WO2018016747A1

WO2018016747A1 - Rechargeable battery

Info

Publication number: WO2018016747A1
Application number: PCT/KR2017/006519
Authority: WO
Inventors: 장명재; 곽승호; 권민형; 변상원
Original assignee: 삼성에스디아이 주식회사
Priority date: 2016-07-18
Filing date: 2017-06-21
Publication date: 2018-01-25
Also published as: KR20180009269A; KR102264702B1

Abstract

A rechargeable battery according to one embodiment of the present invention comprises: an electrode assembly in which electrodes having coated and non-coated tabs are arranged and wound on both sides of a separator; a case for accommodating the electrode assembly; a cap plate coupled to an opening of the case; a top insulator arranged between the electrode assembly and cap plate; and electrode terminals disposed on the cap plate and connected to the non-coated tabs, wherein the non-coated tabs are in a plurality of groups and are connected to the electrode terminals, passing around the periphery of the top insulator in a width-wise direction of the cap plate and past the central part of the electrode terminals in the width-wise direction.

Description

Secondary battery

The present disclosure relates to a secondary battery, and more particularly, to a secondary battery connecting an electrode assembly with a plurality of plain tabs to an electrode terminal.

A rechargeable battery is a battery that repeatedly performs charging and discharging, unlike a primary battery. Small capacity secondary batteries can be used in portable electronic devices such as mobile phones, notebook computers and camcorders, and large capacity secondary batteries can be used as power sources for driving motors of hybrid vehicles and electric vehicles.

For example, the secondary battery includes an electrode assembly for charging and discharging, a case accommodating the electrode assembly, a cap plate coupled to the opening of the case, and an electrode terminal for drawing the electrode assembly out of the cap plate.

One electrode assembly may be accommodated in one case, but a plurality of electrode assemblies may be provided and accommodated in the case. A top insulator interposed between the electrode terminal and the electrode assembly electrically insulates the electrode assembly from the top plate. The plain tabs connected to the electrode assembly are then welded to the electrode terminals by turning the side of the top insulator.

The uncoated tabs have a loose structure between the electrode terminal and the electrode assembly. Accordingly, in the process of inserting the electrode assembly integrally connected with the cap plate to the case, the tabs of the uncoated portion may be folded in the opening of the case, and may be inserted into the case in a folded state to contact different electrodes in the case. That is, the uncoated taps may generate a short circuit and a cell event.

One aspect of the present invention is to provide a secondary battery that prevents folding of a plurality of tabs tabs when inserting an electrode assembly into a case, and prevents a short circuit and a cell event by the tabs of the tabs inside the case.

According to an exemplary embodiment of the present invention, a secondary battery includes an electrode assembly wound by placing electrodes having a coating portion and a tab portion on both sides of a separator, a case accommodating the electrode assembly, and a cap plate coupled to the opening of the case. And a top insulator disposed between the electrode assembly and the cap plate, and an electrode terminal mounted on the cap plate and connected to the plain tabs, wherein the tabs are formed of a plurality of groups, It is connected to the electrode terminal via the outer side of the top insulator in the width direction and beyond the center of the electrode terminal in the width direction.

The electrode assembly may include a first assembly and a second assembly disposed side by side in a width direction of the cap plate, and the tabs of the uncoated region may be formed by connecting the first tab group and the second assembly to the electrodes of the first assembly. It may include a second tap group connected to the electrodes.

The first tap group is connected to the electrode terminal beyond the center of the electrode terminal via the top insulator on the first side (rear side) in the width direction, and the second tab group is opposite to the first tap group in the width direction. It may be connected to the electrode terminal beyond the center of the electrode terminal via the top insulator on the second side (front).

The electrode terminal may include a rivet part installed in the terminal hole of the cap plate, an outer plate installed outside the rivet part and connected to the rivet part, and an inner plate integrally connected to the inside of the rivet part. The first tab group and the second tab group may be welded to the inner plate.

The first tab group is disposed on the lower surface of the inner plate at the first side, is extended and welded to a position via the center of the inner plate, and the second tab group is the lower surface of the inner plate at the second side. It is disposed, and can be welded extending to a position via the center of the inner plate.

