Cylindrical battery and method for manufacturing a cylindrical battery
By employing a cylindrical outer can with strategically arranged protrusions on its surface, the uneven welding current distribution issue is addressed, resulting in stable and efficient connection strength between the tab and the outer can, thereby improving the discharge capacity and stability of cylindrical batteries.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- FDK CORP
- Filing Date
- 2021-11-19
- Publication Date
- 2026-05-26
AI Technical Summary
In cylindrical batteries, welding tabs to the inner side surface of the outer casing can lead to uneven distribution of welding current, resulting in large variations in connection strength between the tab and the outer can, which reduces the discharge capacity and stability.
The outer can is designed with a first surface featuring three or more groups of protrusions on its circumference and a second projection at the center, with the connection area between the first group of protrusions and the inner surface greater than that of the second projection, ensuring uniform distribution of welding current.
This design suppresses variations in connection strength between the curved inner side surface of the outer can and the tab, enhancing the discharge capacity and stability of the cylindrical battery.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a cylindrical battery and a method for manufacturing the same.
Background Art
[0002] There is known a battery in which a power generation element (battery element) including positive and negative electrodes is housed inside an exterior can. Regarding such a battery, there is known a technique of connecting the exterior can and the power generation element using a conductive member (lead, tab, etc.) inside the exterior can.
[0003] For example, a technique of connecting a lead drawn from one of the positive and negative electrode plates to the inner bottom surface of a battery case that houses an electrode group including positive and negative electrode plates (Patent Document 1), or a technique of connecting a lead plate derived from one of the positive and negative electrode plates to the inner bottom of a battery container that houses an electrode group including positive and negative electrode plates, with a metal material having higher weldability interposed therebetween than when directly welding them (Patent Document 2). In addition, in a battery in which a lead plate connected to the current collector of one of the positive and negative electrode plates is welded to the inner bottom surface of a battery can that houses an electrode group including positive and negative electrode plates, there is known a technique of providing a plurality of protrusions on the welded portion of the lead plate (Patent Document 3).
[0004] Also, at least three protrusions are provided within the hollow area at the center of a lower current collector connected to the lower end of a plate group including positive and negative electrode plates housed in a bottomed case made of metal, and the bottom surface of the bottomed case and the lower current collector are welded through at least one of them (Patent Document 4). In addition, there are known techniques of arranging projections at a plurality of locations on concentric circles within a region between a portion facing the hollow cylindrical portion of the plate group and the peripheral portion of the lower current collector or the metal case, arranging projections also on the portion facing the hollow cylindrical portion, and making the height of this projection lower than the height of the projections at a plurality of locations on the concentric circles (Patent Document 5).
[0005] Furthermore, a technique is known in which projection welding protrusions are formed on conductive connection tabs joined to battery elements, and the conductive connection tabs are welded by bringing these projection welding protrusions into contact with the inner wall surface of the battery can (Patent Document 6). In addition, a technique is known in which current collecting leads connected to one of the positive or negative electrode plates are welded to the inner surface of the side wall of a cylindrical metal case housing an electrode group including positive and negative electrode plates (Patent Document 7), and a technique is known in which the cross section perpendicular to the longitudinal direction of the region of the lead member connected to the inner wall of a cylindrical battery can is made into a V-shape at a predetermined angle (Patent Document 8). [Prior art documents] [Patent Documents]
[0006] [Patent Document 1] Japanese Patent Publication No. 2011-228153 [Patent Document 2] Japanese Patent Publication No. 2006-32072 [Patent Document 3] Japanese Patent Application Publication No. 6-275253 [Patent Document 4] Japanese Patent Publication No. 2008-282696 [Patent Document 5] Japanese Patent Publication No. 2005-100949 [Patent Document 6] Japanese Patent Publication No. 2002-216739 [Patent Document 7] Japanese Patent Publication No. 2014-222670 [Patent Document 8] Japanese Patent Publication No. 2010-108870 [Overview of the project] [Problems that the invention aims to solve]
[0007] Incidentally, in a cylindrical battery in which a winding of electrode groups that serve as power generation elements is housed in a cylindrical outer casing, and conductive tabs connected to the winding are welded (connected) to the inner bottom surface of the outer casing by resistance welding, it is necessary to create a hole space in the center of the winding to allow the welding electrode rod to pass through from the upper opening of the outer casing to the inner bottom surface when welding the tab to the inner bottom surface of the outer casing. As a result, the volume of the winding that can be housed in the outer casing is reduced by the amount of such a hole space is created in the winding, and the discharge capacity is reduced. On the other hand, when the tab is welded to the inner side surface of the outer casing, it is not necessary to create a hole space for the welding electrode rod to pass through the winding, which has the advantage of increasing the volume of the winding that can be housed in the outer casing and thus increasing the discharge capacity.
[0008] However, when welding tabs to the inner side surface of a cylindrical outer can, the welding current can become concentrated in certain areas due to the curved inner surface, resulting in large variations in welding strength (connection strength). If multiple projections, called projections, are placed on the surface of the tab to be resistance welded to the inner side surface of the outer can, and the welding current is concentrated on these projections, depending on the arrangement of these projections, the welding of the projections to the inner side surface of the outer can may become uneven, resulting in large variations in the connection strength between the tab and the outer can.
[0009] In one aspect, the present invention aims to reduce variations in the connection strength between the curved inner surface of the cylindrical battery casing and the tab. [Means for solving the problem]
[0010] In one embodiment, the outer can is cylindrical and has a first surface facing the curved inner side surface of the outer can, and the first surface 、 Three or more groups of first protrusions located on the circumference centered on the reference point of the first surface. And the second projection located at the aforementioned reference point The first group of protrusions is provided and the second projection and a tab connected to the inner side surface Furthermore, in a plan view taken from the tab toward the inner surface, the connection area of each connection between the first group of protrusions and the inner surface is greater than the connection area of the connection between the second protrusion and the inner surface. A cylindrical battery is provided.
[0011] In another aspect, a step of preparing a cylindrical outer can, having a first surface facing the curved inner side surface of the outer can, and on the first surface 、 three or more first protrusion groups located on a circumference centered on the reference point of the first surface And the second projection located at the aforementioned reference point is provided The height of the second projection relative to the first surface is lower than the height of the first group of projections relative to the first surface. a step of preparing a tab, and connecting the tab to the inner side surface with the first protrusion group and the second projection is provided, and a method for manufacturing a cylindrical battery is provided.
Advantages of the Invention
[0012] On one side, it becomes possible to suppress variations in the connection strength between the curved inner side surface of the outer can of the cylindrical battery and the tab.
