Note: Descriptions are shown in the official language in which they were submitted.
1078008
This invention relates to means for filling and
hermetically sealing electric cells and more particularly to
ultraminiature cylindrlcal cells utilizing a lithium anode
~nd a high ener~y density cathode material.
In my U.S Patent ~os. 4,028,138 and 4,091,188
I described an ultraminiature eell which is useful in many
applications where space limitations make such an ultra-
miniature eell especially beneficial. The invention
described therein utilizes the high energy content that can
be obtained with a lithium-silver chromate system. That
application was directed to construction of miniature eells
and to a method of making sueh miniature eells having dimensions
on the order of a diameter of 0.1 inch and a length of 0.75
inch and to eells with a volume up to 0.~1 ineh3 . In the cells
dlselosed therein, advantage is taken of the high energy content
that ean be disposed, in this small volume, by using a lithium
anode and a silver ehromate eathode.
However, one of the major problems in manufaeturing
any closed electrie cell is encountered in sealing the eell. In
the construction of a miniature cell of the dimensions here
involvea, the sealing problem is espeeially diffieult. ~'oreover,
the preSence of lithium or any other chemically active alkali metal
as an element or component in the cell requires that all of the
~ssembly work be done in a dry atmosphere sinee the presence of
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any water would introduce hazardous conditions because of the
extreme activity of lithium in the presence of moisture. The
necessity o~ assembling and sealin~ the cell in a dry atmosphere
introduces complications in the handling, the sealing and the
filling operations.
The present invention provides both a design
construction and a method of assembly and filling which
assures the formation and maintenance of an hermetic seal,
and which permits filling an already sealed cell container
without destroying the seal. The resulting cell will
maintain hermeticity and prevent leakage of volatile
electrolyte, thereby retaining the electrolyte needed for the
proper performance of the cell.
In accordance with one embodiment of the invention,
described in my U.S, Patent Nos. 4,02~,138 and 4,091,188
the ultraminiature cell is constructed with a container
casing formed from thin hollow tubing on whose inner surface a
porous layer of an active cathode material such as silver
chromate (Ag2CrO4) is formed.
A small, elon~ated, cylindrical anode of lithium
metal i5 formed around a linear, metallic hollow tube which
is used as current collector, as support for the lithium, and
as electrolyte ~ill ort. The anode thus formed is enwrapped
in one or more layers of thin, insulating, separator material,
such as microporous polypropylene, and this assembly of anode
and separator ls then axially inserted into the axially
disposed space within the surrounding cvlindrical cathode layer.
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In order to seal the ultraminiature cells of the
present invention, the outer extending end of the anode
collector tube is anchored in a cell top by a glass to metal
seal, prior to or during the preparation of the lithium anode.
The hollow tube or needle is joined by an insulative glass
member or ring to a metal ring, which can be either the entire
cell top or just a portion thereof (in larger cells). The
metal ring is hermetically sealed to the cell casing or to the
cell top itself if the metal ring is only a portion thereof.
The hollow tube serves both as the filling conduit
and as an anode collector pin which supports the body of the
lithium anode material, and is permanently disposed and sealed
in the cell top. After the cell has been filled with the
desired amount of electrolyte the input end of the hollow
needle, outside of the cell, is closed off and welded at its
outer end. This completes the seal for the cell.
According to a broad aspect of the present invention,
there is provided an electrochemical cell having an hermetic
seal assembly for closing the open end of the container for
the cell. The hermetic seal assembly comprises a metal rod,
a ring shaped glass member concentrically sealed to the metal
rod at its upper end, and a metal member sealed to the glass
member. The metal rod has liquid passage means therethrough
and is an electrical terminal for the cell and an electrolyte
fill port, with the upper end of the rod having been closed
after the introduction of the electrolyte to close the liquid
passage. The metal rod is in contact with an active electrode
material of the cell and is formed of a metal which is different
from but chemically compatible with the active electrode mater-
ial. The glass member has a thermal coefficient of expansion
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substantially similar to the metal comprising the tube. Theglass member is inert with respect to material contained with-
in the cell and the metal member is hermetically permanently
sealed to the container at the said open end.
The construction of the cell, and the method of
forming, sealing and filling the cell are explained in more
detail in the following specification and are illustrated in
the accompanying drawings in which:
Figure 1 is a vertical cross-section view of a
cell utiliziny a glass to metal seal as the hermetic closure
and cell top.
Figure 2 is a second embodiment of a glass-to-metal
hermetic seal for an electrochemical cell.
Figure 3 is a third embodiment of the invention
wherein the cell has two glass-to-metal feed throughs.
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In the embodiment of the invention shown in ~igure 1
a glass tQ metal seal is used to hermetically seal a cell 110
haying a hollow tantalum tube 112 which acts as current
collector for a concentric, axially disposed lithi~m anode 114.
