Prepration Of Manganses Dioxide And Investigation On The Performance Of Supercapacitor

In the past yeas, the supercapacitors characterized by high power and long-life have attracted global attentions.However, the energy density of supercapacitors is still much less than that of recharge batteries. Thus, many researches on the supercapacitors aim to increase energy density of supercapacitors. According to the equation E=1/2CV², two effective approaches can be used to improve the energy density of supercapacitors. One is to develop hybrid system with higher work voltage(V), the other is to develop nano-structure electrode with high capacitance(C).Electrochemical supercapacitors based on manganese dioxide as active electrode materials are currently attracting a lot of interest due to the relatively low cost of raw materials and the fact that it makes use of environmentally friendly aqueous electrolytes. In the current work we explore in more detail the effects of the multilayer microstructure on MONS/MWCNT film conductivity and overall electrochemical capacitance. The dual role of each monolayer including the effect to the structure of multilayer thin film material and the electrochemical properties were investigated, especially for the crucial effects of MWCNTs. And we introduce a simple, one-pot synthesis route to prepare Na_0.55Mn₂O₄·1.5H₂O and Mn₃O₄ composite with controllable phase compositions, nanostructures and morphologies. An asymmetric electrochemical capacitor was successfully assembled. The main contens as follows:1. Multilayer self-sustained films of MWCNT and MONS are assembled on ITO glass substrates by the layer-by-layer assembly technique. The presence of MWCNT monolayer that was introduced into the multilayer films by layer-by-layer method were to give controllable self-sustain structure and increased electrical conductivity of the electrode, which subsequently resulted in the formation of a self-sustained structure on the inner surface of the MONS film and a significant improvement of the electron injection efficiency. This enabled a higher penetration depth of the electric field into the nanoporous layer compared to MONS films, improving the adsorption/desorption process of cations at the material surface and an insertion/extraction process of cations into the inner parts of the films. Electrochemical measurements of these electrodes indicated an excellent capacitive behavior. The specific capacitance and energy density increased by increasing the number of the MWCNT layer, which also leads to higher power density. These results indicate that the MWCNT self-sustained structure had a profound influence on the electrochemical performance of the capacitors.2. We introduce a simple, one-pot synthesis route to prepare Na_0.55Mn₂O₄·1.5H₂O and Mn₃O₄ composite (labeled Na_0.55Mn₂O₄·1.5H₂O/Mn₃O₄) with controllable phase compositions, nanostructures and morphologies. The specific capacitance of the composite electrode at a current of 0.2 mA is 150 F/g. The cycle life analyses shows that this material can be charged/discharged through a wide potential window (1.2 V) at least thousands of times without any significant fade in capacity, and it remains almost constant during the cycling life. The activated carbon electrode was prepared using an activated carbon sample prepared from the ZnCl2 activation of waste tea leaves at 700°C. The specific capacitance of the AC electrode material was 80 F/g.3. An asymmetric electrochemical capacitor with Na_0.55Mn₂O₄·1.5H₂O/Mn₃O₄ as anode and AC as cathode, and Na2SO4 aqueous solution as electrolyte was successfully assembled. This asymmetric electrochemical capacitor delivers an excellent cycling behavior with energy density of 30 Wh/kg at 300 W/kg. This asymmetric aqueous AC//Na_0.55Mn₂O₄·1.5H₂O/Mn₃O₄ capacitor is a promising candidate for the power sources of electric vehicles and other large power devices owning to its low price, excellent rate behavior and easy preparation of the composite material. Furthermore, the combination of Na_0.55Mn₂O₄·1.5H₂O/Mn₃O₄ and AC within aqueous electrolyte proves a long cycle life of Na-ion intercalation compounds as the battery electrode material, which may provide a new study field for Na-ion insertion/extraction compound in aqueous solution.