Cylindrical secondary battery

Abstract

A battery comprises: an electrode body in which a long positive electrode, having a positive electrode core body and a positive electrode mixture layer, and a long negative electrode (12), having a negative electrode core body (41) and a negative electrode mixture layer (42), are wound with a separator therebetween; and an outer can that houses the electrode body. A negative electrode core body exposed part (41a) is provided to a winding outer surface (12a) on the outermost circumference of the electrode body where the negative electrode core body (41) is exposed. The tensile elongation of a first portion (51) in which the negative electrode core body exposed part (41a) of the negative electrode core body (41) is provided is higher than the tensile elongation of a second portion (52) in which the negative electrode mixture layer (42) is formed on both the winding outer surface (12a) and a winding inner surface (12b) of the negative electrode core body (41).

Description

Cylindrical secondary battery

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

[0002] A conventional cylindrical secondary battery is described in Patent Document 1. This cylindrical secondary battery includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a bottomed cylindrical outer can that houses the electrode assembly, and a sealing body that closes the opening of the outer can. The positive electrode of the electrode assembly is electrically connected to the bottom surface of the sealing body via a positive electrode lead, and a terminal cap that forms the top plate of the sealing body serves as the positive electrode terminal. Meanwhile, the outermost periphery of the electrode assembly includes a negative electrode core exposed portion that is pressure-welded to the inner circumferential surface of the outer can, and the outer can electrically connected to the negative electrode core exposed portion serves as the negative electrode terminal.

[0003] Japanese Patent Application Publication No. 11-204130

[0004] The present inventors have found that, in a cylindrical secondary battery having a negative electrode substrate exposed portion provided on the outermost periphery of an electrode assembly, repeated charge / discharge cycles may cause breakage in the negative electrode substrate exposed portion, resulting in a corresponding decrease in current collection performance, etc. Therefore, an object of the present disclosure is to provide a cylindrical secondary battery in which breakage is less likely to occur in the negative electrode substrate exposed portion provided on the outermost periphery of the electrode assembly.

[0005] In order to solve the above problems, the cylindrical secondary battery according to the present disclosure includes 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, and an outer can that houses the electrode body, wherein a negative electrode core exposed portion where the negative electrode core is exposed is provided on the outermost winding surface of the electrode body, and the tensile elongation of a first portion of the negative electrode core where the negative electrode core exposed portion is provided is higher than the tensile elongation of a second portion of the negative electrode core in which the negative electrode mixture layer is formed on both the outer winding surface and the inner winding surface.

[0006] According to the cylindrical secondary battery according to the present disclosure, it is possible to prevent the occurrence of breaks in the exposed portion of the negative electrode substrate at the outermost periphery of the electrode assembly.

[0007] Fig. 1 is an axial cross-sectional view of a cylindrical secondary battery according to an embodiment of the present disclosure; Fig. 2 is a perspective view of an electrode body of the cylindrical secondary battery; Fig. 3(a) is a plan view showing the outer surface of the wound negative electrode when the negative electrode is unfolded into a long shape, and Fig. 3(b) is a plan view showing the inner surface of the wound negative electrode when the negative electrode is unfolded into a long shape; Fig. 4 is a plan view showing the outer surface of the wound negative electrode at the end of the winding termination side of a cylindrical secondary battery of a reference example after charge-discharge cycles.

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

[0009] 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 designated by the same reference numerals in the drawings, and redundant descriptions are omitted. Furthermore, multiple drawings include schematic diagrams, and the dimensional ratios of the length, width, height, and other dimensions of each component between different drawings do not necessarily match. In this specification, the sealing body 17 side in the axial direction (height direction) of the cylindrical secondary battery 10 is referred to as "upper," and the bottom 35 side of the outer can 16 in the axial direction is referred to as "lower." Furthermore, among the components described below, components not recited in the independent claims representing the highest concept are optional components and not essential components. Furthermore, the present disclosure is not limited to the following embodiments and variations thereof, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0010] Fig. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment of the present disclosure, and Fig. 2 is a perspective view of an electrode assembly 14 of the cylindrical secondary battery 10. As shown in Fig. 1, the cylindrical secondary battery (hereinafter simply referred to as battery) 10 includes a wound electrode assembly 14, a non-aqueous electrolyte (not shown), a cylindrical metal outer can 16 with a bottom that houses the electrode assembly 14 and the non-aqueous electrolyte, and a sealing body 17 that closes the opening of the outer can 16. As shown in Fig. 2, the electrode assembly 14 has a wound structure in which a long positive electrode 11 and a long negative electrode 12 are wound with two long separators 13 interposed therebetween.

