Cylindrical secondary battery

Abstract

A battery (10) is provided with: an electrode body (14) in which a positive electrode (11) and a negative electrode (12) are wound with a separator (13) in between; a bottomed cylindrical outer can (16) that accommodates the electrode body (14); a sealing body (17) that is swaged so as to be fixed onto an opening of the outer can (16) via a gasket (28); and an upper insulating plate (18) that is disposed between the electrode body (14) and the sealing body (17) in the axial direction. The upper insulating plate (18) has a thick portion (41) on the radially inner side. The thick portion (41) protrudes toward the electrode body (14) and is disposed along the circumferential direction.

Description

Cylindrical secondary battery

[0001] The present disclosure relates to a cylindrical secondary battery.

[0002] A conventional cylindrical secondary battery is described in Patent Document 1. This cylindrical secondary battery includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a bottomed cylindrical outer can that houses the electrode assembly, and a sealing body that closes the opening of the outer can. The outer can has a cylindrical portion and a bottom, and the cylindrical portion includes an annular groove portion and an annular shoulder portion. The groove portion is formed by recessing a portion of the cylindrical portion radially inward. The shoulder portion extends radially inward at the upper end of the cylindrical portion. The sealing body is crimped and fixed to the outer can by being sandwiched between the groove portion and the shoulder portion via a gasket.

[0003] The positive electrode of the electrode body is electrically connected to the bottom surface of the sealing body via a positive electrode lead, and the negative electrode of the electrode body is electrically connected to the bottom of the outer can via a negative electrode lead. The electrode body is housed in the outer can on the bottom side of the grooved portion. An upper insulating plate is disposed between the grooved portion and the electrode body. The upper insulating plate is provided mainly to prevent contact between the positive electrode and the outer can and between the negative electrode and the sealing body.

[0004] Japanese Patent Application Laid-Open No. 2000-048825

[0005] As described in the embodiments below, the present inventors have discovered a phenomenon in which a cylindrical secondary battery tends to expand in the height direction (positive electrode width direction) on the inner periphery of an electrode assembly after repeated charge and discharge cycles. In light of this background, if the length of the positive electrode becomes longer than the length of the negative electrode after repeated charge and discharge cycles, and the positive electrode exceeds the separator, there is a risk that the positive electrode may come into contact with the negative electrode. Therefore, an object of the present disclosure is to provide a cylindrical secondary battery that can suppress expansion of the positive electrode in the height direction.

[0006] In order to solve the above problems, the cylindrical secondary battery according to the present disclosure comprises an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a cylindrical outer can with a bottom that houses the electrode body, a sealing body that is crimped and fixed to the opening of the outer can via a gasket, and an insulating plate that is arranged between the electrode body and the sealing body in the axial direction, wherein the insulating plate has a thick portion on the radially inner side that protrudes toward the electrode body and is arranged along the circumferential direction.

[0007] According to the cylindrical secondary battery according to the present disclosure, the expansion of the positive electrode in the height direction can be suppressed.

[0008] 2A and 2B are axial cross-sectional views of a cylindrical battery according to an embodiment of the present disclosure. (a) is a bottom view of an upper insulating plate as viewed from below, (b) is a cross-sectional view of the upper insulating plate in the axial direction (thickness direction) passing through the radial center of the upper insulating plate, and (c) is a schematic cross-sectional view of the upper structure of the electrode body after repeated charge and discharge. (b) is a bottom view corresponding to FIG. 2A in a first modified example. (c) is a bottom view corresponding to FIG. 2A in a second modified example.

[0009] Hereinafter, an embodiment of a cylindrical secondary battery according to the present disclosure will be described in detail with reference to the drawings. The cylindrical secondary battery according to the present disclosure may be a battery using an aqueous electrolyte or a battery using a nonaqueous electrolyte. Hereinafter, a nonaqueous electrolyte secondary battery (lithium ion battery) using a nonaqueous electrolyte will be exemplified as a cylindrical secondary battery 10 according to one embodiment, but the cylindrical secondary battery according to the present disclosure is not limited thereto.

