CA2105952C - Additives for electrochemical cells having zinc anodes - Google Patents
Additives for electrochemical cells having zinc anodes Download PDFInfo
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- CA2105952C CA2105952C CA002105952A CA2105952A CA2105952C CA 2105952 C CA2105952 C CA 2105952C CA 002105952 A CA002105952 A CA 002105952A CA 2105952 A CA2105952 A CA 2105952A CA 2105952 C CA2105952 C CA 2105952C
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- cell
- zinc
- group
- anionic
- surfactant
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- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 title claims abstract description 69
- 239000011701 zinc Substances 0.000 title claims abstract description 67
- 229910052725 zinc Inorganic materials 0.000 title claims abstract description 62
- 239000000654 additive Substances 0.000 title description 7
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 claims abstract description 59
- 229910052753 mercury Inorganic materials 0.000 claims abstract description 59
- 239000003349 gelling agent Substances 0.000 claims abstract description 45
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 37
- 239000003945 anionic surfactant Substances 0.000 claims abstract description 30
- 229910001297 Zn alloy Inorganic materials 0.000 claims abstract description 29
- 239000002736 nonionic surfactant Substances 0.000 claims abstract description 29
- 238000000034 method Methods 0.000 claims abstract description 24
- 239000002245 particle Substances 0.000 claims abstract description 12
- 230000002401 inhibitory effect Effects 0.000 claims abstract description 7
- 239000012670 alkaline solution Substances 0.000 claims abstract 2
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 45
- 239000000203 mixture Substances 0.000 claims description 39
- 125000000129 anionic group Chemical group 0.000 claims description 17
- NUJOXMJBOLGQSY-UHFFFAOYSA-N manganese dioxide Chemical compound O=[Mn]=O NUJOXMJBOLGQSY-UHFFFAOYSA-N 0.000 claims description 15
- 229920002125 Sokalan® Polymers 0.000 claims description 13
- 239000003792 electrolyte Substances 0.000 claims description 12
- 229910052738 indium Inorganic materials 0.000 claims description 12
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 claims description 12
- 125000000217 alkyl group Chemical group 0.000 claims description 10
- 230000015572 biosynthetic process Effects 0.000 claims description 10
- 125000003118 aryl group Chemical group 0.000 claims description 8
- 229920000578 graft copolymer Polymers 0.000 claims description 8
- 239000002253 acid Substances 0.000 claims description 7
- 125000001931 aliphatic group Chemical group 0.000 claims description 7
- 125000002877 alkyl aryl group Chemical group 0.000 claims description 6
- 229910019142 PO4 Inorganic materials 0.000 claims description 5
- 239000010452 phosphate Substances 0.000 claims description 5
- 229920002472 Starch Polymers 0.000 claims description 4
- 125000004432 carbon atom Chemical group C* 0.000 claims description 4
- 239000006182 cathode active material Substances 0.000 claims description 4
- 150000003839 salts Chemical class 0.000 claims description 4
- 235000019698 starch Nutrition 0.000 claims description 4
- 239000008107 starch Substances 0.000 claims description 4
- 229920002126 Acrylic acid copolymer Polymers 0.000 claims 3
- 125000003010 ionic group Chemical group 0.000 claims 2
- 206010011416 Croup infectious Diseases 0.000 claims 1
- 229910045601 alloy Inorganic materials 0.000 claims 1
- 239000000956 alloy Substances 0.000 claims 1
- 201000010549 croup Diseases 0.000 claims 1
- 239000004094 surface-active agent Substances 0.000 abstract description 55
- 239000002002 slurry Substances 0.000 abstract description 22
- 239000006183 anode active material Substances 0.000 abstract description 20
- 229910052739 hydrogen Inorganic materials 0.000 abstract description 17
- 239000001257 hydrogen Substances 0.000 abstract description 17
- 210000004027 cell Anatomy 0.000 description 149
- 239000000243 solution Substances 0.000 description 26
- 229920000642 polymer Polymers 0.000 description 11
- 239000000843 powder Substances 0.000 description 10
- GPRLSGONYQIRFK-MNYXATJNSA-N triton Chemical compound [3H+] GPRLSGONYQIRFK-MNYXATJNSA-N 0.000 description 9
- 239000007864 aqueous solution Substances 0.000 description 8
- 239000012528 membrane Substances 0.000 description 8
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 7
- IAYPIBMASNFSPL-UHFFFAOYSA-N Ethylene oxide Chemical compound C1CO1 IAYPIBMASNFSPL-UHFFFAOYSA-N 0.000 description 7
- -1 ethoxyl fluoroalcohol Chemical compound 0.000 description 7
- 150000001875 compounds Chemical class 0.000 description 6
- 238000002156 mixing Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 239000007789 gas Substances 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 239000001768 carboxy methyl cellulose Substances 0.000 description 4
- 235000010948 carboxy methyl cellulose Nutrition 0.000 description 4
- 239000008112 carboxymethyl-cellulose Substances 0.000 description 4
- 229940105329 carboxymethylcellulose Drugs 0.000 description 4
- 210000003850 cellular structure Anatomy 0.000 description 4
- 235000019441 ethanol Nutrition 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 3
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 3
- 239000010405 anode material Substances 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 150000002894 organic compounds Chemical class 0.000 description 3
- 150000003014 phosphoric acid esters Chemical class 0.000 description 3
- 229920001223 polyethylene glycol Polymers 0.000 description 3
- XLOMVQKBTHCTTD-UHFFFAOYSA-N zinc oxide Inorganic materials [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 3
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 2
- 239000003513 alkali Substances 0.000 description 2
- 239000001913 cellulose Substances 0.000 description 2
- 229920002678 cellulose Polymers 0.000 description 2
- 235000010980 cellulose Nutrition 0.000 description 2
- 239000008151 electrolyte solution Substances 0.000 description 2
- 125000001301 ethoxy group Chemical group [H]C([H])([H])C([H])([H])O* 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 230000002209 hydrophobic effect Effects 0.000 description 2
- AQYSYJUIMQTRMV-UHFFFAOYSA-N hypofluorous acid Chemical class FO AQYSYJUIMQTRMV-UHFFFAOYSA-N 0.000 description 2
- 239000003112 inhibitor Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229920002401 polyacrylamide Polymers 0.000 description 2
- 239000004584 polyacrylic acid Substances 0.000 description 2
- 230000002829 reductive effect Effects 0.000 description 2
- HEMHJVSKTPXQMS-UHFFFAOYSA-M sodium hydroxide Inorganic materials [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 2
- 125000000547 substituted alkyl group Chemical group 0.000 description 2
- SMZOUWXMTYCWNB-UHFFFAOYSA-N 2-(2-methoxy-5-methylphenyl)ethanamine Chemical compound COC1=CC=C(C)C=C1CCN SMZOUWXMTYCWNB-UHFFFAOYSA-N 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N 2-Propenoic acid Natural products OC(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- CERQOIWHTDAKMF-UHFFFAOYSA-N Methacrylic acid Chemical compound CC(=C)C(O)=O CERQOIWHTDAKMF-UHFFFAOYSA-N 0.000 description 1
- 229920003171 Poly (ethylene oxide) Polymers 0.000 description 1
- 239000004372 Polyvinyl alcohol Substances 0.000 description 1
- 229920000297 Rayon Polymers 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 150000008052 alkyl sulfonates Chemical class 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 125000003277 amino group Chemical group 0.000 description 1
- 239000012874 anionic emulsifier Substances 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 125000005619 boric acid group Chemical group 0.000 description 1
- 125000000837 carbohydrate group Chemical group 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 1
- 230000002301 combined effect Effects 0.000 description 1
- 229920001577 copolymer Polymers 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 239000008240 homogeneous mixture Substances 0.000 description 1
- 230000002045 lasting effect Effects 0.000 description 1
- 229920001684 low density polyethylene Polymers 0.000 description 1
- 239000004702 low-density polyethylene Substances 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 230000007257 malfunction Effects 0.000 description 1
- 125000000956 methoxy group Chemical group [H]C([H])([H])O* 0.000 description 1
- 229920000609 methyl cellulose Polymers 0.000 description 1
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 description 1
- 239000001923 methylcellulose Substances 0.000 description 1
- 235000010981 methylcellulose Nutrition 0.000 description 1
- 239000012875 nonionic emulsifier Substances 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 229920002239 polyacrylonitrile Polymers 0.000 description 1
- 229920005597 polymer membrane Polymers 0.000 description 1
- 229920002451 polyvinyl alcohol Polymers 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 239000002964 rayon Substances 0.000 description 1
- 230000000979 retarding effect Effects 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229920002994 synthetic fiber Polymers 0.000 description 1
- 230000008719 thickening Effects 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- 238000009736 wetting Methods 0.000 description 1
- 239000000230 xanthan gum Substances 0.000 description 1
- 229920001285 xanthan gum Polymers 0.000 description 1
- 229940082509 xanthan gum Drugs 0.000 description 1
- 235000010493 xanthan gum Nutrition 0.000 description 1
- SZKTYYIADWRVSA-UHFFFAOYSA-N zinc manganese(2+) oxygen(2-) Chemical compound [O--].[O--].[Mn++].[Zn++] SZKTYYIADWRVSA-UHFFFAOYSA-N 0.000 description 1
- 229960001296 zinc oxide Drugs 0.000 description 1
Classifications
-
- 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
- H01M4/24—Electrodes for alkaline accumulators
- H01M4/244—Zinc electrodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M6/00—Primary cells; Manufacture thereof
- H01M6/22—Immobilising of electrolyte
-
- 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
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Battery Electrode And Active Subsutance (AREA)
- Primary Cells (AREA)
Abstract
The invention relates to a method for inhibiting the occurrence of load voltage instability in zinc anodic alkaline cells. The anode active material contains a gelled slurry of zinc alloy particles, a gelling agent, an aqueous alkaline solution and a mixed surfactant containing an anionic surfactant and a nonionic surfactant. The celled anode active material inhibits the occurrence of load voltage instability and simultaneously reduces hydrogen evolution even though the cell contains no added amounts of mercury.
