Note: Descriptions are shown in the official language in which they were submitted.
Background of the Invention
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This application is a divisional of our Serial Number
266,233, filed November 22, 1976.
It is generally known that conventional primary and
secondary electric cells and batteries are subject to serious
limitation on their use where substantial power is required, for
example, as a power source for automobiles or for the
propulsion of marine craft such as submarines. Widely used
lead-acid batteries of the automobile industry are sturdy
and generally dependable but have power/weight ratios which
are far too low for the substantial power requirements for
propulsion. This is also true of zinc type batteries and
other commercially available electric cells. In general,
the problem is to achieve energy density (watt hrs./lb) and
current density (watts/lb.) ratios in an electric cell or
battery, which will be of such order as to meet the necessary
power requirements.
Since the electrolyte (and its dissolved charge
trans~er agent) is a principal factor in the weight of a
battery, considerable reseaxch energy and time have been
expended in efforts to substitute lower density organic
solutions for the aqueous solutions principally used. The
use of electrolytes employing organic solvents also suggest use
in electric cells of highly reactive metals of low molecular
weight, such as the lighter alkali and alkaline earth metals
(hereinafter "alkaline metals"), especially lithium, sodium,
potassium, magnesium, and calcium. Electric cells based on
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use of these materials, theoretically at least, enable
substantially higher power/weight ratios to be obtained than
in the more conventional batteries. By way of illustration,
a complete lithium battery should be capable of achieving
current and energy density ratios of the order of ten to 20
times that obtained with the conventional lead-acid battery.
However, to date, and despite the obvious benefits to be
obtained, no commercially successful battery or electric
cell has been developed wherein the lighter alkaline metals
are utilized in an electrolyte as the charge transfer agent
between the electrodes. In general, these alkaline metals
are so reactive, particularly in the presence o~ moisture or
atmospheric`air (including nitrogen as well as oxygen),
that they not only present hazards but also require
expensive equipment and handling procedures for their use.
By way of illustration, known lithium sulfur dioxide batteries
are not only excessively expensive to fabricate (principally
because of the problems in handling the metallic lithium),
but also suffer the further difficulty that they are not
designed to be rechargeable. Mor~over, for the reasons noted
above, aqueous electrolyte solutions cannot ~e used at all
with lithium, sodium or others of the reactive metals, and
would not be suitable in any event because of the relatively
low power/weight ratios necessarily attending their use.
A further particular problem commonly encountered in
electric cells and batteries, is a high degree of inherent
internal resistance to current flow. This internal resistance
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leads to overheating and consequent ineffectiveness of the
battery in use, as evidenced by the well known "burn out"
under conditions of severe or continued loading.
Based on the foregoing, it will be apparent that
the development of an improved battery cell and system is
grea-tly to be desired, particularly as respects present
limitations on maximum energy and current density ratios obtain-
able in the cell, the relatively low power/weight ratios
available, and the avoidance of difficulties associated with
handling highly reactive but potentially highly successful
charge transfer materials.
Summary of the Invention
This invention relates generally to high energy
battery cells of primary and secondary nature, and more
particularly to an ambient temperature alkaline metal cell
wherein a dithionite radical of the alkaline metal is used
as the charge transfer agent. It specifically relates to a
secondary battery system utilizing an anhydrous solvent
containing freshly dissolved lithium dithionite as the
electrolyte.
In general, the present invention provides a new and
improved primary or secondary cell based on use of alkaline
metal dithionites or mixtures thereof, as the charge transfer
agent.
The present invention further provides primary and
secondary cells of the type described which achieve maximum
power/weight ratios, through use of highly reactive alkaline
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metals of low molecular weight, such as lithium, sodium,
potassium, magnesium and calcium.
According to a still further feature o~ the invention
there are provided new methods for both manufacturing and
operating such improved primary and secondary cells, which
enable effective use while avoiding the risks and difficulties
of handling the specified, highly reactive alkaline metals.
According to another and specific feature of the
invention there are provided improved primary or secondary cells
of the above character which make possible power/weight ratios
sufficient to meet the power requirements for propulsion of
primary vehicles and marine craft, such as automobiles, trucks,
power boats`and submarines.
