AU594661B2

AU594661B2 - Cell corrosion reduction

Info

Publication number: AU594661B2
Application number: AU53248/86A
Authority: AU
Inventors: Purush Chalilpoyil; Frank Eric Parsen; Jesse Randolph Rea; Chih-Chung Wang
Original assignee: Duracell International Inc
Current assignee: Duracell Inc USA
Priority date: 1985-02-12
Filing date: 1986-02-06
Publication date: 1990-03-15
Anticipated expiration: 2006-02-06
Also published as: AU5324886A; FR2577351A1; DK66886A; BR8600570A; DE3603342A1; NO169098C; NO169098B; CH671304A5; GB2200791B; MX163835B; IE57432B1; GB2170946B; ES551801A0; BE904216A; GB2200791A; NL8600347A; GB8802013D0; ES8706854A1; IE860198L; DK66886D0

Description

,594661I FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE SPECIFICATION FOR OFFICE USE: Class Int. Class Application Number: .*o"Lodged:

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S ?33 0 S S Complete Specification Lodged: Accepted: Accepted: Published: riority: 'Priority: :..elated Art:

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S 0 0O amedin s m. r| Section 49 and is corrcct for printing S. 0 00 Name of Applicant: Address of Applicant: Actual Inventor: DURACELL INTERNATIONAL INC.

SOUTH BROADWAY SUNNYSIDE LANE TARRYTOWN, NEW YORK, U.S.A.

PURUSH CHALILPOYIL, FRANK ERIC PARSEN, JESSE RANDOLPH REA CHIH-CHUNG WANG Address for Service: Shelston Waters, 55 Clarence Street, Sydney Complete Specification for the Invention entitled: "CELL CORROSION REDUCTION" The following statement Is a full description of this Invention, Including the best method of performing It known to me/us:awls -2- This invention relates to methods and materials used for reducing gassing in electrochemical cells as well as the amount of mercury required in anode amalgamations for such cells.

Metals such- as zinc have been commonly utilized as anodes in electrochemical cells, particulairly in cells with aqueous alkaline elec'trolytes. In such cells the zinc is amalgamated with mercury in order to prevent or reduce the extent of reaction of the zinc with the aqueous electrolyte with the detrimental evolution. of hydrogen gas. In the past it has been necessary to utilize about 6-7% by weight of mercury amalgamation in the anode to reduce the amount of "gassing" 5 to acceptable levels. However, because of environmental considerations it has become desirable to eliminate or, at the very least, reduce the amount of mercury utilized well 0 in such cells but without concomitant increase in cell gassing. Various expedients have been utilized, to "ad:%achieve such mercury reduction, such as special to0 treatment of the zinc, the use of additives and exotic amalgamation methods. However, such methods have either had economic drawbacks or limited success.

It is an object of the present invention to provide 0 an economic means for reduction of gassing in electrochemical cells.

It is a further object of the present invention to provide a relatively economic means for permitting the reduction of amounts of mercury used in amalgamation of 'ALi

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-2aaqueous -lectrochemical anode metals without significant concomitant increase in cell gassing or reduction of cell performance.

In accordance with the present invention there is provided a method for making an electrochemical cell, with reduced gassing, with said cell having a polycrystalline metal anode subject to gassing, said method comprising the steps of: a) reducing the number of grains in said polycrystalline metal to one third or less of the original number of grains; b) forming said polycrystalline metal, with reduced number of grains, into an anode for said cell; .and c) placing said formed polycrystalline metal anode into said cell. Preferably, the polycrystalline metal is heated at an elevated temperature, below the melting point of said metal, for a time sufficient to reduce the number of grains in said polycrystalline S. 20 metal to one third or less, of the original number of grains. More preferably, the polycrystalline metal is a. selected from the group consisting of zinc, cadmium, nickel, magnesium, aluminum, manganese, calcium, copper, iron, lead, tin and mixtures thereof. In a preferred embodiment, the polycrystalline metal is zinc and Swherein said zinc is heated at a temperature of between C to 419.5 C for a minimum period of time ranging between five minutes and two hours. The method may 2b further comprise the step of adding a surface active hetero polar material additive having a polar affinity to said anode to said cell and the polycrystalline metal may be converted to single crystals. The single crystals referred to represent particles wherein the grain number has been reduced to one. Thus single crystals are the extreme case where the number of grains in a particle have been reduced to the greatest extent. The surface active hetero polar material additive may comprise an organic phosphate ester having the formula: [RO(EtO)n] P 0

(OM)

Y

where x y 3 SM H, ammonia, amino, or an alkali or alkaline earth metal i and R phenyl or alkyl or alkylaryl of 6-28 carbon atoms.

