Cylindrical non-aqueous electrolyte secondary battery

Abstract

The purpose of the present disclosure is to effectively prevent, in a cylindrical non-aqueous electrolyte secondary cell, short-circuiting between an electrode group and a positive electrode lead due to a variation in the position at which the positive electrode lead is folded with respect to an insulating plate. The secondary cell according to an embodiment of the present disclosure includes an exterior can, a sealing body closing one end of the exterior can, an electrode group disposed inside the exterior can, and an insulating plate disposed between the sealing body and the electrode group. In the electrode group, a positive electrode and a negative electrode are wound in a spiral shape with a separator interposed between. The insulating plate is shaped as a disc having a lead hole (27) penetrated by a positive electrode lead (16) drawn out from the electrode group, and a center hole (29) penetrating the center part of the insulating plate. The outer edge of the lead hole (27) includes a curve part positioned along an arc that is concentric with respect to the outer circumference 26a of the insulating plate as seen in plan view, and linear parts (28a, 28b) positioned along a chord linking the two ends of the arc.

Description

[Technical Field]

[0001] The present disclosure relates to a cylindrical non-aqueous electrolyte secondary battery. [Background technology]

[0002] Conventionally, in cylindrical secondary batteries using a positive electrode plate with a positive electrode lead, an upper insulating plate with a central hole is placed on the electrode group to prevent short circuits due to contact between the positive electrode lead and the electrode group. The central hole penetrates the center of the upper insulating plate and is used to discharge high-pressure gas generated inside the secondary battery through the upper insulating plate or to inject electrolyte into the electrode group. The electrode group is placed inside an outer can, and one end of the outer can is closed with a sealing body.

[0003] Patent Document 1 discloses a cylindrical secondary battery having an upper insulating plate, with a central hole, a lead hole through which a positive electrode lead passes, and multiple openings formed in the half opposite the lead hole. The lead hole has a roughly semicircular arc shape in plan view, with two straight lines extending roughly radially at both circumferential ends. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 054312 Summary of the Invention [Problem to be solved by the invention]

[0005] In the configuration described in Patent Document 1, the positive electrode lead may extend from one end of the lead hole in the upper insulating plate in the arc direction toward the sealing body. In this case, if the portion of the positive electrode lead extending from the upper insulating plate toward the sealing body is bent toward the upper insulating plate, the conductive portion of the positive electrode lead will likely face the electrode group via the other end of the lead hole in the arc direction. Therefore, during secondary battery manufacturing, depending on the bending position of the positive electrode lead relative to the center of the upper insulating plate, batteries that are at risk of future short circuits may be rejected as defective, increasing battery manufacturing costs. In particular, the larger the arc direction of the lead hole, the more strict the bending position of the positive electrode lead must be. However, because the arc direction size of the lead hole affects the ease of inserting the positive electrode lead into the lead hole, a shape that does not excessively restrict this size is desired.

[0006] An object of the present disclosure is to provide a cylindrical nonaqueous electrolyte secondary battery that can effectively prevent short circuits between an electrode group and a positive electrode lead caused by variations in the bending position of the positive electrode lead relative to an insulating plate. [Means for solving the problem]

[0007] The cylindrical nonaqueous electrolyte secondary battery according to the present disclosure is a cylindrical nonaqueous electrolyte secondary battery including an outer can, a sealing body that closes one end of the outer can, an electrode group disposed inside the outer can, and an insulating plate that is disposed between the sealing body and the electrode group, in which the electrode group is formed by spirally winding a positive electrode and a negative electrode with a separator interposed therebetween, and the insulating plate is a circular plate having a lead hole through which a positive electrode lead extending from the electrode group passes and a center hole that passes through the center, and in which the outer edge of the lead hole includes, in a plan view, a curved portion that is disposed along an arc that is concentric with the outer circumferential circle of the insulating plate, and a straight portion that is disposed along a chord connecting both ends of the arc. [Effects of the Invention]

[0008] The cylindrical nonaqueous electrolyte secondary battery according to the present disclosure can effectively prevent short circuits between the electrode group and the positive electrode lead caused by variations in the bending position of the positive electrode lead relative to the insulating plate. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery according to an embodiment. [Figure 2] FIG. 2 is a diagram showing a schematic view of a portion of the electrode group near the inner end in the winding direction in the AA cross section of FIG. [Figure 3] FIG. 3 is a diagram showing the facing relationship between the positive electrode and the negative electrode, with the portion of the electrode group shown in FIG. 2 near the inner end in the winding direction developed. [Figure 4] FIG. 4 is a schematic diagram of FIG. 3 as viewed from above. [Figure 5A] FIG. 5A is a plan view of the upper insulating plate shown in FIG. [Figure 5B] FIG. 5B is an enlarged view of part B in FIG. 5A. [Figure 6] FIG. 6 is a diagram showing the positional relationship between the positive electrode lead and the lead hole when the upper insulating plate is viewed from above in a cylindrical nonaqueous electrolyte secondary battery of a comparative example, in a case where the positive electrode lead is led out from the circumferential center position of the lead hole. [Figure 7] FIG. 7 is a view corresponding to FIG. 6 showing a cylindrical nonaqueous electrolyte secondary battery of a comparative example in which the positive electrode lead is led out from one circumferential end of the lead hole. [Figure 8] FIG. 8 is a diagram showing differences between the lead hole shape of the upper insulating plate of the embodiment and the lead hole shape of the comparative example. [Figure 9] FIG. 9 is a diagram corresponding to FIG. 7 in the embodiment. [Figure 10] FIG. 10 is a view corresponding to FIG. 5 of the upper insulating plate of the cylindrical nonaqueous electrolyte secondary battery of Experimental Example 3. In FIG. [Figure 11] FIG. 11 is a diagram comparing the shape of the upper insulating plate, the aperture ratio relative to the area within the outer circumferential circle of the upper insulating plate, and the rupture rate of the battery case in cylindrical nonaqueous electrolyte secondary batteries according to Experimental Examples 1 to 4. [Figure 12] FIG. 12 is a view corresponding to FIG. 1 in another embodiment. [Figure 13] FIG. 13 is a view corresponding to FIG. 7 in another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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 examples for facilitating understanding of the present invention and can be appropriately changed according to the specifications of the nonaqueous electrolyte secondary battery. Furthermore, in the following, the term "substantially" is used to mean, for example, not only the case where something is completely the same, but also the case where something can be considered to be substantially the same.

