Cylindrical battery

Abstract

In this cylindrical battery, if a portion of a winding outer surface of a negative electrode (12) that extends toward the winding start side from a position (A1) facing a positive electrode starting end (40) with a separator (13) being interposed therebetween in the radial direction of an electrode body (14) is defined as a first surface (S1) and a portion of a winding inner surface of the negative electrode (12) that extends toward the winding start side from a position (A2) facing the positive electrode starting end (40) with the separator (13) being interposed therebetween in the radial direction is defined as a second surface (S2), a tape (50) is affixed to the first surface (S1) or the second surface (S2). The winding end (E1) of the tape (50) is disposed on a negative electrode mixture layer (12b) at a position which is away from the facing position (A1) toward the winding start side by 0.5 turns or less. The thickness of the tape (50) is 50% to 100% inclusive of the thickness of a flat part of the portion where positive electrode mixture layers (11b) are formed on both surfaces of a positive electrode (11).

Description

Cylindrical battery

[0001] The present disclosure relates to a cylindrical battery.

[0002] Conventionally, as a cylindrical battery, there is one described in Patent Document 1. This cylindrical battery includes an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween. In this cylindrical battery, on the negative electrode, a negative electrode lead is attached to a portion wound in a state of not facing the positive electrode through the separator for one or more turns from the inner end in the winding direction, and an insulating tape is attached to the negative electrode core so as to cover the surface of the negative electrode lead. Thereby, deformation of the electrode plate accompanying the charge-discharge cycle in the electrode body is suppressed.

[0003] International Publication No. 2018 / 180748

[0004] The inventor of the present invention has found that when the cylindrical battery is charged and discharged, the gap between the negative electrodes near the starting end of the positive electrode in the electrode body becomes small, and there is a possibility that the voltage drops due to the separator interposed in the gap being pressed from near the center in the width direction of the starting end of the positive electrode. Therefore, an object of the present disclosure is to provide a cylindrical battery capable of suppressing a voltage drop accompanying charge and discharge.

[0005] The first cylindrical battery according to the present disclosure includes an electrode body in which a strip-shaped positive electrode having a positive electrode core and a positive electrode mixture layer and a strip-shaped negative electrode having a negative electrode core and a negative electrode mixture layer are wound with a separator interposed therebetween, a bottomed cylindrical outer can for housing the electrode body, and a sealing body for closing the opening of the outer can. Among the outer winding surfaces of the negative electrode, when a portion extending from the facing position in the radial direction of the electrode body with respect to the starting end of the positive electrode on the starting side of winding to the starting side is defined as the first surface, and a portion extending from the facing position in the radial direction of the electrode body with respect to the starting end of the positive electrode on the starting side of winding to the starting side among the inner winding surfaces of the negative electrode is defined as the second surface, a tape is attached to the first surface or the second surface, and the end of winding of the tape is disposed on the negative electrode mixture layer at a position separated from the facing position in the negative electrode by 0.5 turns or less to the starting side, and the thickness of the tape is 50% or more and 100% or less of the thickness of the flat portion of the portion where the positive electrode mixture layers are formed on both surfaces of the positive electrode.

[0006] The second cylindrical battery according to this disclosure comprises an electrode body in which a strip-shaped positive electrode having a positive electrode core and a positive electrode mixture layer, and a strip-shaped negative electrode having a negative electrode core and a negative electrode mixture layer are wound via a separator, a bottomed cylindrical outer casing for housing the electrode body, and a sealing body for closing the opening of the outer casing, wherein the portion of the outer surface of the negative electrode winding that extends from the position facing the positive electrode start end radially across the separator toward the winding start side is defined as the first surface, and the inner surface of the negative electrode winding that extends from the position facing the positive electrode start end radially across the separator toward the winding start side When the portion extending towards the starting side is considered the second surface, the first tape is attached to the first surface and the second tape is attached to the second surface. The first and second tapes have overlapping regions that overlap each other radially in the electrode body via a separator. The end of the winding of the overlapping region is positioned on the negative electrode mixture layer at a distance of 0.5 turns or less from the positive electrode starting end toward the winding starting side. The total thickness of the first and second tapes in the overlapping region is 50% to 100% of the thickness of the flat portion where the positive electrode mixture layer is formed on both sides of the positive electrode.

[0007] According to the cylindrical battery described herein, the reduction in the gap between the negative electrodes near the positive electrode starting point during charging and discharging can be suppressed by using a tape that fills the gap between the negative electrodes. As a result, stress concentration from the positive electrode starting point to the separator is alleviated, and the voltage drop associated with charging and discharging is suppressed.

