CA1128121A

CA1128121A - Cadium compound additive for cells using divalent silver oxide

Info

Publication number: CA1128121A
Application number: CA322,622A
Authority: CA
Inventors: Robert F. Scarr
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1978-03-30
Filing date: 1979-02-28
Publication date: 1982-07-20
Also published as: CH633913A5; DE2912496A1; NL7902460A; DK129279A; GB2019078B; BE875189A; AU531064B2; AU4557979A; DE2912496C2; JPS54132733A; GB2019078A; FR2421475A1; HK37783A; FR2421475B1

Abstract

CADMIUM COMPOUND ADDITIVE FOR
CELLS USING DIVALENT SILVER
OXIDE ELECTRODES

ABSTRACT OF THE INVENTION

An alkaline silver oxide cell having a negative electrode, an alkaline electrolyte and a positive electrode comprising a major amount of divalent silver oxide and wherein a minor amount of a cadmium compound, such as cadmium oxide, is incorporated into the electrolyte and/or positive electrode to improve the chemical stability of the divalent silver oxide in contact with the alkaline electrolyte.

S P E C I F I C A T I O N

1.

Description

~ Z ~ ~ 2 ~

FIELD OF THE II~VENTION

Th~ invention relates to a silver oxide alkaline cell employing a divalent silver oxide containing positive el.Qctrode and wherein a minor amount of a cadmiu~ compound, such as cadmium oxide, is incorporated into the positive electrode and/or the electrolyte so as to improve the chemical stability of the divalent silver oxide in contact with the alkaline electrolyteO In addition, the cadmium compound can be employed as an overbalance depolarizer in a divalent silver oxide/zinc/alkaline cell so as to substantially prèvent hydrogen gassing from the cathode upon complete discharge of the cell.

BACKGROUND OF THE _~VENTION

The battery has become ,a primary power source for many portable electronic devices such as radios, hearing aids, watches, calculators and the like. In order to maintain the overall &lectronic device as compact as possible the electronic devices are usually designed with caviti~s to accom~odateminiature cells as their source of powerO The cavities are usually made so that a cell can be snugly positioned therein thus making electronic contact with appropriate terminals within the device. A major potential problem in the use of a high energy density cell such as a divalent silver oxide/æinc/alkaline cell, is that if the cell bulges, it usually becomes wedged within the cavity of the device which sometimes can result in da~age to the device. In addition, when the cell bul~es it may disturb the seal whereupon the electrolyte might escape to cause damage to the device and/or oxygen from the atmosphere may enter which could cause wasteful corrosion of the anode.

2~ 11426 ~n the other hand, if the seal of the cell is maintain2d, high internal gas pressure may develop which could cause no~ only bulging of the cell but even possible disassembly of ~he cell.
Although divalent silver oxide is a good high capacity pos-itive active material when used in alkaline cells, it is rather unstable when in con~act with an aqueous al'~aline e lec-trolyte~ Specifically, diYalent silver oxide is a highly oxi-dizing material and as such it is capable of decompoqing the water in an aqueous alkaline electrolyte thereby yielding oxy-gen gas. ~n addition, divalent silver oxide will liberate oxy-gen when it tecomposes to ~orm monovalent silver oxide when in con~act with the aqueous alkaline electrolyte. Divalent silver oxide can also attack cellulosic materials in the cell, such as the separator, to form carbonate ion at the expense of even more electrolyte.. These are undesirable processes because they lead to bulging of the cell, deterioration of its parts and loss of service.
U. S. Patent 3,853,623 discloses one approach to stabilize divalent silver oxide in a silver oxide/zinc/ alkaline cell through ~he use of gold ions incorporated into the alkaline elec roly~e on the positive side of the cell's separator or gold oxide added t~ the positive active material of ~he cell.
Filed co~currently herewith by applicant is Canadian application Serial No.
_3519 which discloses an alkaline ~ilver oxide cell employing a divalent sil~er oxide-containing elec~rode wherein an alum-inum additive is incorporated in the cell to improve ~he chemical s~ability o the divalent silver oxide when in contact .~ ~

