US3844838A - Alkaline cells with anodes made from zinc fibers and needles - Google Patents
Alkaline cells with anodes made from zinc fibers and needles Download PDFInfo
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- US3844838A US3844838A US00233951A US23395172A US3844838A US 3844838 A US3844838 A US 3844838A US 00233951 A US00233951 A US 00233951A US 23395172 A US23395172 A US 23395172A US 3844838 A US3844838 A US 3844838A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/24—Alkaline accumulators
- H01M10/26—Selection of materials as electrolytes
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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
Definitions
- the zinc [58] Field of Search 136/30, 31, 125, 126, 76; fibers and needles are prepared by the electrolysis of a 204/10, 14, 55 R soluble zinc salt-containing electrolyte solution under conditions of extremely high cathode current density.
- This invention relates to zinc filaments in general and more particularly to novel zinc fibers and needles and to a process for their preparation.
- the invention relates to galvanic cell anodes fabricated from the novel zinc fibers and needles and to both primary and secondary galvanic cells using such anodes especially, though not exclusively, in conjunction with an alkaline electrolyte.
- Galvanic cells of the type employing a zinc anode and an alkaline electrolyte generally require that the anode possess a high surface area. This requirement is essential for reducing the tendency of zinc to passivate in the alkaline environment and furthermore to obtain satisfactory high rate discharge, particularly at low temperatures, by a more efficient utilization of the active zinc material.
- Prior art high surface area zinc anodes for use in alkaline galvanic cells have been made using conventional zinc powder.
- the zinc powder is suspended within a suitable gelling agent such as carboxymethyl cellulose containing the alkaline electrolyte, these particular anodes being often referred to as gelled powder anodes.
- the difficulty with anodes of this type is that the gelling agent, which is electrochemically inactive and thus capable of performing no useful purpose other than to support the zinc powder, takes up considerable space which might otherwise be occupied by the active material and consequently its use necessarily reduces the volumetric efficiency of the cell.
- the zinc powder from which these anodes are made usually contains substantial amounts of metallic impurities. These metallic impurities are capable of forming local cell couples with zinc which can give rise to wasteful corrosion of the anode and to the generation of gas during storage of the cell.
- High surface area anodes have also been fabricated from a dendritic zinc sponge produced by electrolytic methods such as disclosed in US. Pat. No. 3,071,638 issued to M. B. Clark et al on Jan. I, 1963. While this dendritic zinc sponge is advantageous in that it can be produced substantially free of impurities, it possesses an extremely high surface area and is pyrophoric and susceptible to spontaneous combustion if proper care is not taken in handling the material during the fabrication of the anode.
- the invention contemplates the provision of novel zinc filaments and in particular novel zinc fibers and needles possessing certain properties which make them ideal for use in fabricating galvanic cell anodes.
- the zinc fibers and needles of the invention are quite readily distinguishable in physical appearance from other forms of zinc material heretofore known in the art.
- the zinc fibers of the invention may best be described as filaments having a thin elongated central spine portion with a number of poly-directional side growths or branches.
- the zinc needles of the invention may best be described as filaments having a fairly smooth central spine portion with only a few or a minimum of poly-directional side growths or branches.
- filament refers in the broadest sense to any thin elongated body whose length may be hundreds or thousands of times greater than its width, and possessing considerable tensile strength, toughness and pliability.
- poly-directional refers to the physical arrangement of the side growths or branches which, during formation, tend to grow in many different directions or along many planes and is used specifically to denote the three dimensional character of the fibers and needles as distinguished.
- novel zinc fibers and needles of the invention are primarily characterized by their stability, unique crystal structure, exceptional purity and high surface area. The zinc fibers and needles are stable in that they do not rapidly oxidize upon exposure to the atmosphere.
- the crystal structure of the zinc fibers and needles is unique and readily distinguishable from any other form of zinc material.
- the zinc fibers and needles may be defined as being composed of one or more single crystals having a preferred orientation. More precisely, the zinc fibers and needles may be defined as filaments the major part of which is composed of a thin elongated crystal spine portion consisting essentially of one or more single crystals p eferentially orientated with an a axis or [010] direction) parallel to the axis' of the filament, i.e.; an a axis coincides with the primary direction of growth.
- the poly-directional side growths or branches are essentially polycrystalline and may be either granular, dendritic or platelet in form.
- the crystals are generally of irregular shape in cross-section and have a fairly large grain size as compared to conventional forms of zinc such as zinc powder.
- the zinc fibers and neeldes are substantially free of metallic impurities, containing only trace amounts of such impurities as aluminum, copper, lead and tin.
- the zinc fibers and needles possess a specific surface area which is intermediate that of conventional zinc powder and pyrophoric zinc sponge.
- the specific surface area of the zinc fibers and needles is between about 0.4 and 0.6 square meter per gram.
