Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery includes: an electrode body (14) in which a positive electrode (11) and a negative electrode (12) are wound with a separator (13) therebetween; and an outer can that accommodates the electrode body (14). The negative electrode (12) has: a negative electrode core body (30); and a mixture layer (32) that is provided to at least one surface of the negative electrode core body (30) and that contains an active material. The negative electrode (12) has a core body exposed part (31) having no mixture layer on either surface of the negative electrode core body (30) at a negative electrode winding initiation-side end part (12a) that is located on the inner circumferential side with respect to a positive electrode winding-initiation end (B1) of the positive electrode (11) and that is closer to the winding initiation-side as compared with the positive electrode winding-initiation end (B1). The core body exposed part (31) has disposed, on at least a portion thereof in the winding direction, a non-tape-covered part (40) that is not covered with a tape on either side thereof in the thickness direction.

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0002] BACKGROUND ART Conventionally, non-aqueous electrolyte secondary batteries have been known that include a wound electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and an outer can that houses the electrode assembly and a non-aqueous electrolyte.

[0003] Patent Document 1 describes that in a nonaqueous electrolyte secondary battery, a core exposed surface is formed at the winding start end of the positive electrode, a positive electrode tab is connected to the core exposed surface, and a protective tape is attached to the positive electrode so as to cover the core exposed surface and the positive electrode tab overlapping the core exposed surface.

[0004] Japanese Patent Application Laid-Open No. 2008-234855

[0005] Similar to the positive electrode having the configuration described in Patent Document 1, in a nonaqueous electrolyte secondary battery, it is conceivable to form an exposed core surface at the winding start end of the negative electrode. At this time, the exposed core surface is covered with insulating tape to prevent an internal short circuit due to contact between the exposed core surface of the negative electrode and the positive electrode. When a negative electrode tab is not connected to the winding start end of the negative electrode, it is also conceivable to provide an exposed core surface at the winding start end and cover the exposed core surface with insulating tape.

[0006] On the other hand, because the portion of the negative electrode where the exposed surface of the substrate is covered with insulating tape is less likely to deform, it is difficult to prevent stress from concentrating on the portion of the negative electrode facing the winding start end of the positive electrode as the charge-discharge cycles of the non-aqueous electrolyte secondary battery progress. This can cause plate deformation such as buckling in the portion of the negative electrode facing the positive electrode, which can cause an internal short circuit.

[0007] Therefore, an object of the nonaqueous electrolyte secondary battery of the present disclosure is to suppress deformation of the negative electrode plate, which can cause an internal short circuit.

[0008] The nonaqueous electrolyte secondary battery according to the present disclosure includes an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator interposed therebetween, and an outer can that houses the electrode assembly. The negative electrode includes a strip-shaped negative electrode core and a mixture layer containing an active material that is provided on at least one surface of the negative electrode core. The negative electrode has a core exposed portion, where the mixture layer is absent on both sides of the negative electrode core, at a negative electrode winding start end portion that is located inward from the positive electrode winding start end of the positive electrode and on the winding start side from the positive electrode winding start end. At least a portion of the core exposed portion in the winding direction is provided with a tape-uncovered portion, where both sides in the thickness direction are not covered with tape.

[0009] In the nonaqueous electrolyte secondary battery according to the present disclosure, a tape-free portion is provided in at least a portion of the winding direction of the exposed core portion at the winding start end of the negative electrode, where the outer periphery does not face the positive electrode. This portion is not covered with tape on both sides in the thickness direction. This makes the tape-free portion of the negative electrode more susceptible to deformation due to charge / discharge cycles, etc., thereby alleviating stress in the portion of the negative electrode facing the winding start end of the positive electrode and suppressing plate deformation in that portion. Furthermore, because the positive electrode does not face the tape-free portion, deformation of the tape-free portion does not cause an internal short circuit. This suppresses plate deformation of the negative electrode, which could cause an internal short circuit.

