Note: Descriptions are shown in the official language in which they were submitted.
` ~79~1~5~
BACKGROU~V OF THE I~VENTION
_ _
This invention relates to the conversion of chemical
energy to electrical energy, and more particularly to a new and
improved lithium-bromine cell and method oE making the same.
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-aqueous
cell. The cell of the present invention includes a lithium anode
and a bromine cathode to utili~e the desirable characteristics
of bromine, among which are a significant degree of chemical
activity, a moderately low molecular weight, and a significant
level of energy density. In making a lithium-bromine cell, it
is necessary to consider, among other factors~ that bromine
normally is in the form of a liquid which emits vapors.
SUMMARY OF THE INVENTION
It is therefor, an object of this invention eO provide
a new and improved lithium-bromine cell and method of making the
same.
In one particular aspect the present invention provldes
20 a method of making a lithium-bromine cell comprising the steps of:
a) providing a casing;
b) placing lithium anode means in said casing;
c) providing a filling element having a passage there-
through;
d) sealing said casing in a manner such that said
filling element is fixed to said casing with one
end of said passage in communication with the inter-
ior of said casing and the other end externally ex-
posed;
e) in~roducing bromine through said passage in said
filling element to the interior of said casing into
operative relationship with said lithium anode means;
and
,~: ~ ',.
~ -2~ ;
.
4~5~
f) closing said passage of said filling element.
In another particular aspect the present invention provides
a lithium-bromine 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 sur~ace portion of said lithium element and
0 extending from said casing;.
d~ means for sealing said conductor means from the
remainder of said cell;
e) a bromine cathode within said casing and in operative
contact with said exposed surface portion oE said lithium
element and with said casing in a manner such that said casing
serves as a cathode current collector;
f) terminal means on said casing and comprising a hollow
element of electrical conducting material having an internal
passage in communication with the interior of said casing and :
0 means closing said passage whereby prior to closing said
passage said element functions to allow introduction of bromine : :
to the interior of said casing into operative relationship with .
said lithium anode element and after closing said passage said
element functiong as an electrical terminal and an electrical
potential difference exists between said terminal and said
conductor means during operation of said ce`ll; and
g) a solid lithium bromide electrolyte formed between `:
said lithium anode.and said bromine cathode.
In a further particular aspect the present invention .
0 provides a lithium-bromine cell compr:Lsing:
a) a casing of electrically conducting material; .
b) anode means positioned within said casing and comprising
a li~hium element having an exposed surface porti.on and another
surface portion; :~
3-
.
.. . . . .
s~
- c) electrical conductor means operatively connected
to said other surface portion of said lithium element and
extending from said casing;
d) means for sealing said conductor means Erom the
remainder of said cell;
e) a bromine cathode within said casing and in operative
contact with said exposed surface portion of said lithium
element and with said casing in a manner such that said casing
serves as a cathode current collector; and
f) a solid lithium bromide electrolyte formed between
said lithium anode and said bromine cathode.
The foregoing and additional advantages and characterizing
features of the present invention will become clearly apparent
upon a reating of the ensuing detailed de-cription
..
.,
~ 20
'.
. ~ .
,.
:
.~ .
jl/ -3a-
::
I ,
,~ . .
'
~Q174~
1 together with the included drawing wherein:
BR _F DESCRIPTIO~ OF THE DRAWIMG FIGURES
Fig. 1 is a perspective view of a lithium-br~mine cell
according to the present inven-tion;
Fig. 2 is a sectional view taken about on line 2-2 in
Fig. l;
Fig. 3 is a fragmentary vertical sectional view
wi-th parts shown in eleva-tion of the cell of Fig. l;
Fig. 4 is a side elevational view with parts removed
illustra-ting a cell at one s-tage in the me-thod of the
present invention;
Fig. 5 is a side elevational view with parts removed
illustrating a cell at another stage in the method of
the present inven-tion;
Fig. 6 is a side eleva-tional view with parts removed
illustrating a cell at a stage in the method according to
another emobdiment of the present inven-tion; and ;;--
Fig. 7 is a fragmentary elevational view illustrating
an alternative means closing the filling elemen-t in the
cell of the present invention.
DETAILED DESCRIPTIO~ OF THE ILLUSTRATED EMBODIME~TS
Referring now to Fig. 1, a lithium-bromine cell
according to the present inven-tion comprises a casing 10
of me-tal such as stainless steel which preferably is shaped
or o-therwise formed to be hollow and generally rectangular
in shape of an in-tegral cons-truction including a cuxved
bo-ttom por-tion 11~ spaced-apart planar side wall por-tions
.