[0011] The negative electrode 12 is formed to have dimensions slightly larger than the positive electrode 11 in order to prevent lithium precipitation. That is, the negative electrode 12 is formed to be longer in the longitudinal direction and width direction (short direction) than the positive electrode 11. Furthermore, the two separators 13 are formed to have dimensions at least slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11. The negative electrode 12 may form the winding start end of the electrode assembly 14. However, in general, the separator 13 extends beyond the winding start end of the negative electrode 12, and the winding start end of the separator 13 becomes the winding start end of the electrode assembly 14.

[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 and positive electrode mixture layers formed on both sides of the positive electrode core. The positive electrode core 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 layer. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be 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, drying the coating, and then compressing it to form positive electrode mixture layers on both sides of the positive electrode core.

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

[0017] The negative electrode 12 has a negative electrode core 41 (see FIGS. 3( a) and 3(b)) and a negative electrode mixture layer 42 (see FIGS. 3(a) and 3(b)) formed on both sides of the negative electrode core 41. For the negative electrode core 41, 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 can be 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 41, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on both sides of the negative electrode core 41.

[0018] 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-containing material containing silicon (Si) as the negative electrode active material. The negative electrode active material may also include metals other than silicon that alloy with lithium, alloys containing such metals, or compounds containing such metals. To increase capacity, the negative electrode active material contained in the negative electrode mixture layer 42 preferably contains graphite and a silicon-containing material, with the silicon-containing material accounting for 6% by mass or more of the negative electrode active material. To suppress expansion and contraction of the corners of the negative electrode 12 during charging and discharging and achieve good durability, the silicon-containing material preferably accounts for 50% by mass or less of the negative electrode active material, and more preferably 30% by mass or less of the negative electrode active material. Examples of silicon-containing materials include a composite material of carbon and silicon (SiC) and a composite material of silicon oxide and silicon (SiO Ｘ ) etc.

[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 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 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 as 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] As shown in Figure 1, a positive electrode lead 20 is joined to the positive electrode 11, and a negative electrode lead 21 is joined to the negative electrode 12. The battery 10 has an upper insulating plate 18 above the electrode body 14 and a lower insulating plate 19 below the electrode body 14. The positive electrode lead 20 is led out from the axially upper side of the electrode body 14 and extends toward the sealing body 17 through a through hole in the upper insulating plate 18. The positive electrode lead 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like. A terminal cap 27 constituting the top plate of the sealing body 17 is electrically connected to the internal terminal plate 23, and the terminal cap 27 serves as a positive electrode terminal.

[0022] The lower insulating plate 19 has a through-hole in the center. The negative electrode lead 21 is led out from the radially inner side and axially lower side of the electrode body 14. The negative electrode lead 21 passes through the through-hole in the lower insulating plate 19 and extends to the bottom 35 of the outer can 16, and then extends along the bottom 35. The portion of the negative electrode lead 21 that extends along the bottom 35 is joined to the bottom 35 by welding or the like, and the outer can 16 serves as a negative electrode terminal.

[0023] As shown in Fig. 2, the positive electrode lead 20 is electrically connected to an intermediate portion, such as the center portion, of the positive electrode core in the winding direction, and the negative electrode lead 21 is electrically connected to the winding start end of the negative electrode core in the winding direction. As shown in Fig. 1, a negative electrode core exposed portion 41a is provided on the outer surface of the outermost periphery of the electrode body 14, and at least a portion of the negative electrode core exposed portion 41a contacts the inner circumferential surface of the outer can 16. In this embodiment, both the winding start end and the winding end end of the negative electrode 12 are electrically connected to the outer can 16 as the negative electrode terminal, thereby shortening the current path of the negative electrode 12 and reducing electrical resistance. When the negative electrode core exposed portion contacts the inner circumferential surface of the outer can, the battery does not need to have a negative electrode lead.

