Cylindrical non-aqueous electrolyte secondary battery

Abstract

The purpose of the present disclosure is to effectively prevent the short circuit between the electrode group and the positive lead caused by the deviation of the bending position of the positive lead relative to the insulating plate in a cylindrical non-aqueous electrolyte secondary battery. The secondary battery involved in one embodiment of the present disclosure includes an outer can, a sealing body that seals one end of the outer can, an electrode group arranged inside the outer can, and an insulating plate arranged between the sealing body and the electrode group. The electrode group winds the positive electrode and the negative electrode into a spiral shape through a separator. The insulating plate is a circular plate having a lead hole (27) through which the positive lead (16) derived from the electrode group passes and a center hole (29) that passes through the center. The outer edge of the lead hole (27) includes a curved portion arranged along an arc concentric with the outer circumference (26a) of the insulating plate and a straight line portion (28a), (28b) arranged along a chord connecting the two ends of the arc when viewed from above.

Description

Technical Field

[0001] The present disclosure relates to a cylindrical nonaqueous electrolyte secondary battery. Background Art

[0002] Traditionally, cylindrical secondary batteries using positive plates with positive leads have been equipped with an upper insulating plate with a central hole to prevent short circuits caused by contact between the positive lead and the electrode group. This hole, which penetrates the center of the upper insulating plate, allows high-pressure gases generated within the secondary battery to escape through the upper insulating plate and allows electrolyte to be injected into the electrode group. The electrode group is placed inside an outer can, one end of which is sealed with a sealing member.

[0003] Patent Document 1 discloses a cylindrical secondary battery with an upper insulating plate. The battery comprises a central hole, a lead hole for the positive electrode lead, and multiple openings formed in the opposite half of the lead hole. The lead hole has a roughly semicircular arc shape when viewed from above, with two straight lines extending approximately radially at either end of the circumference.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2019 / 054312 Summary of the Invention

[0007] -Problems to be solved by the invention-

[0008] In the structure described in Patent Document 1, the positive lead is sometimes led out from one end of the lead hole in the upper insulating plate in the arc direction to the sealing body side. In this case, if the portion of the positive lead that is led out from the upper insulating plate to the sealing body side is bent toward the upper insulating plate, the conductive portion of the positive lead becomes easily opposed to the electrode group across the other end of the lead hole in the arc direction. Therefore, when manufacturing secondary batteries, secondary batteries that are worried about short circuiting in the future are discharged as defective products based on the bending position of the positive lead relative to the center of the upper insulating plate, thereby increasing the manufacturing cost of the battery. In particular, the larger the size of the lead hole in the arc direction becomes, the more strictly the bending position of the positive lead needs to be managed. However, the size of the lead hole in the arc direction affects the insertability of the positive lead into the lead hole, so it is desirable not to excessively restrict the shape of this size.

[0009] An object of the present disclosure is to provide a cylindrical nonaqueous electrolyte secondary battery that can effectively prevent a short circuit between an electrode group and a positive electrode lead caused by a deviation in the bending position of the positive electrode lead relative to an insulating plate.

[0010] -Methods for solving the problem-

[0011] The cylindrical non-aqueous electrolyte secondary battery disclosed herein comprises: an outer can body; a sealing body that seals one end of the outer can body; an electrode group arranged inside the outer can body; and an insulating plate arranged between the sealing body and the electrode group, wherein the electrode group is a positive electrode and a negative electrode wound into a spiral shape with an isolating member interposed therebetween, and the insulating plate is in the shape of a circular plate having a lead hole through which a positive electrode lead led out of the electrode group passes and a center hole that passes through the center portion, and the outer edge portion of the lead hole includes, when viewed from above: a curved portion arranged along an arc concentric with the outer circumference of the insulating plate; and a straight portion arranged along a chord connecting the two ends of the arc.

[0012] -Effects of the Invention-

[0013] According to the cylindrical nonaqueous electrolyte secondary battery of the present disclosure, a short circuit between the electrode group and the positive electrode lead caused by a deviation in the bending position of the positive electrode lead relative to the insulating plate can be effectively prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery according to an example of the embodiment.

[0015] Figure 2 It is schematically represented Figure 1 FIG. 2 is a diagram of the inner end portion of the electrode group in the winding direction, taken along the AA cross section.

[0016] Figure 3 It will Figure 2 The winding direction of the electrode group shown is a diagram showing the opposing relationship between the positive electrode and the negative electrode, with the inner end portion being developed.

[0017] Figure 4 It is from Figure 3 Schematic diagram observed above.

[0018] Figure 5A yes Figure 1 A top view of the upper insulating plate is shown.

[0019] Figure 5B yes Figure 5A Enlarged view of part B.

[0020] Figure 6 This figure shows the positional relationship between the positive electrode lead and the lead hole when viewing the upper insulating plate from above, when the positive electrode lead is led out from the circumferential center of the lead hole in a cylindrical nonaqueous electrolyte secondary battery of a comparative example.

[0021] Figure 7 The results are similar to those in the case where the positive electrode lead is led out from one circumferential end of the lead hole in the cylindrical nonaqueous electrolyte secondary battery of the comparative example. Figure 6The corresponding figure.

[0022] Figure 8 It is a diagram showing the difference between the lead wire hole shape of the upper insulating plate of the embodiment and the lead wire hole shape of the comparative example.

[0023] Figure 9 In the implementation mode Figure 7 The corresponding figure.

[0024] Figure 10 This is a diagram corresponding to FIG. 5 , showing the upper insulating plate of the cylindrical nonaqueous electrolyte secondary battery of Experimental Example 3.

[0025] Figure 11 This graph compares the shape of the upper insulating plate, the opening ratio relative to the area within the outer circumference of the upper insulating plate, and the crack rate of the battery case in the cylindrical nonaqueous electrolyte secondary batteries according to Experimental Examples 1 to 4.

