Cylindrical secondary battery

Abstract

This battery comprises: an electrode body (14) in which a long positive electrode (11), having a positive electrode core body (30) and a positive electrode mixture layer (32), and a long negative electrode (12), having a negative electrode core body (40) and a negative electrode mixture layer (42), are wound with a separator therebetween; and an outer can that houses the electrode body (14). In the negative electrode (12), a negative electrode core body exposed portion (41) in which the negative electrode core body (40) is exposed faces a start end (11a) on the winding start side of the positive electrode (11) in the radial direction on the winding inner side. According to the battery of the present disclosure, in the electrode body (14), good circularity is easily maintained around at least one end of the positive electrode (11) in the longitudinal direction of the positive electrode, thereby facilitating suppression of electrode deformation.

Description

Cylindrical secondary battery

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

[0002] A conventional cylindrical secondary battery is described in Patent Document 1. This cylindrical secondary battery includes an electrode assembly in which a long positive electrode and a long negative electrode are wound with a separator interposed therebetween, and an outer can housing the electrode assembly. The positive electrode has a core exposed portion on both the outer and inner surfaces of the winding at the winding start end in the longitudinal direction of the positive electrode, where no mixture layer is disposed. A portion of the core exposed portion on the outer surface of the winding and a portion of the core exposed portion on the inner surface of the winding are covered with an insulating protective member.

[0003] Patent Document 1 describes that it is preferable to provide protective members at a location on the outer surface of the roll adjacent to the starting end of the mixture layer on the winding start side and at a location on the inner surface of the roll adjacent to the starting end of the mixture layer on the winding start side. It also describes that providing such protective members can protect the exposed core portion on the winding start side, which is susceptible to deformation due to pressure caused by steps due to expansion and contraction associated with charging and discharging, and can prevent micro-short circuits from occurring due to wrinkles or bending.

[0004] Japanese Patent Application Laid-Open No. 2006-134760

[0005] The present inventors have found that it is difficult to maintain good circularity around the starting end of the positive electrode on the winding start side of the wound electrode body of a cylindrical secondary battery, and that this problem tends to become more pronounced particularly when a protective member is placed around the starting end of the positive electrode on the winding start side, as in the cylindrical secondary battery of Patent Document 1 above.

[0006] If the circularity of the positive electrode is low near the starting end of the winding, stress concentration is likely to occur near the starting end during charging and discharging, making the electrode more likely to deform, and reliability and battery characteristics are likely to deteriorate. This problem can also occur near the end of the winding. Therefore, an object of the present disclosure is to provide a cylindrical secondary battery in which the electrode body is likely to maintain good circularity around at least one end of the positive electrode in the longitudinal direction, and electrode deformation is likely to be suppressed.

[0007] To solve the above problems, the present disclosure provides a cylindrical secondary 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; and an exterior can that houses the electrode assembly, wherein an exposed portion of the negative electrode core in the negative electrode faces radially inside at least one of a starting end of the positive electrode on a winding start side and a terminal end of the positive electrode on a winding end side. Here, the radial direction is the radial direction of the exterior can and the radial direction of the cylindrical secondary battery.

[0008] In the cylindrical secondary battery according to the present disclosure, the electrode body tends to maintain good circularity around at least one end of the positive electrode in the longitudinal direction of the positive electrode, and electrode deformation around this end is easily suppressed.

[0009] 1 is a cross-sectional view in the axial direction of a cylindrical secondary battery according to an embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view when an electrode body is cut in a plane perpendicular to its height direction. FIG. 3 is a schematic cross-sectional view when both a positive electrode portion and a negative electrode portion located around a starting end on a winding start side in the longitudinal direction of a positive electrode are developed into a long shape, and is a schematic cross-sectional view when the positive electrode portion and the negative electrode portion are cut in a plane including the positive electrode longitudinal direction and the positive electrode thickness direction. FIG. 4 is a schematic cross-sectional view corresponding to FIG. 3 of a battery of a reference example, and is a schematic cross-sectional view illustrating a problem of the present disclosure. FIG. 5 is a schematic cross-sectional view corresponding to FIG. 3 of a battery of the above embodiment, and is a schematic cross-sectional view illustrating why the problem can be improved. FIG. 6 is a schematic cross-sectional view corresponding to FIG. 3 of a cylindrical secondary battery of a first modified example. FIG. 7 is a schematic cross-sectional view when both a positive electrode portion and a negative electrode portion located around a winding end side on a winding end side in the longitudinal direction of a positive electrode in a cylindrical secondary battery of a second modified example are developed into a long shape, and is a schematic cross-sectional view when the positive electrode portion and the negative electrode portion are cut in a plane including the positive electrode longitudinal direction and the positive electrode thickness direction.

