Cylindrical battery and method for producing same

Abstract

This cylindrical battery includes an electrode body in which an elongated positive electrode (11), having a positive electrode core body (11a) and a positive electrode mixture layer (11b), and an elongated negative electrode, having a negative electrode core body and a negative electrode mixture layer, are wound together with a separator therebetween. The positive electrode mixture layer (11b) has a recess (44) that includes the center of a winding start-side end in the width direction of the positive electrode mixture layer (11b) corresponding to a winding axis direction of the electrode body, and that is formed in a range separated from both ends in the width direction of the positive electrode mixture layer (11b).

Description

Cylindrical battery and its manufacturing method

[0001] The present disclosure relates to cylindrical batteries and methods for manufacturing the same.

[0002] A cylindrical battery includes a wound electrode assembly in which a positive electrode and a negative electrode are spirally wound with a separator interposed therebetween. Repeated charge-discharge cycles in a cylindrical battery can cause the positive electrode and negative electrode to expand and contract, resulting in localized deformation of at least one of the positive electrode and negative electrode, resulting in electrode plate deformation.

[0003] For example, Patent Document 1 discloses a cylindrical battery equipped with a wound electrode body having an insulating tape attached to the negative electrode so as to straddle the surface of the negative electrode lead in the winding direction in order to suppress deformation of the joint portion of the negative electrode lead.

[0004] International Publication No. 2018 / 180748

[0005] In cylindrical batteries, the winding start end of the positive electrode forms a large step along the winding direction, and therefore the negative electrode portion facing the inner side of the winding start end of the positive electrode may deform during charge / discharge cycles. If this deformation of the negative electrode portion occurs, the distance between the positive and negative electrodes may vary, causing uneven charge / discharge reactions and deteriorating cycle characteristics.

[0006] The insulating tape of Patent Document 1 may not be able to sufficiently suppress deformation of the negative electrode portion facing the inner winding side of the winding start end of the positive electrode, which causes the above-mentioned step. Alternatively, it may be possible to provide a thin-walled portion at the winding start end of the positive electrode mixture layer that is thinner than the remaining portions of the positive electrode mixture layer. However, providing a thin-walled portion across the entire winding start end of the positive electrode mixture layer may result in a significant decrease in battery capacity. Furthermore, the inventors' extensive analysis revealed that the degree of deformation of the negative electrode portion varies across the width of the positive electrode mixture layer. Based on these analysis results, the objective of the present disclosure is to realize a cylindrical battery and a manufacturing method thereof that can effectively suppress plate deformation of the negative electrode portion facing the inner winding side of the winding start end of the positive electrode while suppressing a decrease in battery capacity.

[0007] The cylindrical battery according to the present disclosure is a cylindrical battery including an electrode body 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, and the positive electrode mixture layer has a recess that includes the center in the width direction of the positive electrode mixture layer, which corresponds to the winding axis direction of the electrode body, among the winding start end portions, and is provided in a range spaced apart from both ends in the width direction of the positive electrode mixture layer.

[0008] A method for manufacturing a cylindrical battery according to the present disclosure is a method for manufacturing a cylindrical battery, in which the cylindrical battery is a cylindrical battery according to the present disclosure, and the recess is formed by irradiating the positive electrode mixture layer with laser light.

[0009] The cylindrical battery and manufacturing method thereof according to the present disclosure can effectively suppress plate deformation of the negative electrode portion facing the inside of the winding start end of the positive electrode while suppressing a decrease in battery capacity.

[0010] 8 is a cross-sectional view of a cylindrical battery according to an embodiment; FIG. 9 is a cross-sectional view of the winding start end portion of the positive electrode and negative electrode when the electrodes are unfolded into a long strip, cut at the widthwise center; FIG. 10 is a perspective view of a longitudinal portion including the winding start end portion of the positive electrode according to an embodiment; FIG. 11 is a cross-sectional view of FIG. 3 taken along the line A-A in FIG. 3; FIG. 12 is a view of the positive electrode as viewed in the direction of arrow B in FIG. 3 according to an embodiment; FIG. 13 is a view of a longitudinal portion including the winding start end portion of the positive electrode as viewed from the inside of the winding in an embodiment; FIG. 14 is a view of the cutting position of the positive electrode intermediate material before it is cut to the dimensions of the positive electrode as viewed from the inside of the winding; FIG. 15 is a view corresponding to FIG. 4 of a positive electrode constituting a cylindrical battery according to another embodiment; FIG. 16 is a view corresponding to FIG. 5 of the positive electrode of FIG.