As described in our application Serial No. 266,233
alkaline metal cells of primary and secondary nature have been
developed, making use of dithionite radical of an alkaline
metal as the charge transfer agent, which are not only capable
of use at ambient temperature but which also avoid the risks
and difficulties normally encountered in the use of highly
reactive alkaline metals. More specifically, the electrolyte
in contact with the electrode is comprised of a suitable
anhydrous solvent in which the alkaline metal dithionite is
dissolved. The electrolyte may additionally contain an ionizing
agent in the form of a salt of the same alkaline metal and
also may be saturated with sulfur dioxide.
According to the present inven-tion there is
provided an electrochemical cell comprising an electrode structure
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which includes an inert negative electrode of conductive
material, an inert positive current-gathering electrode o~
conductive material, and a liquid mixture in contact with said
electrodes, said liquid mixture consisting essentially of
at least one substantially inert, anhydrous, organic liquid
solvent having therein a charging agent selected from the active
metal dithionites and mixtures thereof, said liquid mixture
during the charging of said cell plating active metal of said
selected active metal dithionite on said negative electrode and
generating sulfur dioxide at said positive electrode, and
means for continuously circulating said liquid mixture into
contact with a source of said charging agent and said negative
and positive electrodes during said charging of the cell.
In another aspect, the present invention relates
to a continuous method of operating an electrochemical system
during the charging and discharging thereof in such fashion
as to minimize internal resistance to current flow while
substantially increasing the energy storage capacity of the
' system, comprising the steps of continuously circulating a
nonaqueous electrolyte t~rough an elongated passage between
closely spaced ad~acent conductive materials forming electrode
surface$ for a battery cell in said system, simultaneously
and continuously circulating said electrolyte from the battery
cell to a circulatory chamber containing a solid charging
agent selected from the active metal dithionites and mixtures
thereof, said charging agent being at least partially
soluble in said electrolyte, continuously discharging
electrolyte containing dissolved charging agent from said
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circulatory chamber and subjecting the same to centrifugal
action to separate entrained solid charging agent from said
circulating electrolyte, and returning the circulating
electrolyte with freshly dissolved charging agent therein to
the elongated passage in said battery cell, said electrolyte
comprising a mixture of at least one organic liquid solvent
containing a current-carrying solute and said charging agent.
In a particular secondary battery system according
to the invention, the electrolyte is circulated through a
highly porous inert spacer between a negative electrode and a
positive current gathering electrode, in a sealed and
evacuated cell. The system is subjected to a charging current
of an energy level sufficient to disassociate the dithionite
(e.g., specifically lithium dithionite) and to plate the
alkaline metal (e.g., lithium) on the negative electrode
~hile releasing the sulfur dioxide at the positive electrode
to further saturate the electrolyte. A continuous supply
of electrolyte containing freshly dissolved dithionite is
obtained through use of an auxiliary dissolving chamber
in conjunction with solids separating means (e.g., centrifugal
separator), thus enabling use of anhydrous solvents in which
the dithionite is only slightly soluble (e.g., acetonitrile,
dimethyl sulfoxide~. The performance of the battery system
can be enhanced by use of a salt of the same alkaline metal
~e.g., lithium perchlorate) as part of the electrolyte, and
as a source of additional alkaline metal.
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Secondary cells as herein described (based on use
of a dithionite radical of the alkaline metal as the charge
transfer agent) are characterized by substantially increased
current and energy density ratios, as compared to conventionally
available secondary cells. sy way of illustration, power/
weight ratios of the order of ten times, or higher, than
those obtained with the conventiona]. lead-acid battery, are
possible. Due to low internal resic;tance, the time
required for recharging the battery will also be greatly
reduced, for example, of the order of one-fifth the time
requiréd in an equivalent lead-acid cell. Besides extremely
low internal resistance to current flow, other particular
advantages of the cells include an unusually long shelf life,
extremely good performance~over a wide range of high and low
temperatures, and a negligible depletion of the active dithio-
nite charge trans.fer agent, despite prolonged cont~inuous use
of the battery`system~ I
~ he invention further contemplates thé assembly and
satisfactory use of primary cell systems, wherein the final
2Q cell potential and discharge characteristics can be enhanced
by replacing the formation electrolyte with other anhydrous
electrolyte`solutions, for éxample, electrolyte solutions
employing or containing, specifically, sulfuryl chloride and
thionyl chloride.
