Manganese Dioxide — Magnesium Perchlorate Batteries

Abstract

The magnesium dry cell consists of a magnesium anode, a manganese dioxide-carbon cathode and an electrolyte — usually magnesium perchlorate or magnesium bromide. The basic cell reaction is $$Mg + 2Mn{O_2} + {H_2}O \to Mg{\left( {OH} \right)_2} + M{n_2}{O_3}$$ A kraft paper separator keeps the anode and cathode apart but permits ionic conduction. The magnesium anode is made up of AZ21 A alloy. The construction of the cell is similar to that of the conventional cylindrical dry cell, with the magnesium anode also serving as the cell container. The cross-section of such a cell is shown in figure 6.1. Present cells have a mechanical seal with a vent for permitting the escape of hydrogen gas formed by the following parasite reaction $$Mg + 2{H_2}O \to Mg{\left( {OH} \right)_2} + {H_2}$$ The magnesium cell has an open-circuit voltage of around 2.0 V as compared to 1.5 V for the zinc dry cell.