The inner plate includes a first connecting portion connected to the rivet portion and a second connecting portion connected to the first tab group and the second tab group, and in a longitudinal direction crossing the width direction and passing through the center of the inner plate, The first length of the first connector may be shorter than the second length of the second connector.

The first tab group and the second tab group may be disposed to have gaps spaced apart from each other in the longitudinal direction on the lower surface of the inner plate.

The first tab group and the second tab group may form a connection start portion connected to the first assembly and the second assembly and a welding end portion welded to the inner plate with the same width.

The first tab group and the second tab group have a length set to a distance protruding from the first assembly and the second assembly, and the length is greater than 1/2 of a distance between the first assembly and the second assembly. Can be set.

The first tab group and the second tab group are formed to have a first width at a connection start portion connected to the first assembly and the second assembly, and a welding end portion welded to the inner plate is smaller than the first width. It can be formed in two widths.

According to an embodiment of the present invention, the tabs of the tabs of the electrode assembly are formed in a plurality of groups, and the tabs of the tabs are connected to the electrode terminals beyond the center of the electrode terminals via the top insulator in the width direction of the cap plate. Can be given.

Therefore, the tensioned tabs are not folded even when the electrode assembly is inserted into the case, and may not be in contact with other electrodes even when inserted into the case. That is, short circuits and cell events caused by the uncoated tabs can be prevented.

1 is a perspective view of a rechargeable battery according to a first exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1.

3 is a cross-sectional view taken along line III-III of FIG. 1.

4 is a perspective view of an electrode assembly applied to FIG. 2.

5 is a perspective view of a state in which an electrode terminal is connected to the electrode assembly of FIG. 2.

6 is a plan view of a state in which the tabs of the uncoated region are connected to the electrode terminal.

FIG. 7 is a plan view of a rechargeable battery according to a second exemplary embodiment of the present invention, in which a plain tab is connected to an electrode terminal.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like elements throughout the specification.

Throughout the specification, when a part is "connected" to another part, it includes not only "directly connected", but also "indirectly connected" between other members. In addition, when a part is said to "include" a certain component, this means that it may further include other components, except to exclude other components unless otherwise stated.

1 is a perspective view of a rechargeable battery according to a first exemplary embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1, and FIG. 3 is a cross-sectional view taken along line III-III of FIG. 1.

1 to 3, the secondary battery 100 according to the first embodiment includes an electrode assembly 10 for charging and discharging current, a case 30 in which the electrode assembly 10 is embedded, and a case 30. A cap plate 40 coupled to the opening 31 of the top plate, a top insulator 20 disposed between the electrode assembly 10 and the cap plate 40, and

electrode terminals

51 and 52.

The case 30 sets a space to accommodate the plate-shaped electrode assembly 10. For example, the case 30 is formed in a substantially rectangular parallelepiped, and has a rectangular opening 31 at one side thereof to insert the electrode assembly 10.

The cap plate 40 is coupled to the opening 31 of the case 30 to seal the case 30 and includes two terminal holes H1 and H2. For example,

electrode terminals

51 and 52 are provided in the terminal holes H1 and H2. As an example, the case 30 and the cap plate 40 may be made of aluminum and welded to each other at the opening 31.

In addition, the cap plate 40 further includes a vent hole 41 and an electrolyte injection hole 42. The vent hole 41 is sealed by the vent plate 411 to discharge the internal pressure caused by the gas generated inside the secondary battery 100 by the charging and discharging action of the electrode assembly 10.

When the internal pressure of the secondary battery 100 reaches the set pressure, the vent plate 411 is cut to open the vent hole 41 to discharge the gas and the internal pressure generated by overcharging. Vent plate 411 has a notch 412 leading to an incision.

The electrolyte injection hole 42 couples and welds the cap plate 40 to the case 30, and then injects the electrolyte into the case 30. After electrolyte injection, the electrolyte injection port 42 is sealed with a sealing stopper 421.

The top insulator 20 is formed of an electrical insulating material and is disposed between the electrode assembly 10 and the cap plate 40 to electrically insulate the electrode assembly 10 and the cap plate 40.

