Electrode group and secondary battery

Abstract

The objective is to provide an electrode group and a secondary battery that suppress short circuits caused by cracking of the positive or negative electrode at the innermost circumference of the electrode group. [Solution] The electrode group of the embodiment is an electrode group with a flattened cross-section in which an electrode member consisting of a positive electrode, a negative electrode, and a separator is wound, and the cross-section of the electrode group has opposing planar portions and opposing curved portions arranged between the planar portions. A recess is provided in at least one of the positive electrode or the negative electrode at the apex of the innermost circumference of the electrode group in the curved portion.

Description

Technical Field

[0001] Embodiments of the present invention relate to an electrode group and a secondary battery.

Background Art

[0002] In recent years, secondary batteries such as lead-acid batteries and nickel-metal hydride batteries have been used as power sources represented by electric vehicles, hybrid vehicles, electric motorcycles, and forklifts. Recently, development towards the adoption of high-energy-density lithium-ion secondary batteries has been actively carried out, with development being carried out while considering long life, safety, etc.

[0003] An electrode group used in a lithium-ion secondary battery (hereinafter referred to as a secondary battery) is, for example, manufactured by winding electrode members including a positive electrode, a negative electrode, and a separator, and integrally pressing and molding them into a flat shape. In such a type of secondary battery, when the positive electrode or the negative electrode is sharply bent by pressure molding at the innermost peripheral portion of the electrode group, there is a possibility that the positive electrode or the negative electrode may crack. And there is a risk that this cracked portion may break through the separator and come into electrical contact with the opposing positive electrode or negative electrode, resulting in a short circuit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the present invention is to provide an electrode group and a secondary battery that suppress a short circuit caused by cracking of the positive electrode or the negative electrode at the innermost peripheral portion of the electrode group.

Means for Solving the Problems

[0006] To solve the above problems, the electrode group of the embodiment is an electrode group with a flattened cross-section in which an electrode member consisting of a positive electrode, a negative electrode, and a separator is wound, and the cross-section of the electrode group has opposing planar portions and opposing curved portions arranged between the planar portions. A recess is provided in at least one of the positive electrode or the negative electrode at the apex of the innermost circumference of the electrode group in the curved portion. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic perspective view showing the electrode group according to the first embodiment. [Figure 2] A partially unfolded perspective view of the electrode group according to the first embodiment, viewed from above. [Figure 3] A schematic cross-sectional view showing the electrode group according to the first embodiment. [Figure 4] An enlarged cross-sectional view schematically showing the innermost part of the electrode group. [Figure 5] A schematic cross-sectional view showing a modified example of the electrode group according to the first embodiment. [Figure 6] A schematic perspective view showing a secondary battery according to the second embodiment. [Modes for carrying out the invention]

[0008] The electrode group and secondary battery of the embodiment will be described below with reference to the drawings.

[0009] (First embodiment) The electrode group 5 of the first embodiment will be described with reference to Figures 1 and 2. Figure 1 is a schematic perspective view of the electrode group 5 according to the first embodiment, and Figure 2 is a partially exploded perspective view of the electrode group 5 according to the first embodiment viewed from above.

[0010] The electrode group 5 is manufactured by winding an electrode member 20 consisting of a positive electrode 100, a negative electrode 200, and a separator 4 positioned between the positive electrode 100 and the negative electrode 200, as shown in Figures 1 and 2. The wound electrode group 5 is manufactured by pressure molding the entire assembly into a flattened cross-sectional shape in the stacking direction (Y direction) of the electrode member 20. This pressure molding reduces the space within the electrode group 5, so when the electrode group 5 is housed in a secondary battery case, for example, more electrode members 20 can be housed in the limited space within the case. The manufacturing method of the electrode group 5 is not limited to these methods; as long as the electrode member 20 is wound, the positive electrode 100 may be wound on the inner circumference side, or the negative electrode 200 may be wound on the inner circumference side.

