CA1056904A - Inorganic separator for alkaline electrochemical cells - Google Patents
Inorganic separator for alkaline electrochemical cellsInfo
- Publication number
- CA1056904A CA1056904A CA250,960A CA250960A CA1056904A CA 1056904 A CA1056904 A CA 1056904A CA 250960 A CA250960 A CA 250960A CA 1056904 A CA1056904 A CA 1056904A
- Authority
- CA
- Canada
- Prior art keywords
- separator
- hydroxide
- mixture
- matrix
- improved
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/417—Polyolefins
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/426—Fluorocarbon polymers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/431—Inorganic material
- H01M50/434—Ceramics
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/491—Porosity
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0002—Aqueous electrolytes
- H01M2300/0014—Alkaline electrolytes
-
- 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
-
- 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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Abstract
ABSTRACT OF THE INVENTION
An improved separator for alkaline electrochemical cells having zinc negative electrodes comprises rare earth inorganic hydroxide in finely divided solid particulate form dispersed uniformly within a shape-retaining non-reactive matrix.
The matrix may be, for example, polytetrafluoroethylene or the like and the separator is insoluble and chemically inert in the cell electrolyte. The separator traps or chemically combines with soluble zinc ions so as to keep the ions within the compart-ment containing the zinc electrode. This reduces the solubility of the zinc electrode. The resultant reduction in shape change reduces the shift in electrical properties which occurs during cycling of the cell. An improved method of making the novel separator is also provided wherein a mixture of the hydroxide and the matrix material is extruded into a thin sheet.
An improved separator for alkaline electrochemical cells having zinc negative electrodes comprises rare earth inorganic hydroxide in finely divided solid particulate form dispersed uniformly within a shape-retaining non-reactive matrix.
The matrix may be, for example, polytetrafluoroethylene or the like and the separator is insoluble and chemically inert in the cell electrolyte. The separator traps or chemically combines with soluble zinc ions so as to keep the ions within the compart-ment containing the zinc electrode. This reduces the solubility of the zinc electrode. The resultant reduction in shape change reduces the shift in electrical properties which occurs during cycling of the cell. An improved method of making the novel separator is also provided wherein a mixture of the hydroxide and the matrix material is extruded into a thin sheet.
Description
BA KGROUND
Field of the Invention .
The pre~ent invention generally relates to improved separators and methods of making the same and more particularly -to improve inorganic separators for alkaline electrochemical cells having zinc negative electrodes.
Prior Art The usual types of alkaline cells and batteries com-prise a positive electrode of, for example, silver oxide, nickel hydroxide or the like and a negative electrode of zinc. The electrolyte may be, for example, concentrated aqueous potassium hydroxide or the like. When such cells are operated, the zinc electrode gradually loses zinc ions into the electrolyte and becomes physically deformed. Certain electrical characteristics of the cell or battery are dependent upon the physical configur-`ation of the electrodes. Any shape change in either electrode results in a change in the electrical properties of the cell, obviously an undesirable development. Moreover, reduction in the size of one of the electrodes, for example the negative electrode places a limit on the durability of the cell. Inasmuch as such cells are relatively expensive, it would be highly desirable to provide means for stabilizing the shape of the electrodes and thus stabilizing the electrical properties of the cell while increasing the usable life of the cell.
SUMMARY OF THE INVENTION
The foregoing needs have now been satisfied by the present invention. In this regard, an improved separator for alkaline electrochemical cells having zinc negative elec-trodes which comprises rare earth inorganic hydroxide in finely X
._ 1 divided solid particulate form dispersed uniformly within a shape-retaining non-reactive matrix is provided. The matrix may be, for example, polytetrafluoroethylene or the like and the separator is insoluble and chemically inert in the cell electro-lyte. The separator traps or chemically combines with soluble zinc ions so as to keep the ions within the compartment contain-ing the zinc electrode. This reduces the solubility of the zinc electrode. The resultant reduction in shape change reduces the shift in electrical properties which occurs during cycling of the cell. An improved method of making the novel separator is also provided wherein a mixture of the hydroxide and the matrix material is extruded into a thin sheet.
