Cylindrical battery

Abstract

A cylindrical battery as one example of an embodiment includes an electrode body having a positive electrode (11), a negative electrode, and a separator, the electrode body being formed by winding the positive electrode (11) and the negative electrode with the separator interposed therebetween, and the positive electrode (11) or the negative electrode being connected to a bottom portion of an exterior can. The positive electrode (11) includes an elongated positive electrode core (30) and a positive electrode mixture layer (31) provided on the positive electrode core (30). For the positive electrode mixture layer (31), in a case where a region including a width direction center of the positive electrode (11) is defined as a central region (312), a region including one end of the width direction of the positive electrode (11) on a sealing body (16) side is defined as a first region (311), and a region including the other end of the width direction of the positive electrode (11) on a bottom portion side of the exterior can (15) is defined as a second region (313), a density of the first region (311) is the same as a density of the central region (312), or is greater than the density of the central region (312), and a density of the second region (313) is less than the density of the central region (312).

Description

Technical Field

[0001] This disclosure relates to cylindrical batteries. Background Technology

[0002] Cylindrical batteries generally include a wound electrode body formed by winding a positive electrode and a negative electrode separated by a separator, a bottomed cylindrical outer can for housing the electrode body, and a sealing body for blocking the opening of the outer can. Patent Document 1 discloses a cylindrical battery having a positive electrode in which the combined positive electrode charge at the top and bottom of the cross-section in the width direction is greater than the combined positive electrode charge at the center, and a negative electrode in which the combined negative electrode charge at the top and bottom of the cross-section in the width direction is smaller than the combined negative electrode charge at the center.

[0003] Prior art literature

[0004] Patent Document 1: Japanese Patent Application Publication No. 2001-15146 Summary of the Invention

[0005] However, in cylindrical batteries, the plates are typically connected to the bottom of the outer casing via welding or other means, with the negative electrode usually connected to the bottom of the outer casing. The inventors' research indicates that repeated charging and discharging of cylindrical batteries increases the difference in surface pressure acting on the plates along their width. This results in plate deformation and reduced capacity retention during charge-discharge cycles. The difference in surface pressure acting along the width of the plates is believed to be due to the plates being fixed to the bottom of the outer casing. In particular, the more extensive the connection between the plates and the bottom of the outer casing, and the stronger the constraint on the plates relative to the bottom, the more likely the aforementioned problems will occur.

[0006] The disclosed cylindrical battery comprises an electrode body, a bottomed cylindrical outer can, and a sealing body. The electrode body has a positive electrode, a negative electrode, and a separator. The positive and negative electrodes are wound together with the separator in between to form the electrode body. The outer can houses the electrode body, and the sealing body blocks the opening of the outer can. The positive or negative electrode is connected to the bottom of the outer can. The positive electrode comprises an elongated positive electrode core and a positive electrode binder layer disposed on the positive electrode core. The characteristic feature is that, for the positive electrode binder layer, when the region containing the center of the positive electrode in the width direction is defined as a central region, the region containing one end of the width direction closer to the sealing body than the central region is defined as a first region, and the region containing the other end of the width direction closer to the bottom of the outer can than the central region is defined as a second region, the density of the first region is the same as or greater than the density of the central region, and the density of the second region is less than the density of the central region.

[0007] The cylindrical battery disclosed herein can suppress the deformation of the plates and suppress the decrease in capacity retention during charge-discharge cycles. Attached Figure Description

[0008] Figure 1 This is a cross-sectional view of the cylindrical battery according to the first embodiment.

[0009] Figure 2 This is a front view of the positive electrode of the first embodiment.

[0010] Figure 3 This is a front view of the positive electrode in the second embodiment.

[0011] Figure 4 This is a diagram illustrating the evaluation method for electrode plate deformation. Detailed Implementation

[0012] Hereinafter, an example of an embodiment of the cylindrical battery of this disclosure will be described in detail with reference to the accompanying drawings. Furthermore, technical configurations formed by selectively combining the constituent elements of the various embodiments and modifications described below are also included within the scope of this disclosure.

[0013] use Figure 1 The cylindrical battery 10 of the first embodiment will be described in detail. Figure 1 This is a schematic diagram showing the cross-sections of the cylindrical battery 10 along its axial and radial directions.