The polycrystalline anode metal may be alloyed with one or more members selected from the group consisting of indium, gallium, thallium, cadmium, bismuth, tin and lead, prior to said reduction of the number of grains thereof or the polycrystalline anode metal may be converted to form said discrete single crystal particles, whereby said one or S S S more members form part of said single crystal.

.i In another aspect of the invention there is provided an electrochemical cell comprising an anode, a cathode and an 9 aqueous electrolyte characterized in that said anode is comprised of single crystal anode metal particles and said cell includes a surface active hetero polar material additive having a polar affinity to said anode. The surface active hetero polar material__

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-2c- Sadditive may be selected from the group consisting of ethylene oxide containing polymers, monocarboxylic acid with at least two ethanolamide groupings, tridecyloxypol(ethylenoxy) ethanol, and organic phosphate esters. The surface active hetero polar material additive may be an organic phosphate ester having the formula: [RO(EtO) nx P O

(OM)

where x y 3 M H, ammonia, amino, or an alkali or alkaline earth metal **and R phenyl or alkyl or alkylaryl of 6-28 carbon atoms.

Further the organic phosphate ester may be comprised of a member of the group consisting of the free acid of an anionic organic phosphate ester based on a linear primary alcohol, and being an unneutralized partial ester of phosphoric acid; the free acid of an :20 anionic complex organic phosphate ester having an aromatic hydrophobe, and being an unneutralized partial ester of phosphoric acid; and an anionic mono substituted ortho phosphate ester. In a further embodiment the organic phosphate ester may be comprised j S*of the free acid of an anionic organic phosphate ester based on a linear primary alcohol, and being an unneutralized partial ester of phosphoric acid.

In yet a further aspect of the present invention

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-2dthere is provided electrochemical cell subject to reduced gassing comprising an aqueous alkaline electrolyte, a cathode and an anode comprised of mercury amalgamated single crystal zinc particles and an organic phosphate ester with said mercury comprising up to 4% by weight of said anode and said organic phosphate ester being comprised of the free acid of an anionic organic phosphate ester based on a linear primary alcohol, and being an unneutralized partial ester of phosphoric acid with said organic phosphate ester comprising from 0.01 to 0.3% by weight of said anode. Preferably, the mercury comprises up to 1.5% by weight of said anode, S. said cathode is comprised of manganese dioxide and said aqueous electrolyte is comprised of a potassium hydroxide solution.

These and other objects, features and advantages of the present invention will become more evident from the following discussion as well as the "drawings" in which: Figure 1 is a photomicrograph of cross sectioned U o0 polycrystalline zinc particles; and Figure 2 is a comparative photomicrograph of cross sectioned polycrystalline zinc as treated in accordance with the present invention.

II- L~LIL JP-- L L_ The present invention may comprise a method for making an electrochemical cell, with reduced gassing. The invention may further comprise the cell containing the treated anode material. The method of the present invention includes reducing the number of grains in the polycrystalline anode metal to one third or less of the original number of grains. Thereafter, the reduced grain anode metal is formed into an anode such as by compression of powder particles either on a substrate or within a cavity. Alternatively, the anode metal may be in the form of a sheet with the anode being convolutely wound in a "jelly roll" configuration together with the cell separator and cathode. The sheet metal may also be used, without winding, in a prismatic cell. If desired, the anode metal (particularly zinc) is amalgamated with mercury after the grained reduction and prior to placement of the anode metal in the cell. In all the aforementioned embodiments, with such extent of grained reduction there is a concomitant reductions in the extent of grain boundaries and a reduction of gassing at such sites.

