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United States Patent (19) (11) 3,816,177 Walsh (45) June 11, 1974

54 SECONDARY CELLS AND BATTERIES 3,576,503 571971 Bloch et at...... 136/83 RX 75 Inventor: Myles A. Walsh, West Falmouth, Primary Examiner-Anthony Skapars Mass. Attorney, Agent, or Firm-Kenway, Jenney & Hildreth 73) Assignee: Eco-Control, Inc., Cambridge, Mass. 22 Filed: Nov. 17, 1972 57 ABSTRACT Secondary cells include a or cadmium electrode, 21 Appl. No.: 307,650 a counter electrode formed of an inert material for holding electrochemically active halogens such as bro 52) U.S. Cl...... 136/24, 136/30, 136/137 mine, chlorine and iodine, an aqueous zinc halide or 51) int. Cl...... HOm 43/00 cadmium halide electrolyte, a quarternary ammonium 58 Field of Search...... 36/24, 30.3, 20.22, 83 R, halide and a depolarizer in the electrolyte. The depo 136/6 R, 6 L, 6 F, 02, 103, 100 R, 137, 154-55 larizer is an organic complexing solvent which dis solves in water, is non-reactive towards the halogen or 56) References Cited halogens in the cell and forms a water insoluble com UNITED STATES PATENTS plex in the presence of quarternary ammonium poly 2,566, 4 8/1951 Bloch...... 136/155 X halides. The quarternary ammonium halides are 3,057,760 1 0 1 1962 Dereska et al...... 36/37 chosed so that at the counter electrode they combine 3,285,781 1 1/1966 Zito, Jr...... 136/30 X with halogens to form polyhalides. 3,352,720 l (1967 Wilson et al...... 136/37 A series-type battery has a plurality of these cells. 3,373,058 3/1968 Bloch...... 136/155 X 3,408,232 10/1968 Blue et al...... 136/30 24 Claims, 7 Drawing Figures

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3,816, 177 1. 2 SECONDARY CELLS AND BATTERES is increased when compared with the prior art cells em ploying such quarternary ammonium halides. A further object of the present invention is to provide BACKGROUND OF THE INVENTION a zinc or cadmium halide cell of the type which in The field of the present invention, in general, is cells 5 cludes a quarternary ammonium halide in the electro and batteries. In particular, the invention pertains to lyte in which polyhalides after being formed become a improved cells and batteries employing zinc or cad part of a stable water insoluble complex. mium and one or more halogens as the electrochemi A further object of the present invention is to provide cally active elements. a zinc or cadmium halide cell of the type which in Although cells which include an aqueous solution of 10 cludes a quarternary ammonium halide in the electro a zinc halide or a cadmium halide as the electrolyte lyte which also includes a depolarizer that is an organic such as zinc- cells are known, with the known complexing solvent which dissolves in water, is non prior art zinc-bromine cells, it is difficult to keep metal reactive towards the halogen or halogens in the cell and lic zinc and liquid bromine apart while simultaneously forms a water insoluble complex in the presence of achieving a structure by which a good percentage of 15 quarternary ammonium halides. the theoretical energy storage capacity can be realized. In connection with the foregoing, the reason why it is DESCRIPTION OF THE DRAWING difficult to keep the liquid bromine apart from the zinc FIG. 1 is a cross-sectional view of a cell in accor is that liquid bromine is soluble in the aqueous zinc bro dance with the present invention; mide electrolyte. Thus, liquid bromine, as it is formed 20 FIG. 2 is a graph showing the increase in perform in the cell, dissolves in the electrolyte. Of course, with ance when zinc cells include a depolarizer bromine dissolved in the electrolyte, it is difficult to in accordance with the present invention; prevent the dissolved bromine from migrating towards FIG.3 is a graph showing cell performance with vari the zinc electrode. The problem of halogen migration ous water soluble quarternary ammonium halides; is also significant in the case of zinc or cadmium cells 25 with aqueous chlorides as the electrolytes. FIG. 4 is a graph showing that the initial level of cell One prior art technique for keeping the metallic zinc performance is insensitive to the choice of depolar 1Zer, and liquid bromine in zinc-bromine cells apart relies on FIG. 5 is a graph showing the improved energy stor the use of quarternary ammonium halides dissolved in 30 age which results from increasing zinc bromide and the electrolyte. In such cells, on charging, elemental quarternary ammonium halide concentrations; bromine is formed by the decomposition of the bro FIG. 6 is a graph showing the effect of the volume of mide, and elemental bromine combines with the quar depolarizer on the cell of the present invention; ternary ammonium halide which is dissolved in the and electrolyte to form solid, water insoluble polybromides. 