DE1671939A1 - Plate electrode for accumulators - Google Patents

Description

. G. EICHENBERG _{4 DÖSSELDORF / den} ... 26 February J968.

DIPL-ING. H. SAUERLAND ckiuenauee η - ~~ "

DRYING. R. KING

PATENT LAWYERS

Mr. Friedrich. August Schneider, 12, Esdoornstraat, Nines, North Brabant, Netherlands

"Plate electrode for accumulators" %

The invention relates to the manufacture of plates for accumulators, in particular to the manufacture of thick negative cadmium plates for alkaline nickel-cadmium accumulators.

British patent 1 024 371 describes positive plates for alkaline nickel-cadmium cells, which are manufactured internally by Grandma using a galvanically produced and stretched nickel grid. The technique of (| stretching one made of thin sheet metal grid can be not only _for nickel but also applicable to other metals and in this respect is of greater importance.

The invention consists in the proposal to produce a plate on the basis of a stack of galvanically produced and stretched metal grids which are connected to one another in parallel and each of which has an adhering porous metal layer.

The gratings can aue each metal, which is stable in the electrolyte, for the di ·

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Electrode plate is to be used. After the hedge the grid is preferably coated with the metal of which it is made, to give the shape of the stretched one Fix the grid and give it greater rigidity. A plate according to the invention can by a Corresponding number of grids are brought to the desired thickness, the grids preferably with one another are connected and are in conductive connection with one another by welding at their edges.

The adhering porous metal layer should preferably be applied to the individual grids before the grids are connected to one another. If this does not happen, an electrode plate with a thickness of the porous metal layer that differs over its thickness cannot be produced, so that some of the advantages explained below are lost.

The tendency of the deposited metal to diffuse from the inside to the outside is reduced if the grids are made of a metal of high conductivity, so that there is a voltage equalization on the surface of each grid when current is drawn from the plate or is placed on the plate. This also means that the electrochemical reactions in the plates in take place at a greater depth.Tension compensation cannot be achieved in sintered plates,

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The specific conductivity differed between the compact ones Grid metal and the porous sintered layer is considerable and of the order of at least 10 s 1 «

The plate according to the invention also has a continuous double porosity. Large pores are formed in the plate by the pockets resulting from the stacking of the grids. In contrast, a fine porosity results within the porous metal layer which form the walls M of the large pores or pockets. The double-porous structure of the plate according to the invention allows the electrolyte to quickly penetrate into the large pores and from there into the fine pores of the porous metal layer. An electrochemical reaction takes place actively in the entire plate, ie in a labyrinth of large pores from which fine pores extend in all directions. Such double porosity also reduces the migration of the deposited metal since it allows electrochemical changes to a greater depth of the plate during charging and discharging than is possible in sintered plates with a simple fine-pore structure.

The grids on the inside of the plate preferably have a thicker layer deposited Metal, than the grid located further out, so that the layer thickness of the deposited metal from the inside out

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decreases on the outside. Such a reduction in layer thickness of the deposited metal to a large extent compensates for any possible metal migration from the inside to the outside, so that the risk of a complete removal of the deposited metal from the center of the plate is reduced or even completely eliminated will. As a result, the interior does not become inactive in the panel according to the invention, so that it has a long service life, i.e. has a high number of charge and discharge cycles.

Overall, the plate according to the invention has a better current distribution inside the plate, a reduced tendency of the active deposited metal to Hike and thus better charging and discharging characteristics as well as a longer service life or a greater number of charge and discharge cycles than conventional electrode plates.

The inventive method is suitable for the production of zinc plates, which are preferably zinc plated mesh, stretched nickel or other metal own, which is not attacked by the electrolyte, are provided for the zinc plates. In this pc-ile, zinc is deposited on the grid. Zinc can be added in the form of a porous layer from a solution of potassium zincate, for example from a solution of 25 to 30 g / l zinc oxide in 25% by weight aqueous potassium hydroxide

