Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery includes: an electrode body (14) in which a first electrode plate and a second electrode plate are wound via a separator; and current collector plates (17, 18) disposed on one side of the electrode body in the winding axis direction. The first electrode plate includes: a first core body made of a metal foil; a first mixture layer formed on at least a first surface of the first core body; and a first core body exposed portion in which the first core body is exposed, and which is provided at an end portion on one side in the short side direction of the electrode plate, the one side being the current collector plate side of the first surface. In a boundary region between the first mixture layer and the first core body exposed portion of the first surface, a protective layer for short circuit suppression is provided in the electrode plate longitudinal direction. The first electrode plate has an unwelded and uncoated region (39) provided in a portion including an inner peripheral-side end portion between a current collector plate welded portion (38) and the protective layer.

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 plate and a negative electrode plate are wound with a separator interposed therebetween, and an exterior housing that houses the electrode assembly and a non-aqueous electrolyte.

[0003] Patent Document 1 describes that in a non-aqueous electrolyte secondary battery, a short circuit between the positive electrode plate and the negative electrode plate is suppressed by applying an insulating layer (protective layer) between the exposed portion of the current collector foil (exposed portion of the core) and the active material layer supporting portion (mixture layer) in the positive electrode plate constituting a wound electrode body.

[0004] Japanese Patent Application Laid-Open No. 2020-72007

[0005] In a non-aqueous electrolyte secondary battery, it is conceivable that an electrode plate constituting a wound electrode body has a core exposed portion where the core is exposed at one end of the electrode plate in the short direction corresponding to the winding axis direction of the electrode body, and that a current collector plate weld portion to be welded to the current collector plate is provided on the core exposed portion in the longitudinal direction of the electrode plate. In this case, it is also conceivable to provide a protective layer for preventing short circuits in the longitudinal direction of the electrode plate between the current collector plate weld portion and the mixture layer.

[0006] However, the inventors have found that with an increase in the number of charge / discharge cycles, the electrode plate may bend near the base of the protective layer, potentially causing a short circuit due to contact with other electrode plates.

[0007] An object of the present disclosure is to prevent short circuits by suppressing bending of the electrode plate near the base of the protective layer, regardless of charge / discharge cycles, in a nonaqueous electrolyte secondary battery in which a protective layer is provided between a collector plate weld portion of the electrode plate and a mixture layer.

[0008] The nonaqueous electrolyte secondary battery according to the present disclosure includes an electrode assembly in which a first electrode plate and a second electrode plate are wound with a separator interposed therebetween, and a current collector plate arranged on one side in the direction of the winding axis of the electrode assembly, wherein the first electrode plate includes a first core made of metal foil, a first mixture layer formed on at least a first surface of the first core, and a first core exposed portion provided on one end of the first surface in the short direction of the electrode plate, which is on the current collector plate side, and exposing the first core, wherein a protective layer for suppressing short circuits is provided in the longitudinal direction of the electrode plate in a boundary region of the first surface between the first mixture layer and the first core exposed portion, and the first electrode plate has a current collector plate welded portion welded to the current collector plate, and a weld-free uncoated region provided in a portion including the inner peripheral end between the current collector plate welded portion and the protective layer.

[0009] In the nonaqueous electrolyte secondary battery according to the present disclosure, the provision of a non-welded uncoated region at the inner circumferential end of the first electrode plate shortens the portion of the first core where the protective layer is provided at the beginning of the charge / discharge cycle. Furthermore, as the secondary battery undergoes more charge / discharge cycles, the elongation of the first core is greater at the inner circumferential end than at other portions. Even if the elongation of the first core is greater at the inner circumferential end, the portion of the first core where the protective layer is provided can be shortened as described above, preventing the portion where the protective layer is provided from becoming excessively long due to elongation. Furthermore, the non-welded uncoated region has lower rigidity and is more easily bent than the portion of the first core where the protective layer is provided. Therefore, even if the non-welded uncoated region elongates, it easily bends to a U-shape or similar cross section. This prevents the elongation of the non-welded uncoated region from affecting the portion where the protective layer is formed and causing it to break. This prevents bending near the base of the protective layer, thereby preventing short circuits.

