Cylindrical secondary battery

Abstract

A cylindrical secondary battery which is one aspect of the present disclosure comprises an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, an electrolytic solution, and a cylindrical outer casing accommodating the electrode body and the electrolytic solution, wherein: an insulator is disposed between the separator and at least one of the positive electrode and the negative electrode; and if the electrode body is divided, in the center in a longitudinal direction of the separator, into a winding inner region on a winding inner side and a winding outer region on a winding outer side, a projected area of the insulator on the separator in the winding inner region is larger than a projected area of the insulator on the separator in the winding outer region.

Description

Cylindrical secondary battery

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

[0002] A cylindrical secondary battery is a battery in which an electrode assembly, in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, is housed in a cylindrical outer casing. Patent Documents 1 and 2 disclose separators having irregularities on their surfaces for the purpose of facilitating the injection of an electrolyte into the outer casing during battery manufacturing.

[0003] Japanese Patent No. 4529903 Japanese Patent Laid-Open No. 2008-226696

[0004] In recent years, efforts have been made to increase the size of cylindrical secondary batteries in order to achieve higher capacity. As a result of extensive research by the present inventors, it has been found that in a wound electrode assembly, uneven distribution of the electrolyte within the electrode assembly can occur, causing a decrease in battery capacity due to repeated charge and discharge, and this tendency is particularly pronounced in large cylindrical secondary batteries. The technologies described in Patent Documents 1 and 2 do not address the issue of increasing battery size, and there is still room for improvement.

[0005] An object of the present disclosure is to provide a cylindrical secondary battery that has a high capacity and excellent charge / discharge cycle characteristics.

[0006] A cylindrical secondary battery according to one aspect of the present disclosure includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, an electrolyte, and a cylindrical exterior body that accommodates the electrode assembly and the electrolyte; an insulator is disposed between the separator and at least one of the positive electrode and the negative electrode; and when the separator is divided at the center in the longitudinal direction into an intra-rolling region on the inside of the roll and an extra-rolling region on the outside of the roll, the projected area of ​​the insulator on the separator in the intra-rolling region is larger than the projected area of ​​the insulator on the separator in the extra-rolling region.

[0007] According to the cylindrical secondary battery according to the present disclosure, it is possible to improve the battery capacity and charge / discharge cycle characteristics.

[0008] Fig. 3 is an axial cross-sectional view of a cylindrical secondary battery according to an example embodiment. Fig. 4 is a perspective view of a wound electrode body provided in the secondary battery shown in Fig. 1. Fig. 5 is a front view showing a separator constituting an electrode body according to an example embodiment in an expanded state, with an insulator projected. Fig. 6 is a plan view of the upper surface of an electrode body including the separator shown in Fig. 3, showing the position where the insulator is arranged.

[0009] In recent years, efforts have been made to increase the size of cylindrical secondary batteries in order to improve battery capacity. However, larger batteries are more likely to have a shortage of electrolyte near the center of the winding of the electrode assembly than conventional batteries, which can lead to poor charge-discharge cycle performance. To address this issue, the present inventors conducted extensive research and found that by disposing an insulator at a predetermined position between the separator and at least one of the positive electrode and negative electrode, it is possible to improve charge-discharge cycle performance while suppressing a decrease in battery capacity. That is, when the separator is divided at the center in the longitudinal direction into an intra-roll region on the inner side of the winding and an extra-roll region on the outer side of the winding, disposing an insulator in the intra-roll region, which is prone to electrolyte shortage, while reducing the projected area of ​​the insulator on the separator in the extra-roll region, which is richer in electrolyte than the intra-roll region, can achieve both good battery capacity and good charge-discharge cycle performance.

[0010] An example of an embodiment of a cylindrical secondary battery according to the present disclosure will be described in detail below with reference to the drawings. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating understanding of the present invention and can be appropriately changed according to the specifications of the cylindrical secondary battery. Furthermore, when multiple embodiments and variations are included in the following description, it is assumed from the outset that the characteristic features of these embodiments and variations can be appropriately combined and used.