[0011] 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 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 battery 10 according to one embodiment, but the cylindrical battery according to the present disclosure is not limited thereto, and the electrolyte may be an aqueous electrolyte.

[0012] 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.

[0013] 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.

[0014] Cylindrical battery 10 further includes a gasket 28 interposed between exterior can 16 and sealing body 17. Gasket 28 is a ring-shaped resin member attached to the outer periphery of sealing body 17, and insulates sealing body 17 from exterior can 16. Gasket 28 seals the gap between exterior can 16 and sealing body 17, sealing the inside of the battery.

[0015] 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 LiPF６ The non-aqueous electrolyte is not limited to a liquid electrolyte, but may be a solid electrolyte.

[0016] 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 than the positive electrode 11 in the longitudinal and width directions. The longitudinal direction corresponds to the winding direction. The width direction corresponds to the winding axis direction of the electrode assembly 14. 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.

[0017] 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 winding 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 winding at the end of winding and the bottom 31 of the outer can 16.

[0018] 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.

[0019] 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.

[0020] Fig. 2 is a cross-sectional view of the winding start end of the positive electrode 11 and the negative electrode 12 when they are developed into a long strip, cut at the center in the width direction. Fig. 3 is a perspective view of a portion in the longitudinal direction including the winding start end of the positive electrode 11.

[0021] As shown in FIGS. 2 and 3 , the positive electrode 11 includes a positive electrode core 11a and positive electrode mixture layers 11b and 11c 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. 3, a core exposed portion 11d is formed on each of both side surfaces in the thickness direction at the longitudinal center of the positive electrode 11, and a positive electrode lead 20 is joined to one of the core exposed portions 11d. The positive electrode mixture layer may be formed only on one surface of the positive electrode core 11a, for example, on the inner wound surface.

[0022] As shown in FIG. 2 , the negative electrode 12 includes a negative electrode core 12a and negative electrode mixture layers 12b and 12c 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 layers 12b and 12c contain a negative electrode active material and a binder, such as styrene-butadiene rubber (SBR) or PVdF, and are preferably formed on both surfaces 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. The negative electrode mixture layer may be formed only on one surface of the negative electrode core 12a, for example, on the outer surface of the wound negative electrode core 12a.

[0023] 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.

[0024] 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 spaced a predetermined distance from the upper end of the outer can 16.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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 Figures 2 to 6. Figure 4 is a cross-sectional view taken along line A-A in Figure 3. Figure 5 is a view of the positive electrode 11 as viewed in the direction of arrow B in Figure 3. Figure 6 is a view of a portion of the positive electrode 11 in the longitudinal direction, including the winding start end, as viewed from the inside of the winding.

[0029] As shown in FIG. 2 , the negative electrode 12 has a non-facing portion 41 in which negative electrode mixture layers 12b, 12c are formed on at least one surface of the negative electrode core 12a at the winding start side of the electrode body 14, and which is wound around the positive electrode 11 by 0.2 turns or more in a state not facing the positive electrode 11.

[0030] The non-facing portion 41 of the negative electrode 12 is preferably wound 0.75 turns or more around the winding start side of the electrode assembly 14. The non-facing portion 41 has the negative electrode mixture layers 12b, 12c, but does not face the positive electrode 11 and therefore does not contribute to the charging and discharging of the battery. On the other hand, the non-facing portion 41 has high rigidity due to the presence of the negative electrode mixture layer 12b, which contributes to stabilizing the shape of the winding core portion of the electrode assembly 14 and ensures a path for exhausting gas generated in the event of a battery abnormality. The separator 13 is not shown in Figure 2.

[0031] In the non-facing portion 41, the negative electrode mixture layers 12b, 12c may be formed on either the inner winding surface of the negative electrode substrate 12a facing the winding center or the outer winding surface of the negative electrode substrate 12a facing the sidewall of the outer can 16, but are preferably formed on both the inner winding surface and the outer winding surface. In this case, the shape stability of the winding core portion is further improved. The non-facing portion 41 is preferably formed with a length of, for example, 0.75 to 1.5 turns, more preferably 0.90 to 1.4 turns, and particularly preferably 1.0 to 1.3 turns. In this case, it is easy to ensure a good exhaust path in the winding core portion.

[0032] The negative electrode 12 has a core exposed portion 12d that is a portion from the starting end 42 to the non-facing portion 41. Like the non-facing portion 41, the core exposed portion 12d is a portion that does not face the positive electrode 11. However, it differs from the non-facing portion 41 in that it does not have the negative electrode mixture layers 12b, 12c and is composed only of the negative electrode core 12a. In this embodiment, a negative electrode lead 21a is joined to the core exposed portion 12d. When the negative electrode lead 21a is disposed on the winding core portion of the electrode body 14, deformation is likely to occur in the facing portion of the positive and negative electrodes during charge and discharge, but this embodiment can effectively suppress such deformation.