Brief Description of the Drawings
[0013] [Figure 1] It is a diagram (part 1) for explaining an example of a cylindrical battery. [Figure 2] It is a diagram (part 2) for explaining an example of a cylindrical battery. [Figure 3] It is a diagram for explaining an example of a power generation element before winding. [Figure 4] It is a diagram for explaining an example of inserting a wound body of a power generation element into an outer can. [Figure 5] It is a diagram for explaining an example of resistance welding. [Figure 6] It is a diagram (part 1) for explaining an example of the arrangement of the protrusion group of the negative tab. [Figure 7] It is a diagram (part 2) for explaining an example of the arrangement of the protrusion group of the negative tab. [Figure 8] It is a diagram (part 3) for explaining an example of the arrangement of the protrusion group of the negative tab. [Figure 9] It is a diagram for explaining the formation of the protrusion of the negative tab. [Figure 10] It is a diagram for explaining a first example of resistance welding between the negative tab and the curved inner side surface of the outer can. [Figure 11] It is a diagram for explaining an example of a negative tab in which the protrusion group is arranged on the circumference and at its center. [Figure 12] This figure illustrates a second example of resistance welding between the negative electrode tab and the curved inner side of the outer can. [Figure 13] This diagram illustrates an example of the condition after resistance welding between the negative electrode tab and the curved inner side of the outer can. [Figure 14] This figure illustrates an example of the shape of a negative electrode tab in which a group of protrusions is arranged on the circumference and at its center. [Modes for carrying out the invention]
[0014] Figures 1 and 2 illustrate an example of a cylindrical battery. Figure 1 schematically shows a perspective view of the main external parts of an example of a cylindrical battery. Figure 2 schematically shows a cross-sectional view of the main parts of an example of a cylindrical battery. Note that Figure 2 is a cross-sectional view taken at plane S0 of Figure 1.
[0015] The cylindrical battery 1 shown in Figures 1 and 2 comprises an outer casing 10, a winding body 20, a positive electrode tab 30, a negative electrode tab 40, an insulating plate 50, an insulating plate 60, a non-aqueous electrolyte 70, a sealing body 80, a gasket 90, and a positive electrode terminal 100.
[0016] The outer container 10 is a cylindrical, bottomed, conductive container with one end open. The outer container 10 is made of a metal material such as stainless steel or nickel-plated iron. The open end of the outer container 10 is sealed by a sealing body 80 on which a positive electrode terminal 100 is provided via a gasket 90.
[0017] The winding body 20 is an example of a power generation element housed in the outer casing 10 of a cylindrical battery 1. The winding body 20 includes an electrode layer, which is an electrode layer, a positive electrode layer 21 and a negative electrode layer 22, and a separator 23 interposed between them. A positive electrode layer 21 containing positive electrode active material is formed on one side of a sheet-like separator 23 made of microporous film or nonwoven fabric, and a negative electrode layer 22 containing negative electrode active material is formed on the other side of the separator 23. This forms a sheet-like laminate in which the positive electrode layer 21, separator 23 and negative electrode layer 22 are stacked in order. This sheet-like laminate is wound spirally to form a cylinder and housed in the outer casing 10 together with a non-aqueous electrolyte 70. Insulating plates 50 and 60 are provided inside the outer casing 10, at its bottom 11 and above the winding body 20 that is housed inside.
[0018] The positive electrode tab 30 and the negative electrode tab 40 are made of a metal material such as nickel. One end of the positive electrode tab 30 is connected to the positive electrode layer 21 of the winding body 20 housed in the outer casing 10, and the other end is connected to the positive electrode terminal 100 provided on the sealing body 80 via a gasket 90. The negative electrode tab 40 is connected to the negative electrode layer 22 of the winding body 20 housed in the outer casing 10, and the other end is connected to the inner side surface 12 of the outer casing 10. The outer casing 10 is connected to the negative electrode layer 22 of the winding body 20 through the negative electrode tab 40 and functions as the negative electrode of the cylindrical battery 1.
[0019] The cylindrical battery 1 can be, for example, a lithium primary battery or a lithium secondary battery. When the cylindrical battery 1 is a lithium primary battery, manganese dioxide or the like is used as the positive electrode active material in the positive electrode layer 21 of the winding body 20, and lithium metal or lithium alloy or the like is used as the negative electrode active material in the negative electrode layer 22 of the winding body 20. When the cylindrical battery 1 is a lithium secondary battery, lithium cobalt oxide or the like is used as the positive electrode active material in the positive electrode layer 21 of the winding body 20, and lithium metal or lithium alloy or the like is used as the negative electrode active material in the negative electrode layer 22 of the winding body 20. The non-aqueous electrolyte 70 of the cylindrical battery 1 is a non-aqueous organic electrolyte obtained by dissolving a lithium salt in a non-aqueous solvent.
[0020] Next, an example of a manufacturing method for the cylindrical battery 1 will be explained with reference to Figures 3 to 5. Figure 3 illustrates an example of a power generation element before winding. Figure 3 schematically shows a plan view of the main parts of an example of a power generation element before winding.
[0021] The winding body 20 of the cylindrical battery 1 is formed by spirally winding a sheet-like power generation element 20a, as shown in Figure 3, into a cylindrical shape. The power generation element 20a includes a sheet-like separator 23, a sheet-like positive electrode layer 21 (not shown in Figure 3) provided on one surface 23a of the separator 23 (the depth side of the paper in Figure 3), and a sheet-like negative electrode layer 22 provided on the other surface 23b of the separator 23 (the front side of the paper in Figure 3).
[0022] One end of the positive electrode tab 30 is connected to the positive electrode layer 21, which is provided on the surface 23a side of the separator 23, and the other end is extended to the outside of the separator 23. The positive electrode tab 30 may be a strip-shaped member in plan view with one end connected to the positive electrode layer 21, or it may be a part of a plate-shaped or mesh-shaped current collector on which the positive electrode material containing the positive electrode active material is formed, extended to the outside of the positive electrode material.
[0023] One end of a strip-shaped negative electrode tab 40 is connected to the negative electrode layer 22, which is provided on the surface 23b side of the separator 23, while the other end is extended to the outside of the separator 23. The portion of the negative electrode tab 40 located inside the separator 23 is protected by insulating tape 24. On the portion of the negative electrode tab 40 that is extended to the outside of the separator 23, a plurality of protrusions 41 (projections) are arranged on the surface 42 facing the inner side surface 12 of the outer casing 10 of the cylindrical battery 1. Note that the arrangement of the group of protrusions 41 shown in Figure 3 and the following Figures 4 and 5 is just one example. Details of the arrangement of the protrusions on the negative electrode tab 40 will be described later.
[0024] Figure 4 illustrates an example of inserting the winding body of the power generation element into the outer casing. Figure 4(A) schematically shows a perspective view of the main parts of an example of the state when the winding body is inserted into the outer casing, and Figure 4(B) schematically shows a perspective view of the main parts of an example of the state after the winding body has been inserted into the outer casing.
[0025] As shown in Figure 3, the sheet-like power generation element 20a is wound spirally into a cylindrical shape to form a winding body 20 as shown in Figure 4(A). The winding body 20 is inserted into a separately prepared bottomed cylindrical outer can 10 from an open end that faces the bottom 11 (Figure 2) of the outer can in the direction of the axis 10a (axial direction) Z. Before inserting the winding body 20, an insulating plate 50 is inserted into the bottom 11 of the outer can 10.
[0026] When the winding body 20 is inserted into the outer can 10, a state is obtained in which the winding body 20 is housed inside the outer can 10, as shown in Figure 4(B). The negative electrode tab 40, which is connected to the negative electrode layer 22 of the winding body 20 and pulled out to the outside of the winding body 20, is welded (connected) to the inner side surface 12 of the outer can 10 by resistance welding via a group of protrusions 41 positioned on it.
[0027] Figure 5 illustrates an example of resistance welding. Figure 5(A) schematically shows a perspective view of the main parts of an example of a welding electrode rod, Figure 5(B) schematically shows a plan view of the main parts of an example of resistance welding, and Figure 5(C) schematically shows a cross-sectional view of the main parts of an example of resistance welding. Note that Figure 5(C) is a VV cross-sectional view of Figure 5(B).