[0010] Hereinafter, an embodiment of a cylindrical secondary battery according to the present disclosure will be described in detail with reference to the drawings. Note that the cylindrical secondary 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 will be exemplified as a cylindrical secondary battery 10 according to one embodiment, but the cylindrical secondary battery according to the present disclosure is not limited thereto.

[0011] It is anticipated from the beginning that new embodiments may be constructed by appropriately combining the features of the embodiments and variations described below. In the following embodiments, the same components are denoted by the same reference numerals in the drawings, and redundant explanations are omitted. Furthermore, multiple drawings include schematic diagrams, and the dimensional ratios of the length, width, height, and other dimensions of each component do not necessarily match between different drawings. In this specification, the sealing body 19 side in the axial direction (height direction) of the cylindrical secondary battery 10 is referred to as "upper," and the bottom 20A side of the outer can 20 in the axial direction is referred to as "lower." Among the components described below, components not recited in the independent claims representing the highest concepts are optional components and not essential components.

[0012] Fig. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment of the present disclosure. As shown in Fig. 1, the cylindrical secondary battery (hereinafter simply referred to as battery) 10 includes an electrode assembly 14, a non-aqueous electrolyte, an outer can 20 that houses the electrode assembly 14 and the non-aqueous electrolyte, and a sealing body 19 that closes an opening located at the upper end of the outer can 20 via an annular gasket 24. In the example shown in Fig. 1, the outer can 20 has a cylindrical shape with a bottom, but the outer can may have openings at both the upper and lower ends, and each opening may be closed with one or more members.

[0013] The electrode assembly 14 includes an elongated positive electrode 11 constituting a first electrode, an elongated negative electrode 12 constituting a second electrode, and two elongated separators 13 interposed between the positive electrode 11 and the negative electrode 12, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with the separators 13 interposed therebetween. The negative electrode 12 is formed to be slightly larger in size than the positive electrode 11. The negative electrode 12 is formed to be longer than the positive electrode 11 in the winding direction and in the axial direction. The two separators 13 are formed to be slightly larger in size 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.

[0014] 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

[0015] 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.).

[0016] The positive electrode 11 has a positive electrode core 30 (see FIG. 3 ) and positive electrode mixture layers 32 (see FIG. 3 ) formed on both sides of the positive electrode core 30. The positive electrode core 30 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 32 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. to the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layers 32 on both sides of the positive electrode core 30.

[0017] 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.

[0018] Examples of the conductive agent contained in the positive electrode mixture layer 32 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 32 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.

[0019] The negative electrode 12 has a negative electrode core 40 (see FIG. 3 ) and a negative electrode mixture layer 42 (see FIG. 3 ) formed on both sides of the negative electrode core 40. For the negative electrode core 40, 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, can be used. The negative electrode mixture layer 42 contains a negative electrode active material and a binder. The negative electrode 12 is produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder, etc., onto the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on both sides of the negative electrode core 40.

[0020] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials include 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 42 may contain a silicon (Si) material as the negative electrode active material. Furthermore, the negative electrode active material may include a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0021] 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 42, 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 42 may also contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0022] 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.