[0033] The length of the core exposed portion 12d is not particularly limited, but from the viewpoint of ensuring a bonding area for the negative electrode lead 21a, it is preferable that the length be 0.5 or more revolutions. The core exposed portion 12d may be formed with a length of 0.5 or more revolutions and less than 1.0 revolutions. The negative electrode lead 21a is, for example, a thin metal plate containing a metal such as nickel as a main component and having a thickness of 50 μm or more and 100 μm or less. The negative electrode lead 21a is bonded to the outer surface of the core exposed portion 12d, for example, at a position away from the starting end 42 and the non-facing portion 41 of the negative electrode 12.

[0034] In this embodiment, as shown in FIGS. 2 to 6 , the positive electrode mixture layer 11b on the inner side of the winding has a recess 44 provided in a range (the range indicated by arrow C2 in FIGS. 5 and 6 ) that includes a center γ ( FIG. 6 ) in the width direction β of the positive electrode mixture layer 11b and is spaced from both ends of the positive electrode mixture layer 11b in the width direction β, within a predetermined range (the range indicated by arrow C1 in FIGS. 2 , 4 , and 6 ) from the winding start end 40 on the winding start side. The recess 44 is thinner than the thickness of a main portion 45 of the positive electrode mixture layer 11b on the inner side of the winding. The main portion 45 of the positive electrode mixture layer 11b is a portion that occupies most of the positive electrode mixture layer 11b other than the recess 44 and has a constant thickness. In the example shown in FIG. 3 , the entire portion of the positive electrode mixture layer 11b other than the recess 44 constitutes the main portion 45. The main portion 45 includes a portion D1 located closer to the end of the winding than the winding start end of the positive electrode mixture layer 11b where the recess 44 is provided, and portions D2 and D3 located outside both ends of the recess 44 in the width direction of the positive electrode mixture layer 11b.

[0035] In this embodiment, the thickness of the positive electrode mixture layer 11b in the recess 44 gradually decreases in the longitudinal direction perpendicular to the width direction β toward the starting end 40, as shown in Fig. 4. For example, as shown in Fig. 4, in a cross section of the positive electrode mixture layer 11b perpendicular to the width direction β, the bottom surface 44a of the recess 44 is linear and inclined with respect to the surface of the core 11a, but the bottom surface 44a may also be curved in an arc shape recessed toward the core 11a.

[0036] As shown in FIG. 5 , the thickness of the positive electrode mixture layer 11b in the recess 44 gradually decreases toward the center γ in the width direction β. In a cross section of the positive electrode mixture layer 11b perpendicular to the longitudinal direction α, the bottom surface 44a of the recess 44 is linear and inclined relative to the surface of the core 11a. However, the bottom surface 44a may also have an arc-shaped curved shape recessed toward the core 11a. The thickness of the positive electrode mixture layer 11b in the recess 44 is minimum at the starting end 40 at the center γ in the width direction β. In this case, the positive electrode mixture layer 11b is formed at the starting end 40 at the center γ in the width direction β, but the thickness of the positive electrode mixture layer 11b at the starting end 40 at the center γ in the width direction β may be zero. The planar shape of the recess 44 as viewed in the thickness direction of the positive electrode mixture layer 11b is semi-elliptical, and the bottom surface 44a of the recess 44 has the shape of a side surface of a semi-elliptical cone.

[0037] Because the content of positive electrode active material per unit area of ​​the recess 44 is smaller than that of the main portion 45, the amount of expansion and contraction of the portion of the negative electrode 12 facing the recess 44 during charge and discharge of the battery is reduced. Furthermore, the provision of the recess 44 prevents the winding start end of the positive electrode 11 from forming a large step along the winding direction. As a result, deformation of the negative electrode portion facing the inner side of the winding start end of the positive electrode during charge and discharge cycles is suppressed.

[0038] As a result of careful analysis by the inventors, it has been found that the negative electrode 12, which faces the inside of the winding start end of the positive electrode 11, tends to be more susceptible to pressure in the widthwise center portion, and that electrode plate deformation is more likely to occur in the widthwise center portion than near both widthwise ends. Therefore, even in a configuration in which the main portion 45 is left on the widthwise outer side of the recess 44 at the winding start end of the positive electrode mixture layer 11b, as in this embodiment, electrode plate deformation of the negative electrode 12 can be effectively suppressed. Furthermore, by leaving the main portion 45 at the winding start end of the positive electrode mixture layer 11b, a decrease in battery capacity can be suppressed.

