Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery includes: a winding-type electrode body in which a first electrode and a second electrode are wound with a separator interposed therebetween; and an exterior body that accommodates the electrode body. The first electrode has a core body and a mixture layer formed on the surface of the core body. A core-body-exposed part where the core body is exposed is formed on the surface of the first electrode, and an electrode tab is joined to the core-body-exposed part. In an expanded state along the planar direction of the first electrode, the surface of the electrode tab in a facing region that faces the core body is a flat surface. In the electrode body, at least one of the core body and the electrode tab is bent to form gaps between the core body and both ends, in the winding direction, of the electrode tab in the facing region, and a protective layer including a material softer than the electrode tab is provided in each of the gaps.

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery, and in particular to a configuration including a wound electrode body in which strip-shaped first and second electrodes having different polarities are wound with a separator interposed therebetween, in which the electrode tab and the core body are joined together while preventing the core body from being cut by the electrode tab.

[0002] Conventionally, a nonaqueous electrolyte secondary battery has been known that includes an electrode assembly and an outer casing that houses the electrode assembly. The electrode assembly is a wound type in which strip-shaped first and second electrodes having opposite polarities are wound with a separator interposed therebetween. One of the first and second electrodes is a positive electrode, and the other is a negative electrode. In such a nonaqueous electrolyte secondary battery, repeated charge and discharge cycles can cause stress associated with the expansion and contraction of the first and second electrodes, which can cause the electrode core to break at the corners of the electrode tabs bonded to the surfaces of each electrode. Breaking of the core increases the electrical resistance of the electrode, which can lead to a deterioration in battery performance.

[0003] Patent Document 1 describes that by providing a protective layer made of a resin layer or the like between a step portion formed on an electrode tab (lead) and the core body (current collector) of the electrode, breakage of the core body due to expansion and contraction of the electrode during charging and discharging is suppressed.

[0004] JP 2014-89856 A

[0005] However, in the configuration described in Patent Document 1, corners of the electrode body in the winding direction at portions of the electrode tab other than the step portion, and corners of the joint with the core body at the boundary with the step portion, are pressed strongly against the core body as the electrode expands and contracts during charging and discharging, which may cause the core body to break. For this reason, the configuration described in Patent Document 1 leaves room for improvement in terms of more reliably preventing the core body from being broken by the electrode tab.

[0006] Therefore, an object of the present disclosure is to provide a nonaqueous electrolyte secondary battery having a configuration including a wound electrode assembly, which can more reliably prevent breakage of the core body due to the electrode tab during charge / discharge cycles.

[0007] The nonaqueous electrolyte secondary battery according to the present disclosure is a nonaqueous electrolyte secondary battery comprising a wound electrode body in which strip-shaped first and second electrodes having opposite polarities are wound with a separator interposed therebetween, and an outer casing that houses the electrode body, wherein the first electrode has a core and a mixture layer formed on the surface of the core, a core exposed portion where the core is exposed is formed on the surface of the first electrode, and an electrode tab is joined to the core exposed portion, and when deployed in the planar direction of the first electrode, the surface of the electrode tab in a facing region that faces the core is flat, and in the electrode body, at least one of the core and the electrode tab is bent so as to form gaps between both ends of the electrode tab in the facing region in the winding direction and the core, and each gap is provided with a protective layer containing a material softer than the electrode tab.

[0008] According to the nonaqueous electrolyte secondary battery according to the present disclosure, in a configuration including a wound electrode assembly, it is possible to more reliably prevent the electrode tab from cutting the core during charge / discharge cycles.

[0009] 9 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure; FIG. 10 is a plan view of a longitudinal intermediate portion of the positive electrode, which is the first electrode of FIG. 1, when viewed in the thickness direction in a state in which the positive electrode is developed along the planar direction; FIG. 11 is an A-A cross-sectional view of FIG. 2; FIG. 12 is an enlarged view of portion B of FIG. 3; FIG. 13 is a view corresponding to FIG. 3, showing the vicinity of the joint between the wound positive electrode and the electrode tab in an electrode body in an embodiment; FIG. 14 is a view corresponding to FIG. 2, showing a nonaqueous electrolyte secondary battery of a first example of comparative example; FIG. 15 is a C-C cross-sectional view of FIG. 6; FIG. 16 is a D-D cross-sectional view of FIG. 6; FIG. 17 is a view corresponding to FIG. 2, showing a nonaqueous electrolyte secondary battery of a second example of comparative example; and FIG. 18 is an E-E cross-sectional view of FIG.