The top insulator 20 has an internal vent hole 27. Since the inner vent hole 27 is formed to correspond to the vent hole 41 provided in the cap plate 40, the inner vent hole 27 is smoothly transferred to the vent hole 41 by the gas generated by the gas generated in the electrode assembly 10. To be discharged.

The top insulator 20 has an internal electrolyte injection hole 28. Since the internal electrolyte injection hole 28 is formed corresponding to the electrolyte injection hole 42 provided in the cap plate 40, the electrolyte through the electrolyte injection hole 42 may be smoothly injected into the top insulator 20.

4 is a perspective view of an electrode assembly applied to FIG. 2. 2 and 4, the electrode assembly 10 includes a first electrode 11 (eg, a cathode) and a second electrode 12 (eg, an anode) on both sides of the separator 13, which is an electrical insulation material. And the cathode 11, the separator 13, and the anode 12 are wound.

The

positive electrodes

11 and 12 are formed of

coatings

111 and 121 coated with active materials on current collectors of metal foils (for example, Cu and Al foils), and current collectors exposed by not applying active materials. And

non-stick tabs

112 and 122. The

uncoated tabs

112 and 122 are disposed at one end of the wound electrode assembly 10 and are disposed to each other at a distance D within the single winding range T of the electrode assembly 10.

That is, the plain tabs 112 of the negative electrode 11 are disposed on one side (left side of FIG. 4) at one end (the upper end of FIG. 4) of the electrode assembly 10 to be wound, and the plain tabs 122 of the positive electrode 12 are arranged. ) Are disposed on each other on the other side (right side of FIG. 4) at a distance D from the same end (top of FIG. 4) of the electrode assembly 10 to be wound.

As described above, the area of the

coating parts

111 and 121 in the

anodes

11 and 12 is maximized, and the area of the plain parts is narrowed to the minimum by the plain tabs 112 and 122. ) Can be increased in capacity.

In addition, since the

tabs

112 and 122 are provided for each winding of the electrode assembly 10 to flow a current to be charged and discharged, the overall resistance of the

tabs

112 and 122 is reduced. Accordingly, the electrode assembly 10 may charge and discharge a high current through the

tabs

112 and 122.

The electrode assembly 10 may be formed as one (not shown) but is formed in two in the first embodiment. That is, the electrode assembly 10 includes a first assembly 101 and a second assembly 102 that are arranged side by side in the width direction (x-axis direction) of the cap plate 40. In addition, the first and

second assemblies

101 and 102 may be formed in a plate shape to form semicircles at both ends in the y-axis direction so as to be accommodated in the case 30 having a substantially rectangular parallelepiped shape.

5 is a perspective view of a state in which an electrode terminal is connected to the electrode assembly of FIG. 2. 2 to 5, the electrode assembly 10, that is, the first and

second assemblies

101 and 102 are arranged in parallel. The electrode terminals 51 and 52 (that is, the first and second electrode terminals) are installed in the terminal holes H1 and H2 of the cap plate 40, respectively, and are connected to each other by the

first tabs

112 and 122. And electrically connected to the second assembly (101, 102).

The

uncoated tabs

112 and 122 may be formed in a plurality of groups. The

non-coating tabs

112 and 122 pass through the outer side of the top insulator 20 in the width direction (x-axis direction) of the cap plate 40 and the first and second electrode terminals 51 in the width direction (x-axis direction). It is connected to the first and

second electrode terminals

51, 52 beyond the center of the, 52.

In the first embodiment, the

non-coating tabs

112 and 122 include first tap groups G11 and G21 and second tap groups G12 and G22. The first tap groups G11 and G21 are connected to the first and

second electrodes

11 and 12 of the first assembly 101, respectively, and the second tap groups G12 and G22 are formed of the second assembly 102. The first and

second electrodes

11 and 12 are respectively connected.

The first tab groups G11 and G21 are formed on the first side (the left side of FIG. 2 and the rear side of FIG. 2) in the width direction (x-axis direction), and the first and the first tab groups G11 and G21 pass through the top insulator 20 from the first side. It is connected to the first and

second electrode terminals

51 and 52 beyond the center of the two

electrode terminals

51 and 52.

