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 and a second electrode, which are belt-shaped and have different polarities from each other, are wound along the longitudinal direction with a separator interposed therebetween; and an exterior body that accommodates the electrode body. The first electrode has a current collector and a mixture layer formed on the surface of the current collector. On the surface of the first electrode, a current collector exposed part of the current collector is formed so as to be in contact with only one end part of both end parts in the transverse direction of the first electrode. A protective tape is adhered so as to cover the current collector exposed part, and a linear recess part extending in the longitudinal direction of the first electrode is formed on the surface of the protective tape.

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] Conventionally, 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 are formed in which a current collector is exposed so as to contact only one of both ends in the short direction of the electrode, leads are welded to these exposed portions, and the leads are then covered with a protective tape.

[0003] Japanese Patent Application Laid-Open No. 2003-068271

[0004] However, during the process of producing a wound electrode assembly, winding misalignment of the electrode assembly may occur, in which the positive electrode and the negative electrode are misaligned relative to each other in the axial direction. From the viewpoint of improving battery reliability, it is desirable that the positive electrode and the negative electrode face each other within a predetermined range. Through research by the present inventors, it has been found that slippage on the surface of the protective tape is one of the causes of winding misalignment of the electrode assembly. The technology disclosed in Patent Document 1 does not consider winding misalignment of the electrode assembly, and there is still room for improvement.

[0005] An object of the present disclosure is to provide a nonaqueous electrolyte secondary battery in which winding misalignment of an electrode assembly is reduced.

[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, and a current collector exposed portion on the surface of the first electrode is formed so as to contact only one of both ends in the shorter direction of the first electrode, and a protective tape is attached so as to cover the current collector exposed portion, and a linear recess extending in the longitudinal direction of the first electrode is formed on the surface of the protective tape.

[0007] The nonaqueous electrolyte secondary battery according to the present disclosure improves the reliability of the battery.

[0008] 2 is an axial cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention; FIG. 3 is a front view showing a positive electrode and a negative electrode constituting an electrode assembly according to an embodiment of the present invention in an expanded state; FIG. 4 is an enlarged view of the protective tape of FIG. 2; and FIG. 5 is a cross-sectional view taken along line AA of 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] The positive electrode 11 and negative electrode 12 constituting the nonaqueous electrolyte secondary battery 10 will be described below with reference to FIGS. 2 to 4. FIG. 2 is a front view showing the positive electrode 11 and negative electrode 12 constituting the electrode assembly 14 according to an example embodiment in a developed state. FIG. 3 is an enlarged view of the protective tape 36 in FIG. 2, and FIG. 4 is a cross-sectional view taken along line A-A in FIG. 3. In this embodiment, 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. Note that while FIG. 2 shows the outer surfaces of the positive electrode 11 and the negative electrode 12, the present invention is not limited to this example, and the inner surfaces of the positive electrode 11 and the negative electrode 12 may have the configuration shown in FIG. 2.

[0017] [Positive Electrode] The positive electrode 11 has a strip-shaped 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] 2 , the positive electrode current collector exposed portion 34 is in contact with only one end side 11 a of both ends in the short side direction of the positive electrode 11, and does not extend to the other end side 11 b in the short side direction of the positive electrode 11. As a result, the positive electrode mixture layer 32 is present between the other end side 11 b in the short side direction of the positive electrode 11 and the positive electrode current collector exposed portion 34, thereby increasing the battery capacity of the secondary battery 10. Note that the form of the positive electrode current collector exposed portion 34 is not limited to the example shown in FIG. 2 . 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 36 is attached to the surface of the positive electrode 11 so as to cover the positive electrode current collector exposed portion 34. In the example shown in Fig. 2 , the protective tape 36 covers the entire positive electrode current collector exposed portion 34 and protrudes from one end side 11a in the short direction of the positive electrode 11.

[0025] Linear recesses 37 extending in the longitudinal direction of the positive electrode 11 are formed on the surface of the protective tape 36. The recesses 37 increase the coefficient of friction on the surface of the protective tape 36, suppressing slippage on the surface of the protective tape 36 and reducing misalignment of the electrode body 14 when wound.

[0026] In the example shown in FIG. 2 , the recess 37 has a zigzag shape extending in the longitudinal direction of the positive electrode 11 in a plan view. The recess 37 extending in the longitudinal direction of the positive electrode effectively reduces winding misalignment of the electrode body 14, in which the positive electrode 11 and the negative electrode 12 are misaligned relative to each other in the axial direction. The zigzag shape of the recess 37 increases the length of the recess, thereby more significantly reducing the effect of reducing winding misalignment of the electrode body 14. Here, a zigzag shape refers to a form in which a straight line is bent multiple times. The line drawn by the recess 37 does not have to be zigzag, and may be, for example, a straight line or a curved line.

[0027] As shown in Fig. 3, it is preferable that two or more recesses 37 are formed on the surface of the protective tape 36. This more significantly reduces the effect of winding misalignment of the electrode body 14. In the example shown in Fig. 3, three recesses 37a, 37b, and 37c are formed on the surface of the protective tape 36, but the number of recesses 37 is not limited to this example and may be, for example, one or more and ten or less.