[0024] The battery 10 further includes a resin gasket 28 disposed between the outer can 16 and the sealing body 17. The sealing body 17 is fixed to the opening of the outer can 16 by crimping via the gasket 28, thereby sealing the interior space of the battery 10. The gasket 28 is sandwiched between the outer can 16 and the sealing body 17 and insulates the sealing body 17 from the outer can 16. The gasket 28 serves as a sealant to maintain airtightness inside the battery and as an insulator to insulate the outer can 16 from the sealing body 17. The outer can 16 has a cylindrical portion 30 and a bottom 35, and the cylindrical portion 30 includes a grooved portion 34 and a shoulder portion 38. The grooved portion 34 can be formed, for example, by spinning a portion of the side surface of the outer can 16 radially inward to form an annular recess radially inward. The shoulder portion 38 is formed by bending the upper end of the outer can 16 inward toward the peripheral edge 39 of the sealing body 17 when the sealing body 17 is fixed to the outer can 16 by crimping.

[0025] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a terminal cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to each other. The internal terminal plate 23 has at least one through-hole 23a. The center of the lower valve body 24 is connected to the center of the upper valve body 26. The insulating member 25 is interposed between the peripheral edges of the lower valve body 24 and the upper valve body 26.

[0026] When the battery 10 generates abnormal heat and the internal pressure of the battery 10 rises, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the terminal cap 27, cutting off 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 and gas is released from the through-hole 27a of the terminal cap 27. This gas release prevents the internal pressure of the battery 10 from rising excessively, which could cause the battery 10 to explode, thereby improving the safety of the battery 10.

[0027] Next, the structure of the negative electrode 12 will be described in more detail using Figure 3. Figure 3(a) is a plan view showing the outer winding surface 12a of the negative electrode 12 when it is unfolded into a long shape, and Figure 3(b) is a plan view showing the inner winding surface 12b of the negative electrode 12 when it is unfolded into a long shape. Note that the hatched areas in Figures 3(a) and 3(b) and Figure 4 below are regions where the negative electrode mixture layer is disposed.

[0028] As shown in Figures 3(a) and (b), the negative electrode 12 has a negative electrode core 41 and a negative electrode mixture layer 42 disposed on both sides of the negative electrode core 41. As shown in Figure 3(a), the outer winding surface 12a of the negative electrode 12 has a negative electrode core exposed portion 41a (see Figure 1) at the end on the winding end side in the longitudinal direction, and a negative electrode core exposed portion 41b at the end on the winding start side in the longitudinal direction. As described above, the negative electrode core exposed portion 41a is located on the outer winding surface 12a of the outermost periphery of the electrode body 14, and at least a portion of the negative electrode core exposed portion 41a contacts the inner circumferential surface of the outer can 16. Note that it is sufficient that the negative electrode core exposed portion 41a is provided on at least a portion of the outer winding surface of the outermost periphery of the negative electrode. Therefore, the area of ​​the negative electrode core exposed portion provided on the winding inner surface 12b of the negative electrode core exposed portion 41a may be smaller than the area of ​​the negative electrode core exposed portion 41a, and it is not necessary to provide a negative electrode core exposed portion on the winding inner surface 12b of the negative electrode core exposed portion 41a.

[0029] The negative electrode lead 21 is joined to the negative electrode substrate exposed portion 41b. In this embodiment, the negative electrode lead 21 is joined to the outer winding surface 12a of the winding start end of the negative electrode 12, but the negative electrode lead 21 may also be joined to the inner winding surface 12b. To prevent short circuits, an insulating tape 55 covering a portion of the negative electrode lead 21 is preferably attached to the negative electrode lead 21 and the negative electrode 12. As shown in FIGS. 3( a) and 3(b) , the negative electrode substrate 41 has a first portion 51 in which the negative electrode substrate exposed portion 41a is provided on the outer winding surface 12a, and a second portion 52 in which the negative electrode mixture layer 42 is disposed on both the outer winding surface 12a and the inner winding surface 12b. The tensile elongation of the first portion 51 is higher than that of the second portion 52.