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Room temperature and a cathode current density of 1 A / dm are deposited. However, the method according to the invention is also suitable for the production of nickel plates, since a stretched nickel lattice can easily be sintered with nickel powder. Such nickel grids can be converted into grids with active nickel oxide, NiO (OH). In this way, nickel oxide electrodes can be made from a stack of activated grids. The porous sintered nickel layer is preferably converted into active nickel oxide by cathodic impregnation with nickel hydroxide from a concentrated nickel nitrate solution according to the McHenry process, which is followed by a charge and discharge cycle in concentrated potassium carbonate Iiö £ * LJig according to the Okinaka process * bin with respect to the nickel economical process is _# that a plurality of compliant nickel mesh coated with nickel powder, and are sintered at lower (temperature, for example 500 ° C. the gratings may then be connected to a Plätte, the temperature at a higher !!, for example, 700 ^ö C is sintered * This creates a solid nickel plate from which a nickel oxide electrode, for example duroh anodisetic oxidation, can be produced in a solution of sodium bicarbonate, which see a treatment in a solution of potassium carbonate according to the British patent application §5 980 / βΤ described procedure connects

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As already mentioned, the method according to the invention is particularly suitable for producing cadmium plates. In alkaline nickel-cadmium cells, pocketed plates are usually used as negative electrodes, which, like the Jungner cell, can be made from perforated steel strip coated with nickel and annealed in hydrogen. The pockets are filled with cadmium oxide CdO or cadmium hydroxide Cd (OH) ₂ , which is then electrolytically reduced to a metallic cadmium sponge. Such a plate, however, does not have the characteristics of a positive sintered plate, ie its service life or the number of charge and discharge cycles is significantly lower than that of a positive sintered plate To deposit cadmium on the inner pore surfaces of a porous body made of sintered copper. However, these attempts did not lead to complete success. The service life of such a plate is also shorter than that of a pocket plate of the same thickness, since there is greater migration of the cadmium metal with a corresponding loss of active surface.It is not possible to coat the porous part of the plate with cadmium in a satisfactory manner, so that it was consequently considered impossible "the electrochemical reaction

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to reverse a cell with such negative plates, without bringing copper into the electrolyte, which affects the performance of the cell. aside from that is the effect of the electrochemical reactions in the formation of active masses within the fine pores of a sintered plate, so that the plate has to be immersed many times in the various solutions to produce a Acceptable amount of Kad ™ precipitation required generate mium hydroxide. The production of such plates ^ is therefore associated with high costs.

In making a nickel-cadmium alkaline cell having a high capacity per unit volume of plate, thick plates should be used provided the cell is not required to have high discharge rates. A positive sintered plate made of nickel may be about 4 mm thick, but at a negative sintered plate of this thickness it is very difficult, the cadmium in the innermost Λ retaining zones lying. Large thickness negative cadmium plates according to the invention have properties, including a large number of charge-discharge cycles, which correspond wholly or substantially to the properties of large thickness positive plates made of sintered nickel.

A cadmium plate according to the invention is preferred made using a copper grid. A Electroplated copper sheet with a thickness of 30 to

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50 microns can be stretched to a uniform thickness of about 0.5 mm. Three of these sheets can then become one about 1 mm thick package can be combined. If the plate thickness is 4 mm, the package consists of 13 sheets of the aforementioned Thickness.

The metallic cadmium is preferably deposited on the stretched metal grids as cadmium black, advantageously following a galvanic coating with hard cadmium from a cyanide or fluoroborate bath. The subsequent deposition of cadmium sponge can be carried out by various known methods. For example, according to US Pat. No. 2,616,939, pasty cadmium oxide can be pressed into the gate, dried and then cathodically converted into cadmium sponge in a solution of potassium hydroxide. However, the grid can also be converted into an aqueous cathode under current as a cathode in accordance with the method according to British patent specification 1,061,463. Solution of cadmium chloride to be immersed. Finally, the grating can be immersed as a cathode in a solution of .Kadmiumsulfat, a current between the grid and a cadmium anode flows. It is important that any oxidation of the cadmium chwamma during washing and drying and a temperature increase above 80 to 90 ° C is avoided.

It is known that the simultaneous Nie- 009887/0466

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derschlagen a precipitate in the form of a cadmium-rich alloy of cadmium and certain other metals yields, the special benefits has "That prevents nickel content of cadmium sponge to 20 ° /> crystal growth, while very small amounts of other metals such as thallium, selenium and silver Increase the mobility of the cadmium ions in cadmium hydroxide and in this way allow a more extensive discharge of the plate. Each of these metals can be deposited from the metal in question together with the cadmium by adding appropriate metal ions to the electrolyte and using an additional anode, whereby the amount of deposited additional metal can easily be adjusted by choosing the currents given to the various anodes.