Tube 112 extends beyond both ends of the anode. A concentric
Ag2CrO4 cathode 116 is supported on the inner wall surface of
an enclosin~ cylindrical, stainless steel can 118, with the
lithium anode 114 and th~ cathode 116 being separated by an
insulating separator 119. The upper end of the hollow tube anode
cux~ent collector 112 is sealed to a glass ring secti~n 121
Which is, in turn, surrounded by and sealed to a stainless steel
metal outer ring 122. The glass to metal bonds between the
glass ring 121 ~nd both the metal tube 112 and the metal ring
122 are hermetic and do not allow any electrolyte seepage to
the exterior of the cell.
The materials comprising the metal can 118 and the
hollow tube feedthrough 112 must be compatible with the
particular cell components with which they are in contact
and additionally the tube metal should be able to form glass
to metal seals. Thus, if the hollow feed-through 112 acts as the
anode current collector for an alkali metal such as lithium,
the particular component metals which are compatible with such
active anode materials include copper, iron, steel, stainless
steel of all types, nickel, titanium, tantalum, molybdenum,
Yanadium~ chromium and tungsten. The metals which are
compatible with a sulfur dioxide active cathode material such
as that disclosed in my U.S. Patent No . 3,945,846 and which
can provide a useful cathode current collector in a Li/S02
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cell system include aluminum~ ~itanium, tantalum, mol~bdenum,
Yanadium~ chromiu~, tungsten (all valve metals), gold and
platinum, Compatible met31s for silyer chromate active cathode
matexials disclosed in my U.S. Patent Nos, a~02~138 and 4,091,188
include titanium, tantalum, molybdenum, vanadium! chrominum,
tungsten (all valve metals except aluminum), gold, platinum
and stainless steel. Though the metals enumerated for the
sulfur dioxide and the silvex chromate materials are useful
as the outer can materials when the anode is placed upon the
holiow feed thxough, the positions and hence the materials
can be reversed when the cathode material is placed on the
hollow feedthrough as described in my U.S. Patent Nos. 4,028,138
and 4,091,188.
A requirement of the seal of the present invention
is that there be compatibility between the metal and glass
members. This involves a consideration of the relative co-
efficients of expansion of these two components. Tantalum
for example, has a coefficient of thermal expansion of about
70 x 10 7 inches per inch per C. The coefficient of expansion
of the glass member may be somewhat greater or somewhat less
than the coefficient o expansion of the met~l member. Thus
in the case of tantalum the coefficient of expansion of the
glass may be as low as about 50 x 10 7 inches per inch perC,
or as high as about 100 x 10 7 inches per inch perC.
Preferably, however, for tantalum, the coefficient of expansion of
the glass should be between about 55 and about 90 x 10 7 inches
per inch perC.
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Depending upon whether the coefficient of exansion
is larger, smaller or ahout the same as the metal member ! the
resulting seal may be res~ectively compression ! tension or
matched. All three of these types of seals are within the
scope of the present invention.
~ lost preferably, the coefficient of thermal expansion
of the glass is between 60 and 80 x l~ 7 inches per inch per
C for tantalum.
The glass also MUSt have the property that it is
essentially unattacked b~ the materials contained in the cell.
~ ny glass meeting the foregoing requirements may
be utili~ed in accordance with the present invention. O~e
exe~plary glass has been found to contain predominately silicon
oxide and minor amounts of sodium oxide, potassium oxide, and
additional oxides in even smaller amounts including one or more
of chromium oxide, manganese oxide, cobalt oxide, lead oxide and/
or ca~iu~ oxide. ~anganese oxide, chromium oxide, cobalt oxide,
silver oxide, lead oxide, calcium oxide, and zinc oxide are
optional substances and in some anplications one or more of these
substances may not be required. Furthermore~ it will be appa~nt
to those skilled in the art that many other glasses either having
some or all o~ the foregoing oxide constituents or different oxide
constituents, which have the necessary properties of coefficient
of expansion and resistance to electrolyte attack may be used in
the present invention.
One exemplary glass meeting the foregoing requirements
is Fusite Corp.'s type GC ~la~s.
The stai~less steel outer ring 122 has a larger
coefficient of expansion than that of the tantalum thereby
providing a compression seal, although other metalliC combinations
may provide matched or tension seals.
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The glass to metal seal is desirably formed prior
to the application of the lithium anode 114 to the tube 112
by placing an annular glass preform having the above-mentioned
characteristics and being of sufficient size to closely fit
within the space between the tantalum tube 112 and the outer
stainless steel ring 122. The assembly of tantalum tube,
steel ring and glass preform is heated to about 100~C to melt
the Preform and to render the viscQsity of the glass such as to
cause the molten glass to flow and when cooled to provide the
gl~ss member 121, The glass of glass member 121 bonds to the
stainless steel ring 122 and the metal tube 112 so as to form
an lntegrated metal-to-glass-to-metal seal,
Though the tube and ring merbers ha~e been described as
being tantalum and stainless steel respectively other metals
as described abo~e can be similarly used with an appropriately
matched expansion glass material.
