Secondary battery and manufacturing method of secondary battery

Abstract

To provide a secondary battery capable of suppressing an influence on a productivity, and releasing a tension stress generated in a tab part where a collector terminal is boned in welding the collector terminal, and provide a manufacturing method of the secondary battery.SOLUTION: A notch 38 is formed on a front surface side of a tab group 34 so as to cross a virtual line VL coupling a first portion P1 that is nearest to one boundary B1 that is closer to a terminal bonding part 34A of a positive electrode in two boundaries B1 and B2 of a flat surface 32A of an outer peripheral surface around a circumference of a winding shaft of an electrode main body part 32 and curvature end surfaces 32B and 32C from a portion to which ends 22U and 22Z in a direction orthogonal to a width direction and a thickness direction of a tab connection part 22A in the terminal bonding part 34A of the positive electrode, and a second portion P2 that is one part of the outermost peripheral part of a part where a mixture material layer is formed in an electrode sheet 40 of the positive electrode having the first portion P1, and is closest to the first portion P1 from a portion corresponding to the one boundary B1.SELECTED DRAWING: Figure 5A

Description

[Technical field]

[0001] The present invention relates to a secondary battery and a method for manufacturing a secondary battery. [Background technology]

[0002] The following Patent Document 1 discloses technology relating to a battery having an electrode winding body (electrode body) in which positive and negative electrode sheets are wound into a flat shape having a flat portion and turn portions on both sides of the flat portion, and positive and negative current collecting members (current collecting terminals) connected to the positive and negative electrode sheets, respectively.

[0003] To put it simply, in this prior art, the electrode wound body has protruding non-coated sections (tab sections) on both ends in the winding axis direction, where no electrode active material layer is formed on the current collecting foil, and positive and negative current collecting members are joined to these non-coated sections. In addition, in at least one of the non-coated sections, cuts are made from the end side in at least two places in the flat section, and a folded-back section is formed in which the current collecting foil between the cuts is folded back along a crease in a direction intersecting the winding axis direction.

[0004] In such a configuration, the difference in thickness between the power generating section (electrode main body section) that constitutes the middle section of the electrode winding in the winding axis direction and the section where the protruding tip ends of the multiple non-coated sections are bundled together can be reduced, thereby reducing the tensile stress (tension) that occurs in the non-coated sections when the protruding tip ends of the multiple non-coated sections are bundled together and the current collecting member is welded. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-186151 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the case of the above-mentioned prior art, not only is the process complicated, but the folded-back portion increases the thickness and makes it easier for misalignment to occur, which is disadvantageous in welding the current collecting member to the non-coated portion, and therefore there is room for improvement in terms of productivity.

[0007] In consideration of the above, an object of the present invention is to provide a secondary battery and a method for manufacturing a secondary battery that can reduce the tensile stress generated in a tab portion to which a current collecting terminal is joined when the current collecting terminal is welded, while minimizing the impact on productivity. [Means for solving the problem]

[0008] A secondary battery according to a first aspect of the present invention includes an electrode assembly in which positive and negative electrode sheets, each having a composite layer formed on a portion of the surface of a sheet-like current collector for a positive and negative electrode, are stacked with a separator sandwiched therebetween and wound flat around a winding axis; a group of positive and negative electrode tabs that constitute a portion of the electrode assembly and are part of the current collector, the group of current collectors having a plurality of tab portions protruding in the axial direction of the winding axis from an electrode main body portion in which the current collector, the composite layer, and the separator are stacked, in the stacking direction, and that are arranged on one side and the other side of the axial direction, and a tab connection portion that is connected to an end of a surface of the foil collecting portion of the group of positive and negative electrode tabs. a first portion, which is the portion closest to one of two boundaries between a flat surface and a curved end surface of the outer peripheral surface of the electrode main body around the winding axis and a curved end surface of the electrode sheet, the first portion being the portion closest to the one of the boundaries that is closer to the terminal joint; and a second portion, which is part of the outermost portion of a portion where the composite layer is formed in the electrode sheet having the first portion and is the portion closest to the first portion among the portions corresponding to the one of the boundaries.

[0009] A secondary battery according to a second aspect of the present invention is the secondary battery according to the first aspect of the present invention, wherein the cut is formed in a shape that is open on the first portion side.

