Joining method

Abstract

This method, for joining a collector plate and a winding electrode group 2 comprising a separator and electrode plate stacked and wound together, involves pressing a jig 32 against the ends of the electrode plates, which are arranged in the radial direction of the electrode group 2, displacing the jig 32 on a curved trajectory so as to bend the ends such that the amount of displacement towards the electrode group 2 gradually increases and the amount of displacement in the radial direction gradually deceases, and joining the bent ends and the electrode plates.

Description

[Technical Field]

[0001] The present disclosure relates to a method for joining an electrode group and a current collector plate. [Background technology]

[0002] Conventionally, batteries have been known in which a wound electrode group and an electrolyte are housed in a cylindrical outer can. Regarding such batteries, Patent Document 1 discloses a method of forming radial slits in the portions at both ends of the electrode group that are not coated with an active material layer, bending the uncoated portions radially outward from the electrode group to form flat welding surfaces, and welding the welding surfaces to current collector plates. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-227137 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors conducted extensive research into methods for joining a current collector plate to a welding surface formed by bending an uncoated portion, and found that there is room for improvement in conventional methods in order to further improve the quality of batteries.

[0005] The present disclosure has been made in light of these circumstances, and one of its objectives is to provide a technology for improving the quality of batteries. [Means for solving the problem]

[0006] One aspect of the present disclosure is a method for joining a current collector plate to a wound electrode assembly in which separators and electrode plates are stacked and wound. This joining method includes pressing a jig against multiple ends of the electrode plates arranged in the radial direction of the electrode assembly, displacing the jig along a curved trajectory so that the amount of displacement toward the electrode assembly gradually increases and the amount of displacement in the radial direction gradually decreases, bending the multiple ends, and joining the bent multiple ends to the current collector plate.

[0007] Any combination of the above components, and conversion of the expression of the present disclosure into a method, device, system, etc., are also valid aspects of the present disclosure. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to improve the quality of batteries. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. [Figure 2] Fig. 2(A) is a diagram showing a process for forming an electrode group, and Fig. 2(B) is a diagram showing a process for processing an electrode group. [Figure 3] Fig. 3(A) is a diagram showing how the end of the electrode group is bent, and Fig. 3(B) is a diagram showing how the electrode group and the current collector plate are joined together. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present disclosure will be described below with reference to preferred embodiments and drawings. The embodiments are illustrative and do not limit the present disclosure, and all features and combinations thereof described in the embodiments are not necessarily essential to the present disclosure. The same or equivalent components, parts, and processes shown in each drawing are designated by the same reference numerals, and redundant descriptions will be omitted where appropriate. The scale and shape of each part shown in each drawing are set for convenience to facilitate explanation and should not be interpreted as limiting unless otherwise specified. Furthermore, when terms such as "first" and "second" are used in this specification or claims, unless otherwise specified, these terms do not indicate any order or importance, but are intended to distinguish one configuration from another. Furthermore, some components that are not important for explaining the embodiments are omitted from each drawing.

[0011] FIG. 1 is a cross-sectional view of a battery 1. The battery 1 is, for example, a rechargeable secondary battery such as a lithium-ion battery, a nickel-metal hydride battery, or a nickel-cadmium battery. As an example, the battery 1 has a structure in which an electrode group 2 is housed in an outer can 4 together with an electrolyte (not shown). As an example, the electrode group 2 is cylindrical, and has a wound structure in which a strip-shaped first electrode plate 6 and a strip-shaped second electrode plate 8 are stacked with a strip-shaped separator 10 sandwiched between them and wound in a spiral shape (see also FIG. 2(A)). In this embodiment, the first electrode plate 6 is a positive electrode plate, and the second electrode plate 8 is a negative electrode plate.