[0008] This is a cross-sectional view of a cylindrical battery according to an embodiment of the present disclosure, along the axial direction. In this embodiment, this is a cross-sectional view perpendicular to the winding axis direction of the electrode body, showing the vicinity of the positive electrode starting end. This is a schematic cross-sectional view showing the positive electrode starting end, which is the end of the positive electrode that is the winding start side, and the end of the negative electrode that is located on the winding side of the positive electrode starting end, unfolded in the longitudinal direction. This is a diagram corresponding to Figure 2 in another embodiment of the cylindrical battery. In another embodiment, this is a schematic cross-sectional view showing the positive electrode starting end and the portion of the negative electrode located on the winding side of the positive electrode starting end, unfolded in the longitudinal direction. This is a diagram corresponding to Figure 2 in another embodiment of the cylindrical battery. In another embodiment, this is a schematic cross-sectional view showing the positive electrode starting end and the portions of the negative electrode located on the winding side and the winding side of the positive electrode starting end, unfolded in the longitudinal direction. This is a diagram corresponding to Figure 7 in another embodiment.

[0009] Hereinafter, embodiments of the cylindrical battery according to this disclosure will be described in detail with reference to the drawings. The cylindrical battery of this disclosure may be a primary battery or a secondary battery. It may also be a battery using an aqueous electrolyte or a battery using a non-aqueous electrolyte. In the following, a non-aqueous electrolyte secondary battery (lithium-ion battery) using a non-aqueous electrolyte will be given as an example of a cylindrical battery 10, which is one embodiment, but the cylindrical battery of this disclosure is not limited to this, and the electrolyte may also be an aqueous electrolyte.

[0010] It is intended from the outset that new embodiments can be constructed by appropriately combining the characteristic features of the embodiments and modifications described below. In the following embodiments, the same reference numerals are used for the same components in the drawings, and redundant explanations are omitted. In addition, multiple drawings include schematic diagrams, and the dimensional ratios such as length, width, and height of each component do not necessarily match between different drawings. In this specification, the side of the cylindrical battery 10 with the sealing body 17 in the axial direction (height direction) is referred to as "upper," and the side of the outer casing 16 with the bottom 31 in the axial direction is referred to as "lower." Furthermore, among the components described below, components that are not described in the independent claim indicating the highest-level concept are optional components and are not essential components.

[0011] Figure 1 is a cross-sectional view along the axial direction of a cylindrical battery 10 according to one embodiment of the present disclosure. As shown in Figure 1, the cylindrical battery 10 comprises an electrode body 14, a bottomed cylindrical outer casing 16 that houses the electrode body 14, and a sealing body 17 that closes the opening of the outer casing 16. The outer casing 16 houses a non-aqueous electrolyte together with the electrode body 14. The outer casing 16 has a shoulder portion 29 at its upper end that is bent radially inward and extends inward. The outer casing 16 has a grooved portion 22 formed in the cylindrical portion 39, and the sealing body 17 is supported by the grooved portion 22 and closes the opening of the outer casing 16.

[0012] The cylindrical battery 10 further includes a gasket 28 interposed between the outer casing 16 and the sealing body 17. The gasket 28 is a ring-shaped resin member attached to the outer circumference of the sealing body 17, and insulates the sealing body 17 from the outer casing 16. The gasket 28 seals the gap between the outer casing 16 and the sealing body 17, thereby sealing the inside of the battery. The gasket 28 is made of, for example, polyolefin.

[0013] The non-aqueous electrolyte has ionic conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte (non-aqueous electrolyte solution), but may also be a solid electrolyte using a gel-like polymer or the like. The cylindrical battery 10 is preferably a lithium-ion battery. The electrolyte salt may be, for example, LiBF ４ LiPF ６ Lithium salts such as the above are used. Non-aqueous solvents include, for example, esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propionate (MP), as well as ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may contain halogen-substituted products in which at least some of the hydrogen atoms of these solvents are replaced with halogen atoms such as fluorine.

[0014] Examples of halogen-substituted compounds include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated linear carbonates, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP). In terms of suppressing the deterioration of the charge-discharge cycle characteristics of non-aqueous electrolyte secondary batteries or improving the input characteristics, the non-aqueous electrolyte preferably contains 5% by mass or more of FEC relative to the mass of the non-aqueous electrolyte, and more preferably contains 5% to 15% by mass of FEC.

[0015] As solid electrolytes, for example, solid or gel-like polymer electrolytes, inorganic solid electrolytes, etc., are used. Polymer electrolytes include, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As matrix polymers, for example, polymer materials that absorb non-aqueous solvents and gel are used. As polymer materials, for example, fluororesins, acrylic resins, polyether resins, etc., are used. As inorganic solid electrolytes, for example, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0016] The electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape via the separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all elongated strip-shaped bodies, and are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed to be slightly larger in dimensions than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the longitudinal and width directions than the positive electrode 11. The separator 13 is formed to be at least slightly larger in dimensions than the positive electrode 11, and for example, two separators are arranged so as to sandwich the positive electrode 11.

[0017] The electrode body 14 is connected to a positive electrode lead 20 and two negative electrode leads 21a and 21b. The positive electrode lead 20 electrically connects the positive electrode 11 to the sealing body 17. The first negative electrode lead 21a is joined to the beginning end of the negative electrode 12, electrically connecting this beginning end to the bottom 31 of the outer container 16. The second negative electrode lead 21b is joined to the end of the negative electrode 12, electrically connecting this end to the bottom 31 of the outer container 16.