Other features and advantages of the invention will
be apparent from the following description taken in conjunction
with the drawing..
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Bri_f Description of the Drawings
Figure 1 is a view in section and elevation of one
embodiment of a secondary battery cell and system, in accord-
ance with the present invention.
Figure 2 is a view in section, along the line 2-2
of Figure 1.
Figure 3 is an enlarged sectional view along the
line 3-3 of Figure 2.
Figure 4 is a greatly enlarged detail view of the
indicated portion of Figure 3.
Figure 5 is an enlarged detail view along the line
5-5 of Figure 1.
Figure 6 is a view in section along the line 6-6 of
Figure 5.
Practical and Theoretical Considerations
In order for a secondary battery to be rechargeable,
both the anode and cathode reactions must be chemically revers-
ible. In order to be a practical secondary cell, these reactions
must also take place in a relatively short period of time. It
is known that the ion exchange reactions of the lower molecular
weight alkaline metals, and particularly the lithium metal/
lithium ion reaction, satisfies both of these conditions and,
moreover, can be carried out in nonaqueous solvents which
provide the further advantage of lower density solutions as
compared to aqueous solutions. The metal ion reactions of
other alkali metals and alkaline earth metals (viz., columns
lA and IIA of the periodic table, herein "alkaline metals")
also satisfy the desired conditions.
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Theoretical considerations related to an alkaline
metal/sulfur dioxide battery suggest that SO2 will be reduced
to S2O2 1 (dithionite) as the battery is discharged. It is
further postulated that a satisfactory battery can be produced
by dissolving an alkaline metal dithionite (e.g., Li2S2O4) in
a nonaqueous solvent to produce the alkaline metal and
dithionite ions in solution (a.g., Li+ and S2O4 ). By passing
a charging current through the solution containing such ions,
the alkaline metal (e.g., Li) will be deposited at one
electrode and SO2 gas will be released at the other. The
advantage is a procedure for employing the highly reactive
alkaline metals in solution without appreciable risk or diffi-
culty in handling, while at the same time releasing sulfur
dioxide gas to saturate the electrolyte.
To verify the foregoing concept with respect to
the preferred alkaline metal, lithium, lithium dithionite
(Li2S2O4) is prepared by the technique of ion exchange.
Specifically, a column of cation exchange resin in the
hydrogen ion (H+) form is converted completely to the lithium
ion (Li+) form by passing a concentrated aqueous solution of
lithium chloride through the column until the effluent is
essentially neutral. The column is rinsed with deionized
water until the excess lithium chloride is removed, as indicated
by the absence of red lithium ion color in a flame test on the
effluent. An aqueous of commercial sodium hyposulfite
(Na2S2O4), which has been deoxygenated by bubbling it with
nitrogen or other inert gas, is then passed through the column.
B~3~
The effluent is collected in deoxygenated ethanol until a flame
test on the effluent indicates the presence of sodium ion.
The lithium dithionite is next precipitated from the ethanol,
and is further washed with deoxygenated ethanol, filtered and
vacuum dried. The lithium dithionite tLi2S2O4) thus produced
is relatively stable when dry and maintained at room temperature.
However, it will rapidly decompose at temperatures near 100C.,
and also reacts rapidly with oxygen when damp or in solution.
The ultraviolet spectrum of the sulEurous oxide ion (S204 )
is used to determine the presence and purity of the alkaline
metal dithionite. While the alkaline metal dithionites are
found to be appreciably soluble only in water, limited
solubility ~less than about 5~) can be achieved in such anhydrous
solvents as acetonitrile and dimethylsulfoxide, among others.
