Rectangular secondary battery

Abstract

The invention provides a rectangular secondary battery which can improve insulation resistance and can fix an insulation protective film and a wound electrode body in consideration of productivity. A rectangular secondary battery is provided with a wound electrode body (3), and an insulating protective film (2) which is wound around the wound electrode body (3) or folded along the outer shape of the wound electrode body to cover the wound electrode body, the insulating protective film (2) has at least side peripheral surface sections (51b, 51c) extending in the circumferential direction of the side peripheral surface of the wound electrode body (3) and covering the wound electrode body (3), and a bottom surface section (52a) covering the bottom surface of the wound electrode body, and an end surface overlapping section (51h) in which the end surface sections on both sides of the insulating protective film (2) overlap is formed on the side peripheral surface of the wound electrode body. The end surface overlapping portion (51h) has through-regions (51f-1, 51G-1) that reach the side peripheral surface of the wound electrode body, and the periphery of the through-regions (51f-1, 51G-1) of the end surface overlapping portion is affixed to the side peripheral surface of the wound electrode body via the through-regions (51f-1, 51G-1) by an electrically insulating adhesive tape (20a).

Description

Technical Field

[0001] The present invention relates to a prismatic secondary battery used in, for example, an electric vehicle or a hybrid vehicle. Background Art

[0002] In recent years, as a power source for electric vehicles or hybrid vehicles, the development of square lithium-ion secondary batteries with high energy density is underway. In secondary batteries for vehicle use, since a large capacity is required compared to mobile phones, multiple secondary batteries are sometimes carried. The square battery contains a flat-shaped wound electrode body as a power generation element in a square battery container (battery can). The wound electrode body is formed by overlapping and winding in an insulated state with a separator between the positive plate and the negative plate.

[0003] A positive electrode collector stack is provided on one side of the winding axis direction of the wound electrode body, and a negative electrode collector stack is provided on the other side of the winding axis direction. A positive electrode connection terminal is joined to the positive electrode collector stack, and a negative electrode connection terminal is joined to the negative electrode collector stack.

[0004] The positive electrode connection terminal and the negative electrode connection terminal are respectively conductively connected to the positive electrode external terminal and the negative electrode external terminal which are arranged on the same surface of the battery container, such as the battery cover, on the outside of the battery container. The battery container is an electrically neutral structure, that is, the battery container has a structure insulated from the wound electrode body.

[0005] In this square battery, in order to prevent the positive collector stacking portion and the negative collector stacking portion of the wound electrode body located inside the battery and the positive electrode connecting terminal and the negative electrode connecting terminal connected thereto from being short-circuited through the inner wall of the battery container, and in order not to damage the surface of the wound electrode body when inserting the wound electrode body into the battery container, various schemes have been proposed for protecting the wound electrode body and the inner wall of the battery container with an insulating protective sheet or film (hereinafter referred to as "insulating film") .

[0006] For example, Japanese Patent Publication No. 2015-11895 (Patent Document 1) discloses a secondary battery provided with an insulating protective film covering the side circumference of a wound electrode body having a substantially rectangular flat shape. The insulating protective film is wound in a manner covering the side circumference of the wound electrode body, and the end faces on both sides of the wound insulating protective film are arranged relative to each other at a predetermined distance. Furthermore, an exposed area is formed in this portion, and in this state, the end faces on both sides and the exposed area of ​​the wound electrode body are attached to each other by adhesive tape.

[0007] In this way, by arranging the end faces of both sides of the insulating protective film to face each other with a predetermined distance therebetween, overlapping of the insulating protective film can be avoided and the thickness can be reduced. Prior art literature Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2015-11895 Summary of the invention Problem that the invention aims to solve

[0009] However, in Patent Document 1, the end surfaces on both sides of the insulating protective film have exposed areas of the wound electrode body (exposed separator), resulting in a structure in which the wound electrode body is not completely covered by the insulating protective film. Therefore, there is room for improvement in fixing the insulating film and the wound electrode body to improve insulation and productivity.

[0010] An object of the present invention is to provide a prismatic secondary battery capable of improving insulation resistance and fixing an insulating protective film and a wound electrode body in consideration of productivity. Technical means of solving problems

[0011] The present invention is characterized in that a square secondary battery has a wound electrode body and an insulating protective film wound on the wound electrode body or folded along the outer shape of the wound electrode body to cover the wound electrode body. In the square secondary battery, the insulating protective film has at least: a circumferential portion extending in the circumferential direction of the side circumferential surface of the wound electrode body and covering the side circumferential surface of the wound electrode body, and a bottom portion covering the bottom surface of the wound electrode body. An end face repeating portion is formed on the side circumferential surface of the wound electrode body with end face portions on both sides of the insulating protective film overlapping, and the end face repeating portion has a through-region reaching the side circumferential surface of the wound electrode body, and the periphery of the through-region of the end face repeating portion is adhered and fixed to the side circumferential surface of the wound electrode body via the through-region by an electrically insulating adhesive tape. Effects of the Invention

[0012] According to the present invention, it is possible to provide a prismatic secondary battery in which insulation resistance can be improved and an insulating protective film and a wound electrode body can be fixed in consideration of productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is an external perspective view showing the external appearance of a rectangular secondary battery. Figure 2 This is an exploded perspective view showing the components of a prismatic secondary battery after it has been disassembled. Figure 3 This is an exploded perspective view showing the constituent components by disassembling the wound electrode body. Figure 4 This is a perspective view of a power generation element assembly having a wound electrode body as a main element. Figure 5 This is a development view of the insulating protective film covering the wound electrode body. Figure 6It is a perspective view showing the positional relationship between the insulating protective film and the power generation element assembly and the method of folding the insulating protective film. Figure 7 This is a front view showing a state in which a side cover portion of an insulating protective film is wound around a power generation element assembly. Figure 8 This is a front view showing a modified example of a state in which a side cover portion of an insulating protective film is wound around a power generation element assembly. Fig. 9A It is a structural diagram showing a first example of a notch portion formed on an end surface of an insulating protective film. Fig. 9B It is a structural diagram showing a second example of the notch portion formed on the end surface of the insulating protection film. Fig. 9C It is a structural diagram showing a third example of the notch portion formed on the end surface of the insulating protection film. Fig.9D It is a structural diagram showing a fourth example of the notch portion formed on the end surface of the insulating protection film. Fig.9E It is a structural diagram showing a fifth example of the notch portion formed on the end surface of the insulating protection film. Fig.9F It is a structural diagram showing a sixth example of the notch portion formed on the end surface of the insulating protection film. Figure 9G It is a structural diagram showing a seventh example of the notch portion formed on the end surface of the insulating protection film. DETAILED DESCRIPTION

[0014] Hereinafter, embodiments of the present invention will be described in detail using the drawings, but the present invention is not limited to the following embodiments, and various modifications and application examples are also included in the technical concept of the present invention.