[0018] In the example shown in Figure 1, the positive electrode lead 20 extends through the opening in the upper insulating plate 18 toward the sealing body 17 and is joined to the lower surface of the sealing body 17. The first negative electrode lead 21a is bent toward the hollow portion 14d of the electrode body 14 through a through hole in the annular lower insulating plate 19. The second negative electrode lead 21b is bent so as to overlap the first negative electrode lead 21a, passing outside the lower insulating plate 19. The overlapping portion of the first negative electrode lead 21a and the second negative electrode lead 21b is resistance welded using a welding rod inserted through the hollow portion 14d of the electrode body 14 and joined to the inner surface of the bottom 31 of the outer can 16.

[0019] When the negative electrode leads 21a and 21b are joined to both ends of the negative electrode 12 in the longitudinal direction, the current collection path of the negative electrode 12 is shortened, thereby reducing the internal resistance of the cylindrical battery 10. Alternatively, the negative electrode leads may be joined only to the end of the negative electrode on the winding end side in the longitudinal direction. Or, the negative electrode leads may be joined only to the end of the negative electrode on the winding start side in the longitudinal direction, and the outermost core exposed portion of the negative electrode core, located at least a part of the outermost circumference of the electrode body, may be in contact with the inner surface of the outer casing 16.

[0020] Figure 2 is a cross-sectional view perpendicular to the winding axis direction of the electrode body, showing the vicinity of the positive electrode start end 40. Figure 3 is a schematic cross-sectional view showing the positive electrode start end, which is the end of the positive electrode 11 on the winding start side, and the end of the negative electrode 12 on the winding start side, located on the winding side of the positive electrode start end, unfolded in the longitudinal direction. Note that the positive electrode start end 40 is the tip of the positive electrode 11 on the winding start side, and the positive electrode start end is the region including the positive electrode start end and its vicinity. In Figures 2 and 3, the cross-section of the positive electrode 11 is shown by the part where the diagonal lines overlap the sandy area. In Figure 2, the separator 13 is shown by a dashed line. In Figure 3, the separator 13 is not shown.

[0021] As shown in Figures 2 and 3, the positive electrode 11 has a positive electrode core 11a and a positive electrode mixture layer 11b formed on both sides of the positive electrode core 11a. The positive electrode core 11a can be made of a metal foil that is stable in the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. The positive electrode mixture layer 11b contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF). For example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, etc., can be used as the positive electrode active material. The positive electrode lead 20 is connected to the positive electrode 11, but it is preferable that it is directly joined to the positive electrode core 11a by ultrasonic welding or the like, and it is preferable that the joint portion with respect to the positive electrode core 11a is covered with insulating tape.

[0022] The negative electrode 12 comprises a negative electrode core 12a and a negative electrode mixture layer 12b formed on both sides of the negative electrode core 12a. The negative electrode core 12a 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 arranged on its surface. The negative electrode mixture layer 12b contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR) or PVdF. For example, graphite or a silicon-containing compound can be used as the negative electrode active material. The negative electrode leads 21a and 21b are preferably directly joined to the negative electrode core 12a by ultrasonic welding or the like, and the joint portion with respect to the negative electrode core 12a is preferably covered with insulating tape. For example, in Figure 3, the first negative electrode lead 21a is joined to the end of the negative electrode 12 on the winding start side, and the joint portion of the first negative electrode lead 21a with respect to the negative electrode core 12a is covered with insulating tape 15.

[0023] In the negative electrode 12, the negative electrode mixture layer 12b formed on at least one side of the negative electrode core 12a has an extended portion 38 that extends from a radially opposing position A1 of the electrode body 14 via a separator 13 with respect to the winding side of the positive electrode start end 40 toward the winding start side of the electrode body 14. The extended portion 38 extends toward the winding start side for, for example, 1 / 5 of a turn or more, preferably 1 / 2 of a turn or more, and more preferably 1 turn or more. When this extended portion 38 is wound toward the winding start side of the electrode body 14 for a predetermined length or more, for example 1 / 2 of a turn or more, from the position A1 opposing the positive electrode start end 40 toward the winding start side of the electrode body 14, it becomes easier to maintain the shape of the hollow portion 14d, which is a cylindrical space formed in the winding core of the electrode body 14.

[0024] Referring to Figure 1, the outer can 16 is generally made of a metal mainly composed of iron, for example, iron plated with nickel, but it may also be made of a metal mainly composed of aluminum or the like. The outer can 16 has a cylindrical portion 39 and a bottom portion 31, and the cylindrical portion 39 includes an annular grooved portion 22 and an annular shoulder portion 29. The grooved portion 22 is formed by spinning a part of the cylindrical portion 39 to create a recess on the radially inward side. The shoulder portion 29 is formed when the upper end (one end in the axial direction) of the cylindrical portion 39 is bent radially inward and crimped to the peripheral edge 33 of the sealing body 17, and extends radially inward at the upper end of the cylindrical portion 39.

