Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates to the conversion of chemical energy
to electrical energy, and more particularly to a solid electrol~te
primary cell having a lithium anode, a chlorine cathode and a
lithium chloride electrolyte.
In recent times a solid electrolyte primary battery has been
developed to provide relatively high voltage and high energy
de~sity in a battery which is especially useful for long life,
low current drain applications. Lithium is generally recognized
as the most satisfactory material for the negative electrode, i.e.
the anode on discharge, in a non-aqueous cell. In selecting a
material for the positive electrode, i.e. cathode on discharge it
- i~ necessary to consider, among other factors, relative chemical
activity and energy density.
SUMMARY OF THE INVENTION
In one particular aspect the present invention provides
a lithium-chlorine cell comprising an anode conRisting essentially
of solid lithium, a sold lithium-chlorine electrolyte and a
` chlorine cathode.
In another particular aspect the present invention provides
a lithium-chlorine cell comprising: a) a casing of electrically
conducting material; b) anode means positioned within said casing
and comprising a lithium element having an exposed surface portion
and another surface portion; c) electrical conductor means
operatively connected to said other surface portion of said
lithium element ànd extending from said casing; d) means for
sealing said conductor means from the remainder of said cell; and
` e) a chlorine cathode within said casing and in operative contact
with said exposed surface portion of said llthium element and
with said casing in a manner such that said casing serves as a
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cathode current collector.
In yet a further particular aspect the present invention
provides a method of making a lithium-chlorine cell comprising
the steps of: a) providing a cell assembly comprislng lithium
anode means within a casing; b~ cooling said assembly to a
temperature sufficiently low to condense chlorine gas; c)
introducing chlorine gas to said casing to provide liquid in
said casing in operative relationship with said litbium anode
means; and d) sealing said casing.
The foregoing and additional advantages and characterizing
features of the present inve~tion will become clearly apparent
upon a reading of the ensuing detailed description tPgether with
the included drawings wherein:
BRIEF DESCRIPTION OF THE DRAWING FIGURES
Fig. 1 is a cross-sectional view of a lithium-chlorine
cell according to one embodiment of the present invention;
Fig. 2 is a side elevationai view wlth parts removed of a
cell according to another embodiment of the present invention at
one stage of assembly;
Fig. 3 illustrates the cell of Pig. 2 at another stage of
assembly; and
Fig. 4 is a fragmentary elevational view of one means
of closing the filling element in the cell of Figs. 2 and 3.
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DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
In the development of solid electrolyte batteries, lithium
is recognized as a very desirable material for the negative
electrode, i.e. the anode on discharge, in a non-aq~eous cell.
The cell of the present invention includes a lithium anode
and a chlorine cathode to utilize the desirable characteristics of
chlorine, among which are a significant degree of chemical
activity,a moderately low molecular weight, and a significant
level of energy density.
Referring now to the drawing, a lithium-chlorine cell accord-
ing to the present invention is generally designated lO and
includes a housing or casing element having a generally cup-shaped
base portion 12 and a peripheral rim or flange portion 14. The
base portion 12 can be of rectangular or circular configuration,
and the casing is of a material which is non-reactive with
chlorine. One form of material found to perform satisfactorily
is a fluoropolymer material commercially available under the
name Halar, a trademark of the Allied Chemical Company. The cell of
the present invention includes an anode in the form of a solid
lithium element 20 and a current collector element 22 contacting a
surface d lithium element 20. The term "solid" is meant to define
the lithium element as being in the solid phase. An anode lead 24
connected such as by welding at one end to current collector 22
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extends out through an aperture in the housing base portion 12
for making external electrical connection to a load circuit. In
forming the anode for the cell of the present invention, current
collector 22 is moved into position adjacent the inner surface of
the base portion 12 and lead 24 is inserted through the opening
and used to draw or pull current collector 22 tightly against the
surface of the housing. If desired, an element or button 26 of
anode material, i.e. lithium, can be placed between collector 22
and the surface of casing 12 as shown in the drawing. The current
collector 22 can comprise No. 12 zirconium mesh having a thickness
of about 0.004 inch and lead 24 can be a relatively thin strip of
zirconium. Then lithium element 20, initially in plate or sheet
form, is placed in casing portion 12 adjacent collector 22. The
entire assembly then is positioned in a suitable holding fixture
and then force is applied to the exposed surface of lithium ele-
ment 22 in a manner forcing or extruding it along the inner sur-
face of casing portion 12 and along the inner surface of casing
portion 1~ so that it conforms to the inner surface of the casing
with a resulting shape as shown in the drawing. A seal or patch
28 of suitable material, for example a fluoropolymer materially
commercially available from the Dupont Company under the trademark
Tefzel, can be placed over the outer surface of the housing around
the aperture through which lead 24 extends and sealed in place by
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a suitable cement such as the cyanoacrylate cement commercially
available from Techni-Tool Inc. under the designation Permabond
100. In addition, the exposed surface of lithium element 20 pre-
ferably is provided with a coating 30 of an organic electron donor
component material, and the nature of coating 30 and its role
in the cell of the present invention will be described in further
detail presently.