To test the concept, a battery cell can be prepared
wherein the electrolyte comprises a suitable nonaqueous sol-
~ent, (i.e., acetonitrile) and wherein the lithium dithionite
is present as a slurry. In one satisfactory cell, a lithium
salt is also present as an ionizing agent, preferably in the
form of a saturated solution, and functions both as an elec-
trolyte and as a source of additional lithium ion. As tests
in aqueous solution show that the perchlorate and dithionite
ions do not react, a saturated solution of lithium perchlor-
ate in acetonitrile is satisfactorily utilized for such
purpose, in the cells just described. Various conductive metals
can be used for the negative electrode, including the
noble metals (gold and silver), aluminum, copper and certain
stainless steels. Conductive material5 usch as finely divided
carbon and sintered aluminum can be used as the positive
current gathering electrode. When current is passed through
these cells, spongy lithium is plated at the negative electrode,
whereas sulfur dioxide gas and the greenish yellow color of
chlorine gas is observed at the other electrode. When the
charging current is discontinued, a constant stable voltage
of (greater than about 4.0) volts is observed. Such cells with
electrode areas of about 15 square centimeters are capable
of lighting flash bulbs for some time. When the bulb is
disconnected, the voltage returns to above 4.0 volts. When
the cell is completely discharged, it is found to be rechargeable
many times. Although the cells can be alternatively operated
with the addition of SO2 gas, the behavior of the cells is
essentially independent of the presence of the added SO2 gas.
However, when the lithium dithionite is omitted from the
electrolyte, the cells fail to charge and produce current.
Successful use of the thionite radical of an alkaline
metal as the charge transfer agent in a secondary battery cell
has led to the development of a full scale cell suitable for
providing power to a primary propulsion system, for example,
in a submarine or automobile. A specific embodiment of such
cell, as used in a battery system, is described below.
Description of Preferred Embodiment
_ _
Referring to Figure 1, reference numeral 10 generally
represents a self-contained battery cell or unit in accordance
~ith the present invention. This cell is-cylindrical in
configuration and includes an outer cylindrical shell 12 and two
generally circular side plates 14 and 16. The side plates
and out~r shell are assembled in leaktight fashion upon an
axial tube 18 which forms a central core for the unit. Assembly
is accomplished by means of a pair of inner circular retaining
washers 20, 22, which are held in place by suitable ~astening
means such as the bolt 24, and a pair of ou-ter circular
retaining flanges 26 and 28 which are held in place by suitable
peripheral fastening means such as a series of bolts 30. In the
assembled condition, the outer casing provides the interior
annular chamber or space 32, defined by the side plates 14, 16,
the outer shell 12 and the inner core 18. Suitable inert
sealing members such as the 0-rings 34 and 36 are positioned
between the described casing members to insure that the annular
space 32 is completely sealed as respects the exterior
environment. As hereinafter described, the space 32 generally
forms a battery chamber for an electric cell including active
(negative) and current gathering (positive) electrodes.
Associated with the battery chamber or cell 10 and
forming part of the electrochemical current producing system of
the present invention is a circulatory chamber 40. This chamber
can take any suitable form such as a cylindrical tank 42 and,
as hereinafter described, generally functions as a reservoir
for circulating anhydrous electrolyte undissolved or partially
dissolved alkaline metal dithionite used to provide the charge
transfer ions. In the illustrated apparatus, the circulatory
chamber 40 is in fluid communication with the battery cell 10
through conduits 44 and 46 connecting an outlet 48 from the
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battery chamber to an inlet 50 of the circulatory chamber,
and through additional conduits 52 and 54 connecting an outlet
56 from the circulatory chamber to an inlet 58 in the battery
chamber. As hereinafter described, circulation of electrolyte
and dissolved charge transfer agent is accomplished by pump
means 60 which generally functions to withdraw spent electrolyte
from the battery chamber 10, to pass the same over a supply
of solid dithionite 62 in the circulatory chamber 40, and to
return electrolyte with freshly dissolved dithionite from the
circulatory chamber to the battery chamber. Thus, referring
specifically to Figure 1, the pump 60 is positioned between
the conduits 44, 46 ~oining the battery and circulating
chambers, and functions to force circulating slurry of
electrolyte and dithionite to a solids separation device 64,
from ~hich electrolyte and dissolved dithionite is charged to
the battery ~hamber through the line 54. IJndissolved solid
dithionite separated in the device 64 is returned to the tank
42 through the line 66, pump 60 and conduit 46. While any
satisfactory solids separation device may be employed (e.g., a
continuous rotary filter), a centrifugal separator is most
conveniently employed in that such apparatus is capable of
acting through fluid flow to both "separate" and return
undissolved dithionite to the circulatory chamber and to deliver
to the battery cell a clear "filtrate" of electrolyte
containing dissolved dithionite.
