Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery according to the present disclosure comprises: an electrode body in which a first electrode (11) and a second electrode that are strip-shaped and have different polarities from each other are wound along the longitudinal direction via a separator; and an exterior body that accommodates the electrode body. The first electrode (11) has a collector (30) and a mixture layer (32) formed on the surface of the collector (30). A collector exposed portion (34) where the collector (30) is exposed is formed on the surface of the first electrode (11), and a protective tape (38) covers the collector exposed portion (34) and is adhered so as to protrude in the lateral direction from the first electrode (11). The outer periphery (38a) of the protective tape (38) is inclined with respect to the lateral direction of the first electrode (11) at an intersection point X1 between the end side (11a) of the first electrode (11) in the lateral direction and the outer periphery (38a) of the protective tape (38).

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery including a wound electrode assembly.

[0002] Non-aqueous electrolyte secondary batteries have been widely used, in which a wound electrode assembly, in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally with a separator interposed therebetween, is housed in an outer casing. Patent Document 1 discloses a technique in which exposed portions where the current collectors are exposed are formed on each of the positive electrode and the negative electrode, leads are welded to these exposed portions, and the leads are then covered with protective tape. Furthermore, in order to cover the entire exposed portions, the protective tape is longer than the exposed portions in the longitudinal and lateral directions of the electrode, and particularly protrudes from the electrode in the lateral direction of the electrode.

[0003] Japanese Patent Application Laid-Open No. 2004-311282

[0004] As the battery is charged and discharged, the electrode body expands and contracts, and the mixture layer is subjected to tensile stress from the protective tape. The inventors' research has revealed that the mixture layer is prone to peeling from the current collector, starting from the intersection of the short-side edge of the electrode and the outer periphery of the protective tape. In particular, in recent years, the active material content in the mixture layer has increased in order to increase the capacity of batteries, making the mixture layer more prone to peeling. Peeling of the mixture layer may lead to a short circuit. The technology disclosed in Patent Document 1 does not consider the risk of short circuits due to peeling of the mixture layer, and there is still room for improvement.

[0005] An object of the present disclosure is to provide a non-aqueous electrolyte secondary battery with a reduced risk of short circuit.

[0006] The nonaqueous electrolyte secondary battery according to the present disclosure comprises an electrode assembly in which strip-shaped first and second electrodes having different polarities are wound longitudinally with a separator interposed therebetween, and an exterior body that houses the electrode assembly, wherein the first electrode has a current collector and a mixture layer formed on the surface of the current collector, a current collector exposed portion where the current collector is exposed is formed on the surface of the first electrode, and a protective tape is attached to cover the current collector exposed portion and protrudes in the short direction from the first electrode, and the outer periphery of the protective tape is inclined with respect to the short direction of the first electrode at the intersection of the short-side edge of the first electrode and the outer periphery of the protective tape.

[0007] The nonaqueous electrolyte secondary battery according to the present disclosure reduces the risk of short circuits and is therefore highly safe.

[0008] 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, showing a positive electrode and a negative electrode constituting an electrode assembly in a developed state, and FIG.

[0009] An example of an embodiment of the present disclosure will be described in detail below. In the following description, specific shapes, materials, directions, numerical values, etc. are examples for facilitating understanding of the present disclosure and can be appropriately changed according to the application, purpose, specifications, etc. Furthermore, when the following description includes multiple embodiments and modified examples, it is assumed from the beginning that the characteristic portions of these embodiments and modified examples will be used in appropriate combination.

[0010] Fig. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment. In the secondary battery 10 shown in Fig. 1, an electrode assembly 14 and a nonaqueous electrolyte (not shown) are housed in an exterior body 15. For ease of explanation, the following description will be given with the sealing body 16 side referred to as "top" and the bottom side of the exterior body 15 referred to as "bottom."

[0011] The electrode assembly 14 has a wound structure in which a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12 are wound longitudinally with a separator 13 interposed therebetween. The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator include olefin-based resins such as polyethylene and polypropylene, and cellulose. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin. Alternatively, the separator 13 may be a multilayer separator including a polyethylene layer and a polypropylene layer, or a separator 13 having a surface coated with a material such as an aramid-based resin or ceramic.

