Cylindrical storage battery with spirally wounded electrode assembly

Abstract: A cylindrical storage battery having a spirally coiled electrode plate assembly in which the shape of the current collector welded to the end part of the electrode plate assembly is improved and the crossing parts of the rib-formed projections of the current collector and the electrode plate terminal edges are welded with sufficient strength permits a high-rate charge and discharge. A storage battery having a spirally coiled electrode plate assembly 5 comprising a positive electrode plate 1, a negative electrode plate 2 and a separator 6, and rectangular current collectors 7 and 8, the respective one of which being welded respectively to the terminal edges 3 and 4 of the electrode 1 and 2 respectively projecting outward from the upper and the lower end planes of the electrode assembly, the current collector welded to the end part of the electrode plate assembly 5 having a flat plate part 7b provided with rectangular cutout parts 7a, in a radial manner and with equal intervals therebetween at 4 places, which extend from the neighborhood of the center to the outer peripheral edge of the plate part, and rib-formed projections 7d which are formed integrally, bent downward, at the two opposed edge parts 7c of the respective cutout parts and are made to cross the terminal edge of the electrode plate and welded thereto.

Description: BACKGROUND OF THE INVENTION The present invention relates to a cylindrical storage battery provided with a spirally coiled electrode plate assembly. In more particular, it relates to an alkaline storage battery which is suitable for, for example, the driving power source of vehicles. The battery is improved in the shape of the current collector welded to the upper and lower parts of the electrode plate assembly to provide high-rate charge and discharge. PRIOR ART Various types of cylindrical alkaline storage batteries are known, representatives of which include nickel-cadmium storage batteries and nickel-metal hydride storage batteries. These batteries are in wide use for various equipment, such as portable telephones and notebook-sized personal computers, because of their high reliability and easy maintenance. In recent years, the development of cylindrical storage batteries suited to high-rate discharge are eagerly awaited as the power source for motor power-assist bicycles, lawn mowers and further electric automobiles and the like. Such a cylindrical storage battery for high-rate discharge has an electrode plate assembly comprising one strip-shaped positive electrode plate and one strip-shaped negative electrode plate which are wound as spiral coils with a separator interposed therebetween, and the assembly is housed in a battery case made of metal. As to the structure of a current collector which is suitable for collecting a large amount of electric current, a type in which respectively one rectangular or nearly circular plate-formed current collector is welded at a plurality of spots to the terminal edge projecting outward from the end plane of the electrode plate assembly (this type being hereinafter referred to as tabless type) is disclosed for example, in U.S.P. Nos. 3732124 and 5238757, and is in generally use at present. Various types have been proposed for such current collectors welded to the terminal part of electrode plate assembly (as in US-A-4,009,053 and JP-A-60 105 166), a representative of which is the current collector 14 shown in Fig. 8. This current collector is provided with a rectangular flat plate part 14a, rib-formed projections 14b formed by bending vertically downward the both side edges stretching along the length direction of the plate part 14a, and two U-shaped cutout parts 14c or punched holes. The welding of the current collector 14 to the electrode plate assembly is effected by making the rib-formed projection 14b to cross the terminal edge of one side electrode projecting upward from the electrode plate assembly, pressing a pair of bar-formed welding electrodes against the upper side of the flat plate parts 14d which hold the cutout part 14c therebetween or against the upper side of the projection 14b, and passing electricity between the electrodes under application of pressure. In the above-mentioned current collector 14, however, the rib-formed projection 14b is formed at the both side edges which extend along the length direction of the plate part 14a. Accordingly, even when welding is conducted by pressing a pair of welding electrodes against the plate part 14a located at the positions which hold the cutout part 14c therebetween and passing electricity under applied pressure, the electric current which flows through the plate part 14a between the pair of welding electrodes (namely, loss current in welding) is large owing to the distance of electricity passage and the electric resistance; on the contrary, the electric current which flows through the crossing part of the pair of projections 14b and the electrode terminal edge is small, so that it is difficult to melt the crossing part of the projection 14b and the electrode terminal edge sufficiency to secure