[0010] 1 is a cross-sectional view taken along the axial direction of a nonaqueous electrolyte secondary battery according to an example embodiment; FIG. 2 is a perspective view showing a portion of an electrode body constituting the nonaqueous electrolyte secondary battery according to an example embodiment developed; FIG. 3 is an enlarged view of part A of FIG. 1 , schematically illustrating a portion at an early stage of a charge-discharge cycle; FIG. 4 is an expanded view of a positive electrode plate constituting the nonaqueous electrolyte secondary battery shown in FIG. 1 ; FIG. 5 is a view corresponding to FIG. 3 when the number of charge-discharge cycles is increased; FIG. 6 is a view showing measurement results of determining the relationship between the number of turns from the innermost circumference and the amount of extension of a positive electrode plate, using a configuration similar to that shown in FIG. 1 ; FIG. 7 is a view corresponding to FIG. 3 when the number of charge-discharge cycles is increased for a nonaqueous electrolyte secondary battery according to a comparative example; FIG. 8 is a view corresponding to FIG. 4 when the number of charge-discharge cycles is increased for a nonaqueous electrolyte secondary battery according to a comparative example;

[0011] In a conventional non-aqueous electrolyte secondary battery, a first mixture layer is formed on at least a first surface of a first substrate made of metal foil, a first substrate exposed portion is provided on one end of the first surface in the short direction of the electrode plate, which is on the current collector plate side, and a current collector plate weld portion to be welded to the current collector plate is provided on the first substrate exposed portion in the longitudinal direction of the electrode plate. In this case, it has been found that if a protective layer for preventing short circuits is provided in the longitudinal direction of the electrode plate between the current collector plate weld portion and the mixture layer, with an increase in the number of charge / discharge cycles, the electrode plate may bend near the base of the protective layer, which may come into contact with another electrode plate, resulting in a short circuit.

[0012] As a result of extensive research, the inventors have found that as the number of charge / discharge cycles increases, the electrode plate elongates particularly at the portion near the innermost periphery of the electrode plate in the electrode assembly, and as a result, the protective layer becomes longer toward the current collector plate, making it more likely to bend near the base of the protective layer. Therefore, the inventors have found that by providing a protective layer on the first surface of the first electrode plate in the boundary region between the first mixture layer and the first substrate exposed portion, and by having the first electrode plate have a current collector plate welded portion welded to the current collector plate and a non-welded, uncoated region in a portion including the inner periphery end between the current collector plate welded portion and the protective layer, it is possible to suppress bending of the electrode plate near the base of the protective layer and thereby suppress short circuits. Specifically, since the first electrode plate has an unwelded, uncoated region at the inner peripheral end between the collector plate weld and the protective layer, even if the number of charge / discharge cycles increases and the first core elongates, the unwelded, uncoated region, which is less rigid and more prone to bending than the portion of the first core provided with the protective layer, becomes longer, while the portion of the first core provided with the protective layer, which is more rigid, does not become excessively long. This prevents bending near the base of the protective layer and prevents short circuits.

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating understanding of the present invention and can be appropriately changed according to the specifications of the nonaqueous electrolyte secondary battery. Furthermore, the term "substantially" is used below to mean, for example, not only completely the same, but also substantially the same. Furthermore, when multiple embodiments and modified examples are included below, it is initially assumed that their characteristic features will be used in appropriate combination.

[0014] Fig. 1 is a cross-sectional view taken along the axial direction of a nonaqueous electrolyte secondary battery 10 according to an embodiment. Fig. 2 is a perspective view showing a partially developed electrode body 14 constituting the nonaqueous electrolyte secondary battery 10. Fig. 3 is an enlarged view of part A in Fig. 1 , schematically illustrating the battery at the beginning of a charge / discharge cycle.