[0015] However, the configuration of the insulating protective film described in Patent Document 1 is indeed a good method to avoid overlapping of the insulating protective film and reduce the length in the thickness direction. However, it is expected that the energy density of single cells and battery packs will need to be increased in the future. That is, by increasing the number of single cells mounted in the battery pack, the total voltage of the battery pack becomes higher. At this time, the problem becomes the insulation resistance between the battery container and the wound electrode body.

[0016] In addition, in order to improve the insulation performance, there is a method of making the end faces of both sides of the insulating protective film overlap to eliminate the exposed area, but in this case, the insulating protective film and the wound electrode body must be fixed to suppress the deviation of the two, and it is necessary to develop a new fixing method that takes productivity into consideration. For example, if there is a deviation between the insulating protective film and the wound electrode body, when the power generation element assembly is inserted into the battery can, the insulating protective film will be rolled between the battery can and the cover, resulting in poor welding during laser welding.

[0017] The present invention can also fully cope with such a problem, and the embodiments of the present invention are described below using the drawings. In the embodiments described below, as an example of a prismatic secondary battery, a lithium ion secondary battery used in a hybrid vehicle or an electric vehicle is described.

[0018] Figure 1 is a perspective view of the appearance of a square secondary battery according to this embodiment. Figure 2 It is an exploded perspective view of the prismatic secondary battery of this embodiment.

[0019] like Figure 1 , Figure 2 As shown, the square secondary battery C1 includes a battery can 1 and a cover (battery cover) 6. The wound electrode body 3 is stored in the battery can 1, and the opening 1a of the battery can 1 is sealed by the cover 6. The cover 6 is joined to the battery can 1 by laser welding to form a battery container sealed by the battery can 1 and the cover 6. The cover 6 is provided with a positive electrode external terminal 8A and a negative electrode external terminal 8B.

[0020] The square secondary battery C1 charges the wound electrode body 3 via the positive electrode external terminal 8A and the negative electrode external terminal 8B, and supplies power to the external load. A gas discharge valve 10 is integrally provided on the cover 6. When the pressure in the battery container rises, the gas discharge valve 10 opens, and the gas is discharged from the inside, reducing the pressure in the battery container and ensuring the safety of the square secondary battery C1.

[0021] The battery can 1 of the square secondary battery C1 is a so-called square, and has a rectangular can bottom 22, a square cylindrical side wall portion (sometimes also indicated as a side peripheral surface) 21 rising from the four sides of the can bottom 22 in the battery height direction (+Y direction), and an opening portion 1a opened in the battery height direction at the upper end of the side wall portion 21. The side wall portion 21 of the battery can 1 has a pair of wide side wall portions 21a separated and opposed to each other in the battery thickness direction (+Z direction) and a pair of narrow side wall portions 21b separated and opposed to each other in the battery width direction (+X direction).

[0022] The wound electrode body 3 is contained in the battery can 1 in a state of being wrapped and covered by the insulating protective film 2 (the insulating protective film 2 will be described later). The wound electrode body 3 has a substantially rectangular flat shape, and has a pair of flat surfaces, and a pair of curved surfaces with arc-shaped cross sections facing each other across the pair of flat surfaces. The wound electrode body 3 is inserted into the battery can 1 from one of the curved surface sides, and is contained in the battery can 1 in a horizontal posture state with the winding axis direction along the battery width direction (+X direction).

[0023] At least a portion of the positive electrode foil connection portion 31d and the negative electrode foil connection portion 32d, which are the electrode foil exposed portions of the wound electrode body 3, are bundled in the flat thickness direction to form a flat plate shape, and are respectively joined to the positive electrode side connection end 42A of the positive electrode collector plate (collector terminal) 4A and the negative electrode side connection end 42B of the negative electrode collector plate (collector terminal) 4B by ultrasonic welding.

[0024] The base ends of the positive collector plate 4A and the negative collector plate 4B are connected to the positive external terminal 8A and the negative external terminal 8B, respectively. The cover 6 is provided with a gasket 5 and an insulating plate 7 to electrically insulate the positive collector plate 4A and the negative collector plate 4B and the positive external terminal 8A and the negative external terminal 8B from the cover 6, respectively.

[0025] Aluminum or aluminum alloy is used as a metal material for the battery can 1 and the lid 6. Aluminum or aluminum alloy is used as a material for the positive electrode collector plate 4A and the positive electrode external terminal 8A. Copper or copper alloy is used as a material for the negative electrode collector plate 4B and the negative electrode external terminal 8B.

[0026] The positive external terminal 8A and the negative external terminal 8B have a welded joint portion welded to a bus bar (not shown) etc. The welded joint portion has a rectangular block shape protruding upward from the cover 6, and is arranged so that the lower surface is opposite to the surface of the cover 6 and the upper surface is parallel to the cover 6 at a predetermined height position.

[0027] The positive electrode connection portion 12A and the negative electrode connection portion 12B protrude from the lower surface of the positive electrode external terminal 8A and the negative electrode external terminal 8B, respectively, and the top end has a cylindrical shape that can be inserted into the positive electrode side through hole 6A and the negative electrode side through hole 6B of the cover 6. The positive electrode connection portion 12A and the negative electrode connection portion 12B penetrate the cover 6, protrude further to the inner side of the battery can 1 than the positive electrode collector plate base 41A and the negative electrode collector plate base 41B of the positive electrode collector plate 4A and the negative electrode collector plate 4B, and the top end is riveted, and the positive electrode external terminal 8A and the negative electrode external terminal 8B, the positive electrode collector plate 4A and the negative electrode collector plate 4B are fixed to the cover 6 as a whole.

[0028] A gasket 5 is interposed between the positive electrode external terminal 8A, the negative electrode external terminal 8B, and the lid 6 , and an insulating plate 7 is interposed between the positive electrode current collecting plate 4A, the negative electrode current collecting plate 4B, and the lid 6 .

[0029] The positive collector plate 4A and the negative collector plate 4B include: a rectangular plate-shaped positive collector plate base 41A and a negative collector plate base 41B, which are arranged opposite to the lower surface of the cover 6; and a positive-side connecting end 42A and a negative-side connecting end 42B, which are bent at the side ends of the positive collector plate base 41A and the negative collector plate base 41B, extend along the wide side of the battery can 1 toward the can bottom 22 side, and are connected in a state of being opposite to and overlapping with the positive foil connecting portion 31d and the negative foil connecting portion 32d of the wound electrode body 3.

