Cylindrical secondary battery

Abstract

Provided is a cylindrical secondary battery (10) comprising: an electrode body (14) in which a band-shaped positive electrode (11) and a band-shaped negative electrode (12) are wound along a longitudinal direction with a separator (13) therebetween; a nonaqueous electrolyte; and a cylindrical outer-casing can (15) that houses the electrode body (14) and the nonaqueous electrolyte, wherein the positive electrode (11) includes a positive electrode core (30), and a positive electrode mixture layer (32) disposed on the surface of the positive electrode core (30), wherein a positive electrode core exposed part (34), where the positive electrode core (30) is exposed, is formed at a portion in contact with only one end of the positive electrode (11) in the lateral direction thereof, and wherein the positive electrode core exposed part (34) is not formed in a range of L / 10 from an outermost winding edge in the longitudinal direction of the positive electrode (11) when L represents the length of the positive electrode (11) in the longitudinal direction.

Description

Cylindrical secondary battery

[0001] The present disclosure relates to a cylindrical secondary battery, and in particular to the structure of an electrode assembly thereof.

[0002] The cylindrical secondary battery includes an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally with a separator interposed therebetween. The positive electrode has a positive electrode core and a positive electrode mixture layer formed on the surface of the positive electrode core.

[0003] For example, in the cylindrical secondary battery disclosed in Patent Document 1, a rectangular positive electrode core exposed portion is formed in a portion that contacts only one of the ends of the positive electrode in the short direction, where the positive electrode current collector plate is exposed, and a positive electrode tab for current collection is joined to the positive electrode core exposed portion.

[0004] Japanese Patent Application Laid-Open No. 2004-311282

[0005] However, as the positive electrode stretches during charging and discharging of the battery, wrinkles may occur in the exposed portion of the positive electrode substrate on the outermost side of the winding in the longitudinal direction. Wrinkles are particularly likely to occur in the exposed portion of the positive electrode substrate on the outermost side of the winding. When wrinkles occur in the exposed portion of the positive electrode substrate, the distance between the positive electrode and the negative electrode may vary, which may increase the resistance value.

[0006] Therefore, an object of the present disclosure is to provide a cylindrical secondary battery that can suppress the occurrence of wrinkles in the exposed portion of the positive electrode substrate.

[0007] The cylindrical secondary battery according to the present disclosure is a cylindrical secondary battery including an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally with a separator interposed therebetween, a non-aqueous electrolyte, and a cylindrical outer can that houses the electrode assembly and the non-aqueous electrolyte, wherein the positive electrode has a positive electrode core and a positive electrode mixture layer arranged on the surface of the positive electrode core, and a positive electrode core exposed portion in which the positive electrode core is exposed is formed in a portion that contacts only one end in the short direction of the positive electrode, and where the length of the positive electrode in the long direction is L, the positive electrode core exposed portion is not formed within a range of L / 10 from the outer side of the winding in the long direction.

[0008] According to the cylindrical secondary battery of the present disclosure, it is possible to suppress the occurrence of wrinkles in the exposed portion of the positive electrode substrate.

[0009] 1 is a longitudinal cross-sectional view of a cylindrical secondary battery according to an embodiment of the present invention;

[0010] An example of an embodiment of the present disclosure will be described in detail below. In the following description, specific shapes, materials, directions, numerical values, etc. are examples for facilitating understanding of the present disclosure, and can be appropriately changed according to the application, purpose, specifications, etc.

[0011] [Cylindrical Secondary Battery] A cylindrical secondary battery (hereinafter, secondary battery 10) as an example of an embodiment will be described using Figure 1. For convenience of explanation, the following description of each component may use the axial direction, radial direction, and circumferential direction. Also, the sealing body 16 side may be referred to as "top" and the bottom side of the outer can 15 as "bottom."

