US 3542600 A
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N ov. 24; 1970 "nu 5 v 3 2- R.POHLMANN 3,542,600, METHOD OF FILLING POROUS ELECTRODE MATRIX'ES WITH Nv.V 2 4,v 1970 R, PQHLMA 3,542,600 METHOD oF FILLING RoU LEC o MATRIxEs WITH l AC'IIV ILL MATER L v Filed Sept. l. 1966 v `2 Sheets-Sheet 2 I t ".llulllh Fig. 3
INVENTOR RE/MA? POHL MAN/V WM j ' AT ORNEYS United States Patent O 3,542,600 METHOD F FILLING POROUS ELECTRODE MATRIXES WITH ACTIVE FILLING MATERIAL Reimar Pohlmann, Darmstadt, Germany, assignor to Varta Aktiengesellschaft, Frankfurt am Main, Germany Filed Sept. 1, 1966, Ser. No. 576,745 Claims priority, application Germany, Sept. Z5, 1965,
V 29,398 Int. Cl. H01m 13/00 U.S. Cl. 136--120 12 Claims 'Ihere are certain difficulties encountered in filling porous electrode matrixes, such as sinter plates, for use in electro-chemical equipment such as batteries and fuel cells because of the Ifine-grained, active filling materials used. Heretofore, the filling was usually done by precipitating the material in the pores of the electrode matrixes, followed by subsequent wash-out of the by-products produced by this process, or by mixing the powder of matrix material and active mass followed by pressing, sintering and pre-treating.
It has been found that the infiuence of ultrasonic energy accelerates diffusion through semi-permeable diaphragms, cell walls, etc. This has been used, for instance, to apply higher amounts of color solutions to textiles or to apply antibacteria agents into wood. All these processes are conditional to true solutions. However, with dispersed materails, those which do not go into solution, only the reverse process has been known to work. -For example, to clean dirty filters completely and rapidly by using ultrasonics, usually only the dispersed substance is removed from the porous body. I have discovered that the reverse process can be used to solve the problems of filling porous electrode matrixes with active material.
The present invention relates to a method which not only simplifies and speeds .up the filling process remarkably, but permits use of a larger amount of filling material than ever before. Briefly, this is done by first laying a thin, even layer of a pasty mixture of the filling material over an ultrasonic oscillator, then placing the electrode matrix upon the pasty layer, and then covering over the matrix with the filling paste while subjecting the system to ultrasonic pressures. It becomes evident that the viscosity of the mixture within the ultrasonic field is substantially lessened because the pasty mass, While showing a remarkable separation of fluid, flows very slightly. Within the range of effect of the ultrasonic lfield, however, the dispersed substance has a tendency to sink down, as the fiuid rises. It is therefore advantageous to treat the porous matrix from the top.
On the other hand, because it is necessary that the means for coupling the ultrasonic energy does not have a too high ultrasonic absorption, it is advisable to keep the applied paste layer between the ultrasonic oscillator and the porous matrix as thin as possible. The consistency of the paste should not be too high because drying of the lower layer, caused by the heat from the ultrasonic energy source, should be prevented. The pasty consistency of the upper mass layer covering the matrix may be substantially higher because the ultrasonic absorption does not interfere here and it is important to bring as little fluid as possible into the pores. The thickness of the entire layer should preferably be so proportioned as to meet the porosity requirements of the matrix. This means, after penetration of the pasty substance, the thickness of the remaining substance should `be close to zero.
The filling method practiced according to this invention may be utilized for all generally known and successfully used electrode matrixes, i.e., metallic or synthetic sinter plates, metallized sinter plates, or plates of fiber material which were obtained by sintering, pressing or Patented Nov. 24, 1970 ICC other methods. In many cases, especially in those of nonpenetrating pores, complete filling may not be possible as the air may, at best, pass only partly out of the pores. It is therefore of advantage to perform the treatment at least part of the time in a vacuum. The vacuum is preferably developed before the ultrasonic treatment starts so that the filling material finds already vacuumized pores at the very start of the ultrasonic oscillations. If the Vacuum is then gradually reduced within the next 30 to 60 seconds, the increasing pressure aids the press-in effect of the ultrasonic oscillations and thereby not only achieves remarkably higher filling amounts, but also results in noticeable time-saving of the filling-process.