[0010] It is anticipated from the beginning that new embodiments may be constructed by appropriately combining the features of the embodiments and variations described below. In the following embodiments, the same components are denoted by the same reference numerals in the drawings, and redundant explanations are omitted. Furthermore, multiple drawings include schematic diagrams, and the dimensional ratios of the length, width, height, and other dimensions of each component between different drawings do not necessarily match. In this specification, the sealing body 17 side in the axial direction (height direction) of the cylindrical secondary battery 10 is referred to as "upper," and the bottom 31 side of the outer can 16 in the axial direction is referred to as "lower." Furthermore, among the components described below, components not recited in the independent claims representing the highest concepts are optional components and not essential components.

[0011] Fig. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment of the present disclosure. As shown in Fig. 1, the cylindrical secondary battery (hereinafter simply referred to as battery) 10 includes a wound electrode assembly 14, a non-aqueous electrolyte (not shown), an outer can 16 that houses the electrode assembly 14 and the non-aqueous electrolyte, and a sealing body 17. The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and two separators 13 interposed between the positive electrode 11 and the negative electrode 12, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with the two separators 13 interposed therebetween.

[0012] The non-aqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The liquid electrolyte (electrolytic solution) includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. The electrolyte salt may include, for example, LiPF ６ Lithium salts such as

[0013] Examples of the solid electrolyte include solid or gel polymer electrolytes and inorganic solid electrolytes. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. Examples of the matrix polymer include a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.).

[0014] A positive electrode lead 20 and a negative electrode lead 21 are connected to the electrode body 14. The positive electrode lead 20 electrically connects the positive electrode 11 to the sealing body 17, and the negative electrode lead 21 electrically connects the negative electrode 12 to the bottom 31 of the outer can 16. In the example shown in FIG. 1 , the positive electrode lead 20 passes through a through-hole 46 (see FIG. 2( a) ) of the upper insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes outside the lower insulating plate 19 and extends toward the bottom 31 of the outer can 16.

[0015] The positive electrode 11 has a positive electrode core and a positive electrode mixture layer formed on at least one surface of the positive electrode core. The positive electrode core is made of a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with the metal disposed on the surface. The positive electrode mixture layer contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is preferably formed on both sides of the positive electrode core. The positive electrode active material is, for example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, or the like. The positive electrode lead 20 is joined to the positive electrode core by ultrasonic welding or the like.

[0016] The negative electrode 12 has a negative electrode core and a negative electrode mixture layer formed on at least one surface of the negative electrode core. The negative electrode core may be made of a foil of a metal stable within the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with such a metal disposed on the surface. The negative electrode mixture layer contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR) or PVdF, and is preferably formed on both surfaces of the negative electrode core. Examples of the negative electrode active material include graphite and silicon-containing compounds. The negative electrode lead 21 is joined to the negative electrode core by ultrasonic welding or the like. The negative electrode 12 may be electrically connected to the outer can 16 by contacting the negative electrode core with the inner surface of the outer can 16.

[0017] The outer can 16 is generally made of a metal primarily composed of iron, such as nickel-plated iron. The outer can 16 may also be made of a metal primarily composed of aluminum or the like. The outer can 16 has a cylindrical portion 39 and a bottom 31. The cylindrical portion 39 includes an annular grooved portion 22 and an annular shoulder portion 29. The grooved portion 22 is formed by spinning a portion of the cylindrical portion 39 to recess it radially inward around the entire circumferential direction. The shoulder portion 29 is formed when the upper end of the cylindrical portion 39 is bent radially inward and crimped onto the peripheral edge portion 33 of the sealing body 17, and extends radially inward at the upper end of the cylindrical portion 39.

[0018] The sealing body 17 is clamped by crimping between the shoulder portion 29 and the grooved portion 22 with the gasket 28 interposed therebetween, and is fixed to the outer can 16. The grooved portion 22 is formed at a position spaced a predetermined length from the upper end of the outer can 16. The predetermined length is, for example, a length equivalent to 1 to 20% of the axial length of the outer can 16. The gasket 28 is compressed by the shoulder portion 29, and a portion of the gasket 28 protrudes radially inward from between the shoulder portion 29 and the sealing body 17.

[0019] The sealing body 17 has a structure in which a terminal plate 23, a lower valve body 24, an insulating plate 25, an upper valve body 26, and a cap 27 are layered in this order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disk or ring shape, and each component except for the insulating plate 25 is electrically connected to one another. The cap 27 has a convex shape with a radially central portion protruding outward. The convex portion 27a of the cap 27 includes a ring-shaped inclined portion and a flat top surface portion surrounded by the inclined portion. One or more air vents 27b are formed in the top surface portion. The convex portion of the cap may have a cylindrical portion instead of the ring-shaped inclined portion.

