Method for manufacturing electric power storage device, and electric power storage device

Abstract

This method for manufacturing an electric power storage device includes: a first preparation step for preparing a wound-type electrode group 50 comprising a first electrode 51 and a second electrode, the first electrode 51 having a metal foil portion 52 exposed at one end in the axial direction of the electrode group 50; a second preparation step for preparing a current collector plate 80 having a central portion 81 and arm portions 82; a third preparation step for preparing a bottomed cylindrical case; a first welding step for welding the metal foil portion 52 and the arm portions 82 at line welded portions LW by means of a line-shaped laser beam formed using a diffractive optical element; and a second welding step for accommodating the electrode group 50 and the current collector plate 80 in the case and welding the central portion 81 and an inner bottom surface of the case at a central welded portion CW. In the first welding step, a spot-shaped melt mark M is formed in a part of the central portion 81 on the outer peripheral side of the central welded portion CW by means of zero-order light emitted from the diffractive optical element. This enables manufacturing costs to be reduced.

Description

Electricity storage device manufacturing method and electricity storage device

[0001] The present disclosure relates to a method for manufacturing an electricity storage device and an electricity storage device.

[0002] Batteries with a so-called end-face current collection structure have been known (see, for example, Patent Document 1). The battery in Patent Document 1 includes a wound electrode group and a current collector plate welded to the protruding foil portion of the electrode group. The welding is performed by, for example, laser welding.

[0003] JP 2010-257851 A

[0004] However, there are many welding points between the protruding foil portion and the current collecting plate, and it takes a certain amount of time to perform laser welding on all of them. This leads to an increase in the manufacturing cost of the battery (or the power storage device). In this situation, one of the objectives of the present disclosure is to reduce the manufacturing cost.

[0005] One aspect of the present disclosure relates to a method for manufacturing an energy storage device, the method comprising: a first preparation step of preparing a wound electrode group having first and second electrodes, the first electrode having a metal foil portion exposed at one axial end of the electrode group; a second preparation step of preparing a current collector plate having a central portion and at least one arm portion extending radially outward from the central portion; a third preparation step of preparing a cylindrical case with a bottom; a first welding step of forming a line-shaped laser beam using a diffractive optical element and welding the metal foil portion and the arm portion together at a line weld using the laser beam; and a second welding step of housing the electrode group and the current collector plate in the case and welding the central portion to an inner bottom surface of the case at a central weld, wherein in the first welding step, zero-order light emitted from the diffractive optical element forms a spot-shaped melt mark in a portion of the central portion that is radially outward from the central weld.

[0006] Another aspect of the present disclosure relates to an energy storage device including: a wound electrode group having a first electrode and a second electrode; a bottomed cylindrical case that houses the electrode group; and a current collector plate electrically connected to the first electrode and the case, wherein the first electrode has a metal foil portion exposed at one axial end of the electrode group, and the current collector plate has a central portion welded to an inner bottom surface of the case by a central weld and at least one arm portion extending from the central portion toward an outer periphery and welded to the metal foil portion by a line weld, and a spot-shaped melt mark is formed in a portion of the central portion that is outer periphery closer to the central weld.

[0007] According to the present disclosure, manufacturing costs can be reduced.

[0008] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present application, will be better understood from the following detailed description taken in conjunction with the drawings.

[0009] 1 is a cross-sectional view schematically illustrating an example of an electricity storage device according to the present disclosure, a bottom view illustrating an electrode group and a negative electrode current collector plate, and a bottom view illustrating another example of an electrode group and a negative electrode current collector plate.

[0010] Examples of embodiments of a manufacturing method for a power storage device and a power storage device according to the present disclosure will be described below. However, the present disclosure is not limited to the examples described below. While specific numerical values ​​and materials may be used in the following description, other numerical values ​​and materials may be used as long as the effects of the present disclosure are obtained.

[0011] (Method for manufacturing an electric storage device) A method for manufacturing an electric storage device according to the present disclosure includes a first preparation step, a second preparation step, a third preparation step, a first welding step, and a second welding step. The electric storage device may be a battery or a capacitor.