[0012] The non-aqueous electrolyte includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent (organic solvent) that can be used include carbonates, lactones, ethers, ketones, and esters, and two or more of these solvents can be mixed together. When two or more solvents are mixed together, it is preferable to use a mixed solvent containing a cyclic carbonate and a chain carbonate. For example, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC) can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) can be used as the chain carbonate. Examples of the electrolyte salt include LiPF ６ , LiBF ４ , LiCF ３ SO ３ etc. and mixtures thereof can be used. The amount of electrolyte salt dissolved in the non-aqueous solvent can be, for example, 0.5 mol / L or more and 2.0 mol / L or less. The non-aqueous electrolyte is not limited to a liquid electrolyte, and may be a solid electrolyte using a gel polymer or the like.

[0013] The opening of the exterior body 15 is closed with the sealing body 16, thereby sealing the interior of the secondary battery 10. Insulating plates 17 and 18 are provided above and below the electrode body 14. The positive electrode lead 19 extends upward through a through hole in the insulating plate 17 and is welded to the underside of the filter 22, which is the bottom plate of the sealing body 16. In the secondary battery 10, the cap 26, which is the top plate of the sealing body 16 and is electrically connected to the filter 22, serves as the positive electrode terminal. On the other hand, the negative electrode lead 20 extends through a through hole in the insulating plate 18 toward the bottom of the exterior body 15 and is welded to the inner bottom surface of the exterior body 15. In the secondary battery 10, the exterior body 15 serves as the negative electrode terminal. Note that if the negative electrode lead 20 is located near the end on the winding end side, the negative electrode lead 20 passes outside the insulating plate 18, extends toward the bottom of the exterior body 15, and is welded to the inner bottom surface of the exterior body 15.

[0014] The exterior body 15 is, for example, a cylindrical metal exterior can with a bottom. A gasket 27 is provided between the exterior body 15 and the sealing body 16 to ensure the airtightness of the interior of the secondary battery 10. The exterior body 15 has a grooved portion 21 that supports the sealing body 16, formed, for example, by pressing the side surface from the outside. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the exterior body 15, and supports the sealing body 16 on its upper surface.

[0015] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are stacked in this order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disk or ring shape, and all components except for the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheral edges. If the internal pressure of the battery increases due to abnormal heat generation, for example, the lower valve body 23 may rupture, causing the upper valve body 25 to bulge toward the cap 26 and separate from the lower valve body 25, thereby cutting off the electrical connection between them. If the internal pressure continues to increase, the upper valve body 25 may rupture, allowing gas to be released from the opening 26a of the cap 26.

[0016] Hereinafter, the positive electrode 11 and negative electrode 12 constituting the nonaqueous electrolyte secondary battery 10 will be described with reference to FIGS. 2 and 3 . FIG. 2 is a front view showing the positive electrode and negative electrode constituting the electrode assembly according to an example of the embodiment in a developed state. FIG. 3 is an enlarged view of the periphery of the exposed portion of the positive electrode current collector in FIG. 2 . FIGS. 2 and 3 show the outer surfaces of the wound positive electrode 11 and negative electrode 12. In this embodiment, a case will be described in which the first electrode is the positive electrode 11 and the second electrode is the negative electrode 12. However, the first electrode may be the negative electrode 12 and the second electrode may be the positive electrode 11. Furthermore, both the positive electrode 11 and the negative electrode 12 may have the configuration of the first electrode.

[0017] [Positive Electrode] The positive electrode 11 has a positive electrode current collector 30 and a positive electrode mixture layer 32 formed on the surface of the positive electrode current collector 30. The positive electrode mixture layer 32 is preferably formed on both sides of the positive electrode current collector 30. The positive electrode current collector 30 can be a foil of a metal such as aluminum that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface layer. The thickness of the positive electrode current collector 30 is, for example, 10 μm or more and 30 μm or less.

[0018] The positive electrode mixture layer 32 includes, for example, a positive electrode active material, a conductive agent, and a binder. The thickness of the positive electrode mixture layer 32 is, for example, 10 μm to 150 μm on one side of the positive electrode current collector 30. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry including a positive electrode active material, a conductive agent, a binder, etc. to the surface of the positive electrode current collector 30, drying the coating, and then rolling the coating to form the positive electrode mixture layer 32 on both sides of the positive electrode current collector 30.