[0010] Hereinafter, embodiments of the nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings.

[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 plan view of a longitudinal intermediate portion of the positive electrode 11 when viewed in the thickness direction in a state in which the positive electrode 11 is developed along the planar direction.

[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 exterior body 15 with a bottom that houses the electrode assembly 14, and a sealing body 16 that closes the opening of the exterior body 15. The exterior body 15 houses a nonaqueous electrolyte together with the electrode assembly 14. The positive electrode 11 corresponds to a first electrode, and the negative electrode 12 corresponds to a second electrode.

[0014] The exterior body 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 body 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 body 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 body 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 a position away from the winding start end and winding end end of the electrode body 14, approximately at the center of the radial direction β of the electrode body 14. The positive electrode tab 19 corresponds to an electrode tab. The positive electrode tab 19 is a strip-shaped conductive member and has a thickness greater than the thickness of the positive electrode core body described below. There are no particular limitations on the material constituting the positive electrode tab, 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 an exposed core portion provided at the winding start end, which is one end of the negative electrode 12 in the longitudinal direction of the electrode plate located at the winding start side 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 underside 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 exterior body 15, and is connected to the inner surface of the bottom of the exterior body 15 by welding or the like, with the exterior body 15 serving as the negative electrode terminal. The negative electrode tab 20 is a strip-shaped conductive member and has a thickness greater than that of the negative electrode core, which will be described later. 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] The negative electrode 12 is disposed on the outermost peripheral surface of the electrode body 14, and the exposed surface of the negative electrode core constituting the negative electrode 12 abuts against the inner peripheral surface of the exterior body 15. This electrically connects both ends of the negative electrode 12 in the longitudinal direction of the electrode plate to the exterior body 15, ensuring good current collection performance.

[0022] Referring to FIG. 2 , the positive electrode 11 has a strip-shaped positive electrode core 31 and a positive electrode mixture layer 30 formed on both sides of the positive electrode core 31. While FIG. 2 only shows the positive electrode mixture layer 30 formed on one thickness-wise surface of the positive electrode core 31, a positive electrode mixture layer is also formed on the other thickness-wise surface (not shown) of the positive electrode core 31. The positive electrode core 31 may 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 31 is a foil of a metal primarily composed of aluminum or an aluminum alloy. The thickness of the positive electrode core 31 is, for example, 10 μm to 30 μm.

[0023] The positive electrode mixture layer 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 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. As described below, the positive electrode tab 19 is directly bonded to the positive electrode core 31 by ultrasonic welding or the like.

[0024] The negative electrode 12 has a negative electrode core and a negative electrode mixture layer formed on both sides of the negative electrode core. The negative electrode core 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 contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR). The thickness of the negative electrode mixture layer 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.

[0025] An annular gasket 27 is interposed between the exterior body 15 and the sealing body 16. The sealing body 16 is fixed by crimping to the upper end portion, which is the open side end portion of the exterior body 15, via the gasket 27. Specifically, the upper end portion of the exterior body 15 is crimped to the peripheral edge portion of the sealing body 16 via the gasket 27. This seals the inside of the battery.

[0026] Furthermore, exterior body 15 has grooved portion 21 formed, for example, by pressing the side surface from the outside, to support sealing body 16. Grooved portion 21 is preferably formed in an annular shape along the circumferential direction of exterior body 15, and supports sealing body 16 on its upper surface.

[0027] 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 is hat-shaped 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.

[0028] When the internal pressure of the battery increases, the lower valve body 23 deforms and breaks, pushing the upper valve body 25 toward the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. When the internal pressure increases further, the upper valve body 25 breaks, and gas is discharged from the opening 26a of the cap 26.