[0010] A third aspect of the secondary battery of the present invention is a secondary battery of the first or second aspect of the present invention, wherein the position where the notch crosses the virtual line is set on the first portion side of the midpoint between the first portion and the second portion.

[0011] A manufacturing method for a secondary battery according to a fourth aspect of the present invention is a method for manufacturing a secondary battery having: an electrode body in which positive and negative electrode sheets, each of which has a composite layer formed on a portion of the surface of a sheet-like current collector for a positive and negative electrode, are stacked with a separator sandwiched therebetween and wound flat around a winding axis; a group of positive and negative electrode tabs constituting a portion of the electrode body and part of the current collector, the group of current collectors including a plurality of tab portions protruding along the axial direction of the winding axis from an electrode main body portion in which the current collector, the composite layer, and the separator are stacked, in the stacking direction, and having a foil collecting portion in which portions of the protruding tip sides of the plurality of tab portions are bundled and stacked, the group of positive and negative electrode tabs being disposed on one side and the other side in the axial direction; and positive and negative electrode current collecting terminals having tab connection portions joined by welding to terminal joining portions on surfaces of the foil collecting portions of the tab groups for the positive and negative electrodes, respectively. the electrode sheet has a first portion, which is a portion closest to one of two boundaries between a flat surface and a curved end surface of the outer peripheral surface around the winding axis of the electrode main body and the curved end surface of the electrode sheet which is closer to the terminal joint portion, among portions where ends of the tab connection portion in a direction perpendicular to the width direction and the thickness direction contact, and a second portion, which is a part of the outermost portion of a portion where the composite layer is formed in the electrode sheet which includes the first portion and is the portion closest to the first portion among portions corresponding to the one boundary; and a welding process, which joins the tab connection portion of the current collecting terminal to the terminal joint portion of the foil collecting terminal by welding after the cutting process, with portions on the protruding tip sides of the multiple tab portions being bundled together.

[0012] A fifth aspect of the present invention relates to a method for producing a secondary battery according to the fourth aspect of the present invention, wherein in the cutting step, the cut is formed so that the first portion side is open.

[0013] A sixth aspect of the present invention is a method for manufacturing a secondary battery according to the fourth or fifth aspect of the present invention, wherein in the cutting step, a cutting blade attached to a welding machine used in the welding step forms the incision, and in the welding step, welding is performed by the welding machine without changing the position of the welding machine when the cutting step is performed.

[0014] A seventh aspect of the present invention is a method for manufacturing a secondary battery according to the sixth aspect of the present invention, wherein the position at which the cut crosses the virtual line in the cutting step is set closer to the first portion than the midpoint between the first portion and the second portion. Effect of the Invention

[0015] In the secondary battery of the first aspect of the present invention, a notch is formed on the surface layer side of the tab group, and this notch is formed to cross an imaginary line connecting a first portion, which is the portion closest to one of two boundaries between the flat surface and the curved end surface of the outer circumferential surface around the winding axis of the electrode body portion and the boundary closer to the terminal joint portion, among the portions where the ends of the tab connection portion in the direction perpendicular to the width direction and the thickness direction contact at the terminal joint portion, and a second portion, which is a part of the outermost portion of the portion where the composite layer is formed in the electrode sheet including the first portion and is the portion closest to the first portion among the portions corresponding to the boundary. Therefore, the notch can reduce the impact on productivity and alleviate the tensile stress generated in the tab portion to which the current collector terminal is joined when the current collector terminal is welded.

[0016] In the secondary battery according to the second aspect of the present invention, the cut is prevented from spreading to the portion of the current collector on the surface of which the composite layer is formed, compared with, for example, a linear cut extending in a direction perpendicular to the imaginary line, and therefore, even if the cut is formed, the effect on performance can be minimized.

[0017] In the secondary battery of the third aspect of the present invention, for example, if a cutting blade is attached to a welding machine during manufacturing, the imaginary line connecting the first and second portions can be crossed with high accuracy even if the length of the cut is set short.