[0011] The positive electrode 100 has a strip-shaped positive electrode current collector 100a with a long side 90 (Z direction) and a short side 92 (X direction). On the positive electrode current collector 100a, there is a positive electrode mixture layer 130 in which the positive electrode mixture is applied parallel to the long side 90, and an uncoated portion 70a of the positive electrode mixture layer where the positive electrode mixture is not applied. The negative electrode 200 has a strip-shaped negative electrode current collector 200a with a long side 90 and a short side 92. On the negative electrode current collector 200a, there is a negative electrode mixture layer 150 in which the negative electrode mixture is applied parallel to the long side 90, and an uncoated portion 70b of the negative electrode mixture layer where the negative electrode mixture is not applied. The separator 4 is also strip-shaped with a long side 90 (Z direction) and a short side 92 (X direction), similar to the positive electrode 100 and the negative electrode 200.

[0012] In the wound electrode group 5 of this embodiment, the uncoated portion 70a of the positive electrode mixture layer protrudes in the opposite direction to the protruding direction of the uncoated portion 70b of the negative electrode mixture layer and is provided at both ends of the electrode group 5. However, the protruding directions of the uncoated portion 70a of the positive electrode mixture layer and the uncoated portion 70b of the negative electrode mixture layer are not limited to these. The uncoated portion 70a of the positive electrode mixture layer and the uncoated portion 70b of the negative electrode mixture layer may protrude in the same direction, and both may be provided at one end of the electrode group 5.

[0013] The electrode group 5 will be described with reference to Figures 3 and 4. Figure 3 is a schematic cross-sectional view (section II shown in Figure 1) of the electrode group 5 according to the first embodiment, and Figure 4 is an enlarged cross-sectional view (section II shown in Figure 1) of the innermost circumference 50 of the electrode group 5. As shown in Figure 3, the electrode group 5 of this embodiment has a flattened cross-sectional shape. In the cross-section of the electrode group 5, the electrode group 5 has opposing flat portions 40 and opposing curved portions 42 positioned between the flat portions 40. Here, the flat portion 40 is the region P shown in Figure 3, and the curved portion 42 is the region Q shown in Figure 3.

[0014] In the curved portion 42 of the electrode group 5 of this embodiment, a recess 54 is provided on at least one of the positive electrode 100 or negative electrode 200 at the apex 52 of the innermost circumference 50 of the electrode group 5. Here, the innermost circumference 50 of the electrode group 5 is defined as the region of the electrode member 20 from the starting point R, where the winding begins, to the ending point R' after one full turn. Furthermore, the apex 52 is defined as the portion of the positive electrode 100 or negative electrode 200 in the curved portion 42 with a high curvature.

[0015] In this embodiment, the electrode group 5 is provided with a recess 54 on at least one of the positive electrode 100 or negative electrode 200 at the apex 52 of the innermost circumference 50 of the electrode group 5. This allows the positive electrode 100 or negative electrode 200 at the innermost circumference 50 of the electrode group 5 to be bent when, for example, the entire electrode group 5 is pressure-molded in the stacking direction (Y direction) of the electrode member 20 after winding, thereby suppressing cracking of the positive electrode 100 or negative electrode 200 in the portion where the recess 54 is provided. This is because, with the recess 54 provided on the positive electrode 100 or negative electrode 200, no positive electrode mixture or negative electrode mixture is provided in the recess 54, resulting in lower electrode strength in the portion where the recess 54 is provided compared to the positive electrode 100 or negative electrode 200 without the recess 54.

[0016] Here, the recesses 54 are preferably provided on both the positive electrode 100 and the negative electrode 200 at the innermost circumference 50 of the electrode group 5, and more preferably on two vertices 52. This allows, for example, the entire electrode group 5 to be pressure-molded in the stacking direction (Y direction) of the electrode members 20 after winding, and even if both the positive electrode 100 and the negative electrode 200 at the innermost circumference 50 of the electrode group 5 are bent, cracking of both the positive electrode 100 and the negative electrode 200 can be suppressed in the portions of the positive electrode 100 and the negative electrode 200 where the recesses 54 are provided.