[0029] In the nonaqueous electrolyte secondary battery 10, a positive electrode tab 19 is connected to the positive electrode 11. A core exposed portion 31a, where the positive electrode core 31 is exposed, is formed on the surface of the positive electrode 11, and the positive electrode tab 19 is joined to this core exposed portion 31a. Consider the case where the positive electrode tab is simply joined to a flat core exposed portion. In this case, repeated charge / discharge cycles of the secondary battery cause the positive and negative electrodes to expand and contract. This expansion and contraction can cause the portion of the positive electrode core adjacent to the joint with the positive electrode tab to bend radially to one side of the joint, potentially causing the corner of the positive electrode tab, or the end in the winding direction, to be strongly pressed against the surface of the positive electrode core. This can cause the positive electrode core to be torn by the end of the positive electrode tab. This tearing can occur both when the positive electrode tab is arranged on the inner surface of the wound positive electrode core and when the positive electrode tab is arranged on the outer surface of the wound positive electrode core.

[0030] On the other hand, as in the configuration described in Patent Document 1, it is also possible to provide a protective layer made of a resin layer or the like between the step portion formed on the electrode tab and the electrode core. However, corners in the winding direction at the portion of the electrode tab other than the step portion, or corners in the winding direction at the joint with the step portion, may be strongly pressed against the surface of the core as the electrode expands and contracts, potentially causing the core to break. Therefore, in this embodiment, as described below, when the electrode is deployed along the planar direction of the electrode, the surface of the facing region of the electrode tab that faces the electrode core is made flat. Then, in the electrode assembly, the electrode core is bent to form gaps between both ends of the electrode tab in the winding direction in the facing region and the core, and protective layers containing a material softer than the positive electrode tab are provided in each gap.

[0031] The configuration of the vicinity of the joint between the positive electrode core 31 and the positive electrode tab 19 will be described in detail below using Fig. 2 and Figs. 3 to 5. Fig. 3 is a cross-sectional view taken along line A-A in Fig. 2. Fig. 4 is an enlarged view of part B in Fig. 3. Fig. 5 is a view corresponding to Fig. 3, showing the vicinity of the joint between the wound positive electrode 11 and the positive electrode tab 19 in the electrode body.

[0032] 2, in a part of the positive electrode 11 in the longitudinal direction X of the electrode plate, for example, in the approximate center, a core exposed portion 31a is formed over the entire length in the lateral direction Y of the electrode plate, where the surface of the metal constituting the positive electrode core 31 is exposed. The core exposed portion 31a is a portion to which the positive electrode tab 19 is joined, and is a portion of the surface of the positive electrode core 31 that is not covered by the positive electrode mixture layer 30. In FIG. 2, the core exposed portion 31a is shown as a sandy portion. The longitudinal direction X of the positive electrode 11 corresponds to the winding direction of the electrode body, and the lateral direction Y of the positive electrode 11 corresponds to the axial direction α of the electrode body (FIG. 1).

[0033] The core exposed portion 31 a of the positive electrode core 31 may be formed in a position other than the center in the longitudinal direction X of the electrode plate, and may be formed, for example, near an end of the electrode plate in the longitudinal direction X. The core exposed portion 31 a is provided, for example, by intermittent application in which the positive electrode mixture slurry is not applied to a part of the positive electrode core 31.

[0034] The positive electrode tab 19 is joined to the core exposed portion 31a by, for example, ultrasonic welding, and extends from one end (upper end) of the positive electrode core 31 in the electrode plate short-side direction Y. As shown in Figures 3 and 4, the positive electrode tab 19 is formed in a strip shape with a substantially rectangular cross section when deployed along the planar direction of the positive electrode 11. As a result, in this deployed state, the surface of the facing region 19a of the positive electrode tab 19 that faces the positive electrode core 31 over the entire length in the electrode plate long-side direction X is a flat surface. The "flat surface" means a surface that does not have any irregularities visible to the naked eye. As described above, the positive electrode tab 19 has a thickness greater than that of the positive electrode core 31.

