US2594713A - Electric accumulator - Google Patents

Description

April 29, 1952 H. G. ANDRE ELECTRIC ACCUMULATOR Filed Nov. 27, 1950 w n i w lk m yf lo o r\ Q l N 0J l CL g (3 O a i II 2 lNVENTOR z: HEN G. ANDRE lg 73m AGE NT Patented Apr. 29, 1952 signorto Yardney'i. International Gorp.,v Newl York, N. Y., av corporation of. New` York` ApplicationNovembe1'27, 1950, Serial No'.

res-nso'.

InFranceNbvemlier 29,1 1949i (o1. 13a-e.)

1V inventionrelates to a. batterykv of" theltype disclosed i'nmy' cci-pending U. S. Application. Ser; No'i $381,702; filed April-1 1947-. Inisuchab'attery, or' reversible;electro-chemical energy generator,- or accumulator; the ionicexclianges between the'.

electro-chemically activejsubstances are eiected. through a semi-permeable material'` which serves as a separator member'- andT is impregnated. with electrolyte:

The invention its* more; particularly-Y directed.' to such accumul'atorsY wherein'` the electro-cliemi-l callyf activematerials of opposite-polarity: are; ap-A plied under pressure against4 tl-'ie oppositev sides.

of sucr'r a semi-permea'lfiley separator or diaphragm member;

The procedureV of applying' electro-chemicallyactive' materia-ls` under pressure aga-inst'- a diaphragm has constituted a decisiveadvanceintle art of reversible electro-chemical energyegenerators; It has madeitpossille' to limit theamount ofelectricity'present' in an accumulator, and-to f'ul'll' its4 operative function; in retention within-f a solidiv material v rather than: in tle` liquid state; which; aside from obvious facilitation of handlingl and' manipulation', has completely altered? the very character of" tlieelectro-cllemicalreactions involved;

However; the, constructionl ofy such accumula.- tors liras until new' raised; certain d'ii'culti'es. Thus, takingy the instance! ofa-n accumulator Whereintli'e electro-chemically active substances are silver;4 anclzincv and the semi-permeakle material' is the` regenerated cellulose sheet'V material known as' cellophane, whereas suoli an accumula .tor i'sea'sy enough-.to makein the'l'aboratory'under theiguidance oa skilled expert andwhen resort-- ingt'ofall thel usual precautions taken in the cone struction of a prototypemodel, tle* resultsare foundM to loe-much less uniform where the pro-4 duction is entrusted to workers, however'skill'e'd',

who cannot be expected t'o'- display the same amount ci care as tl'ieengineer or scientist.. if onlyffor..y considerations offoutput.

It. has been sought forsome timetofascert'ain the; causesfo such lack of uniformityiandtexf plain why, While some'V off the accumulators pro` duced do possess theY characteristics expectedi off them, ai number of specimens" were ordinarily producedA in which either the capacity wastoolowv or the useful life tooV short; even though no diierences in structure could be detected' as compared to the'satsfactoryunits.

Whileit had beenV seen that the successi-utoperation of theaccumulator depended ontl'i'e pres"- sure' prevailing'in it betweenV theactve materials 2 andy the diaphragms.. it wasbelieved; that this pressure; could: be allowed to.` vary over quite a.

wide range: without,4 producingf any critical modify lcations in. the.A characteristics of, the; unitiv As.' the: said. pressure results. from; al swelling ofv the semi-permeable. materialowing; toits; impregna.

tion.y by. electrolyte... itl wasV endeavored to;.optain.. a: satisfactory operative pressure byf suitably se.-v

lectng,. an. approximate:ina-nner,Y thejthickness( orf depth of the semi-permeable member. in. its. dry' state relativelyj to. thet clearance reserved: for.' it in the tank by the active materalspsuchl. that.. after swelling, the resulting. pressure.:` would; approximate thatfwhich was; bvelijevedvto prevailin apreviously: constructed accumulator whichrhaddisplayedlgoudresults.

