US1836847A - Dip for dry cell cores - Google Patents

Description

Dec. 15, 1931. J. M. HENDERSON DIP FOR DRY CELL vCORES Filed Nov. 2, 1928 vPatented Dec. l5, 1931 UNITED STATES PATENT OFFICE JOSEPH M. HENDERSON, OF MADISON, WISCONSIN, ASSIGNOR T0 BURG-ESS BATTERY COMPANY, OF MADISON, WISCONSIN, A CORPORATION OF WISCONSIN DIP FOR DRY CELL CORES lApplication led November 2, 1928. Serial No. 316,827.

This invention relates to an improved covering to envelop the cathode core in the bag type of dry cell.

The ordinary bag type dry cell, as illustrated in the single figure of the drawing, comprises a zinc shell 1, a core 2 of-depolarizing mixture of manganese dioxide or other depolarizer, powdered graphite, sal ammoniac, zinc chloride, and water. A carbon rod 3, having a brass cap 4, is embedded in the depolarizing mixture. The core 2 with its embedded carbon rod 3 may be termed a cathode core, or simply a cathode. The core is set in a gelatinous electrolyte 5 which contacts with the zinc shell 1. The gelatinous electrolyte may be that described in United States Patent No. 1,292,764. It usuallyY consists of sal ammoniac, zinc chloride, a cereal such as starch, and water. A seal 6 of sealing wax or pitch, resting on washer 7 closes the top'of the cell. An expansion space 8 may be left between the washer 7 and the top of the electrolyte 5.

In the production of core 2, a quantity of moist loose depolarizing mixture is compressed about the carbon rod in a mold. Usually there is no further cohesive force than that caused by the moisture and compression. As a result, during factory manipulation particles of the mixture become dislodged at the surface of the core. These particles may bridgethe intervening annular space occupied by electrolyte 5 and make contact with zinc shell 1, causing short circuit and local action within the cell. Prior to the gelatinization 'of the electrolyte, the core 2 absorbs moisture therefrom and gradually becomes soggy to the point where if the gelatinization is greatly delayed, it disintegrates with the result that the cell is rendered useless.

To avoid such disintegration and short circuits, it is common practice to envelop the core 2 in a closely adherent bibulous wrapper, usually of cheesecloth. The cost of such a wrapper, together withtthe labor to apply it represents a considerable item in the cost of the dry cell. Cells have been made without such a wrapper but the omission of the wrapper calls for a careful technique and even then the percentage of rejects is high and the quality of the cells is questionable.

It is an object of this invention to provide a retaining covering or dip for dry cell cathode cores which is 4less expensive and gives better results than the present cheesecloth wrapper and is an improvement over the dips which have been used in the past.

It is a further object of the invention to provide an improved covering for cathode cores which imparts advantages to the dry cell such as greater capacity, less internal resistance, longer life, less accumulation of gas and bursting of seals.

The gauze wrapper is, in itself, expensive. It must be cut into rectangular sections of a size suiiicient to encircle a core twice. It must be treated with an adhesive and must be carefully wrapped about the core to secure it in the proper position. Although the gauze may be replaced by cheap tissue paper the results are not entirely satisfactory.

Many attempts have been made to provide a dip or cathode covering formed directly thereon by dipping the cathode in a liquid suspension but none has been entirely satisfactory. Such a dip is described in United States Patents Nos. 1,316,597 and 1,370,052. Such dips have been made of a non-conductive material, such as plaster of Paris, with or without an adhesive such as glue, starch and the like. To be of any service the coating of the core must be so thick as to result in excessive electrical resistance. If the coating is thin it does not provide the desired protection for the core especially after coming in contact with the liquid electrolyte prior to gelatinization.

My improved retaining covering consists of a liquid medium or dip into which the core is dipped and which, upon removal of the core,

adheres thereto to form a conductive layer 9 of uniform thickness thereon. The covering,

after being allowed to dry, becomes suiciently tough, cohesive, and water resistant to prevent sogginess and the dislodgment of particles of depolarizing mixture from the body of the core and allows the necessary handling and stacking which the cores receive in the regular course of factory operations. It re- 100 tains its conductivity so that the internal resistance of the cells is not increased appreciably.

My liquid covering medium comprises a liquid suspension of a web-formin material such as wood pulp fibres and a fine y divided conductive flake material such as powdered graphite in a liquid suspension of a suitable colloid such as starch. The web-forming material may be any fibrous material such as cotton linters, asbestos, hair and others but I prefer a long fibered wood pulp such as is obtained from the ordinary sulphite pulp mill. I have discovered that if a flaky filler is used in the coating it becomes water resistant whereas an ordinary powdered filler such as talc, clay or plaster of Paris in the coating makes for the rapid disintegration of the coating and consequently of the core also. The flake material may be powdered mica, aluminum bronze or other similar material but, because of its conductive properties and resistance to attack by the electrolyte of the cell, I prefer to usel powdered graphite. Even finely divided artificial graphite is flaky enough for the purpose. Any suitable colloid may be used which will prevent settling of the ingredients of the liquid suspension and act as a binder and will not have a deleterious effect upon the action of the cell. I prefer to use an ordinary cereal such as starch because it is inexpensive and readily available. The starch also functions to increase the Viscosity of the covering medium and assist in forming a deposit of uniform thickness upon the core.