[0026] Figure 12 In other examples of the implementation mode Figure 1 The corresponding figure.

[0027] Figure 13 In other examples of the implementation mode Figure 7 The corresponding figure. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, specific shapes, materials, numerical values, numbers, directions, etc. are provided for illustrative purposes only to facilitate understanding of the present invention and can be appropriately modified to accommodate the specifications of the non-aqueous electrolyte secondary battery. Furthermore, the term "substantially" will be used to encompass situations that may be considered substantially the same, in addition to situations that are completely identical.

[0029] <Example of Implementation>

[0030] Figure 1 1 is a schematic cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery 10 according to an embodiment. Figure 2 It is schematically represented Figure 1 FIG. 2 is a diagram of the inner end portion of the winding direction of the electrode group 14 in the AA cross section. Figure 1 、 Figure 2 As shown, the cylindrical non-aqueous electrolyte secondary battery 10 includes a wound electrode group 14 and a non-aqueous electrolyte (not shown). Figure 2 As shown, the electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator 13. The positive electrode 11 and the negative electrode 12 are wound in a spiral shape with the separator 13 interposed therebetween. Figure 2In order to easily understand the configuration relationship, the negative electrode 12 is represented by a solid line, the positive electrode 11 is represented by a dotted line, and the separator 13 is represented by a single-dot chain line. Figure 2 In FIG, the gaps between the positive electrode 11, the negative electrode 12, and the separator 13 are exaggerated. Figure 1 , the electrode group 14 is shown as the shape viewed from the outer peripheral side. Hereinafter, one side of the electrode group 14 in the winding axis direction is sometimes referred to as "upper," and the other side in the winding axis direction is sometimes referred to as "lower." The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte and may also be a solid electrolyte using a gel-like polymer or the like. Hereinafter, the cylindrical non-aqueous electrolyte secondary battery 10 is referred to as the secondary battery 10.

[0031] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode group 14 are all formed into a strip shape and are spirally wound so as to be alternately stacked in the radial direction of the electrode group 14. In the electrode group 14, the longitudinal direction of each electrode becomes the winding direction, and the width direction of each electrode becomes the winding axis direction. Figure 1 As shown in the figure, the positive electrode lead 16 electrically connecting the positive electrode 11 to the positive electrode terminal is provided, for example, at approximately the center between the inner end and the outer end of the electrode group 14, and can be connected from the upper end ( Figure 1 Lead out the negative electrode lead 40 ( Figure 3 ) is provided at the winding start side end of the electrode group 14, and the lower end of the negative electrode lead 40 is joined to the bottom of the bottomed cylindrical outer can 20. Figure 1 In the embodiment, the negative electrode 12 is exposed on the outermost surface of the electrode group 14 and is in contact with the inner surface of the outer can 20. Thus, both ends of the negative electrode 12 are connected to the outer can 20, which functions as a negative electrode terminal of the secondary battery 10.

[0032] The positive lead 16 and the negative lead 40 are rectangular strip-shaped conductive members that are thicker than the core of the electrode. The thickness of each lead is, for example, 3 to 30 times the thickness of the core, and is generally 50 μm to 500 μm. The constituent material of each lead is not particularly limited. The positive lead 16 is preferably formed by a metal with aluminum as the main component, and the negative lead is preferably formed by a metal with nickel or copper as the main component, or a metal including both nickel and copper. In addition, the negative electrode 12 may not be exposed on the outermost peripheral surface of the electrode group 14, but the negative lead may be joined to the end of the winding end side of the negative electrode core, and the negative lead may be extended from the lower end (α) of the winding axis direction of the electrode group 14. Figure 1 The negative electrode lead 40 is led out to the bottom of the outer can 20.

[0033] The positive electrode 11 and negative electrode 12 are described in more detail. The positive electrode 11 comprises a strip-shaped positive electrode core and a positive electrode mixture layer formed on the core. For example, the positive electrode mixture layer is formed on both sides of the positive electrode core. The positive electrode core can be made of, for example, a foil of a metal such as aluminum, or a film having the metal disposed on the surface. A preferred positive electrode core is a foil primarily composed of aluminum or an aluminum alloy. The thickness of the positive electrode core is, for example, 10 μm to 30 μm.

[0034] The positive electrode mixture layer is preferably formed on both sides of the positive electrode core, covering the entire area except for the non-textured area where the positive electrode lead is connected. The positive electrode mixture layer preferably includes a positive electrode active material, a conductive agent, and a binder. The positive electrode is manufactured by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both sides of the positive electrode core, followed by drying and rolling.

[0035] Examples of the positive electrode active material include lithium-containing transition metal oxides containing transition metal elements such as Co, Mn, and Ni. The lithium-containing transition metal oxide is not particularly limited, but is preferably a transition metal oxide having the general formula Li 1+x A composite oxide represented by MO2 (wherein, -0.2<x≤0.2, M includes at least one of Ni, Co, Mn, and Al).

[0036] As the example of the above-mentioned conductive agent, carbon materials such as carbon black (CB), acetylene black (AB), Ketjen black, graphite, etc. can be enumerated. As the example of the above-mentioned binder, fluorine-based resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, polyolefin resins, etc. can be enumerated. In addition, these resins and carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), etc. can also be adopted simultaneously. These materials can be used alone or in combination of two or more.

[0037] The negative electrode 12 comprises a strip-shaped negative electrode core and a negative electrode mixture layer formed on the negative electrode core. For example, the negative electrode mixture layer is formed on both sides of the negative electrode core. The negative electrode core can be made of, for example, a metal foil such as copper, or a thin film with the metal disposed on the surface. The thickness of the negative electrode core is, for example, 5 μm to 30 μm.

