Cylindrical battery

Abstract

A cylindrical battery (10) comprises an electrode body (14) formed by winding a positive electrode (11) and a negative electrode (12) with a separator (13) therebetween. The negative electrode (12) has a negative electrode core-exposed portion (44). The negative electrode core-exposed portion (44) is joined to a current collecting member (18). The cylindrical battery (10) is characterized in that a width A, a width B, and a width C satisfy the relationships represented by formula (I) and formula (II), where the width A is the width of the positive electrode (11) at a position X where the width of the positive electrode (11) is the largest in a range from the innermost turn to the fifth turn of the positive electrode (11) in a cross-sectional image of the cylindrical battery (10) subjected to 100 cycles of a charge-discharge cycle test, the width B is the width of the positive electrode (11) at the outermost turn of the positive electrode (11), and the width C is the width of the positive electrode 11 at the position X in a cross-sectional image of the cylindrical battery (10) before the charge-discharge cycle test.　Formula (I): (A-C)×100 / C ≥ 1.2; Formula (II): (A-B)×100 / B ≥ 1.2

Description

Cylindrical battery

[0001] The present disclosure relates to cylindrical batteries.

[0002] Conventionally, cylindrical batteries have been known that include an electrode assembly having a positive electrode and a negative electrode, a nonaqueous electrolyte, a cylindrical outer can with a bottom that houses the electrode assembly and the nonaqueous electrolyte, and a sealing member that closes the opening of the outer can. Generally, the positive electrode is formed by disposing a positive electrode mixture layer on a positive electrode core, and the negative electrode is formed by disposing a negative electrode mixture layer on a negative electrode core. The sealing member is supported by the upper surface of a groove provided on the side of the outer can and is fixed to the top of the outer can by being crimped to the opening of the outer can.

[0003] From the viewpoint of improving the output characteristics, etc. of a cylindrical battery, a technique is known in which a negative electrode core exposed portion where the negative electrode core is exposed is provided on the axial lower end side of the electrode body, and the negative electrode core exposed portion is joined to an outer can or a current collecting member (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2000-77054

[0005] In cylindrical batteries in which the exposed portion of the negative electrode substrate is bonded to an outer can or a current collector, the diffusibility of the nonaqueous electrolyte tends to decrease during repeated charge and discharge, particularly in the lower region of the outer can. This can lead to Li deposition on the negative electrode in the lower region of the electrode assembly. Li deposition on the negative electrode increases the thickness of the negative electrode and increases the internal stress of the electrode assembly. As a result, deformation such as buckling of the electrode plate can occur in the lower region of the electrode assembly, potentially resulting in a decrease in cycle performance.

[0006] As a result of the inventors' investigations, it has become clear that the electrode plates expand along the axial direction of the electrode assembly during repeated charge and discharge, thereby reducing the surface pressure inside the electrode assembly, thereby suppressing deformation such as buckling of the electrode plates even during repeated charge and discharge, and ensuring cycle characteristics.

[0007] On the other hand, a grooved portion of an outer can, which is electrically connected to a negative electrode, is generally disposed on the upper portion of the outer periphery of the electrode assembly. Therefore, if the positive electrode disposed on the outer periphery of the electrode assembly extends upward along the axial direction of the electrode assembly, the positive electrode is likely to come into contact with the grooved portion, which may cause an internal short circuit. In other words, simply extending the electrode plate along the axial direction of the electrode assembly to reduce the surface pressure inside the electrode assembly may cause an internal short circuit.

[0008] A cylindrical battery according to one aspect of the present disclosure is a cylindrical battery including an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a non-aqueous electrolyte, and a cylindrical outer can that houses the electrode assembly and the non-aqueous electrolyte and has a bottom, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, and the negative electrode has a negative electrode core exposed portion at the end on the bottom side of both widthwise ends of the negative electrode where the negative electrode mixture layer is not disposed, and the negative electrode core exposed portion is disposed at the bottom or between the electrode assembly and the bottom In a cross-sectional image of a cylindrical battery that has been subjected to 100 charge-discharge cycle tests, the width of the positive electrode at position X within the fifth circumference from the innermost circumference of the positive electrode is defined as width A, the width of the positive electrode at the outermost circumference of the positive electrode is defined as width B, and in a cross-sectional image of the cylindrical battery before the charge-discharge cycle test, the width of the positive electrode at position X is defined as width C, where width A, width B, and width C satisfy the relationships represented by the following formulas (I) and (II): Formula (I): (A-C) x 100 / C ≥ 1.2 Formula (II): (A-B) x 100 / B ≥ 1.2

[0009] According to a cylindrical battery according to one aspect of the present disclosure, it is possible to suppress the occurrence of internal short circuits while suppressing deformation such as buckling of the electrode plates, thereby providing a cylindrical battery that suppresses the occurrence of internal short circuits while exhibiting excellent cycle characteristics.