[0011] <Example of embodiment> FIG. 1 is a schematic cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery 10 according to an embodiment. FIG. 2 is a schematic view of a portion of an electrode group 14 near the inner end in the winding direction, taken along the line AA in FIG. 1 . As shown in FIGS. 1 and 2 , the cylindrical nonaqueous electrolyte secondary battery 10 includes a wound electrode group 14 and a nonaqueous electrolyte (not shown). As shown in FIG. 2 , 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 spirally wound with the separator 13 interposed therebetween. In FIG. 2 , to facilitate understanding of the relative positions, the negative electrode 12 is indicated by a solid line, the positive electrode 11 by a dashed line, and the separator 13 by a dashed line. In FIG. 2 , the gaps between the positive electrode 11, the negative electrode 12, and the separator 13 are exaggerated. In FIG. 1 , the electrode group 14 is shown as viewed from the outer periphery. Hereinafter, one side of the electrode group 14 in the direction of the winding axis may be referred to as the "upper" and the other side of the electrode group 14 in the direction of the winding axis may be referred to as the "lower." The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous electrolyte is not limited to a liquid electrolyte, and may be a solid electrolyte using a gel polymer or the like. Hereinafter, the cylindrical nonaqueous electrolyte secondary battery 10 will be referred to as a secondary battery 10.

[0012] The positive electrodes 11, negative electrodes 12, and separators 13 that make up the electrode group 14 are all formed in strip shapes and spirally wound to form alternate stacks in the radial direction of the electrode group 14. In the electrode group 14, the longitudinal direction of each electrode corresponds to the winding direction, and the width direction of each electrode corresponds to the winding axis direction. As shown in FIG. 1 , a positive electrode lead 16 electrically connecting the positive electrode 11 to a positive electrode terminal is provided, for example, approximately at the center between the inner and outer winding ends of the electrode group 14 and extends from the upper end of the electrode group 14 in the winding axis direction α (upper side in FIG. 1 ). A negative electrode lead 40 ( FIG. 3 ) electrically connecting the negative electrode 12 to a negative electrode terminal is provided, for example, at the winding start end of the electrode group 14, and the lower end of the negative electrode lead 40 is joined to the bottom of a cylindrical outer can 20 with a bottom. In FIG. 1 , the negative electrode 12 is exposed at the outermost peripheral surface of the electrode group 14, and the outermost peripheral surface of this negative electrode 12 is in contact with the inner peripheral surface of the outer can 20. As a result, both ends of the negative electrode 12 are connected to the exterior can 20 which functions as the negative electrode terminal of the secondary battery 10 .

[0013] The positive electrode lead 16 and the negative electrode lead 40 are rectangular, strip-shaped conductive members that are thicker than the electrode core. 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 materials of each lead are not particularly limited. Preferably, the positive electrode lead 16 is made of a metal primarily containing aluminum, and the negative electrode lead is made of a metal primarily containing nickel or copper, or a metal containing both nickel and copper. Alternatively, the negative electrode 12 may not be exposed on the outermost peripheral surface of the electrode group 14, and the negative electrode lead may be joined to the end of the winding termination side of the negative electrode core, and the negative electrode lead may be led out from the lower end of the winding axis direction α of the electrode group 14 (the lower side in FIG. 1) and joined to the bottom of the outer can 20 together with the negative electrode lead 40.

[0014] The positive electrode 11 and the negative electrode 12 will be described in more detail. The positive electrode 11 has a strip-shaped positive electrode core body and a positive electrode mixture layer formed on the core body. For example, the positive electrode mixture layer is formed on both sides of the positive electrode core body. For the positive electrode core body, a metal foil such as aluminum or a film with the metal disposed on the surface layer is used. A preferred positive electrode core body is a metal foil mainly composed of aluminum or an aluminum alloy. The thickness of the positive electrode core body is, for example, 10 μm to 30 μm.

[0015] The positive electrode mixture layer is preferably formed over the entire area excluding the non-coated portion where the positive electrode lead is joined on both sides of the positive electrode core body. The positive electrode mixture layer preferably contains a positive electrode active material, a conductive agent, and a binder. The positive electrode is produced 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 body, followed by drying and rolling.

[0016] 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 composite oxide represented by the general formula Li , , ,

[0017] ,

[0016] , , , , , ,

[0015] ,

[0018] MO2 (where -0.2 < x ≦ 0.2 and M contains at least one of Ni, Co, Mn, and Al).

[0017] Examples of the above-mentioned conductive agent include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. Examples of the above-mentioned binder include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, and polyolefin resins. Further, these resins may be used in combination with carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), etc. These may be used alone or in combination of two or more.