- the length of the zinc fibers and needles may vary from relatively short fibers of about /8 inch to long fibers of about 2 inches while the needles may vary from short needles of about Va inch to long needles of up to about 4 inches in length.
- the average diameter of width or the fibers and needles is about six thousandths of an inch.
- the novel zinc fibers and needles are prepared by the electrolysis of a soluble zinc salt-containing electrolyte under conditions of extremely high cathode current density.
- the cathode current density should be at least about 500 amperes per square foot.
- novel zinc fibers as defined hereinabove are prepared when the electrolysis is carried out at a temperature of about 25C.
- the novel zinc needles are prepared when the electrolysis is carried out at an elevated temperature. The temperature at which the zinc needles can be formed will vary depending upon the particular electrolyte employed.
- the process for preparing the novel zinc fibers and needles of the invention may be carried out in a typical electrolysis cell using a conventional zinc pig anode and a thin cathode suspended in the electrolyte bath.
- the fibers or needles electroform at the cathode and may be broken off and collected at the bottom of the bath or if the fibers of needles are not removed and the electrolysis is allowed to proceed, the fibers or needles tend to electrodeposit in the form of an interconnected skeletal zinc fibrous mat.
- This interconnected skeletal zinc fibrous mat consists basically of multiple fibers or needles joined to one or more neighboring fibers or needles throughout the mat.
- electroform or electroformation as used herein is meant the production of zinc fibers and needles by electrodeposition.
- Galvanic cell anodes can be readily fabricated from the novel zinc fibers and needles using conventional compression molding techniques.
- the novel zinc fibers or needles prepared as described above are placed within the mold and then compression molded to form an anode compact of the desired size and configuration.
- the interconnected skeletal zinc fibrous mats are preferably used. If the individual zinc fibers or needles are used, it is essential that they should be thoroughly intermingled when placed within the mold.
- the fibers or needles readily interlock or interknit with one another producing a highly cohesive anode body which is capable of supporting its own weight and retaining the shape in which it is molded.
- Anode compacts fabricated as described above may be advantageously used in a variety of both primary and secondary galvanic cell systems.
- Primary LeC- lanche type dry cells employing a manganese dioxide cathode may be made using an anode compact of the invention.
- One advantage of the anode compact in this dry cell system is that of improved resistance to leakage.
- the liquid cell reaction products can readily be absorbed by the zinc fibers or needles and thus become effectively immobilized within the cell.
- anode compacts fabricated in accordance with the invention are most advantageously used in both primary and seconary alkaline zinc galvanic dry cell systems.
- One of the principal advantages of anode compacts in such cell systems is that they afford a very high active surface area for a more efficient utilization of the anode material.
- FIG. 1 is a schematic view of a typical electrolysis cell used for preparing the zinc fibers and needles in accordance with the invention
- FIG. 2 is an isometric view showing the hexagonal crystal lattice of zinc
- FIG. 3 is an X-ray diffraction pattern of conventional zinc powder
- FIG. 4 is an X-ray diffraction pattern of zinc fibers prepared in accordance with the invention.
- FIGS. 5 and 6 are polarization curves showing the performance of high surface area galvanic cell anodes made from zinc fibers as compared with conventional types of anodes known in the art;
- FIG. 7 is an elevational sectional view of a typical alkaline zinc galvanic dry cell employing an anode compact in accordance with the invention.
- FIG. 8 is a perspective view of the anode compact used in the cell of FIG. 7;
- FIG. 9 is an elevational sectional view of a typical miniature button type alkaline zinc galvanic dry cell employing an anode pellet in accordance with the invention.
- FIG. 10 is a perspective view of the anode pellet used in the cell of FIG. 9;
- FIG. 11 is a graph showing the relationship between cell voltage and current of typical primary alkaline zinc manganese dioxide galvanic dry cells employing the anode compact as compared with similar cells using a gelled powder anode at various temperatures;
- FIG. 12 is a graph showing the discharge voltage of a typical primary alkaline zinc-manganese dioxide galvanic dry cell employing the anode compact as compared with a similar cell using a gelled powder anode of the conventional type;
- FIG. 13 is a graph showing the discharge voltage of a typical primary alkaline zinc-manganese dioxide galvanic dry cell employing a gelled powder anode as compared with the potential of the gelled powder anode versus a reference electrode; and FIG. 14 is a graph showing the discharge voltage of a typical primary alkaline zinc-silver oxide galvanic dry cell employing the anode compact as compared with a similar cell using a gelled powder anode of the prior art.
- FIG. 1 shows schematically a typical electrolysis cell for preparing zinc fibers and needles in accordance with the invention.
- the cell consists of an open tank 10 which is approximately three-quarters filled with a soluble zinc salt-containing electrolyte bath 12.
- a high purity zinc pig anode 14 such as is conventionally used in the electroplating art.
- a wire cathode 16 is dipped just below the surface of the electrolyte bath 12.