[0012] The secondary battery 10 includes an electrode assembly 14, a non-aqueous electrolyte (not shown), and an outer can 15 that houses the electrode assembly 14 and the non-aqueous electrolyte. 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. The positive electrode 11, the negative electrode 12, and the separator 13 are all strip-shaped, long bodies that are spirally wound along the longitudinal direction and are alternately stacked in the radial direction of the electrode assembly 14. The separator 13 is formed to be slightly larger than the positive electrode 11 and the negative electrode 12, and two separators 13 are arranged to sandwich the positive electrode 11.

[0013] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets 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. Alternatively, the separator 13 may be a multilayer separator including a polyethylene layer and a polypropylene layer, and the surface of the separator 13 may be coated with a material such as an aramid-based resin or ceramic.

[0014] The non-aqueous electrolyte has 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] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. 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. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0016] The sealing body 16 seals the opening at the top end of the outer can 15, 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 tab 19 extends vertically through a through-hole in the insulating plate 17 and connects a filter 22, which is the bottom plate of the sealing body 16, to the positive electrode 11 included in the electrode body 14. This connects the positive electrode 11 to the sealing body 16, and 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 a positive electrode terminal. The positive electrode tab 19 is, for example, an aluminum tab.

[0017] On the other hand, a negative electrode core exposed portion protrudes from the lower side of the negative electrode 12 (one end in the short direction of the negative electrode 12), where the negative electrode core is not provided with a negative electrode mixture layer. The negative electrode core exposed portion is formed from the inner end of the winding to the outer end of the winding in the longitudinal direction of the long negative electrode plate. A negative electrode current collector 20 is provided on the lower side of the electrode body 14, and the negative electrode core exposed portion is joined to the negative electrode current collector 20. This electrically connects the negative electrode 12 and the negative electrode current collector 20. Furthermore, the negative electrode current collector 20 is joined to the inner surface of the bottom of the outer can 15, electrically connecting the negative electrode current collector 20 and the outer can 15. This connection allows the outer can 15 to function as a negative electrode external terminal.

[0018] The negative electrode of the present disclosure is not limited to the end surface current collection structure described above. For example, a negative electrode tab may be provided near the inner end of the negative electrode 12, and the negative electrode tab may be led out from the underside of the negative electrode 12 and connected to the outer can 15. At the same time, a negative electrode substrate exposed portion may be formed at the outer end of the negative electrode 12, and this negative electrode substrate exposed portion may be brought into contact with the inner circumferential surface of the outer can 15, thereby electrically connecting the vicinity of the outer end of the negative electrode 12 to the outer can 15.

[0019] The outer can 15 is a cylindrical metal container with a bottom and an opening on one axial side. A gasket 27 is provided between the outer can 15 and the sealing body 16 to ensure the sealing of the interior of the secondary battery 10. The outer can 15 has a groove 21 that supports the sealing body 16 and is formed, for example, by pressing the side surface from the outside. The groove 21 is preferably formed in an annular shape along the circumferential direction of the outer can 15, and supports the sealing body 16 on its upper surface.

[0020] 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 break, causing the upper valve body 25 to swell toward the cap 26 and separate from the lower valve body 23, thereby cutting off the electrical connection between them. If the internal pressure continues to increase, the upper valve body 25 may break, and gas may be released from the opening 26A of the cap 26.

[0021] [Positive Electrode] A positive electrode 11, which is an example of an embodiment, will be described with reference to Fig. 2. Hereinafter, the positive electrode 11 may be described using the longitudinal direction and the transverse direction. In this case, the longitudinal direction is the winding direction of the positive electrode 11, and the transverse direction is the axial direction. The longitudinal direction may also be described using the inner side and the outer side of the winding.

[0022] The positive electrode 11 has a positive electrode core 30 and a positive electrode mixture layer 32 disposed on the surface of the positive electrode core 30. A positive electrode core exposed portion 34, where the positive electrode core 30 is exposed, is disposed on the surface of the positive electrode 11. The positive electrode core exposed portion 34 contacts only one of both widthwise end portions of the positive electrode 11.