The construction of a plate from a stack of individual grids preferably takes place by pressing the grid edges together, for example spot welding the ™ Edges connects to establish electrical contact between the grids. The outer surfaces of the grid stack can be protected during pressing in that the stack is galvanically produced between two grooved Copper sheets with a thickness of 0.1 mm, for example, are arranged, which are, for example, 3 up to 5 microns thick cadmium layer are coated. A suitable grooved plate is, for example, under the designation

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Nung Veco No, 40/10 in the trade and has a free _: surface of 40 ^B />, a groove size of 0.32 χ 1.92 mm and a weight per unit area of 160 g / m .. The grooves are right-angled. and run zigzag in order not to unduly weaken the sheet metal

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coated sheet metal are larger on one side than on. the other side of the sheet. The grid stack is between. . see two such sheets arranged, each of which is arranged to _t, that the larger groove sides are outside · Subsequently, the individual layers of the, stack, welded together, so that the sheets ^ form an integral part of the plate ...

^ BI

Another method for
of the grid stack during pressing

flat a single thread Ghemiefasej £ gejWÄbjemüi £ ^^^

then to cover this with a fabric. The tissue with square meshes, and one that the free surface

for example square meshes with one edge length

of 2 mm and be made of a 0.25 mm thick wire , so that there is a frl & ift ^^^^ ffy

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The fabric should be slightly narrower than the grid while the wire mesh is the same size as the grids should, so that when pressing and welding the Stacking edges the wire mesh forms an integral part of the panel and the mesh is fully integrated with the panel is connected.

The porous cadmium layer of each grid should be protected in some way until the plate is used in a cell. This can be done by coating each grid with a polymer after its production and prior to welding to the other grids of the stack, which prevents oxidation of the porous layer, but is destroyed when the cell is started up. Suitable polymers are vinyl acetate-crotonic acid polymers which are wholly or partially neutralized with organic amines and are commercially available as aerosols in the form of hairspray. Such polymers need only to the ä prepared grating sprayed, and then to be dried; they are immediately removed from the grids in alkaline solution during the first charge-discharge cycle of the cell in alkaline solution.

The invention is described below using exemplary embodiments of the nearer explained.

Example 1 From three electroplated and stretched

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A 1 mm thick plate was made of copper grids. Each Grid was made by stretching a 30 to 50 micron thick sheet. ' After stretching, the distance was between the lattice tips about 0.4 mm. The stretched grid was plated with copper, the thickness of the sheet being up It grew 200 to 120 microns so that the total thickness was about 0.5 ρ. Each grid was made with a 3 to 5 mm thick layer of cadmium coated from a standard cyanide bath with 100 μl NaCN and 23 μl CdO and one Temperature of 25 ° C possessed. The grid was immersed in the bath and connected as cathode at a current density of 2 A / dm, based on the actual grid surface. Each grating was then made using the method described in British Patent 1,061,463 Covered with cadmium sponge. The weight of the coating the outer grid of the plate was 5 g / dm of the geometric surface and that of the inner ones Grids 7 »5 g / dm of the geometric surface. All in all was the weight of the deposited cadmium sponge 17.5 g / da · The three grids were then pressed together and connected at their edges by spot welding The plate produced in this way had a capacity of 3.5 Ah / dm.

Example 2
From thirteen stretched and after the

0 0 9 8 8 7/0 Λ 6 6

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In connection with the method described in Example 1, copper grids produced by electroplating, a 4 now thick plate was produced. The thickness of the cadmium sponge precipitate changed from the inside out, the weight of the precipitate on the central grid being 5 g / dm. Starting from the middle grid, the precipitation weights of the grids on both sides were 4j 3.5 $ 3> 5ϊ μ 3ί 2.5 and 2.5 g / dm with a total weight of the cadmium of the plate of 43 g

ο The capacity of the plate was 8 Ah / dm or

0.185 ampere hours per gram of cadmium sponge. Before the application of the cadmium sponge, the porosity of the 4 mm thick plate was 80 μ and was thus at least as great as that of the best sintered plates. ■

Example 3

Out of nine stretched and after the Λ

Example T described method electroplated copper grids, a 3 mm thick plate was made. The cadmium sponge was applied under modified conditions and contained $ 1.7 nickel. The bath was buffered with a borax buffer at a pH value of 6 and contained 62 g / l CdCl ₂ · Η ₂ 0, 90 g / l KOl, 12 g / l H ₃ BO ₃ , .0.5 g / l Na ₂ B ^ 0 "and 7" 2 g / l NiCl ₂ · 6Η ₂ 0. The bath temperature was 55 ⁰ C. The anode current was in a cadmium