[0010] 1 is an axial cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure;

[0023] FIG. 2 is a schematic diagram showing the positional relationship of the positive electrode, negative electrode, and separator at the winding start portion of the electrode assembly shown in FIG. 1 in a state in which the positive electrode, negative electrode, and separator are linearly stretched;

[0024] FIG. 3 is an enlarged corresponding view of FIG. 3, showing a state in which deformation has occurred in a tape-uncovered portion of the winding start end of the negative electrode, with the separator omitted;

[0025] FIG. 4 is a view corresponding to FIG. 2, of an electrode assembly of a non-aqueous electrolyte secondary battery according to a comparative example;

[0026] FIG. 5 is a view corresponding to FIG. 2, of an electrode assembly of a non-aqueous electrolyte secondary battery according to another example of the embodiment;

[0027] FIG. 6 is a view corresponding to FIG. 2, of an electrode assembly of a non-aqueous electrolyte secondary battery according to another example of the embodiment.

[0011] It is anticipated from the beginning that new embodiments may be constructed by appropriately combining the features of the embodiments and variations described below. In the following embodiments, the same components are designated by the same reference numerals in the drawings, and redundant explanations are omitted. Furthermore, multiple drawings include schematic diagrams, and the dimensional ratios of the length, width, height, etc. of each component between different drawings do not necessarily match. Furthermore, among the components described below, components that are not recited in the independent claims representing the highest concept are optional components and are not essential components. Furthermore, the present disclosure is not limited to the following embodiments and variations thereof, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0012] Fig. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment. Fig. 2 is a schematic diagram showing the positional relationship of a positive electrode 11, a negative electrode 12, and a separator 13 at a winding start portion when the positive electrode 11, the negative electrode 12, and the separator 13 are linearly extended. Fig. 3 is a schematic diagram showing a cross section perpendicular to the central axis O of an outer can 15 at the winding start portion of an electrode assembly 14.

[0013] 1 , the nonaqueous electrolyte secondary battery 10 includes a strip-shaped positive electrode 11 and negative electrode 12 having opposite polarities, a separator 13, and a wound electrode assembly 14 in which the positive electrode 11 and negative electrode 12 are wound with the separator 13 interposed therebetween. The nonaqueous electrolyte secondary battery 10 also includes a cylindrical outer can 15 with a bottom that houses the electrode assembly 14, and a sealing body 16 that closes the opening of the outer can 15. The outer can 15 houses a nonaqueous electrolyte together with the electrode assembly 14.

[0014] The exterior can 15 is a cylindrical metal container with a bottom, and has a tubular portion 15a and a bottom provided at one end of the tubular portion 15a in the axial direction α. ​​The exterior can 15 has a grooved portion 21 (described below) formed on the other end in the axial direction α, which is the open end of the tubular portion 15a, and the sealing body 16 is supported by the grooved portion 21 to close the opening of the exterior can 15. Hereinafter, for convenience of explanation, the sealing body 16 side of the nonaqueous electrolyte secondary battery 10 will be referred to as the top, and the bottom side of the exterior can 15 will be referred to as the bottom.

[0015] The nonaqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous electrolyte is not limited to a liquid electrolyte (nonaqueous electrolytic solution), and may be a solid electrolyte using a gel polymer or the like. The nonaqueous electrolyte secondary battery 10 is preferably a lithium ion battery. The electrolyte salt may be, for example, LiBF ４ , LiPF ６ Examples of the non-aqueous solvent include esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propionate (MP), ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted product in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine.

[0016] Examples of halogen-substituted compounds include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP). From the viewpoint of suppressing a decrease in the charge-discharge cycle characteristics of a nonaqueous electrolyte secondary battery or improving the output characteristics, the nonaqueous electrolyte preferably contains 5% by mass or more of FEC, and more preferably 5% by mass to 15% by mass of FEC, relative to the mass of the nonaqueous electrolyte.

[0017] Examples of the solid electrolyte include solid or gel polymer electrolytes and inorganic solid electrolytes. 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. Examples of the matrix polymer include a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.).

[0018] As described above, the electrode assembly 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all long, strip-like bodies that are spirally wound and alternately stacked in the radial direction β of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the longitudinal and lateral directions of the electrode plate. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and, for example, two separators 13 are arranged to sandwich the positive electrode 11.

[0019] A positive electrode tab 19 and a negative electrode tab 20 are connected to the electrode body 14. The positive electrode tab 19 electrically connects the positive electrode 11 and the sealing body 16. The positive electrode tab 19 is provided, for example, at the center of the positive electrode 11 in the longitudinal direction of the electrode plate, at approximately the center of the electrode body 14 in the radial direction β, which is a position away from the winding start end and winding end end of the electrode body 14. The positive electrode tab 19 is a strip-shaped conductive member. There are no particular limitations on the material of the positive electrode tab 19, but it is preferable that the positive electrode tab 19 be made of a metal containing aluminum as its main component.