[0015] As shown in FIGS. 1 to 3 , the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte (not shown), an exterior body 15 that is a metal can, and a sealing body 16. The wound electrode assembly 14 has a positive electrode plate 11, a negative electrode plate 12, and a separator 13. As shown in FIG. 2 (described later), the positive electrode plate 11 and the negative electrode plate 12 are spirally wound with the separator 13 interposed therebetween. Hereinafter, one axial side of the electrode assembly 14 may be referred to as the "upper" side, and the other axial side as the "lower" side. The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. Hereinafter, the nonaqueous electrolyte secondary battery 10 will be referred to as a secondary battery 10.

[0016] 2 , the electrode assembly 14 has a wound structure in which a long positive electrode plate 11 and a long negative electrode plate 12 are wound with a long separator 13 interposed therebetween. The positive electrode plate 11 protrudes upward beyond the negative electrode plate 12 and the separator 13, and the negative electrode plate 12 protrudes downward beyond the positive electrode plate 11 and the separator 13.

[0017] The positive electrode plate 11 has a positive electrode core exposed portion 34 where the positive electrode core 30 is exposed without the positive electrode mixture layer 32 at an upper end portion, which is one end portion in the winding axis direction (hereinafter sometimes referred to as the axial direction) of the long positive electrode plate 11 from the winding start end to the winding end end in the electrode plate longitudinal direction. Furthermore, at the upper end portion of the positive electrode plate 11, a positive electrode protective layer 36 is provided between the positive electrode mixture layer 32 and the positive electrode core exposed portion 34 to prevent short circuits of the positive electrode core 30. In this embodiment, as described below, the width of the positive electrode protective layer 36 in the electrode plate short direction varies in the electrode plate longitudinal direction. Furthermore, as described below, the positive electrode plate 11 has a current collector weld portion 38 ( FIG. 3 ) and a non-welded, uncoated region 39 ( FIG. 3 ) between the current collector weld portion 38 and the positive electrode protective layer 36.

[0018] The negative electrode plate 12 has a negative electrode core exposed portion 44 where the negative electrode core 40 is exposed without the negative electrode mixture layer 42 provided, at the lower end portion which is the other end portion in the axial direction from the winding start end to the winding end end in the longitudinal direction of the long negative electrode plate 12. Therefore, the upper end portion in the axial direction of the electrode body 14 is constituted by the positive electrode core exposed portion 34, and the lower end portion in the axial direction of the electrode body 14 is constituted by the negative electrode core exposed portion 44.

[0019] In this embodiment, the positive electrode plate 11 corresponds to the first electrode plate, and the negative electrode plate 12 corresponds to the second electrode plate. The positive electrode core 30 corresponds to the first core, and the positive electrode mixture layer 32 corresponds to the first mixture layer. The negative electrode core 40 corresponds to the second core, and the negative electrode mixture layer 42 corresponds to the second mixture layer. Note that the first electrode plate may be the negative electrode plate 12, and the second electrode plate may be the positive electrode plate 11.

[0020] The non-aqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte includes 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 (nonaqueous electrolytic solution), and may be a solid electrolyte using a gel polymer or the like. The 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.

[0021] 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 input 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.

[0022] 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.).

[0023] The positive electrode plate 11 includes a positive electrode core 30 and a positive electrode mixture layer 32 formed on both sides of the positive electrode core 30. The positive electrode core 30 may be made of a metal foil, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode plate 11, or a film with such a metal disposed on the surface. The thickness of the positive electrode core 30 is, for example, 10 μm to 30 μm. The positive electrode mixture layer 32 includes a positive electrode active material, a conductive agent, and a binder. The positive electrode plate 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc., to the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 32 on both sides of the positive electrode core 30. The positive electrode mixture layer 32 may be formed on only one side of the positive electrode core 30. The thickness of the positive electrode mixture layer 32 on one side of the positive electrode substrate 30 is, for example, 10 μm or more and 150 μm or less.

