View source for Silver oxide battery

{{Short description|Battery using silver oxide as the cathode material}}
{{More citations needed|date=May 2008}}
{{for|the rechargeable cell based on silver(I,III) oxide and zinc|Silver zinc battery}}
{{Infobox battery
| image   = Silver oxide batteries.jpg
| caption = Silver oxide cells
| EtoW    = 130 Wh/kg<ref name="duracell">{{cite web|url=http://www.duracell.com/Procell/chemistries/silver.asp|title=ProCell Silver Oxide battery chemistry|publisher=[[Duracell]]|access-date=2009-04-21|archive-url=https://web.archive.org/web/20091220201115/http://www.duracell.com/procell/chemistries/silver.asp|archive-date=2009-12-20}}</ref>
| EtoS    = 500 Wh/L<ref name="duracell" />
| EtoCP   = Low
| PtoW    = High
| CtoDE   = N/A
| TD      = High
| CD      = N/A
| NomV    = 1.55V
}}
[[File:Button cells and 9v cells (3).png|thumb|Several sizes of button and coin cells, some of which are silver oxide]]

A '''silver oxide battery''' [[Battery nomenclature#IEC_electrochemical system codes for primary batteries|(IEC code: S)]] is a [[primary cell]] 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.<ref name=":0">{{cite web |title=Silver Oxide Batteries |url=https://www.murata.com/en-eu/products/batteries/micro/sr |website=muRata |access-date=25 November 2020}}</ref> They are available in small sizes as [[button cell]]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 mil. out of 212 million in February 2020).<ref>{{cite web|url=http://www.baj.or.jp/e/statistics/02.php|title=Monthly Battery Sales Statistics|website=Baj.or.jp|publisher=MoETI|date=May 2020|access-date=2020-08-07|archive-date=2010-12-06|archive-url=https://web.archive.org/web/20101206075143/http://www.baj.or.jp/e/statistics/02.php|url-status=dead}}</ref>

== History ==
A silver oxide cell was first constructed by [[Alessandro Volta]] in late 1800.<ref>{{Cite web |title=Zinc/silver oxide batteries |url=https://www.doitpoms.ac.uk/tlplib/batteries/batteries_zn_ag.php |access-date=2024-11-09 |website=www.doitpoms.ac.uk}}</ref> This consisted of a circle of cups of a liquid saline electrolyte, containing alternating zinc and silver strips connected by wire. It is claimed that 20 such cups were sufficient for the [[hydrolysis]] of water.<ref>{{Cite journal |last=R. |first=A. |date=February 1923 |title=Bibliographical History of Electricity and Magnetism, Chronologically Arranged |url=http://dx.doi.org/10.1038/111142a0 |journal=Nature |volume=111 |issue=2779 |pages=142 |doi=10.1038/111142a0 |issn=0028-0836}}</ref>

Large silver oxide batteries were used on early ICBM's and satellites because of their high energy-to-weight ratio. For example the [[Corona (satellite)|Corona reconnaissance satellites]] used them, as did the [[RM-81 Agena|Agena-D rocket upper stage]].<ref>{{cite web |date=June 1966 |title=Feasibility Study, Final Report, Geodetic Orbital Photographic Satellite System, Volume 2 |url=http://www.nro.gov/foia/CAL-Records/Cabinet4/DrawerE/4%20E%200007.pdf |url-status=dead |archive-url=https://web.archive.org/web/20120316120722/http://www.nro.gov/foia/CAL-Records/Cabinet4/DrawerE/4%20E%200007.pdf |archive-date=2012-03-16 |access-date=2011-01-28 |publisher=NRO}}</ref> Later, they were also used in the [[Apollo Lunar Module]] and [[lunar rover]].<ref>{{Cite web |last=Clemens |first=Kevin |date=2019-07-05 |title=The Batteries That Powered the Lunar Module |url=https://www.designnews.com/aerospace/batteries-powered-lunar-module |access-date=2021-02-02 |website=designnews.com |language=en}}</ref><ref name="Lyons1988">Lyons, Pete; "10 Best Ahead-of-Their-Time Machines", ''Car and Driver'', Jan. 1988, p.78</ref>