[0023] An upper insulating plate 15 is disposed above the electrode body 14, and an annular lower insulating plate 16 is disposed below the electrode body 14. In the example shown in FIG. 1 , a positive electrode lead 17 attached to the positive electrode 11 passes through a through hole in the upper insulating plate 15, extends toward the sealing body 19, and is connected to the underside of the sealing body 19 by welding or the like. On the other hand, a negative electrode lead 18 attached to the negative electrode 12 passes through a through hole in the lower insulating plate 16, extends toward the bottom 20A of the outer can 20, and is connected to the inner surface of the bottom 20A by welding or the like. The sealing body 19 to which the positive electrode lead 17 is connected serves as a positive electrode terminal, and the outer can 20 to which the negative electrode lead 18 is connected serves as a negative electrode terminal.

[0024] A gasket 24 is provided between the outer can 20 and the sealing body 19 to ensure sealing of the battery interior and insulation between the outer can 20 and the sealing body 19. The outer can 20 has a cylindrical portion 20B and a bottom portion 20A. The cylindrical portion 20B includes an annular grooved portion 28 and an annular shoulder portion 29. The grooved portion 28 is formed by spinning a portion of the cylindrical portion 20B to recess it radially inward. The shoulder portion 29, on the other hand, is formed when the upper end of the cylindrical portion 20B is bent radially inward and crimped to a flange portion (peripheral portion) 31 of the sealing body 19, and extends radially inward. The crimping causes the sealing body 19 to be sandwiched between the shoulder portion 29 and the grooved portion 28 via the gasket 24, and the sealing body 19 is fixed to the outer can 20.

[0025] Sealing body 19 is equipped with a current interruption mechanism. Sealing body 19 has a structure in which, in order from the electrode body 14 side, a metal terminal plate 21, an annular insulating plate 23, and a metal rupture plate 22 are stacked. Rupture plate 22 forms a valve body and is disposed opposite terminal plate 21 with insulating plate 23 sandwiched between them. Insulating plate 23 has an opening 23A formed in its radial center, and an air vent 23B provided in a portion overlapping with air vent 21C of terminal plate 21.

[0026] The rupture plate 22 has a valve portion 22A at the radial center that ruptures in response to an increase in battery internal pressure. The terminal plate 21 has an annular portion 21A and a central portion 21B that is connected to the radially inner end of the annular portion 21A and is located at the radial center. The central portion 21B has a disk shape and is thinner than the annular portion 21A.

[0027] Valve portion 22A is joined by welding or the like to central portion 21B of terminal plate 21 through opening 23A of insulating plate 23. Valve portion 22A includes a protruding portion 33 provided in the radial center and protruding downward, and a thin-walled portion 34 provided radially outward of protruding portion 33. The thickness of thin-walled portion 34 becomes thinner as it extends radially outward.

[0028] The thickness of the thin-walled portion 34 becomes thinner radially outward, so that an annular space 39 is provided below the thin-walled portion 34. The insulating plate 23 is disposed radially outward of the protruding portion 33 so as to surround the entire periphery of the protruding portion 33. The insulating plate 23 is located between the rupture plate 22 and the terminal plate 21.

[0029] Rupture plate 22 holds insulating plate 23, and insulating plate 23 holds terminal plate 21. Specifically, rupture plate 22 includes an annular thick-walled portion 35 connected to the radially outer end of thin-walled portion 34, and thick-walled portion 35 has an annular protruding portion 37 protruding downward. The outer peripheral surface of insulating plate 23 is fitted and fixed to the inner peripheral surface of annular protruding portion 37. Insulating plate 23 also has an annular protruding portion 38 protruding downward on the outer peripheral side, and the inner peripheral surface of annular protruding portion 38 is fitted and fixed to the outer peripheral surface of terminal plate 21. Insulating plate 23 includes a clamping portion that is clamped radially between annular protruding portion 37 and terminal plate 21.

[0030] The vent hole 21C is provided in the annular portion 21A. The positive electrode lead 17 is joined to the lower surface of the annular portion 21A. The terminal plate 21 to which the positive electrode lead 17 is connected is electrically connected to the rupture plate 22, thereby forming a current path connecting the electrode body 14 to the rupture plate 22.

