US2547909A - Primary cell - Google Patents

Description

April 3, 1951 P. F. GEORGE ET AL PRIMARY CELL Filed May 7,' 194g 2 Sheets-Sheet l f n. 9 v, .l F 0 W 5 W my m m 7. 6 f/o a O OO 0 6x52@ m0 IN VEN TORS. E Geo erc (9e 5. Fry

April 3, 1951 P. F. GEORGE ETAL 2,547,909

" PRIMARY CELL v 51/ 429.' 5 Mg olloyedOJ F29. 5

to 0.7% of Hg, Fe (0.007% JNVENToRs.

Percy E GPO/:9e Ashford 5. Fry Roy C. K/'r'/ BY A fro/wf YS Patented Apr. 3, 1.951

nui'rsn stares PRIMARY CELL Delaware Application May 7, 1949, Serial No.`91,928

The invention relatesto primary cell anodes.

It more particularly concerns an improved primary cell anode employing an aqueous electrolyte and magnesium in the anode material.

g- Inasmuch as magnesium is an abundant and readily available metal high in the electromotive force series of metals numerous attempts have been made heretofore to utilize the metal -as the anode material in primary cells, especially those employing an aqueous electrolyte.- However, the anodes` in such cells have not generally exhibited a satisfactoryY electrochemical elciency. That is to say the actual number of coulombs of electricity produced per gram ofthe anode material consumed falls far short of 7940, the theoretical number` of coulombs per gram of magnesium.

VIt is the principal object of the invention to provide an improved primary cell anode employing magnesium as the anode material with enhanced eciency. Other objects and advantages will appear as the description of the invention proceeds.

The invention is predicated upon the discovery that by alloying a smallv amount of mercury i. e.

between about 0.16 fand 0.7 per cent by weight with the magnesium and limiting the iron content ofthe resulting alloy to less than about 0.007 per` cent, as by using purified magnesium, a

greatly enhanced electrochemical eiciency isV obtained on using the alloy as anode material in a primary cell having an aqueous electrolyte. The invention then consists of the improved pri- 2 Claims. (Cl. 13G- 100) mary cell anode hereinafter fully described and particularly pointed out in the claims.

In carrying out the invention, magnesium 'from atmospheric attack by the usual saline ux.

The melt preferably is stirred after the addition or" the mercury to insureuniformity ofdistribution of the mercury throughout the magnesium.

In general the mercury content may be between 0.16 and 0.7 per cent as aforesaid, however best results appear to be obtained when the mercury content is about 0.5 per cent and the iron content not over about 0.002 per cent. After alloyng, the melt may be cast and worked into -any desired shape of anode by any of the conventional fabrication proceduresv known in the art of work-A ing magnesium alloys, such as extrusion, rolling, and forging and combinations of these operations.

Primary cells of either the wet or dry type may be constructed employing the anode material of the invention in combination with any suitable cathode and in aqueous electrolyte. As electrolytes any of the various aqueous electrolytes that have been suggested heretofore for voltaic systems employing a magnesium or magnesium base alloy anode may be used with the anode of the invention. The preferred electrolyte is that disclosed in our patent application Serial No. 73,063

-led January 27, 1949, when the electrolyte is used, in combination with a manganese dioxide depolarized cathode.

The aqueous electrolyte of the said patent application comprises a bromide of an alkali or alkaline earth metal, the electrolyte advantageously containing corrosion inhibiting amounts of a chromic acid salt of a base consisting of an alkali metal base or an alkaline earth metal base including magnesium and ammonium. Of the Various bromides above indicated which may be used in solution in water as the electrolyte, magnesium bromide either alone or in combination with lithium bromide is to be preferred.

Suitable concentrations are from about 150 to A500 grams per liter, the upper limit of concentration being the solubility of the bromide in water. A generally suitable concentration is about 300 grams `per liter. While various electronic conductors that are not attacked by the electrolyte may be .used for the cathode such as carbon, graphite, platinum, we prefer to use carbon. The invention may be further explained by reference to the accompanying drawing in which:

Fig. l is a graph showing the relationship between the eiiciency ofthe anode material in per cent and the percentage of mercury in the anode, the iron content of the anode being about 0.002 per cent. f

Fig. 2 is an end elevation of a wet test cell embodying the anode of the invention.

