JP2020123552A - Power storage device - Google Patents

Abstract

To provide a power storage device capable of suppressing fatigue cracks in bent portions of a positive electrode tab and a negative electrode tab due to spring back.SOLUTION: In a power storage device, a base end portion is formed by gathering together each of a plurality of positive electrode tabs 20a and a plurality of negative electrode tabs 21c at one end of an electrode assembly 12 in a stacking direction. In a state before forming an extension, a bend corresponding portion 24c corresponding to a bent portion in a plurality of the positive electrode tabs 20a and a plurality of the negative electrode tabs 21c is provided with a first slit 51 extending in a first direction A.SELECTED DRAWING: Figure 2

Description

The present invention relates to a power storage device.

Conventionally, a power storage device as described in Patent Document 1 is known.
The above power storage device includes an electrode assembly in which a plurality of sheet-shaped positive electrodes and a plurality of sheet-shaped negative electrodes are stacked in a state of being insulated by a plurality of separators, a case for housing the electrode assembly, and a case. It has a positive electrode terminal and a negative electrode terminal that are fixed and that exchange electricity with the electrode assembly.

The positive electrode of the above-mentioned electrode assembly has a sheet-shaped positive electrode metal foil (for example, aluminum foil), and a positive electrode active material layer provided on both surfaces of the positive electrode metal foil. The negative electrode of the above electrode assembly has a sheet-shaped negative electrode metal foil (for example, copper foil) and a negative electrode active material layer provided on both surfaces of the negative electrode metal foil.

The electrode assembly includes a positive electrode tab group in which positive electrode tabs protruding from a part of one side of the positive electrode metal foil forming the positive electrode are gathered, and a part of one side of a negative electrode metal foil forming the negative electrode. And a group of negative electrode tabs that are gathered together. The positive electrode tab group includes a positive electrode base end portion in which a plurality of positive electrode tabs are gathered toward one end in the stacking direction of the electrode assembly, and a positive electrode bent portion bent from the positive electrode base end portion to the other end in the stacking direction of the electrode assembly. And have. In addition, the positive electrode tab group extends along the tab-side end surface where the positive electrode tab group and the negative electrode tab group of the electrode assembly are present from the side opposite to the positive electrode base end portion of the positive electrode curved portion toward the other end in the stacking direction of the electrode assembly. And a positive electrode extension portion that extends and is fixed to the positive electrode terminal. The negative electrode tab group includes a negative electrode base end portion in which a plurality of negative electrode tabs are gathered toward one end in the stacking direction of the electrode assembly, and a negative electrode bending portion bent from the negative electrode base end portion toward the other end in the stacking direction of the electrode assembly. And have. The negative electrode tab group extends along the tab-side end surface of the electrode assembly from the side opposite to the negative electrode base end portion of the negative electrode curved portion toward the other end in the stacking direction of the electrode assembly and is fixed to the negative electrode terminal. And a negative electrode extension portion.

In the plurality of positive electrode tabs and the plurality of negative electrode tabs, the plurality of positive electrode tabs and the plurality of negative electrode tabs are located at one end in the stacking direction of the electrode assembly, in the root portion closer to the tab side end surface than the positive electrode base end portion and the negative electrode base end portion. A root portion is included that has a bend that bends in a gathered direction.

JP, 2015-32549, A

By the way, in the power storage device having the above configuration, the electrode assembly is housed in the case, and the positive electrode terminal and the negative electrode terminal are fixed to the case and the positive electrode extension part and the negative electrode extension part of each tab group. Therefore, residual stress acts on the positive electrode bent portion of the positive electrode tab group and the negative electrode bent portion of the negative electrode tab group. The positive electrode tab group and the negative electrode tab group try to return so as to extend straight from the bent state around the positive electrode curved portion and the negative electrode curved portion. That is, springback occurs in the positive electrode tab group and the negative electrode tab group. Therefore, in the state where the electrode assembly is housed in the case and the residual stress acts on the positive electrode bent portion of the positive electrode tab group and the negative electrode bent portion of the negative electrode tab group, the power storage device vibrates, and the positive electrode bent portion and When a repeated load is applied to the negative electrode curved portion, the load is transmitted to the curved portions of the plurality of positive electrode tabs and the plurality of negative electrode tabs, and fatigue fatigue cracks may occur in the curved portions of the plurality of positive electrode tabs and the plurality of negative electrode tabs. There is. As a result, the electric resistance of the positive electrode tab and the negative electrode tab in which the fatigue crack has occurred increases, and the performance of the power storage device deteriorates.

The present invention has been made by paying attention to the problems existing in such a conventional technique, and an object thereof is a power storage device capable of suppressing fatigue cracks in the curved portions of the positive electrode tab and the negative electrode tab due to springback. Is to provide.