[0020] The negative electrode tab 20 is joined to a core exposed surface 31a (FIG. 2) of a core exposed portion 31 (described below) provided at the negative electrode winding start end, which is one longitudinal end of the negative electrode 12. In the example shown in FIG. 1, the positive electrode tab 19 passes through the opening of the upper insulating plate 17 and extends toward the sealing body 16 and is joined to the lower surface of the sealing body 16, with the sealing body 16 serving as the positive electrode terminal. The negative electrode tab 20 passes through a through hole in the annular lower insulating plate 18, is bent to fit along the inner surface of the bottom of the outer can 15, and is connected to the inner surface of the bottom of the outer can 15 by welding or the like, with the outer can 15 serving as the negative electrode terminal. The negative electrode tab 20 is a strip-shaped conductive member. The material of the negative electrode tab 20 is not particularly limited. The negative electrode tab 20 is preferably made of a metal primarily composed of nickel or copper, or a metal containing both nickel and copper.

[0021] An exposed portion of the surface of the negative electrode core that constitutes the negative electrode 12 is disposed on the outermost peripheral surface of the electrode body 14, and the negative electrode core abuts against the inner peripheral surface of the outer can 15. This electrically connects the winding start end of the negative electrode 12 and the winding end end of the negative electrode 12 to the outer can 15, ensuring good current collection.

[0022] 2, the positive electrode 11 has a strip-shaped positive electrode core 41 and a positive electrode mixture layer 42 formed on both sides of the positive electrode core 41. The positive electrode core 41 can be a foil of a metal such as aluminum or an aluminum alloy that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface layer. A suitable positive electrode core 41 is a foil of a metal whose main component is aluminum or an aluminum alloy. The thickness of the positive electrode core 41 is, for example, 10 μm to 30 μm.

[0023] The positive electrode mixture layer 42 preferably contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is formed on both sides of the positive electrode core. The thickness of the positive electrode mixture layer 42 is, for example, 40 μm to 100 μm. The positive electrode active material may be, for example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, or the like. The positive electrode tab 19 is directly bonded to the positive electrode core 41 by ultrasonic welding or the like.

[0024] The positive electrode 11 is produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both sides of the positive electrode substrate 41, followed by drying and rolling.

[0025] Examples of the positive electrode active material include lithium-containing transition metal oxides containing transition metal elements such as Co, Mn, and Ni. The lithium-containing transition metal oxides are not particularly limited, but include those represented by the general formula Li １＋ｘ MO ２ (wherein, −0.2<x≦0.2, and M contains at least one of Ni, Co, Mn, and Al) is preferred.

[0026] Examples of the conductive agent include carbon black (CB) such as acetylene black (AB) and Ketjen black, and carbon materials such as graphite. Examples of the binder include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, and polyolefin resins. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. These may be used alone or in combination of two or more.

[0027] The positive electrode tab 19 is formed on one surface of the positive electrode 11 and is joined, for example, by ultrasonic welding, to the exposed surface of the positive electrode core 41 that is exposed from the positive electrode mixture layer 42. In this state, the positive electrode tab 19 extends from the upper end, which is one end in the width direction of the positive electrode core 41.

[0028] The negative electrode 12 has a strip-shaped negative electrode core 30 and a negative electrode mixture layer 32 formed on both sides of the negative electrode core 30. The negative electrode core 30 can be made of a foil of a metal, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. The negative electrode mixture layer 32 contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR). The thickness of the negative electrode mixture layer 32 is, for example, 40 μm or more and 100 μm or less. For example, graphite, a Si-containing material, or the like is used as the negative electrode active material. The negative electrode tab 20 is preferably directly bonded to the negative electrode core by ultrasonic welding or the like.

[0029] The negative electrode 12 is produced by applying a negative electrode mixture slurry containing, for example, a negative electrode active material, a binder, water, and the like, to both sides of the negative electrode substrate 30, followed by drying and rolling.