[0019] The positive electrode active material is composed, for example, of a lithium transition metal composite oxide as a main component. Elements other than Li contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, Si, and P. An example of a suitable lithium transition metal composite oxide is a composite oxide containing at least one of Ni, Co, and Mn. Specific examples include a lithium transition metal composite oxide containing Ni, Co, and Mn, and a lithium transition metal composite oxide containing Ni, Co, and Al.

[0020] Examples of conductive agents contained in the positive electrode mixture layer 32 include carbon black (CB) such as acetylene black (AB) and ketjen black, carbon nanotubes (CNT), graphene, graphite, and other carbon-based particles. These may be used alone or in combination of two or more. Examples of binders contained in the positive electrode mixture layer 32 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide-based resins, acrylic resins, polyolefin-based resins, and polyacrylonitrile (PAN). These may be used alone or in combination of two or more.

[0021] A positive electrode current collector exposed portion 34, where the positive electrode current collector 30 is exposed, is formed on the surface of the positive electrode 11, and a positive electrode lead 19 is connected to the positive electrode current collector exposed portion 34. The positive electrode current collector exposed portion 34 is a portion of the surface of the positive electrode current collector 30 that is not covered with the positive electrode mixture layer 32, and is provided, for example, by intermittent application of the positive electrode mixture slurry to a portion of the positive electrode current collector 30. The positive electrode current collector exposed portion 34 is preferably provided on both sides of the positive electrode 11 so as to overlap in the thickness direction of the positive electrode 11. The positive electrode lead 19 is joined to the positive electrode current collector exposed portion 34 by, for example, ultrasonic welding.

[0022] 2, the positive electrode current collector exposed portion 34 is formed in the middle in the longitudinal direction of the positive electrode 11. The position of the positive electrode current collector exposed portion 34 is not limited to this example, but from the viewpoint of current collection performance, it is preferable that the positive electrode current collector exposed portion 34 be provided at a position that is approximately equidistant from the winding start end and the winding end end of the positive electrode.

[0023] In the example shown in FIG. 2 , the positive electrode current collector exposed portion 34 contacts only one end edge 11 a of the positive electrode 11 in the short-side direction, and does not extend to the other end edge 11 b of the positive electrode 11 in the short-side direction. This allows the positive electrode mixture layer 32 to be present between the other end edge 11 b of the positive electrode 11 in the short-side direction and the positive electrode current collector exposed portion 34, thereby increasing the battery capacity of the secondary battery 10. The configuration of the positive electrode current collector exposed portion 34 is not limited to the example shown in FIG. 3 . The positive electrode current collector exposed portion 34 may extend from one end edge 11 a to the other end edge 11 b of the positive electrode 11 in the short-side direction, and contact both end edges of the positive electrode 11 in the short-side direction. Alternatively, a plurality of positive electrode current collector exposed portions 34 may be formed on the surface of the positive electrode 11, and a positive electrode lead 19 may be connected to each of the plurality of positive electrode current collector exposed portions 34.

[0024] A protective tape 38 is attached to the surface of the positive electrode 11 so as to cover the positive electrode current collector exposed portion 34 and protrude in the lateral direction from the positive electrode 11. In the example shown in Fig. 2 , the protective tape 38 protrudes from one end side 11a of the positive electrode 11 in the lateral direction while covering the entire positive electrode current collector exposed portion 34.

[0025] 2, the protective tape 38 has an arc-shaped side that protrudes from the positive electrode 11, and the start and end of this arc shape are located on the positive electrode mixture layer 32. Note that the shape of the protective tape 38 is not limited to the example shown in FIG. 2 as long as θ, which will be described later, is within a predetermined range.

[0026] 2 , the protective tape 38 is attached to the outer surface of the wound positive electrode 11. In a wound electrode body, tensile stress is applied to the outer surface of the wound electrode, so by attaching the protective tape 38 having the characteristics described below to the outer surface of the wound electrode, the effect of suppressing peeling of the mixture layer becomes more pronounced. Note that the protective tape 38 may be attached only to the inner surface of the wound electrode, or the protective tape 38 may be attached to both the inner and outer surfaces of the wound electrode.

[0027] The protective tape 38 has, for example, a base layer and an adhesive layer formed on the surface of the base layer. The protective tape 38 is attached to the surface of the positive electrode mixture layer 32 by the adhesive layer.

