Alkaline storage battery

Abstract: An alkaline storage battery such as a sealed nickel-cadmium storage battery has an improved current col­ lector tab structure connected as a current path to the mar­ ginal edge of a spirally coiled electrode of an electrode assembly [54]. The current collector tab structure comprises either a plurality of current collector tabs [1,2] or a single current collector tab [25] comprising a current collecting tab and a lead tab [7,8] thicker [26] than the current collecting tab. With this arrangement, the internal resistance of the stor­ age battery is reduced, and high-rate discharge performance is achieved.

Description: The present invention relates to an alkaline storage battery such as a sealed nickel-cadmium storage battery or the like, and more particularly to an alkaline storage battery having an improved current collector tab structure for increased high-rate discharge performance. One conventional alkaline storage battery is shown in FIGS. 6 and 7 of the accompanying drawings. The known alkaline storage battery has an electrode assembly 34 comprising a positive electrode 32 and a negative electrode 33 which are wound as spiral coils with a separator 31 interposed therebetween. The electrode assembly 34 is housed in a nickel-plated steel case 35 which doubles as the negative terminal of the storage battery. The positive electrode 32 has a terminal edge 36 projecting from one end of the electrode assembly 34, whereas the negative electrode 33 has a terminal edge 37 projecting from the other end of the electrode assembly 34. The terminal edge 36 is connected to an upper current collector tab 38 which comprises a circular collecting tab 39 welded to the terminal edge 36 and a rectangular lead tab 40 extending from the circular collecting tab 39, the rectangular lead tab 40 having a width smaller than the diameter of the circular collecting tab 39. The lead tab 40 is spot-welded to a sealing cover 41 of the case 35, the sealing cover 41 serving as the positive terminal of the storage battery. The terminal edge 37 is connected to a lower current collector tab 42 which comprises a circular collecting tab 43 welded to the terminal edge 37 and a tongue-shaped lead tab 44 attached to the center of the circular collecting tab 43. The lead tab 44 is spot-welded to the inner surface of the bottom of the case 35 at the center of the circular collecting tab 43. It is known that the high-rate discharge performance of the alkaline storage battery of such a construction greatly varies depending on the internal resistance of the storage battery. The current collector tabs 38, 42 are spot-welded to the terminal edges 36, 37, respectively, of the electrode assembly 34. To spot-weld such a current collector tab to a terminal edge of an electrode assembly, one surface of the current collector tab is held against the terminal edge of the electrode assembly, and a pair of spot-welding electrodes is disposed on the other surface of the current collector tab. The welding current which is supplied between the spot-welding electrodes flows from the terminal edge of the electrode assembly to the electrode assembly itself through the current collector tab. If the current collector tab, with its current collecting tab and lead tab having the same thickness, is increased in its overall thickness to reduce the electric resistance thereof, then when the current collector tab is welded to the terminal edge of the electrode assembly, the loss current flowing through the current collector tab is increased, thereby reducing the welding current flowing through the joint between the terminal edge of the electrode assembly and the current collector tab. As a result, the joint cannot be welded effectively. It is therefore preferable to reduce the thickness of the current collector tab in order to minimize the loss current which flows during the welding process. If the current collector tab is thinned, however, the electric resistance of the lead tab on which the current is concentrated is increased. Consequently, it is impossible to reduce the electric resistance of the lead tab and hence the entire current collector tab. US-A-4322484 discloses an alkaline storage battery according to the pre-characterising part of claim 1. According to the present invention there is provided an alkaline storage battery comprising: an electrode assembly including a positive electrode plate and a negative electrode plate, said plates being spirally wound with a separator interposed therebetween; a case housing said electrode assembly therein and serving as a negative terminal, said case having an opening; a sealing cover mounted in said opening with an insulating gasket therebetween, said sealing cover serving as a positive terminal; negative electrode current collector means electrically connecting an edge of said negative electrode plate to said case; positive electrode current collector means electrically connecting an edge of said positive electrode plate to said sealing cover, said positive electrode current collector means including first and second current collectors each having a current collecting part attached to said edge of the positive electrode plate and a lead part attached to said sealing cover, characterised in that said first and second current collectors define an opening therebetween in the region of the center of said electrode assembly. Embodiments of battery in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a longitudinal cross-sectional view of an alkaline storage battery according to a first embodiment of the present invention; Fig. 2 is a perspective view of an internal structure of the alkaline storage battery shown in Fig. 1, showing upper current collector