Description
ADDITIVES FOR ELECTROCHEMICAL
CELLS HAVING ZINC ANODES
The invention relates to alkaline electrochemical cells with zinc anodes and additives, particularly containing mixtures of anionic and non-ionic surface active agents, which improve performance of such cells by inhibiting the occurrence of load voltage instability and retarding hydrogen formation.
Electrochemical cells, such as alkaline cells, typically contain zinc anode active material, alkaline electrolyte, a manganese dioxide cathode active material, and a permeable separator film, typically of cellulose or synthetic material. The anode active material has in the past contained as much as loo by weight mercury in the form of amalgamated zinc particles. The mercury improves conductivity between the zinc particles and reduces the amount of hydrogen gas produced in the cell. The anode active material is typically formed into a gelled slurry using conventional gelling agents, such as carboxy-methylcellulose. The gelled slurry holds the zinc particles in place and in contact with each other. A
conductive metal pin or nail known as the anode collector, is typically inserted into the anode active material. The cathode is typically of manganese dioxide and may include small amounts of carbon or graphite to increase conductivity. The alkaline electrolyte is typically an aqueous solution of potassium hydroxide, but other alkali solutions such as aqueous solutions of sodium or lithium hydroxide may also be employed.
Conventional alkaline cells are encased in a steel container to retain the cell components and reduce the chance of leakage.
Because of environmental concerns and regulations, manufacturers of alkaline cells have been trying to reduce the content of mercury to under to by weight of the anode active material and more recently to less than 50 parts mercury per million parts (ppm) by total cell weight. This requires that a substitute for mercury be found which can prove at least as effective in inhibiting the formation of hydrogen gas during cell discharge.
(During discharge hydrogen gas forms as the water contained in the electrolyte solution contacts and reacts with zinc. The evolution of hydrogen gas can cause leakage of the cell's components or otherwise interfere with the cell's performance.) Problems in addition to increased gassing can occur when mercury content is significantly reduced. One such problem is a phenomenon known as load voltage instability (LVI). LVI can occur during normal use of the cell when the mercury content in the cell is less than about 50 parts per million parts by total weight of the cell. This phenomenon can occur periodically when the cell is tapped, bumped or otherwise jolted during normal discharge. Under such conditions a sudden drop in voltage as high as several hundred millivolts can occur. The drop in voltage is typically transitory lasting for a fraction of a second, but occasionally can last for several seconds. The drop in voltage, albeit transitory, can cause the device being powered to noticeably malfunction.
It is not known with certainty why this phenomenon occurs. It is conjectured that the physical jolt may momentarily diminish contact between enough of the zinc particles to cause a temporary break in conduction of electrons from the zinc particles to the anode collector.
CELLS HAVING ZINC ANODES
The invention relates to alkaline electrochemical cells with zinc anodes and additives, particularly containing mixtures of anionic and non-ionic surface active agents, which improve performance of such cells by inhibiting the occurrence of load voltage instability and retarding hydrogen formation.
Electrochemical cells, such as alkaline cells, typically contain zinc anode active material, alkaline electrolyte, a manganese dioxide cathode active material, and a permeable separator film, typically of cellulose or synthetic material. The anode active material has in the past contained as much as loo by weight mercury in the form of amalgamated zinc particles. The mercury improves conductivity between the zinc particles and reduces the amount of hydrogen gas produced in the cell. The anode active material is typically formed into a gelled slurry using conventional gelling agents, such as carboxy-methylcellulose. The gelled slurry holds the zinc particles in place and in contact with each other. A
conductive metal pin or nail known as the anode collector, is typically inserted into the anode active material. The cathode is typically of manganese dioxide and may include small amounts of carbon or graphite to increase conductivity. The alkaline electrolyte is typically an aqueous solution of potassium hydroxide, but other alkali solutions such as aqueous solutions of sodium or lithium hydroxide may also be employed.
Conventional alkaline cells are encased in a steel container to retain the cell components and reduce the chance of leakage.
Because of environmental concerns and regulations, manufacturers of alkaline cells have been trying to reduce the content of mercury to under to by weight of the anode active material and more recently to less than 50 parts mercury per million parts (ppm) by total cell weight. This requires that a substitute for mercury be found which can prove at least as effective in inhibiting the formation of hydrogen gas during cell discharge.
(During discharge hydrogen gas forms as the water contained in the electrolyte solution contacts and reacts with zinc. The evolution of hydrogen gas can cause leakage of the cell's components or otherwise interfere with the cell's performance.) Problems in addition to increased gassing can occur when mercury content is significantly reduced. One such problem is a phenomenon known as load voltage instability (LVI). LVI can occur during normal use of the cell when the mercury content in the cell is less than about 50 parts per million parts by total weight of the cell. This phenomenon can occur periodically when the cell is tapped, bumped or otherwise jolted during normal discharge. Under such conditions a sudden drop in voltage as high as several hundred millivolts can occur. The drop in voltage is typically transitory lasting for a fraction of a second, but occasionally can last for several seconds. The drop in voltage, albeit transitory, can cause the device being powered to noticeably malfunction.
It is not known with certainty why this phenomenon occurs. It is conjectured that the physical jolt may momentarily diminish contact between enough of the zinc particles to cause a temporary break in conduction of electrons from the zinc particles to the anode collector.
Generally, environmentally safe substitutes to completely replace mercury in alkaline cells, without sacrifice in cell performance, have been difficult to find.
~ 2105952 U.S. Patents 4,939,048 and 4,942,101 are directed to inhibiting the occurrence of load voltage instability in a mercury free alkaline cell containing a gelled zinc anode.
U.S. Patent 4,939,048 discloses use of an anode current collector comprising a bundle of conductive fibers and U.S
Patent 4,942,101 discloses use of an anode current collector of various configurations with fittings thereon designed to increase its surface area. Both references disclose including from 1 to 1000 ppm of an organic stabilization compound selected f=rom polyfluoride compounds of the ethoxyl fluoroalcohol type and compounds of the polyethoxylalcohol and alcoyl sulfide type. There is no disclosure or suggestion of mixing anionic and non-anionic surface active agents or that any particular benefits can be obtained from such mixing.
The following prior art discloses a number of organic compounds that reduce the formation of hydrogen gas in alkaline cells. The use of these: materials has allowed for a reduction of mercury content: to environmentally safe levels. However, none of these materials has been disclosed to have an effect on load voltage instability.
U.S. Patent 4,195,120 discloses the addition of an organic phosphate ester surfactant to the anode, cathode or electrolyte of an alkaline cell having zinc anodes containing mercury. Examples of such surfactants are disclosed as available under the trade designation GAFAC*
RE610, GAFAC RA600, and KLEARFAC* AA-040. The addition of the phosphate eater surfactant reduces the hydrogen evolution, thereby increasing t:he shelf-life and useful discharge life of the cell.
U.S. Patent 4,455,358 discloses the use of a starch-graft copolymer as gelling agent for the zinc anode comprising an * Trade-marks A
amalgamated zinc powder containing about 7% mercury. The gelling agent is composed of a carbohydrate backbone which has a water soluble side chain grafted onto it. The gelling agent is reported to increase the practical discharge capacity of the anode while reducing the amount of hydrogen evolution from the cell.
Canadian Patent 1,154,081 discloses the use of a gelling composition formed preferably of a mixed gelling agent containing a starch-graft copolymer and yet another gelling agent, for example, carboxymethylcellulose. The mixed gelling agent is used to gel conventional amalgamated zinc powder for Zn-alkaline-Mn02 cells. The mixed gelling agent is reported to inhibit internal shorting of the cell, which can occur if carboxymethylcellulose alone is employed.
US Patent 3,057,944 discloses the addition of a surface active agent which is heteropolar substance admixed either into the electrolyte or the silver cathode of an electrochemical cell.
US Patent 3,847,669 discloses the addition of an ethylene oxide polymer to a zinc-manganese dioxide cell.
The ethylene oxide polymer may be used to wet the separator or may be added to the zinc during preparation of the zinc anode gel. The ethylene oxide polymer is reported as allowing for a reduction in the amount of mercury required to be added to the zinc anode.
US Patent 4,230,549 discloses a novel polymer.
membrane to be used as separator membrane in electrochemical cells. The membrane is preferably composed of a cross-linked low density polyethylene base grafted with methacrylic acid. Before use, the polymer membrane is immersed in a solution containing surfactants which may be a mixture of an anionic and non-ionic emulsifier such as Ultrawet* KX (a sodium linear alkyl sulfonate) and Triton* X100 (isooctyl phenoxyl polyethoxy ethanol). The treatment of the membrane with the surfactants is reported to have the effect of lowering the electrolytic resistance of the membrane as well as imparting to it better wetting characteristics. There is no discussion with respect to load voltage instability or the effect of these surfactants on hydrogen evolution.
