Secondary battery

Abstract

A cylindrical battery (10) is provided with a wound electrode body (14) and an outer can (16) for accommodating the electrode body (14), and has a structure in which a negative electrode (12) is disposed on an outer peripheral surface (14s) of the electrode body (14) and is in contact with an inner surface of the outer can (16). A mesh sheet (50) having a plurality of through holes (51) is disposed between the outer peripheral surface (14s) of the electrode body (14) and the inner surface of the outer can (16). The negative electrode (12) disposed on the outer peripheral surface (14s) of the electrode body (14) is in contact with the inner surface of the outer can (16) via the through holes (51) of the mesh sheet (50).

Description

secondary battery

[0001] This disclosure relates to a secondary battery, and more particularly to a secondary battery comprising an electrode body having a wound structure, and an outer casing housing the electrode body.

[0002] Conventionally, secondary batteries comprising a wound electrode body in which a positive electrode and a negative electrode are wound in a spiral shape with a separator in between, and an outer casing housing the electrode body, are widely known. Furthermore, Patent Document 1 discloses a secondary battery in which silicon material and graphite are used as the negative electrode active material, and a core exposed portion that contacts the inner surface of the outer casing is provided at the end of the winding of the negative electrode constituting the wound electrode body. The secondary battery of Patent Document 1 has a large-area current collection structure in which the core exposed portion of the negative electrode that forms the outer surface of the electrode body is in contact with the inner surface of the outer casing, and therefore has excellent output characteristics.

[0003] Patent No. 6652125

[0004] On the other hand, suppressing battery heat generation in the event of abnormalities such as external short circuits is an important challenge. However, high-capacity batteries with excellent output characteristics, especially those employing low-resistance current collection structures, tend to generate significant heat during abnormalities. The purpose of this disclosure is to provide a secondary battery that can effectively suppress heat generation during abnormalities while ensuring good output characteristics during normal use.

[0005] The secondary battery according to this disclosure comprises an electrode body in which a positive electrode and a negative electrode are wound with a separator between them, and an outer casing that houses the electrode body, wherein the positive electrode or the negative electrode is disposed on the outer circumferential surface of the electrode body and in contact with the inner surface of the outer casing, wherein a resin layer having a plurality of through holes is disposed between the outer circumferential surface of the electrode body and the inner surface of the outer casing, and the positive electrode or the negative electrode disposed on the outer circumferential surface contacts the inner surface of the outer casing through the through holes of the resin layer.

[0006] The secondary battery described herein can effectively suppress heat generation in the event of an abnormality while ensuring good output characteristics during normal use.

[0007] This is an axial cross-sectional view of a cylindrical battery, which is one example of an embodiment. This is a perspective view of an electrode body, which is one example of an embodiment. This is a diagram showing a cross-section of a cylindrical battery near the resin layer. This is a perspective view of an electrode body, which is another example of an embodiment.

[0008] Hereinafter, an example of an embodiment of the secondary battery according to this disclosure will be described in detail with reference to the drawings. The embodiment described below is merely an example, and this disclosure is not limited to the embodiments described below. Furthermore, forms obtained by selectively combining the various components of the multiple embodiments and modifications described below are included in this disclosure.

[0009] In the following, a cylindrical battery 10 equipped with a bottomed cylindrical outer casing 16 is given as an example of an embodiment of the secondary battery according to the present disclosure, but the battery casing is not limited to a cylindrical outer casing. The secondary battery according to the present disclosure only needs to be equipped with a wound electrode body and an outer casing that houses the electrode body, and may be a rectangular battery equipped with a rectangular outer casing, for example. However, the configuration of the present disclosure is particularly preferred for cylindrical batteries.

[0010] Figure 1 is a schematic diagram showing an axial cross-section including the central axis of the cylindrical battery 10. Note that the mesh sheet 50 and winding tape 60 are omitted from the illustration in Figure 1. As shown in Figure 1, the cylindrical battery 10 comprises an electrode body 14 having a wound structure, an electrolyte, and a bottomed cylindrical outer casing 16 that houses the electrode body 14 and the electrolyte. The electrode body 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 wound in a spiral shape via the separator 13. The outer casing 16 is a bottomed cylindrical metal container with one side open in the axial direction, and the opening of the outer casing 16 is sealed by a sealing body 17. In the following explanation, for convenience, the side of the cylindrical battery 10 with the sealing body 17 is considered the top, and the bottom side of the outer casing 16 is considered the bottom.

[0011] As will be described in more detail later, a positive electrode 11 or a negative electrode 12 is arranged on the outer circumferential surface of the electrode body 14, and the positive electrode 11 or negative electrode 12 contacts the inner surface of the outer casing 16 and is electrically connected. In this embodiment, the negative electrode 12 is arranged on the outermost circumferential surface of the electrode body 14, and the exposed core portion 42 of the negative electrode 12 contacts the inner surface of the outer casing 16 through through holes 51 in the mesh sheet 50, which is a resin layer (see Figure 3, described later). The mesh sheet 50 is configured to melt when the temperature of the cylindrical battery 10 exceeds a predetermined temperature, thereby reducing the opening area of ​​the through holes 51.

[0012] The electrolyte may be an aqueous electrolyte, but in this embodiment, a non-aqueous electrolyte is used. The non-aqueous electrolyte has lithium-ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolyte solution) or a solid electrolyte. The cylindrical battery 10 is, for example, a non-aqueous electrolyte secondary battery, and among these, a lithium-ion battery is preferred.

