Note: Descriptions are shown in the official language in which they were submitted.
10420~ 8894
Back~round of the Invention
This invention relates to flat, electric
current-producing cells using an alkaline electrolyte,
and more particularly to improvements in flat alkaline
cells of the type wherein the active cell elements are
enclosed within a sealed envelope made of a liquid
impervious, plastic film.
Alkaline cells of both the primary and secondary
type are well knawn. Alkaline cells in general po6sess a
number of outstanding advantages over cells using other
types of electrolytes such as the more familiar Leclanche
dry cell using an ammonium chloride electrolyte. One
advantage of alkaline cells is that they exhibit a high
current discharge capacity under continuous load for a
relatively long period. Moreover, alkaline cells have a
substantially more level voltage discharge curve.
Additionally, they have a relatively high ratio of
energy ~o cell volume and are not as adversely affected
by changes in temperature. Typical examples of primary
. .
-; 20 alkaline cells are those utilizing electrode systems of
-` zinc/manganese dioxide, zinc/mercuric oxide and zincj
` silver oxide. Secondary or rechargeable alkaline cells
may also be constructed utilizing a number of different
electrode sy~tems. Of course, the most familiar of
these cells i8 the rechargeable nickel-cadmium cell.
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~O~ZOti7
There is an increasing demand today in the
electronics industry for various types of alkaline cell
batteries. Alkaline cell batteries, for instance, are
ideally suited for use as the power source in many portable
electronic devices such as electronic calculators, radios,
television sets, tape recorders and the like. For most of
these applications, flat alkaline cell batteries would be
preferred because of their potentially higher capacity
per unit volume as compared to conventional round or button
cell batterieg. Thi~ is an important consideration since
most portable electronic devices today could be made more
-~ compact if less space were required to accommodate the
batteries~
One flat cell construction that has been used
successfully with electrolytes other than alkaline electro-
lytes is the type wherein the active cell elements are
enclosed within a sealed envelope made of a liquid
impervious plastic film. Such a cell envelope may be
madej for example, from two plastic films which are
joined tightly together around the marginal borders
thereof such as by heat sealing. Suitable external
connections with the cell electrodes may be made, for
example, by an electrical lead extending through the
marginal border seal or through the provision of an
opening in the plastic film envelope which exposes an
electrode or a current collector such as a thin metal
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lO~ZO~7
foil. Numerous flat cell construction~ of this type are
known in the art, reference being made for example to
Soltis, U.S, Patent No. 2,870,235 and Nagorski, U.S.
Patent No. 2,847,495.
Various attempts have been made to manufacture
flat cell constructions of the type described utilizing an
alkaline electrolyte. So far, however, these attempts
have failed ma~nly due to the difficulty in sealing such
- flat cell constructions against leakage of alkaline
electrolyte. Generally, cells utilizing an alkaline
electrolyte are the most difficult to seal owing to the
ability of the electrolyte to readily wet most surfaces,
including both plastic and metal surfaces, and actually
creep through the interface between a seal and certain
parts of the cell.
In Tamminen, U.S. Patent No. 3,708,340, a flat
cell construction of the type described utilizing an
alkaline electrolyte i8 disclosed. In this flat cell
- construction, external connection with one of the
electrodes iB attained through the provision of an
opening in the plastic film envelope. A seal composed of
a sticky and water-repellent material, such as soft
microcrystalline wax, polyisobutylene or silicone grease,
- surround~ the immediate periphery of the opening at the
interface between one of the electrodes and the plastic
- film. The problem with this flat cell construction,
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~0420G7 8894
however, is that the seal, although made of a water-
- repellent materisl, is nonetheless penetrated by the
alkaline electrolyte and leakage occurs through creepage
of the electrolyte past the seal and out through the
opening in the plastic film envelope.
It is therefore the principal object of this
invention to provide an improved flat cell construction
utilizing an alkaline electrolyte.
A more ~pecific object of the invention is to
provide a flat alkaline cell construction which can be
effectively sealed against leakage of the alkaline
electrolyte.
Still another object of this invention is to
provide a flat alkalinelcell construction which can be
readily assembled and which is economical to manufacture.