The separator prevents the migration of zinc ions from the compartment containing the -la-1 zinc negative electrode in an alkaline electrochemical cell.
The separator accomplishes this by either trapping or chemically combining with those zinc ions. Accordingly, the rate of removal of zinc from the electrode in the form of zinc ions solubilized in the electrolyte is depressed. The net effect is that the zinc electrode retains its shape over a substantially greater period of time during cycling of the cell than is the case with conventional cells and exhibits greater stability of electrical properties than do conventional cells.
The separator may employ any one or a mixture of rare earth inorganic hydroxides such as cerium hydrate, yttrium hydroxide and hydroxides of neodymium, samarium, gadolinum, terbium and the like. The hydroxide is disposed in finely divided particulate form within a non-reactive matrix such as polytetra-fluoroethylene, vinyl acetate and ethylene copolymer resin, poly-vinyl chloride polymer or the like to form the desired separator sheet, which sheet is then placed around the negative electrode in each cell. Further details of the present invention are set forth in the following detailed description and the accompanying drawings.
DRAWINGS
Figure 1 is a schematic perspective view of a preferred embodiment of an electrochemical battery employing the improved inorganic separator of the invention, portions being broken away to illustrate certain internal features of the battery.
DETAILED DESCRIPTION
An improved inorganic separator is made in accordance with the present invention utilizing rare earth inorganic hydroxide in finely divided solid particulate form. The -` ~056904 1 hydroxide may be any one or more of the rare earth hydroxides.
Normally, the average particle diameter of the hydroxide is no greater than about 2 microns and the average density may vary, but for cerium hydrate, for example, is usually no greater than about 0.9 gm/cm3.
This fine powder is mixed intimately with a suitable binder-forming inert matrix material which is non-reactive with the usual alkaline cell electrolytes and which may be, for example, polytetrafluoroethylene emulsion, a low molecular weight poly-olefin resin, a mixture of vinyl acetate and a copolymer ofethylene and vinyl acetate, polyvinyl fluoride resin, fluorinated .
polyethylene or polyvinyl chloride polymer.
The resulting mixture has the rare earth hydroxide uniformly dispersed therein; for example, when polytetrafluoroethy-lene emulsion is used, drying can take place in an oven at 100C
for four hours. If the matrix material is in solid form initially, it is utilized as a finely divided powder and is merely mixed uniformly with the hydroxide. The resulting dry mixture is then ready for formation into a separator configuration of desired average pore diameter and porosity.
Forming of the separator is usually accomplished by extruding the dry mixture of the rare earth hydroxide and matrix forming material through a suitable shape nozzle to form a sheet of material approximately, for example, 0.010" thick. Other thicknesses such as 0.002", 0.005", 0.015" and 0.030" are also suitable. Such extrusion may, for example, be carried out under the following conditions utilizing the following equipment:
The previously described powder mix is mixed and compounded with an extrusion aid (lubricant) such as propylene glycol, methyl alcohol, isopropyl alcohol, ethyl alcohol, acetone i or the like in a mixer such as Patterson Kneadmaster mixer Model CK453. The resultant dough is extruded using, for example, a Patterson Extruder having an auger diameter of three (3) inches J
and an extrusion nozzle opening of 6" wide x 0.010" thick. The lubricant can be present in the extruded dough in a weight concentration of, for example, about 10 - 20 percent. Following extrusion, the sheet is passed through a curing oven at a tempera-ture of 3600F for about 1 - 10 minutes so as to drive off the lubricant and cure the matrix material.
The sheet material thus formed by extrusion is then cut to size and normally used directly as a separator in an alkaline cell of the type described. Preferably, the extruded sheet material has a very low average pore diameter, for example, below about 200 angstroms and a high volume porosity, preferably above about 50%. It will be understood that for special applica-tions the separator material may be formed having other ranges of physical characteristics. Generally, however, a very low pore diameter with high porosity is desired so that efficient contain-ment of solubilized zinc ions can be achieved. The improved separator may be utilized in any suitable way, for example, in the containment surrounding the zinc electrode in the cell or as follows:
The sheet may be placed directly on the zinc electrode so as to act not only as a negative interseparator but also as a support structure for the zinc active material. In this case, the improved inorganic separator material which has been cut to dimensions larger than that of the negative electrode....
is pressed on and into the zinc electrode structure during the latter's fabrication.