[0031] In the above configuration, if the battery 10 generates abnormal heat and the internal battery pressure rises, the valve portion 22A flips around the annular end 22B, which is the radially outer, less rigid part of the thin-walled portion 34, as a fulcrum, so that it becomes convex axially upward. Simultaneously with this flip, the center portion 21B is separated from the annular portion 21A or disengages from the valve portion 22A. Because the valve portion 22A is insulated from the annular portion 21A by the insulating plate 23, this flip interrupts the current path. This interruption suppresses heat generation in the battery 10. If the internal battery pressure rises further, the annular end 22B of the thin-walled portion 34 breaks, forming a gas exhaust port. As a result, high-temperature gas and molten material are exhausted to the outside of the battery 10, restoring the battery 10 to a safe state.

[0032] In the above description, the sealing body 19 includes a terminal plate 21, a rupture plate 22, and an insulating plate 23 positioned therebetween. However, the sealing body may have a laminated structure including two rupture plates (a lower valve body and an upper valve body) and may further include a convex terminal cap covering the two rupture plates. The sealing body may also be composed of only a rupture plate. Alternatively, the sealing body may not include 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.

[0033] 1 , the battery 10 has one positive electrode lead 17 extending from an intermediate portion, such as the center portion in the radial direction, of the electrode body 14 toward the sealing body 19. However, the battery may have multiple positive electrode leads (e.g., eight positive electrode leads) that electrically connect the positive electrode of the electrode body and the sealing body, and one end of each of the multiple positive electrode leads may be joined to the positive electrode at intervals from one another in the longitudinal direction of the positive electrode.

[0034] In this case, the positive electrode current path is effectively shortened, thereby increasing the effect of reducing electrical resistance. Therefore, it is preferable that the battery include six or more positive electrode leads, and more preferably eight or more positive electrode leads. Furthermore, when the battery includes three or more positive electrode leads, the positive electrode current path is effectively shortened, thereby increasing the effect of reducing electrical resistance. Therefore, it is preferable that the centers of the three or more positive electrode leads in the positive electrode longitudinal direction are arranged at approximately equal intervals in the positive electrode longitudinal direction. Furthermore, one axial end of the electrode body may be formed by a strip-shaped positive electrode core exposed portion, and this positive electrode core exposed portion may be joined to a positive electrode current collector plate. The positive electrode core exposed portion may then be electrically connected to the sealing body via the positive electrode current collector plate.

[0035] The battery 10 has one negative electrode lead 18 extending from the radial end of the electrode assembly 14 at the winding start side toward the bottom 20A. However, the battery may have multiple negative electrode leads electrically connecting the negative electrode of the electrode assembly to the bottom of the outer can, with one end of each of the multiple negative electrode leads joined to the negative electrode at intervals in the negative electrode longitudinal direction. Alternatively, one axial end of the electrode assembly may be formed as a strip-shaped negative electrode core exposed portion, and this negative electrode core exposed portion may be joined to a negative electrode current collector plate. The negative electrode core exposed portion may then be electrically connected to the bottom of the outer can via the negative electrode current collector plate.

[0036] At least a portion of the outermost peripheral surface of the electrode assembly may be formed by a negative electrode substrate exposed portion, and the negative electrode substrate exposed portion may be in contact with the inner peripheral surface of the outer can. In this case, the winding start end of the negative electrode of the electrode assembly may be electrically connected to the bottom of the outer can via a negative electrode lead. This effectively shortens the current path on the negative electrode side, effectively reducing electrical resistance. While the case where the positive electrode is electrically connected to the sealing member and the negative electrode is electrically connected to the outer can has been described, the negative electrode may also be electrically connected to the sealing member and the positive electrode may also be electrically connected to the outer can.

[0037] Fig. 2 is a schematic cross-sectional view of the electrode assembly 14 cut along a plane perpendicular to its height. Fig. 3 is a schematic cross-sectional view of both the positive electrode portion and the negative electrode portion located around the end portion on the winding start side in the longitudinal direction of the positive electrode, developed into a long strip, and cut along a plane including the positive electrode longitudinal direction and the positive electrode thickness direction. Note that separators are omitted from Fig. 2 and the following Figs. 3 to 7.

