Battery pack and method for producing the same

Abstract

To produce a battery pack in which two cylindrical battery cells arranged linearly are electrically connected in series.SOLUTION: A battery pack 1 has battery cells 10A, 10B linearly arranged in series, each having a conductive and cylindrical exterior tube 13. A battery tab is disposed between a positive electrode terminal of one battery cell and a negative electrode terminal of the other battery cell to electrically connect the two battery cells in series. The battery tab includes a welded plate portion disposed between the two battery cells, and a powered plate portion continuous with the welded plate portion and located outside the battery cells in a radial direction. The welded plate portion has two protrusions fixed to the negative electrode terminal by projection welding on a surface facing the negative electrode terminal of the other battery cell.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a battery pack and a method for manufacturing the same, and more particularly to a battery pack in which battery cells are arranged in a straight line and electrically connected in series, and a method for manufacturing the same. [Background technology]

[0002] Conventionally, the following method has been used to linearly connect two cylindrical battery cells in a battery pack: Linearly connecting cylindrical battery cells in series means arranging two battery cells electrically connected in series so that the central axis of one battery cell is aligned with the central axis of the other battery cell.

[0003] First, two battery cells are arranged in parallel so that the positive terminal of one battery cell is close to the negative terminal of the other battery cell in a direction approximately perpendicular to the central axis. Next, the positive and negative terminals of the two battery cells located on one side are series-welded with battery tabs to electrically connect the two battery cells in series. After that, the battery tabs are folded in the middle to arrange them in a straight line. Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional battery packs, the battery cell arrangement is changed from parallel to linear by bending the series-welded battery tabs. This makes it difficult to align the central axes of adjacent battery cells in the axial direction when arranging cylindrical battery cells in a linear arrangement along their central axis, which can lead to misalignment.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a battery pack in which series-connected battery cells can be easily arranged in a straight line, and a method for manufacturing such a battery pack. [Means for solving the problem]

[0006] In order to achieve the above object, the battery pack of the present invention is an assembled battery including first and second battery cells, each having a conductive cylindrical outer tube, arranged in a straight line, and electrically connected in series, the battery pack including a battery tab disposed between the positive terminal of the first battery cell and the negative terminal of the second battery cell, electrically connecting the first battery cell and the second battery cell, the battery tab including a welding plate portion located between the first battery cell and the second battery cell, and a conductive plate portion continuous with the welding plate portion and located radially outward of the first battery cell or the second battery cell, the welding plate portion having at least two protrusions on a surface facing the negative terminal of the second battery cell, the protrusions being fixed to the negative terminal of the second battery cell by projection welding between the battery tab and the negative terminal of the second battery cell.

[0007] Furthermore, the present invention also provides a method for producing an assembled battery in which first and second battery cells, each having a cylindrical exterior tube, are linearly arranged and electrically connected in series, the method comprising the steps of: welding a battery tab to a positive terminal of the first battery cell; the battery tab having a welding plate portion fixed to the positive terminal of the first battery cell and a conducting plate portion continuous with the welding plate portion and located radially outward of the first battery cell; spot-welding the welding plate portion to the positive terminal; and spot-welding the battery tab welded to the first battery cell. The method includes the steps of: bringing the negative terminal of the second battery cell into contact with a contact plate portion to align the second battery cell in a straight line with the first battery cell; and projection welding the welding plate portion to the negative terminal of the second battery cell with the first and second battery cells aligned in a straight line, with an insulator interposed between the conductive plate portion and the outer casing tubes of the first and second battery cells, wherein the first and second battery cells connected in series are arranged in a straight line. [Effects of the Invention]