An electricity storage device that solves the above problems is an electrode assembly in which a plurality of sheet-shaped positive electrodes and a plurality of sheet-shaped negative electrodes are stacked in a state of being insulated by a separator, and a case which accommodates the electrode assembly. Provided with a positive electrode terminal and a negative electrode terminal that are fixed to the case and that exchange electricity with the electrode assembly,
The positive electrode is a sheet-shaped positive electrode metal foil, a positive electrode active material layer provided on at least one of both surfaces of the positive electrode metal foil, and a positive electrode tab protruding from a part of one side of the positive electrode metal foil. And have
The negative electrode is a sheet-shaped negative electrode metal foil, a negative electrode active material layer provided on at least one of both surfaces of the negative electrode metal foil, and a negative electrode tab protruding from a part of one side of the negative electrode metal foil. And have
The electrode assembly includes a positive electrode tab group in which the plurality of positive electrode tabs are gathered together, and a negative electrode tab group in which the plurality of negative electrode tabs are gathered together,
The positive electrode tab group includes a positive electrode base end portion in which the plurality of positive electrode tabs are gathered toward one end in the stacking direction of the electrode assembly, and a positive electrode base end portion from the positive electrode base end portion to the other end in the stacking direction of the electrode assembly. And a positive electrode bent portion that bends, and a stack of the electrode assembly from the side opposite to the positive electrode base end portion of the positive electrode bent portion along the tab-side end surface where the positive electrode tab group and the negative electrode tab group of the electrode assembly are present. A positive electrode extension portion fixed to the positive electrode terminal while extending toward the other end in the direction,
The negative electrode tab group includes a negative electrode base end portion in which a plurality of the negative electrode tabs are gathered toward one end in the stacking direction of the electrode assembly, and a negative electrode base end portion from the other end in the stacking direction of the electrode assembly. And a negative electrode bent portion that bends along the tab-side end surface of the electrode assembly, and extends from the side opposite to the negative electrode base end portion of the negative electrode bent portion toward the other end in the stacking direction of the electrode assembly. A negative electrode extension portion fixed to the negative electrode terminal,
In the plurality of positive electrode tabs and the plurality of negative electrode tabs, the plurality of positive electrode tabs and the plurality of negative electrode tabs are included in the root portion provided closer to the tab side end surface than the positive electrode base end portion and the negative electrode base end portion. Includes the root portion having a curved portion that is bent in a state of being gathered at one end in the stacking direction of the electrode assembly,
The positive electrode base end portion and the negative electrode base end portion are formed by gathering each of the plurality of positive electrode tabs and the plurality of negative electrode tabs at one end in the stacking direction of the electrode assembly to form the positive electrode extension portion and the negative electrode. In the state before forming the extending portion, the positive electrode tab group and the negative electrode tab group correspond to the positive electrode curved portion and the negative electrode curved portion of the plurality of positive electrode tabs and the plurality of negative electrode tabs, respectively. A first slit extending along a first direction, which is a direction orthogonal to the tab-side end surface of the electrode assembly, is provided in the curved portion.

According to this, in the state before providing the positive electrode extension part of the positive electrode tab group and the negative electrode extension part of the negative electrode tab group, the plurality of positive electrode tabs and the plurality of negative electrode tabs forming the positive electrode tab group and the negative electrode tab group are bent. The corresponding portion is provided with a first slit extending along the first direction. Therefore, when the positive electrode extension portion of the positive electrode tab group and the negative electrode extension portion of the negative electrode tab group are formed, and the positive electrode curved portion of the positive electrode tab group and the negative electrode curved portion of the negative electrode tab group are formed, they are provided at the corresponding portions. The first slit is deformed so as to open in a direction orthogonal to the first direction and the stacking direction of the electrode assemblies. By bending the positive electrode tab group and the negative electrode tab group, stress is generated in the positive electrode bent portion and the negative electrode bent portion, but by deforming so as to open the first slit, the positive electrode bent portion and the negative electrode tab group of the positive electrode tab group The stress generated in the negative electrode bent portion can be released. That is, the springback in which the positive electrode tab group and the negative electrode tab group try to return from the bent state so as to extend straight is suppressed. Therefore, fatigue cracks in the curved portions of the positive electrode tab and the negative electrode tab due to springback can be suppressed.

In the above power storage device, the first slit may penetrate the positive electrode tab and the negative electrode tab.
According to this, when forming the positive electrode extension part of the positive electrode tab group and the negative electrode extension part of the negative electrode tab group, the first slit opens toward the first direction and a direction orthogonal to the stacking direction of the electrode assembly. It becomes easy to deform like this. Therefore, the stress generated in the positive electrode bent portion of the positive electrode tab group and the negative electrode bent portion of the negative electrode tab group can be more easily released.

In the above power storage device, it is preferable that a plurality of the first slits be provided in the song corresponding portion, and the plurality of the first slits be arranged in a staggered arrangement.
According to this, by providing the plurality of first slits, it is possible to increase the deformation amount in the first direction of the curved corresponding portions of the positive electrode tab and the negative electrode tab and the direction orthogonal to the stacking direction of the electrode assembly. it can. Therefore, the stress generated in the positive electrode tab and the negative electrode tab can be easily released. In addition, since the plurality of first slits are arranged in a zigzag manner, stress can be released to a wider area of the curved portion of the positive electrode tab and the negative electrode tab. Therefore, the stress generated in the positive electrode bent portion of the positive electrode tab group and the negative electrode bent portion of the negative electrode tab group can be released in a wider range.

In the above power storage device, a direction orthogonal to the first direction and the stacking direction, and a width direction of the positive electrode tab and the negative electrode tab is a second direction, and a plurality of the first slits are provided in the second direction. Is staggered so that the first end portions of the positive electrode tab and the negative electrode tab and the second end portion opposite to the first end portion are not continuous in a straight line along the second direction. Good.

According to this, the plurality of first slits are always provided in the second direction in the curved portions of the positive electrode tab and the negative electrode tab. That is, the plurality of first slits are provided so that the positions thereof are displaced along the second direction, and the plurality of first slits are overlapped with each other along the first direction. Therefore, there is no portion that does not deform in the second direction in the music corresponding portion. Therefore, the stress generated in the positive electrode bent portion of the positive electrode tab group and the negative electrode bent portion of the negative electrode tab group can be more efficiently released in the second direction.

In the above power storage device, a state before forming the positive electrode base end portion and the negative electrode base end portion by gathering each of the plurality of positive electrode tabs and the plurality of negative electrode tabs at one end in the stacking direction of the electrode assembly. In the above, it is preferable that a second slit extending in the first direction is provided in the bending corresponding portion corresponding to the bending portion of each of the positive electrode tab and the negative electrode tab.

