Cylindrical battery

Abstract

A negative electrode mixture layer (12b) has an extension section (38) that extends to the winding starting side from the winding inside of a starting end (40) on the winding starting side of a positive electrode (11). A first distance (d1) between the center (40a) of the starting end (40) in the width direction and a mixture layer starting end (50) on the winding starting side of the negative electrode mixture layer (12b) is greater than at least one of a second distance (d2) between one end (40b) of the starting end (40) in the width direction and the mixture layer starting end (50), and a third distance (d3) between the other end (40c) of the starting end (40) in the width direction and the mixture layer starting end (50).

Description

Cylindrical battery

[0001] The present disclosure relates to cylindrical batteries.

[0002] A conventional cylindrical battery is described in Patent Document 1. This cylindrical battery includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween. In this cylindrical battery, the winding start ends of the positive electrode and the negative electrode are asymmetrically shaped to prevent the winding start ends of the positive electrode and the negative electrode from breaking through the separator.

[0003] Japanese Patent Application Laid-Open No. 2001-160411

[0004] The present inventors have discovered that repeated charge and discharge cycles can cause a voltage drop due to the positive electrode starting end near the center in the width direction pressing against the separator. Therefore, an object of the present disclosure is to provide a cylindrical battery that can suppress voltage drops due to charge and discharge.

[0005] In order to solve the above problems, the cylindrical battery according to the present disclosure includes an electrode assembly in which an elongated positive electrode having a positive electrode core and a positive electrode mixture layer, and an elongated negative electrode having a negative electrode core and a negative electrode mixture layer 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, wherein the negative electrode mixture layer has an extension that extends from the inner side of the winding of the starting end on the winding start side of the positive electrode to the winding start side, and a first distance between the widthwise center of the starting end and the mix layer starting end on the winding start side of the negative electrode mix layer is longer than at least one of a second distance between one widthwise end of the starting end and the mix layer starting end, and a third distance between the other widthwise end of the starting end and the mix layer starting end.

[0006] The cylindrical battery according to the present disclosure can suppress voltage drops that occur during charging and discharging.

[0007] 2A is a cross-sectional view in the axial direction of a cylindrical battery according to an embodiment of the present disclosure; FIG. 2B is a schematic plan view of the end portion on the winding start side of the inner surface of the winding when the positive electrode is unfolded into a long shape; and FIG. 2B is a schematic plan view of the end portion on the winding start side of the outer surface of the winding when the negative electrode is unfolded into a long shape. FIG. 2C is a schematic plan view of the end portion on the winding start side of the inner surface of the winding of a positive electrode of a comparative example unfolded into a long shape. FIG. 2D is a schematic plan view of a positive electrode of a first modified example corresponding to FIG. 2A; and FIG. 2E is a schematic plan view of a positive electrode of a second modified example corresponding to FIG. 2A.

[0008] Hereinafter, an embodiment of a cylindrical battery according to the present disclosure will be described in detail with reference to the drawings. The cylindrical battery according to the present disclosure may be a primary battery or a secondary battery. It may also be a battery using an aqueous electrolyte or a battery using a non-aqueous electrolyte. Hereinafter, a non-aqueous electrolyte secondary battery (lithium ion battery) using a non-aqueous electrolyte will be exemplified as a cylindrical battery 10 according to one embodiment, but the cylindrical battery according to the present disclosure is not limited thereto, and the electrolyte may also be an aqueous electrolyte.

[0009] It is anticipated from the beginning that new embodiments will be constructed by appropriately combining the features of the embodiments and variations described below. In the following embodiments, the same components are designated by the same reference numerals in the drawings, and redundant explanations will be omitted. Furthermore, multiple drawings include schematic diagrams, and the dimensional ratios of the length, width, height, etc. of each component between different drawings do not necessarily match. In this specification, the side of the sealing body 17 in the axial direction (height direction) of the cylindrical battery 10 is referred to as "upper," and the side of the bottom 31 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.