Summary of the Invention
; This invention resides in a flat alkaline cell
construction comprising an electrode assembly including
at least a pair of flat electrode elements of opposite
polarity, a porous bibulous separator containing the
; alkaline electrolyte, interposed between and in contact
with the pair of electrode elements, and a current
-~ collecto~ which may be a flat ~hin metal plate or foil,
disposed adjacent to and in electrical connection with
at least one of the pair of electrode elements at one end
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~0~ ZO ~7 8894
of the electrode assembly. All of the cell elements are
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
is formed with an opening adjacent to the current collector
which exposes the collector for making external electrical
connection, for example, between adjacent cells in a stack
of flat cells forming a battery. ~n adhesive sealant which
is non-wettable by the alkaline electrolyte, surrounds the
periphery of the opening at the interface between the
current collector and the plastic film. Preferably, the
adhesive ~ealant is applied to the entire face of the
current collector in order to tightly seal the plastic
film to the collector and also to extend substantially
the leakage path and thereby increase the resistance
to creepage of the alkaline electrolyte from its location
inside the cell. The adhesive sealant preferably used in
the practice of the invention is a sealant formulated from
the general class of compounds known as "fatty polyamides".
The fatty polyamide used in the sealant material preferably
should have an amine number of above about 9.
Although the invention is widely applicable to
flat alkaline cell constructions in general, it will be
more fully described hereinafter with particular reference
to a rechargeable nickel-cadmium cell. Such a rechargeable
nickel-cadmium cell comprises a positive electrode containing
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104~067 8894
an electrochemically oxidizable active material such as
nickel hydroxide, a negative electrode containing an
electrochemically reducible active material such as
cadmium oxide or cadmium hydroxide, and a porous bibulous
separator containing the alkaline electrolyte, interposed
between and in contact with both the positive and the
negative electrodes. The positive and negative electrodes
will be so balanced electrochemically with the active
materials as to prohibit the generation of excessive gas
or gases upon overcharge of the cell. In addition, the
positive electrode may also incorporate an antipolar mass
in order to prevent electrode polarity reversal upon over-
discharge. It will be understood, of course, that the
flat alkaline cell construction of the invention may
utilize other electrode systems such as the zinclmanganese
dioxide system as will readily occur to those skilled in
the art.
The invention will be hereinfurther described in
detsil by reference to the specific embodiments of the
flat cell construction illustrated in the accompanying
drawings.
Brief Description of the Drawin~s
Fig. 1 is a perspective view of one embodiment of
the flat alkaline cell construction of the invention;
Fig. lA is a cross-sectional view of the flat
cell illustratsd in Fig. 1, taken along the line lA-LA;
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104Z067 8894
Fig. 2 is a perspective view of another embodiment
of the flat alkaline cell construction;
Fig. 2A is a cross-sectional view of the flat
cell illustrated in Fig. 2, taken along the line 2A-2A;
Fig. 3 is a perspective view of another embodi-
ment of the flat alkaline cell construction;
Fig. 3A is a cross-sectional view of the flat cell
illustrated in Fig. 3, taken along the line 3A-3A;
Fig. 4 is a perspective view of still another
embodiment of the flat alkaline cell construction;
Fig. 4A is a cross-sectional view of the flat
cell illustrated in Fig. 4, taken along the line 4A-4A;
Fig. 5 is a perspective view of a further embodi-
ment of the flat alkaline cell construction; and
Fig. 5A is a cross-sectional view of the flat
cell illustrated in Fig. 5, taken along the line 5A-5A.
- Description of the Preferred Embodiments
; Figs 1 and lA illustrate a rechargeable flat
nickel-cadmium cell made in accordance with the invention.
The cell comprises a pO8 itive electrode plate 10, a
negative electrode plate 11, and a porous separator 12
containing an alkaline electrolyte sandwiched between and
in facial contact with the positive and negative electrode
. .
plates 10, 11, forming a conventional electrode stack
. assembly. The positive and negative electrode plates 10,
11 and the separator 12 are rectangular in shape and are
1 0 4 Z 0 ~ 7 8~94
of sub~tantially the same size such that the electrode
plates 10, 11 and separator 12 are Rtacked congruently.
