Cylindrical battery

Abstract

A cylindrical battery comprises an electrode body in which a positive electrode (11) that includes a positive electrode core body (41) and a positive electrode mixture layer (42) and a negative electrode that includes a negative electrode core body and a negative electrode mixture layer are wound with a separator therebetween. At the winding start-side end portion of the positive electrode (11), the thickness of the positive electrode mixture layer (42) decreases toward the winding start. When the position at which the thickness of the positive electrode mixture layer (42) begins to decrease in the longitudinal direction of the positive electrode (11) is defined as a reference position (a), a winding inner-side surface length (L1) between the winding inner-side starting end (b1) of the positive electrode mixture layer (42) and the reference position (a) on the winding inner side of the positive electrode (11) is shorter than a winding outer-side surface length (L2) between the winding outer-side starting end (b2) of the positive electrode mixture layer (42) and the reference position (a) on the winding outer side of the positive electrode (11).

Description

Cylindrical battery

[0001] The present disclosure relates to cylindrical batteries.

[0002] A typical cylindrical battery has an electrode assembly in which a positive electrode having a positive electrode core and a positive electrode mixture layer and a negative electrode having a negative electrode core and a negative electrode mixture layer are wound with a gasket interposed therebetween. Patent Document 1 discloses that the roundness of the electrode assembly can be increased by thinning the end portion on the winding start side of the positive electrode mixture layer and the end portion on the winding start side of the negative electrode mixture layer.

[0003] JP 2011-198483 A

[0004] High circularity of the electrode body leads to excellent reliability and battery characteristics of the cylindrical battery. An object of the present disclosure is to provide a cylindrical battery having a high circularity of the electrode body.

[0005] The cylindrical battery according to the present disclosure includes 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 longitudinally with a separator interposed therebetween, and the thickness of the positive electrode mixture layer at the end of the winding start side of the positive electrode decreases toward the winding start side, and when the position in the longitudinal direction of the positive electrode where the thickness of the positive electrode mixture layer starts to decrease is taken as a reference position, the length of the inner side surface of the winding from the reference position on the inner side of the winding of the positive electrode to the inner side starting end of the positive electrode mixture layer is shorter than the length of the outer side surface of the winding from the reference position on the outer side of the winding of the positive electrode to the outer side starting end of the positive electrode mixture layer.

[0006] According to the cylindrical battery according to the present disclosure, the circularity of the electrode body can be increased.

[0007] Fig. 1 is a cross-sectional view in the axial direction of a cylindrical battery according to an embodiment of the present disclosure; Fig. 2 is a schematic cross-sectional view of a starting end portion of a winding start side of a positive electrode unfolded into a long shape, cut along a plane including the longitudinal direction and thickness direction of the positive electrode; Fig. 3 is a schematic cross-sectional view corresponding to Fig. 2 of a positive electrode of a first modified example; Fig. 4 is a schematic cross-sectional view corresponding to Fig. 2 of a positive electrode of a second modified example.

[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. Furthermore, the cylindrical battery according to the present disclosure may be a battery using an aqueous electrolyte or a battery using a non-aqueous electrolyte. Hereinafter, a cylindrical lithium-ion secondary 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.

[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 description will be omitted. Furthermore, multiple drawings include schematic diagrams, and the dimensional ratios of the length, width, height, and other dimensions of each component do not necessarily match between different drawings. In this specification, the sealing body 17 side in the axial direction (height direction) of the cylindrical battery 10 is referred to as the "upper" side, and the bottom 31 side of the outer can 16 in the axial direction is referred to as the "lower" side. Furthermore, in the following description, the inner surface lengths L1, L1', and L1" refer to the length of the inner surface portion indicated by the bold line on the inner side of the winding in Figures 2 to 4, and the outer surface lengths L2, L2', and L2" refer to the length of the outer surface portion indicated by the bold line on the outer side of the winding in Figures 2 to 4. Furthermore, among the components described below, components not recited in the independent claims representing the highest concepts are optional 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 nonaqueous electrolyte (not shown), a cylindrical outer can 16 with a bottom that houses the electrode assembly 14 and the nonaqueous electrolyte, and a sealing body 17 that closes the opening of the outer can 16 via a gasket 28. The gasket 28 may be made of, for example, polyolefin. The outer can may have openings on both axial ends, and the cylindrical battery may have a configuration in which the top and bottom openings of the outer can are closed.