-4-
1~748~l~
1 123 13 extending from the bottom portionl and spaced-
apart curved end wall portions 14, 15 also extending
from bottom por-tion 11 and joining corresponding ones
of the side wall por-tions 12, 13. The bottom portion
11 is of compound curvature in that i-t is curved both
in a direc-tion between -the side wall portions 12, 13
and also is curved in a direc-tion be-tween t~e end wall
por-tions 14~ 15. This latter curva-ture of bot-tom
port~on 11 is of the same degree as the curvature of
the end wall portions 14~ 15 -thereby defining a con-
tinuousJ curved surface around c~long the casing. The
side wall portions 12~ 13 are generally parallel.
The casing has an opened top or end opposite the bottom
por-tion 11 which is sealed closed by means of a lid 17
also of me-tal such as stainless steel.
Referring now to Figs. 2 and 3, the cell of the
present invention further includes anode means com-
prising a pair of lithium elements or plates 22, 24
having an anode current collector elemen-t 26 sandwiched
or positioned therebetween. ~s shown in detail in Fig.
3, current collec-tor 26 is a relatively -thin, preferably
a sheet of no. 12 mesh zirconium metal. A conductor
strip 28 of nic~el or suitable metal is spot welded
to collector element 26 along one edge thereol and
an e1ectrical conduc-tor 30 which can be of nickelJ
platinum or suitable metal is welded at one end to the
strip 28 and is of su~ficient leng~h allowing it to
-5-
~41~S~l
1 extend out from the casing for making external electri-
cal connection -thereto. Conductor 30 is sealed from
the remainder of -the cell by means including an in-
sula-tor element generally designa-ted 32 which surrounds
lead 30 and has a first por-tion 34 which is sand-
wiched between -the lithium plates 22, 24 and a
secondor body portion 36 which is cylindrical and lo-
cated between the lithium plates and lid 17 when the
cell is completed. The insulator 32 is of a material
which in addition to being a non-conduc-tor of electri-
city also is non-reactive with bromine. One form of
material ~ound to per~orm s-tatifac-torily is a 1uoro-
polymer material commercially available under t~e name
Halar~ a trademark of -the Allied Chemical Company.
O~ course~ other materials having -these characteris-
tics can be used for the insula-tor 32.
The anode assembly comprising -the li-thium elements
22, 24 and current collector 26 is fitted within an
anode holding means or frame in the form of a s-trap
40 which embraces the anode assembly in a manner ex-
posing at least one lithium surface. Strap 40 is of
the aforementîoned Halar material or any similar ma-
terial which is non-reac-tive wi-th bromine. In ~he
present illus-tration, s-trap 40 surrounds the peri-
pheral edges of -the lithit~ elements or plates 22,
24 in a snu~ sealing relationship. The opposi-te ends
of s-trap 40 are provided with apertures of a si~e
suf~icient to receive the insulator portion 34~ and
:
~7~
1 these ends are overlapped adjacent the insulator portion
34 as shown in Fig. 3. A ferrule 44 o~ metal such as
stainless s-teel encloses a further portion of lead 30.
Ferxule 44 is threaded at one end ~not shown~ and is con-
nected into insulator portion 36, -the inner surface of
which also is threaded. Ferrule 44 is of generally
hollow cylindrical shape, and the region between ferrule
44 and conductor 30 is filled by a g:Lass seal 46 formed
therein to provide a metal-glass hermetic seal.
One illustrative method of forming the anode assembly
is as follows. First there is provided a subassembly in-
cluding lead 30 within the combination of insulator 32
and ferrule 44. Strap 40 then is assembled into place
with the ends overlapped to align -the openings therein -
which then are fit-ted onto insulator por-tion 34. The
overlapping ends joined to insulator portion 34 can be
sealed in place with a suitable cement which is non-
reactive with bromine such as cyanoacryla-te cement
commercially available under the name Permabond 101.
Similarly, the ~nction between insulator portion 36 and
-the bot-tom portion of ferrule 44 can be cemented. Current
collector 26~ conducting strip 28 and the end o~ lead 30
are spot welded -toge-ther whereupon -the lithium plates
22, 24 are positioned wi-thin strap 40 on opposite sides
of the collector element 26 and insula-tor portion 34.
The subassembly -then is placed wi-thin a suitable fixture
or support and is prassed together wi-th a suitable force,
for example abou-t 3,000 lbs. The current collector 26,
1 strip 28, insulator portion 34 and the portion of lead 30 con-
tained therein are sealed within the lithium elements 22, 24.