[0030] The positive electrode current collector plate base portion 41A and the negative electrode current collector plate base portion 41B are respectively formed with a positive electrode side opening hole 43A and a negative electrode side opening hole 43B through which the positive electrode connecting portion 12A and the negative electrode connecting portion 12B are inserted.

[0031] The positive electrode external terminal 8A and the positive electrode collector plate 4A constitute the positive electrode side terminal component, and the negative electrode external terminal 8B and the negative electrode collector plate 4B constitute the negative electrode side terminal component. Furthermore, these positive electrode side terminal component and negative electrode side terminal component are assembled into one body with the cover 6 via the gasket 5 and the insulating plate 7, thereby constituting a cover assembly. Then, by assembling the wound electrode body 3 in the cover assembly, a power generation element assembly is formed (see Figure 4 ).

[0032] The wound electrode body 3 is supported between the positive electrode collector plate 4A and the negative electrode collector plate 4B of the cover assembly, with the winding axis extending parallel to the cover 6 and the flat surface extending in a direction perpendicular to the bottom of the cover 6. A pair of curved surfaces of the wound electrode body 3 are separately arranged on the cover 6 side and the bottom 22 side of the battery can 1.

[0033] The insulating protective film 2 covers the wound electrode body 3 assembled on the cover assembly together with the positive electrode collector plate 4A and the negative electrode collector plate 4B from the outside, and is interposed between the side wall portion 21 and the bottom 22 in the battery can 1 .

[0034] The insulating protective film 2 is made of an insulating synthetic resin material, and insulates the battery can 1 from the wound electrode body 3, the positive electrode collector plate 4A, and the negative electrode collector plate 4B. In addition, the insulating protective film 2 protects the wound electrode body 3, the positive electrode collector plate 4A, and the negative electrode collector plate 4B in a manner that prevents the wound electrode body 3, the positive electrode collector plate 4A, and the negative electrode collector plate 4B from directly contacting the battery can 1 when an impact or vibration is applied to the square secondary battery C1 from the outside. The structure and function of the insulating protective film 2 will be described in detail later.

[0035] The battery can 1 has a size and shape such that when the wound electrode body 3 is inserted into the battery can 1 from the opening 1a in a state where the insulating protective film 2 covers the periphery of the wound electrode body 3, a pair of flat surfaces of the wound electrode body 3 and the wide side wall portion 21a of the side wall portion 21 of the battery can 1 abut with the insulating protective film 2 sandwiched therebetween, and the battery can 1 can be inserted by pressing with a certain pressing force. In addition, a certain gap is formed between the end surfaces on both sides of the winding axis direction of the wound electrode body 3 and the narrow side wall portion 21b of the side wall portion 21 of the battery can 1.

[0036] The opening 1a of the battery can 1 is closed by a cover 6, and the cover 6 is laser welded to the battery can 1 to be sealed. Then, the battery can 1 is filled with an electrolyte. The electrolyte is injected into the battery can 1 from the injection port 9 of the cover 6. After the electrolyte is injected, the injection port 9 is closed by an injection plug 11, and the injection plug 11 is laser welded to the cover 6 to be sealed.

[0037] Figure 3 It is an exploded perspective view showing a state in which a part of the wound electrode body 3 is unfolded.

[0038] The wound electrode body 3 is an electrode body wound into a flat shape by overlapping the positive electrode body 31 and the negative electrode body 32 with the separator 33 in the middle, and the positive electrode mixture layer 31b, the positive electrode foil exposed portion 31c not coated with the negative electrode mixture layer 32b, and the negative electrode foil exposed portion 32c are respectively arranged on the end faces on both sides of the axis C (winding axis) direction of the wound electrode body 3. The outermost electrode body of the wound electrode body 3 is the negative electrode body 32, and the separator 33 is wound on the outside.

[0039] The separator 33 is formed by placing a winding end portion 33a (see Figure 4 ), using the adhesive tape 20a as the diaphragm fixing tape (refer to Figure 4 ) is used to fix the winding end portion 33a, thereby maintaining the winding state. In the wound electrode body 3, two separators 33 are used, and the winding end portions 33a are overlapped and arranged at the same position.

[0040] like Figure 4 As shown, the winding end 33 a of the separator 33 is arranged on one flat surface of the wound electrode body 3 from one curved surface side toward the other curved surface side and is located closer to the other curved surface side than the center position of the wound electrode body 3 .

[0041] The separator 33 has the function of insulating the positive electrode body 31 from the negative electrode body 32. The negative electrode mixture layer 32b of the negative electrode body 32 is formed larger than the positive electrode mixture layer 31b of the positive electrode body 31 in the width direction. In addition, the positive electrode body 31 and the negative electrode body 32 overlap in a manner that the two ends of the positive electrode mixture layer 31b are arranged on the inner side than the two ends of the negative electrode mixture layer 32b, so that the entire surface of the positive electrode mixture layer 31b is always opposite to the negative electrode mixture layer 32b. The separator 33 is a porous polyethylene resin with a thickness of 20 to 30 μm. The thickness of the separator 33 is preferably 0.01 mm to 0.50 mm, and more preferably 0.03 mm to 0.20 mm.

[0042] The positive electrode body 31 is formed by coating positive electrode mixture layers 31b on both sides of a positive electrode foil 31a, and has an uncoated positive electrode foil exposed portion 31c on one side in the width direction of the positive electrode foil 31a. The negative electrode body 32 is formed by coating negative electrode mixture layers 32b on both sides of a negative electrode foil 32a, and has an uncoated negative electrode foil exposed portion 32c on the other side in the width direction of the negative electrode foil 32a. The positive electrode foil exposed portion 31c and the negative electrode foil exposed portion 32c are respectively arranged on opposite sides in the winding axis direction.

[0043] The positive electrode foil 31a is an aluminum alloy foil with a thickness of about 20 to 30 μm, and the negative electrode foil 32a is a copper alloy foil with a thickness of about 15 to 20 μm. The positive electrode active material is a lithium-containing transition metal composite oxide such as lithium manganate, and the negative electrode active material is a carbon material such as graphite that can reversibly absorb and release lithium ions.

[0044] Figure 4 1 is a perspective view of a power generation element assembly. The power generation element assembly is formed by integrating a wound electrode body 3 and a lid 6 .