Such. ani empirical procedure, inV additicnl to'. the irregular: results '.to whicnit isf conductive.; as"- mentionedhereabove;.provides no means of trans,=

ferri'ng. pro duction` from' onei type: of; accumulator,`

tof4 another type; dii'eringf from the; rst. in; ejlec trical powerv capacitm. orxby itsaloility for rapid',-

discharge, etc. It; is anoljectofrthis;invention tomelet. thisvinadequacyoithe prior'art. It isaanlobjgec't toprovide'. anaccumulatoriof the type;specified.wherein` tliey electro-chemically active substances are aplpliedl under: pressure afgainstgoppositesides or a semiepermealole"v member.;`v may be.l expected.. with.v pos-itix/'eAv certainty. to.-- yieldcptimum; results,-

regardless.l of: its: capacity.. Another; object isto.A4

providaia, meansof; selectingfv auw-ill... from; among. the various. known lorrnsv ofelectroneconstruee;

tion.. that? particularformY which; will lend; itself.

to easy' construction while; leading toithe.: .'iesiredl result,.witlioutanydangei' ofsuch selection-.being adversely` rene'cte'd in. characteristics; of; the? apparatus, contrarlly to; what almost inevitably' occurred-heretoforel.`

Systematic testsliave been conducted-. to` as@ certain' tlieA` conditions to be fulfilled infordeiv t@ olitan' withcertainty successiur'operation`v an l accumulator" oiY t'liej specie'd type. Flor1 this? pur={A pose., it has beensou'glit to definethe-structural characteristics to` be imparted to tlie` electrodes and', more specifically, ti'ie relativetliicltness or. depth dimensions, to. 'bel imparted to. tle acltye 'substancesJ and; diaphragms'in or'c l`er` to-seciirep. within. the.iin-ishod` accumulator-,- apredeterniined J value-of-thepressure underrwhich.tnegactivesuhstances are applied1 against: theqopposite sides; ot.

saiddiaphragms; Y

Irrthe.accompanyingtdifawing: Y Eig; 11 illustrateaatestingf device-.whiclnisgusefulf 3 in the construction of a battery according to the invention;

Fig. 2 is a pressure diagram obtained with the device of Fig. l;

Figs. 3 and 4 are further diagrams illustrating important characteristics of a battery according to the invention; and

Fig. 5 is a fragmentary section through a battery representing an embodiment of the invention, enough being shown of the battery to illustrate the relative arrangement of its component parts.

An accumulator of the type specified comprises a multiplicity of layers or laminae of positive substance alternating with a multiplicity of layers or laminae of negative substances, each pair of adjacent layers or laminae of opposite polarity being separated by a diaphragm and the entire laminated assembly being disposed in a container.

Let l be the distance between the parallel sides of the container extending in a direction parallel with the layers of active substances and the diaphragms, and e the combined thickness of the layers of active substances in the dry state; then the said pressure which prevails after the electrolyte has been added depends on the ratio c of the difference (Z-e) or clearance i, left free in the container by the active substances for receiving the diaphragms, to the sum total of the thickness dimensions d of said diaphragms in the dry state.

The curve representing the variations of said pressure AP versus those of the ratio a has been plotted. For this purpose, the device diagrammatically illustrated in Fig. 1 has been designed. This apparatus essentially consists of a boxshaped container i two of the side walls of which are shown at I I and I2 and the bottom at I3. The walls and the bottom have sucient rigidity such that they may be regarded as undeformable under the operating pressures developed.

Secured to the upper surfaces of said side walls II and I2 is a cross member I4 formed in its center with a hole I for guiding a piston rod I6 having rigidly secured to its lower end a piston Il substantially rectangular in horizontal cross section, and adapted for sliding movement in the container I0, suii'icient clearance being provided in the sliding fit of the piston in the container for allowing substance, especially liquid, to pass from one to the other of the two chambers or compartments I8 and I9 defined by the piston in the container. Upstanding on the container is a structure 2B including two uprights 2I and 22 and an upper cross-bar 23 which supports at its center a preferably threaded rod 24 cooperating with a complementary hole formed in the cross-bar 23. The rod 24 carries at its base a small plate 25 which serves as an abutment for a -compression coil spring 26 of calibrated resiliency, and abutting at its lower end against a plate 21 rigid with the piston rod I6. The plate 21 supports a pointer 28 adapted to cooperate with a scale of calibrations 29 supported from the crossbar 23.