3 isa iront elevation of the anode of the cell of Fig. 2.

l is a preferred orm wet cell embodying ie invention and cut away to show structure.

5 is a sectional elevation of a dry cell embodying the anode of the invention.

In vligs. 2 and like numerals designate like parts. l U

Referring more particularly to the drawing there is shown in Figs. 2 and 3 a wet cell designed particularly for test purposes having case I containing an electrolyte 2. Subinerged in the electrolyte 2 is the anode 3 which is held upon the insulating plate 4 by beeswax 5, which also covers the edge S of the anode so that only the face 'I is exposed to the electrolyte. The plate 4 may be formed of glass, synthetic resin or the like. It is convenient to make the anode face circular and 1 inch in diameter. A suitable insulated lead 8 is provided for making electrical connection to the anode. Spaced 0.6 inch away from the face 'I of the anode is the cathode plate 9. For the p-urpose of making eiciency tests, the cathode may have a rectangular shape 3 x 4 inches with the long dimension vertical as shown in Fig. 4. A suitable lead I is provided for making electrical connection with the cathode. For measuring the ampere hours output of the test cell an ammeter I I connected in series with the variable resistance I2 may be used, as shown in Fig. 2.

Fig. 4 represents a preferred form of a wet cell assembled with the improved anode. As shown, the cell consists of a jar I3 of insulating material, such as glass or molded plastic, divided into an anode compartment I4 and a cathode compartment I5 by a partition I6. Partition I6 consists of a board or plate of insulating material such as glass or plastic, which is conveniently molded of phenol-formaldehyde resin. It is provided with a plurality of perforations I'I arranged in a regular pattern to permit the passage of electric current from one compartment to the other. On the cathode side of partition I6 is a porous lter medium IS such as a sheet of lter paper, which serves as a liquid-permeable retainer for the contents of the cathode compartment I5. In compartment vI4 is disposed the anode I9 consisting of a-plate of the magnesiummercury-alloy aforementioned, to Which is secured a terminal rod 20, the plate I9 being immersed in a body of aqueous electrolyte 2 I. Cathode 22 in compartment I5 is a carbon rod having a terminal 23. The carbon rod 22 is embedded in a mass 24 of a depolarizer mix composed of manganese dioxide and nely divided carbon moisened with electrolyte.

In the dry cell shown in Fig. 5 the magnesium-rnercury alloy anode constitutes the container 25. The cathode 26 is a carbon rod having a terminal cap 2l packed in a bobbin 28 of a depolarizer mass of manganese dioxide and carbon moistened with any suitable aqueous electrolyte such as one of those aforementioned. Between depolarizer 28 and the sides of the container is a body of gelled electrolyte 29. An insulating cup 30 of waxed paper, paper board or the like separates the depolarizer bobbin 28 from the bottom ISI of the container. A disc 32 of similar insulating material covers the top of the bobbin. A vent space 33 is provided above disc 32 which is closed by a vented insulating cover 34 of wax or resln.

The performance of the anode material of the invention is well illustrated by a series of tests employing a test cell having the form shown in Fig. 2, with the anode of Fig. 3, a cathode of carbon and having an electrolyte composed of an aqueous solution containing 150 grams of animonium bromide and 5 grams of ammonium chromate per liter. The results of such tests are plotted in Fig. 1.

In each of the tests of the series using the form of cell of Fig. 2 a different anode was used. each being in the form of a circular piece of rolled plate 1 inch in diameter. Each such anode differed one from the other as regards the mercury content which ranged in small increments from a blank with no mercury to 1.5 per cent by weight of mercury while iron content was about 0.002 per cent in each anode.

