Defining high power EMD through porosimetry

High power electrolytic manganese dioxide (HPEMD), offers distinct performance advantages in alkaline-MnO2 cells compared to the best conventional alkaline EMD materials previously available. Advantages are seen mainly on heavy continuous and heavy pulse drains. No comprehensive model to explain the chemical and structural basis for the improved performance of HPEMD has yet emerged. Hydrothermal electrolytic plating of EMD at 120–125 °C has given rise to several exceptional materials including two samples with excellent high power discharge performance. A systematic study of physico-chemical properties of all of the hydrothermally produced materials as well as commercial EMD samples, including HPEMD, has shown that superior high power performance is linked to porosimetry. By employing the needed plating conditions, one can produce a superior HPEMD material having BET area in the range 20–31 m2 g−1 and simultaneously a micropore area (deBoer “t” method) greater than 8.0 m2 g−1, all within the context of a typical pore volume of 0.035–0.050 cm3 g−1 and a calculated meso–macropore radius greater than 32 Å (cylindrical pore model). A qualitative model explaining the need for a balance between BET area and micropore area is proposed. A possible explanation regarding the physico-chemical nature of the micropores and their relation to cation vacancies, as supported by stepped potential electrochemical spectroscopy (SPECS) investigations of heat treated EMDs, is given.