[0035] 2, the surfaces of the positive electrode tab 19 and the exposed core portion 31a are covered with a protective tape 40. Portions of the protective tape 40 are attached to the surfaces of the positive electrode mixture layers 30 arranged on both sides of the exposed core portion 31a of the positive electrode 11 in the longitudinal direction X of the electrode plate. The protective tape 40 is an insulating tape having insulating properties.

[0036] On the other hand, as shown in Fig. 5 , in the electrode assembly, the positive electrode core 31 is bent so as to form gaps 70 between the positive electrode core 31 and both ends of the positive electrode tab 19 in the winding direction (the direction of arrow γ in Fig. 5 ) in the facing region 19a. A protective layer 50 containing a material softer than the positive electrode tab 19 is provided in each gap 70. For this reason, the positive electrode core 31 is formed with a protrusion 32 that protrudes toward the middle of the positive electrode tab 19 in the winding direction in the facing region 19a. The top 33 of the protrusion 32 is joined by ultrasonic welding or the like to a contact portion 42 in the facing region 19a of the positive electrode tab 19 that abuts against the positive electrode core 31.

[0037] Furthermore, in order to give the positive electrode core 31 the above-described shape, as shown in FIGS. 2 to 4 , in the positive electrode 11 before the electrode assembly 14 is fabricated, a protrusion 32 is formed on the positive electrode core 31, protruding toward the middle of the facing region 19a of the positive electrode tab 19 in the electrode plate longitudinal direction (the direction of the arrow X in FIG. 3 ). As shown in FIG. 2 , the protrusion 32 is formed over the entire length of the positive electrode core 31 in the electrode plate short direction (the direction of the arrow Y in FIG. 2 ). As shown in FIG. 3 , the protrusion 32 has a trapezoidal cross section with inclined portions 34 at both ends in the electrode plate longitudinal direction X, inclined in a direction away from the facing region 19a. As shown in FIG. 4 , curved portions A1 and A2 with an arc-shaped cross section are formed at both ends of the inclined portion 34 in the electrode plate longitudinal direction X. In this manner, the cross section of the inclined portion 34 may have a curved shape. By connecting the curved portions A1 to both sides of the top 33 in the electrode plate longitudinal direction X, which corresponds to the winding direction of the protrusions 32, it is possible to more effectively prevent the positive electrode core 31 from being broken due to contact with the positive electrode tab 19. On the other hand, the curved portions A2 are connected to the base portions 35 on both sides of the top 33 of the positive electrode core 31, along planes parallel to the top 33.

[0038] The protective layer 50 is an adhesive tape using a resin for the base layer 51, has an adhesive layer 52 on the positive electrode core 31 side of the base layer 51, and is adhered to the positive electrode core 31. Examples of adhesive tapes include PP (polypropylene) tape, PI (polyimide) tape, and PET (polyethylene terephthalate) tape. The protective layer is not limited to this, and may have an adhesive layer only on the positive electrode tab side of the base layer, or on both the positive electrode tab side and the positive electrode core side, and be adhered to one or both of the positive electrode core and the positive electrode tab. Using adhesive tape as the protective layer 50 in this way facilitates the work of providing the protective layer 50 in the gap 70 between the positive electrode core 31 and the positive electrode tab 19.

[0039] The protective layer is not limited to the above configuration, and may be configured to include a material softer than the positive electrode tab 19, such as a resin layer or nonwoven fabric. The resin layer may be a resin film. For example, the resin film may be a resin-coated film formed by coating a resin such as a polyvinylidene fluoride (PVDF) film.

[0040] According to the nonaqueous electrolyte secondary battery 10 described above, in a configuration including a wound electrode assembly 14, when the positive electrode 11 and the negative electrode 12 expand and contract during charge and discharge cycles, ends E1 and E2 ( FIG. 5 ), which are corners of the positive electrode tab 19 in the winding direction γ, do not come into contact with the surface of the core exposed portion 31 a of the positive electrode core 31, but a portion including the end of the protective layer 50, which is softer than the positive electrode tab 19, comes into contact. This makes it possible to more reliably prevent the positive electrode core 31 from being cut by the positive electrode tab 19 during charge and discharge cycles, while achieving bonding between the positive electrode tab 19 and the positive electrode core 31.

