WO2012014510A1 - Secondary cell - Google Patents

Abstract

A secondary cell is provided with an electrode group that is charged with and discharges electricity, a can that has an opening and houses the electrode group therein, a lid that is welded to the opening of the can and seals the opening, a positive-electrode connection member and a negative-electrode connection member that each have one end electrically connected to the electrode group and the other end passing through the lid and protruding to the outside of the lid, and a positive-electrode external terminal and a negative-electrode external terminal that are respectively connected to the positive-electrode connection member and the negative-electrode connection member by caulking on the outside of the lid. In each of the positive-electrode connection member and the negative-electrode connection member, a caulked portion the diameter of which is enlarged is formed on the outside of the lid, and in the caulked portion, thin sections which can be laser spot welded are locally formed, and the thin sections are laser spot welded.

Description

Secondary battery

The present invention relates to a secondary battery such as a lithium secondary battery.

2. Description of the Related Art In recent years, large capacity (Wh) lithium secondary batteries have been developed as power sources for hybrid vehicles, electric vehicles, etc. Among them, prismatic lithium secondary batteries with high energy density (Wh / kg) are attracting attention. .

A square lithium secondary battery is formed by flattening a positive electrode plate coated with a positive electrode active material on a positive electrode metal foil and a negative electrode plate coated with a negative electrode active material on a negative electrode metal foil with a separator interposed therebetween. It has a wound electrode group formed into a shape. The electrode group is housed in a can, and a positive external terminal and a negative external terminal that are provided on a lid and exposed to the outside are electrically connected to the electrode group. Further, the can and the lid are sealed and welded, and the inside of the can is filled with an electrolyte injected from a liquid injection port provided in the lid. An injection plug is inserted into the injection port, and the injection port is sealed and welded by laser welding.

The sealed battery described in Patent Document 1 has a cylindrical connection terminal. The connection terminal is inserted into an opening formed in each of the insulating member, the lid, the gasket, and the current collector plate, and the connection terminal is extended from the central axis to the outer peripheral side, and each member is fixed by caulking. A thin-walled portion is provided on the entire outermost periphery of the caulked portion, and a method of joining the thin-walled portion and the current collector plate by laser welding is shown.

JP 2009-87693 A

In the sealed battery of Patent Document 1, each member is fixed by caulking, and the peripheral portion of the caulking portion is thinned to ensure the quality of laser welding. For this reason, there is a possibility that the caulking strength, that is, the strength for fixing each member may be lowered.

The secondary battery according to the first aspect of the present invention includes an electrode group for charging and discharging electricity, an opening, a can in which the electrode group is accommodated, and welded to the opening of the can, A lid for sealing the part, a positive electrode connecting member and a negative electrode connecting member, one end of which is electrically connected to the electrode group and the other end of which penetrates the lid and protrudes to the outside of the lid, The positive electrode connecting member and the negative electrode connecting member are provided with a positive external terminal and a negative external terminal connected to the positive electrode connecting member and the negative electrode connecting member, respectively, by caulking, and the positive electrode connecting member and the negative electrode connecting member are spread outside the lid. In the secondary battery, a caulking portion having a diameter is formed, a thin portion capable of laser spot welding is locally formed in the caulking portion, and the thin portion is laser spot welded.
A secondary battery according to a second aspect of the present invention is the secondary battery according to the first aspect, wherein the positive electrode external terminal and the negative electrode external terminal are electrically insulated from the lid; and the positive electrode connection And a gasket that seals a gap between the negative electrode connecting member and the lid; and the positive and negative electrode connecting members pass through the insulating member and the gasket and are caulked and fixed to the positive and negative external terminals. Secondary battery.
A secondary battery according to a third aspect of the present invention is the secondary battery according to the first or second aspect, wherein the thin portion is formed in plural.
The secondary battery according to a fourth aspect of the present invention is the secondary battery according to any one of the first to third aspects, wherein the thin portion is connected to another battery of the positive electrode external terminal and the negative electrode external connection terminal. It is the secondary battery arrange | positioned at the side which a connection means (for example, screw connection part and weld connection part with a bus-bar) faces.
A secondary battery according to a fifth aspect of the present invention is the secondary battery according to any one of the first to fourth aspects, wherein the thin portion is a circular shape.
A secondary battery according to a sixth aspect of the present invention is the secondary battery according to any one of the first to fourth aspects, wherein the thin portion is an ellipse.
The secondary battery according to a seventh aspect of the present invention is the secondary battery according to any one of the first to sixth aspects, wherein the electrode group is a sheet-like positive and negative electrode in which an active material is applied to both surfaces of a metal foil. An electrode group in which plates are wound in a flat shape around a winding axis with a separator interposed therebetween, and the metal foil exposure of the positive and negative electrode plates where the active material is not applied to both ends in the winding axis direction Each of the positive and negative electrode connecting members is a secondary battery electrically connected to the exposed metal foil portion of the positive and negative electrode plates.
A secondary battery according to an eighth aspect of the present invention is the secondary battery according to the fourth aspect, wherein the electrode group includes a sheet-like positive and negative electrode plate in which an active material is applied on both sides of a metal foil, In the electrode group wound in a flat shape around the winding axis with a separator interposed therebetween, the metal foil exposed portions of the positive and negative electrode plates to which the active material is not applied are provided at both ends in the winding axis direction, respectively. The positive and negative electrode connecting members include a positive and negative current collector plate electrically connected to the exposed metal foil portion of the positive and negative electrode plate, and a cylindrical positive and negative electrode connection welded to the other end of the positive and negative electrode current collector plate. The positive and negative electrode connection terminals include a terminal, the tip of the positive and negative electrode connection terminal penetrates the lid and is caulked to the positive and negative electrode external terminal, and the thinned portion is formed in the caulked portion.
A secondary battery according to a ninth aspect of the present invention is the secondary battery according to any one of the first to eighth aspects, wherein the thin portion is formed flat.