[0011] The electrode assembly 14 includes a long positive electrode 11, a long negative electrode 12, and two long 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 longitudinally with the separators 13 interposed therebetween. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. The negative electrode 12 is formed to be longer than the positive electrode 11 in the winding direction and the axial direction. The two separators 13 are formed to be slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11. The separators 13 protrude above and below the positive electrode 11 and the negative electrode 12.

[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] The positive electrode 11 has a positive electrode core 41 (see FIG. 2 ) and positive electrode mixture layers 42 (see FIG. 2 ) formed on both sides of the positive electrode core 41. The positive electrode core 41 can be made of a metal foil, 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 42 contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 is produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc., onto the positive electrode core 41, drying the coating, and then compressing it to form the positive electrode mixture layers 42 on both sides of the positive electrode core 41.

[0015] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0016] Examples of the conductive agent contained in the positive electrode mixture layer 42 include carbon black such as acetylene black and ketjen black, and carbon materials such as graphite. Examples of the binder contained in the positive electrode mixture layer 42 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0017] The negative electrode 12 has a negative electrode core and negative electrode mixture layers formed on both sides of the negative electrode core. The negative electrode core can be made of a metal foil, 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 layer. The negative electrode mixture layer contains a negative electrode active material and a binder. The negative electrode 12 is produced, for example, by applying a negative electrode mixture slurry containing the negative electrode active material and the binder onto the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the negative electrode core.

[0018] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials are graphites such as natural graphite, such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite, such as lump artificial graphite and graphitized mesophase carbon microbeads. The negative electrode mixture layer may contain a silicon (Si) material as the negative electrode active material. In addition, the negative electrode active material may be a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0019] As in the case of the positive electrode 11, fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like may be used as the binder contained in the negative electrode mixture layer, but styrene-butadiene rubber (SBR) or a modified product thereof is preferably used. In addition to SBR or the like, the negative electrode mixture layer may also contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0020] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0021] An upper insulating plate 18 is disposed above the electrode body 14, and a lower insulating plate 19 is disposed below the electrode body 14. In the example shown in Fig. 1 , a positive electrode lead 20 attached to the positive electrode 11 passes through a through-hole in the upper insulating plate 18, extends toward the sealing body 17, and is joined to the lower surface of the sealing body 17. On the other hand, a negative electrode lead 21 attached to the negative electrode 12 passes outside the lower insulating plate 19, extends toward the bottom 31 of the outer can 16, and is joined to the inner surface of the bottom 31.

[0022] In this embodiment, one positive electrode lead 20 is joined to an intermediate portion, such as the center portion, of the positive electrode 11 in the longitudinal direction, and one negative electrode lead 21 is joined to the winding end portion of the negative electrode 12. However, the cylindrical battery may have multiple positive electrode leads joined at intervals along the longitudinal direction of the positive electrode. Alternatively, the cylindrical battery may have one negative electrode lead joined to the winding start end portion of the negative electrode 12, and at least a portion of the outer circumferential surface of the electrode body may be formed by an exposed negative electrode core portion. The exposed negative electrode core portion may then contact the inner circumferential surface of the outer can. Alternatively, the cylindrical battery may have multiple negative electrode leads joined at intervals along the longitudinal direction of the negative electrode.

[0023] 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.

[0024] 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 strongly 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.

[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 terminal 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 terminal cap 27 has a convex shape with a radially central portion protruding outward. The convex portion 27a of the terminal 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 terminal cap 27 may have a cylindrical portion instead of the ring-shaped inclined 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. When a cylindrical battery 10 generates abnormal heat and the battery's internal pressure rises, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the terminal cap 27, interrupting the current path between the lower valve body 24 and 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 terminal cap 27.

[0027] In this embodiment, one end of the positive electrode lead 20 is connected to the underside of the terminal plate 23 by welding, ultrasonic welding, or the like, and the terminal 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.

[0028] 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 terminal cap 27 that covers the two rupture plates. 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.