[0018] The negative electrode 12 has 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. For the negative electrode core, a foil of a metal such as copper, or a film with such a metal disposed on the surface layer, is used. The thickness of the negative electrode core is, for example, 5 μm to 30 μm.

[0019] The negative electrode mixture layer can be formed on almost the entire surface of both sides of the negative electrode core, except for the uncoated portion to which the negative electrode lead 40 is bonded. The negative electrode mixture layer preferably contains a negative electrode active material and a binder. The negative electrode 12 is produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, water, etc. to both sides of the negative electrode core, followed by drying and rolling.

[0020] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions. For example, carbon materials such as natural graphite and artificial graphite, metals that alloy with lithium such as Si and Sn, or alloys or composite oxides containing these, can be used. The binder contained in the negative electrode mixture layer is, for example, the same resin as that used in the positive electrode 11. When preparing the negative electrode mixture slurry using an aqueous solvent, styrene-butadiene rubber (SBR), CMC or a salt thereof, polyacrylic acid or a salt thereof, polyvinyl alcohol, etc. can be used. These materials may be used alone or in combination of two or more.

[0021] FIG. 3 is a diagram showing the opposing relationship between the positive electrode 11 and the negative electrode 12 by developing a portion of the electrode group 14 shown in FIG. 2 near the inner end in the winding direction. FIG. 4 is a schematic diagram seen from above in FIG. 3. As shown in FIGS. 2 to 4, of the positive electrode 11 and the negative electrode 12, only the negative electrode 12 is disposed at the winding start portion of the electrode group 14. Specifically, the negative electrode 12 includes a non-facing portion 12a that is wound 1.25 or more times from the inner end in the winding direction (point E1 in FIG. 2), which is the winding start end of the electrode group 14, in a state where it does not face the positive electrode 11 via the separator 13. In FIG. 2, the negative electrode 12 includes a non-facing portion 12a that is wound 1.5 times from the inner end in the winding direction E1, and a facing portion 12b that is wound continuously from the non-facing portion 12a and faces the positive electrode 11 via the separator 13. The non-facing portion 12a is a portion of the negative electrode 12 shown in FIG. 2 that extends from the inner end E1 in the winding direction to a point E2 along the winding direction.

[0022] 2, the line passing through E2 is drawn so as to be the shortest 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, and the intersection E2 between the line and the negative electrode 12 corresponds to the outer end of the non-facing portion 12a in the winding direction. In addition, the line passing through E1 is drawn so as to be positioned on an extension of the line passing through E2.

[0023] On the other hand, the non-facing portion 12a has a negative electrode mixture layer forming portion 12c and a negative electrode substrate exposed portion 12d. The negative electrode mixture layer forming portion 12c is a portion in which a negative electrode mixture layer is formed on at least one surface, continuing from the outer end of the non-facing portion 12a in the winding direction (point E2 in FIG. 2) toward the inside in the winding direction. The negative electrode substrate exposed portion 12d is a portion in which a negative electrode mixture layer is not formed on either surface, continuing from the inner end of the non-facing portion 12a in the winding direction (point E1 in FIG. 2) toward the outside in the winding direction. In FIG. 2, the negative electrode substrate exposed portion 12d is indicated by a thin solid line, and the negative electrode mixture layer forming portion 12c is indicated by a thick solid line. The negative electrode mixture layer forming portion 12c is wound 0.75 turns or more. The example in FIG. 2 shows a case in which the negative electrode mixture layer forming portion 12c is wound 0.8 turns. This makes it possible to realize, at low cost, a structure that can ensure an exhaust passage for the winding core of the electrode group 14 in the event that the secondary battery 10 catches fire, as will be described later.

[0024] Furthermore, the secondary battery 10 includes an outer can 20, which is a cylindrical metal container with a bottom, and a sealing body 22, which constitute a battery case 18 that houses the electrode group 14 and the non-aqueous electrolyte. The sealing body 22 closes the open end of the outer can 20. A gasket 24 is provided between the outer can 20 and the sealing body 22, ensuring airtightness within the battery case 18. The outer can 20 has a protruding portion 21 that supports the sealing body 22 and is formed, for example, by pressing the side surface from the outside. The protruding portion 21 is preferably formed in an annular shape along the circumferential direction of the outer can 20, and supports the sealing body 22 on its upper surface.

[0025] In FIG. 1 , the sealing body 22 is shown as a circular plate with a rectangular cross section. However, in reality, the sealing body 22 has an internal pressure-activated 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 cap, stacked in this order from the electrode group 14 side. Each component of the sealing body 22 has, for example, a circular or ring shape, and all 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 centers, with an insulating member interposed between their respective peripheral edges. When abnormal heat generation causes the internal pressure of the battery to rise and reach a predetermined first pressure, the lower valve body, for example, breaks, causing the upper valve body to swell toward the cap and separate from the lower valve body, thereby cutting off electrical connection between them. When the internal pressure further rises to a predetermined second pressure, the upper valve body breaks, releasing the generated gas through an opening formed in the cap. The upper and lower valve bodies form an exhaust valve.