According to the present invention, good welding quality and high caulking strength can be obtained.

1 is an exploded perspective view showing a winding group in a first embodiment of a secondary battery according to the present invention. The perspective view which shows the lid | cover assembly which assembled | attached the winding group of FIG. The perspective view which shows the secondary battery which assembled | attached the cover assembly of FIG. The partial exploded perspective view which shows the state before the assembly of the lid | cover and terminal assembly for the lid | cover assembly of FIG. The longitudinal cross-sectional view which shows the state before the crimping process after components assembly | attachment of the lid | cover and terminal assembly of FIG. FIG. 6 is a longitudinal sectional view showing a first caulking step of the lid / terminal assembly of FIG. 5. FIG. 7 is a longitudinal sectional view showing a second caulking step of the lid / terminal assembly of FIG. 6. FIG. 8 is a longitudinal sectional view showing a third caulking step of the lid / terminal assembly of FIG. 7. The perspective view which shows the state after the crimping process of the lid | cover and terminal assembly of FIG. The perspective view which shows the state which implemented the welding process to the lid | cover and terminal assembly of FIG. The longitudinal cross-sectional view of FIG. The perspective view which shows the lid | cover and terminal assembly after the welding process of FIG. The perspective view which shows the lid | cover and terminal assembly in 2nd Embodiment of the secondary battery by this invention. The perspective view which shows the lid | cover and terminal assembly in 3rd Embodiment of the secondary battery by this invention. The perspective view which shows the state after the 3rd crimping process of the lid | cover and terminal assembly in 4th Embodiment of the secondary battery by this invention. The perspective view which shows the state after the welding process in the lid | cover and terminal assembly of FIG.

An embodiment of a secondary battery according to the present invention will be described with reference to the drawings.
1 to 12 show a prismatic secondary battery according to the first embodiment. The secondary battery of the embodiment is a battery in which a wound electrode group is housed in a thin battery can, and is particularly suitable for a secondary battery that drives a rotating electric machine of a hybrid vehicle or an electric vehicle.

[First Embodiment]
[overall structure]
As shown in FIG. 3, the secondary battery 100 is configured by sealing the can 33 after inserting the lid assembly 35 into the can 33. As shown in FIG. 2, the lid assembly 35 is obtained by assembling the wound electrode group 6 to the lid / terminal assembly 200. The lid / terminal assembly 200 is attached to the lid 11 as shown in FIG. The positive and negative external terminals 13 and 32 and the positive and negative current collecting plates 14 and 31 are mounted. The lid 11 is provided with a liquid injection port 11b. After sealing the can 33, an electrolyte (not shown) is injected into the can 33 from the liquid injection port 11b. Are sealed and welded.

The positive and negative external terminals 13 and 32 are provided with through holes 13b and 32b. The positive and negative external terminals 13 and 32 are connected to a bus bar (not shown) by bolts (not shown) inserted through the through holes 13b and 32b. The peripheral edge of the lid 11 is welded to the can 33, whereby the can 3 is sealed.

