Secondary battery

Abstract

A cylindrical battery (10) is provided with an electrode body (14) that includes a positive electrode (11), a negative electrode (12), and a separator (13), and that is obtained by winding the positive electrode (11) and the negative electrode (12) with the separator (13) interposed therebetween. The separator (13) has a folded portion (50) formed closer to the winding center side than the winding start side end portion of the positive electrode (11), and an extended portion (51) extending from the folded portion (50) toward the winding end side of the electrode body (14) and covering the winding start side end portion of the positive electrode (11) from both sides.

Description

Technical Field

[0001] The present application relates to a secondary battery, and more specifically, to a secondary battery including a wound electrode assembly. Background Art

[0002] Conventionally, secondary batteries comprising a spirally wound electrode assembly comprising a positive electrode, a negative electrode, and a separator, the positive and negative electrodes being wound with the separator interposed therebetween, are widely known (see, for example, Patent Document 1). In a spirally wound electrode assembly used in lithium-ion batteries and other applications, the negative electrode is typically formed one turn larger than the positive electrode, with the winding start end of the negative electrode positioned closer to the winding center than the winding start end of the positive electrode.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-92064 Summary of the Invention

[0006] Wound electrode bodies expand and contract radially during charging and discharging. This can cause deformation, such as bending of the negative electrode, near the positive electrode's winding start point. Stress caused by the electrode body's expansion and contraction is thought to be concentrated near the positive electrode's winding start point. If this stress increases, the bending of the negative electrode may increase, potentially rupturing the separator at the bent portion and causing an internal short circuit.

[0007] An object of the present application is to sufficiently reduce the risk of a short circuit that may occur near the winding center of an electrode assembly in a secondary battery including a wound electrode assembly.

[0008] The secondary battery of the present application is characterized in that it has an electrode body, which includes a positive electrode, a negative electrode and a separator, and is formed by winding the positive electrode and the negative electrode with the separator sandwiched therebetween, and the separator has a folded portion formed closer to the winding center side than the end portion of the positive electrode on the winding start side, and an extended portion extending from the folded portion toward the winding end side of the electrode body and covering the end portion of the positive electrode on the winding start side from both sides.

[0009] The secondary battery of the present application can significantly reduce the risk of short circuits that may occur near the winding center of the electrode assembly. Even if deformation such as bending of the negative electrode occurs near the winding start end of the positive electrode during charging and discharging of the secondary battery, contact between the negative and positive electrodes due to separator rupture can be more reliably prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a cross-sectional view of a secondary battery as an example of an embodiment.

[0011] Figure 2This is a diagram showing the winding center and its vicinity of an electrode assembly as an example of an embodiment.

[0012] Figure 3 yes Figure 2 Enlarged view of part A in .

[0013] Figure 4 This is a diagram showing an example of a conventional electrode assembly.

[0014] Figure 5 It is a diagram for explaining a method for manufacturing an electrode assembly as an example of an embodiment. DETAILED DESCRIPTION

[0015] Hereinafter, an example of an embodiment of the secondary battery of the present application will be described in detail with reference to the accompanying drawings. It should be noted that configurations formed by selectively combining the components of the various embodiments and modifications described below are within the scope of the present application.

[0016] The following embodiments illustrate a cylindrical battery 10 in which a wound electrode assembly 14 is housed in a bottomed cylindrical outer can 16. However, the outer can is not limited to a cylindrical outer can. Other embodiments of the secondary battery of the present application include a prismatic battery having a prismatic outer can, and a pouch-type battery having an outer can composed of a laminate sheet containing a metal layer and a resin layer.

[0017] Figure 1 Schematically shows an axial cross section of a cylindrical battery 10 as an example of an embodiment. Figure 1 As shown, the cylindrical battery 10 includes a wound electrode body 14, an electrolyte, a bottomed cylindrical outer can 16 that houses the electrode body 14 and the electrolyte, and a sealing member 17 that seals the opening of the outer can 16. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a spirally wound structure in which the positive electrode 11 and the negative electrode 12 are interposed with the separator 13. For ease of description, the battery's sealing member 17 side is considered top, and the bottom side of the outer can 16 is considered bottom.