[0011] FIG. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment. The secondary battery 10 shown in FIG. 1 includes an electrode assembly 14 and an electrolyte (not shown) housed in a cylindrical outer casing 15. The electrode assembly 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. Examples of nonaqueous solvents (organic solvents) for the electrolyte include carbonates, lactones, ethers, ketones, esters, and the like. Two or more of these solvents can be mixed together. When two or more solvents are mixed together, a mixed solvent containing a cyclic carbonate and a chain carbonate is preferably used. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and the like can be used as the chain carbonate. The electrolyte salt of the electrolyte solution is LiPF ６ , LiBF ４ , LiCF ３ SO ３ etc., and mixtures thereof can be used. The amount of electrolyte salt dissolved in the non-aqueous solvent can be, for example, 0.5 to 2.0 mol / L. For convenience of explanation, the following description will be given with the sealing body 16 side as the "top" and the bottom side of the exterior body 15 as the "bottom."

[0012] The open end of the exterior body 15 is sealed with the sealing body 16, thereby sealing the interior of the secondary battery 10. Insulating plates 17 and 18 are provided above and below the electrode body 14. The positive electrode lead 19 extends upward through a through hole in the insulating plate 17 and is welded to the underside of a filter 22, which is the bottom plate of the sealing body 16. In the secondary battery 10, a cap 26, which is the top plate of the sealing body 16 and is electrically connected to the filter 22, serves as the positive electrode terminal. On the other hand, the negative electrode lead 20 extends through a through hole in the insulating plate 18 to the bottom side of the exterior body 15 and is welded to the inner bottom surface of the exterior body 15. In the secondary battery 10, the exterior body 15 serves as the negative electrode terminal. Note that when the negative electrode lead 20 is provided at the outer end of the winding, the negative electrode lead 20 passes outside the insulating plate 18, extends to the bottom side of the exterior body 15, and is welded to the inner bottom surface of the exterior body 15.

[0013] The exterior body 15 is, for example, a cylindrical metal exterior can with a bottom. A gasket 27 is provided between the exterior body 15 and the sealing body 16 to ensure the airtightness of the interior of the secondary battery 10. The exterior body 15 has a grooved portion 21 that supports the sealing body 16, formed, for example, by pressing the side surface from the outside. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the exterior body 15, and supports the sealing body 16 on its upper surface.

[0014] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are stacked in this order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disk or ring shape, and all components except for the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheral edges. If the internal pressure of the battery increases due to abnormal heat generation, for example, the lower valve body 23 may rupture, causing the upper valve body 25 to bulge toward the cap 26 and separate from the lower valve body 25, thereby cutting off the electrical connection between them. If the internal pressure continues to increase, the upper valve body 25 may rupture, allowing gas to be released from the opening 26a of the cap 26.

[0015] 2 to 4, the electrode body 14 will be described. The diameter of the electrode body 14 is preferably 20 mm or more. This allows the battery capacity of the secondary battery 10 to be increased.

[0016] FIG. 2 is a perspective view of the electrode assembly 14. As described above, the electrode assembly 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all formed in a strip shape and spirally wound around a winding core disposed along a winding axis 28, resulting in an alternating stacking state in the radial direction of the electrode assembly 14. In the electrode assembly 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 corresponds to the winding direction, and the lateral direction of the positive electrode 11 and the negative electrode 12 corresponds to the axial direction. The positive electrode lead 19 extends axially from approximately the center in the radial direction between the center and the outermost periphery at the upper end of the electrode assembly 14. The negative electrode lead 20 extends axially from the lower end of the electrode assembly 14 near the winding axis 28.

[0017] The positive electrode 11 has a strip-shaped positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. The positive electrode mixture layer is preferably formed on both sides of the positive electrode current collector. The positive electrode current collector can be a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on its surface.

[0018] The positive electrode mixture layer may contain a positive electrode active material, a conductive agent, a binder, etc. The positive electrode mixture layer can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both sides of a positive electrode current collector, drying the slurry, and then rolling the slurry.