[0017] Furthermore, in this embodiment, as shown in Figure 3, it is preferable that recesses 54 are provided in the curved portion 42 at least one of the positive electrode 100 or negative electrode 200 at the apex 52 of the second circumference 55, which extends one full turn of the electrode member 20 from the innermost circumference 50, and at least one of the positive electrode 100 or negative electrode 200 at the apex 52 of the third circumference 60, which extends another full turn of the electrode member 20 from the second circumference. Here, the second circumference 55 of the electrode group 5 is defined as the region of the electrode member 20 from the endpoint R' of the innermost circumference 50 to the endpoint S', which extends one full turn from the starting point S. The third circumference 60 of the electrode group 5 is defined as the region of the electrode member 20 from the endpoint S' of the second circumference 55 to the endpoint T', which extends one full turn from the starting point T.

[0018] In the electrode group 5 of this embodiment, recesses 54 may be provided not only on the apex 52 of the innermost circumference 50 of the electrode group 5, but also on at least one of the positive electrode 100 or negative electrode 200 at the apex 52 of the second circumference 55 and the third circumference 60. This allows for, for example, the entire electrode group 5 to be pressure-molded in the stacking direction (Y direction) of the electrode member 20 after winding, and even if the positive electrode 100 or negative electrode 200 in the second circumference 55 and the third circumference 60, as well as the innermost circumference 50 of the electrode group 5, is bent, cracking of the positive electrode 100 or negative electrode 200 can be suppressed in the portion of the positive electrode 100 or negative electrode 200 where the recess 54 is provided.

[0019] Here, the recess 54 is preferably provided not only in the innermost peripheral portion 50 of the electrode group 5 but also in the second peripheral portion 55 and the third peripheral portion 60 of both the positive electrode 100 and the negative electrode 200, and more preferably provided at two vertex portions 52. Thereby, for example, after winding the electrode member 20, the entire electrode group 5 is pressure-molded in the stacking direction (Y direction) of the electrode member 20. Even when both the positive electrode 100 and the negative electrode 200 in the second peripheral portion 55 and the third peripheral portion 60 are bent, not only in the innermost peripheral portion 50 of the electrode group 5, cracks in both the positive electrode 100 and the negative electrode 200 can be suppressed at the portions where the recess 54 is provided in the positive electrode 100 and the negative electrode 200.

[0020] Furthermore, the recess 54 of the electrode group 5 of the present embodiment may be provided not only at the vertex portions 52 of the innermost peripheral portion 50, the second peripheral portion 55, and the third peripheral portion 60 of the electrode group 5 but also at the vertex portions 52 of the fourth peripheral portion, the fifth peripheral portion, and the outermost peripheral portion after the third peripheral portion 60. Thereby, even when the positive electrode 100 or the negative electrode 200 in the fourth peripheral portion, the fifth peripheral portion, and the outermost peripheral portion of the electrode group 5 is bent, cracks in the positive electrode 100 or the negative electrode 200 can be suppressed at the portions where the recess 54 is provided in the positive electrode 100 or the negative electrode 200.

[0021] The recess 54 of the present embodiment is provided by a laser, a blade, or an adhesive tape, and more preferably provided by a laser. By using a laser, it is possible to suppress damage to the positive electrode current collector 100a under the positive electrode mixture layer 130 and the negative electrode current collector 200a of the negative electrode mixture layer 150, and a galvanolaser is particularly preferable. By using a galvanolaser, the recess 54 can be provided on the surface of the positive electrode 100 or the negative electrode 200 with high precision and high speed.

[0022] By using a laser, the binder contained in the positive electrode mixture or the negative electrode mixture may be decomposed, and a plurality of air bubbles may be formed on the surface of the positive electrode 100 or the negative electrode 200, but these air bubbles are not defined as the recess 54.

[0023] Next, the depth of the recess 54 will be explained. In the electrode group 5 of this embodiment, by providing the recess 54, neither the positive electrode mixture nor the negative electrode mixture is provided in the recess 54, and the electrode strength in the portion of the positive electrode 100 or negative electrode 200 where the recess 54 is provided will be lower than that of the positive electrode 100 or negative electrode 200 where the recess 54 is not provided. Therefore, the depth of the recess 54 must be such that the electrode strength in the portion of the positive electrode 100 or negative electrode 200 where the recess 54 is provided is lower than that of the positive electrode 100 or negative electrode 200 where the recess 54 is not provided, and furthermore, the depth must also ensure the overall battery capacity of the electrode group 5.