Referring to Figures 1 and 2, an electric battery
cell 70 is positioned within the chamber 10 so as to sub-
stantially fill the interior annular space 32. In general terms,
the battery cell 70 includes an elongate active electrode
of conductive material tnegative electrode) arranged in
adjacent configuration to an elongate passive current gathering
electrode (positive electrode) such that a passage is provided
therebetween for the flow of electrolyte solution. In
the illustrative apparatus, and as described in our related
3~Y,/~3
divisional application ~ Serial No. ~GG, ~, this passage
between the elongate electrodes may be maintained by positioning
highly porous inert spacing means between the adjacent electrodes
so as to insure a continuous unobstructed pathway for the
circulating electrolyte and dissolved charge transfer agent.
In more specific terms, the two electrodes and intermediate
spacing means are arranged in an increasing spiral configuration
advancing from an inner electrode terminal 72, adjacent the
central core 18, to an outer electrode terminal 74, adjacent
the outer shell 12. The inner terminal 72 is connected to the
active (negative~ electrode whereas the outer terminal 74 is
connected to the current gathering (positive) electrode. In
each instance, the terminal is mounted within a leak tight
sealing device 76, to maintain the sealed integrity of the
battery cell 10.
The construction and adjacent configuration of the
electrodes in the spiral arrangement of the battery cell 70,
is shown in the sectional view of Figure 3, In general, the
conductive material of the active electrode, represented at
80, may comprise any suitable conductive materials, for example,
a bare metal such as copper, certain stainless steels, aluminum
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and the noble metals. ~n elongate strip of perforated copper
or copper screen is particularly suited for the purpose. The
current gathering electrode, represented at 82, may likewise
comprise any suitable conductive material, for example, finely
divided carbon or graphite, sintered aluminum or the like. In
general, the electrode 82 is formed as an elongate strip
which is generally contiguous with the electrode 80. As
previously noted, an elongate highly porous insert spacer,
represented at 84, is positioned between the electrodes 80
and 82. The construction of the spacer 8~ should be such that
the electrolyte is free to circulate through the battery cell
and between the spaced electrodes, to thereby reduce internal
resistance to current flow (and the potential for heat gain).
While various inert spacing materials can be employed, inert
plastic materials in open lattice form (e.g., crossed strands
of polypropylene or like alkali resistant fiber-forming plastics)
are to be preferred. In general, the inert spacing means should
be insoluble in the anhydrous organic salts used in the
electrolyte solution, and capable of being formed in highly
porous configurations of the type described. In general, the
porous spacing member 84 provides for free flow of electrolyte
through the cell 70 in the battery chamber 10. To enhance
this electrolyte flow, suitable flow pathways 85 can also be
provided on the inner surfaces of the side plates 14 and 16
(See Figure 2).