[0023] When the longitudinal length of the positive electrode 11 is L, the positive electrode substrate exposed portion 34 is not formed within a range of L / 10 from the outer side of the winding in the longitudinal direction, more preferably not formed within a range of L / 6 from the outer side of the winding in the longitudinal direction. In other words, the outermost positive electrode substrate exposed portion 34 is formed from a position L / 10 from the outer side of the winding in the longitudinal direction, more preferably from a position L / 6 from the outer side of the winding in the longitudinal direction. This makes it possible to suppress the occurrence of wrinkles in the positive electrode substrate exposed portion 34 on the outer side of the winding in the longitudinal direction due to elongation of the positive electrode 11 during charging and discharging of the secondary battery 10.

[0024] The positive electrode substrate exposed portion 34 is preferably formed within a range of L / 4 from the outer side of the winding in the longitudinal direction of the positive electrode 11. This makes it possible to suppress an increase in the resistance value of the secondary battery 10. Furthermore, the length L of the positive electrode 11 in the longitudinal direction is preferably 3000 mm or more.

[0025] A plurality of positive electrode substrate exposed portions 34 are preferably arranged on the surface of the positive electrode 11. The number of positive electrode substrate exposed portions 34 is preferably six or more. Since one of the positive electrode tabs 19 is connected to each of the positive electrode substrate exposed portions 34, the current collection ability of the positive electrode 11 is improved, and the output characteristics of the secondary battery 10 are improved. Furthermore, when there are a plurality of positive electrode substrate exposed portions 34, particularly six or more, the positive electrode substrate exposed portions 34 on the outer side of the winding in the longitudinal direction are likely to be formed in the range of L / 10 from the outer side of the winding, which can suppress the occurrence of wrinkles.

[0026] The positive electrode core exposed portion 34, the positive electrode tab 19, and a portion of the positive electrode mixture layer 32 adjacent to the positive electrode core exposed portion 34 are covered with a protective member 36. In other words, the protective member 36 covers the positive electrode tab 19, the positive electrode core exposed portion 34, and a portion of the positive electrode mixture layer 32. The protective member 36 is an insulating member that prevents an internal short circuit between the positive electrode tab 19 and the positive electrode core exposed portion 34 and the opposing negative electrode mixture layer if the separator 13 is torn.

[0027] The protective member 36 is, for example, an adhesive tape having a substrate and an adhesive portion formed on one surface of the substrate. A heat-resistant layer containing inorganic particles such as metal oxide can be provided between the substrate and the adhesive portion. The substrate can be made of any insulating resin, such as PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PI (polyimide), PP (polypropylene), PET (polyethylene terephthalate), or PBT (polybutylene terephthalate). The thickness of the substrate is, for example, 5 μm or more and 50 μm or less.

[0028] The adhesive portion is a portion for adhering the protective member 36 to the surface of the positive electrode 11. The thickness of the adhesive portion is, for example, 1 μm or more and 30 μm or less. The adhesive portion may contain at least one of a rubber-based polymer and an acrylic-based polymer. The rubber-based polymer and the acrylic-based polymer have adhesive properties, and therefore can adhere the protective member 36 to the surface of the positive electrode 11. The adhesive portion may further contain, for example, a silicone-based polymer.

[0029] A foil of a metal such as aluminum that is stable within the potential range of the positive electrode, a film with such a metal disposed on the surface, or the like can be used for the positive electrode core 30. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less.

[0030] The positive electrode mixture layer 32 is preferably formed on both sides of the positive electrode core 30. The thickness of the positive electrode mixture layer 32 is, for example, 10 μm or more and 150 μm or less on one side of the positive electrode core 30. The positive electrode mixture layer 32 contains, for example, 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. to both sides of the positive electrode core 30, drying the coating, and then rolling the coating using a roller or the like.

[0031] The positive electrode active material contained in the positive electrode mixture layer 32 can be, for example, a lithium transition metal composite 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 O４ , 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, and 0<x≦1.2, 0<y≦0.9, and 2.0≦z≦2.3). These may be used alone or in combination.

[0032] The positive electrode active material preferably contains a lithium nickel composite oxide, since this can increase the capacity of the secondary battery 10. The lithium nickel composite oxide is preferably Li ｘ NiO ２ , 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) The higher the Ni content of the lithium nickel composite oxide, the higher the capacity.

