Patent Application
20220336861
The present disclosure relates to a non-aqueous electrolyte secondary battery.
Conventionally widely used is a non-aqueous electrolyte secondary battery comprising: a wound electrode assembly in which a band-shaped positive electrode and a band-shaped negative electrode are wound with a separator interposed therebetween, and the outermost circumference surface thereof is wound and fixed with a fixing tape; and an exterior housing body that houses the electrode assembly. In such a battery, a negative electrode lead, which is projected from a winding initial end part of the negative electrode, is connected to the exterior housing body to allow the exterior housing body to be a negative electrode terminal. Patent. Literature 1 discloses a non-aqueous electrolyte secondary battery in which: a negative electrode lead provided on a winding initial end part of a negative electrode is connected to an exterior housing body, and a current collector exposed part that is in contact with an inner wall surface of the exterior housing body is provided on a winding terminal end part of the negative electrode, for improvement in output characteristics of the battery.
PATENT LITERATURE 1: International Publication No. 2016/147564
Although the non-aqueous electrolyte secondary battery described in Patent Literature 1 requires not less than a certain contacting pressure between the electrode assembly and the exterior housing body, the electrode assembly with repeated charging and discharging expands, which results in increased contacting pressure. Since the fixing tape is attached to the outermost circumference surface of the electrode assembly, deformation such as flexure may occur on a positive electrode or negative electrode constituting the electrode assembly from an end part of the fixing tape, where the stress is likely to concentrate.
An object of the present disclosure is to provide a non-aqueous electrolyte secondary battery that can prevent the deformation, such as flexure, of the positive electrode and negative electrode from the fixing tape when the electrode assembly expands.
The non-aqueous electrolyte secondary battery of an aspect of the present disclosure is a non-aqueous electrolyte secondary battery, comprising: a wound electrode assembly in which a band-shaped positive electrode and a band-shaped negative electrode are wound with a separator interposed therebetween; and a metallic exterior housing body that houses the electrode assembly. The positive electrode or the negative electrode is exposed on the outermost circumference surface of the electrode assembly, the fixing tape having a substrate layer and an adhesive layer is attached to the positive electrode or the negative electrode by means of the adhesive layer, and the substrate layer has a surface roughness (Sa) of 40 μm or more on a region having a width of at least 1 mm from the end part.
The non-aqueous electrolyte secondary battery according to the present disclosure can prevent the deformation, such as flexure, of the positive electrode and negative electrode from the fixing tape when the electrode assembly expands.
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, values, directions, and the like, which are examples for facilitating understanding of the present invention, may be appropriately modified with specifications of cylindrical secondary batteries. The exterior housing body is not limited to being in cylindrical form, and may be in rectangular form or the like. When a plurality of embodiments and modified examples are included in the following description, use in appropriate combination of characteristic portions thereof are anticipated in advance.
An opening end of the exterior housing body 15 is capped with the sealing assembly 16 to seal inside the secondary battery 10. Insulating plates 17 and 18 are provided on the upper and lower sides of the electrode assembly 14, respectively. A positive electrode lead 19 extends upward through a through hole of the insulating plate 17, and welded with the lower face of a filter 22, which is a bottom plate of the sealing assembly 16. In the secondary battery 10, a cap 26. which is a top plate of the sealing assembly 16 electrically connected to the filter 22, becomes a positive electrode terminal. Meanwhile, a negative electrode lead 20 extends through a through hole of the insulating plate 18 toward the bottom side of the exterior housing body 15, and welded with a bottom inner face of the exterior housing body 15. In the secondary battery 10, the exterior housing body 15 becomes a negative electrode terminal.
The exterior housing body 15 is a bottomed cylindrical metallic exterior housing can. The exterior housing body 15 is hard and barely deforms when an external stress is applied to the battery, and may protect the inside. Meanwhile, since the metallic exterior housing body 15 is hard and barely deforms, a contacting pressure generated between an electrode assembly 14 and the exterior housing body 15 increases when the electrode assembly 14 expands due to repeated charges and discharges.