[0026] An upper insulating plate 26 is disposed between the sealing body 22 and the electrode group 14. While FIG. 1 illustrates the upper insulating plate 26 as being spaced apart from the electrode group 14, in reality, the upper insulating plate 26 is disposed so as to contact the upper end of the electrode group 14. The positive electrode lead 16 is a conductive member for electrically connecting the positive electrode core and a positive electrode terminal, and extends from the upper end of the electrode group 14 to one side of the electrode group 14 in the winding axis direction α (upper side in FIG. 1). One end of the positive electrode lead 16 is joined, for example, to a portion of the positive electrode core that is located approximately in the center of the electrode group 14 in the radial direction β. The other end of the positive electrode lead 16 (upper end in FIG. 1) is joined near the center of the lower surface of the sealing body 22. In this state, the positive electrode lead 16 extends toward the sealing body 22 through a lead hole 27 (described below) in the upper insulating plate 26. In the secondary battery 10, the top plate of the sealing body 22 or a cap located at the upper end serves as the positive electrode terminal.

[0027] When forming the secondary battery 10, the positive electrode lead 16 extending from the electrode group 14 is placed on the sealing body 22. The positive electrode lead 16 is then welded to the sealing body 22 by laser welding or the like. An insulating tape is attached to the portion of the positive electrode lead 16 extending from the electrode group 14, on the electrode group 14 side. In FIG. 1, the diagonal grid portion of the positive electrode lead 16 indicates the portion to which the insulating tape is attached. Therefore, the plain portion of the extending portion of the positive electrode lead 16 in FIG. 1 is the exposed conductive portion that is exposed from the insulating tape.

[0028] After the positive electrode 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 time, the positive electrode lead 16 is bent toward the upper insulating plate 26 at a position adjacent to the lead hole 27 to form a first curved portion 16a. Furthermore, the positive electrode lead 16 is folded back at a position opposite the first curved 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 curved portion 16b. In order not to interfere with welding of the sealing body 22 and the positive electrode lead 16, the insulating tape is preferably attached to the positive electrode lead 16 from the electrode group 14 side toward the sealing body 22 side in an area not exceeding the inflection point of the second curved portion 16b. Note that the insulating tape may be attached not only to the portion of the positive electrode lead 16 extending from the electrode group 14 but also to a portion of the portion disposed inside the electrode group 14, or may be attached only to the surface facing the upper insulating plate 26. Alternatively, the insulating tape may be applied to the positive electrode lead 16 so as to be wound spirally around the diagonal grid portion of FIG.

[0029] The secondary battery 10 may be deformed so as to be compressed in the direction of the central axis O during a crushing test or the like. The direction of the central axis O of the secondary battery 10 coincides with the winding axis direction α of the electrode group 14. In this case, if the upper insulating plate 26 has a lead hole 27 through which the positive electrode lead 16 passes, as described below, depending on the shape of the lead hole 27, the exposed part of the positive electrode lead 16 from the insulating tape may come into contact with the electrode group 14 through the lead hole 27, causing a short circuit. In this embodiment, to effectively prevent this short circuit, the shape of the lead hole 27 is regulated as described below.

[0030] Furthermore, a lower insulating plate (not shown) is disposed inside the exterior can 20 between the lower end of the electrode group 14 and the bottom of the exterior can 20. A through-hole is formed in the center of the lower insulating plate. A negative electrode lead 40 (FIG. 3), one end of which is joined to the negative electrode core, is led out to the lower side of the lower insulating plate through the through-hole in the lower insulating plate or through the outer periphery of the lower insulating plate, and is joined to the bottom of the exterior can 20 by welding.

[0031] The upper insulating plate 26 will be described in detail using Figures 5A and 5B. Figure 5A is a plan view of the upper insulating plate 26. Figure 5B is an enlarged view of part B in Figure 5A. The upper insulating plate 26 is a thin, circular plate. The upper insulating plate 26 is formed from an insulating material such as a polyolefin resin. Polyolefin resins are preferable in terms of reducing manufacturing costs, and polypropylene resins can be used, for example, as the polyolefin resin.

[0032] The upper insulating plate 26 is used to prevent short-circuiting between the electrode group 14 and the positive electrode lead 16 and the like extending from the electrode group 14. For this reason, it is preferable that the upper insulating plate 26 cover almost the entire upper end of the electrode group 14. Therefore, the outer diameter d1 (FIG. 5A) of the upper insulating plate 26 is equal to the inner diameter d2 (FIG. 1) of the outer can 20 before use of the secondary battery 10, or is slightly smaller than the inner diameter d2 in consideration of ease of insertion into the outer can 20 during assembly. 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%.

[0033] A central hole 29 is formed in the center of the upper insulating plate 26. The central hole 29 is generally rectangular with rounded corners, but may also be circular, oval, or another polygonal shape. The maximum width of the central hole 29 is preferably smaller than the width W (FIG. 9) of the positive electrode lead 16 so as to prevent a short circuit caused by the positive electrode lead 16 coming into contact with the electrode group 14 through the central hole 29.

[0034] Electrode group 14 Spool A columnar space (not shown) is formed along the winding axis direction α inside the innermost circumferential surface, which is the center including the center. When viewed from the direction of the central axis O of the secondary battery 10, the central hole 29 preferably faces this columnar space and does not face the electrode group 14. In this case, even if an exposed portion of the positive electrode lead 16 from the insulating tape is present directly above the central hole 29, the positive electrode lead 16 will not come into contact with the electrode group 14 through the central hole 29, and a short circuit between the electrode group 14 and the positive electrode lead 16 can be effectively prevented.

[0035] A lead hole 27 having a substantially semicircular arc shape is formed in one half of the upper insulating plate 26 (the lower half of FIG. 5A ) so as to avoid the center hole 29. It is preferable that the center hole 29 and the lead hole 27 are large in order to improve the exhaust performance when gas is generated inside the secondary battery 10.