[0024] Specifically, the ratio of the depth of the recess 54 is preferably 0.02 or more and 1.0 or less with respect to the thickness of the positive electrode mixture layer 130 and the negative electrode mixture layer 150. Here, the depth of the recess 54 and the thickness of the positive electrode mixture layer 130 and the negative electrode mixture layer 150 are measured with the wound electrode group 5 unwound into strip-shaped positive electrode 100 and negative electrode 200, and are defined as the longest distance in the direction parallel to the height direction (Y direction) of the positive electrode 100 and the negative electrode 200.

[0025] The ratio of the depth of the recess 54 to the thickness of the positive electrode mixture layer 130 and the negative electrode mixture layer 150 is 0.02 or more. This ensures that the portion of the positive electrode 100 or negative electrode 200 with the recess 54 has lower electrode strength than the portion of the positive electrode 100 or negative electrode 200 without the recess 54. For example, even if the entire electrode group 5 is pressure-molded in the stacking direction (Y direction) of the electrode member 20 after winding, and the positive electrode 100 or negative electrode 200 at the innermost circumference 50 of the electrode group 5 is bent, cracking of the positive electrode 100 or negative electrode 200 can be suppressed in the portion of the positive electrode 100 or negative electrode 200 with the recess 54. Furthermore, since the depth ratio of the recess 54 is 1.0 or less to the thickness of the positive electrode mixture layer 130 and the negative electrode mixture layer 150, the battery capacity of the entire electrode group 5 can be sufficiently ensured even though neither the positive electrode mixture nor the negative electrode mixture is provided in the recess 54.

[0026] As described above, the recess 54 in this embodiment is formed by a laser, a blade, or adhesive tape. However, if a laser is used, for example, in addition to forming the recess 54 in the positive electrode 100 or negative electrode 200, the binder contained in the positive electrode mixture or negative electrode mixture may be decomposed. Due to the formation of the recess 54 and the decomposition of the binder, the electrode strength of the positive electrode 100 or negative electrode 200 on which the recess 54 is formed is weakened. Therefore, the ratio of the depth of the recess 54 formed by the laser to the thickness of the positive electrode mixture layer 130 and the negative electrode mixture layer 150 is sufficient to be 0.02 or more.

[0027] On the other hand, when a blade or adhesive tape is used to form the recess 54, it is more preferable that the ratio of the depth of the recess 54 to the thickness of the positive electrode mixture layer 130 and the negative electrode mixture layer 150 is 0.05 or more. This allows for sufficient removal of the positive electrode mixture or the negative electrode mixture, and sufficiently weakens the electrode strength of the positive electrode 100 or negative electrode 200 in which the recess 54 is provided.

[0028] In this embodiment, the electrode group 5 is manufactured by winding an electrode member 20 consisting of a positive electrode 100, a negative electrode 200, and a separator 4 placed between the positive electrode 100 and the negative electrode 200. The recess 54 is provided in a direction parallel to the winding axis of the electrode group 5 (X direction). As a result, even if the entire electrode group 5 is pressure-molded in the stacking direction of the electrode member 20 (Y direction) after winding the electrode member 20, and the positive electrode 100 or negative electrode 200 is bent in the innermost circumference 50, second circumference 55, or third circumference 60 where the recess 54 is provided, cracking of the positive electrode 100 or negative electrode 200 can be suppressed in the entire X direction where the recess 54 is provided on the positive electrode 100 or negative electrode 200.

[0029] Furthermore, the length of the recess 54 in the Z direction is preferably 0.01 mm or more and 50 mm or less. If it is 0.01 mm or more, the electrode strength in the portion of the positive electrode 100 or negative electrode 200 where the recess 54 is provided will be lower than in the positive electrode 100 or negative electrode 200 where the recess 54 is not provided. If it is 50 mm or less, even though the positive electrode mixture or negative electrode mixture is not provided in the recess 54, the overall battery capacity of the electrode group 5 can be sufficiently ensured.

