CA2037898C - Rechargeable nickel electrode containing electrochemical cell and method - Google Patents

Abstract

ABSTRACT
A sealed rechargeable nickel electrode containing electrochemical cell has a pasted negative electrode having paste layers adhered to a nonforaminous conductive substrate (40), which retards growth (swelling) of the nickel electrode on cycling. In particular in a sealed rechargeable electrochemical cell having a nickel positive electrode, a pasted negative counter electrode comprised of an electrically conductive substrate and an electrochemically active material secured through adhesion to at least one face of the substrate, a separator interposed between the positive and negative electrodes, and an electrolyte, the improvement comprising the combination:
the nickel positive electrode formed of a porous conductive substrate defining passageways laterally across the positive electrode through which the electrolyte communicates, and an electrochemically active nickel based material adhered to the substrate and interconnected through the passageways to opposite sides of the positive electrode, and the electrically conductive substrate of the pasted negative electrode being substantially nonforaminous, whereby, in charging of the cell, the normal tendency of the nickel electrode to swell is retarded.

Description

` 2037~98 :

RECHARGEABLE NICKEL ELECTRODE CONTAINING
~-ELECTROCHEMICAL CELL AND_METHOD
Backqround_of the Inventlon -- The present lnventlon relates to an electrode assembly -~ for a rechargeable electrochemlcal cell having a nlckel posltlve electrode subject to swelllng on recharglng, and a pasted negatlve electrode, and ln one aspect to an electrode assembly of the fore~
golng type whereln a portlon of an exterlor face of a substrate of - that portlon of an electrode plate deflnlng the outermost or perl-pheral layer or wrap of the electrode assembly ls substantlally - exposed and contacts at least a portlon of a contalner as assem-bled ln a sealed electrochemlcal cell.
Conventlonally, electrode assemblles for electrochemlcal cells are formed from two separate electrode plates of opposlte polarlty with a layer of lnterposed separator materlal. The nega-tlve electrode plate can be of a pressed or pasted deslgn. An aqueous mlxture of an electrochemlcally actlve materlal and a blnder may be applled to each face of an electrlcally conductlve, , perforated substrate and pressed on to the substrate, for example t, 20 by passlng the substrate between rollers. The substrate can be stlppled to lmprove adheslon between the substrate and the elec-trochemlcally actlve materlal.
The posltlve nlckel electrode may be of a slntered deslgn. A perforated or wlre mesh nlckel or nlckel-plated steel substrate of, for example, 2-3 mlls thlckness, ls slntered wlth a carbonyl nlckel powder layer or layers to form a porous electrode ; plaque of, for example, 20-30 mlls thlckness. The resultant por-~ ous plaque ls conventlonally lmpregnated wlth a solutlon of an i, X

~, 20378q8 - la 28718-4 electrochemlcally actlve materlal precursor, typlcally nlckel nltrate. The electrochemlcally actlve nlckel hydroxlde materlal ls preclpltated out of solutlon wlthln the plate.