3~ Preferably, the improved separator is, in use, disposed 1 between protective layers of conventional separator material, such as polypropylene film having the following characteristics:
average pore diameter = 400 - 600 microns; average thickness =
5.0 mils. Such films can be, if desired, of such materials as the following: cellophane, porous irradiated polyethylene, rayon, dynel,* nylon, etc.
Now referring more particularly to Fig. 1 of the accompanying drawings, a typical alkaline battery having zinc negative electrodes and the improved separator material of tO the invention is schematically illustrated. Thus, a battery 10 is shown which includes a container 12 having a hollow interior 14 and a closed top 16 through which a filler and vent tube 18 and the positive and negative terminals 20 and 22, respectively, of the battery extend.
A pair of negative electrodes 24 of zinc in the form of plates are disposed in spaced relation within interior 14 of container 12 and are connected to the negative terminal 22 by a pair of leads 26. A sheet 28 of the improved separator 30 of the invention is wrapped around each negative electrode 24 in container 12 and is disposed between two sheets 32 and 34 of poly-propylene separator material to form therewith containment bag 36 for each negative electrode. Bag 36 has an open upper end 38 through which the leads 26 protrude.
The negative electrodes 24 in their containment bags 36 are sandwiched between three positive electrodes 40 in the form of plates connected by leads 42 to the positive terminal 20.
An electrolyte 44 in the form of concentrated (about 40%) aqueous potassium hydroxide (solution) is also disposed in interior 14 of container 12 below the upper end 38 of each containment bag 36. It will be understood that other arrangements of the improved * Trade mark for a copolymer of vinyl chloride and acrylonitrile ** Registered trade mark for a film produced from wood pulp by the viscose process ~05~;904 1 separator within alkaline electrochemical cells and batteries can be provided. The following specific Examples further illus-trate certain features of the present invention:
EXAMPLE I
Cerium hydrate is passed through a 325 mesh screen so that it has an average particle size of less than 2 microns.
This fine powder is then mixed with sufficient polytetrafluoro-ethylene emulsion so that the solids by weight ratio of the polymer to the hydroxide is about 1:4. The mixing is accomplished for a sufficient period of time until the mixture is uniform.
The resulting product is then dried in an air convection oven at 100C for 4 hours. Four parts (by weight) of the dried mixture are then mixed with one part of propylene glycol and the resulting dough is extruded through a nozzle under 1200 psi at about 85C to obtain a sheet which, after curing in an oven at about 360F for about 5 minutes, has an average thickness of about 0.010". This finished sheet has an average pore diameter of less than 200 angstroms and a volume porosity of about 55%.
The finished sheet is cut into two appropriately sized sheets and installed in a battery having the configuration shown in Figure 1. The battery has two zinc negative electrodes in the form of plates, each plate having the following dimensions:
1.625" wide x 1.50" high x 0.042" thick. Three silver oxide positive electrodes are spaced between and outside the two zinc electrodes. The positive electrodes are each in the form of a plate having the following dimensions: 1.625" wide x 1.50 " high x 0.034" thick. The electrodes are disposed in a casing of styrene-acrylonitrile plastic sold under the trademark Lustran 400 of Monsanto Co., St. Louis, Mo.
