Electrode for electrochemical cells

p0001The invention relates to an electrode for electrochemical cells, in particular negative electrode for rechargeable batteries, in particular lead batteries, consisting of a grid plate, which serves as a carrier for the active material and the current supply and discharge.

p0002It is known that an electrochemical energy store, which is also referred to as an electrochemical cell of three basic components, namely the active masses, grids for receiving and holding the active materials and an electrolyte located between the grating. In general, the positive and negative grids are still separated from each other by separators.

p0003The grid plate in the electrochemical cell is used both as a bulk carrier and for guiding the electron current in the charging and discharging reactions in the active masses. The electron current is delivered during the discharge to a consumer and is supplied to the active materials on the grid plates during charging from a power source.

p0004It is already known to produce grid plates in particular for the negative electrodes of lead accumulators of metal. The production of grid plates takes place usually by casting of lead, or also through the use of expanded copper metal which is subsequently coated with lead-tin and / or lead (DE-A 33 12 550).

p0005A problem with the known grid plates is that they are relatively heavy and that the realizable grid forms by the casting process or the preparation of expanded copper metal are limited.

p0006To reduce the amount of lead in batteries, it is already known (DE-C 27 16 131) to use a plastic mesh as a base for the grid plate and on to arrange a fan-shaped structure made of lead wires, which is connected by heating the plastic grid. Here, then, the functions of the carrier material for the active material and the power line on two different components of the grid plate are distributed, resulting in a complicated production and low efficiency. It is further known (US-PS 3,607,412) to coat a conventionally constructed, flat plastic mesh by spraying molten lead and to thereby render it conductive.

p0007A general problem with the use of plastic grids as grid plate is that generally even sufficient and on the surface evenly distributed electrical conductivity is given when a metal coating is present, and the absorption capacity of the active material is limited. Further, the distances between the active mass of the conductive parts of the grid plate are often so large that the efficiency is insufficient. The mechanical attachment of the active material is unsatisfactory.

p0008The aim of the invention is therefore to provide an electrode of the aforementioned type, which is particularly economical to manufacture, has a low weight as possible, in a variety of well complicated shapes can be produced and has a particularly good electrochemical efficiency, with a good and electrically effective mounting of the active material is to be ensured.

p0009To achieve this object the invention is based on a trained as a plastic network grid plate, the plastic network preferably consists of a highly conductive thin metal layer, in particular of copper coated plastic threads and to form a three-dimensional structure with preferably produced by thermoforming, distributed over its surface, hump-like depressions and / or elevations is provided, is increased in the region of which the distance between the plastic threads. Such, particularly suitable for the purposes of the present invention plastic networks are described in the simultaneously filed Shared patent application and HOECHST AG entitled "Electrodes for galvanic primary and secondary elements". (DE-A 39 22 425).

p0010To achieve the above object is provided according to the present invention is that the plastic network with at least one further coating of a lead-tin alloy or lead is plated and in at least one intended for the uptake of the active storage area where a plurality of recesses and / or elevations is, and is divided into at least one Stromleitbereich where the plastic network has a flat, two-dimensional structure. It is advantageous if the plastic network in the storage area at all points is preferably largely moved in two dimensions at the same rate substantially, while it is non-coated in Stromleitbereich. Further, it is advantageous if in the storage area only the plastic threads of the lead-tin alloy or lead are coated and the mesh openings remain free, while in the Stromleitbereichen the mesh between the plastic threads of the lead-tin alloy or lead are filled. The inventive idea is thus to be seen in, thereby embodying an image formed from plastic threads plastics network in an optimal manner as the negative electrode, in particular a lead-acid battery that serves primarily the inclusion of the active mass, through a three-dimensional filigree structure having storage areas, which additionally also is divided nor the waste and feed the streams of the active material or the active material used, and current conducting, which are preferably arranged suitably distributed between the memory areas and are due to the close-meshed and the shorter current paths particularly suited to the current directing from the storage areas to connecting tab or from the terminal lug to the storage areas in low-resistance manner possible. Due to the close-meshed the plastic net structure in the Stromleitbereichen the mesh of the plastic network with lead-tin or lead are filled there, which is for the purpose of low-resistance possible power line important. On the other hand, the mesh in the storage areas are preferably continuous so far that there only the plastic thread coated with lead-tin or lead, while the meshes remain free itself. Thus, the active material can not only between the walls of the depressions or elevations, but also in the remaining open mesh firmly anchor, and there is a large surface for the current transition of the active material in the grid plate and vice versa available.