[0028] For resistance welding between the negative electrode tab 40, which is connected to the negative electrode layer 22 of the winding body 20 and pulled out to the outside of the winding body 20, and the curved inner side surface 12 of the outer can 10, a pair of welding electrode rods 210 and 220, as shown in Figure 5(A), are used. The tip 211 of one welding electrode rod 210 is in contact with the negative electrode tab 40 on the inside of the outer can 10, and the tip 221 of the other welding electrode rod 220 is in contact with the outside (outer side surface) of the outer can 10, and current is passed between the welding electrode rods 210 and 220.
[0029] The welding electrode rod 210 is a cylindrical member whose cross-section in a direction parallel to the surface 46 of the negative electrode tab 40 against which it abuts (the surface opposite to the surface 42 on which the group of protrusions 41 is arranged, and the surface before the tip portion 211 of the welding electrode rod 210 abuts). The tip portion 211 of the welding electrode rod 210 that abuts against the negative electrode tab 40 inside the outer can 10 has a curved surface (curved surface, spherical surface, or R surface) that is convex toward the surface 46 of the negative electrode tab 40.
[0030] During resistance welding, as shown in Figures 5(B) and 5(C), the negative electrode tab 40 is positioned such that the surface 42 on which the group of protrusions 41 are arranged faces the curved inner side surface 12 of the outer can 10. A welding electrode rod 210 is brought close to the negative electrode tab 40 and its tip 211 contacts it, and a welding electrode rod 220 is brought close to the outside of the outer can 10 and its tip 221 contacts it. The negative electrode tab 40 is pressed by the welding electrode rod 210 toward the inner side surface 12 of the outer can 10 with a predetermined pressure, and the outer can 10 is pressed toward the negative electrode tab 40 with a predetermined pressure by the welding electrode rod 220. The group of protrusions 41 on the negative electrode tab 40 are arranged as described later (arranged on the circumference 44), and when the tip 211 of the curved surface of the welding electrode rod 210 contacts it, pressure is applied uniformly to the curved inner side surface 12 of the outer can 10.
[0031] In this state, a predetermined current (welding current) is passed between the welding electrode rod 210 and the welding electrode rod 220, thereby welding (resistance welding) the group of protrusions 41 on the negative electrode tab 40 to the curved inner side surface 12 of the outer can 10.
[0032] Furthermore, after welding the negative electrode tab 40 to the inner side surface 12 of the outer casing 10, an insulating plate 60 is inserted into the upper part of the winding body 20 inside the outer casing 10. In addition, the positive electrode tab 30, which is connected to the positive electrode layer 21 of the winding body 20 and pulled out to the outside of the winding body 20, is connected to the positive electrode terminal 100, which is provided on the sealing body 80 via a gasket 90, by resistance welding or the like. Then, the sealing body 80 is connected to the open end of the outer casing 10 by laser welding or the like, and the outer casing 10 is sealed. This results in a cylindrical battery 1 as shown in Figures 1 and 2 above.
[0033] Next, we will describe the group of protrusions located on the negative electrode tab 40 of the cylindrical battery 1. Figures 6 to 8 illustrate examples of the arrangement of the protrusions on the negative electrode tab. Figures 6(A) to 6(C), 7(A) to 7(C), 8(A), and 8(B) schematically show a plan view of the main part of an example of a negative electrode tab as seen from the side where the protrusions are arranged.
[0034] Figures 6(A) to 6(C) show an example of an arrangement in which a group of protrusions 41 are arranged linearly along the axis 40a of the negative electrode tab 40 on the surface 42 of the negative electrode tab 40 that faces the curved inner side surface 12 of the cylindrical outer can 10 during resistance welding. Here, the axis 40a of the negative electrode tab 40 is the axis in a direction parallel to the axial direction Z of the outer can 10 when the negative electrode tab 40 is welded to the inner side surface 12 of the outer can 10, and is the axis that passes through the center of the width of the surface 42 in a direction X perpendicular to the axial direction Z of the outer can 10.
[0035] In the example shown in Figure 6(A), two groups of protrusions 41 are arranged in a row on the axis 40a of the negative electrode tab 40. In the example shown in Figure 6(B), three groups of protrusions 41 are arranged in a row on the axis 40a of the negative electrode tab 40. In the example shown in Figure 6(C), three groups of protrusions 41 are arranged in a row parallel to the axis 40a on both sides of the axis 40a of the negative electrode tab 40.
[0036] Furthermore, Figures 7(A) to 7(C) show an example of an arrangement in which the group of protrusions 41 are located on a circle 44 centered on a reference point 43 on the axis 40a of the surface 42 of the negative electrode tab 40 that faces the inner side surface 12 of the outer can 10 during resistance welding.
[0037] In the example shown in Figure 7(A), three groups of protrusions 41 are arranged on a circle 44 centered on the reference point 43 of the negative electrode tab 40. For example, in Figure 7(A), one of the three groups of protrusions 41 is positioned on the axis 40a, and the other two are positioned on either side of the axis 40a, such that the distance between adjacent groups of protrusions 41 is equal.
[0038] In the example shown in Figure 7(B), four groups of protrusions 41 are arranged on a circle 44 centered on the reference point 43 of the negative electrode tab 40. For example, in Figure 7(B), two groups of protrusions 41 are arranged on each side of the axis 40a, and the distance between adjacent groups of protrusions 41 is equal.
[0039] In the example shown in Figure 7(C), six groups of protrusions 41 are arranged on a circle 44 centered on the reference point 43 of the negative electrode tab 40. For example, in Figure 7(C), two of the six groups of protrusions 41 are arranged on the axis 40a, and the remaining four are arranged two on each side of the axis 40a, so that the distance between adjacent protrusions 41 is equal.
[0040] Furthermore, Figures 8(A) and 8(B) show examples of arrangements in which an additional projection 45 is provided at the position of the reference point 43, which is the center of the circumference 44 where the group of projections 41 shown in Figures 7(A) and 7(B) are located.
[0041] The negative electrode tab 40 shown in Figures 6(A) to 6(C), Figures 7(A) to 7(C), Figure 8(A), and Figure 8(B) is shaped such that, in a plan view from the side of the surface 42 where the group of protrusions 41, or the group of protrusions 41 and the protrusions 45, are arranged, it is symmetrical with respect to its axis 40a.
[0042] In Figures 7(A) to 7(C), 8(A), and 8(B), the distance between adjacent groups of protrusions 41 arranged on the circumference 44 of the negative electrode tab 40 is set to be narrower than the width of the surface 42 in the direction X perpendicular to the axial direction Z of the outer can 10.
[0043] Figure 9 illustrates the formation of protrusions on the negative electrode tab. Figures 9(A) and 9(B) schematically show cross-sectional views of key parts of an example of a negative electrode tab with protrusions formed on it. The negative electrode tab 40 has, for example, a recess 47 on the surface 46 opposite to the surface 42 of the negative electrode tab 40, as shown in Figure 9(A), and a projection-shaped protrusion on the surface 42 at a position corresponding to the recess 47, which is extruded by the recess 47, and this projection-shaped protrusion is provided as a projection 41. For example, by a partial punching process (projection punching), a punch is pressed into the flat negative electrode tab 40 from the surface 46 side, thereby pushing out the projection-shaped protrusion (bulge) to the opposite surface 42 side, thereby forming the projection 41. The amount of indentation from the surface 46 side and the amount of extrusion to the surface 42 side of the negative electrode tab 40 of a predetermined thickness T0 are adjusted to form a projection 41 of a predetermined height H0.
