Energy Storage Mechanism Of Manganese Dioxide Electrode Material And Its Application In Micro Supercapacitor

MnO₂ is a common metal oxide.As the electrode material of supercapacitor,Mn O₂has the advantages of wide voltage window,low price and easy access.However,due to the low electronic conductivity and poor cycle stability,the further development of materials is seriously limited.In this paper,Mn O₂ with different morphologies are prepared by a simple and efficient method as the electrode material of supercapacitor,and the energy storage mechanism of Mn O₂ in the process of electrochemical reaction is studied.At the same time,it is applied to micro-supercapacitor to further improve its practicability.Crystalline/amorphous ultra-thin MnO₂ nanosheets with ultra-high specific surface area were synthesized by a mild liquid phase reaction.The existence of ultrahigh specific surface area(317.56 m²g^-1)and amorphous state can provide more electrochemical active sites at the electrode reaction interface.In addition,the ultrathin nanosheet structure can effectively improve the reaction kinetics and realize rapid ion/electron transport.Through the spectroscopic characterization of Mn O₂ nanosheets electrode before and after cycling,it found that the electrode material changes from crystalline phase to amorphous phase in the process of charge and discharge.At the same time,because the two-dimensional structure of the material has excellent flexibility,ultrathin Mn O₂ nanosheets are used as electrode materials,sodium alginate hydrogel as solid electrolyte,and flexible micro-supercapacitors prepared by mask-assisted filtration method.The working voltage reached 1.4 V,showing high area capacitance and energy density.In addition,the device is no obvious capacity attenuation at different bending angles,showing great flexibility.In order to explore the energy storage mechanism of manganese dioxide in alkaline electrolyte,Mn O₂ nanospheres are synthesized by liquid-liquid interface redox reaction.Moreover,the Mn O₂@r GO core-shell structure is designed by electrostatic self-assembly to improve conductivity and cycle stability.According to ex-situ XRD,Raman characterization and first principle analysis,it is found that during the first cycle,with the insertion of K⁺ionsδ-Mn O₂,the bond length of Mn-O bond in Mn O₆ structural unit gradually becomes longer and losses oxygen.Resulting in a large number of oxygen vacancies promotes the phase transition from layered Mn O₂ to spinel-Mn₃O₄.In the subsequent cycle process,Mn₃O₄ can be further oxidized toλ-Mn O₂ with three-dimensional tunnel structure,and finally realized the reversible de-intercalation process of K⁺inλ-Mn O₂.The all-solid-state micro-supercapacitors were prepared via simple mask assisted filtration,and displays excellent electrochemical properties.The energy density and power density are 1.01μWh cm^-2 and 0.12 m W cm^-2,respectively.Moreover,there is no obvious capacity attenuation after 8700 cycles.