A laminated pile of cellophane sheet elements, in the dry state, of measured thickness in the uncompressed condition, is inserted into the container I0 under the piston I1. The said thickness or depth of the pile in uncompressed condition, referred to as d, may, indeed, be measured in the apparatus itself, by reading first the position of the pointer 28 when the piston I1 rests on the bottom I3 of the container, and then its new position with the piston resting on the top of the pile of laminated sheets substantially under zero pressure. Starting from this condition, the piston i1 is raised by a vertical distance i, this distance being ascertained by means of the pointer 28 cooperating with the calibrated scale 29. The vertical position of the plate 25 is then so adjusted that, for this position, the compression of the spring is nil, while as soon as the plate is raised above this position the spring will be subjected to compression.

The swellingly acting electrolyte, e. g. a water solution of potassium hydroxide, is then introduced into the compartment I9 by the simple procedure of pouring it onto the piston I1 whence it flows into the lower compartment through the clearance intentionally provided between the sides of the piston and the walls of the container I0.

The cellophane sheet elements contained in the compartment I9 swell; the stack increases in thickness until it reaches up to the under face of the piston I'I, and thereafter, on further swelling, pushes up the piston against the action of the spring 26 which contracts. The sag of the spring may be indicated by the displacement of the pointer 2 over the scale 29; this reading yields, with due allowance for the initial adjustment, an indication of the pressure P. The curve of variation of this pressure as a function of the above-defined factor a may thus be plotted. A typical such curve has been shown at A in Fig. 2, wherein the values of the factor a are plotted in abscissae and the pressures P (expressed in kg./sq. dm.) in ordinates. It can be ascertained from this curve that the pressure increases as` the fourth power of the factor a.

This surprising discovery explains the irregu` lar results obtained in the past in the construction of such accumulators, in that it shows that a very small difference in the thickness of the diaphragms relatively to the total clearance, providedfor them in the container by the active substances, can entail very considerable differences in the operating pressures.

Thus, in this connection, the invention is based upon the discovery of the critical character of said diaphragm thickness, and of the need for selecting such thickness with the utmost care and accuracy. From this it can be inferred that an essential specication in the manufacture of accumulators designed for operation in the man.-

ner described lies in the number of sheets of regenerated cellulose or cellophane (since their individual thickness is, in practice, very nearly constant) which are to be interposed, .whether rolled or packed around or otherwise, between the active substances of opposite polarity in the accumulator. Y

Actually the pressure under which the active substances of opposite polarity are applied against the diaphragms within the accumulator is not, strictly speaking, the pressure defined by the above-described curve A as a function of the factor a; thus, allowance must be made,in the first place, for the contraction or shrinkage of the active substances which occurs in the course of operation of the accumulator, and, moreover, for the slight distortion assumed by the container under the action of the forces developed against its opposite walls. The compression curves which make allowance for both these factors have also been plotted.

To take into account the compression of the acti-ve substances, completey accumulatori have-been dismantled, which present structuralLA y measured; and it; was found-thatai certain degreci ofvv contraction hasv occurred.. therein rela-1 tively to the thickness. of sai-d electrodesin. the: drystate.v

The; corrected compression curve which maires: allowance for this-contraction is shown atHB in Fig. 2', andity is seen. that: itsy general" shape. is: exactly.' similar tothat of the-curve-fr, and; that: it. can-be-:regarded'as being the curveA merely shifted a direction parallel to: the. axisy of. abscissae. shows that, in. the instance under` investigation, the f contraction of. the active substances amounts to about'. 10%..

Lastly, the corrected curve. which, in*` addition to theicontraction ofthe activev substances, at the same time takes into account the slight expansion of the container is shownv as the curve lC, whichmay also be seen as resulting from the curves A and'B by a translation parallel, to the axis of abscissae.