[0010] 1 is a perspective view of an electrode assembly included in a cylindrical battery according to an embodiment of the present invention;

[0011] Hereinafter, an example of an embodiment of a cylindrical battery according to the present disclosure will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present disclosure is not limited to the following embodiment. Furthermore, the present disclosure also includes configurations obtained by selectively combining the components of the embodiments described below.

[0012] The configuration of a cylindrical battery 10, which is one example of an embodiment, will be described with reference to Figures 1 and 2. Figure 1 is a schematic diagram showing a cross section of the cylindrical battery 10, and Figure 2 is a perspective view of an electrode assembly 14 that constitutes the cylindrical battery 10. Note that Figures 1 and 2 show fewer windings than in the actual case to make it easier to understand the relative positions of the positive electrode 11, negative electrode 12, and separator 13 in the electrode assembly 14.

[0013] 1 and 2 , cylindrical battery 10 includes an electrode assembly 14 in which a positive electrode 11 and a negative electrode 12 are wound with separator 13 interposed therebetween, a non-aqueous electrolyte (not shown), an outer can 16 that houses electrode assembly 14 and the non-aqueous electrolyte, and a sealing body 17 that closes the opening of outer can 16. In this specification, the sealing body 17 side of cylindrical battery 10 is referred to as the "top" and the bottom 16A side of outer can 16 is referred to as the "bottom."

[0014] The electrode assembly 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and has a 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 constituting the electrode assembly 14 are all long strips, and are spirally wound so that they are 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 longitudinal direction and width 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.

[0015] The outer diameter of the electrode body 14 is preferably 40 mm or more, and more preferably 42 mm or more. When the outer diameter of the electrode body 14 is 40 mm or more, the volumetric energy density of the cylindrical battery 10 can be increased, making it easier to achieve high capacity. Furthermore, when the outer diameter of the electrode body 14 is 40 mm or more, deformation such as buckling of the electrode plates, as described below, is likely to occur, and therefore the effects of the present disclosure are significantly exhibited.

[0016] The positive electrode 11 has a positive electrode core 30 and a positive electrode mixture layer 32 formed on the positive electrode core 30. The positive electrode core 30 can be made of 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 the surface layer. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less.

[0017] The positive electrode mixture layer 32 contains a positive electrode active material, a conductive agent, and a binder, and is formed on both sides of the positive electrode core 30 except for an exposed portion of the positive electrode core (not shown) to which the positive electrode lead 20 is welded. 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 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc. onto the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 32 on both sides of the positive electrode core 30.

[0018] The positive electrode mixture layer 32 contains particulate lithium metal composite oxide as a positive electrode active material. The lithium metal composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal element constituting the lithium metal composite oxide is, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among these, it is preferable to contain at least one selected from Co, Ni, and Mn. Examples of suitable composite oxides include lithium metal composite oxides containing Ni, Co, and Mn, or lithium metal composite oxides containing Ni, Co, and Al.

[0019] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, and other carbon materials. Examples of the binder contained in the positive electrode mixture layer 32 include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, and the like. Furthermore, these resins may be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0020] As described above, the positive electrodes 11 are stacked in the radial direction of the electrode body 14, with the separators 13 and negative electrodes 12 interposed therebetween. Here, the distance between the positive electrodes 11 adjacent to each other in the radial direction of the electrode body 14 is preferably greater on the inner circumferential side of the electrode body 14 than on the outer circumferential side of the electrode body 14. In other words, the positive electrodes 11 arranged on the inner circumferential side of the electrode body 14 are preferably wound with a gap therebetween compared to the positive electrodes 11 arranged on the outer circumferential side of the electrode body 14.

[0021] Specifically, in a cross-sectional image of the cylindrical battery 10 before the charge-discharge cycle test, the ratio (D2) of the distance (D1) from the inner peripheral surface of the positive electrode 11 arranged at the outermost periphery to the outer peripheral surface of the positive electrode 11 arranged at the outermost periphery and the positive electrode 11 arranged at the outermost periphery and the inner peripheral surface of the positive electrode 11 arranged at the innermost periphery and the positive electrode 11 arranged at the innermost periphery and the positive electrode 11 arranged at the electrode body 14 in the radial direction of the adjacent (D2) is preferably greater than 1.0, more preferably 1.02 or greater. The cross-sectional image of the cylindrical battery 10 is, for example, an X-ray CT image taken using an inspeXio SMX-255CT FPD HR manufactured by Shimadzu Corporation.