[0030] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions. For example, carbon materials such as natural graphite and artificial graphite, metals that alloy with lithium such as Si and Sn, or alloys or composite oxides containing these, can be used. The binder contained in the negative electrode mixture layer is, for example, the same resin as that used in the positive electrode 11. When preparing the negative electrode mixture slurry using an aqueous solvent, styrene-butadiene rubber (SBR), CMC or a salt thereof, polyacrylic acid or a salt thereof, polyvinyl alcohol, etc. can be used. These may be used alone or in combination of two or more.

[0031] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. The separator 13 is preferably made of an olefin resin such as polyethylene or polypropylene. The thickness of the separator 13 is, for example, 10 μm to 50 μm. Separators 13 tend to be thinner as batteries become higher in capacity and power output. The separator 13 has a melting point of, for example, about 130°C to 180°C.

[0032] An annular gasket 27 is interposed between the exterior can 15 and the sealing body 16. The sealing body 16 is fixed by crimping to the upper end portion, which is the open end portion of the exterior can 15, via the gasket 27. Specifically, the upper end portion of the exterior can 15 is crimped to the peripheral edge of the sealing body 16 via the gasket 27. This seals the inside of the battery.

[0033] The exterior can 15 has a grooved portion 21 formed, for example, by pressing the side surface from the outside, that supports the sealing body 16. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the exterior can 15, and supports the sealing body 16 on its upper surface.

[0034] The sealing body 16 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are layered. Each component constituting the sealing body 16 has, for example, a disk or ring shape, and each component except for the insulating member 24 is electrically connected to each other. The cap 26 has an annular flange on its outer periphery and a hat-like shape with a cylindrical portion in the center with a closed upper end. The internal terminal plate 22 has a central hole that penetrates vertically. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, and the insulating member 24 is interposed between their respective peripheral edges. The components constituting the sealing body 16 are stacked axially on the flange portion of the sealing body 16.

[0035] When the internal pressure of the battery increases and reaches a predetermined value, the lower valve body 23 deforms and pushes the upper valve body 25 toward the cap 26, causing it to break, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. When the internal pressure further increases and reaches a predetermined value, the upper valve body 25 breaks, causing gas to be discharged from the opening 26a of the cap 26.

[0036] The configuration of the negative electrode winding start end 12a, which is the winding start end of the negative electrode 12, will be described in detail below using Figures 2 and 3. The negative electrode winding start end 12a is a portion of the negative electrode 12 located inward from the positive electrode winding start end B1 of the positive electrode 11 and closer to the winding start side than the positive electrode winding start end B1. The negative electrode 12 has a core exposed portion 31 at the negative electrode winding start end 12a, where the negative electrode core 30 has no negative electrode mixture layer 32 on either side. The core exposed portion 31 is provided in a predetermined range from the negative electrode winding start end B2 toward the winding end side of the negative electrode 12. Therefore, on both sides of the core exposed portion 31, core exposed surfaces 31a, 31b without the negative electrode mixture layer 32 are provided from the negative electrode winding start end B2 toward the winding end side. Of the core exposed surfaces 31 a, 31 b, the negative electrode tab 20 is joined to the core exposed surface 31 a on the outer side of the winding, facing the outer periphery, by ultrasonic welding, etc. In this state, the negative electrode tab 20 extends from the lower end, which is one end in the width direction of the negative electrode core 30.

[0037] An insulating tape 34 is attached to the core exposed surface 31a on the outer side of the winding so as to cover the surface of the core exposed surface 31a and the negative electrode tab 20 overlapping the core exposed surface 31a. The insulating tape 34 is an adhesive tape having a base layer on the outer surface side of the negative electrode 12 and an adhesive layer formed on the surface of the base layer facing the core exposed portion 31. 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 may be made of any insulating resin, such as PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PI (polyimide), PP (polypropylene), PET (polyethylene terephthalate), or PBT (polybutylene terephthalate).

[0038] The adhesive layer may contain at least one of a rubber-based polymer and an acrylic-based polymer, and may further contain, for example, a silicone-based polymer.

[0039] The insulating tape 34 is provided on the core exposed surface 31 a from the winding start end toward the winding end side, but as will be described later, does not reach the negative electrode mixture layer 32 on the outer side of the winding. As a result, a portion of the core exposed portion 31 that is not covered with the insulating tape is provided between the negative electrode tab 20 and the negative electrode mixture layer 32.