[0030] The tensile elongation of the negative electrode core 41 can be adjusted by heat treatment of the negative electrode core 41. For example, the above-described negative electrode core 41 can be produced by making the heat treatment time of the first portion 51 longer than the heat treatment time of the second portion 52. Increasing the heat treatment time applied to the negative electrode core increases the tensile elongation of the negative electrode core.

[0031] The tensile elongation is measured in accordance with known standards, such as IPC-TM-650 and JIS Z2241:2011. The tensile elongation can be measured using a known tensile testing machine, for example, an autograph AGS-5kNX manufactured by Shimadzu Corporation. The tensile elongation measurement is performed, for example, under an environment of room temperature (5°C or higher and 35°C or lower) and room humidity (relative humidity 45% or higher and 85% or lower). A test piece for measuring the tensile elongation is prepared, for example, by cutting a measurement target portion of the negative electrode core into a strip. The dimensions of the test piece can be, for example, 3 cm x 3 cm. The dimensions of the test piece may be set to any size that allows the test to be performed.

[0032] The test piece was pulled until it broke, and the tensile elongation was calculated using the test piece length (mm) at break and the original (before test) test piece length (mm) according to the following formula (1): Tensile elongation (%) = [test piece length at break - original test piece length] / [original test piece length] (1)

[0033] Next, the problems discovered by the present inventors and the effects achieved by the battery 10 of the present disclosure will be described. Fig. 4 is a plan view showing the outer winding surface 112a of the winding end side end of the negative electrode 112 of a battery (cylindrical secondary battery) 110 of a reference example after charge / discharge cycles. In the battery 110, a negative electrode substrate exposed portion 141a is provided on the outer winding surface 112a of the outermost periphery of the electrode body (not shown). Furthermore, the negative electrode substrate 141 has a constant tensile elongation regardless of the position in the longitudinal direction of the negative electrode 112.

[0034] When a negative electrode substrate exposed portion 141a is provided on the outermost wound surface 112a of the electrode body of the battery 110, it has been experimentally found that if the tensile elongation of the negative electrode substrate 141 is constant regardless of the position in the longitudinal direction of the negative electrode 112, a cut 160 extending approximately in the longitudinal direction of the negative electrode may occur at the end of the negative electrode substrate exposed portion 141a in the negative electrode width direction after charge / discharge cycles, as shown in Figure 4. In this context, if a cut occurs in the negative electrode substrate exposed portion 141a, there is a risk that the current collection performance on the negative electrode side will decrease and the electrical resistance will increase.

[0035] In contrast, in the battery 10 of this embodiment, the tensile elongation of the first portion 51 is higher than the tensile elongation of the second portion 52. In other words, the flexibility of the first portion 51 is higher than the flexibility of the second portion 52. Therefore, even after charge / discharge cycles, the occurrence of breakage in the first portion 51 is suppressed.

[0036] When the tensile elongation of the first portion 51 is A and the elongation of the second portion 52 is B, A can be set to 110% or more and 140% or less, and B can be set to 101% or more and 105% or less, assuming that A > B is satisfied. Furthermore, in order to effectively prevent breakage of the first portion 51, A / B is preferably 1.05 or more. Furthermore, in order to prevent the positive electrode 11 from approaching the grooved portion 34 due to expansion of the electrode body 14 during charging and discharging, A / B is preferably 1.30 or less.

[0037] The tensile elongation of the negative electrode substrate 41 increases with increasing crystal grain size. In other words, by making the number of crystal grains per unit area of ​​the first portion smaller than the number of crystal grains per unit volume of the second portion, the flexibility of the first portion increases. The crystal grain size of the negative electrode substrate 41 can be controlled by adjusting the heat treatment time and temperature. The negative electrode substrate 41 may be a rolled copper foil manufactured by hot rolling a high-purity ingot or an electrolytic copper foil manufactured by electroplating. In the case of electrolytic copper foil, the crystal grain size can be controlled by adjusting the type, concentration, deposition rate, etc. of additives. The number of copper crystal grains per unit area of ​​the first portion 51 is preferably 50% to 90% of the number of copper crystal grains per unit area of ​​the second portion 52.

