Separating material for dry cells.

The present invention relates to the manufacture of dry cells electro-chemical and, more particularly, to the use of polyacrylamide as a material separator for dry cell batteries.

The dry cells are composed essentially of an anode-consumable metal such as zinc, a set cathode depolarizer such as manganese dioxide, and an electrolyte such as an aqueous solution containing a LEEs acid metal containing halogen, especially, but not exclusively, a zinc salt such as zinc chloride,

The dry cell primary L-remove the creases from conventionally used as source of power in flashlights and other portable electric apparatuses, comprises a zinc anode, cathode depolarizer comprising a mixture of manganese dioxide and a conductive material such as carbon black or graphite, and an electrolyte consisting of an aqueous solution of zinc chloride and ammonium chloride. Various corrosion inhibitors such as mercuric chloride, chromate, andc... may also be employed in the electrolyte in a relatively small amount.

Another type of dry cell primary which has retained considerable attention during recent years is the dry cell magnesium. The system dry cell is very close to the conventional Leclanché dry cell. In fact, the dry cell magnesium comprises a magnesium anode, cathode depolarizer a mixture containing manganese dioxide and a conductive material, and an electrolyte.

The electrolyte consists essentially of an aqueous solution containing a magnesium salt such as magnesium chloride, magnesium perchlorate or magnesium bromide.

It was proposed in the foregoing technique to produce primary dry cells by employing a zinc anode and an electrolyte of zinc chloride in solution. Such a system of dry cell differs from the conventional crushed dry Leclanché primarily by the absence of ammonium chloride of the electrolyte. Has been found that this system of dry cell, that commonly referred to as "system all zinc chloride", has a service capability higher than that of the conventional dry cell Leclanché.

The term "dry cell" involves unterstanding most of the electrolyte of the cell is embedded in a layer of material interposed antrum the anode and the cathode of the cell. This layer is generally referred to as the separator and is a member or a physical structure retaining the electrolyte solution, which provides the means for maintaining the anode in operative connection with the cathode and still maintain a physical separation between the anode and the cathode.

It is well known in the technique of making dry cell battery separators with different materials like gelatin slurry obtained with starch, flour or methylcellulose, which each may be used with or without paper or other backing material or filling.

Although these materials have been used extensively, they are not without disadvantages and has long sought suhstitution materials. The degradation of paper coatings in the acidic electrolyte systems has been long a problem.

Examples of materials which can serve as separator, has been proposed to link branched vinyl polymers, comprising polyacrylamide. United States Patent no. 3 * 018.316 of Higgin and Al reveals that the polyacrylamide hydrophilic gels to partially branched linker are of good separators in dry cell batteries Leclanché type.

The binding agent of the present invention branched, proposed to obtain the polyacrylamide gel partially branched linker is formaldehyde (formalin).

The formaldehyde, as well as many other branched binding agents, are effective for binding branched polyacrylamide to form a stable gel. However difficulties have occurred to maintain accurate control of the time of action of the polyacrylamide branch linkage since the most effective binding agents branched operate too quickly to provide the necessary refueling techniques for mass production factory. Moreover, the polyacrylamide gels obtained by employing several of these binding agents branched and particularly formaldehyde have low-temperature stability.

Especially with respect to the present invention it has previously been suggested to employ ion trivalent chromium as a binding agent for the polyacrylamide branched. It has been discovered that the trivalent chromium is a branched linker effective, particularly when using EOM chromic chloride salt. This binder branched is both effective and rapid, properties that would normally be desirable for binding of a branched polymer.

However it has been found that the agent does not allow the degree ' control of the branched linker which is necessary for the production of cells on a large scale. To enhance the usefulness of the polyacrylamide as a separator for batteries, it is necessary that this branched linker does not go to completion and that the time of operation with the polymer before gelation sufficient to allow compose large batches of material storing to and used in a state fairly fluid. If it is desired to further a branched linker fast polyacrylamide, a means must be provided for this purpose.

Patent Application CanadaINorwayfUSA - ^ Jnis no. 226, 03 $, filed on

14 February 1972, describes some of the difficulties that result from the use of the polyacrylamide in dry cell batteries, and reports problems are encountered in the control of the viscosity of the polyacrylamide gel during the manufacture of the battery. It has been suggested that the viscosity control can be maintained with an acrylamide monomer from and controls both the polymerization and the in situ connection, technique that does hardly suitable to the production of modern batteries, fully mechanized high efficiency.

Whereby, an object of the present invention is

to provide a method of making a cell separator polyacrylamide materials for use in the production of bulk dry cells.