[0018] The electrolyte can be an aqueous electrolyte, but in this embodiment, a non-aqueous electrolyte is used. A non-aqueous electrolyte has ion conductivity (for example, 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 lithium-ion battery.

[0019] The liquid electrolyte (electrolyte) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more thereof. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents thereof. The non-aqueous solvent may contain a halogen-substituted product (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms in these solvents are replaced with halogen atoms such as fluorine. Examples of the electrolyte salt include lithium salts such as LiPF6.

[0020] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. The polymer electrolyte, for example, contains a lithium salt and a matrix polymer, or contains a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that gels after absorbing a non-aqueous solvent can be used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used. As the inorganic solid electrolyte, for example, materials known in all-solid-state lithium-ion secondary batteries (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) can be used.

[0021] The positive electrode 11, the negative electrode 12, and the separator 13 that constitute the electrode body 14 are all long strips that are wound into a spiral shape and are alternately stacked along the radial direction of the electrode body 14. In order to prevent the precipitation of lithium, the negative electrode 12 is formed to be one circle larger than the positive electrode 11. That is, the negative electrode 12 is formed longer in the length and width directions than the positive electrode 11. The separator 13 is formed to be one circle larger than the positive electrode 11 and the negative electrode 12, and two pieces are arranged in a manner that sandwiches the positive electrode 11. The electrode body 14 has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.

[0022] The positive electrode 11 includes a positive electrode core 30 and a positive electrode mixture layer 31 disposed on the positive electrode core 30. The positive electrode core 30 can be made of a metal foil, such as aluminum, aluminum alloy, stainless steel, or titanium, that is stable within the potential range of the positive electrode 11, or a film having such a metal disposed on the surface. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent, and a binder, and is preferably provided on both surfaces of the positive electrode core 30. The positive electrode active material is a lithium transition metal composite oxide containing transition metal elements such as Ni, Co, and Mn.

[0023] The negative electrode 12 includes a negative electrode core 40 and a negative electrode mixture layer 41 disposed on the negative electrode core 40. The negative electrode core 40 can be made of a foil of a metal that is stable in the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, nickel alloy, or a film having the metal disposed on the surface. The negative electrode mixture layer 41 contains a negative electrode active material and a binder, and is preferably provided on both sides of the negative electrode core 40 excluding the portion to which the negative electrode lead 21 is bonded. The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. The negative electrode active material can also use elements such as Si and Sn that alloy with Li, or materials containing such elements.

[0024] The separator 13 is made of a porous sheet that is ion-permeable and insulating. Specific examples of porous sheets include microporous films, woven fabrics, and non-woven fabrics. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 can have either a single-layer or multi-layer structure. For example, the separator 13 can have a multi-layer structure comprising a thermoplastic resin layer such as a polyolefin and a cellulose fiber layer, a two-layer structure of polyethylene (PE) / polypropylene (PP), or a three-layer structure of PE / PP / PE.

[0025] A filler layer containing an inorganic filler may be formed on the surface of the spacer 13. Examples of inorganic fillers include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphate compounds. The filler layer can be formed by applying a slurry containing the filler to the surface of the spacer 13. Furthermore, a layer (heat-resistant layer) of a highly heat-resistant resin such as an aramid resin may be disposed on the surface of the spacer 13. For example, the spacer 13 may include a base material made of a porous sheet and a filler layer or heat-resistant layer disposed on the base material.

[0026] The outer can 16 is a bottomed, cylindrical metal container open at one axial end. The upper opening of the outer can 16 is sealed by a sealing member 17. The cylindrical battery 10 includes an upper insulating plate 18 disposed between the electrode body 14 and the sealing member 17. Furthermore, the cylindrical battery 10 includes a lower insulating plate 19 disposed between the electrode body 14 and the inner surface of the bottom of the outer can 16. Specifically, insulating plates are disposed above and below the electrode body 14.

[0027] In this embodiment, the positive electrode lead 20 passes through the through-hole 60 of the upper insulating plate 18 and extends toward the sealing body 17. The negative electrode lead 21 passes through the outside of the lower insulating plate 19 and extends toward the bottom of the outer can 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or other means. The lid 27, which serves as the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or other means, with the outer can 16 serving as the negative electrode terminal.