European Patent Publication 0 474 382 A1 relates to an alkaline cell having a zinc containing anode and is substantially mercury free, i. e. the mercury content is less than 50 parts per million per total call weight. This reference discloses additives that inhibit the corrosion of zinc. One such additive is an el~hylene oxide polymer, such as phosphate esters of ei~hylene oxide polymers, perfluorinated organic compounds of the ethoxylated fluoroalcohol type, and alkyl and polyethoxyalcohol sulphides. The preferred ethylene oxide polymers are the polyethylene glycols and methoxy polyethylene glycols having a molecular weight from about 300 to 700. (P. 5, line 27-42.) It is stated in broad brush that the ethylene oxide polymers can be used singly or in combination. (P. 5, line 42.) There is no disclosure or suggestion of any particular benefit accruing to the use of any particular type of ethylene oxide polymers in combination. The anode mixture contains electrolyte and optionally an electrolyte-swellable binder such as a polyacrylic acid, for example, Carbopol* 940 gelling agent. (P. 4, line 35.) The cells are reported to exhibit insufficient bulge due to hydrogen gas formation to cause leakage of t:he cell components. (P.7, lines 13-17.) There is no discussion or recognition in this reference of the problem of load voltage instability occurring in alkaline cells which contain zero added mercury. There are also no specific examples which include more than one ethoxylated polymer and in fact all * Trade-marks A' _ 2~o595z the specific examples read on only one ethylene oxide polymer, namely a methoxylated polyethylene oxide (CARBOWAX* 550).
U.S. Patent 4,606,984 discloses the addition of a fluorinated organic compound, of the ethoxylated fluoroalcohol type to an anode of a primary electrochemical cell containing zinc, aluminum or magnesium. A preferred compound of this type is disclosed as available under the trade designation FORAFAC* 1110. The fluorinated compound when added to the anodic material in percentage between 0.01% and 1% by weight of th~~ metal therein, acts as inhibitor causing a reduction in hydrogen gas evolution from the cell. The hydrogen evolution rate is reported at various levels of mercury content in the cell, i.e., from 0% to 5% mercury content with :respect to zinc in a zinc anodic alkaline cell. When the fluorinated compound was added to zinc anodic material, the rate of hydrogen evolution decreased at all levels of mercury content compared to the same anodic material with no inhibitor.
Accordingly it is desirable to find an environmentally safe, disposable substitute for mercury in electrochemical cells, particularly in zinc anodic alkaline cells, that both inhibits hydrogen gas formation and load voltage instability.
It is desirable to find an additive for cells that inhibit the occurrence of load voltage instability during normal discharge of the cell, particularly in zinc anodic alkaline cells having a mercury content of less than about 50 parts per million parts by total weight of the cell.
It is desirable to find additives for cells that simultaneously retard or inhibit hydrogen evolution, particularly in zinc anodic alkaline cells having a mercury content of less than about 50 parts mercury per million parts by * Trade-mark A
total weight of the cell.
The following figures show representative comparative discharges graphs illustrative of the performance of the invention.
Fig. 1 is a graphical plot of the voltage discharge profile (voltage versus service hour) of the alkaline cell described in Example 5 as the cell was tapped at regular one minute intervals as it was discharged under a load of 3.9 ohms.
Fig. 2 is a graphical plot of the voltage discharge profile (voltage versus service hour) of the alkaline cell described in Example 8 as the cell was tapped at regular one minute intervals as it was discharged under a load of 3.9 ohms.
It has been discovered that the addition of a mixture of an anionic and a non-ionic surfactant to the cell, preferably to the zinc anode, inhibits the occurrence of load voltage instability even when there is no mercury added to the cell, e.g., when the mercury content in the cell is below about 50 parts and even less than 10 parts per million parts by total weight of the cell. It is surprising that the problem of load voltage instability in such cells can be overcome simply by adding a mixture of surfactants, since the surfactants themselves are not electrically conductive. It is unexpected that the mixture of anionic and non-ionic surfactants have a combined effect in both inhibiting load voltage instability and simultaneously reducing gassing than either class of surfactants alone. Also, it has been determined that the mixture of surfactants in such cells give cell performance, e.g. in terms of discharge voltage profile and service hours, similar to that obtained in conventional alkaline cells of same composition, but containing an added amount of mercury and no surfactants. In fact for most applications the performance between the two cells is virtually indistinguishable.
The mixture of an anionic surfactant and a non-ionic surfactant have been determined to also significantly reduce the amount of hydrogen gas produced in the cell.
Conventional gelling agents alone have some effect in reducing hydrogen evolution. However, it has been determined that the addition of the surfactants to the zinc slurry along with the gelling agent greatly reduces the amount of hydrogen evolution, particularly in alkaline cells that contain no added amounts of mercury, for example, less than 50 parts mercury per million parts by weight of the cell. The resultant effect is that when a mixture of anionic and non-ionic surfactants is added to the zinc slurry, the occurrence of load voltage instability is inhibited and hydrogen evolution fram the cell is reduced to a level that does not noticeably interfere with the cell's performance or shelf-life, even though the cell contains no added mercury and less than 50 parts mercury per million parts cell weight.
It should be understood that residual amounts of mercury may be present in commercially available pure zinc or in any of the other cell components.
(Commercially pure zinc typically has less than 100 parts mercury per billion parts zinc.) The term "substantially mercury free" is defined herein as a mercury content of less than about 50 parts mercury per million parts total cell weight. The term "essentially mercury free" shall be defined herein as a mercury content less than about 10 parts mercury per million parts by total weight of the cell. Both "substantially mercury free" and "essentially mercury free" cells fall within the definition of "zero-added mercury" cells. "Zero-added mercury" cells contain no added amounts of mercury. Such cells are defined as containing only the residual amount of mercury present in commercially available pure zinc, including the residual amount o:E mercury, if any, present in the other cell components.
The surfactant mixture of the invention to be added to zinc anode active material for alkaline cells is comprised of at least one anionic surfactant and at least one non-ionic surfactant. The anionic and non-ionic surfactants each have a polyethoxy chain - (CHZ-CHZ-O) n- which typically forms the hydrophilic portion of the molecule. The anionic surfactant can be represented generally by the formula (A), Rl(CH2_CH2_O)n _Xl (A) where R1 represents alkyl, aryl, alkylaryl (including substituted alkyl or aryl groups) and these groups normally form the hydrophobic portion of 'the molecule. The group R1 is typically an alkyl chain composed of 4 to 28 carbon atoms. The average number of ethoxy groups, n, is typically between 3 and 40. The molecule terminates at the other end with the anionic group, X1. The anionic group, X, may typically be selected from acid or salt moieties such as those derived from pho:~phoric acid moieties (-O-P03H2) , boric acid moieties (-O-BOzHz) , carboxylic moieties (-COOH) and salts thereof . The anionic surfactant may also be selected from polyethoxy phosphate esters of the type described in U.S. Patent 4,195,1:?0. The anionic surfactants represented by the formula (A) may be selected in their entirety from the organic phosphate esters of the type described in U.S. Patent 4,195,120. The anionic surfactant may typically have a molecular weight of between 200 and 2000.
A preferred anionic surfactant for use in the present invention is available under the trade designation GAFAC
RA600 organic phosphate ester surfactant from Rhone Poulenc.
A
The non-ionic surfactant can be represented generally by the formula (B), RZ- (CHZ-CHz-O) n-X2 (B) where R2 represents hydrogen, alkyl, aryl, alkylaryl (including substituted alkyl or aryl groups), fluorinated aliphatic groups (including substituted fluorinated aliphatic groups), fluorinated aliphatic groups containing amino groups, e.g. sufonamido gz-oups, and any combinations thereof. The group, R2, normally forms the hydrophobic portion of the molecule. The group, R2, typically contains between about 3 and 16 carbon atoms when fluorinated and between 4 and 28 carbons when not fluorinated. The average number of ethoxy groups, n, typi~~ally is between 3 and 250.
The molecule terminates with the' nonionic group, X2, which may typically be hydrogen or methyl. The non-ionic surfactant may typically have a molecular weight of between about 200 and 10000.
Preferred non-ionic surfactants for use in the present invention is TRITON X100 (isooctyl phenoxyl polyethoxy ethanol) from Rohm and Haas Co., ZONYL* FSN and ZONYL FSO
(both of which are fluorinated aliphatic polyethoxy ethanols) from E.I. DuPont and FLUORAD* FC-170C (a fluorinated alkyl polyethoxy ethanol) from 3M Company.
TRITON X100 surfactant has the formula C8H1.,C6H4 (OCzH4) loOH.
ZONYL FSN and ZONYL FSO surfactants have the general formula RfCH2CH20 (CHzCH20) XH, where Rf=F (CFZCFZ) Z and z=3 to 8 .
FLUORAD FC-170C surfactant has the general formula RfSO2N (CzHs) (CHzCHzO) XH where Rf=C"Fzn+1 and n has an average value of about 8.
The preferred anode active material is composed of a gelled zinc slurry containing a mixture of at least one anionic surfactant and one' non-ionic surfactant, advantageously from the pre:Eerred surfactants above described, typically in amounts comprising between about 25 and 200 ppm of each, preferably about 75 ppm of each as * Trade-marks 10 A
compared to the amount of zinc alloy in the slurry.
The gelling agents for the zinc slurry can be selected from a variety of known gelling agents activated by alkaline mixtures. Preferred gelling agents are substantially insoluble in the cell electrolyte so that the gelling agent does not migrate between the anode and cathode. The preferred gelling agents also do not lose water when the gelled zinc slurry is left in storage.
Suitable gelling agents, for example, are carboxymethyl cellulose or crosslinked carboaymethyl cellulose, methyl cellulose, Xanthan gum, crosslinked polyacrylamides, crosslinked acrylic acid copolyners such as CARBOPOL C-940 from B.F.Goodrich Co., starch-graft copolymers such as WATER-LOCK* A221 starch-graft copolymer of polyacrylic acid and polyacrylamide from Grain Processing Co., and alkali hydrolyzed polyacrylonitrile such as WATER-LOCK A 400 from Grain Processing Co. The gelling agent can be used alone or in mixture with other known gelling or thickening components. Although any of these gelling agents can be employed alone or in combination, at least one of the gelling agents may advantageously be selected from crosslinked acrylic acid polymer such as CARBOPOL C940 or SIGMA POLYGEL 4P gelling agents or a starch graft copolymer such as WATER-LOCK A-221 copolymer.