[0028] The substrate layer may be made of any insulating resin, such as polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyimide (PI), polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). Among these, PI, which has a relatively high hardness, is preferred for the purpose of protecting the positive electrode current collector exposed portion 34. The thickness of the substrate layer may be, for example, 5 μm or more and 50 μm or less, or 10 μm or more and 25 μm or less.

[0029] The adhesive layer is a portion for attaching the protective tape 38 to the positive electrode 11. The adhesive layer is formed, for example, over the entire surface of one of the substrate layers. The thickness of the adhesive layer is, for example, 1 μm or more and 30 μm or less, and may be 1 μm or more and 10 μm or less. The adhesive layer may contain at least one of a rubber-based polymer and an acrylic-based polymer. The rubber-based polymer and the acrylic-based polymer have adhesive properties, and therefore can adhere the protective tape 38 to the surface of the positive electrode 11. The adhesive layer may further contain, for example, a silicone-based polymer. In the protective tape 38, a heat-resistant layer containing inorganic particles such as metal oxide may be provided between the substrate layer and the adhesive layer.

[0030] 3 , at the intersection X1 between the short-side edge 11a of the positive electrode 11 and the outer periphery 38a of the protective tape 38, the outer periphery 38a of the protective tape 38 is inclined with respect to the short-side direction of the positive electrode 11, and the inclination angle θ of the outer periphery 38a of the protective tape 38 with respect to the short-side direction of the positive electrode 11 satisfies θ > 0°. This reduces the tensile stress applied to the positive electrode mixture layer 32 at the intersection X1, thereby suppressing peeling of the positive electrode mixture layer 32 and improving the safety of the battery. If the outer periphery 38a of the protective tape 38 is not a straight line, θ is determined based on the tangent to the outer periphery 38a of the protective tape 38 at the intersection X1.

[0031] The outer periphery 38a of the protective tape 38 is preferably inclined at an angle of 10° to 80° with respect to the short-side direction of the positive electrode 11. That is, in FIG. 3, θ preferably satisfies 10°≦θ≦80°. θ more preferably satisfies 30°≦θ≦60°. The shape of the protective tape 38 is not limited to the example shown in FIG. 3 . For example, the width of the protruding portion of the protective tape 38 may be larger than the width of the portion of the protective tape 38 attached to the surface of the positive electrode 11. In this case, the outer periphery 38a of the protective tape 38 intersects with the short-side direction of the positive electrode 11 counterclockwise at an angle of θ.

[0032] 3, the protective tape 38 has a shape that is approximately symmetrical in the left-right direction. At another intersection X2 between the short-side edge 11a of the positive electrode 11 and the outer periphery 38a of the protective tape 38, θ satisfies θ>0°, preferably 10°≦θ≦80°, and more preferably 30°≦θ≦60°, as described above. The shape of the protective tape 38 is not limited to left-right symmetry; it is sufficient that the θ of at least one of X1 and X2 satisfies θ>0°, and it is preferable that the θ of both X1 and X2 satisfies θ>0°.

[0033] In an embodiment in which the positive electrode current collector exposed portion 34 is provided over the entire length of the positive electrode 11 in the short-side direction, the protective tape 38 preferably also protrudes from the other end side 11b of the positive electrode 11. In this case, there are four intersections between the short-side end sides 11a, 11b of the positive electrode 11 and the outer periphery 38a of the protective tape 38, and it is sufficient that θ at one or more of these intersections satisfies θ > 0°, and it is preferable that θ at all of the intersections satisfies θ > 0°.

[0034] [Negative Electrode] The negative electrode 12 includes a strip-shaped negative electrode current collector 40, a negative electrode mixture layer 42 formed on both sides of the negative electrode current collector 40, and a negative electrode current collector exposed portion 43 where the negative electrode current collector 40 is exposed. The thickness of the negative electrode current collector 40 is, for example, 5 μm or more and 30 μm or less. 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 current collector 40. The negative electrode current collector 40 may be a foil of a metal such as copper that is stable within the potential range of the negative electrode 12, or a film having such a metal disposed on its surface layer. The negative electrode mixture layer 42 includes, for example, a negative electrode active material, a binder, etc. The negative electrode 12 is produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and a solvent such as water to the surface of the negative electrode current collector 40, drying the coating, and then rolling the coating to form a negative electrode mixture layer 42 on both sides of the negative electrode current collector 40.

