Note: Descriptions are shown in the official language in which they were submitted.
105~S9 9579-1
BackQround of the Inventlon
Thi8 lnventlon relates to flat alkaline cells
ln goncr~l and more partlcularly to a flat alkallne cell
construction whereln the active elements are encloset
withln a ~ealed, liquld-lmpervious plastic fllm envelope
nd whereln the envelope 1B provlded with both posltlve
nd negstive terminal connections and a thlrd terminal
connection for an auxlliary electrode. In one a~pect
of the inventlon, a flat rech~rgeable cell enclosed withln
a sealed pla~tic fllm envelope and having both positive
and negative terminal connections 18 provided with a
thlrd term~nal connection for an oxygen or hydrogen
~ensIng electrode or a voltsge reference elec~rode.
In our corresponding application now U. S.
Patent 3,871,921, issued M~rch 18, 1975, entitled '~lat
Alkaline Cell Construction And Method For Assembling
me Same," filed April 1, 1974, there is disclosed and
claimed a flat alkaline cell wherein at least a pair
of flat electrode elements of opposite polarity having
a porous separator containing the alkaline electro-
lyte interposed therebetween are arranged in the form
of a conventional electrode stack assembly. This
electrode assembly is enclosed within a sealed, liquid- -
impervious plastic film envelope having a terminal
connection provided in one wall thereof adjacent to one
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105'~859
end of the electrode assembly. The terminal connection is
made using both internal and external current collectors
which are disposed ad3acent to the inner and outer sides
respectively of the wall of the sealed envelope and which
overlie an opening in the wall. The internal current
collector is disposed adjacent to the end of the electrode
assembly and i9 in electrical connection with one of the
electrode elements. A thin layer of an adhesive sealant
is lnterposed between the internal current collector and
the inner surface of the wall of the sealed envelope and
another thin layer of the adhesive sealant is interposed
between the external current collector and the outer
surface of the wall. Both laye~s of adhesive sealant
cover substantially the entire face of both current
collector~, except for a small area coincid~ng with the
opening in the wall. Suitable means are provided for
making electrical connection between the internal and
external current collectors through the opening, such
as a spot weld.
Alkaline electrolytes are notoriously known
for their ability to readily wet most metal and plastic
surfaces and to creep past seals conventionally used in
current-producing electrochemical cells. Our flat cell
construction as described above effectively solves this
problem through the use of an adhesive sealant which is
-3-
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l~S'~859
non-wettable by the alkaline electrolyte. The thin layers
of adhesive sealant u~ed to tightly bond both current
collectors to the plastic film envelope actually re~ist
creepage of the electrolyte past the sealing interfaces
and out through the opening in the wall of the envelope.
Preferably, the adhesive sealant is chosen from the class
of compounds known as "fatty polyamides", although other
adhesive sealants which are not readily wet by the
alkaline electrolyte can also be used.
Still another advantage of our flat cell
construction resides in the provision of an extended
leakage path over which the electrolyte must travel in
order to escape from the cell. This extended leakage
path comprises both of the sealing interfaces between
the internal and external current collectors and the
inner and outer sides of the wall of the sealed envelope
or in other word8, the leakage path traverses approximately
the total width or length of each collector.
In a typical flat cell construction made in
accordance with our above referred to copending applica-
tlon, the 8ealed envelope i8 advantageou81y formed by a
pair of plastic film wall members arranged such that each
wall member overlies an end of the electrode assembly,
both plàstic film wall members being sealed together
along their ~arginal borders such as by a heat seal. A
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lO5Z859
positive terminal connection is provided in one of the
plastic film w811 members ad~acent one end of the electrode
assembly and a negative terminal connection i8 provided
in the other plastic film wall member adjacent to the
other end of the electrode assembly. Both positive and
negative terminal connections are made in the same
manner as described hereinabove using internal and
external current collectors tightly adhered to the
plastic film wall members by a thin layer of the
adhesive sealant. The arrangement of the terminal
connections is such that a plurality of the individual
flat cells may be stacked together with the positive
terminal connection of one cell being in electrical
connection with the negative terminal connection of an
ad~acent cell in the stacked assembly to constitute a
series-connected battery. Flat cells with this arrangement
of the terminal connections can also be assembled into
parallel and series-parallel connected batteries.
It has already been proposed in the prior art
to employ so-called "auxiliary electrodes" in current-
producing electrochemical cells. These auxiliary
electrodes are used in con~unction with the working
electrodes, i.e., positive and negative electrodes, to
perform certain valuable functions in operation of the
cells. Such auxiliary electrodes have been used, for
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~OS%859
instance, in rechargeable cells to detect or sense the
presence of exce8sive a unts of either oxygen or hydrogen
gas that may be generated under certain conditions such
as when the cells are overcharged.
In U. S. Pat. No. 3,462,303 to H. Reber, there
i8 disclosed a sealed rechargeable cell wherein an
auxiliary electrode is maintained in contact with a gas
space and the liquid electrolyte. The auxiliary
electrode will form with the negative electrode of the
cell a voltage differential the value of which will be
dependent on the partial oxygen pressure in the gas
space of the sealed cell. When the cell is subjected
to overcharging, the partial oxygen pressure in the ga3
space will rise, a change in the voltage differential
will occur and this change is utilized for actuating
control devices for terminating the charging current and
thereby prohibiting the build-up of an excessive gas
pressure inside the cell.