Both the positlve and negative electrode plates 10, 11
may be sintered type electrode~ fabricAted from a sintered
metal plaque which may be made, for example, by sintering
: B layer of metal powder, e.g. nickel, onto both sides of
an open or porous substrate such as 8 nickel screen, which
serves as a mechanlcal support and electrlcal path. The
sintered metal plaque 18 impregnated with the electro~
chemically sctive material in accordance with conventional
methot~ well known in the art. The ~orous separator 12
containing the alkaline electrolyte may be made from a
conventional separatGr material such as a non-woven organic ~ -
fiber matte. A preferred type is made from nylon fiber under -
the tradename "Pellon", a trademark of Union Carbide CorPora-
tion. The alkaline electrolyte used in the cell may be, for
example, a 30 percent by weight solution of potassium hydroxide. ;~
At each ent of the electrode stack assembly ~s
provided one of a pair of current collector members 13, 14. -
The~current collector 13 is poaitioned in contact with the
po~itive electrode plate 10 whlle the other current
collector 14 i8 po~ltioned in contact with ~he negative
; electrode plate 11. These current collectors 13, 14 are
made from an electrlcally conductlve metal, preferably in
the form of thin me~sl foll, which i8 lnert to the alkaline
electrolyte such a~ nick~l or nickel plated steel.
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~0~06~ 8894
All of the cell elements including the positive
and negative electrode plates 10, 11, separator 12 with
absorbed electrolyte, and the current collectors 13, 14
are sealed within a liquid-impervious, electrically non-
conductive, plastic film envelope 15. The envelope 15
fits tightly around the side walls of the electrode stack
assembly and al90 around the opposite ends thereof forming
a pair of end walls 16, 17. These end walls 16, 17 do not
completely cover the current collectors 13, 14 but rather
~- 10 overlap only the outer margin thereof forming a pair of
openings 18, 19 which expose the center of each current
collector 13, 14, respectively. As shown in both Figs 1
and lA, a metal terminal lead 20 is secured ~uch as by welding
to the exposed center of the current collector 13 and
- constitutes the positive terminal for the cell. Similarly,
a metal terminal lead 21 is secured to the exposed center
of the current collector 14 and constitutes the negative
terminal for the cell.
- Substantially the entire outer surface of each
current collector 13, 14, except for the exposed center
.. . .
thereof, is cdated with a layer of adhesive sealant 22,
23 respectively, in accordance with the invention. The
adhesive sealant 22, 23 tightly seals the interface between
each of the pair of end walls 16, 17 of plastic film and
,
the current collectors 13, 14 against leakage of alkaline
electrolyte. Suitably, the adhesive sealant 22, 23 should
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la~z0~7
be an organic resin which will adhesively bond to both the
plastic film and metal collectors. Preferably the adhesive
sealant employs a fatty polyamide which is chemically
resistant to and not readily wet by the alkaline electrolyte.
The adhesive sealant 22, 23 is first applied as a thin
layer over the outer surface of each collector 13, 14,
prior to assembly.
The envelope 15 is made from a tubular heat -
shrinkable plastic film such as a vinyl film. In assembly
of the cell, the positive and negative plates 10, 11, ~-
separator 12 and current collec~ors 13, 14 are first
stacked together in the manner as described above and
then inserted inside the heat shrinkable tube with the
outer ends of the tube protruding beyond the current
- collectors 13, 14. The plastic film tube is then heated
and is caused to shrink down tightly around the side
walls of the electrode stack and at the same time, the
protruding ends of the tube shrink down forming the pair
~ of end walls 16, 17. Additional heat and pressure may be
i 20 required to establish the final adhesive bond.
Figs. 2-5 and the corresponding Figs. 2A-5A
inclusive, illustrate a number of other embodiments of the
flat cell construction in accordance with the invention.
In all of these embodiments, the cell elements may be
basically the same as those just described, that is, the
same sintered type positive and negative electrodes may be
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~0420~7
used together with the same porous, ~ibulous separator
containing the alkaline electrolyte, interposed between
the electrodes to form the electrode stack assembly. For
the sake of convenience, the same reference numerals will
denote identical cell elements in the following description.
In the embodiment of the invention illustrated in
Figs. 2 and 2A, one of the pair of current collectors 13,
14 used in the previous flat cell is eliminated and replaced
with a terminal lead 24, suitably made of a metal foil,
which is secured at one end to the negative electrode
plate 11, such as by welding. The cell elements are
enclosed within a sealed, liquid-impervious, electrically
non-conductive, plastic film envelope 25. This envelope
25 is also made from a tubular heat shrinkable plastic film
material. In this case, however, the tube is heat shrunk
.~
tightly over both ends of the electrode stack assembly.
The open ends of the tube are then heat sealed to one another
and also around the protruding terminal lead 24, to form
the liquid-tight seams 26, 27.
