Electrochemical cell having a safety vent closure

A safety blow-out vent closure for galvanic cells, such as nonaqueous oxyhalide cells, which comprises the employment of a conductive tubular member secured to the cell's housing and surrounding a vent orifice in the cell's housing and wherein a deformable member is force-fitted in said vent orifice and adapted to at least partially be ejected from the vent orifice upon the build up of a predetermined internal gas pressure within the cell. The invention is also directed to a method for assembling an electrochemical cell with the above-described safety vent closure.

FIELD OF THE INVENTION 
This invention relates to a safety, non-resealable vent closure for 
galvanic cells, such as nonaqueous cells, which comprises the employment 
of a conductive tubular member disposed about and secured over a vent 
orifice in the cell's housing and wherein a deformable member is 
force-fitted within the vent orifice thereby providing a normally 
fluid-tight seal at said vent orifice. The invention also relates to a 
method of producing the safety vent closure of this invention. 
BACKGROUND OF THE INVENTION 
Galvanic cells may generate large quantities of gas under certain 
conditions during use. Since many such cells are required to be tightly 
sealed in order to prevent loss of electrolyte by leakage, high internal 
gas pressures may develop. Such pressures may cause leakage, bulging or 
possible rupture of the cell's container under abusive conditions if not 
properly vented. 
In the past, several different types of resealable pressure relief vent 
valves have been used for releasing high internal gas pressures from 
inside a sealed galvanic cell. One type of valve that has been commonly 
used consists basically of a valve member such as a flat rubber gasket 
which is biased into sealing position over a vent orifice by means of a 
resilient member such as a helical spring. The resilient member or spring 
is designed to yield at a certain predetermined internal gas pressure so 
as to momentarily break the seal and allow the gas to escape through the 
vent orifice. 
In U.S. Pat. No. 3,664,878 to Amthor issued on May 23, 1972, a resealable 
vent is disclosed which comprises a resilient deformable ball of 
elastomeric material positioned to overlie a vent orifice provided within 
the cell's container. A retainer means is positioned over the resilient 
ball for maintaining the ball in place over the vent orifice and in 
contact with a valve seat provided around the peripheral edge portions of 
the vent orifice and for compressing and deforming the resilient ball into 
a flattened configuration forming a normally fluid-tight seal between the 
flattened ball and the valve seat. The resilient ball is capable of 
undergoing further temporary deformation upon the build up of a 
predetermined high internal gas pressure inside the container so as to 
momentarily break the seal and allow gas to escape through the vent 
orifice. 
However, with the continuing development of portable electrically powered 
devices such as tape recorders and playback machines, radio transmitters 
and receivers, and the like, a new type of reliable, long service life 
cells or batteries has been developed. These newly developed 
electrochemical cell systems provide a long service life by utilizing 
highly reactive anode materials such as lithium, sodium and the like, in 
conjunction with high energy density nonaqueous liquid cathode materials 
and a suitable salt. 
It has recently been disclosed in the literature that certain materials are 
capable of acting both as an electrolyte carrier, i.e., as solvent for the 
electrolyte salt, and as the active cathode for a non-aqueous 
electrochemical cell. U.S. application Ser. No. 439,521 by G. E. Blomgren 
et al filed Feb. 4, 1974, which is a continuation-in-part of application 
Ser. No. 212,582 filed on Dec. 27, 1971, discloses a nonaqueous 
electrochemical cell comprising an anode, a cathode collector and a 
cathode-electrolyte, said cathode-electrolyte comprising a solution of an 
ionically conductive solute dissolved in an active cathode depolarizer 
wherein said active cathode depolarizer comprises a liquid oxyhalide of an 
element of Group V or Group VI of the Periodic Table. The "Periodic Table" 
is the Periodic Table of Elements as set forth on the inside back cover of 
the Handbook of Chemistry and Physics, 48th Edition, The Chemical Rubber 
Co., Cleveland, Ohio, 1967-1968. For example, such nonaqueous cathode 
materials would include sulfuryl chloride, thionyl chloride, phosphorous 
oxychloride, thionyl bromide, chromyl chloride, vanadyl tribromide and 
selenium oxychloride. 
Another class of liquid cathode materials would be the halides of an 
element of Group IV to Group VI of the Periodic Table. For example, such 
nonaqueous cathode material would include sulfur monochloride, sulfur 
monobromide, selenium tetrafluoride, selenium monobromide, thiophosphoryl 
chloride, thiophosphoryl bromide, vanadium pentafluoride, lead 
tetrachloride, titanium tetrachloride, disulfur decafluoride, tin bromide 
trichloride, tin dibromide dichloride and tin tribromide chloride. 
