Secondary battery

Abstract

A secondary battery according to an example of an embodiment of the present invention comprises: an electrode body (14) that has a positive electrode (11) including a positive electrode core body (30) and positive electrode mixture layers (31), a negative electrode (12), and a separator (13), and that is formed by the positive electrode (11) and the negative electrode (12) being wound with the separator (13) interposed therebetween; an exterior body that accommodates the electrode body (14); and a sealing body that closes an opening of the exterior body. The positive electrode (11) has: a facing part (51) in which a positive electrode mixture layer (31) is formed on both surfaces of the positive electrode core body (30) and which faces the negative electrode (12) with the separator (13) interposed therebetween; and a non-facing part (51) which extends from a starting end (50x) of a facing part (50) to a winding center (Z) side of the electrode body (14), the facing part (50) facing a starting end (12x) of the negative electrode (12) located on a winding start side of the electrode body (14) with the separator interposed therebetween. The non-facing part (51) is characterized in that an insulating layer (52) is formed on both surfaces of the positive electrode core body (30).

Description

secondary battery

[0001] The present disclosure relates to secondary batteries, and more particularly to secondary batteries with wound electrodes.

[0002] In recent years, secondary batteries such as lithium-ion batteries have been widely used in applications requiring high capacity, high durability, rapid charging performance, etc., such as in-vehicle applications and power storage applications. In general, a secondary battery includes a wound electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, an exterior body that houses the electrode assembly, and a sealing body that closes the opening of the exterior body.

[0003] The positive and negative electrodes, which are the main components of a secondary battery, have a significant effect on the above-mentioned performance, and therefore many studies have been conducted on the positive and negative electrodes. For example, Patent Document 1 discloses a nonaqueous electrolyte secondary battery in which a heat dissipation material layer is formed on at least one of the positive and negative electrodes in order to reduce the temperature difference in the radial direction of the wound electrode body.

[0004] JP 2013-157219 A

[0005] In wound electrode assemblies, the diameter of the electrode assembly tends to increase as the battery size increases. The inventors' research has revealed that increasing the diameter of the electrode assembly increases the heat capacity and thermal resistance, resulting in localized heat concentration at the center of the electrode assembly. As a result, there is a problem of a decrease in capacity retention during charge-discharge cycles due to material degradation at the center of the electrode assembly. Furthermore, expansion of the negative electrode during charge-discharge cycles and reaction force from the electrode plate located at the innermost periphery of the winding increase the surface pressure of the electrode plate near the center of the winding, resulting in deformation of the electrode plate. The nonaqueous electrolyte secondary battery described in Patent Document 1 cannot solve this problem.

[0006] The secondary battery according to the present disclosure includes an electrode assembly having a positive electrode including a positive electrode core and a positive electrode mixture layer, a negative electrode, and a separator, the positive electrode and the negative electrode being wound with the separator interposed therebetween, an exterior housing that houses the electrode assembly, and a sealing body that closes the opening of the exterior housing. The positive electrode has positive electrode mixture layers formed on both sides of the positive electrode core, and has a facing portion that faces the negative electrode across the separator, and a non-facing portion that extends from a starting end of the facing portion that faces, across the separator, a starting end of the negative electrode located at the winding start side of the electrode assembly toward the winding center of the electrode assembly. The non-facing portion is characterized in that an insulating layer is formed on both sides of the positive electrode core.

[0007] According to the secondary battery of the present disclosure, it is possible to effectively suppress deformation of the electrode plates while suppressing a decrease in capacity retention rate during charge-discharge cycles caused by local heat concentration at the center of the winding of the electrode body.

[0008] 1 is an axial cross-sectional view of a cylindrical battery according to an example of an embodiment; FIG. 2 is a radial cross-sectional view of an electrode body according to an example of an embodiment; FIG. 3 is a front view of a positive electrode according to an example of an embodiment; and FIG. 4 is a diagram illustrating a method for evaluating electrode plate deformation.

