Preparation Of Iron-Cobalt Metal Oxide Electrode Materials For High-performance Supercapacitors

Supercapacitors?SCs?,as a kind of energy storage and conversion device between traditional capacitors and batteries,have solved the storage problem of renewable energy well.It not only has the fast charge-discharge performance of traditional capacitor,but also has the energy storage properties of batteries,and has been used in electronic equipment,transportation,aerospace and other fields.With the advent of the Internet of Things and 5G era,the energy storage level of supercapacitors is insufficient to meet the further development of society at this stage.The development of supercapacitor electrode materials with high-quality,high energy density,high power density,good reversibility and high cycle stability is currently another challenge for human beings.Compared with carbon electrode materials,transition metal oxide electrode materials have become the focus of attention due to their advantages of high energy density and environmental protection.However,the transition metal oxide electrode materials have some problems,such as easy agglomeration and pulverization of particles,slow electron conduction rate and low ion mobility.Therefore,improving the conductivity and electrochemical performance has become one of the current focuses of transition metal oxides.Based on the systematic description of supercapacitors and electrode materials,this paper proposes the idea of introducing other heterogeneous elements?Fe?to prepare Co₃O₄-based binary transition metal oxide electrode materials with excellent electrochemical performance by hydrothermal/solvothermal methods.The specific contents are as follows:?1?In the aqueous solution of urea and ammonium fluoride,urchin-like Fe-doped Co₃O₄microspheres were successfully prepared by a combination of hydrothermal and calcination methods.XRD,EDS,and XPS characterization results confirmed that the prepared sample was Fe-doped Co₃O₄ phase,and divalent and trivalent iron ions were present in the sample.The effects of urea dosage on the micromorphology and size of the samples were studied during the reaction.Without the addition of iron salts,pure Co₃O₄ electrode materials were prepared for comparison.The Fe-doped Co₃O₄ electrode delivers a specific capacitance of 710 F g^-1,higher than that of Co₃O₄(551 F g^-1)at the current density of 1 A g^-1.When the current density increases to 15 A g^-1,the rate capabilities of two electrodes are 79.3%and 76%,respectively.The above data show that metal doping can improve the electrochemical performance of electrode materials,which may be related to the introduction of Fe to increase more redox reactions.?2?In order to further compensate for the problem of low doping ion content and uneven distribution caused by the ion doping method,FeCo₂O₄ was successfully synthesized by using elemental substitution of Co₃O₄ with low-cost and active chemical transition metal Fe.The effects of different solvent ratios on the microstructure of electrode materials such as morphology and size were investigated.The specific surface areas of FeCo₂O₄ microspheres?FeCo₂O₄ MSs?and FeCo₂O₄ nanosheets?FeCo₂O₄ NSs?are 40.9 and 38.5 m² g^-1,respectively.FeCo₂O₄ MSs exhibits a specific capacitance of 583.6 Fg^-1 at 1 A g^-1 and a cycling stability of71.9%after 5000 cycles at 5 A g^-1.In contrast,FeCo₂O₄ NSs possesses better electrochemical performance with a specific capacitance of 852.9 F g^-1 at 1 A g^-1 and a rate capability of 77.8%at 13 A g^-1.FeCo₂O₄ NSs//AC asymmetric supercapacitor?ASC?exhibits a specific capacitance of 90.7 F g^-1 at 1 A g^-1 and a high energy density of 32.26 W h kg^-1 at 807.08 W kg^-1.After 5000cycles at 5 A g^-1,it exhibits a specific capacitance retention of 102.2%.Such excellent performance indicates that FeCo₂O₄ NSs has broad application prospects in the field of energy storage.