It has been found that when employing high energy density liquid cathode 
materials in nonaqueous cell systems, the cells exhibit higher voltages 
than cells employing conventional aqueous systems which results in fewer 
cell units being required to operate a particular battery-powered device. 
In addition, many of the oxyhalide and halide nonaqueous cells display 
relatively flat discharge voltage-versus-time curves. Thus these cells can 
be employed to produce batteries that will provide a working voltage 
closer to a designated cut-off voltage than is practicable with some 
conventional aqueous systems which generally do not exhibit flat discharge 
voltage-versus-time curves. 
However, one possible disadvantage in the use of oxyhalide and halide 
liquid cathode nonaqueous cells is that it may be possible that during 
storage or use, some of the oxyhalide, halide or their reaction products 
may escape from the cell. This escape of liquids and/or gases could cause 
damage to the device employing the cell or to the surface of a compartment 
or shelf where the cell is stored. On the other hand, if the seal of the 
cell is effectively permanently secured, then it is possible that the 
build up of internal pressure within the cell could cause the cell's 
container to rupture which may cause property and/or bodily damage. To 
prevent rupture of the cell's container from possible internal pressure 
build up caused under abusive conditions, such as charging and exposure to 
a high temperature environment, it is necessary to vent the cell at some 
predetermined pressure. It has been reported that some oxyhalides such as 
thionyl chloride and sulfuryl chloride should be vented at pressures below 
about 500 psi and preferably between about 150 and 300 psi. 
It is, therefore, an important object of this invention to provide a safety 
non-resealable vent closure for electrochemical cells, specifically 
oxyhalide cells. 
It is another object of this invention to provide a safety non-resealable 
vent closure for cylindrical cells employing, for example, oxyhalides as 
the active cathodic material. 
It is another object of this invention to provide a safety non-resealable 
vent closure for nonaqueous cells that is inexpensive to manufacture and 
easy to assemble. 
It is another object of the present invention to provide a method for 
assembling the solid components of the cell in a container followed by 
closing the container with a cover and then adding the liquid components 
of the cell prior to assembling the safety vent closure of this invention 
onto the cell's housing. 
The foregoing and additional objects will become fully apparent from the 
following description and the accompanying drawings. 
SUMMARY OF THE INVENTION 
The invention relates to an electrochemical cell in which the active 
components of the cell are assembled within a housing comprising a 
container sealed at its open end by a cover, and having at least one vent 
orifice; the improvement being a safety vent closure comprising a 
conductive tubular member secured to the housing and surrounding the vent 
orifice, a deformable member force-fitted within the vent orifice thereby 
providing a normally fluid-tight seal over said vent orifice; and wherein 
said deformed member is adapted to be at least partially expelled from the 
vent orifice upon a build up of a predetermined internal gas pressure 
inside the cell thereby providing a permanent vent passage. 
Preferably, a layer of a sealant material such as asphalt or wax could be 
disposed within the tubular member over the deformable member and the area 
of the housing defining the vent orifice surrounded by the tubular member. 
The advantage of the sealant material is that it will provide maximum 
leakage resistance as well as further increase reliability to vent after a 
predesignated pressure builds up. Suitable sealing materials could include 
halocarbon wax which is a saturated low-molecular weight polymer of 
chlorotrifluoroethylene having the general formula: --(CH.sub.2 
--CFCl).sub.n --, asphalt, epoxy or any materials which are resilient to 
moisture, have reasonable adhesion to metal and can be applied easily. 
Preferably the material should be applied in liquid form and then set to a 
solid. 
The invention also relates to a method for assembling an electrochemical 
cell having a safety vent closure which comprises the steps: 
(a) placing the solid components of a cell within the container of a cell's 
housing, said housing comprising the container having secured at its open 
end a cover and said housing having at least one vent orifice; 
(b) feeding the liquid component of the cell through the vent orifice into 
the housing; and 
(c) force-fitting a deformable member into the vent orifice thereby 
providing a fluid-tight seal over said vent orifice. 
In the above-described method step (d) could be added as follows. 
(d) placing a layer of a sealant over the deformable member and the area of 
the housing defining the vent orifice. 