[0009] Hereinafter, an example of an embodiment of a secondary battery according to the present disclosure will be described in detail with reference to the drawings. Note that configurations obtained by selectively combining the components of the multiple embodiments and modifications described below are included within the scope of the present disclosure.

[0010] In the embodiment described below, a cylindrical battery in which a wound electrode assembly 14 is housed in a cylindrical outer can 15 with a bottom is exemplified as the secondary battery, but the outer can of the battery is not limited to a cylindrical outer can. Other embodiments of the secondary battery according to the present disclosure include a prismatic battery equipped with a prismatic outer can.

[0011] A cylindrical battery as an example of this embodiment will be described in detail with reference to Fig. 1. Fig. 1 is a schematic diagram showing a cross section of a cylindrical battery 10 taken along the axial and radial directions.

[0012] As shown in FIG. 1 , the cylindrical battery 10 includes a positive electrode 11, a negative electrode 12, and a separator 13. The positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween, forming an electrode assembly 14, and a cylindrical outer can 15 with a bottom that houses the electrode assembly 14. The cylindrical battery 10 also includes an electrolyte housed in the outer can 15 and a sealing body 16 that closes the opening of the outer can 15. The outer can 15 has a groove 21 formed in its side wall, and the sealing body 16 is supported by the groove 21 to close the opening of the outer can 15. The positive electrode 11 or the negative electrode 12 is connected to the bottom of the outer can 15. For ease of explanation, the sealing body 16 side of the cylindrical battery 10 will be referred to as the top, and the bottom side of the outer can 15 will be referred to as the bottom.

[0013] The electrolyte may be an aqueous electrolyte, but in this embodiment, a non-aqueous electrolyte is used. The non-aqueous electrolyte has lithium ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The cylindrical battery 10 is, for example, a non-aqueous electrolyte secondary battery, and preferably a lithium ion battery.

[0014] The liquid electrolyte (electrolytic solution) contains 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. Examples of the electrolyte salt include 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 a 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] 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 long, strip-like bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the length direction and width direction (winding axis direction) than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and for example, two separators 13 are arranged to sandwich the positive electrode 11.

[0017] The positive electrode 11 has a long positive electrode core 30 and a positive electrode mixture layer 31 provided on the positive electrode core 30. The positive electrode core 30 can be a foil of a metal that is stable within the potential range of the positive electrode 11, such as aluminum, an aluminum alloy, stainless steel, or titanium, or a film with such a metal disposed on the surface layer. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is preferably formed on both sides of the positive electrode core 30. For example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, or the like is used as the positive electrode active material.

[0018] The thickness of the positive electrode 11 is, for example, 160 μm or more and 200 μm or less. In this embodiment, the thickness of the positive electrode 11 is substantially constant except for the positive electrode core exposed portion to which the positive electrode lead 20 is connected. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less. The thickness of the positive electrode mixture layer 31 is, for example, 70 μm or more and 100 μm or less on one side of the positive electrode core 30. The positive electrode 11 can be produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode core 30.

[0019] In this embodiment, the positive electrode 11 has a positive electrode core exposed portion where the positive electrode mixture layer 31 is not present and the surface of the positive electrode core 30 is exposed. The positive electrode core exposed portion is provided, for example, in the center portion in the longitudinal direction of the positive electrode 11. A positive electrode lead 20 that connects the sealing body 16 and the positive electrode core exposed portion is joined to the positive electrode core exposed portion. Note that the positive electrode lead 20 is preferably joined directly to the positive electrode core exposed portion by ultrasonic welding or the like.

[0020] The negative electrode 12 has a long negative electrode core 40 and a negative electrode mixture layer 41 provided on the negative electrode core 40. For the negative electrode core 40, a foil of a metal that is stable within the potential range of the negative electrode 12, such as copper, a copper alloy, stainless steel, nickel, or a nickel alloy, or a film having such a metal disposed on its surface can be used. The negative electrode mixture layer 41 contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR), and is preferably formed on both sides of the negative electrode core 40. For example, graphite, a Si-containing material, or the like is used as the negative electrode active material.