A zinc slurry is preparecL by mixing a zinc alloy powder (e.g. 99.9% zinc alloy powder containing about 500 ppm indium) with a suitable gelling agent using a blender or other similar mixing equipmE:nt. (The zinc powder may typically contain between about 50 and 1000 parts indium per million parts by weight of the particles.) Suitable gelling agents are then added to the blender. The gelling agents may advantageously be se:Lected from the list above described. The zinc powder and gelling agent are then blended until a homogeneous mixture is * Trade-marks A
obtained. The electrolyte solution, typically an aqueous solution of KOH (40 wto KOH, 2 wt% ZnO, remainder H20) and the surfactants are then added to the mix while blending.
(Alternatively, the surfactants may be added directly to the zinc powder before blending the zinc powder with the gelling agent.) The mixture is then transferred to a closed storage tank. The gelled zinc slurries having the various compositions set forth in the ensuing examples are prepared in accordance with the above described procedure.
The following examples illustrate the invention and advantages derived therefrom. (All compositions are by weight unless otherwise specified.) Example 1 (Comparative Example):
A conventional zinc/manganese dioxide alkaline size AA cell is prepared with conventional cathode active material, electrolyte and separator membrane. The cell contains zero-added mercury and is "essentially mercury free" (containing less than 10 parts mercury per million parts total cell weight). The cathode active material in the cell is composed of electrolytic manganese dioxide (86 wto), graphite (8 wto) and a 7 Normal aqueous solution of KOH (6 wto). The separator membrane is a conventional electrolyte permeable membrane containing polyvinyl alcohol/rayon material. The electrolyte is an aqueous solution of KOH containing about 40 wto KOH and 2 wt% ZnO, hereinafter referred to as "aqueous 40 wt% KOH
solution". The anode active material is a zinc slurry without any surfactants and having the following composition:
Zinc alloy powder (99.9 wto zinc alloy containing 500 ppm indium) (64.6 wto); aqueous 40 wto KOH solution (34.7 wt%); CARBOPOL C940 gelling agent (0.4 wt%); and WATER-LOCK A-221 gelling agent (0.3 wt%).
The cell in this example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals over the cell discharge life. A voltage drop usually between about 250 and 750 millivolts (average about 500 millivolts) typically occurs upon impact giving a discharge curve similar to the one shown in Fig. 1.
The cell in this example evolves 2.6 milliliters of hydrogen at 71°C over a period of 4 weeks before discharge. (Holding cells at 71°C (160°F) for a period of one week is generally regarded as equivalent to one year of shelf-life of such cells at room temperature.) This volume of hydrogen gas evolution is considered to be unacceptably high.
Example 2 The same AA alkaline cell as in Example 1 is prepared "essentially mercury free" but with an anionic surfactant included in the zinc anode active material.
The zinc anode active material is a zinc slurry having the following composition:
Zinc alloy powder (99.9 wto zinc alloy containing 500 ppm indium) (64.5 wto); aqueous 40 wt% KOH solution (34.6 wto); CARBOPOL C940 gelling agent (0.4 wt%); WATER
LOCK A-221 gelling agent (0.3 wto); aqueous surfactant) solution containing GAFAC RA600 anionic surfactant (0.2 wt%) .
Notes:
(1) The aqueous surfactant solution contains about 150 ppm by weight GAFAC RA600 anionic surfactant with respect to the zinc alloy and thus the aqueous solution contains about 6 wt% GAFAC RA600 surfactant and 94 wto H20.
The cell in this example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals over the cell discharge life. A voltage drop typically between about 250 and 750 millivolts (average about 500 millivolts) occurs upon impact giving a discharge curve similar to the one shown in Fig. 1.
The cell in this example evolves about 0.9 milliliters of hydrogen at 71°C over a period of 4 weeks before discharge. This gassing level is acceptable, but the load voltage instability described above is not.
Example 3:
The same AA alkaline cell as in Example 1 is prepared but with an anionic and non-ionic surfactant included in the anode active material. The anode active material is a zinc slurry having the following composition:
Zinc alloy powder (99.9 wt% zinc alloy containing 500 ppm indium) (64.5 wto); aqueous 40 wto KOH solution (34.6 wto); CARBOPOL C940 gelling agent (0.4 wt%); WATER-LOCK A-221 gelling agent (0.3 wto); aqueous surfactant) solution containing GAFAC RA600 anionic surfactant and TRITON X100 non-ionic surfactant (0.2 wto).
Notes:
(1) The aqueous surfactant solution contains about 75 ppm by weight GAFAC RA600 anionic surfactant and 75 ppm by weight TRITON X100 non-ionic surfactant with respect to the zinc alloy. Thus, the aqueous surfactant solution contains about 3 wto GAFAC RA600 surfactant, 3 wto TRITON
X100 surfactant and 94 wt% H20.
The cell in this example produces a nominal voltage of about 1.5 volts and is discharged using a 3.9 ohm load. The cell is tapped and jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals during the cell discharge life. There are no detectable load voltage instabilities over' the discharge life of the cell. The discharge curve is similar to the one shown in Fig. 2.
The cell in this example evolves 1.2 milliliters of hydrogen at 71°C over a period of 4 weeks before discharge. This is an acceptable level of hydrogen gas evolution.
The performance of the cell of this example in terms of its discharge voltage profile and service life is similar to conventional Zn/Mn02 alkaline cells of same composition, but containing added amounts of mercury and no surfactants.
Examble 4:
The same AA alkaline cell as in Example 1 is prepared but with a non-ionic surfactant included in the zinc anode active material. The zinc anode active material is a zinc slurry having the following composition:
Zinc alloy powder (99.9 wto zinc alloy containing 500 ppm indium) (64.5 wt%); aqueous 40 wt% KOH solution (34.6 wta); CARBOPOL C940 gelling agent (0.4 wt%); WATER-LOCK A-221 gelling agent (0.3 wt%); aqueous surfactant) solution containing TRITON X100 non-ionic surfactant (0.2 wt%).
Notes:
(1) The aqueous surfactant solution contains about 150 ppm by weight TRITON X100 non-ionic surfactant with respect to the zinc alloy and thus the aqueous solution contains about 6 wto TRITON X100 surfactant and 94 wto H20 .
The cell in this example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals over the cell discharge life. There are no detectable load voltage instabilities over the discharge life of the cell. Although there are no load voltage instabilities, the service hours of the cell in this example is 10 percent less than the cell in Example 3 if the discharge service of both cells are carried out at 0°C. This performance loss is unacceptably high.
The cell in this example evolves about 1.2 milliliters of hydrogen at 71°C over a period of 4 weeks before discharge.
Example 5 (Comparative Example):
The same conventional AA alkaline cell as in Example 1 is prepared "essentially mercury free" except that the anode active material is composed of a gelled zinc slurry without surfactants and has the following composition:
Zinc alloy powder (99.9 wto zinc alloy containing 500 ppm indium) (64.5 wto); aqueous 40 wto KOH solution (34.7 wto); and SIGMA POLYGEL 4P gelling agent (0.8 wt%).
The cell in the above example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals over the cell discharge life. An average voltage drop of about 700 millivolts occurs upon impact.
A representative profile (voltage versus service hours) as the cell is tapped at regular one minute intervals during discharge is shown in Figure 1.
The hydrogen gas evolution from the cell in this and the three following examples is determined by performing the following out of cell gassing test. A quantity of 1) the zinc anode composition specified in each example, 2) electrolyte, and 3) anode collector material are sealed in a container in about the same proportion that they are present in an actual cell. The container is stored at 71°C for four weeks. Thereafter, the amount of hydrogen gas contained in the head space is analyzed and adjusted by proration to take into account the difference between the absolute quantity of materials in the test versus the amount in the actual cell. The gas amounts reported here are the adjusted amounts.
The AA alkaline cell gas evolution (assuming storage of the cell for 4 weeks at 71°C and atmospheric pressure) is determined to be 3.6 milliliters at these conditions.
This amount of hydrogen gas evolution is considered to be unacceptably high.
Example 6:
The same conventional AA alkaline cell as in Example 1 is prepared except that the anode active material in the cell is composed of a gelled zinc slurry having the following composition:
Zinc alloy powder (99.9 wt% zinc alloy containing 500 ppm indium) (64.5 wto); aqueous 40 wto KOH solution (34.5 wto); SIGMA POLYGEL 4P gelling agent (0.8 wto);
aqueous surfactant solutions containing GAFAC RA600 anionic surfactant and ZONYL FSN non-ionic surfactant (0.2 wto) .
Notes:
(1) The aqueous surfactant solution contains about 75 ppm by weight GAFAC RA600 anionic surfactant and 75 ppm by weight ZONYL FSN non-ionic surfactant with respect to the zinc alloy. Thus, the aqueous surfactant solution contains about 3 wt% GAFAC RA600 surfactant, 3 wt o ZONYL
FSN surfactant and 94 wt% H20.
The cell in the above example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals over the cell discharge life. There is no detectable load voltage instability over the discharge life of the cell. The discharge curve is similar to the one shown in Fig. 2.
The performance of the cell of this example in terms of its discharge voltage profile and service life is similar to a conventional Zn/Mn02 alkaline cells of same composition, but containing added amounts of mercury and no surfactants.