While I comprehend a considerable variation in the proportions of the ingredients of my liquid coating medium, I have found the following proportions, by weight, to be particularly suitable; 1500 parts of water, 20 parts of long fibered wood pulp, parts of starch and 300 parts of powdered graphite. A suspension of such proportions results in a tough, cohesive coating which permits im- :q mersion of the core in water for at least ten minutes and usually several hours without disintegration. Since gelatinization of the electrolyte requires several minutes, my covering delays disintegration of the core until gelatinization has taken place, after which the gelatinous electrolyte supports the core. The ordinary wrapped or dipped core starts disintegrating within several minutes and often within one minute. In varying the proportions of the ingredients of my covering, I may use from 1000 to 2500 parts of water; 10 to 30 parts of wood pulp, 100 to 400 parts of powdered graphite, and 25 to 200 parts of starch.

In the preparation of my preferred coating suspension, I introduce 20 parts of long fibered wood pulp into 450 parts of water and agit-ate the mixture by stirring to completely separate the pulp fibers and distribute them uniformly throughout the volume of water. Fifty parts of starch are then added and the mixture boiled and stirred until the starch is completely gelatinized. At this point, 1050 additional parts of water and 300 parts of powdered graphite are added and the entire mass vigorously stirred until a smooth consistency is attained and all lumps have disappeared. The suspension is allowed to cool to room temperature and is now ready for use. The above is the preferred method of compounding but this procedure may be varied greatly.

The coating suspension is inexpensive and cheaply prepared. The operation of coating the cores is likewise simple and inexpensive. A plurality of cores may be gripped about the protruding carbon rods by means of a spring clip device. The cores are then immersed in the suspension and immediately withdrawn and suspended in air to dry. More uniform thickness of covering is secured by up-ending the moist cores and supporting them in this position to dry. Drying may be accelerated by circulating a current of warm air about the cores. The thickness of coating 9 is of the order of that of a web of ordinary paper. In fact the formation of the coating is quite comparable to the formation of a web of paper since a portion of the moisture undoubtedly soaks into the core immediately upon immersiom.

leavingl a web of pulp and other material upon t e surface of the core. After the coating is dried the core may be dipped into a wax dip to insulate the bottom of the core and form a spacing collar 10 thereon. This wax collar l10 prevents contact between the zinc can and the core. Instead of forming the insulating bottom over the core, an insulating washer may be used in the bottom of the can.

My improved covering presents many advantages over the bibulous gauze wrapping and dips used inthe past. It is entirely pervious to the electrolytic action between the electrodes of the cell and offers little resistance to the flow of current. Under specific test, cells using my improved coating medium show less internal resistance than do cells containing gauze wrapped cores. My covering provides increased protection against breaking off of loose particles of mixture both before and after the cores are in the cells.' Because of the presence of the scale-like particles the electrolyte does not soak through my covering rapidly and the core does not become soggy and disintegrate. This gradual action results in increased capacity in the later stages of the cells life. Gases do not accumulate and generate pressure sufficient to dislodge the seal of the cell. |The probable explanation for these advantages is that the graphite fiakes overlie one another like shingles on a roof and retard the progress of moisture into the core, the

other forms of dry cells, as for instance, those used in the plate type of battery. The method of application may also be varied. It may be applied to the different types of cathodes by Y painting, spraying or by any other suitable' metho Iclaim:

1. A composition for coating dry cell cathodes comprising a liquid suspension of parts of long fibered wood pulp and 300 parts finely powdered graphitein 1500 parts of water containing 50 parts of gelatinized starch. i

2. A composition for coating dry cell i cathodes comprisinga liquid suspension of.

10 to 30 parts of long fibered wood pulpand 100 to 400 parts finely powdered graphite in 1000 to 2500 partsof water containing 25 to 200 parts of gelatinized starch.

3. A, composition for coating dry cell cathodes comprising wood pulp and pow- 'dered graphite in a liquid suspension of gelatinized starch and water.

4. A composition for coating dry cell cathodes comprising wood pulp and' powdered graphite in a liquid suspension of a suitable colloid in water.

f 5. A composition for coating dry cell 4U cathodescomprising fibrous material and powdered graphite in a l'quid suspension of gelatinized starch and water.

6. A composition for coating dry cell cathodes comprising wood pulp and a finely divided conductive scale-like solid in a liquid suspension of a suitable colloid and water.

7. A composition for coating dryk cell cathodes comprising fibrous material and a finely divided scale-like solid in a liquid sus- 'pension of a suitable colloid and water.

11. A dry cell cathode having a coating comprising ami'xture of wood pul powdered graphite, and gelatinized starch.

12. A dry cell cathode having a coating comprising a mixture of a web forming material, a conductive scale-like solid, and a colloid. Y

13. A dry cell having Aa conductive partition between the cathode core and the gelatinous electrolyte comprising a fibrous material, graphite and a binder.

In testimony whereof I affix my signature.

JOSEPH M. HENDERSON.

8. A composition for coating. dry cell cathodes comprising a web-forming material and a finely divided scale-like solid in a liquid suspension of a suitable colloid and water.

9. A dry cell cathode having a coating comprising long fibered wood pulp, finely powdered graphite and gelatinized starch in the ratio of 10 to 30 parts of said pulp to 100 to 400 parts of said graphite to 25 to 200 parts of said gelatinized starch.

10. dry cell cathode laving a coating comprlsmg wood pulp, finely powdered i graphite, and gelatinized starch in the ratio of 20 parts of said pulp to 300 parts of said 65 graphite to 50 parts of said starch.

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