[0019] The positive electrode active material contained in the positive electrode mixture layer can be, for example, a lithium transition metal oxide containing a transition metal element such as Co, Mn, or Ni. ｘ CoO ２ , Li ｘ NiO ２ , Li ｘ MnO ２ , Li ｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Co ｙ M １－ｙ O ｚ , Li ｘ Ni １－ｙ M ｙ O ｚ , Li ｘ Mn ２ O ４ , Li ｘ Mn ２－ｙ M ｙ O ４ , LiMPO ４ , Li ２ MPO ４ F (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0<x≦1.2, 0<y≦0.9, 2.0≦z≦2.3). These may be used alone or in combination of two or more. In terms of increasing the capacity of the secondary battery 10, the positive electrode active material is preferably Li ｘ NiO２ , Li ｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Ni １－ｙ M ｙ O ｚ (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B; 0<x≦1.2, 0<y≦0.9, 2.0≦z≦2.3) or other lithium nickel composite oxides.

[0020] Examples of the conductive agent contained in the positive electrode mixture layer include carbon-based particles such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotubes (CNT), graphene, graphite, etc. These may be used alone or in combination of two or more.

[0021] Examples of binders contained in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide-based resins, acrylic-based resins, polyolefin-based resins, and polyacrylonitrile (PAN). These may be used alone or in combination of two or more.

[0022] The negative electrode 12 has a strip-shaped negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector. The negative electrode mixture layer is preferably formed on both sides of the negative electrode current collector. The negative electrode current collector can be a foil of a metal such as copper or a copper alloy that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface layer.

[0023] The negative electrode mixture layer may contain a negative electrode active material, a binder, etc. The negative electrode mixture layer can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and a solvent such as water to both surfaces of a negative electrode current collector, drying the mixture, and then rolling the mixture.

[0024] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly absorb and release lithium ions, and generally, a carbon material such as graphite is used. The graphite may be any of natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads.

[0025] The negative electrode active material preferably contains a silicon-containing material. This can improve the battery capacity of the secondary battery 10. The negative electrode 12 containing a silicon-containing material is prone to a shortage of electrolyte at the center of the winding of the electrode body 14 due to large volume changes caused by charging and discharging the battery. However, the effects of the present disclosure can improve the charge-discharge cycle characteristics. Examples of silicon-containing materials include SiO ｘ (0.5≦x≦1.6), Li ２ｙ SiO （２＋ｙ） Examples of such a silicon-containing compound include a silicon-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by (0<y<2) and a silicon-containing compound in which fine particles of Si are dispersed in a carbon phase.

[0026] Examples of binders contained in the negative electrode mixture layer include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof, and polyvinyl alcohol (PVA). These may be used alone or in combination of two or more.

[0027] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include olefin-based resins such as polyethylene and polypropylene, and cellulose. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin, or may be a multilayer separator including a polyethylene layer and a polypropylene layer.

[0028] The separator 13 may have a heat-resistant layer on at least one surface. In other words, the separator 13 may have a heat-resistant layer on at least one of the surface facing the positive electrode 11 and the surface facing the negative electrode 12. The heat-resistant layer is preferably provided on at least the surface facing the positive electrode 11. The heat-resistant layer is provided on, for example, the entire surface of the separator 13.

[0029] The heat-resistant layer contains, for example, a filler and a binder. Examples of fillers include metal oxide particles such as aluminum oxide, metal nitride particles, metal fluoride particles, metal carbide particles, and sulfide particles. These may be used alone or in combination of two or more. Examples of binders 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 a salt thereof, polyacrylic acid (PAA) or a salt thereof, and polyvinyl alcohol (PVA). These may be used alone or in combination of two or more.

[0030] In the electrode assembly 14, an insulator 30 is disposed between at least one of the positive electrode 11 and the negative electrode 12 and the separator 13. This allows the electrolyte to easily penetrate the separator 13, thereby improving charge / discharge cycle characteristics. FIG. 3 is a front view showing the separator 13 constituting the electrode assembly 14 according to an example embodiment in a developed state, with the insulator projected. In this embodiment, the insulator 30 has a linear shape extending in the lateral direction of the separator 13. In other words, the linear insulator 30 is disposed approximately parallel to the lateral direction of the separator 13, and the length of the insulator 30 is approximately the same as the length of the separator 13 in the lateral direction.