[0036] As shown in FIG. 5A , the outer edge of the lead hole 27 is defined based on a circular arc concentric with the outer circumferential circle 26a of the upper insulating plate 26 and a chord connecting both ends of the circular arc. The outer edge of the lead hole 27 includes an outer curved portion 27a, an inner curved portion 27b, and straight portions 28a and 28b. In a plan view, the outer curved portion 27a is disposed along the reference arc, and the straight portions 28a and 28b are disposed along a chord connecting both ends of the reference arc. The outer curved portion 27a may coincide with the reference arc. In this case, the straight portions 28a and 28b are directly connected to both ends of the outer curved portion 27a. The reference arc is preferably a minor arc smaller than a semicircle. The inner curved portion 27b is disposed so as to avoid the center hole 29. The inner curved portion 27b is also preferably disposed along an arc concentric with the outer circumferential circle 26a of the upper insulating plate 26. Depending on the relative positions of the lead hole 27 and the center hole 29, the inner curved portion 27b may be omitted. In this case, the straight line portions 28a and 28b form one straight line.

[0037] 5B, when a rounded portion 30 is interposed between the outer curved portion 27a and the straight portion 28a, the reference arc can be identified 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 rounded portion 30, which connects the outer curved portion 27a and the straight portion 28a, preferably has a chamfered shape at the connection between the reference arc and the chord. The same applies to the rounded portion 31 interposed between the straight portions 28a, 28b and the inner curved portion 27b.

[0038] Furthermore, in the upper insulating plate 26, the total aperture ratio, which is the total area of ​​the central hole 29 and the lead holes 27, relative to the area within the outer circumferential circle 26a of the upper insulating plate 26 (including the inside of the central hole 29 and the lead holes 27) is not particularly limited, but is preferably 11% or more. If the aperture ratio is less than 11%, the exhaust path when gas is generated on the electrode group 14 side of the secondary battery 10 becomes small, resulting in insufficient exhaust performance. The upper limit of the aperture ratio can be determined appropriately depending 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.

[0039] The thickness of the upper insulating plate 26 is, for example, 0.2 mm or more and 0.5 mm or less. If the thickness is less than 0.2 mm, the strength of the upper insulating plate 26 decreases, 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 more than 0.5 mm, the internal volume of the battery will be reduced, resulting in a significant decrease in the capacity of the battery.

[0040] The above-described secondary battery 10 can effectively prevent short circuits between the electrode group 14 and the positive electrode lead 16 due to variations in the bending position of the positive electrode lead 16 relative to the upper insulating plate 26. To explain this effect, we will first explain the disadvantages of the comparative example. FIG. 6 is a diagram showing the positional relationship between the positive electrode lead 16 and the lead hole 46 when the upper insulating plate 45 is viewed from above in a case where the positive electrode lead 16 is led out from the circumferential center position of the lead hole 46 in the secondary battery of the comparative example. FIG. 7 is a diagram corresponding to FIG. 6 in a 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.

[0041] An upper insulating plate 45 of the comparative example shown in FIG. 6 has a planar shape similar to that of the upper insulating plate described in Patent Document 1. Specifically, the upper insulating plate 45 has a central hole 29 formed in the center, a lead hole 46 having a substantially semicircular arc shape formed in one half (the lower half of FIG. 6), and outer peripheral holes 48 formed at multiple positions in the circumferential direction in the other half (the upper half of FIG. 6). The outer edge of the lead hole 46 also has an outer curved portion 46a arranged along an arc concentric with the outer peripheral circle 45a of the upper insulating plate 45. However, unlike the present embodiment, straight line portions 47a, 47b interposed between the outer curved portion 46a and the inner curved portion 46b are arranged along the radial direction connecting the both ends and the center of the arc, rather than along the chord direction connecting the both ends of the reference arc.

[0042] When assembling the secondary battery, it is preferable that the positive electrode lead 16 that passes through the lead hole 46 be bent toward the central axis O of the secondary battery, as shown by the positive electrode lead 16 drawn with a two-dot chain line in Fig. 6. In Figs. 6 and 7, the hatched areas of the positive electrode lead 16 indicate the areas where insulating tape is attached, and the plain areas indicate the exposed conductive areas from the insulating tape.

[0043] During the above bending, there is a possibility that the positive electrode lead 16 may be bent toward a position shifted from the central axis O, as shown by the positive electrode lead 16 drawn with a solid line in Fig. 6. Even in this case, if the positive electrode lead 16 is led out upward from the circumferential center position of the lead hole 46 as shown in Fig. 6, the exposed portion of the positive electrode lead 16 on the opposite side to the lead-out portion is unlikely to face the lead hole 46.

[0044] On the other hand, during assembly of the secondary battery, depending on the relationship between the lead-out position of the positive electrode lead 16 from the electrode assembly and the circumferential position of the upper insulating plate 45, as shown in FIG. 7, the positive electrode lead 16 may be led out upward from one circumferential end of the lead hole 46 (the left end in FIG. 7). In this case, if the positive electrode lead 16 is bent toward the central axis O of the secondary battery as shown by the positive electrode lead 16 indicated by the two-dot chain line in FIG. 7, the exposed portion of the positive electrode lead 16 will not face the electrode assembly through the lead hole 46. On the other hand, as shown by the positive electrode lead 16 indicated by the solid line in FIG. 7, if the positive electrode lead 16 is bent in a direction from the central axis O toward the other circumferential end of the lead hole 46 (the right end in FIG. 7), the exposed portion of the positive electrode lead 16 is likely to face the other circumferential end of the lead hole 46. As a result, if the secondary battery is deformed so as to be compressed in the direction of the central axis O, the exposed portion of the positive electrode lead 16 may come into contact with the electrode assembly through the lead hole 46, resulting in a short circuit. Therefore, during the production of secondary batteries, defective products that may cause short circuits in the future are discarded, which increases the production costs of the batteries.