~28~2~ 11426 with the cell's alkaline electrolyte.
It is an object of the present invention to provide a divalent silver oxide cell that will minimize internal gas pressure ~uildup so as to effectively eliminate distortion of the cell's housing.
It is another object of the present inven~ion to provide a divalent silver oxide cell wherein a cadmium compound, such as cadmium oxide, is incorporated into the cell's elec~rolyte and/or the positive electrode so as to effectively control gas pressure buildup within the cell and t~ereby effectively eliminate distortion of the cell's housing.
I~ is another object of the present invention to incorporate a cadmium compound, such as cadmium oxide.in a divalent silver oxide cell to chemically stabilize ~he divalent silver oxide when in contact with the cell's aqueou~ electrolyte.
It is another ob;ect of the present invention to incorporate a cadmium compound, such as cadmium oxide, in a divalent silver oxide/zinc cell as an overbalance depolarizer to effectively prevent hydrogen gassing from the cathode upon complete discharge of the cell.
The foregoing and additional objects will become more fully apparent ~rom the following description.

SUk~RY OF THE I~VENTION

The invention relates to a silver oxide cell having a negative electrode, an aqueous alkaline electrolyte, a positive electrode comprising a major portion of divalent ~ ~ 2 ~ ~ 2 ~

silver oxide and a separa~or between said negative and positive electrodes~the im~rovement comprising the incorporation of a minor amount of a cadmium compound, such as cadmium oxide, into the positive electrode and/or into the electrolyte of the cell to improve the stability of the divalent silver oxide-containing electrode in contact wi~h the aqueous alkaline electrolyte.
As used herein, a positive electrode or a sil~er electrode shall mean an electrode wherein the active cathode material is divalent silver oxide (AgO) ox an elec~rode wherein the major active m~terial is divalent silver oxide in conjunction with an amount below 50% by weight of monovalent silver oxide CAg2O) and/or some other electro-chemically active positive material.
The cadmium compound, such as cadmium oxide, may be added in the solid positive electrode and/or dissolved in the elec~rolyte. The cadmium compound added to the positive electrode may be either admixed with the divalent silver oxide ~r incorporated within the diva~ent silver oxide crystallites themselves through coprecipitation or absorption during synthesisO Admixture of the cadmium compound and divalen~ silver oxide material has the ad~antage of greater flexibility in the choice of the divalent silver ~xide material with regard to particle size, purity and the like.
The minor amount of the cadmium compound additive for use in the positive electrode of this invention to improve the stability of the divalent silver oxide when 2 ~

` in con~act with ~he cell's aqueous alkaline electroly~e should be between about 0.01 and about 5 per cent based on the dry weight of the divalent silver oxide in the positive electrode and preferably between about 0.1 and about 0.3 weight per cent based on the dry weight of the divalent silver oxide in the positive elec~rode. An amount of the cadmium compound less than, for example, about O.Olweight per cènt9 would not provide sufficient material ~o effectively improve the stability of the divalent silver oxide material when in contact with the aqueous alkaline elec~rolyte. An amount of the cadmium compound more than, for example, about 5 weight per cen~ added to the positive electrode would not further improve the stability of the divalent silver oxide when in contact with the aqueous alkaline electrolyte.
The cadmium compound to be added to the electrolyte in accordance with this invention should be added in an amount between about 0.0001 per cent and up to saturation of the cadmium compound in the electrolyte. For example, when using a 33 per cent potassium hydroxide solution, the upper limit would be about 0.00125 per cent based on the weight of the electrolyte. An amount of the cadmium oxide less than, for example, about 0.0001 per cent would not provide sufficient material to effectively improve the stabili~y of the divalent ~ilver oxide material when in contact wi~h the aqueous alkaline electrolyte.
In addition to its use as a stabilizing agent, cadmium oxide may also be used in larger amounts ranging ~2~