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, ' W~1/015~3 In addition, an ultra high porosity nick~7 8~8 positive electrode plate can be utilized in which an electro-~emically active nickel material may be bonded to a porous substrate such as a highly porous metal foam or fibrous mat by, for example, pressing a slurry or paste containing the active material on to and within interstices of the substrate. The substrate may then be compacted to form a positive nickel electrode plate having a desired thickness.
In sealed rechargeable nickel electrode-containing cells, such as commercial sealed nickel-cadmium cells employing sintered nickel electrodes, the nickel electrode ; increases in thickness during cycling. Thickening is believed to be related to the ratio of gamma nickel lS hydroxide present to beta III nickel hydroxide, the gamma form occupying more space. Such swelling tends to significantly shorten cell life, oftentimes because of premature shorting of the electrode plates. Various efforts have been made in the past to eliminate or inhibit this swelling phenomenon. Only limited success has been realized.
~; Accordingly, it is an object of this invention to produce a rechargeable nickel electrode-containing electrochemical cell in which means are incorporated to retard the normal tendency of the nickel electrode to swell during the life of the cell.
It is a further object of the present invention to provide a wound or nonwound electrode assembly for use in a sealed nickel electrode-containing electrochemical cell having means retarding swelling of the nickel electrode and which provides for direct electrical contact between a portion of the substrate of the negative electrode plate thereof and a portion of the cell container.
Another object of the present invention is to provide a wound electrode assembly which can be easily - manufactured and as assembled within a sealed nickel electrode-containing electrochemical cell will result in a substantially higher coulombic cell capacity and improved - cell performance characteristics including extended life due to retardation of short circuiting.
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SummarY of the Inventlon Accordlng to one aspect of the present lnventlon there ls provlded ln a sealed rechargeable electrochemlcal cell havlng a nlckel posltlve electrode, a pasted negatlve counter electrode comprlsed of an electrlcally conductlve substrate and an electrochemlcally actlve materlal secured through adheslon to at least one face of the substrate, a separator lnterposed between the posltlve and negatlve electrodes, and an electrolyte, the .~ lmprovement comprlslng the comblnatlon:
the nlckel posltlve electrode formed of a porous conductlve substrate deflnlng passageways laterally across the posltlve electrode through whlch the electrolyte communlcates, and an ; electrochemlcally actlve nlckel based materlal adhered to the substrate and lnterconnected through the passageways to opposlte sldes of the posltlve electrode, and the electrlcally conductlve substrate of the pasted negative electrode belng substantlally nonforamlnous, whereby, ln charglng of the cell, the normal tendency of the nlckel electrode to swell ls retarded.
In another aspect the foregolng sealed rechargeable electrochemlcal cell ls housed ln a multl component contalner, one component of the contalner servlng as the negatlve termlnal of the cell, and an end portlon of the nonforamlnous substrate of the negatlve electrode belng substantlally free of the electrochemically actlve materlal on a face thereof, such end portlon maklng conductlve contact wlth the component of the ~, contalner servlng as the negatlve cell termlnal.

2037~9~
3a 25145-222 In yet another aspect, the inventlon ls directed to a method for preparlng a negatlve electrode plate for use ln a rechargeable nlckel electrode-contalnlng electrochemlcal cell, lncludlng the steps of 1) advanclng an electrlcally conductlve strlp substrate at least a portlon of whlch ls nonforamlnous lnto and through a coatlng means; 11) preferentlally applylng a paste mixture of electrochemlcally active materlal and a vehlcle on to the advanclng strlp such that both opposed ma~or faces of the strlp bear paste along a flrst transverse portlon of the strlp, and only one of such ma~or faces bears paste along a second transverse portlon of the strlp leavlng a bare substrate portlon;
111) transversely severlng the thus pasted strlp lnto a plurallty of component strlps sultable ' `.

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WO ~1/01573 - - 4 - ~ 98 as electrodes, the base substrate portion of each component strip adapted to make electrical contact to a terminal of the electrochemical cell; and iv) removing vehicle from the component strip.

Brief Description of the Drawinqs The accompanying drawings, which are incorporated in and form part of the specification, illustrate the embodiments of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:
FIGURE 1 is a cross-sectional view of one embodiment of a wound electrode assembly of the present invention as installed within a container of a sealed nickel electrode-containing electrochemical device;
FIGURE 2 is a cross-sectional view of another embodiment of a wound electrode assembly of the present - invention as installed within a container of a sealed nickel electrode-containing electrochemical device;
FIGURE 3 is a graphical illustration of the increased electrochemical cell capacity obtained with the wound electrode assembly of the present invention for a sealed nickel-cadmium cell;
FIGURE 4 is a schematic representation of an extrusion coating process for producing negative electrode plates in accordance with the invention;
~ FIGURE 5 is a sectional view of the pasted - substrate strip of FIG. 4 taken along 5-5; and FIGURE 6 is a cross-sectional view similar to FIG.
5 showing an alternative embodiment of a negative electrode plate made in accordance with the invention.