Ba8ically the same auxiliary electrode arrange-
ment may be used in a rechargeable cell such as describedabove to sense the pressure of hydrogen gas pres~ure in
the cell. In this instance, the auxiliary electrode which
will form with the positive electrode of the cell a
voltage`differential whose value will be dependent on the
partial hydrogen pressure in the gas space under
9579-1
~OSZ859
conditions where hydrogen gas may be evolved during
, operation of the cell.
Auxiliary electrodes may also be incorporated
in current-producing electrochemical cells as a voltage
reference device. It is possible for instance to
electrochemically couple the positive or negative
electrode of a rechargeable nickel-cadmium cell to an
auxiliary reference electrode and study the discharge
behavior of either electrode independently of the other.
Auxiliary electrodes in these applications are a
valuable tool to the researcher since he can carry out
his ~tudies without having to dismantle the cell
construction.
Provision must of course be made in the
sealed a~sembly of the current-producing electrochemical
cell for making external electrical connection with the
auxiliary electrode. Such means usually comprises a
separate or third terminal connection in the sealed
a~sembly in addition to both the positive and negative
terminal connections. Basically the same type of
construction is used for the third terminal connection
regardless of whether the auxiliary electrode is employed
as an oxygen or hydrogen sensing electrode or voltage
reference electrode.
The principal object of this invention is the
~oS2859
9579-1
provi~ion of a flat alkaline cell contruction of the
character described in U. S. Patent No. 3,871,921
referred to earlier wherein there is provided both posi-
tive and negative terminal connections in the walls of
the plastic film envelope and a third terminal connec-
tion for an auxiliary electrode.
Sum~arY of the Invention
This invention resides in a flat alkaline cell
construction wherein at least a pair of flat electrode
elements of opposite polarity having a porous separator
containing the alkaline electrolyte interposed there-
between are arranged in the form of a conventional
electrode stack assembly. The electrode assembly is
enclosed within a sealed envelope made of a liquid
impervious plastic film and preferably a plastic film
which is electrically non-conductive. The sealed
envelope i8 formed with first and second wall members,
one of which i~ dispo~ed ad~acent to one end of the
electrode assembly and the other of which is disposed
ad~acent to the other end thereof. The first wall member
is provlded with at least one opening and the second wall
member is psovided with at least a pair of openings
which are spaced apart from one another. Firs~ internal
snd external current collectors are disposed adjacent
to the inner and outer sides respectively of the first
-8-
957g-1
~0S'~8 59
wall member overlying the opening, the first internal
current collector being also disposed adjacent to one end
of the electrode assembly and being in electrical
connection with one of the pair of electrode elements.
Second internal and external current collectors are
disposed ad~acent to ~he inner and outer side8 respectively
of the second wall member overlying one of the pair of
openings, the second internal current collector being
also di8po8ed ad3acent to the other end of the
electrode assembly and being in electrical connection
with the other of the pair of electrode elemen~s. Third
internal and external current collectors are disposed
ad~acent to the inner and outer sides respectively of
the second wall member overlying the other opening, the
third internal current collector being also disposed
ad~acent to the other end of the electrode assembly and
being in electrical connection with an auxiliary electrode.
A thin layer of adhe8ive sealant which is non-wettable by
the alkaline electrolyte, preferably a fatty polyamide
8ealant, is interposed between the first internal current
collector and the inner surface of the first wall member,
and another thin layer of the adhesive sealant is
interpo8ed between the first external current collector
and the outer surface of the first wall member. Similarly,
a thin layer of the same adhesive sealant is interposed
betweén the second and third internal current collectors
_g_
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105'~859
and the inner surface of the second wall member and
ahother layer of the same adhesive is lnterposed between
the second and third external current collectors and the
outer surface of the second wall member. All layers of
adhesive ~ealant preferably cover substantially the
entire face of the internal and external current
collectors, except for a small area coinciding with the
openings in the first and second wall members. Suitable
means such as a spot weld are provided for making electrical
connection between the respective pairs of internal and
external current collectars through the openings in the
first and second wall members.
With the flat cell construction of the
invention, the first, second and third terminal connections
are tightly sealed against leakage of the alkaline
electrolyte from inside the cell. The thin layers of
adhesive sealant tightly bond the internal and external
current collectors to the first and second wall members
and seal the interfaces between the current collectors
and both sides of the wall members forming the sealed
envelope. There is also provided in accordance with the
invention an extended leakage path which traverses
approximately the total width or length of each internal
and external current collector.
In the assembly of the flat cell construction
of the invention, the internal electrical connections
-10-
lOS;~8S9 9579-l
between the first and second internal collectors and the
pair of electrode elements of oppo~ite polarity may be
arranged 5uch that the first or second terminal connection
constitutes the positive terminal while the other of the
first or second terminal connection constitutes the
negative terminal of the cell.