[0033] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon-based particles such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotubes (CNT), graphene, and graphite. These may be used alone or in combination of two or more.

[0034] Examples of the binder contained in the positive electrode mixture layer 32 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide-based resins, acrylic-based resins, polyolefin-based resins, etc. These may be used alone or in combination of two or more.

[0035] The negative electrode 12 includes a negative electrode current collector and a negative electrode mixture layer disposed on the surface of the negative electrode current collector. The negative electrode current collector may be a foil of a metal, such as copper, that is stable within the potential range of the negative electrode, or a film having such a metal disposed on its surface. The thickness of the negative electrode current collector is, for example, 5 μm to 30 μm.

[0036] The negative electrode mixture layer is preferably formed on both sides of the negative electrode current collector. The thickness of the negative electrode mixture layer is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode current collector. The negative electrode mixture layer contains, for example, 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, a binder, etc. to both sides of the negative electrode current collector, drying the coating, and then rolling the coating using a roller or the like.

[0037] 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.

[0038] As the negative electrode active material, metals that can be alloyed with Li, such as Si and Sn, metal compounds containing Si, Sn, etc., and lithium-titanium composite oxides may be used. For example, SiO ｘ Si-containing compounds represented by (0.5≦x≦1.6), Li ２ｙ SiO （２＋ｙ） A Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by (0<y<2), or a Si-containing compound in which Si is dispersed in a carbon material, may be used in combination with graphite.

[0039] 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 (PAA-Na, PAA-K, etc., or a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0040] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0041] Example 1 [Preparation of Positive Electrode] As the positive electrode active material, LiNi ０．８８ Co ０．０９ Al ０．０３ O ２ Aluminum-containing lithium nickel cobalt oxide represented by the formula (I) was used. 100 parts by mass of the positive electrode active material, 1 part by mass of acetylene black (AB), and 1 part by mass of polyvinylidene fluoride (PVDF) 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 core made of aluminum foil with a thickness of 15 μm so that six positive electrode core exposed portions were formed. As shown in FIG. 2, the positive electrode core exposed portions were in contact with only one end of the positive electrode in the width direction. Furthermore, when the longitudinal length of the positive electrode is L, the outermost positive electrode core exposed portion was formed at a position L / 6 from the outer side of the winding in the longitudinal direction.

[0042] The coating was dried and rolled. Next, the electrode was cut to a predetermined electrode plate size to prepare a positive electrode having a positive electrode mixture layer formed on both sides of the positive electrode core. After that, an aluminum positive electrode tab was welded to each of the six positive electrode core exposed portions, and insulating tape was applied so as to cover the positive electrode core exposed portions, the positive electrode tab, and a portion of the positive electrode mixture layer adjacent to the positive electrode mixture layer.

[0043] [Preparation of Negative Electrode] 95 parts by mass of graphite, 5 parts by mass of Si oxide (SiO), 1 part by mass of sodium carboxymethyl cellulose (CMC-Na), 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 core made of copper foil with a thickness of 8 μm, dried, rolled, and cut to a predetermined electrode plate size to prepare a negative electrode having a negative electrode mixture layer formed on both sides of the negative electrode core. A negative electrode core exposed portion where the negative electrode mixture layer was not provided was provided on the lower side of the negative electrode (one end in the short direction of the negative electrode), and a nickel negative electrode current collector was welded to the negative electrode core exposed portion.

[0044] [Preparation of non-aqueous electrolyte] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 3:7, and lithium hexafluorophosphate (LiPF ６ A non-aqueous electrolyte was prepared by dissolving 1.5 mol / L of ammonium hydroxide in water.

[0045] [Preparation of Test Cell] A wound electrode assembly was prepared by spirally winding a positive electrode and a negative electrode with a polyethylene microporous membrane separator interposed therebetween. This electrode assembly was housed in a cylindrical outer can with a bottom, and the negative electrode tab was welded to the bottom of the cylindrical outer can with a bottom, and the positive electrode tab was welded to a sealing member. After pouring a nonaqueous electrolyte into the outer can, the opening of the outer can was sealed with a sealing member via a gasket to prepare a cylindrical test cell.

