A silver-oxide battery (IEC code: S) is a

primary cell A primary battery or primary cell is a battery (a galvanic cell) that is designed to be used once and discarded, and not recharged with electricity and reused like a secondary cell (rechargeable battery). In general, the electrochemical reaction ...

using silver oxide as the cathode material and zinc for the anode. These cells maintain a nearly constant nominal voltage during discharge until fully depleted. They are available in small sizes as

button cell A button cell, watch battery, or coin battery is a small single-cell battery shaped as a squat cylinder typically in diameter and high — resembling a button. Stainless steel usually forms the bottom body and positive terminal of the cell; insu ...

s, where the amount of silver used is minimal and not a prohibitively expensive contributor to the overall product cost. Silver-oxide primary batteries account for 30% of all primary battery sales in Japan (64 out of 212 million in February 2020). Silver-oxide batteries were used on Apollo program lunar missions for the

lunar module The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed ...

and

lunar rover A lunar rover or Moon rover is a space exploration vehicle designed to move across the surface of the Moon. The Apollo Program's Lunar Roving Vehicle was driven on the Moon by members of three American crews, Apollo 15, 16, and 17. Other rov ...

power supplies because of their high energy-to-weight ratio.Lyons, Pete; "10 Best Ahead-of-Their-Time Machines", ''Car and Driver'', Jan. 1988, p.78

Chemistry

A silver-oxide battery uses

silver(I) oxide Silver oxide is the chemical compound with the formula Ag2O. It is a fine black or dark brown powder that is used to prepare other silver compounds. Preparation Silver oxide can be prepared by combining aqueous solutions of silver nitrate and a ...

as the positive

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

(

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

as the negative electrode (

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...

), plus an

alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...

electrolyte, usually

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...

(NaOH) or

potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...

(KOH). The

silver Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...

is reduced at the cathode from Ag(I) to Ag, and the

is oxidized from Zn to Zn(II). The

half-cell reaction A half reaction (or half-cell reaction) is either the oxidation or reduction reaction component of a redox reaction. A half reaction is obtained by considering the change in oxidation states of individual substances involved in the redox reaction. ...

at the positive plate: : Ag2O + 2H+ + 2e- -> 2Ag (v) + H2O,

(E^\circ = +1.17\text)

The reaction in the electrolyte: : 2H2O -> 2H+ + 2OH-,

(E^\circ = -0.83\text)

The

at the negative plate: : + 2OH^- -> \overset + 2e-,

(E^\circ = -1.22\text)

Overall reaction: : Zn + H2O + Ag2O -> Zn(OH)2 + 2Ag(v),

(E^\circ = +1.56\text)

Overall reaction (anhydrous form): : Zn + Ag2O -> ceZnO + 2Ag (v)

Mercury content

Miyota caliber 6S21 quartz chronograph movement

Until recently, all silver-oxide batteries contained up to 0.2%

mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

. The mercury was incorporated into the zinc anode to inhibit its continuous corrosion in the alkaline environment, which would otherwise occur regardless of whether or not the battery was providing power. Sony started producing the first silver-oxide batteries without added mercury in 2004.World’s First Environmentally Friendly Mercury Free Silver Oxide Batter
September 29, 2004.

References

External links

SR (Silver Oxide Battery)
from Maxell {{Galvanic cells Disposable batteries

Chemistry

Mercury content

See also

References

External links