[0021] The thickness of the negative electrode 12 is, for example, 170 μm or more and 210 μm or less. In the present embodiment, the thickness of the negative electrode 12 is substantially constant except for a negative electrode core exposed portion described later. The thickness of the negative electrode core 40 is, for example, 5 μm or more and 15 μm or less. The thickness of the negative electrode mixture layer 41 is, for example, 70 μm or more and 110 μm or less on one surface side of the negative electrode core 40. The negative electrode 12 can be produced, similarly to the positive electrode 11, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layers 41 on both surfaces of the negative electrode core 40.

[0022] In this embodiment, the negative electrode 12 has a strip-shaped negative electrode core exposed portion, where the surface of the negative electrode core 40 is exposed, formed along the length of the negative electrode 12 at a widthwise end portion located on the bottom side of the outer can 15. The negative electrode core exposed portion is provided, for example, over a range from the end on the winding start side to the end on the winding end side in the longitudinal direction of the long negative electrode 12.

[0023] The negative electrode core exposed portion is connected to the bottom of the outer can 15 directly or via the lower current collector 17. For example, the negative electrode core exposed portion is joined to the upper surface of the lower current collector 17 by welding or the like. Note that the cylindrical battery 10 may not include the lower current collector 17, and the negative electrode core exposed portion may be joined to the inner surface of the bottom of the outer can 15 by welding or the like. The width of the negative electrode core exposed portion is, for example, 2 mm or more and 20 mm or less.

[0024] Furthermore, the negative electrode 12 does not necessarily have to have a band-shaped negative electrode core exposed portion at its lower end in the axial direction. In that case, a negative electrode core exposed portion in which the negative electrode mixture layer 41 is not present and the surface of the negative electrode core 40 is exposed may be formed at one end in the longitudinal direction. The negative electrode core exposed portion is provided at one end in the longitudinal direction of the negative electrode 12 located at the winding start side or the winding end side of the electrode body 14. A negative electrode lead is connected to the negative electrode core exposed portion, and the negative electrode lead is connected to the outer can 15.

[0025] An insulating plate 18 is disposed on the electrode body 14. In the example shown in Fig. 1, a positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 16. The positive electrode lead 20 is connected to the underside of an internal terminal plate 22 of the sealing body 16 by welding or the like, and a cap 26, which is the top plate of the sealing body 16 and is electrically connected to the internal terminal plate 22, serves as the positive electrode terminal.

[0026] A lower current collector 17 is disposed below the electrode assembly 14. The lower current collector 17 is a metal member. As described above, the exposed portion of the negative electrode core that constitutes the negative electrode 12 is joined to the upper surface of the lower current collector 17. The lower surface of the lower current collector 17 is welded to the inner surface of the bottom of the outer can 15. This allows the outer can 15 to function as a negative electrode terminal. The shape of the lower current collector 17 is not particularly limited, and may, for example, have a generally circular shape when viewed from above.

[0027] The outer can 15 is a cylindrical metal container with a bottom. A gasket 27 is provided between the outer can 15 and the sealing body 16 to seal the interior of the battery. The outer can 15 has a groove 21 formed, for example, by pressing the side surface from the outside to support the sealing body 16. 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. The upper end of the outer can 15 is bent inward and crimped to the periphery of the sealing body 16. The outer diameter of the outer can 15 may be 10 mm or more and 70 mm or less, or 20 mm or more and 60 mm or less. An example outer diameter of the outer can 15 is 46 mm.

[0028] The sealing body 16 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked. Each member constituting the sealing body 16 has, for example, a disk or ring shape, and each member except for the insulating member 24 is electrically connected to one another. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, and the insulating member 24 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 23 deforms and breaks, pushing the upper valve body 25 toward the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. When the internal pressure further increases, the upper valve body 25 breaks, and gas is discharged from the opening 26a of the cap 26.