[0024] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0025] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode mixture layer 32 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0026] A positive electrode protective layer 36 is provided on both sides of the upper end of the positive electrode core 30, between the positive electrode mixture layer 32 and the positive electrode core exposed portion 34. The positive electrode protective layer 36 can be, for example, an inorganic filler protective layer containing an inorganic material additive such as alumina, a resin such as a water-insoluble polymer such as polyvinylidene fluoride (PVdF), and a conductive additive such as acetylene black (AB) or carbon black (CB) in a predetermined ratio. For example, the positive electrode protective layer 36 can be configured to contain an inorganic material such as alumina, a resin such as polyvinylidene fluoride (PVdF), and a conductive additive in a mass ratio of 100:16.7:0.5. The conductive additive may be omitted from the positive electrode protective layer 36. The positive electrode protective layer 36 can be provided on the surface of the positive electrode core 30, and various materials can be used as long as they have the function of suppressing short circuits in the positive electrode core 30.

[0027] The negative electrode plate 12 includes a negative electrode core 40 and a negative electrode mixture layer 42 formed on both sides of the negative electrode core 40. The negative electrode core 40 may be made of a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode plate 12, or a film with such a metal disposed on the surface. The thickness of the negative electrode core 40 is, for example, 5 μm to 30 μm. The negative electrode mixture layer 42 contains a negative electrode active material and a binder. The negative electrode plate 12 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on both sides of the negative electrode core 40. The negative electrode mixture layer 42 may be formed on only one side of the negative electrode core 40. The thickness of the negative electrode mixture layer 42 is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode substrate 40 .

[0028] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials include natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. The negative electrode mixture layer 42 may contain a silicon (Si) material as the negative electrode active material. Furthermore, the negative electrode active material may include a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0029] As in the case of the positive electrode plate 11, fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like may be used as the binder contained in the negative electrode mixture layer 42, but styrene-butadiene rubber (SBR) or a modified product thereof is preferably used. In addition to SBR or the like, the negative electrode mixture layer 42 may also contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0030] 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. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0031] 1 , the secondary battery 10 has a metallic negative electrode current collector 17 made of nickel, nickel alloy, or the like, on the axially lower side of the electrode body 14. A negative electrode core exposed portion 44 protruding from the electrode body 14 is joined to the negative electrode current collector 17, which is joined to the inner surface of the bottom plate of the exterior body 15. The exterior body 15 to which the negative electrode core exposed portion 44 is electrically connected via the negative electrode current collector 17 serves as a negative electrode terminal.

[0032] The secondary battery 10 has a metallic positive electrode current collector 18 made of aluminum, aluminum alloy, or the like, on the axially upper side of the electrode body 14. A positive electrode core exposed portion 34 protruding from the electrode body 14 is joined to the positive electrode current collector 18. The secondary battery 10 has a circular insulating plate 19 on the axially upper side of the positive electrode current collector 18.

[0033] One end of a positive electrode connection lead 20 is joined to the upper surface of the positive electrode current collector 18 by welding or the like, the positive electrode connection lead 20 passes through a through-hole in the insulating plate 19 and extends toward the sealing body 16, and the other end of the positive electrode connection lead 20 is connected to the underside of a filter 22 of the sealing body 16 by welding or the like. A cap 26 that forms the top plate of the sealing body 16 is electrically connected to the filter 22. This electrically connects the positive electrode current collector 18 to the cap 26, and the cap 26 serves as a positive electrode terminal. The positive electrode connection lead 20 is a conductive member made of a metal primarily composed of aluminum or the like.

[0034] The secondary battery 10 further includes a resin gasket 27 disposed between the exterior body 15 and the sealing body 16. The gasket 27 is sandwiched between the exterior body 15 and the sealing body 16, and insulates the sealing body 16 from the exterior body 15. The gasket 27 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the exterior body 15 from the sealing body 16. The exterior body 15 has an annular groove 21 in part of its axial direction.

[0035] The grooved portion 21 can be formed, for example, by spinning a portion of the side surface radially inward to create a recess radially inward. The exterior body 15 has a bottomed tubular portion including the grooved portion 21 and an annular shoulder portion. The bottomed tubular portion houses the electrode assembly 14 and the nonaqueous electrolyte, and the shoulder portion is bent radially inward from the end of the open side of the bottomed tubular portion and extends inward. The shoulder portion is formed when the upper end of the exterior body 15 is bent inward and crimped to the peripheral edge of the sealing body 16. The sealing body 16 is crimped and fixed to the exterior body 15 with a gasket 27 interposed between the shoulder portion and the grooved portion 21. In this manner, the internal space of the secondary battery 10 is sealed.

