DE1671939B2 - DOUBLE POROUS PLATE ELECTRODE FOR ACCUMULATORS, IN PARTICULAR FOR ALKALINE NICKEL-CADMIUM ACCUMULATORS - Google Patents

Description

The invention relates to a double-porous plate electrode for accumulators, in particular for the production of thick negative cadmium plates for alkaline nickel-cadmium batteries.

An accumulator cell with plate electrodes is known from German patent specification 899 214, whose positive electrode consists of a porous metal foil, in whose surface pores nickel or Cobalt hydroxide is embedded and its negative electrode is made of zinc foil with enlarged fine pores Surface in the form of a porous zinc layer. Furthermore are from the French patent specification 1 348 135 and British Patent 1024 371 plate electrodes for alkaline nickel-cadmium cells known that by re-sintering a galvanically generated and stretched metal lattice, in particular a nickel grid.

ίο Furthermore, in the French patent specification 350 098 describes a method for producing accumulator plates, in which a thin layer of an active material on a conductive support, for example a metal mesh or a perforated metal foil is deposited. Finally, there are also double-pore electrodes and Carrier known; for example, in Swiss patent specification 278 111, a carrier made of a pore-containing, load-bearing gross skeleton described, its components mechanically at their points of contact are firmly connected and whose pores are at least partially covered with a fine-pored, electrically conductive fine skeleton are filled. British patent 848 706 refers to it to a method for producing double-pore electrodes in which externally fused particles applied in two superimposed layers of different densities on a carrier will.

Based on the aforementioned prior art, the invention consists in a double-pore structure Plate electrode, which is made from a stack of galvanically produced and stretched, conductive in parallel interconnected metal grids, each with a firmly adhering porous layer made of electroplated metal and their double porosity due to the stacking pockets created by the lattice and the fine pores located within the porous metal layer is.

The grid can consist of any metal that is stable in the electrolyte for the the electrode plate is to be used. After stretching, the lattice preferably becomes with that Plated metal of which it is itself made to define the shape of the stretched lattice and to give it greater rigidity. A plate according to the invention can be replaced by a corresponding Number of grids can be brought to the desired thickness, the grids preferably with one another are connected and are in a conductive connection to one another by welding at their edges. The adherent porous metal layer should preferably be applied prior to joining the grids together can be applied to the individual grids. If this does not happen, no electrode plate can be left over make their thickness of different thickness of the porous metal layer, so some explained below Advantages are lost.

The tendency of the deposited metal to diffuse from the inside out is then reduced, if the grids are made of a metal of high conductivity, so that a voltage equalization on the surface of each grid when electricity is drawn from the plate or applied to the plate will. This also means that the electrochemical reactions in the plates are greater Depth take place. A tension equalization can be

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cannot be achieved in sintered plates, since the analysis according to the McHenry process is in active Nikschied the specific conductivity between the keloxid converted, which is a loading and uncompacting Lattice metal and the porous sinter-charging cycle in a concentrated potassium carbonate dissolving layer is considerable and of the order of magnitude of the Okinaka process. A of at least 10: 1. 5 more economical process with regard to nickel

The plate according to the invention further consists in that several expanded nickel grids with a continuous double porosity. Large pores are coated with nickel powder and at a low temperature in the plate through which the door is sintered when the door is stacked, for example 500 ° C. The lattice-yielding pockets are formed. A fine porous lattice can then be connected to form a plate, on the other hand, within the porous media, which is sintered at a higher temperature of, for example, the walls of the large pores or sometimes 700 ° C. This creates a form of seeing. The double-porous structure of the nickel plate, which is solid according to the invention, allows the electrolyte to penetrate rapidly, for example by anodic oxidation, into the large pores and from these into the pores of the porous metal layer made from a solution of sodium bicarbonate. 15 who can undergo a treatment in a solution An electrochemical reaction takes place actively in that of potassium carbonate,
entire plate, ie in a labyrinth of large po- As already mentioned, the invention is suitable instead, from which fine pores extend in all moderate methods, in particular for producing directions. Such a double porosi cadmium plate. Alkaline nickel-cadmium also reduces the migration of the deposited metal cells, since they use electrochemical changes in plates as negative electrodes, which, like a greater depth of the plate during charging in the Jungner cell, also reduce the migration of the deposited metal. made of perforated steel strip and unloading is permitted, as this can be done in sintered plates, which can be coated with nickel with a simple, fine-pored structure and annealed in hydrogen. The bags will be is. 25 with cadmium oxide CdO or cadmium hydroxide