[0020] The lower valve body 24, insulating plate 25, and upper valve body 26 constitute a current interruption mechanism. The lower valve body 24 and upper valve body 26 are connected at their respective centers, with the insulating plate 25 interposed between their respective peripheral edges. If an abnormality occurs in the battery 10 and the internal pressure rises, the lower valve body 24 deforms and pushes the upper valve body 26 toward the cap 27, causing it to break, interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 breaks, causing gas to be discharged through the vent hole 27b in the cap 27.

[0021] In this embodiment, the positive electrode lead 20 is connected to the underside of the terminal plate 23 by welding, ultrasonic welding, or the like, and the cap 27, which is the top plate of the sealing body 17 electrically connected to the terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom 31 of the outer can 16 by welding, ultrasonic welding, or the like, and the outer can 16 serves as the negative electrode terminal.

[0022] In the above description, the sealing body 17 has a laminated structure including two rupture plates (lower valve body 24 and upper valve body 26) and a convex cap 27 that covers the rupture plate. However, the sealing body may be composed of only a rupture plate, or may have a structure in which an internal terminal plate, an insulating plate, and a rupture plate are laminated in this order from the electrode body side. Alternatively, the sealing body may not have a rupture plate, and the bottom of the outer can may have a thin, easily breakable portion that breaks when the battery generates abnormal heat.

[0023] 2(a) is a bottom view of the upper insulating plate 18 as viewed from below, FIG. 2(b) is a cross-sectional view in the axial direction (thickness direction) passing through the radial center of the upper insulating plate, and FIG. 2(c) is a schematic cross-sectional view of the upper structure of the electrode body 14 after repeated charge and discharge. In FIGS. 2(a) and 2(b) (and the following FIGS. 3 and 4), the dark gray area indicates the area where the thick portion 41 of the upper insulating plate 18 exists, and the light gray area indicates the area where the thin portion 42 of the upper insulating plate 18 exists. In FIG. 2(c), the positive electrode 11 is shown in gray, and the negative electrode 12 is shown in white. The separator 13 is not shown in FIG. 2(c).

[0024] 2( a), the upper insulating plate 18 has a thick portion 41 and a thin portion 42. The upper insulating plate 18 has a circular outer edge 43 and a cylindrical through-hole 45 having a center that substantially coincides with the center of the outer edge 43. This through-hole 45 is provided to allow high-temperature gas released from the electrode body 14 in the event of abnormal heat generation to flow toward the sealing body 17, and to quickly fill the electrode body 14 with non-aqueous electrolyte.

[0025] The thick portion 41 is disposed radially inward of the upper insulating plate 18 and protrudes toward the electrode body 14. More specifically, the thick portion 41 has a protruding portion 41a that protrudes downward further than the thin portion 42. The thick portion 41 is disposed along the circumferential direction. The protruding portion 41a faces a predetermined range on the inner circumferential side of the electrode body 14. In this embodiment, the thick portion 41 is disposed along the outer periphery of the through hole 45 and has an annular shape. The upper insulating plate 18 further has a through hole 46 radially outward of the thick portion 41, through which the positive electrode lead 20 passes.

[0026] Next, the effects achieved by providing the thick portion 41 on the upper insulating plate 18 will be described. The inventors have discovered that when a cylindrical secondary battery is repeatedly charged and discharged many times, a phenomenon occurs in which the positive electrode 11 expands in the height direction (positive electrode width direction) at the inner periphery of the electrode body 14. This phenomenon is schematically illustrated in FIG. 2( c). It is believed that this phenomenon occurs due to the following mechanism.

[0027] As the negative electrode active material expands and contracts during charging and discharging, the negative electrode 12 expands and contracts in the radial and height directions (axial direction). During charging, the radial expansion of the negative electrode 12 increases the radial surface pressure that the positive electrode 11 receives from the negative electrode 12. Therefore, when the negative electrode 12 expands in the height direction, the positive electrode 11 is pulled in the height direction by the negative electrode 12, causing the positive electrode 11 to elongate in the height direction.