35 The use of quarternary ammonium halides, however, FIG. 7 is a graph showing the performance of chlo has not proved fully satisfactory, primarily because of rine cells constructed in accordance with the pres the instability of the solid polybromide and the fact that ent invention. solid polybromides distant from the inert electrode are DESCRIPTION OF THE PREFERRED not readily available for electrochemical reaction. Of 40 EMBODIMENTS course, such removal of bromine from the electro At the outset, it is desirable to comment on certain chemical system decreases the life of the cell. terms that are used throughout this specification and SUMMARY OF THE INVENTION claims. For example, the terms "Zinc electrode' and “bromine electrode' are not intended to imply that the The difficulties associated with zinc-bromine storage 45 electrode elements are formed of these materials exclu cells and batteries are significantly reduced by the zinc sively. As is conventional practice, the terms are used or cadmium-halogen secondary cell and battery of the merely to indicate the electrochemically active element present invention which includes an organic complex reacting. ing solvent depolarizer dissolved in the electrolyte The zinc or cadmium-halogen electrodes are prefera which is non-reactive towards the halogen or halogens 50 bly porous, electrically conductive, and non-corrosive. in the cell system and forms a stable, water insoluble Carbon in its various forms is a preferred material. The complex in the presence of solid quarternary ammo carbon of the zinc or cadmium electrode serves as a nium polyhalides. With such a depolarizer present in plating surface for zinc or cadmium. It may be desirable the cell, not only is the problem of halogen migration to utilize either porous carbon or graphite to form zinc reduced, but also the complex which results from the 55 or cadmium electrodes. combination of the polyhalide and the depolarizer is Furthermore, although reference is made to one stable. Furthermore, with such a depolarizer, the counter and one zinc electrode, it is obvious that cells amount of halogen that is removed from the electro in accordance with the present invention may include chemical system is reduced. more than one pair of electrodes. Moreover, the inven Accordingly, it is an object of the present invention 60 tion includes batteries of two or more cells constructed to provide a zinc or cadmium halide cell in which the in accordance with the present invention. In addition, problem of halogen migration is reduced. since cadmium is chemically similar to zinc, it is obvi It is another object of the invention to provide a zinc ous that the zinc in the electrode and the electrolyte of or cadmium halide cell and battery of the type which any example which follows can be replaced by cad includes a quarternary ammonium halide in the elec 65 mium. In the case of the halogen electrodes, it is neces trolyte; but, in which the amount of halogen that re sary that substantial amounts of one or more halogens mains available in the cell, as polyhalides are formed, selected from the group of bromine, chlorine and io 3,816, 177 3 4 dine be stored in the pores of the electrode. As is ex It might be noted that those solvents listed above, plained in detail below, such storage is accomplished which when dissolved in the electrolyte enhance per by storing quarternary ammonium polyhalides in the formance, are cyclic and non-cyclic hydrocarbons with pores of the halogen electrode. It is accordingly, pre one or more heteroatoms and are partially water solu ferred that the halogen electrode be formed of porous ble due to the aprotic dipole in the molecule. carbon, or graphite felt. A suitable graphite felt for Those complexing solvents which are usable in the forming the halogen electrodes in accordance with the cells of the present invention for complexing with poly present invention UCAR grade WDF graphite felt sold halides were determined by preparing a 10 percent by by