Magnesium Battery | Chemistry Construction of Magnesium Battery

This article covers a legacy, non-rechargeable battery that uses magnesium and manganese dioxide (Mg/MnO₂). Magnesium is a light, relatively low-cost anode material with a more negative electrode potential than zinc. Historical Mg/MnO₂ designs could provide about twice the capacity of a same-size zinc/manganese dioxide cell and retain useful capacity after high-temperature storage. Magnesium batteries of this type gained shelf life from a passive surface film on the magnesium anode.
Discharge disrupts that film and can increase corrosion. As a result, partially discharged Magnesium batteries store less reliably and are poor choices for long-term intermittent duty.

Chemistry of Magnesium Battery

In this primary-cell chemistry, a magnesium alloy forms the negative anode and manganese dioxide is the positive cathode active material. Acetylene black improves conductivity in the cathode mix. Historical formulations used aqueous magnesium perchlorate electrolyte, barium chromate and lithium chromate as corrosion inhibitors, and magnesium hydroxide as a pH buffer. These chromate-containing formulations describe older cell designs, not a current construction recommendation.

At the magnesium anode, oxidation releases electrons as shown by the following half-reaction.


At the manganese dioxide cathode, reduction consumes electrons as shown by the next half-reaction.

The overall discharge reaction is shown below.


A conventional cell has an open-circuit voltage near 2 V, below its theoretical potential of about 2.8 V because of passivation and reaction losses.
In aqueous electrolyte, the magnesium surface can develop a thin Mg(OH)₂ film. An intact film slows corrosion during storage but also resists current when discharge begins.

This magnesium hydroxide film passivates the magnesium. Historical chromate treatments strengthened corrosion control, but the passive layer also causes a temporary voltage delay while the cell activates. Once discharge damages the film, magnesium corrosion can produce hydrogen gas.


These linked discharge and corrosion processes describe the basic chemistry of magnesium battery.

Construction of Magnesium Battery

A conventional cylindrical Mg/MnO2 dry cell resembles a zinc-carbon cell. Its magnesium-alloy can contains small amounts of aluminium and zinc and serves as the negative electrode. The cathode mix contains manganese dioxide and acetylene black for conductivity and moisture retention. Historical mixes also used barium chromate as an inhibitor and magnesium hydroxide as a pH buffer. An aqueous magnesium perchlorate solution with lithium chromate served as electrolyte, a carbon rod collected current from the cathode and electrolyte-wet kraft paper separated the electrodes. The seal had to retain water while safely relieving hydrogen generated during discharge. One legacy design placed a small vent beneath a retainer ring so internal pressure could open a gas path.

The magnesium can formed the outer negative electrode in the standard design. An alternative construction of magnesium battery used a conductive carbon cup as the outer positive current collector and a magnesium cylinder as the inner negative electrode. Paper separators isolated the magnesium from cathode mix on both sides. The mix contained manganese dioxide, carbon black and an aqueous magnesium bromide or magnesium perchlorate electrolyte. The carbon cup connected to the positive terminal, the magnesium drum connected to the negative terminal and a crimped tin-plated steel jacket enclosed the assembly. These details document historical cells; they are not instructions for building or modifying a battery.

Advantage of Magnesium Battery

1. A historical battery design could offer shelf life of up to five years at 20^oC, subject to its construction and storage conditions.
2. Some same-size designs provided about twice the capacity of a Leclanche zinc-carbon cell.
3. Cell voltage was higher than that of a comparable zinc-carbon cell.
4. Magnesium and manganese dioxide supported moderate material cost for specialised primary cells.

Disadvantages of Magnesium Battery

1. The passive anode film can cause voltage delay when discharge starts.
2. Corrosion after activation can evolve hydrogen during discharge.
3. Discharge and corrosion can generate heat.
4. Partial discharge reduces storage performance and increases corrosion risk.

This page describes historical Mg/MnO2 dry-cell technology. Commercial availability and specifications can change, so product selection must use current manufacturer data.

Historical Sizes and Types of Mg/MnO₂ Batteries