In the preferred embodiment of the invention, a
flat alkaline cell is constructed using a sealed envelope
composed of two parts, a plastic film cupped container
in which the electrode assembly is placed and a plastic
film cover, both the cupped container and cover being
sealed tightly together along their marginal borders
such as by a heat seal. Both the cover and the bottom
wall of the cupped container are provided with sealed
terminal connections, i.e., positive and negative
terminal connections, respectively, and a third terminal
connection for the auxiliary electrode is provided in
either the cover or container bottom. All of the
terminal connections are made using both internal and
external current collectors in the same manner as
hereinabove described.
In the assembly of a flat cell in accordance
with the preferred embodiment of the invention, the
cupped container, cover and the collectors are first
assembled as composite units. Both the internal and
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9579-1
~xternal current collector~ for the fir~t, econd and
thlrd ter~in-l connectlon~ are tightly bonded to the $nner
and outer s~des rcspectlvely of the container bottom wall
~nd cover uslng the th$n layers of adhe~lve ~ealant. The
electrode stack assembly 18 placed inslde the ~o-formed
compo~lte cupped container-collector wlth all approprlate
internal electrode connections being made at one end of
the electrode assembly. The composite cover-collector $s
then placed over the open end of the cupped container-
collector with 811 appropriate internal electrode
connections be~ng made at the opposite end of the
electrode assembly. The sealed envelope is then completed
by tightly sealing together the marginal borders of both
the composite container-collector and cover-collector
such ~8 by a heat 8eal. The method of assembling the
flat cell is more fully disclosed in the above referred
to U. S. Patent No. 3,871,921.
Although the invention is widely applicable to
flat alkallne cells in general, it will be more fully
described hereinafter with particular reference to a
rechargeable nickel-cadmium cell. It will be understood,
of course, that the flat alkaline cell con~truc~ion of
the invention may utilize other electrode systems such
a~ the zinc/manganese dioxide system as will be readily
seen to those skllled in the art.
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lOS'~859 9579-l
Brie~ De~criPtion of the DrawinR
Fig. 1 is an elevational view in cross-sec~ion
of a flat alkaline cell construction made in accordance
with the invention;
Fig. 2 is a perspective view of the composite
cupped container-collector used in the flat cell of
Fig. l;
Fig. 3 is a perspective view of the underneath
8ide of the compo~ite cover-collector also used in the
flat cell of FiB. l;
Fig. 4 i8 a cro8s-sectional view of the
compo8ite cover-collector taken along the line 4-4 in
Fig. 3;
Fig. 5 is a view similar to Fig. 1 showing
another embodiment of a flat cell construction made in
accordance with the invention;
Fig. 6 is a perspective view of the composite
cupped container-collector used in the flat cell of
Fig. 5; and
Fig. 7 is a croQs-sectional view of the composite
cupped container-collector taken along the lines 7-7 in
Fig. 6.
De8cription of the Preferred ~mbodiments
Fig. 1 illu~trates a rechargeable flat nickel-
cadmium cell made in accordance with the invention. The
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105~859 9579-1
cell comprises a pair of flat thin positive electrode
plates 10, 11 and 8 pair of flat thin negative electrode
plates 12, 13 having a porous separator 14 containing
the alkaline electrolyte interpo~ed therebetween, the
pairs of positive and negative electrode plates 10-13 and
separator 14 being arranged in the form of a conventional
electrode stack assembly. The pairs of positive and
negative electrode plates 10-13 are arranged in alternate
fashion with the positive electrode plate 10 being
located at one end o~ the electrode assembly, the negative
electrode plate 12 placed between the pair of positive
electrode plates 10, 11 and with the negative electrode
plate 13 being located at the opposite end of the
electrode assembly. The porous separator 14, which is
thoroughly soaked with the alkaline electrolyte, is
sandwiched between and in contact with the pairs of
electrode plates of opposite polarity, that is, between
the positive electrode plate 10 and negative electrode
plate 12, and between the positive electrode plate 11
and each of the negative electrode plates 12, 13.
Preferably, the porous separator 14 is in the form of
a continuous strip of the separator material which is
wound completely around the negative electrode plate 12
and then interposed between the positive electrode plate
11 and the negative electrode plate 13. All of the
-14-
105~859 9579-1
electrode plates 10-13 are rectangular in shape and are of
substsntially the same size such that the electrode plates
are congruent with one another in the electrode s~ack
assembly.
The positive electrode plates 10, 11 contain an
electrochemically oxidizable active material such as
nickel-hydroxide while the negative electrode plates 12,
31 contain an electrochemically reducible active material
such as cadmium oxide or cadmium hydroxide. In accordance
with the conventional practice in the art, the negative
electrode plates 12, 13 contain additional active material
in order to provide an overcharge reserve which will
prohibit the harmful generation of hydrogen gas on over-
charge of the cell. Similarly, the positive electrode
plates 10, 11 may contain some negative active material
as antipolar mass in order to provide an overdischarge
reserve which will substantially delay harmful generation
of hydrogen gas on overdischarge of the cell. Both the
positive electrode plateæ 10, 11 and negative electrode
plates 12, 13 may be sintered type electrodes fabricated
from a sintered metal plaque which may be made, for
example, by sintering a layer of metal powder, e.g.,
nickel powder, onto both sides of an open, porous
substrate such as a nickèl screen, which serves as a
mechanical support. The sintered metal plaque is
105'~359 9579-1
lmpregnatet wlth the electrochemically actlve material in
accort~nce with methods well known ln the art. The
~eparator 14 contalning alkaline electrolyte, may be made
from a conventional separator material such as a non-
woven organic fiber matte. A preferret type 1B mate
from nylon fiber under the trademark "Pell~n." Suitablyj
the alkaline elèctrolyte u~ed in the cell 1B a 30 percent
by weight solution of potassium hydroxide.