[0014] like Figure 1 As shown, the cylindrical battery 10 includes an electrode body 14 and a bottomed cylindrical outer casing 15 that houses the electrode body 14. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13. The positive electrode 11 and the negative electrode 12 are wound together with the separator 13 to form the electrode body 14. The cylindrical battery 10 also includes an electrolyte housed in the outer casing 15 and a sealing body 16 that blocks the opening of the outer casing 15. The outer casing 15 has a groove 21 formed in its sidewall, and the sealing body 16 is supported by the groove 21 to block the opening of the outer casing 15. Furthermore, the positive electrode 11 or the negative electrode 12 is connected to the bottom of the outer casing 15. Hereinafter, for ease of explanation, the sealing body 16 side of the cylindrical battery 10 will be considered upper, and the bottom side of the outer casing 15 will be considered lower.

[0015] The electrolyte can be an aqueous electrolyte, but a non-aqueous electrolyte is used in this embodiment. The non-aqueous electrolyte has lithium-ion conductivity. The non-aqueous electrolyte can be a liquid electrolyte (electrolyte) or a solid electrolyte. The cylindrical battery 10 is, for example, a non-aqueous electrolyte secondary battery, preferably a lithium-ion battery.

[0016] Liquid electrolytes (electrolytes) contain a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Non-aqueous solvents can include, for example, esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may contain halogen-substituted derivatives (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are replaced by halogen atoms such as fluorine. The electrolyte salt is, for example, a lithium salt such as LiPF6.

[0017] As a solid electrolyte, examples include solid or gel-like polymer electrolytes and inorganic solid electrolytes. As an inorganic solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. Polymer electrolytes may contain, for example, lithium salts and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As a matrix polymer, for example, a polymer material that gels by absorbing a non-aqueous solvent can be used. Examples of polymer materials include fluoropolymers, acrylic resins, and polyether resins.

[0018] As described above, the electrode body 14 has a spiral structure in which a positive electrode 11 and a negative electrode 12 are wound together in a spiral shape with a separator 13 in between. The positive electrode 11, negative electrode 12, and separator 13 are all strip-shaped elongated bodies, alternately stacked in the radial direction of the electrode body 14 by being wound into a spiral. To prevent lithium deposition, the negative electrode 12 is formed to be one size larger than the positive electrode 11. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the length and width directions (winding axis direction). The separator 13 is formed to be at least one size larger than the positive electrode 11, for example, two sheets are arranged to sandwich the positive electrode 11.

[0019] The positive electrode 11 has an elongated positive electrode core 30 and a positive electrode binder layer 31 disposed on the positive electrode core 30. The positive electrode core 30 can be made of a foil of a metal that is stable within the potential range of the positive electrode 11, such as aluminum, aluminum alloy, stainless steel, or titanium, or a thin film of the same metal disposed on its surface. The positive electrode binder 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. The positive electrode active material is, for example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, etc.

[0020] 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 exposed portion 32 of the positive electrode core connected to the positive electrode lead 20. 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 binder 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 manufactured as follows: a positive electrode binder slurry containing a positive electrode active material, a conductive agent, and a binder is coated onto the positive electrode core 30, the coating is dried, and then compressed to form the positive electrode binder layer 31 on both sides of the positive electrode core 30.

[0021] In this embodiment, the positive electrode 11 has a positive electrode core exposed portion 32 on the surface of the positive electrode core 30 where the positive electrode binder layer 31 is absent. A positive electrode lead 20, connecting the sealing body 16 and the positive electrode core exposed portion 32, is bonded to this positive electrode core exposed portion 32. Furthermore, the positive electrode lead 20 is preferably directly bonded to the positive electrode core exposed portion 32 by means of ultrasonic welding or the like.

[0022] The negative electrode 12 has an elongated negative electrode core 40 and a negative electrode binder layer 41 disposed on the negative electrode core 40. The negative electrode core 40 can be a foil of a metal stable within the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, or nickel alloy, or a thin film of the metal disposed on its surface. The negative electrode binder 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. The negative electrode active material can be, for example, graphite or a Si-containing material.

[0023] The thickness of the negative electrode 12 is, for example, 170 μm or more and 210 μm or less. In this embodiment, the thickness of the negative electrode 12 is substantially constant except for the exposed portion of the negative electrode core 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 binder layer 41 is, for example, 70 μm or more and 110 μm or less on one side of the negative electrode core 40. The negative electrode 12, like the positive electrode 11, can be manufactured as follows: a negative electrode binder slurry containing a negative electrode active material and a binder is coated onto the negative electrode core 40, the coating is dried and then compressed to form the negative electrode binder layer 41 on both sides of the negative electrode core 40.