[0041] In the above-described FIG. 5 , in the wound state of the positive electrode 11, the positive electrode tab 19 is joined to the inside of the winding (upper side in FIG. 5 ) of the positive electrode core 31. The positive electrode tab may be joined to the outside of the winding of the positive electrode core. In this case, a protrusion is formed on the positive electrode core that protrudes toward the middle of the winding direction in the facing region of the positive electrode tab that faces the positive electrode core. The apex of the protrusion is joined to a contact portion that abuts against the positive electrode core in the facing region of the positive electrode tab, and a protective layer is provided in the gap between the positive electrode core and both ends of the positive electrode tab in the winding direction in the facing region.

[0042] Fig. 6 is a view of a nonaqueous electrolyte secondary battery of a first example of comparative examples, corresponding to Fig. 2. Fig. 7 is a cross-sectional view taken along CC in Fig. 6. Fig. 8 is a cross-sectional view taken along DD in Fig. 6.

[0043] 6 to 8 corresponds to the configuration described in Patent Document 1, and a step portion 19c is formed at the longitudinal end of the positive electrode tab 19b in a facing region facing the positive electrode core 61. A protective layer 55 including a resin layer is provided between the step portion 19c and the core exposed portion 61a of the positive electrode core 61.

[0044] 8 , in this comparative example, ends E3 and E4 in the winding direction, which form corners of the positive electrode tab 19b, are located on the surface of the core exposed portion 61a of the positive electrode core 61. As a result, as the positive electrode 11a and the negative electrode expand and contract during charge and discharge, the ends E3 and E4 are pressed strongly against the core exposed portion 61a, which may cause breakage of the positive electrode core 61. For example, as the negative electrode expands, compressive stress is generated in the positive electrode core 61 in the radial direction from the outer and inner sides of the winding, and stress is also generated in the positive electrode core 61 in the direction extending in the winding direction, which may cause breakage of the positive electrode core 61 along both ends E3 and E4 of the positive electrode tab.

[0045] Fig. 9 is a view of a nonaqueous electrolyte secondary battery of a second example of the comparative example, corresponding to Fig. 2. Fig. 10 is a cross-sectional view taken along the line EE in Fig. 9.

[0046] 9 and 10 also correspond to the configuration described in Patent Document 1. In this comparative example, a stepped portion 19f that is recessed in a substantially U-shape along the outer edge of the positive electrode tab 19e is formed in a facing region of the positive electrode tab 19e that faces the positive electrode core 61 in the longitudinal direction. A substantially U-shaped protective layer 56 is provided between the stepped portion 19f and the core exposed portion 61a of the positive electrode core 61.

[0047] In this second comparative example, protective layers 56 are disposed adjacent to both ends in the winding direction of the contact portion 43 of the positive electrode tab 19e that contacts the positive electrode core 61. However, corners E5 and E6 at the boundary between the step portion 19f of the positive electrode tab 19e and the contact portion 43 are located on the surface of the core exposed portion 61a. When the positive electrode 11b and the negative electrode expand and contract, the protective layer 56, which includes a resin layer that is softer than the positive electrode tab 19e, is more likely to deform than the positive electrode tab 19e. For this reason, the corners E5 and E6 of the positive electrode tab 19e are pressed strongly against the surface of the core exposed portion 61a, which may cause the positive electrode core 61 to break.

[0048] According to the above embodiment, the ends E1, E2 in the winding direction, which form the corners of the positive electrode tab 19, do not come into contact with the surface of the core exposed portion 31 a. Therefore, unlike the examples of the comparative examples shown in FIGS. 6 to 10 , breakage of the positive electrode core 31 can be more reliably prevented.

[0049] In the above embodiment, the positive electrode core 31 is bent so as to form a gap between both ends of the positive electrode tab 19 in the winding direction and the positive electrode core 31, and a protective layer 50 is provided in the gap. On the other hand, in the electrode assembly, both the positive electrode core and the positive electrode tab, or only the positive electrode tab, may be bent so as to form a gap between both ends of the positive electrode tab in the winding direction and the positive electrode core, and a protective layer may be provided in the gap. For example, in the embodiment shown in FIG. 5 , both ends of the positive electrode tab in the winding direction may be bent more inward than in the winding direction, and a protective layer may be provided between both ends and the positive electrode core along the winding direction.

