Zinc Air Batteries

Zinc air batteries are a type of metal-air batteries. These are of two types: The primary cell types, an example of which is the button cell, and the secondary (rechargeable) type. These batteries have high energy densities and are relatively inexpensive to produce in the non-rechargeable form. Sizes can range from very small button cells used in hearing aids to very huge batteries suitable for electric vehicles.

Operation

The principle of operation is best understood by referring to the discharge first. The anode is of porous zinc metal which is saturated with an alkaline electrolyte, normally potassium hydroxide. At the cathode, oxygen from the air (so presence of air and entry into the battery is essential) reacts with the electrolyte to give hydroxyl ions which diffuse into the anode and form a zincate releasing water. Electrons released in this reaction travel to the cathode. To learn more about how it works read here

Voltage

A theoretical open circuit voltage of 1.65 V is indicated but in practice it is around 1.35 V. Load voltage can be as low as 1.2 V

Recharge

Since zinc is being consumed and oxygen is obtained from the air, rechargeable operation is possible by physically replacing the zinc electrodes.

Applications

The smaller button cells (non-rechargeable) are used in devices like watches, calculators, and hearing aids.
Larger cells are used in remote location operation of warning lights, etc.
Zinc Air battery is being investigated as an electric vehicle battery and as large-scale energy storage.

Shortcomings

This battery is sensitive to humidity and temperature extremes.
Carbon dioxide present in the air forms a carbonate which can reduce conductivity.
The zinc air battery suffers from high self-discharge.
Battery life is short as the chemical tends to dry out.
Recharging is feasible only at large scales.
Internal resistance is high which means limited current for given size.

Advantage

Low cost.