Common electrolyte manifold battery

A common electrolyte manifold battery that includes at least one module having a plurality of cells, at least one common electrolyte manifold traversing the cells for transporting a low conductivity electrolyte, an anode and a cathode. The one module includes a collector plate, the collector plate has an end exposed to the common electrolyte manifold, and one of the cells. The one cell comprises a first bipolar plate, positioned in parallel with the collector plate, that has an end proximal to the manifold and an end distal to the manifold, the distal end being connected to the anode. In addition, a second bipolar plate is provided, positioned parallel with the anode plate, that has an end proximal to the manifold and an end distal to the manifold, the distal end being connected to the cathode. The one cell further comprises a layer of insulator enveloping each of the proximal end of the first bipolar plate and the second bipolar plate. The insulator layers are contiguous with the common electrolyte manifold, wherein each of the insulator layers has an anode portion that is directed toward the anode and a cathode portion that is directed toward the cathode, whereby the collector plate exposed end minimizes voltage imbalance of the one cell, the insulator layers minimize short circuiting of the one cell, and the low conductivity electrolyte minimizes leakage currents.

TECHNICAL FIELD 
This invention relates to batteries, and more particularly, to a common 
electrolyte manifold battery. 
BACKGROUND ART 
Common electrolyte manifold batteries are common in the art. In such 
batteries, leakage currents are invariably present which cause the 
degradation of a battery's efficiency and ultimately lead to the 
self-discharge of the battery. Minimizing leakage currents, therefore, is 
an attribute sought by the inventors of prior art batteries. In addition 
to the leakage current problem, short circuiting of the bipolar-plate 
stack is also an inevitable consequence. Short circuiting of the bipolar 
plates occurs because dendrites have grown to such an extent that two 
adjacent plates are bridged. Minimizing or retarding the growth of such 
dendrites is also a desired goal of prior art battery inventors. 
To alleviate these disadvantages, prior art techniques included either 
filling each battery cell individually with a compressed gas or 
ventilating the electrolyte manifold with such a compressed gas in order 
to eliminate leakage currents. These techniques, in turn, are not 
efficient in that the resultant manifold arrangement tended to be rather 
complex when individual cells are required to be filled. In addition, the 
ventilation or blowing out of the manifold not only reduced the 
sensitivity of the battery as to its orientation but also created 
difficulties in controlling the leaking of the electrolyte back into the 
manifold. Thus, the two goals of minimizing internal electrical losses and 
retarding growth of dendrites were not readily achieved in the prior art. 
DISCLOSURE OF THE INVENTION 
An ideal common electrolyte manifold battery having bipolar-plate stack 
configuration should be capable of not only minimizing the presence of 
leakage currents but also retarding the growth of dendrites. 
It is a major object of present invention to provide a common electrolyte 
manifold battery that minimizes internal electrical losses. 
It is another object of the present invention to provide a common 
electrolyte manifold battery that minimizes the formation of dendrites, 
thereby minimizing the potential for electrical short circuiting. 
It is a further object of the present invention to provide a common 
electrolyte manifold battery that is capable of manipulating the growth of 
dendrite at a harmless location, thereby preventing electrical short 
circuiting. 
In order to accomplish the above and still further objects, the present 
invention provides a common electrolyte manifold battery that includes at 
least one module having a plurality of cells, at least one common 
electrolyte manifold traversing the cells for transporting a low 
conductivity electrolyte, an anode and a cathode. The one module includes 
a collector plate, the collector plate has an end exposed to the common 
electrolyte manifold, and one of the cells. The one cell comprises a first 
bipolar plate, positioned in parallel with the collector plate, that has 
an end proximal to the manifold and an end distal to the manifold, the 
distal end being connected to the anode. In addition, a second bipolar 
plate is provided, positioned parallel with the anode plate, that has an 
end proximal to the manifold and an end distal to the manifold, the distal 
end being connected to the cathode. The one cell further comprises a layer 
of insulator enveloping each of the proximal end of the first bipolar 
plate and the second bipolar plate. The insulator layers are contiguous 
with the common electrolyte manifold, wherein each of the insulator layers 
has an anode portion that is directed toward the anode and a cathode 
portion that is directed toward the cathode, whereby the collector plate 
exposed end minimizes voltage imbalance of the one cell, the insulator 
layers minimize short circuiting of the one cell, and the low conductivity 
electrolyte minimizes leakage currents. 
