FI63501C - ELEKTRISK ACKUMULATORCELL MED MINST EN LOESNINGSELEKTROD - Google Patents

Description

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Sweden-Sweden (SE) 7508111-7 (71) Aktiebolaget Tudor, S-172 8l Sundbyberg, Sweden-Sweden (SE) (72) Otto von Krusenstierna, Stockholm, Mats Reger, Äkersberga,

Sweden-Sweden (SE) (7 * 0 Oy Borenius & Co Ab (5 * 0 Electric battery cell with at least one soluble electrode -Elektrisk ac accumulatorcell med minst en lösningselektrod

The invention relates to an electric battery cell having at least one soluble electrode containing a metal which, on discharge, forms a chemical compound soluble in the electrolyte, and a body carrying this metal, an insoluble substantially inert material having at least one central conductive layer and at least one an outer layer which is so much smaller than the central layer that there is a free edge around the entire circumference of this central layer, whereby all the layers are perforated or otherwise punctured. In addition to this, of course, the cell contains other components necessary for its operation, i.e. counter-electrodes, electrolyte and separators, etc. The invention also relates to cells in which the chemical compound formed during discharge is actually soluble in the electrolyte used, but which therefore immediately precipitates as a solid compound. Such special conditions may be, for example, supersaturation of the electrolyte or the addition of other substances which with metal approx

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2 63501 form compounds which are insoluble in the electrolyte. For example, the invention can be applied quite successfully to battery cells with zinc electrodes. These, as a result of the discharge in the basic electrolyte, form compounds which are soluble in the electrolyte. However, the electrolyte may supersaturate, causing the zinc released from the electrode during discharge to precipitate in the electrolyte as solid zinc oxide. The chemical reactions that occur with the discharge of different soluble electrodes in different electrolytes are not fully known. The above and the following have therefore disregarded certain short-lived intermediate reaction products which may be formed in connection with chemical reactions.

An essential problem with cells with soluble electrodes is to achieve a satisfactory cell life. This is mainly related to the conditions that prevail when charging discharged electrodes. The active material of the soluble electrodes then tends to form dendrites which grow from the electrode towards the counter electrode and then easily cause a short circuit. When the active material precipitates again, some edge phenomena, so-called "Shaping" phenomena. This results in the layer of active material tending to grow thicker mainly at the outer edges of the electrode than at other points on the electrode. Various experiments have been carried out to solve this problem, which have also led to an improvement in the service life of the cells, although satisfactory results have still not been obtained. The measures taken have in many cases led to more complex and thus more expensive cell structures, and have also imposed requirements such as electrolyte concentration and other conditions in the cell that have limited the usefulness of the cells and also resulted in expensive cells. The object of the invention is therefore to solve this problem and to develop a cell with a satisfactory service life by means of structural measures which do not restrict the usability of the cell and which also make these cells more economically competitive than previously known structures.

The structure of the soluble electrode in such a cell will be quite essential. It has surprisingly been found that by constructing the electrodes according to the invention in such a way that they have a multilayer body, a fairly reproducible electrode can be obtained, in addition to eliminating or almost completely eliminating the tendency to "shaping" the dendritic formation by combining such a cell structure. to avoid, a cell with very good life characteristics is obtained.

It is already known to form soluble electrodes on a body which is a material other than an electrochemically active material. It is also known to use such bodies which are permeable to the electrolyte and have an even larger active surface area. The ability to penetrate the electrolyte is achieved either by using perforated plates or by assembling the body from a fibrous material, e.g. a wire mesh. In order to achieve a larger active surface of the body, this body has, for example, been proposed to be made of a plate, which can be pressed or stamped so that a number of protrusions and recesses are formed on its surface. Another way to achieve an uneven surface is to use a sheet metal that is different in thickness at different points. In a body assembled from fibers, these fibers may be arranged, e.g., to form a woven network, or that the fibers are located in a disordered manner, such as in a mat of a nonwoven type. A body of the latter type can be made thicker than the final thickness, after which the body is mechanically compressed so as to increase its strength while maintaining a large active surface. The most commonly used method to prevent the detrimental effects of dendritic formation is to surround the soluble electrode with a separator that is so dense that dendrites cannot penetrate it. The use of such dense separators, of course, limits the electrochemical properties of the cell and thus its usefulness. It has also been found that the service life of such separators is not long enough to achieve the required service life of the cell 4 63501. The use of such separators thus allows limited growth of the dendrites, which is thus stopped by a solid wall. Another way to limit growth is to make scrapers or similar devices in the cell that move along the surface of the soluble electrode and scrape off the protruding dendrites. Instead of such scratching members, e.g., rollers can be used, which can be made so that the protruding dendrites do not tear off the electrode, but only become pressed onto this electrode, so that they can still act as an active material. Stationary scratching members or other mechanical devices and electrodes movable relative thereto may also be used. However, it has been shown that the requirements for cells cannot be fully met in this way either. Finally, it has also been proposed to vibrate the soluble electrodes and / or separators or spacers. The formation of dendrites is prevented by the effect of the turbulence which then develops in the electrolyte closest to the surface of the electrode.