The negative electrodes are each enclosed in an open 1 topped containment bag comprising an inner and an outer layer of polypropylene, each about 5 mils thick and having an average pore diameter of about 500 microns,and a middle layer comprising a sheet of the improved separator of the invention. An electro-lyte comprising a 40% aqueous solution of potassium hydroxide is disposed in the battery below the open top of each containment bag. The battery (A) exhibits great durability and stability of electrical properties in contrast to a battery (B) fabricated in the same way utilizing the same materials except for the absence of the cerium hydrate-containing separator of the invention, as shown in the following table:
TABLE
Characteristics Battery A Battery B
life at ngrmal load 160 102 (at 140 F) days maximum number of cycles 56 22 percent negative electrode 20 70 shape change EXAMPLE II
An improved separator in accordance with the present invention is fabricated by intimately and uniformly mixing together 85 parts by weight of yttrium hydroxide with 15 parts by weight of powdered polyethylene resin having an average particle diameter of about 0.2 microns. The yttrium hydroxide is in particulate form having an average particle diameter of about 1 micron and a bulk density of about 1.6 gm/cm3. The mixing is continued until a spongy mixture is obtained, whereupon the mixture is blended into a dough with methyl alcohol (6 parts of mixture to 1 part of alcohol, by weight) and the dough is extruded at 85C and 1000 psi into a sheet which, after curing in an oven at about 350F for about 10 minutes, has a thickness of 1 ~bout 10 mils. The finished sheet has an average pore diameter of 20~ - 300 and a volume porosity of about 40%.
The separator sheet is cut into two sheets and utilized in a battery (C) identical to battery A of Example I in place of the cerium hydrate-containing separator sheets thereof.
Battery C is co~lpared in electrical characteristics with a battery (B) which is identical except for the absence of a rare earth hydroxide-containing separator. The results of the comparison are set forth in the table below:
TABLE
Electrical CharacteristicsBattery C Battery B
battery life (at 140Fo) days 102 35 maximum cycles (at 70 F) 40 22 percent negative electrode 55 70 shape change As in Example I, comparative tests show that improved electrical stability and durability are achieved by using the rare earth hydroxide-containing separator of the invention.
When parallel tests are conducted substituting equivalent amounts of other rare earth hydroxides for the cerium hydrate of Example I and the yttrium hydroxide of this Example in the separator of the invention, comparable improved results are obtained. Substitution in separate tests of polypropylene, vinyl acetate-ethylene copolymers, polyvinylidene fluoride, fluorinated ethylene-propylene resin and polyvinyl chloride for the polytetrafluoroethylene emulsion and the polyethylene resin of Examples I and II, respectively, is made without varying the results, when the separator average pore diameter and total pore volume, as well as the weight ratio of such matrix material to the rare earth hydroxide are substantially as set forth above.
Accordingly, an improved separator is economically formed in accordance with the present method, utilizing effective concentrations of rare earth hydroxides in finely divided particle form uniformly dispersed in a suitable matrix. Such separators when used in containment around the zinc negative electrodes of the cell, effectively reduce the loss of soluble zinc ions from the contained area and thus reduce the loss of zinc from the zinc electrode during operation of the electro-chemical cell. Such loss reduction results in improved longevity for the cell and more stable electrical characteristics, as demonstrated in the tables of Examples I and II. Accordingly, improved alkaline cells and batteries having zinc negative elec-trodes can be provided in an economical manner through the use of the improved separator of the invention.
Various modifications, changes, alterations and additions can be made in the present separator, its components, and in the present method and its steps and parameters. All such modifications, changes, alterations and additions as are within the scope of the appended claims form part of the present invention.
_ 9 _
Field of the Invention .
The pre~ent invention generally relates to improved separators and methods of making the same and more particularly -to improve inorganic separators for alkaline electrochemical cells having zinc negative electrodes.
Prior Art The usual types of alkaline cells and batteries com-prise a positive electrode of, for example, silver oxide, nickel hydroxide or the like and a negative electrode of zinc. The electrolyte may be, for example, concentrated aqueous potassium hydroxide or the like. When such cells are operated, the zinc electrode gradually loses zinc ions into the electrolyte and becomes physically deformed. Certain electrical characteristics of the cell or battery are dependent upon the physical configur-`ation of the electrodes. Any shape change in either electrode results in a change in the electrical properties of the cell, obviously an undesirable development. Moreover, reduction in the size of one of the electrodes, for example the negative electrode places a limit on the durability of the cell. Inasmuch as such cells are relatively expensive, it would be highly desirable to provide means for stabilizing the shape of the electrodes and thus stabilizing the electrical properties of the cell while increasing the usable life of the cell.