[0046] [Charge-Discharge Cycle] At an ambient temperature of 25° C., the test cell was charged at a constant current of 0.3 C until the battery voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value reached 0.01 C. Thereafter, the test cell was discharged at a constant current of 0.5 C until the battery voltage reached 2.5 V, and this charge-discharge cycle was counted as one cycle.

[0047] [Evaluation of DC Resistance] The DC resistance (DCIR) was calculated from the closed circuit voltage (CCV) 10 seconds after discharge and the current value (I10s) 10 seconds after discharge according to the following formula: DCIR = (OCV - CCV) / I10s The resistance of 100 test cells was measured and the average value was calculated, and the average resistance value of Comparative Example 1 was set to 1.00 to calculate the values ​​of each Example and Comparative Example.

[0048] [Evaluation of Occurrence of Wrinkles in Exposed Portion of Positive Electrode Substrate] After the above charge-discharge cycle, 100 test cells were disassembled, and the number of test cells in which wrinkles had occurred in the exposed portion of the positive electrode substrate was counted.

[0049] Example 2 A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the positive electrode, the outermost positive electrode substrate exposed portion was formed at a position L / 5.3 from the outer side of the winding in the longitudinal direction.

[0050] Example 3 A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the positive electrode, the outermost positive electrode substrate exposed portion was formed at a position L / 5L from the outer side of the winding in the longitudinal direction.

[0051] Example 4 A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the positive electrode, the outermost positive electrode substrate exposed portion was formed at a position L / 4.5L from the outer side of the winding in the longitudinal direction.

[0052] Example 5 A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the positive electrode, the outermost positive electrode substrate exposed portion was formed at a position L / 4 from the outer side of the winding in the longitudinal direction.

[0053] Example 6 A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the positive electrode, the outermost positive electrode substrate exposed portion was formed at a position L / 10 from the outer side of the winding in the longitudinal direction.

[0054] <Comparative Example 1> A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the positive electrode, the outermost positive electrode substrate exposed portion was formed at a position L / 16.7 from the outer side of the winding in the longitudinal direction.

[0055] <Comparative Example 2> A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the positive electrode, the outermost positive electrode substrate exposed portion was formed at a position L / 11 from the outer side of the winding in the longitudinal direction.

[0056] <Comparative Example 3> A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the positive electrode, the outermost positive electrode substrate exposed portion was formed at a position L / 3.3 from the outer side of the winding in the longitudinal direction.

[0057] <Comparative Example 4> A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the positive electrode, the outermost positive electrode substrate exposed portion was formed at a position L / 2.8 from the outer side of the winding in the longitudinal direction.

[0058] Table 1 shows the evaluation results of the test cells according to the examples and comparative examples.

[0059]

[0060] As shown in Table 1, in the test cells of Examples 1-6, the resistance value was suppressed while the occurrence of wrinkles in the positive electrode substrate exposed portion was suppressed. On the other hand, in the test cells of Comparative Examples 1-2, the resistance value was suppressed but the occurrence of wrinkles in the positive electrode substrate exposed portion was not suppressed. Furthermore, in the test cells of Comparative Examples 3-4, the occurrence of wrinkles in the positive electrode substrate exposed portion was suppressed but the resistance value was not suppressed.

[0061] It should be noted that the present disclosure is not limited to the above-described embodiments and their variations, and it goes without saying that various modifications and improvements are possible within the scope of the matters described in the claims of the present application.