[0038] The negative electrode mixture layer can be formed on almost the entire surface of both sides of the negative electrode core, excluding the non-textured portion where the negative electrode lead 40 is bonded. The negative electrode mixture layer preferably includes a negative electrode active material and a binder. The negative electrode 12 is manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and water to both sides of the negative electrode core, followed by drying and rolling.

[0039] As the negative electrode active material, there is no particular limitation as long as it is a material that can reversibly absorb and release lithium ions. For example, carbon materials such as natural graphite and artificial graphite, metals such as Si and Sn that are alloyed with lithium, or alloys and composite oxides thereof can be used. The binder included in the negative electrode mixture layer can use, for example, the same resin as that in the case of the positive electrode 11. When an aqueous solvent is used to prepare the negative electrode mixture slurry, styrene-butadiene rubber (SBR), CMC or its salt, polyacrylic acid or its salt, polyvinyl alcohol, etc. can be used. These materials can be used alone or in combination of two or more.

[0040] Figure 3 It will Figure 2 The diagram shows the opposing relationship between the positive electrode 11 and the negative electrode 12 , with the winding direction of the electrode group 14 being developed toward the inner end. Figure 4 It is from Figure 3 The schematic diagram observed above. Figures 2 to 4 As shown, only the positive electrode 11 and the negative electrode 12 are arranged at the winding start portion of the electrode group 14. Specifically, the negative electrode 12 includes the positive electrode 11 and the negative electrode 12 from the winding start end of the electrode group 14, that is, the inner end in the winding direction ( Figure 2 The non-opposing portion 12a is wound for more than 1.25 turns in a state where the separator 13 is not opposed to the positive electrode 11. Figure 2 In the embodiment, the negative electrode 12 includes: a non-opposing portion 12a wound 1.5 times from the inner end E1 in the winding direction; and an opposing portion 12b continuously wound from the non-opposing portion 12a and opposing the positive electrode 11 via the separator 13. The non-opposing portion 12a is Figure 2 The negative electrode 12 shown is a portion extending from the inner end E1 in the winding direction to a point E2 along the winding direction.

[0041] exist Figure 2 In the figure, a straight line passing through E2 is drawn so that the distance from the inner end of the positive electrode 11 in the winding direction to the negative electrode 12 on the inner side of the positive electrode 11 is the shortest. This straight line corresponds to the intersection E2 of the negative electrode 12 and the outer end of the non-opposing portion 12a in the winding direction. In addition, a straight line passing through E1 is drawn so as to be arranged on the extension line of the straight line passing through E2.

[0042] On the other hand, the non-opposing portion 12a includes a negative electrode mixture layer forming portion 12c and a negative electrode core exposed portion 12d. The negative electrode mixture layer forming portion 12c is formed from the outer end ( Figure 2 The negative electrode core exposed portion 12d is formed from the inner end of the non-opposing portion 12a in the winding direction ( Figure 2 The portion of the negative electrode mixture layer which is continuous from point E1) to the outside in the winding direction and not formed on both sides. Figure 2In FIG. 1 , the negative electrode core exposed portion 12d is indicated by a thin solid line, and the negative electrode mixture layer formed portion 12c is indicated by a thick solid line. The negative electrode mixture layer formed portion 12c is wound more than 0.75 turns. Figure 2 The example in FIG. 1 shows a case where the negative electrode mixture layer forming portion 12c is wound 0.8 turns. As described below, this structure can be implemented at low cost to ensure an exhaust path for the winding core of the electrode group 14 in the event of fire in the secondary battery 10.

[0043] Furthermore, the secondary battery 10 comprises a battery case 18 for housing the electrode group 14 and the non-aqueous electrolyte, which is formed by an outer can 20 and a sealing body 22, which are metal containers with a bottom. The sealing body 22 seals the open end of the outer can 20. A gasket 24 is provided between the outer can 20 and the sealing body 22 to ensure the airtightness of the battery case 18. The outer can 20 has, for example, an extension 21 formed by pressing the side surface from the outside to support the sealing body 22. The extension 21 is preferably formed in an annular shape along the circumferential direction of the outer can 20, and supports the sealing body 22 with its upper surface.

[0044] exist Figure 1 In the figure, the sealing body 22 is schematically represented by a circular plate with a rectangular cross section. On the other hand, the sealing body 22 is actually a structure with an internal pressure-operated safety valve. For example, the sealing body 22 is composed of a filter, a lower valve body, an insulating member, an upper valve body and a gap that are stacked in sequence from the electrode group 14 side. The components that constitute the sealing body 22 have, for example, a circular plate shape or a ring shape, and the components except the insulating member are electrically connected to each other. The lower valve body and the upper valve body are connected to each other at their respective central parts, and an insulating member is sandwiched between their respective peripheral parts. If the internal pressure of the battery rises due to abnormal heat and reaches a given first pressure, for example, the lower valve body breaks, and the upper valve body expands toward the gap side and leaves the lower valve body, thereby cutting off the electrical connection between the two. Furthermore, if the internal pressure rises to a given second pressure, the upper valve body breaks, and the gas generated inside is released through the opening formed in the gap. The upper valve body and the lower valve body form an exhaust valve.

[0045] An upper insulating plate 26 is disposed between the sealing member 22 and the electrode group 14. Figure 1 In the figure, the upper insulating plate 26 is shown as being separated from the electrode group 14. In reality, the upper insulating plate 26 is arranged in contact with the upper end of the electrode group 14. The positive electrode lead 16 is a conductive member for electrically connecting the positive electrode core to the positive electrode terminal. It extends from the upper end of the electrode group 14 to one side in the winding axis direction α of the electrode group 14 ( Figure 1 One end of the positive lead 16 is connected to a portion of the positive electrode core body that is approximately in the center of the electrode group 14 in the radial direction β. Figure 1The upper end of the sealing member 22 is bonded to the center of the lower surface of the sealing member 22. In this state, the positive lead 16 passes through a lead hole 27, described later, in the upper insulating plate 26 and extends toward the sealing member 22. In the secondary battery 10, the top plate of the sealing member 22 or the gap at the upper end serves as the positive electrode terminal.