[0039] Similar to the positive electrode mixture layer 11b on the inside of the winding, the positive electrode mixture layer 11c on the outside of the winding may also have a recess.

[0040] Furthermore, the adhesion strength of the positive electrode mixture layer 11b to the positive electrode core 11a is higher in the recess 44 than in the main portion 45. This makes it possible to prevent the positive electrode mixture layer 11b from peeling off from the positive electrode core 11a in the recess 44, thereby ensuring the durability of the battery.

[0041] In order to increase the adhesive strength of the positive electrode mixture layer 11b in the recesses 44, in the manufacturing method of the cylindrical battery of this embodiment, the recesses 44 are formed by irradiating the positive electrode mixture layer 11b with laser light.

[0042] FIG. 7 is a view of the cut position of the positive electrode intermediate material 50 before being cut to the dimensions of the positive electrode 11, viewed from the inside of the winding, in one embodiment. The recess 44 can be formed, for example, by irradiating the positive electrode intermediate material 50 with laser light. Specifically, the laser light is irradiated to a portion of the positive electrode mixture layer 11b in the width direction, including the center of the width direction, so that an elliptical conical recess is formed in the width direction, with the center being the deepest, centered on the cut position indicated by the dashed-dotted line δ. At this time, the irradiation position of the laser light may be moved back and forth in the width direction or longitudinal direction of the positive electrode intermediate material 50 while adjusting the output and focus of the laser light. This removes a portion of the surface of the positive electrode mixture layer 11b with the laser light, forming the recess 49. Then, by cutting the positive electrode intermediate material 50 along the dashed-dotted line δ, a positive electrode 11 is obtained in which the recess 44 is formed in a predetermined range from the starting end of the positive electrode mixture layer 11b on the winding start side. At this time, as shown in Fig. 5, recesses are formed not only at the end of the positive electrode mixture layer 11b on the winding start side but also at the end of the positive electrode mixture layer 11b on the winding end side. Note that in the area of ​​the positive electrode mixture layer 11b irradiated with the laser light, the binder melts and solidifies due to the heat of the laser light. This increases the adhesion strength of the positive electrode mixture layer 11b to the positive electrode substrate 11a in the recesses 44 compared to the main portion 45.

[0043] Furthermore, unlike the present embodiment, when a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and a dispersion medium is applied to a positive electrode core to form a positive electrode mixture layer, the amount of positive electrode mixture slurry applied in the range where the recess 44 is to be formed may be made smaller than that of the main portion 45, thereby forming the recess 44.

[0044] The ratios of lengths L2 and L3 (FIG. 6) from the widthwise center γ to both widthwise ends of the recess 44 to the entire widthwise length L1 (FIG. 6) of the positive electrode mixture layer 11b are preferably 20% or more and 40% or less. More preferably, the ratios of lengths L2 and L3 to length L1 are 25% or more and 40% or less.

[0045] The length of the recess 44 in the longitudinal direction of the positive electrode 11 is preferably a winding length of 0.05 or more and less than 1 revolution. Furthermore, at the widthwise center γ, the average thickness of the positive electrode mixture layer 11b in the recess 44 in the longitudinal direction of the positive electrode 11 is preferably 70% or less of the thickness of the main portion 45. If the average thickness is 70% or less of the thickness of the main portion 45, the effect of suppressing plate deformation of the negative electrode 12 is enhanced.

[0046] FIG. 8 is a view corresponding to FIG. 4 of a positive electrode 111 constituting a cylindrical battery according to another embodiment. FIG. 9 is a view corresponding to FIG. 5 of the positive electrode 111. In the configuration of this example, a recess 47 is provided at the winding start end of the positive electrode mixture layer 11b1 on the inner side of the winding, in a range spaced apart from both ends of the positive electrode mixture layer 11b1 in the width direction, including the width center of the positive electrode mixture layer 11b1. Specifically, the positive electrode mixture layer 11b1 has the recess 47 in a longitudinal range (the range indicated by arrow C1 in FIG. 7 ) from the starting end on the winding start side, and in a predetermined range in the width direction (the range indicated by arrow C2 in FIG. 8 ) including the width center. In this example, the bottom surface 47a of the recess 47 is a flat surface parallel to the surface of the positive electrode core 11a. In this example, too, by providing the recess 47, it is possible to effectively suppress plate deformation of the portion of the negative electrode 12 that faces the inside of the winding start end of the positive electrode 111, while suppressing a decrease in battery capacity. As in the manufacturing method of the cylindrical battery of this embodiment described with reference to FIGS. 1 to 6 , the recess 47 can be formed by irradiating the positive electrode mixture layer 11b1 with laser light. This increases the adhesion strength of the positive electrode mixture layer 11b to the positive electrode substrate 11a in the recess 47 compared to the main portion 45.