Union Carbide Corporation, Carbon Products Divi weight solution of the complexing solvent in water. A sion, 270 Park Ave., New York, N.Y. 10017. UCAR O few grams of a polyhalide was the added to a test tube grade WDF graphite felt has a minimum carbon assay containing the water-complexing solvent solution. Visi of 99.6 percent. ble evidence of the formation of an insoluble oil-like In all cases, the carbon forming the electrode should complex indicated that the solvent is usable as a com possess sufficient structural integrity to permit handling plexing solvent in accordance with the present inven and mounting as a unitary element. Thus, the elec 15 tion. trodes may include reinforcing elements such as cloth and fibers, which are substantially chemically inert. Fi Although the exact chemistry of the complex forma berglass and asbestos constitute preferred reinforcing tion is not certain, some chemical bonding is believed materials, although certain plastics, particularly fluoro to exist between the polyhalide, the complexing solvent carbon polymers, may also be employed. 20 and the water. However, as stated above, the nature of A distinct feature of the present invention is that the the bond between the constituents which form the electrolyte contains a depolarizer. The term "depolar complex is not understood and could be ionic, covalent izer" is narrowly defined as any water soluble com or merely the result of van der Waals forces between pound which is capable of combining with either bro the three constituents. mine, chlorine or iodine containing polyhalides to form 25 water insoluble complexes rich in these halogens. As In one test to determine the nature of the bond in the will be more fully understood by reference to the fol complex, a few grams of tetramethyl ammonium bro lowing detailed description, the addition of a depolar mide was added to a ten percent propylene carbonate izer defined in this manner results in improved cell per in water solution. As a result, a red oil-like complex was formance, improved energy-storage capacity, and 30 formed. Appropriate measurements of the complex in longer cell life. dicated that a definite stoichiometric relationship be The depolarizer is an organic solvent, but not neces tween the polyhalide, the complexing solvent and the sarily a liquid, and may be any of the organic solvents water exists. In this case, the resulting complex had the which are water soluble, non-reactive to either bro following molecular relationship; mine, chlorine or iodine and which are good solvents 35 for quarternary ammonium polyhalides. Stated another tetramethyl ammonium bromide 2 parts way, the cells of the present invention include a depo propylene carbonate 2 parts larizer which can be placed in the electrolyte and which Water l part combines with the polyhalides that are formed in the cell to form insoluble complexes. By way of illustration, 40 examples of suitable organic complexing solvents are: That a definite molecular relationship exists is predi cated on the result of measurements by nuclear mag netic resonance. As a result of these measurements, propylene carbonate O some shifting of bonding was recorded which implies a 45 definite complex formation between the three constitu sy ents. lch, At this point it should be noted that many organic solvents, such as amines, react with halogens, particu larly bromine. For example, cannot be used as dimethyl carbonate O 50 a solvent in the bromine cells of the present invention MeoloMe because acetone reacts with bromine. Any water-soluble quarternary ammonium halide triethylphosphate (Eto) P=o where the halide are chloride, bromide or iodide 55 ions is effective for practicing the present invention. dimethylsulfate TT (Meoso, The substituents on the nitrogen of the quarternary ammonium halide are hydrogen, alkyl or aryl groups or sulfolane TTT o o - any combination of these functionalities. The alkyl or 60 aryl groups may be further functionalized with groups which enhance water such as acids, alcohols, amines, carbonates, esters, ketones, sulfones, sulfox ides, sulfates, phosphates, ammonium groups, amides, 1,4-butane sulfane thioesters, carbamates, acetals, ketals, or any combina V A(6 65 tion of these functionalities. The nitrogen of the quar ternary ammonium halide may be part of one or more cyclic structures. The quarternary ammonium halide may also be a water soluble polymer.