The cell of the present invention further comprises a chlor-
ine cathode including a region of cathode material 32 within the
assembly and operatively contacting lithium element 20 and a
cathode current collector 34 operatively contacting the cathode
material 32. According to a preferred mode of the present inven-
tion, the cathode material 32 comprises a charge transfer complex
of an organic donor component and chlorine. A preferred organic
donor component is polyvinyl pyridine polymer and in particular
two vinyl pyridine polymer. Cathode material 32 preferably com-
prises a mixture of chlorine and poly-two-vinyl pyridine prepared
in a manner which will be described in detai~ presently. A
quantity of the cathode material is placed in the assembly in
contact with the coated lithium element 20 and in an amount filling
the open interior region. A cathode current collector and lead
combination is positioned in the assembly and in contact with
the cathode material. Cathode current collector 34, which can
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comprise No. 12 mesh platinum metal, is secured at the periphery
such as by welding to one end of a cathode lead 36 which can be
a thin strip of platinum iridium alloy, which is enclosed by a
sheet of insulating material 38, for example the aforementioned
Halar~material, which lead 36 extends out from the periphery of
the casing for making external electrical connection thereto.
Then a casing closure element 40 in the form of a sheet of suit-
able material is placed over the end of the assembly in contact
with the peripheral rim or flange 14 and the components are then
heat sealed together. The marginal or peripheral portion of
sheet 40 and the rim or flange 14 therefore must be of a material
which is heat sealable, and this requirement is satisfied by the
aforementioned Halar~material. Heat sealing is performed by
placing the assembly in a suitalbe fixture and applying a heated
platen to the peripheral end or flange portion at a temperature
of about 495F + 5F and at a force of about 60 pounds + 10
pounds which have been found suitable to provide an adequate seal.
While heat is being applied to the periphery of the assembly, the
remainder of the cell assembly can be subjected to low temperature
refrigeration or gas to prevent expansion and leakage of the
cathode material 32.
The lithium-chlorine cell according to the present invention
operates in the following manner. As soon as the chlorine-contain-
;~ ing cathode material 32 placed in the assembly operatively contacts
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lithium element 20, a solid lithium-chlorine electrolyte begins
to form at the interface, and an electrical potential difference
will exist be~ween the anode and cathode electrical leads 24 and
36, respectively, when the current collectors are in operative
position. The mechanism by which the foregoing is accomplished
is believed to include migration of lithium ions through the
electrolyte whereby lithium is the ionic species in the cell.
The following illustrative example explains in further detail
a method of making the cathode material 32 and the operation of
the cell.
Example I
One gram of poly-two-vinyl pyridine was placed in a 200 ml.
pressure reactor, and the sealed vessel was pressurized with
chlorine gas to 85 p.s.i.g., the tank pressure being 85 p.s.i.g.
maximum. The reaction was allowed to proceed for 20.75 hours,
and then the excess chlorine was vented and the vessel was opened.
About 50 to 75 percent of the so~id material in the vessel had a
purplish black color, but the physical condition of the material
otherwise resembled that of the polymer material initially placed
in the vessel. The crude weight of the reaction product was 2.0
grams, and therefore during the reaction 1.0 gram of chlorine had
been consumed or absorbed. The mole ratiot of C12 to poly-2-vinyl
pyridine monomer was .0141/.0095 = 1.48. The dark reaction product
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was bottled loosely and allowed to stand over a weekend, Then
20 drops of propylene glycol were introduced to the product and
the bottle or container was tightly stoppered. After about one
hour the entire mass turned black and was observed to be sticky
and self-adhering, i.e. in a somewhat agglutinated condition.
The mass was placed in a cell assembly similar to that illustrated
in Fig. 1 wherein the lithium anode was unscraped but coated with
organic ~lectron donor component material as described in connec-
tion with Fig. 1. Instead of heat sealing ~osure element 40 and
flange 14 as in the assembly of Fig. 1, a current collector screen
and flat plastic sheet were used to close the cell which was
held together by mere finger pressure. Initially a cell voltage of
3.0 volts open circuit was measured, and this was observed to
build rapidly. After a few minutes, the measured open circuit
voltage was greater than 3.2 volts and observed to be climbing.
Then the cell was taped shut all around and measured voltage was
3.64 volts and climbing. The cell was preserved for further
observation in a sealed vessel containing a dessicant or similar
material to maintain a dry atmosphere.