Preferably, the inside of the plate have Cd (OH) ₂ filled, which is then electrolytically closed

a thicker layer of metallic cadmium sponge is deposited on the lattice,

metal than the grids further out. Such a plate, however, does not have the cha-

that the layer thickness of the never-beaten metal characteristics of a positive sintered plate, d. i.e., their life

decreases from the inside out. Such a duration or the number of charging and discharging cycles

reduction of the layer thickness of the deposited clink is considerably less than that of a positive

Metal compensates to a large extent for any possible ven sintered plate. Numerous attempts are made

Metal wall from the inside reveals the outside, so that the represents to negative sintered plates by cutting off

Risk of complete removal of the deposited thin layer of metallic cadmium

Metal from the center of the plate or the inner pore surfaces of a porous body

is completely eliminated. As a result, sintered copper is deposited with the invention. This ver

according to the plate, the interior is not inactive, so that searches did not lead to complete success,

they have a long service life, d. H. a high number The life of such a plate is also

of charge and discharge cycle. lower than that of one with a pocket plate

Overall, the plate according to the invention has a 40 ben thickness, since a thicker wall of the Kad-

better current distribution inside the plate, a vermiummetalls with a corresponding loss

decreased inclination of the active precipitated me- more active surface results. It is not possible that

tails to hike and thus a better loading-porous part of the plate with cadmium in satisfied-

and discharge characteristics, as well as a greater number of places to coat, so that it accordingly

longevity or a larger number of charging and 45 was considered impossible, the electrochemical reaction

Discharge cycles than usual electrode plates. a cell with such negative plates.

The inventive method is suitable for sweeping without bringing copper into the electrolyte, the manufacture of zinc plates, preferably thereby reducing cell performance made of zinc-plated, expanded nickel or tigt. Also, the effect of the electrochemical one have another metal that is produced by the elec- trical reactions in the formation of active masses Trolyte is not attacked for the zinc plat- within the fine pores of a sintered plate th are provided. In this case it will be on the low, so that the plate many times in the different grids Zinc deposited. Zinc can be immersed in the form of a solution that has to be immersed in order to be partially porous Layer of a solution of potassium zincate, acceptable amount of precipitation required for example from a solution of 25 to 30 g / l 55 of cadmium hydroxide. The production Zinc oxide in 25 per cent by weight of aqueous caustic plates of this type is therefore lithium hydroxide at high cost at room temperature and one cathode.

the current density of 1 A / dir ^{2 can be} deposited. In the production of an alkaline nickel cad- The method according to the invention is, however, also suitable for the production of nickel plates with a high capacity per unit volume, since thick plates should be used, provided that the nickel lattice is slightly re-sintered with nickel powder, that the cell cannot become highly discharged. Such nickel grids may have to have in grids. A positive sintered plate made from nickel converted with active nickel oxide, NiO (OH), can be about 4 mm thick, with a negative one. In this way, nickel oxide electro-sintered plates of this thickness are very difficult to get the cadmium in the innermost zones made from a stack of activated grids. The porous sintered nickel layer is held back. Negative cadmium plates large, preferably by cathodic i impregnation with Nik thickness according to the invention have properties kelhydroxid from a concentrated nickel nitrate solution including a large number of charge-discharge

Cycles which wholly or essentially correspond to the properties of positive plates of great thickness made of sintered Nickel match.

A cadmium plate according to the invention is preferably made using a copper grid. An electroplated copper sheet with a thickness of 30 to 50 microns can be applied to a uniform Thickness of about 0.5 mm can be stretched. Three of these sheets can then be about 1 mm thick package. If the panel thickness is 4 mm, the package consists of 13 sheets of the aforementioned thickness.

The metallic cadmium is preferably used as a cadmium sponge on the stretched metal grids deposited, advantageously following a galvanic coating with hard cadmium a cyanide or fluoroborate bath. The subsequent deposition of cadmium sponge can be done by various known methods. For example, according to the USA 2 616 939 pasty cadmium oxide pressed into the grid, dried and then cathodically in a solution of potassium hydroxide can be converted into cadmium sponge. However, the grid can also under current as cathode according to the method according to the British patent specification 1,061,463 are immersed in an aqueous solution of cadmium chloride. Finally, the grid can be immersed as a cathode in a solution of cadmium sulfate, with a current flowing between the grid and a cadmium anode flows. It is important that any oxidation of the cadmium sponge Avoided during washing and drying and a temperature increase above 80 to 90 ° C will.