p0011At most could still remain smaller non-covered areas that affect the mount and power feed of the active material does not appreciably between puckered elevations and depressions.

p0012A particularly good current conduction is obtained when the plastic threads consist in particular of a plurality of relatively fluffy adjacent thin monofilaments made of synthetic material, so that, because of coating of these monofilaments with the well conducting metal, in particular copper has a large metal surface area and therefore a relatively large cross-section is created for the Stromleitbahnen. Further, in this way, the liquid lead / tin or lead penetrate into the interstices between the many monofilaments of plastic fibers and there also contribute to the creation of the largest possible current conducting metal cross-section. In addition, the lead / tin or lead is particularly well-rooted in the plastic network.

p0013The plastic threads can be connected either by weaving or by other techniques to a plastic network. Next several each consisting of many monofilaments yarns may be twisted together or entangled, wherein the application of the highly conductive metal layer is carried out only after completion of the plastic net structure including recesses and / or elevations.

p0014A ever smaller diameter monofilaments used in the plastic threads and the more monofilaments are provided per plastic threads, an even greater surface is the recording of the highly conductive metal layer and also for the installation of lead / tin or lead in the spaces available.

p0015Since plastics have a much lower specific gravity than metals, the grid plate according to the invention is characterized by a particularly low weight.

p0016Nevertheless Stromleit- and electrochemical properties are superior to those of conventional grids because of formed by many monofilaments polymer threads existing networks can be particularly finely designed and thus is a particularly large effective surface for application of metal coatings. As can be plastic networks in any way deformed bend also from the flat training derogation or otherwise, the grid plate according to the invention can be implemented in any desired shape and be configured for example in the form of a coil.

p0017The coating of the plastic thread with the highly conductive thin metal layer is preferably carried out by first example, a metal film of copper in a thickness of 0.5 to 2 microns is applied, and then an electrolytic copper plating is performed until a metal coating of 1 to 200, in particular 5 to 100 and preferably 10 to 50 microns is present. As material for the Kunststöffäden can be advantageously used polyester, wherein the plastic network is expediently dimensionally stabilized by means of thermal or thermosets. For this is, in particular phenolic resin and acrylic resin.

p0018An advantageous embodiment of the inventive electrode characterized in that the further coating of a lead-cadmium selenium-arsenic-antimony alloy, in particular a lead-tin alloy with preferably 20 to 90% lead, more preferably about 80 to 90% lead (is characterized Rest tin), which preferably has a thickness of 5 to 20, more preferably about 10 .mu.m, if yet another lead coating is applied, and a thickness of 30 to 150 microns, preferably 40 to 60 .mu.m, in particular 50 microns has, if only one layer is applied from a lead-tin alloy.

p0019it if is applied to the highly conductive metal layer or preferably onto the further coating is a lead layer having a thickness of preferably 30 to 70, in particular 40 to 60 and preferably about 50 microns is particularly advantageous. Of the further coatings to be applied by electroplating at least the first.

p0020The galvanic coating of the plastic network is advantageous because in this case the plastic does not undergo heating which might entail a melting or even decomposition by itself.

