Secondary battery

Abstract

The present disclosure relates to a secondary battery that realizes better joining of a wound electrode body and an electrode terminal. In a cross section of the secondary battery disclosed herein that is orthogonal to a winding axis of the wound electrode body (20), in an inner peripheral region (20i), a first separator (25) and a second separator (26) respectively extend more to an inner side of the wound electrode body (20) than an electrode plate. A portion of one of the separators that constitutes an innermost periphery of the wound electrode body (20) is bent in a first bent portion (20b1), and an inner peripheral side end portion (25e) of the one separator is disposed around the winding axis of the wound electrode body (20) between a joining portion of the electrode plate and the electrode terminal and a first bent apex (P). In addition, a portion of the other of the separators that constitutes the innermost periphery of the wound electrode body (20) is bent in a second bent portion (20b2), and an inner peripheral side end portion (26e) of the other separator is disposed around the winding axis of the wound electrode body (20) between the joining portion and a second bent apex (Q).

Description

Technical Field

[0001] This disclosure relates to secondary batteries. Background Technology

[0002] Japanese Patent No. 4630855 discloses a secondary battery comprising an electrode body as a power generation element, a battery casing housing the electrode body, and electrode terminals connecting the electrode body and the battery casing. The secondary battery disclosed in this publication comprises a wound electrode body formed by overlapping and winding strip-shaped separators, strip-shaped negative electrode plates, and strip-shaped positive electrode plates in the winding axis direction. The wound electrode body is formed in the winding axis direction such that a portion of the electrode plate protrudes outward from the separator. Furthermore, the electrode terminals of the corresponding electrodes are engaged with this protruding portion.

[0003] On the other hand, Japanese Patent Application Publication No. 2008-204781 discloses a method for manufacturing a wound electrode body. In this method, a strip-shaped separator, a strip-shaped negative electrode plate, and a strip-shaped positive electrode plate are first overlapped and wound to form a vortex-shaped electrode body. Next, the vortex-shaped electrode body is extruded to become flat. At this point, it is described that the starting end of the winding of the sheet constituting the wound electrode body is positioned at a predetermined position on the innermost circumference of the electrode body.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 4630855

[0007] Patent Document 2: Japanese Patent Application Publication No. 2008-204781 Summary of the Invention

[0008] However, the inventors considered it desirable to achieve a better connection between the wound electrode body and the electrode terminals.

[0009] The disclosed secondary battery includes: a battery casing with a flat, rectangular prism-shaped receiving space; a wound electrode body housed within the battery casing; and a first electrode terminal and a second electrode terminal connected to the battery casing and the wound electrode body. The wound electrode body comprises a strip-shaped first separator, a strip-shaped first electrode plate, a strip-shaped second separator, and a strip-shaped second electrode plate. The first separator, the first electrode plate, the second separator, and the second electrode plate are aligned in the longitudinal direction and overlap sequentially, wound around a winding axis provided in the width direction of the first electrode plate, and the cross-section orthogonal to the winding axis is shaped to have a rectangular portion and a first and a second curved portion that clamp the rectangular portion, and is housed within the receiving space of the battery casing. A portion of the first electrode plate protrudes from the first and second separators on a first side along the winding axis, and is bundled along a direction orthogonal to the winding axis and engaged with the first electrode terminal. A portion of the second electrode plate is exposed from the first and second separators on the second side along the winding axis, and is bundled along a direction orthogonal to the winding axis to engage with the second electrode terminal.

[0010] In a cross-section orthogonal to the winding axis, in the inner circumferential region of the winding electrode body, the first separator and the second separator extend further inward than the first electrode plate and the second electrode plate, respectively. Furthermore, the innermost circumferential portion of one of the first and second separators is bent in the first bend. The inner circumferential end of this separator is disposed around the winding axis of the winding electrode body between the first joint where the first electrode plate and the first electrode terminal are joined, or the second joint where the second electrode plate and the second electrode terminal are joined, and the first bend apex of the first bend. In addition, the innermost portion of the separator of the first separator and the second separator is bent in the second bend, and the inner peripheral end of the other separator is disposed around the winding shaft of the winding electrode body between the first joint or the second joint and the second bend vertex of the second bend.