[0013] A liquid electrolyte (electrolyte solution) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include 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 also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0014] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. As the inorganic solid electrolyte, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0015] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode body 14 are all elongated strips that are wound in a spiral shape and alternately stacked in the radial direction of the electrode body 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 than the positive electrode 11 in both the length and width (short side) directions. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and two separators are arranged so as to sandwich the positive electrode 11. The cylindrical battery 10 includes insulating plates 18 and 19 arranged above and below the electrode body 14, respectively.

[0016] 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. In this embodiment, the positive electrode lead 20 is connected to the longitudinal center of the positive electrode 11, and the negative electrode lead 21 is connected to the longitudinal end of the negative electrode 12 located on the winding center side of the electrode body 14. Although there is one positive electrode lead 20 and one negative electrode lead 21 in this embodiment, multiple positive electrode leads 20 may be provided. For example, multiple positive electrode leads 20 may be connected at predetermined intervals along the longitudinal direction of the positive electrode 11.

[0017] The positive electrode 11 comprises 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 that is stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal disposed on its surface. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent, and a binder, and is preferably formed on both sides of the positive electrode core 30, excluding the portion where the positive electrode lead 20 is welded (core exposed portion). The positive electrode 11 can be manufactured by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode core 30. The thickness of the positive electrode mixture layer 31 is, for example, 60 μm to 100 μm on one side of the positive electrode core 30.

[0018] The positive electrode composite layer 31 contains particulate lithium metal composite oxide as the positive electrode active material. The lithium metal composite oxide is a composite oxide containing metal elements such as Ni, Co, Mn, and Al in addition to Li. The metal elements constituting the lithium metal composite oxide are, 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 Ni, Co, and Mn. Examples of suitable composite oxides include lithium metal composite oxides containing Ni, Co, and Mn, and lithium metal composite oxides containing Ni, Co, and Al.

[0019] The negative electrode 12 comprises 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 metal foil that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal disposed on its surface. The negative electrode mixture layer 41 contains a negative electrode active material, a binder, and optionally a conductive agent, and is preferably formed on both sides of the negative electrode core 40, excluding the first and second core exposed portions described later. The negative electrode 12 can be manufactured 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 41 on both sides of the negative electrode core 40. The thickness of the negative electrode mixture layer 41 is, for example, 60 μm to 100 μm on one side of the negative electrode core 40.

[0020] The negative electrode composite layer 41 contains a carbon material as the negative electrode active material that reversibly intercepts and releases lithium ions. A suitable example of the carbon material is graphite, such as natural graphite or artificial graphite. Alternatively, a material containing elements that alloy with Li, such as Si and Sn, may be used as the negative electrode active material. Among these, a composite material containing Si is preferred. A suitable Si-containing composite material is a composite particle containing an ion-conducting phase and a Si phase dispersed in the ion-conducting phase. Furthermore, a carbon material and a Si-containing composite material may be used in combination as the negative electrode active material. In this case, it becomes easier to achieve both high capacity and high durability.

[0021] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A heat-resistant resin layer, such as 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.

[0022] A negative electrode 12 is positioned on the outer circumferential surface of the electrode body 14, and a core exposure portion 42 is formed where the surface of the negative electrode core body 40 is exposed. The core exposure portion 42 may be formed on a part of the outer circumferential surface of the electrode body 14, but preferably it is formed over the entire surface of the negative electrode that constitutes the outer circumferential surface. The core exposure portion 42 may be formed not only on the radially outward-facing surface of the electrode body 14, but also on both sides of the negative electrode core body 40. Since a negative electrode lead 21 is connected to the longitudinal end of the negative electrode 12 opposite to the core exposure portion 42, first and second core exposure portions are formed at both longitudinal ends.

[0023] In the cylindrical battery 10, the exposed core portion 42 (second exposed core portion) of the negative electrode 12 contacts the inner circumferential surface of the outer casing 16, and the negative electrode lead 21 is connected to the inner surface of the bottom of the outer casing 16 by welding or the like. As described above, a mesh sheet 50 is placed between the electrode body 14 and the outer casing 16, so the exposed core portion 42 contacts the inner circumferential surface of the outer casing 16 through the through hole 51 of the mesh sheet 50. The positive electrode lead 20 extends towards the sealing body 17 through the through hole of the insulating plate 18 and is connected to the lower surface of the internal terminal plate 23, which is the bottom plate of the sealing body 17, by welding or the like. For this reason, in this embodiment, the sealing body 17 becomes the positive electrode external terminal, and the outer casing 16 becomes the negative electrode external terminal.

[0024] As described above, the outer casing 16 is a bottomed cylindrical metal container with one side open in the axial direction. A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure airtightness inside the battery and insulation between the outer casing 16 and the sealing body 17. The outer casing 16 has a grooved portion 22 formed on a part of its side surface that protrudes inward. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The sealing body 17 is fixed to the upper part of the outer casing 16 by the grooved portion 22 and the open end of the outer casing 16 which is crimped to the sealing body 17.

