GALVANIC CELL COMPRISING A METAL CAN, AND METHODS FOR MAKING SUCH A CELL

Abstract: The invention relates to a galvanic cell comprising two electrodes and an electrolyte within a closed case, in which the electrodes have each been connected to an external pole and in which the case comprises a metal can which has been separated from the electrolyte by an electrically insulating organic layer. The galvanic cell is characterised in that the organic layer has been applied by lacquering, paint coating, spray coating or film coating of sheet metal material which has subsequently been formed to a can. The invention also relates to a method of making a galvanic cell.

Description: GALVANIC CELL COMPRISING A METAL CAN, AND METHODS FOR MAKING SUCH A CELL The invention relates to a galvanic cell comprising two electrodes and an electrolyte within a closed case, in which the electrodes have each been connected to an external pole and in which the case comprises a metal can which has been separated from the electrolyte by an electrically insulating organic layer. Also the invention relates to methods and materials of making such a cell. Galvanic cells of this type are often used as rechargeable batteries. The invention shall more specifically be described with regard to the application for rechargeable batteries, although it shall not be restricted thereto. The invention can thus also be applied to the Nickel Metal Hydride (NiMh) type cell. This type of galvanic cells differs from for instance non-rechargeable batteries in which in many cases the metal can forms one of the electrodes. Currently nickel coated steel is used to make cylindrical cans for various types of rechargeable batteries, such as NiCd batteries. The cans are then produced by deepdrawing of nickel coated steelplate. In the case of the NiCd rechargeable battery, the positive and negative electrodes with a separator in between are folded into a roll pack. Current collection at the negative electrode is performed at the bottom end of the can through the use of a negative current collector. This is usually resistance welded at the bottom of the roll pack to the negative electrode which is shifted slightly exposing the steel grid to which the collector is attached/welded. The current collection of the positive electrode is performed at the positive end cap, which is connected to the positive electrode via a welded positive current connector. The positive end cap of a rechargeable battery is historically a metal disk surrounded by a plastic ring-shaped containment ring. The plastic ring prevents electrical contact between the positive pole cap and the battery can. Present technology dictates the use of a tar like substance (brai) to seal the plastic ring to the metal wall of the can and prevent creeping of the electrolyte. A problem with the current batterydesign is that iron from the battery case can dissolute in the electrolyte, such as KOH, which iron thereupon can migrate and deposit within the electrodes. The result of this phenomenon is the poisoning of the cell and loss of performance, which in turn results in a reduced cycle life. This problem has been solved by using a metal can which has been separated from the electrolyte by an electrically insulating organic layer. The organic layer can be designed to chemically separate the electrolyte and the metal can, whereby it is prevented that iron from the metal can can dissolute in the electrolyte and migrate to the electrodes. It is an object of the invention to provide a galvanic cell with an electrically insulating organic layer inside its metal can, which can be made in a relatively simple and cheap way. Although the creeping of electrolyte through the seal between the positive end cap and the battery can is usually prevented by the use of a substance such as brai, the application of such a substance can lead to complications in the assembly and in the use and disposal of the batteries. Over time brai can lose some of its sealing effectiveness due to drying and pressure creep leakage. It therefore is a further object of this invention to prevent the use of substances such as brai. According to the invention in the galvanic cell of the known type the organic layer has been applied by lacquering, paint coating, spray coating or film coating of sheet metal material which has subsequently been formed to a can. By coating the sheet metal material before the cans are formed by for instance deep drawing, it is easy and cheap to coat the sheet, and it is not necessary to coat each metal can on its inside, which would be cumbersome and time consuming. Various types of organic layer-material can be used, including thermosetting and thermoplastic synthetic resins. For many applications in the production of the new cells it has been found that there is a preference