[0031] When the separator 13 is divided at the center in the longitudinal direction into an intra-roll region 13a on the inside of the roll and an extra-roll region 13b on the outside of the roll, the projected area of ​​the insulator 30 on the separator 13 in the intra-roll region 13a is larger than the projected area of ​​the insulator 30 on the separator 13 in the extra-roll region 13b. This makes it possible to minimize the volume of the insulator 30 while suppressing a shortage of electrolyte at the intra-roll center, thereby achieving both battery capacity and charge / discharge cycle characteristics. Although the placement of the insulator 30 reduces the volume of the positive electrode 11 and negative electrode 12 that can be accommodated in the exterior body 15, thereby reducing battery capacity, the placement of more insulator 30 in the intra-roll region 13a than in the extra-roll region 13b makes it possible to achieve both battery capacity and charge / discharge cycle characteristics. The projected area of ​​the insulator 30 in the intra-winding region 13a onto the separator 13 is preferably 0.1% to 50%, more preferably 0.1% to 20%, even more preferably 0.1% to 10%, and particularly preferably 0.1% to 5%, of the area of ​​the intra-winding region 13a.

[0032] In the present embodiment shown in FIG. 3 , five insulators 30 having the same width are arranged at equal intervals only in the in-winding region 13 a, and no insulators 30 are arranged in the out-winding region 13 b. FIG. 4 is a plan view of the top surface of the electrode assembly 14 including the separator 13 shown in FIG. 3 , showing the positions at which the insulators 30 are arranged. As shown in FIG. 4 , the insulators 30 are arranged toward the center of the winding. Note that the arrangement of the insulators 30 is not limited to this example. The number of insulators 30 is not particularly limited, and the insulators 30 may have different widths and may be spaced apart from one another. In addition, the insulators 30 may be arranged in the out-winding region 13 b.

[0033] The width of the linear insulator 30 is, for example, 1 mm or less. The lower limit of the width of the linear insulator 30 is, for example, 0.01 mm. The height of the linear insulator 30 is, for example, 0.5 μm to 1 mm. The cross-sectional shape of the linear insulator 30 is not particularly limited and may be, for example, a circular shape or a rectangular shape.

[0034] The shape of the insulators 30 is not limited to the example in FIG. 3 , and the insulators 30 may have a dot-like shape. The outer shape of the dot-like insulators 30 is, for example, φ1 mm or less. The lower limit of the outer shape of the dot-like insulators 30 is, for example, 0.01 mm. The height of the dot-like insulators 30 is, for example, 0.5 μm to 1 mm. The shape of the dot-like insulators 30 is not particularly limited, and may be, for example, a circular or rectangular shape when viewed from the front.

[0035] The material of the insulator 30 is not particularly limited as long as it is insulating, and may be, for example, ceramic or resin. The material of the insulator 30 is preferably resin. Examples of resins used for the insulator 30 include fluorine-based resins such as PET (polyethylene terephthalate), PI (polyimide), PP (polypropylene), PBT (polybutylene terephthalate), and polytetrafluoroethylene (PTFE), and acrylic resins such as polyacrylic acid, polymethacrylic acid, polyacrylic acid ester, and polymethacrylic acid ester. These may be used alone or in combination of two or more. For example, PET fibers can be used as the linear insulator 30. For example, the dot-shaped insulator 30 can be formed on the surface of the positive electrode 11, the negative electrode 12, or the separator 13 by dissolving the resin in a solvent and using an inkjet method or the like.