[0012] The first electrode plate 6 and the second electrode plate 8 have a structure in which an electrode active material layer is laminated on a current collector. In a typical lithium-ion secondary battery, the current collector is made of aluminum foil or the like for the positive electrode, and copper foil or the like for the negative electrode. The electrode active material layer can be formed by applying an electrode mixture to the surface of the current collector using a known coating device, followed by drying and rolling. The electrode mixture is obtained by kneading and uniformly dispersing materials such as the electrode active material, binder, and conductive material in a dispersion medium. In a typical lithium-ion secondary battery, the electrode active material is lithium cobalt oxide or lithium iron phosphate or the like for the positive electrode, and graphite or the like for the negative electrode.

[0013] The first electrode plate 6 has a first uncoated portion 12, which is not coated with the electrode composite, at one end in the width direction A (the direction intersecting the longitudinal direction of the strip). The first uncoated portion 12 is an exposed portion of the current collector of the first electrode plate 6 where no electrode active material layer is laminated. The second electrode plate 8 has a second uncoated portion 14, which is not coated with the electrode composite, at the other side in the width direction A, i.e., the end opposite the side from which the first uncoated portion 12 protrudes. The second uncoated portion 14 is an exposed portion of the current collector of the second electrode plate 8 where no electrode active material layer is laminated.

[0014] As described above, the electrode group 2 has a structure in which the first electrode plate 6 and the second electrode plate 8 are wound. Therefore, multiple ends of the first electrode plate 6 and the second electrode plate 8 in the width direction A are aligned in the radial direction B of the electrode group 2. Therefore, the electrode group 2 has multiple first uncoated portions 12 aligned in the radial direction B and multiple second uncoated portions 14 aligned in the radial direction B. Each first uncoated portion 12 has a curved portion 16 at its tip that is bent in a curved shape toward the winding center C of the electrode group 2. Each second uncoated portion 14 has a curved portion 18 at its tip that is bent in a curved shape toward the winding center C. Note that the electrode group 2 may have only one of the curved portions 16 and the curved portion 18.

[0015] Separator 10 is made of a microporous film made of, for example, polypropylene resin, and is interposed between first electrode plate 6 and second electrode plate 8.

[0016] A first current collector plate 20 is disposed on the side of the electrode group 2 from which the first uncoated portion 12 protrudes. The first current collector plate 20 is made of, for example, aluminum. At least a portion of each curved portion 16 is in surface contact with the first current collector plate 20. In other words, the formation of the curved portions 16 increases the contact area between each first uncoated portion 12 and the first current collector plate 20. Each curved portion 16 and the first current collector plate 20 are then joined to each other by laser welding or the like. This electrically connects the current collector of each winding layer of the first electrode plate 6 to the first current collector plate 20.

[0017] A second current collector plate 22 is disposed on the side of the electrode group 2 from which the second uncoated portions 14 protrude. The second current collector plate 22 is made of, for example, copper, nickel, nickel-plated copper, or nickel-plated iron. At least a portion of each curved portion 18 is in surface contact with the second current collector plate 22. That is, the formation of the curved portions 18 increases the contact area between each second uncoated portion 14 and the second current collector plate 22. The curved portions 18 and the second current collector plate 22 are then joined to each other by laser welding or the like. This electrically connects the current collector of each winding layer of the second electrode plate 8 to the second current collector plate 22.

[0018] The electrode group 2, in which the first current collector plate 20 and the second current collector plate 22 are joined, is housed together with the electrolyte in a cylindrical outer can 4 with a bottom. The outer can 4 is made of, for example, copper, nickel, iron, or an alloy of these. The second current collector plate 22 is joined to the inner bottom surface of the outer can 4 by welding or the like. A metal sealing plate 26 is fitted into the opening of the outer can 4 with an insulating gasket 24 interposed between them. This seals the electrode group 2 and the electrolyte inside the outer can 4. The first current collector plate 20 is joined to the sealing plate 26 by welding or the like.