[0025] The sealing body 17 is fixed to the outer can 16 by crimping, with a gasket 28 between the shoulder portion 29 and the grooved portion 22. The grooved portion 22 is formed at a predetermined distance from the upper end of the outer can 16. The predetermined length is, for example, 1 to 20% of the winding axial length of the outer can 16.

[0026] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating plate 25, an upper valve body 26, and a sealing plate 27 are stacked in this 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 plate 25 is electrically connected to one another. The sealing plate 27 has a convex shape with its radial center portion protruding outward. The convex portion 27a of the sealing plate 27 includes an annularly formed inclined portion and a flat top portion surrounded by the inclined portion. One or more ventilation holes 27b are formed in the top portion.

[0027] The lower valve body 24, the insulating plate 25, and the upper valve body 26 constitute a current interruption mechanism. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, with the insulating plate 25 interposed between their respective peripheries. When an abnormality occurs in the cylindrical battery 10 and the internal pressure rises to a predetermined value, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the sealing plate 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further and reaches a predetermined value, the upper valve body 26 ruptures, and gas is discharged from the vent hole 27b of the sealing plate 27.

[0028] In this embodiment, the positive lead 20 is connected to the lower surface of the internal terminal plate 23 by laser welding or ultrasonic welding, and the sealing plate 27, which is the top plate of the sealing body 17 electrically connected to the internal terminal plate 23, becomes the positive terminal. The outer casing 16 to which the negative leads 21a and 21b are joined becomes the negative terminal.

[0029] In this embodiment, in order to suppress the voltage drop associated with the charging and discharging of the cylindrical battery 10, insulating tape 50 is attached to the outer surface of the negative electrode 12 such that the end of the winding is positioned slightly away from the positive electrode start end 40 towards the winding start side on the outer surface of the negative electrode 12.

[0030] Specifically, the portion of the outer surface of the negative electrode 12 that extends from the position A1 facing the inner side of the positive electrode start end 40 via the separator 13 in the radial direction of the electrode body 14 toward the winding start side is defined as the first surface S1. The portion of the inner surface of the negative electrode 12 that extends from the position A2 facing the outer side of the positive electrode start end 40 via the separator 13 in the radial direction of the electrode body 14 toward the winding start side is defined as the second surface S2. In this example, an insulating tape 50 is attached only to the first surface S1, with the winding end E1 positioned at a position slightly away from the positive electrode start end 40, specifically at a position 0.5 turns or less away from the opposing position A1 on the negative electrode 12 toward the winding start side.

[0031] The insulating tape 50 is an adhesive tape having a base layer and an adhesive layer formed on the side of the base layer that adheres to the negative electrode 12. A heat-resistant layer containing inorganic particles such as metal oxides can be provided between the base layer and the adhesive layer. The base layer can be any insulating resin, such as PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PI (polyimide), PP (polypropylene), PET (polyethylene terephthalate), PBT (polybutylene terephthalate), etc. A conductive adhesive tape may be used instead of the insulating tape.

[0032] The adhesive layer may contain at least one of a rubber-based polymer or an acrylic-based polymer. The adhesive layer may further contain, for example, a silicone-based polymer.

[0033] The insulating tape 50 only needs to be attached to at least a portion of the width direction of the negative electrode 12, which coincides with the winding axis direction of the first surface S1 of the negative electrode 12, but it is preferable that it is attached so as to include the center of the negative electrode in the width direction. Furthermore, it is preferable that the length of the insulating tape in the width direction of the negative electrode is at least 1 / 3 of the total length in the width direction of the negative electrode and at or below the total length in the width direction.

[0034] The winding end E1 of the insulating tape 50 is located on the negative electrode mixture layer 12b at a distance of 0.5 turns or less from the radially opposing position A1 of the electrode body 14 with respect to the positive electrode start end 40, towards the winding start side. Therefore, the distance La in the winding direction between the winding end E1 and the positive electrode start end 40 is 0.5 turns or less in circumference.

[0035] The thickness T2 of the insulating tape 50 (Figure 3) is 50% to 100% of the thickness T1 (Figure 3) of the flat portion 11c in the area where the positive electrode mixture layer 11b is formed on both sides of the positive electrode 11. The flat portion 11c is the part that has no irregularities or inclined surfaces on both sides in the thickness direction and has a uniform thickness.

[0036] During charging and discharging of the cylindrical battery 10, the electrode body 14 tends to bulge near the center in the winding axis direction compared to the ends in the winding axis direction, and the pressure tends to be higher near the center in the winding axis direction. In this embodiment, the insulating tape 50 can suppress deformation of the negative electrode 12 and reduction of the gap between the negative electrodes 12 near the positive electrode start end 40 during charging and discharging of the cylindrical battery 10. This is because the insulating tape 50 is positioned to fill the gap between the first surface S1 and the second surface S2 of the negative electrode 12 without going through the positive electrode 11, on the winding start side from the positive electrode start end 40. This reduces stress concentration from the positive electrode start end 40 to the separator 13. Therefore, the cylindrical battery 10 suppresses voltage drop associated with charging and discharging.