[0012] In the first preparation step, a wound electrode group having a first electrode and a second electrode is prepared. The first electrode of the electrode group has a metal foil portion exposed at one axial end of the electrode group. The electrode group may be formed by winding the first electrode and the second electrode with a separator interposed therebetween. The outer shape of the electrode group may be, for example, cylindrical or prismatic. One of the first electrode and the second electrode is a positive electrode, and the other of the first electrode and the second electrode is a negative electrode.

[0013] The first electrode may have a long sheet-like (or strip-like) first current collector and a first active material layer formed on the surface of the first current collector. When the first electrode is the negative electrode of a lithium-ion secondary battery, the first current collector may be made of copper foil or copper alloy foil. When the first electrode is the negative electrode of a lithium-ion secondary battery, the first active material layer may include a negative electrode active material (such as a carbonaceous material or a silicon-containing material), a conductive agent, and a binder. The first active material layer may not necessarily be provided.

[0014] The second electrode may have a second current collector in the form of a long sheet (or a strip) and a second active material layer formed on the surface of the second current collector. When the second electrode is a positive electrode of a lithium-ion secondary battery, the second current collector may be made of aluminum foil or aluminum alloy foil. When the second electrode is a positive electrode of a lithium-ion secondary battery, the second active material layer may include a positive electrode active material (e.g., a lithium-containing transition metal oxide), a conductive agent, a binder, etc.

[0015] The separator may be made of a porous sheet having ion permeability and insulating properties, such as a thin film, woven fabric, or nonwoven fabric having micropores.

[0016] In the second preparation step, a current collector plate is prepared, which has a central portion and at least one arm portion extending from the central portion toward the outer periphery (or radially outward). The current collector plate may be made of, for example, a metal whose main component is iron. The central portion may be, for example, a circular or polygonal flat plate. The arm portions may extend radially outward from the outer edge of the central portion. The number of arm portions is not particularly limited, but may be, for example, three or more and six or less.

[0017] In the third preparation step, a cylindrical case with a bottom is prepared. The case may have an opening at one end. The case may be made of, for example, a metal containing iron as a main component. The cylindrical portion of the case may have, for example, a cylindrical or rectangular shape.

[0018] In the first welding step, a diffractive optical element is used to form a line-shaped (or linear) laser beam, and the metal foil portion and the arm portion are welded together at a line weld using the laser beam. The number of line-shaped laser beams may be the same as the number of arm portions, in which case one line beam is irradiated onto each arm portion. The line weld can also be referred to as a linear weld. In this way, by welding the metal foil portion and the arm portion together using a line-shaped laser beam, the time required for the welding can be shortened, and ultimately the manufacturing cost of the electricity storage device can be reduced.

[0019] In the second welding step, the electrode group and the current collector plate are housed in a case, and the central portion of the current collector plate is welded to the inner bottom surface of the case at a central weld. This welding can be performed, for example, by laser welding. The central weld may be formed in a region including the center of the central portion. The central portion and the inner bottom surface of the case may be welded directly or indirectly via some kind of conductive member. In this specification, both of these cases are considered to be included in the weld between the central portion of the current collector plate and the inner bottom surface of the case.

[0020] In the first welding step, the zero-order light emitted from the diffractive optical element forms a spot-shaped fusion mark in a portion of the central portion of the current collecting plate that is closer to the outer periphery than the central weld. In the first welding step, as described above, the diffractive optical element forms a line-shaped laser beam, and the output of the original laser is relatively high. Therefore, the energy of the zero-order light, which is inevitably generated when using a diffractive optical element, is also somewhat high. Here, as is well known to those skilled in the art, the first welding step uses a presser plate to tightly attach the electrode group and the current collecting plate to each other. If the presser plate is irradiated with the zero-order light, the presser plate will be damaged each time the first welding step is performed, eventually requiring replacement. However, in the first welding step of the present disclosure, the zero-order light forms a spot-shaped fusion mark in the aforementioned portion of the central portion. This can be achieved by providing the presser plate with an opening that allows the zero-order light to pass through. In other words, in the first welding step of the present disclosure, the presser plate is not irradiated with the zero-order light, and therefore does not need to be replaced due to damage caused by the zero-order light. This further reduces the manufacturing cost of the power storage device.