[0010] Fig. 1 is an axial cross-sectional view of a cylindrical battery 10 according to one embodiment of the present disclosure. As shown in Fig. 1, the cylindrical battery 10 includes an electrode assembly 14, a cylindrical outer can 16 with a bottom that houses the electrode assembly 14, and a sealing body 17 that closes the opening of the outer can 16. The outer can 16 houses a nonaqueous electrolyte together with the electrode assembly 14. The outer can 16 has a shoulder 29 at its upper end that is bent radially inward and extends inward. The outer can 16 has a groove 22 formed in its side wall, and the sealing body 17 is supported by the groove 22 to close the opening of the outer can 16.

[0011] The cylindrical battery 10 further includes a gasket 28 interposed between the exterior can 16 and the sealing body 17. The gasket 28 is a ring-shaped resin member attached to the outer periphery of the sealing body 17, and insulates the sealing body 17 from the exterior can 16. The gasket 28 seals the gap between the exterior can 16 and the sealing body 17, sealing the inside of the battery. The gasket 28 is made of, for example, polyolefin.

[0012] The non-aqueous electrolyte 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. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and mixed solvents thereof. Examples of the electrolyte salt include LiPF ６ The non-aqueous electrolyte is not limited to a liquid electrolyte, but may be a solid electrolyte.

[0013] The electrode assembly 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all long, strip-shaped bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the longitudinal direction and width direction than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and for example, two separators 13 are arranged to sandwich the positive electrode 11.

[0014] A positive electrode lead 20 and two negative electrode leads 21 a, 21 b are connected to the electrode body 14. The positive electrode lead 20 electrically connects the positive electrode 11 and the sealing body 17. The first negative electrode lead 21 a is joined to the end of the negative electrode 12 at the start of winding, and electrically connects the end of the negative electrode 12 at the start of winding and the bottom 31 of the outer can 16. The second negative electrode lead 21 b is joined to the end of the negative electrode 12 at the end of winding, and electrically connects the end of the negative electrode 12 at the end of winding and the bottom 31 of the outer can 16.

[0015] 1 , the positive electrode lead 20 passes through the opening of the upper insulating plate 18 and extends toward the sealing body 17, and is joined to the lower surface of the sealing body 17. The first negative electrode lead 21a passes through a through-hole in the annular lower insulating plate 19 and is bent toward the hollow portion 14a of the electrode body 14. The second negative electrode lead 21b passes outside the lower insulating plate 19 and is bent so as to overlap the first negative electrode lead 21a. The overlapping portion of the first negative electrode lead 21a and the second negative electrode lead 21b is resistance-welded using a welding rod inserted into the hollow portion 14a of the electrode body 14, and is joined to the inner surface of the bottom 31 of the outer can 16.

[0016] When the negative electrode leads 21a, 21b are joined to both longitudinal ends of the negative electrode 12, the current collection path of the negative electrode 12 is shortened, thereby reducing the internal resistance of the cylindrical battery 10. The negative electrode lead may be joined only to the longitudinal end of the negative electrode at the end where winding ends. Alternatively, the negative electrode lead may be joined only to the longitudinal end of the negative electrode at the start of winding, and an outermost core exposed portion of the negative electrode core located at at least a part of the outermost periphery of the electrode body may contact the inner circumferential surface of the exterior can 16.

[0017] Fig. 2(a) is a schematic plan view of the end portion of the winding start side on the inner surface of the winding when the positive electrode 11 is unfolded into a long shape, and Fig. 2(b) is a schematic plan view of the end portion of the winding start side on the outer surface of the winding when the negative electrode 12 is unfolded into a long shape. Note that the shaded area in Fig. 2(a) is the positive electrode material mixture layer forming area, and the shaded area in Fig. 2(b) is the negative electrode material mixture layer forming area.

[0018] As shown in FIG. 2( a), the positive electrode 11 includes a positive electrode core 11a and a positive electrode mixture layer 11b formed on at least one surface of the positive electrode core 11a. The positive electrode core 11a can be 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 such a metal disposed on the surface. The positive electrode mixture layer preferably 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 11a. The positive electrode active material may be, for example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, or the like. The positive electrode lead 20 is connected to the positive electrode 11, but is preferably directly bonded to the positive electrode core 11a by ultrasonic welding or the like, and the joint with the positive electrode core 11a is preferably covered with insulating tape.