p0021but it is also possible that at least one and preferably the last applied of the further coatings by immersion in a molten bath of the coating metal, in particular, the immersion times the network is while in the molten bath are so short that the melting point of the plastic material, from which the plastic network is made is not exceeded. The temperature of the molten bath thereby to 400 to 700 ° K, in particular 500 to 600 ° C and the immersion time 1-4, be particularly 1 to 2 sec.. It is also possible that already galvanically briefly immersed with a highly conductive metal plated plastic network in a lead or lead-tin alloy melt, provided that the immersion times are sufficient short. The highly conductive metal layer in this case acts advantageously as a heat conductor.

p0022A preferred development of the invention is that prior to applying the further coating, the coated with the well conducting metal grid plate in a cleaning bath preferably comprising an aqueous solution of citric acid, which is in particular 20% strength to saturated, there is, is subjected to a cleaning process. The residence time in the cleaning is expected to reach 2 to 10 and especially 4 to 8 and preferably 5 sec.. The cleaning bath is in the range of 250 ° to 350 °, in particular 290 ° to 320 °, and preferably at about 300 ° K. The use of a cooled cleaning bath is particularly advantageous because this excessive heating of the plastic network is counteracted in a subsequent coating in the melt.

p0023At least on the side of the grid plate, where the power loss occurs, should be provided a Stromleitbereich. It is preferred if the terminal lug of the grid plate is designed as Stromleitbereich. In particular, the running around the grid plate around the edge region can be formed as Stromleitbereich.

p0024Advantageously, street-like extending current conducting located between island-arranged storage areas. From the site, in particular corner of the grid plate, where the connecting lug is arranged to extend to the opposite corner, a diagonal Stromleitbereich. In this way it is achieved that the current conducting zones are distributed over the surface of the grid plate that are guaranteed from and to all memory areas of particularly low-resistance current supply or discharge lines.

p0025The preparation of the electrode according to the invention or of formed therefrom disk sets can be particularly economical that several grids are formed as a continuous band which is folded into a disk set.

p0026Due to the use of a deformable easily plastic network as a grid plate may consist in a further embodiment that the plastic network edge preferably by 90 ° from the plane of the plate and in particular alternately in one or other direction perpendicular bent to faces mass supporting webs which expediently about as far from the plate plane as the depressions or elevations rise and also represent current conducting. By mass supporting webs which seated in the wells or on the increases active composition can laterally be kept particularly low from below and from above.

p0027Further, it is advantageous if the current conducting zones are at least partially formed groove- or channel-shaped, the longitudinal direction of the grooves or channels is substantially in the current flow direction, and that the grooves or channels are at least partially filled with the lead-tin alloy or lead or filled with active mass. In this way, the metallic cross section of the current conducting zones is increased, and thus the resistance is further decreased.

p0028Another embodiment is configured such that a plurality are provided by current conducting separate memory areas and all current conducting zones are directly related to each other. This simplifies the manufacture of the electrodes in a continuous process churning is made possible.

p0029The invention is described in the following example with reference to the drawing; This shows:<dl id="dl0001"><dt>Fig. 1</dt><dd>a schematic plan view of an electrode according to the invention,</dd><dt>FIG. 2</dt><dd>a highly schematic enlarged section along line II-II in Fig. 1,</dd><dt>Fig. 3</dt><dd>an enlarged schematic section along line III-III in Fig. 1 a provided with a groove-like Stromleitbereich electrode,</dd><dt>Fig. 4</dt><dd>a magnified image of the area IV in FIG. 2,</dd><dt>Fig. 5</dt><dd>an enlarged plan view of a part of the electrode in the memory area,</dd><dt>Fig. 6</dt><dd>a corresponding plan view in Stromleitbereich,</dd><dt>Fig. 7</dt><dd>a highly schematic production apparatus for an electrode according to the invention,</dd><dt>Fig. 8</dt><dd>a further advantageous embodiment of such Herstellungsvorrichtun, </dd><dt>Fig. 9</dt><dd>a perspective view of the combination of an electrode with separator,</dd><dt>Fig. 10</dt><dd>a schematic perspective view of the combination of FIG. 9 gestelltem in ready condition</dd><dt>Fig. 11</dt><dd>a plan view of electrodes configured as a coherent tape according to the invention and</dd><dt>Fig. 12</dt><dd>a perspective view of a deformed to a disk set electrode band to FIG. 11.</dd></dl>