The grain-size of the active mass filling-material should be as fine as possible, at least eq-ually fine to the capillarydimensions of the porous electrode matrix. However, a large amount of fluid will still be pressed into the matrix. It is therefore desirable to replace the volume of the fluid as much as possible with active massjIn the present invention, the ultrasonic treatment is therefore continued until a temperature is reached at which at least part of the fluid vaporizes during the treatment. This results in a bakingin of the pasty mass into the internals of the matrix. The process may be additionally aided by using a vacuum. The vaporizing may be still further accelerated by choosing a fluid with a high vapor-pressure, for instance, lower alcohols, as ether or acetone. The chemical properties of the fluid should naturally match the ones of the filling material.
To obtain, as far as possible, a fool-proof, repeatable and complete ultrasonic treatment, it is advisable to press the porous electrode matrix and the pasty mass applied thereon to the ultrasonic oscillator. The pressing-on should preferably be performed by a body whose oscillation resistance is Very different from that of the paste, for example, a dry wood-block, In this case, the ultrasonic oscillations do not penetrate the pressure block, but are reflected back into the treatment area and increase the effect. Instead of a wood pressure block, other Inaterials such as steel or copper can be used. As the oscillation resistance of wood is substantially lower, the oscillation resistance of the above cited metals is substantially higher than that of the pasty filling material. In both cases, a substantial reflection of the ultrasonic oscillations will be effected at the pressure block. Metal has proved especially sutiable because it has excellent heat-conductivity, which is necessary if a liquid vehicle is added to make the active filling material more easily spread. The Viscosity of such a vehicle can be said to grow with increasing temperature, which again leads to substantial difiiculties in filling the pores at higher heat degrees. So in particular when liquid vehicles are used, it is recommended that the ultrasonic oscillator be cooled as effectively as possible and also the lower layer, the pressure block and consequently, the upper layer. A substantial heat-up would then only be likely in the porous electrode matrix itself, which might even be desired in the final state of the filling process for vaporizing the fluid from the electrode matrix. Switching off the cooling system near the end of the filling process also aids the vaporizing.
An especially sutiable design of the pressure block is to provide it with holes, grooves and channels on its pressing side, to encourage the fiuids tendency to flow from the area of treatment'to the pressure body. If certain precautions are overlooked, the intensive ultrasonic treatment and the pressure may have the unpleasant result of tightly baking together the oscillator, the paste, the electrode matrix and the pressure block so that upon removal of the pressure block, a substantial amount of the active filling material is torn from the pores, or the electrode matrix may even be damaged. This may be prevented by taking the precaution of covering the pressing side of the block with an anti-adhesive to prevent the baking-on. An especially effective prevention method is to place a thin foil of material, such as plastic, between the filling material and the pressure block. Thus, the pressure block is easily lifted off the foil and the foil itself may be removed by simply pulling it off. In the same sense that in the process according to this invention it is preferable to use a pressure block which is penetrable by the fluid, a foil should be used which likewise can be penetrated by the fiuid.
The filled electrode matrix is taken out by sliding the plate parallel to the surface of the working ultrasonic oscillator. The upper side of the electrode may be cleaned by a spring-stripper.
EXAMPLE A porous electrode matrix, for example, a sinter-plate of nickel or synthetic powder or a fiber plate should be filled with electro-chemically active mass, like Cd mass. The mass is pulverized to microparts of 1 micron to 10 microns and mixed homogeneously with the respective fluid until a paste having a consistency of ready-to-spread soft butter is formed. If the electrode matrix has a thickness of about 2 mm., the applied layer on the ultrasonic oscillators should not be thicker than 2 to 3 mm. The ultrasonic oscillator should be well cooled, for the content of fiuid in the mass and therefore the consistency of the lower layer should not alter after the application of the paste. Then the matrix is layed on the layer and covered with a 3 to 4 mm. layer of paste. Subsequently this upper layer is covered with a perforated thin synthetic foil, the pressure body put on, and the air eventually removed by a vacuum pump. After reaching the vacuum limit, the pressure body will be pressed on by about 0.15 kp./cm.2 and the ultrasonic oscillator is switched on. Shortly after turning on the oscillator, the vacuum is gradually decreased until a atmospheric pressure is reached. The whole filling process takes about 10 minutes Without application of a vacuum, and 5 minutes with application of the vacuum. After the filling process is completed, which, for example, may be controlled by the extent to which particles flow off With the fluid, the pressure body is lifted up and the synthetic foil is removed. The ultrasonic oscillator now carries the pasty active mass, in which the electrode matrix is embedded, filled with very dry mass. This cake itself is intimately connected with the ultrasonic oscillator. The filled electrode matrix is picked up by a gripping device and slid along parallel to the oscillator surface after the ultrasonic oscillator has been put into operation again, and at the same time the layer on top of the matrix will be removed by a scraper. The process of removal is now possible, as the frictional force between the tightly baked together substances decreases in the order of magnitude during the start of the ultrasonics and the filled matrix slides relatively easy on the oscillator during the ultrasonic oscillation, even if previously tightly baked together with the oscillator. After a finishing drying, the electrodes are ready to be assembled. To visualize this method, the accompanying drawings show in schematic form the operation of equipment designed for filling porous electrode matrixes with active materials wherein:
FIG. 1 shows the overall basic construction of the equipment;
FIG. 2 illustrates the steps of the filling process; and
FIG. 3 shows the filling method utilizing a vacuum.