[0011] In the secondary battery with the above-described structure, the starting end of the wound electrode body is bent at the first or second bend, and the inner circumferential end of the first or second separator is positioned between the first or second bend apex and the first or second joint. Therefore, even if the inner circumferential end of the first or second separator slightly deviates from a predetermined position, it is not likely to affect the engagement between the electrode terminals and the wound electrode body. In the secondary battery disclosed herein, the engagement between the electrode terminals and the wound electrode body is not easily hindered by the mutual offset of the separators. Attached Figure Description

[0012] Figure 1 This is a partial cross-sectional view of the secondary battery 100.

[0013] Figure 2 yes Figure 1 Section II-II.

[0014] Figure 3 This is a schematic diagram illustrating the structure of the wound electrode body 20.

[0015] Figure 4 This is a schematic diagram of the manufacturing method of the wound electrode.

[0016] Figure 5 It is a schematic diagram of a cross-section orthogonal to the winding axis of the winding electrode body 20.

[0017] Figure 6 This is a schematic diagram of a portion of a cross-section orthogonal to the winding axis of the winding electrode body 220.

[0018] Figure 7 This is a schematic diagram of a portion of a cross-section orthogonal to the winding axis of the winding electrode body 320.

[0019] (Symbol Explanation)

[0020] 10: Battery casing; 12: Casing body; 14: Cover; 20: Winded electrode body; 21: Positive electrode plate; 22: Negative electrode plate; 22a: Negative electrode current collector foil; 25: First separator; 26: Second separator; 30: Positive terminal; 40: Negative terminal; 71: Washer; 72: Insulator; 91: First joint; 92: Second joint; 100: Secondary battery; 220, 320: Winded electrode body. Detailed Implementation

[0021] The following describes one embodiment of the secondary battery disclosed herein. This embodiment is not intended to limit the invention. Unless otherwise specified, the technology disclosed herein is not limited to the embodiment described herein. The accompanying drawings are schematic and do not necessarily reflect the actual product. Furthermore, unless otherwise specified, the designations "A to B," etc., indicating numerical ranges, mean "above A and below B," and also include the meaning of "above A and below B." In addition, in the accompanying drawings described below, the same symbols are used for components and parts that perform the same function, and repeated descriptions are sometimes omitted or simplified. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect actual dimensional relationships.

[0022] In this specification, "secondary battery" refers to a general energy storage device that generates a charging and discharging reaction by the movement of charge carriers between a pair of electrodes (positive and negative electrodes) via an electrolyte. The aforementioned secondary batteries include not only so-called storage batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, but also capacitors such as electric double-layer capacitors. The following describes an embodiment using a lithium-ion secondary battery as the object.

[0023] Implementation Method 1

[0024] <100 Secondary Batteries>

[0025] Figure 1 This is a partial cross-sectional view of a secondary battery 100. Figure 1 The image depicts a state in which the interior is exposed along a wide surface on one side of the roughly rectangular shell body 12. Figure 2 yes Figure 1 Section II-II. Figure 2 The image depicts a narrow section along one side of the roughly rectangular shell body 12, exposing the interior. (Example) Figure 1 , 2 As shown, the secondary battery 100 includes a battery casing 10, a wound electrode body 20, and a positive terminal 30 and a negative terminal 40. Furthermore, the positive terminal 30 is an example of a first electrode terminal in the secondary battery disclosed herein. The negative terminal 40 is an example of a second electrode terminal in the secondary battery disclosed herein.

[0026] <Battery casing 10>

[0027] Battery casing 10 Figure 1 , 2 As shown, the housing body 12 has a generally rectangular, cuboid shape and a side opening, and a cover 14 is mounted on the opening. In this embodiment, from the viewpoint of ensuring lightweight and the required rigidity, the housing body 12 and the cover 14 are respectively formed of aluminum or an aluminum alloy with aluminum as the main component.