[0025] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. 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 peripheral edges. When a malfunction occurs in the battery and the internal pressure rises, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 upward toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0026] Figure 2 is a perspective view of the electrode body 14. Figure 3 is a cross-section of the cylindrical battery 10 near the mesh sheet 50. As shown in Figures 2 and 3, a mesh sheet 50, which is a resin layer having a plurality of through holes 51, is placed between the outer circumferential surface 14s of the electrode body 14 and the inner circumferential surface of the outer casing 16. The exposed core portion 42 of the negative electrode 12, which is placed on the outer circumferential surface 14s of the electrode body 14, is in contact with the inner circumferential surface of the outer casing 16 through the through holes 51 of the mesh sheet 50. In addition, a winding stopper tape 60 is attached to the outer circumferential surface 14s of the electrode body 14 to fix the winding end 12x of the negative electrode 12 and maintain the winding structure of the electrode body 14. Two strip-shaped winding stopper tapes 60 are attached to the outer circumferential surface 14s of the electrode body 14.

[0027] The re-wrapping tape 60 is attached so that its length is aligned with the circumferential direction of the electrode body 14. Preferably, the two re-wrapping tapes 60 are attached to the axial ends of the electrode body 14, separated from each other in the axial direction. The re-wrapping tape 60 is attached so as to straddle the end end 12x of the negative electrode 12, and fixes the end end 12x to the portion located inside the winding of the end end 12x. The re-wrapping tape 60 has a length of, for example, 30% to 80% of the circumference of the outer surface 14s. The lengths of the two re-wrapping tapes 60 may be different, but in this embodiment they are substantially the same.

[0028] The winding stopper tape 60 has a width of, for example, 5% or more of the width of the negative electrode 12. The width of the winding stopper tape 60 is, for example, 5% to 25% or 10% to 20% of the width of the negative electrode 12. The widths of the two winding stopper tapes 60 may be different from each other, but in this embodiment they are substantially the same. The thickness of the winding stopper tape 60 is, for example, 15 μm to 40 μm, preferably 20 μm to 30 μm.

[0029] The re-wrapping tape 60 includes a tape base material and an adhesive layer provided on one side of the tape base material. The re-wrapping tape 60 is, for example, an insulating tape that is substantially non-conductive. The tape base material is composed of a single-layer or multi-layer resin base material. The re-wrapping tape 60 may contain inorganic fillers such as titania, alumina, silica, and zirconia, and a layer containing inorganic fillers may be provided separately from the tape base material and adhesive layer.

[0030] Examples of resins constituting the tape substrate include polyester such as polyethylene terephthalate (PET), polyolefins such as polypropylene (PP), polyimide (PI), polyphenylene sulfide (PPS), polyetherimide (PEI), and polyamide. The adhesive layer is formed, for example, by coating one side of the tape substrate with adhesive. The adhesive constituting the adhesive layer may be a hot-melt type that becomes tacky when heated or a thermosetting type that hardens when heated, but from the viewpoint of productivity, it is preferable to have adhesive properties at room temperature. Examples of adhesives include acrylic adhesives and synthetic rubber adhesives.

[0031] The mesh sheet 50 covers the area of ​​the outer circumferential surface 14s of the electrode body 14 that does not overlap with the winding tape 60. In this case, the overlap between the mesh sheet 50 and the winding tape 60 prevents the diameter of the electrode body 14 from increasing, thereby increasing the volume of the electrode group and enabling higher capacity. Since the winding tape 60 is positioned at both axial ends of the electrode body 14, the mesh sheet 50 is positioned in the axial center of the electrode body 14, sandwiched between the two winding tapes 60. It is preferable that the mesh sheet 50 broadly covers the core exposed portion 42 that forms the outer circumferential surface 14s of the electrode body 14, so it is positioned close to the winding tape 60 without leaving a large gap between the tape and the mesh sheet 50 in the area that does not overlap with the tape 60.

[0032] The mesh sheet 50 is preferably formed in a cylindrical shape and covers the outer surface 14s over substantially the entire length of the outer surface 14s in the circumferential direction. The ends of the mesh sheet 50 may overlap, but from the viewpoint of increasing capacity, the overlap width is preferably 1 mm or less. The circumference of the mesh sheet 50 may be less than or equal to the circumference of the outer surface 14s, but it is preferably 95% or more of the circumference of the outer surface 14s. If the length of the winding tape 60 is shorter than the circumference of the outer surface 14s, there will be portions that are not covered by the mesh sheet 50 and the winding tape 60 at positions aligned with the winding tape 60 in the circumferential direction of the outer surface 14s.

[0033] Figure 4 shows a modified example of the mesh sheet 50. The embodiment illustrated in Figure 4 differs from the embodiment illustrated in Figure 3 in that the mesh sheet 50 is also placed in the portion that overlaps with the winding tape 60. In the embodiment illustrated in Figure 4, a wider area of ​​the outer peripheral surface 14s, including the portion to which the winding tape 60 is attached, is covered by the mesh sheet 50. The mesh sheet 50 is placed along the entire axial length of the electrode body 14, and substantially covers the entire area of ​​the outer peripheral surface 14s. Note that if the thickness of the winding tape 60 is small, even if the mesh sheet 50 is placed so as to overlap with the winding tape 60, the effect on the battery capacity is small.

