Preparation And Properties Of Electrode Materials For Wide Potential Supercapacitors

With high power density and long cycle life,supercapacitor is a rising star in the field of energy storage.However,the low energy density seriously hinders its practical application and development.Based on this,from the perspective of optimizing electrode materials,this paper aims to prepare electrode materials of wide potential supercapacitor,so as to greatly improve the energy density.Firstly,the preparation and properties of negative materials for wide potential supercapacitors are studied.A three-dimensional self-assembled Fe₂O₃nanoparticles/reduced graphene oxide（Fe₂O₃/r GO）hydrogel composite electrode material was designed by a simple solvothermal method.The effects of different solvent-thermal reaction time on the morphology,loading capacity,pore structure and electrochemical properties of hydrogel materials were systematically studied.With this hydrogel as the self-supporting anode material of supercapacitor,the voltage window can reach-1.2 V-0 V,and it shows A high specific capacitance of 1090 F/g at the current density of 2 A/g,with excellent rate performance（531 F/g at the high current density of10 A/g）.On this basis,the charge storage mechanism of Fe₂O₃/r GO hydrogel was deeply analyzed and revealed.Secondly,the preparation and properties of positive materials for wide potential supercapacitors are studied.Lamellar Na⁺intercalated MnO₂ nanosheets(CNFs/Na_0.5MnO₂)were grown on hollow porous and lightweight electrospun carbon nanofiber nonwoven（CNFs）by electrodeposition and electrochemical oxidation.The effects of different electrodeposition time and electrolyte concentration on the morphology of nanosheets were investigated.Using CNFs/Na_0.5MnO₂ with optimal parameters as cathode material for supercapacitor,its electrochemical properties and the embedding/exiting process of Na⁺were investigated.Based on the synergistic effect of the embedding/exiting of Na⁺in the electrochemical reaction process and the electroactive CNFs substrate,CNFs/Na_0.5MnO₂ exhibited excellent electrochemical performance,which was stable in the range of 0-1.25 V,and a high specific capacitance of 365 F/g was obtained at a current density of 2 A/g.Finally,a flexible wide potential positive material was prepared on this basis.First,a vertical graphene（VG）array was grown in situ on a flexible carbon cloth by plasma enhanced chemical vapor deposition（PECVD）.Then,the layered Na⁺intercalated MnO₂ nanosheets(CC-VG/Na_0.5MnO₂)were loaded by electrochemical method on this flexible substrate.The unique structure of three-dimensional VG not only increases the contact area between the electrode material and the electrolyte,but also reduces the diffusion distance of ions in the electrolyte,thus improving electrode dynamics.The electrochemical properties of CC-VG/Na_0.5MnO₂ cathode materials for flexible supercapacitors were then systematically studied.The results show that CC-VG/Na_0.5MnO₂ can operate stably in a wide potential window of 0-1.3 V,and exhibit a high specific capacity of 525 F/g at 2 A/g.The specific capacitance is as high as 392 F/g even at a high current density of 30 A/g,indicating an excellent rate capability.What’s more,the capacity retention rate is 87.3%after 1000 cycles,which means a good cycling stability.The electrode material structure design method proposed in this thesis effectively improves the electrochemical performance,which provides a new idea for the preparation of electrode materials for supercapacitors with wide potential and high capacitance.