[0037] The winding length Lb of the tape 50 is preferably 0.1 turns or more and 1.0 turn or less. If the winding length Lb is less than 0.1 turns, the effect of relieving the stress concentration described above will be small. On the other hand, if the winding length Lb is 1.0 turn or more, the tightening force by the tape 50 on the inner circumference side of the electrode body 14 tends to increase. Preferably, the winding length of the portion of the tape 50 located on the negative electrode mixture layer 12b is 0.1 turns or more.

[0038] Next, the experimental results obtained by the inventors of the present invention to confirm the effects of the embodiments will be described. The experiments were conducted using 12 types of cylindrical batteries, including the cylindrical batteries of Comparative Examples 1 to 9 and the cylindrical batteries of Examples 1 to 3. It should be noted that this disclosure is not limited to the following embodiments.

[0039] <Example 1> [Fabrication of the positive electrode] As the positive electrode active material, LiNi ０．８８ Co ０．０９ Al ０．０３ O ２Lithium nickel cobalt aluminum oxide represented by was used. 100 parts by mass of the positive electrode active material, 1 part by mass of acetylene black (AB), and 0.9 part by mass of polyvinylidene fluoride (PVdF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode binder slurry. Next, the positive electrode binder slurry was applied to both sides of a strip-shaped positive electrode core made of aluminum foil with a thickness of 15 μm so that core exposed portions were formed. After drying this coating film at a temperature of 100 to 150°C in a dryer to remove NMP, it was rolled by a roll press machine. Then, it was cut into a predetermined electrode plate size to produce a positive electrode 11 having positive electrode binder layers 11b formed on both sides of the positive electrode core 11a. The positive electrode 11 had a thickness of 180 μm. Then, a positive electrode lead 20 made of aluminum was welded to the core exposed portion.

[0040] [Fabrication of Negative Electrode] After mixing 95 parts by mass of graphite powder and 5 parts by mass of silicon oxide (SiO), 1 part by mass of sodium carboxymethyl cellulose (CMC-Na) and 1 part by mass of styrene-butadiene rubber (SBR) were mixed, and an appropriate amount of water was added to prepare a negative electrode binder slurry. Next, the negative electrode binder slurry was applied to both sides of a strip-shaped negative electrode core made of copper foil with a thickness of 8 μm, dried, and then rolled using a roller. Then, it was cut into a predetermined electrode plate size to produce a negative electrode 12 having negative electrode binder layers 12b formed on both sides of the negative electrode core 12a. The negative electrode 12 had a thickness of 202 μm. Then, core exposed portions where the binder layer was not present and the surface of the negative electrode core was exposed were provided at the starting end and the ending end of the winding side of the negative electrode 12, and nickel negative electrode leads 21a and 21b were welded to the core exposed portions.

[0041] Also, an insulating tape 50 was adhered to a first surface S1, which is a portion extending from the positive electrode starting end 40 to the starting side of the winding, among the outer winding surfaces of the negative electrode 12. At this time, the thickness of the insulating tape 50 was set to 90 μm. For this reason, the thickness of the insulating tape 50 is 50% of the thickness (180 μm) of the flat portion 11c of the portion where the positive electrode binder layers 11b are formed on both sides of the positive electrode 11.

[0042] [Preparation of Non-aqueous Electrolyte] 100 parts by mass of a mixed solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 1:3 was added with 5 parts by mass of vinylene carbonate (VC), and lithium hexafluorophosphate (LiPF ６ 6) was dissolved at a concentration of 1.5 mol / liter to prepare a non-aqueous electrolyte.

[0043] [Preparation of Sealing Body] As shown in FIG. 1, an internal terminal plate 23, a lower valve body 24, an insulating plate 25, an upper valve body 26, and a sealing plate 27 were laminated in the vertical direction, and the contact portions of the internal terminal plate, the lower valve body 24, the upper valve body 26, and the sealing plate 27 were joined to each other by welding to prepare a sealing body 17.

[0044] [Preparation of Secondary Battery] A wound electrode body 14 was prepared by winding a positive electrode 11 and a negative electrode 12 in a spiral shape through a separator 13 made of a microporous polyethylene film. Insulating plates were respectively arranged above and below the electrode body 14, and the electrode body 14 was housed in an exterior can 16. Negative electrode leads 21a and 21b were welded to the bottom of the bottomed cylindrical exterior can 16, and a positive electrode lead 20 was welded to the lower side surface of the internal terminal plate 23 of the sealing body 17, respectively. After injecting a non-aqueous electrolyte into the exterior can 16, the opening of the exterior can 16 was sealed with the sealing body 17 through a gasket 28 to prepare the cylindrical battery 10 of Example 1. At this time, in the electrode body 14, the distance in the winding direction between the winding end E1 of the insulating tape 50 and the positive electrode starting end 40 was 0.10 turns in terms of the circumference. Also, the diameter of the hollow portion 14d of the electrode body 14 was 4 mm.