[0036] The sealing body 16 has a structure in which a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked in this order from the electrode body 14 side. Each member constituting the sealing body 16 has, for example, a disk or ring shape, and each member except for the insulating member 24 is electrically connected to one another. The filter 22 has at least one through-hole. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, with the insulating member 24 interposed between their respective peripheral edges.

[0037] When the secondary battery 10 generates abnormal heat and the internal pressure of the secondary battery 10 rises, the lower valve body 23 deforms and ruptures, 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. If the internal pressure rises further, the upper valve body 25 ruptures and gas is discharged from the through-hole 26a of the cap 26. This gas discharge prevents the internal pressure of the secondary battery 10 from rising excessively, which could cause the secondary battery 10 to explode, thereby improving the safety of the secondary battery 10.

[0038] Next, the structure of the periphery of the joint between the electrode body 14 and the positive current collector plate 18 at the top of the secondary battery 10, and the structure of the positive plate 11 will be described with reference to Figures 3 and 4. Figure 3 is an enlarged view of part A in Figure 1, showing a schematic view of the secondary battery 10 in its shipping state, which is the early stage of a charge / discharge cycle. Figure 4 is an exploded view of the positive plate 11 that constitutes the secondary battery 10.

[0039] As shown in FIG. 3 , the positive electrode core 30 has an axially extending portion 37 extending substantially parallel to the axial direction of the electrode assembly 14 from the upper end of a coated portion 35, on both sides of which a positive electrode mixture layer 32 is provided. The current collector weld portion 38 is bent at approximately 90 degrees from the upper end of the axially extending portion 37 toward the inner periphery and extends parallel to the lower surface of the positive current collector plate. The current collector weld portion 38 is welded to the lower surface of the positive current collector plate 18. A positive electrode protective layer 36 is provided on both sides of a portion of the axially extending portion 37 near the upper end of the coated portion 35. The width of the positive electrode protective layer 36 in the short-side direction of the electrode plate increases toward the outer periphery of the electrode assembly 14. The positive electrode plate 11 has the current collector weld portion 38 welded to the positive current collector plate 18 and an uncoated region 39 (no welding) provided in a portion including the inner periphery end between the current collector weld portion 38 and the positive electrode protective layer 36. In Figure 3, the current collector plate weld 38 and the underside of the positive current collector plate 18 are shown separated from each other, but in reality, the upper surface of each current collector plate weld 38 in each circumferential portion of the positive current collector plate 11 is welded in contact with the underside of the positive current collector plate 18.

[0040] Furthermore, the current collector plate welds 38 in adjacent winding portions of the positive electrode plate 11 partially overlap, thereby reducing the electrical resistance between the positive electrode plate 11 and the positive current collector plate 18. Note that the current collector plate welds 38 in adjacent winding portions of the positive electrode plate 11 may not overlap.

[0041] 4 shows the positive electrode plate 11 in an expanded state, showing a first surface S1 which is one side surface in the thickness direction of the positive electrode plate 11. A positive electrode core exposed portion 34 where the positive electrode core 30 is exposed is provided at the upper end of the first surface S1 which is one side in the short side direction of the electrode plate, that is, on the positive electrode current collector plate 18 side. In FIG. 4, the positive electrode core exposed portion 34 is shown as a plain portion.

[0042] Furthermore, on the first surface S1, a positive electrode protective layer 36 is provided in the boundary region between the positive electrode mixture layer 32 and the positive electrode substrate exposed portion 34 in the longitudinal direction of the positive electrode plate 11. In Fig. 4, the positive electrode protective layer 36 is represented by a sandy portion. Also in Fig. 4, the positive electrode mixture layer 32 is represented by a diagonal grid portion.

[0043] 4, the upper edge of the positive electrode protective layer 36 is inclined upward toward the winding end with respect to the longitudinal direction of the electrode plate so that the width of the positive electrode protective layer 36 in the lateral direction of the electrode plate increases toward the outer periphery of the electrode body 14. As a result, the width of the positive electrode protective layer 36 in the lateral direction of the electrode plate varies in the longitudinal direction of the electrode plate.