[0029] The positive electrode 11 of the electrode assembly 14 will be described in detail below with further reference to Figures 2 and 3. Figure 2 is a diagram schematically showing a cross section of the electrode assembly 14 along the radial direction. In Figure 2, the separator 13 is omitted for clarity of the drawing. Figure 3 is a front view of the positive electrode 11 and the negative electrode 12. In Figure 3, the positive electrode core exposed portion and the negative electrode core exposed portion are omitted for clarity of the drawing.

[0030] As shown in FIG. 2 , the positive electrode 11 has a facing portion 50 in which a positive electrode mixture layer 31 is formed on both sides of a positive electrode core 30 and faces the negative electrode 12 via the separator 13, and a non-facing portion 51 that extends toward the winding center Z of the electrode body 14 so as not to face the negative electrode 12 via the separator 13, and in which the positive electrode mixture layer 31 is not formed on both sides of the positive electrode core 30.

[0031] The non-facing portion 51 extends from a starting end 50x of the facing portion 50 that faces the starting end 12x of the negative electrode 12 on the inside of the winding with the separator 13 interposed therebetween toward the winding center Z of the electrode body 14. As described above, in the non-facing portion 51, the insulating layer 52 is formed on both sides of the positive electrode core 30. That is, as shown in FIG. 2 , the positive electrode 11 having the insulating layer 52 is located at the innermost periphery of the wound electrode body 14.

[0032] The non-facing portion 51 has the positive electrode substrate 30, but has an insulating layer 52 on its surface, and therefore does not contribute to the charging and discharging of the battery. That is, the non-facing portion 51 does not generate heat due to the battery reaction. On the other hand, the non-facing portion 51 is located at the innermost periphery of the wound electrode body 14, functions as the winding core of the electrode body 14, and contributes to suppressing a decrease in the capacity retention rate during charge and discharge cycles due to heat concentration at the winding center of the electrode body 14. Furthermore, the non-facing portion 51 stabilizes the shape of the winding core portion and contributes to suppressing electrode plate deformation by mitigating stress generated by expansion and contraction of the electrode body 14 during charge and discharge.

[0033] In this specification, the starting end 11x of the positive electrode 11 refers to one end in the length direction of the positive electrode 11 located on the winding start side (closer to the winding center Z) of the electrode body 14. Similarly, the starting end 12x of the negative electrode 12 refers to one end in the length direction of the negative electrode 12 located on the winding start side of the electrode body 14. The starting end 11x of the positive electrode 11 is located closer to the winding center Z than the starting end 12x of the negative electrode 12.

[0034] The non-facing portion 51 may be wound 0.5 to 2 turns, or 0.75 to 1.75 turns, from the starting end 50x of the facing portion 50. It is preferable that the non-facing portion 51 is wound one or more turns from the starting end 50x of the facing portion 50.

[0035] The insulating layer 52 is not particularly limited as long as it is made of an insulating material, but it preferably contains a binder in terms of the mechanical strength and adhesiveness of the insulating layer 52. The insulating layer 52 contains, for example, an inorganic material. Alternatively, the insulating layer 52 may be formed by applying an insulating heat-dissipating paint.

[0036] The inorganic material contained in the insulating layer 52 includes, for example, at least one selected from a metal oxide, a metal hydroxide, a metal nitride, a metal fluoride, and a metal carbide.

[0037] Examples of inorganic materials in the insulating layer 52 include metal oxides such as aluminum oxide, titanium oxide, zirconium oxide, silicon oxide, manganese oxide, magnesium oxide, and nickel oxide, metal hydroxides such as aluminum hydroxide and magnesium hydroxide, metal nitrides such as titanium nitride, boron nitride, aluminum nitride, magnesium nitride, and silicon nitride, metal fluorides such as aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, and barium fluoride, and metal carbides such as silicon carbide, boron carbide, titanium carbide, and tungsten carbide. In terms of chemical stability against the electrolyte, the inorganic material preferably contains at least one of aluminum oxide, titanium oxide, and magnesium oxide.