[0019] Next, the formation of the electrode group 2, processing of the end portion of the electrode group 2, and bonding of the electrode group 2 and the current collector plate will be described. FIG. 2(A) is a diagram showing the process of forming the electrode group 2. In FIG. 2(A), the first uncoated portion 12 and the second uncoated portion 14 are omitted. FIG. 2(B) is a diagram showing the process of processing the electrode group 2. In FIG. 2(B), a cross section of a portion of the end portion of the electrode group 2 is shown. FIG. 3(A) is a diagram showing how the end portion of the electrode group 2 is bent. FIG. 3(B) is a diagram showing the state after bonding of the electrode group 2 and the current collector plate. In FIG. 3(B), a first current collector plate 20 is shown as an example.

[0020] 2(A), a strip-shaped first electrode plate 6, a strip-shaped second electrode plate 8, and a strip-shaped separator 10 are prepared. Then, the strip-shaped separator 10, the strip-shaped first electrode plate 6, the strip-shaped separator 10, and the strip-shaped second electrode plate 8 are stacked in this order. The resulting stack is wound spirally to form a wound electrode group 2.

[0021] Next, as shown in FIG. 2(B), the electrode group 2 is set in a processing device 28. The processing device 28 includes a stage 30, a pair of jigs 32, a cam mechanism 34, and a frame 36. The stage 30 has a mounting surface 30a on which the electrode group 2 is placed. As an example, the mounting surface 30a has a circular groove (not shown) into which an end of the electrode group 2 fits, and the electrode group 2 is fixed by fitting the end into this groove. Note that the method for fixing the electrode group 2 is not particularly limited. The electrode group 2 is oriented so that the winding center C extends in the normal direction to the mounting surface 30a. The electrode group 2 shown in FIG. 2(B) is oriented so that the second uncoated portion 14 faces the mounting surface 30a and the first uncoated portion 12 faces away from the mounting surface 30a. The stage 30 can rotate the electrode group 2 around the winding center C.

[0022] A pair of jigs 32 are arranged at positions facing the mounting surface 30a with the electrode group 2 in between. Each jig 32 has a pressing surface 32a facing the electrode group 2. The pressing surface 32a abuts against a plurality of uncoated portions (first uncoated portions 12 in FIG. 2(B)) of the electrode group 2 facing the opposite side to the mounting surface 30a. Each jig 32 is supported by a frame 36 in a state where it can move toward and away from the electrode group 2. In addition, a drive unit (not shown) that moves each jig 32 toward and away from the electrode group 2 is supported by the frame 36.

[0023] The cam mechanism 34 is disposed at a position farther from the electrode group 2 than the pressing surface 32a, and is supported by the frame 36. The cam mechanism 34 has a plate 38, a pair of cam grooves 40, and a pair of cam followers 42. The plate 38 is fixed to the frame 36. The pair of cam grooves 40 are provided in the plate 38. The pair of cam grooves 40 are disposed so as to sandwich the winding center C when viewed from the direction in which the winding center C extends (i.e., the width direction A). One end of each of the pair of cam followers 42 is connected to the corresponding jig 32. The other end of one cam follower 42 is slidably inserted into one cam groove 40. The other end of the other cam follower 42 is slidably inserted into the other cam groove 40.

[0024] Each cam groove 40 extends obliquely so as to approach the electrode group 2 from the outside toward the inside in the radial direction B of the electrode group 2. In addition, each cam groove 40 is curved so that the amount of displacement in the direction approaching the electrode group 2 gradually increases as it moves inward in the radial direction B.

[0025] Each jig 32 is displaced by a cam mechanism 34. That is, while each jig 32 is pressed against the plurality of first uncoated portions 12 aligned in the radial direction B of the electrode group 2, the drive unit advances each jig 32 toward the electrode group 2. Then, the cam followers 42 slide along the cam grooves 40, and each jig 32 is displaced toward the winding center C while approaching the electrode group 2. At this time, as shown in FIG. 3(A), each jig 32 is displaced along a curved trajectory so that the amount of displacement (amount of displacement per unit time) in the direction approaching the electrode group 2 gradually increases and the amount of displacement in the radial direction B of the electrode group 2 gradually decreases. As a result, the tips of the plurality of first uncoated portions 12 are bent inward in the radial direction B, forming a plurality of curved portions 16.