[0034] The mesh sheet 50 is a sheet formed in a mesh-like structure with numerous through-holes 51. The exposed core portion 42 is electrically connected to the inner circumferential surface of the outer casing 16 via the through-holes 51. However, the mesh sheet 50 softens when the temperature of the cylindrical battery 10 exceeds a predetermined temperature, reducing the opening area of ​​the through-holes 51. That is, during normal use of the battery, the electrical connection between the exposed core portion 42 and the outer casing 16 is ensured via the through-holes 51. However, if an abnormality occurs in the battery and the temperature rises, the opening area of ​​the through-holes 51 decreases, hindering or interrupting the electrical connection. As a result, the temperature rise in the event of an abnormality in the cylindrical battery 10 is effectively suppressed.

[0035] The mesh sheet 50 softens and deforms, for example, when the temperature of the cylindrical battery 10 exceeds 90°C. As a result, the opening area of the through hole 51 decreases, and the aperture ratio of the mesh sheet 50 also decreases. The through hole 51 may be completely blocked. Also, the mesh sheet 50 may melt when the temperature of the battery exceeds 90°C. In this specification, the term "softening" is used as a superordinate concept of "melting".

[0036] The temperature of the battery at which the mesh sheet 50 softens and the opening area of the through hole 51 begins to decrease is, for example, 90°C or higher and 150°C or lower, preferably 90°C or higher and 120°C or lower. Here, the temperature of the battery means the temperature of the outer peripheral surface of the outer can 16. When the temperature of the battery is 90°C or lower, it is preferable that the mesh sheet 50 does not soften and the opening area of the through hole 51 does not change. In this case, during normal use of the battery, while ensuring good electrical connection between the core body exposed portion 42 and the outer can 16, when an abnormality such as an external short circuit occurs and the temperature of the battery rises, the opening area of the mesh sheet 50 can be rapidly decreased.

[0037] The heat deflection temperature of the material constituting the mesh sheet 50 is, for example, 70°C or higher and 120°C or lower, more preferably 70°C or higher and 110°C or lower, and particularly preferably 80°C or higher and 110°C or lower, in a state where a load of 0.45 MPa is applied. If the heat deflection temperature of the material constituting the mesh sheet 50 is within this range, for example, when an abnormality occurs such that the battery exceeds a predetermined temperature, the electrical connection between the core body exposed portion 42 and the outer can 16 is rapidly inhibited or interrupted. The heat deflection temperature is measured by the method described in the examples below.

[0038] The volume resistivity of the material constituting the mesh sheet 50 is preferably 1.0×10 １２ Ω·cm or more at 25°C, more preferably 1.0×10 １３ Ω·cm or more, and particularly preferably 1.0×10 １５It is particularly preferable that it is Ω·cm or more. If the volume resistivity of the constituent material of the mesh sheet 50 is within this range, when an abnormality occurs in the battery, the electrical connection between the core body exposed portion 42 and the outer can 16 can be more effectively suppressed. The volume resistivity is measured by the method described in the examples below.

[0039] The mesh sheet 50 is mainly composed of a resin having the above physical properties, but may contain an inorganic filler or the like. The mesh sheet 50 may be made of the same resin as the winding tape 60, or may be made of a resin having a lower heat deflection temperature than the tape. The mesh sheet 50 is composed of, for example, a resin selected from polyolefins such as polyethylene (PE), polypropylene (PP), copolymers of ethylene and / or propylene and α-olefins, fluororesins such as polytetrafluoroethylene (PTFE), polyamides, or composite materials thereof. An example of a suitable resin constituting the mesh sheet 50 is a polyolefin, and among them, PE or PP is preferable.

[0040] The mesh sheet 50 preferably covers 50% or more of the outer peripheral surface 14s of the electrode body 14. In this case, the heat generation of the battery when an abnormality such as an external short circuit occurs can be more effectively suppressed. The coverage rate of the outer peripheral surface 14s by the mesh sheet 50 is preferably 60% or more, more preferably 65% or more, and particularly preferably 70% or more from the viewpoint of suppressing heat generation during an abnormality. Here, the coverage rate means the ratio of the area of the region covered by the mesh sheet 50 to the total area of the outer peripheral surface 14s, and the total area of the outer peripheral surface 14s includes the region covered by the winding tape 60.

[0041] The mesh sheet 50 and the winding tape 60 may be arranged so as not to overlap each other, and 60% or more, or 70% or more of the outer peripheral surface 14s may be covered by the mesh sheet 50 and the winding tape 60, or substantially the entire area of the outer peripheral surface 14s may be covered. The coverage rate of the outer peripheral surface 14s by the winding tape 60 is, for example, 10% or more and 30% or less. The coverage rate of the outer peripheral surface 14s by the mesh sheet 50 and the winding tape 60 is preferably 70% or more, more preferably 80% or more, and may be substantially 100%.

[0042] The thickness of the mesh sheet 50 is, for example, 10 μm or more and 250 μm or less, preferably 20 μm or more and 180 μm or less, more preferably 25 μm or more and 100 μm or less, and particularly preferably 30 μm or more and 70 μm or less. If the thickness is too small, it is difficult to close the through-hole 51 when an abnormality such as an external short circuit occurs, and the heat generation suppression effect tends to be small. If the thickness of the mesh sheet 50 is within the above range, it is possible to effectively suppress heat generation during the occurrence of an abnormality while suppressing a decrease in capacitance. The thickness of the mesh sheet 50 is measured by using a pin-type measuring head of a digital length measuring instrument (manufactured by NIKON Corporation, MH-15M) and reading it with a counter (manufactured by NIKON Corporation, TC-101A).