[0044] Furthermore, when a group of protrusions 41 is placed on the negative electrode tab 40, the formation of such a group of protrusions 41 by projection processing may be performed all at once or individually. Also, when a group of protrusions 41 is placed on the circumference 44 and a protrusion 45 is placed at the center of the circumference 44, the protrusion 45 can similarly be formed together with the group of protrusions 41 or individually by such projection processing.
[0045] Furthermore, the negative electrode tab 40 may be formed by creating a projection 41 on the surface 42 of a flat negative electrode tab 40, rather than by projection processing as described above, for example, as shown in Figure 9(B). For example, the projection 41 can be formed by press working from the surface 42 side of the flat negative electrode tab 40, by cutting the surface 42 side, or by depositing the same or different type of metal material onto the surface 42 of the negative electrode tab 40. When the projection 41 is formed by depositing a different type of metal material onto the surface 42 of the negative electrode tab 40, the metal material may be, for example, a metal material with better weldability to the inner side surface 12 of the outer can 10 than the metal material of the negative electrode tab 40.
[0046] Furthermore, when a group of protrusions 41 is arranged on the negative electrode tab 40, the formation of such a group of protrusions 41 by pressing, cutting, or depositing metal material may be carried out in batches or individually. Also, when a group of protrusions 41 is arranged on the circumference 44 and a protrusion 45 is placed at the center of the circumference 44, the protrusion 45 can similarly be formed together with the group of protrusions 41 or individually by pressing, cutting, or depositing metal material.
[0047] For example, the negative electrode tab 40 shown in Figures 6(A) to 6(C), 7(A) to 7(C), 8(A), and 8(B) above is resistance-welded to the curved inner side surface 12 of the outer can 10.
[0048] Figure 10 illustrates a first example of resistance welding between the negative electrode tab and the curved inner side surface of the outer can. Figures 10(A) and 10(B) schematically show a plan view of the main parts of an example of the state during resistance welding between the negative electrode tab and the inner side surface of the outer can, respectively.
[0049] Figures 10(A) and 10(B) schematically show a plan view of the main part of the outer can 10 as seen from the axial direction Z, as an example of the state during resistance welding between the negative electrode tab 40 and the inner side surface 12 of the outer can 10. For convenience, Figures 10(A) and 10(B) show three groups of protrusions 41 in a plan view of the outer can 10 as seen from the axial direction Z, but are not limited to this.
[0050] During resistance welding, for example, as shown in Figure 10(A), the negative electrode tab 40 is positioned such that the surface 42 on which the group of protrusions 41 are arranged faces the curved inner side surface 12 of the outer can 10. The tip 211 of the welding electrode rod 210 is in contact with the negative electrode tab 40, and the tip 221 of the welding electrode rod 220 is in contact with the outside (outer side surface) of the outer can 10. The negative electrode tab 40 is pressed by the welding electrode rod 210 with a predetermined pressure toward the inner side surface 12 of the outer can 10. The negative electrode tab 40 can take on a curved shape along the curved surface as it is pressed by the curved surface of the tip 211 of the welding electrode rod 210. The outer can 10 is also pressed toward the negative electrode tab 40 by the welding electrode rod 220 with a predetermined pressure. In this state, a predetermined welding current is passed between the welding electrode rod 210 and the welding electrode rod 220.
[0051] The welding current flowing through the negative electrode tab 40 tends to concentrate on the group of protrusions 41 (or the group of protrusions 41 and protrusions 45) of the negative electrode tab 40. By concentrating the welding current on the group of protrusions 41 of the negative electrode tab 40 and generating heat, the negative electrode tab 40 becomes easier to weld to the curved inner side surface 12 of the outer can 10 compared to when the group of protrusions 41 is not provided.
[0052] As resistance welding progresses, for example, as shown in Figure 10(B), the tips of the group of protrusions 41 on the negative electrode tab 40 melt and are welded to the curved inner side surface 12 of the outer can 10. As a result, the conductivity resistance between the negative electrode tab 40 and the outer can 10 (between the welding electrodes 210 and 220) decreases, and the height of the group of protrusions 41 decreases. In this way, the group of protrusions 41 on the negative electrode tab 40 and the curved inner side surface 12 of the outer can 10 are welded together.
[0053] In this example, resistance welding between the group of protrusions 41 on the negative electrode tab 40 and the curved inner side surface 12 of the outer can 10 was used. However, similarly, if a protrusion 45 is positioned at the center of the circumference 44 where the group of protrusions 41 is located, a welding current flows through the protrusion 45, and the protrusion 45 and the curved inner side surface 12 of the outer can 10 can be welded together.
[0054] In the case of a negative electrode tab 40 having a group of protrusions 41 arranged on a circumference 44, and a protrusion 45 located at the center of the circumference 44, as shown in Figures 7(A) to 7(C), Figure 8(A), and Figure 8(B), when the curved surface of the tip 211 of the welding electrode rod 210 comes into contact with it, the group of protrusions 41, or the group of protrusions 41 and the protrusion 45, are uniformly pressurized against the curved inner side surface 12 of the outer can 10. For example, when the apex of the curved surface of the tip 211 of the welding electrode rod 210 comes into contact with a point on the circumference 44 of the negative electrode tab 40 corresponding to a reference point 43 (the position where the protrusion 45 is placed), the group of protrusions 41, or the group of protrusions 41 and the protrusion 45, are uniformly pressurized against the curved inner side surface 12 of the outer can 10.
[0055] The negative electrode tab 40 may take on a curved shape during and after welding its group of protrusions 41, or the group of protrusions 41 and protrusions 45, to the curved inner side surface 12 of the outer can 10. That is, the negative electrode tab 40 may take on a curved shape along the curved surface of the tip 211 of the welding electrode rod 210, or a curved shape along the curved inner side surface 12 of the outer can 10, due to the pressure applied by the welding electrode rod 210 to which it is in contact, or the joining force with the inner side surface 12 after welding. For example, the negative electrode tab 40 may be made of a material that exhibits such flexibility during and after welding. Alternatively, the thickness of the negative electrode tab 40 may be set to exhibit such flexibility.
[0056] Next, we will describe the results of evaluating the welding strength (connection strength) and its variation with the curved inner side surface 12 of the outer can 10 for the eight types of negative electrode tabs 40 shown in Figures 6(A) to 6(C), 7(A) to 7(C), 8(A), and 8(B).
[0057] Here, eight types of negative electrode tabs 40, as shown in Figures 6(A) to 6(C), Figures 7(A) to 7(C), Figure 8(A), and Figure 8(B), were used. These negative electrode tabs 40 were made of nickel with a thickness T0 = 0.1 mm (Figure 9(A)), and projection processing was applied so that a group of protrusions 41 with a height H0 = 0.15 mm (Figure 9(A)) was formed at predetermined positions. The surface 42 of each of the eight types of negative electrode tabs 40 formed in this way, on which the group of protrusions 41, or the group of protrusions 41 and the protrusion 45, was provided, was placed facing the curved inner side surface 12 of the nickel-plated iron outer casing 10. Then, using welding electrodes 210 and 220, a welding current of 1.6 kA was applied, and resistance welding was performed on the group of protrusions 41, or the group of protrusions 41 and the protrusion 45 of the negative electrode tab 40 against the curved inner side surface 12 of the outer casing 10. The tensile strength between each of the eight types of welded negative electrode tabs 40 and the outer can 10 was measured and defined as the weld strength.
