The Effect of Varying the Ionic Conductivity, Discharge Rate, Electrode Composition and Thickness on Alkaline MnO2 Cathode

Zinc-manganese dioxide (Zn-MnO₂) batteries have a long shelf life, have a high energy density and are inexpensive compared to other rechargeable batteries. Yet a rechargeable Zn-MnO₂ battery does not exist which is able to recharge more than five hundred times because MnO₂ is not rechargeable after its first electron reaction. This research was focused on understanding the discharge behavior of MnO₂ electrode in a Zn-MnO₂ battery under various conditions. Hence, the effect of ionic conductivity, discharge rates, electrode composition, MnO₂ material supplier and electrode thickness on the accessible discharge capacity is studied and analyzed. The MnO₂ electrode was discharged to its 1-electron reaction (i.e. 100% depth of discharge, DOD). A galvanostatic technique is used to discharge the MnO₂ electrodes in classical three electrode half-cell experiments. In these experiments, the ionic conductivity, controlled by the electrolyte concentration (potassium hydroxide, KOH), was varied by varying the electrolyte concentration from 0wt% to 45wt% KOH.  The effect of discharged rates (C-rates) was studied from 1C to C/20 rate in 30 wt% KOH electrolyte. As MnO₂ is not conductive, graphite was added to improve the electronic conductivity. The effect of graphite content was studied on the discharge behavior. This research was able to find the best electrolyte concentration, electrode composition and studied the effect of C-rates on the discharge capacity.