[0018] In the method for producing a secondary battery according to the fourth aspect of the present invention, a cut is formed on the surface layer side of the tab group so as to cross an imaginary line connecting a first portion, which is the portion closest to one of two boundaries between the flat surface and the curved end surface of the outer peripheral surface around the winding axis of the electrode body portion and the boundary closer to the terminal joint portion, and a second portion, which is a part of the outermost portion of the portion where the composite layer is formed in the electrode sheet including the first portion and is the portion closest to the first portion among the portions corresponding to the boundary, among the portions where the ends of the tab connection portion in the direction perpendicular to the width direction and the thickness direction contact each other, in the terminal joint portion. Then, the tab connection portion of the current collecting terminal is joined to the terminal joint portion of the collecting foil portion by welding while the protruding tip side portions of the multiple tab portions are bundled together. During the welding of the current collecting terminal, the tensile stress generated in the tab portion to which the current collecting terminal is joined can be alleviated by the cut. In addition, since the cut is only formed on the surface layer side of the tab group, the effect on productivity is suppressed.

[0019] In the method for producing a secondary battery according to the fifth aspect of the present invention, compared with, for example, a linear cut extending in a direction perpendicular to the imaginary line, the cut is prevented from spreading to the portion of the current collector on the surface of which the composite layer is formed after the cutting step, and therefore, even if a cut is formed, the effect on performance can be minimized.

[0020] In the manufacturing method for a secondary battery of the sixth aspect of the present invention, the relative positional accuracy of the welding position of the tab connection portion of the current collecting terminal to the terminal joint portion of the foil collecting portion in the tab group and the formation position of the notch on the surface side of the tab group can be improved.

[0021] In the method for manufacturing a secondary battery according to the seventh aspect of the present invention, even if the length of the cut is set short, it can cross the imaginary line connecting the first portion and the second portion with high accuracy. [Brief description of the drawings]

[0022] [Figure 1] 1 is a partially exploded perspective view of a secondary battery according to an embodiment; [Diagram 2]1 is a schematic diagram showing the configuration of an electrode body according to an embodiment, with a part cut away and simplified; [Diagram 3] 3 is a cross-sectional view showing a schematic view of a part in the thickness direction and width direction taken along line 3L-3L in FIG. 1. [Figure 4] 2 is a cross-sectional view showing a schematic view of a vertical center portion of the positive electrode tab group in FIG. 1 cut horizontally. FIG. [Figure 5A] 2 is a simplified front view showing the electrode body and the current collecting terminal in FIG. 1 in an exploded state. FIG. [Figure 5B] 5B is an enlarged view of the cut in FIG. 5A and its surrounding area. FIG. [Figure 5C] 5B is a simplified front view showing a state in which a current collecting terminal is joined to the electrode body of FIG. 5A. FIG. [Figure 6] 2 is a side view showing in a simplified form the current collecting terminal of the positive electrode in FIG. 1. [Figure 7] 2 is a side view showing a schematic outline of an upper portion of a side surface of the electrode body in FIG. 1. [Figure 8] FIG. 2 is a schematic diagram showing a configuration in which a cutting blade is attached to a welding machine for welding a current collecting terminal to an electrode body. [Figure 9] FIG. 1 is a cross-sectional view showing a part of a cross section on the outer periphery side of an electrode body according to a conventional technique. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] A secondary battery and a method for manufacturing the secondary battery according to the embodiment will be described with reference to Figs. 1 to 9. The secondary battery according to the embodiment is, for example, a lithium ion secondary battery constituting a battery module used as an on-board power source for an electric vehicle or the like. Note that an arrow X shown as appropriate in the drawings indicates the axial direction of a winding axis 30L (see Fig. 2) around which the electrode body 30 is wound, an arrow Y indicates the winding direction of the electrode body 30 around the winding axis, and an arrow Z indicates the thickness direction of the electrode body 30. The direction indicated by the arrow X is the direction that coincides with the battery width direction, which is the width direction of the secondary battery 10, and the direction indicated by the arrow Z is the direction that coincides with the thickness direction of the secondary battery 10. In the following description, when the configurations of the positive electrode side and the negative electrode side are collectively indicated, they may be expressed as "positive and negative electrodes".

[0024] [Configuration of secondary battery 10] Fig. 1 shows a perspective view of a secondary battery 10 according to an embodiment in a partially disassembled state. As shown in Fig. 1, the secondary battery 10 has a lid assembly 20, an electrode body 30, and a battery case 70. Note that in Fig. 1, the lid assembly 20 and the electrode body 30 are shown in a joined state.

[0025] (battery case 70) The battery case 70 is formed in a rectangular box shape that is open at the top and is elongated in the width direction of the battery. The battery case 70 contains the electrode assembly 30 and an electrolyte.