[0046] When forming the secondary battery 10, the positive electrode lead 16 extending from the electrode group 14 is arranged to overlap the sealing body 22. The positive electrode lead 16 is welded to the sealing body 22 by laser welding or the like. An insulating tape is applied to the portion of the positive electrode lead 16 extending from the electrode group 14 on the electrode group 14 side. Figure 1 The oblique grid portion of the positive lead 16 indicates the portion where the insulating tape is attached. Figure 1 The non-textured portion becomes the exposed portion of the conductive portion exposed from the insulating tape.

[0047] After the positive lead 16 is connected to the sealing body 22 as described above, the sealing body 22 is attached to the open end of the outer can 20. At this point, the positive lead 16 is bent toward the upper insulating plate 26 at a position adjacent to the lead hole 27, forming a first bent portion 16a. Furthermore, the positive lead 16 is folded back at a position opposite the first bent portion 16a with respect to the central axis O of the secondary battery 10, which is perpendicular to the sealing body 22, to form a second bent portion 16b. Insulating tape is preferably applied to the positive lead 16 from the electrode group 14 side toward the sealing body 22 side, but not exceeding the inflection point of the second bent portion 16b, to prevent obstruction of welding between the sealing body 22 and the positive lead 16. Furthermore, the insulating tape may be applied not only to the portion of the positive lead 16 extending from the electrode group 14 but also to a portion of the portion disposed within the electrode group 14, or only to the surface facing the upper insulating plate 26. Alternatively, the insulating tape may be attached to the positive electrode lead 16 so as to be spirally wound. Figure 1 The oblique lattice part.

[0048] During a crush test or other tests, the secondary battery 10 may deform and become compressed in the direction of its central axis O. The central axis O of the secondary battery 10 coincides with the winding axis α of the electrode group 14. In this case, as described later, if the upper insulating plate 26 includes a lead hole 27 through which the positive lead 16 passes, the shape of the lead hole 27 may cause the portion of the positive lead 16 exposed from the insulating tape to contact the electrode group 14 after passing through the lead hole 27, resulting in a short circuit. In this embodiment, to effectively prevent this short circuit, the shape of the lead hole 27 is restricted, as described later.

[0049] Furthermore, a lower insulating plate (not shown) is disposed inside the outer can 20 between the lower end of the electrode group 14 and the bottom of the outer can 20. A through hole is formed in the center of the lower insulating plate. A negative lead 40 ( Figure 3 ) passes through the through hole of the lower insulating plate or the outer peripheral side of the lower insulating plate and is led out to the lower side of the lower insulating plate, and is joined to the bottom of the outer can body 20 by welding.

[0050] use Figure 5A 、 Figure 5B The upper insulating plate 26 will be described in detail. Figure 5A It is a top view of the upper insulating plate 26 . Figure 5B yes Figure 5A Enlarged view of part B. Upper insulating plate 26 is a thin, circular plate. Upper insulating plate 26 is formed from an insulating material such as a polyolefin resin. Polyolefin resins are preferred for reducing manufacturing costs. For example, polypropylene resin can be used as the polyolefin resin.

[0051] The upper insulating plate 26 is used to prevent short circuits between the electrode group 14 and the positive lead 16 and the like led out from the electrode group 14. Therefore, the upper insulating plate 26 preferably covers almost the entire upper end of the electrode group 14. Figure 1 ) or the insertability of the outer can body 20 during assembly, the outer diameter d1 of the upper insulating plate 26 ( Figure 5A For example, the outer diameter d1 of the upper insulating plate 26 is preferably 98% to 100% of the inner diameter d2 of the outer can 20, and more preferably 98% to 99.8%.

[0052] A center hole 29 is formed in the center of the upper insulating plate 26. The center hole 29 is a generally rectangular shape with each corner rounded to an arc shape, but it can also be a circle, an oblong, or other polygonal shape. The maximum width of the center hole 29 is preferably greater than the width W ( Figure 9 ) is small so that the positive electrode lead 16 does not pass through the central hole 29 and contact the electrode group 14 to cause a short circuit.

[0053] A columnar space (not shown) is formed inside the innermost circumference of the electrode group 14, which includes the center portion of the winding axis. This space extends along the winding axis direction α. ​​The center hole 29 preferably faces this columnar space when viewed from the center axis O of the secondary battery 10, rather than facing the electrode group 14. In this case, even if a portion of the positive lead 16 is exposed from the insulating tape directly above the center hole 29, the positive lead 16 will not pass through the center hole 29 and contact the electrode group 14, effectively preventing a short circuit between the electrode group 14 and the positive lead 16.

[0054] On one side half of the upper insulating plate 26 ( Figure 5A A substantially semicircular arc-shaped lead hole 27 is formed in the lower half of the secondary battery 10, avoiding the center hole 29. In order to improve the exhaust performance when gas is generated inside the secondary battery 10, the center hole 29 and the lead hole 27 are preferably enlarged.

[0055] like Figure 5A As shown, the outer edge of lead hole 27 is defined by an arc concentric with the outer circumference 26a of upper insulating plate 26 and a chord connecting its ends. The outer edge of lead hole 27 includes an outer curved portion 27a, an inner curved portion 27b, and straight portions 28a and 28b. When viewed from above, outer curved portion 27a is arranged along the reference arc, while straight portions 28a and 28b are arranged along the chord connecting the ends of the reference arc. Outer curved portion 27a may also coincide with the reference arc. In this case, straight portions 28a and 28b directly connect the ends of outer curved portion 27a. The reference arc is preferably a smaller arc than a semicircle. Inner curved portion 27b is arranged to avoid center hole 29. Inner curved portion 27b is also preferably arranged along an arc concentric with outer circumference 26a of upper insulating plate 26. Depending on the positional relationship between lead hole 27 and center hole 29, inner curved portion 27b may be omitted. In this case, the straight line portions 28a and 28b form a straight line.