[0008] According to the present invention, by projection welding the cathode terminal of the second battery cell to the battery tab fixed to the positive terminal of the first battery cell, the central axes of the first battery cell and the second battery cell connected in series can be aligned in a straight line with high precision. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view of a battery pack according to an embodiment; [Figure 2] 2A and 2B show a battery cell included in the battery pack shown in FIG. 1, in which (A) is a front view and (B) is a plan view. [Figure 3] 2A, 2B, 2C, and 2D are perspective, plan, side, and front views, respectively, of a battery tab included in the battery pack shown in FIG. 1. [Figure 4] 4 is an enlarged view of an area IV surrounded by a dotted line in FIG. 3, showing a protrusion formed on a battery tab. [Figure 5] FIG. 10(A) shows a step of spot welding a battery cell to a first battery cell, and FIG. 10(B) shows a step of projection welding a second battery cell to a battery tab fixed to the first battery cell. DETAILED DESCRIPTION OF THE INVENTION

[0010] The embodiments will be described below with reference to the drawings.

[0011] As shown in Figure 1, an assembled battery 1 according to one embodiment includes a first battery cell 10A and a second battery cell 10B connected in series and arranged in a straight line. In the following description, the A and B attached to the reference characters indicating the battery cells and their components refer to the first battery cell and the second battery cell, and when A or B is not included, the battery cell and its component are referred to as the corresponding battery cell. Specifically, a battery tab 20 is disposed between the positive terminal 11A of the first battery cell 10A and the negative terminal 12B of the second battery cell 10B. The first battery cell 10A and the second battery cell 10B are electrically connected in series via the battery tab 20, and are arranged in a straight line in this order: first battery cell 10A, battery tab 20, and second battery cell 10B.

[0012] The battery cell 10 is an AA-size bare cell and includes a conductive outer tube 13. The outer tube 13 has a cylindrical shape with one open end and a central axis X. The diameter D1 of the outer tube 13 is 13.9 mm, and the length L1 in the tube axis direction is 48.8 cm. A positive terminal 11 is attached to the open end of the outer tube 13 via a sealing member. The positive terminal 11 is cylindrical with a diameter D2 of 7 mm and is attached concentrically with the outer tube 13. The length L2 of the positive terminal 11 protruding from one end of the outer tube 13 is 0.7 mm. The bottom wall corresponding to the other end of the outer tube 13 functions as a negative terminal 12. In this embodiment, the first battery cell 10A has a positive terminal 11A at one end of the outer tube 13A in the direction of the central axis XA, and a negative terminal 12A at the other end. The second battery cell 10B has a positive electrode terminal 11B at one end of the outer casing 13B in the direction of the central axis XB, and a negative electrode terminal 12B at the other end.

[0013] The battery tab 20 electrically connects the first battery cell 10A and the second battery cell 10B, and also functions as a welding electrode receptacle for assembling the battery pack 1. The battery tab 20 is made of a nickel plate with a roughly rectangular outline. As shown in FIGS. 3(A) and 3(C), the battery tab 20 is bent at a parallel linear portion that is closer to one short side than the other short side, forming a bent portion 21. The bent portion 21 divides the battery tab 20 into a welding plate portion 22 and a conductive plate portion 23. In this embodiment, the conductive plate portion 23 is bent from the bent portion 21 so that it extends in a direction roughly perpendicular to the in-plane direction of the welding plate portion 22.

[0014] As shown in Figures 3(B) and 3(D), the weld plate portion 22 has a substantially rectangular shape with a long side length L3 of 11.2 mm and a short side length L4 of 7.5 mm. The short side length L4 of the weld plate portion 22 can be any value as long as it is smaller than the diameter D1 of the outer casing 13. The weld plate portion 22 also has two projections 24, 24 for projection welding on one surface 22A, and the other surface 22B is flat. As shown in Figure 4, the projections 24 have a dome shape with a diameter of 1 mm. The projections 24 are welded to the negative terminal 12B of the battery cell 10B by projection welding, electrically connecting the battery tab 20 to the battery cell 10B.