According to this, in the state before the positive electrode base end portion of the positive electrode tab group and the negative electrode base end portion of the negative electrode tab group are provided, the plurality of positive electrode tabs and the plurality of negative electrode tabs forming the positive electrode tab group and the negative electrode tab group are curved. The corresponding portion is provided with a second slit extending along the first direction. Therefore, when the positive electrode base end portion of the positive electrode tab group and the negative electrode base end portion of the negative electrode tab group are formed, the second slits provided in the bending corresponding portion are orthogonal to the first direction and the stacking direction of the electrode assembly. It transforms to open in the direction. Although stress is generated in the curved portion by bending the positive electrode tab and the negative electrode tab, the stress generated in the curved portion of the positive electrode tab and the negative electrode tab can be released by deforming the second slit so as to open. That is, the springback in which the curved portions of the positive electrode tab and the negative electrode tab return from the bent state so as to extend straight is suppressed, and thus residual stress acting on the curved portions of the positive electrode tab and the negative electrode tab can be suppressed. Therefore, fatigue cracks in the curved portions of the positive electrode tab and the negative electrode tab due to springback can be suppressed.

In the above power storage device, the second slit may penetrate the positive electrode tab and the negative electrode tab.
According to this, when forming the positive electrode base end part of the positive electrode tab group and the negative electrode base end part of the negative electrode tab group, the second slit opens toward the first direction and the direction orthogonal to the stacking direction of the electrode assemblies. It becomes easy to deform like this. Therefore, the stress generated in the curved portions of the positive electrode tab and the negative electrode tab can be more easily released.

In the above power storage device, a plurality of the second slits are provided in the bending corresponding portion,
The plurality of second slits may be staggered.
According to this, the amount of deformation can be increased by providing the plurality of second slits in the bending corresponding portion. Therefore, the stress generated in the positive electrode tab and the negative electrode tab can be easily released. In addition, since the plurality of second slits are arranged in a zigzag manner, stress can be released to a wider area of the curved corresponding portions of the positive electrode tab and the negative electrode tab. Therefore, the stress generated in the curved portions of the positive electrode tab and the negative electrode tab can be released in a wider range.

In the above power storage device, a second direction is a direction orthogonal to the first direction and the stacking direction, and a width direction of the positive electrode tab and the negative electrode tab is a second direction, and a plurality of the second slits are provided in the second direction. Is staggered so that the first end portions of the positive electrode tab and the negative electrode tab and the second end portion opposite to the first end portion are not continuous in a straight line along the second direction. Good.

According to this, the plurality of second slits are always provided in the second direction in the curved corresponding portions of the positive electrode tab and the negative electrode tab. That is, the plurality of second slits are provided so that their positions are displaced along the second direction B, while the plurality of second slits are overlapped with each other along the first direction. Therefore, there is no portion that does not deform in the second direction in the bending corresponding portion. Therefore, the stress generated in the curved portions of the positive electrode tab and the negative electrode tab can be more efficiently released in the second direction.

According to the present invention, fatigue cracks in the curved portions of the positive electrode tab and the negative electrode tab due to springback can be suppressed.

FIG. 3 is an exploded perspective view of a power storage device. The exploded perspective view of an electrode assembly. (A), (b) is sectional drawing of a power storage device. FIG. 5 is a schematic view of a tab before forming an extension portion. FIG. 5 is a schematic view of the tab before forming the proximal end portion. The front view which showed the slit before forming a base end part and an extension part. The front view which showed the slit after forming a base end part and an extension part.

Hereinafter, an embodiment in which a power storage device is embodied as a secondary battery will be described with reference to FIGS.
As shown in FIG. 1, a secondary battery 10 as a power storage device includes a case 11. The secondary battery 10 includes an electrode assembly 12 housed in a case 11 and an electrolytic solution (not shown). The case 11 has a case body 13 in the shape of a square cylinder with a bottom, and a plate-like lid 14 that closes the opening 13 a of the case body 13. The case main body 13 and the lid 14 that form the case 11 are both made of metal (for example, stainless steel or aluminum). Further, the secondary battery 10 of the present embodiment is a prismatic battery having a prismatic appearance. Further, the secondary battery 10 of the present embodiment is a lithium ion secondary battery.

The secondary battery 10 includes a positive electrode terminal 15 and a negative electrode terminal 16 that exchange electricity with the electrode assembly 12. The positive electrode terminal 15 and the negative electrode terminal 16 are exposed to the outside of the case 11 through a pair of holes 14a that are arranged in parallel in the lid 14 at a predetermined interval. Further, the positive electrode terminal 15 and the negative electrode terminal 16 are attached with ring-shaped insulating rings 17 a for insulating the case 11 from each other. Thereby, the positive electrode terminal 15 and the negative electrode terminal 16 are fixed to the case 11. The positive electrode terminal 15 and the negative electrode terminal 16 have a positive electrode conductive member and a negative electrode conductive member having the same polarity, respectively.

The lid 14 is provided with a round hole-shaped injection port 14c penetrating in the thickness direction. The injection port 14c is used to inject the electrolytic solution into the case 11. The liquid injection port 14c is sealed by the sealing member 19, and the sealing property of the liquid injection port 14c is maintained.

As shown in FIG. 2, FIG. 3A, and FIG. 3B, the electrode assembly 12 has a plurality of sheet-shaped positive electrodes 20, a plurality of sheet-shaped negative electrodes 21, and a sheet shape. It has a plurality of separators 23. The electrode assembly 12 is configured by stacking a plurality of positive electrodes 20 and a plurality of negative electrodes 21 in a state of being insulated by a separator 23. The stacking direction of the positive electrode 20, the negative electrode 21, and the separator 23 is the stacking direction of the electrode assembly 12.

As shown in FIG. 2, the positive electrode 20 includes a sheet-shaped positive electrode metal foil (for example, aluminum foil) 20a, a positive electrode active material layer 20b provided on both surfaces of the positive electrode metal foil 20a, and a positive electrode metal foil 20a. It has a strip-shaped positive electrode tab 20c protruding from a part of one side. The positive electrode tab 20c is composed of the positive electrode metal foil 20a itself.

The negative electrode 21 includes a sheet-shaped negative electrode metal foil (for example, copper foil) 21a, negative electrode active material layers 21b provided on both surfaces of the negative electrode metal foil 21a, and a part of one side of the negative electrode metal foil 21a. It has a protruding negative electrode tab 21c. The negative electrode tab 21c is composed of the negative electrode metal foil 21a itself. The plurality of positive electrode tabs 20c and the plurality of negative electrode tabs 21c are present at positions where the positive electrode tab 20c and the negative electrode tab 21c do not overlap each other when the positive electrode 20 and the negative electrode 21 are stacked.