[0045] <Example 2> A secondary battery was prepared in the same manner as in Example 1, except that the distance in the winding direction between the winding end E1 of the insulating tape 50 adhered to the first surface S1 of the negative electrode 12 and the positive electrode starting end 40 in the electrode body was 0.25 turns in terms of the circumference.

[0046] <Example 3> A secondary battery was prepared in the same manner as in Example 1, except that the distance in the winding direction between the winding end E1 of the insulating tape 50 adhered to the first surface S1 of the negative electrode 12 and the positive electrode starting end 40 in the electrode body was 0.40 turns in terms of the circumference.

[0047] <Comparative Example 1> A secondary battery was manufactured in the same manner as in Example 1, except that the thickness of the insulating tape attached to the first surface of the negative electrode in the electrode body was 30 μm. The thickness of the insulating tape in Comparative Example 1 is 17% of the thickness of the flat portion (180 μm) of the positive electrode where the positive electrode mixture layer is formed on both sides.

[0048] <Comparative Example 2> A secondary battery was manufactured in the same manner as in Comparative Example 1, except that the distance in the winding direction between the end of the insulating tape winding and the start of the positive electrode in the electrode body was set to 0.25 turns in circumference.

[0049] <Comparative Example 3> A secondary battery was manufactured in the same manner as in Comparative Example 1, except that the distance in the winding direction between the end of the insulating tape winding and the start of the positive electrode in the electrode body was set to 0.40 turns in circumference.

[0050] <Comparative Example 4> A secondary battery was manufactured in the same manner as in Comparative Example 1, except that the distance in the winding direction between the end of the insulating tape winding and the start of the positive electrode in the electrode body was set to 0.60 turns in circumference.

[0051] <Comparative Example 5> A secondary battery was manufactured in the same manner as in Example 1, except that the thickness of the insulating tape attached to the first surface of the negative electrode in the electrode body was 60 μm. The thickness of the insulating tape in Comparative Example 5 is 33% of the thickness of the flat portion (180 μm) of the part where the positive electrode mixture layer is formed on both sides of the positive electrode.

[0052] <Comparative Example 6> A secondary battery was manufactured in the same manner as in Comparative Example 5, except that the distance in the winding direction between the end of the insulating tape winding and the start of the positive electrode in the electrode body was set to 0.25 turns in circumference.

[0053] <Comparative Example 7> A secondary battery was manufactured in the same manner as in Comparative Example 5, except that the distance in the winding direction between the end of the insulating tape and the start of the positive electrode in the electrode body was set to 0.40 turns in circumference.

[0054] <Comparative Example 8> A secondary battery was manufactured in the same manner as in Comparative Example 5, except that the distance in the winding direction between the end of the insulating tape winding and the start of the positive electrode in the electrode body was set to 0.60 turns in circumference.

[0055] <Comparative Example 9> A secondary battery was manufactured in the same manner as in Example 1, except that the distance in the winding direction between the end of the insulating tape attached to the first surface of the negative electrode and the start end of the positive electrode was set to 0.60 turns in circumference.

[0056] [Evaluation of Deformation of the Negative Electrode] (Evaluation Method) For each prepared battery, constant current charging at 0.3C was performed in a 45°C environment until the voltage reached 4.2V, and then constant voltage charging at 4.2V until the current value reached 0.02C. After that, discharge was performed at a constant current of 0.5C until the battery voltage reached 2.85V. One charge-discharge cycle was performed in this manner. Subsequently, for the secondary batteries, cross-sectional observation was performed using an X-ray CT apparatus at a cross section perpendicular to the winding axis direction of the electrode body to check for deformation of the negative electrode near the positive electrode start end. The results of the check are shown in Table 1.

[0057]

[0058] As shown in Table 1, in Comparative Examples 1 to 8, deformation occurred in the negative electrode regardless of the change in the distance in the winding direction between the end of the insulating tape and the start of the positive electrode. This is thought to be because the thickness of the insulating tape was less than 50% of the thickness of the flat portion where the positive electrode mixture layer was formed, so the gap between the negative electrodes near the start of the positive electrode was not sufficiently filled by the insulating tape. Thus, in Comparative Examples 1 to 8, deformation of the negative electrode near the start of the positive electrode occurs, and the gap between the negative electrodes near the start of the positive electrode becomes smaller, which is thought to cause a voltage drop due to stress concentration from the start of the positive electrode to the separator.

[0059] Furthermore, in Comparative Example 9, although the thickness of the insulating tape was 50% of the thickness of the flat portion where the positive electrode mixture layer was formed, deformation occurred in the opposing portions of the positive and negative electrodes. This is thought to be because the distance between the starting end of the positive electrode and the end of the insulating tape was 0.60 turns in circumference, so the gap between the negative electrodes near the starting end of the positive electrode was not sufficiently filled by the insulating tape. Therefore, similar to Comparative Examples 1 to 8, in Comparative Example 9 as well, the gap between the negative electrodes near the starting end of the positive electrode becomes smaller, which is thought to cause a voltage drop due to stress concentration from the starting end of the positive electrode to the separator.