The application of lithium to the tube is accomplished
in the manner described in my U.S. Patent Nos. 4,028,138 and
4,091,188 and the entire sub-assembly comprising rod 112 having
rings 121, 122 and anode 114 secured thereto is then fitted into
the cell cavity formed in the cathode, also as described above.
The sub-assembly is welded to the container 118 at its upper
periphery by suitable means such as electron beam or laser welding,
with the weld being effected between the steel container 118
and the metal ring 122 ~t their point of contact 123. The
metallic outer ring 122 is in the shape of a truncated cone
having a concave base, with the periphery of the base of the
ring 122 sized to fit the open end of the container 118 at its
upper periphery 123 so that only a minimal point of contact
is made between the ring 122 and the container 118 to thereby
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minimize cell component damage that could be caused from the
heat of welding.
This is an especially important feature in s~all
cells because of rapidity of heat transfer in such cells. The
electrolyte (Lr~ LiAlC14 in an equivolume mixture of tetrahydro-
furan and propylene carbonate) is introduced into the cell by
injection, as with a syringe, through the fluid passage 113 in
rod 112.
The rod 112 is of greater length than anode 114 and
extends completely therethrough so that a predetermined
amount of electrolyte fluid can be introduced through the
hollow tube 112 (e.g. by means of a syringe) to exit from the
botto~ of said tube 112 into the operating space between the
lithium anode 114 and the cathode 116. After the filling
operation, the combination tube and anode collector is
separated from the filling source, closed above the glass to
metal æsemblY, and sealed by tungsten inert gas (TIG) welding
in the manner described in my U.S. Patent Nos. 4,028,138 and
4,091,188 in which a welder with a tungsten cathode is
positioned just above the hollow tube end to be sealed, a gas
is passed through said electrode, and, on triggering the welder,
hot gas melt the tip of the tube to form a round bead of metal
thus sealing the tube.
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In a second embodiment of the invention shown in Figure 2 where-
in the cell is larger than cell 110 of Figure 1, a glass to metal, hollow
tube, feedthrough assembly having a tube 212, a glass sealing member 221
and an outer metal ring member 222 is only a part of cell top 225. Top
225 has a preformed, opening 230 concentrically positioned thereon into
which sealing assembly 211 is placed. Once assembly 211 is properly
positioned it is attached by welding or other similar means to the cell
top 225 at the periphery of the opening 230. The other components of the
cell can be placed in the cell in the same manner as described with ref-
erence to Example 1.
In another embodiment of the invention, shown in Figure 3,
there is provided a versatile cell 310 which is capable of use with a
container formed of a material which is not compatible with the active
cell components (for example, the electrolyte when in contact with a
lithium anode~. Such incompatible materials include the following
metals: aluminum, zinc, tin, magnesium, gold, platinum and silver.
It is possible to use such material by providing two glass to metal
feedthroughs as shown in Figure 3 so that it is unnecessary to use
the cell container as a terminal. In this embodiment, the cell top
325 has two preformed open circular areas 330 and 331 for the accomo-
dation of two glass to metal feedthrough assemblies 311a and 311b.
Only one feedthrough 311a is shown as being hollow for use as means
for introduction of the electrolyte solution. The other feedthrough
311b is shown as a solid rod, but both feedthroughs can have fluid
passageways therein if desired. In this way, and depending on the
location of the materials with the cell, one of the feedthroughs
becomes the negative terminal when in contact with the anodic mat-
erial, and the other becomes the positive terminal when in contact
with the cathodic material. In this embodiment the container does
not operate as a current collector and is not in contact with the
corrosive cell materials. Accordingly, metals such as aluminum can
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be used in the formation of tlle cell container. Though not shown in the draw-
ing, the electrode materials are not placed directly upon rods 312a or 312b
which function as terminals for the electrode but not as current collectors,
and the cell components are separated from the container walls by one or more
insulating separators. Suitable electrode materials for this type of cell
would include spirally wound layers of alternate lithium and carbonaceous
ribbons with an S02 or thionyl chloride solution.
While the above disclosure has described the invention with ref-
erence to lithium, it will be obvious that other anode materials, such as
the active metals of Groups IA and IIA, can also be used. In addition it
will be recognized by these skilled in the art that many organic electrolyte
solvents may be used. For example organic solvents that may be used include
tetrahydrofuran, propylene carbonate, dimethyl sulfite, dimethyl sulfoxide,
N-nitrosodimethylamine, gamma-butyrolactone, dimethyl carbonate, methyl
formate, butyl formate, dimethoxyethane, acetonitrile and N:N dimethyl
formamide, and electrolyte salts for such cells include light metal salts
such as perchlorates, tetrachloroaluminates, halides, hexafluophosphates,
and hexafluoarsenates.
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