Lithium ion secondary battery

Abstract

To provide a lithium ion secondary battery capable of suppressing application of a load to an end portion of a cell during expansion of a cell laminate.SOLUTION: In a lithium ion secondary battery, a plurality of unit cells each including a cell stacked body in which cells each including a positive electrode layer, an electrolyte layer, and a negative electrode layer are stacked, and an exterior body that accommodates the cell stacked body are stacked. The exterior body includes two planar portions that are in contact with both of the cells at an outermost end in a stacking direction of the cell stacked body, a stretched portion in which a planar portion is stretched outward from the side surface of the cell stacked body along a plane on at least two sides of the cell stacked body viewed from the stacking direction, and a side surface portion that connects the two stretched portions. The side surface portion has a margin capable of following the contraction and expansion of the cell laminate, and the extending portion is bonded to the extending portion of the exterior body of the adjacent unit cell.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a lithium ion secondary battery. [Background technology]

[0002] A lithium-ion secondary battery is composed of a plurality of stacked unit cells, each of which has a cell stack sealed inside an exterior housing. The cell stack is composed of stacked cells, each of which has a positive electrode layer, an electrolyte layer, and a negative electrode layer. A known conventional exterior housing for a secondary battery has a pair of opposing surfaces and an outer periphery connecting the opposing surfaces, the outer periphery having a folded structure, and the outer periphery being variable in a direction that changes the distance between the opposing surfaces (Patent Document 1, paragraph

[0010] , Figure 2). The exterior housing for a secondary battery according to this embodiment improves the cycle characteristics of a secondary battery using it. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-139872 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-described exterior body, a load is applied to the cell ends when the cell stack expands, which may cause damage to the ends or short circuits.

[0005] Therefore, an object of the present invention is to provide a lithium ion secondary battery that can suppress the load applied to the cell ends when the cell stack expands. [Means for solving the problem]

[0006] To achieve the above object, the present invention provides a lithium-ion secondary battery in which a plurality of unit cells are stacked, the unit cells including a cell stack formed by stacking cells each having a positive electrode layer, an electrolyte layer, and a negative electrode layer, and an exterior housing that houses the cell stack, the exterior housing having two flat portions in contact with both of the cells at the outermost ends in the stacking direction of the cell stack, extension portions on at least two sides of the cell stack as viewed from the stacking direction, where the flat portions extend outward beyond the side surfaces of the cell stack along the surfaces of the flat portions, and side portions connecting the two extension portions together, the side portions having a margin that can accommodate contraction and expansion of the cell stack, and the extension portions are bonded to the extension portions of the exterior housing of adjacent unit cells. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress the load from being applied to the cell end when the lithium ion secondary battery expands. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of a cell that constitutes a lithium ion secondary battery according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the lithium ion secondary battery according to the embodiment of the present invention, viewed from the first direction shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view of the lithium ion secondary battery taken along the AA plane shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view showing a lithium ion secondary battery according to an embodiment of the present invention, illustrating the configuration when the battery is in a discharged state. [Figure 5] FIG. 5 is a cross-sectional view showing a lithium ion secondary battery according to an embodiment of the present invention, illustrating the configuration when the battery is in a charged state. [Figure 6] FIG. 6 is a cross-sectional view showing a first modification of a cell constituting a lithium ion secondary battery according to an embodiment of the present invention. [Figure 7]FIG. 7 is a cross-sectional view showing a modified example 2 of a cell constituting a lithium ion secondary battery according to an embodiment of the present invention. [Figure 8] FIG. 8 is a cross-sectional view showing a third modification of a cell constituting a lithium ion secondary battery according to an embodiment of the present invention. [Figure 9] FIG. 9 is a cross-sectional view showing a fourth modified example of a cell constituting a lithium ion secondary battery according to an embodiment of the present invention. [Figure 10] FIG. 10 is a cross-sectional view showing a fifth modification of the lithium ion secondary battery according to the embodiment of the present invention. [Figure 11] FIG. 11 is a cross-sectional view showing a sixth modification of the lithium ion secondary battery according to the embodiment of the present invention. [Figure 12] FIG. 12 is a cross-sectional view showing a seventh modification of the lithium ion secondary battery according to the embodiment of the present invention. [Figure 13] FIG. 13 is a cross-sectional view showing Modification 8 of the lithium ion secondary battery according to the embodiment of the present invention. [Figure 14] FIG. 14 is a cross-sectional view showing a ninth modification of the lithium ion secondary battery according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown here are merely examples for embodying the technical concept of the present invention and are not intended to limit the present invention. Therefore, all other possible forms, examples, and operational techniques that can be conceived by those skilled in the art without departing from the spirit of the present invention are included in the scope and spirit of the present invention, as well as in the scope of the inventions described in the claims and their equivalents.