[0026] (Lid Assembly 20) The lid assembly 20 has a lid member 21, positive and negative current collecting terminals 22, 24 for inputting and outputting electric power from the electrode body 30, and external terminals 26, 28 for external connection. Of the pair of current collecting terminals 22, 24, the current collecting terminal 22 on the one side in the width direction of the battery is a current collecting terminal for the positive electrode, and the external terminal 26 electrically connected to this current collecting terminal 22 is an external terminal for the positive electrode. Moreover, of the pair of current collecting terminals 22, 24, the other current collecting terminal 24 on the width direction of the battery is a current collecting terminal for the negative electrode, and the external terminal 28 electrically connected to this current collecting terminal 24 is an external terminal for the negative electrode.

[0027] The lid member 21 is formed in a rectangular plate shape that is long in the battery width direction. The lid member 21 is attached so as to cover the opening of the battery case 70. The lid member 21 is provided with a safety valve 21A and a cap 29 that covers the injection port 21B. The safety valve 21A is configured to open when the internal pressure of the battery case 70 reaches a predetermined pressure, and to discharge gas generated inside the battery case 70. The injection port 21B is a through hole formed through the lid member 21 in the plate thickness direction, and is used when injecting an electrolyte into the battery case 70.

[0028] The positive electrode collector terminal 22 and the positive electrode external terminal 26 are made of, for example, an aluminum alloy, and the negative electrode collector terminal 24 and the negative electrode external terminal 28 are made of, for example, a copper alloy. The positive and negative electrode collector terminals 22, 24 are each a plate-like member having a portion bent in a crank shape (approximately Z-shape). The positive and negative electrode collector terminals 22, 24 are joined to the electrode body 30. This will be described in detail later. The positive and negative electrode external terminals 26, 28 are exposed to the outside of the cover member 21. The positive electrode external terminal 26 is disposed on the same side as the positive electrode collector terminal 22 in the battery width direction, and the negative electrode external terminal 28 is disposed on the same side as the negative electrode collector terminal 24 in the battery width direction.

[0029] (Electrode body 30) The electrode body 30 has an electrode main body 32 constituting the widthwise middle portion, and positive and negative electrode tab groups 34, 36 provided on both widthwise sides. Fig. 2 shows a simplified schematic diagram of the electrode main body 32 with a part cut away. Fig. 3 shows a schematic cross-sectional view of a part in the thickness direction and width direction cut along line 3L-3L in Fig. 1.

[0030] The electrode body 30 is formed by stacking the positive and negative electrode sheets 40, 50, each of which has a composite layer 44, 54 formed on a portion of the surface of the sheet-like positive and negative electrode collectors 42, 52 shown in Fig. 3, with a separator 60 sandwiched between them, and then winding the electrode sheets 40, 50 in a flat shape around the winding axis 30L as shown in Fig. 2. For convenience, the eight layers shown in Fig. 3 are not shown in detail in Fig. 2. The electrode body 32 is formed by stacking the current collectors 42, 52, the composite layers 44, 54, and the separator 60. The separator 60 is formed of an insulating material such as polypropylene.

[0031] The positive electrode current collector 42 shown in FIG. 3 is made of, for example, a foil of an aluminum alloy or the like. A composite layer 44 is applied to both sides of the current collector 42 except for a portion along one edge in the width direction. The composite layer 44 is configured to contain at least an active material that constitutes the positive electrode. The negative electrode current collector 52 is made of, for example, a foil of a copper alloy. A composite layer 54 is applied to both sides of the current collector 52 except for a portion along the other edge in the width direction. The composite layer 54 is configured to contain at least an active material that constitutes the negative electrode.

[0032] FIG. 4 shows a schematic cross-sectional view of the positive electrode tab group 34 in FIG. 1 cut horizontally at the vertical center. The positive electrode tab group 34 is a part of the positive electrode current collector 42 shown in FIG. 3, and includes a plurality of tabs 42T protruding from the electrode main body 32 along the axial direction of the winding shaft in the lamination direction of eight layers shown in FIG. 3, and has a foil collection part 34X in which the protruding tip side parts of the plurality of tabs 42T shown in FIG. 4 are bundled and laminated, and is disposed on one side of the axial direction of the winding shaft. The protruding tip side of the tabs 42T is brought closer to the center position (see dashed line CL) in the thickness direction of the electrode body 30, and is bent in a stretched state. The tabs 42T are bent more toward the outer periphery.