[0038] 2 and 3 , a negative electrode core exposed portion 41 where the negative electrode core 40 is exposed in the negative electrode 12 faces the starting end 11a on the winding start side of the positive electrode 11 in the radial direction (radial direction of the outer can 20) on the inside of the winding. In this embodiment, if the position in the negative electrode longitudinal direction that faces the starting end 11a on the winding start side of the positive electrode 11 on the inside of the winding in the radial direction of the negative electrode 12 is defined as the starting end facing position 12a, the starting end 12b on the outside of the winding is located outside the starting end facing position 12a. As shown in FIG. 2 , the negative electrode 12 extends from the starting end facing position 12a to the inside of the winding for two or more turns.

[0039] In this way, by winding the negative electrode 12 from the opposing start position 12a to the inside of the winding for two or more turns, a core can be formed on the inside of the winding of the electrode body 14 in the two or more turns, and the rigidity of the radially inner end of the electrode body 14 can be increased. Therefore, even if a radially inward force is applied to the electrode body 14, the electrodes 11 and 12 inside the electrode body 14 are less likely to move radially inward, and good circularity of the electrode body 14 is more likely to be maintained.

[0040] 3 , the battery 10 includes an insulating tape 71 that covers the inner surface 61 of the positive electrode 11 from a winding start point 61 a at the winding start side to a facing position 61 b ​​that is radially facing a winding end point 41 b at the negative electrode substrate exposed portion 41 that is closer to the winding end than the winding end point 41 a. The insulating tape 71 is an example of an insulating protective portion. The insulating tape 71 may be made of an insulating material, and for example, the base material may be made of a polyimide film and the adhesive material may be made of silicone.

[0041] In a cross section of the positive electrode 11 in the thickness direction, the end surface 11c on the winding start side of the positive electrode 11 is surrounded by a protective portion (insulating portion) and is covered from the outside. In this embodiment, the insulating tape 71 is attached from the opposing position 61b on the winding inner surface 61 to the winding start end 61a, and extends to a position beyond the winding start end 61a. In addition, an insulating tape 72 is attached to a portion of the winding outer surface 62 that substantially corresponds to the longitudinal range of the positive electrode to which the insulating tape 71 is attached.

[0042] The insulating tape 72 is attached from a position 62b on the outer winding surface 62 that substantially corresponds to the opposing position 61b to a starting end 62a on the winding start side of the outer winding surface 62, and extends to a position beyond the starting end 62a. The tip of the insulating tape 71 that extends beyond the starting end 61a and the tip of the insulating tape 72 that extends beyond the starting end 62a are attached to each other. As a result, in the cross sections shown in Figures 2 and 3, the end face 11c on the winding start side of the positive electrode 11 is surrounded by the insulating tape 71 and the insulating tape 72 and is covered from the outside.

[0043] Next, the effects of the battery 10 of the present disclosure will be described. The present inventors discovered that unless countermeasures are taken, it is difficult to maintain good circularity around the starting end of the winding side of the positive electrode of the wound electrode body of a cylindrical secondary battery, and that this problem is particularly pronounced when a protective member is disposed around the starting end of the winding side of the positive electrode, as in the cylindrical secondary battery of Patent Document 1.

[0044] More specifically, as shown in Figure 4, which is a schematic cross-sectional view corresponding to Figure 3 of the reference example battery 310 and which explains the problems of the present disclosure, a step occurs at the starting end 311a on the winding start side of the positive electrode 311 of the wound electrode body 314 of the battery 310, and when protective members 371, 372 are placed around the starting end on the winding start side of the positive electrode 311, the radial length of the step becomes even larger.

[0045] In this context, in the conventional configuration, when radially inward stress indicated by arrow A occurs around the starting end of the positive electrode due to charging and discharging, a large radially outward stress indicated by arrow B is likely to occur due to a large step, making the electrode around the starting end of the positive electrode more likely to deform.

[0046] 5, which is a schematic cross-sectional view of battery 10 corresponding to FIG. 3 and illustrates why the problem can be improved, according to battery 10 of the present disclosure, negative electrode substrate exposed portion 41, which has a thin thickness and low rigidity, faces radially inward from winding start end 11a of positive electrode 11. Therefore, even if radially inward stress indicated by arrow C occurs around the positive electrode start end, negative electrode 12 can easily flexibly deform radially inward in the direction indicated by arrow D, which releases that force. Therefore, even after multiple charge / discharge cycles, good roundness is likely to be maintained, resulting in a battery 10 with high reliability and battery characteristics.