To further reduce the extent of gassing a small amount of a surface active hetero polar substance (surfactant) of a type that will act as a hydrogen evolution inhibitor is added tc the cell. Because of the hetero polar nature of th6 surfactant it is generally at least slightly soluble in the cell electrolyte and has a polar affinity to the surface of the anode metal particles with a coating being formed thereby. Such affinity is particularly marked with respect to zinc particles commonly utilized in anodes of alkaline electrolyte cells. The surfactant may be effectively incorporated in

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3 i the cell in various ways. For example, it may be added to the anode, incorporated in the electrolyte, or in the separator by pre-wetting or impregnating the separator with the additive. The surfactant may even be added to the cathode. In all such instances the surfactant migrates to the surface of the anode metal particles to form the requisite hydrogent gas inhibiting coating.

Adding the surfactant to the anodic material is by direct addition to the powdered metal (amalgamated or unamalgamated) to form a surface coating for the anode.

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654 55 0S 3a vill provide Aost effective heating and as a result, with properly designed calciner, less than ten minutes at temperatures above 370*C is sufficient to effect sufficient grais reduction. Recrystallization and grain coarsening depends upon many factors sach as temperature, time, strain energy within the material, and the purity. As a result, exact heat treatment parameters are determined in accordance with the specific heat treatment equipment being utilized. For clarity, the effective heat and temperature, hereinafter referred to, relate to a direct application of heat to the material. In all events, a reduction of the number of grains in the material to one third or 3.0 less of the original material is the desired result.

The heat treatment of the polycrystalline anode material is effective with both powdered material generally used in the construction of compressed anodes in cells having a bobbin type structure, and such treatment is also effective with respect to the treatment of metal strips or sheets utilized in prismatic or convolutely wound cell structures.

The purity of the initial polycrystalline anode material determines, in part, the length of time required to provide the requisite reduction of grains or conversely the temperature at which the material should be heated for a given period of time; the lower the purity, the higher the temperature or the longer the time period required. The most common anode material for electrochemical cells is zinc with the most common impurity contained therein go**j being lead. Other, less common, anode materials incllude cadmium, nickel, magnesium, aluminum, manganese, calcium, copper, iron, lead, tin and mixtures thereof including mixtures with zinc.

The alkaline electrolyte solution in which the anode material is placed and which generally is a factor in the gas generation (usually the anode reacts with the electrolyte with resultant gas formation) is usually an aqueous solution of a hydroxide of alkali or alkaline earth metals such as NaOH and KOH. Common cathodes for the alkaline cells include manganese dioxide, cadmium oxide and hydroxide, mercuric oxide, lead oxide, nickel oxide and hydroxide, silver oxide and air. The reduced grain number anodes of the present invention however are also of utility in cells having other electrolytes in which gassing of the anode is problematical such as in acid type electrolytes.

i L ii--L lli:~~-Y1_141 -r Common alkaline type cells contain compressed polycrystalline zinc particles having an average particle size of about 100 microns. Each of such particles has about 16 or more grains and in accordance with the present invention the number of grains in each of the particles is reduced by heating the zinc particles at an effective temperature between about to 419.5 0 C (the latter being the melting point of zinc) for a minimum period of time ranging from about two hours at 50 0 C to about five minutes at 419.5°C to reduce the amount of grains to an average of about 3 to grains per particle. Zinc particles having lead impurities require a temperature of about 100 0 C for the minimum two hour period to achieve a similar reduction in number of grains.

Useful surfactants, which may in a preferred embodiment be added to the cell, in accordance with the present invention in order to further reduce the degree of gassing, include ethylene oxide containing polymers 20 such as those having phosphate groups, saturated or 00 a unsaturated monocarboxylic acid with at least two ethanolamide groupings; tridecyloxypoly(ethytlenoxy) ethanol; and most preferably organic phosphate esters.

The preferred organic phosphate esters generally are monoesters or diesters having the following formula: [RO(EtO)n] P 0 i (OM)y where x y 3

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16. The cell of claim 15 wherein said mercury comprisises up to 1.5% by weight of said anode, said cathode is comprised of manganese dioxide and said aqueous electrolyte is comprised of a potassium hydroxide solution.

DATED this 29th day of December, 1989 DURACELL INTERNATIONAL INC.