[0033] The negative electrode tab group 36 shown in Fig. 1 is not shown in detail, but is a part of the negative electrode current collector 52 shown in Fig. 3, and includes a plurality of tab portions 52T protruding from the electrode main body portion 32 along the axial direction of the winding shaft in the lamination direction of eight layers shown in Fig. 3, and has a foil collecting portion 36X (see Fig. 1) in which the protruding tip side portions of the plurality of tab portions 52T (only one tab portion 52T is shown in Fig. 3) are bundled and laminated, and is disposed on the other side of the axial direction of the winding shaft. Supplementally, the negative electrode tab group 36 shown in Fig. 1 is disposed in a state substantially similar to that of the positive electrode tab group 34 shown in Fig. 4, which is inverted left and right.

[0034] The tab connection portion 22A of the positive electrode current collector terminal 22 shown in Figures 5A and 5C is joined by welding to the terminal joint portion 34A (portion surrounded by a two-dot chain line) on the surface of the foil collecting portion 34X of the positive electrode tab group 34 shown in Figure 5A. In each figure, the tab portion 42T to which the tab connection portion 22A of the positive electrode current collector terminal 22 is joined is indicated by "42T1" in parentheses after the reference symbol 42T. The tab connection portion 24A of the negative electrode current collector terminal 24 shown in Figures 5A and 5C is joined by welding to the terminal joint portion 36A on the surface of the foil collecting portion 36X of the negative electrode tab group 36 shown in Figure 5A.

[0035] 6 shows a simplified side view of the positive electrode current collector terminal 22. As shown in FIG. 6, the tab connection portion 22A of the current collector terminal 22 is formed in a flat shape. A ridge line extending in the width direction (direction perpendicular to the paper surface of FIG. 6) is formed at the end (here, the upper end) 22U opposite to the end 22Z on the tip side of the tab connection portion 22A. Note that, although a simplified side view of the negative electrode current collector terminal 24 (see FIG. 1) is omitted, the shape of the current collector terminal 24 (see FIG. 1) is, for example, substantially the same shape as the positive electrode current collector terminal 22.

[0036] As shown in FIG. 5A, among the portions at the terminal joint 34A of the positive electrode where the ends 22U, 22Z in the direction perpendicular to the width direction and thickness direction of the tab connection portion 22A are in contact, a first portion P1 is the portion closest to one boundary B1 closer to the terminal joint 34A of the positive electrode, of the two boundaries B1, B2 between the flat surface 32A of the outer peripheral surface around the winding axis of the electrode main body 32 and the curved end faces 32B, 32C, and a second portion P2 is a part of the outermost portion of the portion where the composite layer 44 (see FIG. 3) is formed in the electrode sheet 40 of the positive electrode having the first portion P1, and is the portion closest to the first portion P1 among the portions corresponding to the one boundary B1. In FIG. 5A, for ease of viewing, the position of the second portion P2 is shown as being the same as the right end of one boundary B1 (the same applies to FIGS. 5B and 5C).

[0037] The cut 38 is formed in a shape (for example, a semicircular shape) that is open on the first portion P1 side. Fig. 5B shows an enlarged view of the cut 38 and its surroundings. As shown in Fig. 5B, the position where the cut 38 crosses the virtual line VL is set on the first portion P1 side of the center point P3 between the first portion P1 and the second portion P2.

[0038] In this embodiment, the curved end faces 32B, 32C of the outer circumferential surface around the winding axis of the electrode main body 32 shown in Fig. 5A are formed in a semicircular arc shape, for example. Therefore, in this embodiment, the vertical position of the boundary B1 between the flat surface 32A of the outer circumferential surface around the winding axis of the electrode main body 32 and the upper curved end face 32B coincides with a position that is lowered downward from the vertex 32T of the upper curved end face 32B by a length obtained by multiplying the thickness t of the electrode main body 32 by 1 / 2, as shown typically in Fig. 7.

[0039] [Welding machine 100 used in manufacturing secondary battery 10] Next, a description will be given of a welding machine used to manufacture the secondary battery 10 shown in Fig. 1. Fig. 8 shows a schematic diagram of a welding machine 100 for welding the current collecting terminals 22, 24 (see Fig. 1) to the electrode body 30 (shown by a two-dot chain line (imaginary line) in the figure).