[0043] A suitable aperture ratio of the mesh sheet 50 varies somewhat depending on the size of the through-hole 51, the thickness of the sheet, etc., but is, for example, 1.0% or more and 50% or less, more preferably 1.5% or more and 40% or less, and particularly preferably 2.0% or more and 10% or less. If the aperture ratio is within the above range, it is possible to effectively suppress heat generation during the occurrence of an abnormality while suppressing an increase in the resistance (hereinafter referred to as "outer peripheral resistance") between the core body exposed portion 42 and the outer can 16 during normal use of the battery. The aperture ratio of the mesh sheet 50 means the ratio of the area of the through-hole 51 to the total area of the sheet.

[0044] The shape of the through-hole 51 may be circular or polygonal. Also, the shapes and sizes of the plurality of through-holes 51 may be different from each other, but in order to exhibit a stable function, it is preferable that the shapes and sizes of each through-hole 51 are the same. It is preferable that a large number of fine through-holes 51 are formed in the mesh sheet 50. In the present embodiment, through-holes 51 having a substantially square shape and the same size are uniformly formed throughout the sheet. The size of each through-hole 51 is 0.5 mm ２ or more and 15 mm ２ or less is preferable, 0.6 mm ２ or more and 10 mm ２ or less is more preferable, and 1.0 mm ２ or more and 5.0 mm ２ or less is particularly preferable.

[0045] The through-hole 51 is a hole that allows a clear view from front to back when the mesh sheet 50 is viewed from a direction parallel to the thickness direction of the sheet. Because the size of the through-hole 51 is small, it may not be visible to the naked eye, but the mesh sheet 50 can be confirmed to have a hole that penetrates straight through in the thickness direction of the sheet by, for example, microscopic observation. Note that the separator does not have through-holes like the through-hole 51. Therefore, for example, if a separator is placed in place of the resin layer of this disclosure, the positive or negative electrode placed on the outer circumferential surface of the electrode body will not come into contact with the inner surface of the outer can.

[0046] The minimum length of the through-hole 51 is, for example, 0.5 mm or more and 10 mm or less, preferably 1.0 mm or more and 4.0 mm or less. If the minimum length of the through-hole 51 is within this range, the increase in outer peripheral resistance during normal use of the battery can be suppressed while effectively suppressing heat generation in the event of an abnormality. The suitable minimum length varies slightly depending on the constituent material and thickness of the mesh sheet 50, but for example, in the case of a PE mesh sheet 50 with a thickness of 30 μm or more and 70 μm or less, it is 1.0 mm or more and 2.0 mm or less, or 1.0 mm or more and 1.5 mm or less. The minimum length refers to the minimum span of the through-hole 51 that passes through the center of the circumscribed circle of the through-hole 51. If the through-hole 51 is rectangular, the minimum length is the shortest distance between opposite sides, and if it is elliptical, the length of the minor axis is the minimum length.

[0047] The ratio of the thickness of the mesh sheet 50 to the minimum length of the through-hole 51 is, for example, 1:5 to 1:50, more preferably 1:10 to 1:40, and particularly preferably 1:10 to 1:20. If the ratio of thickness to minimum length is within this range, it is possible to suppress the increase in peripheral resistance during normal use of the battery while effectively suppressing heat generation in the event of an abnormality.

[0048] Furthermore, instead of the mesh sheet 50, a resin layer may be provided between the outer circumferential surface 14s of the electrode body 14 and the inner circumferential surface of the outer can 16, with through-holes formed in an arrangement, size, or shape that cannot be described as mesh-like. The physical properties of the resin layer, such as the temperature of deflection under load, thickness, and size of the through-holes, are preferably the same as those of the mesh sheet 50. The through-holes in the resin layer may be, for example, slit-shaped, wave-shaped, or dot-shaped.

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

[0050] <Example 1> [Preparation of the positive electrode] Lithium cobalt oxide was used as the positive electrode active material. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 98:1:1, and a positive electrode mixture slurry was prepared using N-methylpyrrolidone (NMP) as the dispersion medium. The slurry was applied to both sides of a long aluminum foil positive electrode core with a thickness of 15 μm, leaving an exposed core portion in the center along its length. The coating was dried and compressed to obtain a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode core. An aluminum positive electrode lead was ultrasonically welded to the exposed core portion.

[0051] [Fabrication of the negative electrode] Graphite was used as the negative electrode active material. The negative electrode active material, styrene-butadiene rubber (SBR) dispersion, and sodium carboxymethylcellulose (CMC-Na) were mixed in a solid content mass ratio of 98:1:1, and water was used as the dispersion medium to prepare a negative electrode mixture slurry. This slurry was applied to both sides of a long copper foil negative electrode core body with a thickness of 8 μm, leaving first and second core body exposed portions at both ends in the longitudinal direction. The coating film was dried and compressed to obtain a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode core body. A nickel negative electrode lead was ultrasonically welded to the first core body exposed portion.