p0030According to FIG. 1 to 6 a grid plate 11 of the invention consists of a preferably woven or braided plastic network whose individual plastic threads 13 of FIG. 4 to 6 of a plurality of monofilaments 13 'persists, which is coated with a thin copper layer of a few microns thick are. It may be connected by braiding or twisting to größerern elongated structures with each other in each case several, for example three plastic threads (Fig. 4). The totality of the monofilaments 13 'of a plastic filament 13 is twisted expedient. In this synthetic threads 13 is a lead or lead-tin alloy coating 24 (Fig. 4, 5) of 40 to 60 microns is applied. The coating 24 penetrates expedient the plastic threads 13 or penetrates at least superficially in this one, so that as large a current interface between the coating 24 and the copper coatings of the monofilaments 13 'is achieved.

p0031Referring to FIGS. 1 and 2, the grid plate 11 of the invention has, for example by deep drawing of Kunststoffnetzwer kes or the plastic threads 13 partially out of the plane of the grid plate 11 alternately to one side and out the other side formed hump-like depressions 32 and elevations 33, which in Figure . 1 2 shown only schematically as circles and in Fig. greatly exaggerated and schematic and together form the memory areas 12, where later the active material is housed. In between and on the edge located in the plane of the grid plate 11 and shown in Figure 1 and 2 at 35 upward or downward bent current conducting 14, are arranged so closely within which the adjacent plastic threads 13 that -. Can be seen from Fig. 6 is - the mesh between the plastic threads 13 are so small that the force applied to the plastic threads 13 lead-tin or lead layer 24 also fills the meshes of the plastic network.

p0032Whereas the periodic and selective removal of the plastic threads 13 or the plastic network out of the plane of the grid plate 11 in particular in FIG. 2 the electrical resistance according to the achieved thereby extending the plastic thread 13 and the creation of metal-free spaces 34 in the mesh (Fig. 5) increases, the electrical resistance in the Stromleitbereichen 14 remains low, said to reduce the resistance in the Stromleitbereichen 14 also contributes the filling of the meshes with lead-tin or lead.

p0033there the gaps 34 in the mesh (Fig. 5) Due to the deep-drawing process to create the depressions 32 and elevations 33 are increased so that an applied example, the dipping process lead coating 24 only the plastic threads 13 covers, the interstices 34, however, does not fill. This benefits a fixed mechanical support of the later introduced active mass of the plastic network. For the good retention of the active material further the wells 32 and the responsible increases 33 bordering the ground except for the side facing away from the plate plane side practically everywhere. The width of the elevations 33 and the depressions 32 in the range of 3 to 10 mm, especially 4 to 6 mm. The depth of the elevations 33 and depressions 32 is 1 to 5 mm, in particular 2 to 3 mm. The ratio of width to depth is in the range 2: 1:. 1 to 3 In this respect, the depth of the ridges 33 and the grooves 32 in FIG. 2 for reasons of clarity of the inventive concept is shown exaggerated. Of particular importance is that the adjacent elevations 33 and recesses 32 adjoin one another, such that the plastic network has moved two-dimensionally in the border areas of neighboring elevations 33 and depressions 32 and are present there, the enlarged interstices 34th Through the alternation of warped in opposite directions increases 33 and recesses 32 is a particularly suitable for absorption of large amounts of active material, a particularly good mechanical attachment of the active material and for a short-way power dissipation from the respectively current injection into the active mass grid plate 11 created.

p0034Also, the bending of the edges of the grid plate 35 of FIG. 1 and 2, alternately on one side and the other side due to a good support of the later introduced active mass from the edge of the grid plate 11 ago.