The rate of hydrogen gas produced in an AA alkaline cell containing the above gelled zinc slurry composition is determined in the same manner as set forth in Example 5. The AA alkaline cell gas evolution (assuming storage of the cell for 4 weeks at 71°C and atmospheric pressure) is determined to be 0.9 milliliters at these conditions, which is an acceptable level of hydrogen gas formation.
Example 7:
The same conventional AA alkaline cell as in Example 1 is prepared except that the anode active material in the cell is composed of a gelled zinc slurry having the following composition:
Zinc alloy powder (99.9 wto zinc alloy containing 500 ppm indium) (64.5 wt%); aqueous 40 vto KOH solution (34.5 wt%); SIGMA POLYGEL 4P gelling agent (0.8 wto);
aqueous surfactant solutions containing GAFAC RA600 anionic surfactant and ZONYL FSO non-ionic surfactant (0.2 wt%).
Notes:
(1) The aqueous surfactant solution contains about 75 ppm by weight GAFAC RA600 anionic surfactant and 75 ppm by weight ZONYL FSO non-ionic surfactant with respect to the zinc alloy. Thus, the aqueous surfactant solution contains about 3 wto GAFAC RA600 surfactant, 3 wto ZONYL
FSO surfactant and 94 wt% E~O.
The cell in the above example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals over the cell discharge life. There is no detectable load voltage instability over the discharge life of the cell. The discharge curve is similar to the one shown in Fig. 2.
The performance of the cell of this example in terms of its discharge voltage profile and service life is similar to conventional Zn/Mn02 alkaline cells of same composition, but containing added amounts of mercury and no surfactants.
The rate of hydrogen gas produced in an AA alkaline cell containing the above gelled zinc slurry composition is determined in the same manner as set forth in Example 5. The AA alkaline cell gas evolution (assuming storage of the cell for 4 weeks at 71°C and atmospheric pressure) is determined to be 0.8 milliliters at these conditions, which is an acceptable level of hydrogen gas formation.
Example 8:
The same conventional AA alkaline cell as in Example 1 is prepared except that the anode active material in the cell is composed of a zinc slurry having the following composition:
Zinc alloy powder (99.9 wt% zinc alloy containing 500 ppm indium) (64.5 wt%); aqueous 40 vt% ROE solution (34.5 wto); SIGMA POLYGEL 4P gelling agent (0.8 wt%);
aqueous surfactant solutions containing GAFAC RA600 anionic surfactant and FC-170C non-ionic surfactant (0.2 wt%).
Notes:
(1) The aqueous surfactant solution contains about 75 ppm by weight GAFAC RA600 anionic surfactant and 75 ppm by weight FC170C non-ionic surfactant with respect to the zinc alloy. Thus, the aqueous solution contains about 3 wt% GAFAC RA600 surfactant, 3 wt% FC-170C surfactant and 94 wto EzO.
The cell in the above example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds at regular one minute intervals over the cell discharge life. There is no detectable load voltage instability over the discharge life of the cell.
A representative profile (voltage versus service hours) as the cell is tapped during discharge is shown in Figure 2.
The performance of the cell of this example in terms of its discharge voltage profile and service life is similar to conventional Zn/Mn02 alkaline cells of same composition, but containing added amounts of mercury and no surfactants.
The rate of hydrogen gas produced in an AA alkaline cell containing the above gelled zinc slurry composition is determined in the same manner as set forth in Example 5. The AA alkaline cell gas evolution (assuming storage of the cell for 4 weeks at 71°C and atmospheric pressure) is determined to be 0.8 milliliters at these conditions, which is an acceptable level of hydrogen gas formation.
Although the present invention is described with respect to specific embodiments, it should be appreciated that other embodiments falling within the scope and the concept of the invention are also possible. Therefore, the invention is not intended to be limited by the specific embodiments, but rather is defined by the claims and equivalents thereof.
~ 2105952 U.S. Patents 4,939,048 and 4,942,101 are directed to inhibiting the occurrence of load voltage instability in a mercury free alkaline cell containing a gelled zinc anode.
U.S. Patent 4,939,048 discloses use of an anode current collector comprising a bundle of conductive fibers and U.S
Patent 4,942,101 discloses use of an anode current collector of various configurations with fittings thereon designed to increase its surface area. Both references disclose including from 1 to 1000 ppm of an organic stabilization compound selected f=rom polyfluoride compounds of the ethoxyl fluoroalcohol type and compounds of the polyethoxylalcohol and alcoyl sulfide type. There is no disclosure or suggestion of mixing anionic and non-anionic surface active agents or that any particular benefits can be obtained from such mixing.
The following prior art discloses a number of organic compounds that reduce the formation of hydrogen gas in alkaline cells. The use of these: materials has allowed for a reduction of mercury content: to environmentally safe levels. However, none of these materials has been disclosed to have an effect on load voltage instability.
U.S. Patent 4,195,120 discloses the addition of an organic phosphate ester surfactant to the anode, cathode or electrolyte of an alkaline cell having zinc anodes containing mercury. Examples of such surfactants are disclosed as available under the trade designation GAFAC*
RE610, GAFAC RA600, and KLEARFAC* AA-040. The addition of the phosphate eater surfactant reduces the hydrogen evolution, thereby increasing t:he shelf-life and useful discharge life of the cell.
U.S. Patent 4,455,358 discloses the use of a starch-graft copolymer as gelling agent for the zinc anode comprising an * Trade-marks A
amalgamated zinc powder containing about 7% mercury. The gelling agent is composed of a carbohydrate backbone which has a water soluble side chain grafted onto it. The gelling agent is reported to increase the practical discharge capacity of the anode while reducing the amount of hydrogen evolution from the cell.
Canadian Patent 1,154,081 discloses the use of a gelling composition formed preferably of a mixed gelling agent containing a starch-graft copolymer and yet another gelling agent, for example, carboxymethylcellulose. The mixed gelling agent is used to gel conventional amalgamated zinc powder for Zn-alkaline-Mn02 cells. The mixed gelling agent is reported to inhibit internal shorting of the cell, which can occur if carboxymethylcellulose alone is employed.
US Patent 3,057,944 discloses the addition of a surface active agent which is heteropolar substance admixed either into the electrolyte or the silver cathode of an electrochemical cell.
US Patent 3,847,669 discloses the addition of an ethylene oxide polymer to a zinc-manganese dioxide cell.
The ethylene oxide polymer may be used to wet the separator or may be added to the zinc during preparation of the zinc anode gel. The ethylene oxide polymer is reported as allowing for a reduction in the amount of mercury required to be added to the zinc anode.
US Patent 4,230,549 discloses a novel polymer.
membrane to be used as separator membrane in electrochemical cells. The membrane is preferably composed of a cross-linked low density polyethylene base grafted with methacrylic acid. Before use, the polymer membrane is immersed in a solution containing surfactants which may be a mixture of an anionic and non-ionic emulsifier such as Ultrawet* KX (a sodium linear alkyl sulfonate) and Triton* X100 (isooctyl phenoxyl polyethoxy ethanol). The treatment of the membrane with the surfactants is reported to have the effect of lowering the electrolytic resistance of the membrane as well as imparting to it better wetting characteristics. There is no discussion with respect to load voltage instability or the effect of these surfactants on hydrogen evolution.
European Patent Publication 0 474 382 A1 relates to an alkaline cell having a zinc containing anode and is substantially mercury free, i. e. the mercury content is less than 50 parts per million per total call weight. This reference discloses additives that inhibit the corrosion of zinc. One such additive is an el~hylene oxide polymer, such as phosphate esters of ei~hylene oxide polymers, perfluorinated organic compounds of the ethoxylated fluoroalcohol type, and alkyl and polyethoxyalcohol sulphides. The preferred ethylene oxide polymers are the polyethylene glycols and methoxy polyethylene glycols having a molecular weight from about 300 to 700. (P. 5, line 27-42.) It is stated in broad brush that the ethylene oxide polymers can be used singly or in combination. (P. 5, line 42.) There is no disclosure or suggestion of any particular benefit accruing to the use of any particular type of ethylene oxide polymers in combination. The anode mixture contains electrolyte and optionally an electrolyte-swellable binder such as a polyacrylic acid, for example, Carbopol* 940 gelling agent. (P. 4, line 35.) The cells are reported to exhibit insufficient bulge due to hydrogen gas formation to cause leakage of t:he cell components. (P.7, lines 13-17.) There is no discussion or recognition in this reference of the problem of load voltage instability occurring in alkaline cells which contain zero added mercury. There are also no specific examples which include more than one ethoxylated polymer and in fact all * Trade-marks A' _ 2~o595z the specific examples read on only one ethylene oxide polymer, namely a methoxylated polyethylene oxide (CARBOWAX* 550).
U.S. Patent 4,606,984 discloses the addition of a fluorinated organic compound, of the ethoxylated fluoroalcohol type to an anode of a primary electrochemical cell containing zinc, aluminum or magnesium. A preferred compound of this type is disclosed as available under the trade designation FORAFAC* 1110. The fluorinated compound when added to the anodic material in percentage between 0.01% and 1% by weight of th~~ metal therein, acts as inhibitor causing a reduction in hydrogen gas evolution from the cell. The hydrogen evolution rate is reported at various levels of mercury content in the cell, i.e., from 0% to 5% mercury content with :respect to zinc in a zinc anodic alkaline cell. When the fluorinated compound was added to zinc anodic material, the rate of hydrogen evolution decreased at all levels of mercury content compared to the same anodic material with no inhibitor.
Accordingly it is desirable to find an environmentally safe, disposable substitute for mercury in electrochemical cells, particularly in zinc anodic alkaline cells, that both inhibits hydrogen gas formation and load voltage instability.