[0030] A more preferable value for the length of the recess 54 in the Z direction is 0.05 mm or more and 5 mm or less. Having a recess 54 with a length of 0.05 mm or more in the Z direction makes it easier to process the surface of the positive electrode 100 or negative electrode 200. Furthermore, in the electrode group 5 of this embodiment, recesses 54 may be provided not only in the innermost circumference 50 of the electrode group 5, but also in the apex portions 52 of the second circumference 55 and the third circumference 60. It is preferable to align the positions of the recesses 54 at the apex portions 52 with those at the innermost circumference 50 in the Z direction. Having a recess 54 with a length of 5 mm or less in the Z direction makes it easier to align the positions of the recesses 54 at the apex portions 52 of the second circumference 55 and the third circumference 60 with those at the apex portion 52 of the innermost circumference 50.

[0031] Furthermore, it is preferable that the recess 54 be provided on the winding axis side (inner circumference side) of the electrode group 5 for each positive electrode 100 or negative electrode 200. In the curved portion 42, the positive electrode mixture or negative electrode mixture is more easily compressed on the winding axis side (inner circumference side) of each positive electrode 100 or negative electrode 200 than on the opposite side (outer circumference side) of each positive electrode 100 or negative electrode 200. If the positive electrode mixture or negative electrode mixture is strongly compressed, the positive electrode current collector 100a or negative electrode current collector 200a may be excessively pulled in the Y direction and break. Therefore, it is preferable to provide the recess 54 on the winding axis side (inner circumference side) of the electrode group 5 for each positive electrode 100 or negative electrode 200 to weaken the electrode strength on the winding axis side (inner circumference side).

[0032] A modified version of the electrode group 5 of this embodiment will be explained using Figure 5. Figure 5 is a schematic cross-sectional view (section II shown in Figure 1) of a modified version of the electrode group 5 according to the first embodiment. As shown in the modified version of Figure 5, the recess 54 may be provided not only on the winding axis side (inner circumference side) of the electrode group 5, but also on the opposite side (outer circumference side) from the winding axis side. As a result, the recess 54 is provided in the positive electrode 100 or negative electrode 200 on both the winding axis side (inner circumference side) and the opposite side (outer circumference side) of the electrode group 5, so that the positive electrode mixture or negative electrode mixture is not provided in the recess 54. In the part of the positive electrode 100 or negative electrode 200 where the recess 54 is provided, the electrode strength is lower than in the positive electrode 100 or negative electrode 200 where the recess 54 is not provided, and cracking of the positive electrode 100 or negative electrode 200 can be suppressed.

[0033] Furthermore, the electrode group 5 is manufactured by winding the electrode member 20, and it is preferable that the recess 54 be provided on at least one of the positive electrode 100 or the negative electrode 200 immediately before the electrode member 20 is wound. In this embodiment, the recess 54 of the electrode group 5 is provided on the apex 52 of the curved portion 42 of the electrode group 5, but since the curvature of the curved portion 42 is different at each apex 52, if multiple recesses 54 are provided, it is necessary to adjust the length (pitch) in the Z direction between the recesses 54. This adjustment can be easily performed by doing so immediately before the electrode member 20 is wound.

[0034] In the electrode group 5 of the first embodiment described above, a recess 54 is provided on at least one of the positive electrode 100 or negative electrode 200 at the apex 52 of the innermost circumference 50 of the electrode group 5. This allows the entire electrode group 5 to be pressure-molded in the stacking direction (Y direction) of the electrode member 20 after winding, and even if the positive electrode 100 or negative electrode 200 at the innermost circumference 50 of the electrode group 5 is bent, cracking of the positive electrode 100 or negative electrode 200 can be suppressed in the portion of the positive electrode 100 or negative electrode 200 where the recess 54 is provided. Therefore, an electrode group 5 can be provided that suppresses short circuits caused by cracking of the positive electrode 100 or negative electrode 200.

[0035] (Second embodiment) The secondary battery 1 of the second embodiment will be described with reference to Figure 6. Figure 6 is a schematic perspective view showing the secondary battery 1 according to the second embodiment.

[0036] As shown in Figure 6, the secondary battery 1 has an outer case 3, and the electrode group 5 of the first embodiment is housed inside the outer case 3. Inside the outer case 3, the electrode group 5 is impregnated with an electrolyte (not shown), and the electrolyte is injected, for example, through an injection port (not shown) provided on the lid member 7, and the injection port is sealed with a sealing plate 19 after the electrolyte has been injected. The electrolyte used is a non-aqueous electrolyte prepared by dissolving an electrolyte (e.g., a lithium salt) in a non-aqueous solvent. The non-aqueous solvent may be used alone or in a mixture of two or more types.