Preferably, in the above-described method the steps (a) and (d) could be 
performed as follows: 
(a) placing the solid components of a cell within the container of a cell's 
housing, said housing comprising the container having secured at its open 
end a cover and wherein at least one tubular member is secured to said 
housing and surrounds at least one vent orifice; and 
(d) placing a layer of a sealant within said tubular member over the 
deformable member and the area of the housing defining the vent orifice 
and surrounded by the tubular member. 
As used herein, the deformable material has to be made of a material or 
coated with a material that is chemically resistant to the cell's 
components, particularly the cell's liquid components, and have a hardness 
greater than 100 on the Shore A scale*. The deformable material shall also 
have a modulus of elasticity (Young's Modulus) between about 
0.01.times.10.sup.6 psi and about 28.times.10.sup.6 psi and preferably 
between about 0.03.times.10.sup.6 and 20.times.10.sup.6 psi. For 
nonaqueous oxyhalide cell systems, the deformable material can be selected 
from the group consisting of polytetrafluoroethylene, fluorinated ethylene 
propylene polymer, perfluoroalkoxyethylene polymer, ethylene 
tetrafluoroethylene polymer and the like. When the deformable material is 
to be coated with a chemically inert material, the said deformable 
material can be selected from the group consisting of nylon, lead, hard 
rubber and the like. Other suitable materials for use in this invention 
but not suitable for some of the oxyhalide cell systems are nylon, 
polypropylene, polycarbonate, acrylic polymers and the like. 
FNT *as measured on a durometer instrument manufactured by the Shore Instrument 
Mfg. Co. 
As used herein, the tubular member can be cylindrical, square, rectangular 
or have any polygonal shaped cross section. In the preferred embodiment, 
the cell will be a cylindrical cell in which the vent orifice is disposed 
in the cell's cover and wherein the conductive tubular member, which 
serves as an electrical terminal for the cell, will be a cylindrical 
member having an outwardly disposed flange at one end which is adapted for 
securing to the cell's cover. The tubular member is ideally suited as an 
element to which conductive strips can be welded to serve as external 
leads. Preferably, the deformable member should have a smooth spherical 
configuration and the wall defining the vent orifice should be 
substantially smooth. 
The safety vent closure of this invention can be made to vent at any 
predetermined pressure build up within the cell by regulating the size of 
the vent opening with respect to the size of the deformable member, the 
material of which the deformable member is made, the degree of deformation 
required of the deformable member upon its insertion into the vent 
orifice, and the shapes of the vent opening and the deformable member. 
Using the teachings of this invention, the deformable member could be 
inserted rapidly into the orifice with a minimum of force to attain a 
reliable and predictable safety vent closure. The use of a controlled 
height dead-stop ram to insert the deformable member would be most 
desirable for automatic assembly operations. 
It has been found that for 0.475 inch diameter cells an ideal safety vent 
closure can be had using a cover thickness of 0.05 inch, a circular vent 
orifice of 0.086 inch diameter, a deformable ball of 
polytetrafluoroethylene measuring 0.094 inch in diameter and a 
conventional ram employing a push-in force of 25 pounds. 
A preferred version of the safety vent closure of this invention utilizes a 
polytetrafluoroethylene ball with a halocarbon wax overseal in which the 
ball is compressed 10 to 15 percent upon insertion into a vent opening in 
a lithium/oxyhalide cell. Once inserted, the ball will assume a 
substantially spherical configuration. Cells of this type were tested and 
found to exhibit no leakage at 25.degree. C. and 100% relative humidity 
over long periods of time. In the abuse testing of these type cells 
wherein the cells were charged at up to 2 amperes and on testing of the 
cells in an incinerator at temperatures as high as 865.degree. C., all the 
cells vented properly without any container rupture. Thus the subject 
invention is ideally suited for lithium/oxyhalide cell systems, 
specifically those employing sulfuryl chloride and/or thionyl chloride. 
The safety non-resealable vent closure of this invention preferably can be 
employed with all size cylindrical cells and is ideally suited for liquid 
cathode cell systems employing, for example, a liquid oxyhalide. In 
addition to providing an excellent and effective safety venting means, the 
invention also permits the initial assembling of the solid components of a 
cell within a container that can be closed in a conventional manner before 
adding the cell's liquid component. When the cell's liquid component is an 
oxyhalide-based liquid cathode, such as thionyl chloride or sulfuryl 
chloride, then these corrosive liquids can be injected into the cell's 
housing through the small vent orifice, e.g., by vacuum filling, after the 
cell cover is secured to the container. This will effectively eliminate 
the corrosion of crimping equipment used to close the cell as well as 
eliminating contamination at the interfaces of the container-gasket and 
gasket-cover of the cell by the oxyhalide. 