[0058] For each of the eight types of negative electrode tabs 40, ten samples were prepared by welding them to the outer can 10, and the average value and variation (standard deviation σ) of the welding strength of these ten samples were determined. In addition, for each of the eight types of negative electrode tabs 40, the presence or absence of perforation in the outer can 10 due to excessive welding current was checked in the ten samples. The results are shown in Table 1.
[0059] [Table 1] Sample No. 1 shown in Table 1 is a sample in which the negative electrode tab 40 shown in Figure 6(A), that is, a negative electrode tab 40 in which two groups of protrusions 41 are arranged in a straight line, is welded to the curved inner side surface 12 of the outer can 10.
[0060] Sample No. 2 shown in Table 1 is a sample in which the negative electrode tab 40 shown in Figure 6(B), that is, a negative electrode tab 40 in which three groups of protrusions 41 are arranged in a straight line, is welded to the curved inner side surface 12 of the outer can 10.
[0061] Sample No. 3 shown in Table 1 is a sample in which the negative electrode tab 40 shown in Figure 6(C), that is, a negative electrode tab 40 in which a total of six negative electrode tabs are arranged in two rows of three groups of protrusions 41 arranged in a straight line, is welded to the curved inner side surface 12 of the outer can 10.
[0062] Sample No. 4 shown in Table 1 is a sample in which the negative electrode tab 40 shown in Figure 7(A), that is, a negative electrode tab 40 in which three groups of protrusions 41 are arranged on the circumference 44, is welded to the curved inner side surface 12 of the outer can 10.
[0063] Sample No. 5 shown in Table 1 is a sample in which the negative electrode tab 40 shown in Figure 7(B), that is, a negative electrode tab 40 in which four groups of protrusions 41 are arranged on the circumference 44, is welded to the curved inner side surface 12 of the outer can 10.
[0064] Sample No. 6 shown in Table 1 is a sample in which the negative electrode tab 40 shown in Figure 7(C), that is, a negative electrode tab 40 in which six groups of protrusions 41 are arranged on the circumference 44, is welded to the curved inner side surface 12 of the outer can 10.
[0065] Sample No. 7 shown in Table 1 is a sample in which the negative electrode tab 40 shown in Figure 8(A), that is, the negative electrode tab 40 which has a total of four protrusions arranged therein, with three groups of protrusions 41 on the circumference 44 and one protrusion 45 in the center, is welded to the curved inner side surface 12 of the outer can 10.
[0066] Sample No. 8 shown in Table 1 is a sample in which the negative electrode tab 40 shown in Figure 8(B), that is, the negative electrode tab 40 which has a total of 5 protrusions arranged therein, with 4 groups of protrusions 41 on the circumference 44 and 1 protrusion 45 in the center, is welded to the curved inner side surface 12 of the outer can 10.
[0067] Table 1 shows that, compared to samples No. 1 to 3 (Figures 6(A) to 6(C)) using negative electrode tabs 40 with protrusions 41 arranged in a straight line, samples No. 4 to 6 (Figures 7(A) to 7(C)) using negative electrode tabs 40 arranged on the circumference 44 tend to have less variation in welding strength against the curved inner side surface 12 of the outer can 10. Comparing samples with the same number of protrusions 41 on the negative electrode tab 40 but differing in whether they are arranged in a straight line or on the circumference 44, for example, sample No. 2 and sample No. 4 (Figures 6(B) and 7(A)), even though the average welding strengths are about the same, sample No. 4, using a negative electrode tab 40 with protrusions 41 arranged on the circumference 44, shows less variation in welding strength. The same can be said for sample No. 3 and sample No. 6 (Figures 6(C) and 7(C)).
[0068] Furthermore, among samples No. 1 to 3, which used negative electrode tabs 40 with groups of protrusions 41 arranged in a straight line, perforation of the outer can 10 was observed in 3 out of 10 samples in sample No. 1 (Figure 6(A)), which used a negative electrode tab 40 with two groups of protrusions 41, and perforation of the outer can 10 was observed in 1 out of 10 samples in sample No. 2 (Figure 6(B)), which used a negative electrode tab 40 with three groups of protrusions 41. In contrast, in samples No. 4 to 6, which used negative electrode tabs 40 with groups of protrusions 41 arranged on the circumference 44, no perforation of the outer can 10 was observed in any of the 10 samples.
[0069] Furthermore, the negative electrode tab 40 of sample No. 7 (Figure 8(A)) corresponds to sample No. 4 (Figure 7(A)) with an additional protrusion 45 placed at the center (reference point 43) of the circumference 44 where the group of protrusions 41 is located. Comparing sample No. 4 and sample No. 7, the average values of their weld strengths are similar, and the variation in weld strength is even smaller for sample No. 7 than for sample No. 4. Similarly, the negative electrode tab 40 of sample No. 8 (Figure 8(B)) corresponds to sample No. 5 (Figure 7(B)) with an additional protrusion 45 placed at the center (reference point 43) of the circumference 44 where the group of protrusions 41 is located. Comparing sample No. 5 and sample No. 8, the average values of their weld strengths are similar, and the variation in weld strength is even smaller for sample No. 8 than for sample No. 5.
[0070] Furthermore, in both sample No. 7 and sample No. 8, no holes were observed in the outer can 10 of the 10 samples. From the results in Table 1, it can be said that using a negative electrode tab 40 with three or more groups of protrusions 41 arranged on the circumference 44 enables stable welding with reduced variation in welding strength, even when welding the curved inner side surface 12 of the outer can 10 by resistance welding. By arranging three or more groups of protrusions 41 of the negative electrode tab 40 on the circumference 44, the force applied when the negative electrode tab 40 is sandwiched between the welding electrode rods 210 and 220 and pressed against the curved inner side surface 12 of the outer can 10 is made uniform, thereby effectively suppressing variations in welding strength.
[0071] Furthermore, the results in Table 1 show that by arranging three or more groups of protrusions 41 on the negative electrode tab 40 on the circumference 44, and also by placing a protrusion 45 at the center of the circumference 44 (reference point 43), it is possible to further suppress variations in welding strength.
[0072] Further explanation will be given regarding a negative electrode tab 40 in which a projection 45 is positioned at the center of the circumference 44 on which the group of projections 41 is arranged. Figure 11 illustrates an example of a negative electrode tab in which a group of protrusions is arranged on the circumference and at its center. Figure 11(A) schematically shows a plan view of the main part of an example of a negative electrode tab, and Figure 11(B) schematically shows a cross-sectional view of the main part of an example of a negative electrode tab. Figure 11(B) is a cross-sectional view taken along line XI-XI in Figure 11(A).
[0073] Figures 11(A) and 11(B) show an example of a negative electrode tab 40 in which four groups of protrusions 41 are arranged on a circumference 44, and a protrusion 45 is positioned at the center of the circumference 44. In a negative electrode tab 40 as shown in Figures 11(A) and 11(B), for example, a punch is pressed into the flat negative electrode tab 40 from the surface 46 side by a partial punching process to form a recess 47, which in turn pushes out a group of protrusions on the opposite surface 42 side, thereby forming the group of protrusions 41 and 45. In a negative electrode tab 40 in which a protrusion 45 is positioned at the center of the circumference 44 on which the groups of protrusions 41 are arranged, the height H2 of the central protrusion 45 can be made lower than the height H1 of the groups of protrusions 41 on the circumference 44, as shown in Figure 11(B).