[0024] In this embodiment, the negative electrode 12 has a strip-shaped negative electrode core exposed portion at its width end located on the bottom side of the outer packaging can 15, which exposes the surface of the negative electrode core 40 along the length direction of the negative electrode 12. The negative electrode core exposed portion is provided, for example, covering the range from the end of the winding start side to the end of the winding end side along the length direction of the strip-shaped negative electrode 12.

[0025] The exposed portion of the negative electrode core is connected directly to or through the lower current collector 17 to the bottom of the outer casing 15. For example, the exposed portion of the negative electrode core is joined to the upper surface of the lower current collector 17 by welding or the like. Alternatively, the cylindrical battery 10 may omit the lower current collector 17, and instead, the exposed portion of the negative electrode core is joined to the inner surface of the bottom of the outer casing 15 by welding or the like. The width of the exposed portion of the negative electrode core is, for example, 2 mm or more and 20 mm or less.

[0026] Alternatively, the negative electrode 12 may not have a strip-shaped negative electrode core exposed portion at its width end on the bottom side of the outer packaging can 15. In this case, a negative electrode core exposed portion may be formed at one end of the negative electrode 12 in the length direction, where the negative electrode compound layer 41 is absent and the surface of the negative electrode core 40 is exposed. The negative electrode core exposed portion is provided at one end of the negative electrode 12 in the length direction, located on the winding start side or winding end side of the electrode body 14. A negative electrode lead is connected to this negative electrode core exposed portion, and the negative electrode lead is connected to the outer packaging can 15.

[0027] An insulating plate 18 is disposed on the electrode body 14. Figure 1 In the example shown, the positive lead 20 extends toward the sealing body 16 through the through hole of the insulating plate 18. The positive lead 20 is connected to the lower surface of the internal terminal plate 22 of the sealing body 16 by welding or the like, and the top plate, i.e., the cover 26, of the sealing body 16, which is electrically connected to the internal terminal plate 22, becomes the positive terminal.

[0028] A lower current collector 17 is disposed below the electrode body 14. The lower current collector 17 is a metal component. As described above, the upper surface of the lower current collector 17 is joined to the exposed portion of the negative electrode core constituting the negative electrode 12. In addition, the lower surface of the lower current collector 17 is welded to the inner surface of the bottom of the outer can 15. Thus, the outer can 15 functions as the negative terminal. There is no particular limitation on the shape of the lower current collector 17; for example, it can have a roughly circular shape when viewed from above.

[0029] The outer can 15 is a bottomed cylindrical metal container. A gasket 27 is provided between the outer can 15 and the sealing body 16 to seal the inside of the battery. The outer can 15, for example, has a groove 21 formed by stamping the side portion from the outside to support the sealing body 16. The groove 21 is preferably formed in a ring shape along the circumference of the outer can 15, and supports the sealing body 16 on its upper surface. In addition, the upper end of the outer can 15 is bent inward and riveted to the periphery of the sealing body 16.

[0030] The sealing body 16 has a structure in which an internal terminal plate 22, a lower valve body 23, an insulating component 24, an upper valve body 25, and a cover 26 are stacked sequentially from the electrode body 14 side. Each component constituting the sealing body 16 has, for example, a circular or annular shape, and all components except the insulating component 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected at their respective central portions, and the insulating component 24 is sandwiched between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heating, the lower valve body 23 deforms and ruptures by pushing the upper valve body 25 towards the cover 26, thereby cutting off the current path between the lower valve body 23 and the upper valve body 25. When the internal pressure rises further, the upper valve body 25 ruptures, and gas is discharged from the opening 26a of the cover 26.

[0031] The following is further reference. Figure 2 The positive electrode compound layer 31 of the positive electrode 11 is described in detail. Figure 2 This is a front view illustrating the positive electrode 11 of the first embodiment.

[0032] As described above, the positive electrode 11 has an elongated positive electrode core 30 and a positive electrode mixture layer 31 disposed on the positive electrode core 30. The positive electrode mixture layer 31 is divided into: a central region 312, which includes the center of the positive electrode 11 in the width direction; a first region 311, which includes one end of the width direction of the central region 312 closer to the sealing body 16; and a second region 313, which includes the other end of the width direction of the central region 312 closer to the bottom side of the outer packaging can 15. The density of the first region 311 is the same as or greater than that of the central region 312, and the density of the second region 313 is less than that of the central region 312, as will be described in detail later.