[0052] [Electrode Body Fabrication] The positive electrode, the negative electrode, and a polyethylene separator were wound in a spiral shape, and a winding-stopping tape was attached to the outermost surface to obtain a wound-type electrode body. At this time, the negative electrode and the other components were wound so that the first exposed core portion to which the negative electrode lead was joined was located on the winding center side of the electrode body, and the second exposed core portion was located on the outermost surface of the winding structure. After forming the winding structure of the electrode body, the winding core was removed to obtain a wound-type electrode body with a hollow portion formed at the winding center. The outer surface of the electrode body formed by the second exposed core portion has a width (axial length of the electrode body) of 64 mm and a circumference of 80 mm. An adhesive tape with a width of 9 mm and a length of 60 mm was used as the winding-stopping tape. The winding-stopping tape was attached to both ends in the width direction with the length direction aligned with the circumferential direction of the outer surface.

[0053] [Preparation of Non-Aqueous Electrolyte] Mix ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:3 (at 25°C) to form a mixed solvent, and add LiPF4 to achieve a concentration of 1.5 mol / L. ６ A non-aqueous electrolyte was prepared by dissolving the substance.

[0054] [Fabrication of Cylindrical Battery] After placing insulating plates above and below the electrode body, the negative electrode lead was welded to the inner surface of the bottom of a bottomed cylindrical outer can, and the positive electrode lead was welded to the internal terminal plate of the sealing body, thereby housing the electrode body inside the outer can. At this time, a resin layer with multiple through holes was placed between the electrode body and the outer can so as to cover the outer surface of the electrode body. Subsequently, the non-aqueous electrolyte was injected into the outer can, and the opening of the outer can was sealed with a sealing body via a gasket to obtain a cylindrical battery.

[0055] The above resin layer has a minimum through-hole length of 1.0 mm, an aperture ratio of 2%, a thickness of 50 μm, a load deflection temperature (0.45 MPa) of 85°C, and a volume resistivity of 1 × 10⁻⁶. １６ A polyethylene (PE) mesh sheet with a density exceeding Ω·cm was used. The mesh sheet was positioned to cover the entire outer surface of the electrode body, including the area where the winding tape was attached. The outer surface of the electrode body (the exposed core of the negative electrode) was in contact with the inner surface of the outer container through the opening in the mesh sheet.

[0056] <Example 2> A cylindrical battery was manufactured in the same manner as in Example 1, except that a polyethylene mesh sheet A2 (with the same physical properties as mesh sheet A1) with a minimum through-hole length of 0.8 m and an opening ratio of 1% was used as the resin layer.

[0057] <Example 3> A cylindrical battery was manufactured in the same manner as in Example 1, except that a polyethylene mesh sheet A3 with an aperture ratio of 40% (other physical properties were the same as mesh sheet A1) was used as the resin layer.

[0058] <Example 4> A cylindrical battery was manufactured in the same manner as in Example 1, except that the mesh sheet A1 was arranged so that the coverage of the outer surface of the electrode body was 40%.

[0059] <Example 5> A cylindrical battery was manufactured in the same manner as in Example 1, except that the mesh sheet A1 was arranged so that the coverage of the outer surface of the electrode body was 70%.

[0060] <Example 6> A cylindrical battery was manufactured in the same manner as in Example 1, except that a polyethylene mesh sheet A6 (with the same physical properties as mesh sheet A1) with a minimum through-hole length of 2.0 m and an opening ratio of 5% was used as the resin layer.

[0061] <Example 7> A cylindrical battery was manufactured in the same manner as in Example 1, except that a polyethylene mesh sheet A7 with a thickness of 175 μm (other physical properties were the same as mesh sheet A1) was used as the resin layer.

[0062] <Example 8> A cylindrical battery was manufactured in the same manner as in Example 6, except that a polyethylene mesh sheet A8 with a thickness of 175 μm (other physical properties were the same as mesh sheet A6) was used as the resin layer.

[0063] <Example 9> The resin layer had a minimum through-hole length of 1.0 mm, an aperture ratio of 2%, a thickness of 175 μm, a load deflection temperature (0.45 MPa) of 120°C, and a volume resistivity of 1 × 10⁻⁶. １８ A cylindrical battery was fabricated in the same manner as in Example 1, except that a polyethylene terephthalate (PTFE) mesh sheet A9 with a resistance exceeding Ω·cm was used.

[0064] <Example 10> A cylindrical battery was manufactured in the same manner as in Example 9, except that a polyethylene terephthalate mesh sheet A10 (with the same physical properties as mesh sheet A9) was used as the resin layer, with a minimum through-hole length of 2.0 mm and an opening ratio of 5%.

[0065] <Example 11> The resin layer had a minimum through-hole length of 2.0 mm, an aperture ratio of 5%, a thickness of 250 μm, a load deflection temperature (0.45 MPa) of 105°C, and a volume resistivity of 1 × 10⁻⁶. １６ A cylindrical battery was fabricated in the same manner as in Example 9, except that a mesh sheet A11 made of polypropylene (PP) with a resistance exceeding Ω·cm was used.

[0066] <Example 12> A cylindrical battery was manufactured in the same manner as in Example 11, except that a polypropylene mesh sheet A12 (with the same physical properties as mesh sheet A11) with a minimum through-hole length of 3.0 mm and an opening ratio of 10% was used as the resin layer.

[0067] <Example 13> A cylindrical battery was manufactured in the same manner as in Example 11, except that a polypropylene mesh sheet A13 (with the same physical properties as mesh sheet A11) was used as the resin layer, with a minimum through-hole length of 8.0 mm and an opening ratio of 64%.

[0068] <Comparative Example 1> A cylindrical battery was manufactured in the same manner as in Example 1, except that a resin layer was not provided.