M H, ammonia, amino, or an alkali or alkaline earth metal R phenyl or alkyl or alkylaryl of 6-28 carbon atoms Specific useful and preferred organic phosphate ester surfactants include materials which can be identified by their commercial designation as GAFAC RA600 (an anionic organic phosphate ester supplied by GAF Corp. as the free acid, based on a linear primary alcohol, and being an unneutralized partial ester of phosphoric acid); GAFAC RA610 (an anionic complex organic phosphate ester supplied by GAS Corp. as the free acid, having an aromatic hydrophole, and being an 0* unneutralized partial ester of phosphoric acid); and

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KLEARFAC AA-040 (an anionic mono substituted ortho phosphate ester supplied by BASF Wyandotte Corp).

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L S a It has been found that the incorporation of a surfactant additive of the type referred to herein in a cell in an amount of from 0.001% to preferably 0.005 to and most preferably 0.01 to 0.3% by weight of the active anode component of the cell, rrecludes or at least significantly inhibits the evolution of hydrogen within the cell, and thereby increase its shelf life and its useful work life.

The additions of the surfactant to cells containing reduced number of anode metal grains or single crystals of such anode metals provides a synergistic further reduction of cell gassing. As hereinbefore defined single crystal refers to particles wherein the grain number has been reduced to one.

Though the use of single crystal anode material and the use of organic phosphate ester surfactants (US Patent o. Nos. 4,487,651 and 4,195,120 owned by the same assignee as 9*99 the present invention) have separately been know to effectively reduce cell gassing or to permit some 20 reduction of mercury content in the anode without detrimental increase in gassing, the effect of the combination has unexpectedly been discovered to be considerably more than additive. Thus, in cells having 9999 9° 9.

amalgamated single crystal zinc anodes, the amount of .9 mercury in the amalgam can be effectively reduced from about 6-7% to abut 4% or stated differently the rate of gassing of polycrystalline zinc amalgam containing mercury can be reduced by about 2-fold with the use of .9 single crystal zinc. Similarly the utilization of an organic phosphate ester surfactant such as GAFACT RA600 with polycrystalline zinc amalgam anodes results in about 3 i.

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IJ C w A cr a 4-fold reduction of gassing with for example 0.1% GAFAC RA600. However, in accordance with the present invention, a combination of the two, i.e. a siigle crystal zinc amalgam, with a surfactant unexpectedly permits the effective reduction of the mercury to about 1.5% with about a 20-fold gassing rate inhibition or about double what might have been expected. As a matter of course, combination of chemical gas reduction expedients does not usually even provide an additive effect no does excessive utilization of additives. The use of the surfactant material with the reduced grain number zinc anode material provides an economical synergistic reduction of cell gassing to above that obtained with single crystal anode material but well below that obtained with the high grain number polycrystalline zinc.

The single crystals of zinc are preferably prepared as described in said US Patent No. 4,487,651, the disclosure of which is incorporated herein by reference thereto. Such procedure involves the formation of a thin *0 skin crucible on each of the zinc particles by oxidation in air at a temperature just below the melting point (419°C) of the zinc, heating of the skin enclosed zinc particles in an inert atmosphere above the melting point of the zinc and slow cooling thereafter with removal of the oxide skins. Zinc particle sizes generally range between 80 and 600 microns for utility in electrochemical cells and such method provides an effective means for 0:66 making single crystal particles of such small dimensions.

S.0. The amount of mercury in the anode amalgam may range from 0 4% depending upon the cell utilization and the degree of gassing to be tolerated.

F -7- 9 i The amalgamated reduced grain number or single crystal metal particles, as herein before defined, with surfactant additives such as GAFAC RA600 are formed into anodes for electrochemical cells particularly alkaline electrochemical cells. Alternatively, the anodes are formed from the reduced grain number or single crystal metal particles and the surfactant migrates thereto from other cell components such a the electrolyte, separator or cathode to which the surfactants have been initially added. Other anode metals capable of being formed into reduced grain number or single crystal powders and which are useful in electrochemical cells include Al, Cd, Ca, Cu, Pb, Mg, Ni, and Sn.

A further additional or alternative expedient for reduction of gassing is the alloying of polycrystalline anode metal particles with indium or other additives prior to anode metal grain reduction or the formation of the 0 r single crystal metal particles, generally in amounts o* ranging between 25-5000 ppm and preferably between 20 100-1000 ppm. The amount of mercury in the anode amalgam may range from 0 4% depending upon the cell utilization and the degree of gassing to be tolerated.