Y 3,816, 177 5 6 By way of example, suitable quarternary ammonium herein by reference. An earlier patent to Bloch is U.S. halides include phenyltrimethyl ammonium bromide, Pat. No. 2,566,114 entitled "Electric Cell," R. Bloch, N,N-dimethyl morpholinum bromide, tetramethylam the teachings of which are also incorporated herein by monium chloride, tetramethyl ammonium bromide and reference. The significance of the foregoing is that the N,N,N,N,N,N-hexamethyl diammonium methylene di present invention is an improvement on the "Bloch' bromide. cell in that the cell of the present invention includes a The electrolyte is generally saturated with more than depolarizer. In this regard, the alkyl-ammonium halides one of the quarternary ammonium halides for most effi such as the tetramethyl and tetraethyl ammonium ha cient energy storage. lides disclosed in U.S. Pat. No. 2,566,114 are usable in Polyhalide ions which are formed in the cells of the 10 the cell of the present invention. Indeed, exhaustive present invention can be represented by a generalized tests in accordance with the present invention have in formula dicated that any prior art cell of the type disclosed in the Bloch patents which includes a quarternary ammo nium halide is improved by the addition of a depolar where X, Y and Z represent either an identical, two 15 izer in accordance with the present invention which liq different or, in the case of the anions, three different uefies and isolates the halogen rich polyhalides. halogen atoms. The sum m + n + p is usually an odd In addition to the depolarizer and one or more quar number than can be 3, 5, 7, or 9. ternary ammonium halides, the electrolyte of the cell Table 1 below lists polyhalide ions of electrovalent of the present invention includes water and a zinc or salts. The list does not include ions of compounds 20 cadmium halide. Other salts, such as zinc sulfate, may whose identification remains doubtful or polyhalide be added to the electrolyte to improve electrolyte con ions identified only in solutions through some sort of ductivity and/or zinc plating characteristics. For most physicochemical measurement. efficient performance, it is generally preferred that the organic solvent constitute from 1 percent to 5 percent TABLE 25 of the total electrolyte volume. A zinc halide or cadmium halide is added in an X X X Xg X X* amount from 0.4 moles/liter to saturation. For most ef la" is l ICl." ficient energy storage, it is generally preferred that the Br Cl Br BrF," molarity range from 3 to 6. C Br F. IF," 30 Br, l, Bra BrC1 On the charging cycle, zinc is deposited on the zinc Cl BrC electrode and elemental bromine, chlorine or iodine is BrC l, BrCl liberated at the counter electrode. The elemental halo BrF 1Bra Bra IBrCl gen immediately combines with the dissolved quarter BrC ICl nary ammonium halide and dissolved organic complex BrCl ICF 35 Cl IF ing solvent (depolarizer) to form a complex which is BrF, substantially insoluble in the electrolyte, and which has CIF a surface tension less than that of the electrolyte. It is preferred that the complex wet the surfaces of the Polyhalide anionic salts are formed mostly easily with counter electrode. Thus, it is desirable that the counter large monovalent cations. 40 electrode be formed of a material which is poorly wet For a discussion of the chemistry of various polyhalo by the electrolyte, such as carbon in its various forms gen complex ions, see the article Popov, "Polyhalogen or graphite. Complex Ions,' which appears in Gutmann, Halogen On the discharge cycle, the halides are reformed with Chemistry, Vol. 1, Academic Press, 1967, pages the generation of power. The cell is completely dis 225-264, the teachings of which are incorporated 45 charged when either the zinc or the complex is entirely herein by reference. Another article which discusses consumed. the chemistry of the perhalides of quarternary ammo nium salts is Chattaway and Hoyle, "Perhalides of Qua In accordance with the present invention, where X is ternary Ammonium Salts," Journal of Chemical Sci either a bromide, chloride or iodide , the depolar ence, Vol. 123, 1923, pages 654-662, the teachings of 50 izer (complexing solvent) reacts at the halide electrode which are also incorporated herein by reference. according to the net reactions: In connection