~etailed Descri~tion of the Preferred Embodiments The invention will be described primarily with respect to wound nickel-cadmium cells for purposes of illustration. It will be understood that the invention applies to any sealed rechargeable electrochemical cell having a nlckel positlve electrode, such as nlckel-cadmlum, nlckel-zlnc, nlckel-hydrogen and nlckel metal hydrlde. Any deslred conflguration may be employed such as splral wound, flat wound, parallel plate (prismatic), tubular plate, button or the llke.
A sealed electrochemlcal cell lllustrated generally at ~; 10 ln FIG. l comprlses a ~ar contalner 12 lnsulated from a con-talner lld 13 houslng a wound electrode assembly 20 whlch ls dlmensloned and conflgured to be posltloned wlthln contalner 12 and be contlguous wlth lts lnner sldewall 14. Contalner 12 may be constructed of any sultable electrlcally conductlve materlal, for example nlckel plated steel, havlng a thlckness of about .010 to about .015 lnches.
^ Electrode assembly 20 ls comprlsed of a posltlve elec-. trode plate 30 contalnlng an electrochemlcally actlve materlal, :
,~ notably nlckel hydroxlde, a negatlve counter electrode plate 40, ~ and a porous, flexlble lnterleaved separator materlal 50 whlch ls .~ posltloned on each face of posltlve electrode 30 to electrlcally lnsulate lt from negatlve electrode plate 40 throughout the entlre cell. Any sultable separator materlal can be employed ln the ~- present lnventlon, for example, unwoven nylon or polypropylene.
Electrode assembly 20 ls formed by wlnding the components thereof about a removable arbor wlthln a nest ~not lllustrated) as more fully descrlbed ln U.S. Patent No. 4,203,206.
- A sultable electrolyte ls absorbed ln the separator and plates, usually ln a starved quantlty, to provlde lnterconnectlng volds and a low tortuoslty path to enhance dlffuslon of gaseous oxygen evolved at the nlckel electrode on overcharge to reach the ,~

20378~8 6 2871~-4 negatlve plate where lt ls consumed through a thln electrolyte layer. Alkallne electrolyte ls preferred, such as 31 percent potasslum hydroxlde.
Negatlve electrode plate 40 ls a pasted plate formed by bondlng or attachlng a layer of a sultable electrochemlcally actlve materlal 42 normally to each face or slde of substrate 15.
By "pasted" plate ls meant a non-slntered, non-electrochemlcally deposlted electrode formed by applylng a paste, slurry, powder mlxture, or the like, wlth or wlthout a vehlcle such as water or organlc solvent, onto at least one face of substrate 15. The electrochemlcally actlve materlal 42 can be afflxed to substrate 15 by presslng sultable paste whlch ls a mlxture prlmarlly of actlve materlal, for lnstance cadmlum oxlde, cadmlum hydroxlde and cadmlum metal, and binder ln the case of a cadmlum electrode onto substrate 15. Aqueous based binders such as ethylene vlnyl ace-tate or dispersed polytetrafluoroethylene may be used. Alter-natlvely, the actlve materlal may be bonded to the substrate by ~,j means of slmultaneously extrudlng from a cross-head dle an organlc slurry contalnlng the actlve materlal ln suspenslon onto both sldes of the substrate to form a layer on each face thereof. In one aspect an elastomerlc blnder ls lncorporated lnto the organic slurry to malntain the electrochemically actlve materlal ln sus-.:
penslon wlthln the organic solvent.
- The preferred elastomeric binders are a styrene-butadiene copolymer manufactured under the trade name of AMERIPOL
by the B.F. Goodrich Company or styrene-ethylene/butylene-styrene block copolymers manufactured under the trade name KRATON by the Shell Chemlcal Co. Sultable organlc solvents useful as a carrler ; ~,, "'`~''``' ~ .
, ` 2037898 6a 28718-4 ~` ln formulatlng such organlc slurrles may lnclude naphthol splrlts, Stoddard solvent, decane, xylenes, lso-parafflns, and mlxtures thereof. After extruslon onto the substrate, the organlc slurry ls dried to remove the organlc solvent and to form a mlcroporous, flexlble coatlng on the substrate whereln partlcles of electro-chemlcally actlve materlal are bound together and to the substrate by means of the elastomeric blnder.
Alternatlvely, another preferred blndlng system employs i~ an alcohol soluble polyamlde, whlch lmparts deslrable cadmlum ~^ 10 agglomeratlng retardatlon characteristlcs to the electrode.
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WO Yl/1~1573 I'CT/US90/03947 - 7 - 20;~ 9~
In accordance with the invention it has been found unexpectedly that the normal tendency of the nickel electrode to swell during recharging is-retarded by ensuring that the electrically conduc~ive substrate 15 of the counter pasted negative electrode 40 is substantially nonforaminous, e.g. imperforate. By "substantially nonforaminous" s meant that the substrate lacks macro holes, reticulation or perforations, and particularly that any micro holes or reticulation pattern present are so small, as "seen" by the positive electrode, that a uniform current density is applied to substantially the entire negative plate on charge and discharge. It has been found that foraminous negative ; plate substrates e.g. those having 2mm diameter perforations spaced about 3-5.2 mm apart (center to center), induce the formation of blisters in a test nickel electrode in an accelerated flooded test cell in the exact pattern of the perforations of the negative counter electrode ' 5 substrate.
Preferably substrate 15 of the negative electrode of the invention is formed of a flat smooth conductive sheet ~' 20 completely free of holes or reticulation to the naked eye, although such imperforate sheet may be stippled, embossed, roughened, etched or otherwise modified to enhance adhesion to the paste of active material. ~owever, micro holes or foramina having a cross dimension on the order of less than about 200, more preferably less than about 100, most preferably less than about 30 percent of the interelectrode distance (measured from the surface of the nickel electrode to the surface of the negative substrate) may be employed without significant deleterious effect.
Although not entirely understood, it is believed ; that perforated substrate negative electrodes of the prior art exhibit nonuniform current densities due to "edge effects" at each perforation. Accordingly, the corresponding area of the nlckel electrode directly across from these perforations receives more charge during recharging and, therefore, forms more gamma nickel hydroxide which causes blistering (swelling) at those sites.
Applicants are unaware of any teaching or suggestion in the prior art that nickel electrode swelling ~ 3 7 8~9 i,~