[0022] Generally, the negative electrode 12 expands during charging and contracts during discharging. Accordingly, the positive electrode 11 tends to expand along the axial direction during charging and contract along the axial direction during discharging. Although the detailed mechanism is unclear, when the positive electrodes 11 are wound with gaps between them, they tend to expand along the axial direction during charging but are less likely to contract along the axial direction during discharging. Therefore, when the distance between adjacent positive electrodes 11 in the radial direction of the electrode body 14 is greater on the inner circumferential side of the electrode body 14 than on the outer circumferential side of the electrode body 14, the positive electrodes 11 located on the inner circumferential side of the electrode body 14 tend to expand along the axial direction compared to the positive electrodes 11 located on the outer circumferential side of the electrode body 14 during repeated charging and discharging. As will be described in detail later, this prevents the positive electrodes 11 from contacting the grooved portions 21 of the outer can 16, even during repeated charging and discharging, thereby suppressing the occurrence of internal short circuits.

[0023] The negative electrode 12 has a negative electrode core 40 and a negative electrode mixture layer 42 formed on the negative electrode core 40. The negative electrode core 40 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. The negative electrode mixture layer 42 contains a negative electrode active material, a binder, and, if necessary, a conductive agent, and is formed on both sides of the negative electrode core 40 except for a negative electrode core exposed portion 44 described below. The negative electrode 12 can be produced by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on both sides of the negative electrode core 40.

[0024] The negative electrode mixture layer 42 generally contains, as the negative electrode active material, a carbon material that reversibly absorbs and releases lithium ions. Suitable examples of the carbon material include natural graphite, such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite, such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). Furthermore, the negative electrode active material may include a material containing at least one of an element that alloys with Li, such as Si or Sn, and a material containing such an element. Among these, a composite material containing Si is preferred.

[0025] A suitable example of a composite material containing Si is SiO２ Examples of the composite material include a material in which Si fine particles are dispersed in a silicate phase such as lithium silicate, or a material in which Si fine particles are dispersed in an amorphous carbon phase. A conductive layer such as a carbon coating is formed on the particle surface of the composite material. The combined use of a carbon material and a Si-containing composite material as the negative electrode active material is preferred from the viewpoint of achieving both high capacity and high durability of the battery.

[0026] As in the case of the positive electrode mixture layer 32, the binder contained in the negative electrode mixture layer 42 can be a fluorine-containing resin, PAN, polyimide, acrylic resin, polyolefin, or the like, but preferably styrene-butadiene rubber (SBR) is used. The negative electrode mixture layer 42 preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. Among these, it is preferable to use a combination of SBR with CMC or a salt thereof, PAA or a salt thereof, or the like. The negative electrode mixture layer 42 may contain a conductive agent such as CNT.

[0027] The negative electrode 12 has a negative electrode core exposed portion 44 at the end (lower end) on the bottom 16A side of both widthwise ends of the negative electrode 12, where the negative electrode mixture layer 42 is not provided and the negative electrode core 40 is exposed. Therefore, the lower end of the axial direction of the electrode body 14 is formed by the negative electrode core exposed portion 44. The negative electrode core exposed portion 44 is formed, for example, from the winding start end to the winding end end in the longitudinal direction of the strip-shaped negative electrode 12. The width of the negative electrode core exposed portion 44 is, for example, 2 mm or more and 20 mm or less.

[0028] When assembling the cylindrical battery 10, the negative electrode substrate exposed portion 44 is bent radially inward of the electrode body 14. The outer surface of the bent negative electrode substrate exposed portion 44 is then joined to the current collecting member 18, which will be described later.

[0029] Furthermore, the negative electrode 12 has a non-facing portion at the winding start side of the electrode body 14 where the negative electrode 12 is wound in a state where it does not face the positive electrode 11 via the separator 13. In other words, the negative electrode 12 extends further toward the winding start side of the electrode body 14 than the position facing the end of the positive electrode 11 at the winding start side.

[0030] The separator 13 is 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 polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13. A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0031] The non-aqueous electrolyte has lithium ion conductivity. The non-aqueous electrolyte 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

[0032] The cylindrical battery 10 includes a metal current collecting member 18 made of nickel, nickel alloy, or the like, on the axially lower side of the electrode assembly 14. The negative electrode substrate exposed portion 44 protruding from the electrode assembly 14 is joined to the upper surface of the current collecting member 18, which is joined to the inner surface of the bottom 16A of the outer can 16. As a result, the outer can 16, which is electrically connected to the negative electrode substrate exposed portion 44 via the current collecting member 18, serves as the negative electrode terminal. Joining the negative electrode substrate exposed portion 44 to the current collecting member 18 increases the contact area, making it easier to achieve low resistance in the cylindrical battery 10. The cylindrical battery 10 may not include the current collecting member 18, and the negative electrode substrate exposed portion 44 may be directly joined to the inner surface of the bottom 16A of the outer can 16.

