Primary Single Use Battery Chemistry

Alkaline Battery Chemistry

Anode : Zinc powder
Cathode : Manganese dioxide (MnO2) powder
Electrolyte : Potassium hydroxide (KOH)

This cell uses an alkaline aqueous solution for the electrolytes. Alkaline battery chemistry was introduced in the early 1960s. Alkaline cell advantages over zinc-carbon includes :

• 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 high discharge rates.

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

Other alkaline cell designs include mercury oxide, silver oxide, and zinc air cells. Mercury and silver give even higher energy densities, but carry a higher cost. They have or are being phased out by pollution regulations because of their high toxicity and heavy metals.