Referring again to the cell of Fig. 1, the material of coat-
ing 30 on lithium element 20 is an organic electron donor material
of the group of organic compounds known as charge transfer complex
donors, The material oi the coating can be the organic donor
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used in preparing the charge transfer complex of the cathode mat-
erial 32, but other materials can be employed. A preferred mater-
ial for the coating is polyvinyl pyridine and it is applied to the
exposed surface of lithium element 20 in the following manner. A
solution of poly-2-vinyl pyridine polymer in anhydrous benzene
or other suitable solvent is prepared. The poly-2-vinyl pyridine
is readily commercially available. The solution is prepared
with 2-vinyl-pyridine present in the range from about 10% to about 20%
by weight with a strength of about 14% by weight of 2-vinyl-pyridine
being preferred. While 2-vinyl pyridine, 4-vinyl pyridine
and 3-ethyl 2-vinyl pyridine can be used, 2-vinyl pyridine is
preferred because of its more fluid characterist~sin solution.
When the solution is prepared at a strength below about 10%
the resulting coating can be undesirably too thin and when the solu-
tion is prepared at a strength greater than about 20% the material
becomes difficult to apply. The solution is applied to the ex-
posed surface of each lithium plate in a suitable manner, for
example simply by application with a brush and this preferably
is done in a dry room having an atmosphere wherein the relative humi-
dity is less than one percent. The presence of the anhydrous
benzene serves to exclude moisture thereby preventing any adverse
reaction with the lithium plate. The coated anode then is ex-
posed to a desiccant in a manner sufficient to remove the benzene
from the coating. In particular the coated anode is placed in a
chamber with barium oxide solid material for a time
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sufficient to remove the benæene, which can be in the neighbor-
hood of 24 hours.
Figs. 2-4 illustrate a lithium-chlorine cell according to
the present invention wherein the cathode material is formed from
liquid chlorine. Fig. 2 illustrates the cell at a stage of
assembly prior to introduction of chlorine. The cell comprises
a casing 44, preferably of electrically conducting material such
as stainless steel, having spaced-apart side walls, one of which
is designated 46, which are joined by spaced apart end walls 48
and 50. Casing 44, being of electrically conducting material,
serves as a cathode current collector. The casing includes a
curved bottom portion 52, and the opposite, open end of casing 44
is sealed closed by a lid member 54 fitted therein which also is
of metal such as stainless steel. A lithium anode means in cas-
ing 44 comprises a pair of plate-like lithium elements, one plate
56 being shown in Fig. 2, sandwiched together against a current
collector element (not shown) and surrounded snugly by a sealing
strap or frame element 58 at the peripheral edges thereof.
Strap 58 is of material which is non-reactive with chlorine, for
example a fluoropolymer material commercially available under the
name Halar, a trademark of Allied Chemical Company.
An anode electrical conductor 60 which is joined at one end
to the current collector (not shown) extends out from the assembly
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of lithium ~ates through aligned openings in the overlapping
ends of strap 58. Conductor 60 is sealed from the remainder
of the cell by means including an insulator element 62 which surr-
ounds conductor 60 and has a first portion (not shown) which is
sandwiched between the lithium plates and a second portion which
is cylindrical and located between the lithium plates and lid 54
when the cell is completed. Insulator 62 is of a material which
in addition to being a non-conductor of electricity also is non-
reactive with chlorine, for example this afore-mentioned Halar~
material. A ferrule 64 of metal such as stainless steel encloses
: a further portion of conductor 60. Ferrule 64 can be threaded
at one end (not shown) and is connected into insulator 62, the
inner surface thereof (not shown) which also can ~e threaded.
Ferrule 64 is of generally hollow cylindrical shape, and the
region between ferrule 64 and conductor 60 can be filled by a
glass seal formed therein to provide a metal-glass hermetic seal.
The exposed end of conductor 60 outwardly of casing 44 provides
external electrical connection to the cell.
The exposed or operative surfaces of the anode lithium
plates are coated with an organic electron donor material as
previously described. In some instances it may be advantageous
to introduce an organic electron donor material into operative
relationship with the lithium anode prior to introducing chlorine.
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An organic electron donor material found to perform satisfactor-
ily is polyvinyl pyridine polymer, in particular two-vinyl pyri-
dine polymer, and as shown in Fig. 2 the material is in the form
of a pellet or wafer, one of which is designated 66 in Fig. 2.
It is preferred to include two such pellet~ or wafers in a cell,
one adjacenteach exposed face of the lithium anode. Alternatively
the organic electron donor material can be introduced in the
form of crystals placed in the cell casing in a measured quantity
adjacent both sides of the lithium anode.