tabs from which lead tabs extend and an electrode assembly; Fig. 3 is a perspective view of an internal structure of an alkaline storage battery according to a second embodiment of the present invention; Fig. 4 is a perspective view of an internal structure of an alkaline storage battery not in accordance with the present invention; Fig. 5 is a graph showing discharge performances of the alkaline storage batteries shown in Figs. 1-4 and a conventional alkaline storage battery; FIG. 6 is a longitudinal cross-sectional view of a conventional alkaline storage battery; and FIG. 7 is a perspective view of an internal structure of the conventional alkaline storage battery. FIGS. 1 and 2 show an alkaline storage battery according to a first embodiment of the present invention. The alkaline storage battery according to the first embodiment is in the form a nickel-cadmium storage battery having the nominal capacity of 1.2 Ah. The alkaline storage battery includes an electrode assembly 54 comprising a positive electrode 52 and a negative electrode 53 which are wound as spiral coils with a separator 51 interposed therebetween. The electrode assembly 54 is housed in a nickel-plated steel case 55 which doubles as the negative terminal of the storage battery. The positive electrode 52 has a terminal edge 56 projecting from one end of the electrode assembly 54, whereas the negative electrode 53 has a terminal edge 57 projecting from the other end of the electrode assembly 54. The alkaline storage battery has two upper current collector tabs 1, 2 connected to the terminal edge 56 of the positive electrode 52. The upper current collector tabs 1, 2 comprise respective semicircular current collecting tabs 5, 6 spot-welded to the terminal edge 56 of the positive electrode 52, and respective rectangular lead tabs 7, 8 extending upwardly from the current collecting tabs 5, 6, respectively. The upper current collector tabs 1, 2 have a thickness of 0.15 mm. The lead tabs 7, 8 are disposed in confronting relation to each other and have distal ends spot-welded to a sealing cover 10 of the case 55, the sealing cover 10 doubling as the positive terminal of the storage battery. The sealing cover 10 is mounted in an end opening of the case 55 with an insulating seal ring 58 therebetween. The terminal edge 57 is connected to a lower current collector tab 62 which comprises a circular collecting tab 63 spot-welded to the terminal edge 57 and a tongue-shaped lead tab 64 attached to the center of the circular collecting tab 63. The lead tab 64 is spot-welded to the inner surface of the bottom of the case 55 at the center of the circular collecting tab 63. The storage battery thus constructed will be referred to as a storage battery A. An electric current supplied from the current collecting tabs 5, 6 of the two current collector tabs 1, 2 flows to the sealing cover 10 through the lead tabs 7, 8 joined to the current collecting tabs 5, 6. According to the storage battery A, the density of the current flowing through the current collecting tabs 5, 6 and the lead tabs 7, 8 is reduced to half, and the electric resistance of the current collector tabs 1, 2 is substantially reduced. The internal resistance of the storage battery A is about 20 % lower than the internal resistance of a conventional nickel-cadmium storage battery. To spot-weld the current collecting tabs 5, 6 to the electrode assembly 54, a pair of welding electrodes is held against the current collecting tabs 5, 6, respectively, and a welding current is passed between the welding electrodes. Therefore, the welding current is concentrated on joints between the current collecting tabs 5, 6 and the terminal edge 56 of the positive electrode 52. Another storage battery, referred to as a storage battery B, according to the first embodiment of the present invention is similar to the storage battery A except that upper current collector tabs have a greater thickness of 0.20 mm. The internal resistance of the storage battery B is about 25 % lower than the internal resistance of a conventional nickel-cadmium storage battery. While two upper current collector tabs are employed in the storage batteries of the first embodiment, more upper current collector tabs and/or a plurality of lower current collector tabs may be employed. FIG. 3 shows an internal structure of an alkaline storage battery according to a second embodiment of the present invention. The alkaline storage battery of the second embodiment is a nickel-cadmium storage battery having the nominal capacity of 1.2 Ah, and differs from the alkaline storage batteries of the first embodiment only with respect to two upper current collector tabs 11, 12. More specifically, the upper current collector tab 11 is positioned underneath the upper current collector tab 12. The upper current collector tab 11 comprises a substantially circular current collecting tab 13 welded to the terminal edge of the positive electrode and a rectangular lead tab 15 raised, by lancing, and extending upwardly from the current collecting tab 13. The other upper current collector tab 12 has a substantially circular current collecting tab 14 including a surface area welded to a portion of the marginal edge of the positive electrode and the other surface area welded to the current collecting tab 13 and a lead tab 16 raised, by lancing, and extending upwardly from the current collecting tab 14. The lead tabs 15, 16 are disposed in confronting relation to each other. The storage battery thus constructed will be referred to as a storage battery C. The internal resistance of the storage battery C is about 30 % lower than the internal resistance of a conventional nickel-cadmium storage battery. For further reducing the internal