- an array of multiple cathodes suspended within the electrolyte bath from a common bus bar may be used, there being only one cathode shown here for the purposes of illustration.
- the anode l4 and cathode 16 are connected respectively through means of wires 18, 20 into an external circuit (not shown).
- the circuit includes a source of direct electrical current and means such as rheostat for controlling the flow of electrical current through the cell.
- the external circuit is closed suitably by means of a switch and electrical current is allowed to flow through the cell.
- the anode is consumed during the Anode: Zn Zn 2e
- the cell electrolyte is invariant in that the anode is continuously replenishing zinc ions into the electrolyte as zinc ions are removed at the cathode.
- cathode current density should be maintained at about at least 500 amperes per square foot. In the preferred practice of the invention, the cathode current density should be maintained at above about 1,000 amperes per square foot. This is considerably higher than that used in the conventional electroplating art for depositing smooth coatings of zinc from an alkaline zinc cyanide bath wherein cathode current densities of from about to 50 amperes per square foot have been reported (Electroplating Engineering Handbook by A. K. Graham, page 2l4, Reinhold Publishing Company).
- cathode current densities of only about 140 amperes per square foot are required. Since the current density is inversely proportional to the cathode surface area for a given current, it is advantageous to employ a cathode of the smallest practical surface area exposed to the electrolyte and preferably a very thin wire cathode is used.
- the zinc first deposits at the cathode in the form of individual fibers of needles which may be easily broken off and then collected at the bottom of the electrolyte bath.
- This skeletal fibrous mat consists basically of multiple fibers or needles joined to one or more neighboring fibers or needles in the mat.
- the electroformation process may be necessary to periodically increase the flow of electrical current through the cell, such as by means of the rheostat, in order to meet the increased current requirements due to the increasingly greater number of fibers or needles being deposited. It is virtually impossible during this period of the process to determine the cathode current density with any degree of accuracy due to the rapidly changing surface area of the zinc deposits.
- the electroformation process may be expediently carried out by properly controlling the amount of electrical current flowing through the cell to provide an estimated cathode current density which is above the minimum requirement to promote the electroformation of the fibers or needles.
- cathode current density can be estimated simply by visual observation of the type of deposit or reaction occuring at the cathode. lf the cathode current density is too low, no fiber or needle deposits can be observed. The deposit in this instance will be of the level, adherent type or the powdery type. if the cathode current density is too high, gas evolution (hydrogen) will be readily observed.
- the electrolyte may contain any zinc salt whose principal requirment is that it be solublein a solvent of high dielectric constant resulting in a solution of sufficient ionic conductivity to permit the maintenance of at least the minimum cathode current density necessary for electroforming the zinc fibers and needles of the invention.
- Suitable soluble zinc salts include the acetate, bromide, chlorate, chloride, formate, iodide, l-phenol-4- sulphonate, sulphate, thiocyanate, borate, bromate, fluogallate, fluoborate, fluosilicate, glycerophosphate, nitrate, phosphate, and sulphonate.
- Suitable solvents for the zinc salt include water, alcohols such as methanol, ethanol, and n-propanol, nitromethane, propylene carbonate and dimethylformamide. Cost and conductivity considerations are the two most important factors upon which the choice of the zinc salt and solvent should be based.
- Zinc chloride and zinc sulphate are the two preferred choices for the zinc salt from the standpoint of cost and conductivity.
- An aqueous solution of zinc chloride is the most preferred electrolyte solution.
- Water is the preferred solvent because of its low cost and freedom from fire hazard and toxicity.
- An additional salt such as ammonium sulphate may be used to increase the conductivity of the electrolyte bath.
- the concentration of the soluble zinc salt in the electrolyte solution is not too narrowly critical so long as enough zinc ions are present in the electrolyte to promote the electroformation of the zinc fibers and needles and further provided that a sufficiently high conductivity is maintained.
- the electrolyte solution should contain at least above about 30 per cent by weight of the soluble zinc salt in solution.
- the zinc fibers of the invention may be electroformed at a temperature of about 25C. under the conditions of extremely high cathode current density, elevated temperatures of above about 25C. are required to form the zinc needles and that the specific temperature at which the Zinc needles will begin to deposit will vary depending on the electrolyte composition and the concentration of the soluble zinc salt used.
- the temperature of the electrolyte must be elevated to about 80C. before zinc needles will be deposited.
- the individual zinc fibers and needles may be advantageously varied in length by properly controlling the cathode current density, that is, by adjusting the amount of electrical current flowing through the cell. It has been found that in addition to the temperature of the electrolyte bath, the current density maintained at the cathode has a profound influence on the nature of the zinc deposit and specifically the maximum length to which the respective individual fibers or needles may grow. By varying the electrical current flowing through the cell and consequently the cathode current density, the length of the fibers or needles may be varied from relatively short to long fibers or needles.