It is desirable to find an additive for cells that inhibit the occurrence of load voltage instability during normal discharge of the cell, particularly in zinc anodic alkaline cells having a mercury content of less than about 50 parts per million parts by total weight of the cell.
It is desirable to find additives for cells that simultaneously retard or inhibit hydrogen evolution, particularly in zinc anodic alkaline cells having a mercury content of less than about 50 parts mercury per million parts by * Trade-mark A
total weight of the cell.
The following figures show representative comparative discharges graphs illustrative of the performance of the invention.
Fig. 1 is a graphical plot of the voltage discharge profile (voltage versus service hour) of the alkaline cell described in Example 5 as the cell was tapped at regular one minute intervals as it was discharged under a load of 3.9 ohms.
Fig. 2 is a graphical plot of the voltage discharge profile (voltage versus service hour) of the alkaline cell described in Example 8 as the cell was tapped at regular one minute intervals as it was discharged under a load of 3.9 ohms.
It has been discovered that the addition of a mixture of an anionic and a non-ionic surfactant to the cell, preferably to the zinc anode, inhibits the occurrence of load voltage instability even when there is no mercury added to the cell, e.g., when the mercury content in the cell is below about 50 parts and even less than 10 parts per million parts by total weight of the cell. It is surprising that the problem of load voltage instability in such cells can be overcome simply by adding a mixture of surfactants, since the surfactants themselves are not electrically conductive. It is unexpected that the mixture of anionic and non-ionic surfactants have a combined effect in both inhibiting load voltage instability and simultaneously reducing gassing than either class of surfactants alone. Also, it has been determined that the mixture of surfactants in such cells give cell performance, e.g. in terms of discharge voltage profile and service hours, similar to that obtained in conventional alkaline cells of same composition, but containing an added amount of mercury and no surfactants. In fact for most applications the performance between the two cells is virtually indistinguishable.
The mixture of an anionic surfactant and a non-ionic surfactant have been determined to also significantly reduce the amount of hydrogen gas produced in the cell.
Conventional gelling agents alone have some effect in reducing hydrogen evolution. However, it has been determined that the addition of the surfactants to the zinc slurry along with the gelling agent greatly reduces the amount of hydrogen evolution, particularly in alkaline cells that contain no added amounts of mercury, for example, less than 50 parts mercury per million parts by weight of the cell. The resultant effect is that when a mixture of anionic and non-ionic surfactants is added to the zinc slurry, the occurrence of load voltage instability is inhibited and hydrogen evolution fram the cell is reduced to a level that does not noticeably interfere with the cell's performance or shelf-life, even though the cell contains no added mercury and less than 50 parts mercury per million parts cell weight.
It should be understood that residual amounts of mercury may be present in commercially available pure zinc or in any of the other cell components.
(Commercially pure zinc typically has less than 100 parts mercury per billion parts zinc.) The term "substantially mercury free" is defined herein as a mercury content of less than about 50 parts mercury per million parts total cell weight. The term "essentially mercury free" shall be defined herein as a mercury content less than about 10 parts mercury per million parts by total weight of the cell. Both "substantially mercury free" and "essentially mercury free" cells fall within the definition of "zero-added mercury" cells. "Zero-added mercury" cells contain no added amounts of mercury. Such cells are defined as containing only the residual amount of mercury present in commercially available pure zinc, including the residual amount o:E mercury, if any, present in the other cell components.
The surfactant mixture of the invention to be added to zinc anode active material for alkaline cells is comprised of at least one anionic surfactant and at least one non-ionic surfactant. The anionic and non-ionic surfactants each have a polyethoxy chain - (CHZ-CHZ-O) n- which typically forms the hydrophilic portion of the molecule. The anionic surfactant can be represented generally by the formula (A), Rl(CH2_CH2_O)n _Xl (A) where R1 represents alkyl, aryl, alkylaryl (including substituted alkyl or aryl groups) and these groups normally form the hydrophobic portion of 'the molecule. The group R1 is typically an alkyl chain composed of 4 to 28 carbon atoms. The average number of ethoxy groups, n, is typically between 3 and 40. The molecule terminates at the other end with the anionic group, X1. The anionic group, X, may typically be selected from acid or salt moieties such as those derived from pho:~phoric acid moieties (-O-P03H2) , boric acid moieties (-O-BOzHz) , carboxylic moieties (-COOH) and salts thereof . The anionic surfactant may also be selected from polyethoxy phosphate esters of the type described in U.S. Patent 4,195,1:?0. The anionic surfactants represented by the formula (A) may be selected in their entirety from the organic phosphate esters of the type described in U.S. Patent 4,195,120. The anionic surfactant may typically have a molecular weight of between 200 and 2000.
A preferred anionic surfactant for use in the present invention is available under the trade designation GAFAC
RA600 organic phosphate ester surfactant from Rhone Poulenc.
A
The non-ionic surfactant can be represented generally by the formula (B), RZ- (CHZ-CHz-O) n-X2 (B) where R2 represents hydrogen, alkyl, aryl, alkylaryl (including substituted alkyl or aryl groups), fluorinated aliphatic groups (including substituted fluorinated aliphatic groups), fluorinated aliphatic groups containing amino groups, e.g. sufonamido gz-oups, and any combinations thereof. The group, R2, normally forms the hydrophobic portion of the molecule. The group, R2, typically contains between about 3 and 16 carbon atoms when fluorinated and between 4 and 28 carbons when not fluorinated. The average number of ethoxy groups, n, typi~~ally is between 3 and 250.
The molecule terminates with the' nonionic group, X2, which may typically be hydrogen or methyl. The non-ionic surfactant may typically have a molecular weight of between about 200 and 10000.
Preferred non-ionic surfactants for use in the present invention is TRITON X100 (isooctyl phenoxyl polyethoxy ethanol) from Rohm and Haas Co., ZONYL* FSN and ZONYL FSO
(both of which are fluorinated aliphatic polyethoxy ethanols) from E.I. DuPont and FLUORAD* FC-170C (a fluorinated alkyl polyethoxy ethanol) from 3M Company.
TRITON X100 surfactant has the formula C8H1.,C6H4 (OCzH4) loOH.
ZONYL FSN and ZONYL FSO surfactants have the general formula RfCH2CH20 (CHzCH20) XH, where Rf=F (CFZCFZ) Z and z=3 to 8 .
FLUORAD FC-170C surfactant has the general formula RfSO2N (CzHs) (CHzCHzO) XH where Rf=C"Fzn+1 and n has an average value of about 8.
The preferred anode active material is composed of a gelled zinc slurry containing a mixture of at least one anionic surfactant and one' non-ionic surfactant, advantageously from the pre:Eerred surfactants above described, typically in amounts comprising between about 25 and 200 ppm of each, preferably about 75 ppm of each as * Trade-marks 10 A
compared to the amount of zinc alloy in the slurry.
The gelling agents for the zinc slurry can be selected from a variety of known gelling agents activated by alkaline mixtures. Preferred gelling agents are substantially insoluble in the cell electrolyte so that the gelling agent does not migrate between the anode and cathode. The preferred gelling agents also do not lose water when the gelled zinc slurry is left in storage.
Suitable gelling agents, for example, are carboxymethyl cellulose or crosslinked carboaymethyl cellulose, methyl cellulose, Xanthan gum, crosslinked polyacrylamides, crosslinked acrylic acid copolyners such as CARBOPOL C-940 from B.F.Goodrich Co., starch-graft copolymers such as WATER-LOCK* A221 starch-graft copolymer of polyacrylic acid and polyacrylamide from Grain Processing Co., and alkali hydrolyzed polyacrylonitrile such as WATER-LOCK A 400 from Grain Processing Co. The gelling agent can be used alone or in mixture with other known gelling or thickening components. Although any of these gelling agents can be employed alone or in combination, at least one of the gelling agents may advantageously be selected from crosslinked acrylic acid polymer such as CARBOPOL C940 or SIGMA POLYGEL 4P gelling agents or a starch graft copolymer such as WATER-LOCK A-221 copolymer.
A zinc slurry is preparecL by mixing a zinc alloy powder (e.g. 99.9% zinc alloy powder containing about 500 ppm indium) with a suitable gelling agent using a blender or other similar mixing equipmE:nt. (The zinc powder may typically contain between about 50 and 1000 parts indium per million parts by weight of the particles.) Suitable gelling agents are then added to the blender. The gelling agents may advantageously be se:Lected from the list above described. The zinc powder and gelling agent are then blended until a homogeneous mixture is * Trade-marks A
obtained. The electrolyte solution, typically an aqueous solution of KOH (40 wto KOH, 2 wt% ZnO, remainder H20) and the surfactants are then added to the mix while blending.
(Alternatively, the surfactants may be added directly to the zinc powder before blending the zinc powder with the gelling agent.) The mixture is then transferred to a closed storage tank. The gelled zinc slurries having the various compositions set forth in the ensuing examples are prepared in accordance with the above described procedure.
The following examples illustrate the invention and advantages derived therefrom. (All compositions are by weight unless otherwise specified.) Example 1 (Comparative Example):
A conventional zinc/manganese dioxide alkaline size AA cell is prepared with conventional cathode active material, electrolyte and separator membrane. The cell contains zero-added mercury and is "essentially mercury free" (containing less than 10 parts mercury per million parts total cell weight). The cathode active material in the cell is composed of electrolytic manganese dioxide (86 wto), graphite (8 wto) and a 7 Normal aqueous solution of KOH (6 wto). The separator membrane is a conventional electrolyte permeable membrane containing polyvinyl alcohol/rayon material. The electrolyte is an aqueous solution of KOH containing about 40 wto KOH and 2 wt% ZnO, hereinafter referred to as "aqueous 40 wt% KOH
solution". The anode active material is a zinc slurry without any surfactants and having the following composition:
Zinc alloy powder (99.9 wto zinc alloy containing 500 ppm indium) (64.6 wto); aqueous 40 wto KOH solution (34.7 wt%); CARBOPOL C940 gelling agent (0.4 wt%); and WATER-LOCK A-221 gelling agent (0.3 wt%).
