-solid-state asymmetric supercapacitor,which had a wide voltage window of 1.7 V and a high energy density of 60.60 W h kg^–1 at a power density of 852.30 W kg^–1.