Preparation Of Manganese Dioxide And Investigation On The Performance Of Supercapacitor

Supercapacitors are new energy storage components between batteries and electrostatic capacitors, because of their excellent properties, such as higher power density compared with rechargeable batteries, larger specific capacitor compared with conventional capacitors, and broad operating temperature range and long cycle life, which could meet the high power need of electric vehicles when starting-up or accelerating. They could also be used as electric components, power sources for small apparatus and direct current switches. Supercapacitors have become a hotspot in research because of their wide potential application.In this dissertation we studied several methods for the preparation of MnO₂electrode material for supercapacitor. The performance of MnO₂ electrode andsupercapacitor was investigated using cyclic voltammetric (CV), constant currentcharge/discharge and electrochemical impedance spectrometry (EIS). X-raydiffraction (XRD), scanning electron microscope (SEM) and transmission electronmicroscope (TEM) were used to analyze the structure of MnO₂. MnO₂ electrodematerial was prepared by potentiodynamical deposition. It was found that whenthe electrolyte was 1 mol/L, the scan rate was 50mV/s, and the scan cycles was200 times, the resulting MnO₂ particulates were small nanowires with diameter inthe range of 100～200 nm and length in the order of 0.5～1.0 μm. In 2mol/L(NH4)₂SO₄ electrolyte solution and the potential range of 0.25～0.95V (vs.SCE),the average discharge specific capacitance of MnO₂ electrode was 505.7 F/g at aconstant current of 10mA. The efficiency of charge-discharge of MnO₂ electrodewas improved after 1000 cycles, and the ESR was as low as 0.26Ω. MnO₂ wasprepared by liquid-phase redox method. The influence of reaction temperature,dispersant and other factors were investigated. The electrochemical tests includedthat CV curves presented favorable characteristic of squareness, and the averagedischarge specific capacitance of MnO₂ electrode were 138.7 F/g (composed ofγ-MnO₂ and α-MnO₂) and 81.3 F/g (α-MnO₂) by constant charge/dischargemeasurements, at a constant current of 5mA. Nano-MnO₂ prepared by sol-gelmethod was composed of α-MnO₂ and γ-MnO₂, and the particle size was about 30nm. A supercapacitor was assembled with MnO₂ electrode, carbon electrode andagar film, and the electrolyte was a mixture of equal volume of 1.0 mol/L(NH₄)₂SO₄ and 1.0 mol/L MgSO₄ solution. In a potential range of 0～1.4V, and the...