[0028] A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the airtightness of the battery interior. The gasket 28 also serves to insulate the outer can 16 from the sealing body 17. The outer can 16 has a groove 22 formed therein, with a portion of the side surface protruding inward, to support the sealing body 17. The groove 22 is preferably formed in an annular shape along the circumference of the outer can 16, with its upper surface supporting the sealing body 17. The sealing body 17 is fixed to the upper portion of the outer can 16 by using the groove 22 and the open end of the outer can 16, which is caulked against the sealing body 17.

[0029] The sealing body 17 has a structure consisting of an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a lid 27 stacked in this order from the electrode body 14 side. Each component of the sealing body 17 has, for example, a disc or ring shape, and all components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, with the insulating member 25 interposed between their respective peripheries.

[0030] When an abnormality occurs in the cylindrical battery 10 and the internal pressure rises, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 toward the lid 27. This breaks the current path between the lower and upper valve bodies 24 and 26. If the internal pressure of the battery rises further, the upper valve body 26 ruptures, allowing high-temperature gas to escape from the opening in the lid 27. In other words, the sealing body 17 is equipped with a current interruption mechanism and a safety valve. The safety valve consists of two valve bodies: the lower valve body 24 and the upper valve body 26.

[0031] Below, with appropriate reference to Figure 2 and Figure 3 At the same time, the structure of the winding center α of the electrode body 14 and its vicinity will be described in detail. Figure 2 1 is a diagram showing the winding center α of the electrode body 14 and its vicinity. Figure 3 yes Figure 2 Enlarged view of part A in .

[0032] like Figure 2 As shown, the electrode body 14 includes a positive electrode 11, a negative electrode 12, and two separators 13, which are wound in a spiral shape. The two separators 13 are arranged so as to sandwich the positive electrode 11 and the negative electrode 12 from both sides. Normally, one separator 13 is sandwiched between the positive electrode 11 and the negative electrode 12. However, two separators 13 are sandwiched between the end of the positive electrode 11 at the start of winding and the negative electrode 12. This significantly reduces the risk of short circuits that may occur near the winding center α of the electrode body 14. This will be described in detail later.

[0033] Near the winding center α of the electrode body 14, the negative electrode start end 12a is located closer to the winding center than the positive electrode start end 11a. In this specification, the positive electrode start end 11a refers to the end of the positive electrode 11 where the winding starts, meaning the longitudinal end of the positive electrode 11 located closer to the winding center of the electrode body 14. Similarly, the negative electrode start end 12a refers to the end of the negative electrode 12 where the winding starts, meaning the longitudinal end of the negative electrode 12 located closer to the winding center of the electrode body 14. The negative electrode 12 extends, for example, from the positive electrode start end 11a toward the winding center α by a length of not less than 0.25 turns and not more than 1 turn.

[0034] For example, a negative electrode lead 21 may be provided near the winding center α of the electrode body 14. However, in this embodiment, the negative electrode lead 21 is provided at the outer peripheral end of the electrode body 14. Furthermore, the positive electrode lead 20 is connected to the longitudinal center of the positive electrode 11. In other words, the positive electrode lead 20 and the negative electrode lead 21 are not provided near the winding center α of the electrode body 14. Figure 2 In FIG, a winding core 60 used for manufacturing the electrode assembly 14 is indicated by a dashed line. The winding core 60 is removed after manufacturing the electrode assembly 14, but the winding core 60 may be left.

[0035] Near the winding center α of the electrode body 14, two separators 13 extend further toward the winding center beyond the negative electrode starting end 12a. The inner circumference of the electrode body 14 is formed by the separators 13, and near the winding center α, only the separators 13 are wound over a length of, for example, one or more turns. That is, a certain amount of excess separator 13 remains near the winding center α of the electrode body 14.

[0036] The separator 13 has a folded portion 50 formed closer to the winding center than the positive electrode starting end 11a. The folded portion 50 is formed, for example, in a roughly Z-shaped shape when viewed from above, reversing the orientation of the starting end 13a of the separator 13. The starting end 13a is the end of the separator 13 where winding begins, meaning the end of the separator 13 in the longitudinal direction located toward the winding center of the electrode body 14. The separator 13 is arranged so that two separators overlap from a position corresponding to the negative electrode starting end 12a to near the starting end 13a. The folded portion 50 is formed by folding the two separators 13 at the same position.