[0033] An insulating plate 19 is disposed above the electrode body 14. The insulating plate 19 has a circular shape in a plan view. A through hole is provided in the radial center of the insulating plate 19. The thickness of the insulating plate 19 is, for example, 0.5 mm or more and 5 mm or less.

[0034] The cylindrical battery 10 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like. The number of positive electrode leads 20 may be one or more. Increasing the number of positive electrode leads 20 can reduce the electrical resistance of the cylindrical battery 10. The positive electrode lead 20 extends toward the sealing body 17 through a through-hole in the insulating plate 19, and the upper end of the positive electrode lead 20 is connected to the underside of the filter 22 of the sealing body 17 by welding or the like. A cap 26 that forms the top plate of the sealing body 17 is electrically connected to the filter 22, and the cap 26 serves as the positive electrode terminal.

[0035] The cylindrical battery 10 has, for example, a discharge capacity of 95 Wh or more. In a cylindrical battery 10 with such a high discharge capacity, the volume of the electrode assembly 14 changes significantly during charging and discharging, and the diffusibility of the nonaqueous electrolyte tends to decrease. This makes it easier for deformation such as buckling of the electrode plates, as described below, to occur, and therefore the effects of the present disclosure are particularly pronounced.

[0036] The outer can 16 is a cylindrical metal container having a bottom 16A and an open end in the axial direction, and the opening of the outer can 16 is closed by a sealing body 17 .

[0037] A gasket 27 is provided between the exterior can 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior can 16 has a grooved portion 21 formed inward at a portion of its side surface that supports the sealing body 17. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the exterior can 16, and supports the sealing body 17 on its upper surface. The length along the axial direction from the upper surface of the electrode body 14 to the lower surface of the grooved portion 21 is, for example, 0.5 mm or more and 10 mm or less. The sealing body 17 is fixed to the top of the exterior can 16 by the grooved portion 21 and the open end of the exterior can 16 that is crimped to the sealing body 17.

[0038] The sealing body 17 has a structure in which a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked in this order from the electrode body 14 side. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 24 is electrically connected to one another. The filter 22 has at least one through-hole. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, with the insulating member 24 interposed between their respective peripheral edges.

[0039] If the cylindrical battery 10 generates abnormal heat and its internal pressure rises, the lower valve body 23 deforms and breaks, pushing the upper valve body 25 toward the cap 26, interrupting the current path between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 breaks and gas is released through the vent hole 26a in the cap 26. This gas release prevents the cylindrical battery 10 from exploding due to an excessive rise in internal pressure, thereby improving the safety of the cylindrical battery 10.

[0040] In a cylindrical battery 10 in which a negative electrode substrate exposed portion 44 is provided at the lower axial end of the electrode assembly 14 and the negative electrode substrate exposed portion 44 is joined to the current collecting member 18, as in the present embodiment, the diffusibility of the nonaqueous electrolyte tends to decrease, particularly in the lower region of the electrode assembly 14, during repeated charge and discharge. This is presumably because the negative electrode substrate exposed portion 44 easily blocks the flow path of the nonaqueous electrolyte at the lower end of the electrode assembly 14. The electrode assembly 14 expands during charge, and the nonaqueous electrolyte is pushed out of the electrode assembly 14, making it difficult for it to flow back into the electrode assembly 14 when the electrode assembly 14 contracts during discharge. Therefore, the amount of nonaqueous electrolyte in the lower region of the electrode assembly 14 decreases with repeated charge and discharge. When the amount of nonaqueous electrolyte in the lower region of the electrode assembly 14 decreases, Li may precipitate on the negative electrode 12. When Li precipitates on the negative electrode 12, the thickness of the negative electrode 12 increases, increasing stress inside the electrode assembly 14. As a result, deformation such as buckling of the electrode plates may occur in the lower region of the electrode assembly 14, which may result in a deterioration in cycle characteristics.

[0041] As a result of investigations by the present inventors, it has become clear that by elongating the positive electrode 11 along the axial direction of the electrode body 14 during repeated charge and discharge, stress inside the electrode body 14 is dispersed and the surface pressure inside the electrode body 14 is reduced. As a result, even if the diffusibility of the non-aqueous electrolyte decreases due to repeated charge and discharge, deformation such as buckling of the electrode plate is suppressed, and good cycle characteristics can be ensured.