with Table 1, it should be noted that 2 X + quarternary ammonium halide + depolarizer the list of polyhalide ions contained therein is a com a complex + 2 et (). prehensive list of polyhalide ions that have been re 55 O ported in the literature. The inclusion of Table 1 in the 2 X 2 X + 2 e (1b). specification is not intended to imply that each and every polyhalide ion listed therein is formed in the vari X + quarternary ammonium halide 2 polyhalide ous embodiments of the present invention. For exam (c). ple, it is not desirable to include fluorides in the elec trolyte since fluorine gas and/or hydrogen fluoride is 60 polyhalide -- depolarizer -e complex (1 d) difficult to handle. Furthermore, as stated above, the use of quarternary ammonium halides in zinc or cad In Equation 1, the arrow to the right indicates the di mium halogen cells is known in this art. A U.S. patent rection of the chemical reaction during charge of the which is directed to such cells is U.S. Pat. No. cell, and the arrow to the left indicates the chemical re 3,373,058 entitled "Primary Cell Comprising an Aque 65 action occurring during discharge. ous Solution Containing Halogen and a Metal Halide,' In accordance with this invention, on the charge cy M. R. Bloch, the teachings of which are incorporated cle, metallic zinc or cadmium is deposited on the zinc 3,816, 177 7 8 or cadmium electrode and water insoluble complexes least 90 percent porous. The polypropylene separator coat the surfaces of the halogen electrode. Both of 17 was roughly 10 mils thick and 50 percent porous. these coatings can be observed with the naked eye. In all examples, electrode 12 served as the zinc elec Charging continues until about 80 percent of the zinc trode, and electrode 14 served as the halogen elec or cadmium halide is decomposed and about 80 per trode. Each electrode was provided with approximately cent of the quarternary ammonium halides are reacted ten square inches of active surface area. according to Equation 2 to form halogen storage com Each cell was vacuum-filled with approximately one plexes. hundred cubic centimeters of electrolyte. Me' + 2 X + quarternary ammonium halide -- de Each cell was charged until more than 80 percent of polarizer (2 Me -- complex W 2. 10 the zinc halide initially in solution was converted into : where Me is either zinc or cadmium Zinc and bromine, chlorine or iodine compounds. Generally, charging densities from about 0.25 to 0.75 Charging current densities ranged typically from 5 to amps per square inch are employed, but higher or 25 amperes/square foot. lower densities can be used if desired. The complex All cells were tested at constant current drain for a thus formed intimately covers the surface of the porous 5 variety of current densities. halogen electrode. This complex chemically stores the EXAMPLE 1. halogen until the time when discharge takes place. On discharge, reaction 2 is reversed and electric po Example 1 indicated the performance of cells filled wer, Zinc or cadmium ions, halide ions, quarternary with the following electrolytes: ammonium halides and the organic solvent depolarizer are produced. Cell Identification Electrolyte As is well understood in the art, repeated charging Letter Composition and discharging or zinc-halogen or cadmium-halogen A 0.4M ZnBr, 0.2M ZnSO, cells causes the formation of zinc or cadmium dendrites in water 25 B 0.4M ZnBr, 0.2M ZnSO which grow from the zinc or cadmium electrode until in 9: by volume water to they short the cell by extending into contact with the propylene carbonate halide electrode. Cells formed according to the present C 0.4M Zn Br, 0.2M ZnSO, invention, however, are longer lived than conventional 0.4M (CH)NBr in water cells. The longer life span of the cell of the present in 30 (CH), NBr in 9:1 by volume vention is due to the retardation of dendritic growth. It water to propylene carbonate is theorized that dendrites, which enter the layer of a halogen-rich complex covering the halogen electrode, The performance of cells A, B, C and D is plotted in tend to be dissolved. This substantially retards the rate FG. 2. of dendritic growth and prolongs the life of the cells. 