Preparation, Modification And Electrochemical Performance Of Manganese Dioxide

Manganese dioxide, the most abundant and nontoxic cathode material, has been widely applied in battery industry. The quality of MnO2 plays a key role in the performance of the Zinc-Manganese batteries. So the improvement on the electrochemical performance of MnO2 is very necessary.MnO2with ultrafme powder displays better electrochemical performance due to its larger specific surface area. In the third chapter, micro-particulate MnO2 was synthesized by reducing KMnO4 with H2O2, and then calcined at various temperatures. The effects of heat treatment on the physical properties and the electrochemical performance of the MnO2 samples were investigated in detail. The experiment results showed that calcination treatment had remarkable effects on the crystal structure and electrochemical performance of the samples. The sample treated at 200 ℃ displayed the best electrochemical performance among all the samples, and its specific discharge capacity is 28.6% higher than that of commercial MnO2 at 250mA g~-1.In the forth chapter, MnO2 was coated with Ca(OH)2 or Sr(OH)2 by a liquid-phase surface treatment method. The SEM photographs of the samples showed that the morphologies of the MnO2 samples were obviously altered by surface treatment. The electrochemical experiments indicated that the surface modification decreased the polarization of MnO2 electrodes, increased the discharge potential, the discharge capacity and cycle stability, which is probably due to the increase of the diffusion coefficient of protons after surface modification.In the fifth chapter, the effects of various additives including Bi, Bi2O3 and Ca(OH)2 on the electrochemical performance of MnO2 were investigated. The results of electrochemical tests showed that the additives of Bi and Bi2O3 increased remarkably the discharge capacity and the cycle stability of MnO2, and the discharge capacity increased with the increase of Bi and Bi2O3 contents. It was also found that the addition of Ca(OH)2 improved the discharge potential, whilethe addition of Bi and Bi2C>3 decreased the discharge potential, and the joint addition of Bi and Ca(0H)2 not only improved the discharge potentials of MnC>2 but also increased its discharge capacity.