[0021] Furthermore, the arm portion of the current collecting plate extends from the center toward the outer periphery (or radially outward). Therefore, the linear laser beam irradiated onto the arm portion also has a shape along the radial direction, and the pattern center of the laser beam coincides with the center of the central portion of the current collecting plate. In contrast, the zeroth-order light is irradiated onto a portion of the central portion of the current collecting plate that is closer to the outer periphery than the central welded portion. In other words, in the first welding step, the diffractive optical element is used so that the irradiation position of the zeroth-order light and the pattern center of the linear laser beam are offset from each other. This increases the diffraction efficiency of the diffractive optical element and enables the laser output required for welding in the first welding step to be reduced.

[0022] The manufacturing method for an energy storage device may further include an evaluation step of alternatively evaluating the state of the line weld by evaluating the state of the melting mark. The state of the melting mark may include the diameter of the melting mark if the melting mark is circular, the shape of the melting mark, or the presence or absence of the melting mark. The state of the line weld may include the joint strength, the presence or absence of defects, or the presence or absence of the line weld. The melting mark is formed simultaneously with the line weld, and both are caused by the same laser beam. Therefore, by evaluating the state of the melting mark, the state of the line weld can be alternatively (or indirectly) evaluated. For example, if the diameter of the spot-shaped melting mark is too small, it can be determined that the joint strength of the line weld is insufficient due to insufficient laser output.

[0023] (Power Storage Device) The power storage device according to the present disclosure may be a battery or a capacitor. Examples of the battery include primary batteries such as lithium primary batteries, and secondary batteries such as alkaline batteries (nickel-metal hydride batteries, nickel-cadmium batteries, etc.), lithium-ion secondary batteries, and lithium metal secondary batteries.

[0024] The power storage device according to the present disclosure has a so-called end face current collection structure, and includes an electrode group, a case, and a current collector plate.

[0025] The electrode group is a wound electrode group having a first electrode and a second electrode. The electrode group may have, for example, a cylindrical or prismatic outer shape. The first electrode has a metal foil portion exposed at one axial end of the electrode group.

[0026] The case is a cylindrical case with a bottom that houses the electrode group. The case may house an electrolyte in addition to the electrode group. The shape of the cylindrical part of the case may be, for example, a cylindrical or rectangular tube.

[0027] The current collector plate is electrically connected to the first electrode and the case. The current collector plate has a central portion and at least one arm portion. The central portion is welded to the inner bottom surface of the case by a central weld. The at least one arm portion extends from the central portion toward the outer periphery and is welded to the metal foil portion by a line weld. This achieves the electrical connection.

[0028] A spot-shaped melt mark is formed in a portion of the center of the current collector plate that is closer to the outer periphery than the central weld. Here, as described above, a presser plate is used in the process of forming the line weld to tightly attach the electrode group and the current collector plate to each other. In the energy storage device according to the present disclosure, a spot-shaped melt mark is formed in the aforementioned portion of the center. In other words, the laser light used to form such a melt mark is not irradiated onto the presser plate. Therefore, there is no need to replace the presser plate due to damage caused by the laser light, and the manufacturing cost of the energy storage device can be reduced.

[0029] As described above, according to the present disclosure, the manufacturing cost of the power storage device can be reduced by forming the line welds all at once. Furthermore, according to the present disclosure, the manufacturing cost of the power storage device can be further reduced by eliminating the need to replace the pressing plate. Furthermore, according to the present disclosure, the condition of the line welds can be alternatively evaluated by evaluating the condition of the spot-like melt marks formed on the current collector plate.