In FIG. 1, a stable table 1 contains a water tank 2, with the ultrasonic oscillators 3 immersed. These may be welded to a carrier plate 4 and surrounded by cooling water 5, which fiows in through feeder pipe 6 and out through exit pipe 7. The oscillators are started by the high frequency input line 8 at a frequency which may, for example, range between 10 and 60 kilocycles. The car- Iier plate 4 is first covered by a layer of active mass 9 which is as near as possible to uniform thickness. Over the bottom layer 9 is the porous electrode matrix 10, which is covered over with a thicker layer 11 of active mass. A thin synthetic foil 12, with perforations 22, is laid between layer 11 and a pressure block 13. Pressure block 13 has grooves 21 on its bottom surface to allow the fluid to drain off easier.
FIGS. 2a and 2b illustrate a manner of charging the equipment and FIG. 2c illustrates a manner of removing the filled electrode matrix. A`V pipe or tube 14 is installed above the filling space and is moved by a sliding device which is arranged vertically to the tube axis and slides over the filling space. The tube has slits, holes and nozzles, through which the active mass may be fed by a pump (not shown). The carrier plate 4 has a free, bright reflection area for the ultrasonic oscillators 3. The paste 16 is applied through tube 14 is spread uniformly by a solid lug 17, whose inclination may be set by an adjustable arresting device 18. If, for instance, the tube 14 is moved in the direction of arrow 40, lug 17 is pushed against by arresting device 18 and provides a layer 9 of uniform thickness on the oscillator surface. After this is performed, the tube 14 is located at the right side of the filling space. Next the porous electrode matrix 10 is laid upon the layer 9 and the filling tube 14 slides from right to left while feeding paste in the manner illustrated in FIG. 2b. The lug 17 is positioned by a second adjustable arresting device 18 which is suitably adjusted to obtain the desired thickness of layer 11 over the electrode matrix. In the final state, the filling tube is again at the left side of the filling space, such as shown in FIG. 2c, and whereby some of the surplus paste may be slid over the edge of the filling space into the drip channel 19 (FIG. l) by lug 17 and may then fiow through the pump 20 back into the supply container.
Afterwards, as earlier described, the perforated foil 12 is applied to the top of layer 11 and the pressure block 13 is pushed down by hydraulic means or a spring tension device or something similar and the ultrasonic oscillator is switched on. The active filling material is substantially liquefied and penetrates through the pores of the electrode matrix. The effect shows mainly a transfer of filling material from the bottom to the top, resulting in a separation of fiuid on top of the layer. For this very reason, the thickness of the top layer is chosen somewhat greater than the lower layer and the pressure body 13 is provided with drain channels 21 to collect the fiuid which passes through the perforation 22 in the foil 12. The perforations 22 should be large enough to allow the fluid to pass through yet small enough so that the smallest particles in the pasty filling material are unable to pass through.
The duration of ultrasonic treatment depends upon the consistency and the like of pasty mass chosen, and may last anywhere from about 20 seconds to 15 minutes. After the ultrasonic oscillator is turned off, the pressure body 13 is lifted up and the foil 12 pulled off. The layers are now substantially shrunken, forming a tightly baked cake containing in its inside the filled electrode matrix.