== Specifications ==

* Cell voltage<ref name=":0" />
** Open circuit voltage = 1.6 V
** Working voltage = 1.2~1.5 V
* Energy density = 130 Wh/kg (60 Wh/lb)<ref name=":0" />
* Service life of several thousand hours (continuous operation)<ref name=":1">{{Cite web |title=Zinc/silver oxide batteries |url=https://www.doitpoms.ac.uk/tlplib/batteries/batteries_zn_ag.php |access-date=2024-11-09 |website=www.doitpoms.ac.uk}}</ref>
* Shelf stable over several years (retaining 90% of initial capacity)<ref>{{Cite web |title=Silver Oxide Batteries (SR)/Alkaline Button Batteries (LR) {{!}} Primary Batteries {{!}} Biz.maxell - Maxell |url=https://biz.maxell.com/en/primary_batteries/sr_coin.html |access-date=2024-11-09 |website=biz.maxell |language=en}}</ref>

Silver oxide cells are a primary battery and do not have a cycle life or a rate of charging and discharging.<ref name=":0" />

Typical silver oxide cells are stable at temperatures below 100°C, at which point leakage can occur.<ref name=":2">{{Cite web |title=Seiko Instruments Inc. Micro Energy Division |url=https://www.sii.co.jp/en/me/battery/support/caution3/ |access-date=2024-11-09 |website=Seiko Instruments Inc. Micro Energy Division |language=en-US}}</ref>

==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 positive plate:
: <chem>Ag2O + H2O + 2e- ->  2Ag + 2OH-</chem>, <math>(E^\circ = +0.34\text{ V})</math>

The [[half-cell reaction]] at the negative plate:
: <chem>{Zn} + 2OH^- -> \overset{Zinc~hydroxide}{Zn(OH)2} + 2e-</chem>,  <math>(E^\circ = -1.22\text{ V})</math> 

Overall reaction:  
: <chem>Zn + H2O + Ag2O -> Zn(OH)2 + 2Ag</chem>, <math> (E^\circ = +1.56\text{ V})</math>

Overall reaction (anhydrous form):
: <chem>{Zn} + Ag2O ->[\ce{KOH/NaOH}] \overset{Zinc~oxide}{ZnO} + 2Ag</chem>

== Construction ==
[[File:LR44 button cell cross section.jpg|thumb|Cross-section of a similarly constructed button cell]]
In order to reduce the cost of manufacture, most commercially available silver oxide cells take the form of [[Button cell|button cells]] with relatively low silver content. These button cells generally follow the same compact design. The bottom portion of the cell is the [[cathode]], which consists of a graphite infused silver oxide. A plastic membrane separates this from an [[anode]] of powdered zinc dissolved in an alkaline electrolyte. An insulating gasket keeps the two contacts apart, facilitating the discharge of the cell.<ref name=":1" />

==Mercury content==
[[File:Miyota caliber 6S21 quartz chronograph movement.jpg|thumb|Silver oxide battery used to power a quartz watch movement; battery is marked as containing no mercury]]
Until 2004, all silver oxide batteries contained up to 0.2% [[Mercury (element)|mercury]], incorporated into the zinc anode to inhibit corrosion from the alkaline environment.<ref>[http://www.azom.com/details.asp?ArticleID=2651 World’s First Environmentally Friendly Mercury Free Silver Oxide Battery]. September 29, 2004.</ref> This corrosion would occur regardless of whether or not the battery was providing power, making shelf life an important consideration with silver oxide batteries. [[Sony]] started producing the first mercury-free silver oxide batteries in 2004. Regulation in the [[European Union]] now dictates that all batteries be virtually mercury-free.<ref>{{Cite web |title=Batteries |url=https://www.zeromercury.org/about-mercury/mercury-in-products/batteries/#:~:text=The%20Minamata%20Convention%20on%20Mercury,with%20a%20mercury%20content%20%3C%202%25 |access-date=2024-11-09 |website=Zero Mercury |language=en-US}}</ref>

Other safety concerns with silver oxide cells stem from their small size, which often leads to accidental swallowing and poisoning, especially by young children.<ref name=":2" />

==See also==
* [[Battery nomenclature]]
* [[Battery recycling]]
* [[Comparison of battery types]]
* [[Fuel cell]]
* [[History of the battery]]
* [[List of battery sizes]]
* [[List of battery types]]

==References==
{{Reflist}}

==External links==
{{Commons category|Silver oxide batteries}}
* [https://biz.maxell.com/en/primary_batteries/sr_coin.html SR (Silver Oxide Battery)] from Maxell

{{Galvanic cells}}

[[Category:Disposable batteries]]