[0019] As shown in FIG. 2( b), the negative electrode 12 includes a negative electrode core 12a and a negative electrode mixture layer 12b formed on at least one surface of the negative electrode core 12a. The negative electrode core 12a can be made of a foil of a metal, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. The negative electrode mixture layer 12b contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR) or PVdF, and is preferably formed on both sides of the negative electrode core 12a. Examples of the negative electrode active material include graphite and silicon-containing compounds. The negative electrode leads 21a and 21b are preferably directly bonded to the negative electrode core 12a by ultrasonic welding or the like, and the bonded portion to the negative electrode core 12a is preferably covered with insulating tape 15.

[0020] 1 , the outer can 16 is generally made of a metal primarily composed of iron, such as nickel-plated iron, but 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 recessing a portion of the cylindrical portion 39 radially inward using a spinning process. The shoulder portion 29 is formed when the upper end (the end on one side in the axial direction) of the cylindrical portion 39 is bent radially inward and crimped to the peripheral edge portion 33 of the sealing body 17, and extends radially inward at the upper end of the cylindrical portion 39.

[0021] The sealing body 17 is clamped by crimping between the shoulder portion 29 and the grooved portion 22 via the gasket 28, and is fixed to the outer can 16. The grooved portion 22 is formed at a position a predetermined length away 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.

[0022] 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 sealing plate 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 sealing plate 27 has a convex shape with a radially central portion protruding outward. The convex portion 27a of the sealing plate 27 includes a ring-shaped sloped portion and a flat top surface portion surrounded by the sloped portion. One or more air vents 27b are formed in the top surface portion.

[0023] 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 cylindrical battery 10 and the internal pressure rises, the lower valve body 24 deforms and pushes the upper valve body 26 toward the sealing plate 27, causing it to break, thereby 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, allowing gas to be released through the vent hole 27b in the sealing plate 27.

[0024] 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 sealing plate 27, which is the top plate of the sealing body 17 electrically connected to the terminal plate 23, serves as the positive electrode terminal. Also, the outer can 16 to which the negative electrode leads 21 a, 21 b are joined serves as the negative electrode terminal.

[0025] Next, the structure of the positive electrode 11 and the position of the positive electrode 11 relative to the negative electrode 12 will be described in detail using Figure 2. As shown in Figures 2(a) and 2(b), the negative electrode mixture layer 12b has an extension portion 38 that extends from the inner side of the winding at the starting end 40 on the winding start side of the positive electrode 11 toward the winding start side of the electrode body 14. The extension portion 38 extends toward the winding start side by, for example, 1 / 5 to 1 turn.

[0026] As shown in Figure 2(a), the starting end 40 of the positive electrode 11 is displaced toward the winding end of the longitudinal direction of the positive electrode 11 as it moves from the lower side (the bottom 31 side of the outer can 16) to the upper side in the axial direction, and the starting end 40 extends on a straight line that is inclined at an acute angle with respect to the width direction of the positive electrode 11. For reasons that will be described later, the distance d0 in the longitudinal direction of the positive electrode 11 between the center 40a in the width direction of the starting end 40 and the tip 42 located at the lower end 40b of the starting end 40 is preferably 0.5 mm or more and 5 mm or less. The tip 42 of the starting end 40 is the portion of the starting end 40 that is located closest to the winding start side, and is preferably provided at at least one of the lower end 40b and the upper end 40c of the starting end 40.

[0027] As shown in FIG. 2( b), the mixture layer starting edge 50 extends substantially parallel to the width direction of the negative electrode 12. As shown in FIGS. 2( a) and 2(b), the first distance d1 between the center 40a of the starting edge 40 and the mixture layer starting edge 50 is longer than the second distance d2 between the widthwise lower end (one end) 40b of the starting edge 40 and the mixture layer starting edge 50. The first distance d1 may be longer than the third distance d3 between the widthwise upper end (the other end) 40c of the starting edge 40 and the mixture layer starting edge 50, and the first distance d1 may be longer than both the second distance d2 and the third distance d3. In this way, by separating the center 40a of the starting edge 40 from the mixture layer starting edge 50 relative to at least one of the widthwise lower end 40b and upper end 40c, it is possible to prevent the separator 13 from being pressed by the center 40a of the starting edge 40 of the positive electrode 11. The first distance d1, the second distance d2, and the third distance d3 are all distances based on the longitudinal direction of the positive electrode 11 (corresponding to the winding direction).