[0028] 3, the recesses 37a, 37b, and 37c have the same shape. The recesses 37a, 37b, and 37c are parallel to one another. The recesses 37a, 37b, and 37c do not intersect with one another and are spaced apart by a distance L in the short-side direction of the first electrode. The shape of the recesses 37 in a plan view is not limited to this example.

[0029] Each of the zigzag recesses 37 shown in Fig. 3 has a bending point 38. The number of bending points 38 is not particularly limited, but may be, for example, 1 to 20 per recess 37. In the example shown in Fig. 3, the bending points 38 are sharp in the lines drawn by the recesses 37, but the invention is not limited to this example, and the bending points 38 may be rounded.

[0030] In the example shown in FIG. 4, the bottom 39 of the recess 37 in cross section is pointed, but is not limited to this example and may be, for example, flat or rounded.

[0031] The depth D of the recess 37 is, for example, 1 μm or more and 5 μm or less, and preferably 1 μm or more and 3 μm or less.

[0032] The protective tape 36 has, for example, a base material layer 36 a and an adhesive layer 36 b formed on the back surface of the base material layer 36 a. That is, a recess 37 is formed on the surface of the base material layer 36 a. The protective tape 36 is attached to the surface of the positive electrode mixture layer 32 by the adhesive layer 36 b.

[0033] The base layer 36a 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 base layer 36a is, for example, 5 μm to 50 μm, and may be 10 μm to 25 μm.

[0034] The material of the recess 37 and the material of the base layer 36a may be different from each other, but in the example shown in Fig. 4, the material of the recess 37 and the material of the base layer 36a are the same. This makes it easier to form the recess 37 on the surface of the base layer 36a. For example, the recess 37 can be formed by laser processing or press processing the surface of the base layer 36a.

[0035] The adhesive layer 36b is a portion for adhering the protective tape 36 to the positive electrode 11. The adhesive layer 36b is formed, for example, over the entire surface of one of the substrate layers 36a. The thickness of the adhesive layer 36b 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 36b 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 36 to the surface of the positive electrode 11. The adhesive layer 36b may further contain, for example, a silicone-based polymer. In the protective tape 36, a heat-resistant layer containing inorganic particles such as metal oxide may be provided between the substrate layer 36a and the adhesive layer 36b.

[0036] [Negative Electrode] As shown in FIG. 2 , 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 44 where the negative electrode current collector 40 is exposed. The thickness of the negative electrode current collector 40 is, for example, 5 μm to 30 μm. The thickness of the negative electrode mixture layer 42 is, for example, 10 μm to 150 μm 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. 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.

[0037] 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 located 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 location of the negative electrode lead 20 is not limited to the end on the winding start side as shown in FIG. 2 , and may be at any position in the longitudinal direction of the negative electrode 12. The negative electrode current collector exposed portion 44 is formed, for example, by intermittent application of the negative electrode mixture slurry to a part of the negative electrode current collector 40. Note that a protective tape 36 may be attached so as to cover the negative electrode current collector exposed portion 44.

[0038] 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.

[0039] 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, resulting in a more pronounced effect of the protective tape 36 according to the present disclosure.

[0040] 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.

[0041] As described above, the nonaqueous electrolyte secondary battery according to the present disclosure can reduce winding misalignment of the electrode assembly caused by slippage on the surface of the protective tape, thereby improving the reliability of the battery.

[0042] The present disclosure is further described by the following embodiments. Aspect 1: A nonaqueous 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 so as to contact only one of both ends in the short direction of the first electrode, and a protective tape is attached so as to cover the current collector exposed portion, and a linear recess extending in the long direction of the first electrode is formed on the surface of the protective tape. Aspect 2: The nonaqueous electrolyte secondary battery according to Aspect 1, wherein the recess has a zigzag shape in a plan view. Aspect 3: The nonaqueous electrolyte secondary battery according to Aspect 1 or 2, wherein two or more recesses are formed on the surface of the protective tape. Configuration 4: The nonaqueous electrolyte secondary battery according to Configuration 3, wherein the two or more recesses have the same shape. Configuration 5: The nonaqueous electrolyte secondary battery according to Configuration 3 or 4, wherein the two or more recesses are parallel to each other. Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 3 to 5, wherein the two or more recesses are spaced apart from each other in the short-side direction of the first electrode.

[0043] REFERENCE SIGNS LIST 10 (nonaqueous electrolyte) secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 exterior body, 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, 36 protective tape, 36a substrate layer, 36b adhesive layer, 37 recess, 38 bending point, 39 bottom, 40 negative electrode current collector, 42 negative electrode mixture layer, 44 exposed portion of negative electrode current collector

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, and a current collector exposed portion on the surface of the first electrode is formed so as to contact only one of both ends in the short direction of the first electrode, and a protective tape is attached so as to cover the current collector exposed portion, and a linear recess extending in the longitudinal direction of the first electrode is formed on the surface of the protective tape.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the recess has a zigzag shape in a plan view.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein two or more recesses are formed on the surface of said protective tape.

4. The nonaqueous electrolyte secondary battery according to claim 3, wherein the two or more recesses have the same shape.

5. The nonaqueous electrolyte secondary battery according to claim 3, wherein the two or more recesses are parallel to each other.

6. The nonaqueous electrolyte secondary battery according to claim 3, wherein the two or more recesses are spaced apart from one another in the short-side direction of the first electrode.

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