With particular reference to the electrolyte solution,
an essential component is a substantially inert anhydrous
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organic solvent for the alka.Line metal dithionite employed
as the charge transfer agent. Preferably, the electrolyte
solvent will also have good properties as a medium for
promoting reactions involving ionization. The solvent should
also be substantially inert with respect to the selected
conductive materials employed as electrodes, viz., copper,
aluminum, carbon etc. The anhydrous electrolyte liquid should
particularly function as a solvent for the selected alkaline
metal dithionite radical employed as the charge transfer agent
and, also, for sulfur dioxide gas. With respect to the
preferred alkaline metal dithionite, lithium dithionite,
particularly satisfactory anhydrous organic solvents include
acetonitrile, dimethylsulfoxide, dimethylformamide, and to a
lesser extent, propylene carbonate, and isopropylamine, among
others. Because of the generally low solubility of the
alkaline metal dithionites in anhydrous organic solvents, it
is also advantageous and desirable to use an additional
electrolyte iiquid as an ionizing agent to promote solubility
and conductivity of the alkaline metal dithionite. Generally,
it has been found that certain:inorganic salts of the same
alkaline metal as used in the dithionite are satisfactory for
this purpose. Specifically, it has been found that the
perchlorate ions of alkaline metals will not react with the
dithionite ions, based on testing and analysis in aqueous
solution. Accordingly, in the case of the preferred lithium
dithionite charge transfer agent, lithium perchlorate has
proved to be very satisfactory as an ionizing component of the
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electrolyte. While alkaline metal bromates, such as lithium
bromate, are also satisfactory ionizing agents, the use of
such compounds is ~uestionable because of the undesired
production of bromine gas. On the other hand, battery cells
have been satisfactorily employed employing lithium dithionite
in a saturated solution of lithl~lm bromite in acetonitrile.
In view of the foregoing considerations, it has
been determined that a preferred electrolyte solutio~ to be
used with lithium dithionite is a mixture of acetonitrile with
lithium perchlorate (viz., Li Cl O4).
A particular advantage of the battery cell and system
of the present invention is that current producing operations
can be carried out at ambient temperatures, that is, without
heating or cooling, and at atmospheric pressure. In an
atmospheric pressure system, it is advantageous to use gaseous
sulfur dioxide to further promote solubility of the alkaline
metal aithionite, and the conductivity of the dithionite radical.
Generally, the electrolyte can be substantially saturated with
gaseous sulfur dioxide which may be added to the system at any
convenient point, for example, in the inlet conduit 46 to the
circulatory chamber or, as illustrated, directly to the tank
42 through the valYed conduit 86. The presence of sulfur
dioxide in the electrolyte solution is beneficial in that the
gas insures removal of any free oxygen or water by reaction
therewith, to thereby avoid undesired reactions with the
alkaline metal or dithionite radicals.
The start up and operation of the battery system
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illustrated in Figures 1 and 2 will now be describe~. Initially,
desired quantities of dried crystalline alkaline metal
dithionite (prepared in the manner herein described) together
with dry crystalline alkaline metal perchlorate are placed in
the circulatory chamber 40, as at 62. Valving in the
circulatory system, represented at 43, 47 and 55 (Figure 1) is
then opened to permit the entire system to be subjected to the
purging effects of a vacuum. Specifically, a vacuum is pulled
on the reservoir chamber 40 by means of a suitable vacuum
pump 90, operatVing through the lines 92 and 94. During such
operation, the valve 96 in the electrolyte solvent supply line
98 is closed, whereas the valves 93 and 95 are open. The battery
system comprising the battery chamber 10 and circulatory chamber
40 are then purged in several cycles involving the pulling of
an appropriate vacuum (i.e., 40 microns) with the vacuum pump
90, and alternatively introducing dry inert gas (viz., argon
or nitrogen) through the valve line 98 with assistance of the
pump 60. These alternative pump and purge cycles (represented
by the arrows 100, 102) serve to free the circulatory system
of oxygen or water vapor such as might react with the alkaline
metal dithionite. The anydrous organic electrolyte solvent is
then introduced to the vacuum outlet (through line 98 and
valve 96) to the reservoir chamber 40, where it mixes with the
dry chemicals in the bottom of the reservoir. Simultaneously,
the organic solvent can be saturated with sulfur dioxide to
insure _emoval of any possible remaining oxygen or water vapor.