[0069] <Comparative Example 2> The resin layer had a thickness of 15 μm, a load deflection temperature (0.45 MPa) of 105°C, and a volume resistivity of 1 × 10⁻⁶. １６ A cylindrical battery was fabricated in the same manner as in Example 1, except that a polypropylene sheet with a capacitance exceeding Ω·cm and without through-holes that allow visibility from front to back was used. This polypropylene sheet is the same separator used in the Examples and Comparative Examples.

[0070] Discharge capacity, AC resistance, and external short-circuit tests were performed on each battery in the examples and comparative examples. The evaluation results are shown in Table 1.

[0071] [Measurement of Discharge Capacity] Each battery was charged at a constant current of 0.5C under a temperature of 25°C until the battery voltage reached 4.2V. Then, it was discharged at a constant current of 0.5C until the battery voltage reached 2.5V, and the discharge capacity at this time was determined. The capacity ratios shown in Table 1 are relative values ​​with the discharge capacity of the battery in Comparative Example 1 as the reference (±0%).

[0072] [Measurement of AC-IR Resistance] The cell was fixed to a fixing jig, and two terminals (HIOKI, pin-type leads 9772) electrically connected to a digital resistance meter (TSURUGA, MODEL 3566) were brought into contact with the top surface of the sealing body and the bottom of the outer casing, and the resistance value (Ω) was measured. This was taken as the actual resistance value. The resistance ratios shown in Table 1 are relative values ​​with the AC-IR of the battery of Comparative Example 1 as the reference (±0%).

[0073] [External Short Circuit Test] The batteries of each example and comparative example were charged with a constant current of 1500mA at 25°C until the battery voltage reached 4.2V. Then, at 60°C, the positive and negative terminals of each charged battery were short-circuited externally using a short-circuit resistor of 40mΩ. After 20 seconds, the circuit was shut off to resolve the short circuit. The temperature of the battery surface after the external short circuit was measured. The temperature differences shown in Table 1 are relative values ​​with the temperature of the outer casing surface of the battery of Comparative Example 1 as the reference (±0°C).

[0074]

[0075] As shown in Table 1, all of the cylindrical batteries in the examples can effectively suppress temperature rise during external short-circuit testing while ensuring low resistance during normal use. Compared to the battery of Comparative Example 1, which does not have a resin layer between the outer surface of the electrode body and the inner surface of the outer casing, the batteries in the examples show an increase in resistance, but compared to the battery of Comparative Example 2, which uses a resin layer without through holes, the increase in resistance is suppressed. Furthermore, the batteries in the examples show a significantly reduced temperature rise during external short-circuit testing compared to the battery of Comparative Example 1, exhibiting the same or even better temperature rise suppression effect as the battery of Comparative Example 2. Moreover, the capacity reduction due to the placement of the resin layer is small, and according to the configuration of the examples, it is possible to realize a battery with high capacity, excellent output characteristics, and the ability to effectively suppress heat generation in the event of an abnormality.

[0076] The resin layer used in the battery of the embodiment softens and deforms when the temperature rises due to an external short circuit, reducing the opening area of ​​the through-holes. As a result, the electrical connection between the exposed core of the negative electrode and the outer casing is inhibited or interrupted, suppressing the temperature rise of the battery. On the other hand, during normal use of the battery, electrical connection is ensured through the through-holes, so low resistance can be ensured and good output characteristics can be obtained. Furthermore, from the evaluation results shown in Table 1, it can be understood that the load deflection temperature of the resin layer, the coverage rate of the outer surface of the electrode body, the thickness, the opening ratio, and the size of the through-holes affect the AC resistance and the heat generation when an abnormality occurs. For example, if the thickness of the resin layer is reduced to the extent that the effect of suppressing heat generation when an abnormality occurs can be achieved, the resistance will decrease and the decrease in battery capacity will also be suppressed.

[0077] Furthermore, if the contact area between the outer surface of the electrode body and the inner surface of the outer casing becomes smaller, the resistance value increases. However, since the resistance value increases inversely proportionally to the contact area, for example, if the entire outer surface is covered with a resin layer that provides almost no contact area, the resistance value will increase sharply. On the other hand, if the opening area created by the through-hole is made too large, the heat generation suppression effect in the event of an abnormality will decrease. For this reason, for example, if the minimum length of the through-hole is 1.0 mm or more and 4.0 mm or less, or 1.0 mm or more and 2.0 mm or less, and the coverage rate of the outer surface by the resin layer including the through-hole is 60% or more, or 70% or more, then a higher level of balance between low resistance and heat generation suppression effect can be achieved.

[0078] Furthermore, as the battery's state of charge (SOC) increases, the volume of the electrode body increases, and the surface pressure acting from the electrode body on the inner surface of the outer casing increases. As a result, the contact area between the outer surface of the electrode body and the inner surface of the outer casing increases, and the effect of the resin layer's coverage of the outer surface becomes more pronounced at high SOC levels. In this embodiment, since current collection on the negative electrode side is ensured by the outer surface of the electrode body and the negative electrode lead, the total resistance of the battery is calculated using the following formula (R1 is the resistance of the positive electrode lead), and is not simply the sum of the negative electrode lead resistance R2 and the outer casing resistance R3. Total battery resistance = R1 + [(R2 × R3) / (R2 + R3)]

[0079] Note that the size of the outer casing is the same for the batteries in the examples and comparative examples. In the batteries of the examples and comparative example 2, the length of the electrodes was shortened and a smaller diameter electrode was created compared to the battery of comparative example 1, which did not have a resin layer, in order to fit the electrode body with the resin layer into the outer casing. The capacity decreases by the amount the electrode length is shortened. The batteries of Examples 1 to 6, in which the thickness of the resin layer is 30 μm or more and 70 μm or less, have only a slight decrease in battery capacity compared to the batteries of comparative examples 1 and 2, and the resistance ratio and / or temperature difference are improved.