[0062] The present disclosure is further described by the following embodiments. Configuration 1: A cylindrical secondary battery including an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally with a separator interposed therebetween, a non-aqueous electrolyte, and a cylindrical outer can accommodating the electrode assembly and the non-aqueous electrolyte, wherein the positive electrode has a positive electrode core and a positive electrode mixture layer disposed on the surface of the positive electrode core, a positive electrode core exposed portion in which the positive electrode core is exposed is formed in a portion of the positive electrode that contacts only one end in the short direction, and the positive electrode core exposed portion is not formed within a range of L / 10 from the outer side of the winding in the long direction, where L is the longitudinal length of the positive electrode. Configuration 2: A cylindrical secondary battery according to configuration 1, wherein six or more positive electrode core exposed portions are formed, and a positive electrode tab is joined to each of the positive electrode core exposed portions. Configuration 3: The cylindrical secondary battery according to configuration 1 or 2, wherein the longitudinal length of the positive electrode is 3000 mm or more.Configuration 4: The cylindrical secondary battery according to any of configurations 1 to 3, wherein the positive electrode substrate exposed portion is not formed within a range of L / 6 from the outer side of the winding of the positive electrode in the longitudinal direction, where L is the longitudinal length of the positive electrode.Configuration 5: The cylindrical secondary battery according to any of configurations 1 to 4, wherein the positive electrode substrate exposed portion is formed within a range of L / 4 from the outer side of the winding of the positive electrode in the longitudinal direction, where L is the longitudinal length of the positive electrode. Configuration 6: The cylindrical secondary battery according to any one of configurations 1 to 5, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer arranged on the surface of the negative electrode core, a negative electrode core exposed portion where the negative electrode core is exposed is formed at one end in the short direction of the negative electrode, and a negative electrode current collector plate is joined to the negative electrode core exposed portion. Configuration 7: The cylindrical secondary battery according to any one of configurations 1 to 5, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer arranged on the surface of the negative electrode core, a negative electrode core exposed portion where the negative electrode core is exposed is formed at one end in the long direction of the negative electrode, and the negative electrode core exposed portion contacts the inner circumferential surface of the outer can.

[0063] REFERENCE SIGNS LIST 10 (cylindrical) secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 outer can, 16 sealing body, 17, 18 insulating plate, 19 positive electrode tab, 20 negative electrode tab, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a opening, 27 gasket, 30 positive electrode core body, 32 positive electrode mixture layer, 34 positive electrode core body exposed portion, 36 protective member

Claims

1. A cylindrical secondary battery comprising: an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound in the longitudinal direction with a separator interposed therebetween, a non-aqueous electrolyte, and a cylindrical outer casing for accommodating the electrode assembly and the non-aqueous electrolyte, wherein the positive electrode has a positive electrode core and a positive electrode mixture layer arranged on a surface of the positive electrode core, a positive electrode core exposed portion in which the positive electrode core is exposed is formed in a portion that contacts only one end in the lateral direction of the positive electrode, and the positive electrode core exposed portion is not formed within a range of L / 10 from the outer side of the winding in the longitudinal direction, where L is the longitudinal length of the positive electrode.

2. A cylindrical secondary battery as claimed in claim 1, wherein six or more positive electrode core exposed portions are formed, and a positive electrode tab is joined to each of the positive electrode core exposed portions.

3. A cylindrical secondary battery according to claim 1, wherein the length of the positive electrode in the longitudinal direction is 3000 mm or more.

4. A cylindrical secondary battery as claimed in claim 1, wherein, when the longitudinal length of the positive electrode is L, the positive electrode core exposed portion is not formed within a range of L / 6 from the outer side of the winding in the longitudinal direction of the positive electrode.

5. A cylindrical secondary battery as claimed in claim 1, wherein the positive electrode substrate exposed portion is formed within a range of L / 4 from the outer side of the winding in the longitudinal direction of the positive electrode, where L is the longitudinal length of the positive electrode.

6. A cylindrical secondary battery according to any one of claims 1 to 5, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer arranged on a surface of the negative electrode core, a negative electrode core exposed portion where the negative electrode core is exposed is formed at one end in the short side direction of the negative electrode, and a negative electrode current collector plate is joined to the negative electrode core exposed portion.

7. A cylindrical secondary battery according to any one of claims 1 to 5, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer arranged on a surface of the negative electrode core, and a negative electrode core exposed portion at which the negative electrode core is exposed is formed at one longitudinal end of the negative electrode, and the negative electrode core exposed portion contacts the inner peripheral surface of the outer can.

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