[0045] In order to prevent such a problem in the comparative example, it is conceivable to shorten the circumferential length of the lead hole 46 overall, but in that case, the ease of inserting the positive electrode lead 16 into the lead hole 46 during assembly of the secondary battery is likely to decrease. According to the embodiment, such a problem can be prevented.

[0046] FIG. 8 illustrates differences between the shape of the lead hole 27 in the upper insulating plate 26 of the embodiment and the shape of the lead hole 46 of the comparative example. In the comparative example shown in FIG. 8( a), the straight line portions 47a and 47b are arranged along the radial direction connecting both ends of the reference arc to the center of the arc, whereas in the embodiment shown in FIG. 8( b), the straight line portions 28a and 28b are arranged along the chord connecting both ends of the reference arc. Due to this difference, the ratio of the length of the inner curved portion 27b to the length of the outer curved portion 27a can be made smaller in the embodiment than in the comparative example. This ensures ease of insertion of the positive electrode lead 16 into the lead hole 27, while making it less likely that the positive electrode lead extending from one end of the lead hole 27 (e.g., the left end in FIG. 8( b)) will face the other end of the lead hole 27 (e.g., the right end in FIG. 8( b)).

[0047] 9 is a diagram corresponding to FIG. 7 in an embodiment. As shown in FIG. 9, according to the upper insulating plate 26 of the embodiment, the linear portions 28a, 28b connecting the outer curved portion 27a and the inner curved portion 27b of the lead hole 27 are arranged along a chord connecting both ends of the reference arc of the outer curved portion 27a. As a result, even when the positive electrode lead 16 extending from one circumferential end of the lead hole 27 (the left end in FIG. 9) is bent toward a position shifted from the central axis O of the secondary battery, as shown by the solid line in FIG. 9, the extending portion of the positive electrode lead 16 can be prevented from facing the electrode group 14 through the lead hole 27. As a result, a short circuit between the electrode group 14 and the positive electrode lead 16, which is caused by variations in the bending position of the positive electrode lead 16 relative to the upper insulating plate 26, can be effectively prevented.

[0048] Furthermore, in this example, the upper insulating plate 26 has only the lead hole 27 and the center hole 29 as through-holes, so that the electrode group 14 and the positive electrode lead 16 can be more effectively prevented from short-circuiting through the through-holes.

[0049] 2 to 4, the non-facing portion 12a of the negative electrode 12, which does not face the positive electrode 11 with the separator 13 interposed therebetween, is wound 1.25 or more times from the inner end of the winding direction of the electrode group 14. Furthermore, of the non-facing portion 12a, the negative electrode mixture layer forming portion 12c on which the negative electrode mixture layer 12f is formed is wound 0.75 or more times. The positive electrode 11 does not face either side of this negative electrode mixture layer forming portion 12c. As a result, when the secondary battery 10 ignites, the negative electrode mixture layer forming portion 12c does not react with the positive electrode 11, and the portion of the negative electrode mixture layer forming portion 12c near the inner end of the winding direction, including the negative electrode core portion, remains cylindrical on the winding core of the electrode group 14. Furthermore, the negative electrode mixture layer forming portion 12c has higher strength than a portion where only the negative electrode core is exposed on both sides. Therefore, the remaining cylindrical portion serves as an exhaust passage, guiding the high-temperature, high-pressure gas generated inside the battery in the event of a fire in an up-and-down direction, allowing it to be efficiently exhausted. This prevents the secondary battery 10 from exploding due to an excessive increase in internal pressure. Furthermore, since there is no need to provide a metal cylindrical member at the winding core of the secondary battery 10 to efficiently exhaust gas, costs can be reduced. This allows a low-cost structure to be realized that ensures an exhaust passage at the winding core of the electrode group 14 in the event of a fire in the secondary battery 10.

[0050] <Experimental Example> The inventors of the present disclosure fabricated secondary batteries 10 of Experimental Examples 1 to 4 as follows and conducted high-temperature overheating tests.

[0051] [Experimental Example 1] [Preparation of positive electrode] As the positive electrode active material, LiNi 0.88 Co 0.09 Al 0.03 The aluminum-containing lithium nickel cobalt oxide represented by O2 was used. 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) were mixed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) solvent to obtain a positive electrode mixture slurry. This paste-like positive electrode mixture slurry was uniformly applied to both sides of a long positive electrode core made of aluminum foil with a thickness of 15 μm. Next, the NMP was removed in a heated dryer at a temperature of 100 to 150 °C, and then the positive electrode was rolled using a roll press to form a positive electrode mixture layer. The rolled positive electrode was then heat-treated by contacting it with a roller heated to 200 °C for 5 seconds. The long positive electrode core with the formed positive electrode mixture layer was then cut to a predetermined electrode size to produce a positive electrode 11. An aluminum positive electrode lead 16 was then attached to the positive electrode core. The fabricated positive electrode 11 has a thickness of 0.144 mm, a width of 62.6 mm, and a length of 861 mm.

