Device for producing battery electrodes and method for producing the same

Abstract: Superimposing strip layers comprising a positive electrode strip (3) and a negative electrode strip (4), which are put into layers together with a separator strip (2) being put between the strips, is spirally wound around an outer circumference of a bobbin (1) having an end cross section similar in shape to a center hole of a spiral electrode to form a substantially circular center hole in the spiral electrode while extracting the bobbin.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a device for producing a battery electrodes comprising a positive electrode strip, a negative electrode strip and a separator strip, all of which are spirally wound. The present invention also relates to a method for producing the same. DESCRIPTION OF THE PRIOR ART Various methods for producing a spiral battery electrodes have been proposed. In Japanese Patent publication JP-B2-4-37549 as well as in EP233813 there are disclosed typical examples of such methods. A conventional method similar to the methods disclosed in the above publications will be described with reference to Figs. 6 and 7. A pair of bobbin pieces having a semi-circular cross section are combined into a single bobbin 1 with an insulator strip such as a separator 2 being put therebetween and then being attached thereto. Then, the bobbin 1 is turned so that the insulator strip is spirally wound around the outer circumference of the bobbin 1. The bobbin 1 is further turned so that a superimposing strip consisting of the separator 2, a positive electrode strip 3 and a negative electrode strip 4 is spirally wound around the circumference of the bobbin 1 to form a spirally wound body (coil). The coil is inserted into a cylindrical metal case 6, and then the bobbin 1 is extracted from the coil to produce a spiral electrodes. In the following producing step, a welding apparatus is inserted into the center hole 9 of the spiral electrodes in order to weld a lead portion on the negative side of the spiral electrodes to the inside of the bottom of the cylindrical metal case 6. In such a case, a "bent portion" of the separator 2 in the center hole 9 as shown in Fig. 7 often interferes with the welding apparatus, so that an inferior battery electrodes is produced. Further, EP 655 793, which document belongs to the state of the art according to Art 54(3) only discloses a method for producing an electrode assembly in which an anode and a cathode are wound together in a unidirectional winding having substantially straight sides by using a correspondingly shaped mandsel. SUMMARY OF THE INVENTION It is an object of the present invention to provide a bobbin for producing spiral battery electrodes having a hole of predetermined shape at a center thereof which solves the above-mentioned problem and of which the hole does not complicate a construction of the battery electrodes and does not interfere with a welding apparatus. Another object of the invention is to provide a method for producing the battery electrodes including a step of extracting a bobbin while forming a center hole of the battery electrodes having a desired shape. These objects are achieved by a bobbin as defined in claim 1 and by a method is defined in claim 2. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic illustration of a spiral electrodes manufactured by means of a bobbin according to a first embodiment of the present invention; Fig. 2 is a schematic illustration of a method for manufacturing the spiral electrodes by means of the bobbin according to the first embodiment of the present invention; Fig. 3 is a side view of the bobbin according to the first embodiment of the present invention; Fig. 4 is a cross-sectional view of the spiral electrodes manufactured by means of the bobbin according to the first embodiment of the present invention; Fig. 5 is a schematic illustration of a bobbin according to a second embodiment of the present invention; Fig. 6 is a schematic illustration of a manufacturing step of welding a lead portion on the negative side of the spiral electrodes to a cylindrical metal case according to the present invention; Fig. 7 is a schematic illustration of a conventional method for manufacturing a spiral electrodes by means of a conventional bobbin; and Fig. 8 is a cross-sectional view of the spiral electrode according to the conventional method. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in further detail by way of two examples with reference to the accompanying drawings. Referring first to a first embodiment of the present invention shown in Figs. 1-3 inclusive, a bobbin 1 comprises one piece 1A of the bobbin 1 and the other piece 1B of the bobbin 1, the one piece 1A having one portion of semi-circular cross section, around which portion an electrodes is spirally wound, and the other portion of a circular cross section with a diameter of 3 mm at a tip thereof, and the other piece 1B having a semi-circular cross section that forms a circular cross section with a diameter of 3 mm when the other piece 1B is placed over the one piece 1A at a bobbin slope 10 of the one piece 1A. A separator strip 2, a positive electrode strip 3, and a negative electrode strip 4 are piled up together and then spirally wound around the outer circumference of the bobbin 1 to form a spiral electrodes 5. As shown in Fig. 1, after the spiral electrodes is completed, the other piece 1B is firstly extracted from the spiral electrodes 5 in the direction indicated by an arrow B, and secondly the spiral electrodes 5 is removed from the one piece 1A toward the direction indicated by an arrow A. The center hole 9 of the spiral electrodes 5 is formed to be substantially circular in shape since the end of the one piece 1A has a circular cross section as shown in Fig. 1. As shown in Fig. 6, the spiral electrodes 5 is inserted into a cylindrical metal case 6 with a lead portion 7 on the negative side of the spiral electrode 5 downwardly, of which the lead portion 7 is welded to the bottom inside 11 of the cylindrical metal case 6. A "bent portion" of the separator strip 2, which is left in the center hole 9 of the spiral electrodes 5, and the deformation of the center hole 9 itself may cause the separator 2 or the spiral electrodes 5 to be interfered with a welding apparatus 8, so that an inferior battery electrodes is produced. According to the embodiment of the present invention, such defects can be prevented. The tapered part of the bobbin 1 prevents the separator 2 from being unnecessarily put between the bobbin pieces 1A, 1B and facilitates the bobbin to be extracted when forming the spiral electrodes 5. Fig. 5 shows a second embodiment of the present invention. A bobbin 1 has guide groove, in which an inclined surface for receiving the separator strip 2 is formed. An insulator strip such as the separator strip 2 is put between the guide groove of the bobbin 1 and attached to the guide groove. The bobbin 1 is turned so that the insulator strip is spirally wound around the outer circumference thereof to form a spiral electrodes. The bobbin is then extracted from the spiral electrodes, so that the center hole of the bobbin is formed to be substantially circular in shape without the "bent portion" of the separator strip 2. In the first and second embodiments, the center hole has substantially a circular shape, however, it may have any other shape such as a rectangular shape or an elliptic shape. In the embodiments, the bobbin consists of two pieces or a single piece, however, it may consists of three pieces or more. If the cross section of the end of the bobbin is not equivalent in shape with that of the center hole, it is possible to form the center hole into a circular shape by extracting the bobbin from the electrodes while turning the bobbin. One thousand spiral electrodes were produced by the method of the first embodiment, and the same number of the spiral electrodes were produced by a conventional method. The spiral electrodes produced by both methods were respectively inserted into a cylindrical iron case, and their lead portions of nickel on the negative side of the spiral electrodes were welded to the inside of the cylinder iron cases. The proportion of rejects due to the interference of the welding apparatus with the separator strip 2 during welding was respectively measured. Under a copper alloy with an outer diameter of 2.8 mm is connected to a capacitor regenerative type welder, the lead portion is welded under a pressure of 5 Kg at a current of 1.38KA during 6.8 msec. An electrodes was considered to be acceptable if fractures are found in the lead portion on the negative side of the electrodes and the lead portion is found to break at a load of 1.2 Kg or more in a tension test. Table 1 gives the results. Proportion of rejects when welding the negative terminal side lead and the inside of the cylindrical iron case Manufacturing method according to first embodiment 3% Conventional manufacturing method 12%