[0045] The wound electrode body 3 is assembled into a power generation element assembly by joining the positive electrode foil connecting portion 31d and the negative electrode foil connecting portion 32d formed by pre-pressing the positive electrode foil exposed portion 31c and the negative electrode foil exposed portion 32c in the thickness direction to the positive electrode collector plate 4A and the negative electrode collector plate 4B of the cover assembly by ultrasonic welding.

[0046] In the power generation element assembly, the wound electrode body 3 is installed in the following manner: on one flat surface, that is, on the flat surface 3a on the front side shown in the +Z direction in the figure, the winding end portion 33a of the diaphragm 33 is arranged in the battery can 1 in a posture state in which the winding end portion 33a is arranged in the direction from the cover 6 side toward the can bottom 22 side of the battery can 1.

[0047] The winding end 33a of the separator 33 is arranged at a position closer to the bottom of the can than the central position of the wound electrode body 3. The insulating adhesive tape 20a is attached to the flat surface 3a on the surface side of the wound electrode body 3 so as to extend from the lid side to the bottom of the can beyond the winding end 33a of the separator 33. In addition, the flat surface 3b on the opposite side (back side) of the flat surface 3a on the surface side of the wound electrode body 3 is covered by the continuous separator 33.

[0048] For example, when the battery can 1 of the prismatic secondary battery C1 constituting the battery pack swells, the center of the wide side wall portion 21a of the side wall portion 21, which is the most swollen part of the battery can 1, is pressed by the restraint, and is therefore preferably as flat as possible without any unevenness.

[0049] Therefore, by arranging the winding end 33a of the separator 33 at a position closer to the other curved surface than the central position of the wound electrode body 3, it is possible to prevent the unevenness caused by the height difference of the winding end 33a from being formed at the central position of the wide side surface of the side wall portion 21.

[0050] Next, use Figure 5 The structure of the insulating protective film 2 is described in detail, and the same is also referred to in conjunction with this description. Figure 7 .

[0051] Figure 5 is a diagram showing the unfolded insulating protective film 2. Figure 7 The front side is shown when the insulating protective film 2 covers the peripheral surface of the wound electrode body 3. In addition, the insulating protective film 2 is shown below as being composed of an opaque member, but it is not limited to being opaque and may be transparent.

[0052] like Figure 5 As shown, the insulating protection film 2 includes a side cover portion 51 covering the side peripheral surface of the wound electrode body 3 and a bottom cover portion 52 covering the curved surface of the can bottom side of the wound electrode body 3 .

[0053] The side cover 51 is wound around the side circumference of the wound electrode body 3 with the direction perpendicular to the winding axis direction of the wound electrode body 3 as the central axis direction, and covers the positive electrode collector plate 4A, the negative electrode collector plate 4B and the side surface of the wound electrode body 3 from the outside. Alternatively, the side cover 51 is folded along the outer shape of the wound electrode body 3, and covers the side surface of the wound electrode body 3 and the positive electrode collector plate 4A and the negative electrode collector plate 4B from the outside.

[0054] The bottom cover 52 is continuous with the side cover 51 , is wound around the wound electrode body 3 with the direction along the winding axis of the wound electrode body 3 as the central axis direction, and has a curved surface covering the bottom side of the case.

[0055] like Figure 5 As shown, the upper horizontally long rectangular portion of the insulating protection film 2 forms a side cover portion 51 , and the lower portion that is continuous with and protrudes from the side cover portion 51 forms a bottom cover portion 52 .

[0056] The side cover 51 has a strip shape extending at a certain width, and has: a back-facing portion 51a (first flat surface facing portion) facing the flat surface 3b (the other flat surface) on the back side of the wound electrode body 3 over the entire surface; and a pair of front-facing portions 51b and 51c (a pair of second flat surface facing portions) that are continuous and protrude from the back-facing portion 51a in a direction away from each other along the longitudinal direction, and face the flat surface 3a (one flat surface) on the front side of the wound electrode body 3. The back-facing portion 51a and the front-facing portions 51b and 51c are regions facing the pair of wide side wall portions 21a of the battery can 1.

[0057] A pair of end surface facing portions 51d and 51e facing the end surfaces of the wound electrode body 3 are provided between the back surface facing portion 51a and the front surface facing portions 51b and 51c. The end surface facing portions 51d and 51e are regions facing the pair of narrow side walls 21b of the battery can 1.

[0058] A pair of front relative portions 51b, 51c are divided into one side and the other side in the long side direction of the side cover portion 51. When the side cover portion 51 is wound on the side circumferential surface of the wound electrode body 3, the front relative portions 51b, 51c overlap and cover the flat surface 3a on the front side of the wound electrode body 3.

[0059] That is, on the flat surface 3a on the front side of the wound electrode body 3, the side end 51g on one side in the long side direction and the side end 51f on the other side in the long side direction are arranged to overlap each other by a predetermined distance D in the winding axis direction of the wound electrode body 3 (see Figure 7 ),like Figure 7 As shown, an end surface overlap portion 51h is formed between the side end portion 51g and the side end portion 51f. The length of the predetermined distance D is arbitrary, but is required to ensure the length of the through region formed by the notch portion described later.

[0060] Here, notches 51g-1 and 51f-1 of a predetermined shape are formed in the winding axis direction of the wound electrode body 3 at the side end 51g on one side in the longitudinal direction and the side end 51f on the other side in the longitudinal direction. In the present embodiment, the notches are formed in a rectangular shape including the side ends 51g and 51f.

[0061] When viewed from the width direction (short side direction) of the side cover 51, the notches 51g-1 and 51f-1 are formed approximately near the center, preferably in the center, and when the side end 51g and the side end 51f overlap each other, the respective notches 51g-1 and 51f-1 are in a positional relationship of being aligned and overlapping. That is, the notches 51g-1 and 51f-1 are formed near the center of the end face overlapping portion 51h.

[0062] Therefore, when the side end 51g on one side in the long-side direction and the side end 51f on the other side in the long-side direction overlap, the notches 51g-1 and 51f-1 overlap in whole or in part, forming a Figure 7 Therefore, the flat surface 3a on the front side of the wound electrode body 3 is exposed through the mutual notch portions 51g-1 and 51f-1.

[0063] And, if Figure 7As shown, across the end face overlap portion 51h, a pair of front facing portions 51b and 51c are bonded and fixed to each other by a rectangular electrically insulating adhesive tape 20b. Furthermore, the adhesive tape 20b is bonded and fixed to the flat surface 3a on the front side of the wound electrode body 3 exposed from the through region 51k of the notch portions 51g-1 and 51f-1.