Another object of the invention is to provide a method for manufacturing cell separators polyacrylamide which are particularly useful for use in combination with electrolytes of "any zinc chloride" - and have good high temperature stability.

Another object of the invention is to provide a method of producing a fuel cell separator polyacrylamide tellessorte that the degree and the bonding time can be predetermined and controlled accurately and that the degradation of the coating of paper is minimal réàui-to-_ Te.

Another object of the invention is to provide a novel method of polyacrylamine branch linkage.

The objects and advantages above exposed, as well as other, are achieved in the present invention via provide a handshake of branched polyacrylamide by adding to an aqueous solution of a chromium-containing compound polyacrylamine wherein a higher proportion of chromium has a valence other than + 3 and a compound that will react with said compound oontenant chromium to produce chromium ions valent + 3. Examples of such compounds are potassium dichromate and potassium thiocyanate.

The theory of the invention is not included entirely for the time being, and the precipitating non-hearing not being limited by a theory of the invention, it appears that, although the chromium ion can have a valence de + 3 or + 6, only ions having the valence + 3 are effective as binding branched for the polyacrylamide. Therefore it is possible to have chromium ions in a PAM without causing the link provided that ions either to a valence + 6. The addition of a compound which will reduce the chromium ion + 6 + 3 to a valenoe will produce the link polyacrylamide. The branched linker proceeds only to the extent where the chromium ions valent + 3 are obtained, thereby enabling an effective contrêle of the degree and speed bond forming branched by monitoring the amount and speed of producing ions ohrome + 3 valence.

The chromium ion may also have a valence de + 2 but is unstable and under oette form is rapidly oxidized to + 3 in the presence of 1' air or in an acidic solution. For oette because the chromium ion + 2 is not recommended for the aims of the present invention.

A succession réaotionnelle as described above will be ready easily to manufacturing techniques for mass production, since one of the ingredients, namely the chromium-containing compound to a valence + 6, may be added to a solution of polyacrylamide long before its use. The other ingredient, namely the compound that will react to reduce the chromium ions to a valenoe de + 3 + 6" may be selected for the reaction rate thereof to allow the desired degree of control over the production of ion to a ohromevalenoe de + 3. In addition, in choissiesant the best time for addition to this simple component, it is ensured that the connection raàifiée begins while most favorable.

It will appear clear to the ordinarily skilled artisan that the separator of the present invention,, like most the DS cell separator materials, operates with a purely physical and does not participate in the electrochemical reaction in the cell. For this reason, the separator according to the invention can be used with a wide variety of anodes, cathodes and combinations of electrolyte, the only criterion for the manual being compatibility of the separator with the material of construction of the stack * and reaction products of the stack. The need compatibility will exclude the use of the separator of the present invention with strongly alkaline electrolytes, since the polyacrylamide gel will degrade quickly at a pH high alkalinity, e.g. above pH 11.

The good anodes comprise alkaline earth metals but are not so limited. The anodes particularly appreciated are formed zinc, magnesium or aluminum.

In general, the materials particularly evident for the cathodes are metal oxides, the manganese dioxide being especially preferred.

The electrolytes suitable for use with the distractor of the present invention are solutions compatible aqueous alkali metal, alkaline earth metal, and ammonium perchlorate balogénures.

Aqueous solutions of zinc chloride, ammonium chloride, magnesium die chloride, magnesium bromide, lithium bromide, calcium chloride, potassium bromide, sodium bromide, potassium iodide, calcium bromide, magnesium perchlorate, lithium perchlorate, potassium perchlorate, ammonium perchlorate, aluminum chloride, nickel chloride, nickel bromide, cobalt chloride, cobalt bromide andc... all suitable for use.

As explained above, the separators of the invention are formed by branched linker polyacrylamide. The molecular weight polyacrylamide useful in the invention is not narrowly limited since different applications will require gels separators with different physical properties and these can be controlled not only in choieiàsanttun polymer of molecular weight higher or lower, but also by making the branched linker to a greater or lesser degree or employing a polymer solution more concentrated or diluted. It will be easy for those skilled in making changes that. could be. a needed to be prepared with a molecular weight higher or lower.

In general the molecular weight polyacrylamide useful in the present invention may be of lbaxlre less 100,000 to greater than 10 or 20 million, but preferably about 15.000.000 to 200, 00.

However most of the separators have been made preferably with a nonionic homopolymer of acrylamide having a molecular weight of approximately 5 to 6 million. This product is marketed under the trade name of P "Cyanamer" PAM 250 of the Cyanamid Company to Américan, of Wayne, U.S." plain.