[0056] like Figure 5B As shown, when an R-shaped portion 30 is interposed between the outer curved portion 27a and the straight portion 28a, the reference arc can be determined by drawing an extension line La from the first end P1 of the outer curved portion 27a along the reference arc. In this case, the R-shaped portion 30, which serves as the connection between the outer curved portion 27a and the straight portion 28a, preferably has a shape where the connection between the reference arc and the chord is chamfered. The same applies to the R-shaped portion 31 interposed between the straight portions 28a and 28b and the inner curved portion 27b.

[0057] Furthermore, in the upper insulating plate 26, the total area of ​​the center hole 29 and the lead wire holes 27, i.e., the total aperture ratio, relative to the area within the outer circumference 26a of the upper insulating plate 26 (including the inner side of the center hole 29 and the lead wire holes 27), is not particularly limited, but is preferably 11% or greater. If the aperture ratio is less than 11%, the exhaust path for gases generated on the electrode group 14 side of the secondary battery 10 is reduced, resulting in insufficient exhaust performance. The upper limit of the aperture ratio can be appropriately determined based on the strength of the upper insulating plate 26, but can be, for example, 60% or less, preferably 40% or less, and more preferably 20% or less.

[0058] The thickness of the upper insulating plate 26 is, for example, not less than 0.2 mm and not more than 0.5 mm. If the thickness is less than 0.2 mm, the strength of the upper insulating plate 26 is reduced, and there is a risk that the electrode group 14 will fly out toward the sealing body 22 when an impact is applied to the secondary battery 10. If the thickness of the upper insulating plate 26 is greater than 0.5 mm, the battery internal volume becomes smaller, thereby significantly reducing the battery capacity.

[0059] The secondary battery 10 described above can effectively prevent short circuits between the electrode group 14 and the positive lead 16 caused by deviations in the bending position of the positive lead 16 relative to the upper insulating plate 26. To illustrate this effect, a disadvantage of the comparative example will first be described. Figure 6 1 and 2 show the positional relationship between the positive electrode lead 16 and the lead hole 46 when viewing the upper insulating plate 45 from above, when the positive electrode lead 16 is led out from the circumferential center of the lead hole 46 in the secondary battery of the comparative example. Figure 7 This is the case where the positive electrode lead 16 is led out from one circumferential end of the lead hole 46 in the secondary battery of the comparative example. Figure 6 The corresponding figure.

[0060] Figure 6 The upper insulating plate 45 of the comparative example shown has the same planar shape as the upper insulating plate described in Patent Document 1. Specifically, the upper insulating plate 45 has: a center hole 29 formed in the center; Figure 6 The lower half of the semicircular arc-shaped lead hole 46 is formed; and the other half ( Figure 6 The lead hole 46 also has outer peripheral holes 48 at multiple locations along the circumference (the upper half of the upper insulating plate 45). The outer edge of the lead hole 46 also has an outer curved portion 46a arranged along an arc concentric with the outer circumference 45a of the upper insulating plate 45. However, unlike the present embodiment, the straight portions 47a and 47b sandwiched between the outer curved portion 46a and the inner curved portion 46b are arranged not along the chord direction connecting the two ends of the reference arc, but along the radial direction connecting the two ends to the center of the arc.

[0061] When assembling secondary batteries, Figure 6 As shown by the positive electrode lead 16 with a two-dot chain line, the positive electrode lead 16 that passes through the lead hole 46 is preferably bent toward the central axis O of the secondary battery. Figure 6 、 Figure 7 In FIG. 1 , the hatched portion of the positive electrode lead 16 indicates a portion to which the insulating tape is applied, and the unpatterned portion indicates a portion where the conductive portion is exposed from the insulating tape.

[0062] In the above bending, if Figure 6 As shown by the solid line positive lead 16, the positive lead 16 may be bent toward a position offset from the central axis O. In this case, as shown in FIG. Figure 6 As long as the positive lead 16 is led out upward from the circumferential center of the lead hole 46 , the exposed portion of the positive lead 16 opposite the lead-out portion is unlikely to face the lead hole 46 .

[0063] On the other hand, when assembling the secondary battery, according to the relationship between the position where the positive electrode lead 16 is led out from the electrode group and the circumferential position of the upper insulating plate 45, as shown in FIG. Figure 7 As shown in FIG. 1 , the positive electrode lead 16 may also be inserted from one end portion ( Figure 7 In this case, as shown in FIG. Figure 7 As with the positive electrode lead 16 shown in the double-dashed line, as long as it is bent toward the central axis O of the secondary battery, the exposed portion of the positive electrode lead 16 will not pass through the lead hole 46 and face the electrode group. Figure 7 As shown by the solid line of the positive lead 16, the positive lead 16 extends from the central axis O to the other end portion ( Figure 7 When the battery is bent in the direction of the right end (of the battery), the exposed portion of positive lead 16 is likely to face the other circumferential end of lead hole 46. Consequently, if the secondary battery is compressed and deformed in the direction of central axis O, the exposed portion of positive lead 16 may pass through lead hole 46 and contact the electrode group, causing a short circuit. Therefore, during secondary battery manufacturing, defective products that may short-circuit in the future are rejected, increasing battery manufacturing costs.