35 Example 1 demonstrates that the use of an electro In actual operation, there is a tendency for hydrogen lyte which is an aqueous solution containing zinc bro gas to be generated at the zinc or cadmium electrode. mide, an organic solvent depolarizer such as propylene It is theorized that hydrogen gas results from the reac carbonate and a quarternary ammonium halide can tion of bromine-chlorine- or iodine- containing acids produce cells whose performance is substantially supe with zinc or cadmium. This hydrogen gas evolution 40 rior to cells containing electrolytes which do not con presents no special problems in the present invention tain such a depolarizer. because the gas can rise along the surface of the zinc or cadmium electrode to the electrolyte surface. This EXAMPLE 2 path remains open at all times because the halogen-rich A test of charge retentivity was performed by bring complex covering the halogen electrode does not com 45 ing cells A, B, C and D formed according to Example pletely fill up the region between the electrodes. It is l to full charge and by measuring the length of time re theorized that this path remains clear because if the quired for the voltage of each cell type to decay to one complex were to touch the zinc or cadmium surface, a half of its original value while delivering no current. direct reaction would take place to form water-soluble The results of these tests are: products which immediately dissolve. 50 Batteries and cells of the present invention are fur Cell Identification Charge Retentivity, ther illustrated by the aid of the following non-limiting Letter hours examples. In each example, a vertical cell 10 of the A. 5 - 10 type shown in crosssection in FIG. 1 was constructed. B - 3 Each cell was formed of a casing 11 which pro 55 C 200 - 250 vided supporting walls for graphite electrodes 12 and D 200 - 400 14, and provided sealing for an electrolyte chamber 16. The quarternary ammonium polyhalides are gener The graphite electrodes 12 and 14 were separated by ally unstable and decompose spontaneously, particu a layer of glass wool 15, a sheet of porous polypropyl 60 larly in contact with aqueous solutions. Comparision of ene 17 and a layer of graphite felt 19. Electrical leads the charge retentivity of cells C and D indirectly dem (not shown) were connected to electrodes 12 and 14 onstrates that the quarternary ammonium polyhalides by means of clips (not shown). can be stabilized by dissolving them in organic liquids, Electrodes 12 and 14 were made of one-eighth inch 65 such as propylene carbonate which are soluble in wa thick molded graphite and had a porosity of 26 percent. ter, nonreactive with bromine and form a water insolu The layer of glass wool 15 and the layer of graphite felt ble oil in the presence of quarternary ammonium poly 19 were both roughly one-eighth inches thick and at halides. 3,816, 177 9 10 EXAMPLE 3 Continued Cell Type Example 3 compares the performance of a plurality Molarity of N of cells formed according to example 1 and filled with CHONBr 0.85 0.4MZnBr, 0.2MZnSO, and quarternary ammonium 5 halide dissolved in 91 by volume water to propylene Peformance of said cells D, NandO is plotted in FIG. carbonate. The quarternary ammonium halides tested 5. Were: Eample 5 illustrates that improved energy storage re 10 sults from increasing zinc bromide and quarternary am Cell identification Quarternary Ammonium monium halide concentrations. Letter Halide EXAMPLE 6 0.4M (CH)NBr 0.4M (CH)NCl Example 6 compares the performance of a plurality 0.4M (CH4)HNCl 0.4M (CH) (CH)NBr 15 of cells formed according to Example 1 and filled with 0.4M (CH)NI 0.4M ZnBr, 0.2M ZnSO, 0.4M (CH)NBr dissolved 0.2M CHNBr. in the following ratios by volume of water to propylene 0.4M. CHONBr carbonate:

Performance of said cells D, E, F, GH, I and J is plot Cell Identification Volume water: Volume ted in FIG. 3. Example 3 illustrates that with the excep Letter propylene carbonate tion of quarternary ammonium iodides, initial level of D 90:10 cell performance is insensitive to the particular choice O 955 R 97:3 of water-soluble quarternary ammonium halide. Cell H S 99: illustrates that performance of the iodides is lower over 25 T 86:14 the entire range of current density. EXAMPLE 4 Performance of said cells D, Q, R, S and T is plotted Example 4 compares the performance of a plurality in FIG. 6. of cells formed according to Example 1 and filled with 30 Example 6 illustrates that performance depends on 