[0028] [Evaluation of Voltage Drop Amount] <Example> The winding start side of the positive electrode was cut so that the starting end of the winding start side of the positive electrode extended in a direction inclined toward the width direction of the positive electrode. As with the positive electrode of the embodiment shown in FIG. 2(a), the upper end of the starting end was positioned closer to the winding end side than the lower end of the starting end. The winding direction distance from the upper end to the lower end of the starting end was 1 mm, and the winding direction distance from the width direction center of the starting end to the lower end of the starting end was 0.5 mm. The negative electrode was fabricated so that the starting end of the mix layer on the winding start side was approximately parallel to the width direction of the negative electrode. An electrode assembly was fabricated by winding the positive electrode and negative electrode with a separator interposed therebetween so that the negative electrode mix layer provided on the outer winding surface of the negative electrode core extended from the inside of the winding start end of the positive electrode toward the winding start side. The electrode assembly was used to fabricate a cylindrical battery of the example.

[0029] Comparative Example A positive electrode was fabricated in the same manner as in the Example, except that the winding start side of the positive electrode 311 was cut so that the winding start end 340 of the positive electrode 311 was approximately parallel to the width direction of the positive electrode 311, as shown in Figure 3. The start end of the positive electrode 311 was positioned at a position corresponding to the width-direction center position of the start end of the positive electrode in the electrode assembly of the Example, and the positive electrode 311 and the negative electrode were wound with a separator interposed therebetween to fabricate an electrode assembly. A cylindrical battery of the Comparative Example was fabricated using this electrode assembly.

[0030] (Evaluation Method) Each of the produced batteries was charged at a constant current of 1 C until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 0.05 C. After the voltage stabilized, each battery was left in a 60°C environment for 150 days. The amount of voltage drop after leaving the battery was evaluated from the voltage measured before and after leaving the battery. The evaluation results are shown in Table 1.

[0031]

[0032] In the battery of the example in which the distance between the widthwise center position of the positive electrode starting end and the mix layer starting end of the negative electrode mix layer was longer than the distance between the bottom end of the positive electrode starting end and the mix layer starting end of the negative electrode mix layer, the amount of voltage drop was significantly reduced to 1 / 10 compared to the battery of the comparative example in which the distance between the positive electrode starting end and the mix layer starting end of the negative electrode mix layer was constant regardless of the widthwise position of the positive electrode starting end.

[0033] The reason why the amount of voltage drop in the battery of the example was smaller than that in the battery of the comparative example is presumably that, in the battery of the example, the distance between the widthwise center of the starting end of the positive electrode and the starting end of the mixture layer of the negative electrode is longer than the distance between the bottom end of the starting end of the positive electrode and the starting end of the mixture layer of the negative electrode, making it more difficult for the widthwise center part of the starting end of the positive electrode to press against the separator than in the battery of the comparative example.

[0034] When the distance in the width direction between the center of the positive electrode starting end in the width direction and the lower end of the positive electrode starting end is 0.5 mm or more, voltage drop can be significantly suppressed. Furthermore, when the distance in the width direction between the center of the positive electrode starting end in the width direction and the lower end of the positive electrode starting end is 5 mm or less, the lower end of the positive electrode starting end does not excessively protrude toward the winding start side. Therefore, the positive electrode, negative electrode, and separator can be smoothly wound.

[0035] 2(b), when the negative electrode lead 21a joined to the bottom 31 of the outer can 16 is joined to the end of the negative electrode 12 on the winding start side, the lower end of the winding start side of the electrode body 14 is less likely to deform. Therefore, in this case, it is preferable that the tip 42 of the starting end 40 of the positive electrode 11 be positioned at the lower end 42b of the starting end 40.