[0028] <Shell Body 12>

[0029] Shell body 12 as Figure 1 , 2 As shown, a wound electrode body 20 is housed, and an opening 12h is provided for housing the wound electrode body 20. The housing body 12 has a flat, rectangular receiving space with a side opening. The housing body 12 is as follows... Figure 1 As shown, it has a generally rectangular base 12a, a pair of wide surfaces 12b, and a pair of narrow surfaces 12c. The pair of wide surfaces 12b stand upright in the base 12a from the long side. The pair of narrow surfaces 12c stand upright in the base 12a from the short side. The opening 12h is formed by being surrounded by the long sides of the pair of wide surfaces 12b and the short sides of the pair of narrow surfaces 12c.

[0030] Alternatively, the housing body 12 may also contain an electrolyte (not shown) together with the wound electrode body 20. As the electrolyte, a non-aqueous electrolyte obtained by dissolving a supporting salt in a non-aqueous solvent can be used. Examples of non-aqueous solvents include carbonate-based solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of supporting salts include fluorinated lithium salts such as LiPF6.

[0031] <Cover 14>

[0032] The cover 14 is installed in the opening 12h of the housing body 12. Furthermore, the periphery of the cover 14 engages with the edge of the opening 12h of the housing body 12. This engagement can be achieved, for example, through seamless, continuous welding. This welding can be achieved, for example, through laser welding. The housing body 12 and the cover 14 have sizes corresponding to the number and dimensions of the wound electrode bodies 20.

[0033] Although detailed illustrations are omitted, in this embodiment, the cover 14 is provided with a gas vent valve and a liquid injection port. The gas vent valve is configured to rupture when the internal pressure of the secondary battery 100 reaches a predetermined value, venting the gas inside the secondary battery 100 to the external thin-walled portion. The liquid injection port is a through hole for injecting electrolyte after the cover 14 is joined to the housing body 12. The liquid injection port is sealed, for example, by a sealing component.

[0034] In this embodiment, a positive terminal 30 and a negative terminal 40 are installed on the cover 14. The battery housing 10 and the wound electrode body 20 are connected through the positive terminal 30 and the negative terminal 40.

[0035] <Electrode terminals>

[0036] The positive terminal 30 has an internal terminal 31 and an external terminal 32. The negative terminal 40 has an internal terminal 41 and an external terminal 42. The internal terminals 31 and 41 are mounted to the inside of the cover 14 via an insulator 72. The external terminals 32 and 42 are mounted to the outside of the cover 14 via a washer 71. The internal terminals 31 and 41 extend into the interior of the housing body 12. The front end of the internal terminal 31 of the positive terminal is connected to the unformed portion 21a1 of the positive current collector foil 21a. The front end of the internal terminal 41 of the negative terminal is connected to the unformed portion 22a1 of the negative current collector foil 22a.

[0037] like Figure 1 , 2 As shown, the internal terminal 31 of the positive electrode includes a base 31a and a connecting piece 31b. The base 31a is, for example, a portion disposed along the inner surface of the cover 14, with the insulator 72 in between. The connecting piece 31b is, for example, a portion extending from one end of the base 31a. In this embodiment, the connecting piece 31b extends toward the inside of the housing body 12. Figure 2 As shown, the end of the connecting piece 31b in the extending direction of the connecting piece 31b is joined to the unformed portion 21a1 of the positive electrode. The joining method is not particularly limited; for example, conventional joining methods such as ultrasonic joining, laser welding, or resistance welding can be used. Furthermore, the internal terminal 41 on the negative electrode side is the same as that on the positive electrode side, so its description is omitted here.

[0038] <Wound Electrode Body 20>

[0039] Figure 3 This is a schematic diagram illustrating the structure of the wound electrode body 20. The wound electrode body 20 is a power generation element of the secondary battery 100, and is housed in the casing body 12 covered by an insulating film (not shown) or the like. Figure 1 , 3 As shown, the wound electrode body 20 includes a strip-shaped first separator 25, a strip-shaped positive electrode plate 21, a strip-shaped second separator 26, and a strip-shaped negative electrode plate 22. Furthermore, the positive electrode plate 21 is an example of the first electrode plate in the secondary battery disclosed herein. The negative electrode plate 22 is an example of the second electrode plate in the secondary battery disclosed herein.