~ssuming that ~he dry chemicals 62 include the
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selected alkaline metal dithionite together with the same alkaline
metal perchlorate, the perchlorate totally dissolves in the
entering solvent to form a saturated solution. However, the
alkaline metal dithionite being only partially soluble/ will
remain substantially undissolved at the bottom of the reservoir
chamber, with the portions of the undissolved dithionite
forming a slurry with the entering solvent. In this "filling"
operation, the solvent pump 104 is operated simultaneously
with the circulatory pump 60 to distribute electrolyte
solution throughout the circulatory system including the battery
cell 10. During such operation, undissolved dithionite
circulating as a slurry with the electrolyte will be removed
from the circulating liquid in the centrifugal separator 64,
and returned through the line 62 to the bottom of the reservoir
chamber. When the system is completely filled, the valve 96
can be closed so that the electrolyte circulates between the
battery cell 10 and reservoir chamber 40 in a more or less steady
state. However, sulfur dioxide gas can be continuously metered
to the system at a controlled rate, under the control of the
yalve 106. At this stage, the battery cell 10 is in an inert
discharge state, with electrolyte solution being continuously
circulated through the porous pathway between the electrodes
80 and 82, provided by the inert strands of the spacing member
84 (see arrows 110 in Figures 3 and 4).
At this point~ the battery cell is subjected to a
charging current capable of supplying the energy level required
to plate the alkalLne metal onto the negative electrode (i.eO,
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the bare metal conductor 80), whlle simultaneously further
saturating the circulating electrolyte with sulfur dioxide
released rom the dithionite radical, at the positive electrode
82 . As particularly illustrated in the enlarged detail view
of Figure 4, the alkaline metal is deposited as a layer 120
on the baxe metal conductors 80. Because of the very low
internal resistance to current flow in the pathway between the
electrodes 80 and 82, the plating o* the alkaline metal ion
continues even though there is a very low proportion of the
available dithionite material in the solution in the circulating
electrolyte. By way of illustration, the electrolyte may be
saturated with dithionite at less than a 5~ solution, say in
a 1% solution, as respects the circulating organic solvent.
However, due to the continuous circulation of clear, freshly
dissolyed dithionite solution through the separator 64, and
into the battery cell 10, a continuous supply of alkaline
metal ion is available for plating on the negative electrode
80. In this operation, it will be appreciated that the lithium
plated onto the conductor 80 itself becomes the conductive
layer so that the alkaline metal ion ~ill continue to plate
onto the conductor and build up in the free space available
between the strands of the inert spacer 84. Because the plating
reaction takes place at the constant ambient temperature, and
in the presence of the circulating medium, there is very
little energy loss due to internal resistance of the battery
cell, and consequently negligible heat gain even at relatively
high loading.
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The discharge state of the described battery cell and
system is best described with respect to a particular battery
cell construction based on use of lithium dithionite as the
charge transfer agent, acetonitrile as the anhydrous organic
solvent, and lithium perchlorate as a disso]~ed ionizing agent.
Thus, a particular battery cell 10, designed to fit within a
sealed exterior opening (cylindrical) of a submarine hull may
have dimensions of the order of 20 inches in diameter and 7-1/2
to 8 inches in thickness. The active (negative) electrode is an
elongate ribbon of copper screening or perforated metal, 78 feet
long, 5 inches wide and approximately 0.08 inches thick. The
passive current gathering (positive) electrode is likewise
formed as an elongate strip of a mix-ture of 80~ carbon with 20~
polyfluorotetraethylene which is 78 feet long, 5 inches wide and
of the order of 0.08 inches in thickness. The inert spacing
member between the electrodes is an elongate strip o~ poly-
propylene lattice-work screening, which similarly is approximately
78 feet long, 5 inches wide and about 0.08 inches in thickness
~individual strand diameter, approx. 0.04 inches). The
resulting sandwich or laminate of copper and carbon electrodes
with an intermediate polypropylene spacer (78 feet long, 5 inches
wide and 1/4 inch thick) is arranged in a spiral extending
outwardly from the central core 18 to the outer cylindrical shell
12. As illustrated in Figures 5 and 6, the active copper
electrode 80 is connected to the outer terminal 74 by means of
an outer electrode clip 75. The carbon electrode 82 is
similarly connected to the inert terminal 72 by means of an inner
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electrode clip (not shown) pos~tioned adjacent the central
core 18.