Similarly, as in the previous flat cell, the
envelope 25 has an opening 28 which exposes the center
of the current collector 13. A metal terminal lead 29 -is
secured such as by welding to the center of the collector
13. Heat shrinking the plastic tube tightly seals the ~ -
interface except for the center thereof, between the
overlapping portions of the plastic film forming the
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. ~04Z~67 8894
envelope 25 and the current collector 13 against leakage
of the alkaline electrolyte. A layer of adhesive sealant
31 is also applied on the surface of the collector and
around the foil terminal lead 24 at the point where it
protrudes through the liquid-tight seam 27. Preferably,
the adhesive sealant used in this embodiment is the same
fatty polyamide sealant which is non-wettable by the
alkaline electrolyte.
In the embodimRnt of the invention illustrated
in Figs. 3 and 3A, the pair of current rollectors 13, 14
are coated on their outer surfaces with a thin layer 32,
33 of a heat sealable organic resin such as polyethylene,
except for a small area which is left exposed at the
- center of each collector for-making external electrical
connection. A thin narrow layer 34, 35 of adhesive sealant,
preferably a fatty polyamide sealant, is applied directly
over the heat sealable layer 32, 33, around the outer
margin of each current collector 13 ? 14. The cell elements
are again enclosed within 8 sealed, liquid impervious,
electrically non-conductive, plastic film envelope 36.
- This envelope 36 is also made rom a heat shrinkable
: plastic film tube but in this case the tube has one
closed and one open end. The tube is heat shrunk tightly
around the side walls of the electrode stack assembly,
except that corresponding with the open end of the tube.
After the tube shrinks down tightly over both ends of the
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8894
104Z067
electrode stack forming the end walls 37, 38, the open
end of the tube is heat sealed together to form the
liquid-tight seam 39. Both end walls 37, 38 are provided
with openings 40, 41 through which the center of each
current collector 13, 14 is exposed. Terminal leads 42,
43 are secured such as by welding to the center of each
collector 13, 14. After the tube is heat shrunk tightly
around the electrode stack in the manner as just described,
the end walls 37, 38 are sealed directly to the respective
10 heat sealable layers 32, 33 on each of the current collec-
tors 13, 14 by application of heat and pressure. The
advantage of this flat cell construction is that the
attainment of a tight seal at the interface between the
plastic film snd the current collectors surrounding the
- opening for making external electrical connection is not
solely dependent upon the adhesive sealant.
Figures 4 and 4A illustrate another embodiment
of the invention wherein the cell elements are sealed
within a liquid impervious, electrically non-conductive,
20 plastic film envelope or housing of a somewhat different
construction. In this embodiment, the current collectors
13, 14 are similarly coated on their outer surfaces with
a thin layer of the adhesive ~ealant 44, 45~ preferably a
fatty polyamide sealant, except for the small area left
- exposed at the center of each collector. The electrode
stack asse~bly is placed inside a rectangular, open ended
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~0~2~7 8894
container 46 which is made of the liquid impervious,
electrically non-conductive plastic film. The container
46 includes side walls 47 and a bottom wall 48 and may be
made, for example, by vacuum forming a flat sheet of the
plastic film material. The electrode stack fits snugly
- inside the container 46 whose open end is sealed off ~y a
cover 49 also made of the same plastic film material.
The cover 49 has its outer peripheral edges heat sealed
to the peripheral edges of the container 46 forming a
continuous liquid-tight seam 50. Both the cover 49 and the
container bottom wall 48 are provided respectively with
openings 51, 52 through which the center of each current
collector 13, 14 is exposed. Terminal leads 53, 54 are
secured such as by welding to the center of each
.- collector. In the final assembly of the cell, both the
cover 49 and the bottom wall 48 are heated ln order to
assure that the layers of adhesive sealant 44, 45 adhesively
bond the film to each of the current collectors 13, 14.