The cell in this example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals over the cell discharge life. A voltage drop usually between about 250 and 750 millivolts (average about 500 millivolts) typically occurs upon impact giving a discharge curve similar to the one shown in Fig. 1.
The cell in this example evolves 2.6 milliliters of hydrogen at 71°C over a period of 4 weeks before discharge. (Holding cells at 71°C (160°F) for a period of one week is generally regarded as equivalent to one year of shelf-life of such cells at room temperature.) This volume of hydrogen gas evolution is considered to be unacceptably high.
Example 2 The same AA alkaline cell as in Example 1 is prepared "essentially mercury free" but with an anionic surfactant included in the zinc anode active material.
The zinc anode active material is a zinc slurry having the following composition:
Zinc alloy powder (99.9 wto zinc alloy containing 500 ppm indium) (64.5 wto); aqueous 40 wt% KOH solution (34.6 wto); CARBOPOL C940 gelling agent (0.4 wt%); WATER
LOCK A-221 gelling agent (0.3 wto); aqueous surfactant) solution containing GAFAC RA600 anionic surfactant (0.2 wt%) .
Notes:
(1) The aqueous surfactant solution contains about 150 ppm by weight GAFAC RA600 anionic surfactant with respect to the zinc alloy and thus the aqueous solution contains about 6 wt% GAFAC RA600 surfactant and 94 wto H20.
The cell in this example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals over the cell discharge life. A voltage drop typically between about 250 and 750 millivolts (average about 500 millivolts) occurs upon impact giving a discharge curve similar to the one shown in Fig. 1.
The cell in this example evolves about 0.9 milliliters of hydrogen at 71°C over a period of 4 weeks before discharge. This gassing level is acceptable, but the load voltage instability described above is not.
Example 3:
The same AA alkaline cell as in Example 1 is prepared but with an anionic and non-ionic surfactant included in the anode active material. The anode active material is a zinc slurry having the following composition:
Zinc alloy powder (99.9 wt% zinc alloy containing 500 ppm indium) (64.5 wto); aqueous 40 wto KOH solution (34.6 wto); CARBOPOL C940 gelling agent (0.4 wt%); WATER-LOCK A-221 gelling agent (0.3 wto); aqueous surfactant) solution containing GAFAC RA600 anionic surfactant and TRITON X100 non-ionic surfactant (0.2 wto).
Notes:
(1) The aqueous surfactant solution contains about 75 ppm by weight GAFAC RA600 anionic surfactant and 75 ppm by weight TRITON X100 non-ionic surfactant with respect to the zinc alloy. Thus, the aqueous surfactant solution contains about 3 wto GAFAC RA600 surfactant, 3 wto TRITON
X100 surfactant and 94 wt% H20.
The cell in this example produces a nominal voltage of about 1.5 volts and is discharged using a 3.9 ohm load. The cell is tapped and jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals during the cell discharge life. There are no detectable load voltage instabilities over' the discharge life of the cell. The discharge curve is similar to the one shown in Fig. 2.
The cell in this example evolves 1.2 milliliters of hydrogen at 71°C over a period of 4 weeks before discharge. This is an acceptable level of hydrogen gas evolution.
The performance of the cell of this example in terms of its discharge voltage profile and service life is similar to conventional Zn/Mn02 alkaline cells of same composition, but containing added amounts of mercury and no surfactants.
Examble 4:
The same AA alkaline cell as in Example 1 is prepared but with a non-ionic surfactant included in the zinc anode active material. The zinc anode active material is a zinc slurry having the following composition:
Zinc alloy powder (99.9 wto zinc alloy containing 500 ppm indium) (64.5 wt%); aqueous 40 wt% KOH solution (34.6 wta); CARBOPOL C940 gelling agent (0.4 wt%); WATER-LOCK A-221 gelling agent (0.3 wt%); aqueous surfactant) solution containing TRITON X100 non-ionic surfactant (0.2 wt%).
Notes:
(1) The aqueous surfactant solution contains about 150 ppm by weight TRITON X100 non-ionic surfactant with respect to the zinc alloy and thus the aqueous solution contains about 6 wto TRITON X100 surfactant and 94 wto H20 .
The cell in this example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals over the cell discharge life. There are no detectable load voltage instabilities over the discharge life of the cell. Although there are no load voltage instabilities, the service hours of the cell in this example is 10 percent less than the cell in Example 3 if the discharge service of both cells are carried out at 0°C. This performance loss is unacceptably high.
The cell in this example evolves about 1.2 milliliters of hydrogen at 71°C over a period of 4 weeks before discharge.
Example 5 (Comparative Example):
The same conventional AA alkaline cell as in Example 1 is prepared "essentially mercury free" except that the anode active material is composed of a gelled zinc slurry without surfactants and has the following composition:
Zinc alloy powder (99.9 wto zinc alloy containing 500 ppm indium) (64.5 wto); aqueous 40 wto KOH solution (34.7 wto); and SIGMA POLYGEL 4P gelling agent (0.8 wt%).
The cell in the above example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals over the cell discharge life. An average voltage drop of about 700 millivolts occurs upon impact.
A representative profile (voltage versus service hours) as the cell is tapped at regular one minute intervals during discharge is shown in Figure 1.
The hydrogen gas evolution from the cell in this and the three following examples is determined by performing the following out of cell gassing test. A quantity of 1) the zinc anode composition specified in each example, 2) electrolyte, and 3) anode collector material are sealed in a container in about the same proportion that they are present in an actual cell. The container is stored at 71°C for four weeks. Thereafter, the amount of hydrogen gas contained in the head space is analyzed and adjusted by proration to take into account the difference between the absolute quantity of materials in the test versus the amount in the actual cell. The gas amounts reported here are the adjusted amounts.
The AA alkaline cell gas evolution (assuming storage of the cell for 4 weeks at 71°C and atmospheric pressure) is determined to be 3.6 milliliters at these conditions.
This amount of hydrogen gas evolution is considered to be unacceptably high.
Example 6:
The same conventional AA alkaline cell as in Example 1 is prepared except that the anode active material in the cell is composed of a gelled zinc slurry having the following composition:
Zinc alloy powder (99.9 wt% zinc alloy containing 500 ppm indium) (64.5 wto); aqueous 40 wto KOH solution (34.5 wto); SIGMA POLYGEL 4P gelling agent (0.8 wto);
aqueous surfactant solutions containing GAFAC RA600 anionic surfactant and ZONYL FSN non-ionic surfactant (0.2 wto) .
Notes:
(1) The aqueous surfactant solution contains about 75 ppm by weight GAFAC RA600 anionic surfactant and 75 ppm by weight ZONYL FSN non-ionic surfactant with respect to the zinc alloy. Thus, the aqueous surfactant solution contains about 3 wt% GAFAC RA600 surfactant, 3 wt o ZONYL
FSN surfactant and 94 wt% H20.
The cell in the above example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals over the cell discharge life. There is no detectable load voltage instability over the discharge life of the cell. The discharge curve is similar to the one shown in Fig. 2.
The performance of the cell of this example in terms of its discharge voltage profile and service life is similar to a conventional Zn/Mn02 alkaline cells of same composition, but containing added amounts of mercury and no surfactants.
The rate of hydrogen gas produced in an AA alkaline cell containing the above gelled zinc slurry composition is determined in the same manner as set forth in Example 5. The AA alkaline cell gas evolution (assuming storage of the cell for 4 weeks at 71°C and atmospheric pressure) is determined to be 0.9 milliliters at these conditions, which is an acceptable level of hydrogen gas formation.
Example 7:
The same conventional AA alkaline cell as in Example 1 is prepared except that the anode active material in the cell is composed of a gelled zinc slurry having the following composition:
Zinc alloy powder (99.9 wto zinc alloy containing 500 ppm indium) (64.5 wt%); aqueous 40 vto KOH solution (34.5 wt%); SIGMA POLYGEL 4P gelling agent (0.8 wto);
aqueous surfactant solutions containing GAFAC RA600 anionic surfactant and ZONYL FSO non-ionic surfactant (0.2 wt%).
Notes:
(1) The aqueous surfactant solution contains about 75 ppm by weight GAFAC RA600 anionic surfactant and 75 ppm by weight ZONYL FSO non-ionic surfactant with respect to the zinc alloy. Thus, the aqueous surfactant solution contains about 3 wto GAFAC RA600 surfactant, 3 wto ZONYL
FSO surfactant and 94 wt% E~O.
The cell in the above example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds (267 Newtons) at regular one minute intervals over the cell discharge life. There is no detectable load voltage instability over the discharge life of the cell. The discharge curve is similar to the one shown in Fig. 2.
The performance of the cell of this example in terms of its discharge voltage profile and service life is similar to conventional Zn/Mn02 alkaline cells of same composition, but containing added amounts of mercury and no surfactants.
The rate of hydrogen gas produced in an AA alkaline cell containing the above gelled zinc slurry composition is determined in the same manner as set forth in Example 5. The AA alkaline cell gas evolution (assuming storage of the cell for 4 weeks at 71°C and atmospheric pressure) is determined to be 0.8 milliliters at these conditions, which is an acceptable level of hydrogen gas formation.