[0033] The width L311 of the first region 311 can be more than 5% and less than 30% of the full width L11 of the positive electrode 11, or it can be more than 10% and less than 25%. As an example of the width L311 of the first region 311, it is 15% of the width L11 of the positive electrode 11.

[0034] The width L313 of the second region 313 can be more than 5% and less than 30% of the full width L11 of the positive electrode 11, or more than 10% and less than 25%. An example of the width L313 of the second region 313 is 15% of the width L11 of the positive electrode 11. An example of the ratio of width L311, width L312, and width L313 is 15:70:15. The full width L11 of the positive electrode 11 is, for example, 70 mm.

[0035] The density of region 311 is the same as or greater than the density of central region 312, and the density of region 313 is less than the density of central region 312. For example, the density of region 311 can be more than 100% and less than 130% of the density of central region 312, or it can be more than 115% and less than 125%. An example of the density of region 311 is 120% of the density of central region 312. The density of region 313 can be more than 70% and less than 100% of the density of central region 312, or it can be more than 75% and less than 95%. An example of the density of region 313 is 80% of the density of central region 312.

[0036] If the density of the first region 311 is too high compared to the density of the central region 312, or if the density of the second region 313 is too low compared to the density of the central region 312, it may be difficult to meet the performance requirements of the electrode body 14, such as peel strength. For example, the density of the first region 311 may be too high if it is 130% or more of the density of the central region 312. Conversely, the density of the second region 313 may be too low if it is 70% or less of the density of the central region 312.

[0037] The average density of the central region 312 is preferably higher than 3.30 g / cc, particularly preferably higher than 3.45 g / cc, and may also be higher than 3.55 g / cc. There is no particular upper limit to the density of the central region 312, but from the viewpoint of improving fast charging performance, it is preferably lower than 3.65 g / cc. An example of a preferred range for the average density of the central region 312 is 3.45 g / cc or higher and 3.65 g / cc or lower, or 3.45 g / cc or higher and 3.55 g / cc or lower.

[0038] The density of the positive electrode additive layer 31 depends primarily on the filling density of the positive electrode active material. Therefore, it can be said that the filling density of the positive electrode active material in the first region 311 is the same as, or higher than, the filling density of the positive electrode active material in the central region 312. Similarly, it can be said that the filling density of the positive electrode active material in the second region 313 is lower than the filling density of the positive electrode active material in the central region 312. The thickness of the positive electrode additive layer 31 is, for example, 70 μm or more and 100 μm or less on one side of the positive electrode core 30. From the viewpoint of homogenizing the battery reaction, it is preferable that the thicknesses of the first region 311, the central region 312, and the second region 313 are substantially the same.

[0039] The positive electrode mixture layer 31 is formed by coating 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 film, and then compressing it. The first region 311, the central region 312, and the second region 313 can be formed, for example, by adjusting the amount of positive electrode mixture slurry applied per unit area.

[0040] As a specific example, when forming the first region 311, the coating amount of the positive electrode slurry is set to be 100% or more and less than 110% of the coating amount when forming the central region 312. Preferably, it is 100%. Additionally, the coating amount may have an error of approximately ±2.5% relative to the target value. When forming the second region 313, the coating amount of the positive electrode slurry is set to be 75% or more and less than 85% of the coating amount when forming the central region 312. Then, the entire region of the positive electrode slurry layer 31 is compressed under the same conditions to homogenize the thickness.

[0041] Alternatively, two types of positive electrode slurry can be used. When forming the first region 311, the same type of positive electrode slurry as the central region 312 can be used. When forming the second region 313, a positive electrode slurry containing a positive active material that is easier to thin out than that in the central region 312 can be used. Alternatively, three types of positive electrode slurry can be used. When forming the first region 311, a positive electrode slurry containing a positive active material that is easier to tightly fill than that in the central region 312 can be used. When forming the second region 313, a positive electrode slurry containing a positive active material that is easier to thin out than that in the central region 312 can be used. The positive electrode slurry can be applied, for example, by a molding process.

[0042] The densities of the central region 312, the first region 311, and the second region 313 in the inner roll region 314, located inside the roll of the electrode body 14, can be smaller than those in the outer roll region 315, located outside the roll of the electrode body 14. For example, the inner roll region 314 is the region spanning 1 / 3 of the total length of the positive electrode 11 from the inner roll end, and the outer roll region 315 is the region spanning 2 / 3 of the total length of the positive electrode 11 from the outer roll end. That is, the densities of the central region 312, the first region 311, and the second region 313 in the inner roll region 314, which spans 1 / 3 of the total length of the positive electrode 11 inside the roll of the electrode body 14, can be smaller than those in the region spanning 2 / 3 of the total length of the positive electrode 11 outside the roll of the electrode body 14. The density of each region in the inner roll region 314 is, for example, greater than 70% and less than 100% of the density of each region in the outer roll region 315. Since the surface pressure of the inner region 314 is higher than that of the outer region 315, the radial surface pressure can be made uniform by making the density of the inner region 314 lower than that of the outer region 315.

