The Preparation Of MnO₂and The Study On Its Application Of Supercapacitors

Supercapacitor as one kind of the potential energy storage device has beenwidely used in aerospace, national defense, military, portable verbal system,electrical vehicles and so on, which comprises several key parts including thecollector, the polarized electrode. Among them, the polarized electrode has asignificant inpact on the electrochemical performance of supercapacitor.Currently, a variety of materials have been used for preparation of the polarizedelectrode such as carbon materials, metal oxide and conducting polymers. Ofthese electrode materials, Environmentally Friendly transition metal oxides aregenerally considered as a candidate of a supercapacitor electrode materialsbecause of their higher theory specific capacitance than carbon materials. Inparticular, manganese dioxide with high abundance in nature and otheroutstanding features used for supercapacitors are of great interests in thedevelopment of good electrochemical performance of electrode materials.In this work, manganese dioxide (MnO2) was successfully synthesized bychemical liquid coprecipitation method with the additive ofpolyvinylpyrrolidone. Experimental results indicates that addingpolyvinylpyrrolidone leads small crystalline and the high specific surface area,and hence the the good performance of the composite materials are anticipated. The morphology and structures of the MnO2were also characterized by X-raydiffraction (XRD) spectrometry and scanning electron microscopy (SEM).Electrochemical performance was investigated as well via cyclic voltammetry(CV)、electrochemical impedance spectroscopy (ESI) and chronopotentiometry(CP).Initailly，the resultant MnO2materials were treated under the differentreaction temperatures ranging from at250℃,350℃,400℃for3h.Among the reaction temperatures examined here, the best capacitiveperformance could be obtained at350℃, indicative of that the reactiontemperature has important effect on their electrochemical behaviors. This couldbe rationized by the morphology and structure of the MnO2characterized byX-ray diffraction (XRD) spectrometry and scanning electron microscopy (SEM)at350℃, which displays the smallest granularity of MnO2with the shape offloccules with the highest fracture area. With optimized condition of reactiontemperature in hand, we next to explore the electrochemical performance ofprepared material in30%wt KOH alkaline electrolyte and neutral(1mol/LNa2SO4). The experimental results shows that the specific capacitancewas437F/g in the30wt%KOH electrolyte when the current density was0.5A/gand voltage ranges from-0.5～0.3V. It is noted that the energy lost only by20%after1000cycles in KOH electrolyte. In addition, experimental findings revealsthat the synthesized MnO2exhibits the good specific capacitance and internalresistance for supercapacitor in KOH electrolyte; wheareas the corresponding that in Na2SO4electrolyte gave excellent ratio characteristics but the lowspecific capacitance.