As described above, the exterior housing body 15 may be in rectangular form. It is to be noted that the exterior housing body 15 in cylindrical form has a disc-shaped cross section in the horizontal direction, resulting in uniform distribution of stress inside the battery. Thus, the exterior housing body 15 in cylindrical form is less likely to expand as compared with a rectangular exterior housing body having an easily-expandable plain part, and the contacting pressure between the electrode assembly 14 and the exterior housing body 15 is likely to increase. Accordingly, the exterior housing body 15 in cylindrical form is likely to cause deformation, such as flexure, of the positive electrode 11 and negative electrode 12 from the fixing tape, and therefore easily exerts the effect of the present disclosure.
A gasket 27 is provided between the exterior housing body 15 and the sealing assembly 16 to achieve sealability inside the secondary battery 10. The exterior housing body 15 has a grooved part 21 formed by, for example, pressing the side part thereof from the outside to support the sealing assembly 16. The grooved part 21 is preferably formed circularly along the circumferential direction of the exterior housing body 15, and supports the sealing assembly 16 with the gasket 27 interposed therebetween and with the upper face of the grooved part 21.
The sealing assembly 16 has a stacked structure of a filter 22, a lower vent member 23, an insulating member 24, an upper vent member 25, and a cap 26 in this order from the electrode assembly 14 side. Each member constituting the sealing assembly 16 has, for example, a disk shape or a ring shape, and each member except for the insulating member 24 is electrically connected each other. The lower vent member 23 and the upper vent member 25 are connected each other at each of central parts thereof, and the insulating member 24 is interposed between each of the circumferential parts of the vent members 23 and 25. If the internal pressure of the battery increases with abnormal heat generation, for example, the lower vent member 23 breaks and the upper vent member 25 expands toward the cap 26 side to be separated from the lower vent member 23, resulting in cutting off of an electrical connection between the both members. If the internal pressure further increases, the upper vent member 25 breaks, and gas is discharged through an opening 26a of the cap 26.
Next, the electrode assembly 14 will he described with reference to
The negative electrode 12 is exposed on the outermost circumference surface of the electrode assembly 14, and a fixing tape 50 is attached through both ends in the axial direction to the negative electrode 12. The fixing tape 50, which is a member for winding and fixing the electrode assembly 14, is attached so as to cover at least a part of a winding terminal end part 12a of the negative electrode 12. A width of the fixing tape 50 is not particularly limited, and for example, 3 mm to 30 mm, and may be 5 mm to 15 mm. A position and number of the fixing tape 50 is not particularly limited as long as it is attached so as to cover a part of the winding terminal end part 12a, which is exposed on the outermost circumference surface of the electrode assembly 14, and for example, the fixing tape 50 may be attached along the axial direction.
For the separator 13, a porous sheet having an ion permeation property and an insulation property is used. Specific examples of the porous sheet include a fine porous thin film, a woven fabric, and a nonwoven fabric. As a material of the separator 13, an olefin resin such as polyethylene and polypropylene is preferable. A thickness of the separator 13 is, for example. 10 μm to 50 μm. The separator 13 has tended to be thinned as higher capacity and higher output of the battery. The separator 13 has a melting point of, for example, approximately 130° C. to 180° C.
Next, the positive electrode 11 and negative electrode 12 constituting the electrode assembly 14 will be described with reference to
The positive electrode 11 has a band-shaped positive electrode current collector 30 and a positive electrode mixture layer 32 formed on both surfaces of the inner peripheral side and outer peripheral side of the positive electrode current collector 30. For the positive electrode current collector 30, a foil of a metal, such as aluminum, a film in which such a metal is disposed on a surface layer thereof, and the like are used, for example. A preferable positive electrode current collector 30 is a foil of aluminum or of a metal mainly composed of an aluminum alloy. A thickness of the positive electrode current collector 30 is, for example, 10 μm to 30 μm.
The positive electrode mixture layer 32 is preferably formed on an entire region of both surfaces of the positive electrode current collector 30 except for a positive electrode current collector exposed part 34, described later. The positive electrode mixture layer 32 preferably includes a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 is produced by: applying a positive electrode mixture slurry including the positive electrode active material, the conductive agent, the binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) on both surfaces of the positive electrode current collector 30; and then drying and compressing the positive electrode mixture layer 32.