- the length of the fibers or needles will vary in inverse proportion to the cathode current so that by increasing the cathode current the length of the fibers of needles will be decreased and conversely by decreasing the cathode current the length of the fibers or needles will be increased. It will thus be seen that long, medium and short fibers or needles may be readily prepared.
- the zinc fibers may be prepared in lengths ranging from relatively short fibers of about 42 inch to long fibers of about 2 inches in length while the zinc needles may be prepared in lengths ranging from relatively short needles of about Va inch to long needles of up to 4 inches in length.
- Table 1 illustrates the effects of both temperature and cathode current upon the nature of the zinc deposit.
- the electrolyte solution used to obtain the data shown in the table was a 47 per cent by weight solution of zinc chloride in water.
- Zinc needles electroform at a temperature of about 80C. using this electrolyte.
- zinc fibers have been prepared using an electrolysis cell similar to that shown in FIG. 1 except that two arrays of seven thin zinc wire cathodes of about 0.312 inch in diameter dipping approximately 0.2 inch into the electrolyte solution were used, one array on each side of a zinc pig anode.
- the electrolyte was a 47 per cent by weight solution of zinc chloride in water and the anode-tocathode distance was about 5 inches.
- the temperature of the electrolyte was maintained at about 25C.
- a current of about 180 amperes flowed through the cell and zinc was observed to electrodeposit at the cathode surfaces in the form of individual fibers.
- electrolysis was allowed to proceed without removing the fibers, more and more fibers were observed to electrodeposit from the surfaces of the fibers initially formed at each cathode and this process continued with each of the fibers joining to one or more neighboring fibers until an interconnected skeletal zinc fiber mat was produced.
- the weight of the fiber mat so produced caused it to be broken off from the cathode surfaces and the mat then fell to the bottom of the electrolyte bath. The process was continued to produce more and more fiber mat.
- Zinc needles have also been prepared using the same electrolyte composition as disclosed in the above example. The process was carried out under essentially the same conditions except that the electrolyte was maintained at a temperature of about 90C.
- FIG. 2 shows diagramatically this hexagonal lattice for zinc with one of the unit cells being shown in darkened outline for purposes of illustration. It will be seen from the drawing that there are two zinc EFFECT OF TEMPERATURE AND CATHODE CURRENT UPON THE NATURE OF ELECTROFORMED ZINC Form of Approx. Length Temperature Cathode Current Electroformed Zinc inches C.
- the unit cell is composed of one eighth of a zinc atom on each of the corners and one zinc atom at a location within the cell. Each corner atom is shared by eight unit cells of adjacent crystals.
- the two axes of the zinc lattice are identified as the a and c axes in the literature and are shown in the diagram of FIG. 2.
- FIG. 3 An X-ray diffraction pattern for conventional zinc powder is shown in FIG. 3.
- the zinc powder shows conthe a axis nearer tinuous lines representing the randomness of crystal orientation and polycrystalline nature in the zinc powder.
- X-ray diffraction data have also been obtained for the zinc fibers and needles of the invention. These data were obtained by the rotating crystal method. The fibers and needles were mounted with their growth direction, i.e., direction along their length, perpendicular to the impinging X-ray beam.
- FIG. 4 shows the X-ray diffraction pattern for zinc fibers prepared in accordance with the invention.
- the X-ray diffraction pattern for the fibers shows the characteristic spots arranged on layer lines when the crystal is aligned with its growth axis perpendicular to the X-ray beam.
- the identity or repeat distance along this crystal growth axis can be calculated from the distance between the layer lines on the film and was found for both the fibers and needles to be 2.665A. This is the same value published in the literature for the distance between zinc atoms along the a axis of the crystal. It will be seen that the zinc fibers and needles of the invention are composed of one or more zinc crystals preferentially orientated with an (1 axis ([lYO] or [010]direction) parallel to the axis of the filament which is coincident with the primary direction of growth.
- Table [1 below gives the X-ray diffraction data for the zinc fibers of the invention.
- the table lists the d values in A for the observed line and the Miller indices (hkl) for a unit cell corresponding to the observed line in the X-ray diffraction pattern.
- the observed locations of reflection on the zinc fiber orientated with its long direction perpendicular to the impinging X-ray beam.
- Crystal grain studies have also been made on the zinc fibers and needles of the invention. The data obtained were compared with results of similar studies conducted on conventional zinc powder. All of the specimens studied were mounted, sectioned, polished and etched to bring out the grain structure. In the case of the zinc fibers and needles, the specimens were all seetioned through a plane taken in a direction perpendicular to the central spine portion of the fibers and needles.
- Crystal grain size measurements were taken on the zinc fibers in a direction essentially perpendicular to the growth axis and the crystals were found to range in size from the largest grain diameter of about 0.01 inch to the smallest grain diameter of about 0.0002 inch (2 X 10*). The average grain diameter of the crystals was determined to be about 0.005 inch.