As shown in FIGS. 3A and 3B, in the secondary battery 10, the negative electrode active material layer 21 b of the negative electrode 21 is the electrode assembly 12 of the positive electrode active material layer 20 b of the positive electrode 20. They must face each other in the stacking direction. Therefore, the negative electrode active material layer 21b of the negative electrode 21 is formed larger than the positive electrode active material layer 20b of the positive electrode 20. Specifically, in the stacking direction of the electrode assembly 12, the positive electrode active material layer 20b provided on the positive electrode metal foil 20a can be covered with the negative electrode active material layer 21b provided on the negative electrode metal foil 21a. Thus, the negative electrode active material layer 21b is set larger than the positive electrode active material layer 20b. For this reason, in the electrode assembly 12, the outer edge portion of the negative electrode active material layer 21b of the negative electrode 21 constitutes the coating extension portion 40 that extends outside the outer edge of the positive electrode active material layer 20b.

As shown in FIG. 3A, the electrode assembly 12 includes a positive electrode tab group 25. The positive electrode tab group 25 is configured by collecting a plurality of positive electrode tabs 20c in the stacking direction of the electrode assembly 12.

The positive electrode tab group 25 includes a positive electrode base end portion 27a in which a plurality of positive electrode tabs 20c are gathered toward one end in the stacking direction of the electrode assembly 12, and a positive electrode base end portion 27a from the other end in the stacking direction of the electrode assembly 12. It has a positive electrode bent portion 24a that is bent toward. In addition, the positive electrode tab group 25 is arranged along the tab-side end surface 12a where the positive electrode tab group 25 and the negative electrode tab group 26 of the electrode assembly 12 are present, from the side opposite to the positive electrode base end portion 27a of the positive electrode bent portion 24a. Has a positive electrode extension portion 28a extending toward the other end in the stacking direction. The tab-side end surface 12a of the electrode assembly 12 is configured by gathering one side of the negative electrode metal foil 21a on which the negative electrode tab 21c is provided and one side of the separator 23 along the stacking direction of the electrode assembly 12. Has been done. The positive electrode conductive member of the positive electrode terminal 15 is fixed to the positive electrode extension portion 28 a of the positive electrode tab group 25.

As shown in FIG. 3B, the electrode assembly 12 includes a negative electrode tab group 26. The negative electrode tab group 26 is configured by collecting a plurality of negative electrode tabs 21c in the stacking direction of the electrode assembly 12.

The negative electrode tab group 26 includes a negative electrode base end portion 27b in which a plurality of negative electrode tabs 21c are gathered toward one end in the stacking direction of the electrode assembly 12, and a negative electrode base end portion 27b from the other end in the stacking direction of the electrode assembly 12. It has a negative electrode bent portion 24b that is bent toward. The negative electrode tab group 26 extends along the tab-side end surface 12a of the electrode assembly 12 from the side opposite to the negative electrode base end portion 27b of the negative electrode bent portion 24b in the stacking direction of the electrode assembly 12. It has a portion 28b. Further, the negative electrode conductive member of the negative electrode terminal 16 is fixed to the negative electrode extension portion 28 b of the negative electrode tab group 26.

As shown in FIGS. 3A and 3B, the plurality of positive electrode tabs 20c and the plurality of negative electrode tabs 21c are arranged closer to the tab side end surface 12a than the positive electrode base end portion 27a and the negative electrode base end portion 27b. It has a root 29. The plurality of root portions 29 includes a root portion 29 having a curved portion 29a that is bent in a state where the plurality of positive electrode tabs 20c and the plurality of negative electrode tabs 21c are gathered together at one end in the stacking direction of the electrode assembly 12. There is. In the present embodiment, the root portions 29 (see FIG. 3A) of all the positive electrode tabs 20c have the curved portion 29a. Of the root parts 29 of the negative electrode tab 21c, the root parts 29 of the plurality of negative electrode tabs 21c have a curved part 29a, except for the one located at one end in the stacking direction of the electrode assembly 12 (see FIG. 4). The negative electrode tab 21c located at one end of the electrode assembly 12 in the stacking direction extends straight toward the lid 14 along the side wall of the case body 13 (see FIG. 3B).

The curved portion 29a of the root portion 29 of the positive electrode tab 20c has a mountain fold portion 20d that is bent so that the positive electrode tab 20c is mountain fold and a valley fold portion 20e that is bent so as to be valley fold. The curved portion 29a of the root portion 29 of the negative electrode tab 21c has a mountain fold portion 21d that is bent so that the negative electrode tab 21c is mountain-folded and a valley fold portion 21e that is bent so as to be valley-folded. Here, the mountain folds 20d and 21d are bent so as to be mountain folds when viewed from the other end of the electrode assembly 12 in the stacking direction along the stacking direction of the electrode assembly 12. The valley folds 20e and 21e are bent from one end in the stacking direction of the electrode assembly 12 so as to form a valley fold when viewed along the stacking direction of the electrode assembly 12.

Here, the positive electrode tab group 25 and the negative electrode tab group 26 try to return from the bent state centering on the positive electrode bent portion 24a and the negative electrode bent portion 24b so as to extend straight. That is, spring back occurs in the positive electrode tab group 25 and the negative electrode tab group 26. Therefore, when the electrode assembly 12 is housed in the case 11, a repeated load is applied to the positive electrode bent portion 24a of the positive electrode tab group 25 and the negative electrode bent portion 24b of the negative electrode tab group 26 while residual stress is applied. Fatigue cracks may occur in the curved portions 29a of the positive electrode tabs 20c and the negative electrode tabs 21c forming the positive electrode tab group 25 and the negative electrode tab group 26.