[0064] The lengths of the front facing portions 51b and 51c of the side cover portion 51 in the long side direction are different from each other. In the present embodiment, the front facing portion 51c is longer than 51b, and the side end portions 51f and 51g are arranged on the flat surface 3a of the wound electrode body 3, and are located at a position more toward one side of the winding axis direction than the central position of the flat surface 3a.

[0065] In addition, by configuring the side end portions 51f and 51g at offset positions, the adhesive tape 20b for fixing the side end portions 51f and 51g can also be configured at offset positions, thereby preventing the thickness of the wound electrode body 3 from being thickened by overlapping the adhesive tape 20b with the adhesive tape 20a for fixing the winding end portion 33a of the separator 33 near the center position of the wound electrode body 3 in the winding axis direction.

[0066] The bottom cover 52 is continuous with the lower end of the back surface facing portion 51a of the side cover 51 and is protruded in a direction perpendicular to the long side direction of the side cover 51. When wound on the curved surface of the can bottom side of the wound electrode body 3, the bottom cover 52 has a curved surface facing portion 52a facing the curved surface of the can bottom side of the wound electrode body 3, a folded piece portion 52b continuous with the curved surface facing portion 52a and facing the flat surface 3a on the front side of the wound electrode body 3, and a pair of folded wing portions 52c continuous with the curved surface facing portion 52a and facing the end surfaces of the wound electrode body 3, respectively.

[0067] The curved surface facing portion 52a has a length substantially equal to the length in the winding axis direction of the wound electrode body 3 and a width that is bent along the curved surface of the wound electrode body 3 and covers the entire curved surface. The folded-back piece portion 52b is formed to be continuous with and protrude from the curved surface facing portion 52a. A pair of folded wing portions 52c are continuous with both side ends of the bottom cover portion 52 and protrude in directions that are separated from each other, are bent by being inserted into the battery can 1, and are respectively interposed between the end surfaces on both sides of the winding axis direction of the wound electrode body 3 and the narrow side wall portion 21b of the side wall portion 21 of the battery can 1.

[0068] When the bottom cover 52 is wound on the curved surface on the can bottom side of the wound electrode body 3, the folded-back piece 52b overlaps with the front facing parts 51b and 51c, and partially covers the flat surface 3a on the front side of the wound electrode body 3. Furthermore, when inserted into the battery can 1, the top end 52d of the folded-back piece 52b is disposed on the flat surface 3a between the flat surface 3a on the front side of the wound electrode body 3 and the wide surface of the side wall 21 of the battery can 1, and is disposed at a position away from the winding end 33a of the separator 33 by a predetermined distance toward the can bottom side.

[0069] As a fixing member for fixing the wound electrode body exposed in the through-region and the insulating film around the through-region, an example of using a fixing sheet such as an adhesive tape or a sticking tape is recorded. In the present embodiment, the adhesive tapes 20a, 20b, and 20c are adhesives applied on one side of a substrate. For example, the substrate uses paper, cloth, film, etc. The adhesive can use a known adhesive. For example, it is a polymer adhesive. In addition, there can also be an adhesive tape with an adhesive applied on the substrate.

[0070] The insulating protective film 2 is composed of a sheet or film member made of a synthetic resin such as PP (polypropylene). The thickness of the insulating protective film 2 is set to be thicker than the thickness of one diaphragm 33 and thinner than the thickness of three diaphragms. In this embodiment, the thickness of one diaphragm 33 is set to 20 to 30 μm, and the thickness of the insulating protective film 2 is set to about twice that, that is, 50 μm.

[0071] In addition, the case of using PP as the material of the insulating protective film 2 is described as an example, but it is not limited to this. For example, any synthetic resin such as PFA (polytetrafluoroethylene), PPS (polyphenylene sulfide), PET (polyethylene terephthalate) or a material that will not react or deteriorate due to the electrolyte will suffice.

[0072] Next, use Figure 6-7 Describes how to install the insulating protective film.

[0073] First, if Figure 6 As shown, the insulating protective film 2 is arranged relative to the power generation element assembly so that the upper end of the insulating protective film 2 is along the lower surface of the cover 6. Furthermore, the insulating protective film 2 is aligned in the following manner: the back surface facing portion 51a of the side cover portion 51 of the insulating protective film 2 is arranged opposite to the flat surface 3b on the back side of the wound electrode body 3, and the boundary portion between the side cover portion 51 and the bottom cover portion 52 is arranged at the lower end of the flat surface 3b on the back side of the wound electrode body 3.

[0074] Then, if Figure 6As shown by arrows A and B, the two ends of the side cover portion 51 of the insulating protective film 2 are wound in a manner to cover the positive electrode collector plate 4A and the negative electrode collector plate 4B from the outside of the wound electrode body 3. When the insulating protective film 2 is wound around the side cover portion 51 on the side of the wound electrode body 3, the side end portion 51f of the front facing portion 51b and the side end portion 51g of the other front facing portion 51c are arranged to overlap each other in the winding axis direction of the wound electrode body 3, and an end face overlapping portion 51h is formed between the side end portion 51g and the side end portion 51f (see Figure 7 ).

[0075] The width D of the end surface overlap portion 51h (see Figure 7 The length of the notches 51g-1 and 51f-1 is arbitrary, but is determined to ensure the length of the through region 51k formed by the notches 51g-1 and 51f-1. The area of ​​the through region 51k is determined by the width D of the end face repeating portion 51h and the length L of the notches 51f-1 and 51g-1 orthogonal thereto.

[0076] In this way, the area of ​​the through region 51k is determined to be an area that can be bonded and fixed to the flat surface 3a on the front side of the wound electrode body 3 and the insulating protective film 2 by the adhesive tape 20b. If the area of ​​the through region 51k is small, the fixing force of the adhesive tape 20b is insufficient, and the insulating protective film 2 is shifted. In this way, since the side end 51f of the front facing portion 51b on one side and the side end 51g of the front facing portion 51c on the other side are overlapped, the flat surface 3a on the front side of the wound electrode body 3 is not exposed, and the insulation resistance can be improved.

[0077] After the side cover 51 is wound, the bottom cover 52 is wound along the curved surface of the can bottom side of the wound electrode body 3 as shown by arrow C. The curved surface facing portion 52a of the bottom cover 52 is curved along the curved portion of the can bottom side of the wound electrode body 3. The folded-back piece 52b is overlapped and arranged outside the front facing portion 51b on one side and the front facing portion 51c on the other side.

[0078] like Figure 7 As shown, the insulating protective film 2 is wound around the wound electrode body 3 and fixed with an electrically insulating adhesive tape 20b and an adhesive tape 20c. The adhesive tape 20c is attached from the folded-back piece 52b of the bottom cover 52 to the front facing portion 51c.