This cur-ve C. provides the. manufacturer' with accuratedata on the thickness which is to be imparted to the semi-permeable.` substance taken inpthedryA state, or, in practica, the numberof sheets of cellophane to be used for. each electrode, in; order toobtain, in the operation of thefaccumulator under construction, a predetermined value for the pressure of application of said active substances against the cellophane separators.

It is found, by way of example, that in order to obtain a normal operating pressure of 2O kg./sq. dm. the combined cellophane thickness should be selected such that the factor a should be slightly higher than 2.30. This information is especially valuable in view of the experimental results, indicated hereafter, provided by very numerous tests carried out with the object of ascertaining the most favorable internal pressure for optimum operation of an accumulator.

With the above teachings in mind, accumulator units have been constructed diiering from one another in their internal operating pressure, that is the pressure of application of the active substances against the separator diaphragme. Then the electric capacities of each of these units was plotted as a function of the said pressure, for various rates of discharges. Curves were thus obtained such as shown at D, E, F on the diagram of Fig. 3, wherein the pressures in lig/sq. dm. are plotted in abscissae and the capacities in amp. hrs. in ordinates.

The curve D was found for complete discharges of the units in .two hours, the curve E .for complete discharges of the units in ten hours, and the curve F for complete discharges in 24 hours. These curvesl show that optimum capacity, in each of the three cases, is for an internal pressure approximating 20 lig/sq. dm., and that this capacity drops ofi but slowly as the pressure is decreased from 20 lig/sq. dm. to 15 lig/sq. dm., while it drops on" at a comparatively very fast rate as the pressure is increased above 20 or 2l kg./sq. dm.

Keeping in mind both the curves of Fig. 2 and those of Fig. 3, the reason why accumulator units produced in an apparently quite similar Comparison between-1` curves. and; B.-

6 manner.: displayed such. wide differences irrsenviot performancev becomes obvious; Itis: seeirthatzitj is suicient` for the internal. pressure; tori/tary. only by one. or two: lig/sq. dm. for the; capa@ to be cut down by 5.0 Now; avariationoij 1401's 2 kg./sq. dm. correspondsv to only a percent.l variation in the: ratiora. In practice, tlsrisinreansv that the insertion of only one or twoy cellophane. sheetsv too many during the. construction org` am; accumulator'is enough gravely-"to: impairfthezultimate operatingcharacteristics ofttl'reiun-ih` Further experiments have been: conduetedon accumulators possessing different; internaligpres? sures: with the, object of' ascertaining theA 'indu-1 ence. ofv such pressure. on servicelife.. The results'. of these tests are summarized-in graphicl forni.. in the curve of Fig. e, wherein internalpressure is plotted in abscissae versus: the: numberf ofi the unit's useful operating: cycles in. ordinates-.fiA The... curve G thus obtained" displaysv a. maximum. a pressureV approximating 20 lig/sq.. din-.3.; which. the number of operatingcycles;attains 400;.. It decays, thoughsl'owly, as. thefpressure.- ist-increased above the said. value; but on. the: other: hand itV fallsA comparatively'rapidly as.: the ternal pressure is reduced' below 20 kg./sq:. dma.

These last-mentioned experiments'vt'hus: dem.-L onstrate: that, Where it; is: desired; to.k obtain an accumulator having'A a: long-service.. lifje,. it'. nec-f essary that. the: pressure bei not; substantially lower thai/1:20 kgr/sqa. For: reasonssimilarto. those explained aboveY in: thediscussionzoi the: curves' D; E, F, itiisr seent that tlielaclc'oifv only-@nef orl two sheets:` cf; cellophane.L has` a; veryadverse@ eiect. onthe; operation of, anzaccumulator;

Now'V to combine;` the teachings resulting; from:v the consideration of Figs. 2 to 4, the necessary conclusion is that both the excess and the denciency of one or two sheets of cellophane result in highly detrimental consequences on the accumulator performance, and that the prescriptions as to the number of cellophane sheets used to wrap the active substances sh-ould be scrupulously followed. Such prescriptions, which are Very easy to observe strictly, by a mere eiort of attention, make it possible to provide accumulators which possess all the high qualities expected of them as resulting from the tests conducted on the prototype model. The simplicity of the improvement provided by this invention, far from detracting from its importance, confers to it an essential value, inasmuch as it makes it possible to achieve considerable improvement in production without increasing the cost of manufacture and without requiring any alteration in plant.