[0015] The conductive plate portion 23 is continuous with the welded plate portion 22 and is located radially outside the outer casing tube 13A of the battery cell 10A when the other surface 22B of the welded plate portion 22 is welded to the positive electrode terminal 11A of the battery cell 10A. The conductive plate portion 23 functions to pass current through the welded plate portion 22 during projection welding.

[0016] In order to reduce the weight of the battery tab 20 itself and make it easily bendable, an opening 25 including a part of the bending portion 21 is formed across the welding plate portion 22 and the conductive plate portion 23.

[0017] Next, a method for electrically connecting the first battery cell 10A and the second battery cell 10B in series will be described.

[0018] (1) Connection between the first battery cell and the battery tab First, the battery tab 20 is fixed to the first battery cell 10A. As shown in FIG. 5A, the battery tab 20 is positioned so that it contacts the positive terminal 11A of the first battery cell 10A. The other surface 22B of the welding plate portion 22 of the battery tab 20 faces the positive terminal 11A, and the conductive plate portion 23 is positioned radially outside the outer casing tube 13A. Next, two electrode rods 30, 30 for spot welding are pressed against one surface 22A of the welding plate portion 22, and the battery tab 20 is spot-welded to the positive terminal 11A of the first battery cell 10A using the electrode rods 30, 30. This fixes the battery tab 20 to the first battery cell 10A and electrically connects it to the first battery cell 10A. After spot welding is complete, the electrode rods are removed. The electrode rods 30, 30 are pressed against the welding plate portion 22 of the battery tab 20, avoiding the protrusions 24.

[0019] (2) Connection between the battery tab and the second battery cell Next, as shown in FIG. 5(B), the second battery cell 10B is positioned so that its negative terminal 12B (the bottom wall of the outer casing 13) contacts the battery tab 20 fixed to the first battery cell 10A. Specifically, the second battery cell 10B is positioned so that its negative terminal 12B abuts against the two protrusions 24, 24 of the welded plate portion 22 of the battery tab 20. Furthermore, the second battery cell 10B is aligned with the first battery cell 10A so that the extension of the central axis XA of the first battery cell 10A overlaps with the central axis XB of the second battery cell 10B. After alignment, the positive side of the second battery cell 10B is pressed toward the first battery cell 10A in the central axis direction.

[0020] Next, the weld plate portion 22 of the battery tab 20 and the second battery cell 10B are projection-welded. Two electrode rods 41, 42 are used for the projection welding. One electrode rod 41 is pressed against the current-carrying plate portion 23 of the battery tab 20 from the radially outer side of the battery cell 10B, and supplies power to the weld plate portion 22 via the current-carrying plate portion 23. The other electrode rod 42 is pressed against the side of the outer casing tube 13 on the opposite side of the weld plate portion 22 with respect to the central axis XB of the second battery cell 10B.

[0021] When current is applied using the electrode rods 41 and 42, the welding plate 22 heats up and softens. At the same time, the second battery cell 10B is pressed toward the first battery cell 10A, causing the protrusion 24 of the welding plate 22 to collapse and become welded to the negative terminal of the second battery cell 10B. When current is stopped, the temperature of the battery tab 20 drops and the weld between the battery tab 20 and the negative terminal of the second battery cell 10B solidifies, so that the welding plate 22 of the battery tab 20 is fixed to the negative terminal 12B of the second battery cell 10B around the protrusion 24 of the battery tab 20. At this time, to prevent current from flowing directly from the conducting plate 23 to the outer casing 13B, an insulator 43 is placed between the conducting plate 23 and the side of the outer casing 13B of the battery cell 10B.

[0022] In this way, the second battery cell 10B is fixed to the battery tab 20 by the protrusion 24 of the battery tab 20, and the second battery cell 10B is electrically connected to the first battery cell 10A via the battery tab 20. In other words, the second battery cell 10B is connected linearly in series with the first battery cell 10A.

