Note: Descriptions are shown in the official language in which they were submitted.
3~ ~ 121~5
FIELD OF THE INVENTION
-The invention relates to a silver oxide
alkaline cell employing a divalent silver oxide-con-
~aining positive electrode and wherein a minor amount
of an aluminum additive is inco~orated into the posi-
tive electrode and/or the electrolyte so as to improve
~he chemical stab~lity of the divalent silver ox~de in
contact with alkaline electrolyte.
BACXGROUND OF THE INYE~T~ON
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 electronic device as
compact as possible the electronic devices are usually
designed with cavities to accommodate miniature cells
as their source of power. The cavieies are usually made
so that a cell can be snugly positioned therein thus
making electronic contact with appropriate terminals
within the de~ice. A maior potential probl~m in the
use of a high energy density cell such as a divalent
silver oxide/zinc/alkaline cell, is that if the cell
bulges, it usually becomes wedged within the cavity of
the device whi.ch sometimes can result in damage to the
device. In addi~ion, when the cell bulges it may
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disturl) ;:he seal whereupon the electrolyte might escape
to cause damage to the device and'or oxygen from the
at~mosphere may enter which could ceuse wasteful
corrosion of the anode. On the other hand, if the seal of
the cell ~s maintained, high internal gas pressure may
develop which could cause not only bulging of the cell
but even possible disassembly of the cell.
Although divalent silver oxide is a good high
capacity positive active material when used in alkal~ne
cells, it is rather unstable when in contact with an
aqueous alkaline electrolyte. Specifically, divalent
silver oxide is a highly oxidizing material and as
such it is capable of decomposing the water in an
aqueous alkaline electrolyte. Divalent silver oxide
can also attack cellulosic materials ~n ehe cell, such
as the separator, to form carbona~e ~on at the expense
- of even more electrolyte. These are undesirable proces-
ses because they lead to bulging of the cell, de~eriora-
tion of its parts, and loss of service.
U.S. Patent 3,853,623 discloses one approach to
stabilizing divalent silver oxide in a silver oxide/-
zinc/alkaline cell through the use of gold ions incor-
porated into the alkaline electrolyte on the positive
side of the cell's separator or gold oxide added to the
positive active material of the cell.
Canadian application Serial Number
~ 335 ~ 12145
322,622 by applicant relates to a divalent
silver oxide cell in which a minor amount of a ca~mium
compound is incorpora~ed in the cell's alkaline electro-
lyte and/or positive elPctrode to improve the chemical
stability of the divalent silver oxide in contact with
the alkaline electrolyt~. Also clisclosed is the ad-
dition of an aluminum additive to the cell in con-
unction with the cadmium c~mpoulld for chemical
stabilization of divalent silver oxide in alkaline
mediums.
It is an object of the present invention to
provide a divalent silver oxide cell that will mini-
mize internal gas pressure buildup so as to effectively
eliminate distortion of the cell's housing.
I~ is another object of the present invention
to provide a divalent silver oxide cell wherein an alum-
inum additive is incorporated into the cell's electrolyte
and/or the positive electrode so as to effectively
control gas pressure buildup within the cell and
thereby effectively eliminate distortion of the cell's
housing.
It is another object of the present invention
to incorporate an aluminum additive in a divalent silver
oxide cell to chemically stabilize the divalent silver
oxide when in contact with the cell's aqueous alkaline
electrolyte.
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The foregoing and additional objects will
become more fully apparent fr~m the follow~ng descip-
tion. -
- SUMMARY OF THE INVENTION
The invention relates to a silver oxide cell
having a negative electrode, an aqueous alkaline elec-
trolyte, a positive electrode co¢prising a m~jor portion
of divalent silver oxide and a separaeor between said
negative and positive electrodes, the improvement
~mprising the incorporation of a minor amount of an
aluminum additive into the positive electrode and/or
into the electrolyte of the cell to improve the stabil-
ity of the divalent silver oxide-containing electrode in
contact with the aqueous alkaline electrolyte.
As used herein, a positive electrode or a silver
oxide electrode shall mean an electrode wherein the
active cathode material is divalent silver oxide (AgO)
or an electrode wherein ~he major active material is
divalent silver oxide in conjunct~on with an smount
below 50% by we~ght of monovalent silver oxide (Ag~O)
and/or some oth~er electrochemically active positive
material.