[0036] [Modifications] The present disclosure is not limited to the above-described embodiment and its modifications, and various improvements and modifications are possible within the scope of the claims of the present application and their equivalents. For example, as shown in FIG. 4, i.e., a schematic plan view of a positive electrode 111 according to a first modification corresponding to FIG. 2(a), a tip 142 on the winding start side at a starting end 140 of the positive electrode 111 may extend substantially parallel to the width direction of the positive electrode 111. According to the second modification, bending of the tip 142 of the positive electrode 111 can be prevented when the positive electrode 111, the negative electrode 12, and the separator 13 are wound.

[0037] 5, that is, a schematic plan view of a positive electrode 211 of a second modified example corresponding to FIG. 2(a), a starting end 240 of the positive electrode 211 may have a convex curved portion 241 in the widthwise center portion on the longitudinal winding end side. A first distance between a center 240a of the starting end 240 and a mixture layer starting end 50 of the negative electrode mixture layer 12b may be longer than a second distance between a lower end (one end in the widthwise direction) 240b of the starting end 240 in the widthwise direction and the mixture layer starting end 50, and may also be longer than a third distance between an upper end (the other end in the widthwise direction) 240c of the starting end 240 in the widthwise direction and the mixture layer starting end 50.

[0038] According to the second modification, the shape of the starting end of the positive electrode 211 approaches a shape symmetrical with respect to a plane (not shown) that bisects the positive electrode 211 in the width direction, which allows for smooth winding of the positive electrode 211, the negative electrode 12, and the separator 13. Furthermore, the leading ends 242a, 242b located at the lower end 240b and the upper end 240c of the starting end 240 of the positive electrode 211 extend substantially in the width direction of the positive electrode 211, which allows for smoother winding of the positive electrode 211, the negative electrode 12, and the separator 13.

[0039] REFERENCE SIGNS LIST 10 Cylindrical battery, 11, 111, 211 Positive electrode, 11a Positive electrode core, 11b Positive electrode mixture layer, 12 Negative electrode, 12a Negative electrode core, 12b Negative electrode mixture layer, 13 Separator, 14 Electrode body, 14a Hollow portion, 15 Insulating tape, 16 Outer can, 17 Sealing body, 18 Upper insulating plate, 19 Lower insulating plate, 20 Positive electrode lead, 21a First negative electrode lead, 21b Second negative electrode lead, 22 Grooved portion, 23 Terminal plate, 24 Lower valve body, 25 Insulating plate, 26 Upper valve body, 27 Sealing plate, 27a Convex portion, 27b Vent, 28 Gasket, 29 Shoulder portion, 31 Bottom portion, 33 Peripheral edge portion, 38 Extension portion, 39 Cylindrical portion, 40, 140, 240 Starting end of positive electrode, 40a, 240a Width direction center of starting end, 40b, 240b Lower end of starting end, 40c, 240c Upper end of starting end, 50 Starting end of negative electrode mixture layer, 141 Curved portion, 42, 142, 242a, 242b Tip end of starting end, d1 First distance, d2 Second distance, d3 Third distance.

Claims

1. A cylindrical battery comprising: an electrode assembly in which a long positive electrode having a positive electrode core and a positive electrode mixture layer, and a long negative electrode having a negative electrode core and a negative electrode mixture layer are wound with a separator interposed therebetween; a bottomed, cylindrical outer can that contains the electrode assembly; and a sealing body that closes the opening of the outer can, wherein the negative electrode mixture layer has an extension that extends from an inner side of a starting end of a winding start side of the positive electrode to the winding start side, and a first distance between a center in the width direction at the starting end and the mix layer starting end of the negative electrode mix layer on the winding start side is longer than at least one of a second distance between one end in the width direction of the starting end and the mix layer starting end, and a third distance between the other end in the width direction of the starting end and the mix layer starting end.

2. The cylindrical battery according to claim 1, wherein the one end in the width direction is an end of the starting end on the bottom side of the outer casing, the first distance is longer than the second distance, and a negative electrode lead is provided joined to the end of the negative electrode on the winding start side.

3. The cylindrical battery according to claim 1 or 2, wherein the first distance is longer than both the second distance and the third distance.

4. A cylindrical battery as described in claim 1 or 2, wherein the tip portion of the starting end that is located closest to the beginning of winding extends along the width direction of the positive electrode.