[0037] A gas discharge valve 21 may be provided on the surface of the lid member 7 together with the sealing plate 19. Furthermore, for example, a pair of positive electrode external terminals 23a and negative electrode external terminals 23b are attached to the surface of the lid member 7, and the external terminals 23a and 23b are electrically connected to the uncoated portion 70a of the positive electrode mixture layer and the uncoated portion 70b of the negative electrode mixture layer of the electrode group 5, respectively. A terminal insulator 35 may be provided between the external terminals 23a and 23b and the lid member 7 to maintain insulation between them.

[0038] The secondary battery 1 of the second embodiment described above is equipped with the electrode group 5 of the first embodiment. As a result, even if, for example, the entire electrode group 5 is pressure-molded in the stacking direction (Y direction) of the electrode member 20 after winding the electrode member 20, and the positive electrode 100 or negative electrode 200 at the innermost circumference 50 of the electrode group 5 is bent, cracking of the positive electrode 100 or negative electrode 200 can be suppressed in the portion of the positive electrode 100 or negative electrode 200 where the recess 54 is provided. Therefore, a secondary battery 1 can be provided that suppresses short circuits caused by cracking of the positive electrode 100 or negative electrode 200.

[0039] According to the electrode group 5 of at least one embodiment described above, a recess 54 is provided on at least one of the positive electrode 100 or negative electrode 200 at the apex 52 of the innermost circumference 50 of the electrode group 5. This allows the entire electrode group 5 to be pressure-molded in the stacking direction (Y direction) of the electrode member 20 after winding, and even if the positive electrode 100 or negative electrode 200 at the innermost circumference 50 of the electrode group 5 is bent, cracking of the positive electrode 100 or negative electrode 200 can be suppressed in the portion of the positive electrode 100 or negative electrode 200 where the recess 54 is provided. Therefore, an electrode group 5 can be provided that suppresses short circuits associated with cracking of the positive electrode 100 or negative electrode 200.

[0040] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0041] 1...Secondary battery, 3...Outer case, 4...Separator, 5...Electrode group, 7...Lid member, 19...Sealing plate, 20...Electrode member, 21...Gas discharge valve, 23...External terminal, 23a...Positive electrode external terminal, 23b...Negative electrode external terminal, 35...Terminal insulator, 40...Flat part, 42...Curved part, 50...Innermost circumference, 52...Apex, 54...Recess, 55...Second circumference, 60...Third circumference, 70a...Uncoated part of positive electrode mixture layer, 70b...Uncoated part of negative electrode mixture layer, 90...Long side, 92...Short side, 100...Positive electrode, 100a...Positive electrode current collector, 130...Positive electrode mixture layer, 150...Negative electrode mixture layer, 200...Negative electrode, 200a...Negative electrode current collector.

Claims

1. An electrode group having a flattened cross-sectional shape, in which electrode members consisting of a positive electrode, a negative electrode, and a separator are wound together, The cross-section of the electrode group has opposing planar portions and opposing curved portions arranged between the planar portions. An electrode group wherein a recess is provided in at least one of the positive electrode or the negative electrode at the apex of the innermost circumference of the electrode group in the curved portion.

2. In the electrode group, the second circumference extends from the innermost circumference to the electrode member, and the third circumference extends from the second circumference to the electrode member, The electrode group according to claim 1, wherein at least one of the positive electrode or the negative electrode is provided with a recess at the apex of the second and third peripheral portions of the electrode group in the curved portion.

3. The positive electrode comprises a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector. The negative electrode comprises a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. The electrode group according to claim 1, wherein the ratio of the depth of the recess to the thickness of the positive electrode mixture layer and the negative electrode mixture layer, in which the recess is provided, is 0.02 or more and 1.0 or less.

4. The electrode group according to claim 1, wherein the recess is provided in a direction parallel to the winding axis of the electrode group.

5. The electrode group according to claim 1, wherein the recess is provided on the winding axis side of the electrode group.

6. The electrode group according to claim 1, A rechargeable battery equipped with an electrolyte.

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