A cell for use in this invention can be the split internal anode/outer 
cathode collector construction as described in U.S. Pat. No. 4,032,696 or 
the split internal cathode collector construction as described in U.S. 
Pat. No. 4,048,389, said U.S. Pat. Nos. 4,032,696 and 4,048,389 being 
incorporated herein by reference. 
Suitable nonaqueous liquid cathode materials for use in cells of this 
invention could be one or more of the liquid oxyhalides of an element of 
Group V or Group VI of the Periodic Table and/or one or more of the 
halides of an element of Group IV to Group VI of the Periodic Table, said 
Periodic Table being the Periodic Table of Elements as set forth on the 
inside back cover of the Handbook of Chemistry and Physics, 48th Edition, 
The Chemical Rubber Co., Cleveland, Ohio, 1967-1968. For example, such 
nonaqueous cathode materials would include sulfuryl chloride, thionyl 
chloride, phosphorous oxychloride, thionyl bromide, chromyl chloride, 
vanadyl tribromide, selenium oxychloride, sulfur monochloride, sulfur 
monobromide, selenium tetrafluoride, selenium monobromide, thiophosphoryl 
chloride, thiophosphoryl bromide, vanadium pentafluoride, lead 
tetrachloride, titanium tetrachloride, disulfur decafluoride, tin bromide 
trichloride, tin dibromide dichloride and tin tribromide chloride. Another 
suitable cathode material would be liquid sulfur dioxide. 
Anodes suitable for use in nonaqueous liquid cathode cell systems can be 
generally consumable metals and include the alkali metals, alkaline earth 
metals and alloys of alkai metals or alkaline earth metals with each other 
and other metals. The term "alloy" as used herein is intended to include 
mixtures; solid solutions such as lithium-magnesium; and intermetallic 
compounds such as lithium monoaluminide. The preferred anode materials are 
the alkali metals and particularly lithium, sodium and potassium. When 
using lithium anodes the anode may be coated with a vinyl resin as 
disclosed in U.S. Pat. No. 3,993,501, said patent incorporated herein by 
reference. 
The cathode collector for use in liquid cathode cell systems has to be 
electronically conductive so as to permit external electrical contact to 
be made with the active cathode material and also provide extended area 
reaction sites for the cathodic electrochemical process of the cell. 
Materials suitable for use as a cathode collector are carbon materials and 
metals such as nickel, with acetylene black being preferable. In addition, 
the cathode collector when made of a particulate material should be 
capable of being molded directly within a can or capable of being molded 
into various size discrete bodies that can be handled without cracking or 
breaking. To impart a cohesive characteristic to some types of cathode 
collectors, such as carbonaceous cathode collectors, a suitable binder 
material, with or without plasticizers and with or without stabilizers, 
can be added to the cathode collector materials. Suitable binder materials 
for this purpose may include vinyl polymers, polyethylene, polypropylene, 
polyacrylics, polystyrene and the like. For example, 
polytetrafluoroethylene would be the preferred binder for cathode 
collectors for use with liquid oxyhalide cathodes. The binder, if 
required, should be added in an amount between about 5% and about 30% by 
weight of the molded cathode collector since an amount less than 5% would 
not provide sufficient strength to the molded body while an amount larger 
than 30% would wetproof the surface of the carbon and/or reduce the 
available surface of the carbon, thereby reducing the activation site 
areas required for the cathodic electrochemical process of the cell. 
Preferably, the binder should be between 10% and 25% by weight of the 
cathode collector. Of importance in selecting the materials for the 
cathode collector is to select materials that will be chemically stable in 
the cell system in which they are to be used. 
A solute for use in liquid cathode cell systems may be a simple or double 
salt which will produce an ionically conductive solution when dissolved in 
a suitable solvent. Preferred solutes for nonaqueous systems are complexes 
of inorganic or organic Lewis acids and inorganic ionizable salts. The 
only requirements for utility are that the salt, whether simple or 
complex, be compatible with the solvent being employed and that it yield a 
solution which is ionically conductive. According to the Lewis or 
electronic concept of acids and bases, many substances which contain no 
active hydrogen can act as acids or acceptors of electron doublets. The 
basic concept is set forth in the chemical literature (Journal of the 
Franklin Institute, Vol. 226, July/December, 1938, pages 293-313 by G. N. 
