Preparation And Capacitive Properties Of Cobalt Ferrite Based Electrode Materials

With the continuous development of social economy,the demand of energy storage devices for human social activities and industrial development is increasing.After long-term development,portable energy storage devices still have many fundamental problems,such as poor mechanical performance and low energy storage.Therefore,a new type of portable energy storage device is needed to solve this problem.Energy storage devices include supercapacitors,lithium ion batteries,solar cells,etc.,and supercapacitors have become a leader in the new generation of energy storage devices due to its high power density and good cycle stability and safety.However,the low specific capacitance and energy density of supercapacitors seriously affect their commercial applications.Therefore,how to improve the specific capacitance and energy density of supercapacitors while maintaining good cycle stability and safety has become a key problem to be solved at present.According to this problem,this paper adopts the different electrode substrate such as carbon fiber cloth plated nickel and nickel foam sponge,through simple synthesis method is carried out on the different substrate coated compound and spraying,such as theory of high specific capacitance of double metal oxide growth of cobalt ferrite on the basal,five high capacitance properties of electrode materials is prepared.The specific capacitance,energy density and cycling stability of the electrode can be improved by adjusting the solvent ratio and structure guide agent.The physical and chemical properties of electrode materials were analyzed by XRD,SEM,XPS and tensile test.Through the electrochemical analysis experiment,the systematic analysis of the three-electrode system and the capacitance performance of the assembled supercapacitor are carried out.Finally,the application of supercapacitors is investigated through the conversion of mechanical energy into electrical energy by the devices assembled into supercapacitors.The specific research content is as follows:Cobalt ferrite microspheres are grown on CFC substrate by simple hydrothermal method.At the current density of 1 A g^-1,the specific capacitance of CoFe₂O₄ microspheres/CFC is320.5 F g^-1.The energy density of the flexible supercapacitor is 25.4 Wh kg^-1.After 2000cycles,the specific capacitance retention rate is 88.9%.In addition,a layer of PEDOT:PSS hydrophilic polymer was sprayed on the surface of CoFe₂O₄/CFC by high-pressure spraying,which improved the hydrophilicity of the electrode,facilitated the electron transfer,and shortened the ion diffusion path.When the current density is 1 A g^-1,the specific capacitance is 213 F g^-1,the energy density of the flexible supercapacitor is 5.36 Wh kg^-1,and the specific capacitance retention rate was 90.2%after 5000 cycles.In order to further improve the specific capacitance and energy density of the electrode,Co OOH nanowire/CoFe₂O₄/NS composite sponge electrode was prepared by a simple two-step hydrothermal method based on NS with good conductivity and elasticity.The material not only retained the high storage performance of CoFe₂O₄,but also increased the specific surface area of the composite sponge material and the active site of electrochemical reaction.The specific capacitance of Co OOH/CoFe2O4/NS is 1201 F g^-1at 1 A g^-1,the maximum energy density and maximum power density can be obtained by assembling the flexible supercapacitor is 54.1 Wh kg^-1 and 374.9 W kg^-1.The average conversion rate of mechanical energy charging is 84%,the highest conversion rate is 95.6%,and the cycle performance of mechanical energy charging is excellent.Aiming at the specific capacitance and energy density of electrode substrate,the electrochemical properties of three kinds of substrate materials are compared,and the conductivity and specific capacitance of nickel foam are found to be the highest.Therefore,using nickel foam as the substrate,CoFe₂O₄ nanomaterials with different nanostructures are grown on nickel foam by controlling the solvent ratio and structure guiding agent,and PEDOT/CoFe2O4/NF nanosphere composite electrode was prepared by electrochemical deposition.As a nuclear material,CoFe₂O₄ nanospheres provide stable support.As a shell material,PEDOT is uniformly coated on the surface of the nanosphere,which improves the conductivity of the electrode and promotes the transfer of electrons and ions.When the current density is 1 A g^-1,the specific capacitance of the electrode material is 1211 F g^-1.After4000 cycles of charging and discharging,the specific capacitance can retain 96.1%of the initial specific capacitance.The energy density and power density of supercapacitor is 81.8Wh kg^-1 and 212.4 W kg^-1.Nickel foam/CoFe₂O₄ nanosheet composites are prepared by solvent ratio and structure-directing agent controllably.Nickel foam/CoFe₂O₄ nanosheet composites are selenized by ion exchange method,and nickel foam/CoFe₂O₄/CoFe₂Se₄ nanosheet structural electrodes are obtained.The electrode material has high specific surface area and controllable morphology,which is conducive to the rapid transfer and diffusion of electrons and ions,thus improving the capacitance performance.When the current density is 1 A g^-1,the specific capacitance of the electrode material is 1334.5 F g^-1.When the current increases to 10 A g^-1,70%of the specific capacitance can still are retained,this has a good multiplier performance.The specific capacitance of supercapacitors is 274 F g^-1 energy density and power density of110 Wh kg^-1 and 524.5 W kg^-1.And it has a very good cycle life,with a retention rate of 99%after 4000 cycles.Nickel foam/CoFe₂O₄/CoFe₂Se₄ nanobox electrode material is successfully prepared by two-step hydrothermal method.The electrode material has a high specific surface area and multistage pore structure,which is conducive to the rapid transfer and diffusion of electrons and ions,so that the active material is fully exposed to the electrolyte,and there are many active sites,so as to improve the capacitance performance.The specific capacitance of nickel foam/CoFe₂O₄/CoFe₂Se₄ nanobox electrode at 1 A g^-1 current density is 2040.8 F g^-1.CCSEC assemble by supercapacitor under the current density of 1 A g^-1 the specific capacitance of463.2 F g^-1,energy density and power density of 164.72 Wh kg^-1 and 500.8 W kg^-1.A mechanical generator is used to charge CCSEC.When charging for 30 min,the car can be driven at a constant speed of 16.4 m and the maximum voltage of mechanical energy storage is 1.61 V.When CCSEC is charged repeatedly with mechanical energy,the car travels for distances of more than 14 m,which indicates that CCSEC has good repeatability and indirectly proves that CCSEC has excellent cyclic stability.