The second tap groups G12 and G22 are formed on the second side (the right side of FIG. 2 and the front of FIG. 4) in the width direction (x-axis direction) opposite to the first tap groups G11 and G21, and the top insulator on the second side. The first and

second electrode terminals

51 and 52 are connected to the first and

second electrode terminals

51 and 52 via the center of the first and

second electrode terminals

51 and 52.

The first and

second electrode terminals

51 and 52 are uncoated to discharge current from the first and

second assemblies

101 and 102 or to charge current to the first and

second assemblies

101 and 102. Connected to

tabs

112 and 122, respectively.

The first and

second electrode terminals

51 and 52 may have the same structure. Referring to the drawings, the first and

second electrode terminals

51 and 52 include

rivet parts

512 and 522,

inner plates

511 and 521, and

outer plates

513 and 523.

The first and

second electrode terminals

51 and 52 are electrically connected to the cap plate 40 through the internal insulating

members

611 and 612 and the

gaskets

621 and 622 between the cap plate 40 and the inner surface thereof. Insulated.

The

inner insulation members

611 and 612 are in close contact with the cap plate 40 on one side, and the

inner plates

511 and 521 and the

rivet portions

512 and 522 of the first and

second electrode terminals

51 and 52 on the other side. Since a part is wrapped, the connection structure between the first and

second electrode terminals

51 and 52 and the

tabs

112 and 122 are stabilized.

The

gaskets

621 and 622 are provided between the

rivet parts

512 and 522 of the first and

second electrode terminals

51 and 52 and the inner surfaces of the terminal holes H1 and H2 of the cap plate 40. Seals and electrically insulates between 512 and 522 and the terminal holes H1 and H2 of the cap plate 40.

In addition, the

gaskets

621 and 622 are further installed between the inner insulating

members

611 and 612 and the inner surface of the cap plate 40 to further seal between the inner insulating

members

611 and 612 and the cap plate 40. do.

The

rivet parts

512 and 522 are inserted into the terminal holes H1 and H2 through the

gaskets

621 and 622, and the coupling holes of the

outer plates

513 and 523 through the external insulating

members

631 and 632. After insertion into the 514 and 524, the

rivet portions

512 and 522 are fixed to the

outer plates

513 and 523 by caulking or welding around the coupling holes 514 and 524. As a result, the first and

second electrode terminals

51 and 52 may be installed in the cap plate 40.

As such, the

rivet parts

512 and 522 are installed in the terminal holes H1 and H2 to protrude out of the cap plate 40.

Rivets

512 and 522 are connected to

inner plates

511 and 521 on the inside of cap plate 40 and to

outer plates

513 and 523 on the outside of cap plate 40. That is, the

rivet parts

512 and 522 mechanically and electrically connect the

inner plates

511 and 521 and the

outer plates

513 and 523 to each other.

The

inner plates

511 and 521 are integrally formed to be wider than the areas of the

rivet portions

512 and 522 and welded to the

plain tabs

112 and 122 with a large area, and are located inside the cap plate 40.

At this time, the

non-coated tabs

112 and 122 of the first and

second assemblies

101 and 102 are divided into the first tap groups G11 and G21 and the second tap groups G12 and G22, so that The top insulator 20 is bent to the side and welded to the

inner plates

511 and 521.

Therefore, the electrode assembly 10, that is, the first and

second assemblies

101 and 102, is moved out of the case 30 through the

tabs

112 and 122 and the first and

second electrode terminals

51 and 52. Can be withdrawn. In addition, since the

tabs

112 and 122 are directly connected to the first and

second electrode terminals

51 and 52, the structure of drawing the electrode assembly 10 out of the case 30 may be simplified.

6 is a plan view of a state in which the tabs of the uncoated region are connected to the electrode terminal. Referring to FIG. 6, the plain tabs 122 of the positive electrode 12 are omitted for convenience and the plain tabs 112 of the negative electrode 11 are described as an example. The non-coating tabs 112 are formed of the first tab group G11 and the second tab group G12 and are connected to the inner plate 511 of the first electrode terminal 51.

The first tap group G11 is connected to the first side (upper side in FIG. 6), is disposed on the lower surface of the inner plate 511 at the first side, and extends to a position via the center CL of the inner plate 511. And the lower surface of the inner plate 511 is welded. The second tab group G12 is connected to the second side (lower side in FIG. 6), is disposed on the lower surface of the inner plate 511 at the second side, and extends to a position via the center CL of the inner plate 511. And the lower surface of the inner plate 511 is welded.