can be retarded by uslng imperforate substrate ln the counter electrode, of the pasted type. Imperforate grld ln cadmlum and other negatlve electrodes ls known per se. See, for lnstance, U.S. Patent nos. 3,783,025 (Klng et al.); 4,460,666 (Dlnkler et al.); and 4,686,013 (Pensabene et al.).
Posltlve electrode plate 30 ls preferably formed by slnterlng a low denslty metal powder, for example, a carbonyl nlckel powder, on each face of a porous substrate 34 whlch can be - any sultable electrlcally conductlve materlal, for example, nlckel ; 10 plated steel, whlch preferably has been perforated to provlde the slnter wlth mechanlcal lnterconnectlon across the perforatlons.
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Conventlonally, the electrode plaque thus formed, of about 80 percent poroslty, ls loaded by lmpregnatlng the plate ln a serles of steps wlth an aqueous solutlon contalnlng an electrochemlcally actlve precursor nlckel materlal preferably nlckel nltrate whlch subsequently ls preclpltated out of solutlon thereby formlng an area on each face of substrate 34 and wlthln the perforatlons . through the substrate which contalns an electrochemlcally actlve materlal, namely nlckel hydroxlde. Thls standard slntered nlckel j:
electrode has exhlblted the aforementioned swelling problem when matched with a negatlve electrode employlng a perforated sub-strate.
- Alternatlvely, posltlve electrode 30 may employ a hlgher poroslty ~e.g. 85-95 percent) substrate, plaque or mat, of metal foam, randomly lntermlngled metal flbers pasted or lmpregnated wlth actlve nlckel materlal, or slmply a perforated sheet sub-strate on whlch ls pressed or pasted a dry powder, slurry or paste contalnlng the actlve materlal. Addltlonal components may be ~ ,, 8a 28718-4 admlxed wlth the actlve materlal such as conductlve powders or flbers, blnders, antlpolar mass, cobalt and the llke as ls well known to those skilled ln the art.
As thus manufactured, the electrode assembly 20 ls lnserted lnto and housed wlthln contalner 12. To electrically connect posltlve electrode plate 30 to a portion of the contalner which ls electrlcally lnsulated ,i~, :' ., :
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_ from sidewall 12, for example, contact button 17 of cover 13, an electrically conductive tab (not illustrated) is formed integrally with or welded to an end portion of ` substrate 19 which is not coated with active material, is dimensioned to extend beyond substrate 19, and is secured in known manner to the cover by any suitable means, such as laser welding.
In accordance with another aspect of the present ~, invention, the exterior face 15' of substrate 15 of the outermost or peripheral layer or wrap of negative electrode plate 40 is exposed and contacts the sidewall 14 of container 12 to electrically connect the outermost or ; peripheral layer or wrap of electrode plate 40 directly to the side wall 14. To expose the exterior face of nonforaminous substrate 15' of the outermost or peripheral layer or wrap of electrode plate 40, outer layer of ; separator material 50, and the layer of active material 42 are removed from the outermost or peripheral layer or wrap of electrode plate 40. The outer layer of separator material is removed while winding the components of the electrode assembly of the present invention about a removable arbor. Prior to winding, the layer of active material 42 can be scarfed from the exterior of the outermost or peripheral layer or wrap of electrode plate 40 thereby exposing substrate 15' so that electrical contact will be made to substantially the entire peripheral surface . of exposed substrate 15' and the sidewall 14 of container 12. This layer of active material 42 can be scarfed by scraping the exterior face of substrate 15' in the outer layer or wrap by suitable means, for example, a blade.
Alternatively, electrode plate 40 is preferably formed such that the outer wrap or layer of substrate 15' does not have a layer of surface active material 32 formed on the exterior face thereof, as will be described hereinafter with respect .~ 35 to FIGS. 4 and 5. Outer wrap of substrate 34 is substantially imperforate and has a layer of surface active material 42' extruded only on the interior face thereof.
The preferred method of forming electrode plate 40, shown in cross section in FIG. 5 as produced, is by the .
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crosshead extrusion coating process illustrated in FIG. 4.
Accordingly, imperforate conductive strip substrate 15 is vertically upwardly advanced through an opening in a crosshead die 60, equipped with an inlet (not shown) for continuously supplying negative active paste. The die opening is shaped to extrusion coat substrate 15 to the pasted configuration of FIG. S; i.e. both opposed major faces of substrate 15 bear paste layers 42 in a first transverse portion 15 of the substrate, while in the adjoining transverse portion one face of portion 15' of the substrate is bare and the opposite face has adhered to it paste layer 42'. An alternative to extrusion coating includes fully pasting both sides of substrate 15 and ;- employing a doctor blade to selectively remove paste from a portion of the substrate.