The embodiment of the invention illustrated in
Figs. 5 and 5A incorporates still another type of construc-
tion for the sealed, liquid impervious, electrically non-
conductive cell envelope. As in the previous flat cell
illustrated in Figs. 3 and 3A, the current collectors 13, -
14 are coated on their outside surfaces with a thin layer
55, 56, respectively, of a heat sealable organic resin,
such as polyethylene, except for a small area left exposed
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104Z~67
at the center of each collector. All of the cell elements
are enclosed within a sealed composite envelope 57 which
in this instance is made from two tubes of a heat
shrinkable plastic film material. The first tube is
heat shrunk down over the electrode stack assembly in
exactly the same manner as described for the cell illus-
trated in Figs. 1 and lA forming both side walls 60 and
end walls 61, 62. Both end walls 61, 62 overlap only the
marginal borders of the pair of current collectors 13,
14 and leave open a substantial portion of each layer 55,
56 of heat sealable resin applied to each current collector
13, 14. After the first tube is heat shrunk around the
electrode stack assembly, the end walls 61, 62 are heat
i sealed to the layers 55, 56 of heat sealable resin tightly
sealing the marginal borders of each current collector 13,
14. The portions of the heat sealable layers 55, 56 which
are left open after the first tube is heat shrunk around
the electrode stack assembly is then coated with layers 63,
64, respectively, of adhesive sealant, preferably a fatty
polyamide, except for a small area coinciding with the
center of each current collector 13, 14 which is left ~
... .
exposed by the layers 55, 56. A second tube of heat
shrinkable plastic film is then heat shrunk down over
the first tube forming side walls 65, 66 which overlap
the end walls 61, 62 formed by the first tube and also
overlapping and bonding tightly to the layers 63, 64 of
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la4 2~ ~7 8894
adhesive sealant. The overlapping portions of the second
plastic tube are formed with openings 67, 68 which coincide
with the small area left exposed at the center of each
current collector 13, 14. Terminal leads 69, 70 are
secured to the exposed center of the collectors 13, 14
such as by welding.
Although not illustrated in the accompanying
drawing, a number of flat alkaline cells constructed in
accordance with the inventio~ can be readily stacked
together, for example, in a columnar form, to constitute a
battery of any desired multiple of single cell voltage.
In constructing such a battery, the positive terminal lead
from each independent cell may be connected, such as by
welding, to the negative terminal lead of an adjacent cell
in the stack to form a series-connected battery. Other
arrangements are of course possible, such as a parallel
or series-paralled connected battery, as will readily
occur to those skilled in the art,
In flat cells of the invention utilizing the
rechargeable nickel cadmium electrode system as in other
cell configurations such as cylindrical and rectangular
cells, gas generation and the consequent build up of
substantial gas pressure inside the cell can occur par-
ticularly if the cell is placed on overcharge for long
- periods of time. On overcharge, oxygen gas may be
liberated at the positive electrode at a faster rate than
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:.
.
it can be recombined at the negative electrode leading to
a build up of high internal gas pre~sure. In addition,
excessive oxygen gas pressures can lead to nearly complete
charging of the negative electrode which results in the
generation of hydrogen gas from the negative electrode.
The evolution of hydrogen gas further increases the gas
- pressure inside the cell since it does not recombine
within the cell as does the oxygen.
In flat cells of this invention the plastic film
envelope which i8 made, for example, of a 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 ~ignificant 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.
Commercial plastic films which may be employed in
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1042~D~ 8894
the practice of this invention include those made of the
following materials: vinyl polymers and copolymers,
polyvinylidene chloride, polyethylene, polypropylene,
nylon, polysulfone, polystyrene, and fluorocarbon polymers.
For use with the preferred fatty polyamide adhesive, films
made of polyethylene, polypropylene, and vinyl polymers
and copolymers are preferred. Regular and shrink-type
films are available in these materials. Desired film
characteristics include the following: low cost, flexibility,
tear and puncture resistance, chemical stability and
resistance to alkaline battery electrolyte, hot-formability,
low oxygen gas and water vapor transmission rates, and of
course strong surface 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 ~ surface metallic coating
on one or both sides providing oif course the film is not
made electrically conductive enough to put a parasitic
current drain on the cell.