[0064] To prevent the aforementioned disadvantages of the comparative example, it is conceivable to shorten the overall circumferential length of the lead hole 46. However, in this case, the insertability of the positive electrode lead 16 into the lead hole 46 is likely to be reduced during assembly of the secondary battery. According to the embodiment, the aforementioned disadvantages can be prevented.

[0065] Figure 8 1 is a diagram showing the difference between the shape of the lead wire hole 27 of the upper insulating plate 26 of the embodiment and the shape of the lead wire hole 46 of the comparative example. Figure 8 In the comparative example shown in (a), the straight line portions 47a and 47b are arranged along the radial direction connecting the center of the reference arc from both ends of the reference arc. Figure 8 In the embodiment shown in (b), the straight portions 28a and 28b are arranged along a chord connecting the two ends of the reference arc. Due to this difference, in this embodiment, the ratio of the length of the inner curved portion 27b to the length of the outer curved portion 27a can be reduced compared to the comparative example. This ensures that the positive lead 16 can be inserted into the lead hole 27, while at the same time, the positive lead 16 can be inserted from one end of the lead hole 27 (for example, Figure 8 The positive electrode lead led out of the left end of (b) is difficult to be connected with the other end of the lead hole 27 (for example Figure 8 (b) is opposite to the right end portion of (b).

[0066] Figure 9 In the implementation mode Figure 7 The corresponding figure. Figure 9 As shown, according to the upper insulating plate 26 of the embodiment, the straight portions 28a and 28b connecting the outer curved portion 27a and the inner curved portion 27b of the lead hole 27 are arranged along a chord connecting the two ends of the reference arc of the outer curved portion 27a. Figure 9 Like the positive electrode lead 16 of the solid line, the lead hole 27 is provided at one end in the circumferential direction ( Figure 9 Even when the positive lead 16 (the left end portion of the positive lead 16) is bent toward a position offset from the central axis O of the secondary battery, the lead portion of the positive lead 16 can be prevented from facing the electrode group 14 through the lead hole 27. This effectively prevents a short circuit between the electrode group 14 and the positive lead 16 caused by a deviation in the bent position of the positive lead 16 relative to the upper insulating plate 26.

[0067] Furthermore, in this example, the upper insulating plate 26 has only the lead hole 27 and the center hole 29 as through holes, thereby more effectively preventing the electrode group 14 and the positive electrode lead 16 from passing through the through holes and causing a short circuit.

[0068] Furthermore, if Figures 2-4As shown, in the negative electrode 12, the non-opposing portion 12a that is not opposed to the positive electrode 11 via the separator 13 is wound more than 1.25 times from the inner end of the electrode group 14 in the winding direction. In addition, the negative electrode mixture layer forming portion 12c in the non-opposing portion 12a, which forms the negative electrode mixture layer 12f, is wound more than 0.75 times. Neither the positive electrode 11 nor the double surface of the negative electrode mixture layer forming portion 12c is opposed to each other. Therefore, since the negative electrode mixture layer forming portion 12c and the positive electrode 11 do not react when the secondary battery 10 catches fire, the portion closer to the inner end in the winding direction, including the negative electrode core portion of the negative electrode mixture layer forming portion 12c, remains in the winding core of the electrode group 14 in a cylindrical shape. In addition, the negative electrode mixture layer forming portion 12c is stronger than the portion where only the negative electrode core is exposed on both sides. Therefore, the portion remaining in the cylindrical shape becomes an exhaust passage, which guides the high-pressure gas in the upward and downward directions at the high temperature generated inside the battery during a fire, thereby efficiently exhausting the gas. Therefore, it is possible to suppress the rupture of the secondary battery 10 caused by an excessive increase in the internal pressure of the secondary battery 10. In addition, there is no need to set a metal cylindrical member on the winding core portion of the secondary battery 10 in order to efficiently exhaust gas, thereby suppressing cost increases. As a result, a structure that can ensure an exhaust passage for the winding core portion of the electrode group 14 in the event of a fire in the secondary battery 10 can be achieved at a low cost.

[0069] <Experimental Example>

[0070] The inventors of the present disclosure prepared secondary batteries 10 of Experimental Examples 1 to 4 as follows, and conducted high-temperature overheating tests.

[0071] [Experimental Example 1]

[0072] [Production of positive electrode]

[0073] As the positive electrode active material, LiNi 0.88 Co 0.09 Al 0.03 Then, 100 parts by weight of LiNi 0.88 Co 0.09 Al 0.03O2, 1.0 parts by weight of acetylene black and 0.9 parts by weight of polyvinylidene fluoride (PVDF) (binder) are mixed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) solvent to obtain a positive electrode mixture slurry. The paste-like positive electrode mixture slurry is evenly applied to both sides of a long positive electrode core composed of aluminum foil with a thickness of 15 μm. Next, in a heated dryer, after removing NMP at a temperature of 100 to 150°C, the positive electrode mixture layer is formed by rolling with a roller press, and the rolled positive electrode is contacted with a roller heated to 200°C for 5 seconds, thereby performing a heat treatment. Moreover, the long positive electrode core with the positive electrode mixture layer formed is cut into an electrode size of a given size to produce a positive electrode 11, and then an aluminum positive electrode lead 16 is installed on the positive electrode core. The fabricated positive electrode 11 had a thickness of 0.144 mm, a width of 62.6 mm, and a length of 861 mm.