The secondary battery 10 of the present embodiment is provided with a configuration that suppresses fatigue cracks in the curved portions 29a of the plurality of positive electrode tabs 20c and the plurality of negative electrode tabs 21c. Hereinafter, a state before the positive electrode extending portion 28a of the positive electrode tab group 25 and the negative electrode extending portion 28b of the negative electrode tab group 26 are formed, and the positive electrode base end portion 27a of the positive electrode tab group 25 and the negative electrode group of the negative electrode tab group 26 are formed. The structure for suppressing the above-described fatigue crack will be described separately for the case where the end portion 27b is not formed yet. The positive electrode base end portion 27a of the positive electrode tab group 25, the negative electrode base end portion 27b of the negative electrode tab group 26, the positive electrode extension portion 28a of the positive electrode tab group 25, and the negative electrode extension portion 28b of the negative electrode tab group 26 have the same configuration. Have Therefore, FIG. 4 illustrates a state before the positive electrode extension portion 28a of the positive electrode tab group 25 is formed, and the description of the negative electrode tab group 26 is omitted.

As shown in FIG. 4, a plurality of positive electrode tabs 20c are gathered together at one end of the electrode assembly 12 in the stacking direction to form a positive electrode base end portion 27a, which is in a state before the positive electrode extension portion 28a is formed. In this state, a positive electrode tab bundle 30 having a plurality of positive electrode tabs 20c gathered together is formed at one end of the electrode assembly 12 in the stacking direction. The positive electrode tab bundle portion 30 includes a positive electrode base end portion 27a provided near the tab side end surface 12a of the electrode assembly 12, and a protruding extension portion 31 extending from the positive electrode base end portion 27a toward the opposite side of the electrode assembly 12. It is configured. The protruding extension part 31 includes an extension corresponding part 28c corresponding to the positive electrode extension part 28a when the protruding extension part 31 is bent, and a bending corresponding part 24c corresponding to the positive electrode bent part 24a when the protrusion extension part 31 is bent. And have.

As shown in FIG. 2, among the plurality of positive electrode tabs 20c and the plurality of negative electrode tabs 21c, the positive electrode tabs 20c and the negative electrode tabs 21c are connected to the curved portions 24c corresponding to the positive electrode curved portions 24a and the negative electrode curved portions 24b. A plurality of lengths extending in a direction projecting from the foil 20a and the negative electrode metal foil 21a, that is, a first direction A orthogonal to the so-called tab-side end surface 12a of the electrode assembly 12 (see FIGS. 3A and 3B). A first slit 51 is provided. The plurality of first slits 51 penetrate the positive electrode tab 20c and the negative electrode tab 21c.

Further, consider a state before the positive electrode base end portion 27a of the positive electrode tab group 25 and the negative electrode base end portion 27b of the negative electrode tab group 26 are formed. In this state, the positive electrode tab 20c and the negative electrode tab 21c project in the first direction A. A plurality of second slits whose lengths extend along the first direction A are provided in the curved corresponding portions 29b corresponding to the curved portions 29a (see FIGS. 3A and 3B) of the positive electrode tab 20c and the negative electrode tab 21c. 52 is provided. The plurality of second slits 52 penetrate the positive electrode tab 20c and the negative electrode tab 21c.

Next, the configurations of the plurality of first slits 51 and the plurality of second slits 52 will be described together with the operation of this embodiment. Although the number of the first slits 51 and the number of the second slits 52 are different from each other in FIG. 2, the arrangement of the plurality of first slits 51 and the plurality of second slits 52 is the same. Therefore, although FIG. 5 is a diagram showing how to arrange the plurality of first slits 51, the description of how to arrange the second slits 52 will also be made using this figure.

As shown in FIG. 5, the plurality of positive electrode tabs 20c and the plurality of negative electrode tabs 21c are gathered together at one end in the stacking direction of the electrode assembly 12 to form the positive electrode base end portion 27a and the negative electrode base end portion 27b, and the positive electrode extension portion. 28a and the negative electrode extension 28b, or the positive electrode tabs 20c and the negative electrode tabs 21c are gathered together at one end of the electrode assembly 12 in the stacking direction to form the positive electrode base end portion 27a and the negative electrode base end portion 27b. In the state before forming the, the plurality of first slits 51 and the plurality of second slits 52 are arranged in a staggered arrangement.

A direction orthogonal to the first direction A and the stacking direction of the electrode assembly 12, and the width direction of the positive electrode tab 20c and the negative electrode tab 21c is referred to as a second direction B. Both ends of the positive electrode tab 20c and the negative electrode tab 21c in the second direction B are referred to as a first end 22a and a second end 22b, respectively. The first end 22a and the second end 22b are ends extending along the first direction A. In the second direction B, the plurality of first slits 51 and the plurality of second slits 52 include the first end 22a of the positive electrode tab 20c and the negative electrode tab 21c, and the second end 22b opposite to the first end 22a. Are arranged in a zigzag manner so that and are not continuous in a straight line along the second direction B. That is, the plurality of first slits 51 are arranged along the first direction A such that the first slits 51 are displaced from each other along the first direction A while being partially displaced from each other. Similarly, the plurality of second slits 52 are also arranged along the first direction A such that some of the second slits overlap each other while shifting their positions along the second direction B. ..

Next, the operation of this embodiment will be described.
As shown in FIG. 6, when the plurality of positive electrode tabs 20c and the plurality of negative electrode tabs 21c are gathered toward one end in the stacking direction of the electrode assembly 12 to form the positive electrode base end portion 27a and the negative electrode base end portion 27b, the positive electrode A curved portion 29a is formed at the root portions 29 of the tab 20c and the negative electrode tab 21c. Along with this, tensile stress acts on the mountain folds 20d and 21d of the curved portion 29a. Further, compressive stress acts on the valley folds 20e and 21e of the curved portion 29a. Here, the 2nd slit 52 provided in the curve corresponding part 29b of the positive electrode tab 20c and the negative electrode tab 21c expands in the 2nd direction B. Therefore, the tensile stress and the compressive stress acting on the curved portion 29a are released in the direction in which the second slit 52 is deformed.