An auxiliary electrode 15 i8 positioned ad~acent
to the positlve electrode plate 10 at one end of the
electrode stack assembly. The auxillsry electrode 15
18 less than hslf the size of the positive and negative
electrode plates 10-13 and 18 preferably placed over the
t~p of one-half section of the positive electrode plate
10 (the left hand half-section of the positive electrode
plate 10 in Fig. 1). A separate porous ~eparator 16,
e.g., "Pellon", thoroughly soaked with the alkaline
electrolyte, is interposed between and in contact with
the positlve electrode plate 10 and the auxiliary
electrode 15.
The auxillary electrode 15 is an oxygen sensing
electrode. It is preferably positioned ad~acent to the
positi~e electrode plate 10 in order to sense ~ore
effectively the beginning of oxygen evolution at this
electrode during charging of the ce$1. The oxygen
-16-
.... . .. .. ... ... .. . . .. .. .. , . , . , . . . _
9579-
105Z859
sens~ng electrode 15 may be composed of nickel, for
example, and preferably i8 made from a sintered nickel
plaque as de8cribed above.
The electrode assembly including the auxiliary
electrode 15 is enclosed within a shallow, rectangular,
cupped container 17. This cupped container 17 is
preferably made by vacuum forming a rectangular cup from
a ~heet of liquid impervious, electrically non-conductive
plastic film, such as a polypropylene film. The cupped
container 17 i8 formed with an opening 18 in the middle
of its bottom wall 19.
A first terminal connection is provided in the
bottom wall 19 of the cupped container 17. This terminal
connection comprises first internal and external current
collector~ 20, 21 which may be in the form of flat, thin
metal plates or foils, suitably a nickel foil, for
example. The internal and external current collectors 20,
21 are placed ad~acent to the inner and outer sides
respectively of the bottom wall 19 of cupped container
17, overlying the opening 18. The collectors 20, 21
are tightly adhered to the inner and outer sides of the
bottom wall 19 by thin layers 22, 23 respectively, of an
adhesive sealant which is chemically resistant to and
non-wettable by the alkaline electrolyte. Preferably,
the layers 22, 23 of adhesive sealant cover substantially
9579~
lO5Z859
the entire surface o~ the collectors 20, 21 tightly
sealing the interfaces between the collectors and the
bottom wall 19. The collectors 20, 21 are electrically
connected to one another through the opening 18 such as
by means of a spot weld 24 or a solder spot. Alternatively,
the collectors 20, 21 may be electrically connected to
one another by means such as th~ use of an electrically
conductive cement. The cupped container 17 and the pair
of collectors 20, 21 are preferably assembled together
in the manner as firs~ described to form a composite
member 8uch as illu8trated in the view of Fig. 2.
A rectangular cover 25 preferably made from the
same liquid impervious, electrically non-conductive
plastic fi~m, is provided for the cupped container 17.
The cover 25 is formed with a pair of spaced a~art
openings 26, 27, each of which is located at the a~proxi-
mate midpoint of each half-section of the cover 25.
A second and third terminal connection is
provided in the cover 25. These two terminal connections
are assembled in basically the same manner as in the
assembly of the first terminal connection hereinabove
described.
The second and third terminal connections
comprise, respectively, second internal and external
current collectors 28, 29 and third internal and external
-18-
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105'~859
current collectors 30, 31, which al80 may suitably be
thin metal plates or foil, e.g., nickel foil. The
internal collectors 28, 30 for each of the two terminal
connections are disposed adjacent to the inner side of
the cover 25 and the external collectors 29, 31 are
dispo~ed ad~acent to the outer side of the cover 25,
overlying the openings 26, 27. The size of the collectors
is smaller than each half-section of the cover 25 such
that the pairs of internal and external collectors 28, 29
10 and 30, 31 are spaced apart from each other at the
midpoint of the cover 25. The second internal and
external collectors 28, 29 are tightly adhered to the
inner and outer sides respectively of the cover 25 by
a thin layer 32, 33 of the non-wetting adhesive sealant
and are electrically connected to one another through
the opening 26 by the spot weld 34. Similarly, the
third internal and external collectors 30, 31 are
tightly adhered to the inner and outer sides respectively
of the cover 25 by a thin layer 35, 36 of the same
20 adhesive sealant and are electrically connected to one
another through the opening 27 by the spot weld 37. The
layers of adhesive sealant cover substantially the entire
face of the internal and external collectors 28-31,
tightly sealing the interfaces between the collectors and
the cover 25. The cover 25 and the collectors 28-31 are
-19-
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105Z8S9
also preferably assembled to form a composite member such
as illustrated in Fig. 3.