Other objects, features, and advantages of the present invention will 
appear from the following detailed description of the best mode of a 
preferred embodiment, taken together with the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to FIG. 1, there is shown a common electrolyte manifold battery, 
designated 12. Battery 12 in the preferred embodiment is a lithium-thionyl 
chloride (Li/SOCl.sub.2) reserve-activated, bipolar, common static 
electrolyte battery. Battery 12 consists of twenty modules 14 each having 
86 cells arranged in an annular configuration. Modules 14 are arranged 
about an axis "X." Traversing through the battery stack of modules 14 are 
two common electrolyte manifolds 16, shown as dotted lines in FIG. 1, 
which are parallel to axis "X" of battery 12. In the preferred embodiment, 
each manifold 16 has a diameter of approximately 1/8 inch. 
More particularly, each battery module 14, as best shown in FIG. 2, 
includes a collector plate 18 and 86 cells 20. As best shown in FIG. 3, 
each cell 20 comprises a pair of bipolar plates 22A and 22B. Positioned 
between bipolar plates 22A and 22B is a separator 24. Positioned 
contiguous to one end of bipolar plates 22A and 22B, the ends which are 
distal to one of the two common electrolyte manifolds 16, are anode 26 and 
cathode 28. Positioned at the other end of bipolar plates 22A and 22B, at 
the end adjacent to common electrolyte manifold 16, are insulation layers 
30A and 30B which envelop plates 22A and 22B, respectively. In addition, a 
layer of insulator 30C is positioned contiguous to collector plate 18, as 
best shown in FIG. 2. 
In the preferred embodiment, bipolar plates 22A and 22B are manufactured 
from nickel clad copper material. Each of bipolar plates 22A and 22B has a 
thickness of approximately 2.5 mils in the preferred embodiment. Separator 
24 is manufactured from a porous material such as ceramic or fiberglass 
paper that prevents the direct contact of anode 26 and cathode 28 while 
permitting ionic conduction between anode 26 and cathode 28. Separator 24 
has an uninstalled thickness of approximately 20.0 mils in the preferred 
embodiment. Moreover, anode 26 is manufactured from a lithium material and 
cathode 28 porous carbon. In the preferred embodiment, anode 26 has a 
thickness of approximately 3-4 1/2 mils, and cathode 28 has an uninstalled 
thickness of approximately 17-19 mils. The total thickness of each cell 20 
is approximately 0.0145 inch in the preferred embodiment. 
The electrolyte used, flowing from manifold 16 into porous separator 24, is 
a thionyl chloride (SOCl.sub.2) solvent having lithium tetrachloralumate 
(LiAlCl.sub.4) and aluminum trichloride (AlCl.sub.3) salts. The chemical 
reaction is as follows. First, lithium metal of anode 26 is oxidized, 
yielding lithium ion, 
EQU 4Li.fwdarw.4Li.sup.+ +e.sup.-. 
At cathode 28, the SOCl.sub.2 solvent is reduced, producing chloride ions, 
elemental sulfur and sulfur dioxide, 
EQU 4e.sup.- +2SOCl.sub.2 .fwdarw.4Cl.sup.- +S+SO.sub.2. 
The overall chemical reaction is 
EQU 4Li+2SOCl.sub.2 .fwdarw.2LiCl+S+SO.sub.2. 
In designing a common electrolyte manifold battery, the two primary 
considerations are (1) leakage current which degrades battery efficiency, 
leading to self discharge of the battery; and (2) the formation of 
elemental lithium which, if it bridges anode 26 and cathode 28, will lead 
to short circuiting. The consequences of short circuiting a cell are 
catastropic in that they generally result in a thermal runaway situation, 
leading eventually to the venting of the battery. 
Since the energy loss associated with the leakage current in manifold 16 of 
the present invention is relatively modest in light of the fact that the 
conductivity of the electrolyte is relatively low, e.g., 55-60 
ohm-centimeter, the loss of energy is generally in the range of 1/2 to 1% 
of the total energy produced by battery 12. 
To analyze the second consideration, the schematic illustrated in FIG. 4 is 
useful in explaining the present invention. In the circuit diagram, 
R.sub.e represents the cell resistance of one cell 20, R.sub.m represents 
the electrolyte resistance in manifold 16, and R.sub.c represents the 
electrolyte resistance in going from manifold 16 to an active cell 20, 
also referred to as the channel resistance. R.sub.l represents the 
external load resistance and R.sub.s represents the shunt resistance. In 
the preferred embodiment, the shunt resistance is provided by collector 
plate 18. Collector plate 18 in the preferred embodiment has a thickness 
of approximately 10 mils. 