The inner plate 511 includes a first connecting portion 51a connected to the rivet portion 512, and a second connecting portion 51b connected to the first tap group G11 and the second tap group G12. In the longitudinal direction (y-axis direction) crossing the width direction (x-axis direction) and passing through the center CL of the inner plate 511, the first length L10 of the first connecting portion 51a is the second connecting portion 51b. It is formed shorter than the second length (L20) of. The second length L20 of the second connecting portion 51b is formed long to enable welding connection between the first tap group G11 and the second tap group G12 along the longitudinal direction (y-axis direction).

The first tap group G11 and the second tap group G12 are disposed with a gap G spaced apart from each other in the longitudinal direction (y-axis direction) on the lower surface of the inner plate 511. The second length L20 of the second connector 51b prevents the interference between the first tap group G11 and the second tap group G12 to be welded by forming a gap G. The gap G is formed to a minimum within the range in which the interference between the first tap group G11 and the second tap group G12 is prevented, and thus the first tap group G11 and the second tap group G12 with respect to the inner plate 511. The welding area of) can be made as wide as possible.

The first tap group G11 and the second tap group G12 have the same width (y) as the connecting start part connected to the first assembly 101 and the second assembly 102 and the welding end part welded to the inner plate 511. Set in the axial direction). Therefore, the first tap group G11 and the second tap group G12 are welded to the inner plate 511 with a rectangular area.

Meanwhile, the first tap group G11 and the second tap group G12 have a length L set to a distance protruding from the first assembly 101 and the second assembly 102, and the length L is the first. It is set to greater than half (L> G2 / 2) of the gap G2 between the assembly 101 and the second assembly 102. That is, the length L of the 1st tap group G11 and the 2nd tap group G12 is set short.

In this way, the first tap group G11 and the second tap group G12 extend the center CL of the inner plate 511 via the top insulator 20 in the width direction (x-axis direction) of the cap plate 40. Since it is connected to the inner plate 511 beyond, the tabs 112 can be tensioned.

Since the tab tabs 112, that is, the first tab group G11 and the second tab group G12 are shortened and tensioned, even when the electrode assembly 10 is inserted into the case 30, the

tab tabs

112 and 122 may be used. Will not be folded. Even when the electrode assembly 10 is inserted into the case 30, the

tabs

112 and 122 are not in contact with the negative and

positive electrodes

11 and 12. That is, short circuits and cell events caused by the

uncoated tabs

112 and 122 can be prevented.

The secondary battery of the second embodiment will be described below. For the sake of convenience, the configurations of the first and second embodiments are compared, and the same configurations will be omitted and different configurations will be described.

FIG. 7 is a plan view of a rechargeable battery according to a second exemplary embodiment of the present invention, in which a plain tab is connected to an electrode terminal. Referring to FIG. 7, in the secondary battery 200 of the second embodiment, the first tap group G31 and the second tap group G32 are connected to the first assembly 201 and the second assembly 202. In the first width (W1) is formed, the welding end portion welded to the inner plate 511 is formed with a second width (W2) smaller than the first width (W1).

Therefore, the first tap group G31 and the second tap group G32 are welded to the inner plate 511 and a trapezoidal area. The first tab group G31 and the second tab group G32 may be welded to a large area on both sides of the inner plate 511 in the x-axis direction without interfering with each other.

Meanwhile, the first tap group G31 and the second tap group G32 have a length L2 set to a distance protruding from the first assembly 201 and the second assembly 202, and the length L2 is the first length. It is set to greater than half (L2> G3 / 2) of the gap G3 between the assembly 201 and the second assembly 202. That is, the length L2 of the 1st tap group G31 and the 2nd tap group G32 is set short.

In this way, the first tap group G31 and the second tap group G32 pass through the top insulator 20 in the width direction (x-axis direction) of the cap plate 40 via the center CL of the inner plate 511. Since it is connected to the inner plate 511 beyond, the tabs 113 can be tensioned.