0.4M ZnBr, 0.2M ZnSO, and 0.4M (CH3)NBr dis the volume of organic complexing solvent dissolved in solved in 9:1 by volume water to an organic complexing the electrolyte Optimal performance for this cell con solvent. The organic complexing solvents tested were: figuration is achieved when propylene carbonate con stitutes from 1 percent to 5 percent of the electrolyte 35 volume. Cell Identification EXAMPLE 7 Letter Organic Liquid Example 7 indicates the performance of cells filled D Propylene carbonate K Sulfolane with the following electrolytes: L Triethyl phosphate 40 M Dimethylsulfate Z Dimethyl carbonate Cell Identification Electrolyte Letter Composition

Performance of said cells D, K, L, M and Z is plotted 45 0.4M (CH), NBr in 9:1 by in FIG. 4. volume water to propylene carbonate Example 4 illustrates that a variety of organic com E 0.4M Zn Br, 0.2M ZnSO, 0.4M (CH), NC) in 9:1 by plexing solvents are available which are water soluble, volume water to propylene non-reactive to bromine, and form complexes with carbonate water and quarternary ammonium polyhalides. FIG. 4 50 0.4M ZnCl, 0.2M ZnSO, 0.4M (CH),NBr in 9:1 by illustrates that the initial level of cell performance is in volume water to propylene sensitive to the particular choice of organic complexing carbonate ().2M ZnCl, 0.2M ZnSO, Nolvent. ().4M (CH), NCI in 9:} by volume water to propylene EXAMPLE 5 carbonate Example 5 compares the performance of a plurality 55 of cells formed according to Example 1 and filled with zinc bromide, 0.2MZnSO and quarternary ammonium The performance of cells D, E, U and V is plotted in halides dissolved in 9:1 by volume water to propylene FIG. 7. Curve V of FIG. 7 demonstrates that the tri chloride ion is unstable in an aqueous solution and carbonate. The molarity of zinc bromide and quarter 60 readily dissociates to chlorine and the chloride ion. nary ammonium halides was varied as follows: Curve U, however, shows that excellent results occure with ZnCl2 as an electrolyte. Comparison of curves U Cell Type and V demonstrate that longer cell life for a zinc chlo Molarity of D N O 65 rine cell results if formation of the trichloride ion is ZnBra 0.4 1.0 50 avoided. (CH)NBr 0.4 0.4 0.30 Each cell was tested for short-circuiting by alterna (CH)NBr 0.5 tively charging and discharging the cells. Cells contain 3,816, 177 12 ing a depolarizer in accordance with the invention did 8. In a secondary cell including an Me electrode not fail through shortcircuiting and hence the number where Me is selected from the group consisting of zinc of cycles in excess of 100 that might be necessary to and cadmium, a halogen counter electrode spaced produce short-circuiting cannot be determined. apart from said Me electrode, an aqueous electrolyte It is appreciated that numerous variations of the pre and a quarternary ammonium halide wherein the im ferred cell, electrolyte composition and battery config provement comprises an organic solvent in the electro uration may be made. For example, the above cells ere lyte which is soluble in water, non-reactive towards the constructed from materials readily available in the lab halogen or halogens in the cell and which forms a water oratory, such as glass casing 11. It is, of course, appar insoluble complex in the presence of quarternary am ent that a commerical cell or battery would be formed O monium polyhalides. of a material more durable than glass. Such cell con 9. The cell as set forth in claim 8 wherein said Me struction techniques, however, are well within the skill electrode is a zinc electrode, said aqueous electrolyte of those in this art and will be readily apparent to those includes zinc bromide and said quarternary ammonium skilled in this art. Thus, the invention may be embodied halide is tetramethyl ammonium bromide. in other specific forms without departing from the spirit 15 10. The cell as set forth in claim 9 also including zinc or essential characteristics thereof. The present em sulfate to improve electrolyte conductivity and zinc bodiments are therefore to be considered in all respects plating characteristics. as illustrative and not restrictive, the scope of the in 11. The cell as set forth in claim 8 wherein said Me vention being indicated by the appended claims rather electrode is a zinc electrode, said aqueous electrolyte than by the foregoing description, and all changes includes zinc bromide and said quarternary ammonium which come within the meaning and range of equiva halide is tetramethyl ammonium chloride. lency of the claims are therefore intended to be em 12. The cell as set forth in claim 11 also including braced therein. zinc sulfate to improve electrolyte conductivity and I claim: zinc plating characteristics. 