Example 8:
The same conventional AA alkaline cell as in Example 1 is prepared except that the anode active material in the cell is composed of a zinc slurry having the following composition:
Zinc alloy powder (99.9 wt% zinc alloy containing 500 ppm indium) (64.5 wt%); aqueous 40 vt% ROE solution (34.5 wto); SIGMA POLYGEL 4P gelling agent (0.8 wt%);
aqueous surfactant solutions containing GAFAC RA600 anionic surfactant and FC-170C non-ionic surfactant (0.2 wt%).
Notes:
(1) The aqueous surfactant solution contains about 75 ppm by weight GAFAC RA600 anionic surfactant and 75 ppm by weight FC170C non-ionic surfactant with respect to the zinc alloy. Thus, the aqueous solution contains about 3 wt% GAFAC RA600 surfactant, 3 wt% FC-170C surfactant and 94 wto EzO.
The cell in the above example produces a nominal voltage of about 1.5 volts and is discharged under a 3.9 ohm load. The cell is tapped or jolted with an impact force of about 60 pounds at regular one minute intervals over the cell discharge life. There is no detectable load voltage instability over the discharge life of the cell.
A representative profile (voltage versus service hours) as the cell is tapped during discharge is shown in Figure 2.
The performance of the cell of this example in terms of its discharge voltage profile and service life is similar to conventional Zn/Mn02 alkaline cells of same composition, but containing added amounts of mercury and no surfactants.
The rate of hydrogen gas produced in an AA alkaline cell containing the above gelled zinc slurry composition is determined in the same manner as set forth in Example 5. The AA alkaline cell gas evolution (assuming storage of the cell for 4 weeks at 71°C and atmospheric pressure) is determined to be 0.8 milliliters at these conditions, which is an acceptable level of hydrogen gas formation.
Although the present invention is described with respect to specific embodiments, it should be appreciated that other embodiments falling within the scope and the concept of the invention are also possible. Therefore, the invention is not intended to be limited by the specific embodiments, but rather is defined by the claims and equivalents thereof.
Claims (20)
1. A method for both inhibiting the occurrence of load voltage instability and controlling the formation of hydrogen gas in an alkaline electrochemical cell having a gelled zinc anode and an aqueous alkaline electrolyte, said method comprising adding a mixture of at least one anionic surfactant having a polyethoxy chain and one non-ionic surfactant having a polyethoxy chain to said zinc anode.
2. The method of claim 1 wherein the cell has a cathode active material therein comprising manganese dioxide and the aqueous alkaline solution comprises potassium hydroxide.
3. The method of claim 1 wherein the anionic surfactant is represented by the formula:
R1(CH2-CH2-O)n-X1 wherein, R1 is selected from the group consisting of alkyl, aryl, alkylaryl and combinations thereof; X1 is selected from an anionic group consisting of an anionic acid group, salt of an anionic acid group, and anionic phosphate ester group; and n is between about 3 and 40.
R1(CH2-CH2-O)n-X1 wherein, R1 is selected from the group consisting of alkyl, aryl, alkylaryl and combinations thereof; X1 is selected from an anionic group consisting of an anionic acid group, salt of an anionic acid group, and anionic phosphate ester group; and n is between about 3 and 40.
4. The method of claim 1 wherein the non-ionic surfactant is represented by the formula:
R2-(CH2-CH2-O)n-X2 wherein, R2 is selected from the group consisting of alkyl, aryl, alkylaryl, fluorinated aliphatic groups and combinations thereof; X2 is a non-ionic group; and n is between about 3 and 250.
R2-(CH2-CH2-O)n-X2 wherein, R2 is selected from the group consisting of alkyl, aryl, alkylaryl, fluorinated aliphatic groups and combinations thereof; X2 is a non-ionic group; and n is between about 3 and 250.
5. The method of claim 3 wherein the group R1 is an alkyl group containing between about 4 and 28 carbon atoms.
6. The method of claim 3 wherein the anionic surfactant has a molecular weight between about 200 and 2000.
7. The method of claim 4 wherein the group R2 is a fluorinated aliphatic group having between about 3 and 16 carbon atoms.
8. The method of claim 4 wherein the non-ionic surfactant has a molecular weight between about 200 and 10000.
9. The method of claim 1 wherein the gelled zinc anode comprises between about 25 and 200 parts anionic surfactant per million parts by weight of a zinc-alloy particle and between about 25 and 200 parts non-ionic surfactant per million parts by weight of a zinc-alloy particle.
10. The method of claim 1 wherein the cell contains less than 50 parts mercury per million parts by weight of the cell.
11. The method of claim 1 wherein the cell contains less than 10 parts mercury per million parts by weight of the cell.
12. The method of claim 9 wherein the zinc-alloy particles comprise an alloy comprising zinc and indium.
13. The method of claim 12 wherein said particles contain between about 50 and 1000 parts indium per million parts by weight of the particles.
14. The method of claim 1 wherein the zinc anode comprises a gelling agent and wherein the gelling agent comprises a gelling component selected from the group consisting of crosslinked acrylic acid copolymers and starch graft copolymers, and mixtures thereof.
15. The method of claim 14 wherein the gelling agent comprises a mixture of CARBOPOL C940 crosslinked acrylic acid copolymer and WATER-LOCK A-221 starch graft copolymer.
16. The method of claim 14 wherein the gelling agent comprises SIGMA POLYGEL 4P (SYNTHALEN M) crosslinked acrylic acid polymer.
17. The method of claim 14 wherein the gelling agent comprises WATER-LOCK A-221 starch graft copolymer.
18. The method of claim 14 wherein the gelling agent comprises CARBOPOL C940 crosslinked acrylic acid copolymer.
19. A method for both inhibiting the occurrence of load voltage instability and controlling the formation of hydrogen gas in an alkaline electrochemical cell having a gelled zinc anode, an aqueous alkaline electrolyte, and "zero added" mercury, said method comprising adding a mixture of at least one anionic surfactant and one nonionic surfactant to said zinc anode, wherein the anionic surfactant is represented by the formula:
R1-(CH2-CH2-O)n-X1 Wherein, R1 is selected from the croup consisting of alkyl, aryl, alkylaryl and combinations thereof; X1 is selected from an anionic acid group consisting of an anionic acid group, salt of an anionic acid group, and anionic phosphate ester group; and n is between 3 and 40, and wherein the non-ionic surfactant is represented by the formula:
R2-(CH2-CH2-O)n-X2 wherein, R2 is selected from the group consisting of alkyl, aryl, alkylaryl, fluorinated aliphatic groups and combinations thereof; X2 is a non-ionic group; and n is between about 3 and 250.
R1-(CH2-CH2-O)n-X1 Wherein, R1 is selected from the croup consisting of alkyl, aryl, alkylaryl and combinations thereof; X1 is selected from an anionic acid group consisting of an anionic acid group, salt of an anionic acid group, and anionic phosphate ester group; and n is between 3 and 40, and wherein the non-ionic surfactant is represented by the formula:
R2-(CH2-CH2-O)n-X2 wherein, R2 is selected from the group consisting of alkyl, aryl, alkylaryl, fluorinated aliphatic groups and combinations thereof; X2 is a non-ionic group; and n is between about 3 and 250.
20. The method of claim 19 wherein the cell contains less than 50 parts mercury per million parts by weight of the cell.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/986,233 US5401590A (en) | 1992-12-07 | 1992-12-07 | Additives for electrochemical cells having zinc anodes |
| US986,233 | 1992-12-07 |
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| CA2105952A1 CA2105952A1 (en) | 1994-06-08 |
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| US4195120A (en) * | 1978-11-03 | 1980-03-25 | P. R. Mallory & Co. Inc. | Hydrogen evolution inhibitors for cells having zinc anodes |
| US4455358A (en) * | 1979-12-26 | 1984-06-19 | Duracell Inc. | Electrochemical cells having a gelled anode-electrolyte mixture |
| US4260669A (en) * | 1980-03-14 | 1981-04-07 | Union Carbide Corporation | Alkaline-MnO2 cell having a zinc powder-gel anode containing starch graft copolymer |
| FR2567328B1 (en) * | 1984-07-04 | 1986-07-11 | Wonder | METHOD FOR STABILIZING PRIMARY ELECTROCHEMICAL GENERATORS WITH REACTIVE ZINC, ALUMINUM OR MAGNESIUM ANODES AND ANODE FOR SUCH A GENERATOR STABILIZED BY THIS PROCESS |
| US4777100A (en) * | 1985-02-12 | 1988-10-11 | Duracell Inc. | Cell corrosion reduction |
| FR2634596B1 (en) * | 1988-07-25 | 1990-10-26 | Cipel | ELECTROCHEMICAL GENERATOR WITH ALKALINE ELECTROLYTE AND ZINC NEGATIVE ELECTRODE |
| FR2634595B1 (en) * | 1988-07-25 | 1995-07-28 | Cipel | ELECTROCHEMICAL GENERATOR WITH ALKALINE ELECTROLYTE AND ZINC NEGATIVE ELECTRODE |
| CA2046148C (en) * | 1990-08-14 | 1997-01-07 | Dale R. Getz | Alkaline cells that are substantially free of mercury |
| JPH0738306B2 (en) * | 1991-04-22 | 1995-04-26 | 松下電器産業株式会社 | Zinc alkaline battery |
-
1992
- 1992-12-07 US US07/986,233 patent/US5401590A/en not_active Expired - Lifetime
-
1993
- 1993-09-10 CA CA002105952A patent/CA2105952C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2105952A1 (en) | 1994-06-08 |
| US5401590A (en) | 1995-03-28 |
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| EEER | Examination request | ||
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