[0040] The welding machine 100 includes an anvil 102 that holds the objects to be welded (in the figure, the foil collecting portion 34X of the electrode body 30 and the tab connection portion 22A of the current collecting terminal 22) and an ultrasonic horn 104, and is capable of ultrasonically welding the objects to be welded while applying pressure to them. The welding machine 100 is equipped with a cutting blade 106 (shown as a block in the figure), and this cutting blade 106 is an electric power tool that is capable of forming the incisions 38 on the surface side of the tab group 34 shown in Fig. 5C etc.

[0041] [Method of manufacturing secondary battery 10] Next, a method for manufacturing the secondary battery 10 will be described.

[0042] First, the positive and negative electrode sheets 40, 50 shown in FIG. 3 are laminated with a separator 60 sandwiched between them, and then wound flat around a winding axis to form the electrode assembly 30 (electrode assembly forming step).

[0043] Next, in the region where the ends 22U, 22Z in the direction perpendicular to the width direction and thickness direction of the tab connection portion 22A contact in the terminal joint 34A of the positive electrode shown in FIG. 5A, a first region P1 is formed on the surface side of the tab group 34 so as to cross a virtual line VL connecting a first region P1, which is the region closest to one boundary B1 closer to the terminal joint 34A of the positive electrode, of two boundaries B1, B2 between the flat surface 32A of the outer peripheral surface around the winding axis of the electrode main body 32 and the curved end faces 32B, 32C, and a second region P2, which is a part of the outermost region of the portion where the composite layer 44 (see FIG. 3) is formed in the electrode sheet 40 of the positive electrode having the first region P1 and is the region closest to the first region P1 among the regions corresponding to the one boundary B1 (cutting process).

[0044] In this cutting step, the cut 38 is formed so that the first portion P1 side is open. Therefore, compared with, for example, a linear cut extending in a direction perpendicular to the virtual line VL, the cut is prevented from spreading to a portion of the positive electrode current collector 42 on whose surface the composite layer 44 (see FIG. 3) is formed after the cutting step. Therefore, even if the cut 38 is formed, the effect on performance (for example, the effect of current interruption) can be minimized.

[0045] In the cutting step, a cutting blade 106 attached to a welding machine 100 shown in Fig. 8, which is used in a welding step described later, forms the incision 38 shown in Fig. 5C. The incision 38 is formed simultaneously with the installation of the current collecting terminals 22, 24. Furthermore, the position where the incision 38 crosses the imaginary line VL in the cutting step is set on the first portion P1 side of the center point P3 between the first portion P1 and the second portion P2, as shown in Fig. 5B. Therefore, even if the length of the incision 38 is set short, the incision 38 can cross the imaginary line VL connecting the first portion P1 and the second portion P2 with high accuracy.

[0046] After the cutting step, as shown in Fig. 4, the protruding tip end portions of the multiple tab portions 42T, 52T (see Fig. 3 for tab portion 52T) are bundled together, and the tab connections 22A, 24A of the current collecting terminals 22, 24 are joined by welding to the terminal joints 34A, 36A of the foil collecting portions 34X, 36X shown in Fig. 5A (welding step). At this time, the tensile stress generated in the tab portion 42T (42T1) to which the tab connection portion 22A of the positive electrode current collecting terminal 22 shown in Fig. 5C etc. is joined can be alleviated by the cuts 38.

[0047] Here, the occurrence of an internal short circuit will be further explained with reference to Fig. 9. Fig. 9 shows a part of a cross section near the outer circumferential side of the electrode body 130 of the conventional technology and a portion corresponding to the second portion P2 (see Fig. 5C) of this embodiment. In Fig. 9, for convenience, the axial direction of the winding shaft around which the electrode body 130 is wound, the positive and negative electrode sheets and their constituent parts, and the separator are given the same reference numerals as in this embodiment.

[0048] In the electrode body 130 of the prior art, when a plurality of tab portions 42T are bundled and pressed by a welding machine, a large tensile stress (tension) is generated in the outermost positive electrode tab portion 42T, which may cause a dimple 140 to be generated in a part of the outermost positive electrode tab portion 42T, which is deformed so as to be warped toward the inside in the stacking direction. The tensile stress is greatest on a line corresponding to the virtual line VL (see FIG. 5C) in this embodiment, and a dimple 140 is generated on the line.