from about 5 per cent ~o about 25 per cent by weight of the dry constituents of the posi~ive electrode, as an overbalance depolarizer in a divalent silver oxide cell. An overbalance depolarizer is that part of the posieive electrode in excess of the stoichiometric amount needed to balance the nega~ive electrode. Its purpose is to augment the positive electrode capacity sufficiently to prevent hydrogen gassing from the ca~hode upon complete discharge of the cell (anode-limited).
Like divalent silver oxide, a cadmium compound, such as ,10 ` cadmium oxide, has limited solubility in alkaline environments, discharges a~ a potential positive to hydrogen, and its volumetric energy density is suffic:iently high so as not to impair the over-all energy density of the silver oxide/anode ~ystem. As an overbalance substitute for divalent silver oxide, its advantages are that it is far less costly and impar~ chemical stabili~y to the divalent silver oxide material when in contact with aqueous alkaline electrolyteO
It is also within the scope o this invention to additionally add zinc oxide or aluminate ions to the elec-trolyte 9 andlor zinc oxide or aluminum oxide to the positiveelectrode. The zinc oxide and aluminate ions can be added to the electrolyte in a range between about 0.5 and about 5 per cent based on the weight of the electrolyte. When incorporated in ehe positive electrode, the zinc oxide and aluminum oxide can be added in an amount between about Q.5 and ~bout 5 and about 0.001 and about 0.1 weight per cent 7 respectively, based on the dry weight of the divalent silver 2 ~

oxide in the positive electrode. Zinc oxide has been found to be more desirable than aluminum oxide. Unexpectedly, the combination of cadmium oxide in the positive electrode and zinc oxide or aluminate ions in the electrolyte produced a synergistic effect on the stability of divalen~ silver oxide in contact with the aqueous alkaline electrolyte.
It is also within the scope of this invention to additionally add a minor amount of a stabilizer, a flow agent and/or a lubricating agent to the active positive mix to further alter the physical charac~eristics of the active po~itive mix for molding purposes to produce ~arious size and type electrodes. Examples of some of these additives are ethylene bis-stearamide, zinc stearate, lead stearate, calcium stearate and the like.
The silver oxide electrodes of this invention may be employed in an aqueous cell system using an anode such as zinc, cadmium, indium or the like, The electrode couple so selected can be employed with a compatible electrolyte and preferably an alkaline electrolyte. Examples of suitable electrolytes include aqueous solutions of alkaline earth metal hydroxides, such as strontium hydroxide and alkali metal hydroxides, exemplified by sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide and cesium hydroxide. Com~atible mixtures of the preceding may be utilized. Preferably, the electrode of this in~ention should be porous so that the walls o the pores and inter~tices of the electrode can become wetted by the electrolyte.

8.

EXAMPLE I
Several lots of test cells were produced each using a divalent silver oxide-containing positive pellet having a density of 90 grams per cubic inch, a negative electrode of zinc, and a 33% KOH electrolyte. The positive electrode was positioned in a cathode collector cup with a zinc screen disposed between the inner surface of the GUp and the positive pellet as disclosed in U. S. Patent No.

3,920,478. Next a dual separator consisting of a cellulosic barrier film and an absorbent layer~ having a gold layer on that site ad;acent the cathode, was disposed on top of the positive pellet followed by the zinc electrode. An anode cup containing the zinc electrode was then placed over the cathode cup and sealed thereto in a conventional manner.
The exact constituents of the positive electrode and any additives to the electrolyte are shown in Table 1.
The cells were stored for three months under various temperature conditions. Thereafter ~he eells were measured fvr any bulging and the results obtained for each test lot were averaged and are shown in Table 2 along with the maximum cell bulge observed in each lot. In addition, the service life to a 1.3 volt cutoff was observed and is also shown in Table 2.

11~26 o o o o o o o _ ~

? O ¢ o ~ O o k~ ¢ ~ , , , , , , , ~ z I C~ Z I ~ I N

~ U~
.~ o C'J _ _ _ . = = _ 00 _~ o _~ _ s ~ - - 3 - - -~ , ~ , ~ o ,,,, .~
? _I o ~ o ~ o ~1 ~1 o ,, E~~C ~ I "~; ~ I ~ -I I ' ' ' o _~ O O U O
¢ , ~ , - 3 - ' u O o a~ o ~D r o ~ o ~ a~
. . . . . . , . o ~ a~
o o - - ~ ~o C~ - - - -~ co r~