[0074] [Production of negative electrode]

[0075] As the negative electrode active material, a mixture of 95 parts by weight of graphite powder and 5 parts by weight of silicon oxide was used. Then, the mixed material, 1 part by weight of carboxymethyl cellulose (CMC) as a thickener, and 1 part by weight of styrene-butadiene rubber as a binder were dispersed in water to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to both sides of a negative electrode core composed of a copper foil with a thickness of 8 μm to form a negative electrode coating portion. At this time, the outermost peripheral surface of the electrode group formed the negative electrode core. Then, after the coating was dried in a heated dryer, it was compressed with a compression roller to adjust the thickness of the negative electrode mixture layer so that the thickness of the negative electrode was 160 μm. Moreover, the long strip of negative electrode core with the negative electrode mixture layer formed was cut into an electrode size of a given size to produce a negative electrode 12 with a negative electrode mixture layer formed on both sides, and then a negative electrode lead 40 made of nickel-copper-nickel was installed on the negative electrode core. The negative electrode 12 after fabrication had a width of 64.2 mm and a length of 959 mm.

[0076] [Fabrication of Battery Electrode Group]

[0077] The positive electrode 11 and the negative electrode 12 are wound into a cylindrical shape with a polyethylene separator 13 interposed therebetween, thereby constituting an electrode group 14 .

[0078] [Preparation of non-aqueous electrolyte]

[0079] Ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed in a volume ratio of 1:3, and 5 parts by weight of vinylene carbonate (VC) are added to 100 parts by weight of the mixed solvent to dissolve LiPF6 in the mixed solvent at a concentration of 1.5 mol / L, thereby preparing a non-aqueous electrolyte.

[0080] [Fabrication of upper insulation board]

[0081] The upper insulating plate 26 is made of a circular plate made of polypropylene resin with a thickness of 0.3 mm. Figure 5A As shown, a lead hole 27 and a center hole 29 are formed, through which the positive electrode lead 16 passes. Center hole 29 has a length of 2.2 mm and a width of 3 mm. Furthermore, lead hole 27, through which the positive electrode lead 16 passes, is formed so that the combined opening ratio of center hole 29 and lead hole 27 is 18.3%.

[0082] [Production of Secondary Batteries]

[0083] An upper insulating plate 26 and a lower insulating plate are respectively arranged above and below the above-mentioned electrode group 14, and the electrode group 14 is housed in the outer can 20. The positive lead 16 is passed through the lead hole 27 of the upper insulating plate 26 and led out from the electrode group 14. The negative lead 40 is welded to the outer can 20 of the battery case 18, and the positive lead 16 is welded to the sealing body 22 having an internal pressure-operated safety valve. Then, a non-aqueous electrolyte is injected into the interior of the battery case 18 by decompression. Finally, the sealing body 22 is riveted to the open end of the upper part of the outer can 20 through the gasket 24, thereby producing the secondary battery 10. The capacity of the secondary battery 10 is 4600 mAh. In addition, in the negative electrode 12, the non-opposing portion 12a that is opposed to the positive electrode 11 without the separator 13 is wound 1.75 times. Furthermore, the negative electrode mixture layer formed portion 12 c where the negative electrode mixture layer 12 f is formed in the non-opposing portion 12 a is wound 0.75 turns, and the negative electrode core exposed portion 12 d is wound 1 turn.

[0084] [Experimental Example 2]

[0085] A secondary battery according to Experimental Example 2 was produced in the same manner as in Experimental Example 1, except that a lead hole 27 was formed for the positive electrode lead 16 to pass through, and the total opening ratio of the center hole 29 and the lead hole 27 was 15.4%. The shape of the upper insulating plate 26 of Experimental Example 2 is shown in the following figure. Figure 11 in the column of Experimental Example 2.

[0086] [Experimental Example 3]

[0087] Figure 10 5 , which is a diagram corresponding to FIG. 5 , of the upper insulating plate 26 of the secondary battery of Experimental Example 3. Figure 10 As shown, in the upper insulating plate 26, in addition to the positive electrode lead 16 ( Figure 1 ) through the lead hole 27, and the structure that the total opening ratio of the center hole 29 and the lead hole 27 is 11.7%, the secondary battery involved in Experimental Example 3 was produced in the same manner as Experimental Example 1. Figure 11The column of Experimental Example 3 also shows the shape of the upper insulating plate 26 of Experimental Example 3. Figure 10 As shown, compared to Experimental Examples 1 and 2, lead hole 27 is significantly smaller, and therefore no inner curved portion is formed in lead hole 27 to avoid center hole 29. Specifically, the outer edge of lead hole 27 includes an outer curved portion 27a arranged along an arc concentric with outer circumference 26a of upper insulating plate 26 in a plan view, and straight portions 28c connected to both ends of outer curved portion 27a via rounded portions 30. Straight portion 28c is arranged along a chord connecting the two ends of the reference arc.

[0088] [Experimental Example 4]

[0089] A secondary battery according to Experimental Example 4 was produced in the same manner as in Experimental Example 1, except that a lead hole 27 through which the positive electrode lead 16 passes was formed and the total opening ratio of the center hole 29 and the lead hole 27 was 5.6%. Figure 11 The column of Experimental Example 4 shows the shape of the upper insulating plate 26 of Experimental Example 4. Like the lead-wire holes 27 of Experimental Example 3, the lead-wire holes 27 of Experimental Example 4 also do not have an inner curved portion.

[0090] [Overheat test]

[0091] Ten secondary batteries from each of Experimental Examples 1 to 4 were charged at a constant current of 1380 mA to a voltage of 4.2 V, followed by a constant voltage charge at 4.2 V to a current of 92 mA. Using these charged secondary batteries, an overheat test was conducted to evaluate their gas venting performance. This test simulated the burning environment of the battery module by overheating ten secondary batteries from each of Experimental Examples 1 to 4 using radiant heat in a 300°C furnace, forcing them into thermal breakdown. The cracking rate of the battery cases was then verified.

