pH-Controlled Electrolysis of Electrolytic Manganese Dioxide (EMD) for Improved Cycle Life of Rechargeable MnO2/Zn Batteries

A systematic study of the effect of acid concentration (0.5–5 M H2SO4) on the electrolysis of electrolytic manganese dioxide (EMD or γ-MnO2) has been performed. All the samples were characterized for their phase and crystallinity, their structural water, the pyrolusitic-to-ramsdellite ratio, BET surface area, pore size range; and were examined for their electrochemical performance. Concentration of the electrolysis acid affects the structural water content and the pyrolusitic-to-ramsdellite ratio of the γ-MnO2 phase as well as the surface area and pore size. The best cycling performance was achieved for the samples prepared with an electrolysis bath containing an acid concentration of about 2 M H2SO4. Electrochemical performance over 100 cycles of the EMD prepared in 2 M H2SO4 has shown higher energy efficiency and improved longer term cycling performance compared to commercial EMD products. Post-mortem analysis of the cycled EMD samples show partial loss of the EMD phase, loss of water content, and growth of irreversible manganese dioxide phases.