[0029] 2 is a schematic cross-sectional view of the starting end of the winding start side of the positive electrode 11, which has been developed into a long strip, cut along a plane including the longitudinal direction and thickness direction of the positive electrode 11. As shown in FIG. 2 , the thickness of the positive electrode mixture layer 42 at the winding start end of the positive electrode 11 decreases toward the winding start side. When the position in the longitudinal direction of the positive electrode 11 where the thickness of the positive electrode mixture layer begins to decrease is defined as reference position a, the inner surface length L1 from reference position a on the inner side of the winding of the positive electrode 11 to inner side starting end b1 of the positive electrode mixture layer 42 is shorter than the outer surface length L2 from reference position a on the outer side of the winding of the positive electrode 11 to outer side starting end b2 of the positive electrode mixture layer 42.

[0030] Specifically, the thickness of the positive electrode mixture layer 42a on the inside side of the winding decreases from reference position a toward the winding start side, and the thickness of the positive electrode mixture layer 42b on the outside side of the winding decreases from position c, which is closer to the winding start side than reference position a, toward the winding start side. Furthermore, the inside side starting end b1 and the outside side starting end b2 of the positive electrode mixture layer 42 are positioned substantially the same in the longitudinal direction of the positive electrode 11. Therefore, the inside side surface length L1 is shorter than the outside side surface length L2. The maximum thicknesses of the positive electrode mixture layer 42a and the positive electrode mixture layer 42a are substantially the same.

[0031] The inner surface length L1 and the outer surface length L2 can be identified by a cross-sectional photograph (cross-sectional image) of a cross section perpendicular to the height direction of the electrode body 14 taken with a scanning electron microscope (SEM). Therefore, the presence or absence of infringement can be determined by checking the cross-sectional photograph (cross-sectional image).

[0032] Next, the effects of the cylindrical battery 10 will be described. The smaller the radius of a circle, the shorter the perimeter. Based on this principle, as in the cylindrical battery 10 of the present disclosure, if the inner surface length L1 of the center side of the electrode body 14 is shorter than the outer surface length L2, an electrode body 14 with high circularity can be produced. Therefore, according to the present disclosure, a cylindrical battery 10 with excellent reliability and battery characteristics can be produced. Since this makes it easier to produce an electrode body with high circularity, it is preferable that the inner surface length L1 be 0.90 to 0.99 times the outer surface length L2.

[0033] 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.

[0034] 3 is a schematic cross-sectional view of the positive electrode 111 of the first modified example, corresponding to FIG. 2. The positive electrode mixture layer 142a on the inside side of the winding may have a thickness at the inside starting end, and the positive electrode mixture layer 142b on the outside side of the winding may also have a thickness at the outside starting end. In the example shown in FIG. 3, both the positive electrode mixture layer 142a on the inside side of the winding and the positive electrode mixture layer 142b on the outside side of the winding have a thickness at their respective starting ends b1′, b2′.

[0035] In the positive electrode 111 of the first modified example as well, when the position in the longitudinal direction of the positive electrode 111 where the thickness of the positive electrode mixture layer 142 arranged on the positive electrode core 141 begins to decrease is taken as reference position a′, by making the inner-side surface length L1′ from the reference position a′ on the inner side of the positive electrode 111 to the inner-side starting end b1′ of the positive electrode mixture layer 142 shorter than the outer-side surface length L2′ from the reference position a′ on the outer side of the positive electrode 111 to the outer-side starting end b2′ of the positive electrode mixture layer 142, an electrode body with high circularity can be produced.

[0036] Fig. 4 is a schematic cross-sectional view of a positive electrode 211 of a second modified example, corresponding to Fig. 2. If the thickness of the positive electrode mixture layer at the positive electrode starting end is gradually reduced down to the positive electrode core, the inner and outer winding surfaces of the positive electrode core are likely to be exposed on the positive electrode starting end side.

[0037] As shown in FIG. 4 , in the positive electrode 211 of the second modified example, an inner side starting end b1" of the inner side positive electrode mixture layer 242a and an outer side starting end b2" of the outer side positive electrode mixture layer 242b are located on the outer side of the starting end d of the positive electrode 211. Furthermore, the inner side mixture layer non-forming portion on the inner side of the positive electrode substrate 241 from the inner side starting end b1" to the starting end d is covered with an insulating protective layer 261a, and the outer side mixture layer non-forming portion on the outer side of the positive electrode substrate 241 from the outer side starting end b2" to the starting end d is covered with an insulating protective layer 261b. It is preferable that a part of the protective layer 261a is disposed between the starting end of the positive electrode mixture layer 242a and the positive electrode substrate 241, and it is preferable that a part of the protective layer 261b is disposed between the starting end of the positive electrode mixture layer 242b and the positive electrode substrate 241.

