Research And Application Of Iron Oxide And Carbon Based Composite Electrode Materials

With the acceleration of industrialization,new generation supercapacitors with high energy density,high power density and excellent cycle stability are seeked in increasing demand for energy.And they are highly desirable for practical applications.To improve the electrochemical performance of supercapacitors,constructions of high performance electrode materials become inevitable.However,low specific capacitances and narrow potential windows restrict the application of supercapacitor electrode materials.Iron oxide（Fe₂O₃ and Fe₃O₄）electrode materials have the advantages of wide potential window,large theoretical specific capacity,non-toxic and environmental protection.As a result,iron oxide is expected to break through the bottleneck of traditional electrode materials and assemble high energy density water system hybrid supercapacitors.However,battery-like iron oxide anode materials take redox reaction as the main energy storage and have poor rate performance at high current density.Therefore,the preparation of a Fe₂O₃ and Fe₃O₄-based anode material with wide potential window,high specific capacity and high rate performance can further promote the application of battery-supercapacitor hybrid energy storage device（BSH）in high power storage.In this paper,iron oxide（Fe₂O₃）and reduced graphene oxide（r GO）composites were prepared by one-step hydrothermal method.By finely modulating the mass ratio of Fe₂O₃ to r GO,the specific capacity of the electrode reaches 413 C g^-1 in the 6 M KOH electrolyte when the potential window is between-0.15 and-1.2 V.At 20 A g^-1 current density,it still has 91.08%superhigh rate capability.In the meantime,the electrode shows good electrochemical properties in terms of potential window,specific capacity and rate performance.In order to further improve the electrochemical performance of BSH energy storage device,La_0.85Sr_0.15Mn O₃@Ni Co₂O₄ perovskite composite material with high specific capacity of 826 C g^-1 is used as positive electrode materials.By matching with the Fe₂O₃/r GO anode,the energy density of the BSH device increased to77.5 Wh kg^-1 and has a good power density of 54,000 W kg^-1.This device has excellent electrochemical behavior,which offers theoretical and experimental basis for the practical application of BSH devices.The traditional coating method introduces non-conductive binder,which results in high contact resistance between the iron oxide and the collector.However,the electrode prepared by in-situ synthesis method has good interfacial contact between active substance and collector with low resistance,which is expected to improve the conductivity of the electrode itself and thus improve the specific capacity.In this paper,an electrode material consisting of carbon material,transition metal oxide and metal skeleton was prepared by sol-gel impregnation method.Fe₃O₄ was grown in situ on iron foam by using gelatin’s self-bonding property and carbon material’s self-derived property.In addition to the C element,the gelatin-derived carbon material also contains abundant doping elements（such as N and O elements）,which can contribute part of specific capacity.C@Fe₃O₄/FeF electrode with the best performance was prepared with area specific capacitance up to 2036.36 m F cm^-2 under the current of 1m A.The energy density of the LSM@NC//C@Fe₃O₄/FeF BSH device is 197.56μWh cm^-2 and the specific capacity retention rate reaches 117%under the current of 100 m A with 10,000cycles.In the off-campus practice,I participated in the cooperative research project of Changchun Up Optotech Co.,Ltd.and designed a kind of anode material suitable for supercapacitor with high energy density.Using Fe₂O₃ as the base material,the electrochemical performance of Fe₂O₃ composited with nitrogen-doped graphene electrode was studied by adding different contents of ammonia water to regulate the nitrogen content of graphene.And design scheme of negative electrode material with larger specific capacity was proposed.