The pair of negative electrode plates 12, 13
are electrically interconnected by means of a thin metal
collector tab 38 which is secured at one end to the
corresponding peripheral edges of both negative electrode
plates 12, 13 such as by welding. At its other end the
tab 38 i9 interposed between and in contact with the
negative electrode plate 13 and the internal collector
20 for the first terminal connection at one end of the
electrode a~sembly. Similarly, the pair of positive
electrode plates 10, 11 are electrically interconnected
by means of a thin metal tab 39 which is secured at one
end to the corresponding peripheral edges of both
positive electrode plates 10, 11. At its other end the
tab 39 i5 interposed between the separator 16 overlying
the positive electrode plate 10 and the internal
collector 28 for the second terminal connection at the
other end of the electrode a~sembly. Tabs 38, 39 are
2 secured such as by welding to the respective collectors
20, 28 during the assembly of the cell as will be
described in greater detail hereinafter.
Both the cupped container 17 and the cover 25
which are preferably made from the same liquid impervious,
electrically non-conductive plastic film, are formed with
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lOS'~859 9579-l
marginal borders 40, 41 respectively, which are secured
together such as by heat sealing to provide a tight
leakage proof seam 42.
The method of assembling the flat cell construc-
tion may now be described in greater detail. As indicated,
the cupped container 17 is first formed as a composite
member with both the first internal and external current
collectors 20, 21 tightly adhered to the inner and outer
sides of the container bottom wall 19 through means of
the thin layers 22, 23 of the adhesive sealant. Similarly,
the cover 25 i8 first formed as a composite member with
the first and second internal and external collectors
28-31 tightly secured to the inner and outer sides of the
cover through means of the thin layers 32, 33 and 35, 36
of the adhesive sealant. Tab 38 is secured such as by
welding to the corresponding ~eripheral edges of the pair
of positive electrode plates 10, 11. A continuous
strip 14 of the separator material, which is a~proximately
three times the length of an electrode plate, is wound
completely around the negative electrode plate 12 with
one end being secured to the port~on of the separator
strip 14 which overlaps the peripheral edge of the
negative electrode plate 12 suitably by a heat seal as
shown at 43 in Fig. 1. Provision is made for passage
of the tab 38 through the strip 14 such as by means of a
-21-
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lOS~859
slot as shown st 44. The free portion 14a of the ~trip
14 which extends beyond the seal 43 is interleaved between
the pair of negative electrode plates 12, 13. Tab 38 is
then secured as by welding to the first internal
collector 20 within the bottom of the cupped container 17
while in a similar manner tsb 39 is secured as by welding
to the second internal collector 28 on the cover 25. The
pair of positive electrode plates 10, 11 are then inter-
leaved with the pair of negative electrode plates 12, 13
with the negative electrode plate 12, which is enveloped
by the separator strip 14, interposed between the pair of
po~itive electrode plates 10, 11 to complete the electrode
assembly. The auxiliary electrode 15 is then secured
such as by welding to the third internal collector 30.
With all of the cell components placed in the manner as
hereinabove described, the cover 25 is placed over the
open end of the cupped container 17 and their marginal
borders 40, 41 are secured together such as by heat sealing
to complete the assembly of the cell.
It will be readily seen from the above
descript~on that the assembly of the first internal and
external collectors 20, 21 constitutes the negative
terminal connection and that the assembly of the second
internal and external collectors 28, 29 constitutes the
positive terminal connection of the flat cell. The
-22-
1 0 ~ 5~ 9579-1
as~embly of the third internal and external collectors 30,
31 constitute~ a third terminal connection which in the
flat cell illustrated is the terminal connection for the
auxiliary oxygen sensing electrode 15.
~ igs. 5-7 illustrate another embodiment of a
flat cell con~truction in sccordance with the invention
wherein like reference numerals denote the same or
similar parts a~ used in the flat cell hereinabove
de8cribed. In this flat cell construction, the third
terminal connection i8 incorporated in the bottom wall
19 of the cupped container 17 instead of in the cover 25.
The electrode assembly used in this flat cell
construction is basically the same arrangement of flat
thin positive electrode plates 10, 11 and flat thin
negative electrode plates 12, 13 arranged in alternate
fashion with the po~itive electrode plate 10 being
located at one end of the electrode assembly, the negative
electrode plate 12 placed between the pair of positive
electrode plates 10, 11 and with the negative electrode
plate 13 being located at the opposite end of the
electrode assembly. The same porous separator xtrip 14,
thoroughly soaked with the alkaline electrolyte, is
sandwiched between the pairs of positive and negative
electr~de plates 10-13.
An auxiliary electrode 45 is positioned adjacent
9579-
lOS'~859
to the negative electrode plate 13 at one ent of the
electrode assembly, Agsln the a~xiliary electrode 45 is
les~ than half the size of the positive and negati~e
electrode plate8 10-13 and i8 preferably placed over the
bottom of one half-section of the negative electrode 13
(the right hand half-section of the negative electrode-13
in Fig. 5). A separate porous separator 46, e.g.,
"Pellon", thoroughly soaked with the alkaline electrolyte,
i8 interposed between and in contact with the negative
electrode plate 13 and the auxiliary electrode 45.