Theoretical considerations may lbe put forward to explain the results yielded by the practical tests described herein. An excessive pressure applying the active substances against the diaphragms tends to retard, and finally completely to inhibit, the ion diffusion and exchanges.

On the other hand, in the case the pressure of application is too low, the electrodes are insufficiently constrained, so that the active substances. including especially the negative active substance, tend to drop to the bottom of the container.

However that may be, it was impossible to predict the decisive importance, from the standpoint of operating performance, of the measurement of the means for obtaining the internal pressure, and this explains the diiculties encountered heretofore and now overcome.

Fig. 5 shows part of a battery according to the invention comprising a casing 2H wherein there are assembled under pressure, as hereinabove set forth, a set of positive electrodes 210 alternating with negative electrodes 2I8. The negative electrodes consist essentially, in the discharged condition of the battery (as disclosed in my above-identied co-pending application) of zinc oxide, the positive electrodes being composed essentially of silver. An alkaline electrolyte (not shown) permeates the sheet material 22B, here indicated to consistof cellophane, which separates adjacent electrodes from one another.

In the light of the foregoing it will, of course, be apparent that the battery shown in Fig. 5 is merely an illustrative example and that departures `therefrom are permissible within the spirit and scope of the appended claims.

l. An electric accumulator, which comprises at least one positive electrode containing silver, at least one negative electrode containing zinc juxtaposed with said positive electrode, a semipermeable material between said electrodes, an alkaline electrolyte impregnating said electrodes and said material and exerting a swelling iniluence on said material, the swelling of said material applying the same against said electrodes under a pressure at least 15 lag/sq. dm.

2. In an electric accumulator, in combination. a casing; a plurality of elements juxtaposed in said casing including at least one positive electrode, at least one negative electrode, a semipermeable material, and means including said material separating electrodes of opposite polarity; and an electrolyte in said casing permeating said electrodes and said material, said electrolyte having a swelling iniluence upon said material,

the ratio of free space, computed as the difference between the dimension of said casing noi-malato said electrodes and the combined thickness of all of said elements other than said material, to the total thickness of said material, when in the dry state, being within a range of substantially from 2 to 3.

3. In an electric accumulator, in combination, a casing; a plurality of elements juxtaposed in said casing including at least one positive electrode containing silver, at least one negative electrode containing zinc, and a semi-permeable material between adjacent electrodes of opposite polarity; and an alkaline electrolyte in said casing permeating said electrodes and said material,` said electrolyte having a swelling influence upon said material, the ratio of free space, computed. as the diierence between the dimension of said.

HENRI GEORGES ANDRE'.

REFERENCES CITED The following references are of -record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,955,115 Drumm Apr. 17, 1934 2,317,711 Andre Apr. 27, 1943 2,339,031 Rosenberg Jan. 11, 1944 2,407,648

Boehm, Jr Sept. 17, 1946

Claims (1)

1. AN ELECTRIC ACCUMULATOR, WHICH COMPRISES AT LEAST ONE POSITIVE ELECTRODE CONTAINING SILVER, AT LEAST ONE NEGATIVE ELECTRODE CONTAINING ZINC JUXTAPOSED WITH SAID POSITIVE ELECTRODE, A SEMIPERMEABLE MATERIAL BETWEEN SAID ELECTRODES, AN ALKALINE ELECTROLYTE IMPREGNATING SAID ELECTRODES AND SAID MATERIAL AND EXERTING A SWELLING INFLUENCE ON SAID MATERIAL, THE SWELLING OF SAID MATERIAL APPLYING THE SAME AGAINST SAID ELECTRODES UNDER A PRESSURE AT LEAST 15 KG./SQ. DM.

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