good welding. Resultantly, the weld part, namely the integrate part formed by the rib-formed projection 14b and the electrode terminal edge, has a high contact resistance and, when the battery is discharged with a large electric current, for example 3c (electric current of three times the battery capacity), the IR drop at the weld part is too large to give a satisfactory battery performance. SUMMARY OF THE INVENTION The main object of the present invention is to provide, overcoming the above-mentioned difficulties, a storage battery which permits charge and discharge at high rate by improving the shape of the current collector welded to the end part of the spirally coiled electrode plate assembly to concentrate the welding current at the crossing part of the rib-formed projection provided to the current collector and the projecting terminal edge of the electrode and thereby to melt the crossing part sufficiently to effect firm welding. According to the present invention, there is provided a cylindrical storage battery according to claim 1. DESCRIPTION OF THE PREFERRED EMBODIMENTS The shape of the current collector is very important for welding it securely to the electrode plate terminal edge projecting outward from the electrode plate assembly. For example, if a pair of electrodes for electric resistance welding are merely held against the flat part, devoid of a cutout part, of a current collector, the loss current, which flows the surface of the flat part between the electrodes and does not contribute to welding, increases, making it difficult to weld securely the rib-formed projection of the current collector to the electrode terminal edge at a plurality of spots. In the present invention, the current collector made of nickel plated steel which is provided with a plurality of cutout parts which reach the outer peripheral edge of the current collector and open there in a radial manner, downward rib-formed sharp projections being integrally formed at the edge parts of the respective cutout parts. Accordingly, the rib-formed projection and the terminal edge of one side electrode plate projecting from the end part of the electrode plate assembly cross each other; therefore, by pressing a pair of welding electrodes against the current collector so as to hold the rectangular cutout part therebetween, the loss current which flows on the current collector surface between the pair of welding electrodes decreases by virtue of the cutout part and the welding current which flows into the crossing part of the projection located on the underside of the cutout part and the terminal edge of the electrode plate is increased, whereby welding is effected securely at a number of crossing parts. The shape of the cutout parts is not limited, for example a rectangular cutout part, a U-shaped cutout part and a trapezoidal cutout part are exemplified. For the convenience of manufacturing the rib-formed projections, a rectangular cutout part is preferable. Cutout parts are preferably formed with equal intervals. The number of cutout parts is preferably 4∼8, more preferably 4∼6. The rib-formed projections may be formed only at the two opposed edge parts of each of the cutout parts. The height (width) and the thickness of the rib-formed projection which is to cross the terminal edge of the electrode plate also are important for securing the crossing part and concentrating the welding current. In the present invention, the length of the rib-formed projection from the plate part should be smaller than the length (width) of the bare part of nickel plated steel perforation sheet which constitutes the projecting terminal edge of the electrode plate; preferably the projection length of the projection is 1/5 to 2/3 of the width of the bare part of perforation sheet so that the projection may not touch the terminal edge of the opposite electrode even at the completion of welding. The thickness of the projection is preferably 2-8 times the thickness of the perforation sheet so that the tip of the projection may be held securely against the end surface of the perforation sheet bare part of electrode plate and the crossing parts may generate heat uniformly by resistance and may be uniformly molten and deformed. The aspect of the present invention described in claim 1 specifies the shape and the state of welding of current collectors for a positive and a negative electrode which are welded to the terminal edges of electrode plates respectively projecting outward from the upper and the lower end of a spirally coiled electrode plate assembly. The current collectors for the positive and the negative electrode are securely welded to the electrode plate terminal edges at a number of spots, whereby a current collecting structure which permits high-rate charge and discharge is provided. The aspects of the present invention described in claims 2-8 specify the specific shape and size of the rib-formed projection and the relation of the size of the projection to the size of the perforation sheet part of the electrode plate terminal edge to be welded thereto, to secure weld parts suited to high-rate discharge. Other details of the present invention and preferred structures of batteries which permit high-rate charge and discharge are described below with reference to accompanying drawings and Examples. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a partially sectional side view of a nickel-cadmium storage battery shown in the Example of the present invention, Fig. 2 is a top view of the current collector of the above-mentioned battery, Fig. 3 is a front view of the current collector of the above-mentioned battery, Fig. 4 is a front view of a current collector of another example, Fig. 5 is a sectional view of the lower end part of the projection of a current collector, Fig. 6 is a front view of a current collector of still another example, Fig. 7 is a top view of the nearly circular plate-formed current collector of the present invention, and Fig. 8 is a perspective view showing a representative current collector of the prior art. DESCRIPTION OF EXAMPLES Some specific examples of the present invention are described below. Fig. 1 is a sectional side view of a nickel-cadmium storage battery provided with a current collector of tabless type shown in the Example of the present invention. The battery A has a diameter of 33 mm, a height of 61.5 mm and a nominal capacity of 5,000 mA. The structure of the battery A is described in detail below. A sintered type nickel positive electrode plate 1 1.0 mm in thickness and a paste type cadmium negative electrode plate 2 0.7 mm in thickness were prepared, the respective electrode plates were provided at their lengthwise terminal edges with bare perforation sheet parts 3 and 4, a separator 6 was interposed between the electrode plates such that the bare perforation sheet parts 3 and 4 respectively project by about 15 mm above and below an electrode plate assembly 5, and the whole was wound spirally to form an electrode plate assembly 5 about 30 mm in diameter and about 50 mm in height. A rectangular current collector 7 having a diagonal length of about 27 mm provided at the central part with a hole was arranged right above the upper end plane of the above-mentioned electrode plate assembly 5, and while keeping a rectangular current collector 8 having the same or a slightly larger diagonal length than the current collector 7 provided at the central part with a connecting tongue-shaped lead used for welding in contact with the bare perforation sheet part 4 of the lower end plane of the electrode plate assembly 5, the current collectors were welded respectively to the bare perforation sheet parts 3 and 4 at a plurality of spots by using a pair of welding electrodes. The details of welding are described later. The electrode plate assembly 5 was inserted into a metal case 9, one welding electrode was passed through the central hole of the current collector 7 so as to press the tongue-shaped lead provided at the center of the current collector 8, and the pressed part was welded to the inner bottom surface of the battery case. Then a predetermined amount of an alkaline electrolyte was poured into the battery case 9 by using the central hole and the cutout parts of the current collector 7, the end of a connecting lead provided to the current collector 7 was welded to the lower surface of a sealing plate 11 which doubles as the positive electrode terminal, and the opening of the case 9 was hermetically sealed with the sealing plate 11. Thus, the battery A of the present invention was obtained. As shown in Fig. 2, the rectangular current collector 7 with projections not formed according to the present inention welded to the upper part of the electrode plate assembly is formed of a flat plate part 7b 0.4 mm in thickness provided at the center with a hole for passing a welding electrode therethrough in a diameter of, for example, 6 mm and provided with rectangular cutout parts 7a which extend from the neighborhood of the hole to the outer peripheral edge in a width of 3 mm at 4 places with equal intervals therebetween and in a radial manner, and of rib-formed projections 7d provided integrally by bending downward at the two opposed edge parts of each of the cutout parts 7a and welded as shown in Fig. 3 (where the projections 7d are not formed according to the present invention) to the bare perforation sheet part 3 of the positive electrode plate 1 crossing therewith. The welding of the projection 7d to the bare perforation sheet part of the electrode plate terminal edge was performed by holding a pair of welding electrode having a rectangular tip against the flat plate part 7b along the edge part 7c so as to hold the cutout part 7a therebetween, and passing an alternate current of about 2,000 A between the pair of electrodes for about 10 µ sec while pressing the welding electrodes against plate part 7b. In this way, the welding current which flows on the flat surface of the current collector 7 between the pair of welding electrodes decreases as the result of obstruction by the rectangular cutout part 7a and increase in distance which the current flows. On the other hand, the distance between the welding electrode through the bare perforation sheet decreases relatively, to increase the welding current