In the cell according to the invention, the soluble electrode is assembled mainly on a body of inert insoluble material, the body having at least one central conductive layer and at least one other layer on both sides thereof. All of these layers are suitably pierced or otherwise punctured. By "inert" in this context is meant that the body does not act as an active material in the electrochemical reactions of the cell. However, such a material alone is not a frame according to the invention, but the invention is characterized in that part of the free edge width of the central layer is surrounded by an edge rim of electrically insulating material, the distance between the inner rim and the outer layer Thus, in addition to both sides of the central body, at least one layer is required, which must be a separate layer and thus must not be directly connected to the entire surface of the central layer. The central layer may suitably be a perforated metal sheet or a metal wire fabric. Such a layer may also be a non-conductive material with a conductive surface layer, e.g. a metal-coated plastic. The additional layer may be the same material as the 5 63501 central layer or another material. These additional layers are suitably made of metal mesh or metal-coated plastic. They can also be made of plastic mesh without any other surface coating, which, however, requires that the active material of the electrode as such has sufficient electrical conductivity. The outer layers are suitably joined together by welding, soldering or some other means, these joints being point-like and made through openings in the central layer. Direct mechanical joining between the central layer and the outer layers shall be avoided or at least limited to a number of points located along only one edge. This mainly depends on the fact that otherwise it is difficult to make the frames completely flat during manufacture. It has also been found that the cells according to the invention make it possible to eliminate the "shaping" phenomenon in a surprisingly simple manner, since the dimension of the outer layers in the electrode plane is smaller than the dimension of the central layer, leaving the edges of this central layer free. In addition, a portion of the free edge must be surrounded by an electrically insulating material so that the conductive surface of the soluble electrode becomes slightly smaller than the conductive surface of the counter electrode. Surfaces in this context refer to the geometric surfaces projected, without taking into account the size of the electrochemically active surface, which, as mentioned above, can be affected by corrugations, perforations or other means. The free edge of the central layer must be so wide that the distance between the insulating material and the outer layers is at least twice the thickness of the outer layers. It has been found that by subjecting the soluble electrodes in the cell according to the invention or the separators or spacers adjacent thereto to an oscillating movement in a plane parallel to the plane of the electrode, very favorable operating conditions of the cell are achieved. Since the oscillation frequency must be relatively high, the oscillating component must be placed in the vertical guide grooves. All electrodes are suitably placed in such guide grooves, it being noted that the insulating material at the outer edge of the central layer must extend beyond the guide groove so that the surface of the soluble electrode 6 63501 is smaller than the surface of the counter electrode. Due to the conditions prevailing in the cell, a very good reproducibility of the charge discharge cycle and a long cell life are thus achieved. This is especially true if the body is dimensioned in such a way that the active material contained in the soluble electrode does not completely cover the openings in the outer layer of the body when the cell is fully charged.

The invention will be explained in the following on the basis of the accompanying figures. In this connection, the advantageous effects which can be achieved thanks to the invention will also be explained in more detail. In particular, a preferred embodiment of the invention will be described, especially in connection with a zinc electrode, since the invention is expected to achieve its main application in cells equipped with such electrodes.

Figure 1 shows a cell according to the invention in section.

Fig. 2 shows a soluble electrode suitable for use in this cell, pa Fig. 3 shows a section of this electrode.

Figure 4 shows some parts of the electrodes in the cell according to the invention and a part of the plate provided with a grooving groove.

Figure 1 shows a section perpendicular to the electrodes of the cell. The cell has a number of soluble electrodes 1 and counter-electrodes and 2. Between these there are separators or spacer members 3. The soluble electrodes are connected to each other by connectors 4 so as to form a common bridge 5. The soluble electrodes are arranged to vibrate so that the shaft 6 is mounted on the cell. to the bearings 8 in the wall. The shaft is made a crankshaft, and the movements are transmitted to the electrodes by means of a yoke 7 and suspension and connection devices 18, 19. The shaft is electrically isolated from the electrodes, e.g. so that the connecting devices are made of an electrically insulating material. The electrodes are connected to the outer pole pin 10 by means of a flexible conductor 17. The counter electrodes are connected to the pole pin 11, but these connections are not shown in the figure because they are of a completely conventional construction.

The electrode shown in Figures 2 and 3 has a body assembled on the central layer 13. The layer 13 is a plate with perforations 21. Attached to this plate are outer layers with a mesh 14 * one 7 63501 mesh on each side of the central plate. The two nets, which may be metal, plastic or metal-coated plastic, are attached to each other by welding or gluing. The fastening is done in dots, and the fastening seams penetrate the perforations in the plate 21.

