CA1063670A - Flexible lead chloride cathode construction - Google Patents

Abstract

Abstract of the Disclosure The invention disclosed relates to a flexible electrode material, consisting essentially of a mesh material selected from the group consisting of woven wire gauze, perforated sheet metal and expanded metal, and lead chloride supported on said mesh material. The absence of any binder in the electrode material permits a higher loading of electrochemically active material in the electrode structure, resulting in a more efficient, longer-life electrode.

Description

~63670 This application i8 a divlsional of applicant's co-pending Canadian application Serial No. 244,744, filed February 2, 1976.
The present invention relates to flexible electrode material, suitable, for example, for use in the manufacture of salt water batteries.
Electrodes are conventionally manufactured by mixing lead chloride powder with a binder and with carbon or other electrically conductive material, and then compacting the mixture around both sides of a metallic conductor, e.g. copper or nickel gauze, perforated sheet or expanded metal.
~lowever, the necessity to include conducting material and a binder -in the mixture reduces the amount of active material which can be included in the electrode, and therefore reduces the electrical efficiency of the electrode. -Furthermore, this prior, conventional process for the manufacture of battery electrodes requires considerable expenditure of labour and may involve difficulties in quality control.
In applicant's Canadian Patent 1,018,246, there is disclosed a method of forming a battery electrode structure ~7hich comprises placing an open-mesh electrically conductive support structure in the form of a copper wire screen in a mold, and casting a mass of electrically active material in 2p the mold around the support structure, the electrically active material comprising, for example, lead chloride.
In another of applicant's co-pending Canadian application Serial No. 229,399~ filed June 16~ 1975, there i8 disclosed a similar method and apparatus for forming a flexible electrode material. The present method \~ and apparatus allows for a smoother and thicker coating of the electrode ; !
l material. The apparatus is also simpler and cheaper to construct and oper- -; j , .
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'~ It is an object of the present invention to proYide a novel and j ;~

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improved flexible electrode material.
According to the present invention there is provided a flexible electrode material, consisting of a mesh material selected from the group consisting of woven wire gauze, perforated sheet metal and expanded metal, and lead chloride supported on said mesh material.
Preferably, the mesh comprises a strip-shaped woven wire gauze, perforated sheet metal or expanded metal, made of copper.
The flexible electrode material of the invention is preferably ~ manufactured according to the method and apparatus as described and claimed 3 in the pa~ent application Serial No. 244,7~4, filed 2 February 1976. Accord-ing to that method, the strip-shaped mesh is guided through a bath of molten ~ lead chloride and upwardly from the bath to deposit the lead chloride in the `~ mesh9 The coated mesh is then cooled to solidify the coating.
When the coating material has been cooled sufficiently to effect solidification thereof, the electrode material may be cut into predetermined lengths, or coiled, e.g. on a spool, as desired.
The apparatus for the manufacture of the flexible electrode material, according to the invention comprises an open-topped container for a bath of molten coating material, means associated with the container for heating and melting the coating material, first guide means for supporting a roll of strip-shaped mesh material above and adjacent one end of the container, second guide means for guiding said strip-shaped material on a path of travel :: :
extending downwardly from the first guide means, and into the container, third guide means above and adjacent the other end of the container for guiding the 3trip-ahaped material upwardly from said second guide means, and ., .
out of the container, means for lowering said second guide means from an elevated position above the container through the open top of the container 1 : :
to an operating position within the container in which a portion of the strip-shaped material is immersed in the bath; and drive means for advancing the strip-shaped material past the first, second and third guide meansO
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The inven~ion will be more readily ~Inderstood from the follow~
ing description of a preferred embodiment thereof given, by way of example, with reference to the accomparlying drawing, which i8 a schematic side view of apparatus in operation fo~ forming flexible lead chloride elec~rode material.
Referring specifically to the drawing, a first guide means in the form of a supply spool 10 i8 provided above and adjacent one end of an open-topped tank 14, for carrying a coil 11 of strip-shaped material, conven-iently in the form of a gauze of a suitable metal or a suitable expanded .. .. .
metal, preferably, a woven copper wire gauze 12. The spool 10 is rotatably mounted on a support arm 13b.
In operation, the woven copper gauze 12 extends from the supply roller 11 on the spool 10 downwardly into the open-topped tank 14 containing .. . .
~ a bath of molten material 15, preferably, lead chloride; around the underside `, of a second guide means in the form of two submerged spaced, freely-rotatable graphite rollers 16, the spacing of which may be adjusted to vary the path length in the molten material upwardly out of the bath of molten material 15 at an exit angle which may be varied to control the run-back of molten material and hence the thickness of the coating, conveniently, of about 45; and over A third guide means in the form of a freely-rotatable guide roller 18 mounted ;~ on the carriage 23; along a substantially horizontal path between a pair of . . ..
i/l driven, slightly spaced water-cooled rollers 25 and 26 to expedite solidifi-:: .
cation of the lead chloride coating on the gauze 12 and through the nip of a -pair of spring-biased rollers 27 and 28 with knur~ed surfaces. The roller x 27 is driven by a drive means comprising a variable speed motor (not shown) ;; to control the speed of advance of the gauze 12 through the apparatus. The j' coated strip material may be collected by any convenient means downstream of the driven roller 27.