[0037] like Figure 2 and Figure 3As shown, the separator 13 includes an extension portion 51 that extends from the folded portion 50 toward the winding end side of the electrode body 14 and covers the winding start end of the positive electrode 11, including the positive electrode starting end 11a, from both sides. The extension portion 51 is formed by two separators 13. Therefore, the winding start end of the positive electrode 11 can be covered from both sides in the thickness direction of the positive electrode 11. The two separators 13 are folded back at the folded portion 50 so that the starting end 13a faces the winding end side. Near the positive electrode starting end 11a, the two separators 13 are divided into the inner and outer sides of the positive electrode 11, covering both sides of the positive electrode 11.

[0038] Figure 4 1 is a diagram showing an example of the structure of a conventional electrode body 100. Figure 4 As shown, in the electrode assembly 100, the two separators 101 extend beyond the negative electrode starting end 12a toward the winding center, which is the same as the separator 13 of the electrode assembly 14. On the other hand, the two separators 101 are not folded back, and their starting ends 101a face the direction of the winding center α, which is different from the separator 13 of the electrode assembly 14. Figure 2 and Figure 4 As shown, the structure of the electrode body 14 of this embodiment is greatly different from the structure of the conventional electrode body 100 .

[0039] The folded portion 50 of the separator 13 can also be formed in the winding core portion of the electrode body 14. The so-called winding core of the electrode body 14 refers to the portion of the winding core 60 when the winding core 60 is present, and refers to the axially extending cavity formed by the trace of the winding core 60 when the winding core 60 is removed. The winding core of the electrode body 14 functions as a gas discharge path, for example, when a battery abnormality occurs. The two separators 13 are bent into a Z-shape in a top view at the folded portion 50, cross the winding core of the electrode body 14, and folded back toward the winding end side of the electrode body 14.

[0040] The extension 51 of the separator 13 extends from the folded portion 50 to the starting end 13a, and a portion thereof overlaps with the portion of the separator 13 facing the folded portion 50. The extension 51 extends beyond the negative electrode starting end 12a and further extends beyond the positive electrode starting end 11a. The extension 51 is formed by stacking two separators 13 from the folded portion 50 to near the positive electrode starting end 11a. As described above, the extension 51 is separated from each other near the positive electrode starting end 11a, with one separator placed on each side of the positive electrode 11.

[0041] The extension portion 51 covers the first surface of the positive electrode 11 facing the inner circumference of the electrode body 14 and the second surface of the positive electrode 11 facing the outer circumference at the winding start end of the positive electrode 11. Because the first and second surfaces of the winding start end of the positive electrode 11 are also covered by the portion of the separator 13 facing the folded portion 50, two separators 13 are interposed between the first and second surfaces of the winding start end and the negative electrode 12. As a result, the winding start end of the positive electrode 11 is protected by separators 13 that are twice as thick as the rest of the electrode.

[0042] The length of the extension portion 51 covering the end portion of the positive electrode 11 on the winding start side is preferably 3 mm or more and 15 mm or less in the longitudinal direction of the positive electrode 11, and more preferably 5 mm or more and 10 mm or less. That is, the positive electrode 11 is protected by the extension portion 51 in the range of 3 mm or more and 10 mm or less in the longitudinal direction from the positive electrode starting end 11a. In this case, the risk of a short circuit that may occur near the winding center α of the electrode body 14 can be sufficiently reduced without substantially compromising the smooth movement of ions between the positive and negative electrodes. Although the volume of the positive electrode 11 changes due to the charge and discharge of the battery, if the extension portion 51 overlaps by more than 3 mm, the situation where the extension portion 51 is separated from the positive electrode 11 can be sufficiently suppressed.

[0043] Figure 5 1 is a diagram for explaining a method for manufacturing the electrode body 14 having the above-mentioned structure. Figure 5 As shown, the electrode assembly 14 can be manufactured by spirally winding the positive electrode 11, negative electrode 12, and separator 13 using a winding core 60. First, the negative electrode 12 is placed between two separators 13. The positive electrode 11 is stacked so that the separator 13 on the inner side of the winding (hereinafter referred to as the "inner separator 13") faces the negative electrode 12. At this time, the negative electrode 12 is arranged so that it extends beyond the position corresponding to the positive electrode starting end 11a, and the separator 13 extends beyond the position corresponding to the negative electrode starting end 12a.

