CA1114894A - Electrochemical cell using a dithionite radical of an alkaline metal as the charge transfer agent - Google Patents
Electrochemical cell using a dithionite radical of an alkaline metal as the charge transfer agentInfo
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- CA1114894A CA1114894A CA358,124A CA358124A CA1114894A CA 1114894 A CA1114894 A CA 1114894A CA 358124 A CA358124 A CA 358124A CA 1114894 A CA1114894 A CA 1114894A
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- electrolyte
- dithionite
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
ABSTRACT OF THE DISCLOSURE
An ambient temperature electric cell of primary and secondary nature, characterized by the use of a dithionite radical of an alkaline metal as the charge transfer agent, and including processes for manufacturing and for operating the same. The dithionite is dissolved in an anhydrous electrolyte comprised of a suitable solvent, which may also contain a salt of the same alkaline metal and be saturated with sulfur dioxide.
A sealed and evacuated cell (negative electrode, inert highly porous space, and positive current gathering electrode) is filled with the electrolyte and subjected to a charging current sufficient to plate the alkaline metal onto the negative electrode while further saturating the electrolyte with sulfur dioxide. In the case of a secondary cell, the electrolyte is capable of redissolving the dithionite produced upon discharge, such procedure being enhanced by a system for forced circulation of the electrolyte. In the case of a primary cell, redissolution is not necessary and the final cell potential and discharge character-istics can be enhanced by replacing the dithionite electrolyte with other anhydrous electrolyte solutions (e.g., sulfuryl chloride or thionyl chloride). The cell is characterized by extremely low internal resistance, long shelf life, excellent performance over a wide temperature range, and negligible depletion of the active dithionite charge transfer agent. In a particular high energy battery system, an electrolyte containing dissolved dithionite is circulated between a battery chamber and an auxiliary chamber containing solid dithionite salt (e.g., lithium dithionite). The electrolyte circulates from the auxiliary chamber through a solids separating means (centrifugal separator) to the battery chamber, where the electrolyte containing freshly dissolved dithionite is passed through a highly porous intermediate passage between an elongate active anode (e.g., copper) and an adjacent elongate current gathering cathode (e.g., finely divided carbon), in such fashion as to minimize internal resistance to current flow while substantially increasing the energy storage capacity of the battery cell.
An ambient temperature electric cell of primary and secondary nature, characterized by the use of a dithionite radical of an alkaline metal as the charge transfer agent, and including processes for manufacturing and for operating the same. The dithionite is dissolved in an anhydrous electrolyte comprised of a suitable solvent, which may also contain a salt of the same alkaline metal and be saturated with sulfur dioxide.
A sealed and evacuated cell (negative electrode, inert highly porous space, and positive current gathering electrode) is filled with the electrolyte and subjected to a charging current sufficient to plate the alkaline metal onto the negative electrode while further saturating the electrolyte with sulfur dioxide. In the case of a secondary cell, the electrolyte is capable of redissolving the dithionite produced upon discharge, such procedure being enhanced by a system for forced circulation of the electrolyte. In the case of a primary cell, redissolution is not necessary and the final cell potential and discharge character-istics can be enhanced by replacing the dithionite electrolyte with other anhydrous electrolyte solutions (e.g., sulfuryl chloride or thionyl chloride). The cell is characterized by extremely low internal resistance, long shelf life, excellent performance over a wide temperature range, and negligible depletion of the active dithionite charge transfer agent. In a particular high energy battery system, an electrolyte containing dissolved dithionite is circulated between a battery chamber and an auxiliary chamber containing solid dithionite salt (e.g., lithium dithionite). The electrolyte circulates from the auxiliary chamber through a solids separating means (centrifugal separator) to the battery chamber, where the electrolyte containing freshly dissolved dithionite is passed through a highly porous intermediate passage between an elongate active anode (e.g., copper) and an adjacent elongate current gathering cathode (e.g., finely divided carbon), in such fashion as to minimize internal resistance to current flow while substantially increasing the energy storage capacity of the battery cell.
Description
Background of the Invention .. .. _ . ...
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 , ' ' ' : ' '.' ' ' " ' . ' ~~3~
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 -- 4 ~
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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 -3'n ~
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..
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.
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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 - , , : :' . . , ' , ' ~,' ' " ': ' , ' ~ 4~
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 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 ,. :
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 tl~
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 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, 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.
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 ' ' ~ ' ' , ~
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
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 , ' ' ' : ' '.' ' ' " ' . ' ~~3~
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 -- 4 ~
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:
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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 -3'n ~
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..
