Non-aqueous electrolyte secondary battery

Abstract

Provided is a highly reliable non-aqueous electrolyte secondary battery in which the occurrence of internal short circuiting is suppressed. A non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure comprises: an electrode body in which a first electrode and a second electrode that are strip-shaped and have different polarities from each other are wound 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. An exposed portion at which the current collector is exposed is formed on the surface of the first electrode, and one end side of an electrode tab is connected to the exposed portion. The electrode tab has a planar shape in which a corner part on one end side is R-chamfered.

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates 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 strip-shaped positive and negative electrodes are stacked and wound, is housed in an outer casing. Patent Document 1 discloses a secondary battery including a wound electrode assembly, and discloses a technology for improving current collection by providing a positive electrode current collector exposed portion, in which the positive electrode current collector is exposed, at a position approximately in the center of the positive electrode in the longitudinal direction, and connecting a positive electrode tab to this positive electrode current collector exposed portion.

[0003] Japanese Patent Application Laid-Open No. 2008-234855

[0004] In recent years, non-aqueous electrolyte secondary batteries have become increasingly high-capacity and high-power. The increased capacity and high-power of batteries has led to an increase in the amount of heat generated when an internal short circuit occurs in the battery, creating a need to reduce the risk of an internal short circuit. In secondary batteries that house a wound electrode assembly in an exterior case, a large stress may be applied to the tip of the electrode tab when the battery receives a strong external impact, potentially damaging the separator facing the tip of the electrode tab and causing an internal short circuit. Prior art, including Patent Document 1, has not adequately considered the shape of the tip of the electrode tab, and there is still room for further consideration.

[0005] An object of the present disclosure is to provide a highly reliable non-aqueous electrolyte secondary battery that suppresses the occurrence of internal short circuits.

[0006] A nonaqueous electrolyte secondary battery according to one aspect of the present disclosure includes an electrode assembly in which strip-shaped first and second electrodes having different polarities are wound 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, an exposed portion where the current collector is exposed is formed on the surface of the first electrode, and one end of an electrode tab is connected to the exposed portion, and the electrode tab has a planar shape with rounded chamfered corners on the one end.

[0007] The nonaqueous electrolyte secondary battery according to the present disclosure can suppress internal short circuits caused by breakage of the separator facing the tip of the electrode tab.

[0008] Fig. 3 is an axial cross-sectional view of a cylindrical secondary battery that is an example of an embodiment. Fig. 4 is a perspective view of a wound electrode body provided in the secondary battery shown in Fig. 1. Fig. 5 is a front view showing a positive electrode and a negative electrode that constitute an electrode body according to an example of an embodiment in a developed state. Fig. 6 is an enlarged view of the vicinity of a positive electrode current collector exposed portion and a positive electrode tab of the positive electrode shown in Fig. 3. Fig. 7 is a view corresponding to Fig. 4 in another example of an embodiment. Fig. 8 is a view corresponding to Fig. 4 in another example of an embodiment.

[0009] Hereinafter, an example of an embodiment of a cylindrical secondary battery according to the present disclosure will be described in detail with reference to the 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 cylindrical secondary battery. Furthermore, when the following description includes multiple embodiments and modified examples, it is assumed from the beginning that the characteristic portions of those embodiments and modified examples can be appropriately combined and used.

[0010] FIG. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment. The secondary battery 10 shown in FIG. 1 includes an electrode assembly 14 and a nonaqueous electrolyte (not shown) housed in an outer casing 15. The electrode assembly 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. Examples of nonaqueous solvents (organic solvents) for the nonaqueous electrolyte include carbonates, lactones, ethers, ketones, esters, and the like. Two or more of these solvents can be mixed together. When two or more solvents are mixed together, a mixed solvent containing a cyclic carbonate and a chain carbonate is preferably used. 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. The electrolyte salt of the non-aqueous electrolyte is LiPF ６ , LiBF ４ , LiCF ３ SO ３etc., 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. For convenience of explanation, the following description will be given with the sealing body 16 side as the "upper" and the bottom side of the exterior body 15 as the "lower".

[0011] 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 tab 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 tab 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 addition, the negative electrode 12 is located on the outermost peripheral surface of the electrode body 14 and is in contact with the exterior body 15. In the secondary battery 10, the exterior body 15 serves as the negative electrode terminal.