25 13. The cell as set forth in claim 8 wherein said Me 1. A secondary cell comprising a casing, an Me elec electrode is a zinc electrode, said queous electrolyte trode where Me is a metal selected from the group con includes zinc bromide and said quarternary ammonium sisting of zinc and cadmium, a counter electrode halide is dimethyl ammonium chloride. spaced apart from said Me electrode, an aqueous elec 14. The cell as set forth in claim 13 also including trolyte, a quarternary ammonium halide and an organic zinc sulfate to improve electrolyte conductivity and solvent which is soluble in water, non-reactive toward zinc plating characteristics. the halogen or halogens in the cell and which forms a 15. The cell as set forth in claim 8 wherein said Me water insoluble complex in the presence of quarternary electrode is a zinc electrode, said aqueous electrolyte ammonium polyhalides. includes zinc bromide and said quarternary ammonium 2. The cell as set forth in claim 1 wherein at the 35 halide is phenyltrimethyl ammonium bromide. counter electrode, the quarternary ammonium halide 16. The cell as set forth in claim 15 also including combines with halogens present in the cell to form zinc sulfate to improve electrolyte conductivity and polyhalides, and the polyhalides combine with the or Zinc plating characteristics. ganic solvent to form insoluble complexes which are 17. The cell as set forth in claim 8 wherein said Me halogen rich. 40 electrode is a zinc electrode, said aqueous electrolyte 3. The cell as set forth in claim 2 wherein the electro includes zinc bromide and said quarternary ammonium lyte is an aqueous salt solution containing a saltse halide is tetramethyl ammonium iodide. lected from the group consisting of zinc bromide, zinc 18. The cell as set forth in claim 17 also including chloride, , , cadmium zinc sulfate to improve electrolyte conductivity and chloride and cadmium iodide. 45 zinc plating characteristics. 4. The cell as set forth in claim 3 wherein said quar 19. The cell as set forth in claim 8 wherein said Me ternary ammonium halides are selected from the group electrode is a zinc electrode, said aqueous electrolyte consistint of phenyltrimethyl ammonium bromide, includes zinc bromide and said quarternary ammonium N,N-dimethyl morpholinum bromide, tetramethyl am halide is CH2N2Nr.Br. monium chloride, tetramethyl ammonium bromide, 20. The cell as set forth in claim 19 also including N,N,N,N,N,N-hexamethyl diammonium methylene di zinc sulfate to improve electrolyte conductivity and bromide, dimethyl ammonium hydrochloride, tetra zinc plating characteristics. methyl ammonium iodide and tetraethyl ammonium 21. The cell as set forth in claim 8 wherein said Me bromide. electrode is a zinc electrode, said aqueous electrolyte 5. The cell as set forth in claim 3 wherein said Me 55 includes zinc bromide and said quarternary ammonium electrode and said counter electrode are formed of po halide is CHONBr. rous carbon, and wherein said electrodes form sites for 22. The cell as set forth in claim 21 also including the electrochemically active elements reacting at the zinc sulfate to improve electrolyte conductivity and electrodes. zinc plating characteristics. 60 23. The cell as set forth in claim 8 wherein said Me 6. The cell as set forth in claim 5 wherein said elec electrode is a zinc electrode, said aqueous electrolyte trolyte also includes zinc sulfate to improve electrolyte includes zinc bromide and said quarternary ammonium conductivity and zinc plating characteristics. halide is tetraethyl ammonium bromide. 7. The cell as set forth in claim 5 wherein said organic 24. The cell as set forth in claim 23 also including solvent is selected from the group consisting of propy 65 zinc sulfate to improve electrolyte conductivity and lene carbonate, dimethyl carbonate, triethyl phos zinc plating characteristics. phate, dimethyl sulfate, sulfolane and 1,4-butane sul 2k xk k k k fone.