which flows into the crossing part of the bare perforation sheet part of the electrode plate and the rib-formed projection 7d. In this instance, in order to weld simultaneously a large number of crossing parts of the projections 7d and the bare perforation sheet part of electrode plate, the terminal shape of the pair of welding electrodes is preferably in the form of rectangle, which makes it possible to hold the welding electrode tip approximately along the length direction of the cutout part 7a. This welding technique was applied not only to the positive electrode current collector 7 but also to the welding of the crossing part of the negative electrode current collector 8 and the bare perforation sheet part 4 of the negative electrode plate. The connecting tongue-shaped lead formed at the center of the negative electrode current collector was welded to the inner bottom center of the battery case while being pressed with the welding electrode passed through the hole located at the center of the positive electrode current collector. For comparison with the battery described above, a battery B of Comparative Example was prepared with the same structure as described above except that the current collector 14 mentioned above was used in place of the current collector 7 welded to the upper part of the electrode plate assembly 5. The current collector 14 is composed, as shown in Fig. 8, of a rectangular flat plate part 14a 0.4 mm in thickness, rib-formed projections 14b of the same thickness formed by bending perpendicularly the both side edges of the plate part 14a, and of cutout parts 14c. The two batteries A and B were respectively charged with an electric current of 5A for 1.5 hours and then discharged with an electric current of 15A (that is, 3C) until the terminal voltage reached 1.0 V. The discharge capacity and the average discharge voltage determined from the test are shown in Table 1. Battery Discharge capacity Average discharge voltage A 5000 mAh 1.18 V B 4700 mAh 1.16 V As shown in Table 1, the discharge capacity of the battery A was 300 mAh higher than that of the battery B, and the average discharge capacity of the battery A was 0.02 V higher than that of the battery B. With a view to verifying the difference in performance, the batteries A and B were disassembled and examined. In the battery A, the positive electrode side current collector 7 welded to the upper part of the electrode plate assembly was found to be firmly welded because, at all of the crossing parts of the rib-formed projections 7d and the bare perforation sheet parts 3, the projection 7d bit into the perforation sheet part 3 and melted as such; the weld part also showed a sufficient tensile strength. In the battery B, on the other hand, the positive electrode side current collector 14 welded to the upper part of the electrode plate assembly was not sufficiently welded at a plurality of spots among the crossing parts of the projections 14b and the bare perforation sheet parts 3, such insufficiently welded parts are readily peeled apart on stretching, and the weld parts as the whole showed an insufficient tensile strength. The fact that the battery B has a plurality of parts where the projection 14b and the bare perforation sheet part 3 are not sufficiently melted and welded signifies that the contact resistance of the weld parts of the projection 14b to the bare perforation sheet part 3 as the whole increases; resultantly, the battery B has an increased internal resistance and hence showed a lower average discharge voltage and lower discharge capacity than the battery A. In the battery A, the rib-formed projection 7d of the current collector 7 is provided integrally, bended downward, at the opposed edge parts 7c of the cutout part 7a; accordingly, when a pair of welding electrodes are held against the current collector, the welding electric current which flows through the plate part 7b of the side more external than the projection 7d is small and most of the welding electric current concentrates to the projection 7d, so that at each of the points where the projections 7d cross the bare perforation sheet parts 3 the projection 7d bit into the bare perforation sheet part 3 and melted as it was, resulting in firm welding of the part. Consequently, the battery had a lower resistance than the battery B, permitting sufficient discharge with a large electric current; resultantly, the value of electric current which can be charged and discharged with the battery A and its discharge capacity were both high. In the above Example, as shown in Fig. 3, a current collector 7 constructed of a rib-formed projection 7d and a plate part 7b both of the same thickness was used. However, another current collector 12 may also be used wherein, as shown in Fig. 4, the rib-formed projections 12a are bended downward at the opposed edge parts of the cutout part while being drawn to reduce their sectional. area, so as to provide a thickness of the projections 12a smaller than that of the plate part 12b, for example, the thickness of the plate part of 0.4 mm and the thickness of the projections 12a of 0.3 mm. This structure is advantageous in that