[0040] <Positive Plate 21>

[0041] Regarding the positive electrode plate 21, in the positive electrode current collector foil 21a (e.g., aluminum foil) of a predetermined width and thickness, except for the unformed portion 21a1 of a certain width set at one end in the width direction, a positive electrode active material layer 21b containing the positive electrode active material is formed on both sides. In lithium-ion secondary batteries, the positive electrode active material is, for example, a lithium transition metal composite material, a material that can release lithium ions during charging and absorb lithium ions during discharging. Generally, various materials other than lithium transition metal composite materials can be proposed for the positive electrode active material, and there is no particular limitation.

[0042] <Negative Plate 22>

[0043] Regarding the negative electrode plate 22, in the negative electrode current collector foil 22a (e.g., copper foil) of a predetermined width and thickness, except for the unformed portion 22a1 with a certain width set on one edge in the width direction, a negative electrode active material layer 22b containing the negative electrode active material is formed on both sides. In lithium-ion secondary batteries, the negative electrode active material is, for example, a material like natural graphite, that can absorb lithium ions during charging and release the lithium ions absorbed during charging during discharging. Generally, various materials other than natural graphite can be proposed for the negative electrode active material, and there is no particular limitation.

[0044] <Separators 25, 26>

[0045] In the first separator 25 and the second separator 26, for example, porous resin sheets through which an electrolyte with the required heat resistance can pass are used. Various other designs may be proposed for the first separator 25 and the second separator 26, and there is no particular limitation.

[0046] like Figure 1 , 3 As shown, the width of the negative electrode active material layer 22b is, for example, wider than that of the positive electrode active material layer 21b. The widths of the first separator 25 and the second separator 26 are wider than those of the negative electrode active material layer 22b.

[0047] Figure 4 This is a schematic diagram illustrating the manufacturing method of a wound electrode. Figure 4 In, it is shown Figure 3This is an example of a method for manufacturing the wound electrode body 20. In the above-described method for manufacturing the wound electrode body, firstly, two strip-shaped separators 25 and 26, a strip-shaped positive electrode plate 21, and a strip-shaped negative electrode plate 22 are prepared, each wound onto a reel (not shown). The two strip-shaped separators 25 and 26, the strip-shaped positive electrode plate 21, and the strip-shaped negative electrode plate 22 are placed on a winding machine and guided along a predetermined path to a reel S. A first slit Sa and a second slit Sb are formed in the reel S. In this embodiment, the reel S is generally cylindrical, and the first slit Sa and the second slit Sb are positioned 180 degrees apart around the winding axis of the reel S. In the manufacturing of the wound electrode body 20, the front end of the first separator 25 is clamped into one of the first slit Sa and the second slit Sb of the reel S, and the front end of the second separator 26 is clamped into the other. Next, the spool S is slightly wound up, and the front end of the positive electrode plate 21 is inserted between the second separator 26 wound onto the spool S and the first separator 25 wound into the spool S. Then, the front end of the negative electrode plate 22 is inserted between the first separator 25 wound onto the spool S and the second separator 26 wound into the spool S. The spool S is then rotated, thereby winding up two strip-shaped separators 25 and 26, the strip-shaped positive electrode plate 21, and the strip-shaped negative electrode plate 22. The cylindrical electrode body wound onto the spool S is then pulled out from the spool S and flattened from the side, thus becoming a flat shape. This is how a flat electrode is manufactured. Figure 3 The flat, wound electrode body 20 is shown.

[0048] like Figure 1 , 3 As shown, in the wound electrode body 20, the unformed portions 21a1 of the positive electrode current collector foil 21a and the unformed portions 22a1 of the negative electrode current collector foil 22a face opposite sides in the width direction. Furthermore, the first separator 25, the negative electrode plate 22, the second separator 26, and the positive electrode plate 21 are aligned in the length direction and overlap sequentially, and are spirally wound around a winding axis WL set in the width direction of the positive electrode plate 21. The negative electrode active material layer 22b covers the positive electrode active material layer 21b with the first separator 25 and the second separator 26 in between. The negative electrode active material layer 22b is covered by the first separator 25 and the second separator 26. A portion of the positive electrode plate 21 (in this embodiment, the unformed portion 21a1) is located along the first side 201 of the winding axis (…). Figure 1 , 3 The left side of the negative electrode plate 22 is exposed from the first separator 25 and the second separator 26. This exposed portion is bundled and engages with the internal terminal 31, for example, along a direction orthogonal to the winding axis WL (e.g., the stacking direction of the electrode plates and separators). A portion of the negative electrode plate 22 (in this embodiment, the unformed portion 22a1) is located on the second side 202 along the winding axis. Figure 1 , 3The right side of the section is exposed from the first separator 25 and the second separator 26. The exposed portion is bundled, for example, along a direction orthogonal to the winding axis WL and engages with the internal terminal 41.