Since the tab tabs 113, that is, the first tab group G31 and the second tab group G32 are shortened and tensioned, even when the electrode assembly 70 is inserted into the case 30, the tab tabs 113 may not be folded. Will not. Even when the electrode assembly 70 is inserted into the case 30, the tab tabs 113 do not come into contact with other electrodes. That is, short circuits and cell events caused by the uncoated tabs 113 may be prevented.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the scope of the invention.

Description of the sign

10, 70: electrode assembly 11: first electrode (cathode)

12: second electrode (anode) 13: separator

20: top insulator 27: internal vent hole

28: internal electrolyte injection hole 30: case

31: opening 40: cap plate

41: vent hole 42: electrolyte injection hole

51, 52: (first and second) electrode terminal 51a: first connection portion

51b second connection portions 100 and 200: secondary batteries

101, 701: first assembly 102, 702: second assembly

111, 121: coating

portions

112, 122, 113: plain tab

411: vent plate 412: notch

421: sealing stopper 511, 521: inner plate

512 and 522: rivet parts 513 and 523: outer plate

514, 524: coupling holes 611, 612: internal insulating member

621, 622: gaskets 631, 632: external insulation member

CL: center D: distance

G: gap G11, G21, G31: 1st tap group

G12, G22, G32: 2nd tap group G2, G3: Spacing

H1, H2: Terminal hole L, L2: Length

L10: First Length L20: Second Length

T: Once winding range W1, W2: First and second widths

Claims

An electrode assembly wound by placing electrodes having a coating portion and a tab portion on both sides of the separator;

A case accommodating the electrode assembly;

A cap plate coupled to the opening of the case;

A top insulator disposed between the electrode assembly and the cap plate; And

An electrode terminal installed on the cap plate and connected to the plain tabs

Including;

The plain tabs

Formed of a plurality of groups,

Via the outside of the top insulator in the width direction of the cap plate,

A secondary battery connected to the electrode terminal beyond the center of the electrode terminal in the width direction.
The method of claim 1,

The electrode assembly is

It includes a first assembly and a second assembly arranged side by side in the width direction of the cap plate,

The plain tabs

A secondary battery comprising a first tab group connected to the electrodes of the first assembly and a second tab group connected to the electrodes of the second assembly.
The method of claim 2,

The first tap group is

Connected to the electrode terminal beyond the center of the electrode terminal via the top insulator on the first side in the width direction;

The second tap group is

A secondary battery connected to the electrode terminal beyond the center of the electrode terminal via the top insulator on the second side in the width direction that is the opposite side of the first tab group.
The method of claim 3,

The electrode terminal

Rivet portion installed in the terminal hole of the cap plate,

An outer plate installed outside the rivet part and connected to the rivet part;

It includes an inner plate which is integrally connected to the inside of the rivet portion,

The first tap group and the second tap group

A secondary battery welded to the inner plate.
The method of claim 4, wherein

The first tap group is

Disposed on the lower surface of the inner plate at the first side, and extended and welded to a position via the center of the inner plate;

The second tap group is

The secondary battery is disposed on the lower surface of the inner plate on the second side, and extended to a position via the center of the inner plate to be welded.
The method of claim 5,

The inner plate is

A first connection part connected to the rivet part and a second connection part connected to the first tab group and the second tab group;

In the longitudinal direction crossing the width direction and passing through the center of the inner plate

The first length of the first connection portion

The secondary battery is formed shorter than the second length of the second connector.
The method of claim 6,

The first tap group and the second tap group

The secondary battery is disposed having a gap spaced apart from each other in the longitudinal direction on the lower surface of the inner plate.
The method of claim 4, wherein

The first tap group and the second tap group

A secondary battery having a same width as a connecting start portion connected to the first assembly and the second assembly and a welding end portion welded to the inner plate.
The method of claim 8,

The first tap group and the second tap group

Has a length set to the distance protruding from the first assembly and the second assembly,

The length is

The secondary battery is set to more than 1/2 of the interval between the first assembly and the second assembly.
The method of claim 4, wherein

The first tap group and the second tap group

A first width is formed at a connection start portion connected to the first assembly and the second assembly,

A secondary battery forming a welding end portion welded to the inner plate to a second width smaller than the first width.