[Lid assembly]
As shown in FIG. 2, the lid assembly 35 includes a lid / terminal assembly 200 and an electrode group 6 connected to the positive and negative current collecting plates 14, 31 in the lid / terminal assembly 200. The positive and negative current collector plates 14 and 31 are welded to the positive and negative electrode bodies 1 and 3 exposed at both ends of the electrode group 6.

The positive and negative electrode current collector plates 14 and 31 are respectively welded with positive and negative electrode connection terminals 15 and 16 at a welded portion 20 (see FIG. 5). Hereinafter, a member in which the positive and negative current collecting plates 14 and 31 and the positive and negative electrode terminals 15 and 16 are integrated is referred to as a positive and negative electrode connecting member as necessary. The positive and negative electrode connection members, that is, the positive and negative electrode connection terminals 15 and 16 penetrate the lid 11 from the inside and protrude to the outside. Positive and negative electrode external terminals 13 and 32 are attached to the positive and negative electrode connection terminals 15 and 16 on the outer surface of the lid 11. Details of the method of attaching the lid / terminal assembly 200, in particular, the positive and negative current collecting plates 14 and 31, and the positive and negative external terminals 13 and 32 to the lid 11 will be described later.

[Turn-up group]
As shown in FIG. 1, the electrode group 6 includes a positive electrode body 1 in which a positive electrode active material 2 is applied on both sides of a positive electrode metal foil, and a negative electrode body 3 in which a negative electrode active material 4 is applied on both sides of the negative electrode metal foil. 5 is wound around in a flat shape. The positive electrode metal foil is made of, for example, aluminum having a thickness of 30 μm, and the negative electrode metal foil is made of, for example, copper having a thickness of 15 μm. The separator 5 is made of, for example, a porous polyethylene resin. Electric power is charged and discharged between the positive electrode active material 2 and the negative electrode active material 4 of the electrode group 6.

[Lid and terminal assembly]
The lid / terminal assembly 200 will be described in detail with reference to FIGS.
In particular, as shown in FIG. 12, the lid / terminal assembly 200 includes a lid 11, positive and negative current collector plates 14 and 31, positive and negative electrode connection terminals 15 and 16, a gasket 10, an insulating member 12, and positive and negative electrodes. External terminals 13 and 32 are provided, and are integrated in a process described later. The positive and negative current collector plates 14 and 31 are metal plates bent along the side surface shape of both end portions in the axial direction of the electrode group 6, and are made of aluminum and copper, which are the same as the material of the positive and negative electrode bodies 1 and 3.

Hereinafter, the configuration on the positive electrode side will be described.
As shown in FIGS. 4 and 5, the positive electrode current collector plate 14 and the positive electrode connection terminal 15 are integrated in advance by a welding portion 20 to form a positive and negative electrode connection member. The lid 11 has a through hole 11a through which the positive electrode connection terminal 15 is inserted. The positive electrode connection terminal 15 has a shaft portion 15a that is inserted into the through hole 11a and protrudes to the outside of the lid 11, and a head portion 15f having a larger diameter than the shaft portion. The positive electrode connection terminal 15 is inserted into the through hole 11a in a state where the gasket 10 is fitted to the shaft portion 15a. After the lid / terminal assembly 200 is manufactured, the gasket 10 is pressed against the inner surface of the lid 11 by the head 15f. That is, a through hole 10 a is formed in the gasket 10, the shaft portion 15 a of the positive electrode connection terminal 15 is inserted into the through hole 10 a, and the shaft portion 15 a penetrates the through hole 11 a of the lid 11 from the lower surface side of the lid 11. Yes. After the penetration, the head portion 15f is pressed into contact with the gasket 10, and the gap between the positive electrode connection terminal 15 and the lid 11 is sealed. Since the gasket 10 is made of an insulating material, it also has a function of electrically insulating the positive and negative electrode connection terminals and the lid.

As shown in FIGS. 4 and 5, the shaft portion 15a of the positive electrode connection terminal 15 is fitted with the positive and negative electrode external terminals 13 through the insulating member 12 outside the lid 11, and then the shaft portion 15a has the shaft portion 15a. A caulking process and a welding process are performed. As a result, the shaft portion 15 a of the positive electrode connection terminal 15 is electrically connected to the positive electrode external terminal 13 while being electrically insulated from the lid 11.

[Caulking process]
The three-step caulking process of the lid / terminal assembly 200 will be described in detail by taking the positive electrode side as an example.