[0012] 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.

[0013] 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.

[0014] Next, the electrode assembly 14 will be described with reference to Fig. 2. Fig. 2 is a perspective view of the electrode assembly 14. As described above, the electrode assembly 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all formed in a strip shape, and are spirally wound around a winding axis, thereby being alternately stacked in the radial direction of the electrode assembly 14. The separator 13 is formed to be at least one size larger than the positive electrode 11, and, for example, two separators 13 are arranged to sandwich the positive electrode 11.

[0015] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets 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, and the surface of the separator 13 may be coated with a material such as an aramid-based resin or ceramic.

[0016] In the radial direction β, the side of the winding axis is called the inner side of the winding, and the opposite side is called the outer side of the winding. In the electrode body 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is called the winding direction γ, and the lateral direction of the positive electrode 11 and the negative electrode 12 is called the axial direction α. ​​In the winding direction γ, the side of the winding axis is called the winding start side, and the opposite side is called the winding end side. The positive electrode tab 19 extends in the axial direction α from approximately the center in the radial direction from the center to the outermost circumference at the upper end of the electrode body 14. Furthermore, the negative electrode tab 20 extends in the axial direction α from near the winding axis at the lower end of the electrode body 14.

[0017] Next, the positive electrode 11 and the negative electrode 12 will be described in detail with reference to FIGS. 3 to 5B. An example in which the positive electrode 11 is the first electrode and the negative electrode 12 is the second electrode will be described below. Note that the present embodiment is not limited to this example. For example, the negative electrode 12 may be the first electrode. Alternatively, the second electrode may have the same characteristics as the first electrode, and both the positive electrode 11 and the negative electrode 12 may have the characteristics of the first electrode.

[0018] 3 is a front view showing the positive electrode 11 and negative electrode 12 constituting an electrode assembly 14 according to an example embodiment in an expanded state. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium precipitation. That is, the negative electrode 12 is formed to be longer in both the lateral and longitudinal directions than the positive electrode 11. As will be described later, since the positive electrode tab 19 faces the negative electrode 12, when a strong external impact is received, stress is concentrated at one end 19a of the positive electrode tab 19, which may damage the opposing separator 13 and cause an internal short circuit.

[0019] 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 current collector 30 may be, for example, a foil of a metal such as aluminum, or a film having such a metal disposed on its surface. A suitable positive electrode current collector 30 is a foil of a metal whose main component is aluminum or an aluminum alloy. The thickness of the positive electrode current collector 30 is, for example, 10 μm or more and 30 μm or less.

[0020] The positive electrode mixture layer 32 is preferably formed on both sides of the positive electrode current collector 30. The thickness of the positive electrode mixture layer 32 is, for example, 10 μm or more and 150 μm or less on one side of the positive electrode current collector 30. The positive electrode mixture layer 32 includes, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 is produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both sides of the positive electrode current collector 30, followed by drying and rolling.

[0021] As the positive electrode active material, a lithium-containing transition metal oxide containing a transition metal element such as Co, Mn, or Ni can be used. The lithium-containing transition metal oxide is not particularly limited, but may be any of the following oxides represented by the general formula: Li １＋ｘ MO ２ (wherein, −0.2<x≦0.2, and M contains at least one of Ni, Co, Mn, and Al) is preferred.

[0022] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon black (CB) such as acetylene black (AB) and Ketjen black, and carbon materials such as graphite. Examples of the binder contained in the positive electrode mixture layer 32 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, and polyolefin resins. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. These may be used alone or in combination of two or more.

[0023] 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. 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.

[0024] 3, a positive electrode current collector exposed portion 34 is provided over the entire length in the short direction at approximately the center 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, the positive electrode current collector exposed portion 34 is preferably provided at a position approximately equidistant from both ends of the winding start side and the winding end side.

[0025] One end 19a of the positive electrode tab 19 is connected to the positive electrode current collector exposed portion 34. The positive electrode tab 19 is joined to the positive electrode current collector exposed portion 34 by, for example, ultrasonic welding. The width of the positive electrode tab 19 is, for example, 1 mm or more and 10 mm or less.