[0010] In addition, for the convenience of illustration and ease of understanding, the drawings attached to this specification may be represented schematically with the scale, aspect ratio, shape, etc. appropriately changed from the actual product, but these are merely examples and do not limit the interpretation of the present invention.

[0011] In this specification, ordinal numbers such as "first" may be used. However, unless otherwise specified, these ordinal numbers are used to identify components for the convenience of explanation and do not specify the number or order.

[0012] <Embodiment> FIG. 1 is a cross-sectional view of a cell 1a constituting a lithium-ion secondary battery 1A (hereinafter also simply referred to as "secondary battery 1A") according to an embodiment of the present invention. FIG. 2 is a plan view of the secondary battery 1A according to the embodiment of the present invention as viewed from a first direction shown in FIG. 1. FIG. 3 is a cross-sectional view of the secondary battery 1A taken along the AA plane shown in FIG. 2. As shown in FIG. 1, the cell 1a constituting the secondary battery 1A includes a cell stack 20 and an exterior body 30.

[0013] The cell stack 20 is composed of a cell having a positive electrode current collector, a positive electrode layer, an electrolyte layer, a negative electrode layer, and a negative electrode current collector, a positive electrode tab 23 connected to the positive electrode layer, and a negative electrode tab 24 connected to the negative electrode layer.

[0014] The stacking direction of the cell stack 20 is defined as a first direction. The outermost surface of the cell stack 20 in the stacking direction is defined as a main surface 21, and the outermost surface in a direction perpendicular to the stacking direction is defined as a side surface 22.

[0015] The positive electrode current collector and the negative electrode current collector are formed in the shape of a rectangular thin plate from a metal material such as aluminum, nickel, iron, stainless steel, titanium, or copper.

[0016] The positive electrode layer is disposed on both main surfaces of the positive electrode current collector. The positive electrode layer contains, as a positive electrode active material, a substance capable of releasing lithium ions during charging and absorbing lithium ions during discharging by utilizing an oxidation-reduction reaction. Examples of materials for the positive electrode active material include lithium-transition metal composite oxides such as LiMn2O4, LiCoO2, LiNiO2, and Li(Ni-Mn-Co)O2, and those in which part of the transition metal is substituted with other elements, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds.

[0017] An example of the electrolyte layer is a solid electrolyte layer. The solid electrolyte layer contains a solid electrolyte as a main component and is a layer interposed between the positive electrode layer and the negative electrode layer. Examples of solid electrolyte materials include sulfide solid electrolytes and oxide solid electrolytes, but sulfide solid electrolytes are preferred. Examples of sulfide solid electrolytes include LPS-based (e.g., argyrodite (Li6PS5Cl)), LGPS-based (e.g., Li 10 GeP2S 12 ) materials are preferred.

[0018] The negative electrode layer is disposed on both main surfaces of the negative electrode current collector. The negative electrode layer is configured to contain at least lithium metal or a substance that forms an alloy with lithium as a negative electrode active material. The term "including lithium metal as the active material in the negative electrode layer" includes cases where lithium metal foil or lithium metal particles are disposed on the main surface of the negative electrode current collector, and cases where lithium metal is deposited on the main surface of the negative electrode current collector using a positive electrode that includes a positive electrode active material such as a lithium-transition metal composite oxide, a lithium-transition metal phosphate compound, or a lithium-transition metal sulfate compound. Furthermore, the term "including a substance that forms an alloy with lithium as an active material in the negative electrode layer" means that the negative electrode layer contains at least one substance selected from the group consisting of In, Al, Si, and Sn.

[0019] Aluminum foil, aluminum alloy foil, copper foil, nickel foil, etc. can be used for the positive electrode tab 23 and the negative electrode tab 24. The positive electrode tab 23 is connected to a positive electrode current collector, and the negative electrode tab 24 is connected to a negative electrode current collector.