[0052] [Preparation of negative electrode] A mixture of 95 parts by weight of graphite powder and 5 parts by weight of silicon oxide was used as the negative electrode active material. This mixture, 1 part by weight of carboxymethyl cellulose (CMC) as a thickener, and 1 part by weight of a styrene-butadiene rubber dispersion as a binder were dispersed in water to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied to both sides of a negative electrode core made of 8 μm-thick copper foil to form a negative electrode coating. The coating was formed so that the outermost surface of the electrode group became the negative electrode core. The coating was then dried in a heated dryer and compressed with a compression roller to adjust the thickness of the negative electrode mixture layer to 160 μm. The long negative electrode core with the negative electrode mixture layer formed thereon was then cut to a predetermined electrode size to produce a negative electrode 12 with a negative electrode mixture layer formed on both sides. A nickel-copper-nickel negative electrode lead 40 was then attached to the negative electrode core. After fabrication, the negative electrode 12 has a width of 64.2 mm and a length of 959 mm.

[0053] [Preparation of battery electrodes] A polyethylene separator 13 was interposed between a positive electrode 11 and a negative electrode 12, and the electrodes were wound into a cylindrical shape to form an electrode group .

[0054] [Preparation of non-aqueous electrolyte] Ethylene carbonate (EC) and dimethyl Carbohydrate To 100 parts by weight of the mixed solvent, 5 parts by weight of vinylene carbonate (VC) was added, and LiPF6 was dissolved in the mixed solvent to a concentration of 1.5 mol / L to prepare a non-aqueous electrolyte solution.

[0055] [Preparation of upper insulating plate] A circular plate made of polypropylene resin and having a thickness of 0.3 mm was used for the upper insulating plate 26, and a lead hole 27 and a central hole 29, through which the positive electrode lead 16 passes, were formed as shown in Fig. 5A. The central hole 29 was 2.2 mm long and 3 mm wide. The lead hole 27 through which the positive electrode lead 16 passes was formed so that the total aperture ratio of the central hole 29 and the lead hole 27 was 18.3%.

[0056] [Secondary battery production] An upper insulating plate 26 and a lower insulating plate were placed above and below the electrode group 14, respectively, and the electrode group 14 was housed in an outer can 20. The positive electrode lead 16 was led out from the electrode group 14 through a lead hole 27 in the upper insulating plate 26. The negative electrode lead 40 was welded to the outer can 20 of the battery case 18, and the positive electrode lead 16 was welded to a sealing member 22 having an internal pressure-activated safety valve. A nonaqueous electrolyte was then injected into the battery case 18 by a reduced pressure method. Finally, the sealing member 22 was crimped to the upper open end of the outer can 20 via a gasket 24, thereby producing a secondary battery 10. The capacity of the secondary battery 10 was 4600 mAh. Furthermore, the non-facing portion 12a of the negative electrode 12, which did not face the positive electrode 11 via the separator 13, was wound 1.75 times. In addition, of the non-facing portion 12a, the negative electrode mixture layer forming portion 12c on which the negative electrode mixture layer 12f was formed was wound 0.75 turns, and the negative electrode substrate exposed portion 12d was wound one turn.

[0057] [Experimental Example 2] A secondary battery according to Experimental Example 2 was fabricated in the same manner as Experimental Example 1, except that the lead hole 27 through which the positive electrode lead 16 penetrated was formed so that the total aperture ratio of the central 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 column for Experimental Example 2 in Fig. 11 described later.

[0058] [Experimental Example 3] FIG. 10 is a diagram corresponding to FIG. 5 of an upper insulating plate 26 of a secondary battery of Experimental Example 3. A secondary battery of Experimental Example 3 was fabricated in the same manner as Experimental Example 1, except that, as shown in FIG. 10, a lead hole 27 through which a positive electrode lead 16 (FIG. 1) penetrates was formed in the upper insulating plate 26 so that the total aperture ratio of the central hole 29 and the lead hole 27 was 11.7%. The shape of the upper insulating plate 26 of Experimental Example 3 is also shown in the column for Experimental Example 3 in FIG. 11 (described later). As shown in FIG. 10, the lead hole 27 is significantly smaller than those in Experimental Examples 1 and 2, and therefore, no inner curved portion is formed in the lead hole 27 to avoid the central hole 29. Specifically, the outer edge of the lead hole 27 includes an outer curved portion 27a arranged along an arc concentric with the outer circumferential circle 26a of the upper insulating plate 26 in a plan view, and straight portions 28c connected to both ends of the outer curved portion 27a via rounded portions 30. The straight portions 28c are arranged along a chord connecting both ends of the reference arc.

[0059] [Experimental Example 4] A secondary battery according to Experimental Example 4 was fabricated in the same manner as Experimental Example 1, except that the lead hole 27 through which the positive electrode lead 16 passes was formed so that the total aperture ratio of the central hole 29 and the lead hole 27 was 5.6%. The column for Experimental Example 4 in FIG. 11 described later shows the shape of the upper insulating plate 26 of Experimental Example 4. Like the lead hole 27 of Experimental Example 3, the lead hole 27 of Experimental Example 4 also does not have an inner curved portion formed.

[0060] [Overheating test] Ten secondary batteries for each of Experimental Examples 1 to 4 were charged at a constant current of 1380 mA until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 92 mA. Using the secondary batteries charged in this manner, an overheating test was conducted to evaluate exhaust performance. In the overheating test, ten secondary batteries for each of Experimental Examples 1 to 4 were overheated by radiant heat in a heating furnace at 300°C, forcing them into thermal runaway and examining the rate of battery case explosion, as a test simulating a battery module combustion environment.