Since short circuiting is dependent on both the electrical contact between 
anode 26 and cathode 28 at different voltage potentials and the growth of 
lithium dendrites, the present invention minimizes these two factors. 
First, since the growth of dendrites is dependent on the totality of the 
channel currents, the channel currents may be reduced by shunted collector 
plate 18 and the channel geometry. The reduction in channel currents may 
be achieved either by reducing the voltage drop across the channel 
resistance, R.sub.c, or by increasing the resistance R.sub.c. 
Theoretically, the channel currents can be driven to zero if the voltage 
drop in manifold 16 (.DELTA.V.sub.1) is made equal to the voltage drop in 
the battery stack (.DELTA.V.sub.2). As best shown in FIGS. 2 and 3, this 
is accomplished by exposing end 32 of collector plate 18 so as to create a 
low shunt resistance R.sub.s which in turn causes the voltage at nodes "A" 
and "B" to be equal and the voltage at nodes "C" and "D" to be equal. 
Furthermore, assuming the R.sub.m 's and the R.sub.e 's are equal for each 
cell 20, the voltage drop across any R.sub.c is zero. Whereas the maximum 
channel currents are approximately 8.2 milliamps, a shunt resistance of 40 
ohms reduces the maximum channel currents to approximately 0.7 milliamps. 
Thus, exposed end 32 of collector plated 18 minimizes the voltage 
imbalance of of cell 20. 
As for channel geometry, the channel resistance, R.sub.c, may be increased 
by minimizing the the space of each channel by employing insulators 30A 
and 30B. Insulators 30A and 30B are manufactured from a 
polytetrafluoroethylene (Teflon) material. Insulators 30A and 30B are 
bonded to the plates by using standard cyanoacrylate adhesives. 
To minimize the possibility of lithium dendrites bridging bipolar plates 
22A and 22B, insulators 30A and 30B of different diameters are used. Since 
lithium dendrites nucleate at anode plate 22A and grow in the direction of 
the channel current, i.e., towards manifold 16, a longer insulator on 
cathode 28 would prevent the dendrites from coming into contact with a 
bare cathode plate 22B. The growth of dendrites is illustrated in FIG. 3 
by the arrow "GD." As best shown in FIG. 3, each of insulators 30A and 30B 
has its cathode portion 34 greater than its anode portion 36. In essence, 
the dendrites are manipulated to nucleate or grow at a harmless location 
on anode plate 22A such that it cannot come into contact with cathode 
plate 22B, which is protected by the longer cathode portion 34 of 
insulator 30B. In the preferred embodiment, both insulators 30A and 30B 
are approximately 2.0 mils in thickness. The diameter of the cathode side 
is approximately 1.0 inch and the anode side 0.5 inch. Although bipolar 
plates 22A and 22B are also referred to as anode plate 22A and cathode 
plate 22B, respectively, each of bipolar plates 22A and 22B is identical. 
They are described in this fashion so as to simplify their functions. In 
actuality, each of bipolar plates 22A and 22B is in contact with anode 26 
and cathode 28. In addition, each of bipolar plates 22A and 22B is either 
the cathode plate or anode plate for an adjacent cell 20. For example, 
bipolar plate 22A is illustrated as being in contact with anode 26 in 
FIGS. 2-3 and is referred to as an anode plate. However, it serves as the 
cathode plate for the next adjacent cell 20 because its other surface is 
in contact with cathode 28, not shown. Similarly, bipolar plate 22B is 
illustrated as a cathode plate in FIGS. 2-3. It, however, serves as the 
anode plate for the next adjacent cell 20 because its other surface is in 
contact with anode 26, not shown. 
In operation, a bipolar stack of 20 modules, each having 86 cells, is used 
to generate 180 kilowatts of energy. If none of the attributes are 
utilized, the battery would vent in approximately 1.7 to 2.6 minutes. If 
Teflon insulators 30A and 30B of equal lengths are used, venting will 
occur at approximately 7.6 to 8.5 minutes. If Teflon insulators 30A and 
30B of equal lengths and shunted collectors 18 are used, venting will 
occur after approximately 34.4 minutes. Last, if all the attributes of the 
present invention are used--insulators 30A and 30B each having longer 
cathode portion 34, and shunted collectors 18, venting does not occur at 
all within 24 hours, the maximum test time. 
It will be apparent to those skilled in the art that various modifications 
may be made within the spirit of the invention and the scope of the 
appended claims.