[0049] If this dimple 140 occurs, the separator 60 may be pinched between the positive electrode tab portion 42T at the outermost periphery and the negative electrode sheet 50 on its inner periphery, which may cause the separator 60 to break. Furthermore, if ultrasonic welding is performed between the current collecting terminal (not shown) and the tab portion 42T in this state, the vibrations generated during joining are transmitted to the dimples 140, making the separator 60 more likely to break. If the separator 60 is broken, there is a possibility that the positive electrode sheet 40 and the negative electrode sheet 50 may come into contact with each other, i.e., an internal short circuit may occur.

[0050] In contrast, in this embodiment, the tensile stress generated in the tab portion 42T (42T1) that is disposed on the outermost periphery among the multiple tab portions 42T shown in Fig. 4 and to which the tab connection portion 22A of the positive electrode current collecting terminal 22 shown in Fig. 5C etc. is joined is relaxed by the cuts 38, so that the occurrence of dimples can be prevented or effectively suppressed. Therefore, the occurrence of an internal short circuit during ultrasonic welding can be prevented or effectively suppressed.

[0051] 8 when the cutting step is performed, the welding machine 100 welds the terminal joint 34A of the foil collecting portion 34X in the positive electrode tab group 34 shown in Fig. 5A to the tab connection portion 22A of the current collecting terminal 22. This makes it possible to improve the relative positional accuracy between the welding position of the tab connection portion 22A of the current collecting terminal 22 to the terminal joint 34A of the foil collecting portion 34X in the positive electrode tab group 34 and the formation position of the cut 38 on the surface layer side of the positive electrode tab group 34.

[0052] 1 is inserted into the battery case 70, and the lid member 21 is joined to the opening of the battery case 70. Then, the electrolyte is poured through the injection port 21B formed in the lid member 21, and the injection port 21B is sealed with a cap 29. In this manner, a rechargeable secondary battery 10 is manufactured.

[0053] As described above, according to this embodiment, it is possible to reduce the impact on productivity while mitigating the tensile stress generated in the tab portion 42T (42T1) to which the positive electrode collector terminal 22 is joined when the positive electrode collector terminal 22 is welded.

[0054] [Supplementary explanation of the embodiment] In the above embodiment shown in Figures 1 to 8, the notch 38 is formed on the surface side of the positive electrode tab group 34, which is prone to deformation due to its material, but a similar notch may be formed on the surface side of the negative electrode tab group 36.

[0055] In the above embodiment, the tab connection parts 22A, 24A of the current collecting terminals 22, 24 are disposed on the upper side of the tab groups 34, 36 in a front view as shown in Fig. 5C etc., but as a modification of the above embodiment, the tab connection parts of the current collecting terminals may be disposed on the lower side of the tab groups in a front view. In the case of such a modification, the first part is the part closest to the lower boundary (B2) in a front view among the parts where the ends of the tab connection parts in the directions perpendicular to the width direction and thickness direction of the terminal joint part contact, and the second part is the part closest to the first part among the parts that are part of the outermost periphery of the part where the composite layer is formed in the electrode sheet having the first part and correspond to the lower boundary (B2) in a front view.

[0056] 5B and the like, the cut 38 is semicircular with the first portion P1 side open, but as a modification of the embodiment, the cut may be substantially V-shaped (preferably V-shaped with an acute angle) or substantially U-shaped with the first portion (P1) side open. As another modification of the embodiment, the cut may not be configured to be open on the first portion (P1) side.

[0057] Furthermore, in the above embodiment, the position where the notch 38 crosses the virtual line VL is set on the first portion P1 side of the midpoint P3 between the first portion P1 and the second portion P2, but it is also possible to adopt a configuration in which the position where the notch crosses the virtual line (VL) is set on the midpoint (P3) between the first portion (P1) and the second portion (P2) or on the second portion P2 side of the midpoint P3.

[0058] In addition, in the cutting process of the above embodiment, the cutting blade 106 attached to the welding machine 100 used in the welding process shown in FIG. 8 forms the incision 38 shown in FIG. 5B, etc., but as a modification of the above embodiment, in the cutting process, a cutting blade that is not attached to the welding machine (100) may form the incision.

[0059] The above-described embodiment and the multiple modified examples can be implemented in appropriate combinations.