[0080] This disclosure is further illustrated by the following embodiments. Configuration 1: A secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound with a separator between them, and an outer casing for housing the electrode body, wherein the positive electrode or the negative electrode is disposed on the outer circumferential surface of the electrode body and in contact with the inner surface of the outer casing, wherein a resin layer having a plurality of through holes is disposed between the outer circumferential surface of the electrode body and the inner surface of the outer casing, and the positive electrode or the negative electrode disposed on the outer circumferential surface contacts the inner surface of the outer casing through the through holes of the resin layer. Configuration 2: The secondary battery according to Configuration 1, wherein the outer casing has a bottomed cylindrical shape, the negative electrode has a negative electrode core, a negative electrode mixture layer disposed on the negative electrode core, and a core exposed portion on the outer circumferential surface of the electrode body in which the surface of the negative electrode core is exposed, and the core exposed portion is in contact with the inner surface of the outer casing through the through holes of the resin layer. Configuration 3: The secondary battery according to Configuration 1 or 2, wherein the resin layer covers 50% or more of the outer surface of the electrode body. Configuration 4: The secondary battery according to any one of Configurations 1 to 3, wherein the load deflection temperature of the material constituting the resin layer is 70°C or more and less than 110°C when a load of 0.45 MPa is applied. Configuration 5: The secondary battery according to any one of Configurations 1 to 4, wherein the thickness of the resin layer is 20 μm or more and 180 μm or less. Configuration 6: The secondary battery according to any one of Configurations 1 to 5, wherein a winding tape is attached to the outer surface of the electrode body, and the resin layer covers the area of ​​the outer surface that does not overlap with the winding tape. Configuration 7: The secondary battery according to any one of Configurations 1 to 6, wherein the minimum length of the through-hole in the resin layer is 1.0 mm or more and 4.0 mm or less. Configuration 8: The secondary battery according to Configuration 7, wherein the ratio of the thickness of the resin layer to the minimum length of the through-hole is 1:10 to 1:40. Configuration 9: The volume resistivity of the material constituting the resin layer is 1.0 × 10 at 25°C. １２ A secondary battery according to any one of configurations 1 to 8, having a resistance of Ω·cm or more. Configuration 10: A secondary battery according to any one of configurations 1 to 9, wherein the resin layer is made of polyolefin.

[0081] 10 Cylindrical battery, 11 Positive electrode, 12 Negative electrode, 12x End of winding, 13 Separator, 14 Electrode body, 14s Outer surface, 16 Outer can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode core body, 31 Positive electrode mixture layer, 40 Negative electrode core body, 41 Negative electrode mixture layer, 42 Core body exposed section, 50 Mesh sheet, 51 Through hole, 60 Winding stopper tape

Claims

1. A secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound with a separator between them, and an outer casing for housing the electrode body, wherein the positive electrode or the negative electrode is positioned on the outer circumferential surface of the electrode body and in contact with the inner surface of the outer casing, wherein a resin layer having a plurality of through holes is disposed between the outer circumferential surface of the electrode body and the inner surface of the outer casing, and the positive electrode or the negative electrode positioned on the outer circumferential surface contacts the inner surface of the outer casing through the through holes in the resin layer.

2. The secondary battery according to claim 1, wherein the negative electrode comprises a negative electrode core, a negative electrode mixture layer disposed on the negative electrode core, and a core exposed portion on the outer circumferential surface of the electrode body in which the surface of the negative electrode core is exposed, and the core exposed portion is in contact with the inner surface of the outer casing through the through-holes in the resin layer.

3. The secondary battery according to claim 1 or 2, wherein the resin layer covers 50% or more of the outer surface of the electrode body.

4. The secondary battery according to claim 1 or 2, wherein the load deflection temperature of the material constituting the resin layer is 70°C or more and less than 110°C when a load of 0.45 MPa is applied.

5. The secondary battery according to claim 1 or 2, wherein the thickness of the resin layer is 20 μm or more and 180 μm or less.

6. The secondary battery according to claim 1 or 2, wherein a winding tape is attached to the outer circumferential surface of the electrode body, and the resin layer covers the area of ​​the outer circumferential surface that does not overlap with the winding tape.

7. The secondary battery according to claim 1 or 2, wherein the minimum length of the through-hole in the resin layer is 1.0 mm or more and 4.0 mm or less.

8. The secondary battery according to claim 7, wherein the ratio of the thickness of the resin layer to the minimum length of the through hole is 1:10 to 1:

40.

9. The volume resistivity of the material constituting the resin layer is 1.0 × 10⁻⁶ at 25°C. １２ A secondary battery according to claim 1 or 2, wherein the value is Ω·cm or greater.

10. The secondary battery according to claim 1 or 2, wherein the resin layer is made of polyolefin.

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