[0049] Figure 5 This is a schematic diagram of a cross-section orthogonal to the winding axis of the wound electrode body 20. For example... Figure 5 As shown, the wound electrode body 20 is shaped into an elliptical shape with a rectangular portion 20a, a first bent portion 20b1, and a second bent portion 20b2 in a cross-section orthogonal to the winding axis WL. The rectangular portion 20a is, for example, located at the center of the long side in the cross-section orthogonal to the winding axis WL, and is sandwiched between the first bent portion 20b1 and the second bent portion 20b2 from both sides in that direction. In this embodiment, the rectangular portion 20a has a wide surface at both ends in the stacking direction of the electrode plate and the separator. For example, the rectangular portion 20a has a first region R1 and a second region R2. The first region R1 is, for example, a location where an electrode terminal (e.g., a connecting piece 31b of the internal terminal 31 of the positive electrode) is disposed in the connection between the electrode terminal and the wound electrode body 20. The second region R2 is, for example, a location where an electrode terminal (e.g., a connecting piece 31b of the internal terminal 31 of the positive electrode) is joined in the connection between the electrode terminal and the wound electrode body 20. The second region R2 is, for example, the location where the joint 91 described later is formed. The first curved portion 20b1 and the second curved portion 20b2 are, for example, locations respectively disposed at the two ends in the aforementioned long side direction, clamping the rectangular portion 20a. The outer surfaces of the first curved portion 20b1 and the second curved portion 20b2 are, for example, formed by curved surfaces.

[0050] However, in such Figure 4 As shown, immediately after winding, a first separator 25 and a second separator 26 are arranged on the innermost circumference of the cylindrical electrode body, with the aforementioned ends of the separators (winding start ends) contacting the spool S. When the spool S is pulled out from the electrode body, the winding start ends of the first separator 25 and the second separator 26 sometimes shift as the spool S is pulled out. If the aforementioned positional shift of the first separator 25 and the second separator 26 occurs, when engaging the electrode terminals with the wound electrode body 20 manufactured as described above, the shifted portions of the first separator 25 and the second separator 26 sometimes interfere with the engagement portion with the electrode terminals. The inventors believe it is desirable to prevent this phenomenon from occurring.

[0051] In the wound electrode body 20 manufactured according to the above process, as Figure 5As shown, in a cross-section orthogonal to the winding axis WL, the winding start end point E1 on the positive electrode side and the winding start end point E2 on the negative electrode side are disposed in the inner peripheral region 20i of the winding electrode body 20. In the inner peripheral region 20i, the winding start end point E1 on the positive electrode side and the winding start end point E2 on the negative electrode side can be disposed at positions symmetrical to the center point C of the winding electrode body 20. Here, the inner peripheral region 20i refers, for example, to the region closer to the center C than the outermost periphery of the winding electrode body 20. The center C can be the midpoint of the line segment PQ connecting the first bending vertex P of the first bending portion 20b1 and the second bending vertex Q of the second bending portion 20b2.

[0052] like Figure 5 As shown, the positive electrode side winding start end E1 includes the inner peripheral end 25e of the first separator 25 and the inner peripheral end 21e of the positive electrode plate 21. In this embodiment, in the positive electrode side winding start end E1, the first separator 25 extends further inward than the positive electrode plate 21 towards the winding electrode body 20. Furthermore, the negative electrode side winding start end E2 includes the inner peripheral end 26e of the second separator 26 and the inner peripheral end 22e of the negative electrode plate 22. In this embodiment, in the negative electrode side winding start end E2, the second separator 26 extends further inward than the negative electrode plate 22 towards the winding electrode body 20.