[0060] On the other hand, according to Examples 1 to 3, no deformation of the negative electrode 12 occurred near the positive electrode start end 40. This is because the thickness of the insulating tape 50 was 50% or more of the thickness of the flat portion 11c where the positive electrode mixture layer 11b was formed, and the distance between the positive electrode start end 40 and the end of the insulating tape 50 was 0.50 turns or less in circumference. Therefore, it is thought that the gap between the negative electrodes 12 near the positive electrode start end 40 was sufficiently filled with the insulating tape 50. Thus, according to Examples 1 to 3, stress concentration from the positive electrode start end 40 to the separator 13 is reduced, and therefore, voltage drop is suppressed.

[0061] [Another Embodiment] Figure 4 is a diagram corresponding to Figure 2 in a cylindrical battery of another embodiment. Figure 5 is a schematic cross-sectional view in the other embodiment showing the positive electrode starting end and the portion of the negative electrode 12 located on the outer side of the winding of the positive electrode starting end, unfolded in the longitudinal direction.

[0062] In this example, of the two surfaces S1 and S2 of the negative electrode 12 constituting the electrode body 14a, an insulating tape 51 is attached only to the second surface S2, at a position close to the positive electrode start end 40. Specifically, the end of the tape is positioned on the negative electrode mixture layer 12a at a distance of 0.5 turns or less toward the winding start side from the radially opposing position A2 of the electrode body 14a with respect to the positive electrode start end 40 on the second surface S2. Therefore, the distance Lc in the winding direction between the end of the tape and the positive electrode start end 40 is 0.5 turns or less in circumference.

[0063] Furthermore, the thickness T3 (Figure 5) of the insulating tape 51 is 50% to 100% of the thickness T1 (Figure 5) of the flat portion 11c where the positive electrode mixture layer 11b is formed on both sides of the positive electrode 11. The material of the insulating tape 51 is the same as that of the insulating tape 50 in Figures 1 to 3. As a result, the insulating tape 51 can suppress the reduction of the gap between the negative electrode near the positive electrode start end 40 in the electrode body 14a due to charging and discharging of the cylindrical battery 10. This reduces stress concentration from the positive electrode start end 40 to the separator 13, thereby suppressing the voltage drop associated with charging and discharging.

[0064] The winding length Ld of the insulating tape 51 is preferably 0.1 turns or more and 1.0 turn or less. If the winding length Ld is less than 0.1 turns, the effect of easing the stress concentration described above will be small. On the other hand, if the winding length Ld is 1.0 turn or more, the tightening force by the insulating tape 51 on the inner circumference side of the electrode body 14a tends to increase. Preferably, the winding length of the portion of the insulating tape 51 located on the negative electrode mixture layer 12b is preferably 0.1 turns or more. In this example, the other configurations and operations are the same as those in Figures 1 to 3.

[0065] Figure 6 is a cylindrical battery of another embodiment, corresponding to Figure 2. Figure 7 is a schematic cross-sectional view of another embodiment, showing the positive electrode starting end and the portions of the negative electrode 12 located on the inside and outside of the winding of the positive electrode starting end, unfolded in the longitudinal direction.

[0066] In this example, a first insulating tape 50a is attached to the first surface S1 of the negative electrode 12 that constitutes the electrode body 14b, and a second insulating tape 51a is attached to the second surface S2 of the negative electrode. The electrode body 14b has an overlapping region Sa in which the first tape 50a and the second tape 51a overlap each other in the radial direction of the electrode body 14b via a separator 13. The overlapping region Sa is the region shown by the oblique grid in Figures 6 and 7, and is a part of the winding direction of the space between the outer and inner surfaces of the winding of the negative electrode 12 where the positive electrode 11 is not interposed. The configuration in this example has a configuration that combines the configurations shown in Figures 1 to 3 and the configurations shown in Figures 4 to 5. In the overlapping region Sa, the total thickness of the two tapes 50a and 51a is defined because it helps to suppress the reduction of the gap between the negative electrodes 12 near the positive electrode starting end 40 in the electrode body 14b.

[0067] The winding end E3 of the overlapping region Sa is located on the negative electrode mixture layer 12b at a position less than 0.5 turns away from the positive electrode start end 40 towards the winding start side. Therefore, the distance Le in the winding direction between the winding end E3 and the positive electrode start end 40 is less than 0.5 turns in circumference.

[0068] In this example, the winding end E3 of the overlapping region Sa coincides with the winding end of the first tape 50a and the second tape 51a. A portion of the first tape 50a extends from the overlapping region Sa towards the winding start side.

[0069] The total thickness (T2a + T3a) of the first tape 50a and the second tape 51a in the overlapping region Sa is 50% or more and 100% or less of the thickness T1 of the flat portion 11c in the area where the positive electrode mixture layer 11b is formed on both sides of the positive electrode 11.