[0026] As will be described in detail later, one end 19a of the positive electrode tab 19 is rounded. Rounded corners refer to rounded corners. Stress is likely to concentrate at the corners of the one end 19a of the positive electrode tab 19 when subjected to a strong external impact. By rounding the one end 19a, stress concentration at the corners can be alleviated, and an internal short circuit due to damage to the separator 13 facing the one end 19a can be suppressed. Note that the present invention is not limited to the example shown in FIG. 3 . For example, 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 tab 19 may be connected to each of the positive electrode current collector exposed portions 34.

[0027] The negative electrode 12 has a strip-shaped negative electrode current collector 40 and a negative electrode mixture layer 42 formed on the surface of the negative electrode current collector 40. The negative electrode current collector 40 may be, for example, a foil of a metal such as copper, or a film having such a metal disposed on its surface. The thickness of the negative electrode current collector 40 is, for example, 5 μm or more and 30 μm or less.

[0028] The negative electrode mixture layer 42 is preferably formed on both sides of the negative electrode current collector 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 current collector 40. The negative electrode mixture layer 42 contains, for example, a negative electrode active material and a binder. The negative electrode mixture layer 42 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 both sides of the negative electrode current collector 40, followed by drying and rolling.

[0029] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release Li 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, or artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. Furthermore, metals that alloy with Li, such as Si and Sn, metal compounds containing Si and Sn, and lithium-titanium composite oxides may also be used as the negative electrode active material. For example, SiO ｘ (x is 0.5 to 1.6), silicon oxide represented by the formula Li ２ｙ SiO （２＋ｙ） A silicon-containing material in which fine particles of Si are dispersed in a lithium silicate phase represented by (0<y<2), a silicon-containing material in which fine particles of Si are dispersed in a carbon phase, or the like may be used in combination with graphite.

[0030] The negative electrode mixture layer 42 contains, for example, graphite as a negative electrode active material and a silicon-containing material. By including the silicon-containing material in the negative electrode 12 together with graphite, the battery capacity can be increased. The content of the silicon-containing material in the negative electrode active material may be 3% by mass or more. In this case, the rate at which the negative electrode 12 expands upon charge and discharge increases, making the effects of the present disclosure more pronounced. The upper limit of the content of the silicon-containing material in the negative electrode active material is, for example, 30% by mass.

[0031] 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 its salts (CMC-Na, CMC-K, CMC-NH ４ and the like, which may be a partially neutralized salt), polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, and the like, which may be a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0032] In the example shown in FIG. 3 , negative electrode current collector exposed portions 44, where the negative electrode current collector 40 is exposed, are formed near the winding start end and winding end end of the negative electrode 12. The negative electrode current collector exposed portions 44 are portions of the negative electrode current collector 40 that are not covered with the negative electrode mixture layer 42. For example, the negative electrode current collector exposed portions 44 are formed by intermittent application of the negative electrode mixture slurry to a portion of the negative electrode current collector 40. A negative electrode tab 20 is connected to the negative electrode current collector exposed portion 44 near the winding start end. The negative electrode current collector exposed portion 44 near the winding end is in direct contact with the outer casing 15. The negative electrode current collector exposed portions 44 are preferably provided on both sides of the negative electrode 12 so as to overlap in the thickness direction of the negative electrode 12. The negative electrode tab 20 is joined to the negative electrode current collector exposed portion 44 by, for example, ultrasonic welding.

[0033] Next, the shape of the tip of the positive electrode tab 19 will be described with reference to Fig. 4. Fig. 4 is an enlarged view of the positive electrode current collector exposed portion 34 of the positive electrode 11 and the vicinity of the positive electrode tab 19 shown in Fig. 3.

[0034] In the example shown in FIG. 4 , one end 19a of the positive electrode tab 19 has a flat portion 50 located in the center of the width of the positive electrode tab 19 and R-chamfered portions 52 located at both ends of the width of the positive electrode tab 19. The flat portion 50 is a straight line substantially parallel to the longitudinal direction of the positive electrode 11. That is, the positive electrode tab 19 has a planar shape in which the corners on the one end 19a side are R-chamfered. The positive electrode tab 19 can be obtained, for example, by R-chamfering the corners of a typical rectangular positive electrode tab. In the example shown in FIG. 4 , the shapes of the two R-chamfered portions 52 are the same, but they may also be different shapes.