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and split a nickel circuit. The ratio of the anodic cadmium current to the Niclcelstrom and the surface area of the cadmium anode to the surface area to the nickel anode was 4: 1. The cathode current density was 4 A / dm of the actual metal surface of the stretched and cadmium-coated copper grid. The total anode current thickness was 1 A / dm. After the galvanic coating, the sponge of the grids were lightly compressed between two plastic plates and the grids were then washed until the water from the water was free of chlorine ions. The cleaned grids were then immediately placed in a drying oven at 80 ° 0. The dried grids were cooled to room temperature and immediately carefully sprayed with a high quality hairspray. The deposit of cadmium sponge on the nine grids changed from the outside to the inside in such a way that it was 1 »3, 4, 5, 5, 5, 4, 3 and 1 g / dm ² in the order of the grids.

The sides of the stack of nine grids were covered with Veco 40/10 j then became the Stack galvanically coated with cadmium in the manner already described and in a lorm to a 3 mm thick Plate with strongly pressed edges, pressed by spot welding were connected to each other »

The plate produced in this way contained 31 g / dm cadmium sponge and possessed when discharged for 5 hours

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a capacity of 10 A / dm or 0.33 ampere-hours per gram of cadmium. These values are, inter alia, about 50 i "conventional above the corresponding values impregnated with cadmium sintered plates.

Example 4

A 3 mm thick plate was produced from nine stretched copper grids produced by electroplating using the method described in Example 1. The grids were coated with cadmium according to the procedure described in Example 3.

The stack, consisting of nine grids, was first covered on both sides with a single-thread nylon fabric, each 5 mm narrower than the stacking surfaces. The mesh size of the square mesh was 330 microns, the thickness of the nylon thread was 136 microns, and the open surface of the nylon fabric was 47 i »*

Finally, both sides of the stack were each with a cadmium-coated copper wire mesh, the dimensions of which corresponded to the stack dimensions. The mesh width of the square mesh was 2 mm, the wire diameter 0.25 mm and the thickness of the cadmium coating 4 microns. The proportion of the free area of the copper wire mesh was 745t

The entire stack was then pressed into a 3 mm thick plate, as in connection with Example 3

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described, the plate dimensions, the. Content of Cadmium sponge and the capacity of the precast board are the same Achieved values like the plate described in Example 3. The capacity of the plate was 10.7 A / dm or 0.34 ampere hours per gram of cadmium sponge.

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Claims (1)

¹ , sheet Mr. Friedrich. August Schneider, 12, Esdoornstraat, Nines, North Brabant, Netherlands Patent claims: Plate electrode for accumulators, especially negative Λ Cadmium plate electrode for alkaline nickel-cadmium cells, characterized, that they are galvanically produced from a stack and stretched, conductively connected to one another in parallel Metal grid, the ^ edes of which with a firmly adhering porous layer of electrodeposited metal is provided. β plate according to claim 1, characterized in that the grids are made of zinc-coated expanded nickel and the coating is made of zinc. 5. Plate according to claim 1, characterized in that the grids are made of nickel and are plated with nickel. Plate according to Claim 1, characterized in that that the grids are made of nickel and have a firmly adhering porous coating of nickel, which consists at least partially of active nickel oxide. 0 9 8 8 7/0466 .. Sheet 5. Plate according to claim 1, characterized that the grids with cadmium or a cadmium-rich alloy are coated 6β plate according to claim 5 »characterized thereby η e t that the grids with a cadmium-rich »nickel, thallium, selenium or silver containing Le- Are coated with alloy «. 7. Plate according to claims 5 or 6, characterized
characterized in that the electroplated grids are made of copper 8. Plate according to claims 5 to 7, characterized in that the grid stack between two cadmium-coated and grooved copper sheets is arranged. 9 · Plate according to claims 5 to 7 »characterized in that the grid stack is arranged between single-thread synthetic fiber fabric pieces
which are cadmium-coated copper wire mesh. 10. Plate according to claims 1 to 9 »characterized in that the grid with one out
a protective layer which is made of a polymer and which can be destroyed during operation of the cell. 009887/0466