[0047] The present disclosure is further described by the following embodiments. Configuration 1: A cylindrical battery including 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, wherein the positive electrode mixture layer has a recessed portion that includes a widthwise center of the positive electrode mixture layer corresponding to the winding axis direction of the electrode assembly, and is provided in a range spaced apart from both ends of the positive electrode mixture layer in the widthwise direction, at a winding start end portion. Configuration 2: The cylindrical battery according to Configuration 1, in which the recessed portion has a higher adhesion strength to the positive electrode core than a main portion other than the recessed portion, which has a constant thickness. Configuration 3: The cylindrical battery according to Configuration 1 or Configuration 2, in which the ratio of the length from the widthwise center to both widthwise ends of the recessed portion to the entire widthwise length of the positive electrode mixture layer is 20% or more and 40% or less. Configuration 4: The cylindrical battery according to any one of Configurations 1 to 3, wherein the thickness of the positive electrode mixture layer in the recessed portion decreases toward the starting end of the positive electrode mixture layer in a longitudinal direction perpendicular to the width direction, and decreases toward the center in the width direction.Configuration 5: The cylindrical battery according to any one of Configurations 1 to 4, wherein the recessed portion has a winding length of 0.05 or more turns but less than one turn.Configuration 6: The cylindrical battery according to any one of Configurations 1 to 5, wherein the recessed portion is provided on the inner side of the wound positive electrode.Configuration 7: The cylindrical battery according to any one of Configurations 1 to 6, wherein, at the center in the width direction, the average thickness of the positive electrode mixture layer in the recessed portion in the longitudinal direction is 70% or less of the thickness of a main portion other than the recessed portion and having a constant thickness.Configuration 8: The method for manufacturing the cylindrical battery according to Configuration 1, wherein the recessed portion is formed by irradiating the positive electrode mixture layer with laser light.

[0048] REFERENCE SIGNS LIST 10 Cylindrical battery, 11, 111 Positive electrode, 11a Positive electrode core, 11b, 11c, 11b1 Positive electrode mixture layer, 11d Core exposed portion, 12 Negative electrode, 12a Negative electrode core, 12b, 12c Negative electrode mixture layer, 13 Separator, 14 Electrode body, 14a Hollow portion, 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 portion, 39 cylindrical portion, 40 starting end, 41 non-opposing portion, 42 starting end, 44 recessed portion, 44a bottom surface, 45 main portion, 47 recessed portion, 47a bottom surface, 49 recessed portion, 50 positive electrode intermediate material

Claims

1. A cylindrical battery comprising an electrode body 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, wherein the positive electrode mixture layer has a recess that includes a center in a width direction of the positive electrode mixture layer corresponding to a winding axis direction of the electrode body among the winding start end portions and is provided in an area separated from both ends of the positive electrode mixture layer in the width direction.

2. The cylindrical battery according to claim 1, wherein the adhesion strength of the positive electrode mixture layer to the positive electrode core is greater in the recess than in a main portion other than the recess and having a constant thickness.

3. The cylindrical battery according to claim 1, wherein the ratio of the length from the center in the width direction to both ends in the width direction of the recess to the entire length in the width direction of the positive electrode mixture layer is 20% or more and 40% or less.

4. The cylindrical battery according to claim 1, wherein the thickness of the positive electrode mixture layer in the recess is smaller toward a starting end of the positive electrode mixture layer in a longitudinal direction perpendicular to the width direction, and is also smaller toward a center in the width direction.

5. The cylindrical battery according to claim 1, wherein the recess has a winding length of 0.05 or more turns but less than 1 turn.

6. The cylindrical battery according to claim 1, wherein the recess is provided on an inner side of the positive electrode.

7. The cylindrical battery according to claim 1, wherein, at the center in the width direction, an average thickness of the positive electrode mixture layer in the recessed portion in the longitudinal direction is 70% or less of a thickness of a main portion other than the recessed portion and having a constant thickness.

8. A method for manufacturing a cylindrical battery according to claim 1, wherein the recess is formed by irradiating the positive electrode mixture layer with laser light.

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