0e 0 *0* 3 0 -7a- <\Th i~ The amalgamated single crystal metal particles with prealloyed inclusions of materials such as indium are then formed into anodes for electrochemical cells particularly alkaline electrochemical cells. Other anode metals capable of being formed into single crystal powders and which are useful in electrochemical cells include Al, Cd, Ca, Cu, Pb, Mg, Ni, and Sn. It is understood that with anodes of these metals the prealloy material is not the same as the anode active material but is less electrochemically active.

In order to more clearly illustrate the effectiveness of the present invention in reducing cell gassing, the following comparative examples are presented. It is understood that such examples are for illustrative purposes only and that details contained therein are not to be construed as limitations on the present invention. Unless otherwise indicated herein and throughout the present specification all parts are parts by weight.

em .e EXIAMPLE 1 Three batches of polycrystalline zinc of average particle size of about 100 microns are heat treated for varying periods of time and temperatures and are then amalgamated with about 4X mercury by weight. A fourth batch of 4% merciry amalgamated polycrystalline zinc is not heat treated and is used as a control. Two grams of each batch are placed in 37% KOH solutions (similar to the electrolyte of alkaline cells) at

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with heating parameters and gassing rates given in Table 1: TABLE 1 Zinc Treatment ml gas (24 hours) al gas (93 hours) Control, not heated 0.62 3.77 114 hours at 400C 0.25 2.07 235 hours at 400*C 0.28 2.78 hours at 419*C 0.28 2.18 It is evident from the above that the heat treatment of the present invention serves to more than halve the gassing rate of amalgamated zinc. It is further evident that continued long term heating does not significantly affect gassing rates and is generally economically undesirable.

-8- EXAMPLE 2 Polycrystalline zinc powder (average particle size of 100 microns) from the New Jersey Zinc Co. (NJZ) is heat treated at 370'C by tumbling for one hour in a rotating calcine furnace. The powder, as received from New Jersey Zinc, has the crystalline structure shown in Figure 1. After the heat treatment the powder has the crystalline structure shown in Figure 2 wherein grain size is markedly increased, the number of grains is reduced and the amount of grain boundaries is concomitantly reduced. The polycrystalline zinc, as received and after heat treatment is amalgamated with 4% mercury and two gram samples of each are tested for gassing as in Example 1. An additional two gram sample of 7% mercury amalgamated zinc from Royce Zinc Co., v:ith similar polycrystalline grain structure and average particle size, *6 is also tested for gassing as an additional control (representing prior art amalgamated zinc) with gassing results given in Table 2: TABLE 2 Zinc Type Gassing (al) after 24 hours at 0 As received from NJZ 4% Hg 0.85 Heated at 370*C for 1 hour 4% Hg 0.4 7% Hg Royce 0.25 ,0 Beat treatment, as described, provides an anode material having markedly superior gassing properties when compared to untreated polycrystalline zinc and slightly worse than prior art amalgamated zinc having considerably more mercury in the amalgam.

EXAMPLE 3 Two grams of each of the amalgamated zinc materials of Example 2 are similarly tested for gassing at 71*C after periods of 7 and 14 days with the results given in Tables 3 and 4: Zinc Type As received from NJZ 4% Hg Heated at 370'C for 1 hour 4% Hg 7% Hg Royce Zinc Type As received from NJZ 4% Hg Heated at 370*C for 1 hour 4% Hg 7% Hg Royce TABLE 3 7 Days (ml gas) 0.98 0.50 0.46 14 days (ml gas) 1.95 1.19 0.95 TABLE 4 Gassing Rate (ul/gm-day) 0-7 Days 7-14 days 0-14 days 70 69 36 49 43 33 35 34 L i- ~2:Ci

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Both the total amount of evolved gas and the gassing rate of heat treated zinc powders, after extended periods of time, are comparable to those of zinc powders amalgamated with significantly more mercury.

It is evident from the photomicrographs of Figure 1 and 2 that the numerous polycrystalline grain boundaries have been reduced in number with a concomitant reduction in the number of polycrystalline grains per particle without general change in the shape of the individual particles.

The number of grains in the heat treated particles is a third or less of that of the original particles.