The material of strap 40 is pressure bondable to lithium with
the result that the peripheral juncture at the edges of the
lithium elements 22, 24 is enclosed or sealed by the strap 40.
If desired, the junction between the inner surface of strap 40
and the periphery of lithium elements 22, 24 can be sealed
further by the aforementioned cement. The completed anode
assembly thus has two exposed surfaces which are oppositely
directed or disposed.
When the anode assembly is completed, the exposed surfaces
of lithium elements 22 and 24 are provided with coatinys 48
and 50, respectively, of an organic electron donor component
material, and the nature of the coatings 48, 50 and their
role in the cell of the present invention will be described in
further detail presently. The completed anode assembly is
positioned in casing 10 as shown in Figs. 2 and 3, with the
anode operative surfaces spaced from the inner surface of casing
10 .
The cell of the present invention further comprises a
bromine cathode including a reyion of cathode material 54 with-
in casing 10 and operatively contacting the exposed surfaces of
the lithium^elements22, 24 and operatively contacting the inner
surface of casing 10. Casing 10, being of electrically con-
ducting material, serves as a cathode current collector. Ac-
cording to a preferred mode of the present invention, the cathode
material 54 comprises the reaction product of liquid bromine
and an organic ~lectron donor material. In particular, the
- 8 -
--
. : .... . , . ... , :.: ., : , . : . .: . .
1~4~
1 cathode material 54 preferably comprises a charge transfer com-
plex of bromine and an organic electron donor component materi-
al. A preferred form of the organic electron donor component
is polyvinyl pyridine polymer and in particular two-vinyl-
pyridine polymer.
The cell of the present invention further comprises an
element 58 on the casing and having a passage 60 therethrough
which at one end thereof is in communication with the interior
of casing 10 and which at the other end is externally exposed.
In particular, element 58 is in the form of a metal tube fixed
to lid membeE 17. Tube 58 preferably a separate element which
is fitted at one end into an aperture provided through lid 17
and welded thereto. Alternatively, the lid 17 and tube 58 could
be formed integrally from a single piece of metal. Lid member
17 is fitted into pla~e in the open end of the casing and is
~ welded at 64 around the peripheral edge thereof to the corres-
- ponding edge o~ the casing. In making the cell according to the
method of the present invention, bromine is introduced through
passage 60 in the filling element 58 to the interior of the
casing and into operative relationship with the lithium anodeO
Then passage 60 is closed by suitable means, for example an
element 66 which can be a plug of material which is non-reactive
with bromine and which is sealed in place by sui-table non-
reactive cement. Other arrangements for closing passage 60
can of course be employed. The metal tube 58 preferably of
nickel also serves as an electrical terminal inasmuch as the
casing 10 ser~es as a ~athode curren-t co~ector.
.
Fi~s. 4-7 illustrate the method according to the present
'
',
~' . - ' , ,. : ~' '' ' '
. . . . , , ,:
48~i8
1 invention for making the lithium-bromine cell illustrated in
Figs. 1-3. Fig. 4 illustrates a cell at a stage of the method
prior to introduction of bromine. Thus, there is provided the
casing 10, preferably of electrically conduc-ting material such
as stainless steel, and the lithium anode means in the casing
including the pair of lithium plates, the one plate 22 being
shown in Fig. 4, surrounded by the strap or frame 40 at the
peripheral edges thereof and having the anode electrical con-
ductor 30 e~tending therefrom and out through the casing being
enclosed and insulated by the insulator element 32 and ferrule
44. The exposed or operative surfaces of the lithium plates are
coated with an organic electron donor material as previously
described. According to a preferred mode of the present in-
vention, an organic electron donor material is introduced into
operative relationship with the lithium anode means prior to
introducing bromine. An organic electron donor material found
to perform satisfactorily is polyvinyl pyriding polymer, in
particular two-vinyl pyridine polymer, and as shown in Fig. 4
the material is in the form of a pellet or wafer, one of which
is designated 70 in Fig. 4. It is preferred to include two such
pellets or wafers in a cell, one adjacent each exposed face of
the lithium anode. By way of example, in a cell wherein the
total weight of li-thium is about 1.0~ grams, each pelle-t or
wafer has a weight of about 0.5 gram and is of a size having an
outer diameter of about 1 3~32 inches and a thickness of about
0.035 inch. Alternati~ely, the organic electron donor material
can be introduced in the form of crystals generally designated
7~ in Fig. 6 placed in the cell in a measured quantity adjacent
- 10 -
. . , - , . .: . . . :
~74~Si~
1 both sides of the lithium anode.