[0043] In this specification, the density of the positive electrode mixture layer 31 is determined by cutting out various regions of the positive electrode mixture layer 31 with a tool and measuring their weight. For example, circular plate shapes are cut out at multiple locations in each of the first region 311, the central region 312, and the second region 313, and their weights are measured, thereby obtaining the average density of each region.

[0044] use Figure 3 The second embodiment will be described in detail. Figure 3 This is a front view illustrating the positive electrode 11 of the cylindrical battery 10 according to the second embodiment. The only difference between the second embodiment and the first embodiment is that a plurality of positive electrode core exposed portions 32 are formed on the positive electrode 11. In the second embodiment, structures identical to those in the first embodiment are labeled with the same reference numerals as in the first embodiment, and descriptions are omitted. Furthermore, in the second embodiment, descriptions of effects and variations identical to those in the first embodiment are omitted.

[0045] In the second embodiment, such as Figure 3 As shown, the positive electrode 11 has multiple exposed positive electrode core portions 32 in the first region 311. Furthermore, positive electrode leads 20 are connected to each of the multiple exposed positive electrode core portions 32. All the positive electrode leads 20 extend in the same direction, protruding from one end of the positive electrode 11 in the width direction. In the second embodiment, one end of each positive electrode lead 20 in the length direction is engaged with the positive electrode 11, and the other end in the length direction is engaged with the internal terminal plate 22 of the sealing body 16. The positive electrode 11 and the internal terminal plate 22 are electrically connected via the positive electrode leads 20.

[0046] There is no particular limitation on the number of positive leads 20; for example, it can be 3 to 15 or 6 to 10. An example of the number of positive leads 20 is 8. The positive leads 20 can be arranged at equal intervals along the length of the positive electrode 11. Alternatively, the positive leads 20 can be arranged at varying intervals, such that multiple positive leads 20 are stacked within the wound electrode body 14. By having multiple positive leads 20 on the positive electrode 11, the resistance can be reduced.

[0047] Furthermore, the above-described embodiments can be appropriately modified within the scope of the objectives of this disclosure. For example, the positive electrode 11 may have a positive electrode core exposed portion 32 at its width-direction end located on the sealing body 16 side, exposing the positive electrode core 30. In this case, the positive electrode core exposed portion 32 is wound in such a way that it extends from the upper end of the electrode body 14. The extended positive electrode core exposed portion 32 is connected to an upper current collector plate disposed on the electrode body by welding or the like. By joining the positive electrode core exposed portion 32 to the upper current collector plate, the contact area between the positive electrode core exposed portion 32 and the upper current collector plate is increased, thereby reducing the internal resistance of the positive electrode 11.

[0048] Example

[0049] The present disclosure will be further illustrated below by way of examples, but the present disclosure is not limited to these examples.

[0050] <Example 1>

[0051] [Preparation of Positive Electrode Slurry]

[0052] Lithium nickel oxide (LiNi) containing cobalt and aluminum is used. 0.88 Co 0.09 Al 0.03 O2) was used as the positive electrode active material. The positive electrode active material, acetylene black and polyvinylidene fluoride were mixed at a solid component mass ratio of 98:1:1, and N-methylpyrrolidone (NMP) was used as the dispersion medium to prepare the positive electrode mixture slurry.

[0053] [The production of the positive electrode]

[0054] A positive electrode slurry is coated onto both sides of a positive electrode core consisting of a 15 μm thick strip of aluminum foil using a die-coating method. A first coating is formed in the region encompassing one end of the positive electrode core in the width direction, a central coating is formed in the region encompassing the center in the width direction, and a second coating is formed in the region encompassing the other end in the width direction. These coatings are then dried. The first coating is formed with the same amount of material as the central coating, and the second coating is formed with 90% of the amount of material used in forming the central coating. Furthermore, the first coating becomes the first region, the central coating becomes the central region, and the second coating becomes the second region.

