Silver-oxide battery


A silver-oxide battery is a primary cell with a very high energy-to-weight ratio. They are available in small sizes as button cells, where the amount of silver used is minimal and not a significant contributor to the product cost.
Silver-oxide primary batteries account for 30% of all primary battery sales in Japan.

Chemistry

A silver-oxide battery uses silver oxide as the positive electrode, zinc as the negative electrode, plus an alkaline electrolyte, usually sodium hydroxide or potassium hydroxide. The silver is reduced at the cathode from Ag to Ag, and the zinc is oxidized from Zn to Zn.
The half-cell reaction at the negative plate:
The reaction in the electrolyte:
The half-cell reaction at the positive plate:
Overall reaction:
Overall reaction :

Characteristics

Silver-oxide batteries have a nominal voltage of 1.55V. Compared to other batteries they have a higher open-circuit voltage than a mercury battery, and a flatter discharge curve than a standard alkaline battery.

Mercury content

Silver-oxide batteries become hazardous on the onset of leakage; this generally takes 5 years from the time they are put into use. Until recently, all silver-oxide batteries contained up to 0.2% mercury. The mercury was incorporated into the zinc anode to inhibit corrosion in the alkaline environment. Sony started producing the first silver-oxide batteries without added mercury in 2004.