[0038] The insulating layer 52 has an electrical resistivity of 1.0×10 ８ [Ω·m] or more, and the electrical resistivity is preferably 1.0×10 １６ The upper limit of the electrical resistivity is not particularly limited, but is preferably 1.0×10 ２４ The electrical resistivity may be expressed in Ω·m. The electrical resistivity is a value measured based on Japanese Industrial Standard JIS C 2139 (Dielectric and Resistive Properties of Solid Electrical Insulating Materials).

[0039] Furthermore, the insulating layer 52 preferably has a thermal conductivity of 3 W / m·K or more, and more preferably 20 W / m·K or more. The upper limit of the thermal conductivity is not particularly limited, but may be 500 W / m·K. The thermal conductivity (unit: W / m / K) is a value measured at a temperature of 25°C using a flash method in accordance with Japanese Industrial Standard JIS R 1611 (Method for measuring thermal diffusivity, specific heat capacity, and thermal conductivity of fine ceramics using a flash method).

[0040] The binder contained in the insulating layer 52 is preferably a substance that dissolves in a solvent such as N-methylpyrrolidone (NMP) or water and is chemically stable in the positive electrode 11. Examples of such a binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyacrylic acid, polyacrylonitrile, polyisobutylene, and polyisoprene.

[0041] The thickness of the non-facing portion 51 is, for example, 30 μm or more and 200 μm or less. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less. The thickness of the insulating layer 52 is preferably, for example, 10 μm or more on one surface side of the positive electrode core 30. Furthermore, the thickness of the insulating layer 52 is preferably 100 μm or less.

[0042] The non-facing portion 51 can be produced by applying an insulating slurry containing an insulating material and a binder onto the positive electrode core 30, drying the coating, and then compressing it to form an insulating layer 52 on both sides of the positive electrode core 30.

[0043] 2 and 3 , when forming the electrode body 14, the negative electrode 12 is wound such that the starting end 12x is positioned closer to the starting end 11x of the positive electrode 11 than the starting end 50x of the facing portion 50 of the positive electrode 11 to prevent lithium deposition. That is, an insulating layer 52 may be formed on a portion of the facing portion 50. The length L51 of the non-facing portion 51 is not particularly limited, and is preferably a length that is wound one or more times from the starting end 50x of the facing portion 50 at the innermost periphery of the electrode body 14 after winding.

[0044] The above-described embodiment can be modified as appropriate within the scope of the object of the present disclosure. For example, the positive electrode 11 may be provided with a positive electrode core exposed portion, where the positive electrode core 30 is exposed, at the widthwise end located on the sealing body 16 side. In this case, the positive electrode core exposed portion is wound so as to extend from the upper end of the electrode assembly 14. The extended positive electrode core exposed portion is joined by welding or the like to an upper current collector plate placed on the electrode assembly 14. By joining the positive electrode core exposed portion to the upper current collector plate, the contact area between the positive electrode core exposed portion and the upper current collector plate increases, thereby reducing the internal resistance of the positive electrode 11.

[0045] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0046] Example 1 Preparation of Positive Electrode Mixture Slurry Lithium nickel oxide (LiNi) containing cobalt and aluminum was used as the positive electrode active material. ０．８８ Co ０．０９ Al ０．０３ O ２ The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a solid content mass ratio of 98:1:1, and N-methylpyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode mixture slurry.

[0047] [Preparation of Positive Electrode] The positive electrode mixture slurry was applied to both sides of the opposing portions of a positive electrode core made of a long aluminum foil with a thickness of 15 μm by a die coating method to form a coating film, which was then dried. Furthermore, an insulating slurry containing aluminum oxide and polyvinylidene fluoride (PVdF) was applied to the non-facing portion of the positive electrode core to form an insulating coating film, which was then dried. As a result, an insulating layer was formed on the non-facing portion. According to the above measurement method, the electrical resistivity of aluminum oxide was 1.0 × 10 １６ [Ω·m] and thermal conductivity was 30 [W / m·K].