SUMMARY OF THE INVENTION
The foregoing needs have now been satisfied by the present invention. In this regard, an improved separator for alkaline electrochemical cells having zinc negative elec-trodes which comprises rare earth inorganic hydroxide in finely X
._ 1 divided solid particulate form dispersed uniformly within a shape-retaining non-reactive matrix is provided. The matrix may be, for example, polytetrafluoroethylene or the like and the separator is insoluble and chemically inert in the cell electro-lyte. The separator traps or chemically combines with soluble zinc ions so as to keep the ions within the compartment contain-ing the zinc electrode. This reduces the solubility of the zinc electrode. The resultant reduction in shape change reduces the shift in electrical properties which occurs during cycling of the cell. An improved method of making the novel separator is also provided wherein a mixture of the hydroxide and the matrix material is extruded into a thin sheet.
The separator prevents the migration of zinc ions from the compartment containing the -la-1 zinc negative electrode in an alkaline electrochemical cell.
The separator accomplishes this by either trapping or chemically combining with those zinc ions. Accordingly, the rate of removal of zinc from the electrode in the form of zinc ions solubilized in the electrolyte is depressed. The net effect is that the zinc electrode retains its shape over a substantially greater period of time during cycling of the cell than is the case with conventional cells and exhibits greater stability of electrical properties than do conventional cells.
The separator may employ any one or a mixture of rare earth inorganic hydroxides such as cerium hydrate, yttrium hydroxide and hydroxides of neodymium, samarium, gadolinum, terbium and the like. The hydroxide is disposed in finely divided particulate form within a non-reactive matrix such as polytetra-fluoroethylene, vinyl acetate and ethylene copolymer resin, poly-vinyl chloride polymer or the like to form the desired separator sheet, which sheet is then placed around the negative electrode in each cell. Further details of the present invention are set forth in the following detailed description and the accompanying drawings.
DRAWINGS
Figure 1 is a schematic perspective view of a preferred embodiment of an electrochemical battery employing the improved inorganic separator of the invention, portions being broken away to illustrate certain internal features of the battery.
DETAILED DESCRIPTION
An improved inorganic separator is made in accordance with the present invention utilizing rare earth inorganic hydroxide in finely divided solid particulate form. The -` ~056904 1 hydroxide may be any one or more of the rare earth hydroxides.
Normally, the average particle diameter of the hydroxide is no greater than about 2 microns and the average density may vary, but for cerium hydrate, for example, is usually no greater than about 0.9 gm/cm3.
This fine powder is mixed intimately with a suitable binder-forming inert matrix material which is non-reactive with the usual alkaline cell electrolytes and which may be, for example, polytetrafluoroethylene emulsion, a low molecular weight poly-olefin resin, a mixture of vinyl acetate and a copolymer ofethylene and vinyl acetate, polyvinyl fluoride resin, fluorinated .
polyethylene or polyvinyl chloride polymer.
The resulting mixture has the rare earth hydroxide uniformly dispersed therein; for example, when polytetrafluoroethy-lene emulsion is used, drying can take place in an oven at 100C
for four hours. If the matrix material is in solid form initially, it is utilized as a finely divided powder and is merely mixed uniformly with the hydroxide. The resulting dry mixture is then ready for formation into a separator configuration of desired average pore diameter and porosity.
Forming of the separator is usually accomplished by extruding the dry mixture of the rare earth hydroxide and matrix forming material through a suitable shape nozzle to form a sheet of material approximately, for example, 0.010" thick. Other thicknesses such as 0.002", 0.005", 0.015" and 0.030" are also suitable. Such extrusion may, for example, be carried out under the following conditions utilizing the following equipment:
The previously described powder mix is mixed and compounded with an extrusion aid (lubricant) such as propylene glycol, methyl alcohol, isopropyl alcohol, ethyl alcohol, acetone i or the like in a mixer such as Patterson Kneadmaster mixer Model CK453. The resultant dough is extruded using, for example, a Patterson Extruder having an auger diameter of three (3) inches J
and an extrusion nozzle opening of 6" wide x 0.010" thick. The lubricant can be present in the extruded dough in a weight concentration of, for example, about 10 - 20 percent. Following extrusion, the sheet is passed through a curing oven at a tempera-ture of 3600F for about 1 - 10 minutes so as to drive off the lubricant and cure the matrix material.