in welding the projection 12a to the electrode terminal edge, the welding current is more readily concentrated to the projection 12a and welding is more securely effected. In the above Example, as shown in Fig. 3, the rib-formed projection 7d (not formed according to the present invention) used was of the same shape over the whole of its height, in this case a rectangular shape. However, another structure wherein, as shown in the sectional view of Fig. 5, the lower end of the projection 7d is shaved to provide a sharp part 7e of the form of knife edge is advantageous in that the tip of the projection more easily bites into the bare perforation sheet part of the electrode terminal edge, the state of welding becomes more secure and resultantly the welding strength increases. Further, a still another current collector 13 wherein the shape viewed from top is the same as that shown in Fig. 2 but, as shown in Fig. 6, the plate part 13a is subjecting to pressing treatment to obtain a thickness smaller than the initial thickness, for example, the thickness is reduced from 0.5 mm to 0.4 mm, the thickness of the projection 13b is selected at 0.5 mm so as to be larger than that of the plate part 13a, and the terminal edge 13c of the projection 13b is sharpened by shaving into the form of knife edge is suited for taking out a large electric current because it can increase particularly the area of the electric current take-out part while giving approximately the same welding effect as in the above Example. Thus, the thickness of the current collector is preferably 0.25-0.5 mm to secure good welding and sufficient sectional area of passage of electricity. The height of the projection, though it depends also on the length (i.e., width) of the projecting part of perforation sheet which the projection crosses and bites into, is preferably about 0.5-0.7 mm when the length of the projecting part is about 0.7-1.8 mm. When the above-mentioned respective dimensions are within the aforesaid ranges, a secure welding can be attained while reducing that part of the electrode plate which does not participate in the electromotive reaction. The shape of the above-mentioned current collector viewed from top is not limited to the rectangular one shown in Fig. 2. A current collector wherein the plate part 7b is nearly circular as shown in Fig. 7 may also be used in accordance with the type of cylindrical storage battery. When such a current collector is welded to the end part of the electrode plate assembly, approximately the same effect can be obtained as in the Example. Further, though a nickel-cadmium storage battery was exemplified in the Example, the present invention may also be applied to other alkaline storage batteries, such as a nickel-metal hydride storage battery, so long as they are of cylindrical type. Thus, according to the present invention, in a cylindrical storage battery having a spirally coiled electrode plate assembly, a rectangular or nearly circular plate-formed current collector welded to the upper part of the electrode plate assembly has a flat plate part provided with a plurality of rectangular cutout parts, in a radial manner and with equal intervals therebetween, which extend from the neighborhood of the center to the peripheral edge of the plate, and rib-formed projections which are formed integrally downward at the two opposed edge parts of respective cutout parts and are to be crossed and welded with the one side electrode terminal edge; so that the terminal edge of the one side electrode and the rib-formed projection of the current collector can be securely melted and firmly welded with each other at a state wherein the two are crossing and biting into each other. Resultantly, a battery which has an excellent current collecting structure and permits high-rate discharge can be provided. A cylindrical storage battery having a spirally coiled electrode plate assembly in which the shape of the current collector welded to the end part of the electrode plate assembly is improved and the crossing parts of the rib-formed projections of the current collector and the electrode plate terminal edges are welded with sufficient strength permits a high-rate charge and discharge. A storage battery having a spirally coiled electrode plate assembly 5 comprising a positive electrode plate 1, a negative electrode plate 2 and a separator 6, and rectangular current collectors 7 and 8, the respective one of which being welded respectively to the terminal edges 3 and 4 of the electrode 1 and 2 respectively projecting outward from the upper and the lower end planes of the electrode assembly, the current collector welded to the end part of the electrode plate assembly 5 having a flat plate part 7b provided with rectangular cutout parts 7a, in a radial manner and with equal intervals therebetween at 4 places, which extend from the neighborhood of the center to the outer peripheral edge of the plate part, and rib-formed projections 7d which are formed integrally, bent downward, at the two opposed edge parts 7c of the respective cutout parts and are made to cross the terminal edge of the electrode plate and welded thereto.