[0047] The starting end of the winding start side on the winding inner surface of the positive electrode does not need to be covered with an insulating protective part. However, the portion of the winding inner surface 61 of the positive electrode 11 covered with the insulating tape (corresponding to the insulating protective part) 71 is not involved in charging and discharging, so if the insulating tape 71 is applied from the starting end 61a on the winding inner surface 61 of the positive electrode 11 to an opposing position 61b that is radially opposite to the position 41b on the winding end side of the end 41a on the winding end side of the negative electrode core exposed portion 41, the same effect can be achieved in principle as if the starting end of the winding start side of the positive electrode 11 were moved outward in the winding to a positive electrode longitudinal position 11b that is opposite to position 41b.

[0048] This achieves the same effect as when the region where the negative electrode mixture layer 42 is disposed is wider than the region where the positive electrode mixture layer 32 is disposed, thereby effectively preventing the generation of lithium dendrites and realizing a highly reliable battery 10. Note that, since it is easy to increase the capacity, it is preferable that the inner winding surface portion 85 of the inner winding surface 61 of the positive electrode 11 that is covered with the insulating tape 71 has a length in the longitudinal direction of the positive electrode that is greater than 0 mm and not more than 5 mm.

[0049] 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.

[0050] 2, the starting end 12b on the outer side of the negative electrode mixture layer 42 is located on the outer side of the winding of the starting end opposing position 12a that faces the starting end 11a of the positive electrode 11 in the radial direction on the inner side of the winding, and the negative electrode substrate 40 extends two or more turns from the starting end opposing position 12a to the inner side of the winding. However, the negative electrode does not have to extend two or more turns from the starting end opposing position that faces the starting end of the positive electrode in the radial direction on the inner side of the winding to the inner side of the winding.

[0051] 6 , a negative electrode core exposed portion 141 at which the negative electrode core 140 is exposed in the negative electrode 112 may be radially opposed to a starting end 111a on the winding start side of the positive electrode 111 on the winding inside. The negative electrode mixture layer 142 may have a negative electrode mixture layer portion 142a arranged on the outer winding surface of the negative electrode core 140 of the negative electrode 112, closer to the winding start side in the negative electrode longitudinal direction than a starting end opposing position 112a of the negative electrode 112 that is radially opposed to the starting end 111a of the positive electrode 111 on the winding inside. The negative electrode mixture layer 142 may also have a negative electrode mixture layer portion 142b arranged on the inner winding surface of the negative electrode core 140 of the negative electrode 112, closer to the winding start side in the negative electrode longitudinal direction than a starting end opposing position 112a of the negative electrode 112 that is radially opposed to the starting end 111a of the positive electrode 111 on the winding inside.

[0052] Furthermore, the problem of difficulty in maintaining good circularity around the starting end of the positive electrode winding may also occur around the terminal end of the positive electrode winding. Therefore, as shown in Figure 7, a negative electrode substrate exposed portion 241 where the negative electrode substrate 240 is exposed in the negative electrode 212 may face the terminal end 211a of the positive electrode 211 on the winding end side on the inner side in the radial direction.

[0053] The battery 210 may also include an insulating tape 271 that covers the area from the end 261a of the inner winding surface 261 of the positive electrode 211 to a facing position 261b that is radially opposed to the position 241b on the negative electrode substrate exposed portion 241 that is closer to the winding start side than the winding start end 241a. The insulating tape 271 is an example of an insulating protective portion. The insulating tape 271 may be made of an insulating material, for example, a polyimide film as a base material and a silicone adhesive material. The battery 210 may also include an insulating tape 272 whose end on the winding end side is bonded to the end on the winding end side of the insulating tape 271 and whose winding start side is bonded to the outer winding surface 262 of the positive electrode 211. The insulating tape 272 may cover the end face 211c on the winding end side of the positive electrode 211 together with the insulating tape 271.