The sheet material thus formed by extrusion is then cut to size and normally used directly as a separator in an alkaline cell of the type described. Preferably, the extruded sheet material has a very low average pore diameter, for example, below about 200 angstroms and a high volume porosity, preferably above about 50%. It will be understood that for special applica-tions the separator material may be formed having other ranges of physical characteristics. Generally, however, a very low pore diameter with high porosity is desired so that efficient contain-ment of solubilized zinc ions can be achieved. The improved separator may be utilized in any suitable way, for example, in the containment surrounding the zinc electrode in the cell or as follows:
The sheet may be placed directly on the zinc electrode so as to act not only as a negative interseparator but also as a support structure for the zinc active material. In this case, the improved inorganic separator material which has been cut to dimensions larger than that of the negative electrode....
is pressed on and into the zinc electrode structure during the latter's fabrication.
3~ Preferably, the improved separator is, in use, disposed 1 between protective layers of conventional separator material, such as polypropylene film having the following characteristics:
average pore diameter = 400 - 600 microns; average thickness =
5.0 mils. Such films can be, if desired, of such materials as the following: cellophane, porous irradiated polyethylene, rayon, dynel,* nylon, etc.
Now referring more particularly to Fig. 1 of the accompanying drawings, a typical alkaline battery having zinc negative electrodes and the improved separator material of tO the invention is schematically illustrated. Thus, a battery 10 is shown which includes a container 12 having a hollow interior 14 and a closed top 16 through which a filler and vent tube 18 and the positive and negative terminals 20 and 22, respectively, of the battery extend.
A pair of negative electrodes 24 of zinc in the form of plates are disposed in spaced relation within interior 14 of container 12 and are connected to the negative terminal 22 by a pair of leads 26. A sheet 28 of the improved separator 30 of the invention is wrapped around each negative electrode 24 in container 12 and is disposed between two sheets 32 and 34 of poly-propylene separator material to form therewith containment bag 36 for each negative electrode. Bag 36 has an open upper end 38 through which the leads 26 protrude.
The negative electrodes 24 in their containment bags 36 are sandwiched between three positive electrodes 40 in the form of plates connected by leads 42 to the positive terminal 20.
An electrolyte 44 in the form of concentrated (about 40%) aqueous potassium hydroxide (solution) is also disposed in interior 14 of container 12 below the upper end 38 of each containment bag 36. It will be understood that other arrangements of the improved * Trade mark for a copolymer of vinyl chloride and acrylonitrile ** Registered trade mark for a film produced from wood pulp by the viscose process ~05~;904 1 separator within alkaline electrochemical cells and batteries can be provided. The following specific Examples further illus-trate certain features of the present invention:
EXAMPLE I
Cerium hydrate is passed through a 325 mesh screen so that it has an average particle size of less than 2 microns.
This fine powder is then mixed with sufficient polytetrafluoro-ethylene emulsion so that the solids by weight ratio of the polymer to the hydroxide is about 1:4. The mixing is accomplished for a sufficient period of time until the mixture is uniform.
The resulting product is then dried in an air convection oven at 100C for 4 hours. Four parts (by weight) of the dried mixture are then mixed with one part of propylene glycol and the resulting dough is extruded through a nozzle under 1200 psi at about 85C to obtain a sheet which, after curing in an oven at about 360F for about 5 minutes, has an average thickness of about 0.010". This finished sheet has an average pore diameter of less than 200 angstroms and a volume porosity of about 55%.
The finished sheet is cut into two appropriately sized sheets and installed in a battery having the configuration shown in Figure 1. The battery has two zinc negative electrodes in the form of plates, each plate having the following dimensions:
1.625" wide x 1.50" high x 0.042" thick. Three silver oxide positive electrodes are spaced between and outside the two zinc electrodes. The positive electrodes are each in the form of a plate having the following dimensions: 1.625" wide x 1.50 " high x 0.034" thick. The electrodes are disposed in a casing of styrene-acrylonitrile plastic sold under the trademark Lustran 400 of Monsanto Co., St. Louis, Mo.