After the anode assembly is placed in casing 44 and the
organic electron donor material, if used, is introduced, the cas-
ing is sealed by means of lid member 54. Lid member 54 is pro-
vided with a filling element 68 in the form of a metal tube fixed
to lid member 54 and having a passage 70 therethrough. Tube 68
preferably is a separate element which is fitted at one end and into
an aperture provided through lid 54 and welded thereto. Alter-
natively, the lid 54 and tube 68 could be formed integrally from
a single piece of metal. Lid 54 is fitted into the open end of
casing 44 with an aperture in lid 54 receiving the ferrule 64 in
a tight-fitting manner whereupon the lid is sealed to the casing
by welding at 72 around the peripheral edge thereof to the corres-
ponding edge of the casing.
The cell is completed by introducing chlorine through
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passage 70 in the filling element 68 into the interior of the
casing into operative relationship with the lithium anode. In
particular, a small dlameter tube or conduit 74 leading from a
supply of chlorine (not shown) is placed in fluid communication
with passage 70, and in the present instance tube 74 is inserted
into and along within element 68 so that the open end of the
tube 74 is within the casing 44. Liquid chlorine in a measured
quantity or volume is conveyed from the supply through the tube
74 into the casing 44, the level of chlorine at this illustrative
stage of assembly being designated 76 in Fig. 3. Tube 74 can
have an outer diameter such that it fits relatively snugly within
the passage 70 to prevent or minimize escape of chlorine gas from
within casing 44 to the outside. If desired, the tube 74 can
carry a suitable seal for engaging the end of filling element 68
or the entire filling assembly and cell can be cooled below the
vapor point of chlorine. The amount of liquid chlorine intro-
duced to casing 44 generally will be sufficient to at least cover
the exposed surfaces of the lithium plates, and often will be
filled to a level above the anode assembly and below the lid 54.
After the predetermined amount of chlorine is introduced to
casing 44, conduit 74 is removed from the filling element 68 and
the passage 70 is sealed closed. As shown in Fig. 4, the outer
end of tube 68 is pinched or otherwise mechanically formed into
a flattened, clamped portion 78 which then can be further sealed
by welding. Other means for sealing the passage 70 can be employed.
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The metal tube 68 preferably of nickel also serves as an electri-
cal terminal inasmuch as the casing 44 serves as a cathode current
collector.
In situations where an organic elec~ron donor material is
introduced prior to the chlorine, i.e. the pellets 66 of poly-2-
vinyl pyridine, the chlorine introduced to the casing reacts with
the organic electron material, and the reaction product is a
charge transfer complex of an organic electron donor component,
i.e. poly-2-vinyl pyridine, and chlorine. Thus, chlorine-containing
cathode material is formed in casing 44 upon introduction or
in;ection of chlorine to the interior thereof.
The lithium-chlorine cell shown in Figs. 2-4 operates in
the following manner. As soon as the chlorine cathode material
operatively contacts the lithium anode elements, a solid lithium-
chlorine electrolyte begins to form at the interface, and an
electrical potential difference will exist between anode lead 60
and cathode terminal 68 when the current collectors are in opera-
tive position. The mechanism by which the foregoing is accom-
plished is believed to include migration of lithium ions through
the electrolyte whereby lithium is the ionic species in the cell.
The following illustrative example explains in further detail
the lithium-chlorine cell of the present invention wherein
the cathode material is formed from liquid chlorine.
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Example II
A cell assembly similar to that shown in Figs. 2 and 3
including a stainless steel casing and lithium anode coated
with poly-2-vinyl pyridine was cooled to a temperature of about
-70C by immersing the cell assembly in a bath of dry ice and
acetone. Gaseous chlorine was bubbled into the cell enclosure by
means of a supply tube inserted into the hollow metal inlet tube
leading from the casing lid similar to the metal tube or filling
element 68 shown in Figs. 2 and 3. In particular, a very fine
syringe needle was attached to one end of a length of small bore
plastic tubing, the other end of which was connected to the outlet of
a chlorine gas cylinder or similar supply. The needle was inserted
in the cell metal inlet tube, and with the cell cooled in the dry
ice-acetone bath, the chlorine gas was slowly introduced. The
gas condensed into liquid chlorine in the call and this is con-
tinued for a time sufficient to provide an adequate volume of
liquid chlorine, usually an amount which will cover the lithium
anode. Thereafter, the cellcasing was cooled further by pouring
liquid nitrogen over it. The supply tube was removed and the
casing metal inlet tube was ~elded shut thereby completely seal-
ing the casing. The difference between 12.0 grams gross weight
and 11.7 grams tare weight indicated about 0.3 gram chlorine in
the cell. The cell open circuit voltage initially was observed
to be 2.973 volts which then fell to 2.90 volts and thereupon
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rose to 3.1 volts in one hour. In the foregoing method, using
the dry ice-acetone system enables the cell itself to serve as
the condensing unit and avoids any freezing in the cell metal
inlet tube.
It is therefore apparent that the present invention accom-
plishes its intended objects. While several embodiments of the
present invention are described in detail, this is for purpose
of illustration, not limitation.
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