The removal of the matrix follows somewhat according to the illustration in FIG. 2c, whereby a third arresting device 18", which may be an altered device 18 of FIG. 2a, adjusts lug 17 to a vertical position so that it is just over the left edge of oscillator plate 4. A locking device 23 on the right side of the filling space is raised against the force of spring 24, until the bottom edge 41 reaches the upper surface of the electrode matrix 10. The ultrasonics are switched on again and the lug 17 and tube 14 are moved from left to right again. As a result of the renewed operation of the ultrasonics, the adhesion between the oscillator and the electrode matrix is substantially lessened, so a speedy pull-out of the matrix 10 is now possible. The remainder of the upper layer 11 is also removed by the bottom edge of the locking device 23. The surplus amount of the mass drips into 25 and may be fed back to the supply container.
FIG. 3 illustrates schematically the manner of working using a vacuum, which may be preferred. Since the basic construction and functions are the same asin FIGS. 1 and 2, similar parts are numbered the same as in FIGS. 1 and 2. The filling process, however, is performed under the vacuum bell jar 26, which is raised and lowered by a roller conveyor 27, supported on a pillar 28 which moves by means of counter-weight 29. Before the vacuum bell jar 26 is lowered, the filling space is loaded. Then the vacuum bell jar 26 is pulled down by grasping puller 30, and pressed tightly on its rubber gaskets 31 to plate 4. By applying a vacuum in the pipe line 32 a powerful suction strength is created. After a short treatment by vacuum has vented the pores of the porous electrode matrix, especially those pores which do not entirely penetrate the matrix, the pressure cylinder 33 is fed through inlet 34 with oil or air pressure which forces piston 35 down on the pressure block 24 to the desired pressure which may be controlled by gauge 36. Now the ultrasonics are switched on and after about to 10 seconds treatment time, the vacuum line is disconnected by valve 37 and the outside air supply switched on to disrupt the vacuum as read off gauge 38. The increasing pressure during the ultrasonic oscillation accelerates the transfer of the pasty mass quite decidedly. Not only is a greater filling weight obtained, but also the filling time is shortened. It is advisable to have the vacuum-bell jar locked in its suction position by locks, not shown, otherwise the pressure in cylinder 33 coupled with elimination of the vacuum within the bell jar 26 may result in the counterweight 29 lifting the bell oi the plate.
1. A method of lling porous electrode matrixes, such as sinter plates, with active material for the use in batteries and the like, comprising the steps of: applying a pasty illing material in a thin even layer over an ultrasonic oscillator, laying the electrode matrix on the thin layer, covering over the matrix with .another layer of filling paste and then treating the entire combination with ultrasonic energy While under pressure.
2. The method according to claim 1, further including the steps of laying a thin foil over the top layer of pasty lilling material and removing the foil after the ultrasonic energy has been terminated.
3. The method according to claim 2, wherein the thin foil is penetrable by fluid from the pasty material.
4. The method according to claim 2, wherein the thin foil is perforated with pores which are smaller than the particles of the pasty lilling material.
5. The method according to claim 4, wherein the pressure is provided by pressing downward on the foil uniformly with a pressing block which has oscillation, res istance substantially different from that of the pasty llmg material, the bottom of the pressing block having grooves, holes and channels through which excess uid passes.
6. The method according to claim 5, further including the step of cooling the pressure block during pressing.
7. The method according to claim 6, further including the step of removing the lled matrix after it has been treated by sliding it parallel to the surface of the oscillator plate and stripping off the remaining top layer of lling material While sliding the matrix out.
8. The method according to claim 7, wherein the conslstency and the thickness of the upper layer on the electrode matrix are greater than those of the lower layer.
9. The method according to claim 8, wherein the treatment is at least part of the time performed in a vacuum.
10. The method according to claim 9, wherein the vacuum is developed before the ultrasonic energy is applied and is gradually reduced after the iilling process has started.
11. The method according to claim 10, wherein the ultrasonic energy is applied until the fluid vaporizes at least partly from the electrode matrix by the heat of the ultrasonic absorption.
12. The method according to claim 11, wherein a uid which is easily vaporized is used.
References Cited UNITED STATES PATENTS 1,197,737 9/1916 Hayden 136-67 2,896,922 7/ 1959 Pohlman 259-1 3,276,975 10/ 1966 Holechek 136-120 X 3,282,732 l1/l966 Bradley et al. 136-l20 X 3,336,423 8/1967 Le Clair et al 136-120 X FOREIGN PATENTS 1,210,417 2/ 1966 Germany.
WINSTON A. DOUGLAS, Primary Examiner O. F. CRUTCHFIELD, Assistant Examiner U.S. Cl. X.R.
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