Further, after the positive electrode base end portion 27a and the negative electrode base end portion 27b are formed by gathering the plurality of positive electrode tabs 20c and the plurality of negative electrode tabs 21c toward one end in the stacking direction of the electrode assembly 12, the positive electrode extension portion 28a is formed. When the positive electrode tab group 25 and the negative electrode tab group 26 are formed by forming the negative electrode extending portion 28b and the negative electrode extending portion 28b, the positive electrode bent portion 24a of the positive electrode tab group 25 and the negative electrode bent portion 24b of the negative electrode tab group 26 are formed. Along with this, tensile stress and compressive stress similarly act on the positive electrode bent portion 24a and the negative electrode bent portion 24b. Here, the plurality of first slits provided in the music corresponding portions 24c corresponding to the positive electrode bent portions 24a and the negative electrode bent portions 24b of the plurality of positive electrode tabs 20c and the negative electrode tabs 21c configuring the positive electrode tab group 25 and the negative electrode tab group 26, respectively. 51 spreads in the second direction B. Therefore, the tensile stress and the compressive stress acting on the positive electrode bent portion 24a and the negative electrode bent portion 24b are released in the direction in which the first slit 51 is deformed.

The amount of deformation of the plurality of first slits 51 and the plurality of second slits 52 increases as they approach the center portions of the positive electrode curved portion 24a, the negative electrode curved portion 24b, and the curved portion 29a in the first direction A and the second direction B. .. Therefore, in a state in which the plurality of first slits 51 and the plurality of second slits 52 are deformed, the first portion in the portion corresponding to the positive electrode bent portion 24a of the positive electrode tab 20c, the negative electrode bent portion 24b of the negative electrode tab 21c, and the curved portion 29a. The end 22a and the second end 22b are in a state of bulging in an arc shape. Then, in the state in which the positive electrode tab group 25 and the negative electrode tab group 26 are formed, the tensile stress and the compressive stress acting on the positive electrode bent portion 24a, the negative electrode bent portion 24b, and the curved portion 29a escape in the second direction B. Maintained at. Therefore, the positive bending portion 24a, the negative bending portion 24b, and the bending portion 29a are maintained in a state in which the tensile residual stress and the compressive residual stress are suppressed.

In this embodiment, the following effects can be obtained.
(1) In this embodiment, the positive electrode extending portion 28a of the positive electrode tab group 25 and the negative electrode extending portion 28b of the negative electrode tab group 26 are formed, and the positive electrode bent portion 24a of the positive electrode tab group 25 and the negative electrode bent portion of the negative electrode tab group 26 are formed. When the portion 24b is formed, the first slit 51 provided in the music corresponding portion 24c is deformed so as to open in the second direction B. By bending the positive electrode tab group 25 and the negative electrode tab group 26, stress is generated in the positive electrode curved portion 24a and the negative electrode curved portion 24b, but the positive electrode curved portion 24a and the negative electrode curved portion 24b are deformed so that the first slit 51 is opened, and the positive electrode curved portion 24a The stress generated in the portion 24a and the negative electrode bent portion 24b of the negative electrode tab group 26 can be released. That is, the spring back that the positive electrode tab group 25 and the negative electrode tab group 26 try to return from the bent state to extend straight is suppressed, and thus the positive electrode bent portion 24a of the positive electrode tab group 25 and the negative electrode bent portion 24b of the negative electrode tab group 26 are suppressed. The residual stress acting can be suppressed. Therefore, fatigue cracks in the curved portions 29a of the positive electrode tab 20c and the negative electrode tab 21c due to springback can be further suppressed.

(2) In the present embodiment, the first slit 51 penetrates the positive electrode tab 20c and the negative electrode tab 21c. Therefore, when forming the positive electrode extending portion 28a of the positive electrode tab group 25 and the negative electrode extending portion 28b of the negative electrode tab group 26, the first slit 51 is easily deformed so as to open in the second direction B. Therefore, the stress generated in the positive electrode bent portion 24a of the positive electrode tab group 25 and the negative electrode bent portion 24b of the negative electrode tab group 26 can be more easily released.

(3) In the present embodiment, the plurality of first slits 51 are staggered. Therefore, by providing the plurality of first slits 51, it is possible to increase the amount of deformation of the curved corresponding portions 24c of the positive electrode tab 20c and the negative electrode tab 21c in the second direction B. Therefore, the stress generated in the positive electrode tab 20c and the negative electrode tab 21c can be easily released. Moreover, since the plurality of first slits 51 are arranged in a staggered arrangement, the stress can be released to a wider area of the curved portion 24c of the positive electrode tab 20c and the negative electrode tab 21c. Therefore, the stress generated in the positive electrode bent portion 24a of the positive electrode tab group 25 and the negative electrode bent portion 24b of the negative electrode tab group 26 can be released in a wider range.

(4) In the present embodiment, in the second direction B, the plurality of first slits 51 include the first end portions 22a of the positive electrode tab 20c and the negative electrode tab 21c, and the second end portions on the opposite side of the first end portion 22a. 22b are arranged in a staggered manner so as not to be continuous in a straight line along the second direction B. Therefore, the plurality of first slits 51 in the second direction B are always provided in the curved portion 24c of the positive electrode tab 20c and the negative electrode tab 21c. That is, the plurality of first slits 51 are provided so that the positions thereof are displaced along the second direction B while the plurality of first slits 51 overlap each other along the first direction A. Therefore, there is no portion of the music corresponding portion 24c that is not deformed in the second direction B. Therefore, the stress generated in the positive electrode bent portion 24a of the positive electrode tab group 25 and the negative electrode bent portion 24b of the negative electrode tab group 26 can be more efficiently released in the second direction B.