[0035] The negative electrode lead 20 is joined to the surface of the negative electrode current collector 40 by, for example, ultrasonic welding. One end of the negative electrode lead 20 is disposed in the negative electrode current collector exposed portion 44, and the other end extends downward from the lower end of the negative electrode current collector exposed portion 44. The position of the negative electrode lead 20 is not limited to the end on the winding start side as shown in FIG. 2 , but may be at any position in the longitudinal direction of the negative electrode 12. The negative electrode current collector exposed portion 44 is provided, for example, by intermittent application in which the negative electrode mixture slurry is not applied to a part of the negative electrode current collector 40.

[0036] The negative electrode active material contained in the negative electrode mixture layer 42 is not particularly limited as long as it can reversibly absorb and release lithium ions, and generally, a carbon material such as graphite is used. The graphite may be any of natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads.

[0037] As the negative electrode active material, metals that can be alloyed with Li, such as Si and Sn, metal compounds containing Si, Sn, etc., and lithium-titanium composite oxides may be used. For example, SiO ｘ (0.5≦x≦1.6) ２ｙ SiO （２＋ｙ） A Si-containing compound in which Si fine particles are dispersed in a lithium silicate phase represented by (0<y<2), or a Si-containing compound in which Si is dispersed in a carbon material, may be used in combination with graphite. The inclusion of a Si-containing compound in the negative electrode mixture layer 42 increases the battery capacity, but also increases the rate at which the electrode body 14 expands and contracts during charging. Therefore, when the negative electrode mixture layer 42 contains a Si-containing compound, a greater tensile stress is applied to the positive electrode mixture layer 32, making the effect of the protective tape 38 according to the present disclosure more pronounced.

[0038] Examples of the binder contained in the negative electrode mixture layer 42 include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, etc., or a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0039] As described above, the nonaqueous electrolyte secondary battery according to the present disclosure can reduce the tensile stress applied to the mixture layer at the intersection of the short-side edge of the positive electrode and the outer periphery of the protective tape, thereby reducing the risk of a short circuit due to peeling of the mixture layer.

[0040] The present disclosure is further described by the following embodiments. Aspect 1: A non-aqueous electrolyte secondary battery including an electrode assembly in which strip-shaped first and second electrodes having opposite polarities are wound longitudinally with a separator interposed therebetween, and an exterior housing that houses the electrode assembly, wherein the first electrode has a current collector and a mixture layer formed on the surface of the current collector, a current collector exposed portion where the current collector is exposed is formed on the surface of the first electrode, and a protective tape is attached to cover the current collector exposed portion and protrudes from the first electrode in the short-side direction, and the outer periphery of the protective tape is inclined with respect to the short-side direction of the first electrode at an intersection of an end side of the short-side direction of the first electrode and the outer periphery of the protective tape. Aspect 2: The non-aqueous electrolyte secondary battery according to Aspect 1, wherein the outer periphery of the protective tape is inclined with respect to the short-side direction of the first electrode at an angle of 10° to 80°. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the protective tape is attached to the outer side of the wound first electrode. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the first electrode is a positive electrode. Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the current collector exposed portion is formed in a longitudinally intermediate portion of the first electrode.

[0041] REFERENCE SIGNS LIST 10 (nonaqueous electrolyte) secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 outer casing, 16 sealing body, 17, 18 insulating plate, 19 positive electrode lead, 20 negative electrode lead, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a opening, 27 gasket, 30 positive electrode current collector, 32 positive electrode mixture layer, 34 exposed portion of positive electrode current collector, 38 protective tape

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode assembly in which strip-shaped first and second electrodes having opposite polarities are wound longitudinally with a separator interposed therebetween, and an exterior housing that houses the electrode assembly, wherein the first electrode has a current collector and a mixture layer formed on the surface of the current collector, a current collector exposed portion where the current collector is exposed is formed on the surface of the first electrode, and a protective tape is attached to cover the current collector exposed portion and protrudes in the short direction from the first electrode, and at the intersection of the short-side edge of the first electrode and the outer periphery of the protective tape, the outer periphery of the protective tape is inclined with respect to the short direction of the first electrode.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the outer periphery of the protective tape is inclined at an angle of 10° to 80° relative to the short-side direction of the first electrode.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the protective tape is attached to the outer surface of the wound first electrode.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first electrode is a positive electrode.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the current collector exposed portion is formed in a longitudinally intermediate portion of the first electrode.

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