- Crystal grain size measurements were taken on the zinc needles and the crystals were found to range from the largest grain diameter of about 0.002 to the smallest grain diameter of about 0.0001 inch. The average grain diameter of the crystals was found to be about 0.0008 inch.
- Crystal grain size measurements were taken on the zinc powder and the grain diameter was found to range from about 0.000004 to 0.001 inch.
- the average grain diameter of the zinc powder was found to be about 0.0002 inch.
- Zinc fibers and needles prepared in accordance with the invention have been found to be an excellent material for use in fabricating anodes for galvanic cells and especially those of the type employing an alkaline electrolyte.
- the fibers and needles possess a high surface area which is far in excess of that of conventional zinc powder but which at the same time is not so highly developed as to be pyrophoric and susceptible to rapid oxidation upon exposure to the atmosphere.
- the fibers and needles contain only trace amounts of impurities and consequently they are less prone to the formation of local corrosion coupled resulting in wasteful corrosion of the anode and gassing during storage of the cells.
- High surface area anodes for use in galvanic cells may be readily fabricated using the zinc fibers and needles of the invention by conventional compression molding techniques.
- the individual fibers or needles are placed within a suitable mold of the size and configuration desired and then compressed under a suitable pressure. say about 40 psi.
- the fibers or needles should be thoroughly intermingled with one another so that they are arranged in randomly orientated fashion within the mold with each of the fibers or needles making contact with as many neighboring fibers or needles as possible.
- the interconnected skeletal zinc fiber mat produced in accordance with the invention is advantageous for use in this molding procedure since the fibers or needles are throughly intermingled and joined to one or more neighboring fibers in the mat.
- the intermingled fibers or needles readily interlock or interknit with one another producing an anode compact of high strength and cohesiveness.
- Anode compacts so produced have been found to possess a number of advantages over anodes of the prior art. They possess a high strength and cohesiveness and are capable of supporting their own weight and consequently they do not require the use of a gelling agent such as carboxymethyl cellulose as employed in conventional gelled powder anodes. Moreover, the zinc fibers and needles contain only trace amounts of metallic impurities and therefore there is less tendency for the establishment of local corrosion couples which might otherwise result in wasteful anode corrosion and gassing during storage of the cells.
- a series of polarization tests were conducted in order to demonstrate the superior performance capabilities of anode compacts made in accordance with the invention.
- the performance of the anode compacts was compared in the test with that of conventional fiat zinc sheet anodes, sprayed zinc anodes (molten zinc sprayed onto a perforated zinc grid), and gelled powder anodes consisting of zinc powder suspended in a carboxymethyl cellulose gel.
- the anode compacts used in the test were made from zinc fibers electroformed from a methanol solution of zinc chloride. The weight of zinc was the same (0.80 gram) in both the anode compacts and gelled powder anodes tested.
- the tests were performed in a polytetrafluoroethylene cell holder using a large excess of a 35.8 per cent by weight potassium hydroxide electrolyte solution containing 4.48 per cent by weight of zinc oxide.
- the anodes were held in a vertical position with an anode face of about 0.78 square inch of apparent area exposed to the electrolyte.
- a large zinc cathode and a cadmium reference electrode were used in the cell.
- Current was provided by a -cycle a.c. interrupter of the type disclosed in the Kordesch et al publication, (Journal of the Electrochemical Society, vol. 107, pages 480-483, June 1960 Substantially resistance-free potential readings were taken and recorded. A Keithley electrometer was used to make these readings.
- FIG. shows a typical alkaline zinc galvanic dry cell employing an anode compact made in accordance with the invention.
- the cell comprises a cupped metallic can 22 surrounded by an insulating jacket 24. The extremities of the jacket are crimped around the outer edges of an insulated top cover 26 and an outer bottom metal cover 28.
- a paper washer 30 electrically insulates the can 22 from the bottom cover 28.
- Snugly fitted within the can 22 is a tubular cathode 32, the innermost surfaces of which are lined with a paper separator 34.
- a metal cap 36 Secured to the top of can 22 is a metal cap 36 serving as the positive cathode terminal.
- the cathode used in the cell may be composed of manganese dioxide or other oxidic depolarizer material.
- the cathode is of the cement-bonded type such as disclosed and claimed in U.S. Pat. No. 2,962,540 issued to K. Kordesch on Nov. 29, 1960.
- anode compact 40 of the invention Separated from the top of can 22 by means of separator 34 and the plastic insulating disc 38 is the anode compact 40 of the invention.
- the anode compact is made by compression molding the zinc fibers or needles into cylindrical form as more particularly shown in FIG. 8.
- the electrolyte for the cell is suitably a concentrated solution of potassium hydroxide, i.e., 30 to 35 per cent by weight solution of KOH.
- the electrolyte is absorbed into the anode compact and soaks the separator 34.