[0053] exist Figure 2 In the illustrated embodiment, when the wound electrode body 20 is housed into the battery housing 10, the first bent portion 20b1 is disposed on the cover 14 side. Additionally, as... Figure 1 , 2 As shown in Figure 5, the innermost circumferential portion of the first separator 25 constituting the wound electrode body 20 is bent in the first bend 20b1. The inner circumferential end 25e of the first separator 25 is disposed around the winding shaft WL of the wound electrode body 20 between the first engagement portion 91 of the positive electrode plate 21 and the positive terminal 30 (e.g., the connecting piece 31b of the internal terminal 31) and the first bend vertex P of the first bend 20b1. The inner circumferential end 25e may, for example, be disposed in the rectangular portion 20a. Figure 5 In the embodiment shown, the inner peripheral end portion 25e is located within the first region R1 of the rectangular portion 20a, between the second region R2 and the first curved portion 20b1.

[0054] like Figure 5As shown, a fold-back portion 25a adjacent to the inner peripheral end 25e of the first divider 25 is disposed on the first bend 20b1. The fold-back portion 25a can, for example, be located on the straight line L1 connecting the first bend vertex P and the second bend vertex Q. The fold-back amount of the first divider 25 is defined by the distance D1 from the fold-back portion 25a to the inner peripheral end 25e. The distance D1 can be less than the distance D2 from the fold-back portion 25a to the end 91a on the cover 14 side of the first joint 91. For example, the ratio of distance D1 to distance D2 (D1 / D2) can be set to 0.2 to 0.95.

[0055] In addition, Figure 2 In the embodiment shown, when the wound electrode body 20 is housed into the battery housing 10, the second bent portion 20b2 is disposed on the bottom surface 12a side of the housing body 12. Additionally, as... Figure 1 , 2 As shown in Figure 5, the innermost circumferential portion of the second separator 26 constituting the wound electrode body 20 is bent in the second bend 20b2. The inner circumferential end 26e of the second separator 26 is disposed around the winding shaft WL of the wound electrode body 20 between the first joint 91 and the second bend vertex Q of the second bend 20b2. The inner circumferential end 26e can, for example, be disposed at the end 91b on the bottom surface 12a side of the first joint 91 (see Figure 5). Figure 1 Between the second curved vertex Q and the second curved vertex.

[0056] like Figure 5 As shown, a fold-back portion 26a adjacent to the inner peripheral end 26e of the second divider 26 is disposed on the second curved portion 20b2. The fold-back portion 26a can, for example, be located on a straight line L1. The fold-back amount of the second divider 26 is defined by the distance from the fold-back portion 26a to the inner peripheral end 26e. The fold-back amount of the second divider 26 is not particularly limited, and may be, for example, the same as the aforementioned distance D1.

[0057] As mentioned above, only the positive electrode side has been described, but the same applies to the negative electrode side, so a detailed explanation is omitted here. Furthermore, Figure 1 The symbol 92 in the figure represents the second joint where the negative plate 22 and the negative terminal 40 (e.g., the connecting piece of the internal terminal 41) are joined.

[0058] In the secondary battery 100, the wound electrode body 20 includes a strip-shaped first separator 25, a strip-shaped positive electrode plate 21, a strip-shaped second separator 26, and a strip-shaped negative electrode plate 22. The first separator 25, the positive electrode plate 21, the second separator 26, and the negative electrode plate 22 are aligned in the length direction and overlap sequentially, and are wound around a winding shaft WL set in the width direction of the positive electrode plate 21. The cross-section orthogonal to the winding shaft WL has a rectangular portion 20a and a first bent portion 20b1 and a second bent portion 20b2 that clamp the rectangular portion 20a, and is received in the receiving space of the battery housing 10. A portion of the positive electrode plate 21 protrudes from the first separator 25 and the second separator 26 on a first side 201 along the winding shaft WL, and is bundled along a direction orthogonal to the winding shaft WL and engaged with the positive terminal 30. A portion of the negative electrode plate 22 is exposed from the first separator 25 and the second separator 26 on the second side 202 along the winding axis WL, and is bundled together in a direction orthogonal to the winding axis WL to engage with the negative terminal 40.