[0030] An example of a method for manufacturing a power storage device and a power storage device according to the present disclosure will be described in detail below with reference to the drawings. The above-described steps and components can be applied to the steps and components of the example method for manufacturing a power storage device and the example of the power storage device described below. The steps and components of the example method for manufacturing a power storage device and the example of the power storage device described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above-described embodiment. Among the steps and components of the example method for manufacturing a power storage device and the example of the power storage device described below, steps and components that are not essential to the method for manufacturing a power storage device and the power storage device according to the present disclosure may be omitted. Note that the diagrams shown below are schematic and do not accurately reflect the shapes and numbers of actual components.

[0031] In the following, first, the electricity storage device 10 of this embodiment will be described, and then a method for manufacturing the electricity storage device of this embodiment will be described.

[0032] (Electricity Storage Device) The electricity storage device 10 of this embodiment is configured as a lithium-ion secondary battery, but is not limited to this. As shown in Figures 1 and 2, the electricity storage device 10 includes a case 20, a sealing unit 30, an electrode group 50, a negative electrode current collector plate 80, and a positive electrode current collector plate 90. Note that the electricity storage device 10 of this embodiment has a so-called end face current collection structure on both the positive electrode side and the negative electrode side, but instead may have a current collection structure via a tab on one of the positive electrode side or the negative electrode side.

[0033] The case 20 is formed in a cylindrical shape with a bottom and an opening at one end (the upper end in FIG. 1 ). The case 20 has a cylindrical side wall portion 21 and a disk-shaped bottom portion 23. A crimping portion 22 for fixing the sealing unit 30 is formed in an area of ​​the side wall portion 21 near the opening. The case 20 in this embodiment is made of a metal whose main component is iron, but is not limited to this.

[0034] The sealing unit 30 seals the opening of the case 20. The sealing unit 30 has a structure in which a filter 31, a lower valve body 32, an insulating member 33, an upper valve body 34, and a cap 35 are stacked in this order from the electrode group 50 side. Each member constituting the sealing unit 30 has, for example, a disk or ring shape, and each member except for the insulating member 33 is electrically connected to each other. The insulating member 33 is made of an insulating resin, and each other member is made of metal. The sealing unit 30 is fixed to a crimped portion of the case 20 via an insulating gasket 40.

[0035] The electrode group 50 is housed in the case 20 and includes a negative electrode 51 and a positive electrode 55. The electrode group 50 is a wound electrode group formed by winding the negative electrode 51 and the positive electrode 55 with a separator 59 interposed therebetween. The electrode group 50 has a cylindrical outer shape. The negative electrode 51 is electrically connected to the bottom 23 of the case 20 via a negative electrode current collector 80. Thus, the case 20 functions as an external negative electrode terminal of the energy storage device 10. The positive electrode 55 is electrically connected to the filter 31 of the sealing unit 30 via a positive electrode current collector 90 and a positive electrode lead 60. Thus, the cap 35 of the sealing unit 30 functions as an external positive electrode terminal of the energy storage device 10. A ring-shaped insulating plate 70 is disposed between the electrode group 50 and the sealing unit 30. The negative electrode 51 is an example of a first electrode, and the positive electrode 55 is an example of a second electrode.

[0036] The negative electrode 51 has a negative electrode metal foil portion 52 exposed at one axial end (the lower end in FIG. 1 ) of the electrode group 50. The negative electrode metal foil portion 52 is a region of the negative electrode current collector where no negative electrode active material layer is formed. The negative electrode metal foil portion 52 is an example of a metal foil portion.

[0037] The positive electrode 55 has a positive electrode metal foil portion 56 exposed at the other axial end (the upper end in FIG. 1 ) of the electrode group 50. The positive electrode metal foil portion 56 is a region of the positive electrode current collector where no positive electrode active material layer is formed.

[0038] The negative electrode current collector 80 is electrically connected to the negative electrode 51 and the case 20. As shown in FIG. 2 , the negative electrode current collector 80 is formed in a generally cross shape. The negative electrode current collector 80 includes a negative electrode central portion 81 and four negative electrode arm portions 82 extending outward from the negative electrode central portion 81. The negative electrode central portion 81 is welded to the bottom 23 of the case 20 at a central weld CW (shown by a two-dot chain line in FIG. 2 ). Each negative electrode arm portion 82 is welded to the negative electrode metal foil portion 52 at a line weld LW. The negative electrode current collector 80 is an example of a current collector, the negative electrode central portion 81 is an example of a central portion, and the negative electrode arm portions 82 are an example of an arm portion.