In obtaining the performance data with the cell of Fig. 2 each anode was weighed before assembling in the cell and the cell was discharged through the variable resistance I2 and ammeer I I as shown in Fig. 2. During the discharge, the variable resistance I2 was constantly adjusted so as to maintain a substantially constant rate of discharge corresponding to a current density of '7 amperes per square foot of electrode (anode) surface exposed to the electrolyte. Each anode was allowed to discharge for minutes. After discharging, each anode was removed from the cell;cleaned and weighed. The difference in the weight of each anode before and after the test compared to the theoretical weight of metal corresponding to the number of coulombs of electricity produced was used in computing the eiciency according to the formula:

c t m n lOOXcoulombs obtairgd from cell per en e me cy 7940Xanode weight loss in grams Elciencies obtained by the foregoing tests were plotted as ordinates in Fig. 1 against the corresponding mercury content of the anode as abscissa. It will be observed that an unexpected increase in anode eiciency is realized when the mercury content of the anode is between about 0.16 and 0.7 per cent and that the maximum efciency is obtained when the mercury content is about 0.5 per cent while the iron content is within the aforesaid range.

Further examples of Wet cells of the form of Fig. 2, are tabulated in Tables I and II using an anode formed of the alloy composed of 0.5 per cent of mercury 0.002 per cent of iron, the balance being magnesium having a purity of 99.98 per cent.

1 With carbon plate cathode.

Referring to Table I, the anode efficiency was determined and computed in the manner already described.

Table II Initial Cell Dcsigna- Electrolyte Composition Concentration Closed tion of Salts in Water Circuit VoltageI l llgp. L. NH4Cl-l-5 g. p. L. (NHm- 0.84

r 4. 2 lcgp. L. NH4Br+29 g. p. L. (NHQz- 0.80

r 4. 3 i 300 g. p. L. SrBrQAHzO-I-Z g. p. L. 0.54

g (NHOzCrOI.

1Using platinized platinum cathode connected through 5 ohm resistor to anode.

As illustrative of dry cells, those tabulated in Table III are examples made up in D size in the form shown in Fig. 5. In each cell the anode (cup 25) was composed of the alloy consisting of about 0.5 per cent of mercury and 0.001 per cent of iron, the balance being magnesium having a purity of 99.98 per cent. The cathode was a carbon rod imbedded in the depolarizer mix of 90 parts of manganese dioxide and 10 parts oi acetylene black.

Table III Initial Cell Dcs- Elcctrolyte Composition Con- Cell Discharge ignation centration of Salts in Water Volt- Tests age B11-301 1 150 g. p. L. NHlBr-I-50 g. p. L. 1. 84 5.9 days.

(NHQZCrOl. 2.-.. 1000 g. p. L. SrBr26H2O-{-0.05 2.03 11.2 days g. p. L. (N Cr 13A-82 3. 1000 g. p. L. SrBr2-0H2O-i-005 2.03 138 hours.

g. p. L. (NHDQCTCH.

1Cell discharged for 4 minutes through a 6% ohm resistor twice each hour for 10 consecutive hours of each day o days a Week until the cell voltage declines to 0.935. Total number of elapsed days from beginning to end of discharge'test is recorded.

2 Cell continuously discharged through a resistor of 83% ohms until cell voltage declined to 1.13 volts. The total number of hours of such discharge is recorded.

We claim: 1. In a primary cell having in combination an REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,771,190 Polcich July 22, 1930 2,445,306 Lawson 1 July 13, 1948 OTHER REFERENCES Robinson, H. A., Trans. Electrochemical Socy., vol. 90 (1946) pages 499, 500.

Claims (1)

1. IN A PRIMARY CELL HAVING IN COMBINATION AN AQUEOUS ELECTROLYTE, AN ANODE, AND A CATHODE, THE IMPROVEMENT WHICH CONSISTS IN FORMING THE ANODE OF MAGNESIUM ALLOYED WITH FROM 0.16 TO 0.7 PER CENT BY WEIGHT OF MERCURY, THE IRON CONTENT OF THE ALLOY NOT EXCEEDING 0.007 PER CENT.

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