The open-topped tank includes angled sldes 30 to allow for ., . ~,, .
l 30 flexibility of exit angle of the gauze 12 from the bath 15.
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~063~;76al The provision of two guide roller~ 16 allows for a sufficient path length in the ~ath 15 to permit the temperature of the gauze to increase somewhat while in the bath, resulting in a more complete coating of the gauze 12.
The gauze 12 is maintained under tension during operation o the apparatus by means of a heavy freely-rotatable roller 13 which rests against the coil 11. The roller 13 is rotatably mounted on one end of a linking arm 13a which, in turn, is pivotably mounted at itx other end on a support arm 13b. Tension is maintained due to the weight of the roller 13.
~ roller 17 is rotatably mounted on one end of a linking arm 17a, the other end of which is pivotably mounted on the carriage 23 and is maintained in the illustrated position by the tension of the gauze. The roller ,i 17 is provided for spreading and smoothening the molten coating over the surface of the gauze 12 prior to solidification.
The open topped tank i8 also provided with a heating-mean~, ~,! conveniently in the form of a heat-insulating jacket 21 containing electrical resistance heating elements 22 which are-energized by an electrical power source S0 means 24 is provided in the area of exit of the coated gauze 12 from the bath 15 to prevent the deposition of scum, which tends to form -,. ~ : , -' on the surface of the bath due to surface oxidation thereof, on the gauze 12.
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Specifically, means 24 comprises a ~heltered passage including an inlet below the surface of the bath and an outlet above the surface of the bath, being defined by a rectangular block provided with an opening 29 therethrough. In the operating position, the block 2~ is partially submerged in the bath 15 in .
such a manner that the gau~e 12 e~its the bath 15 through the opening 29.

The block 24 is mounted on the carriage 23, and may be pre-heated by means i not shown to reduce so~ification prior to smoothening and distribution of j, the coatin~ over the surface of the Mesh by roller 17. ~ -`~ 30 The freely rotatable graphite rollers 16 as well as rollers 17 :,~. .~ . , :
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and 18 are mounted on a carriage 23 which i9 provided wlth means (not ~hown) for raising and lowering the carriage such that the rollers 16 and means 2 may be raised out of and lowered into the bath 150 A fume hood including exhaust fans (not shown) is provided over the apparatus to exhaust toxic lead chloride fumes arising from surface oxidation of the bath. The fumes are directed to a water-spray scrubbing unit (not shown) before being exhausted to the atmosphere.
In operation of the above described apparatus, the electric resistance heating elements 22 are energized to pre-heat the lead chloride until the latter becomes molten and the mesh 12 is threaded onto the system of rollers with the apparatus in the elevated position, that is, above the bath. The carriage 23 is then lowered from the elevated position to the operating position shown in the drawing, such that the rollers 16 are sub-merged in the bath of molten material 15 to enable the mesh 12 to be guided 1 along a path therethrough; and such that the block 24 is partially submerged in the bath 15 in the area of exit of the mesh from the bath.
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The mesh 12 exits from the bath 15 at an angle which may be varied by adjustment of the positioning of the roller 18, and is guided past the remaining rollers as defined above.
The mesh is kept under tension by means of roller 13 which is i~ - now positioned as in the drawing.
I The driven roller 27 must be activated before or shortly after ,, the mesh is lowered into the bath to prevent corrosion of the gauze by the ~! bath.
, The energization of the electric resistance heater elements 22 ;
::ï, is controlled to maintain the temperature of the molten lead chloride within ... .
' the range of about 510C to about 60~C, the fusion point of lead chloride being about 501C.
,~ It was found that the following parame~ers affect the thickness of the coating obtained:
(1) varying the speed of advance of the mesh through the `' apparatus .1, .
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~63~7~3 (2~ varying the temperAture of the bath of molten material (~) varyLng the exit flngle of the mesh from the bath (4) varying the roughness and size of the openings in the substrate mesh, and (5~ quick cooling and solldification of the coatings.