EXAMPLE 4 Zinc powder amalgams containing 1.5% mercury are made with standard grain polycrystalline zinc alone, standard grain polycrystalline zinc with 0.1% RA600 as an additive element, single crystal zinc, and single crystal zinc with 0.1% RA600 as an additive element. Equal amounts of the amalgam powders are then placed in equal amounts of 37% KOH alkaline solution (typical electrolyte solution of alkaline cells) and tested for gassing at a temperature of 71*C. The 0.1% GAFAC RA600 is added to the alkaline solution and stirring of the zinc in such solution results in the deposition of the surfactant on the zinc. The amount of gassing, measured in microliters/gram per day (uL/g-day) and the rate reduction factors (with the polycrystalline zinc control being 1) are set forth in Table TABLE ANODE MATERIAL GASSING RATE RATE REDUCTION FACTOR Polycrystalline zinc, 1.5% Hg 295 1 Polycrystalline zinc. 1.5% Rg 80 3.7 0.1% RA600 Single crystal zinc, 1.5% Hg 140 2.1 Single crystal zinc, 1.5% Hg 15 19.7 0.1% RA600 A rate reduction factor (if any) would at most have been expected to be about 7.8 (3.7 x 2.1) for a combined utilization of single crystal zinc and RA600 with a gassing rate reduction to about 38 uL/g-day. The combination however synergistically reduces the gassing to about double the expected reduction.

i i EXAMPLE Zinc powder amalgams of polycrystalline and single crystal zinc with and without the 0.1% GAFAC RA600 additive are tested as in Example 3 but with 0.5% mercury amalgams. The amount of gassing, measured in microliters/gram per day (uL/g-day) and the rate reduction factors (with the polycrystalline zinc control being 1) are set forth in Table 6: TABLE 6 ANODE MATERIAL GASSING RATE RATE REDUCTION FACTOR Polycrystalline zinc, 0.5% Hg 720 1 Polycrystalline zinc, 0.5% Hg 130 0.1Z RA600 Single crystal zinc, 0.5% Hg 265 2.7 *ooo Single crystal zinc, 0.5% Hg 26 28 0.1% RA600 A rate reduction factor (if any) would at most have been expected to be about 14.9 (5.5 x 2.7) for a combined utilization of single crystal zinc and RA600 with a gassing rate reduction to about 48 uL/g-day. The

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combination however synergistically reduces the gassing to nearly double

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the expected reduction.

t is evident from the above examples and tables that the single crystal zinc with one or more additives of the present invention is markedly effective in permitting large mercury reductions without increase in cell gassing.

EXAMPLE 6 Polycrystalline zinc is prealloyed with 550 ppm of gallium and 100 ppm of indium. A first sample thereof is then amalgamated with 1.5Z mercury. A second sample is made into individual single crystal alloy particles, as described above, prior to the amalgamation with mercury. Two grams of each of the samples are placed in a 37Z KOH electrolyte solution with gassing at the end of 24 and 48 hours being measured at 900C as being representative of corrosion. As control an amalgam is made with polycr stalline zinc with 7% mercury similar to that commonly used in alkaline type cells. Results of such tests are given in Table 7.

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TABLE 7 SAMPLE VOLUME OF GAS 90 C 24 Hours 48 Hours polycrystalline alloy 0.7 1.9 single crystal alloy 0.3 control Hg) 0.2 EXAMPLE 7 A first portion of polycrystalline zinc powder containing 0.042 lead is amalgamated with 22 Hg and a second portion is converted to individual single crystal particles prior to the amalgamation. The amalgams are then tested for corrosion rate in 10M KOH containing 2Z ZnO. The gassing rates at 71*C are 225 uL/gm per day and 80 mL/gm per day respectively.

It is evident that the corrosion reduction of anode metals such as zinc by the prealloying with corrosion reducing additive materials is greatly enhanced by the formation of single crystals from the anode metal-additive alloy.

It is understood that the above examples are illustrative in nature and that changes in material treatment, material proportions, the specific materials, cell construction and the like are within the scope of the present invention as defined in the following claims.