[0038] The number of crystal grains per unit area of ​​the first portion 51 can be calculated by dividing the number of crystal grains present in a first predetermined region by the area of ​​the first predetermined region in a scanning electron microscope (SEM) image of a cross section of the first predetermined region included in the first portion 51. Similarly, the number of crystal grains per unit area of ​​the second portion 52 can be calculated by dividing the number of crystal grains present in a second predetermined region by the area of ​​the second predetermined region in an SEM image of a cross section of the second predetermined region included in the second portion 52.

[0039] Example The battery 10 described with reference to FIGS. 1 to 3 was fabricated using the negative electrode 12 in which the tensile elongation of the first portion 51 was set to 1.15 times the tensile elongation of the second portion 52 .

[0040] <Comparative Example> A comparative example battery was fabricated in the same manner as the example battery, except that a negative electrode was used whose tensile elongation was constant regardless of the position in the longitudinal direction and whose tensile elongation was consistent with that of the first portion 51 of the example battery.

[0041] (Confirmation of Presence or Absence of Breaks in the Exposed Portion of the Negative Electrode Substrate) Each of the produced batteries was charged in a 45°C environment at a constant current of 0.3 C until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 0.02 C. Thereafter, the battery was discharged at a constant current of 0.5 C until the voltage reached 2.5 V. This charge / discharge cycle was counted as one cycle, and the charge / discharge cycle was repeated 500 times. Thereafter, each battery was disassembled, and it was visually confirmed whether or not breaks had occurred in the exposed portion of the negative electrode substrate at the outermost periphery of the electrode body.

[0042]

[0043] The test results are shown in Table 1. In Table 1, each tensile elongation is shown as a relative value when the tensile elongation of the second portion of the example is set to 100. As shown in Table 1, breakage of the first portion was confirmed in the battery of the comparative example, whereas breakage of the first portion was not confirmed in the battery of the example. This confirmed that breakage of the first portion after multiple cycles can be suppressed by making the tensile elongation of the first portion higher than the tensile elongation of the second portion.

[0044] The negative electrode active material contained in the negative electrode mixture layer includes graphite and a silicon-containing material. When the content of the silicon-containing material is 6% by mass or more relative to the negative electrode active material, the capacity can be increased, but the expansion and contraction of the negative electrode during charge and discharge becomes significant. Therefore, the effect of the battery of the present disclosure, which is to suppress breakage of the first portion, is remarkable. Furthermore, when the number of crystal grains per unit area of ​​the first portion is smaller than the number of crystal grains per unit volume of the second portion, the flexibility of the first portion is increased, and breakage of the first portion after multiple cycles can be effectively suppressed.

[0045] REFERENCE SIGNS LIST 10 Battery, 11 Positive electrode, 12 Negative electrode, 12a Outer winding surface, 12b Inner winding surface, 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, 23 Internal terminal plate, 23a Through hole, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Terminal cap, 27a Through hole, 28 Gasket, 30 Cylindrical portion, 34 Grooved portion, 35 Bottom portion, 38 Shoulder portion, 39 Peripheral portion, 41 Negative electrode core, 41a, 41b Negative electrode core exposed portion, 42 Negative electrode mixture layer, 51 First portion, 52 Second portion, 160 cuts.

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 a negative electrode core exposed portion where the negative electrode core is exposed is provided on the outermost winding surface of the electrode assembly; and wherein the tensile elongation of a first portion of the negative electrode core where the negative electrode core exposed portion is provided is higher than the tensile elongation of a second portion of the negative electrode core in which the negative electrode mixture layer is formed on both the outer winding surface and the inner winding surface.

2. The cylindrical secondary battery according to claim 1, wherein the negative electrode active material contained in the negative electrode mixture layer comprises graphite and a silicon-containing material, and the content of the silicon-containing material is 6 mass% or more relative to the negative electrode active material.

3. The cylindrical secondary battery according to claim 1 or 2, wherein the number of crystal grains per unit area of ​​the first portion is smaller than the number of crystal grains per unit volume of the second portion.

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