[0036] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0037] [Preparation of Positive Electrode] 95 parts by mass of LiNi ０．８ Co ０．１５ Al ０．０５ O ２2.5 parts by mass of acetylene black (AB) and 2.5 parts by mass of polyvinylidene fluoride (PVDF) having an average molecular weight of 1.1 million were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a strip-shaped positive electrode current collector made of aluminum foil, dried, rolled, and cut to a predetermined electrode plate size to produce a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode current collector. A positive electrode exposed portion in which no mixture layer was present and the current collector surface was exposed was provided in approximately the center of the longitudinal direction of the positive electrode, and an aluminum positive electrode lead was welded to the positive electrode exposed portion.

[0038] [Preparation of Negative Electrode] 94 parts by mass of graphite, 6 parts by mass of SiO , 1 part by mass of carboxymethyl cellulose (CMC), and 1 part by mass of styrene butadiene rubber (SBR) were mixed, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a strip-shaped negative electrode current collector made of copper foil, dried, rolled, and cut to a predetermined electrode plate size to prepare a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode current collector. A negative electrode exposed portion where no mixture layer was present and the current collector surface was exposed was provided at the inner end of the winding, and a nickel negative electrode lead was welded to the negative electrode exposed portion.

[0039] [Preparation of Electrolyte Solution] Five parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent consisting of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio of EC:DMC = 1:3). LiPF was added to the mixed solvent to a concentration of 1 mol / L. ６ was dissolved to prepare an electrolyte solution.

[0040] [Fabrication of Secondary Battery] Ten PET fibers with a diameter of 0.1 mm were evenly arranged on the surface of the positive electrode over the entire area corresponding to the in-winding region of the separator, and one PET fiber with a diameter of 0.1 mm was placed in the center of the area corresponding to the out-winding region of the separator. The projected area of ​​one PET fiber on the separator was 0.05% of the area of ​​the in-winding region (or the out-winding region). The positive and negative electrodes were then wound with a polyethylene separator between them to fabricate an electrode assembly. Insulating plates were placed on the top and bottom of the electrode assembly, and the electrode assembly was housed in a cylindrical outer casing. The negative electrode lead was then welded to the bottom of the outer casing, and the positive electrode lead was welded to a sealing member. An electrolyte was then injected into the inner casing by vacuum injection, and the open end of the outer casing was crimped to the sealing member via a gasket to fabricate a secondary battery.

[0041] Example 2 A secondary battery was produced in the same manner as in Example 1, except that, in the production of the secondary battery, the arrangement of the PET fibers was changed so that, of the ten PET fibers arranged on the surface of the positive electrode in Example 1, only two fibers from the winding center side remained, and the positive electrode and negative electrode were lengthened so that the diameter of the electrode body became the same as the diameter of the electrode body in Example 1.

[0042] Example 3 A secondary battery was fabricated in the same manner as in Example 1, except that in fabricating the secondary battery, the number of PET fibers arranged on the positive electrode surface in a region corresponding to the intra-wound region of the separator was changed to 20 so that the distance between the PET fibers was half that of Example 1, and the positive electrode and negative electrode were shortened so that the diameter of the electrode body was the same as that of the electrode body of Example 1.

[0043] Example 4 A secondary battery was produced in the same manner as in Example 1, except that in the production of the secondary battery, PET fibers were not disposed in a portion of the positive electrode surface corresponding to the outer region of the separator, and the positive electrode and negative electrode were lengthened so that the diameter of the electrode body was the same as the diameter of the electrode body of Example 1.

[0044] <Comparative Example 1> A secondary battery was produced in the same manner as in Example 1, except that in the production of the secondary battery, PET fibers were not placed on the surface of the positive electrode, and the positive electrode and the negative electrode were lengthened so that the diameter of the electrode body was the same as the diameter of the electrode body of Example 1.

[0045] Comparative Example 2 A secondary battery was fabricated in the same manner as in Example 1, except that in the fabrication of the secondary battery, 10 PET fibers were evenly arranged over the entire area of ​​the positive electrode surface corresponding to the outer region of the separator, and the positive electrode and negative electrode were shortened so that the diameter of the electrode body became the same as the diameter of the electrode body of Example 1.