[0042] Specifically, in a cross-sectional image of a cylindrical battery 10 that has undergone 100 charge-discharge cycle tests (for example, an X-ray CT image taken using an inspeXio SMX-255CT FPD HR manufactured by Shimadzu Corporation), the width of the positive electrode 11 at position X where the width of the positive electrode 11 is greatest within the range from the innermost circumference to the fifth circumference of the positive electrode 11 is defined as width A. Then, in a cross-sectional image of the cylindrical battery 10 before the charge-discharge cycle test, the width of the positive electrode 11 at position X is defined as width C. At this time, if the width A and the width C satisfy the following formula (I), the surface pressure inside the electrode body 14 can be sufficiently reduced. Formula (I): (A-C) x 100 / C ≥ 1.2

[0043] The specific conditions for the charge-discharge cycle test in this specification are as follows: in a temperature environment of 45°C, charging to 4.2 V at a constant current of 0.3 C, followed by charging at a constant voltage of 4.2 V until the current value reaches 0.02 C, and then discharging to 2.85 V at a constant current of 0.5 C; this constitutes one cycle.

[0044] When the value of {(A-C) x 100 / C} is 1.2 or more, the positive electrode 11 can be sufficiently elongated along the axial direction of the electrode assembly 14 when charge and discharge are repeated. In other words, when the value of {(A-C) x 100 / C} is less than 1.2, the positive electrode 11 does not elongate sufficiently, the stress inside the electrode assembly 14 is not dispersed, and the surface pressure inside the electrode assembly 14 cannot be sufficiently reduced. As a result, when the diffusibility of the non-aqueous electrolyte decreases due to repeated charge and discharge, deformation such as buckling of the electrode plate is likely to occur, and cycle characteristics may be reduced.

[0045] The value of {(A-C) x 100 / C} should be 1.2 or greater, preferably 1.5 or greater, and more preferably 2.0 or greater. In this case, the surface pressure inside the electrode assembly 14 can be further reduced. As a result, deformation such as buckling of the electrode plate is further suppressed, making it easier to ensure cycle characteristics. The upper limit of the value of {(A-C) x 100 / C} is not particularly limited, but is, for example, 10.

[0046] The value of {(A-C) x 100 / C} can be adjusted, for example, by the hardness of the positive electrode core 30. For example, if the material of the positive electrode core 30 is changed and the hardness of the positive electrode core 30 is reduced, the positive electrode 11 becomes more likely to extend along the axial direction of the electrode body 14 when charge and discharge are repeated, and the value of {(A-C) x 100 / C} increases. Furthermore, for example, if the hardness of the positive electrode core 30 is increased by performing heat treatment on the positive electrode core 30, the positive electrode 11 becomes less likely to extend along the axial direction of the electrode body 14 when charge and discharge are repeated, and the value of {(A-C) x 100 / C} decreases.

[0047] Meanwhile, as described above, the grooved portion 21 of the outer can 16 is disposed above the outer periphery of the electrode body 14. Because the grooved portion 21 of the outer can 16 is electrically connected to the negative electrode 12, if the positive electrode 11 extending along the axial direction of the electrode body 14 comes into contact with the grooved portion 21, an internal short circuit will occur.

[0048] Therefore, the inventors conducted further studies and found that by making the width A and the width C satisfy formula (I) and setting the difference between the amount of elongation of the positive electrode 11 arranged on the inner periphery and the amount of elongation of the positive electrode 11 arranged on the outer periphery during repeated charging and discharging to a specific value or more, it is possible to reduce the surface pressure inside the electrode body 14 and prevent the positive electrode 11 from contacting the grooved portion 21.

[0049] Specifically, in a cross-sectional image of a cylindrical battery 10 that has undergone 100 charge-discharge cycle tests, when the width of the positive electrode 11 at the outermost periphery of the positive electrode 11 is defined as width B, if the width A and width B satisfy the following formula (II), the contact pressure inside the electrode body 14 can be reduced while preventing the positive electrode 11 from contacting the grooved portion 21. Formula (II): (A-B) x 100 / B ≥ 1.2

[0050] When the value of {(A-B) x 100 / B} is 1.2 or more, the positive electrode 11 arranged on the inner periphery of the electrode body 14 extends more along the axial direction than the positive electrode 11 arranged on the outer periphery of the electrode body 14. As a result, the positive electrode 11 is prevented from coming into contact with the grooved portion 21, and the occurrence of an internal short circuit is suppressed.

[0051] The value of {(A-B) x 100 / B} may be 1.2 or more, preferably 1.25 or more, and more preferably 1.3 or more. In this case, the positive electrode 11 extending along the axial direction of the electrode body 14 is further prevented from contacting the grooved portion 21, and the occurrence of an internal short circuit is further suppressed. The upper limit of the value of {(A-B) x 100 / B} is not particularly limited, but is, for example, 10.