[0074] Figure 12 illustrates a second example of resistance welding between the negative electrode tab and the curved inner side surface of the outer can. Figures 12(A) and 12(B) schematically show a plan view of the main parts of an example of the state during resistance welding between the negative electrode tab and the inner side surface of the outer can, respectively.
[0075] Figures 12(A) and 12(B) schematically show a plan view of the main part of the outer can 10 as seen from the axial direction Z, as an example of the state during resistance welding between the negative electrode tab 40 and the inner side surface 12 of the outer can 10, as shown in Figures 11(A) and 11(B) above.
[0076] During resistance welding, as shown in Figure 12(A), the negative electrode tab 40 is positioned such that the surface 42 on which the group of protrusions 41 on the circumference 44 and the central protrusion 45 are located faces the curved inner side surface 12 of the outer can 10. At this time, the group of protrusions 41 on the circumference 44 of the negative electrode tab 40 are in contact with the curved inner side surface 12 of the outer can 10, while the central protrusion 45, which is lower in height than the group of protrusions 41, may not be in contact with the inner side surface 12. The tip 211 of the welding electrode rod 210 is brought into contact with the negative electrode tab 40, and the tip 221 of the welding electrode rod 220 is brought into contact with the outside (outer side surface) of the outer can 10. The negative electrode tab 40 is pressed by the welding electrode rod 210 with a predetermined pressure toward the inner side surface 12 of the outer can 10. The negative electrode tab 40 can be curved along the curved surface of the tip 211 of the welding electrode rod 210 when it comes into contact with the curved surface and is pressed. The outer can 10 is also pressed against the negative electrode tab 40 by the welding electrode rod 220 with a predetermined pressure. In this state, a predetermined welding current is passed between the welding electrode rod 210 and the welding electrode rod 220.
[0077] The welding current flowing through the negative electrode tab 40 first concentrates on the group of protrusions 41 that are relatively high before welding and in contact with the curved inner side surface 12 of the outer can 10. As a result, as shown in Figure 12(B), the tips of the group of protrusions 41 melt and are welded to the curved inner side surface 12 of the outer can 10, and the height of the group of protrusions 41 decreases. As the welding of the group of protrusions 41 progresses in this way, the central protrusion 45, which was relatively low before welding and was not in contact with or not sufficiently in contact with the curved inner side surface 12 of the outer can 10, comes into contact with the inner side surface 12, as shown in Figure 12(B). Then, welding current flows to the central protrusion 45, and the protrusion 45 is welded to the curved inner side surface 12 of the outer can 10. In a negative electrode tab 40 having a group of protrusions 41 arranged on the circumference 44 and a protrusion 45 located at the center of the circumference 44, welding to the curved inner side surface 12 of the outer can 10 is performed in this manner, for example.
[0078] In the case of a negative electrode tab 40 having a group of protrusions 41 arranged on the circumference 44 and a protrusion 45 located at the center of the circumference 44, before the central protrusion 45 contacts the inner side surface 12, the curved surface of the tip 211 of the welding electrode rod 210 comes into contact with it, causing the group of protrusions 41 on the circumference 44 to be uniformly pressed against the curved inner side surface 12 of the outer can 10. After the central protrusion 45 contacts the inner side surface 12, the tip 211 of such a welding electrode rod 210 comes into contact with it, causing the group of protrusions 41 and the protrusion 45 to be uniformly pressed against the curved inner side surface 12 of the outer can 10. For example, when the apex of the curved surface of the tip 211 of the welding electrode rod 210 comes into contact with a reference point 43 (the position where the projection 45 is placed) on the circumference 44 of the negative electrode tab 40 and pressurizes, the group of projections 41, or the group of projections 41 and projection 45, are uniformly pressurized against the curved inner side surface 12 of the outer can 10.
[0079] The negative electrode tab 40 may take on a curved shape during and after welding its projections 41 and 45 to the curved inner side surface 12 of the outer can 10. That is, the negative electrode tab 40 may take on a curved shape along the curved surface of the tip 211 of the welding electrode rod 210, or a curved shape along the curved inner side surface 12 of the outer can 10, due to the pressure applied by the welding electrode rod 210 to which it is in contact, or the joining force with the inner side surface 12 after welding.
[0080] Figure 13 illustrates an example of the state after resistance welding between the negative electrode tab and the curved inner side surface of the outer can. Figure 13 schematically shows a plan view of the main part of the outer can 10 as seen from the axial direction Z, as an example of the state after resistance welding of the negative electrode tab 40 and the inner side surface 12 of the outer can 10, as shown in Figures 11(A) and 11(B) above. Furthermore, Figure 13 schematically shows a plan view of the main part of the welded portion (connection portion) between the negative electrode tab 40 and the inner side surface 12 of the outer can 10, as seen in the direction from the negative electrode tab 40 toward the inner side surface 12.
[0081] In the case of a negative electrode tab 40 in which a projection 45 is positioned at the center of the circumference 44 where the group of projections 41 is arranged, and the height of the projection 45 before welding is lower than the height of the group of projections 41 before welding, as shown in Figure 13, after welding the negative electrode tab 40 to the inner side surface 12 of the outer can 10, the welded portion 48 between the group of projections 41 and the inner side surface 12 and the welded portion 49 between the projection 45 and the inner side surface 12 may have different shapes.
[0082] For example, as described above, when welding of a group of protrusions 41, which have a relatively high height before welding, is followed by welding of a group of protrusions 45, which have a relatively low height before welding, to the curved inner side surface 12 of the outer can 10, the welding area AR1 (connection area) of the welded portion 48 between the group of protrusions 41 and the inner side surface 12 will be larger than the welding area AR2 (connection area) of the welded portion 49 between the protrusions 45 and the inner side surface 12. Also, for example, when welding of a group of protrusions 41, which have a relatively high height before welding, is followed by welding of a group of protrusions 45, which have a relatively low height before welding, to the curved inner side surface 12 of the outer can 10, as described above, the maximum distance L1 from opposite ends to end of the welded portion 48 between the group of protrusions 41 and the inner side surface 12 will be longer than the maximum distance L2 from opposite ends to end of the welded portion 49 between the protrusions 45 and the inner side surface 12. Due to the difference in height between them, a difference in shape may occur between the welded portion 48 between the group of protrusions 41 and the inner side surface 12, and the welded portion 49 between the protrusion 45 and the inner side surface 12, after welding.
[0083] Furthermore, even if the heights of the projection group 41 and the projection 45 are the same, depending on the curvature of the inner side surface 12 of the outer can 10, the curvature of the tip 211 of the welding electrode rod 210, and the applied pressure, a difference in shape may occur between the welded portion 48 of the projection group 41 and the welded portion 49 of the projection 45, as shown in Figure 13.