It is known that when cadmium and certain others Metals a deposit in the form of a cadmium-rich alloy results, which has particular advantages owns. A nickel content of up to 20% in the cadmium sponge prevents crystal growth while very small amounts of other metals, such as thallium, selenium and silver, reduce the mobility of cadmium ions in cadmium hydroxide, thus allowing the plate to continue unloading. Each of these metals can be combined with the cadmium by adding appropriate metal ions for the electrolyte and using an additional anode from the metal in question The amount of additional metal deposited can be easily changed by choosing the one on the various Currents given to anodes can be adjusted.

The construction of a plate from a stack of individual grids is preferably carried out by pressing the grid edges together, followed by spot welding of the edges, for example, in order to establish electrical contact between the grids. The outer surfaces of the grid stack can be protected during pressing by placing the stack between two grooved electroplated copper sheets with a thickness of 0.1 mm, for example, which are coated with a cadmium layer, for example 3 to 5 microns thick. A suitable grooved plate has, for example, a free surface of 40%, a groove size of 0.32 × 1.92 mm and a weight per unit area of 160 g / m ² . The grooves are arranged at right angles and run in a zigzag shape so as not to unduly weaken the sheet metal. Electroplating is done by depositing cadmium from an electrode on only one side of the sheet so that the grooves in the coated sheet are larger on one side than on the other side of the sheet. The grid stack is arranged between two such sheets, each of which is arranged so that the larger groove sides

ίο lie outside. Then the individual Layers of the stack are welded together so that the sheets are an integral part of the Form plate.

Another method of protecting the outer surfaces of the lattice stack during pressing is to to apply a single-thread synthetic fiber fabric to each surface and then with a Covering cadmium-coated copper wire mesh. The fabric can be made of nylon, for example with square meshes with a mesh width of 330 microns and a thread thickness of 44 Microns so that the free surface area is 46%. The wire mesh can, for example, be square Have meshes with an edge length of 2 mm and consist of a 0.25 mm thick wire, so that there is a free surface of 74%.

The mesh should be slightly narrower than the grids, while the wire mesh should be the same size as should have the grid, so that when the stack edges are pressed and welded together, the Wire mesh forms an integral part of the plate and the mesh forms an integral part of the plate 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 in that each grid after its manufacture and is coated with a polymer prior to welding to the remaining grids of the stack, which oxidation of the porous layer is prevented, but is destroyed when the cell is started up. Suitable Polymers are vinyl acetate-crotonic acid polymers that are wholly or partially with organic amines are neutralized and sold as aerosols in the form of hairspray. Such polymers need just to be sprayed onto the prepared grids and then dried; you will be in alkaline solution during the first charge-discharge cycle immediately removed from the grids of the cell in alkaline solution.

The invention is explained in more detail below on the basis of exemplary embodiments.

example 1

A 1 mm thick plate was made from three electroplated and stretched copper grids. Each grid was made by stretching a 30 to 50 micron thick sheet. After this Stretching, the distance between the lattice peaks was about 0.4 mm. The stretched grid was with Copper plated, the thickness of the sheet increasing to 200 to 120 microns, making the total thickness was about 0.5 mm. Each grid was covered with a 3 to 5 mm thick layer of cadmium Standard cyanide bath coated with 100 g / l NaCN and 23 g / l CdO and a temperature of 25 ° C. The grid was immersed in the bath and at

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a current density of 2 A / dm ² , based on the tat- washed until the wash water is free of chlorine ions neuter grid surface, connected as the cathode. was. The cleaned grids were then immediately placed in a drying oven at 80 ° C. Each grid was then placed in the UK. The processes described in patent specification 1061463 with dried grids were provided with a coating of cadmium sponge at room temperature. 5 cools and immediately carefully sprayed with a high-quality hairspray. The cadmium precipitation on the plate was 5 g / dm ^2. The geometric upper sponge on the nine grids changed from the surface and in the inner grids 7.5 g / dm ² outside in such a way that it was in the Reider geometric surface . In total, the order of the grids was 1, 3, 4, 5, 5, 5, 4, 3 and 1 g / dm ^{2. The} weight of the deposited cadmium sponge was 10.