- the closure for the cell may be of the type disclosed and claimed in U.S. Pat. No. 3,042,734 issued to J.L.S. Daly et al on July 3, 1962.
- a closure comprises an inner metal bottom 42 sealed within the open end of can 22 by means of a nylon gasket 44 having a central opening 46.
- This opening is of a diameter slightly smaller than the external diameter of a rivet 48 so that when the rivet is driven through the opening 46 the gasket will be radially compressed between the inner bottom member 42 and the rivet head, thereby furnishing a tight mechanical seal thereat.
- the anode collector 50 Prior to driving rivet 48 through the cover and gasket, the same is passed through a central opening in the anode collector 50.
- This anode collector may be formed by a pair of rod-like members 52 formed integrally with a head plate 54 in which the central opening is provided for the rivet 48, the pair ofrod-like members 52 being embedded within the anode compact 40.
- an anode compact for use in a D-size alkaline zinc-manganese dioxide galvanic dry cell of a construction such as shown in FIG. 7 may be made by compression molding 15.5 grams of zinc fibers into a cylindrical shape approximately 1.6 inches high and 0.85 inch in diameter.
- Such an anode compact has a void volume of about 85.8 percent of the total volume which is more than sufficient for the subsequent absorption of the electrolyte.
- FIG. 9 shows a typical miniature button type alkaline zinc galvanic dry cell employing an anode compact of the invention.
- the cell comprises a metallic cup 56 which serves as the positive terminal.
- a thin wafer-like cathode 58 Within the cup 56 and in contact with its bottom wall is a thin wafer-like cathode 58.
- the cathode may be composed of any oxidic depolarizer material such as manganese dioxide, nickel oxide or silver oxide, for example.
- the anode is in the form of a thin pellet 60 and is disposed on top of the cathode 58 separated therefrom by at least one layer of a suitable separator material 62.
- a metallic top closure 64 is placed within the open end of the cup 56 and is pressed downwardly into contact with the top of the anode pellet 60.
- the top closure 64 is sealed around its outer periphery by a generally L-shaped plastic insulating grommet 66 and serves as the negative terminal of the cell.
- the anode pellet used in the button type cell of FIG. 9 is made by compression molding the zinc fibers or needles as described hereinabove.
- FIG. 10 shows the anode pellet prior to assembly in the cell.
- the anode compacts can be readily fabricated using the zinc fibers and needles without the need for any suspension or gelling agent such as used in gelled powder anodes of the prior art.
- the elimination of the gelling agent is highly advantageous from the standpoint of providing optimum volumetric cell efficiency since the gelling agent used in prior anodes, i.e., carboxymethyl cellulose, is electrochemically inactive and performs no useful purpose other than to support the zinc powder. Its elimination thus allows for more active material to be incorporated into the anode structure and conseqently the cell discharge capabilities are substantially increased.
- Performance of the two types of cells was compared by progressively switching each of the cells for l5-second intervals across load resistors of IO, 2, l, 0.5, 0.337 and 0.252 ohms. The voltages were continuously recorded on a potentiometric recorder. The voltage at the end of each l5-second interval was then used together with the known load resistor to calculate the current. Testing was conducted at temperatures of 25C C. and 20C. The voltage versus current relationship of the cells tested is shown in FIG. 11. It will be readily seen that for all the temperatures at which the cells were tested, the cells employing the interlocked zinc fiber anode compacts exceeded the performance of the cells employing the gelled zinc powder anodes of the prior art.
- Amalgamation of the zinc powder prior to fabricating the gelled powder anode with usually about 8 per cent by weight of mercury has proven effective in prohibiting or substantially reducing the evolution of gas caused by the establishment of local gassing couples due to the presence of impurities in the zinc. It has now been found, however, that the level of amalgamation required with the present anodes may be reduced below that necessary with the gelled powder anode. This is at least partially due to the fact that the zinc fibers and needles contain only trace amounts of impurities, notably iron for example. Reduction in the level of amalgamaton in the case of the present anodes, however, depends largely upon the nature of the cathode material.
- the cathode material contains only a limited amount of major impurities which might otherwise migrate through the cell electrolyte to the anode and establish local gassing couples thereat, then the level of amalgamation in the case of the present anodes may be substantially reduced below that required for the gelled powder anode.
- test cells were then placed in the bottom of a Pyrex beaker filled with paraffin oil so that any leaks in the sealed cell system could be easily detected by gas bubbling through the paraffin oil.
- a Pyrex tube having an open bottom end and equipped with a stopcock was placed within the beaker surrounding the cell and its pressure gauge.
- An extremely sensitive pressure test apparatus was thus provided for measuring the quantity of gas evolved from the cells. The sensitivity of the measurements was exceedingly high in that 7 X 10 moles of gas could be easily detected. This is equivalent to 1.4 X 10" grams of hydrogen or a local couple current of 0.2 milliamtest was thus solely attributable to the establishment of O Bere-hOur magnitude.