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.
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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 - , , : :' . . , ' , ' ~,' ' " ': ' , ' ~ 4~
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 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 ,. :
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 tl~
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 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, 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.
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 ' ' ~ ' ' , ~
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 .. . .
': ' , :
.
, ' "' , :' :
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.
.
'', ' ~ ..
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 .
.
: . , ~ . . :
' ' ~ ' . '' ~
.
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 .. . .
': ' , :
.
, ' "' , :' :
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.
.
'', ' ~ ..
Claims (22)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrochemical cell comprising an electrode structure which includes an inert neyative electrode of conductive material, an inert positive current-gathering electrode of 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.
2. An electrochemical cell as in claim 1 wherein said charging agent is lithium dithionite.
3. An electrochemical cell as in claim 2 wherein said inert negative electrode initially comprises a copper structure substantially free of the same active metal as said selected active metal dithionite.
4. An electrochemical cell as in claim 2 which includes SO2 dissolved in said solvent.
5. An electrochemical cell as in claim 4 wherein said solvent is selected from acetonitrile, propylene carbonate and mixtures thereof.
6. An electrochemical cell as in claim 2 wherein said negative electrode includes a layer of active metal plated thereon from said liquid mixture.
7. An electrochemical cell as in claim 6 wherein said liquid mixture comprises an electrolyte mixture including a current-carrying solute dissolved in substantially inert, anhydrous organic liquid solvent.
8. An electrochemical cell as in claim 7 wherein said liquid mixture solvent and said solute solvent include at least one solvent in common.
9. An electrochemical cell as in claim 8 wherein said solute is lithium perchlorate, and said common solvent is selected from acetontrile, propylene carbonate and mixtures thereof.
10. An electrochemical cell as in claim 9 which includes SO2 dissolved in at least one of said solvents.
11. An electrochemical cell as in claim 1 wherein said liquid mixture comprises an electrolyte mixture including a current-carrying solute dissolved in said solvent.
12. An electrochemical cell as in claim 11 wherein said solute is a salt of the same active metal as in the active metal dithionite selected as the charging agent.
13. An electrochemical cell as in claim 12 wherein said charging agent is lithium dithionite and said solute is lithium perchlorate.
14. An electrochemical cell as in claim 13 which includes SO2 dissolved in said solvent.
15. An electrochemical cell as in claim 12 wherein said anhydrous organic liquid solvent is acetonitrile, said charging agent is lithium dithionite, and said solute is lithium perchlorate.
16. An electrochemical cell as in claim 12 including a source of sulfur dioxide gas and means to introduce said sulfur dioxide gas into said solvent.
17. An electrochemical cell as in claim 12 wherein said negative electrode is metallic copper.
18. An electrochemical cell as in claim 17 wherein said copper anode includes a layer of active metal plated thereon from said mixture.
19. An electrochemical cell as in claim 12 wherein said positive current gathering electrode is finely divided carbon.
20. 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 through an elongated passage between closely spaced adjacent conductive materials forming electrode surfaces 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 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.
21. A method as in claim 20 wherein said current-carrying solute comprises a member selected from the group consisting of active metal perchlorates and mixtures thereof.
22. A method as in claim 20 wherein sulfur dioxide is continuously introduced into said circulating electrolyte to dehydrate the same and to enhance the operation of said electrochemical system.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA358,124A CA1114894A (en) | 1976-09-13 | 1980-08-12 | Electrochemical cell using a dithionite radical of an alkaline metal as the charge transfer agent |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US722,548 | 1976-09-13 | ||
| US05/722,548 US4154902A (en) | 1976-09-13 | 1976-09-13 | Electric battery cell, system and method |
| CA266,233A CA1089929A (en) | 1976-09-13 | 1976-11-22 | Electrochemical cell using a dithionite radical of an alkaline metal as the charge-transfer agent |
| CA358,124A CA1114894A (en) | 1976-09-13 | 1980-08-12 | Electrochemical cell using a dithionite radical of an alkaline metal as the charge transfer agent |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1114894A true CA1114894A (en) | 1981-12-22 |
Family
ID=27164787
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA358,124A Expired CA1114894A (en) | 1976-09-13 | 1980-08-12 | Electrochemical cell using a dithionite radical of an alkaline metal as the charge transfer agent |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1114894A (en) |
-
1980
- 1980-08-12 CA CA358,124A patent/CA1114894A/en not_active Expired
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