[0055] In this embodiment, the ratio of the width of the first region, the width of the central region, and the width of the second region is adjusted to 15:70:15. The average width of the first region is 10 mm, the average width of the central region is 50 mm, and the average width of the second region is 10 mm. Eight exposed positive electrode core portions without a positive electrode binder layer are provided in the first region, and aluminum positive electrode leads are welded to these exposed positive electrode core portions.

[0056] Next, the coating (positive electrode additive layer) is compressed using a roller, and the positive electrode core is cut into predetermined electrode sizes, resulting in a positive electrode with positive electrode additive layers formed on both sides of the positive electrode core. The average thickness of the positive electrode additive layer is 70 μm on one side of the positive electrode core, and the first region, the central region, and the second region have substantially the same thickness. The density of the first region is the same as that of the central region, and the density of the second region is 90% of that of the central region. According to the above measurement method, the average density of the first region is 3.55 g / cc, the average density of the central region is 3.55 g / cc, and the average density of the second region is 3.20 g / cc.

[0057] [Making the negative electrode]

[0058] Graphite powder and Si-containing materials were mixed at a mass ratio of 95:5 to serve as the negative electrode active material. A negative electrode active material, a dispersion of styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed at a solid component mass ratio of 98:1:1, using water as the dispersion medium to prepare a negative electrode slurry. This slurry was coated onto both sides of a negative electrode core consisting of a strip of copper foil with a thickness of 8 μm. The coating was dried and compressed to obtain a negative electrode with a negative electrode slurry layer formed on both sides of the negative electrode core. Additionally, at the lower end of the negative electrode in the width direction, a strip-shaped exposed portion of the negative electrode core, extending from the beginning to the end of winding, was provided along the length direction of the negative electrode, where no negative electrode slurry layer was present.

[0059] [Fabrication of Electrodes]

[0060] The positive electrode, the negative electrode, and the polyethylene diaphragm are wound into a spiral shape using a cylindrical core component, and a winding fixing tape is attached to the outermost circumferential surface to obtain a wound electrode body. After forming the wound structure of the electrode body, the core component is removed to obtain a wound electrode body with holes formed in the core portion.

[0061] [Preparation of non-aqueous electrolytes]

[0062] A non-aqueous electrolyte was prepared by adding 5 parts by mass of vinylene carbonate (VC) to 100 parts by mass of a mixed solvent consisting of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:3 (25°C) to dissolve LiPF6 at a concentration of 1.5 mol / L.

[0063] [Making of Cylindrical Batteries]

[0064] An insulating plate is placed on top of the aforementioned electrode body, and a negative current collector plate is placed below the electrode body. The exposed portion of the negative electrode core extending from the lower end of the electrode body is welded to the upper surface of the lower current collector plate, and the lower surface of the lower current collector plate is welded to the inner surface of the bottom of the outer can. Then, the positive electrode lead is welded to the internal terminal plate of the sealing body, and the electrode body is housed inside the outer can. Next, a non-aqueous electrolyte is injected into the outer can under reduced pressure, and the opening of the outer can is sealed with the sealing body through a gasket, thereby obtaining a cylindrical battery.

[0065] <Example 2>

[0066] In the fabrication of the positive electrode, the electrode body and cylindrical battery were fabricated in the same manner as in Example 1, except that the density of the second region was 80% of the density of the central region.

[0067] <Example 3>

[0068] In the fabrication of the positive electrode, the electrode body and cylindrical battery were fabricated in the same manner as in Example 1, except that the density of the first region was 110% of the density of the central region.

[0069] <Example 4>

[0070] In the fabrication of the positive electrode, the electrode body and cylindrical battery were fabricated in the same manner as in Example 1, except that the density of the first region was 120% of the density of the central region and the density of the second region was 80% of the density of the central region.

[0071] <Comparative Example 1>

[0072] In the fabrication of the positive electrode, the electrode body and cylindrical battery were fabricated in the same manner as in Example 1, except that the density of the second region was 100% of the density of the central region.

[0073] <Comparative Example 2>

[0074] In the fabrication of the positive electrode, the electrode body and cylindrical battery were fabricated in the same manner as in Example 1, except that the density of the second region was 110% of the density of the central region.

[0075] <Comparative Example 3>

[0076] In the fabrication of the positive electrode, the electrode body and cylindrical battery were fabricated in the same manner as in Example 1, except that the density of the first region was 90% of the density of the central region and the density of the second region was 100% of the density of the central region.

[0077] <Comparative Example 4>

[0078] In the fabrication of the positive electrode, the electrode body and cylindrical battery were fabricated in the same manner as in Example 1, except that the density of the first region was 110% of the density of the central region and the density of the second region was 100% of the density of the central region.