[0070] In this example, the overlapping region Sa of the first tape 50a and the second tape 51a can suppress the reduction in the gap between the negative electrodes 12 near the positive electrode start end 40 in the electrode body 14b during charging and discharging of the cylindrical battery. As a result, stress concentration from the positive electrode start end 40 to the separator 13 is alleviated, and the voltage drop associated with charging and discharging can be suppressed.

[0071] The winding length Lf of the overlapping region Sa is preferably 0.1 turns or more and 1.0 turns or less. In the overlapping region Sa, it is more preferable that the winding length Lf of the portion where each of the first tape 50a and the second tape 51a is located on the negative electrode mixture layer 12b is 0.1 turns or more. In this example, the other configurations and operations are the same as those in Figures 1 to 3, or Figures 4 to 5.

[0072] Figure 8 is a diagram corresponding to Figure 7 in another embodiment. In this example, unlike the configurations in Figures 6 and 7, a portion of the first tape 50b extends from the overlapping region Sb toward the winding end, and a portion of the second tape 51b extends from the overlapping region Sb toward the winding start. In this example, the other configurations and operations are the same as those in Figures 6 and 7.

[0073] Furthermore, the second tape may extend from the overlapping region shown in Figures 6 to 8 toward the end of the winding, and the first tape may extend from the overlapping region toward the beginning of the winding.

[0074] This disclosure is not limited to the embodiments and their variations, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0075] 10 Cylindrical battery, 11 Positive electrode, 11a Positive electrode core, 11b Positive electrode mixture layer, 11c Flat section, 12 Negative electrode, 12a Negative electrode core, 12b Negative electrode mixture layer, 13 Separator, 14, 14a, 14b Electrode body, 14d Hollow section, 15 Insulating tape, 16 Outer can, 17 Sealing body, 18 Upper insulating plate, 19 Lower insulating plate, 20 Positive electrode lead, 21a First negative electrode lead, 21b Second negative electrode lead, 22 Grooved section, 23 Terminal plate, 24 Lower valve body, 25 Insulating plate, 26 Upper valve body, 27 Sealing plate, 27a Protrusion, 27b Ventilation hole, 28 Gasket, 29 Shoulder section, 31 bottom, 33 peripheral edge, 38 extension, 39 cylindrical part, 40 positive terminal start end, 50, 51 insulating tape, 50a, 50b first tape, 51a, 51b second tape.

Claims

1. The electrode body comprises a strip-shaped positive electrode having a positive electrode core and a positive electrode mixture layer, and a strip-shaped negative electrode having a negative electrode core and a negative electrode mixture layer, wound via a separator; a bottomed cylindrical outer can containing the electrode body; and a sealing body closing the opening of the outer can, wherein the outer surface of the negative electrode is defined as the first surface, and the portion extending from the position facing the positive electrode start end on the winding start side of the electrode body via the separator in the radial direction is defined as the second surface, and a tape is attached to the first surface or the second surface, and the end of the tape is positioned on the negative electrode mixture layer at a distance of 0.5 turns or less from the opposing position on the negative electrode towards the winding start side. A cylindrical battery in which the thickness of the tape is 50% or more and 100% or less of the thickness of the flat portion of the positive electrode where the positive electrode mixture layer is formed on both sides of the positive electrode.

2. The electrode body comprises a strip-shaped positive electrode having a positive electrode core and a positive electrode mixture layer, and a strip-shaped negative electrode having a negative electrode core and a negative electrode mixture layer, wound around a separator; a bottomed cylindrical outer can containing the electrode body; and a sealing body closing the opening of the outer can, wherein the portion of the outer surface of the negative electrode winding that extends from the position facing the positive electrode start end on the radial direction of the electrode body via the separator toward the winding start side is designated as the first surface, and the portion of the inner surface of the negative electrode winding that extends from the position facing the positive electrode start end on the radial direction via the separator toward the winding start side is designated as the second surface, a first tape is attached to the first surface, and a second tape is attached to the second surface, and the first tape and the second tape have overlapping regions that overlap each other radially via the separator. A cylindrical battery wherein the winding end of the overlapping region is positioned on the negative electrode mixture layer at a distance of 0.5 turns or less from the positive electrode start end toward the winding start side, and the total thickness of the first tape and the second tape in the overlapping region is 50% or more and 100% or less of the thickness of the flat portion of the positive electrode mixture layer formed on both sides of the positive electrode.

3. The cylindrical battery according to claim 1, wherein the length of the tape in the winding direction is 0.1 turns or more and 1.0 turn or less.

4. The cylindrical battery according to claim 3, wherein the length in the winding direction of the portion of the tape located on the negative electrode mixture layer is 0.1 turns or more.

5. The cylindrical battery according to claim 2, wherein the winding length of the overlapping region is 0.1 turns or more and 1.0 turn or less.

6. The cylindrical battery according to claim 5, wherein in the overlapping region, the winding length of the portion where each of the first tape and the second tape is located on the negative electrode mixture layer is 0.1 turns or more.

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