[0020] The outer casing 30 is formed from a flexible material, such as a resin film such as polyethylene or polypropylene, or a resin-metal thin film laminate material in which both sides of a metal foil such as aluminum are laminated with a resin such as polyethylene or polypropylene.

[0021] The exterior body 30 has a flat portion 31, an extension portion 32, and a side surface portion 33. The cell 1a has a structure in which the cell stack 20 is sealed inside the exterior body 30.

[0022] The planar portion 31 is in contact with the main surface 21 of the cell stack 20. That is, the exterior body 30 has two planar portions 31 that are in contact with the main surfaces 21 of both cells at the outermost ends of the cell stack 20 in the stacking direction.

[0023] The extension portions 32 are portions of the planar portions 31 that extend along the surface outward beyond the side surfaces 22 of the cell stack 20. The extension portions 32 are arranged on at least two sides of the cell stack 20 when viewed from the first direction. In this embodiment, as shown in FIG. 2 , the exterior body 30 has the extension portions 32 on two opposing sides of the cell stack 20 when viewed from the first direction. However, the present invention is not limited to this, and the extension portions 32 may be provided on two adjacent sides of the cell stack 20.

[0024] On the two sides that do not have the extension portion 32, a portion of the positive electrode tab 23 and a portion of the negative electrode tab 24 extend from the cell stack 20 when viewed from the first direction. In detail, one end of the positive electrode tab 23 is disposed inside the exterior body 30, and the other end is located outside the exterior body 30. Similarly, one end of the negative electrode tab 24 is disposed inside the exterior body 30, and the other end of the negative electrode tab 24 is located outside the exterior body 30.

[0025] 3 , the two sides that do not have the extension portion 32 are configured so that the positive electrode tab 23 and the negative electrode tab 24 are sandwiched by the exterior body 30 from the first direction. With this configuration, when sealing the exterior body 30 by heat welding or the like, the exterior body 30 can be sealed without wrinkles on the two sides that have the positive electrode tab 23 and the negative electrode tab 24. Since the two flat portions 31 are bonded to each other on the two sides that do not have the extension portion 32, the cell stack 20 can be sealed inside the exterior body 30.

[0026] The side surface portion 33 connects the two extension portions 32 together. In this embodiment, the side surface portion 33 has a U-shape during discharge. The outer peripheral edge direction of the cell stack 20 is oriented so as to be the open end of the U-shape of the side surface portion 33. The side surface portion 33 has two main surfaces 331 parallel to the main surface 21 and a side surface 332 parallel to the side surface 22.

[0027] The end of the main surface 331 on the open end side is connected to the end of the extension portion 32. In this embodiment, of the two planar portions 31, one above the other in the first direction, the end of the extension portion 32 is folded from the main surface 331 on the lower side in the first direction to be connected. Hereinafter, the folded and connected portion will be defined as the folded portion. On the main surface 331 on the upper side in the first direction, the end of the extension portion 32 is sealed and connected to the end of the main surface 331 with adhesive 34 or the like. Hereinafter, the sealed and connected portion will be defined as the sealed portion. The area where the main surface 331 and the extension portion 32 are sealed is only the end side of the area where the main surface 331 and the extension portion 32 contact each other.

[0028] The end of the main surface 331 on the cell stack 20 side is connected to the side surface 332, and the side surface 332 is in contact with the side surface 22 of the cell stack 20. The main surface 331 is also in contact with the extension portion 32. The side surface portion 33 and the extension portion 32 are not bonded to each other except at the ends, so the side surface portion 33 has a margin that allows it to accommodate contraction and expansion due to charging.

[0029] 4 is a cross-sectional view showing a lithium-ion secondary battery 1A according to an embodiment of the present invention, illustrating the configuration when the battery is in a discharged state. The secondary battery 1A is composed of a plurality of cells 1a stacked in a first direction. The extension portion 32 of one cell 1a is bonded to the extension portion 32 of the exterior body 30 of the adjacent cell 1a with an adhesive 35 or the like.