[0079] The adhesive tape 20b is attached from the side end 51f of one side of the front facing portion 51b to the side end 51g of the other side of the front facing portion 51c, across the end face overlap portion 51h. Furthermore, the adhesive tape 20b is set to a size that covers the entire through region 51k formed by the notch 51f-1 of the side end 51f of the front facing portion 51b and the notch 51g-1 of the side end 51g of the other side of the front facing portion 51c, and is arranged at a position covering the through region 51k, and is adhered and fixed to the flat surface 3a on the front side of the wound electrode body 3.

[0080] Thus, the adhesive tape 20b adheres and fixes the surface of the side end 51f of the front facing portion 51b, the surface of the other side end 51g of the front facing portion 51c, and the surface of the flat surface 3a on the front side of the wound electrode body 3. Figure 7 It can be seen that the area of ​​the adhesive tape 20 b is set sufficiently larger than the area (hatched portion) of the through region 51 k formed in the end surface overlapping portion 51 h of the insulating protection film 2 .

[0081] Thus, since the side end 51f of one side facing portion 51b and the side end 51g of the other side facing portion 51c overlap to form the end face overlapping portion 51h, the flat surface 3a on the front side of the wound electrode body 3 is not exposed, which can improve the insulation resistance.

[0082] In addition, a through area 51k is formed by forming a notch portion 51f-1 on the side end portion 51f on one side of the front relative portion 51b, and a notch portion 51g-1 on the side end portion 51g on the other side of the front relative portion 51c, so that the adhesive tape 20b and the flat surface 3a on the front side of the wound electrode body 3 are bonded and fixed to each other, so that the insulating protective film 2 and the flat surface 3a on the front side of the wound electrode body 3 can be fixed by a simple operation process, thereby improving productivity.

[0083] Furthermore, since the through region 51h where the flat surface 3a on the front side of the wound electrode body 3 is exposed is covered with the adhesive tape 20b having electrical insulation, the insulation resistance of the through region 51h formed to simplify the above-mentioned working steps can be improved.

[0084] The adhesive tapes 20a, 20b, and 20c are arranged at positions separated from each other in the direction along the flat surface 3a of the wound electrode body 3. The adhesive tapes 20b and 20c are preferably arranged at positions offset from the center of the flat surface 3a in the battery height direction or the battery width direction.

[0085] Below, according to Figure 8 A modification example in which the formation positions of the notches 51f-1 and 51g-1 are changed will be described.

[0086] exist Figure 8 In the embodiment, the notch 51f-1 of the side end 51f of the front facing portion 51b and the notch 51g-1 of the side end 51g of the other side facing portion 51c are formed close to the top end 52d of the folded back piece 52b. That is, the notches 51f-1 and 51g-1 are formed close to one side from the center of the end face overlapping portion 51h. Therefore, the through area 51k formed by the notch 51f-1 and the notch 51g-1 is formed at a position close to the top end 52d of the folded back piece 52b, which is an adjacent position here.

[0087] The adhesive tape 20b is bonded from the side end 51f of one side of the front facing portion 51b to the side end 51g of the other side of the front facing portion 51c, across the end face overlapping portion 51h. In addition, the adhesive tape 20b is also attached to the surface of the top end 52d of the folded back piece 52b. Furthermore, the adhesive tape 20b is arranged in a manner to cover the entire through area 51k formed by the notch 51f-1 of the side end 51f of one side of the front facing portion 51b and the notch 51g-1 of the side end 51g of the other side of the front facing portion 51c, and is bonded and fixed to the surface of the flat surface 3a on the front side of the wound electrode body 3.

[0088] In this way, the adhesive tape 20b adheres and fixes the surface of the side end 51f on one side of the front facing portion 51b, the surface of the side end 51g on the other side of the front facing portion 51c, the surface of the top end 52d of the folded-back piece 52b, and the surface of the flat surface 3a on the front side of the wound electrode body 3 to each other.

[0089] Thus, since the side end 51f of one side facing portion 51b and the side end 51g of the other side facing portion 51c overlap to form the end face overlapping portion 51h, the flat surface 3a on the front side of the wound electrode body 3 is not exposed, which can improve the insulation resistance.

[0090] In addition, a through area 51k is formed by a notch portion 51f-1 formed on the side end portion 51f on one side of the front relative portion 51b, and a notch portion 51g-1 formed on the side end portion 51g on the other side of the front relative portion 51c, so that the adhesive tape 20b and the flat surface 3a on the front side of the wound electrode body 3 are bonded and fixed to each other, so that the insulating protective film 2 and the flat surface 3a on the front side of the wound electrode body 3 can be fixed by a simple operation process, thereby improving productivity.

[0091] Furthermore, the through region 51h where the flat surface 3a on the front side of the wound electrode body 3 is exposed is covered by the insulating adhesive tape 20b, so that the insulation resistance of the through region 51h can be improved. In addition, since the adhesive tape 20b is also attached to the surface of the top end portion 52d of the folded-back piece 52b, it is possible to prevent the top end portion 52d of this part from being rolled up.

[0092] exist Figure 8 In the modified example, a through region shown by a dashed square frame may be formed in the region above the end surface overlap portion 51h. This allows the insulating protective film 2 and the flat surface 3a on the front side of the wound electrode body 3 to be more firmly bonded and fixed.

[0093] Next, the shapes of the notch formed on the side end 51f of one side of the front facing portion 51b and the notch formed on the other side end 51g of the front facing portion 51c are described. In addition, since the shapes of the notches formed on the two side ends 51f and 51g are the same, the notch formed on the other side end 51g of the front facing portion 51c is described below.

[0094] FIG. 9 shows an example of notches formed in the end surface portions on both sides of the insulating film 2 .

[0095] Fig. 9A yes Figure 5 The notch 51g-1 of the insulating protective film 2 shown is rectangular in shape. The depth D1 and width L of the notch 51g-1 are arbitrary, but as mentioned above, the through area 51k needs to be determined to a size that can ensure sufficient area for bonding and fixing by the adhesive tape 20b.

[0096] Fig. 9B The notch 51g-2 is formed by a combination of the arc portion 53 and the straight portion 54. The notch 51g-2 is a substantially U-shaped notch formed by the substantially parallel straight portions 54 connected to the end of the arc portion 53.

[0097] In addition, the depth D1 and the width L of the notch 51g-2 are arbitrary, but as described above, the through area 51k needs to be determined to a size that can ensure sufficient bonding and fixing by the adhesive tape 20b. In addition, since there are no corners (edges) compared to a rectangular notch, the mold for forming the notch is less worn, and insufficient cutting of the notch can be improved.