[0040] Of the core exposed surfaces 31a, 31b, the core exposed surface 31b on the inner side of the winding, facing the inner periphery, is not covered with insulating tape. As a result, in the negative electrode 12, a core exposed portion 31 is provided at the negative electrode winding start end 12a, which is located inward from the positive electrode winding start end B1 and toward the winding start side of the positive electrode winding start end B1, where there is no material mixture layer on either side of the negative electrode core 30. Furthermore, the core exposed portion 31 is provided at a part in the winding direction with a tape-uncovered portion 40, where both sides in the thickness direction are not covered with tape. The tape-uncovered portion 40 is provided between the negative electrode tab 20 and the negative electrode material mixture layer 32 in the winding direction of the negative electrode 12.

[0041] 2, the portion of the negative electrode 12 where the negative electrode mixture layer 32 is provided on both sides is indicated by arrow A1, the range where the negative electrode mixture layer 32 is provided on only one side is indicated by arrow A2, and the combined range of arrows A3 and A4 indicates the core exposed portion 31. Of the core exposed portion 31, the range where the insulating tape 34 is provided is indicated by arrow A3, and the range of the tape-uncovered portion 40 where neither side is covered with tape is indicated by arrow A4.

[0042] In this example, the winding start end of the anode mixture layer 32 on the inside of the winding is located closer to the winding start end than the winding start end of the anode mixture layer 32 on the outside of the winding, but the winding start ends of both the outside and inside of the winding anode mixture layer 32 may be aligned in the winding direction or may be different.

[0043] As described above, in this embodiment, the exposed core portion 31 of the negative electrode winding start end 12a has a portion 40 without tape coating along a part of the winding direction. This makes the uncovered portion 40 of the negative electrode 12 more susceptible to deformation due to charge / discharge cycles, etc., and relieves stress in the portion of the negative electrode 12 that faces the positive electrode winding start end B1. This makes it possible to suppress electrode plate deformation of the negative electrode 12 that could cause an internal short circuit.

[0044] The effects of this embodiment will be described in detail with reference to FIG. 4 . FIG. 4 is an enlarged view of FIG. 3 , showing the state in which deformation has occurred in the non-tape-covered portion 40 of the negative electrode winding start end 12 a of the negative electrode 12, with the separator omitted. In this example, as described above, the non-tape-covered portion 40 is provided at the negative electrode winding start end 12 a. Therefore, while the portion of the negative electrode winding start end 12 a covered with insulating tape 34 is less likely to deform, the non-tape-covered portion 40 is more likely to deform. As a result, as shown in FIG. 4 , the non-tape-covered portion 40 far removed from the positive electrode winding start end B1 easily deforms due to loads applied to the negative electrode 12 from the positive electrode winding start end B1, resulting in, for example, a bent portion 50. This relieves stress in the portion of the negative electrode 12 facing the positive electrode winding start end B1, thereby suppressing electrode plate deformation in that portion. 3, the positive electrode 11 does not face the non-tape-coated portion 40 on the outer and inner periphery, even with the separator 13 interposed therebetween, and only another portion of the negative electrode 12 faces the outer periphery via the separator 13. Therefore, deformation of the non-tape-coated portion 40 does not cause an internal short circuit. Therefore, electrode plate deformation of the negative electrode 12, which can cause an internal short circuit, can be suppressed.

[0045] 1 to 4, a portion 40 not covered with tape is provided between the negative electrode tab 20 and the negative electrode mixture layer 32. This allows stress to be alleviated in the portion of the negative electrode 12 that faces the vicinity of the positive electrode winding starting end B1 while protecting the negative electrode tab 20 with the insulating tape 34. The portion not covered with tape can also be provided on the negative electrode winding starting end 12a closer to the winding starting side than the negative electrode tab 20.

[0046] 3 and 4 , in the embodiment, the non-tape-coated portion 40 is preferably located at a position 0.1 to 1 turn toward the winding start from the position C1 facing the positive electrode winding start B1 on the inner circumferential side in the winding direction of the negative electrode 12. This preferred configuration facilitates more effective relief of stress concentrated in the portion of the negative electrode 12 facing the vicinity of the positive electrode winding start B1. On the other hand, if the non-tape-coated portion is located at a position less than 0.1 turn toward the winding start from the facing position C1, the portion of the negative electrode facing the vicinity of the positive electrode winding start B1 may be more susceptible to deformation of the non-tape-coated portion. Furthermore, if the non-tape-coated portion is located at a position more than 1.0 turn toward the winding start from the facing position C1 in the negative electrode 12, the distance in the winding direction between the non-tape-coated portion and the vicinity of the positive electrode winding start B1 becomes excessive, making it difficult to effectively relieve stress in the portion of the negative electrode facing the vicinity of the positive electrode winding start B1.