Lewis). 
A suggested reaction mechanism for the manner in which these complexes 
function in a solvent is described in detail in U.S. Pat. No. 3,542,602 
wherein it is suggested that the complex or double salt formed between the 
Lewis acid and the ionizable salt yields an entity which is more stable 
than either of the components alone. 
Typical Lewis acids suitable for use in conjunction with liquid oxyhalide 
cathodes include aluminum fluoride, aluminum bromide, aluminum chloride, 
antimony pentachloride, zirconium tetrachloride, phosphorus pentachloride, 
boron fluoride, boron chloride and boron bromide. 
Ionizable salts useful in combination with the Lewis acids include lithium 
fluoride, lithium chloride, lithium bromide, lithium sulfide, sodium 
fluoride, sodium chloride, sodium bromide, potassium fluoride, potassium 
chloride and potassium bromide. 
It will be obvious to those skilled in the art that the double salts formed 
by a Lewis acid and an ionizable salt may be used as such or the 
individual components may be added to the solvent separately to form the 
salt or the resulting ions in situ. One such double salt, for example, is 
that formed by the combination of aluminum chloride and lithium chloride 
to yield lithium aluminum tetrachloride. 
If desired, and specifically for the halides, a cosolvent should be added 
to the liquid active reducible cathode and solute solution to alter the 
dielectric constant, viscosity or solvent properties of the solution to 
achieve better conductivity. Some examples of suitable cosolvents are 
nitrobenzene, tetrahydrofuran, 1,3-dioxolane, 3-methyl-2-oxazolidone, 
propylene carbonate, .gamma.-butyrolactone, sulfolane, ethylene glycol 
sulfite, dimethyl sulfite, benzoyl chloride, dimethoxyethane, dimethyl 
isoxazole, diethyl carbonate, sulfur dioxide and the like. 
Suitable separators for use with liquid cathodes in nonaqueous cells 
suitable for use in nonaqueous liquid cathode cell systems are the 
nonwoven glass separators, preferably those separators that incorporate 
long glass fibers along with the short glass fibers since such a 
combination increases the tear strength of the separators thereby making 
them easier to handle. 
The container of the cell could be made of stainless steel, iron, nickel, 
plastic, coated metals or some other suitable material. 
Some preferred combinations of nonaqueous cathode materials and anodes 
would be as follows: 
(1) sulfuryl chloride/Li or Na; 
(2) thionyl chloride/Li or Na; 
(3) phosphorus oxychloride/Li or Na; 
(4) sulfur monochloride/Li or Na; 
(5) sulfur monobromide/Li or Na; 
(6) selenium tetrafluoride/Li or Na. 
Preferably, the cells for use in this invention would be liquid oxyhalide 
cells using sulfuryl chloride, thionyl chloride or mixtures thereof with a 
lithium anode. 
It is to be understood that the safety vent closure of this invention could 
be used in other cell systems such as, for example, Leclanche dry cells, 
zinc chloride cells, lithium-MnO.sub.2 cells, lithium-iron sulfide cells, 
alkaline-MnO.sub.2 cells, nickel-cadmium cells, and lead-acid cells. 
The present invention will become more apparent from the following 
description thereof when considered together with the accompanying drawing 
which is set forth as being exemplary of embodiments of the present 
invention and is not intended in any way to be limitative thereof and 
wherein.

Referring in detail to FIG. 1, there is shown a cross sectional view of a 
cylindrical cell comprising a cylindrical container 2 having disposed 
therein a cathode collector shell 4 in contact with the inner upstanding 
circumference of the container 2 thereby adapting the container as the 
cathodic or positive terminal for the cell. Disposed within and in contact 
with the inner circumference of cathode collector 4 is a separator liner 6 
with its bottom separator or disc 10. If desired, the cathode collector 
material could be extruded within the container 2, rolled with the 
container material or composed of one or more segments to form a 
cylindrical tube and then placed in the can. 
A two member anode 12 is shown in FIGS. 1 and 2 comprising a first half 
cylindrical annular member 14 having flat end faces 16 and 18 and a second 
half cylindrical annular member 20 having flat end faces 22 and 24. When 
the flat end faces of each cylindrical half member are arranged in an 
opposing fashion as shown in FIGS. 1 and 2, an axial cavity 26 is defined 
between the cylindrical half annular members 14 and 20. 