[0079] <Comparative Example 5>

[0080] In the fabrication of the positive electrode, the electrode body and cylindrical battery were fabricated in the same manner as in Example 1, except that the density of the first region was 120% of the density of the central region and the density of the second region was 100% of the density of the central region.

[0081] The following methods were used to evaluate the batteries of the examples and comparative examples, and the evaluation results are shown in Table 1. The positive electrode binder layer density shown in Table 1 represents the ratio of the densities of each region when the density of the central region is set to 100%.

[0082] [Evaluation of plate deformation (bending)]

[0083] The batteries of both the examples and comparative examples were charged at a constant current of 0.5C at 25°C until the battery voltage reached 4.2V. Then, they were discharged at a constant current of 0.7C until the battery voltage reached 2.5V. After 500 charge-discharge cycles, the batteries were brought to a charging state, and the area near the core of the electrode was observed using an X-ray CT apparatus (Shimadzu Corporation, SMX-225CT FPD HR).

[0084] like Figure 4 As shown, near the positive electrode starting end in the CT image of the electrode body, deformation is determined to be present if deformation (bending) of the electrode plate (at least one of the positive electrode 11 and negative electrode 12) with an angle α of less than 150° is confirmed. In Examples 1-4 and Comparative Examples 1-5, 10 batteries were evaluated respectively.

[0085] [Evaluation of capacity maintenance rate]

[0086] The batteries of the examples and comparative examples were charged at a constant current of 1C at 25°C until the battery voltage reached 4.2V. Then, they were discharged at a constant current of 0.5C until the battery voltage reached 2.5V. This charge-discharge cycle was counted as one cycle, and 500 cycles were performed. The discharge capacity of the first cycle and the discharge capacity of the 500th cycle were calculated, and the capacity retention rate was calculated using the following formula.

[0087] Capacity retention rate (%) = (500th cycle discharge capacity ÷ 1st cycle discharge capacity) × 100

[0088] If the calculated capacity retention rate is below 90%, it is determined that the capacity cannot be maintained and is included in the count. That is, the numerator of the capacity retention rate in Table 1 is the number of cells with a capacity retention rate below 90% after 500 cycles. In Examples 1-4 and Comparative Examples 1-5, 10 cells were evaluated respectively.

[0089] Table 1

[0090]

[0091] As shown in Table 1, in Examples 1-4, both suppression of bending and suppression of capacity retention rate reduction were achieved simultaneously. In particular, Example 4, where the density of the first region was 120% of that of the central region and the density of the second region was 80% of that of the central region, more effectively suppressed deformation of the negative electrode and reduction in capacity retention rate. On the other hand, in Comparative Examples 1-5, both suppression of bending and suppression of capacity retention rate reduction were not achieved simultaneously.

[0092] The present disclosure will be further described through the following embodiments.

[0093] Technical component 1: A cylindrical battery comprising an electrode body, a bottomed cylindrical outer can, and a sealing body.

[0094] The electrode body has a positive electrode, a negative electrode, and a diaphragm, with the positive electrode and the negative electrode wound together with the diaphragm in between to form the electrode body.

[0095] The outer can houses the electrode body.

[0096] The sealing body blocks the opening of the outer can.

[0097] The positive electrode or the negative electrode is connected to the bottom of the outer can.

[0098] The positive electrode comprises a strip-shaped positive electrode core and a positive electrode compound layer disposed on the positive electrode core.

[0099] Regarding the positive electrode mixture layer, if the region containing the center of the positive electrode in the width direction is defined as the central region, the region containing one end in the width direction closer to the sealing body than the central region is defined as the first region, and the region containing the other end in the width direction closer to the bottom side of the outer can than the central region is defined as the second region, then...

[0100] The density of the first region is the same as, or greater than, the density of the central region.

[0101] The density of the second region is less than the density of the central region.

[0102] Technical configuration 2: The cylindrical battery according to technical configuration 1 or 2,

[0103] The negative electrode comprises a strip-shaped negative electrode core and a negative electrode mixture layer disposed on the negative electrode core.

[0104] At the width-direction end of the negative electrode located on the bottom side of the outer packaging can, a strip-shaped negative electrode core exposure portion is formed along the length direction of the negative electrode, exposing the surface of the negative electrode core.

[0105] The exposed portion of the negative electrode core is directly or indirectly connected to the bottom of the outer can through the negative electrode current collector.