[First caulking process]
As shown in FIG. 5, the tip portion of the shaft portion 15a is a cylindrical portion 15b, and a bottomed hole 15g that opens toward the tip is formed.
As shown in FIG. 6, in the first caulking process among the three stages, the tip-shaped conical mold 22 is press-fitted into the bottomed hole 15g with the head 15f supported by the planar mold 21. Is done. Thereby, the cylindrical part 15b is expanded. Thus, the positive electrode current collector plate 14, the gasket 10, the positive electrode external terminal 13, and the insulating member 12 are temporarily fixed to the lid 11.

[Second caulking process]
As shown in FIG. 7, in the second caulking step, the mold 24 having the annular groove 24a formed at the tip is formed in the cylindrical portion 15b with the head 15f supported by the planar mold 23. Pressed. At this time, the cylindrical portion 15b is pushed and expanded in a substantially disk shape within the annular groove 24a, and the diameter thereof is expanded, thereby forming a substantially disk-shaped caulking portion 15d. As a result, the positive electrode current collector plate 14, the gasket 10, the positive electrode external terminal 13, and the insulating member 12 are fastened and fixed to the lid 11 and integrated.

[The third caulking process]
As shown in FIG. 8, in the third caulking step, the die 26 is pressed against the periphery of the caulking portion 15d while the head 15f is supported by the flat die 25. The mold 26 has a plurality of (for example, four equally circumferentially) circular protrusions 26a formed at the tip, and a circular indentation (thin flat surface) formed by the protrusions 26a on the periphery of the caulking part 15d. Part) 15e are formed at equal intervals.

As shown in FIG. 9, the thin flat portions 15e are set to a minimum area and number so that the shaft portion 15a is fixed to the positive electrode external terminal 13 with necessary and sufficient strength by laser spot welding. Therefore, the thin flat portion 15e is locally and intermittently formed. Since the thin flat portion 15e is not formed around the entire periphery of the caulking portion 15d, a portion that is not thin remains and the caulking strength of the entire caulking portion 15d is high.

In the case of an in-vehicle lithium secondary battery, vibration load and impact load act on the battery during use. In particular, when the assembled battery is configured, since the positive electrode external terminal 13 is connected to the adjacent unit cell by the bus bar, a large load acts on the caulking portion 15 d of the positive electrode external terminal 13. In the present embodiment, an assembled battery that can withstand such a load can be configured by increasing the strength of the caulking portion 15d.

[Welding process]
Welding of the caulking portion 15d on the positive electrode side of the lid / terminal assembly 200 after the three-step caulking process is performed.
As shown in FIGS. 10 and 11, the positive electrode connection terminal 15 and the positive electrode external terminal 13 are electrically connected by laser welding, and a welded portion 30 is formed in the thin flat portion 15e. As described above, the caulking portion 15d has a sufficient caulking strength, so that the adhering strength between the positive electrode connecting terminal 15 and the positive electrode external terminal 13 is basically sufficient only by caulking. Therefore, it is not necessary to strictly control the fixing strength between the positive electrode connection terminal 15 and the positive electrode external terminal 13 under welding conditions.

In laser welding, a plurality of (four) thin flat portions 15e are irradiated with laser, and the thin flat portions 15e and the positive electrode external terminal 13 are welded. In addition, the quantity of the thin flat part 15e which is a welding location, a welding area, etc. are determined based on the electrical property at the time of charging / discharging of a secondary battery. If there are many thin flat parts 15e, the connection resistance of the thin flat part 15e and the positive electrode external terminal 13 can be reduced. In laser welding, for example, a YAG laser welder is used. For example, spot welding is performed with a pulse energy of 20 J. In addition, since only the welded portion is pressed locally, there is no gap between the thin flat end portion 15e and the positive electrode external terminal 13, and there is an effect that the welding quality is improved.

Since the positive electrode connection terminal 15 on the positive electrode side is made of aluminum, the thin flat portion 15e15e has a high reflectance with respect to the laser beam. In order to increase the absorption rate of the laser beam, it is necessary to make the laser beam enter perpendicularly to the thin flat portion 15e15e, and it is desirable to minimize the inclination of the thin flat portion 15e and make the surface as flat as possible.

The insulating member 12 is disposed in the vicinity of the welded portion 30, but the insulating member 12 is made of resin and has a low melting point. For this reason, it is necessary to perform welding with as little energy as possible and prevent the insulating member 12 from melting. In order to reduce the welding energy, the thin flat portion 15e may be made as thin as possible. In the present embodiment, a good result was obtained by setting the thickness of the thin flat portion 15e to 0.3 mm.