[0047] 3 and 4 , in a cross section of the electrode assembly 14 taken along a plane perpendicular to the central axis O of the outer can, the electrode assembly 14 is divided by a radial line L passing through the positive electrode winding starting end B1 and the central axis O, defining a first side portion D1 including the positive electrode winding starting end portion extending from the positive electrode winding starting end B1 toward the winding end, and a second side portion D2 on the opposite side of the line L from the first side portion D1. In this case, the non-tape-coated portion 40 is provided in the second side portion D2. This makes it easy to appropriately reduce the distance in the winding direction between the non-tape-coated portion 40 and the portion of the negative electrode 12 facing the vicinity of the positive electrode winding starting end B1, thereby easing stress in the portion of the negative electrode 12 facing the vicinity of the positive electrode winding starting end B1.

[0048] More preferably, the non-tape-coated portion 40 is located in the second side portion D2, and is located at a position 0.1 to 1 turn toward the winding start side from the position C1 facing the positive electrode winding start end B1 on the inner circumferential side in the winding direction of the negative electrode 12. In other words, the non-tape-coated portion 40 is more preferably located at a position 0.1 to 0.5 turns toward the winding start side.

[0049] FIG. 5 is a diagram corresponding to FIG. 2 of an electrode assembly 14a of a comparative nonaqueous electrolyte secondary battery. In the comparative example shown in FIG. 5, at the negative electrode winding start end 12a, the entire substrate exposed portion 31, where no negative electrode mixture layer is present on either side of the negative electrode substrate 30, is covered with insulating tape 34. In this case, the entire substrate exposed portion 31 at the negative electrode winding start end 12a is less likely to deform. In this case, it becomes difficult to alleviate stress concentrated near the positive electrode winding start end B1 of the negative electrode 12 through deformation of other portions of the negative electrode 12 over the course of charge / discharge cycles. As a result, in the comparative example, electrode plate deformation may occur in the portion of the negative electrode 12 facing the positive electrode winding start end B1, which could cause an internal short circuit. The embodiments shown in FIGS. 1 to 4 can prevent such problems.

[0050] 6 is a view corresponding to FIG. 2 of an electrode body 14b of a nonaqueous electrolyte secondary battery according to another embodiment. In the configuration of this example, at the negative electrode winding start end 12a, both sides of the core exposed portion 31, where there is no negative electrode mixture layer on either side of the negative electrode core 30, are not entirely covered with insulating tape. As a result, the tape-uncovered portion 40a is provided along the entire winding direction of the core exposed portion 31. In this example, the negative electrode tab is not provided at the negative electrode winding start end 12a, but is provided at the winding end end or an intermediate portion in the winding direction of the negative electrode 12. Furthermore, if the outermost peripheral surface of the winding end end of the negative electrode 12 contacts the inner peripheral surface of the outer can 15, the negative electrode tab can be omitted.

[0051] 1 to 4, the configuration of this example also makes the non-tape-covered portion 40a more easily deformable, thereby alleviating stress in the portion of the negative electrode 12 that faces the vicinity of the positive electrode winding start end B1, thereby suppressing plate deformation of the negative electrode 12 that could cause an internal short circuit. Other configurations and functions of this example are the same as those of the configurations of Figures 1 to 4. Note that this example may also be configured such that a negative electrode tab is joined to one of the exposed surfaces of the core exposed portion 31, and the negative electrode tab is not covered with insulating tape.

[0052] 7 is a view corresponding to FIG. 2 of an electrode body 14c of a nonaqueous electrolyte secondary battery according to another example of the embodiment. In the configuration of this example, unlike the configurations of FIGS. 1 to 4, in the exposed core portion 31 of the negative electrode 12, the exposed core surface 31a on the outer side of the winding is covered with an insulating tape 34a covering the negative electrode tab 20 and an insulating tape 34b adjacent to the negative electrode mixture layer 32, and the two insulating tapes 34a, 34b are provided spaced apart in the winding direction of the negative electrode 12. As a result, at the negative electrode winding start end 12a, a tape-uncovered portion 40b is provided between the two insulating tapes 34a, 34b in the winding direction, and both sides in the thickness direction are not covered with tape.