[0028] On the other hand, during discharge, the radial surface pressure that the positive electrode 11 receives from the negative electrode 12 decreases due to radial contraction of the negative electrode 12. Therefore, when the negative electrode 12 contracts in the height direction, the positive electrode 11 may not be able to contract in the height direction and may remain in an elongated state. Therefore, it is presumed that repeated charge and discharge cycles result in the positive electrode 11 gradually elongating in the height direction compared to the negative electrode 12. This phenomenon is particularly likely to occur on the inner periphery of the electrode body, where the surface pressure that the positive electrode 11 receives from the negative electrode 12 is high.

[0029] In view of this background, in the battery 10 of the present disclosure, the upper insulating plate 18 has a thick portion 41 that is disposed radially inward along the circumferential direction and protrudes downward. The protruding portion 41a of the thick portion 41 fills the axial gap between the upper insulating plate 18 and the inner periphery of the electrode body and prevents deformation of the upper insulating plate, making it difficult for the negative electrode 12 to expand upward during charging. This prevents the positive electrode 11 from being pulled upward by the negative electrode 12, thereby suppressing elongation of the positive electrode 11.

[0030] Furthermore, the upper insulating plate 18 has the thin portion 42, which is thinner than the thick portion 41 and located radially outward of the thick portion 41, so that the volume occupied by the upper insulating plate 18 within the outer can 16 is reduced. This prevents an increase in the internal pressure of the battery 10 and prevents unnecessary operation of the current interruption mechanism.

[0031] Furthermore, the upper insulating plate 18 has a thin portion 42 on the radially outer side, which prevents the upper insulating plate 18 from blocking a wide area of ​​the upper end surface of the electrode body 14. This ensures a path to the rupture plate for high-temperature gas released from the upper end surface of the electrode body 14 when the battery 10 generates abnormal heat, allowing the rupture plate to break smoothly in the event of abnormal heat generation.

[0032] 1 and 2 , all of the through holes 45 axially overlap the hollow portion 14a of the electrode body 14. In order to effectively suppress extension of the positive electrode 11 on the inner circumferential side of the electrode body 14, when the radial length of the electrode plate group 60 composed of the positive electrode 11 and the negative electrode 12 is d (see FIG. 2( c )), it is preferable that at least a part of the thick portion 41 be located radially outward from a position located 15% of d (0.15d) from the radial inner end 65 of the electrode plate group 60.

[0033] Furthermore, in order to reduce the volume occupied by the upper insulating plate 18 within the outer can 16 and to make it easier to ensure a path for high-temperature gas to reach the rupture plate in the event of abnormal heat generation, it is preferable that all of the thick-walled portion 41 be located radially inward from the radial inner end 65 of the plate pack 60 at a length that is 40% of d (0.4d) radially outward.

[0034] The present disclosure is not limited to the above-described embodiments and their modifications, and various improvements and modifications are possible within the scope of the claims of the present application and their equivalents.

[0035] Although the case where the upper insulating plate 18 has the through holes 45 and 46 has been described, the upper insulating plate may have through holes other than the through holes 45 and 46, or may not have the central through hole 45.

[0036] Although the above description concerns a case in which the upper insulating plate 18 has a thick portion 41 that is annular in plan view, the thick portion 41 does not have to be annular. For example, as shown in FIG. 3 , the upper insulating plate 118 may have a thick portion 141 and a thin portion 142, and the thick portion 141 may be C-shaped in plan view. Alternatively, as shown in FIG. 4 , the upper insulating plate 218 may have a thick portion 241 and a thin portion 242, and the thick portions 241 may be arranged intermittently in the circumferential direction. More specifically, the thick portion 241 of the upper insulating plate 218 may be composed of a plurality of fan-shaped portions 241 a arranged at intervals in the circumferential direction, or more preferably, a plurality of fan-shaped portions 241 a arranged at equal intervals in the circumferential direction. The thick portion 241 may have a radial shape in plan view.

[0037] 3 is used, groove 155 arranged between both circumferential ends of upper insulating plate 118, which is C-shaped in plan view, serves as a path that communicates with central through-hole 145. Therefore, high-temperature gas released from the upper end surface of electrode body 14 during abnormal heat generation in the battery can be smoothly guided to the rupture plate via groove 155 and through-hole 145, allowing the rupture plate to be smoothly broken.

[0038] 4 is used, grooves 255 are formed between adjacent sectorial portions 241a in the circumferential direction. Therefore, even in this case, high-temperature gas released from the upper end surface of the electrode body 14 when the battery abnormally heats up can be smoothly guided to the rupture plate via the grooves 255 and through-holes 245 formed at intervals in the circumferential direction, allowing the rupture plate to be smoothly broken.