[0054] Furthermore, the inner winding surface portion 285 of the inner winding surface 261 of the positive electrode 211 that is covered with the insulating tape 271 may have a length in the positive electrode longitudinal direction that is greater than 0 mm and less than 5 mm. According to this modification, even after numerous charge / discharge cycles, the electrode assembly 214 is likely to maintain a high degree of circularity around the end portion on the winding end side of the positive electrode 211, and high reliability and battery performance are likely to be maintained. Note that the structure of the electrode assembly of the present disclosure that makes it easy to maintain good circularity may be employed at only one end of the positive electrode in the positive electrode longitudinal direction, or may be employed at both end portions of the positive electrode in the positive electrode longitudinal direction.

[0055] 10,210 Battery, 11,111,211 Positive electrode, 11a,111a Starting end of positive electrode on winding start side, 11c End face of positive electrode on winding start side, 12,112,212 Negative electrode, 12a,112a Position opposite to starting end of negative electrode, 12b Starting end of negative electrode mixture layer on outer side of winding, 13 Separator, 14,214 Electrode body, 15 Upper insulating plate, 16 Lower insulating plate, 17 Positive electrode lead, 18 Negative electrode lead, 19 Sealing body, 20 Outer can, 20A Bottom, 20B Cylindrical portion, 21 Terminal plate, 21A Annular portion, 21B Central portion, 21C Vent, 22 Rupture plate, 22A Valve portion, 22B Annular end portion, 23 Insulating plate, 23A Opening, 23B Ventilation hole, 24 Gasket, 28 Grooved portion, 29 Shoulder portion, 30 Positive electrode core, 32 Positive electrode mixture layer, 33 Protruding portion, 34 Thin portion, 35 Thick portion, 37, 38 Annular protruding portion, 39 Space, 40, 140, 240 Negative electrode core, 41, 141, 241 Negative electrode core exposed portion, 41a End of negative electrode core exposed portion on winding end side, 41b Position of negative electrode core exposed portion on winding end side relative to end of negative electrode core exposed portion on winding end side, 42, 142 Negative electrode mixture layer, 61, 261 Inner surface of positive electrode winding, 61a Starting end of inner surface of positive electrode winding on winding start side, 61b Opposing position of inner surface of positive electrode winding, 62, 262 outer winding surface of positive electrode, 62a: starting end of winding start side of outer winding surface of positive electrode, 62b: location on outer winding surface of positive electrode roughly corresponding to the opposing position, 71, 72, 271, 272: insulating tape, 85, 285: inner winding surface, 142a, 142b: negative electrode mixture layer portion, 211a: terminal end of winding end side of positive electrode, 211c: end face of winding end side of positive electrode, 241a: winding start side end of negative electrode core exposed portion, 241b: position on the negative electrode core exposed portion closer to winding start side than the winding start side end, 261a: terminal end of inner winding surface of positive electrode, 261b: opposing position on inner winding surface of positive electrode.

Claims

1. A cylindrical secondary 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; and an outer can that houses the electrode assembly, wherein an exposed portion of the negative electrode core at which the negative electrode core is exposed faces at least one of the starting end of the positive electrode on the winding start side and the ending end of the positive electrode on the winding end side in the radial direction on the inside of the winding.

2. A cylindrical secondary battery as described in claim 1, wherein the negative electrode substrate exposed portion faces the starting end of the positive electrode in the radial direction on the inner side of the winding, and is provided with an insulating protective portion that covers the area from the starting end on the inner side of the winding of the positive electrode to a position that faces radially toward the end of the winding of the negative electrode substrate exposed portion.

3. The cylindrical secondary battery according to claim 1, wherein the negative electrode substrate exposed portion faces the end of the positive electrode in the radial direction on the inner surface of the winding, and is provided with an insulating protective portion that covers the area from the end of the positive electrode on the inner surface of the winding to a position that faces radially toward the start of winding of the negative electrode substrate exposed portion relative to the end of the start of winding.

4. A cylindrical secondary battery according to claim 2 or 3, wherein the inner surface of the positive electrode that is covered by the protective portion has a length in the longitudinal direction of the positive electrode that is greater than 0 mm and not greater than 5 mm.

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