The auxiliary electrode 45 in this instance may
be a hydrogen sensing electrode. The auxiliary electrode
45 is preferably po~itioned adjacent to the negative
electrode plate 13 in order to sen8e more effectively any
hydrogen gas that may be evolved at this electrode
particularly during deep discharge of the cell. The
hydrogen sensing electrode 45 may be made from a porous
sintered nickel plaque impregnated with a suitable
hydrogen catalyst such as a platinum group metal, e.g.,
platinum, palladium and radium.
A fir8t terminal connection is provided in the
cover 25 and comprises both internal and external
current collectors 47, 48 which ma~ also be flat thin
metal plates or foil, e.g., nickel foil. The internal
and external collectors 47, 48 are placed adjacent to
-24-
~ 0 5'~ 8 S9 9579-1
the inner and outer s~de~ respectively of the cover 25,
overlying an opening 49 located at the midpoint of the
cover 25. The collectors 47, 48 are again tightly adhered
to the inner and outer sides of the cover 25 by thin
layers 50, 51 respectively of the non-wetting adhesive
sealant. The layers 50, 51 of adhesive sealant preferably
cover substantially the entire surface of each collector
47, 48 tightly sealing the interfaces between the
collectors and the cover 25. Both of the collectors 47,
48 are electrically connected to one another through
the opening 49 by means of the spot weld 52. Similar
to the flat cell illustrated in Figs. 1-4, the cover 25
and collectors 47, 48 are preferably assembled to form a
composite member as hereinabove described.
A second and third terminal connection are
provided in the bottom wall 19 of the cupped container
17. The two terminal connections are also assembled in
basically the same manner as hereinabove described.
The second and third terminal connections
comprise, respectively, second internal and external
current collectors 53, 54, which overlie an opening 55
located at the approximate midpoint of one half-section
of the bottom wall 19, and third internal and external
current collectors 56, 57, which overlie an opening 58
located at the approximate midpoint of the other half-
-25-
9579-1
~05Z859
section of the bottom wall 19. The internal and external
collectors 53, 54 and 56, 57 are also sultably thin metal
plates or foil, e.g., nickel foll. The internal
collectors 53, 56 for each of the two terminal connections
are disposed adjacent to the inner side of the bottom
wall 19 and the external collector~ 54, 57 are disposed
ad~acent to the outer side of the bottom wall 19, over-
lying the openings 55, 58. Again the size of the
collectors is smaller than each half-section of the
bottom wall 19 such that the pairs of internal and
external collectors 53, 54 and 56, 57 are spaced apart
from each other at the midpoint of the bottom wall 19,
The second internal and external collectors 53, 54 are
tightly adhered to the inner and outer sides respectively
of the bottom wall 19 by a thin layer 59, 60 of the
non-wetting adhesive sealant and are electrically
connected to one another through the opening 55 by the
spot weld 61. In the same manner, the third internal
and external collectors 56, 57 are tightly adhered to
the inner and outer sides respectively of the bottom
wall 19 by a thin layer 62, 63 of the same adhesive
sealant and are also electrically connected to one
another through the opening 58 by the spot weld 64. The
layers of adhe~ive sealant cover substantially the entire
surface of the internal and external collectors 53, 54
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1~5'~859 9579-1
and 56, 57, tightly seallng the interfaces between the
collectors and the bottom wall 19. The cupped container
17 and the collector~ 53, 54 and 56, 57 are also
preferably assembled to form a composite member such as
illustrated in Figs. 6 and 7.
The flat cell of this embodiment of the
invention is as~embled in basically the same manner a~
the assembly of the flat cell construction illustrated
in Figs. 1-4. The pair of positive electrode plates 10,
11 are electrically interconnected by means of a thin
metal collector tab 65 which is secured at one end to
the corre~ponding peripheral edges of both positive
electrode plates 10, 11 such as by welding. At its
other end the tab 65 is interposed between and in
contact with the positive electrode plate 10 and the
internal collector 47 for the first terminal connection
at one end of the electrode assembly. Similarly, the
pair of negative electrode plates 12, 13 are electrically
interconnected by means of a thin metal tab 66 which is
secured at one end to the corresponding peripheral edges
of both negative electrode plates 12, 13. The tab 66 at
its other end i~ interposed between the separator 46,
overlying the negative electrode plate 13, and the
internal collector 53 for the second terminal connection
at the opposite end of the electrode assembly. Tabs 65,
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1 9579-1
~S'~Sg
66 are securet such a~ by welding to the respective
collectors 47, 53 during the assembly of the cell.
Auxiliary electrode 45 is maintained in electrical
connection with the internal collector 56 for the third
terminal connection. Preferably, auxiliary electrode 45
is secured such a~ by welding to the collector 56 also
during assembly of the cell as hereinabove described.