Examples of the positive electrode active material may include a lithium-containing transition metal oxide containing a transition metal element such as Co, Mn, and Ni. The lithium-containing transition metal oxide is hot particularly limited, and preferably a composite oxide represented by the general formula Li1+xMO2 (in the formula, −0.2<x≤0.2 and M includes at least one of the group consisting of Ni, Co, Mn, and Al).
Examples of the conductive agent include carbon materials such as carbon black (CB), acetylene black (AB), Ketjenblack, and graphite. Examples of the binder include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), a polyimide (PI), an acrylic resin, and a polyolefin resin. With these resins, carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like may be used in combination. These materials may be used singly, or may be used in combination of two or more thereof.
In the example illustrated in
Onto the positive electrode current collector exposed part 34, one end of the positive electrode lead 19 is connected with ultrasonic welding or the like. The positive electrode current collector exposed part 34 is preferably provided on both surfaces of the positive electrode 11 to be stacked in the thickness direction of the positive electrode 11 from a viewpoint of operability of connecting the positive electrode lead 19. The positive electrode lead 19 is preferably provided at a position of substantially same distance from the winding initial end part and the winding terminal end part 11a from a viewpoint of current collectability. The other end of the positive electrode lead 19 extends upward from the end surface in the width direction at a medial position in the radial direction of the electrode assembly 14 when wound as the electrode assembly 14. The position of the positive electrode lead 19 to be disposed is not particularly limited to the example illustrated in
The negative electrode 12 has the band-shaped negative electrode current collector 40 and the negative electrode mixture layer 42 formed on both surfaces of the negative electrode current collector 40. For the negative electrode current collector 40, a foil of a metal such as copper, a film in which such a metal is disposed on a surface layer thereof, or the like is used, for example. A thickness of the negative electrode current collector 40 is, for example, 5 μm to 30 μm.
The negative electrode mixture layer 42 is preferably formed on an entire region of both surfaces of the negative electrode current collector 40 except for a negative electrode current collector exposed part 44, described later. The negative electrode mixture layer 42 preferably includes a negative electrode active material and a binder. For example, the negative electrode 12 is produced by: applying a negative electrode mixture slurry including the negative electrode active material, the binder, water, and the like on both surfaces of the negative electrode current collector 40; and drying and compressing the negative electrode mixture layer 42.
The negative electrode active material is not particularly limited as long as it may reversibly occlude and release lithium ions, and for example, carbon materials such as natural graphite and artificial graphite, metals that form an alloy with lithium such as Si and Sn, or an alloy or oxide including them may be used. For the binder included in the negative electrode mixture layer 42, the resin similar to the positive electrode 11 is used, for example. When the negative electrode mixture slurry is prepared in an aqueous solvent, styrene-butadiene rubber (SBR), CMC or a salt thereof, polyacrylic acid or a salt thereof, polyvinyl alcohol, and the like may be rued. These materials may be used singly, and may be used in combination of two or more thereof.
In the example illustrated in
Onto the negative electrode current collector exposed part 44 of the winding initial end part, one end of the negative electrode lead 20 is connected with ultrasonic welding or the like. The negative electrode current collector exposed part 14 is preferably provided on both surfaces of the negative electrode 12 to be stacked in the thickness direction of the negative electrode 12 from a viewpoint of operability of connecting the negative electrode lead 20. The other end of the negative electrode lead 20 extends downward from the end surface in the width direction near the winding axial center of the electrode assembly 14 when wound as the electrode assembly 14. The position of the negative electrode lead 20 to be disposed is not particularly limited to the example illustrated in
The negative electrode current collector exposed part 44 of the winding terminal end part 12a is positioned on the outermost circumference surface of the electrode assembly 14, and is in contact with the exterior housing body 15. Thus, a current pathway to the negative electrode terminal is achieved in addition to the negative electrode lead 20, resulting in improvement in output characteristics of the battery.
