Design,preparation And Electrochemical Performance Of Manganese-based Oxide Self-supporting Electrodes

Supercapacitors possess the advantages of higher delivery of power density and longer cycling stability than metal ion batteries,and thus have attracted great interest in the field of energy storage research.For example,as one kind of energy storage device with high safety and environmental friendliness,and low cost,aqueous supercapacitors have great application potential.Nevertheless,their practical application faces a tough challenge due to the limited energy density?E?which is usually between 5 and 15 Wh kg^–1.Accordingly,increasing E is key to facilitating the application.Following the equation of E=1/2 CV²,energy density can be boosted by increasing the specific capacitance?C?and/or voltage window?V?of a supercapacitor.Among various materials,some transition metal oxides are considered as the ideal electrode materials for supercapacitors due to their high theoretical capacitance and environmental friendliness.However,the intrinsically low electrical conductivity and limited specific surface area for bulk metal oxides severely restrict the actual delivering of electrochemical performance.To address this issue,the strategy of integrating nanostructured metal oxides with conductive carbon materials to build composite structures is usually adopted.Based on the systematic investigation and careful review of the relevant literatures,design,preparation and electrochemical performance of manganese-based oxide self-supporting electrodes for supercapacitor applications are conducted.The main research contents of this thesis are as follows:?1?Preparation of porous?-MnO₂ with a hierarchical interconnected nanosheet structure on graphite paper?GP?and application in aqueous supercapacitors.Using highly conductive GP as substrates,the GP surface is first modified by electrochemical roughness.Then,the electrodeposition method is introduced to prepare porous?-MnO₂with a hierarchical interconnected nanosheet structure on electrochemically roughened graphite paper to form the composite self-composite electrode.It is found that a broad potential of 0–1.4 V?vs Ag/AgCl?can be achieved for the composite self-supporting electrodes in the 5 M NaNO₃ aqueous electrolyte.Meanwhile,a capacitance of⁴07.6F g^–1 at 1 A g^–1 and 90.7%capacitance retention after 5000 cycles at 8 A g^–1 are delivered.For the assembled asymmetric aqueous supercapacitors with the configuration of?-MnO₂//activated carbon,a broad voltage window of 0–2.4 V and E of³8.4 Wh kg^–1 at 599.7 W kg^–1 are achieved.?2?Preparation of NiMn₂O₄ nanoflowers on carbon fiber cloth and application in aqueous supercapacitors.Using hydrophilization-treated highly conductive carbon fiber cloth?CF?as substrates,the CF surface is first coated with Mn?OH?₂ nanosheets by electrodeposition,and then NiMn₂O₄ nanoflower structure is formed by the hydrothermal method.The experimental results show that the electrochemical performance of the NiMn₂O₄/CF composite self-supporting electrode prepared at the hydrothermal temperature of 180?is optimal and a specific capacitance of⁸67.0 F g^–1 is delivered at 1 A g^–1 in the 1 M KOH aqueous electrolyte.When the current density increases from 1 A g^–1 to 10 A g^–1,the capacitance retention is up to⁵5.4%.Finally,the aqueous hybrid supercapacitors of 1.5 V are assembled with the configuration of NiMn₂O₄//activated carbon,and an energy density of 25.6 Wh kg^–1 is obtained at 375.6W kg^–1.