` It will be readily seen from the above
description of the flat cell of this embodiment that the
a~sembly of the first internal and external collectors
47, 58 constitutes the positive terminal connectlon
and that the assembly of the second internal and external
collectors 53, 54 constitutes the negative terminal
connection of the flat cell. The assembly of the third
internal and external collectors 56, 57 constitutes a
third terminsl connection which in this embodiment of the
flat cell is the terminal connection for the auxiliary
hydrogen sensing electrode 45,
In cells utilizing the rechargeable nickel-
cadmium electrode system, gas generation and the consequentbuild up of substan~ial gas pressure inside the cell can
occur particularly if the cell is placed on overcharge
or long periods of time. On overcharge, oxygen gas may
be initially liberated at the positive electrode at a
faster rate than it can be recombined at the negative
~ 8S9 9579-1
electrode leading frequently to a build ~p of high
internal gas pressure. Hydrogen gas can be evolved, for
example, when the cell is subjected to deep discharge.
The evolution of hydrogen gas further increases the gas
pressure inside the cell since it does not normally
rec~mbine within the cell as does the oxygen.
In flat cells of this invention, the plastic
film envelope which is made, for example, of a poly-
propylene or vinyl film is flexible and fairly weak.
The cell can rupture, although without danger, if the
internal gas pressure is allowed to build up to any
signi~icant level such as 160 psi, for example. In order
to avoid this problem, it has been found desirable to
provide a mechanism for preventing the generation of
hydrogen at the negative electrode while at the same time
facilitating the recombination of oxygen. Accordingly,
in the preferred embodiment of a rechargeable nickel-
cadmium flat cell, the positive and negative electrodes
are balanced electrochemically with respect to one
another such that the capacity of the negative electrode
is greater than that of the positive electrode. Preferably,
the capacity of the negative electrode is at least one
and one-half times greater than that of the positive
electrode and may be as great as three times the positive
capacity.
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95~9-
lOS;~859
: As a further deter,rent against cell rupture due
to the build up of excessive internal gas pressure, flat
cells of the construction disclosed and claimed in our
above referred to copending application may incorp~rate
an auxiliary oxygen or hydrogen sensing electrode together
with a third terminal connection in accordance w th the
invention. In the instance where the auxiliary electrode
i8 an oxygen sensing electrode, the auxiliary electrode
. forms with the negative electrode a voltage differential
whose value will depend on the partial oxygen pressure
that is.developed inside the cell. Conversely, in the
case where the auxiliary electrode is a hydrogen sensing
electrode, the auxiliary electrode forms with the positive
electrode a voltage differential whose value will depend
on the partial hydrogen pressure inside the cell. Under
conditions where the cell evolves copious quan~ities of
oxygen gas on overcharge, for instance, the partial
oxygen pressure will rise inside the cell, the voltage `
differential will change and this change can be utilized
as a signal for actuating a control device in ~he charge
circuit to cut off the charging current and thereby ~
prohibit the further build up of gas pressure inside the~ -
cell. Charging circuits utilizing such control devices
- ~ ~
are of course well kno~n to those skilled in the art.
In assembling batteries of flat cells of the
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105~859 9579-1
type referred to in U. S. Patent 3,871,921, only one
cell incorporates a third terminal connection and
auxiliary oxygen or hydrogen sensing electrode and
this cell is utilized as a so-called "control cell," it
being understood that the remaining battery cells will
be maintained in approximately the same state of charge
or discharge. Such batteries may be assembled with the
flat cells interconnected in series, parallel or series
parallel arrangement. In assembling a series-connected
battery, for instance, the flat cells may be stacked
one on top of another with the positive términal con-
nection in one wall of each cell making electrical
contact with the negative terminal connection in the
opposite wall of the next cell. The control cell may
then be placed at either end of the battery stack of
cells in order to more readily facilitate the elec-
trical connection of the control cell into the charging
circuit. other arrangements of the battery assembly and
control cell are o~ course possible as will readily
occur to those skilled in the art.
Flat cells utilizing a third terminal connection
in accordance with the invention may also incorporate
an auxiliary electrode which functions as a voltage
reference device. Such applications are particularly
useful to the researcher 8ince the auxiliary electrode can
-31-
~05'~859 9579-l
.
be utilized to study the behavior of either the posltive
or negative electrode without the necessity of dis-
assembling the cell structure. In the two embodiments
of the flst cell illustrated in the drawing, the
auxiliary electrode can be readily itilized as a voltage
reference device. It is only necessary to make the proper
external electrical connections between the positive or
negaeive and the third terminal connections of the cell.