[0048] Next, the coating film (positive electrode mixture layer, insulating layer) was compressed using a roller, and the positive electrode core was cut to a predetermined electrode size to obtain a positive electrode with a positive electrode mixture layer and an insulating layer formed on both sides of the positive electrode core. The average thickness of the positive electrode mixture layer was 70 μm on one side of the positive electrode core, and the average thickness of the insulating layer was 10 μm on one side of the positive electrode core. At this time, the insulating layer was formed in a region 30 mm from the starting end of the positive electrode with a total length of 3800 mm, and the positive electrode mixture layer was formed in the remaining region. The positive electrode had eight positive electrode core exposed portions at the width direction end where no positive electrode mixture layer was present, and aluminum positive electrode leads were welded to the positive electrode core exposed portions.

[0049] [Fabrication of Negative Electrode] A mixture of graphite powder and a Si-containing material in a mass ratio of 95:5 was used as the negative electrode active material. Graphite had an electrical resistivity of 2.8×10 according to the measurement method described above. －８The electrical conductivity was 60 [Ω·m] and thermal conductivity was 60 [W / m·K]. The negative electrode active material, a dispersion of styrene butadiene rubber, and sodium carboxymethyl cellulose were mixed in a solids mass ratio of 98:1:1, and a negative electrode mixture slurry was prepared using water as a dispersion medium. The slurry was applied to both sides of a negative electrode core made of a long copper foil with a thickness of 8 μm, and the coating was dried and compressed to obtain a negative electrode with a negative electrode mixture layer formed on both sides of the negative electrode core. A strip-shaped negative electrode core exposed portion was provided at the lower end of the width direction of the negative electrode, where the negative electrode mixture layer was not present from the start end to the end of the winding along the length of the negative electrode. The total length of the negative electrode was 4000 mm.

[0050] [Fabrication of Electrode Assembly] The positive electrode, the negative electrode, and a polyethylene separator were spirally wound around a cylindrical winding core member, and a stop tape was applied to the outermost surface to obtain a wound electrode assembly. The positive electrode was positioned so that the non-facing portion with an insulating layer was located at the center of the winding. At the start of the winding of the electrode assembly, the positive electrode extended from the starting end of the facing portion that faced the starting end of the negative electrode and the separator toward the inside of the winding, providing a non-facing portion that did not face the negative electrode. After forming the winding structure of the electrode assembly, the winding core member was removed to obtain a wound electrode assembly with a cavity formed in the winding core portion. The positive electrode with an insulating layer was located at the innermost periphery of the winding (winding core portion).

[0051] [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 1:3 (25°C), and LiPF ６ was dissolved in a concentration of 1.5 mol / L to prepare a non-aqueous electrolyte solution.

[0052] [Fabrication of Cylindrical Battery] An insulating plate was placed on the electrode assembly, and a negative electrode current collector was placed underneath. The exposed portion of the negative electrode core extending from the lower end of the electrode assembly was welded to the upper surface of the lower current collector, and the lower surface of the lower current collector was welded to the inner surface of the bottom of the outer can. Furthermore, a positive electrode lead was welded to the internal terminal plate of the sealing member, and the electrode assembly was housed in the outer can. A nonaqueous electrolyte was then injected into the outer can under reduced pressure, and the opening of the outer can was sealed with the sealing member via a gasket, thereby obtaining a cylindrical battery.

[0053] Example 2 In the production of a positive electrode, magnesium oxide (electrical resistivity: 1.0×10) was used for the insulating layer instead of aluminum oxide. １６ An electrode assembly and a cylindrical battery were fabricated in the same manner as in Example 1, except that an insulating slurry containing an insulating material containing 100% ethylenediaminetetraacetic acid (Fe2O3, Cr2O4 ...