[0044] Furthermore, a current collector weld 38 having a constant width in the short-side direction is formed along the long-side direction at the upper end, which is one end of the positive electrode substrate exposed portion 34 in the short-side direction. The positive electrode plate 11 also has a non-welded uncoated region 39 located between the current collector weld 38 and the positive electrode protective layer 36, including the inner peripheral end. Because the width of the positive electrode protective layer 36 in the short-side direction varies along the long-side direction, the width of the non-welded uncoated region 39 in the short-side direction continuously decreases from the winding start end of the innermost circumferential portion toward the winding end end of the outermost circumferential portion. As a result, the width of the non-welded uncoated region 39 in the short-side direction increases toward the innermost circumferential portion in each winding portion A1, A2, A3, and A4 of the positive electrode plate, as shown in FIG. 3 .

[0045] The maximum width of the uncoated region 39 in the short direction of the electrode plate is W2, which is greater on the inner side than W1, based on the center C1 in the longitudinal direction of the electrode plate. Furthermore, the average width of the uncoated region 39 in the short direction of the electrode plate is Wm1, which is the average width from the innermost periphery to the fifth turn, which is greater than Wm2, which is the average width from the sixth turn to the outermost periphery. In Figure 4, T1 indicates the winding end of the fifth turn.

[0046] According to the secondary battery 10 described above, the positive electrode plate 11 has a non-welded uncoated region 39 in a portion including the inner peripheral end between the current collector plate weld 38 and the positive electrode protective layer 36. This allows the portion of the positive electrode core 30 where the positive electrode protective layer 36 is provided to be shorter at the inner peripheral end of the positive electrode plate 11 at the initial stage of a charge / discharge cycle due to the non-welded uncoated region 39. Furthermore, as the secondary battery 10 undergoes more charge / discharge cycles, the positive electrode core 30 elongates more at the inner peripheral end than at other portions. Even if the positive electrode core 30 elongates more at the inner peripheral end, the portion of the positive electrode core 30 where the positive electrode protective layer 36 is provided can be shortened as described above, thereby preventing the portion where the positive electrode protective layer 36 is provided from becoming excessively long due to elongation. Furthermore, the non-welded uncoated region 39 has lower rigidity and is more flexible than the portion of the positive electrode substrate 30 where the positive electrode protective layer 36 is provided, so even if the non-welded uncoated region 39 stretches, it easily bends so that the cross section becomes U-shaped or the like. This prevents the portion where the positive electrode protective layer 36 is formed from being affected and broken by the stretching of the non-welded uncoated region 39. This prevents breaking near the base of the positive electrode protective layer 36, thereby preventing short circuits.

[0047] FIG. 5 is a diagram corresponding to FIG. 3 when the number of charge-discharge cycles is increased. As shown in FIG. 5 , when the number of charge-discharge cycles of the secondary battery 10 is increased, the positive electrode core 30 provided with the positive electrode mixture layer 32 elongates in the vertical direction due to repeated charge-discharge cycles. At this time, the elongation is greater on the inner circumferential side than on the outer circumferential side of the electrode assembly 14. This is thought to be because the outer circumferential side is restricted by the outer circumferential body 15, but the inner circumferential side is permitted to elongate due to the presence of a cavity near the winding axis of the electrode assembly 14. Therefore, as in the embodiment, the maximum width of the uncoated region 39 in the transverse direction of the electrode plate is greater (W2) than (W1) on the inner circumferential side, based on the center C1 in the longitudinal direction of the electrode plate. This suppresses folding near the base of the positive electrode protective layer 36 and thus prevents short circuits. Furthermore, the positive electrode protective layer 36 can be enlarged on the outer circumferential side, thereby enhancing the short circuit prevention effect.