[0023] The first battery cell 10A and the second battery cell 10B are positioned when the second battery cell 10B is projection-welded to the battery tab 20, and subsequent processes do not involve deformation of the battery tab 20. Therefore, the battery pack 1 can be fabricated while maintaining the first battery cell 10A and the second battery cell 10B in a positioned state.

[0024] In this way, when two battery cells are linearly arranged and electrically connected in series, a battery tab consisting of a welding plate portion and a current-carrying plate portion is used to projection-weld the negative terminal of one battery cell to battery tab 20 fixed to the positive terminal of the other battery cell, thereby enabling the two battery cells to be electrically connected in series to be linearly arranged with high precision in a manner simpler than conventional methods. Linear arrangement means that the central axes of the two cylindrical battery cells form a straight line.

[0025] Furthermore, compared to conventional assembled batteries that are fabricated by spot welding a single battery tab to the paired positive and negative terminals at one end of parallel-arranged battery cells and then bending the battery tab to change the linear arrangement, this method allows for accurate linear series connection of two battery cells, thereby improving the dimensional accuracy of the assembled battery 1 with a simpler process than conventional methods.

[0026] Furthermore, projection welding is simple because it only requires that electrode rods be brought into contact with the conductive plate portion of the battery tab located radially outward of the battery cell and with the side surface of the battery cell exterior tube to be welded to the battery tab.

[0027] In the above embodiment, the bent portion of the battery tab can be positioned as appropriate.

[0028] The number of projections provided on the battery tab for projection welding may be three or more.

[0029] Furthermore, the present disclosure is not limited to cylindrical battery cells, but can also be applied to cylindrical battery cells that have a shape that requires alignment of the central axis of the outer casing between two adjacent battery cells, such as rectangular battery cells that are electrically connected in series in a linear manner. [Explanation of symbols]

[0030] 1 battery pack 10A, 10B battery cells 11A, 11B Positive terminal 12A, 12B negative terminal 13A, 13B Exterior pipe 20 Battery tab 22 Welded plate section 23 Conductive plate part 24 protrusions 43 Insulator

Claims

1. A battery pack including first and second battery cells, each having a conductive cylindrical outer tube, arranged in a straight line and electrically connected in series, a battery tab disposed between the positive terminal of the first battery cell and the negative terminal of the second battery cell to electrically connect the first battery cell and the second battery cell; the battery tab has a welding plate portion located between the first battery cell and the second battery cell, and a conducting plate portion that is continuous with the welding plate portion and located radially outward of the first battery cell or the second battery cell, the welding plate portion has at least two protrusions on a surface facing the negative electrode terminal of the second battery cell, the protrusions being fixed to the negative electrode terminal by projection welding between the battery tab and the negative electrode terminal of the second battery cell.

2. A method for producing a battery pack in which first and second battery cells, each having a cylindrical outer tube, are connected in series, comprising: a step of welding a battery tab to a positive electrode terminal of the first battery cell, the battery tab having a welding plate portion fixed to the positive electrode terminal of the first battery cell and a conducting plate portion contiguous with the welding plate portion and located radially outward of the first battery cell, the step of spot-welding the welding plate portion to the positive electrode terminal; a step of bringing the negative electrode terminal of the second battery cell into contact with a welding plate portion of the battery tab welded to the first battery cell, and aligning the second battery cell in a straight line with the first battery cell; projection-welding the welding plate portion to the negative terminal of the second battery cell, with the first battery cell and the second battery cell aligned in a straight line, with an insulator interposed between the current-carrying plate portion and the outer casing tubes of the first battery cell and the second battery cell; wherein the first battery cell and the second battery cell connected in series are arranged in a straight line.

3. 3. The method according to claim 2, wherein the welding plate portion has at least two protrusions on a surface facing the negative terminal of the second battery cell, the protrusions being fixed to the negative terminal of the second battery cell by projection welding between the welding plate portion and the negative terminal of the second battery cell.

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