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
Nominal cell voltage	1.55V

A silver-oxide battery (IEC code: S) is a primary cell with a very high energy-to-weight ratio. They maintain a nearly constant nominal voltage during discharge until fully depleted. 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 (64 out of 212 million in February 2020).

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):

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

Mercury content

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

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

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

External links

• SR (Silver Oxide Battery) from Maxell