[0059] In a cross-section orthogonal to the winding axis WL, in the inner peripheral region 20i of the wound electrode body 20, the first separator 25 and the second separator 26 extend further inward than the positive electrode plate 21 and the negative electrode plate 22, respectively. The innermost portion of the first separator 25 constituting the innermost periphery of the wound electrode body 20 is bent in the first bend 20b1. The inner peripheral end 25e of the first separator 25 is disposed around the winding axis WL of the wound electrode body 20 between the first joint 91 that connects the positive electrode plate 21 and the positive terminal 30 or the second joint 92 that connects the negative electrode plate 22 and the negative terminal 40, and the first bend vertex P of the first bend 20b1. Furthermore, in a cross-section orthogonal to the winding axis WL, the innermost portion of the second separator 26 constituting the winding electrode body 20 is bent in the second bend 20b2, and the inner peripheral end 26e of the second separator 26 is disposed around the winding axis WL of the winding electrode body 20 between the first joint 91 or the second joint 92 and the second bend apex Q of the second bend 20b2.

[0060] In other words, in the secondary battery 100, the starting end of the winding of the electrode body 20 is bent at the first bend 20b1 or the second bend 20b2 and positioned between the first bend vertex P or the second bend vertex Q and the first joint 91 or the second joint 92. Even if the inner circumferential end 25e of the first separator 25 or the inner circumferential end 26e of the second separator 26 is slightly offset from a predetermined position, it is not likely to affect the engagement between the electrode terminals and the winding electrode body 20. Therefore, the engagement between the electrode terminals and the winding electrode body 20 is not easily hindered by the mutual offset of the separators.

[0061] By bending the winding start end of the wound electrode body 20 at either the first bend 20b1 or the second bend 20b2, the inner circumferential portions of the first bend 20b1 and the second bend 20b2 become thicker. Therefore, during the fabrication of the wound electrode body 20, appropriate pressure is applied to the bend, and the bend further becomes an obtuse angle, changing from line contact to surface contact, thus reducing the aforementioned pressure. Therefore, poor pressure resistance can be mitigated. Furthermore, the thickening of the inner circumferential portions of the first bend 20b1 and the second bend 20b2 softens the curvature in the bend, suppressing the peeling of the electrode active material layer. For example, if the peeling of the negative electrode active material layer 22b is suppressed, the deposition of metallic lithium is also suppressed.

[0062] Furthermore, in this embodiment, the inner peripheral end 25e of the first separator 25 is located within the first region R1 of the rectangular portion 20a and is disposed between the second region R2 and the first curved portion 20b1. Even though the inner peripheral end 25e of the first separator 25 is located within the first region R1 of the rectangular portion 20a, it is positioned closer to the first curved portion 20b1 than the second region R2, thus achieving the effect of suppressing the connection obstruction between the electrode terminals and the wound electrode body 20.

[0063] In the above embodiment, the first electrode plate is a positive electrode plate 21 and the second electrode plate is a negative electrode plate 22, but this is not a limitation. Alternatively, the first electrode plate may be a negative electrode plate 22 and the second electrode plate a positive electrode plate 21. In this case, the electrode plate included in the winding start end E1 of the first curved portion 20b1 disposed on the side of the cover 14 within the battery casing 10 becomes the negative electrode plate 22. This structure is preferably suitable for suppressing the peeling of the negative electrode active material layer 22b.

[0064] In addition, in the above embodiment, the inner peripheral end 25e of the first separator 25 is disposed on the side of the first bend 20b1, but it is not limited thereto. Alternatively, the inner peripheral end 26e of the second separator 26 may be disposed on the side of the first bend 20b1, and the inner peripheral end 25e of the first separator 25 may be disposed on the side of the second bend 20b2.

[0065] Implementation Method 2

[0066] In the first embodiment described above, the inner peripheral end portion 25e of the first separator 25 is disposed within the first region R1 of the rectangular portion 20a. However, the placement of the inner peripheral end portion 25e is not limited to this. Figure 6 This is a schematic diagram of a portion of a cross-section orthogonal to the winding axis WL of the wound electrode body 220. The secondary battery according to the second embodiment is the same as the secondary battery 100 according to the first embodiment, except that the wound electrode body 220 is used as a power generation element. Therefore, descriptions that are repeated for the secondary battery 100 are omitted.