[0084] Figure 14 illustrates an example of the shape of a negative electrode tab in which the group of protrusions is arranged on the circumference and at its center. Figure 14 schematically shows a cross-sectional view of the main part of an example of a negative electrode tab. Figure 14 shows an example of a negative electrode tab 40 in which a projection 45 is positioned at the center of the circumference 44 where the group of projections 41 are arranged, and the height of the projection 45 before welding is lower than the height of the group of projections 41 before welding. In the negative electrode tab 40 shown in Figure 14, for example, a punch is pressed into the flat negative electrode tab 40 from the surface 46 side by a partial punching process to form a recess 47, which in turn pushes out a group of projection-shaped protrusions to the opposite surface 42 side, thereby forming the group of projection-shaped protrusions as the group of projections 41 and the projection 45. The amount of pressure applied to the flat negative electrode tab 40 from the surface 46 side (or the amount of extrusion to the surface 42 side) is adjusted to form a group of projections 41 of a predetermined height H1 and a projection 45 of a predetermined height H2.
[0085] Here, it is preferable that the overall thickness M of the negative electrode tab 40 after the formation of the protrusions 41 and 45 is set to be less than 0.27 mm. It is preferable that the ratio M / T0 of the overall thickness M to the thickness T0 of the negative electrode tab 40 before the formation of the protrusions 41 and 45 (or after formation but in the part where the protrusions 41 and 45 have not been formed) is set to be less than 2.7.
[0086] In other words, the total thickness M = T0 + H1 of the projection 41 group formation area on the negative electrode tab 40 is preferably less than 0.27 mm, and when T0 = 0.1 mm, the ratio of the total thickness M to the thickness T0, M / T0, is less than 2.7. Similarly, the total thickness M = T0 + H2 of the projection 45 formation area on the negative electrode tab 40 is preferably less than 0.27 mm, and when T0 = 0.1 mm, the ratio of the total thickness M to the thickness T0, M / T0, is less than 2.7.
[0087] When forming the group of protrusions 41 and 45 by pressing the surface 46 side of the flat negative electrode tab 40 and pushing it out towards the surface 42 side, if the amount of pressing from the surface 46 side (or the amount of pushing towards the surface 42 side) is large, the thickness (wall thickness) of the negative electrode tab 40 may become partially thinner in the areas of the group of protrusions 41 and 45 (especially in their middle sections). In the group of protrusions 41, which are formed by pressing in a larger amount to make them higher than the protrusions 45, this partial thinning of the thickness of the negative electrode tab 40 is more likely to occur compared to the protrusions 45.
[0088] As described above, by setting the overall thickness M of the projection 41 group formation area and the projection 45 formation area to be less than 0.27 mm, or by setting the ratio of the overall thickness M to the thickness T0, M / T0, to be less than 2.7, it becomes possible to suppress the degree to which the thickness of the negative electrode tab 40 is partially thinned by the formation of the projection 41 group and the projection 45. For example, in either the projection 41 group or the projection 45, the difference between the thickness T1 (wall thickness) of that area and the thickness T0 can be kept to 20% or less, and the overall thickness distribution (or thickness variation) of the negative electrode tab 40 can be made uniform.
[0089] By making the overall thickness distribution of the negative electrode tab 40 uniform, such as to be 20% or less of the thickness T0, the localized concentration of the welding current and the resulting temperature rise during resistance welding can be suppressed. For example, due to the symmetrical arrangement of the group of protrusions 41 relative to the protrusion 45, the welding current is distributed to two or more locations, suppressing the localized concentration of the welding current and the resulting temperature rise. By suppressing the localized concentration of the welding current and temperature rise in this way, explosive spatter can be effectively suppressed.
[0090] Furthermore, even if the heights of the protrusions 41 and 45 are the same, by making the overall thickness distribution of the negative electrode tab 40 uniform, such as to be 20% or less of the thickness T0, explosive flying can be effectively suppressed in the same way.
[0091] Next, we will describe the results of evaluating the relationship between the height of the central projection 45, the welding strength (connection strength) with the curved inner side surface 12 of the outer can 10, and its variation, for a negative electrode tab 40 in which a projection 45 is positioned at the center of the circumference 44 where the group of projections 41 is arranged.
[0092] Here, resistance welding was performed against the curved inner side surface 12 of the outer casing 10 for two types of negative electrode tabs 40: one with four groups of protrusions 41 arranged on a circumference 44 and a protrusion 45 positioned at the center of the circumference 44, and another with varying heights of the central protrusion 45. The welding current was increased from 1.6kA to 2.7kA. For comparison, resistance welding was similarly performed against the curved inner side surface 12 of the outer casing 10 for a negative electrode tab 40 without four groups of protrusions 41 arranged on a circumference 44 and no protrusion 45 positioned at the center of the circumference 44, with the welding current increased to 2.7kA. The tensile strength between the welded negative electrode tab 40 and the outer casing 10 was measured and defined as the weld strength. For each negative electrode tab 40, ten samples were prepared by welding them to the outer casing 10, and the average value and variation (standard deviation σ) of the weld strength of these ten samples were determined. Furthermore, for each negative electrode tab 40, the presence or absence of perforations in the outer casing 10 of 10 samples was checked. The results are shown in Table 2.
[0093] [Table 2] Sample No. 5, shown in Table 2, is a sample in which the negative electrode tab 40 shown in Figure 7(B), that is, a negative electrode tab 40 in which four groups of protrusions 41 are arranged on the circumference 44, is welded to the curved inner side surface 12 of the outer can 10. This sample No. 5 is a comparative sample using a negative electrode tab 40 in which a protrusion 45 is not arranged at the center of the circumference 44.
[0094] Sample No. 8, shown in Table 2, is a sample in which a negative electrode tab 40, as shown in Figure 8(B), is welded to the curved inner side surface 12 of the outer can 10. This negative electrode tab 40 has a total of five protrusions: four groups of protrusions 41 on the circumference 44 and one protrusion 45 in the center. Sample No. 8 is a reference sample using a negative electrode tab 40 in which the height of the group of protrusions 41 on the circumference 44 (H0; Figure 9(A)) and the height of the central protrusion 45 are equal.
[0095] Similarly, samples No. 8a to 8e shown in Table 2 are samples in which a negative electrode tab 40, as shown in Figure 8(B), is welded to the curved inner side surface 12 of the outer can 10. This negative electrode tab 40 has a total of five protrusions arranged on it: four groups of protrusions 41 on the circumference 44 and one protrusion 45 in the center. These samples No. 8a to 8e use a negative electrode tab 40 in which the height of the central protrusion 45 (H2; Figure 11(B)) is lower than the height of the groups of protrusions 41 on the circumference 44 (H1; Figure 11(B)).
[0096] In Table 2, the height [mm] of the central projection 45 is the height H2 shown in Figure 11(B), and the ratio [%] is the ratio of the height H2 of the central projection 45 to the height H1 of the projection 41 on the circumference 44 (or H0 = 0.150 mm in Figure 9(A)).
[0097] Table 2 shows that under the condition of increasing the welding current from 1.6kA to 2.7kA, sample No. 5, which uses a negative electrode tab 40 in which no protrusion 45 is positioned at the center of the circumference 44, shows a large variation in welding strength, while sample No. 8, which uses a negative electrode tab 40 in which a protrusion 45 of the same height as the group of protrusions 41 on the circumference 44 is positioned at the center, shows a reduced variation in welding strength. However, in sample No. 8, when the welding current was increased, the welding current concentrated on the central protrusion 45, and perforation occurred in the outer can 10 (the part corresponding to the protrusion 45 (center)) in 4 out of 10 samples. Similarly, in sample No. 8a, which used a negative electrode tab 40 in which the ratio of the height of the central projection 45 to the height of the group of projections 41 on the circumference 44 was 80%, the variation in welding strength was suppressed, but due to the concentration of the welding current on the central projection 45, holes were formed in the outer can 10 (the part corresponding to the projection 45 (center)) in 2 out of 10 samples.