for the use of thermoplastic resins, such a polyesters, polyolefmes and polyamides and/or copolymers and mixtures thereof. A further improvement according to the invention consists in that the organic layer is applied to at least part of the inner side of the metal can. If at the place were the organic layer is affixed to the metal can an electrical connection is provided this then can not result in leakage of electrolyte between the organic layer and the metal can. However, it is also possible not to apply a coating or lacquer at the place of the sheet metal where eventually an electrical connection has to be made to the metal can. On the other hand, a similar effect is achieved if according to the invention the organic layer is affixed to the entire inner surface of the metal can. This organic layer can also be maintained on the inner surface of the constructed end cap. All of the subsequent qualities achieved in the can may also be realised in the end cap. Various constructions are possible for connecting the negative electrode electrically to the bottom of the metal can in order that said bottom can form the negative pole. According to the invention a simple construction is achieved if the negative electrode is connected to a negative current collector which is welded through the organic layer to the inner side of the metal can, said metal can forming the external negative pole. As explained before the place of this welding connection may be the bottom of the can, but also the wall. This concept is also true with the end cap and the positive current collector. Spot welding of coated metal sheets is a technique which is generally known in the art. Providing an organic layer separating the metal can and the electrolyte can also facilitate the making of a galvanic cell of the type in which the positive electrode is connected by a positive current collector to a cap-shaped positive pole which is, electrically insulated, affixed to the upper rim of the metal can. According to the invention the outer rim of the positive pole is provided with a plastic ring-shaped element which is clamped within the upper rim portion of the metal can and is affixed thereto by the intermediate organic layer. In case the organic layer comprises a thermosetting resin, this can be made to further harden and bond in between the plastic ring-shaped element and the rim portion of the metal can, and also the inside surface of the positive end cap if the organic layer is provided there. In the case the organic layer comprises a thermoplastic resin temporally locally heating of the contact region of the plastic ring-shaped element with the rim portion of the metal can may cause the thermoplastic resin to melt and to glue the ring-shaped element and the rim portion together, along with the inside surface of the positive end cap if the organic layer is provided there, and to produce a leakage-free closure of the battery. Although the organic layer may be a coating upon an untreated metal surface, a more corrosion resistant product may be obtained if, according to the invention, the metal can consists of a metal from the group comprising low carbon steel, extra- or ultra-low carbon steel, Boron-, Titanium- or Niobium-stabilised low-carbon steel, interstitial-free steel, high-strength steel with a tensile strength of more than 350N/mm 2 , Aluminium and Al-alloys, which metal is metallically coated on at least the inside of the can with a coating from the group comprising one or more of nickel, nickel-cobalt, tin, conversion coatings and electrocoated chromium. This group may also comprise other metal coatings such as Au, Ag, Mo, Ir, Rh, W, Zn, Sn, B, Mn, Fe, Si, In, Ge, Ln, Ti, P, Ga and their alloys with Ni and/or Kobalt and possibly combined with organic substances. Preferably also the outside of the metal can, apart from the bottom portion, has been provided with an organic coating. Advantageously this outside coating of the metal can is a printable material upon which names, markings etc. can be printed. Apart from the galvanic cell itself, the invention also relates to the making of such cells. According to a first method of making a galvanic cell of a type as described above and comprising the steps of preparing a metal can with an organic layer covering the inner surfaces of the cell, which layer is affixed to at least the bottom of said inner surface, filling the metal can with a positive and a negative electrode, connecting these electrodes by means of current collectors to external poles, providing an electrolyte inside the cell and closing the cell, the novel method is characterised in that prior to providing the electrolyte, the negative current collector is electrically connected to the inner side of the metal can by spot-welding through the organic layer. This inner side may be