[0053] According to the configuration of this example, it is easy to accurately adjust the position at the negative electrode winding start end 12a where deformation is likely to occur. In this example, the other configurations and operations are the same as those of the configurations of FIGS.

[0054] In the above embodiments, the case where the negative electrode mixture layer is provided on both sides of the negative electrode core has been described, but the negative electrode mixture layer may be provided on only one side of the negative electrode core.

[0055] The present disclosure is further described by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery comprising: an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator interposed therebetween; and an outer can housing the electrode assembly, wherein the negative electrode comprises: a strip-shaped negative electrode core; and a mixture layer containing an active material provided on at least one surface of the negative electrode core, wherein the negative electrode has a core exposed portion in which the mixture layer is absent on both surfaces of the negative electrode core at a negative electrode winding start end portion located inward from the positive electrode winding start end of the positive electrode and on the winding start side from the positive electrode winding start end, and wherein at least a portion in the winding direction of the core exposed portion is provided with a tape-uncovered portion in which both sides in the thickness direction are not covered with tape. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein a negative electrode tab covered with insulating tape is joined to the core exposed portion, and the tape-uncovered portion is provided between the negative electrode tab and the mixture layer in the winding direction of the negative electrode. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the non-tape-coated portion is located at a position 0.1 to 1 revolution toward the winding start end of the positive electrode from a position facing the winding start end of the positive electrode in the winding direction of the negative electrode.Configuration 4: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein, in a cross section of the electrode body cut along a plane perpendicular to the central axis of the outer can, the electrode body is divided by a radial line passing through the positive electrode winding start end and the central axis, and a first side portion including a positive electrode winding start end portion extending from the positive electrode winding start end toward the winding end end, and a second side portion on the opposite side of the first side portion with the line between them, the non-tape-coated portion is located at the second side portion.Configuration 5: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the non-tape-coated portion is located along the entire winding direction of the core exposed portion.

[0056] REFERENCE SIGNS LIST 10 non-aqueous electrolyte secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14, 14a, 14b, 14c electrode body, 15 outer can, 15a cylindrical portion, 16 sealing body, 17 upper insulating plate, 18 lower insulating plate, 19 positive electrode tab, 20 negative electrode tab, 21 grooved portion, 22 internal terminal plate, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 27 gasket, 30 negative electrode core, 31 core exposed portion, 31a, 31b core exposed surface, 32 negative electrode mixture layer, 34, 34a, 34b insulating tape, 40 tape-uncovered portion, 41 core exposed portion, 41a, 41b core exposed surface, 42 positive electrode mixture layer, 50 folded portion.

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator interposed therebetween; and an outer can housing the electrode assembly, wherein the negative electrode comprises a strip-shaped negative electrode core; and a mixture layer containing an active material provided on at least one surface of the negative electrode core, wherein the negative electrode has a core exposed portion at a negative electrode winding start end portion located inward from a positive electrode winding start end of the positive electrode and on the winding start side of the positive electrode, where the mixture layer is absent on both surfaces of the negative electrode core, and wherein at least a portion in the winding direction of the core exposed portion is provided with a tape-uncovered portion where both sides in the thickness direction are not covered with tape.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein a negative electrode tab covered with insulating tape is joined to the exposed core portion, and the tape-uncovered portion is provided between the negative electrode tab and the material mixture layer in the winding direction of the negative electrode.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-tape-coated portion is located at a position 0.1 to 1 turn away from the winding start end of the positive electrode in the winding direction of the negative electrode.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein, in a cross section of the electrode body cut along a plane perpendicular to the central axis of the outer can, the electrode body is divided by a radial line passing through the positive electrode winding start end and the central axis, and a first side portion including the positive electrode winding start end portion extending from the positive electrode winding start end toward the positive electrode winding end end, and a second side portion on the opposite side of the first side portion with the line in between, the non-tape-coated portion is provided in the second side portion.

5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-tape-coated portion is provided over the entire core exposed portion in the winding direction.

Images