Silver oxide battery

For the rechargeable cell based on silver(I,III) oxide and zinc, see Silver zinc battery.

Silver oxide battery

Silver oxide cells
Specific energy	130 Wh/kg
Energy density	500 Wh/L
Specific power	High
Charge/discharge efficiency	N/A
Energy/consumer-price	Low
Time durability	High
Cycle durability	N/A

A silver-oxide battery (IEC code: S) 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 over 20% of all primary battery sales in Japan (67,000 out of 232,000 in September 2012).

Chemistry

A silver-oxide battery uses silver(I) oxide as the positive electrode (cathode), zinc as the negative electrode (anode), plus an alkaline electrolyte, usually sodium hydroxide (NaOH) or potassium hydroxide (KOH). The silver is reduced at the cathode from Ag(I) to Ag, and the zinc is oxidized from Zn to Zn(II).

The half-cell reaction at the negative plate:

${\ce {Ag2O + 2H+ + 2e- -> 2Ag (v) + H2O}}$, $(E^{\circ }=+1.17{\text{ V}})$

The reaction in the electrolyte:

${\ce {2H2O -> 2H+ + 2OH-}}$, $(E^{\circ }=-0.83{\text{ V}})$

The half-cell reaction at the positive plate:

${\ce {{Zn}+2OH^{-}->{\overset {Zinc~hydroxide}{Zn(OH)2}}+2e-}}$, $(E^{\circ }=+1.22{\text{ V}})$

Overall reaction:

${\ce {Zn + H2O + Ag2O -> Zn(OH)2 + 2Ag(v)}}$, $(E^{\circ }=+1.56{\text{ V}})$

Overall reaction (anhydrous form):

${\ce {Zn + Ag2O ->[{\ce {KOH/NaOH}}] ZnO + 2Ag (v)}}$

Characteristics

Compared to other batteries, a silver-oxide battery has a higher open-circuit voltage than a mercury battery, and a flatter discharge curve than a standard alkaline battery.

Mercury content

Several sizes of button and coin cells, some of which are silver-oxide

Silver-oxide batteries become hazardous on the onset of leakage; this generally takes 5 years from the time they are put into use (which coincides with their normal shelf life). 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.

See also

• History of the battery
• Fuel cell
• Battery recycling
• List of battery types
• List of battery sizes
• Comparison of battery types
• Battery nomenclature