[0052] The value of {(A-B) x 100 / B} can be adjusted, for example, by changing the distance between the positive electrodes 11 adjacent to each other in the radial direction of the electrode body 14 between the inner and outer circumferential sides of the positive electrodes 11. The value of {(A-B) x 100 / B} can be increased by winding the positive electrodes 11 arranged on the inner circumferential side with a larger gap than the positive electrodes 11 arranged on the outer circumferential side. From the viewpoint of making the value of {(A-B) x 100 / B} 1.2 or more, in a cross-sectional image of the cylindrical battery 10 before the charge-discharge cycle test, the ratio (D2 / D1) of the distance (D2) from the outer peripheral surface of the positive electrode 11 arranged at the innermost periphery to the inner peripheral surface of the positive electrode 11 arranged at the innermost periphery and ..., relative to the distance (D1) from the inner peripheral surface of the positive electrode 11 arranged at the outermost periphery to the outer peripheral surface of the positive electrode 11 adjacent in the radial direction of the electrode body 14, is preferably greater than 1.0, and more preferably 1.02 or more.

[0053] As a method for changing the distance between adjacent positive electrodes 11 in the radial direction of the electrode body 14 between the inner and outer sides of the positive electrode 11, for example, a method of adjusting the length of the non-facing portion of the negative electrode 12 that is wound at the start of winding of the electrode body 14 without facing the positive electrode 11 via the separator 13 can be mentioned.

[0054] The non-facing portion is preferably wound 0.3 or more times, more preferably 0.4 or more times. If the non-facing portion is wound less than 0.3 times, the shape of the winding core portion of the electrode body 14 may not be maintained during repeated charge and discharge. As a result, gas inside the battery may not be able to be smoothly vented to the outside during abnormal heat generation of the battery. Furthermore, the non-facing portion is preferably wound 1.0 or less times, more preferably 0.9 or less times. The longer the non-facing portion, the smaller the distance between the positive electrodes 11 on the inner circumferential side tends to be. Therefore, by winding the non-facing portion 1.0 or less times, the distance between the positive electrodes 11 on the inner circumferential side can be increased. As a result, the positive electrodes 11 on the inner circumferential side are more likely to elongate along the axial direction. Therefore, the non-facing portion is preferably wound 0.3 or more times but 1.0 or less times, more preferably 0.4 or more times but 0.9 or less times.

[0055] Another method for varying the distance between adjacent positive electrodes 11 in the radial direction of the electrode body 14 between the inner and outer circumferential sides of the positive electrodes 11 is to vary the magnitude of the tension applied to the positive electrodes 11 in the longitudinal direction when winding the positive electrodes 11. Specifically, by making the tension on the inner circumferential side (winding start side) of the positive electrodes 11 smaller than the tension on the outer circumferential side (winding end side) of the positive electrodes 11, the positive electrodes 11 arranged on the inner circumferential side can be wound with a larger gap between them than the positive electrodes 11 arranged on the outer circumferential side.

[0056] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0057] Example 1 Preparation of Positive Electrode 100 parts by mass of a positive electrode active material, 1 part by mass of acetylene black (AB), and 0.9 parts 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. ０．８８ Co ０．０９ Al ０．０３ O ２ The aluminum-containing lithium nickel cobalt oxide represented by the formula:

[0058] Next, the positive electrode mixture slurry was applied to both sides of a positive electrode core made of aluminum foil with a thickness of 15 μm and a width of 67.1 mm. The coating was applied so as to form eight positive electrode core exposed portions. The coating was dried, rolled, and cut to a predetermined electrode plate size to produce a positive electrode having a positive electrode mixture layer with a thickness of 17 μm on each side formed on both sides of the positive electrode core. Then, an aluminum positive electrode lead was fixed to each of the positive electrode core exposed portions by ultrasonic welding.

[0059] [Preparation of Negative Electrode] 95 parts by mass of graphite, 5 parts by mass of silicon 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.

[0060] Next, the negative electrode mixture slurry was applied to both sides of a negative electrode core made of copper foil with a thickness of 19 μm and a width of 75 mm so as to form a negative electrode core exposed portion with a width of 5 mm. This coating was dried, rolled, and cut to a predetermined electrode plate size to produce a negative electrode having a negative electrode mixture layer formed on both sides of the negative electrode core.

[0061] [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.

[0062] [Preparation of Test Cell (Cylindrical Battery)] An electrode assembly was prepared by spirally winding a positive electrode and a negative electrode with a polyethylene microporous membrane separator interposed therebetween. At this time, the electrode assembly was prepared so that the non-facing portion of the negative electrode was wound 0.5 turns at the start of winding of the electrode assembly. The outer diameter of the electrode assembly was 40 mm.