p0035The storage areas 12 each comprise a wide variety of immediately adjacent elevations 33 and depressions 32 between which no two-dimensional current conducting zones are preferably present. The current conducting 14 are rather merely present at some or all limits of storage areas 12th All current conducting 14 are directly related, so that from any point of a Stromleitbereiches 14 at least one additional current conducting only takes 14 containing current path for connecting lug 15th

p0036As is apparent from FIG. 1, the storage spaces 12 as large as possible arranged like islands within the relatively narrow current conducting 14 such that there are between the individual storage areas 12 each narrow street like current conducting 14 which are all connected, so that a flawless and low-resistance power line is guaranteed to and from the terminal lug 15th Overall, the storage areas 12 and the current conducting zones 14 are distributed over the surface of the grid plate 11, that on the one hand the greatest possible storage capacity for the active material is ensured, on the other hand sufficiently low resistance current conducting lead of the individual memory areas 12 to terminal lug 15, which is also just , that is, formed as Stromleitbereich.

p0037If the terminal lug 15 arranged as shown in FIG. 1 in a corner of the grid plate 11, so to lead 14 to the opposite corner 16 a straight and diagonally extending Stromleitbereich. A corresponding arrangement is also advantageous if the terminal lug 15 is moved slightly more towards the center of the grid plate 11 back.

p0038According to FIG. 3, the street-like current conducting 14 may be groove-shaped and is poured, for example, lead 23, whereby the electrical conductivity is increased in these areas. Instead, the channel 14 to pour with lead, it can be completed in accordance with active mass.

p0039According to FIG. 7, the production of the electrode plate according to the invention can economically take place in that an already deformed and copper-plated plastic network 11 'in strip form is successively passed continuously through a cleaning bath 19, a galvanic lead-Zinnlegierungsbad 20 and a galvanic lead bath 21st Via electrically conductive rollers 25, which will be the result of a negative voltage while the tape 11 'negatively charged. In cooperation with an existing in the baths lying at positive potential electrode 26 as a deposition of a lead-tin alloy in the bath 20 and of lead in the bath 21 is ensured on the belt 11 '. The light emerging from galvanic lead bath 21 band is thus provided with a copper layer, a lead-tin alloy layer and a layer of lead.

p0040According to FIG. 8, the copper-plated and already with the storage areas 12 and the Stromleitbereichen 14 provided band 11 "passed by carrying through the cleaning bath 19 and the galvanic lead-tin alloy bath 20 by a lead melt 22. The arranged in the melt refractory deflecting 27 is in this case relatively near the surface of molten lead 22 so that the tape 11 'only very briefly dips into the molten lead 22nd In this manner, melting or even decomposition of the synthetic threads of the plastic network 11 'effectively avoided.

p0041To 'to avoid excessive heating of the ribbon 11 in the molten lead 22, the guide roller 27 may be according to the invention also cooled by, for example, a cooling liquid is passed through schematically indicated axial Kühlkänale 28 of deflecting 27th

p0042Further, it is expedient if immediately 11 takes place following the exchange of the grid plate from the molten bath, cooling of the grid plate 11 and the belt 11 '. This can be 8, for example, be done by a provided with cooling channels 31 cooling roll 30 is used for the deflection of the tape 11 'of FIG..

p0043It is not absolutely necessary to provide a galvanic pre-coating of the network shown in FIGS. 7 and 8 after cleaning. A more economical and faster production can be realized in that takes place immediately after cleaning the brief immersion of the grid plate 11 and the belt 11 'into the molten lead 22 (Fig. 8).

p0044For the plastic material not harmful lead covering of the grid plate (in the melt) the lead temperature, dwell time and the subsequent cooling is decisive.