[0060] While one example of the present invention has been described above, the present invention is not limited to the above, and it goes without saying that the present invention can be implemented in various modified forms without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0061] 10 Secondary battery 22 Current collector terminal 22A Tab Connection 24 Current collector terminal 24A Tab Connection 30 Electrode body 30L winding shaft 32 Electrode body 32A flat surface 32B curved end face 32C curved end face 34 Tabs 34A terminal joint 34X Foil Collection Section 36 Tabs 36A terminal joint 36X Foil collecting section 38 Cutting 40 Electrode sheet 42 Current collector 42T Tab section 44 Mixed material layer 50 Electrode Sheet 52 Current collector 52T Tab section 54 Mixed material layer 60 Separator 100 Welding Machine 106 Cutting edge B1 Boundary (one side boundary) B2 boundary P1 first part P2 second part P3 center point VL Virtual Line X Axial direction of the winding shaft

Claims

1. an electrode body in which positive and negative electrode sheets, each of which has a composite layer formed on a portion of the surface of a sheet-like current collector for a positive or negative electrode, are stacked with a separator sandwiched therebetween and wound flat around a winding axis; a group of positive and negative electrode tabs constituting a part of the electrode body, the group being a part of the current collector, the group having a plurality of tab portions protruding in the axial direction of the winding shaft from an electrode main body portion in which the current collector, the composite layer, and the separator are laminated, the group having a foil collecting portion in which protruding tip end portions of the plurality of tab portions are bundled and laminated, and the group being disposed on one side and the other side in the axial direction; current collecting terminals of positive and negative electrodes, the tab connection portions of which are joined by welding to terminal joining portions on the surfaces of the foil collecting portions of the tab groups of the positive and negative electrodes; A secondary battery having a second portion of the electrode sheet including the first portion, the second portion being a part of the outermost periphery of a portion where the composite layer is formed and being the part closest to the first portion among the portions corresponding to the one boundary between the flat surface and the curved end surface of the outer peripheral surface around the winding axis of the electrode main body, and the second portion being the part closest to the first portion among the portions corresponding to the one boundary, the first portion being the part closest to the first portion among the portions where the ends of the tab connection portion in a direction perpendicular to the width direction and the thickness direction contact at the terminal joint.

2. The secondary battery according to claim 1 , wherein the cut is formed in a shape that is open on the first portion side.

3. The secondary battery according to claim 1 , wherein a position where the cut crosses the virtual line is set on the first portion side of a center point between the first portion and the second portion.

4. a method for manufacturing a secondary battery comprising: an electrode body in which positive and negative electrode sheets, each of which has a composite layer formed on a portion of the surface of a sheet-like current collector for positive and negative electrodes, are stacked with a separator sandwiched therebetween and wound flat around a winding axis; a group of positive and negative electrode tabs constituting a portion of the electrode body, which is a portion of the current collector, the group of current collectors having a foil collecting portion in which the protruding tip end portions of the plurality of tab portions are bundled together and stacked, the group of positive and negative electrode tabs being disposed on one side and the other side of the axial direction; and positive and negative electrode current collecting terminals having tab connection portions joined by welding to terminal joint portions on the surfaces of the foil collecting portions of the group of positive and negative electrode tabs, a cutting process for forming a cut on a surface layer side of the tab group so as to cross an imaginary line connecting a first portion, which is a portion closest to one of two boundaries between a flat surface and a curved end surface of an outer circumferential surface of the electrode body around the winding axis and which is closer to the terminal joint portion, among portions where an end of the tab connection portion in a direction perpendicular to the width direction and the thickness direction is in contact with the terminal joint portion, and a second portion, which is a part of the outermost portion of a portion where the composite layer is formed in the electrode sheet including the first portion and is a portion closest to the first portion among portions corresponding to the one boundary; a welding step of joining the tab connection portion of the current collecting terminal to the terminal joint portion of the foil collecting portion by welding in a state in which the protruding tip side portions of the plurality of tab portions are bundled together after the cutting step; A method for manufacturing a secondary battery having the above structure.

5. The method for manufacturing a secondary battery according to claim 4 , wherein in the cutting, the cut is formed so that the first portion side is open.

6. In the cutting step, a cutting blade attached to a welding machine used in the welding step forms the cut, The method for manufacturing a secondary battery according to claim 4 , wherein in the welding step, welding is performed by the welding machine without changing the position of the welding machine when the cutting step is performed.

7. The method for manufacturing a secondary battery according to claim 6 , wherein a position where the incision crosses the virtual line in the incision process is set closer to the first portion than a center point between the first portion and the second portion.

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