(5) In the present embodiment, when the positive electrode base end portion 27a of the positive electrode tab group 25 and the negative electrode base end portion 27b of the negative electrode tab group 26 are formed, the second slit 52 provided in the bending corresponding portion 29b is the second. It deforms so as to open toward the direction B. Although stress is generated in the curved portion 29a by bending the positive electrode tab 20c and the negative electrode tab 21c, the stress generated in the curved portion 29a of the positive electrode tab 20c and the negative electrode tab 21c by deforming so that the second slit 52 opens. Can escape. That is, the springback that tries to return the curved portions 29a of the positive electrode tab 20c and the negative electrode tab 21c so as to extend straight from the bent state is suppressed, and the residual stress acting on the curved portions 29a of the positive electrode tab 20c and the negative electrode tab 21c is suppressed. Can be suppressed. Therefore, fatigue cracks in the curved portions 29a of the positive electrode tab 20c and the negative electrode tab 21c due to springback can be suppressed.

(6) In the present embodiment, the second slit 52 penetrates the positive electrode tab 20c and the negative electrode tab 21c. Therefore, when forming the positive electrode base end portion 27a of the positive electrode tab group 25 and the negative electrode base end portion 27b of the negative electrode tab group 26, the second slit 52 is easily deformed so as to open in the second direction B. Therefore, the stress generated in the curved portions 29a of the positive electrode tab 20c and the negative electrode tab 21c can be more easily released.

(7) The plurality of second slits 52 are staggered. Therefore, by providing the plurality of second slits 52 in the bending corresponding portion 29b, it is possible to increase the deformation amount of the curved corresponding portion 24c of the positive electrode tab 20c and the negative electrode tab 21c in the second direction B. Therefore, the stress generated in the positive electrode tab 20c and the negative electrode tab 21c can be easily released. In addition, since the plurality of second slits 52 are arranged in a staggered arrangement, stress can be released in a wider area of the corresponding curved portions 29b of the positive electrode tab 20c and the negative electrode tab 21c. Therefore, the stress generated in the curved portions 29a of the positive electrode tab 20c and the negative electrode tab 21c can be released in a wider range.

(8) In the present embodiment, in the second direction B, the plurality of second slits 52 include the first end portions 22a of the positive electrode tab 20c and the negative electrode tab 21c, and the second end portions on the side opposite to the first end portion 22a. 22b are arranged in a zigzag manner so as not to be continuous in a straight line along the second direction B. Therefore, the curved corresponding portions 29b of the positive electrode tab 20c and the negative electrode tab 21c are always provided with the plurality of second slits 52 in the second direction B. That is, the plurality of second slits 52 are provided so that the positions thereof are displaced along the second direction B while the plurality of second slits 52 overlap each other along the first direction A. Therefore, there is no portion of the bending corresponding portion 29b that is not deformed in the second direction B. Therefore, the stress generated in the curved portions 29a of the positive electrode tab 20c and the negative electrode tab 21c can be more efficiently released in the second direction B.

The present embodiment can be modified and implemented as follows. The present embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
In the second direction B, the plurality of second slits 52 have the first end 22a of the positive electrode tab 20c and the negative electrode tab 21c and the second end 22b opposite to the first end 22a in the second direction B. The lines were arranged in a staggered manner so as not to be continuous with a straight line, but the arrangement is not limited to this. For example, you may change as follows.

As shown in FIG. 7, the plurality of first slits 51 and the plurality of second slits 52 may be arranged so as not to overlap along the first direction A while shifting their positions along the second direction B. ..

The plurality of first slits 51 and the plurality of second slits 52 may be arranged so as to be aligned along the first direction A and the second direction B.
The number of first slits 51 and the number of second slits 52 may be changed appropriately. For example, it may be one. In this case, the first slit 51 may be provided along the first direction A over the entire length of the curved portion 24c of the positive electrode tab 20c and the negative electrode tab 21c. The second slit 52 may be provided along the first direction over the entire length of the curved corresponding portion 29b of the positive electrode tab 20c and the negative electrode tab 21c. In addition, when the number of the first slits 51 and the second slits 52 is increased, it is preferable to increase the number within a range in which the cross-sectional areas of the positive electrode tab 20c and the negative electrode tab 21c become small and the conductivity does not decrease.

The first slit 51 and the second slit 52 may have a groove shape that does not penetrate the positive electrode tab 20c and the negative electrode tab 21c.
The configuration in which the first slit 51 is provided in the positive electrode tab 20c and the negative electrode tab 21c but the second slit 52 is not provided may be adopted.

In the positive electrode 20, the positive electrode active material layer 20b may be present only on one surface of the positive electrode metal foil 20a. In the negative electrode 21, the negative electrode active material layer 21b may be present only on one surface of the negative electrode metal foil 21a. That is, the positive electrode active material layer 20b and the negative electrode active material layer 21b may be provided on at least one of the positive electrode metal foil 20a and the negative electrode metal foil 21a.

The curved portion 29a was not provided in the root portion 29 of the negative electrode tab 21c, which is located at one end in the stacking direction of the electrode assembly 12 among the plurality of negative electrode tabs 21c constituting the negative electrode tab group 26, but is not limited thereto. Absent. For example, the position of forming the negative electrode base end portion 27b of the negative electrode tab group 26 is slightly moved from the present embodiment toward the central portion of the electrode assembly 12 so that the negative electrode tab located at one end of the electrode assembly 12 in the stacking direction is located. A curved portion 29a is also formed on 21c. Also in this case, it is preferable to provide the second slit 52 in the bending corresponding portion 29b corresponding to the bending portion 29a. The configurations of the positive electrode tab group 25 and the negative electrode tab group 26 may be reversed.

The secondary battery 10 may be a secondary battery other than the lithium ion secondary battery. In short, any material can be used as long as the ions move between the positive electrode active material layer 20b and the negative electrode active material layer 21b, and the charge is transferred.

The power storage device may be applied to another power storage device such as an electric double layer capacitor instead of the secondary battery 10.
Next, the technical ideas that can be understood from the above-described embodiment and other examples will be added below.

(1) When the first slit has a groove shape that does not pass through the positive electrode tab and the negative electrode tab, the first slit has a storage portion provided in a bent portion such that the curved portion is a mountain fold. apparatus.