the bottom of the can. In the same way, the positive current collector can be electrically connected to the inner side of the end cap by spot welding through the organic layer, if the organic layer is present on the inner side of the end cap. According to a further improvement of a method of making a galvanic cell of a type as described above, comprising the steps of preparing a metal can with an organic layer covering the inner surface of the can, filling the metal can with a positive and a negative electrode, connecting these electrodes by means of current collectors to external poles, providing an electrolyte inside the cell and closing the cell by means of a cap-shaped positive pole which is, electrically isolated, affixed to the upper rim of the metal can, this improvement further comprises that the outer rim of the cap-shaped positive pole is provided with a plastic ring-shaped element, that the upper rim of the metal can is formed to a closeable seat for the cap-shaped positive pole, that upon closing the cell said positive pole is placed on said seat whereby the organic layer separates the positive pole and the rim portion of the metal can, whereupon the rim portion of the metal can is forced around the plastic ring- shaped element and heat is supplied to the forced rim portion of the metal can in order to locally soften the organic layer until the plastic rim-shaped element and the forced rim portion are affixed to each other. The invention is further illustrated by some figures. Figure 1 shows a longitudinal section of a rechargeable battery. Figure 2 shows detail II of Fig. 1 on a larger scale. Figure 3 shows the negative current collector of Fig. 1. In Fig. 1 reference numeral 1 indicates a steel can which has been obtained by deepdrawing of nickel coated steel sheet material. Metal can 1 is provided at its inner surface with an organic layer 2. In the case as shown the steel sheet material has been coated with an organic film consisting of, for instance, polypropylene (PP) or PET. The coated steel sheet has been deepdrawn to form the can 1 in a way generally known in the art. A positive electrode 6 and a negative electrode 3 have been folded in a roll pack with an isolating separator (not shown) in between them. Electrodes 3 and 6 are somewhat shifted relatively in axial direction. In that way the negative electrode can be connected to negative current collector 5 and the positive electrode to positive current collector 7. Negative current collector 5 has been shaped as shown in Fig. 1 and in a top-view in Fig. 3. A central portion 13 has been deepened, which rests on the bottom 4 of metal can 1. By spotwelding, indicated by cross 14 the central portion 13 has been welded to the bottom 4. The weld penetrates the coating layer 2, which creates an electric contact between current collector 5 and the bottom 4. This results in that said bottom 4 can operate as the negative external pole of the battery. However, it is also possible (not shown) to provide the steel sheet material with an organic layer having openings at certain spots. During the deepdrawing of metal sheet these openings in the organic layer can be located at the bottom of the deepdrawn metal cans, and the negative current collector can be welded to the bottom in the normal way, without having to penetrate the coating layer. Instead of coating the sheet metal material with PP or PET, the sheet metal can also be coated by a lacquer or paint. Depending on the type of organic layer used, the organic layer can be applied by lacquering, paint coating, spray coating or film coating. The positive cuπent collector 7 is electrically connected by means 11 to the cap-shaped positive pole 8. In Fig. 2 is indicated that the outer rim of positive pole 8 is provided with a plastic ring-shaped element 12, which serves to electrically isolate the positive pole 8 from the metal can 1. The upper rim of the coated metal can 1 has been shaped with a seat 9 upon which the positive pole rests with ring-shaped element 12. After positioning the positive pole 8 the upper rim of the metal can is folded inward (see 10). The organic layer 2 thereby separates the metal can 1 and the ring-shaped element 12. The battery is finally closed by forcing upper rim 10 towards the seat 9. Simultaneously heat is supplied sufficiently to partly melt the organic layer between the rim portion of the metal can and the ring-shaped element 12. After cooling down a closure is obtained which prevents that electrolyte may wick around the positive pole and weep from the cell. This closure facilitates the elimination of the use of a tar-like product and will allow closer tolerances. This again removes a huge variable from the assembly process. It was found that the new seal also remains hermetic during disposal and recycling of the battery.