[0044] Next, the winding core 60 is installed between the starting ends 13a of the two separators 13 and the starting end 12a of the negative electrode, sandwiching the two separators 13. To ensure that the two separators 13 form an extended portion 51 of sufficient length, the portion on the starting end 13a side is extended significantly from the winding core 60. At this time, it is preferable that the separator 13 on the outer side of the winding (hereinafter referred to as the "outer separator 13") of the two separators 13 be extended longer than the inner separator 13. This makes it easier to completely cover both surfaces of the winding start end of the positive electrode 11 with the inner and outer separators 13.

[0045] By Figure 5In the illustrated state, the winding core 60 is rotated in the direction of the arrow, forming a folded portion 50 in the portion of the separator 13 held by the winding core 60. The portion extending from the winding core 60 to the starting end 13a is folded back toward the winding end, forming an extended portion 51 extending toward the positive electrode starting end 11a. As the winding core 60 rotates, the positive electrode starting end 11a is inserted between the two separators 13, resulting in a state where the first surface of the winding start end of the positive electrode 11 is covered by the inner separator 13 and the second surface is covered by the outer separator 13. By continuing to rotate the winding core 60, a wound electrode assembly 14 is obtained.

[0046] As described above, according to the cylindrical battery 10 having the electrode body 14, the risk of a short circuit that may occur near the winding center α of the electrode body 14 can be substantially reduced. The electrode body 14 expands and contracts in the radial direction during charging and discharging. At this time, stress is concentrated near the positive electrode starting end 11a, and deformation such as bending of the negative electrode 12 may occur near the positive electrode starting end 11a. This deformation of the negative electrode 12 can occur on both the inner and outer sides of the positive electrode starting end 11a. However, according to the electrode body 14, both sides of the end portion of the positive electrode 11 on the winding start side are covered by the extension portion 51 of the separator 13, and both sides are protected by two separators 13. Therefore, it is possible to more reliably prevent the separator 13 from being broken at the bent portion of the negative electrode 12 and coming into contact with the positive electrode 11.

[0047] The above deformation of the negative electrode 12 becomes more likely to occur with the increase in the capacity of the cylindrical battery 10 and the thinning of the separator 13. It is expected that the importance of the above structure of the electrode body 14 will further increase in the future.

[0048] It should be noted that the above embodiments can be appropriately modified in design without prejudice to the purpose of this application. For example, Figure 2 and Figure 3 In the example shown, the extended portion 51 of the separator 13 covers each surface of the winding start end of the positive electrode 11 with substantially the same length. However, the inner separator 13 may cover more of the positive electrode 11 than the outer separator 13. Alternatively, the outer separator 13 may cover more of the positive electrode 11 than the inner separator 13.

[0049] Description of Reference Numerals

[0050] 10 Cylindrical battery, 11 Positive electrode, 11a Positive electrode start, 12 Negative electrode, 12a Negative electrode start, 13 Separator, 13a Start, 14 Electrode body, 16 Outer can, 17 Sealing body, 18 Upper insulating plate, 19 Lower insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Slot, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Lid, 28 Gasket, 30 Positive electrode core, 31 Positive electrode mixture layer, 40 Negative electrode core, 41 Negative electrode mixture layer, 50 Fold-back portion, 51 Extension portion, 60 Winding core, 100 Electrode body, 101 Separator, α Winding center.

Claims

1. A secondary battery comprising an electrode body comprising a positive electrode, a negative electrode, and a separator, wherein the positive electrode and the negative electrode are wound with the separator interposed therebetween. The separator includes a folded portion formed closer to the winding center than the winding start end of the positive electrode, and an extended portion extending from the folded portion toward the winding end of the electrode assembly and covering the winding start end of the positive electrode from both sides.

2. The secondary battery according to claim 1, wherein The length of the extended portion of the separator covering the winding start-side end portion of the positive electrode is 3 mm to 10 mm in the longitudinal direction of the positive electrode.

Images