[0067] The wound electrode body 220, for example, includes the inner circumferential end 25e of the first separator 25 and the inner circumferential end 21e of the positive electrode plate 21 at the starting end E21 on the positive electrode side. Figure 6 As shown, the inner peripheral end 25e of the first separator 25 is positioned closer to the first curved portion 220b1 than the first region R1 of the rectangular portion 220a. In this embodiment, the inner peripheral end 25e is positioned away from the second region R2 of the rectangular portion 220a, thus achieving a better effect of suppressing the engagement obstruction between the electrode terminals and the wound electrode body 220. Furthermore, regarding the wound electrode body 220, except as described above, the description is the same as that of the wound electrode body 20 in the first embodiment described above. Therefore, the description here is omitted. Additionally, Figure 6 The symbol 220i in the figure represents the inner circumferential region of the wound electrode body 220.

[0068] Third Implementation Method

[0069] Figure 7 This is a schematic diagram of a portion of a cross-section orthogonal to the winding axis WL of the wound electrode body 320. The secondary battery according to the third embodiment is identical to the secondary battery 100 according to the first embodiment, except that the wound electrode body 320 is used as a power generation element. Therefore, descriptions that are repeated for the secondary battery 100 are omitted.

[0070] The wound electrode body 320, for example, includes the inner circumferential end 25e of the first separator 25 and the inner circumferential end 21e of the positive electrode plate 21 at the winding start end E31 on the positive electrode side. Figure 7 As shown, the inner peripheral end 25e of the first separator 25 is disposed in the first bent portion 320b1. In this embodiment, the inner peripheral end 25e is disposed further away from the second region R2 of the rectangular portion 320a, so the effect of suppressing the engagement obstruction between the electrode terminals and the wound electrode body 320 can be better achieved. Furthermore, regarding the wound electrode body 320, except as described above, it is the same as the description of the wound electrode body 20 in the first embodiment described above, so the description here is omitted. Additionally, Figure 7 The symbol 320i in the figure represents the inner circumferential region of the wound electrode body 320.

[0071] The above describes one embodiment of the technology disclosed herein. Furthermore, the above embodiment illustrates an example of a secondary battery applying the technology disclosed herein, and is not intended to limit the scope of the technology disclosed herein.

Claims

1. A secondary battery, comprising: The battery casing has a flat, rectangular prism-shaped storage space; The wound electrode body is housed within the battery casing; and The first electrode terminal and the second electrode terminal are connected to the battery casing and the wound electrode body. The wound electrode body includes a strip-shaped first separator, a strip-shaped first electrode plate, a strip-shaped second separator, and a strip-shaped second electrode plate. The first separator, the first electrode plate, the second separator, and the second electrode plate are aligned and overlapped sequentially in the length direction, and are wound around a winding axis set in the width direction of the first electrode plate. Furthermore, a cross-section orthogonal to the winding axis forms a shape having a rectangular portion and a first and a second curved portion that clamp the rectangular portion, and is thus housed within the receiving space of the battery casing. A portion of the first electrode plate protrudes from the first and second separators on a first side along the winding axis, and is bundled along a direction orthogonal to the winding axis to engage with the first electrode terminal. A portion of the second electrode plate protrudes from the first and second separators on a second side along the winding axis, and is bundled along a direction orthogonal to the winding axis to engage with the second electrode terminal. In a cross-section orthogonal to the winding axis, In the inner circumferential region of the wound electrode body, the first separator and the second separator extend further inward than the first electrode plate and the second electrode plate, respectively, and the innermost circumference of the wound electrode body is formed by the first separator and the second separator. The innermost portion of one of the first and second separators, constituting the innermost circumference of the wound electrode body, is bent in the first bend. The inner circumferential end of this separator is disposed around the winding shaft of the wound electrode body between the first joint where the first electrode plate and the first electrode terminal are joined, or the second joint where the second electrode plate and the second electrode terminal are joined, and the first bend apex of the first bend. The innermost portion of the separator of the first separator and the second separator that forms part of the innermost circumference of the wound electrode body is bent in the second bend, and the inner circumferential end of the other separator is disposed around the winding shaft of the wound electrode body between the first joint or the second joint and the second bend vertex of the second bend.

Images