10 ~

o o o o o o o, ~ ~ U~

- S~ ~ o~ oc~ o C~ ~ C:
¢ ;~l æ

~:
o ~

~::: :::-::::
o ~a ~ v ~ ~: ,~: - : : ~: : I
o o ~ C~
~I
o: ~ : o ~
E~ ~ ~ ~ O o o o ~.~ .
~ ~~ ~
~ : ~ : : : : ~ - :: : ~
<~ C~
.
. o C5~: 00: - ~0: c~ _ _ : : O~ .,~
bO ~1 ~
¢ ~ ¢
. ~ . ~C~g ~
S~ rl C
~ V 3 oo C~ V
u~ U~
bD ~ - ¢ ~ C~
¢ oo o ~ CS~
o~ ~ ~ h ~ ~X
11 ~8~ ~~

o h ~ O
~Z
O ~ o -~ ~ ,Q ¢ O ~a q~ ~
s~
h O ~ C~

U~U~ o U~ o o o U~ ~ o U~ o U~ o o ~ ~ c~ ~~ i~ `D O ~ ~
~ o~ ~ o ,~

X o ~ o ~ U~ o o U~ ~ O ~Lr~ O O O o o t~
U~~,1 ~ ,~ ~ ~ C~ ~ ~~ C~l ~ C`l ~q o C _I . ~ ~~D O ~0 ~D 00 1~ ~ ~ ~O r~ ~o ~ ~ ~ dl c~ ~ . ~ . . . . . . . . . o . .
¢ ~ O ~1 0 0 ~1 ~ ~ O ~ ~1 0 c~

al . x O O ~ O u~ O o u~ o ~ c~ ~ o o U~ O O Ln O
¢ ~1 E~ ~ ~ ~ ~1 0 0 0 0 ~ ~ O ~ ~ ~ O

~ o o o o o o o o o o o o o o -~ o~ o~ o~ -' I I I

x u~o ~ u~u~ o ~ o o o u~ o y~ 3 o o o o ~ .. . ~. . . . . . . o o o ~ .
~ o o o o o o o o ~ o o ~l o ~
~D ~ OO ~ O ~c~ O~ ~ ~ --I ~ ~ d' `
l ~

,~
~ ~ Q~
~ 3: c~ ~ ~D
C~
3:

X o u~ o o L~ In O U~ O ~L~
~ ~ C'~
~ 00 ,~ o r~ ~ ~ O U~
3 ~ ~ ~, o ~ o a~

X Lr~ o U~ o U~ U~ o U~ U~ o o o U~ ~
:~ ~ C~ ~ o ~ o ~1 ~ ~ 'D O ~ o C~
.. ~ ¢ o ,~ ,~ o ,~ o ,~ ~ ~ ~ o o U~

O O
c~ ~a ~
~3 o o ~! ~ x u~ o ,~ o ul o o ~ o u~ ?
0~ ~ o o' ~ o ,~
L~ ~ _I o ~1 c~ O ~` C`~ Cd h ¢ o o ~1 o O O o o O o 0, 0 ~ 0`0 o ,~
. ~ ~ ~
o u~ u~7 0 u~ oO In In C~ U~ O ~
O O O ~i 0 0 'I -I ~ o bO
.~0 ~ ~ ~ O ~ O ~ O C`l ~ c~
~ 3 o o o o ~ o o o o o o o o ~
. ~ ~ , o~
b~

~Z ~ sU ~ ~
a~ O o ~ ~ ~ ~ ~ ~ ~ oo ~ o -- ~ I

~ 2~L

The results of the data shown in Table 2 illustrate that using the teachings of this invention9 a cadmium compound additive with or without zinc oxide and aluminum additives can be effecl:ively used to stabilize divalent ~ilver oxide when in contact with an aqueous alkaline electrolyte so as to reduce cell bulging. As also illustrated, the combination of a cadmium com-pound ;n the positive electrode and zinc oxide or al~minate ions in the electrolyte produced a synergistic effect on the stability of divalent silver oxide in contact with aqueous alkaline electrolyte.
That i~, the addition of both a cadmium compound in the po~itive electrode and zinc oxide or aluminate ions to the electrolyte reduced bulge more than the composite of either material acting alone. This i9 shown Eor example by comparing te~t Lot 23 with Lots 16, 17, and 19 for Z~10 addition to the electrolyte, and by comparillg Lot 22 with Lots 16, 18, and 19 for aluminate addition to the electrolyte.