[0061] [Test Results] Fig. 11 is a diagram comparing the shape of upper insulating plate 26, the aperture ratio relative to the area of ​​the outer circumferential circle of upper insulating plate 26, and the rupture rate of the battery case in the secondary batteries according to Experimental Examples 1 to 4. As shown in Fig. 11, Experimental Examples 1 to 3, in which the total aperture ratio of lead hole 27 and center hole 29 relative to the area of ​​the outer circumferential circle of upper insulating plate 26 was 11% or more, were able to reduce the rupture rate of the battery case in the overheat test to zero. On the other hand, Experimental Example 4, in which this aperture ratio was less than 11%, caused the battery case to rupture in the overheat test. This confirmed that by setting the aperture ratio to 11% or more, it is possible to realize a secondary battery with higher safety, which can quickly release gas generated inside the battery.

[0062] <Another embodiment> FIG. 12 is a view corresponding to FIG. 1 in another example of the embodiment. FIG. 13 is a view corresponding to FIG. 7 in another example of the embodiment. In the secondary battery 10a of this example, a plurality of (four in FIG. 13 ) outer peripheral holes 32 as through holes are formed in a circumferentially aligned manner in the half of the upper insulating plate 26 opposite the lead hole 27. Furthermore, when the distance from the central axis O of the secondary battery 10a to the second curved portion 16b of the positive electrode lead 16 (the distance to the portion of the second curved portion 16b that is farthest from the central axis O) is defined as L1, and the distance from the central axis O of the secondary battery 10a to the outer peripheral hole 32 (the distance to the portion of the outer peripheral hole 32 that is closest to the central axis O) is defined as L2, L1 and L2 are regulated so that L2 > L1. This prevents the exposed portion of the positive electrode lead 16 from coming into contact with the electrode group 14 through the outer peripheral hole 32 and causing a short circuit, even when the upper insulating plate 26 is formed with the outer peripheral hole 32 as another through hole in addition to the lead hole 27 and the central hole 29. Furthermore, the ability to discharge internal gas can be improved by increasing the number of through holes in upper insulating plate 26. In this manner, the configuration of the present disclosure also allows for the formation of through holes other than lead holes 27 and center hole 29 in upper insulating plate 26. In this example, the other configurations and functions are the same as those in FIGS. 1 to 5 and 9.

[0063] In the configurations of Figures 12 and 13, when other through holes besides the lead hole 27 and the central hole 29 are formed in the upper insulating plate 26, if the maximum width of the other through holes is made smaller than the width W (Figure 9) of the positive electrode lead 16, the distance L2 from the central axis O of the secondary battery 10 to the other through holes can also be made less than the distance L1 from the central axis O of the secondary battery 10 to the second curved portion 16b of the positive electrode lead 16. [Explanation of symbols]

[0064] 10, 10a cylindrical nonaqueous electrolyte secondary battery (secondary battery), 11 positive electrode, 12 negative electrode, 12a non-facing portion, 12b facing 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 curved portion, 16b second curved portion, 18 battery case, 20 outer can, 21 protruding portion, 22 sealing body, 24 gasket, 26 upper insulating plate, 26a outer circumferential circle, 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 circumferential hole, 40 negative electrode lead, 45 upper insulating plate, 46 lead hole, 48 outer circumferential hole.

Claims

1. A cylindrical nonaqueous electrolyte secondary battery comprising: an outer can; a sealing body closing one end of the outer can; an electrode group disposed inside the outer can; and an insulating plate disposed between the sealing body and the electrode group, The electrode group is formed by spirally winding a positive electrode and a negative electrode with a separator interposed therebetween, the insulating plate is in the shape of a disk having a lead hole through which a positive electrode lead extending from the electrode group passes and a center hole passing through the center of the insulating plate; an outer edge portion of the lead hole includes, in a plan view, a curved portion arranged along an arc concentric with an outer circumferential circle of the insulating plate, and a straight portion arranged along a chord connecting both ends of the arc, The arc is a minor arc smaller than a semicircle. Cylindrical non-aqueous electrolyte secondary battery.

2. 2. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, 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. Cylindrical non-aqueous electrolyte secondary battery.

3. 3. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, the insulating plate has only the lead holes and the center hole as through holes; Cylindrical non-aqueous electrolyte secondary battery.

4. 4. The cylindrical nonaqueous electrolyte secondary battery according to claim 3, the sealing body is configured to release the generated gas inside when the internal pressure reaches a predetermined pressure; when viewed from the direction of the winding axis of the electrode group, the central hole does not face the electrode group, and the total opening ratio of the lead hole and the central hole is 11% or more with respect to the area within the outer circumferential circle of the insulating plate. Cylindrical non-aqueous electrolyte secondary battery.

5. 5. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, The insulating plate is made of a polyolefin resin. Cylindrical non-aqueous electrolyte secondary battery.

6. 6. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, The thickness of the insulating plate is 0.2 mm or more and 0.5 mm or less. Cylindrical non-aqueous electrolyte secondary battery.

7. 7. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, The negative electrode is a non-facing portion wound 1.25 times or more around an inner end of the electrode group in a winding direction, the inner end being wound with the separator interposed therebetween, so as not to face the positive electrode; the non-facing portion has a negative electrode mixture layer forming portion on at least one surface thereof, the negative electrode mixture layer being formed continuously from an outer end in the winding direction to an inner end in the winding direction; The negative electrode mixture layer forming portion is wound 0.75 turns or more. Cylindrical non-aqueous electrolyte secondary battery.

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