- The thus pasted substrate is then advanced to knife means 62, 64 which cross cut the pasted substrate into electrodes 40a, 40b, 40c, etc. of desired width.
Subsequently the plates are dried or heated to drive off the ; 20 paste vehicle e.y. water or solvent.
Use of imperforate substrate in accordance with the invention also simplifies this manufacturing process since the transversely cut edges 66, 68 of each electrode are free of burrs or raw edges (as in the case of transversely cutting through perforations), which if present lead to shorting in finished cells (in this respect, reference is also made to col. 1, lines 26-65 of U.S. Patent no. 4,105,832 (Sugalski)).
Alternatively nonforaminous substrate 15 can be pasted only on one side thereof, or on both sides with paste layers 70 and 72, to form electrode 80, as shown in FIG.
6. Electrodes made in either of these fashions are especially suited for use in parallel plate cells (prismatic), the former embodiment allowing conductive contact to be made with the inside wall of a flat walled conductive container.
In the alternative, less preferred embodiment o~
FIG. 2, only the outer wrap portion 41' of substrate 41 of negative plate 20' is imperforate, to make a good electrical ~J Yl~UI~ r~ ~u ~u/u.
X0~371~3~3 connection to inner wall 14 of container 12. The greater the proportion of substrate 41 which is nonforaminous (and imperforate) the greater the swelling inhibition imparted to - the juxtoposed nickel electrode 30 during cycling (repeated charge and recharge).
The electrode assembly of FIGS. 1 and 2 of the present invention, and analogous arrangements in other cell configurations such as prismatic, result in improved contact between the negative electrode plate and the container of an electrochemical cell. In addition the volume normally occupied by separator and active material on the outside surface of the outer wrap of conventional wound electrode assemblies now becomes available for introducing additional positive and~or negative electrode active material in the same volume. The amount of additional electrochemically active material and the attendant increase in electrical capacity of a given electrochemical cell are a function of the thickness of each component of the electrode assembly of the present invention and the diameter or cross dimension of the container into which the assembly is positioned. FIG. 3 is a graphical illustration of the increase in cell capacity obtained with a wound electrode assembly of the present invention for a nickel-cadmium cell. Calculations were based on a positive plate thickness of .030 inch and a width of 1.575 inches, a negative plate thickness of .021 inch, separator thickness of .006 inch, and an arbor diameter of .187 inch. Curve A of FIG. 3 represents the electrical capacity of a conventionally manufactured nickel-cadmium cell, curve B represents the electrical capacity of a nickel-cadmium cell utilizing the wound electrode assembly of the present invention, and curve C represents the - percentage of increase of cell capacity obtained in utilizing the wound electrode assembly of the present - invention. The increase in cell capacity utilizing the wound electrode assembly of the present invention is greater for smaller diameter cells. As illustrated, the increase in cell capacity for a AA sized cell is greater than 20%.
The followinq examples describe the manner and process of making and using the present invention and set W~ YU/ ~lSY4 i - 12 - 2037~
forth the best mode contemplated by the inventor of carrying out the invention but are not to be construed as limiting the scope thereof.
ExamDle 1 Several cylindrical, sealed nickel cadmium AA size cells were each wound in accordance with the present invention on a 0.187 inch arbor from a conventionally sintered positive electrode plate impresnated with nickel ~` 10 hydroxide and an extrusion coated elastomer bonded cadmium oxide negative electrode plate. The positive and negative electrode plates were interposed with a non-woven nylon j separator. The negative electrode plate was formed such that the exterior surface of the outer layer or wrap thereof was substantially free of elastomer bonded cadmium oxide and the outer layer of separator was sized so that the substrate of the outer layer or wrap, which was formed of smooth imperforate nickel coated steel sheet 0.059 mm thick, was exposed. The resultant wound electrode assembly was positioned within a cylindrical cell container such that the exposed substrate of the outer layer or wrap of negative electrode plate contacted the container side wall. Prior to ;~ sealing the cells, 1.95 milliliters of 27 weight percent KOH
was added thereto. The cells were then sealed and formed at 25 70 milliamperes for 24 hours and discharged at 700 milliamperes. Cell capacities for these cells are summarized below in Table 1.