The separator material of the invention is fabricated by forming a mixture of an aqueous electrolyte salts, a polyacrylamide, a chromium compound comprising chromium at a valentfe other than + 3, a reducing agent for the chromium and the special additives that could

be desired or necessary for a particular application. These special additives may be corrosion inhibitors, fillers such as mineral silicates, tissues, or paper fibers, c...

The amount of polyacrylamide required will generally be between 1 and 20 percent by weight based on the total weight of the mixture excluding fillers.

The K ' any chromium-containing compound to a valence de + 6 it can be used to form the separator of the present invention with compatibility with the other components of the stack and reaction products of the stack which will be required to use. The chromium compounds preferred are those containing the ^ ^ O-Cr ion ", e.g. alkali metal, metal hiohromatesalealind earth and ammonium. The sodium dichromate, potassium dichromate, and so forth are typical examples.

The reducing agent for converting the Cr ion⁺ ^ cr⁺ ^ may be a compound that is compatible containing ' anions which are more electropositive than the ^ ^ * O-Cr ion. Examples of such compounds include sulfite, bisulfite and salts thiocyai " Te of alkali metals, metals aloalino earth and ammonia.

Gum it has been indicated above, the filler material such that the mineral silicates, the fibers of fabric or paper, may be added to the mixture forming separator.

Especially good results were obtained with mineral silicates such as the pillowcase, fibrous talc and asbestos. Such a material increases the strength of the separator and further enhances the physical separation between anode and depolarizing the cell's.

In some cases, as for a miniature battery or for those which employs only a thin layer of polyacrylamide gel, the filler material can be omitted. In other cases, as for the stacks engages the high usage or those which employ a low concentration polyacrylamide, it may be desirable to employ a substituent of the polyacrylamide gel " being appropriate substitute materials are fine paper as O (- cellulose or other materials commonly used for the separators for stack.

Those skilled in the manufacture of batteries will be aware of various techniques for separators quality suitable for use determined according Oe is exposed above.

The following examples illustrate the invention and are not limiting.

EXAMPLE 1

Prepared a cell string size test "D." using separators according to the present invention. These stacks are made with 10 boxes zinc for cell anode and cathode 52 grams of a mixture consisting of electrolytic manganese dioxide sprayed, acetylene black powder and an aqueous solution of zinc chloride of 32 percent by weight in a weight ratio of approximately 6 / ΐ / 3. The construction method used is the method designated

" spin-Paste voor is rotated individually the boxes of zinc and is injected four milliliters of a mixture forming separator in each box by means of a syringe. A rotation continued for a few seconds allows the mixture forming separator coating the bottom and sides of the box. The coated cans are then placed in an oven at 70 °c during 10 minutes for drying the coating, are introduced shall keep paper " ^ - cellulosic, cathode mix is fed into the boxes and a strip coated carbon cathode collector is introduced in the center of the mixture. Added two milliliters of an aqueous solution of zinc chloride to 32 weight percent to each cell, and the cell is sealed.

The mixture forming separator is made with 100 milliliters of an aqueous solution of zinc chloride to 3 percent by weight, to which is added 0.40 grams of potassium dichromate, 0.40 grams of potassium thiocyanate, resin polyacrylamide and a small amount of corrosion inhibitors commonly employed. In addition, some mixtures contain talc as a filler. The PAM resin, employed in each stack test is F "Cyanamer" PAM 250 that has a molecular weight in the range of 5 to 6 million. Table I shows the composition of each divider tried.

I-TATA.BISA.U

4®1 Each consisting of 100 ml of a mixture of an aqueous solution of 3 $ZnClj, 0.40 g of 2^2 Κ Ο 7, the O, 40 grams KSCF, and Î designation

WITH

B

C

D

E

P

G

H

I

J

The polyacrylamide

3

3

3

3

5

5

5

7

7

7

Talcum

0

20

23

28

0

23

17

0

23

17

The discharge data for fresh batteries employing the various mixtures separators Table I, in continuous discharge, are shown in Table II.

We can see from the table above that good performance is achieved with stacks made with each of the different mixtures forming separator. with or without the addition of talc. Even the stack the j, de relatively low voltage waveforms, gave good performance for a long period of time.

EXAMPLE 2

An array of cells is prepared in the same manner as in, the example 1, except that employed 57? 4 grams of cathode mixture and non-coated paper. the composition of each of the dividers is indicated at Table III.