After completion of the positive electrode side welding, the negative electrode side welding is performed.
On the negative electrode side, the gasket 10, the lid 11, the insulating member 12, and the negative electrode external terminal 32 are caulked and fixed by the negative electrode connection terminal 16, and then the negative electrode connection terminal 16 and the negative electrode external terminal 32 are spot welded by laser. Weld. Since both the negative electrode connection terminal 16 and the negative electrode external terminal 32 are made of copper, the reflectance with respect to the laser is lower than that of aluminum, and welding is performed with an energy of 50 J, for example.

[Second Embodiment]
A second embodiment of the secondary battery according to the present invention will be described with reference to FIG. In the figure, the same or corresponding parts as those in the first embodiment are designated by the same reference numerals, and the differences will be mainly described.
In the secondary battery of the second embodiment, the number of thin flat portions is three, which is a smaller number than the secondary battery of the first embodiment.

As shown in FIG. 13, like the positive electrode connection terminal 15 of the first embodiment, the caulking process similar to the first and second caulking processes of the first embodiment is performed on the shaft portion 17a of the positive electrode connection terminal 17. To implement.
In the third caulking step, three thin flat portions 17e are formed on the caulking portion 17d formed on the shaft portion 17a, and further, the thin flat portion 17e is formed by a welding step similar to the first embodiment. A weld 30 is formed.

The welded portion 30 is arranged in the range of the circumferential angle of 180 ° of the caulking portion 17d at every circumferential angle of 90 °, and the arrayed range of the welded portion 30 faces the through hole 13b in the positive electrode external terminal 13. As described above, the bus bar is connected to the through hole 13b. When the electrode group 6 charges and discharges electric power, the current passes through the positive electrode connection terminal 15 and the positive electrode current collector plate 14, and at this time, a current path CF from the welded portion 30 toward the through hole 13b is formed. This current path CF is the shortest and the connection resistance is reduced by arranging the three welds 30 on the side facing the through hole 13b in the caulking part 17d.

In addition, if the range of the welded portion 30 is set to a narrower circumferential angle range and all the welded portions 30 are brought closer to the through hole 13b, the electric resistance is further reduced. However, the bias of the caulking portion 17d is increased, which may be disadvantageous with respect to the caulking strength.

This embodiment has an effect that the manufacturing cost of the welding process can be reduced in addition to the effect of the first embodiment.

[Third Embodiment]
A third embodiment of the secondary battery according to the present invention will be described with reference to FIG. In the figure, the same or corresponding parts as those in the first and second embodiments are denoted by the same reference numerals, and differences will be mainly described.
In the third embodiment, the number of thin flat portions is one, which is a smaller number than in the first embodiment.

As shown in FIG. 13, the same caulking process as the first caulking process of the first embodiment with respect to the shaft portion 17a of the positive electrode connecting terminal 17 similar to the positive electrode connecting terminal 15 of the first embodiment. To implement.
In the third caulking step, one thin flat portion 17e is formed on the caulking portion 17d formed on the shaft portion 17a, and further, the thin flat portion 17e is formed by a welding step similar to that of the first embodiment. A weld 30 is formed.

The welded portion 30 is disposed at a position closest to the through hole 13b in the caulking portion 17d, and the current path CF is the shortest. In addition to the effects of the first embodiment, the present embodiment provides the effect of minimizing electrical resistance with a minimum welding process cost.

[Fourth Embodiment]
A fourth embodiment of the secondary battery according to the present invention will be described with reference to FIGS. In the figure, the same or corresponding parts as those in the first and second embodiments are denoted by the same reference numerals, and differences will be mainly described.
In the fourth embodiment, the thin flat portion has an elliptical shape in the same welded portion arrangement as that of the second embodiment.

As shown in FIG. 15, the same caulking process as the first caulking process of the first embodiment with respect to the shaft portion 17a of the positive electrode external terminal 17 similar to the positive electrode connecting terminal 15 of the first embodiment. To implement.
In the third caulking step, three oval thin flat portions 17f are formed on the caulking portion 17d formed on the shaft portion 17a. In the third caulking step, a mold 26 (see FIG. 8) having three elliptical protrusions 26a formed at the tip is used. Thereafter, an elliptical welded portion 30 is formed on the thin flat portion 17f by the same welding process as in the first embodiment.

By making the welded portion 30 elliptical, the weld area at the welded portion 30 increases, which is effective in reducing electrical resistance.
In addition to the effects of the first embodiment, this embodiment has the effects that the manufacturing cost of the welding process can be reduced and the electrical resistance is relatively small.

