Study On The Supercapacitive Properties Of MnO₂/C Materials In Molten Nitrates

With the development of economy, energy and environmental problems become the pressing problems to be solved. Today,more and more new energies entered into our lives,if the transfer and utilization can be implemented between new energy and electric energy, the application scope of new energy can be enlarged. Supercapacitor is a new element between the conventional capacitor and the secondary battery, which becomes a hot research because of the advantages such as high conductivity,rapid charge-discharge,good cycle stability,etc.Today supercapacitor draws more attention among the researchers, and has more and more utilization direction. Supercapacitor has a widely applications in the aerospace, military,industrial, defense aspects. This article focused on the study of the electrode material, molten nitrate was choosed as the electrolyte originated from the advantages of low melting point,low toxicity, little corrosion and cheap price, etc.In this thesis, SEM has been used to analyse the morphologies of samples prepared by us,and XRD was used to analyse the composition, cyclic voltammetry, constant current charge-discharge method and AC impedance method were used to study the electrochemical properties of the electrode materials.1. The electrochemical properties of activated carbon electrode on different collectors and different nitrate electrolytes were studied, and then the most suitable collector and the electrolyte with best performance were selected. The results illustrated that: at 150°C, for the activated carbon electrode, the electrochemical stability was best when using nickel foam as collector, and the best ratio of nitrate was NaNO₃-LiNO₃-KNO₃ （17:30:53 wt.%）. Within the potential range of -0.8～0.6 V, the specific capacity was 183 F/g at 2 mV/s, and at 8 mA/cm² the discharge capacity was 242 F/g.2. MnO₂ was prepared by hydrothermal method, the results shown that: the optimal condition was the reaction temperature of 140℃, the reaction time of 6 h, the specific capacity of MnO₂ was maximized. Within the potential range of -0.2～0.8 V, at 15 mA/cm² the discharge capacity was 365 F/g at 150℃. In the cycle performance test, the specific capacity only decayed 8.9% when cycled 500 times, which means that it has a good cycling stability.Then composite material of MnO₂ and activated carbon was prepared, when the mass ratio [C:MnO₂] was 1:4, the electrode has the maximum specific capacity, and the performance was the best. It was showed that the performance was improved through compositing the materials.3. MnO₂ and activated carbon electrode materials were studied, and made the MnO₂/AC,[MnO₂/AC]/AC,MnO₂/MnO₂ and AC/AC supercapacitors. The results showed that the potential can reach to 1.4 V. By the electrochemical test, which showed that: at 150℃, in the cyclic voltammetry test, the specific capacity were 43 F/g, 48 F/g, 76 F/g and 41 F/g at 2 mV/s, respectively. The leakage current were 0.005 A, 0.002 A, 0.003 A and 0.003 A,respectively. These types of capacitor all have good electrochemical performance.