If desired, arcuate type backing sheets 15 and 17, such as inert 
electrically conductive metal screens or grids, could be disposed against 
the inner surface wall of the anode bodies 14 and 20, respectively, to 
provide uniform current distribution over the anode. This will result in a 
substantially uniform consumption or utilization of the anode while also 
providing a substantially uniform spring pressure over the inner wall 
surface of anode as will be discussed below. 
An electrically conductive spring strip 28 is appropriately bent into a 
flattened elliptically shaped member having an extending end 30. When 
inserting the spring strip 28 into a container, the legs 32, 34 of the 
conductive strip 28 are squeezed together and forced into the axial 
opening between the two screen backed anode members arranged in a 
container as shown in FIGS. 1 and 2. The inserted conductive spring strip 
28 resiliently biases the two anode members 14 and 20 via backing screens 
15 and 17 so as to provide a substantially uniform and continuous pressure 
contact over the inner wall of the anode members. The extended end 30 of 
spring strip 28 is shown projected above the surface of anode members 14 
and 20. An insulating gasket 36 has a central opening 38 through which the 
projected end 30 of the spring strip 28 passes, whereupon the end 30 is 
then welded to a cover 40 thereby adapting the cover 40 as the anodic or 
negative terminal of the cell. 
Secured to the cover 40 is a cylindrical cap 42. Specifically, the 
cylindrical cap comprises a cylindrical segment 41 terminating at one end 
with an outwardly oriented flange 44 which is secured to cover 40. 
The insulating gasket 36 has a peripheral depending skirt 52 disposed 
between the cover 40 and the upper inner wall of the container 2 for 
closing the cell through conventional crimping techniques. As shown in 
FIG. 1, the cylindrical cap is secured to the cover 40 and the cell is 
closed using conventional crimping techniques with all of the solid 
components of the cell assembled within the container 2. After the cell is 
assembled with the solid components, a hypodermic needle 54 or the like is 
used to inject the liquid component into the assembled cell. Specifically, 
a cathode-electrolyte comprising a suitable salt dissolved in an 
oxyhalide, a halide with a cosolvent or mixtures thereof can be dispensed 
through the cover vent orifice 25 into cavity 26 using the hypodermic 
needle 54 whereupon it can penetrate through the separator and cathode 
collector of the cell. 
As shown in FIG. 3, with the cell's liquid component fed into the 
container, a polytetrafluoroethylene deformable ball 56 is disposed over 
opening 25 in cover 40 and then a ram member 58 is used to force ball 56 
into vent orifice 25 as shown in FIG. 4. After removal of the ram 58, a 
layer of a sealant 60 is disposed over ball 56 and cover 40 within 
cylindrical member 42 producing a fully sealed cell employing the safety 
vent closure of this invention. 
Preferably prior to the adding of the liquid component of the cell, a 
vacuum could be created within the cell whereupon the liquid component 
could then be drawn effectively into the cell and uniformly distributed 
therein. 
The safety vent closure of this invention will provide a means for venting 
of rapidly generated high pressure gas built up within a cell thereby 
preventing the rupture of the cell's container. 
The following examples are illustrative of the present invention and are 
not intended in any manner to be limitative thereof. 
EXAMPLE 1 
Several cells were made in accordance with FIGS. 1 to 5 using the following 
components: 
anode of lithium, 
cathode collector of polytetrafluoroethylene-bonded acetylene black, and 
thionyl chloride containing 1.5 M LiAlCl.sub.4. 
Each cell measured 0.475 inch diameter and was 1.63 inches long. The vent 
orifice measured 0.109 inch in diameter and was 0.05 inch long. The 
polytetrafluoroethylene ball was 0.125 inch in diameter and was 
forcefitted into the vent orifice as shown in FIG. 4. A layer of 
halocarbon wax (obtained from Halocarbon Industries, New Jersey) was 
deposited over the polytetrafluoroethylene ball and the area defining vent 
orifice as shown in FIG. 5. 
Several of the above-described cells were heated in a direct flame at a 
temperature up to about 865.degree. C. All of the cells vented without 
rupturing the cells' containers. Contrary to this, cells using the 
above-identified components and sealed in a conventional manner would 
generally show some container rupture when subjected to the same test 
conditions. 
EXAMPLE 2 
Several cells were constructed using the same components as in Example 1 
and employing the resealable vent closure of this invention. The cells 
were charged at 2 amperes and all were observed to vent without rupturing 
of the cells' containers. Contrary to this, cells using the 
above-identified components and sealed in a conventional manner would 
generally show some container rupture when subjected to the same test 
conditions.