- the cells were then placed on TABLE V ANODE SHELF DATA Pressure (Psig) After Storage at 24C. (months) Pressure (Psig) After Storage at 54C.
- the anodes were cylindrical as shown in FIG. 8.
- a 41 man by weight mafia?the'pbms tnfia'iiyaroxide was used as the electrolyte for all the cells and the electrolyte volume was the same, i.e., 12.8 milliliters.
- the electrolyte was previously shaken thoroughly with zinc fibers for the purpose of removing any trace heavy metal impurities that may have been originally present in the potassium hydroxide solution.
- a control lot of OOOOOCN shelf storage within the test apparatus and were separated into two groups. One group of cells was maintained at a temperature of 24C. while the other group was maintained at a temperature of 54C. Pressure data were periodically obtained by measuring the quantity of gas evolved from the cells. The test was carried out 55 for a period of up to 2 /2 years/Table V below summarizes the results of these tests.
- alkaline zinc galvanic cells Many different types have been made using anodes fabricated from the zinc fibers and needles in accordance with the invention. Besides the primary alkaline zinc galvanic dry cells used in the above experiments, a number of secondary or rechargeable galvanic dry cells have also been constructed. These cells differ from those of primary type only in the specific composition of the cathode material and the electrolyte.
- Rechargeable alkaline zinc-nickel oxide galvanic dry cells employing the anode of the invention have been tested for prolonged periods of time with repeated cycling, i.e., charge and discharge, and have shown a superior performance in that the cells were capable of attaining a state of full charge after discharge over a greater number of cycles than possible with rechargeable cells employing the conventional gelled zinc powder anode.
- This is believed due to the fact that the anode of the invention more readily permits rapid oxygen recombination with the active material since there is no gelling agent which normally restricts the passage of gas throughout the anode structure. In addition, no oxidizable organic gelling agent is present to deteriorate.
- the rechargeable alkaline zinc-nickel oxide galvanic dry cells described above were of the miniature button type construction using a zinc fiber anode pellet as illustrated in FIGS. 9 and I0. 1
- One advantage in the manufacture of these miniature button type dry cells is that the anode pellet can be assembled in the cell container in the dry state followed by metering of the desired amount of electrolyte rather than by the more complicated procedure of metering a wet gelled powder anode into the cell container. Moreover, there is less tendency for leakage of the electrolyte which is a major problem with these button type cells since the anode pellet is highly absorbent and soaks up and holds the electrolyte.
- FIG. 14 shows the discharge performance at room temperature of such a cell compared with the performance of a similar cell using a gelled zinc powder anode.
- an electrolyte consisting of a concentrated solution of potassium hydroxide, suitably a 30 to 35 per cent solution of KOI-l. It has now been found, however, that with such rechargeable dry cells employing the anode of the invention the cycle life can be substantially increased by using a more highly concentrated solution of potassium hydroxide together with a high concentration of zinc oxide dissolved therein. Specifically, the molar ratio of KOH to ZnO should be of the order of about 6 to 1. Analysis of these electrolytes falls in the range of about 4-5 to 50 per cent potassium hydroxide and 12.5 to 15 per cent zinc oxide. The improved performance of these electrolytes can be attributed to the reduction in the formation of zinc dendrites formed during cell charging.
- the formation of zinc dendrites on charging may be substantially reduced and the cycle life of the cells significantly improved. It has been fu thermore found that the formation of these zinc dendrites may be even further reduced by incorporating in the cell electrolyte one or more additives selected from the group consisting of lead, arsenic, molybdenum and tungsten. In the alkaline solution, these additives will be present as the plumbite, arsenate, molybdate and tungstate. These additives should be present in the cell electrolyte in an amount of at least 20 ppm although a concentration of at least 1,000 ppm is preferred.
- electrolytes most suitable for use in rechargeable alkaline Zinc galvanic dry cells employing an anode made in accordance with the invention are highly concentrated solutions of 40 to 45 per cent potassium hydroxide containing about 12.5 to 15 per cent zinc oxide dissolved therein and having added thereto, in an amount of at least 20 ppm one or more additives selected from the group consisting of lead, arsenic, molybdenum, and tungsten.
- separator system consisting of multiple layers of a non-woven open pore material which is highly retentive of the electrolyte.
- This separator system is resistant to the penetration of zinc dendrites formed at the anode and thus serves to further improve the cycle life of the cell.
- Suitable separator materials for this purpose include Viskon-Vinyon* or other synthetic fiber batts.
- a number of miniature button type rechargeable alkaline zinc-nickel oxide galvanic dry cells utilizing the electrolytes of the invention have been made.
- the cell construction was basically the same as that shown in FIG. 9.
- the anodes for each cell were fabricated by compression molding zinc needles into the form of a wafer-like pellet (FIG. 10).