After the organic electron donor material is placed in
casing 10 in operative relationship with the lithium anode, the
casing is sealed in a manner such tha-t the filling element or
tube 58 is fixed to the casing with one end of the passage 60
in communication with the interior of the casing and the other
end externally exposed. As i~ustrated in Fig. ~, the filling
element 58 is fixed to lid 17, which, in turn, is fitted into
the open end of casing 10 with the aperture in the lid receiv-
ing ferrule 44 whereupon the lid is sealed to the casing bymeans of the weld 64 as previously described.
The next step in the method of the present invention is in-
troducing bromine through passage 60 in the filling element 58
to the interior of the casing into operative relationship with
the lithium anode. In particular, a small diameter tube or
conduit 78 leading from a supply of bromine (not shown) is placed
in fluid communication with passage 60, and in the present illus-
tration tube 78 is insarted into and along with element 58 so
that the open end of the tube 78 is within the casing 10. Liq-
uid bromine in a measured quantity or volume is conveyed fromthe supply through the tube 78 into the casing 10, the level of
bromine at this illustrative stage of the method being designated
80 in Fig. 5. Tube 78 can have an outer diameter such that it
fits relatively snugly within the passage 60 to prevent or mini-
mize escape of bromine vapors from within casing 10 to the out-
side. If desired, the tube 78 can carry a suita~le seal for
engaging the end of filling element 58. One illustrative form
of supply and dispenser is a hypodermic syringe where conduit
- 11 -
:
8~i3
1 78 is the needle thereof. The amount of liquid bromine intro-
duced to casing 10 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 17. After the predetermined amoun-t of bromine is introduced
to casing 10, conduit 78 is removed from the filling element 58
and the passage 60 is closed as previously described. ~nother
means for closing tube 5~ is illustrated in Fig. 7 wherein the
outer end is pinched or otherwise mechanically formed into a
flatened, clamped portion 84 which then can be further sealed
by welding.
The liquid bromine in casing 10 reacts at room temperature
with the organic electron material, i.e. poly-2-vinyl pyridine,
and the reaction product is a charge transfer complex of an
organic electron donor component, i.e. poly~2-vinyl pyridine,
and bromine. Thus, the bromine-containing cathode material is
formed in casing 10 upon introduction or in~ection of bromine
to the interior thereof.
The lithium-bromine cell according to the present invention
operates in the following manner. As soon as the bromine-
containlng cathode material, for example the cathode material ;
54 in Figs. Z and 3, operatively contacts a lithium element, a
solid lithium-bromine electrolyte begins to form at the inter-
~ace. In the present illustration this occurs at the outer or
oppositely-disposed surfaces of the two lithium elements 22 and
24. An electrical~potential difference will exist between the ~ -
anode lead 30 and the cathode terminal 58 because casing 10 is
of electrically conductive ma-terial and operatively contacts
- 12 -
~0~
1 the bromine-containing cathode material -to serve as a cathode
current collector. 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 method of the present invention is efficient, effec-
tive, relatively easy to perform, and utilizes bromine in its
natural or uncombined form as a starting product. Liquid
bromine is introduced through a passage in a filling element to
the interior of a sealed casing containing other cell components
wherein the bromine-containing cathode material, i.e. a charge
transfer complex of poly-2-vinyl pyridine and bromine, is formed
in situ. Introducing or injecting bromine into a sealed cas-
ing, i.e. after the casing lid is welded in place, avoids re-
lease of bromine vapor to the surroundings thereby preventing
contamination of the atmosphere with bromine vapor and prevent-
ing interference of the bromine vapor with the weld.
In the cell of the present invention all parts of the anode -
current collector 26 and conductor 30 are shielded or sealed
from cathode material 54 and from the metal casin~ 10, 17. As
a result, no insulation is needed between the cathode material
54 and the metal casing thereby enabling the metal casing 10, 17
to contact the bromine-containing cathode material and function
as a very large cathode current collector. This improves cell
performance and increases theoretical energy density due to
the relatively large amo~nt of cathode material in contact with
the curren~ collector. Another advantage of the foregoing ar
rangement is that b~ having the filling element 58 selectri-
- 13 -
S8
1 cally conducting material, after in~ection of bromine and the
closing of passage 60, the element provides another impor-tant
function in serving as a cathode electrical terminal for the
cell.
Table I presents electrical data obtained from a lithium-
bromine cell according to the present invention as a function
of cell life in hours. For example, the data entered in the
first row of Table I was obtained sixteen hours after the cell
was placed in operation. The impedance quantities indicate
impedance measured at 100 hertz, add impedance measurements
were made with a 100 kilohm resistance connected in parallel
with the cell under test.