The aluminum additive may be added in the solid
posi~ive electrode and/or dissolved in the electrolyte.
The aluminum adlditive, such as aluminum oxide, incDr-
porated in the positive electrode may be either admixed
~ ~3~ ~ 12145
with the divalent silver oxide or incorporated withîn
the divalent silver oxide crystallites th~mselves
through coprecipitation or absorption during synthesis.
Admixture of the aluminum additive and divalent silver
oxide material has the advantage oi- greater flexibiltty
in the choice of the divalent silver ox de material with
regard to particle size, purity and the like.
The minor amount of the aluminum additive,
such as aluminum oxide, for use in the positive electrode
lb of this invention to improve the stability of the diva~ent
silver oxide when in contac~ with the cell's aqueous
alkaline electrolyte should be between about 0 OOl and about 5 per
ce~t based on the dry weight of the divalent silver
oxide in the positive electrode and preferably between
about 0.005 and about 0.05 weight per cent based on ~he
dry weight of the divalent silver oxide in the positive
electrode. An amount of the aluminum additive less
than, for example, about O.OOlweight per cent, would not
provide sufficient material to effectively improve the
stability of the divalent silver oxide material when in
contact with the aqueous alkaline electrolyte. An
amount of the aluminum additive more tha~, ~or example,
about 5 weight per cent added to the positive elec-
trode would not further improve the stability of the
divalent silver oxide when in contact with the aqueous
alkaline electrolyte and would replace too mNch of the high
capaclty silver oxide material.
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The aluminum additive, such as aluminate ion~, in
accordancs with this invention ~hould be added in an amount between
about 0. Ol and about lO per cent based on the weight of the aqueous
alkaline electrolyte, preferably between about 0. 5 and about 2. 0 per
cent based on the weight of the electrolyte, An amount of the aluminum
additive less then, for example, about 0. 01 pe~ cent would not provide
- sufficie~t material to effectively improve the ~tability of the divalent
~ilver oxide material when in contact with the aqueous al~aline
electrolyte. An amount of the aluminum additive more than, for
example 10 per cent would not be soluble in the aqueous alkaline
slectrolyte.
Electrolytes containing the aluminum additive can be
prepared either by saturation of the electrolyte with Al203, or by
dissolution of sodium or potassium aluminate.
It i9 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 character-
istics of the active positive mix for molding purposes to produce various
Qize 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,
cadmiumt indiu~n or the like. The electrode
.. : .~, . : -
~ ~3~ 12145
couple so selected can be employed with a compatible
electrolyte and preferably an alkaline electrolyte.
Examples of suitable electrolytes include aqueous sol-
utions of alkaline earth metal hydroxides, such as
stron~ium hydroxide and alkali metal hydroxides, exempli-
fied by sodium hydroxide, potassium hydroxide, lithi~m
hydroxide, rubidium hydroxide and cesium hydroxide.
Compatible mixtures of the preceding may be
utilized. Preferably, the electrode of this invention
should be porous so that the walls of the pores and
interstices of the electrode can become wetted by the electrolyte
EXAMPLE I
Several lots of test cells were produced each
using a divalent silver oxide-containing positive pellet
having a density o~ 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 lnner surface of ~he
cup and the positive pellet as disclosed in U.S. Patent
3,920,478.
Next a dual separator consisting of a cellulosic
barrier film and an absorbent layer was disposed on top
of the positive pellet containing divalent silver oxide, An
anode cup containing the zinc electrode was then placed
over the cathode cup and seal thereto in a conventlonal
manner. ~
~ 3~'7~ 12145
The exact constituents of the positive electrode
and any additives to the electrolyte are shown in
Table 1.
The cells were stored :Eor three months under
various temperature conditions. Thereafter the cells
were meaured for any bùlging 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 cu~off was
observed for most cells and is also shown in Table 2.
~L~IL3~5'7~
12145
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S78 12145
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~3~
12145
The results of the data shown in Table 2
illustrate~ ~hat using the teaching of this invention
an aluminum additive cian be added to a divalent silver
oxide cell to improve the chemical stability of the di-
~alent silver oxide when it contacts the cell's alkaline
electrolyte.
Numerous variations and modificat~ons of the
invention herein described can be made without departing
from the ~pirit iqnd scope thereof, and, accordingly, ~he
sime is not limited to lts specific embodiments disclosed
herein except as in the appended claims.
12.