[0039] Although not shown, the outer edge of the thick portion may be polygonal, for example, a regular polygonal, in a bottom view when the upper insulating plate is viewed from below in the axial direction. If the thick portion is not formed around the entire circumference, it is preferable that the thick portion be formed over 70% or more of the circumferential area, and more preferably, over 80% or more of the circumferential area, in order to effectively suppress extension of the positive electrode 11 on the inner circumferential side of the electrode body.

[0040] For example, when the upper insulating plate 218 shown in Figure 4 is used, in a bottom view when the upper insulating plate 218 is viewed from below, with respect to a circle 280 whose center coincides with the center of the upper insulating plate 118 and passes through the thick portion 241, it is preferable that the length of the portion passing through the thick portion 241 shown by the solid line be 70% or more of the total circumference of the circle 280, and more preferably 80% or more of the total circumference of the circle 280.

[0041] The cylindrical secondary battery of the present disclosure may also have the following configurations. Configuration 1: A cylindrical secondary battery comprising: an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; a bottomed, tubular outer can housing the electrode assembly; a sealing body crimped and fixed to the opening of the outer can via a gasket; and an insulating plate arranged axially between the electrode assembly and the sealing body, wherein the insulating plate has a thick portion on its radially inner side, the thick portion protruding toward the electrode assembly and arranged along the circumferential direction. Configuration 2: The cylindrical secondary battery according to Configuration 1, in which the thick portion is arranged continuously in the circumferential direction. Configuration 3: The cylindrical secondary battery according to Configuration 1, in which the thick portion is arranged intermittently in the circumferential direction. The cylindrical secondary battery of any one of the preceding embodiments, wherein the insulating plate has a through hole at the center, all of the through holes axially overlapping with the hollow portion of the electrode body, and at least a portion of the thick portion is located radially outward from a position located 15% of the radial length of the electrode plate assembly from the radial inner end of the electrode plate assembly composed of the positive electrode and the negative electrode. The cylindrical secondary battery of any one of the preceding embodiments, wherein the thick portion is located radially inward from a position located 40% of the radial length of the electrode plate assembly from the radial inner end of the electrode plate assembly composed of the positive electrode and the negative electrode.

[0042] REFERENCE SIGNS LIST 10 battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 14a hollow portion, 16 outer can, 17 sealing body, 18, 118, 218 upper insulating plate, 19 lower insulating plate, 20 positive electrode lead, 21 negative electrode lead, 22 grooved portion, 23 terminal plate, 24 lower valve body, 25 insulating plate, 26 upper valve body, 27 cap, 28 gasket, 29 shoulder portion, 31 bottom portion, 33 peripheral portion, 39 cylindrical portion, 41, 141, 241 thick portion, 41a protruding portion, 42, 142, 242 thin portion, 43 outer edge, 45, 46, 145, 245 through hole, 60 Plate group, 65 Radial inner end of plate group, 155, 255 Groove, 241a Fan-shaped portion, 280 Yen.

Claims

1. A cylindrical secondary battery comprising: an electrode assembly in which a positive electrode and a negative electrode are wound with a separator between them; a bottomed cylindrical outer can containing the electrode assembly; a sealing body that is crimped and fixed to the opening of the outer can via a gasket; and an insulating plate that is arranged axially between the electrode assembly and the sealing body, wherein the insulating plate has a thick portion on its radially inner side that protrudes toward the electrode assembly and is arranged along the circumferential direction.

2. The cylindrical secondary battery according to claim 1, wherein the thick-walled portion is disposed continuously in the circumferential direction.

3. The cylindrical secondary battery according to claim 1, wherein the thick-walled portions are arranged discontinuously in the circumferential direction.

4. A cylindrical secondary battery as described in any one of claims 1 to 3, wherein the insulating plate has a through hole in the center, all of the through holes overlap with the hollow portion of the electrode body in the axial direction, and at least a part of the thick portion is located radially outward from a point located radially outward from the radial inner end of the electrode plate group constituted by the positive electrode and the negative electrode by a length that is 15% of the radial length of the electrode plate group.

5. A cylindrical secondary battery as described in any one of claims 1 to 3, wherein all of the thick portions are located radially inward of a point located radially outward from the radial inner end of the electrode plate group composed of the positive electrode and the negative electrode by a length that is 40% of the radial length of the electrode plate group.

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