[0030] The lithium ion secondary battery 1A contains at least lithium metal or a material that forms an alloy with lithium as the negative electrode active material, so that the lithium ion secondary battery 1A expands and contracts in a first direction as lithium ions are absorbed and released during charging and discharging.

[0031] Here, the functions of the cell stack 20 and the exterior body 30 when the lithium ion secondary battery 1A expands will be described with reference to Fig. 5. Fig. 5 is a cross-sectional view showing the lithium ion secondary battery 1A in an embodiment of the present invention, and shows the configuration when the battery is in a charged state.

[0032] When the lithium-ion secondary battery 1A is charged, the cell stack 20 expands in the first direction. At this time, stress also acts on the exterior body 30 housing the cell stack 20. The extension portions 32 of the exterior body 30 are bonded to the extension portions 32 of adjacent cells 1a, preventing the cell stack 20 from collapsing when it expands. Furthermore, because the side portions 33 have a margin where they are not bonded to the cell stack 20, this margin expands preferentially during expansion. That is, as shown in FIG. 5 , the bonded portions between the extension portions 32 remain approximately perpendicular to the first direction, and the side portions 33 follow the expansion of the cell stack 20. This configuration prevents the exterior body 30 from applying a load to the end of the cell stack 20 when it expands due to charging.

[0033] Since the side surface 22 of the cell stack 20 having the extension portion 32 is in contact with the side surface portion 33 of the exterior body 30, cracks at the end portion of the cell stack 20 can be prevented.

[0034] The above describes an embodiment of the present invention. In this embodiment, the extension portions 32 are configured to be bonded to the extension portions 32 of adjacent cells 1a. However, in addition to the extension portions 32, the flat portions 31 may also be bonded to the flat portions 31 of adjacent cells 1a. This configuration strengthens the bond between the cells 1a, and can prevent the cells 1a from shifting in a direction perpendicular to the first direction due to charge and discharge.

[0035] Modifications of the embodiment will be described below. Differences from the lithium ion secondary battery 1A of the embodiment will be mainly described, and the same components as those of the lithium ion secondary battery 1A of the embodiment will be assigned the same reference numerals and will not be described again.

[0036] <Variation 1> A first modification of the embodiment of the present invention will be described with reference to Fig. 6. In this embodiment, the side surface portion 33 contacts the side surface 22 of the cell stack 20, but the present invention is not limited to this.

[0037] 6, the side surface portion 33 may not be in contact with the cell stack 20. Even with this configuration, it is possible to prevent a load from being applied from the exterior body 30 to the end of the cell stack 20 when the cell stack 20 expands due to charging.

[0038] <Variation 2> Next, a second modification of the embodiment of the present invention will be described with reference to FIG.

[0039] In this embodiment, on the main surface 331 on the lower side in the first direction, the end of the extension portion 32 is folded from the main surface 331 and connected thereto, and on the main surface 331 on the upper side in the first direction, the end of the extension portion 32 is sealed and connected to the end of the main surface 331 with adhesive 34 or the like, but this is not limited to this.

[0040] 7, the upper main surface 331 in the first direction may have a folded portion and a sealed portion. That is, of the two upper main surfaces 331 in the first direction, one main surface 331 may be folded and connected to the extension portion 32, and the other main surface 331 may be sealed with adhesive 34 or the like and bonded to the extension portion 32. Even with this configuration, it is possible to prevent load from being applied from the exterior body 30 to the end of the cell stack 20 when the cell stack expands due to charging. Furthermore, in the configuration of Modification 2, the exterior body 30 can be made from a single piece of material.

[0041] <Variation 3> Next, a third modification of the embodiment of the present invention will be described with reference to FIG.

[0042] 8, a configuration may be adopted in which both the upper and lower main surfaces 331 in the first direction are sealed and connected to the ends of the extension portions 32 with adhesive 34 or the like. In this case, the area where the main surfaces 331 and the extension portions 32 are sealed is only the end side of the area where the main surfaces 331 and the extension portions 32 contact each other. Even with this configuration, it is possible to prevent a load from being applied from the exterior body 30 to the ends of the cell stack 20 when the cell stack expands due to charging.

[0043] <Variation 4> Next, a fourth modification of the embodiment of the present invention will be described with reference to FIG.