[0063] A current collecting member was placed under this electrode assembly, and the exposed portion of the negative electrode substrate at the lower end of the electrode assembly was bent radially inward and welded to the current collecting member. The electrode assembly was then housed in a bottomed cylindrical outer can, the current collecting member was welded to the bottom of the bottomed cylindrical outer can, and the positive electrode lead was welded to a sealing member. A groove was then formed in the opening of the outer can by pressing. A nonaqueous electrolyte was then poured into the outer can, and the opening of the outer can was sealed with a sealing member via a gasket, to produce a cylindrical test cell.

[0064] X-ray CT images of the fabricated test cell were taken using an inspeXio SMX-255CT FPD HR manufactured by Shimadzu Corporation. As a result, the ratio (D2 / D1) of the distance (D1) from the positive electrode arranged at the outermost periphery to the positive electrode arranged at the innermost periphery and the positive electrode adjacent to the positive electrode arranged at the innermost periphery in the radial direction of the electrode body to the distance (D2) from the positive electrode arranged at the innermost periphery to the positive electrode adjacent to the positive electrode arranged at the innermost periphery in the radial direction of the electrode body was 1.02.

[0065] [Charge-Discharge Cycle Test] The test cell was charged to 4.2 V at a constant current of 0.3 C in a temperature environment of 45° C., then charged at a constant voltage of 4.2 V until the current value reached 0.02 C, and then discharged to 2.85 V at a constant current of 0.5 C. This constitutes one cycle, and 100 cycles were performed. The discharge capacity of the test cell of Example 1 at the first cycle was 98 Wh.

[0066] X-ray CT images of the test cells after the charge-discharge cycle test were taken in the same manner as above. Then, the presence or absence of deformation such as buckling of the electrode plates inside the electrode assembly was evaluated from the X-ray CT images of the test cells after the charge-discharge cycle test.

[0067] Furthermore, from the X-ray CT image of the test cell after the charge-discharge cycle test, the width (A) of the positive electrode at the position X where the width of the positive electrode was greatest within the range of the fifth circumference from the innermost circumference of the positive electrode, and the width (B) of the positive electrode at the outermost circumference of the positive electrode were measured. Furthermore, from the X-ray CT image before the charge-discharge cycle test, the width (C) of the positive electrode at the position X was measured.

[0068] Example 2 A test cell was prepared and evaluated in the same manner as the test cell of Example 1, except that the tension applied to the positive electrode in the longitudinal direction during winding was adjusted so that the value of (D2 / D1) above would be the value shown in Table 1. The discharge capacity of the test cell of Example 2 at the first cycle was 98 Wh.

[0069] Example 3 A test cell was prepared and evaluated in the same manner as the test cell of Example 1, except that in preparing the negative electrode, the thickness of the negative electrode mixture slurry was changed and the discharge capacity of the test cell in the first cycle was adjusted to 90 Wh.

[0070] <Comparative Examples 1 and 2> In the preparation of the positive electrode, the positive electrode core used in Example 1 was subjected to heat treatment to adjust the hardness of the positive electrode core, and in the preparation of the test cell, the tension applied in the longitudinal direction of the positive electrode during winding was adjusted so that the above-mentioned (D2 / D1) value would be the value shown in Table 1. Test cells were prepared and evaluated in the same manner as the test cell of Example 1. The discharge capacities at the first cycle of the test cells of Comparative Examples 1 and 2 were each 98 Wh.

[0071] The presence or absence of deformation such as buckling of the electrode plates and the evaluation results for the test cells of the examples and comparative examples are shown in Table 1. The table also shows the values ​​of (D2 / D1), {(A-C) × 100 / C}, and {(A-B) × 100 / B} obtained from X-ray CT images.

[0072]

[0073] As shown in Table 1, the test cells of the examples in which the widths A, B, and C satisfy {(A-C) x 100 / C} ≥ 1.2 and {(A-B) x 100 / B} ≥ 1.2 did not experience deformation such as buckling of the electrode plates even after the charge-discharge cycle test. Furthermore, in the test cells of the examples, the positive electrode did not come into contact with the grooved portion even after the charge-discharge cycle test. On the other hand, the test cells of the comparative examples in which {(A-C) x 100 / C} ≥ 1.2 and {(A-B) x 100 / B} ≥ 1.2 were not satisfied experienced deformation such as buckling of the electrode plates after the charge-discharge cycle test.