resistance of the storage battery, a stack of more current collector tabs which are successively welded may be employed. Furthermore, two or more lower current collector tabs may be employed and arranged in the same manner as the upper current collector tabs. FIG. 4 shows an internal structure of an alkaline storage battery not in accordance with the present invention. The alkaline storage battery of Fig. 4 is a nickel-cadmium storage battery having the nominal capacity of 1.2 Ah, and differs from the alkaline storage battery shown in FIG. 1 in that only a single upper current collector tab 24 is employed. The upper current collector tab 24 comprises a substantially circular current collecting tab 25 welded to the terminal edge of the positive electrode and a rectangular lead tab 26 connected to and extending upwardly from the current collecting tab 15. The current collecting tab 25 has a thickness of 0.15 mm, and the lead tab 26 has a thickness of 0.50 mm. The thicker lead tab 26 has a reduced electric resistance to the passage of a current therethrough. The storage battery illustrated in FIG. 4 will be referred to as a storage battery F. The internal resistance of the storage battery F is about 20 % lower than the internal resistance of a conventional nickel-cadmium storage battery. The lower current collector tab may be identical in configuration to the upper current collector tab 24. The concept of using a thicker lead tab in the illustrated in Fig. 4 is applicable to the Fig. 1-3 embodiments. Fig. 5 shows the discharge voltages of the storage batteries A, B, C, F and a conventional storage battery G, the discharge voltages being plotted against time after the storage batteries have fully recharged and then discharged with a current of 20 A flowing from the storage batteries. It can be seen from Fig. 5 that the storage batteries A, B, C, F with the reduced internal resistance exhibit higher high-rate discharge performances and higher discharge voltages than the conventional storage battery G. (Discharge curves D and E should be ignored as they do not relate to illustrated embodiments of battery). With the present invention, as described above, because the electric resistance of the current collector tab or tabs is reduced, the alkaline storage battery has higher high-rate discharge performance, i.e. can keep a higher discharge voltage upon a high-rate discharge.

Claims: An alkaline storage battery comprising: an electrode assembly (54) including a positive electrode plate (52) and a negative electrode plate (53), said plates being spirally wound with a separator (51) interposed therebetween; a case (55) housing said electrode assembly (54) therein and serving as a negative terminal, said case having an opening; a sealing cover (10) mounted in said opening with an insulating gasket (58) therebetween, said sealing cover serving as a positive terminal; negative electrode current collector means (62) electrically connecting an edge (57) of said negative electrode plate (53) to said case (55); positive electrode current collector means (1, 2) electrically connecting an edge (56) of said positive electrode plate (52) to said sealing cover (10), said positive electrode current collector means including first and second current collectors (1, 2, 11, 12) each having a current collecting part (5, 6, 13, 14) attached to said edge (56) of the positive electrode plate (52) and a lead part (7, 8, 15, 16) attached to said sealing cover (10), characterised in that said first and second current collectors (1, 2) define an opening therebetween in the region of the center of said electrode assembly (54). An alkaline storage battery as claimed in claim 1, wherein said opening is of generally polygonal shape. An alkaline storage battery as claimed in claim 2, wherein said opening is of generally square shape. An alkaline storage battery as claimed in any of the preceding claims, wherein said opening is defined by recesses formed in the current collecting parts (5, 6, 13, 14) of the first and second current collectors (1, 2, 11, 12). An alkaline storage battery as claimed in claim 4, wherein the lead part (7, 8, 15, 16) of each current collector (1, 2, 11, 12) is formed by deforming it out of the plane of the current collecting part (5, 6, 13, 14) of its respective current collector to form a said recess in the current collecting part. An alkaline storage battery as claimed in any of the preceding claims, wherein said first and second current collectors (1, 2, 11, 12) are arranged with their lead parts (7, 8, 15, 16) in confronting relation to each other, and wherein said opening is defined between said confronting lead parts. An alkaline storage battery as claimed in any of the preceding claims, wherein a portion of the current collecting part (13, 14) of one of the current collectors (11, 12) is positioned over a portion of the current collecting part of the other of the current collectors. An alkaline storage battery as claimed in claim 7, wherein the current collecting parts of said first and second current collectors (11, 12) are welded together. An alkaline storage battery as claimed in any of the preceding claims, wherein more than two current collectors (1, 2, 11, 12) are provided. An alkaline storage battery as claimed in any of the preceding claims, wherein the lead part (7, 8, 15, 16) of at least one of said first and second current collectors (1, 2, 11, 12) is thicker than its respective current collecting part (5, 6, 13, 14).

Inventors: HOSHINO KENICHI, MARUYAMA HIROMI, ODA SENNOSUKE, SUZUKI NORIO, HOSHINO, KENICHI, MARUYAMA, HIROMI, ODA, SENNOSUKE, SUZUKI, NORIO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1989
Main classification: H01M2
IPC codes: H01M2, H01M10