[Modification]
In the second and third embodiments, the position of the welded portion 30 is arranged on the side facing the through hole 13b or in a close position, but welding bolts and other means are adopted as means for connecting to other batteries. In such a case, it is preferable to arrange the welded portion 30 on the side facing the connecting means or on a close position.

The electrode group has been described as a wound electrode group in which a long positive and negative electrode body is wound together with a separator, but the present invention can also be applied to a rectangular sheet-shaped laminated electrode group.
Although the secondary battery according to the present invention has been described as a secondary battery for driving a rotating electric machine of a hybrid vehicle or an electric vehicle, it can be used as a driving power source for various rotating electric machines of a railway vehicle or a construction machine. Or it can utilize also as a battery cell of the power supply device for electric power storage.

The secondary battery described above is an example, and the present invention is not limited to the above-described embodiments and modifications. That is, the present invention includes an electrode group housed in a battery can, a positive and negative external terminal that is exposed outside the battery can in order to connect the electrode group to an external load, an electrode group, and a positive and negative electrode The present invention can be applied to various secondary batteries having positive and negative electrode connecting members that electrically connect external terminals. Therefore, the shape, structure, arrangement, and the like of the electrode group, the positive and negative external terminals, and the positive and negative electrode connecting members are not limited to the embodiments. For example, in the embodiment, an example in which a separate positive and negative current collector plate and positive and negative electrode connection terminals are integrated by welding has been described. However, the positive and negative current collecting plates and the positive and negative electrode connecting terminals may be made from one material.

The disclosure of the following priority application is hereby incorporated by reference.
Japanese patent application 2010 No. 167995 (filed on July 27, 2010)

Claims (9)

Secondary battery
An electrode group for charging and discharging electricity;
A can having an opening and storing the electrode group;
A lid welded to the opening of the can to seal the opening;
A positive electrode connecting member and a negative electrode connecting member, one end of which is electrically connected to the electrode group and the other end of which penetrates the lid and protrudes outside the lid;
Outside the lid, the positive electrode connecting member and the negative electrode connecting member, respectively, provided with a positive external terminal and a negative external terminal connected by caulking,
The positive electrode connecting member and the negative electrode connecting member are formed with a caulked portion whose diameter is increased outside the lid, and the caulked portion is locally formed with a thin portion capable of laser spot welding, and the thin wall The part is laser spot welded. The secondary battery according to claim 1,
An insulating member that electrically insulates the positive electrode external terminal and the negative electrode external terminal from the lid;
A gasket for sealing a gap between the positive electrode connecting member and the negative electrode connecting member and the lid;
The positive and negative electrode connecting members pass through the insulating member and the gasket and are caulked and fixed to the positive and negative electrode external terminals. The secondary battery according to claim 1 or 2,
A plurality of the thin portions are formed. The secondary battery according to any one of claims 1 to 3,
The thin-walled portion is disposed on the positive electrode external terminal and the negative electrode external connection terminal on the side facing the connection means with another battery. The secondary battery according to any one of claims 1 to 4,
The thin portion is circular. The secondary battery according to any one of claims 1 to 4,
The thin part is oval. The secondary battery according to any one of claims 1 to 6,
The electrode group is an electrode group in which a sheet-like positive and negative electrode plate in which an active material is applied on both surfaces of a metal foil, and a separator interposed between them and wound in a flat shape around a winding axis, The metal foil exposed portions of the positive and negative electrode plates to which the active material is not applied are provided at both ends in the winding axis direction, respectively.
The one ends of the positive and negative electrode connecting members are electrically connected to the exposed metal foil portions of the positive and negative electrode plates, respectively. The secondary battery according to claim 4,
The electrode group is an electrode group in which a sheet-like positive and negative electrode plate in which an active material is applied on both surfaces of a metal foil, and a separator interposed between them and wound in a flat shape around a winding axis, The metal foil exposed portions of the positive and negative electrode plates to which the active material is not applied are provided at both ends in the winding axis direction, respectively.
The positive and negative electrode connecting members include a positive and negative current collector plate electrically connected to the exposed metal foil portion of the positive and negative electrode plate, and a cylindrical positive and negative electrode connection welded to the other end of the positive and negative electrode current collector plate. Terminal and
The leading ends of the positive and negative electrode connecting terminals penetrate through the lid and are caulked to the positive and negative electrode external terminals, and the thin portion is formed in the caulking portion. The secondary battery according to any one of claims 1 to 8,
The thin portion is formed in a flat shape.

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