[0046] [Evaluation of Initial Discharge Capacity and Capacity Retention Rate] The secondary batteries of the Examples and Comparative Examples were charged to 4.2 V at a constant current of 1 C at an ambient temperature of 25° C., and then charged at a constant voltage of 4.2 V until the current value reached 0.05 C. After leaving the batteries for 20 minutes, they were discharged to 2.5 V at a constant current of 1 C. This charge / discharge cycle was counted as one cycle, and 200 cycles were performed. The capacity retention rate of the secondary batteries of the Examples and Comparative Examples in the charge / discharge cycles was calculated using the following formula. The discharge capacity at the first cycle was taken as the initial discharge capacity. Capacity retention rate = (discharge capacity at the 200th cycle / discharge capacity at the first cycle) × 100

[0047] Table 1 shows the evaluation results of the initial discharge capacity and capacity retention rate of the secondary batteries of Examples and Comparative Examples. The initial discharge capacities of the secondary batteries of Examples 1 to 4 and Comparative Example 2 are expressed relative to the initial discharge capacity of the secondary battery of Comparative Example 1, which is set to 100. Table 1 also shows the ratio of the projected area of ​​the insulator in the inner-winding region and the outer-winding region to the area of ​​the inner-winding region (or the outer-winding region).

[0048]

[0049] The secondary batteries of the Examples were able to achieve both good initial discharge capacity and good charge-discharge cycle characteristics. On the other hand, the secondary battery of Comparative Example 1, in which no insulators were disposed, had poor charge-discharge cycle characteristics, and the secondary battery of Comparative Example 2, in which the same number of insulators were disposed in the outer-winding region as in the inner-winding region, had poor initial discharge capacity. This shows that by arranging the insulators so that the projected area of ​​the insulators on the separator in the inner-winding region is larger than the projected area of ​​the insulators on the separator in the outer-winding region, the battery capacity and charge-discharge cycle characteristics are improved.

[0050] REFERENCE SIGNS LIST 10 secondary battery, 11 positive electrode, inner winding end, 12 negative electrode, 13 separator, 13a inner winding region, 13b outer winding region, 14 electrode body, 15 outer casing, 16 sealing body, 17, 18 insulating plate, 19 positive electrode lead, 20 negative electrode lead, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a opening, 27 gasket, 28 winding shaft, 30 insulator

Claims

1. A cylindrical secondary battery comprising an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, an electrolyte, and a cylindrical exterior body that accommodates the electrode assembly and the electrolyte, an insulator is disposed between at least one of the positive electrode and the negative electrode and the separator; a cylindrical secondary battery in which, when the separator is divided at a center in a longitudinal direction into an intra-roll region on an inner side of the roll and an extra-roll region on an outer side of the roll, a projected area of ​​the insulator on the separator in the intra-roll region is larger than a projected area of ​​the insulator on the separator in the extra-roll region.

2. The cylindrical secondary battery according to claim 1 , wherein the separator has a heat-resistant layer on at least one of a surface facing the positive electrode and a surface facing the negative electrode.

3. The cylindrical secondary battery according to claim 1 , wherein the insulator has a linear shape extending in a lateral direction of the separator.

4. The cylindrical secondary battery according to claim 3 , wherein the insulator has a width of 1 mm or less.

5. The cylindrical secondary battery according to claim 1 , wherein the insulator has a dot-like shape.

6. 6. The cylindrical secondary battery according to claim 5, wherein the insulator has an outer diameter of φ1 mm or less.

7. 3. The cylindrical secondary battery according to claim 1, wherein a projected area of ​​the insulator in the inner-winding region onto the separator is 0.1% to 50% of an area of ​​the inner-winding region.

8. The cylindrical secondary battery according to claim 1 , wherein the insulator is not disposed in the outer wound region.

9. 3. The cylindrical secondary battery according to claim 1, wherein the insulating material is a resin.

10. The cylindrical secondary battery according to claim 1 or 2, wherein the negative electrode comprises a silicon-containing material as a negative electrode active material.

11. 3. The cylindrical secondary battery according to claim 1, wherein the electrode body has a diameter of 20 mm or more.