[0098] Fig. 9C51g-3 is a notch formed by an arc portion 53. The depth D1 and width L of the notch 51g-3 are arbitrary, but as described above, the through area 51k needs to be determined to a size that can ensure sufficient area for bonding and fixing by the adhesive tape 20b. In addition, since there is no corner (edge) compared to a rectangular notch, the mold for forming the notch is less worn, which is preferred.

[0099] Fig.9D The notch 51g-4 is a triangular shape. The depth D1 and width L of the notch 51g-4 are arbitrary, but as described above, the through region 51k needs to be determined to a size that can ensure an area that is sufficiently bonded and fixed by the adhesive tape 20b.

[0100] Fig.9E The notch 51g-5 is a trapezoidal shape. The depth D1 and width L of the notch 51g-5 are arbitrary, but as described above, the through region 51k needs to be determined to a size that can ensure an area that is sufficiently bonded and fixed by the adhesive tape 20b.

[0101] The notch portion described above is a notch including the side end portions 51f and 51g, but the notch portion described below is a notch (a form of a through hole) not including the side end portions 51f and 51g.

[0102] Fig.9F The rectangular through hole 51g-6 is used as a notch. The length D1 of the bottom side and the length L of the height of the through hole 51g-6 are arbitrary, but as mentioned above, the through area 51k needs to be determined to a size that can ensure sufficient bonding and fixing by the adhesive tape 20b.

[0103] Figure 9G The circular through hole 51g-7 is used as a notch. The diameter L of the through hole 51g-7 is arbitrary, but as described above, the through region 51k needs to be determined to a size that can ensure an area sufficient for bonding and fixing by the adhesive tape 20b.

[0104] In addition, the shape of the through hole portion is not limited to this, and various shapes such as a triangle shape, a trapezoidal shape, and an elliptical shape may be adopted.

[0105] In addition, the length of the notch, for example, D1, is greater than L. When the width direction (X direction) of the battery C1 is longer than the height direction (Y direction), it is preferable to deal with the situation where the wound electrode body 3 is subjected to stress due to expansion. Alternatively, L is longer than D1. In the case of assembly in which the wound electrode body 3 is inserted into a container, it is preferable to deal with the situation where an external force is applied. As described above, the present invention, for example, has the following configuration.

[0106] (1) A square secondary battery, comprising a wound electrode body and an electrically insulating insulating film wound on the wound electrode body or folded along the outer shape of the wound electrode body to cover the wound electrode body 3, in which the insulating film has at least a portion extending in the circumferential direction of the side circumference of the wound electrode body and covering the side circumference of the wound electrode body, and a bottom portion covering the bottom surface of the wound electrode body 3, an end face repeating portion in which end face portions on both sides of the insulating film overlap is formed on the side circumference of the wound electrode body, and the end face repeating portion has a through region reaching the side circumference of the wound electrode body, and the periphery of the through region of the end face repeating portion and the side circumference of the wound electrode body 3 are fixed by an electrically insulating fixing sheet via the through region.

[0107] This makes it possible to provide a prismatic secondary battery that can improve insulation resistance and that can fix the insulating protective film and the wound electrode body in consideration of productivity.

[0108] (2) In the square secondary battery described in (1), the side circumferential surface of the wound electrode body has at least two flat surfaces facing each other, and the end surface overlap portion is formed on one of the flat surfaces and further formed at a position closer to one side of the flat surface than the other flat surface. Thus, it is possible to prevent the unevenness caused by the height difference of the winding end from being formed at the center of the flat surface, which is the part of the wound electrode body most likely to expand due to charge and discharge.

[0109] (3) In the square secondary battery described in (2), the area of ​​the fixing sheet is set to be sufficiently large relative to the area of ​​the through-region formed on the end face repeating portion of the insulating film. For example, the area of ​​the fixing sheet has an area overlapping with the side circumference that is greater than the area of ​​the through-region. It is preferred to improve the fixation of the insulating film. For example, the area of ​​the fixing sheet has an area overlapping with the side circumference that is less than 10 times the area of ​​the through-region. It is preferred to minimize the fixing sheet arranged between the insulating film and the inner wall of the battery can.

[0110] (4) In the prismatic secondary battery described in (3), the through region is formed by a notch portion formed in the end surface portions on both sides of the insulating film.

[0111] When the insulating protective film overlaps one side end in the longitudinal direction with the other side end in the longitudinal direction, all or part of the notches overlap to form a through region. Therefore, the flat surface of the front side of the wound electrode body is exposed in the through region.

[0112] (5) A square secondary battery, comprising: a flat wound electrode body, in which a positive electrode body and a negative electrode body are wound with a separator sandwiched between them; a battery can with a bottom, which accommodates the wound electrode body; a cover, which seals an opening portion that is opposite to and opens to the bottom of the battery can; and an insulating film, which is interposed between the battery can and the wound electrode body, the insulating film having a side cover portion that is wound on the wound electrode body with a direction perpendicular to the winding axis direction of the wound electrode body as a central axis direction and covers the side circumference of the wound electrode body, the side cover portion having a pair of flat surface opposing portions that are respectively opposite to the flat surface of one side of the wound electrode body, the side ends of each of the pair of flat surface opposing portions forming an end surface repeating portion that overlaps with each other in the winding axis direction of the wound electrode body, and the end surface repeating portion having a through region that reaches the flat surface of one side of the wound electrode body, and the periphery of the end surface repeating portion and the flat surface of one side of the wound electrode body are fixed via the through region by an electrically insulating fixing sheet. This makes it possible to provide a prismatic secondary battery that can improve insulation resistance and that can fix the insulating protective film and the wound electrode body in consideration of productivity.

[0113] (6) In the square secondary battery described in (5), the through-region is formed by a notch formed on each of the side ends of the pair of flat surface opposing portions. When the side end on one side of the long side direction of the insulating protective film overlaps with the side end on the other side of the long side direction, all or part of the notches overlap to form a through-region. Therefore, the flat surface on the front side of the wound electrode body is exposed in the through-region portion.

[0114] (7) In the square secondary battery described in (6), the fixing sheet is fixed from the side end portion of one side to the side end portion of the other side across the end face repeating portion, and further, the fixing sheet is set to a size that covers the entire through area formed by the notch portion of the side end portion of one side and the notch portion of the side end portion of the other side, and is arranged at a position covering the through area and fixed to the surface of the flat surface of one side of the wound electrode body. Thus, a square secondary battery can be provided that can improve insulation resistance and can fix the insulating protective film and the wound electrode body in consideration of productivity.