TABLE I
Open Circuit Voltage Cell Impedance
Cell Life in HoursIn Volts ~n Ohms
16 3.373 90
64 3.417 76
88 3.422 81
112 3.424 84
The cell from which the foregoing data was obtained included a
total lithium weight of about 1.2 grams and a total weight of -
about 1.0 gram for two pellets of poly-2-vinyl pyridine. The
. :
weight of the anode assembly was 2.24 grams prior to coating and
2.28 grams after coating. The completed cell wei~hed 13.09
grams before introduction of bromine and 27.03 grams after in-
troduction of bromine. This ne-t weight of 13.94 grams bromine
at 0.335 ampere-hours per gram energy density for bromine gives
a stoichiometric energy capacity of 4O6 ampere hours. At a
- 14 -
358
1 utilization ra-te of 76 percen-t, the cell has a nominal energy
capacity of 3.5 ampere hours. With an output voltage of 3.4
volts and a cell weight of 27 grams, the energy density of the
cell is 450 watt-hours/Kilogram [3.4 volts x 3 5 ampere hours]
The weight ratio of bromine to organic electron donor material,
i.e. poly-2-vinyl pyridine, in the completed cell is 13.94
grams: 1:04 grams or 13.3:1.
It is important that the bromine-containing cathode materi-
al 54 is not allowed to come in contact directly with any por-
tion of the electrical conducting means connected to the lithi-
um elements of the anode, in particular anode current collector
26 and leads 28,30. Otherwise, this will cause an electronic
conduction between the cathode material 54 and the anode current
collector 26 or leads 29, 30 creating an electrical short
circuit condition in the cell. In particular, any migration of
the bromine-containing cathode material 54 directly to anode cur-
; rent co~ector 26 or directly to leads 28, 30 instead of first
reacting with a lithium element of the anode will result in
a condition of electronic conduction thereby creating a short
circuit in the cell. On the other hand, when the bromine-con-
taining material 54 contacts only the lithium portion of the
anode this gives rise first to a condition of ionic conduction
and results in proper cell operation.
In the cell of the present invention, all parts of the
anode current collector 26 and leads 28, 30 are sealed from
cathode material 54 and from the metal casing. Anode current
collector 26 and its connection through strip 28 to lead 30
are sealed within the sandwiched or pressure bonded assembly of
~L07~5~
1 lithium plates 22, 24. This seal is enhanced by the strap 40
which is of Halar or similar material which is non-reactive with
bromine.
The foregoing arrangement together with the provision of
insulator 32 and ferrule 44 with glass seal 46 provides an
anode structure which is comple-tely sealed with the exception
of the oppositely-directed operative lithium surface portions
; of the anode which are available to the cathode material 54.
All parts of anode current collector 26 and leads 28, 30 are
shielded from the cathode material and from the cell casing. ~ ~ -
Furthermore, the sealed anode assembly can be completed before
the entire cell is assembled for efficiency in manufacturing.
The foregoing advantages are provided in a cell which is
relatively simple in construction.
The material of coatings 48 and 50 on lithium elements 22 ;
and 2~, respectively, is an organic electron donor material of -~
the group of organic compounds known as charge transfer complex
donors. The material of the coatings can be the organic elec-
; tron donor material introduced into the cell casing prior to
introducing bromine which then reacts to form the charge trans-
fer complex of the cathode material 54, but other materials can
be employed. A preferred material for the coatings is polyvinyl
pyridine and it is applied to the exposed surfaces of lithium
elements 22 and 24 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 com-
mercially available. The solution is prepared ~ith 2-vinyl-
pyridine present in the range from about 10% to abou-t 20% by
_ 16 -
~7~858
1 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 pre-
ferred because of its more fluid characteristics in solution.
When the solution is prepared at a strenc3th below about 10% the
resulting coating can be undesirably too thin and ~hen the solu-
tion is prepared at a stren~th greater than about 20% the materi-
al becomes difficult to apply. The solution is applied to the
exposed surface of each lithium plate in a suitable manner, for
example simply by application with a brush. The presence of
the anhydrous benzene serves to exclude moisture thereby pre-
ventin~ any adverse reaction with the lithium plate. The coated
anode then is exposed 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 sufficient to remove the benzene, which can be in the
neighborhood of 24 hours. The foregoin~ procedure can be re-
peated to provide multiple coatin~s or layers~ for example
three, on each lithium plate.
~t is therefore apparent that the present invention ac-
complishes its intended objects. While several embodiments of
the present invention have been described in detail, this is
for the purpose of illustration, not limitation.
.
.: . .
.. .. . . . . .. .