: Exam~le 2 , 30 A high energy density positive electrode plate was manufactured by filling a high porosity nickel foam - structure with a slurry of nickel hydroxide and other active materials and drying and compressing the electrode plate to a thickness set forth in Table 1. The resultant positive electrode plate was employed with the components of and wound, activated, and formed in accordance with Example 1 to form a plurality of cells. Cell capacities for such cells are summarized below in Table 1.

W~ 1S73 PCT1US90/U3947 - 13 - ~037898 ExamDle 3 A plurality of cells were constructed, activated and formed in accordance with Example 2 except that cadmium S oxide and separator were present on the exterior of the substrate of the outer layer or wrap of the negative electrode plate in accordance with conventional practice.
The negative electrode plate had a nickel tab attached to edge of the plate which was welded to the bottom of the cell container.
The results of Examples l, 2, and 3 are summarized below in Table l. Cell capacities are set forth both as a value which is typical of the measured values and as a value - rated on a "C" rate scale, i.e., a one hour rate.
(Insert Table l) ., As evident from the results set forth above, the length of separator necessary to construct the electrode assemblies o Examples l and 2 in accordance with the present invention was substantially less than that necessary to construct the conventional cells of Example 3. This . resulted in a significant increase in the length of both the positive and negative electrode plates in the wound electrode assemblies and in the capacities of the cells employing such electrode assemblies according to the invention.
Examples 4 and 5, set forth below, compare the ; swelling tendencies of sintered nickel electrodes in flooded test cells against control cadmium electrodes employing ; perforated substrates (Example 4), and the same electrodes employing imperforate substrates according to the invention (Example 5).
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ExamDle 4 A test cell was constructed by providing a rectangular flat nickel test electrode, wrapping this electrode in standard nylon separator, sandwiching the test ,. WO 91/01~73 PCr~9;~/~3B498 - 13a-.
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, , ~037s~8 nlckel plate and separator between a palr of rectangular cadmium counter electrodes, followed by wrapplng the thus formed sandwlch ln addltlonal separator, and provldlng a polyvlnyl chlorlde fllm backlng on the outslde of the outer most separator layer faces.
The test cells were then held ln compresslon by two small paper blnder cllps, and the thus formed test cells were placed ln ; plastlc rectangular open contalners whlch were fllled wlth 31 welght percent potasslum hydroxlde to ~ust above the top of the test cell, and approprlate electrlcal connectlons made to allow dlscharge and charge of the test cell.
The partlcular speclflcatlons of the test cell were as - follows. The posltlve test plate electrode was a standard slntered nlckel electrode. The overall dlmenslons of the test electrode were 3.2 cm long by 3.1 cm wlde by 0.731 mm thlck. The test plate employed a perforated nlckel plated steel substrate havlng a thlckness 0.0635 mm and perforatlons whose hole lnslde dlameter was 1.1 mm. A standard slntered nlckel matrlx havlng a bulk denslty of 0.083 g/cm was present on both ma~or faces of the substrate. The porous slntered nlckel was lmpregnated wlth ~ 20 electrochemlcally actlve nlckel hydroxlde at a loadlng level of - 0.1588 g/cm2.
~ The palr of negatlve counter electrodes were ldentlcal . . .
pasted cadmlum electrodes employlng perforated nlckel plated steel substrates havlng a thlckness of 0.059 mm, hole lnternal dlameters of 2 mm and a hole pattern present such that 12 holes were contalned per cm of substrate area. The dry welghts of the cadmlum paste lngredlents ln percent by welght were: 91.1 percent cadmlum oxlde; 5 percent cadmlum metal partlcles; 1.12 percent 14a 25145-222 - nlckel hydroxlde; 1.25 percent zlrconlum oxlde; 1 percent - polyamlde blnder/anti-agglomerant (Henkel 6200); and 0.5 percent polyethylene flber. The actlve materlal welght was 0.1 g/cm2.
The outslde dlmenslons of the pasted cadmlum counter electrode were 3.2 cm long by 3.2 cm wlde by 0.55 mm thlck.