[0044] As shown in Fig. 9, the entire area where the main surface 331 and the extension portion 32 are in contact may be sealed with adhesive 34 or the like, leaving a margin on the side surface 332. In Modification 4, the main surface 331 is bonded to the extension portion 32 and does not have a margin, but the margin on the side surface 332 follows the expansion of the cell stack 20. Therefore, even with this configuration, it is possible to prevent a load from being applied from the exterior body 30 to the end of the cell stack 20 when it expands due to charging. Furthermore, in Modification 4, the area of ​​the sealed portion is large, which further prevents the extension portion 32 from collapsing when it expands due to charging.

[0045] <Variation 5> Next, a fifth modification of the embodiment of the present invention will be described with reference to FIG.

[0046] As shown in Fig. 10, the contact portions of the main surface 331 and the extension portions 32 may be folded together. In Modification 5, the contact portions of the main surface 331 and the extension portions 32 are folded at the center so that the ends face the first direction. Even with this configuration, it is possible to prevent a load from being applied from the exterior body 30 to the ends of the cell stack 20 when the cell stack expands due to charging. Furthermore, in Modification 5, by folding the contact portions of the main surface 331 and the extension portions 32, it is possible to reduce the area occupied by the cell stack 20 in terms of the projected area as viewed from the first direction, thereby improving the volumetric energy density.

[0047] <Variation 6> Next, a sixth modification of the embodiment of the present invention will be described with reference to FIG.

[0048] As shown in Fig. 11, the contact portion between the main surface 331 and the extension portion 32 may be folded multiple times. In Modification 6, the contact portion between the main surface 331 and the extension portion 32 is folded five times so that the end of the contact portion between the main surface 331 and the extension portion 32 is rolled inward. Even with this configuration, it is possible to prevent a load from being applied from the exterior body 30 to the end of the cell stack 20 when the cell stack expands due to charging. Furthermore, in Modification 6, by folding the contact portion between the main surface 331 and the extension portion 32 multiple times, it is possible to further reduce the occupied area in the projected area as viewed from the first direction, thereby further improving the volumetric energy density.

[0049] <Variation 7> Next, a seventh modification of the embodiment of the present invention will be described with reference to FIG.

[0050] As shown in FIG. 12 , two sides of the lithium-ion secondary battery 1A that do not have the extension portion 32 as viewed from the first direction may be bonded to adjacent exterior bodies 30 via reinforcing members 40. In Modification 7, reinforcing members 40 made of a material such as plastic are bonded with adhesive 41 to the two sides of the secondary battery 1A that do not have the extension portion 32 as viewed from the first direction. The reinforcing members 40 apply a force to the exterior body 30 in a direction toward the outside of the cell stack 20. This configuration also prevents a load from being applied from the exterior body 30 to the ends of the cell stack 20 when the cell stack 20 expands due to charging. Furthermore, in Modification 7, even when the interior of the exterior body 30 is vacuum-sealed, a load from being applied from the exterior body 30 to the ends of the cell stack 20 can be prevented.

[0051] <Variation 8> Next, an eighth modification of the embodiment of the present invention will be described with reference to FIG.

[0052] As shown in FIG. 13 , two sides of the lithium-ion secondary battery 1A that do not have the extensions 32 as viewed from the first direction may have resin members 50 inside the exterior housing 30. In Modification 8, the spaces between the exterior housing 30 and the cell stack 20 on the two sides of the secondary battery 1A that do not have the extensions 32 as viewed from the first direction are filled with resin. The resin members 50 are made of a soft resin that follows the expansion and contraction of the secondary battery 1A. The resin members 50 apply a force to the exterior housing 30 in the direction outward from the cell stack 20. This configuration also prevents a load from being applied from the exterior housing 30 to the ends of the cell stack 20 when the cell stack 20 expands due to charging. Furthermore, in Modification 8, even when the interior of the exterior housing 30 is vacuum-sealed, a load from being applied from the exterior housing 30 to the ends of the cell stack 20 can be prevented.

[0053] <Variation 9> Next, a ninth modification of the embodiment of the present invention will be described with reference to FIG.