[0050] In the above embodiment, the first electrode is a positive electrode, but the first electrode may be a negative electrode, a negative electrode tab is joined to a core exposed portion where the negative electrode core is exposed, and the surface of the negative electrode tab in a facing region facing the negative electrode core is a flat surface when the negative electrode is deployed in the planar direction. In the electrode assembly, at least one of the negative electrode core and the negative electrode tab is bent so as to form gaps between the negative electrode core and both ends in the winding direction of the facing region, and a protective layer containing a material softer than the negative electrode tab is provided in each gap.

[0051] The present disclosure is further described by the following embodiments. Configuration 1: A nonaqueous electrolyte secondary battery including a wound electrode assembly in which strip-shaped first and second electrodes having opposite polarities are wound with a separator interposed therebetween, and an exterior housing that houses the electrode assembly, wherein the first electrode has a core and a mixture layer formed on the surface of the core, a core exposed portion where the core is exposed is formed on the surface of the first electrode, and an electrode tab is joined to the core exposed portion, when the first electrode is deployed in a planar state, a surface of a facing region of the electrode tab that faces the core is flat, and in the electrode assembly, at least one of the core and the electrode tab is bent to form gaps between the core and both ends of the electrode tab in the winding direction in the facing region, and each of the gaps is provided with a protective layer containing a material softer than the electrode tab. Configuration 2: The nonaqueous electrolyte secondary battery according to Configuration 1, wherein the protective layer is an adhesive tape using a resin for a base layer and is attached to the at least one member.Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the one member is the core body.Configuration 4: The nonaqueous electrolyte secondary battery according to Configuration 3, wherein the core body has a protrusion that protrudes toward a middle portion in the winding direction in the facing region of the electrode tab, and the protrusion has an apex joined to the electrode tab and inclined portions connected to both ends of the apex in the winding direction.

[0052] 10 Non-aqueous electrolyte secondary battery, 11, 11a, 11b Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Exterior body, 16 Sealing body, 17 Upper insulating plate, 18 Lower insulating plate, 19, 19b, 19e Positive electrode tab, 19a Facing area, 19c, 19f Step portion, 20 Negative electrode tab, 21 Grooved portion, 22 Internal terminal plate, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Opening, 27 Gasket, 30 Positive electrode mixture layer, 31 Positive electrode core, 31a Core exposed portion, 32 Protrusion, 33 Top, 34 Inclined portion, 35 Base portion, 40 Protective tape, 42, 43 Contact portion, 50 Protective layer, 51 Base layer, 52 Adhesive layer, 55, 56 protective layer, 61 positive electrode core, 61a core exposed portion, 70 gap.

Claims

1. A non-aqueous electrolyte secondary battery comprising: a wound electrode assembly in which strip-shaped first and second electrodes having opposite polarities are wound with a separator interposed therebetween; and an exterior housing that houses the electrode assembly, wherein the first electrode has a core and a mixture layer formed on the surface of the core; a core exposed portion where the core is exposed is formed on the surface of the first electrode, and an electrode tab is joined to the core exposed portion; in a state where the first electrode is deployed in the planar direction, the surface of the electrode tab in a facing region that faces the core is flat; and in the electrode assembly, at least one of the core and the electrode tab is bent so as to form gaps between the core and both ends of the electrode tab in the facing region in the winding direction, and each of the gaps is provided with a protective layer containing a material softer than the electrode tab.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the protective layer is an adhesive tape using a resin as a base layer, and is attached to at least one of the members.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the one member is the core body.

4. The nonaqueous electrolyte secondary battery according to claim 3, wherein the core body has a protrusion that protrudes toward a middle portion in the winding direction in the region facing the electrode tab, and the protrusion has an apex joined to the electrode tab and inclined portions connected to both ends of the apex in the winding direction.

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