[0115] (8) In the prismatic secondary battery described in (7), the area of ​​the fixing piece is set to be sufficiently larger than the area of ​​the through region formed in the end surface overlapping portion of the insulating film.

[0116] (9) In the square secondary battery described in (1) or (5), the through-region is formed near the center of the end face repeating portion. For example, the through-region is formed to include a central partition when the width of the wound electrode body in the height direction (Y direction) is divided into three parts. This is preferred in order to cope with external forces in the lateral peripheral direction.

[0117] (10) In the square secondary battery described in (1) or (5), the through-region is formed from the center of the end face repeating portion close to one end side. For example, it is formed on the side close to the terminal. It is preferred when it is presumed that the wound electrode body expands less when it is close to the external terminal side. For example, it is formed on the side away from the external terminal. It is preferred when it is presumed that the wound electrode body expands less when it is close to the external terminal side. In addition, specifically, for example, the through-region is formed to not include the center of the width of the wound electrode body in the height direction (Y direction). Alternatively, the through-region is formed to include the area outside the central partition when the width of the wound electrode body in the height direction (Y direction) is divided into three parts.

[0118] (11) In the square secondary battery described in (4) or (6), the shape of the notch is any one of a rectangular shape, an arc shape, a triangular shape, a trapezoidal shape, a circular shape, and a roughly U-shaped shape composed of roughly parallel straight lines connected to the ends of the arc.

[0119] In addition, the present invention is not limited to the above-mentioned embodiments, and includes various modified examples. The above-mentioned embodiments are described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to all the structures described. In addition, a part of the structure of some embodiments can be replaced with the structure of other embodiments, and the structure of other embodiments can be added to the structure of some embodiments. For the structure of each embodiment, other structures can also be added, deleted, or replaced. Explanation of symbols

[0120] C1…rectangular secondary battery, 1…battery can, 1a…opening, 2…insulating protective film, 3…wound electrode body, 3a…flat surface on the front side, 3a…flat surface on the back side, 4A…positive electrode collector plate, 4B…negative electrode collector plate, 5…gasket, 6…cover, 6A…positive electrode side through hole, 6B…negative electrode side through hole, 7…insulating plate, 8A…positive electrode external terminal, 8B…negative electrode external terminal, …liquid port, 10…gas discharge valve, 11…liquid injection plug, 12A…positive electrode Connecting portion, 12B…negative electrode connecting portion, 20a…adhesive tape, 20b…adhesive tape, 20c…adhesive tape, 21…side wall portion, 22…bottom of tank, 31…positive electrode body, 32…negative electrode body, 33…diaphragm, 51…side cover portion, 51a…flat surface opposite portion, 51b, 51c…front surface opposite portion, 51f, 51g…side end portion, 51f-1, 51g-1…notch portion, 52…bottom cover portion, 52b…folded back sheet portion, 52d…top end portion.

Claims

1. A rectangular secondary battery comprising: a wound electrode body, and an electrically insulating insulating film wound on the wound electrode body or folded along the outer shape of the wound electrode body to cover the wound electrode body, The square secondary battery is characterized in that: The insulating film has at least a side peripheral surface portion extending in the circumferential direction of the side peripheral surface of the wound electrode body and covering the side peripheral surface of the wound electrode body, and a bottom surface portion covering the bottom surface of the wound electrode body. An end face repeating portion in which end face portions on both sides of the insulating film overlap is formed on the side circumferential surface of the wound electrode body, and the end face repeating portion has a through-region reaching the side circumferential surface of the wound electrode body, and the periphery of the through-region of the end face repeating portion and the side circumferential surface of the wound electrode body are fixed via the through-region by an electrically insulating fixing sheet.

2. The square secondary battery according to claim 1, characterized in that: The side circumferential surfaces of the wound electrode body include at least flat surfaces facing each other, The end surface overlapping portion is formed on one of the flat surfaces and is formed at a position closer to one side of the one flat surface than the other flat surface.

3. The square secondary battery according to claim 2, characterized in that: The area of ​​the fixing piece is set to be sufficiently large relative to the area of ​​the through region formed on the end surface overlapping portion of the insulating film.

4. The square secondary battery according to claim 3, characterized in that: The through region is formed by notch portions formed in the end surface portions on both sides of the insulating film.

5. A square secondary battery, comprising: A flat wound electrode body, which is formed by winding a positive electrode body and a negative electrode body with a separator sandwiched between them; a battery can having a bottom, which accommodates the wound electrode body; a cover that seals an opening that faces and opens to the bottom of the battery can; and an insulating film interposed between the battery can and the wound electrode body, The square secondary battery is characterized in that: The insulating film has a side cover portion that is wound around the wound electrode body with a direction perpendicular to the winding axis direction of the wound electrode body as a central axis direction and covers the side peripheral surface of the wound electrode body. The side cover portion has a pair of flat surface opposing portions respectively opposing the flat surface of one side of the wound electrode body, and the side ends of each of the pair of flat surface opposing portions form an end surface repeating portion that overlaps with each other in the winding axis direction of the wound electrode body, and the end surface repeating portion has a through-region that reaches the flat surface of one side of the wound electrode body, and the periphery of the end surface repeating portion and the flat surface of one side of the wound electrode body are fixed via the through-region by an electrically insulating fixing sheet.

6. The square secondary battery according to claim 5, characterized in that: The through region is formed by a notch portion formed at each of the side end portions of the pair of flat surface facing portions.

7. The square secondary battery according to claim 6, characterized in that: The fixing piece is fixed across the end surface overlapping portion from the side end portion on one side to the side end portion on the other side. Furthermore, the fixing sheet is set to a size that covers the entire through-area formed by the notch portion at one side end portion and the notch portion at the other side end portion, and is arranged at a position covering the through-area and fixed to the surface of the flat surface of one side of the wound electrode body.

8. The square secondary battery according to claim 7, characterized in that: The area of ​​the fixing piece is set to be sufficiently large relative to the area of ​​the through region formed on the end surface overlapping portion of the insulating film.

9. The square secondary battery according to claim 1 or 5, characterized in that: The through region is formed near the center of the end surface overlapping portion.

10. The square secondary battery according to claim 1 or 5, characterized in that: The through region is formed from the center of the end surface overlapping portion toward one end side.

11. The square secondary battery according to claim 4 or 6, characterized in that: The shape of the cutout portion is any one of a rectangular shape, an arc shape, a triangular shape, a trapezoidal shape, a circular shape, and a roughly U-shaped shape consisting of roughly parallel straight lines connected to the ends of the arc.

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