; Parameters 2 to 5 are first specified to minimize run-back of coating material. ~he thickness of the coating material may then be sufficiently controlled by varying the speed of advance of the mesh through the bath.
j More specifically, the amount of lead chloride deposited on the mesh 12 may be increased by increasing the speed of travel of the mesh 12, and thus the speed of rotation of the roller 27~ However, the speed of advance must be sufficient to prevent corrosion or melting of the mesh.
It was found that the heaviest coatings were achieved when the bath temperature was kept jus~ above the melting point of lead chloride.
I This is apparently due to the viscosity of the molten lead chloride. Speci-fically, since viscosity decreases as the temperature increases, if the bath -is maintained just above the melting point of lead chloride a higher viscosity will result than if the temperature of the bath was higher. The higher ~is-cosity reduces the run-back of molten material from the mesh. Thus, a bath -temperature of about 525 C is preferred~ However, temperatures of up to _ about 600C will also produce useul electrode material, but with lighter ., , ,l deposition of coating. As mentioned above, the exit angle may be ~aried by i adjusting the position of r~ller 18 to control the amount of run-back of molten material. Conveniently, an angle of about 45 was chosen.
~ It was also found that the run-back of coating material could ;~ be minimized by providing cooling rollers i.e. water-cooled by tap water.
In addition, the size of the copper gauze, when employed as the mesh, is also an important factor in determining the amount of lead chloride which will be deposited. Gauze having a greater roughness or larger openings will be capable of picking up a heavier loading of lead chloride. ~owever, there ma~ be an upper limit on the mesh size which will not enable it to .,; ~, ` .
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retain the coating.
Therefore, for very heavy lead chloride coatings, it may be necessary to use expanded or perforated sheet metal substrates instead of ~oven wire gauze. However, the less expensive gauze ls preferred when it is required to minimize the cost of production.
Successful results have been obtained, for example, using copper gauzes of 32-28 mesh size, made Erom wire of 0.007 - 0.012 inch diameter. The width of the gauzes may be from 2-6 inches depending upon the require~Zent, and the processing speed may be in the range of about 2.5 ft/min to about 100 ft/min the molten lead chloride bath temperature being held at about 510-600C, preferably at about 525 C~ -Electrodes obtained by this process were flexible and could readily be rolled into a cylindrical diameter of about 1 centimeter. The lead chloride coating adhered qulte well to the gau7e, although~ the elec-~I trode material is intentionally flexed in a repeated back and forth manner, it was found that the coating would eventually crack and loosen.
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in view of an "edge effect" which causes uneven coating at the edges of the gauze. Thus, if the requirement i8 for a 3~' electrode, the edges may be cut ` 20 off to eliminate the unevenly coated portion of the mesh.
`I Tablç I contains results of coverage of lead chloride coatings on a 4~", 28 mesh, .012 diameter copper wire gauze at a bath temperature of about 525 C.

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COVERAGE SPEED
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.61 62 Zi .52 55 i! .20 35 `,i; 30 .12 20 The fle~ible electrode material obtained as described above ; was examined to determinc its suitability for use in sea water batteries for . ! ' .

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~L~63670 sonobuoy~, nnd electrodes conta:Lni.ng a COfltillg of about 0.23 gmtcm were found to be capable of discharge for about 4-5 hours under conditions ppropriate to sonobuoy battery i~pplications. More heavily coated electrodes (i.e. about 0.6 gm/cm ) dischargecl for up to 20 hours at sonobuoy battery rates~
While lead chloride has been referred to as the coating material ernployed in the illustrated appara.us, it will be appreciated by those skilled in the art that other coating materials, such as cooper chloride, silver chloride or a mixture thereof with lead chloride, which melts without decomposition and whi~h has a melting point lower than that of the metal of the mesh, usually cooper, may be employedO

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Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A flexible electrode material, consisting of a mesh material selected from the group consisting of woven wire gauze, perforated sheet metal and expanded metal, and lead chloride supported on said mesh material.

2. Flexible electrode material according to claim 1, wherein the mesh material is woven copper wire gauze.

3. Flexible electrode material according to claim 2, wherein the gauze is 32-28 mesh and of 0.007 - 0.012 diameter copper wire.

4. Flexible electrode material according to claim 1, 2 or 3, wherein the amount of lead chloride supported on said mesh material is about 0.12 to about 0.6 gm/cm2.