(2) When the second slit has a groove shape that does not penetrate the positive electrode tab and the negative electrode tab, the second slit has a storage portion provided in a bent portion such that the curved portion is a mountain fold. apparatus.

10... Secondary battery as power storage device, 11... Case, 12... Electrode assembly, 12a... Tab side end surface, 15... Positive electrode terminal, 16... Negative electrode terminal, 20... Positive electrode, 20a... Metal foil for positive electrode, 20b... Positive electrode Active material layer, 20c... Positive electrode tab, 21... Negative electrode, 21a... Negative metal foil, 21b... Negative electrode active material layer, 21c... Negative electrode tab, 22a... First end portion, 22b... Second end portion, 23... Separator, 24a... Positive electrode bent portion, 24b... Negative electrode bent portion, 24c... Bending corresponding portion, 25... Positive electrode tab group, 26... Negative electrode tab group, 27a... Positive electrode base end portion, 27b... Negative electrode base end portion, 28a... Positive electrode extension Output part, 28b... Negative electrode extension part, 29... Root part, 29a... Bending part, 29b... Bending corresponding part, 51... 1st slit, 52... 2nd slit, A... 1st direction, B... 2nd direction.

Claims (8)

An electrode assembly in which a plurality of sheet-shaped positive electrodes and a plurality of sheet-shaped negative electrodes are stacked in a state of being insulated by a separator,
A case accommodating the electrode assembly,
The positive electrode terminal and the negative electrode terminal fixed to the case and transmitting and receiving electricity to and from the electrode assembly are provided.
The positive electrode is a sheet-shaped positive electrode metal foil, a positive electrode active material layer provided on at least one of both surfaces of the positive electrode metal foil, and a positive electrode tab protruding from a part of one side of the positive electrode metal foil. And have
The negative electrode is a sheet-shaped negative electrode metal foil, a negative electrode active material layer provided on at least one of both surfaces of the negative electrode metal foil, and a negative electrode tab protruding from a part of one side of the negative electrode metal foil. And have
The electrode assembly includes a positive electrode tab group in which the plurality of positive electrode tabs are gathered together, and a negative electrode tab group in which the plurality of negative electrode tabs are gathered together,
The positive electrode tab group includes a positive electrode base end portion in which the plurality of positive electrode tabs are gathered toward one end in the stacking direction of the electrode assembly, and a positive electrode base end portion from the positive electrode base end portion to the other end in the stacking direction of the electrode assembly. And a positive electrode bent portion that bends, and a stack of the electrode assembly from the side opposite to the positive electrode base end portion of the positive electrode bent portion along the tab-side end surface where the positive electrode tab group and the negative electrode tab group of the electrode assembly are present. A positive electrode extension portion fixed to the positive electrode terminal while extending toward the other end in the direction,
The negative electrode tab group includes a negative electrode base end portion in which a plurality of the negative electrode tabs are gathered toward one end in the stacking direction of the electrode assembly, and a negative electrode base end portion from the other end in the stacking direction of the electrode assembly. And a negative electrode bent portion that bends along the tab-side end surface of the electrode assembly, and extends from the side opposite to the negative electrode base end portion of the negative electrode bent portion toward the other end in the stacking direction of the electrode assembly. A negative electrode extension portion fixed to the negative electrode terminal,
In the plurality of positive electrode tabs and the plurality of negative electrode tabs, the plurality of positive electrode tabs and the plurality of negative electrode tabs are included in the root portion provided closer to the tab side end surface than the positive electrode base end portion and the negative electrode base end portion. Includes the root portion having a curved portion that is bent in a state of being gathered together at one end in the stacking direction of the electrode assembly,
The positive electrode base end portion and the negative electrode base end portion are formed by gathering each of the plurality of positive electrode tabs and the plurality of negative electrode tabs at one end in the stacking direction of the electrode assembly to form the positive electrode extension portion and the negative electrode. In a state before forming the extending portion, the positive electrode tab group and the negative electrode tab group correspond to the positive electrode curved portion and the negative electrode curved portion of the plurality of positive electrode tabs and the plurality of negative electrode tabs, respectively. The power storage device is characterized in that the bending corresponding portion is provided with a first slit extending along a first direction which is a direction orthogonal to the tab-side end surface of the electrode assembly. The power storage device according to claim 1, wherein the first slit penetrates the positive electrode tab and the negative electrode tab. A plurality of the first slits are provided in the music corresponding portion,
The power storage device according to claim 1 or 2, wherein the plurality of first slits are arranged in a staggered arrangement. A direction orthogonal to the first direction and the stacking direction, and a width direction of the positive electrode tab and the negative electrode tab is a second direction,
In the second direction, the plurality of first slits have first ends of the positive electrode tab and the negative electrode tab and a second end opposite to the first end along the second direction. The power storage device according to claim 3, wherein the power storage devices are arranged in a staggered manner so as not to be continuous in a straight line. In a state before forming the positive electrode base end portion and the negative electrode base end portion by gathering each of the plurality of positive electrode tabs and the plurality of negative electrode tabs at one end in the stacking direction of the electrode assembly, the positive electrode tab and A second slit extending along the first direction is provided in a bending corresponding portion corresponding to the bending portion of each of the negative electrode tabs, and the second slit is provided. The power storage device according to 1. The power storage device according to claim 5, wherein the second slit penetrates the positive electrode tab and the negative electrode tab. A plurality of the second slits are provided in the bending corresponding portion,
The power storage device according to claim 5 or 6, wherein the plurality of second slits are arranged in a staggered arrangement. A direction orthogonal to the first direction and the stacking direction, and a width direction of the positive electrode tab and the negative electrode tab is a second direction,
In the second direction, the plurality of second slits have first end portions of the positive electrode tab and the negative electrode tab and a second end portion opposite to the first end portion along the second direction. The power storage device according to claim 7, wherein the power storage devices are arranged in a staggered manner so as not to be continuous in a straight line.