- the electrolyte composition was varied from a standard solution of 35 per cent KOH plus 1.5 per cent ZnO to electrolyte compositions containing 47.5 per cent KOl-l and 12.5 per cent ZnO with and without the addition of 1,000 ppm of lead.
- the separator used in the cells employing the electrolytes of the invention consisted of ten layers of 0.008 inch Viskon-Vinyon.
- the cells were subjected to deep discharge to 0.9 volt at the 1 /2 hour rate followed by constant current charging at the 4-hour rate plus 50 per cent minimum overcharge. The cells were considered to have reached the end of their useful cycle life when the cell capacity dropped off to 50 per cent of the ini-
Abstract
Description
Claims (9)
Priority Applications (1)
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US00233951A US3844838A (en) | 1970-04-03 | 1972-03-13 | Alkaline cells with anodes made from zinc fibers and needles |
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US2549070A | 1970-04-03 | 1970-04-03 | |
US00233951A US3844838A (en) | 1970-04-03 | 1972-03-13 | Alkaline cells with anodes made from zinc fibers and needles |
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US3844838A true US3844838A (en) | 1974-10-29 |
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Cited By (7)
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US4579791A (en) * | 1983-04-06 | 1986-04-01 | Duracell Inc. | Cell anode |
US4777100A (en) * | 1985-02-12 | 1988-10-11 | Duracell Inc. | Cell corrosion reduction |
US4840644A (en) * | 1987-11-24 | 1989-06-20 | Duracell Inc. | Cell corrosion reduction |
US5158643A (en) * | 1988-12-16 | 1992-10-27 | Matsushita Electric Industrial Co., Ltd. | Method for manufacturing zinc oxide whiskers |
US20030170543A1 (en) * | 2002-02-26 | 2003-09-11 | Alltrista Zinc Products Company, L.P. | Zinc fibers, zinc anodes and methods of making zinc fibers |
US20070141466A1 (en) * | 2004-04-23 | 2007-06-21 | Harunari Shimamura | Alkaline battery |
US8491768B2 (en) | 2010-06-23 | 2013-07-23 | International Business Machines Corporation | Method of purifying nanoparticles in a colloid |
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US2655472A (en) * | 1949-12-16 | 1953-10-13 | Robert V Hilliard | Process of extracting and recovering metals by leaching and electrolysis |
US2820077A (en) * | 1953-03-17 | 1958-01-14 | Accumulateurs Fixes | Electrodes for galvanic cells and method of making same |
US3071638A (en) * | 1959-06-25 | 1963-01-01 | Union Carbide Corp | Dendritic zinc electrodes |
US3226260A (en) * | 1963-03-01 | 1965-12-28 | Union Carbide Corp | Rechargeable alkaline cell |
US3291707A (en) * | 1963-02-19 | 1966-12-13 | Abbey Automation Systems Inc | Bright zinc electroplating technique |
US3326783A (en) * | 1963-08-21 | 1967-06-20 | Tennessee Corp | Process for the production of electrolytic zinc powder |
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US2655472A (en) * | 1949-12-16 | 1953-10-13 | Robert V Hilliard | Process of extracting and recovering metals by leaching and electrolysis |
US2820077A (en) * | 1953-03-17 | 1958-01-14 | Accumulateurs Fixes | Electrodes for galvanic cells and method of making same |
US3071638A (en) * | 1959-06-25 | 1963-01-01 | Union Carbide Corp | Dendritic zinc electrodes |
US3291707A (en) * | 1963-02-19 | 1966-12-13 | Abbey Automation Systems Inc | Bright zinc electroplating technique |
US3226260A (en) * | 1963-03-01 | 1965-12-28 | Union Carbide Corp | Rechargeable alkaline cell |
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Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
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US4579791A (en) * | 1983-04-06 | 1986-04-01 | Duracell Inc. | Cell anode |
US4777100A (en) * | 1985-02-12 | 1988-10-11 | Duracell Inc. | Cell corrosion reduction |
US4840644A (en) * | 1987-11-24 | 1989-06-20 | Duracell Inc. | Cell corrosion reduction |
US5158643A (en) * | 1988-12-16 | 1992-10-27 | Matsushita Electric Industrial Co., Ltd. | Method for manufacturing zinc oxide whiskers |
US20030170543A1 (en) * | 2002-02-26 | 2003-09-11 | Alltrista Zinc Products Company, L.P. | Zinc fibers, zinc anodes and methods of making zinc fibers |
US20070141466A1 (en) * | 2004-04-23 | 2007-06-21 | Harunari Shimamura | Alkaline battery |
US7553586B2 (en) * | 2004-04-23 | 2009-06-30 | Panasonic Corporation | Alkaline battery |
US8491768B2 (en) | 2010-06-23 | 2013-07-23 | International Business Machines Corporation | Method of purifying nanoparticles in a colloid |
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