[0048] As shown in Figure 5, as the number of charge / discharge cycles increases, the coated portion 35 of the positive electrode mixture layer 32 stretches significantly in the vertical direction toward the inner periphery. Even in this case, as shown in Figure 3, the uncoated region 39 without welding is larger on the inner periphery, so the uncoated region 39 without welding on the inner periphery bends more than the outer periphery. However, the stretching of the coated portion 35 on the inner periphery can be absorbed by the area below the current collector plate weld 38. This prevents the portion of the positive electrode protective layer 36, which has higher rigidity than the uncoated region 39 without welding, from being sandwiched vertically between the current collector plate weld 38 and the coated portion 35 and bending in the axial direction. This prevents bending near the base of the positive electrode protective layer 36, thereby preventing short circuits.

[0049] Furthermore, as will be described later, measurements by the inventors have revealed that the average elongation of the positive electrode plate 11 from the innermost circumferential portion to the fifth winding is greater than the average elongation of the positive electrode plate 11 from the sixth winding to the outermost circumferential portion. Figures 1, 3, and 5 are schematic diagrams of the electrode assembly 14, and the actual number of windings of the positive electrode plate 11 is significantly greater than those shown in Figures 1, 3, and 5. Even when the average elongation of the positive electrode plate 11 from the innermost circumferential portion to the fifth winding is greater than the average elongation of the other portions, as described above, the average width of the uncoated region 39 in the short-side direction of the electrode plate, i.e., the average width Wm1 from the innermost circumferential portion to the fifth winding is greater than the average width Wm2 from the sixth winding to the outermost circumferential portion, as in the embodiment, thereby enhancing the short-circuit suppression effect.

[0050] FIG. 6 shows the results of measurements performed using a configuration similar to that shown in FIG. 1 to determine the relationship between the number of turns from the innermost periphery of the positive electrode plate 11 and the amount of elongation. In FIG. 6, the horizontal axis represents the number of turns from the innermost periphery of the positive electrode plate 11, and the vertical axis represents the amount of elongation of the positive electrode plate 11. The dashed line E1 in FIG. 6 indicates the state of the secondary battery 10 at the time of shipment, which is the initial stage of the charge-discharge cycle. The thin solid line E2 in FIG. 6 indicates the state after 170 charge-discharge cycles, and the thick solid line E3 indicates the state after 300 charge-discharge cycles. The measurement results in FIG. 6 reveal that the more charge-discharge cycles there are, the greater the amount of elongation of the positive electrode plate 11, and that the inner portion tends to elongate more than the outer portion. The measurement results in FIG. 6 also reveal that the average elongation from the innermost periphery to the fifth turn of the positive electrode plate 11 is greater than the average elongation from the sixth turn to the outermost periphery. This demonstrates that the embodiment achieves a high short-circuit suppression effect.

[0051] Fig. 7 is a diagram corresponding to Fig. 3 at the beginning of a charge / discharge cycle of the secondary battery of the comparative example. Fig. 8 is a diagram corresponding to Fig. 3 when the number of charge / discharge cycles of the secondary battery of the comparative example increases. As shown in Fig. 7 , in the comparative example, the positive electrode plate 11a constituting the electrode body 14a does not have an uncoated region without welding between the current collector plate weld 38 welded to the positive current collector plate 18 and the positive electrode protective layer 36, and the entire upper surface of the positive electrode substrate exposed portion 34 is joined by welding to the positive current collector plate 18 as the current collector plate weld 38.

[0052] In this comparative example, as shown in FIG. 8 , if the number of charge / discharge cycles increases and the inner circumferential side of the positive electrode plate 11a expands significantly in the vertical direction, the portion of the positive electrode plate 11a where the positive electrode protective layer 36 is provided is sandwiched between the current collector plate weld 38 and the coating 35 of the positive electrode mixture layer 32 and is pushed from the coating 35 toward the current collector plate weld 38. As a result, the portion of the positive electrode plate 11 where the positive electrode protective layer 36 is provided tends to bend in the axial direction near its base and fall toward the negative electrode plate 12. In this case, the positive electrode plate 11 may break through the separator 13 and come into contact with the negative electrode plate 12, resulting in a short circuit. The above-described embodiment can prevent such a problem.