[0039] 2, a spot-shaped fusion mark M is formed in a portion of the negative electrode central portion 81 that is closer to the outer periphery than the central weld CW. As will be described later, this spot-shaped fusion mark M can be formed by zero-order light emitted from a diffractive optical element used to form each line weld LW.

[0040] The negative electrode current collector plate 80 may be formed in a rectangular shape, as shown in Fig. 3 . In this case, the negative electrode current collector plate 80 includes a negative electrode central portion 81 and two negative electrode arm portions 82 extending radially outward from the negative electrode central portion 81. The negative electrode central portion 81 is welded to the bottom 23 of the case 20 at a central weld CW (shown by a two-dot chain line in Fig. 3 ). Each negative electrode arm portion 82 is welded to the negative electrode metal foil portion 52 at two line welds LW.

[0041] The positive electrode current collector 90 is electrically connected to the positive electrode 55. Like the negative electrode current collector 80, the positive electrode current collector 90 is formed in a generally cross shape. The positive electrode current collector 90 includes a positive electrode center portion and four positive electrode arm portions (not shown) extending outward from the positive electrode center portion. Each positive electrode arm portion may be welded to the positive electrode metal foil portion 56 by a line weld (not shown).

[0042] (Method for manufacturing the power storage device) Next, a method for manufacturing the power storage device of this embodiment will be described. The method for manufacturing the power storage device of this embodiment can not only manufacture the power storage device 10 of this embodiment described above, but can also manufacture other types of power storage devices. The method for manufacturing the power storage device includes a first preparation step, a second preparation step, a third preparation step, a first welding step, a second welding step, and an evaluation step.

[0043] In the first preparation step, a wound electrode group 50 is prepared, which includes a positive electrode 55 and a negative electrode 51. The electrode group 50 may be as described above.

[0044] In the second preparation step, there is prepared a negative electrode current collector plate 80 having a negative electrode central portion 81 and four negative electrode arm portions 82. The negative electrode current collector plate 80 may be the one described above.

[0045] In the third preparation step, a bottomed cylindrical case 20 is prepared. The case 20 may be the one described above.

[0046] In the first welding step, a diffractive optical element (not shown) is used to form a line-shaped laser beam, and the laser beam is used to weld the negative electrode metal foil portion 52 of the electrode group 50 and the negative electrode arm portion 82 of the negative electrode current collector 80 at the line weld LW. At this time, a presser plate (not shown) having an opening is used to press the negative electrode current collector 80 against the negative electrode metal foil portion 52. In the first welding step, simultaneously with this welding, zero-order light emitted from the diffractive optical element forms a spot-shaped molten mark M in a portion of the negative electrode central portion 81 that is outer circumferentially closer to the central weld CW. At this time, the zero-order light passes through the opening in the presser plate and is irradiated onto that portion of the negative electrode central portion 81.

[0047] In the second welding step, the electrode group 50 and the negative electrode current collector plate 80 are housed in the case 20, and the negative electrode central portion 81 is welded to the bottom 23 of the case 20 at the central weld CW. Laser welding can be used for this welding.

[0048] In the evaluation process, the state of the spot-shaped fusion mark M is evaluated to alternatively evaluate the state of the line weld LW. Some specific examples of this evaluation are shown below. First, if the diameter of the fusion mark M is within a predetermined tolerance range, it can be determined that the line weld LW was formed properly. Next, if the diameter of the fusion mark M exceeds the tolerance range, it can be determined that the line weld LW was not formed properly because the laser output was excessive or the focal position was misaligned. On the other hand, if the diameter of the fusion mark M is below the tolerance range, it can be determined that the line weld LW was not formed properly because the laser output was insufficient. Alternatively, if the shape of the fusion mark M is abnormal, for example, if a portion of an originally circular shape is missing, it can be determined that the line weld LW was not formed properly because of an abnormality in the laser profile. Finally, if no fusion mark M is present, it can be determined that the line weld LW was not formed properly because laser irradiation was not performed.