The auxiliary voltage reference electrode in this
instance may be camposed of a sintèred nickel plaque
impregnated with a metal hydroxide as the active material
Ie will of course be understood that the
auxiliary electrode used in the two embodiments of the
invention described herein may be either oxygen or
hydrogen sensing electrodes. Thus in the embodiment of
the flat cell illustrated in Figs. 1-4, the auxiliary
electrode 45 may be a hydrogen sensing electrode,
although it is preferred to position this electrode
ad3acent to the negative electrode. ~ ~-
Commerical plastic films which may be utilized
in forming the sealed envelope in flat cells of the
invention include those made of the following materials:
vinyl polymers and copolymers, polyvinylidene chloride,~
polyethylene, polypropylene, nylon, polysulfone, poly~
8tyrene, and fluorocarbon polymers. For use with the
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9579-
lO5~S9
preferred fatty polyamide adhesive, films mate of poly-
ethylene, polypropylene, nd v$~yl polymers and copolymers
are preferred. Regular snd shrink-type films are ava~lable
in these materials. Desired film characteristics include
the following: low cost, flexibility, tear and puncture
resistance, chemical stability and resistance to alkaline
b~ttery elecerolyte, hot-formability, low oxygen gas and
water vapor transmission rates, and of course strong
8urface adherence with fatty polyamide or equivalent
adhesive To reduce the gas and water vapor transmission
rate of the plastic film, it may be vacuum metallized or
otherwise given a ~urface metallic coating on one or
both sides providing of course the film is not made
electrlcally conductive enough to put a parasitic current
drain on the cell.
Although there are probably a number of
organic compounds which exhibit a non-wetting characteristic
when in contact with an alkaline electrolyte, the most
preferred adhesive sealant for use in`the practice of
the invention are the fatty polyamides. Such fatty
polyamide sealants are disclosed in U. S. Patent No.
3,922,178 issued to J. Winger on November 25, 1975 and
assigned to the common assignee hereof. As disclosed
in this patent application, fatty polyamides
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9579-1
1052859
~re produced by rescting a polyb~sic acid with a poly-
function~l ~mine. Generally, the fatty polyamides useful
ln the practice of the ~nvention are those having an
amine number of above about 9. The amine number is the
number of milligrRms of KOH e~uivalent to one grsm of
fatty polyamide and is determined by procedures well
known in the art The fatty polyamide sealants can be
mixed w$th extenders ant modifiers in order to modify
the physical properties of the fatty polyamide. In
constructing flat cells in accord with the inventior"
the fatty polyamide sealant can be applied as a hot-melt
or from solution in a solvent such as an alcohol/aromatic
hydrocarbon mixture. A ng the specific commercially
available fatty polyamides that are particularly useful
in constructing fl-t cells of the invention are those
produced unter the trademarks of VERSALON and GENBOND,
General Mills, Inc. and Swift's Z-610, Swift and Co~p~ny.
It has been found that during the assembly of
flat cells of the invention the preferred adhesi~e
~ealants, i.e., fatty polyamides, do not readily wet some
types of pla~tic film and accordingly a li~uid tight ~-
8eal between the cupped container and cover and the metal
collector foils is sometimes difficult to attain. This
d$fficulty m~y be overcome and the bond be een the
plastic film and the collector foils substantially
, : ~
- -34-
lOS;~8S9 957g-l
improved if the plastic film i8 first subJected to 8uc-
cessive heat and corona discharge treatments. The
process for treating the plastic film i8 disclosed and
claimed in U. S. Patent No. 3,914,521 issued on
November 21, 1975. In this process, the pla8tic film
i8 heated to an elevated temperature, about 120C in
the case of a polyprop~lene film for a period of about
one half minute, optionally cooling the plastic film to
ambient temperature and then su~jecting the film to a
high intensity corons discharge in the area of the film
where the collector foils are to be adhered.
Although the invention has been described herein
with particular reference to rechargeable flat cell systems
such as the nickel-cadmium cell wherein an auxiliary
electrode is used as an oxygen or hydrogen sensing
electrode, it will be understood that the invention is
not so limited and is applicable as well to primary flat
cells wherein the auxiliary electrode is utilized as a
voltage reference electrode.
Primary flat alkaline cells which are believed
to be readily adaptable to the flat cell construction
herein described include the following: alkaline
~anganese dioxide-zinc, silver oxide-zinc, and mercuric
oxide-zinc.
Electrodes and other materials employed would
-35-
~ J ~
lO5Z859
of course be those requlred by and compatible with the
cell system employed. For example, the collector plateg
! used with the slkaline manganese dloxlde-zinc system would
preferably be of copper or brass rather than steel.
Similarly the flat electrodes employed could be of the
well known pressed powder type on an open or expanded
conductive substrate rather than of the impregnated porous
sinter type.
It is obvious that the flat cell construction
of the invention need not be limited to the rectangular
format. Other shapes of cell such as square, circular,
elliptical, hexagonal, and various irregular figures
could be encased in plastic film and provided with a
positive, negat~ve and a third terminal connection by
the technique herein disclosed.
Although t illustrated in the drawing, it is
evident that certain variants in the flat cell construction
are possible. For example~ it would be within the scope
of the invention to construct a thicker cell than that
illustrated by encasing the cell in two opposed and
sealed cupped assemblies rather than using the cup and
cover assemblies illustrated. Similarly a thinner eell
could be encased in two cover assemblies. It is also
possible to construct the flat cell with the first,
8econd and third terminal connections incorporated in one
-36-
lOS'~859 9579-l
wall of the sealed envelope, e.g., the bottom wall of the
cupped container or the cover. Suitable means such as
collector tabs can be used to make electrical connection
between the positive, negative and auxiliary electrodes
and the terminal connections in one wall of the sealed
envelope. Additionally, the external current collectors
need not be flat metal plates or foil but can be suitably
made of any other configuration such as a curved plate or
the like.
-37-
