Silver oxide battery

Japanese: 酸化銀電池 - さんかぎんでんち（英語表記）silver oxide battery

This button-type alkaline primary battery uses monovalent silver oxide _Ag2O powder with a conductive agent added as the positive electrode active material, zinc powder mixed with a gelling agent as the negative electrode active material, and a highly concentrated 20-45% aqueous solution of potassium hydroxide KOH or sodium hydroxide NaOH with added zinc oxide ZnO as the electrolyte. It was developed in the United States in the 1960s. Using KOH as the electrolyte provides good high-rate discharge characteristics and low-temperature discharge characteristics. Using NaOH reduces these characteristics slightly, but improves leakage resistance. The electromotive reaction is (positive electrode)
Ag ₂ O＋H ₂ O＋2e ^- -→2Ag＋2OH ^-
(Negative electrode)
Zn＋2OH ^- -→Zn(OH) ₂ +2e ^-
(whole)
Ag ₂ O＋Zn＋H ₂ O―→2Ag＋Zn(OH) ₂
The electromotive force is 1.594 volts and the battery voltage is 1.55 volts. Conductive metallic silver is deposited during discharge, resulting in little polarization and good utilization of the active material. In addition, the energy density is high at 85-95Wh/kg, and the operating temperature range is wide, from -30°C to 60°C. The discharge voltage is extremely flat, except in the case of large current discharge.

When divalent silver oxide (AgO) is used as the positive electrode active material, the discharge capacity per unit weight can be increased because the oxidation number is 2. However, in the positive electrode, 2AgO＋H ₂ O＋2e ^- ―→Ag ₂ O＋2OH ^-
The reaction proceeds, and the reaction of the whole battery is 2AgO＋Zn＋H ₂ O―→Ag ₂ O＋Zn(OH) ₂
The reaction proceeds. Therefore, after the discharge voltage of about 1.8 volts, which is the battery voltage equivalent to 1.856 volts of this electromotive force, a discharge voltage of 1.55 volts is obtained due to Ag ₂ O generated by the discharge of AgO. However, this two-stage discharge characteristic is not desirable in practice, and since AgO is unstable in alkaline electrolyte, there are problems with the storage life. Therefore, if the surface of the AgO particles is covered with Ag ₂ O, the Ag generated by the discharge of the Ag ₂ O on the surface reacts with the AgO inside to generate Ag ₂ O, and the discharge capacity can be increased accordingly. Furthermore, since the discharge voltage is only due to Ag ₂ O, it is a single stage of 1.55 volts instead of two stages, and a high energy density can be achieved. In addition, the zinc of the negative electrode active material is alloyed with other metals or an organic corrosion inhibitor is added to increase the hydrogen overvoltage, making it less likely to self-discharge.

Silver oxide button batteries are used in electronic watches, cameras, calculators, electronic toys, and electronic thermometers, but because silver is expensive, their market share is gradually being taken over by alkaline button batteries and button lithium batteries.

Silver-zinc oxide batteries can also be used as storage batteries, but because they are expensive and have a short charge-discharge cycle life, they are limited to use as a power source for special applications such as space development, marine development, and military use, where their characteristics of high output and high energy density can be utilized, and production volumes are low.

[Mitsuru Asano]

"Electrochemistry" edited by Zenpachi Ogumi (2000, Ohmsha)" ▽ "Electrochemical Society, ed., "Electrochemistry Handbook" (2000, Maruzen)" ▽ "Battery Handbook" edited by the Battery Handbook Editorial Committee (2001, Maruzen)"

[Reference] | Primary battery | Storage battery | Batteries | Lithium batteries

Silver oxide battery structure
©Shogakukan ">

Silver oxide battery structure

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

正極活物質には1価の酸化銀Ag₂O粉末に導電剤を加えたもの、負極活物質には亜鉛粉末にゲル化剤を混合したものを用い、電解液には酸化亜鉛ZnOを添加した20～45％の高濃度の水酸化カリウムKOHあるいは水酸化ナトリウムNaOH水溶液を用いたボタン形アルカリ一次電池。1960年代にアメリカで開発された。電解液にKOHを用いると高率放電特性や低温放電特性がよい。NaOHを用いるとそれらの特性はすこし劣るが耐漏液性を向上することができる。起電反応は
　（正極）
　　Ag₂O＋H₂O＋2e^-―→2Ag＋2OH^-
　（負極）
　　Zn＋2OH^-―→Zn(OH)₂＋2e^-
　（全体）
　　Ag₂O＋Zn＋H₂O―→2Ag＋Zn(OH)₂
であって、起電力は1.594ボルト、電池電圧は1.55ボルトである。放電により導電性の金属銀が析出するので分極は少なく、活物質の利用率はよい。またエネルギー密度が85～95Wh/kgと高く、使用温度範囲がマイナス30℃～60℃と広い。放電電圧は大電流放電の場合を除き、きわめて平坦(へいたん)である。

　2価の酸化銀AgOを正極活物質に用いると、酸化数が2であるので単位重量当りの放電容量を増すことができる。しかし正極では
　　2AgO＋H₂O＋2e^-―→Ag₂O＋2OH^-
の反応が進行し、電池全体として
　　2AgO＋Zn＋H₂O―→Ag₂O＋Zn(OH)₂
の反応が進む。このため、この起電力の1.856ボルトに相当する電池電圧である約1.8ボルトの放電電圧に続き、AgOの放電により生成したAg₂Oによる1.55ボルトの放電電圧が得られることになる。しかしこの2段階の放電特性は実用上好ましくなく、またAgOはアルカリ性電解液中で不安定であるので、保存寿命に課題が生じる。そのためAgO粒子の表面をAg₂Oで被覆すると、表面のAg₂Oの放電により生成したAgが内部のAgOと反応してAg₂Oが生成することになり、その分だけ放電容量を高めることができる。さらに放電電圧はAg₂Oのみによるため2段階でなく1.55ボルトの1段階となり、高エネルギー密度化を実現できる。なお、負極活物質の亜鉛はほかの金属と合金化したり、また有機防食剤を添加して水素過電圧を高め、自己放電がおきにくくされている。