The negative electrodes are each enclosed in an open 1 topped containment bag comprising an inner and an outer layer of polypropylene, each about 5 mils thick and having an average pore diameter of about 500 microns,and a middle layer comprising a sheet of the improved separator of the invention. An electro-lyte comprising a 40% aqueous solution of potassium hydroxide is disposed in the battery below the open top of each containment bag. The battery (A) exhibits great durability and stability of electrical properties in contrast to a battery (B) fabricated in the same way utilizing the same materials except for the absence of the cerium hydrate-containing separator of the invention, as shown in the following table:
TABLE
Characteristics Battery A Battery B
life at ngrmal load 160 102 (at 140 F) days maximum number of cycles 56 22 percent negative electrode 20 70 shape change EXAMPLE II
An improved separator in accordance with the present invention is fabricated by intimately and uniformly mixing together 85 parts by weight of yttrium hydroxide with 15 parts by weight of powdered polyethylene resin having an average particle diameter of about 0.2 microns. The yttrium hydroxide is in particulate form having an average particle diameter of about 1 micron and a bulk density of about 1.6 gm/cm3. The mixing is continued until a spongy mixture is obtained, whereupon the mixture is blended into a dough with methyl alcohol (6 parts of mixture to 1 part of alcohol, by weight) and the dough is extruded at 85C and 1000 psi into a sheet which, after curing in an oven at about 350F for about 10 minutes, has a thickness of 1 ~bout 10 mils. The finished sheet has an average pore diameter of 20~ - 300 and a volume porosity of about 40%.
The separator sheet is cut into two sheets and utilized in a battery (C) identical to battery A of Example I in place of the cerium hydrate-containing separator sheets thereof.
Battery C is co~lpared in electrical characteristics with a battery (B) which is identical except for the absence of a rare earth hydroxide-containing separator. The results of the comparison are set forth in the table below:
TABLE
Electrical CharacteristicsBattery C Battery B
battery life (at 140Fo) days 102 35 maximum cycles (at 70 F) 40 22 percent negative electrode 55 70 shape change As in Example I, comparative tests show that improved electrical stability and durability are achieved by using the rare earth hydroxide-containing separator of the invention.
When parallel tests are conducted substituting equivalent amounts of other rare earth hydroxides for the cerium hydrate of Example I and the yttrium hydroxide of this Example in the separator of the invention, comparable improved results are obtained. Substitution in separate tests of polypropylene, vinyl acetate-ethylene copolymers, polyvinylidene fluoride, fluorinated ethylene-propylene resin and polyvinyl chloride for the polytetrafluoroethylene emulsion and the polyethylene resin of Examples I and II, respectively, is made without varying the results, when the separator average pore diameter and total pore volume, as well as the weight ratio of such matrix material to the rare earth hydroxide are substantially as set forth above.
Accordingly, an improved separator is economically formed in accordance with the present method, utilizing effective concentrations of rare earth hydroxides in finely divided particle form uniformly dispersed in a suitable matrix. Such separators when used in containment around the zinc negative electrodes of the cell, effectively reduce the loss of soluble zinc ions from the contained area and thus reduce the loss of zinc from the zinc electrode during operation of the electro-chemical cell. Such loss reduction results in improved longevity for the cell and more stable electrical characteristics, as demonstrated in the tables of Examples I and II. Accordingly, improved alkaline cells and batteries having zinc negative elec-trodes can be provided in an economical manner through the use of the improved separator of the invention.
Various modifications, changes, alterations and additions can be made in the present separator, its components, and in the present method and its steps and parameters. All such modifications, changes, alterations and additions as are within the scope of the appended claims form part of the present invention.
_ 9 _
Claims (17)
1. An improved separator for alkaline electrochemical cell having zinc negative electrodes, said separator comprising rare earth inorganic hydroxide in finely divided solid particulate form dispersed within a shape-retaining non-reactive matrix.