[0092] [Test results]

[0093] Figure 11 This figure compares the shape of the upper insulating plate 26, the opening ratio relative to the outer circumference of the upper insulating plate 26, and the crack rate of the battery case in the secondary batteries involved in Experimental Examples 1 to 4. Figure 11 As shown, in Experiments 1 to 3, where the combined opening ratio of the lead holes 27 and the center hole 29 relative to the outer circumference of the upper insulating plate 26 was 11% or greater, the battery case rupture rate during the overheat test was reduced to zero. On the other hand, in Experiment 4, where the opening ratio was less than 11%, the battery case ruptured during the overheat test. This confirms that achieving an opening ratio of 11% or greater allows for the rapid discharge of gases generated within the battery, resulting in a safer secondary battery.

[0094] <Other Examples of Implementation>

[0095] Figure 12 In other examples of the implementation mode Figure 1 The corresponding figure. Figure 13 In other examples of the implementation mode Figure 7 In the secondary battery 10a of this embodiment, a plurality of (in the half of the upper insulating plate 26 opposite to the lead hole 27) Figure 13 The outer peripheral holes 32 (four in the example) are arranged in a circumferential direction. Furthermore, the distance from the central axis O of the secondary battery 10a to the second bend 16b of the positive lead 16 (the distance to the portion of the second bend 16b farthest from the central axis O) is L1, and the distance from the central axis O of the secondary battery 10a to the outer peripheral holes 32 (the distance to the portion of the outer peripheral holes 32 closest to the central axis O) is L2. In this case, L1 and L2 are constrained to satisfy L2>L1. Thus, even when the upper insulating plate 26 includes the outer peripheral holes 32 as additional through-holes in addition to the lead holes 27 and the central hole 29, it is possible to prevent the exposed portion of the positive lead 16 from passing through the outer peripheral holes 32 and contacting the electrode group 14, causing a short circuit. Furthermore, since the number of through-holes in the upper insulating plate 26 can be increased, the discharge of internal gas can be improved. In this way, the structure disclosed in the present invention can also form through holes other than the lead hole 27 and the center hole 29 in the upper insulating plate 26. In this example, other structures and functions are the same as Figure 1 ~5, Figure 9 The structure is the same.

[0096] In addition, Figure 12 、 Figure 13 In the structure of the upper insulating plate 26, when other through holes other than the lead hole 27 and the center hole 29 are formed, as long as the maximum width of the other through holes is larger than the width W of the positive lead 16 ( Figure 9 ) is small, the distance L2 from the central axis O of the secondary battery 10 to the other through-holes can be made smaller than the distance L1 from the central axis O of the secondary battery 10 to the second bent portion 16b of the positive electrode lead 16.

[0097] -Explanation of symbols-

[0098] 10, 10a cylindrical non-aqueous electrolyte secondary battery (secondary battery), 11 positive electrode, 12 negative electrode, 12a non-opposing portion, 12b opposing portion, 12c negative electrode mixture layer forming portion, 12d negative electrode core exposed portion, 12f negative electrode mixture layer, 13 separator, 14 electrode group, 16 positive electrode lead, 16a first bent portion, 16b second bent portion, 18 battery casing, 20 outer can body, 21 extending portion, 22 sealing body, 24 gasket, 26 upper insulating plate, 26a outer circumference, 27 lead hole, 27a outer curved portion, 27b inner curved portion, 28a, 28b, 28c straight portion, 29 center hole, 30, 31 R portion, 32 outer peripheral hole, 40 negative electrode lead, 45 upper insulating plate, 46 lead hole, 48 outer peripheral hole.

Claims

1. A cylindrical non-aqueous electrolyte secondary battery, comprising: an outer can; a sealing body that seals one end of the outer can; an electrode group that is disposed inside the outer can; and an insulating plate that is disposed between the sealing body and the electrode group. The electrode group is formed by winding the positive electrode and the negative electrode into a spiral shape with a separator interposed therebetween. The insulating plate is in the shape of a disk having a lead hole through which a positive lead led out from the electrode group passes and a center hole that passes through the center. When the outer edge of the lead hole is viewed from above, include: a curved portion arranged along an arc concentric with the outer circumference of the insulating plate; and a straight line portion arranged along a chord connecting both ends of the arc, The arc is a minor arc smaller than the semicircle, The positive electrode lead is bent toward the insulating plate at a position adjacent to the lead hole to form a first bent portion, The positive electrode lead is folded back at a position on the opposite side of the first bent portion with respect to the central axis of the secondary battery that is orthogonal to the sealing body to form a second bent portion.

2. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, in, The connection portion between the curved portion and the straight portion has a shape in which the connection portion between the arc and the chord is chamfered in a plan view.

3. The cylindrical nonaqueous electrolyte secondary battery according to claim 1 or 2, in, The insulating plate has only the lead hole and the center hole as through holes.

4. The cylindrical nonaqueous electrolyte secondary battery according to claim 3, in, The sealing body is configured to release the generated gas inside when the internal pressure reaches a predetermined pressure. When the center hole is viewed from the winding axis direction of the electrode group, the center hole does not face the electrode group, and the total opening ratio of the lead hole and the center hole is 11% or more relative to the area within the outer circumference of the insulating plate.

5. The cylindrical nonaqueous electrolyte secondary battery according to claim 1 or 2, in, The insulating plate is made of polyolefin resin.

6. The cylindrical nonaqueous electrolyte secondary battery according to claim 1 or 2, in, The insulating plate has a thickness of 0.2 mm or more and 0.5 mm or less.

7. The cylindrical nonaqueous electrolyte secondary battery according to claim 1 or 2, in, The negative electrode includes a non-opposing portion wound 1.25 turns or more from the inner end of the electrode group in the winding direction in a state where the separator is interposed and the positive electrode is not opposed to the positive electrode. The non-opposing portion includes a negative electrode mixture layer forming portion on at least one surface of which a negative electrode mixture layer is formed continuously from an outer end in the winding direction to an inner side in the winding direction. The negative electrode mixture layer forming portion is wound at least 0.75 times.

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