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June 16, 2022

Alkaline Battery Chemistry FAQ

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Alkaline Cells

Anode: Zinc powder

Cathode: Manganese dioxide (MnO2) powder

Electrolyte: Potassium hydroxide (KOH)

Applications: Radios, toys, photo-flash applications, watches, high-drain applications

Alkaline cells use the same manganese dioxide and zinc electrodes as the carbon-zinc, with a different electrolyte and construction. This cell design gets its name from its use of alkaline aqueous solutions as electrolytes. Alkaline battery chemistry was first introduced in the early ’60s. The alkaline cell has grown in popularity, becoming the zinc-carbon cell's greatest competitor. Alkaline cells have many acknowledged advantages over zinc-carbon, including a higher energy density, longer shelf life, superior leakage resistance, better performance in both continuous and intermittent duty cycles, and lower internal resistance, which allows it to operate at high discharge rates over a wider temperature range.

Zinc in a powdered form increases the surface area of the anode, allowing more particle interaction. This lowers the internal resistance and increases the power density. The cathode, MnO2, is synthetically produced because of its superiority to naturally occurring MnO2. This increases the energy density. Just as in the zinc carbon cell, graphite is added to the cathode to increase conductivity. The electrolyte, KOH, allows high ionic conductivity. Zinc oxide is often added to slow down corrosion of the zinc anode. A cellulose derivative is thrown in as well as a gelling agent. These materials make the alkaline cell more expensive than the zinc-carbon, but its improved performance makes it more cost effective, especially in high drain situations where the alkaline cell's energy density is much higher.

The half-reactions are:

Zn + 2 OH- —> ZnO + H2O + 2 e-

2 MnO2 + H2O + 2 e- —>Mn2O3 + 2 OH-

The overall reaction is:

Zn + 2MnO2 —> ZnO + Mn2O3 E=1.5 V

There are other cell designs that fit into the alkaline cell category, including the mercury oxide, silver oxide, and zinc air cells. Mercury and silver give even higher energy densities, but cost a lot more and are being phased out through government regulations because of their high toxicity as heavy metals. The mercury oxide, silver oxide, and zinc air (which is being developed for electronic vehicles) are all discussed below.

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