2. The improved separator of claim 1 wherein said separator has an average pore diameter below about 200 angstroms, and a volume porosity above about 50 percent.
3. The improved separator of claim 1 wherein said particles of said inorganic hydroxide have an average particle diameter not in excess of about 2 microns and a bulk density not in excess of about 0.9 gm/cm3.
4. The improved separator of claim 1 wherein said hydroxide comprises cerium hydrate.
5. The improved separator of claim 1 wherein said hydroxide comprises yttrium hydrate.
6. The improved separator of claim 2 wherein said matrix comprises a dried polytetrafluoroethylene emulsion.
7. The improved separator of claim 1 wherein said matrix is present in a solids concentration in said separator of about 5 - 50 percent by weight of said separator.
8. The improved separator of claim 7 wherein said separator has an average thickness of about 10 mils.
9. A method of making an improved separator for zinc electrode-containing alkaline electrochemical cells, said method comprising uniformly mixing a rare earth inorganic hydroxide in finely divided particulate form with binder-forming inert matrix material and thereafter extruding the mixture, curing it and recovering a thin shape-retaining separator.
10. The method of claim 9 wherein said matrix material comprises an emulsion of polytetrafluoroethylene and wherein said mixture is dried before said extrusion.
11. The method of claim 9 wherein said matrix is present in said mixture in a solids concentration of about 5 to about 50 percent by weight of said mixture.
12. The method of claim 9 wherein said mixture is extruded to an everage thickness of about 10 mils, an average pore diameter below about 200 angstroms, a volume porosity above about 50 percent and a bulk density not in excess of about 0.9 gm/cm3.
13. The method of claim 12 wherein said hydroxide comprises cerium hydrate.
14. The method of claim 12 wherein said hydroxide comprises yttrium hydroxide.
15. The method of claim 9 wherein said matrix material
15. The method of claim 9 wherein said matrix material
Claim 15 continued:
and hydroxide are mixed dry to a uniform and spongy mixture which is then heated and extruded.
and hydroxide are mixed dry to a uniform and spongy mixture which is then heated and extruded.
16. The method of claim 15 wherein said mixture is blended with a minor concentration of an extrusion lubricant and the resultant dough is extruded and cured to form a separator sheet about 10 mils thick.
17. The method of claim 15 wherein said matrix material comprises a polyolefin resin.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US57694875A | 1975-05-12 | 1975-05-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1056904A true CA1056904A (en) | 1979-06-19 |
Family
ID=24306665
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA250,960A Expired CA1056904A (en) | 1975-05-12 | 1976-04-23 | Inorganic separator for alkaline electrochemical cells |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS51140143A (en) |
| CA (1) | CA1056904A (en) |
| DE (1) | DE2614248A1 (en) |
| FR (1) | FR2311415A1 (en) |
| GB (1) | GB1495867A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5051157A (en) * | 1988-02-29 | 1991-09-24 | University Of Victoria | Spacer for an electrochemical apparatus |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2851950A1 (en) * | 1978-12-01 | 1980-06-12 | Varta Batterie | Flat battery using alkaline electrolyte - where negative electrode is zinc sheet surrounding manganese di:oxide positive electrode in plastic case |
-
1976
- 1976-01-13 GB GB1210/76A patent/GB1495867A/en not_active Expired
- 1976-03-09 FR FR7606702A patent/FR2311415A1/en not_active Withdrawn
- 1976-04-02 DE DE19762614248 patent/DE2614248A1/en not_active Withdrawn
- 1976-04-09 JP JP51039459A patent/JPS51140143A/en active Granted
- 1976-04-23 CA CA250,960A patent/CA1056904A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5051157A (en) * | 1988-02-29 | 1991-09-24 | University Of Victoria | Spacer for an electrochemical apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5626944B2 (en) | 1981-06-22 |
| JPS51140143A (en) | 1976-12-02 |
| GB1495867A (en) | 1977-12-21 |
| FR2311415A1 (en) | 1976-12-10 |
| DE2614248A1 (en) | 1976-12-02 |
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