[0026] At the beginning of the displacement, each jig 32 is displaced more in the direction toward the winding center C than in the direction toward the electrode group 2. Then, during the displacement process, the amount of displacement in the direction toward the electrode group 2 gradually increases, and the amount of displacement in the radial direction B of the electrode group 2 gradually decreases. As a result, at the later stage of the displacement, each jig 32 is displaced more in the direction toward the electrode group 2 than in the direction toward the winding center C. In other words, the displacement mode of each jig 32 transitions from a state in which the amount of displacement in the radial direction B is larger than the amount of displacement in the direction toward the electrode group 2 to a state in which the amount of displacement in the direction toward the electrode group 2 is larger than the amount of displacement in the radial direction B.

[0027] In this way, by displacing each jig 32 on a curved trajectory, in the early stage of the displacement of each jig 32, it is possible to preferentially apply to each first uncoated portion 12 a force that causes the portion to collapse inward in the radial direction B, rather than a pushing force. Then, in the later stage of the displacement, it is possible to strongly push each first uncoated portion 12 that has been guided to collapse inward in the radial direction B. This allows the tip of each first uncoated portion 12 to be bent while aligning the collapse direction.

[0028] Furthermore, each jig 32 bends a plurality of first uncoated portions 12 in a partial region in the circumferential direction of the electrode group 2. In the first stage of the processing step, the pair of jigs 32 of the present embodiment press each first uncoated portion 12 in a straight line passing through the winding center C when viewed from the extension direction of the winding center C. Subsequently, in the second stage, the electrode group 2 is rotated 90° around the winding center C, and the pair of jigs 32 again press each first uncoated portion 12 in a straight line passing through the winding center C. As a result, a cross-shaped curved portion 16 is formed in the electrode group 2.

[0029] After the cross-shaped curved portions 16 are formed, as shown in FIG. 3(B), laser welding or the like is performed at positions where the bent first uncoated portions 12, i.e., the multiple curved portions 16, and the first current collector plate 20 overlap, forming joints 44. This bonds the electrode group 2 and the first current collector plate 20. The electrode group 2 with the bonded first current collector plate 20 is oriented so that the second uncoated portions 14 face away from the mounting surface 30a and fixed to the stage 30. Then, the pair of jigs 32 performs the above-described processing on the second uncoated portions 14. As a result, cross-shaped curved portions 18 are formed on the electrode group 2. The multiple curved portions 18 and the second current collector plate 22 are then bonded by laser welding or the like.

[0030] The electrode group 2, in which the first current collector plate 20 and the second current collector plate 22 are joined together, is housed in an outer can 4 together with an electrolyte. Subsequently, processes such as joining the second current collector plate 22 to the outer can 4, joining the first current collector plate 20 to a sealing plate 26, and fitting the sealing plate 26 into the opening of the outer can 4 are carried out, thereby obtaining a battery 1.

[0031] As described above, the method for joining the electrode group 2 and the current collector plate in this embodiment includes pressing the jig 32 against multiple ends of the electrode plate (at least one of the first uncoated portion 12 and the second uncoated portion 14) that are aligned in the radial direction of the electrode group 2, displacing the jig 32 in a curved trajectory so that the amount of displacement in the direction toward the electrode group 2 gradually increases and the amount of displacement in the radial direction of the electrode group 2 gradually decreases, thereby bending the multiple ends, and joining the bent multiple ends to the current collector plate (at least one of the first current collector plate 20 and the second current collector plate 22).

[0032] The inventors discovered that when bending multiple uncoated portions, if the jig 32 is displaced linearly and a load is applied to each uncoated portion, the buckling positions and buckling directions of each uncoated portion become non-uniform, making it difficult to uniformly bend each uncoated portion in the same direction. If the uncoated portions are bent in a non-uniform manner, the quality of the weld between the electrode group 2 and the current collector plate may deteriorate. In contrast, in this embodiment, the jig 32 is displaced in a curved path to apply a load to each uncoated portion. This allows each coated portion to be bent in the same direction and have a uniform curved shape at the tip. This improves the quality of the weld between the electrode group 2 and the current collector plate, thereby improving the quality of the battery 1.