It will be evident from the foregoing that the
invention provides a flat alkaline cell construction of
the type wherein the active cell elements are enclosed
`; within a liquid impervious, plastic film envelope which is
~ effectively sealed against leakage of the alkaline
; electrolyte. One important feature of the invention~ of
course, is the use of an adhesive sealant which is chemically
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8894
lQ~Z0~7
resistant to and non-wettable by the alkaline electrolyte,
surrounting at least the immediate periphery of the
- opening in the plastic film envelope for making external
electrical connection. Although there are probably a
number of orgflnic compounds which exhibit a non-wetting
characteristic when in contact with an alkaline electrolyte,
the most preferred edhesive sealant for use in the practice
of the invention are the fatty polyamides. Such fatty
- polyamide sealants for use in alkaline cells are already dis-
closed in U.S.Patent No. 3,922,178, issued to J.Winger, filed
on November 25, 1975. As disclosed therein, fatty polyamides
are produced by reacting a polybasic acid with a poly-
functional amlne. Generally, the fatty polyamides useful
in the practice of the invention are those having an
amine number of above about 9. The amine number is the
number of milligrams of KOH equivalent to one gram of fatty
polyamide and is determined by procedures well known in
; the art. The fatty polyamide sealants can be mixed with
extender~, modifiers, ant hardeners such as epoxy resins,
in order to modify the physical properties of the fatty
polyamite. In constructlng flat cells in accord with the -~
lnvention, the fstty polyamide sealant can be appl~ed as
a hot-melt or from solutlon in a solvent such as an alcohOl/
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8894
~04Z067
aromatic hydrocarbon mixture. Among the specific commer-
cially available fatty polysmides that sre particularly
useful in constructing flat cell~ of the invention ~re
those produced under the tradename~ of VERSALON and
GENBOND, trademarks of General Mills, Inc. and Swift's
Z-610, a trademark of Swift and Company.
It has been found that during the as~embly of
flat cells of the invention the preferred adhesive 6ealants,
i.e. fAtty polyamide6, do not readily wet some types of
plastlc film and accordingly a liquid tight seal between
the cupped contsiner snd cover snd the metal collector is
somet~me6 dlfflcult to atta~n. This dlfficulty may be
overcome and the bond between the plastic film and the
collector ~ubstaneially improved if the pl~stic film is
f~rst sub~ected to successive heat and corona discharge
treatu~nts. The proce8s for treating the plastic film is
disclosed and claimed ln our copending Canadian Patent
application Ser. No. 221,747, filed on March 10, 1975. In this
proces~, the plastic film i6 heated to an elevated tem-
; 20 per~ture, about 120C ln the case of a polypropylene film,
for a per~od of about one half mlnute, optionally cooling
the plastic film to ~mbient temperature ant then sub~ecting
Ithe film to a high inten~ity corona discharge in the area
of the film where the oetal collector i~ to be adhered.
Another ~port~nt feature of the invention re~ides ~ -
~n the provl~ion of a oeal for ~ flat ~lkal~ne dry cell
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which is so constructed and arranged as to constitute an
extended leakage path to resist creepage of the alkaline
electrolyte from its location inside the cell. It will
be noted in all of the preferred embodiments of the flat
cell described that the adhesive sealant or heat sealable
resin is applied as a coating or layer over one entire
face of each collector, except for the small area which is
left exposed at the center thereof, and tightly bonds the
whole interface between the plastic film and the collectors.
Since the alkaline electrolyte can only leak out from the
cell by penetrating the adhesive seal over this extended
creepage path, there is little likelihood of leakage
occuring from inside the cell.
Flat cells of the invention exhibit certain
; other advantages over the prior art and particularly the
conventional metal-encased round or cylindrical cells and
button cells.
Metal containers and covers are heavy, costly,
and wasteful of space. They are not readily adaptable
` 20 to rectangular cells. Such cells withstand high internal
pressure, but if they do rupture they can be hazardous.
Multi-cell rectangular batteries composed of an assembly
of round unit cells are inherently burdened with unused
space.
By contrast the improved plastic film encased
flat cells of the invention overcome all of the foregoing
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10420~i'7
objections. The plastic film adds little additional bulk
and weight. It will withstand reasonable operating
pressures and if the film does rupture under pressure no
hazard exists. The rectangular embodiments illustrated
can be readily fitted as s~ngle cells or multiple cell
stacks into rectangular battery compartments or enclosures
to provide the full energy density practically attainable
in the cell system employed. ~ost of the flat cell
embodiments shown can be readily adapted to cell shapes
other than square or rectangular, for example, circular,
elliptical, hexagonal, triangular as well as a variety of
irregular geometric figures. The flat cells may thus be
tailored to fit special cavities or holders, thus
preserving the high energy density capability of the
system.
Primary or secondary alkaline cell systems which
are believed to be readily adaptable to the novel fla~
cell constructions herein described include the following:
alkaline-manganese dioxide, silver oxide-zinc, nickel
cadmium, nickel zinc, and mercuric oxide-zinc.
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