[0106] Technical configuration 3: A cylindrical battery according to any one of technical configurations 1 to 3,

[0107] The density of the second region is less than 90% of the density of the central region.

[0108] Technical configuration 4: A cylindrical battery according to any one of technical configurations 1 to 4,

[0109] The density of the first region is more than 110% of the density of the central region.

[0110] Technical configuration 5: A cylindrical battery according to any one of technical configurations 1 to 5,

[0111] The positive electrode forms multiple positive electrode core exposed portions, where a portion of the surface of the positive electrode core is exposed in the first region.

[0112] The exposed portion of the positive electrode core has a positive electrode lead that connects the sealing body and the exposed portion of the positive electrode core.

[0113] Technical configuration 6: A cylindrical battery according to any one of technical configurations 1 to 5,

[0114] The width of the first region is more than 5% and less than 30% of the full width of the positive electrode.

[0115] Technical configuration 7: A cylindrical battery according to any one of technical configurations 1 to 6,

[0116] The width of the second region is more than 5% and less than 30% of the full width of the positive electrode.

[0117] Technical configuration 8: A cylindrical battery according to any one of technical configurations 1 to 7,

[0118] The density of the central region, the first region, and the second region is smaller in the region located on the inner side of the roll of the positive electrode, which is one-third of the total length of the positive electrode, than in the region located on the outer side of the roll of the positive electrode, which is two-thirds of the total length of the positive electrode.

[0119] Explanation of reference numerals in the attached figures

[0120] 10 Cylindrical battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Outer can, 16 Sealing body, 17 Lower current collector plate, 18 Insulating plate, 20 Positive lead, 21 Slot, 22 Internal terminal plate, 23 Lower valve body, 24 Insulating component, 25 Upper valve body, 26 Cover, 26a Through hole, 27 Gasket, 30 Positive electrode core, 31 Positive electrode binder layer, 32 Positive electrode core exposed portion, 40 Negative electrode core, 41 Negative electrode binder layer, 42 Negative electrode core exposed portion, 311 First region, 312 Central region, 313 Second region, 314 Inner region, 315 Outer region.

Claims

1. A cylindrical battery comprising an electrode body, a bottomed cylindrical outer can, and a sealing body. The electrode body has a positive electrode, a negative electrode, and a diaphragm, with the positive electrode and the negative electrode wound together with the diaphragm in between to form the electrode body. The outer can houses the electrode body. The sealing body blocks the opening of the outer can. The positive electrode or the negative electrode is connected to the bottom of the outer can. The positive electrode comprises a strip-shaped positive electrode core and a positive electrode compound layer disposed on the positive electrode core. Regarding the positive electrode mixture layer, if the region containing the center of the positive electrode in the width direction is defined as the central region, the region containing one end in the width direction closer to the sealing body than the central region is defined as the first region, and the region containing the other end in the width direction closer to the bottom side of the outer can than the central region is defined as the second region, then... The density of the first region is the same as, or greater than, the density of the central region. The density of the second region is less than the density of the central region.

2. The cylindrical battery according to claim 1, The negative electrode comprises a strip-shaped negative electrode core and a negative electrode mixture layer disposed on the negative electrode core. At the width-direction end of the negative electrode located on the bottom side of the outer packaging can, a strip-shaped negative electrode core exposure portion is formed along the length direction of the negative electrode, exposing the surface of the negative electrode core. The exposed portion of the negative electrode core is directly or indirectly connected to the bottom of the outer can through the negative electrode current collector.

3. The cylindrical battery according to claim 1, The density of the second region is less than 90% of the density of the central region.

4. The cylindrical battery according to claim 1, The density of the first region is more than 110% of the density of the central region.

5. The cylindrical battery according to claim 1, The positive electrode forms multiple positive electrode core exposed portions, where a portion of the surface of the positive electrode core is exposed in the first region. The exposed portion of the positive electrode core has a positive electrode lead that connects the sealing body and the exposed portion of the positive electrode core.

6. The cylindrical battery according to claim 1, The width of the first region is more than 5% and less than 30% of the full width of the positive electrode.

7. The cylindrical battery according to claim 1, The width of the second region is more than 5% and less than 30% of the full width of the positive electrode.

8. The cylindrical battery according to any one of claims 1 to 7, The density of the central region, the first region, and the second region is smaller in the region located on the inner side of the roll of the positive electrode, which is one-third of the total length of the positive electrode, than in the region located on the outer side of the roll of the positive electrode, which is two-thirds of the total length of the positive electrode.

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