In this way, the three layers of the body are kept together as a unit, without a fixed mechanical connection between the outer layers and the central layer. Along the outer edge of the board there is an electrically insulating layer, which may be, for example, a U-profile of suitable plastic, or an insulating lacquer layer. The dimension of the nets is so much smaller than the dimension of the board that a free edge is formed in the board between the outer edge of the nets and the insulating layer, the dimension of which must be at least twice the thickness of the nets.

Fig. 4 shows a number of soluble electrodes 1 and counter electrodes 2, the second vertical side of which is arranged in the guide grooves 32 in the plate 51. For the sake of clarity, only some parts of the electrodes are shown. The complete cell has two plates with guide rollers, one on each side of the electrode array. The guide grooves can also be part of the cell wall. It can be seen from the figure that the insulating layer on the outer edge of the soluble electrode extends to the electrode to such an extent that this layer also covers a small part of the electrode outside the guide groove. In this way, the soluble electrodes have a slightly narrower and smaller electrochemically active surface than the counter electrodes. This can also be achieved due to the special design of the plate 31 with guide grooves, which, however, leads to technical difficulties.

An electrode according to the invention was made of perforated iron plate. The plate was 0.5 mm thick, 200 mm high and 140 mm wide. Circular holes with a diameter of 6 mm and a number of such that the free surface was about 50 # were punched into the plate. A nickel-plated wire mesh with a wire thickness of 0.5 mm and a distance between wires of about 2 mm was placed on both sides of the plate. These nets were 185 mm high and 125 mm wide and were centrally located on both sides of the plate. Thus, a 7.5 mm wide free edge was formed around the plate. The nets were attached to each other by welding them together through some perforations in the plate. The number of welding points was 20. The joint 4 was attached to the frame, after which the outer edge of the plate was insulated to a width of 5 mm on both sides by brushing the insulating varnish. The mesh loops were filled to about 50% with an active material suitable for zinc electrodes β '63501, after which the electrodes were placed in a cell vessel together with counter-electrodes, which were conventional "type" nickel electrodes. Separators were placed between the electrodes, that the edges of the electrode were covered up to the dashed line 22. The cell electrolyte was, as usual, an aqueous solution of potassium hydroxide with conventional additives.

An electrode body was prepared as described above, but no active material was placed. The body was placed in a cell vessel with counter electrodes and vibrated. The cell vessel contained 6 moles of potassium hydroxide and 100 g of zinc oxide per liter as electrolyte. The cell thus obtained was charged with a current of 15 A, whereupon zinc was found to precipitate on the electrode body. In this case, it turned out that in the initial stage, a zinc coating was formed only on the plate inside the mesh loops. A certain cover also formed on the free edge outside the net. Hydrogen gas was found to develop to some extent near the nets, but no zinc coating was formed. After about 15 minutes, the coating also began to form on the nets. However, this cover was quite thin on the front of the net and had no protruding dendrites. A zinc coating was also formed along the edge, which, however, was not larger in size than the coating in the nets, and no protruding dendrites were formed near the edges.

A cell having four soluble electrodes and nickel oxide type counter electrodes of conventional construction was prepared as described above. These counter electrodes were dimensioned so that in order to achieve a corresponding capacity on the soluble electrodes, so much active material was precipitated that approximately half of the volume of the mesh loops was filled with zinc. This cell was charged and discharged several times according to the prescribed diagram. Thus, during each such charging and discharging cycle, the active layer of the soluble electrode dissolves completely or partially and re-forms. The properties of the capped cells of the invention were still essentially unchanged after 800 cycles.

As can be seen from the previous examples, a surprising increase in service life has been achieved with the cells according to the invention. This is because the formation of dendrites in the electrodes is avoided, and that the electrodes

Claims (5)

9 The "shaping" phenomenon at the edges is removed. The claims An electric battery cell having at least one soluble electrode containing a metal which, upon discharge, forms a chemical compound soluble in the electrolyte, and a body carrying this metal, an insoluble substantially inert material having at least one central conductive layer (13) and on both sides thereof. at least one outer layer (14) so much smaller than the central layer that there is a free edge around the entire circumference of this central layer, all layers being routed material, netting, etc., characterized in that part of the width of the free edge of the central layer is electrically insulating surrounded by an edge rim (15) of material, wherein the distance between the inner edge of the rim and the outer edge of the outer layer is at least twice the thickness of the outer layer. A cell according to claim 1, characterized in that the outer layers are connected to each other by welding, soldering or in some other way, the joints being point-like and penetrating the openings in the central layer. Cell according to Claim 1 or 2, characterized in that the central layer is a routed plate of iron or steel and in that the outer layer is a mesh of the same material or plastic, in which case all the layers can be nickel-plated. 1. Electric accumulator cells with a minimum of one or more electrodes in the metal and an electrolyte in the form of a single core of a metal or an electrode