[0054] Example 3 In the production of a positive electrode, aluminum nitride (electrical resistivity: 1.0×10) was used for the insulating layer instead of aluminum oxide. １６ An electrode assembly and a cylindrical battery were fabricated in the same manner as in Example 1, except that an insulating slurry containing an insulating material containing 1,000 sulphur dioxide and 1,000 sulphur dioxide (SiO 2 , thermal conductivity: 150 [Ω·m], thermal conductivity: 150 [W / m·K]) was applied.

[0055] Example 4 In the production of a positive electrode, an insulating layer was formed using an insulating slurry having an electrical resistivity of 1.0×10 １６ An electrode body and a cylindrical battery were produced in the same manner as in Example 1, except that an insulating heat-dissipating paint (UV-curable thermally conductive insulating coating agent, manufactured by Fujifilm Wako Co., Ltd.) with a viscosity of 1000 psi (Ω m) and a thermal conductivity of 5 W / m K was applied to the electrode body and the insulating coating was cured by UV irradiation.

[0056] <Comparative Example 1> An electrode body and a cylindrical battery were produced in the same manner as in Example 1, except that in producing the electrode body, the positive electrode did not have a non-facing portion or an insulating layer extending from the starting end of the facing portion, and the positive electrode, negative electrode, and separator were wound so that the negative electrode was located at the innermost periphery of the winding (winding core portion).

[0057] The batteries of the examples and comparative examples were evaluated by the following methods, and the evaluation results are shown in Table 1.

[0058] [Evaluation of electrode plate deformation] Each battery of the examples and comparative examples was charged at a constant current of 0.5 C in a temperature environment of 25° C. until the battery voltage reached 4.2 V. Thereafter, the battery was discharged at a constant current of 0.7 C until the battery voltage reached 2.5 V. After 500 cycles of this charge / discharge, the battery was placed in a charged state, and the vicinity of the winding core of the electrode body was observed using an X-ray CT device (Shimadzu Corporation, SMX-225CT FPD HR).

[0059] As shown in Figure 4, when deformation (buckling) of the electrode plate (at least one of the positive electrode 11 and the negative electrode 12) was confirmed near the starting end of the positive electrode in the CT image of the electrode body, where the angle α was 150° or less, it was determined that deformation had occurred. In Examples 1 to 4 and Comparative Example 1, evaluation was performed on 20 batteries each.

[0060] [Evaluation of Capacity Retention Rate] Each battery of the Examples and Comparative Examples was charged at a constant current of 1 C in a temperature environment of 25° C. until the battery voltage reached 4.2 V. Thereafter, the battery was discharged at a constant current of 0.5 C until the battery voltage reached 2.5 V. This cycle of charge and discharge was counted as one cycle, and 500 cycles were repeated. The discharge capacity at the first cycle and the discharge capacity at the 500th cycle were determined, and the capacity retention rate was calculated according to the following formula: Capacity retention rate (%) = (Discharge capacity at 500th cycle / Discharge capacity at first cycle) × 100

[0061] The capacity retention rate was calculated for 20 batteries for each of Examples 1 to 4 and Comparative Example 1, and the average values ​​are shown in the table.

[0062]

[0063] As shown in Table 1, the batteries of Examples 1 to 4 were less susceptible to plate deformation than the battery of Comparative Example 1. Furthermore, the batteries of Examples 1 to 3 exhibited improved capacity retention rates compared to the battery of Comparative Example 1. The relatively high thermal conductivity of the graphite contained in the negative electrode mixture layer can somewhat suppress the decrease in capacity retention rate due to heat concentration at the winding center. However, as is clear from the results of Comparative Example 1, plate deformation is more likely to occur. It is believed that stress generated by the expansion and contraction of the electrode assembly during charge and discharge is absorbed by the winding core portion of the electrode assembly, suppressing plate deformation. However, the position of the negative electrode having the negative electrode mixture layer in the winding core portion increases the rigidity of the winding core portion, which is thought to prevent sufficient stress relaxation and lead to plate deformation.