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Claims

1. A method for making an electrochemical cell, with reduced gassing, with said cell having a polycrystalline metal anode subject to gassing, said method comprising the steps of: a) reducing the number of grains in said polycrystalline metal to one third or less of the original number of grains; b) forming said polycrystalline metal, with reduced number of grains, into an anode for said cell; and c) placing said formed polycrystalline metal anode into said cell.

2. The method of claim 1 wherein said polycrystalline metal is heated at an elevated temperature, below the melting point of said metal, for a time S* sufficient to reduce the number of grains in said polycrystalline metal to one third or less, of the original number of grains. S.

3. The method of claim 2 wherein said polycrystalline metal is selected from the group consisting of zinc, cadmium, nickel, magnesium, aluminum, manganese, calcium, copper, iron, lead, tin and mixtures thereof.

4. The method of claim 3 wherein said polycrystalline metal is zinc and a* wherein said zinc is heated at a temperature of between 50*C to 419.5°C for a minimum period of time ranging between five minutes and two hours.

The method of claim 1 wherein said method further comprises the step of adding a surface active hetero polar material additive having a polar affinity to said anode to said cell.

6. The method of claim 5 wherein said polycrystalline metal is converted to single crystals.

7. The method of claims 5 and 6 wherein said surface active hetero polar material additive comprises an organic phosphate ester having the formula: [RO(EtO)n] P 0 nx (OM) y where x y 3 M H, ammonia, amino, or an alkali or alkaline earth metal and R phenyl or alkyl or alkylaryl of 6-28 carbon atoms. -13- I-A

8, The method of claims 1 and 5 wherein said polycrystalline anode metal is alloyed with one or more members selected from the group consisting of indium, gallium, thallium, cadmium, bismuth, tin and lead, prior to said reduction of the number of grains thereof.

9. The method of claim 8 wherein said polycrystalline anode metal is converted to form said discrete single crystal particles, whereby said one or more members form part of said single crystal.

An electrochemical cell comprising an anode, a cathode and an aqueous electrolyte characterised in that said anode is comprised of single crystal anode metal particles and said cell includes a surface active hetero polar material additive having a polar affinity to said S* anode, wherein the single crystal anode metal particles are a result of reducing the number of grains of polycrystalline particles.

11. The cell of claim 10 wherein said surface active hetero polar material additive is selected from the group consisting of ethylene oxide containing polymers, monocarboxylic acid with at least two ethanolamide groupings, tridecyloxypoly(athylenoxy) ethanol, and organic phosphate esters.

12. The cell of claim 11 wherein said surface active hetero polar material additive is an organic phosphate ester having the formula: LRo(Eto)J x -P 0o where x y= 3 i -24 M H, ammonia, amino, or an alkali or alkaline earth metal and R phenyl or alkyl or alkylaryl of 6-28 carbon atoms.

13. The cell of claim 12 wherein said organic phosphate ester is comprised of a member of the group consisting of the free acid of an anionic organic phosphate ester based on a linear primarj alcohol, and being an unneutralized partial ester of phosphoric acid; the free acid of an anionic complex organic phosphate ester having an aromatic hydrophobe, and being an unneutralized partial ester of phosphoric acid; and an anioric mono substituted ortho phosphate ester. 0

14. The cell of claim 13 wherein said organic phosphate ester is comprised of the free acid of an anionic organic phosphate ester based on a linear primary alcohol, and being an unneutralied partial ester of phosphoiic acid. An electrochemical cell subject to reduced gassing comprising an aqueous alkaline electrolyte, a cathode and an anode comprised of mercury amalgamated single crystal zinc particles and an organic phosphate ester with said mercury comprising up to 4% by weight of said anode and said organic phosphate ester being comprised of the free acid of an anionic organic phosphate ester based on a "f linear primary alcohol, and being an unneutralized partial ester of phosphoric acid with said organic phosphate ester comprising from 0.01 to 0.3% by weight of said anode, wherein said single crystal zinc particles are a result of reducing the number of grain of polycrystalline particles.

15 c i I

16. The cell of claim 15 wherein said mercury comprisises up to 1.5% by weight of said anode, said cathode is comprised of manganese dioxide and said aqueous electrolyte is comprised of a potassium hydroxide solution. DATED this 29th day of December, 1989 DURACELL INTERNATIONAL INC. Attorney: IAN T. ERNST Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS oe 0S Suo S So 3,