17.5 g / dm ^2. The three grids were then pressed together. The sides of the stave consisting of nine grids and pels were connected at their edges with the above-described grooved plate. The plate produced in this way covers; then the stack in which it already possessed a capacity of 3.5 Ah / dm ² . described way galvanically with cadmium over-. 15 pulled and pressed in a form to form a 3 mm thick plate Example Z _{with strongly verpre} ß _th edges that through

From thirteen stretched and after being joined together in spot welding,

In connection with the procedure described in Example 1, the plate produced in this way contained 31

vanisch produced copper grids was a 4 mm g / dm ² cadmium sponge and possessed at 5 hours

thick plate made. The thickness of the precipitate ao discharge has a capacity of 10 A / dm ² or 0.33

from cadmium sponge changed from the inside to ampere-hours per gram of cadmium. These values

outside, with the weight of the precipitation on the lying around 50% above the corresponding value

average grid was 5 g / dm ² . Starting from the ten conventional sin-

The middle grids were the rainfall weights of the plates.

the grid 4 lying on both sides; 3.5; 3.5; 3; 35 Example 4
2.5 and 2.5 g / dm ² with a total weight of the

Cadmium of the plate of 43 g. Out of nine stretched and after the

The capacity of the plate was 8 Ah / dm ² or the method described in Example 1 galvanically

0.185 ampere-hours per gram of cadmium-provided copper grids became 3 mm thick

sponge. The porosity of the 4 mm thick plate is established. The grilles were after the

carried out procedures with cadmium described in Example 3 prior to application of the cadmium sponge

80%> and was thus at least as large as in the case of the overdrawn.

best sintered plates. The stack consisting of nine grids was

Example 3 next on both sides with a single thread

35 meshes of nylon covered, each by 5 mm

Out of nine stretched and after which in the frame it was narrower than the stacking areas. The mesh example 1, galvanically expanding the square mesh was 330 meshes Copper mesh has a 3 mm thick crown, the thickness of nylon thread 136 microns, and Plate made. The cadmium sponge was un- the open surface of the nylon fabric was enclosed Applied under modified conditions and 40 47 ° / o.

held 1.7 per cent nickel. The bath was filled with a Bo- Finally, both sides of the stack were buffered with rax buffer each at a pH value of 6 and a cadmium-coated copper wire mesh contained 62 g / l CdCl ₂ -H ₂ O, 90 g / l KCl, 12 g / l covers, the dimensions of which corresponded to the stack dimensions H ₃ BO ₃ , 0.5 g / l Na ₂ B ₄ O ₇ and 7.2 g / l NiCl ₂ · 6 H ₂ O. The mesh size of the square meshes. The bath temperature was 55 ° C. The anode current 45 was 2 mm, the wire diameter 0.25 mm and the thickness of the cadmium coating was 4 microns in a cadmium and a nickel current. The circle divided. The ratio of the anodic proportion of the free area of the copper wire mesh to the nickel current and the surface area was 74 per cent.

the cadmium anode to the surface to the nickel- The entire stack then became a 3mm anode was 4: 1. The cathode current density was 50 thick pressed plate, as described in connection with 4 A / dm ^{2 of} the actual metal surface of Example 3, the plate dimensions being unstretched and cadmium-coated copper mesh, the cadmium sponge content and the hangover. The total anode current density was 1 A / dm ² . The same values as the plate described in Example 3 were achieved after electroplating. The capacity of the grating between two plastic plates was 10.7 A / dm ² or 0.34 A slightly compacted and the grating was then per hour per gram of cadmium sponge.

Claims (10)

Patent claims: 1. Double-porous plate electrode for accumulators, characterized in that that they are galvanically produced from a stack and stretched, in parallel connection with one another conductive connected metal grid, each of which is made with a firmly adhering porous layer electroplated metal is provided and the double porosity due to the stacking pockets created by the grid and the fine ones located within the porous metal layer Pores is formed. 2. Plate electrode according to claim 1, characterized in that the thickness of the porous Layer of electrodeposited metal from the grid inside the plate decreases in the direction of the outer grid. 3. Plate electrode according to claim 1 or 2, characterized in that the porous metal layer consists of cadmium or a cadmium-rich alloy. 4. Plate electrode according to claim 3, characterized in that the cadmium-rich alloy Contains nickel, thallium, selenium or silver. 5. Plate electrode according to claim 3 or 4, characterized in that the galvanically produced Grids are made of copper. 6. Plate electrode according to claims 3 to 5, characterized in that the grid stack arranged between two cadmium-coated and grooved copper sheets is. 7. plate electrode according to claims 3 to 5, characterized in that the grid stack is arranged between single-thread synthetic fiber fabric pieces on which cadmium-coated Copper wire mesh. 8. plate electrode according to claim 1, characterized in that its grid with zinc coated nickel and the coating is made of zinc. 9. Plate electrode according to claim 1, characterized in that its grids are made of nickel and are plated with nickel. 10. Plate electrode according to claim 1, characterized in that the grids are made of nickel and have an adherent, porous coating of nickel, some of which is active Nickel oxide consists.