Claims: CLAIMS 1. Galvanic cell comprising two electrodes and an electrolyte within a closed case, in which the electrodes have each been connected to an external pole and ' < in which the case comprises a metal can which has been separated from the electrolyte by an electrically insulating organic layer, characterised in that the organic layer has been applied by lacquering, paint coating, spray coating or film coating of sheet metal material which has subsequently been formed to a can. !. Galvanic cell according to claim 1 , characterised in that the organic layer consists of a thermoplastic resin. 3. Galvanic cell according to claim 1 or 2, characterised in that the organic layer has been affixed to at least part of the inner side of the metal can. 4. Galvanic cell according to any of claims 1-3, characterised in that the organic layer has been affixed to the entire inner surface of the metal can. 5. Galvanic cell according to any of claims 1-4, characterised in that the organic layer is a coating upon the inner surface of the metal can of the group comprising lacquers, paint coatings and spray coatings. 6. Galvanic cell according to any of the claims 1-5, characterised in that the negative electrode is connected to a negative current collector which is welded through the organic layer to the inner side of the metal can, said metal can forming the external negative pole. 7. Galvanic cell according to any of the preceding claims 1-6 of the type in which the positive electrode is connected by a positive current collector to a cap- shaped positive pole which is, electrically insulated, affixed to the upper rim of the metal can, characterised in that the outer rim of the positive pole is provided with a plastic ring-shaped element which is clamped within the upper rim portion of the metal can and is affixed thereto by the intermediate organic layer. 8. Galvanic cell according to any of the preceding claims in which the metal can consists of a metal from the group comprising low carbon steel, extra-low carbon steel, ultra-low carbon steel, Boron-, Titanium- or Niobium-stabilised low-carbon steel, interstitial-free steel, high-strength steel with a tensile strength of more than 350 N/rnm 2 , Aluminium and Al-alloys, which metal is metallically coated on at least the inside of the can with a coating from the group comprising one or more of nickel, nickel cobalt, tin, conversion coatings and electrocoated chromium. 9. Galvanic cell according to any of the preceding claims in which also the outside of the metal can, apart from the bottom portion, is provided with an organic coating. 10. Galvanic cell according to any of the preceding claims in which the cell is of the type of a rechargeable battery. 11. Method of making a galvanic cell of the type of claim 6, comprising the steps of preparing a metal can with an organic layer covering the inner surface of the can, which layer is affixed to at least the bottom of said inner surface, filling the metal can with a positive and a negative electrode, connecting these electrodes by means of cuπent collectors to external poles, providing an electrolyte inside the cell and closing the cell, characterised in that prior to providing the electrolyte, the negative current collector is electrically connected to the inner side of the metal can by spot-welding through the organic layer. 12. Method of making a galvanic cell of the type of claim 7, comprising the steps of preparing a metal can with an organic layer covering the inner surface of the can, filling the metal can with a positive and a negative electrode, connecting these electrodes by means of current collectors to external poles, providing an electrolyte inside the cell and closing the cell by means of a cap-shaped positive pole which is, electrically isolated, affixed to the upper rim of the metal can, characterised in that the outer rim of the cap-shaped positive pole is provided with a plastic ring-shaped element, that the upper rim of the metal can is formed to a closeable seat for the cap-shaped positive pole, that upon closing the cell said positive pole is placed on said seat whereby the organic layer separates the positive pole and the rim portion of the metal can, whereupon the rim portion of the metal can is forced around the plastic ring-shaped element and heat is supplied to the forced rim portion of the metal can in order to locally soften the organic layer until the plastic rim-shaped element and the forced rim portion are affixed to each other.

Inventors: STOSKY ROBERT STANLEY, VAN HAASTRECHT GIJSBERTUS CORN, STOSKY, ROBERT, STANLEY, VAN HAASTRECHT, GIJSBERTUS, CORNELIS
Applicants: CORUS TECHNOLOGY BV, HAASTRECHT GIJSBERTUS CORNELIS, STOSKY ROBERT STANLEY, STOSKY, ROBERT, STANLEY, VAN HAASTRECHT, GIJSBERTUS, CORNELIS
Application year: 2000
Main classification: H01M2
IPC codes: H01M2