[0064] As a result of investigations by the inventors, it was found that by forming an insulating layer on the non-facing portion of the positive electrode and positioning the positive electrode having the insulating layer on the winding core portion of the electrode body, as in the battery of the example, it is possible to effectively suppress plate deformation while suppressing a decrease in capacity retention rate due to local heat concentration.

[0065] The present disclosure will be further described by the following embodiments. Configuration 1: A secondary battery including an electrode assembly having a positive electrode including a positive electrode core and a positive electrode mixture layer, a negative electrode, and a separator, the positive electrode and the negative electrode being wound with the separator interposed therebetween, an exterior body accommodating the electrode assembly, and a sealing body closing an opening of the exterior body, wherein the positive electrode has the positive electrode mixture layer formed on both sides of the positive electrode core, and has a facing portion facing the negative electrode across the separator, and a non-facing portion extending from a starting end of the facing portion facing a starting end of the negative electrode located on the winding start side of the electrode assembly with the separator interposed therebetween toward the winding center of the electrode assembly, and an insulating layer formed on both sides of the positive electrode core in the non-facing portion. Configuration 2: A secondary battery including an insulating layer having an electrical resistivity of 10 ８ The secondary battery according to the first aspect of the present invention, wherein the insulating layer has an electrical resistivity of 10 [Ω·m] or more. １６ The secondary battery according to configuration 1 or 2, wherein the thermal conductivity of the insulating layer is 3 W / m K or more. Configuration 4: The secondary battery according to any one of configurations 1 to 3, wherein the thermal conductivity of the insulating layer is 3 W / m K or more. Configuration 5: The secondary battery according to any one of configurations 1 to 4, wherein the thermal conductivity of the insulating layer is 20 W / m K or more. Configuration 6: The secondary battery according to any one of configurations 1 to 5, wherein the exterior body has a cylindrical shape with a bottom, and the exterior body has an outer diameter of 20 mm or more.

[0066] 10 Cylindrical battery, 11 Positive electrode, 11x Starting end of positive electrode, 12 Negative electrode, 12x Starting end of negative electrode, 13 Separator, 14 Electrode body, 15 Outer can, 16 Sealing body, 17 Lower current collector plate, 18 Insulating plate, 20 Positive electrode lead, 21 Grooved portion, 22 Internal terminal plate, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Through hole, 27 Gasket, 30 Positive electrode core, 31 Positive electrode mixture layer, 40 Negative electrode core, 41 Negative electrode mixture layer, 50 Opposing portion, 50x Starting end of opposing portion, 51 Non-opposing portion, 51x Starting end of non-opposing portion, 52 Insulating layer

Claims

1. A secondary battery comprising: an electrode assembly having a positive electrode including a positive electrode core and a positive electrode mixture layer, a negative electrode, and a separator, the positive electrode and the negative electrode being wound with the separator interposed therebetween; an exterior housing that houses the electrode assembly; and a sealing body that closes an opening of the exterior housing, wherein the positive electrode has: a facing portion in which the positive electrode mixture layer is formed on both sides of the positive electrode core and which faces the negative electrode across the separator; and a non-facing portion that extends from a starting end of the facing portion that faces, via the separator, a starting end of the negative electrode located on the winding start side of the electrode assembly, towards the winding center of the electrode assembly, and an insulating layer is formed on both sides of the positive electrode core in the non-facing portion.

2. The electrical resistivity of the insulating layer is 10 ８ The secondary battery according to claim 1 , wherein the resistance is Ω·m or more.

3. The electrical resistivity of the insulating layer is 10 １６ The secondary battery according to claim 1 , wherein the resistance is Ω·m or more.

4. The secondary battery according to claim 1, wherein the thermal conductivity of the insulating layer is 3 W / m·K or more.

5. The secondary battery according to claim 1, wherein the thermal conductivity of the insulating layer is 20 W / m·K or more.

6. The secondary battery according to any one of claims 1 to 5, wherein the exterior body has a cylindrical shape with a bottom, and the exterior body has an outer diameter of 20 mm or more.

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