EXAMPLE XI
Several test lots of cells were produced as de~cribed in Example I except that the cathode and electrolyte compositions employed are as shown in Table 3. The result~ of the data shown in Table 3 zo illu~trate the benefits as expressed above in Example I in that the cadmium co~npound additive reduces cell bulging. Both Example I
and Example II show that the addition of the cadmium compound by admixture gives slightly better bulge control than by coprecipitation.

14.

7~. o o u~ o u~ o 11426 x~ L2 ~L
O ~L ~ o u~
?
_l ~ oo o ,r, 7*~
~ ~ o u~ o o o a~
_I bC I~ o~
~4 *

* u~
~1 ~
~1 ~1 O
~I
**xl ~1 ~ ~ ~ ~ ~ ~ ~ ~
d E
~ ~ 5~ ~ ~
a) '~.c ~ ~ o ,E o ~ ~1 ? ¦ ~1 0 e~l ~ O O C~ ri C
~3 5'' ~ '~ C~
D u~

o ~¦ ~
r~ Z r~ P~Z; ~,~ r,.n 1~ ~ è~ E
~:3 ¢
,.C ~ ~ X-, m u ~ o ~
L, ,~ O ~ f~ C
O ~ ¢ ~ ~ ~ ~ ~ ~ ~0 O O O O
,~ h O ~ ~ ~
CO ~ -é U
~ h ~ td r3 Q) " cd ~ O ~a 11 ? ~ 13 0 ~i O O ~ td ra ~ ~ 11 11 ~ cd t~
r~ ~! ~ ~ ~7 ~ ~ O ~ J~ 13 ? ~
~d <1 ~~
-1 0 ~ ~ ~ ~*
lC C *
~Z
~q d~ O ,~
E~ ~

15,

Claims

WHAT IS CLAIMED IS:

1. A silver oxide cell having a negative electrode, an aqueous alkaline electrolyte, a positive electrode com-prising a major portion of divalent silver oxide and a separator between said negative electrode and positive electrode, the improvement comprising the addition of cadmium oxide into the positive electrode to improve the stability of the divalent silver oxide-containing electrode in contact with the aqueous alkaline electrolyte, said cadmium oxide being present in the positive electrode in an amount between about 0.01 and 0.5 weight per cent based on the dry weight of the divalent silver oxide in the positive electrode.

2. The silver oxide cell of claim 1 wherein the cadmium oxide is present in an amount between about 0.1 and about 0.3 weight per cent based on the dry weight of the divalent silver oxide in the positive electrode.

3. The silver oxide cell of claim 1 wherein the positive electrode contains less than 50 per cent by weight of monovalent silver oxide based on the dry weight of the divalent silver oxide in the positive electrode.

4. The silver oxide cell of claim 3 wherein the cadmium oxide is present in the positive electrode in an amount between about 0.01 and about 0.3 weight per cent based on the dry weight of the divalent silver oxide in the positive electrode.

5. The silver oxide cell of claim 4 wherein the cadmium oxide is present in an amount between about 0.1 and about 0.3 weight per cent based on the dry weight of the divalent silver oxide in the positive electrode.

16.

6. The silver oxide cell of claim 1 wherein the positive electrode contains a minor amount of zinc oxide or aluminum oxide.

7. The silver oxide cell of claim 1 wherein the aqueous alkaline electrolyte contains a minor amount of zinc oxide or aluminate ions.

8. The silver oxide cell of claim 1 wherein the positive electrode contains a minor amount of a material selected from the group consisting of ethylene bis-stearamide, zinc stearate, lead stearate and calcium stearate.

9. The silver oxide cell of claim 1 wherein the negative electrode is selected from the group consisting of zinc, cadmium and indium.

10. The silver oxide cell of claim 1 wherein the negative electrode is zinc.

11. The silver oxide cell of claim 1 wherein the negative electrode is zinc and the electrolyte comprises aqueous potassium hydroxide.

12. The silver oxide cell of claim 1 wherein the negative electrode is zinc and the electrolyte comprises aqueous sodium hydroxide.

17.