[0033] Another method for making each uncoated portion easier to bend is to provide slits in the uncoated portion, as in the prior art. However, this method may generate cutting waste from the uncoated portion when the slits are formed. If this cutting waste gets mixed into the electrode group 2, it may lead to a decrease in the quality of the battery 1, so measures to deal with the cutting waste are necessary. In contrast, the joining method of this embodiment makes it possible to form uniformly shaped curved portions without providing slits in the uncoated portions. This allows for further improvement in the quality of the battery 1.

[0034] Furthermore, in the joining method of this embodiment, the uncoated portion is bent in a partial region in the circumferential direction of the electrode group 2. This allows the unbent region to absorb the circumferential deflection caused by the bending of the uncoated portion. This improves the welding quality between the electrode group 2 and the current collector plate, thereby improving the quality of the battery 1.

[0035] Furthermore, in the joining method of this embodiment, the jig 32 is displaced by the cam mechanism 34. This allows the jig 32 to be displaced with high precision using a simple configuration, thereby further improving the quality of the battery 1.

[0036] The embodiments of the present disclosure have been described in detail above. The above-described embodiments merely illustrate specific examples of implementing the present disclosure. The content of the embodiments does not limit the technical scope of the present disclosure, and many design modifications, such as changing, adding, or deleting components, are possible within the scope of the invention defined in the claims. A new embodiment with design modifications will combine the effects of the combined embodiments and modifications. In the above-described embodiments, content that allows such design modifications is emphasized by using notations such as "in this embodiment" or "in this embodiment," but design modifications are also permitted even in content without such notation. Furthermore, any combination of components included in each embodiment is also valid as an aspect of the present disclosure. Hatching on cross sections in the drawings does not limit the material of the hatched object.

[0037] The embodiments may be specified by the following items. [Item 1] A method for joining a wound electrode group (2) in which a separator (10) and electrode plates (6, 8) are stacked and wound, to current collector plates (20, 22), comprising the steps of: a jig (32) is pressed against a plurality of end portions (12, 14) of the electrode plates (6, 8) arranged in the radial direction of the electrode group (2), and the jig (32) is displaced along a curved path so that the amount of displacement in a direction approaching the electrode group (2) gradually increases and the amount of displacement in the radial direction gradually decreases, thereby bending the plurality of end portions (12, 14); and joining the bent end portions (12, 14) to current collector plates (20, 22). Joining method. [Item 2] bending the ends (12, 14) in a partial region in the circumferential direction of the electrode group (2); Item 1. The joining method. [Item 3] The jig (32) is displaced by a cam mechanism (34). Item 3. The bonding method according to item 1 or 2. [Industrial Applicability]

[0038] The present disclosure can be used in a method for joining an electrode group and a current collector plate. [Explanation of symbols]

[0039] 1 battery, 2 electrode group, 6 first electrode plate, 8 second electrode plate, 10 separator, 12 first uncoated portion, 14 second uncoated portion, 20 first current collector plate, 22 second current collector plate, 32 jig, 34 cam mechanism.

Claims

1. A method for joining a wound electrode group, in which separators and electrode plates are stacked and wound, to a current collector plate, comprising the steps of: a jig is pressed against a plurality of ends of the electrode plates arranged in a radial direction of the electrode group, and the jig is displaced along a curved path so that the amount of displacement in a direction approaching the electrode group gradually increases and the amount of displacement in the radial direction gradually decreases, thereby bending the plurality of ends; and joining the bent end portions to the current collector plate. Joining method.

2. bending the end portions in a partial region in the circumferential direction of the electrode group; The joining method according to claim 1 .

3. The jig is displaced by a cam mechanism. The joining method according to claim 1 or 2.

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