[0049] <<Appendix>> The above embodiments disclose the following technology: (Technology 1) A method for manufacturing an electricity storage device, comprising: a first preparation step of preparing a wound electrode group having first and second electrodes, the first electrode having a metal foil portion exposed at one axial end of the electrode group; a second preparation step of preparing a current collector plate having a central portion and at least one arm portion extending radially outward from the central portion; a third preparation step of preparing a cylindrical case with a bottom; a first welding step of shaping a line-shaped laser beam using a diffractive optical element and welding the metal foil portion and the arm portions at line welds using the laser beam; and a second welding step of housing the electrode group and the current collector plate in the case and welding the central portion to an inner bottom surface of the case at a central weld, wherein in the first welding step, zero-order light emitted from the diffractive optical element forms a spot-shaped melt mark in a portion of the central portion that is radially outward of the central weld. (Technology 2) The manufacturing method of the electricity storage device according to Technology 1, further comprising an evaluation step of alternatively evaluating a state of the line weld by evaluating a state of the fusion mark. (Technology 3) An electricity storage device comprising: a wound electrode group having a first electrode and a second electrode; a bottomed cylindrical case that houses the electrode group; and a current collector plate electrically connected to the first electrode and the case, wherein the first electrode has a metal foil portion exposed at one axial end of the electrode group, and the current collector plate has a central portion welded to an inner bottom surface of the case by a central weld, and at least one arm portion extending from the central portion toward the outer periphery and welded to the metal foil portion by a line weld, and a spot-like fusion mark is formed in a portion of the central portion that is outer periphery side of the central weld.

[0050] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0051] The present disclosure can be used for a manufacturing method of an electricity storage device and for an electricity storage device.

[0052] 10: Energy storage device 20: Case 21: Side wall portion 22: Caulking portion 23: Bottom portion 30: Sealing unit 31: Filter 32: Lower valve body 33: Insulating member 34: Upper valve body 35: Cap 40: Gasket 50: Electrode group 51: Negative electrode (first electrode) 52: Negative electrode metal foil portion (metal foil portion) 55: Positive electrode (second electrode) 56: Positive electrode metal foil portion 59: Separator 60: Positive electrode lead 70: Insulating plate 80: Negative electrode current collector plate (current collector plate) 81: Negative electrode center portion (center portion) 82: Negative electrode arm portion (arm portion) 90: Positive electrode current collector plate CW: Center weld LW: Line weld M: Melt mark

Claims

1. A method for manufacturing an electricity storage device, comprising: a first preparation step of preparing an electrode group of a wound type having a first electrode and a second electrode, the first electrode having a metal foil portion exposed at one axial end of the electrode group; a second preparation step of preparing a current collecting plate having a central portion and at least one arm portion extending outward from the central portion; a third preparation step of preparing a cylindrical case with a bottom; a first welding step of forming a line-shaped laser beam using a diffractive optical element and welding the metal foil portion and the arm portion at a line weld portion using the laser beam; and a second welding step of housing the electrode group and the current collecting plate in the case and welding the central portion to an inner bottom surface of the case at a central weld portion, wherein in the first welding step, a spot-shaped melt mark is formed in a portion of the central portion that is closer to the outer periphery than the central weld portion by zero-order light emitted from the diffractive optical element.

2. The method for manufacturing an energy storage device according to claim 1, further comprising an evaluation step of alternatively evaluating a state of the line weld by evaluating a state of the molten trace.

3. An electricity storage device comprising: a wound electrode group having a first electrode and a second electrode; a bottomed cylindrical case that houses the electrode group; and a current collector plate electrically connected to the first electrode and the case, wherein the first electrode has a metal foil portion exposed at one axial end of the electrode group, and the current collector plate has a central portion welded to the inner bottom surface of the case by a central weld, and at least one arm portion extending from the central portion to the outer periphery and welded to the metal foil portion by a line weld, and a spot-like melt mark is formed in a portion of the central portion that is outer periphery than the central weld.

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