Claims: A bobbin (1) for producing spiral battery electrodes comprising a positive electrode strip (3), a negative electrode strip (4) and a separator strip (2), said bobbin comprising a winding portion of predetermined cross-sectional shape, which is adapted to attach thereto said separator strip (2) and to spirally wind said electrodes (3, 4) together with said separator strip (2) put therebetween around an outer circumference therof, and being extractable from said spiral battery electrodes while leaving a center hole (9) characterized in that said bobbin further comprises: an end portion having a cross-sectional shape differing from that of said predetermined cross-sectional shape and being adapted to a desired shape of said center hole (9) and a tapered portion (10) arranged between said end portion and said winding portion for facilitating extraction of said bobbin (1) from said spiral battery electrodes. A method for producing spiral battery electrodes comprising a negative electrode strip, a positive electrode strip and a separator strip put therebetween, said method comprising the steps of attaching a bent portion of said separator strip to a winding portion of a bobbin according to claim 1, spirally winding said negative electrode strip said positive electrode strip and said separator strip around an outer circumference of said winding portion and forming a center hole in the likewise produced spiral battery electrodes of a desired cross-sectional shape by extracting said bobbin from said spiral electrodes by passing said tapered portion and said end portion through said spiral battery electrodes to thereby displace outwardly said bent portion.

Inventors: KANEDA YOSHIMITU, MIYATA KYOSUKE, YONEDA TAKASHI, KANEDA, YOSHIMITU, MIYATA, KYOSUKE, YONEDA, TAKASHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1996
Main classification: H01M6
IPC codes: H01M6, H01M2, H01M10