[0098] In contrast, in sample No. 8b, which used a negative electrode tab 40 in which the ratio of the height of the central projection 45 to the height of the group of projections 41 on the circumference 44 was 60%, even when the welding current was increased to 2.7kA, the variation in welding strength was suppressed, and the perforation of the outer can 10 due to the concentration of the welding current on the central projection 45 was also suppressed. Similarly, in sample No. 8c, which used a negative electrode tab 40 in which the ratio of the height of the central projection 45 to the height of the group of projections 41 on the circumference 44 was 50%, sample No. 8d, which used a negative electrode tab 40 with a height ratio of 30%, and sample No. 8e, which used a negative electrode tab 40 with a height ratio of 20%, both the variation in welding strength and the perforation of the outer can 10 were suppressed.
[0099] From the results in Table 2, when using a negative electrode tab 40 for resistance welding to the curved inner side surface 12 of the outer can 10, in which a projection 45 is positioned at the center of the circumference 44 where the group of projections 41 is arranged, it is preferable that the height of the central projection 45 be in the range of 20% to 60% of the height of the group of projections 41 on the circumference 44. By setting the height of the central projection 45 in this range of 20% to 60% of the height of the group of projections 41 on the circumference 44, it is possible to effectively suppress variations in welding strength and perforation of the outer can 10. Even when relatively high welding current conditions are used during resistance welding, if the height of the projection 45 of the negative electrode tab 40 is within this range, variations in welding strength and perforation of the outer can 10 can be suppressed.
[0100] In the above description, we have mainly shown a configuration in which both the group of protrusions 41 and the protrusion 45 are welded to the inner side surface 12 of the outer can 10, when using a negative electrode tab 40 in which the group of protrusions 41 is arranged and the protrusion 45 is lower in height than the group of protrusions 41 before welding. However, it is also possible that the group of protrusions 41 on the circumference 44 is welded to the inner side surface 12, while the central protrusion 45 is not welded to the inner side surface 12. Furthermore, even if the heights of the group of protrusions 41 and the protrusion 45 are the same, it is also possible that the group of protrusions 41 on the circumference 44 is welded to the inner side surface 12, while the central protrusion 45 is not welded to the inner side surface 12. Whether or not the central projection 45 is welded to the inner side surface 12 may be influenced by the specifications of the cylindrical battery 1 and the welding electrode rod 210, such as the curvature of the inner side surface 12 of the outer casing 10, the curvature of the tip 211 of the welding electrode rod 210, and the pressure applied.
[0101] Furthermore, in the above explanation, an example was given in which, in a cylindrical battery 1 in which the outer casing 10 functions as the negative electrode, the negative electrode tab 40 connected to the negative electrode layer 22 of the winding body 20 housed inside the outer casing 10 is connected to the curved inner side surface 12 of the outer casing 10 by resistance welding.
[0102] In addition, the cylindrical battery 1 may be configured such that the outer casing 10 functions as the positive electrode. In this configuration, the positive electrode tab connected to the positive electrode layer 21 of the winding body 20 housed inside the outer casing 10 can be configured as described for the negative electrode tab 40, and connected to the curved inner side surface 12 of the outer casing 10 by resistance welding. Furthermore, in this case, the negative electrode tab connected to the negative electrode layer 22 of the winding body 20 can be configured as described for the positive electrode tab 30, and connected to the negative electrode terminal provided on the sealing body 80 via a gasket 90 instead of the positive electrode terminal 100. The connection technique between the negative electrode tab 40 and the curved inner side surface 12 of the outer casing 10 described above can also be similarly applied to the connection between the positive electrode tab and the curved inner side surface 12 of the outer casing 10. [Explanation of Symbols]
[0103] 1. Cylindrical battery 10 outer cans 10a,40a axis 11 Bottom 12 Medial side 20 Winding body 20a power generation element 21 Positive electrode layer 22 Negative electrode layer 23 Separator 23a,23b,42,46 sides 24 Insulating Tape 30 Positive Tabs 40 Negative Electrode Tabs 41,45 protrusion 43 Reference point 44 Circumference 47 Recess 48,49 Welded parts 50, 60 Insulating board 70 Nonaqueous electrolyte 80 Sealing body 90 Gasket 100 Positive terminal 210,220 Welding electrode rods 211,221 Tip AR1, AR2 Welding Area H0, H1, H2 Height L1,L2 maximum distance M Overall thickness S0 side T0, T1 thickness
Claims
1. A cylindrical outer can, The outer can has a first surface facing the curved inner side surface, and the first surface comprises three or more groups of first protrusions located on the circumference centered on a reference point of the first surface, and a second protrusion located at the reference point, and the tab is connected to the inner side surface by the groups of first protrusions and the second protrusion. Includes, A cylindrical battery characterized in that, in a plan view taken from the tab toward the inner side surface, the connection area of each connection portion between the first group of protrusions and the inner side surface is larger than the connection area of the connection portion between the second protrusion and the inner side surface.
2. The outer container contains an electrode layer, The cylindrical battery according to claim 1, characterized in that one end of the tab is connected to the inner side surface and the other end is connected to the electrode layer.
3. The cylindrical battery according to claim 1 or 2, characterized in that, in a plan view when viewed from the tab toward the inner side surface, the maximum distance between the opposing ends of each connection portion between the first group of protrusions and the inner side surface is greater than the maximum distance between the opposing ends of the connection portion between the second protrusion and the inner side surface.
4. The aforementioned reference point is located at the center of the width of the tab in a direction perpendicular to the axial direction of the outer can. The cylindrical battery according to any one of claims 1 to 3, characterized in that the tab has a shape that is symmetrical when viewed from the first surface side with respect to an axis that is parallel to the axial direction of the outer casing and passes through the reference point.
5. The cylindrical battery according to any one of claims 1 to 4, characterized in that the distance between adjacent members of the first group of protrusions is equal to each other.
6. The cylindrical battery according to any one of claims 1 to 5, characterized in that the tab has a group of recesses on a second surface opposite to the first surface, and a group of protruding portions on the first surface corresponding to each of the recesses.
7. The process of preparing the cylindrical outer can, The process of preparing a tab having a first surface facing the curved inner side surface of the outer can, the first surface comprising three or more groups of first protrusions located on a circle centered on a reference point of the first surface, and a second protrusion located at the reference point, wherein the height of the second protrusion relative to the first surface is lower than the height of the group of first protrusions relative to the first surface, The steps include connecting the tab to the inner surface with the first group of protrusions and the second protrusions. A method for manufacturing a cylindrical battery, characterized by including the following:
8. The method for manufacturing a cylindrical battery according to claim 7, characterized in that the height of the second projection relative to the first surface is in the range of 20% to 60% of the height of the first group of projections relative to the first surface.
9. The aforementioned tab is The second surface opposite to the first surface has a group of recesses, and the first surface has a group of protruding parts corresponding to each of the recesses, The method for manufacturing a cylindrical battery according to claim 7 or 8, characterized in that the difference in thickness between any protrusion of the group of protrusions and the thickness between the first surface and the second surface is 20% or less.