[0053] Fig. 9 is a view of a secondary battery according to another example of the embodiment, corresponding to Fig. 4. In the configuration of this example, as shown in Fig. 9, in the expanded state of the positive electrode plate 11b, the width of the positive electrode protective layer 36 in the short-side direction of the electrode plate increases toward the outer periphery of the electrode body 14, so that the upper edge of the positive electrode protective layer 36 gradually changes upward toward the winding end in the long-side direction of the electrode plate.

[0054] As a result, the positive electrode plate 11b has a non-welded, uncoated region 39a in a portion including the inner peripheral end between the current collector plate weld 38 and the positive electrode protective layer 36. Because the width of the positive electrode protective layer 36 in the short-side direction of the plate changes in stages as described above, the width of the non-welded, uncoated region 39a in the short-side direction of the plate gradually decreases from the winding start end of the innermost portion toward the winding end end of the outermost portion. A secondary battery including such a positive electrode plate 11b can also achieve a high short-circuit suppression effect even with a large number of charge / discharge cycles, similar to the configurations shown in FIGS. 1 to 6 . Other configurations and functions of this example are the same as those of the configurations shown in FIGS. 1 to 6 .

[0055] In the above examples, the positive electrode plates 11 and 11b are provided with unwelded, uncoated regions 39 and 39a. Alternatively, a negative electrode protective layer may be provided on a portion of the negative electrode plate that protrudes downward from the negative electrode mixture layer of the negative electrode core. In this case, the negative electrode plate may have a collector plate welded to the negative electrode current collector 17 and a welded, uncoated region provided in a portion including the inner peripheral end between the collector plate weld and the negative electrode protective layer. Even in this case, similar to the effect of the positive electrode plates 11 and 11a in the above embodiment, a high short-circuit suppression effect can be achieved by suppressing breakage of the portion of the negative electrode core where the negative electrode protective layer is provided, even with many charge / discharge cycles.

[0056] 10 Non-aqueous electrolyte secondary battery (secondary battery), 11, 11a, 11b Positive electrode plate, 12 Negative electrode plate, 13 Separator, 14, 14a Electrode body, 15 Exterior body, 16 Sealing body, 17 Negative electrode current collector plate, 18 Positive electrode current collector plate, 19 Insulating plate, 20 Positive electrode connection lead, 21 Grooved portion, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Through hole, 27 Gasket, 28 Negative electrode connection lead, 30 Positive electrode core, 32 Positive electrode mixture layer, 34 Positive electrode core exposed portion, 35 Coated portion, 36 Positive electrode protective layer, 37 Axial extension portion, 38 Current collector plate welded portion, 39, 39a Uncoated area without welding, 40 Negative electrode core, 42 Negative electrode mixture layer, 44 Negative electrode core exposed portion, 46 negative electrode protective layer.

Claims

1. An electrode body in which a first electrode plate and a second electrode plate are wound with a separator interposed therebetween, and a current collector plate disposed on one side in the winding axis direction of the electrode body, The first electrode plate includes a first core made of a metal foil, a first binder layer formed on at least a first surface of the first core, and a first core exposed portion provided at one end of the electrode plate in the short side direction on the current collector plate side on the first surface, where the first core is exposed, A protective layer for suppressing short circuit is provided in the longitudinal direction of the electrode plate in a boundary region between the first binder layer and the first core exposed portion on the first surface, The first electrode plate has a current collector welding portion welded to the current collector plate and a non-welded and non-coated region provided in a portion including an inner peripheral side end between the current collector welding portion and the protective layer, A non-aqueous electrolyte secondary battery.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the maximum width of the non-welded and non-coated region in the short side direction of the electrode plate is larger on the inner peripheral side than on the outer peripheral side with respect to the center in the longitudinal direction of the electrode plate.

3. The non-aqueous electrolyte secondary battery according to claim 2, wherein the average width of the non-welded and non-coated region in the short side direction of the electrode plate is larger from the innermost peripheral portion to the fifth winding portion than from the sixth winding portion to the outermost peripheral portion.

4. The non-aqueous electrolyte secondary battery according to claim 2, wherein the width of the non-welded and non-coated region in the short side direction of the electrode plate continuously or stepwise decreases from the start side end of the innermost peripheral portion to the end side end of the outermost peripheral portion.

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