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W~IJU1573 PC~/U~90/03947 - 15 - Z0~7S~98 - Separator layers were formed of nonwoven mats of 67 percent nylon 66 and 33 percent nylon 6. The separator , layers had a length of 10 cm, a width of 5 cm and weight of 70 g/m2 and a thickness such that the interelectrode spacing - 5 in the test cell was 0.17 mm.
The electrolyte utilized was 31 weight percent potassium hydroxide.
The test cell was cycled by discharging at a current of 0.055 amperes for one hour, followed by charging at a current of 0.055 amperes for 19.87 hours. Upon conclusion of this discharge/charge regime, the test plates were removed from the cell holder container and washed to remove the potassium hydroxide. The thickness of the test plate wa~ then promptly measured in the wet state and found ^ 15 to be 0.909 mm. This represented a 24.3 percent increase in thickness compared to the original thickness of 0.731 mm.

Example 5 ,.
The same test cell apparatus and components were used as in Example 4 which measured thickness increase of .~ the test electrode matched with the control negative counter electrodes employing perforated substrate. The sole exception is that in this example the cadmium electrode ;~ 25 substrate was imperforate, without any holes. The only , other difference was a slight difference in measured thickness of the positive test plate. In this example the measured thickness was 0.732 mm. Upon conclusion of the test performed identically as described in Example 4, the nickel test electrode was removed from the test cell and washed to remove potassium hydroxide, and the wet thickness of the electrode measured in the same manner as in Example 4. It was found that the nickel test electrode had increased in thickness from the initial 0.732 mm to a finai wet thickness of 0.768 mm. This represented an increase in thickness of only 4.9 percent, compared to the control perforated electrode of Example 4 which had undergone swelling of 24.3 percent.

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- 16 - ~)37~9~3 While the preferred embodiments have been fully described and depicted for the purpose of explaining the . principles of the present invention, it will be appreciated by those skilled in the art that various modifications and -~ 5 changes may be made thereto without departing from the scope of the invention set forth in the appended claims.

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Claims (16)

What is claimed is:

1. In a sealed rechargeable electrochemical cell having a nickel positive electrode, a pasted negative counter electrode comprised of an electrically conductive substrate and an electrochemically active material secured through adhesion to at least one face of the substrate, a separator interposed between the positive and negative electrodes, and an electrolyte, the improvement comprising the combination:
the nickel positive electrode formed of a porous conductive substrate defining passageways laterally across the positive electrode through which the electrolyte communicates, and an electrochemically active nickel based material adhered to the substrate and interconnected through the passageways to opposite sides of the positive electrode, and the electrically conductive substrate of the pasted negative electrode being substantially nonforaminous, whereby, in charging of the cell, the normal tendency of the nickel electrode to swell is retarded.

2. The cell of Claim 1 wherein the substrate of the negative electrode is an imperforate sheet.

3. The cell of Claim 2 wherein the sheet is provided with means on its surface enhancing the adhesion between the electrochemically active material and the substrate of the negative electrode.

4. The cell of Claim 1 wherein the substrate of the positive electrode is formed of a perforated sheet bearing a sintered low density metal powder on each face of such substrate and mechanically interconnected through the perforations.

5. The cell of Claim 1 wherein the substrate of the positive electrode is formed of 85-95 percent porous metal foam.

6. The cell of Claim 1 including a multicomponent container for housing the cell elements, one component of the container serving as the negative terminal of the cell, and an end portion of the nonforaminous substrate of the negative electrode being substantially free of said electrochemically active material on a face thereof, and making conductive contact with said component of the container serving as the negative cell terminal.

7. The cell of Claim 6 wherein the container is cylindrical and the electrodes and separator are spirally wound and the nonforaminous substrate of the outer negative electrode makes contact with the container.

8. The cell of Claim 1 wherein the electrically conductive substrate of the pasted negative electrode has micro holes therethrough, of a cross dimension less than about 200 percent of the distance from the surface of such substrate to the adjacent surface of the nickel positive electrode.

9. The cell of Claim 1 wherein the electrically conductive substrate of the pasted negative electrode has microholes therethrough, of a cross dimension less than about 100 percent of the distance from the surface of such substrate to the adjacent surface of the nickel positive electrode.

10. The cell of Claim 1 in which the negative counter electrode is cadmium.

11. The cell of Claim 1 in which the negative counter electrode is zinc.

12. The cell of Claim 1 in which the negative counter electrode is hydrogen.

13. The cell of Claim 1 in which the negative counter electrode is metal hydride.

14. A method for preparing a negative electrode plate for use in a rechargeable nickel electrode-containing electrochemical cell comprising the steps of:
advancing an electrically conductive strip substrate at least a portion of which is nonforaminous into and through a coating means;
preferentially applying a paste mixture of electrochemically active material and a ??

vehicle onto the advancing strip such that both opposed major faces of the strip bear paste along a first transverse portion of the strip, and only one of such major faces bears paste along a second transverse portion of the strip leaving a base substrate portion;
transversely severing the thus pasted strip into a plurality of component strips suitable as electrodes, the base substrate portion of each component strip adapted to make electrical contact to a terminal of the electrochemical cell; and removing vehicle from the component strip.

15. The method of Claim 14 wherein said bare substrate portion is nonforaminous.

16. The method of Claim 14 wherein the strip substrate is an imperforate metallic sheet.