p0045According to FIG. 9, the grid plate 11 may be provided via two living hinges 29 with two equal-area separator 17, which practically made of the same, but not metal coated plastic network as the grid plate 11. In order to be of sufficient thickness for the separator 17 ensure they can be deformed in total in a manner similar to the grid plate 11 in the memory areas 12th

p0046By around flap of the separator 17 to the folding hinges 29 in the direction of arrows in Fig. 9, the arrangement can be brought in from FIG. 10 position shown, so that with one and the same plastic network an overall arrangement of a negative electrode forming grid plate 11, and two disposed on opposite sides of said separator plates grating plate 11 is realized 27th It is also conceivable to produce a folded bag from two separator and adjust in this case a tie plate separately manufactured 11th

p0047According to FIG. 11 as one piece, for example, by the manufacturing method according to FIG. 7 or 8 numerous grids inventive band-11 are produced. After production then more of the band-contiguous grid plates 11 cut and folded according to FIG. 12 to a set of plates 18, the individual plates are on the hinges in fluid communication so that only at one or both ends of connecting lugs 15 must be present.

p0048It is essential that the preparation of the lattice plate is made for use in an accumulator formed by coating lead-tin or lead only if the already is already present with the Stromleitbereichen 14 and the storage areas 12 preformed and with copper plated polymer network structure.

p0049The geometric grid structure is no longer limited by casting technology limits or by the prescribed forms of expanded metals when applying the inventive method. The inventive method does not allow the production of previously impossible structures.

p0050The mechanical adhesion of the active materials on the grid plates is a known problem in the production of electrodes for rechargeable batteries. The properties of the above described electrodes according to the invention are so far improved in this respect, as by the use of a large number of through the plastic threads or fibers formed thin grid webs instead of fewer thicker webs in conventional grids greatly increases the contact area between the grid and the active material is. As the grid bars formed by the plastic threads and in particular all monofilaments contained therein are thoroughly coated with copper, thus the electrical conductivity is also influenced. Further, the utilization of the active material in the electrode of the invention is significantly improved.

p0051For the advantages of the electrode of the invention, inter alia, the close basic mesh size of typical plastic lattice structure networks is decisive, which is greatly increased in the region of the depressions 32 and elevations 33rd

p0052Except an aqueous citric acid solution, aqueous solutions of other hydroxycarboxylic acids may be used for the cleaning. The immersion time in the cleaning bath is preferably 2 to 10 sec ..

p0053After cleaning, adhering to the grid plate residues of cleaning bath still should be removed by means of compressed air. The complete removal of residues of the cleaning bath prior to coating with lead-tin or lead is therefore important in order to obtain a complete and continuous coating in the subsequent step.

p0054If a relatively brittle active material is used, the recesses 32 and projections 33 are narrower than when a more viscous mass is applied.

p0055The active material may for example be applied by rollers on both sides of the electrode of the invention. It all depends on the mixture evenly over all depressions and elevations as well as possibly. To distribute in the gutters of the current conducting zones. For leveling and compaction of the active material, an ultrasonic irradiation to be applied, which leads to a liquefaction of the ground and thus to a verbeserten flow process. If the mass is relatively low viscosity and / or is irradiated by ultrasound, can also be a one-sided application, in which case the mass occurs to the other side through the mesh of the storage areas throughout.

p0056As active material, all producible with a pasty or unctuous consistency compositions are suitable. Particularly in the production of electrodes for lead-acid batteries can be carried out with a basic mass density of 3 to 5.7 g / ml. The paste can be coated here, either by hand or machine. To improve weight distribution, the use of ultrasound for temporary liquefaction of the ground is possible.

p0057In particular, in dense networks is a double-sided pasting advantageous in order to achieve a complete wrapping of all network parts. Furthermore, a complete coating of a dense network by using more liquid mixtures and subsequent pressing with an absorbent non-woven material which will be used later in the finished cell as an acid reservoir, done.

p0058The elevations 33 and depressions 32 may, according to circumstance have different shapes, for example, the shape of cones or truncated cones, pyramids or truncated pyramids having different polygonal bases, cylinders, prisms, spherical segments, etc. It is particularly preferred, even if the vertices or - all surfaces of the elevations lie in a plane and parallel to the base surface, which, mutatis mutandis, also applies to the wells.