TABLE TTIS

Each consists of 4®1 100 ml of a mixture of an aqueous solution of ZnCl 3 $,,, the O ^ ^ KjCr 0.40 grams, 0.40 grams KSCL^T , and:

Designating the polyacrylamide talcum

3, 28 1.4 23 K.

7, 17 M.

THE M 5' 17

0, 5 20

The discharge data cells employing the different mixtures of the separators Table III after one week of storage at 25 °c are given in table 17.

TABLE 17

Continuous discharge 2.25 ohm after one week

Designating a circuit court_has s voltage waveforms

the flash circuit is open cells

We can see from the table ITs hereinafter dessas■that good performance was obtained with pilee according to the present invention, m8me in the absence of paper or continuous separator substituent other than that which is done with the mixture separator of the invention.

3 SXEMPLS

Is manufactured according to the present invention a ' number of dry cells "any zinc chloride" by the process called "pasted". In this fabrication method commonly employed, mixture forming a separator is provided in the FO ^ d of a box and a coil zinc cathode depolarizer prefabricated carbon strip having a manifold in its center is inserted into the box, the mixture forming pouesant separator on the sides of the box for filling the void between the box and the coil.

the stacks test were made each with 9 gauge zinc cans that were provided cell anode. Each box has been added 6 milliliters of a mixture forming separator obtained by mixing 100 milliliters of a solution of zinc chloride to 25 weight percent, 0.40 g of potassium dichromate, 0.40 g ' of potassium thiocyanate, 21 g of talc, resin polyacrylamide and a small amount of corrosion inhibitor. The amount of polyacrylamide used was 4 for oentoent.en weight based on the total weight of the other components, a homopolyaère polyacrylamide having a molecular weight of 5 to 6 million.

A mixture cathode depolarizer was made 6000 grams

natural manganese dioxide, acetylene black and 1500 grams 4000 milliliters of a solution of zinc chloride to 32 weight percent.

Forty-six grams of EO mixture have been cast around a carbon strip to form the coil and have been introduced into the box of zino containing the mixture forming separator, which has been pushed back into the void between the coil and the box, the stack was then closed in a conventional manner and discharged continuously to 2.25 ohm. The open circuit voltage was 1.58 volts; the closed circuit voltage was 1.38 volts. It was a 25 minutes to the stack to 1.1 volts, 108 minutes to reach 1 volts, 175 minutes to reach 0.9 volts and 280 minutes to reach Ο, 65 volts.

4 SINGLE

A number of stacks Leclancbé were prepared according to the method "pasted" described in the example 3 * the mixture cathode depolarizer was in 46 grams of a mixture of manganese dioxide natural to 58.64 weight percent, 15 weight percent ammonium chloride, 5) 41 weight percent zinc chloride, 8.39 percent by weight of acetylene black and water for the rest. The mixture forming separator differed from that of the example 3 only in that 24 percent by weight of ammonium chloride and 6.5 percent by weight of zinc chloride were substituted 25 weight percent zinc chloride

in the example 3.

After one month of shopping to 25 °c, the stacks test scientifically an open circuit voltage of 1.60 3.4 volts and current flash an amps.

In continuous discharge of 2.25 ohm, a closed circuit voltage of 1.23 volts was obtained. In 50 minutes at the voltage was 1 volts; in 10 $0.9 min volts; and 200 min Ο, 65 volts.

After shopping for a month to 71 °c, 1" same discharge yielded 1.57 volts open circuit voltage rating, 1.22 volts voltage rating of closed circuit and 3) an amps of current pop 3. Had to 26 minutes to the stack to 1 volts, 60 minutes to reach 0.9 volts and 162 minutes to reach 0.65 volts. The stacks LeclanbSé pulp separator having a conventional type and used as control have not survived a magazine of one month to 71 °c.

EXAMPLE 5

Test cells were prepared by employing boxes magnesium anode of 0.0762 mm thickness, measuring approximately 24.5 mm diameter and 78.40 mm in length. The separator was an paper coating and a substrate coated with a synthetic fiber "onth forming separator by adding to 100 ml of an aqueous solution of magnesium perchlorate, 4 percent by weight of" Cyanamer " w 250 polycarylamide, 0.4 g of potassium thiocyanate, 0.4 g of potassium dichromate. The mixture contained more than 28 g of talc for 100 g of solution of magnesium perchlorate.

The mixture cathode depolarizer was in an aqueous solution of magnesium perchlorate, acetylene black, manganese dioxide and corrosion inhibitors which are normally used.

■this stack had a duration of 63 hours, being discharged alternatively to 3.55 ohm during 2 minutes and 72.2 ohm during 18 min, voltage cutoff 1.25 volts.