[0035] Next, another embodiment of the positive electrode 11 will be described with reference to Figures 5A and 5B. Figures 5A and 5B are views corresponding to Figure 4 in another example of the embodiment.

[0036] In the example shown in Fig. 5A, one end 19a of the positive electrode tab 19 is rounded entirely. That is, the positive electrode tab 19 has a planar shape in which the entire one end 19a is rounded entirely. Because the entire one end 19a is rounded, the one end 19a does not have a flat portion and only has an R-chamfered portion 52. This more significantly reduces the effect of alleviating stress applied to the vicinity of the one end 19a when an external impact is received. The shape of the one end 19a is preferably a curved shape that convexly extends outward from the positive electrode tab 19, for example, a semicircular arc with the width of the positive electrode tab 19 as its diameter.

[0037] 5B , the positive electrode current collector exposed portion 34 is in contact with only one end 11a of the positive electrode 11 in the short-side direction, and the length L1 of the positive electrode current collector exposed portion 34 in the short-side direction of the positive electrode 11 is equal to or less than half the length L2 of the positive electrode 11 in the short-side direction. By shaping the positive electrode current collector exposed portion 34 as described above, the one end 19a of the positive electrode tab 19 is surrounded by the positive electrode mixture layer 32 not only in the long-side direction but also in the short-side direction of the positive electrode 11, thereby reducing stress acting near the one end 19a when subjected to an external impact. Furthermore, the center of the positive electrode 11 in the short-side direction expands more than the both ends of the positive electrode 11 in the short-side direction due to battery charge / discharge, and is therefore more susceptible to large stress when subjected to an external impact. By setting L1 / L2≦½, it is possible to prevent one end 19 a from being positioned at the center in the short-side direction of positive electrode 11, and therefore the effect of alleviating stress acting near one end 19 a when subjected to external impact becomes more pronounced. Note that in the example shown in Fig. 5B, one end 19 a is entirely rounded as in the example shown in Fig. 5A, but the shape of one end 19 a is not limited to this example.

[0038] As described above, according to the nonaqueous electrolyte secondary battery of the present disclosure, it is possible to alleviate the stress acting in the vicinity of one end 19 a when subjected to an external impact, thereby suppressing an internal short circuit caused by damage to the separator facing the tip of the electrode tab.

[0039] 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 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, an exposed portion where the current collector is exposed is formed on the surface of the first electrode, and one end of an electrode tab is connected to the exposed portion, and the electrode tab has a planar shape in which a corner on the one end side is rounded and chamfered. Aspect 2: The non-aqueous electrolyte secondary battery according to Aspect 1, wherein the electrode tab has a planar shape in which the entire one end side is rounded and chamfered. Aspect 3: The non-aqueous electrolyte secondary battery according to Aspect 1 or 2, wherein the exposed portion is in contact with only one of both ends in the short side direction of the first electrode, and the length of the exposed portion in the short side direction of the first electrode is half or less of the length of the first electrode in the short side direction. 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 first electrode or the second electrode contains graphite as a negative electrode active material and a silicon-containing material, and the content of the silicon-containing material in the negative electrode active material is 3 mass% or more.

[0040] REFERENCE SIGNS LIST 10 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 tab, 19a One end, 20 Negative electrode tab, 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 Positive electrode current collector exposed portion, 40 Negative electrode current collector, 42 Negative electrode mixture layer, 44 Negative electrode current collector exposed portion, 50 Flat portion, 52 R-chamfered portion

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode assembly in which a band-shaped first electrode and a second electrode having mutually different polarities are wound with a separator interposed therebetween, and an exterior body housing the electrode assembly, wherein the first electrode has a current collector and a mixture layer formed on the surface of the current collector, an exposed portion where the current collector is exposed is formed on the surface of the first electrode, and one end side of an electrode tab is connected to the exposed portion, and the electrode tab has a flat shape with a rounded chamfered corner on the one end side.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the electrode tab has a flat shape with the one end entirely chamfered with a radius.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the exposed portion contacts only one of both ends in a short side direction of the first electrode, and the length of the exposed portion in the short side direction of the first electrode is equal to or less than half the length of the first electrode in the short side direction.

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 first electrode or the second electrode contains graphite as a negative electrode active material and a silicon-containing material, and the content of the silicon-containing material in the negative electrode active material is 3 mass % or more.

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