Claims: A cylindrical storage battery (A) comprising a spirally coiled electrode plate assembly (5) consisting essentially of a positive electrode plate (1), a negative electrode plate (2) and a separator (6) each in the form of strip, the terminal edge (3) of one electrode plate (1) projecting upward and the terminal edge (4) of the other electrode plate (2) projecting downward, current collectors (7, 8; 13) each formed essentially of a rectangular or nearly circular plate respectively welded to the respective terminal edges of the respective electrode plates projecting from the upper part or the lower part of the electrode plate assembly (5), a metal case (9) which houses the electrode plate assembly (5) and the current collectors (7, 8; 13) therein, and a sealing plate (11) provided with a cap-formed terminal at the top which seals the case (9), wherein the respective current collectors (7, 8; 13) welded to the respective terminal edges of the respective electrode plates (1, 2) are provided with a plurality of cutout parts (7a) in a radial manner, and with downward rib-formed projections (7d; 13b) respectively formed integrally at the edge parts (7c) of the respective cutout parts, and the respective projections and the terminal edges of the electrode plates crossing each other and being welded with each other at a plurality of spots while the projections partly biting into the terminal edges of the electrode plates, characterized in that said cutout parts extend from the neighborhood of the center to the outer peripheral edge of the plate (7, 8; 13), and said terminal edge (7e; 13c) of the downward projection (7d; 13b) is shaved sharp and its thickness reduces in the direction away from the cutout parts or exhibits reduced sectional area so as to provide a thickness of the projections (13c) smaller than that of the plate part (13b). The cylindrical storage battery according to claim 1 wherein the downward projection (7d; 13b) of the current collector (7; 13) is formed in the same thickness as the plate part (7b; 13a). The cylindrical storage battery according to claim 1 wherein the downward projection (13b) of the current collector (13) is formed in a thickness larger than that of the plate part (13a). The cylindrical storage battery according to claim 1 wherein the parts (3, 4) projecting upward and downward of the spirally coiled electrode plate assembly (5) consists essentially of bare parts of respective perforation sheets of the positive and the negative electrode plates (1, 2) and the projection (7d; 13b) of the current collector (7; 13) welded to the terminal edge of the perforation sheet bare part has a thickness 2-8 times that of the perforation sheet. The cylindrical storage battery according to claim 1 wherein the projection length of the current collector (7; 13) from the plate part (7b; 13a) falls within the range of 1/5 to 2/3 of the length of the bare perforation sheet part (3, 4). The cylindrical storage battery according to claim 1 wherein the current collector (7; 13) welded to the terminal edge of one side electrode plate (3) projecting upward of the spirally coiled electrode plate assembly (5) is welded to one end of a rectangular lead piece (10) and the other end of the lead piece is welded to the under surface of the sealing plate (11) at at least one place. The cylindrical storage battery according to claims 1 to 6 wherein said positive electrode (1) comprises a sintered type nickel substrate and an active material held thereon, said negative electrode (2) comprises a paste-like electrode material coated on the both sides thereof. The cylindrical storage battery according to claim 7 wherein said metal case (9) doubles as the output-input terminal of the negative electrode (2), and said sealing plate (11) is electrically insulated from the case (9) and doubles as the input-output terminal of the positive electrode (1). The cylindrical storage battery according to claim 8 wherein said rib-formed projections (7d; 13b) are formed integrally by bending at the edge parts of respective cutout parts. The cylindrical storage battery according to claim 9 wherein the negative electrode current collector (8) is provided with a tongue-shaped lead formed by cutting out a part thereof at the central part, said lead being welded to the inner bottom of the battery case (9). The cylindrical storage battery according to claim 10 wherein the length of the perforation sheet projecting parts (3, 4) formed in the positive and the negative electrode plates (1, 2) is about 0.7-1.8 mm, and the length of the rib-formed projections (7d; 13b) from the plate part provided integrally at the respective cutout parts of the positive electrode current collector (7; 13) and the negative electrode current collector (8) is about 0.4-0.7 mm. The cylindrical storage battery according to claim 10 wherein the positive and the negative current collectors (7, 8; 13) are both formed essentially of a nickel-plated iron flat plat and the lead piece (10) welded at one end to the positive electrode current collector (7; 13) is formed essentially of a nickel plate.

Inventors: EGUCHI TOSHIHIDE, NAKAMARU HISAO, ONISHI MASATO, SUZUKI NORIO, EGUCHI, TOSHIHIDE, NAKAMARU, HISAO, ONISHI, MASATO, SUZUKI, NORIO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1998
Main classification: H01M2
IPC codes: H01M4, H01M2, H01M10