[0038] In the positive electrode 211 of the second modified example as well, when the position in the longitudinal direction of the positive electrode 211 where the thickness of the positive electrode mixture layer 242 begins to decrease is taken as reference position a'', the inner side surface length L1'' from the reference position a'' on the inner side of the positive electrode 211 to the inner side starting end b1'' of the positive electrode mixture layer 242 is made shorter than the outer side surface length L2'' from the reference position a'' on the outer side of the positive electrode 211 to the outer side starting end b2'' of the positive electrode mixture layer 242, thereby making it possible to produce an electrode body with high circularity.

[0039] The protective layers 261a and 261b contain an insulating material as a main component. Examples of insulating materials include resin materials and inorganic materials. The resin material is preferably a polymeric material. Examples of resin materials include fluorine-based resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyimide resins, polyamide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts, and polyvinyl alcohol (PVA). The exemplified materials may be used alone, or two or more of the exemplified materials may be used in combination. The inorganic material is preferably a metal oxide. The insulating material constituting the protective layers 261a and 261b may be composed solely of a resin material, or may contain a resin material and an inorganic material.

[0040] The positive electrode 211 can be produced, for example, by applying a slurry containing an insulating material to the winding start end portions of the inner and outer winding surfaces of the positive electrode core 241, and then applying the positive electrode slurry to both the inner and outer winding surfaces so that the tip of the winding start side is positioned on the resin-coated portion. If a cylindrical battery is produced using the positive electrode 211, exposure of the positive electrode core 241 at the winding start end portion of the positive electrode 211 can be prevented, thereby increasing the roundness of the electrode body and reliably preventing a short circuit at the exposed portion of the positive electrode core 241.

[0041] 2 to 4 , the positions of the inside winding starting ends b1, b1′, b1″ of the positive electrode mixture layers 42, 142, 242 in the longitudinal direction of the positive electrodes 11, 111, 211 approximately coincide with the positions of the outside winding starting ends b2, b2′, b2″ of the positive electrode mixture layers 42, 142, 242. However, the position of the inside winding starting end of the positive electrode mixture layer in the longitudinal direction of the positive electrode may differ from the position of the outside winding starting end of the positive electrode mixture layer.

[0042] REFERENCE SIGNS LIST 10 Cylindrical battery, 11, 111, 211 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18 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 Terminal cap, 27a Convex portion, 27b Vent, 28 Gasket, 29 Shoulder portion, 31 Bottom portion, 33 Peripheral portion, 39 Cylindrical portion, 41, 141, 241 Positive electrode core body, 42, 142, 242 Positive electrode mixture layer, 42a, 142a, 242a Inner side positive electrode mixture layer of winding; 42b, 142b, 242b outer side positive electrode mixture layer of winding; 261a, 261b protective layer; a, a', a'' reference position; b1, b1', b1'' inner side starting end of positive electrode mixture layer of winding; b2, b2', b2'' outer side starting end of positive electrode mixture layer of winding; d starting end of positive electrode.

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 longitudinally with a separator interposed therebetween, wherein the thickness of the positive electrode mixture layer at the winding start end of the positive electrode decreases toward the winding start side, and when the position in the longitudinal direction of the positive electrode where the thickness of the positive electrode mixture layer starts to decrease is taken as a reference position, the length of the inner surface of the winding from the reference position on the inner side of the winding of the positive electrode to the inner side starting end of the positive electrode mixture layer is shorter than the length of the outer surface of the winding from the reference position on the outer side of the winding of the positive electrode to the outer side starting end of the positive electrode mixture layer.

2. The cylindrical battery according to claim 1, wherein the inner winding starting end and the outer winding starting end are located closer to the winding end than the starting end of the positive electrode, and an inner winding mixture layer non-forming portion on the inner winding surface of the positive electrode substrate from the inner winding starting end to the starting end of the positive electrode, and an outer winding mixture layer non-forming portion on the outer winding surface of the positive electrode substrate from the outer winding starting end to the starting end of the positive electrode, are covered with a protective layer having an insulating material as a main component.

3. The cylindrical battery according to claim 2, wherein a portion of the protective layer is disposed between the starting end of the positive electrode mixture layer and the positive electrode substrate.

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