[0074] The present disclosure will be further described by the following embodiments. Configuration 1: A cylindrical battery including an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a non-aqueous electrolyte, and a cylindrical outer can accommodating the electrode assembly and the non-aqueous electrolyte and having a bottom, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, and the negative electrode has a negative electrode core exposed portion at the end of the negative electrode on the bottom side, where the negative electrode mixture layer is not disposed, and the negative electrode core exposed portion is provided at the bottom or a collector disposed between the electrode assembly and the bottom. A cylindrical battery having a cross-sectional image of the cylindrical battery joined to an electrode member and subjected to 100 charge-discharge cycle tests, wherein width A denotes the width of the positive electrode at position X within five turns from the innermost periphery of the positive electrode at which the width of the positive electrode is greatest, width B denotes the width of the positive electrode at the outermost periphery of the positive electrode, and width C denotes the width of the positive electrode at position X in a cross-sectional image of the cylindrical battery before the charge-discharge cycle tests, and the widths A, B, and C satisfy the relationships represented by the following formulas (I) and (II): Formula (I): (A-C) x 100 / C ≥ 1.2 Formula (II): (A-B) x 100 / B ≥ 1.2 Configuration 2: The cylindrical battery according to Configuration 1, wherein the negative electrode has a non-facing portion wound around the separator at a winding start side of the electrode body so as not to face the positive electrode, and the non-facing portion is wound 0.3 to 1.0 turns in total. Configuration 3: The cylindrical battery according to Configuration 1 or 2, wherein, in a cross-sectional image of the cylindrical battery before the charge-discharge cycle test, the ratio (D2 / D1) of the distance (D2) from the outer peripheral surface of the positive electrode arranged at the innermost periphery to the inner peripheral surface of the positive electrode arranged at the innermost periphery and the radially adjacent positive electrode of the electrode body to the distance (D1) from the inner peripheral surface of the positive electrode arranged at the outermost periphery to the outer peripheral surface of the positive electrode radially adjacent to the positive electrode arranged at the outermost periphery of the electrode body is greater than 1.0. Configuration 4: The cylindrical battery according to any one of Configurations 1 to 3, wherein the outer diameter of the electrode body is 40 mm or more. Configuration 5: The cylindrical battery according to any one of Configurations 1 to 4, wherein the discharge capacity of the cylindrical battery is 95 Wh or more.

[0075] REFERENCE SIGNS LIST 10 Cylindrical battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 16A Bottom, 17 Sealing body, 18 Current collecting member, 19 Insulating plate, 20 Positive electrode lead, 21 Grooved portion, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Vent, 27 Gasket, 30 Positive electrode core, 32 Positive electrode mixture layer, 40 Negative electrode core, 42 Negative electrode mixture layer, 44 Negative electrode core exposed portion.

Claims

1. A cylindrical battery comprising: an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; a non-aqueous electrolyte; and a cylindrical outer can accommodating the electrode assembly and the non-aqueous electrolyte and having a bottom, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, and of both widthwise end portions of the negative electrode, the end portion on the bottom side is provided with a negative electrode core exposed portion where the negative electrode mixture layer is not disposed and the negative electrode core is exposed, and the negative electrode core exposed portion is joined to the bottom or to a current collecting member disposed between the electrode assembly and the bottom, and in a cross-sectional image of the cylindrical battery after 100 charge-discharge cycle tests have been performed, width A denotes the width of the positive electrode at position X where the width of the positive electrode is greatest within the range of five turns from the innermost periphery of the positive electrode, and width B denotes the width of the positive electrode at the outermost periphery of the positive electrode, A cylindrical battery in which, when the width of the positive electrode at the position X in the cross-sectional image of the cylindrical battery before the charge-discharge cycle test is defined as width C, the width A, the width B, and the width C satisfy the relationships represented by the following formulas (I) and (II): Formula (I): (A-C) x 100 / C ≥ 1.2 Formula (II): (A-B) x 100 / B ≥ 1.2 2. The cylindrical battery according to claim 1, wherein the negative electrode has a non-facing portion wound around the electrode body at the winding start side thereof so as not to face the positive electrode with the separator interposed therebetween, and the non-facing portion is wound 0.3 to 1.0 turns in total.

3. The cylindrical battery according to claim 1, wherein in a cross-sectional image of the cylindrical battery before the charge-discharge cycle test, the ratio (D2 / D1) of the distance (D2) from the outer peripheral surface of the positive electrode arranged at the innermost periphery to the inner peripheral surface of the positive electrode arranged at the innermost periphery and ...

4. The cylindrical battery according to claim 1, wherein the outer diameter of the electrode body is 40 mm or more.

5. The cylindrical battery according to claim 1, wherein the discharge capacity of the cylindrical battery is 95 Wh or more.

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