[0054] As shown in FIG. 14 , a configuration may be adopted in which a plate member 60 is provided in contact with the cell 1a located at the outermost end of the lithium-ion secondary battery 1A, and the extension portion 32 and the plate member 60 are bonded to each other. In Modification 9, plate members 60 are arranged on both sides of the lithium-ion secondary battery 1A in the first direction. The extension portion 32 of the cell 1a located at the outermost end of the lithium-ion secondary battery 1A is bonded to the plate member 60 with an adhesive 36 or the like. The plate member 60 may be provided for the purpose of restraining the secondary battery 1A or for the purpose of cooling or dissipating heat from the secondary battery 1A. Even with this configuration, it is possible to prevent a load from being applied from the exterior body 30 to the end of the cell stack 20 during expansion due to charging. Furthermore, Modification 9 can prevent the outer extension portion 32 of the outermost cell 1a from collapsing when multiple cells 1a are stacked.

[0055] Although the embodiments and modifications of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and the technical scope of the present invention is not intended to be limited to the specific configurations of the above embodiments. Furthermore, the above embodiments can be combined as appropriate.

[0056] The following embodiments are also included within the scope of the present invention: a lithium ion secondary battery 1A according to claim 2 having the features of claim 3; a lithium ion secondary battery 1A according to any one of claims 2 to 5 having the features of claim 6; a lithium ion secondary battery 1A according to any one of claims 2 to 6 having the features of claim 7; a lithium ion secondary battery 1A according to any one of claims 2 to 7 having the features of claim 8; a lithium ion secondary battery 1A according to any one of claims 2 to 8 having the features of claim 9; and a lithium ion secondary battery 1A according to any one of claims 2 to 9 having the features of claim 10. [Explanation of symbols]

[0057] 1A…Secondary battery 1a...single battery 20...Cell stack 21...Main surface 22...Side 30...Exterior body 31...Plane part 32...Extension part 33...Side part 331...Main surface 332...Side 40...Reinforcing member 50...Resin material 60...Plate member

Claims

1. A lithium ion secondary battery in which a plurality of unit cells are stacked, the unit cells including a cell stack in which cells each having a positive electrode layer, an electrolyte layer, and a negative electrode layer are stacked, and an exterior body that houses the cell stack, The exterior body has two planar portions in contact with both cells at the outermost ends in the stacking direction of the cell stack; an extension portion on at least two sides of the cell stack as viewed from the stacking direction, the extension portion being formed by extending the planar portion along a surface thereof outward beyond the side surface of the cell stack; and a side surface portion connecting the two extension portions, the side surface portion has a margin that can follow the contraction and expansion of the cell stack, The lithium ion secondary battery, characterized in that the extension portion is bonded to the extension portion of the exterior body of an adjacent one of the single cells.

2. The lithium ion secondary battery according to claim 1 , wherein the side surface of the cell stack having the extension portion is in contact with the side surface portion of the exterior body.

3. 2. The lithium ion secondary battery according to claim 1, wherein two sides of the cell stack as viewed from the stacking direction do not have the extension portion, and the two flat portions are bonded together.

4. The lithium-ion secondary battery according to claim 3, characterized in that the side of the cell stack that does not have the extension portion when viewed from the stacking direction is bonded to the side of the outer casing of the adjacent single battery that does not have the extension portion by a reinforcing member.

5. 4. The lithium-ion secondary battery according to claim 3, wherein a resin member is disposed between the exterior body and the cell stack on two sides of the cell stack that do not have the extension portion when viewed from the stacking direction.

6. The extension portion and the side surface portion are in contact with each other, The end side of the extension part is bonded, 2. The lithium ion secondary battery according to claim 1, wherein the flat portion side of the extension portion is not bonded.

7. a plate member in contact with the two unit cells located at the outermost ends in the stacking direction; 2. The lithium ion secondary battery according to claim 1, wherein the extension and the plate member are bonded together.

8. 2. The lithium ion secondary battery according to claim 1, wherein the contact portion between the extension portion and the side surface portion includes a portion where the extension portion and the side surface portion are both folded.

9. 2. The lithium ion secondary battery according to claim 1, wherein the exterior bodies of adjacent cells are bonded together at all of their contacting portions.

10. Of the two planar portions, the extension portion extending from one of the planar portions is bonded to the side surface portion, The lithium ion secondary battery according to claim 1, characterized in that the extension portion extending from the other flat portion is made of the same material as the side portion, and the side portion is folded and connected at the end of the extension portion.

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