Upon discharge o~ a fully charged cell o~ the type
described (represented by plating lithium on the copper
electrode to a thickness of 0.04 inches) the practical
discharge capacity of the cell closely approaches the theor-
etical capacity, that is, 4800 ampere hours for each 785 grams
of lithium dithionite. The described battery cell thus has
a discharge capacity approximating 16 times the practical
limit of the conventional lead-acid cell of corresponding space
dimensions and weight. This is computed as follows: lithium
will be plated on the negative electrode to a thickness of
0.0025 inches for each 785 grams of lithium dithionite delivered,
representing 300 ampere hours. Since the available space for
plating of lithium in the described battery cell is 0.04 inches,
the available watt hours per pound will be:
0.0400 x 300 ampere hours = 4800 ampere hours
~0~
In general terms, 300 ampere hours of energy storage is
equivalent to 16 watt hours per pound of available plated lithium.
A total of 4800 ampere hours is therefore 16 times the limit
of the conyentional lead-acid cell of similar weight and
dimensions.
In a particular application of the described battery
cell, designed to proYide a 240 volt/300 ampere hour system,
78 individual battery cells are operated in series to provide
the essential propulsive power. Each cell, including battery
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chamber 10 and circulatory chamber 40 has a total volume of
1600 ml (cell volume lOa ml and reservoir volume 1500 ml).
The electrolyte comprises 1600 ml of acetonitrile, saturated
with SO2, and circulating over 15 grams of Li2S2O4 and 75
grams of Li Cl O~ initially placed in the circulatory chamber
40. In a test sequence, involving several 10 second charge
and discharge cycles to assure continuity and a 10 minute
charge at 0.5 amps, discharge characteristics wi-th respect
to a 150 ohm load and a current flow o~ 0.02+ amps, are
represented in Table I below:
Table I
Discharge Discharge
T e _ _ Voltage_ _
0 2.947
1 min. 2.939
2 min. 2.929
5 min. 2.904
10 min. 2.848
In general, ~perational characteristics were excellent,
with a cell life of 1.5 hours before recharging, and a peak
amperage of 300 amps.
It has been determined that the improved battery
cell and system of the present invention provides many advantages.
Specifically, because there is no build up or scaling within
the cell, the battery cell is found to be rechargeable many
times. Recharging of the cell is easily accomplished because
of the presence of dissolved SO2 gas within the electrolyte
solution, permitting easier reversibility to the alkaline metal
dithionite. Moreover~ the circulation of the electrolyte over
a gross supply of solid dithionite permits a large capacity
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battery with battery cell size limitations which are,
conversely, quite small. The battery cell is particularly
advantageous in that it can be operated at constant ambient
temperatures and at atmospheric pressures. Improved battery
cells employing the alkaline metal clithionite provide a further
advantage in enabling use of low molecular weight alkaline
metals such as lithium, sodium, potassium, magnesium and
calcium, without concern as to problems of exposure to air or
necessity of using controlled atmospheres or mineral oils in
admixture with the alkaline metal. Moreover, the charging
sequence is entirely new in that the reactive alkaline metal
is plated directly on an electrode during charging of the battery
so as to be`available for discharge. The battery cell thus has
application for primary as well as secondary cells. Thus,
following plating of the lithium on the electrode, the lithium
dithionite electrolyte can be evacuated from the cell and be
replaced with an electrolyte of improved discharge charac-
teristics, for example, sulfuryl chloride or thionyl chloride.
The advantage of this procedure in a primary cell is a higher
voltage on discharge.
A principal advantage of the improved dithionite
battery cells resides in the provision of maximum energy and
current density ratios as well as power~weight ratios (generally
10 to 20 times those previously available with conventional
battery cells~, thus making possible for the first time the
potential for battery operation and propulsion of primary
yehicles and marine craft such as automobiles, trucks, power
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boats and submarines. Other advantages inherent in the use
of the improved battery cells and systems herein disclosed
will be apparent to those skilled in the art to which the
invention pertains, which is not intended to be limited to the
specific disclosures herein except as limited by the appended
claims.
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