On the outermost circumference surface of the electrode assembly 14, the negative electrode 12 is exposed to achieve the current pathway to the negative electrode terminal of the winding terminal end part 12a, but the negative electrode current collector 40 is preferably exposed as an example of an embodiment. The negative electrode current collector 40 is more preferably exposed on an entire surface of the outermost circumference surface of the electrode assembly 14. Thus, a contacting area of the negative electrode current collector exposed part 44 and the exterior housing body 15 increases, resulting in improvement in output characteristics of the battery. When the negative electrode current collector 40 is exposed on the entire surface of the outermost circumference surface of the electrode assembly 14, a length in the longitudinal direction of the negative electrode current collector exposed part 11 may be larger than a length of the outermost circumference of the electrode assembly 14.
Although a case where the exterior housing body 15 is the negative electrode terminal in
Next, the fixing tape 50, which is a member for winding and fixing the electrode assembly 14, will be described with reference to
The substrate layer 52 has an uneven shape on the surface thereof as illustrated in
The substrate layer 52 has a surface roughness (Sa) of 40 μm or more on a region having a width of at least 1 mm from the end part. Setting the surface roughness (Sa) near the end part of the fixing tape 50, which is likely to concentrate a stress due to the contacting pressure between the electrode assembly 14 and the exterior housing body 15, to be 40 μm or more relaxes the stress, and may prevent the deformation, such as flexure, of the positive electrode 11 and negative electrode 12. Here, the surface roughness (Sa) is defined by ISO25178, and may be measured with a commercially available microscope such as VR-3200 manufactured by KEYENCE.
An entire surface of the substrate layer 52 preferably has the surface roughness (Sa) of 40 μm or more. As a result, not only a surface near the end part of the substrate layer 52 but also the entire surface of the substrate layer 52 relaxes the stress; thus, the deformation, such as flexure, of the positive electrode 11 and negative electrode 12 is more certainly prevented.
The surface roughness (Sa) on the substrate layer 52 is preferably 150 μm or less from a viewpoint of maintenance of battery characteristics. A larger surface roughness (Sa) on the substrate layer 52 increases a thickness of the fixing tape 50, resulting in a decreased space for housing the electrode assembly 14 and the electrolyte in the exterior housing body 15.
The substrate layer 52 may be appropriately selected from viewpoints of strength, resistance against the electrolyte liquid, processability, cost, and the like, and for example, PP (polypropylene), PI (polyimide), PET (polyethylene terephthalate), or the like may be used. The adhesive layer 54 is preferably a resin having adhesiveness at room temperature, and for example, an acrylic resin and a rubber resin may be used.
In
A method of producing the uneven shape on the surface of the substrate layer 52 is not particularly limited, and the uneven shape may be produced by, for example, pressing the fixing tape 50 in which a laminated paper is adhered to the adhesive layer 54 against a roller having an uneven shape on a surface thereof. The surface roughness (Sa) on the substrate layer 52 may be regulated with a surface roughness (Sa) of the roller and a pressing pressure of the roller. For example, pressing a roller having a surface roughness (Sa) of 200 μm to 400 μm with a linear pressure of 10 kgf/cm to 100 kgf/cm enables to produce the fixing tape 50 having the surface roughness (Sa) of 40 μm or more.
The present disclosure will be further described below with Examples, but the present disclosure is not limited to these Examples.
[Production of Specimen]
Mixing of 95 parts by mass of graphite, 5 parts by mass of SiO, 1 part by mass of carboxymethyl cellulose (CMC), and 1 part by mass of styrene-butadiene rubber (SBR) was performed, and an appropriate amount of water was added thereto to prepare a negative electrode mixture slurry. Then, the negative electrode mixture slurry was applied on one surface of a band-shaped negative electrode current collector made with a copper foil having a thickness of 8 μm, and then the applied film was dried. The dried applied film was compressed by using a roller, and then cut to a predetermined electrode size to produce a negative electrode in which a negative electrode mixture layer was formed on the one surface of the negative electrode current collector.
An adhesive layer of an acrylic adhesive was applied with 10 μm on a substrate layer made with polypropylene (PP) having a thickness of 20 μm to produce a flat-plate tape. Then, a polypropylene (PP) laminated paper on which a mold releasing agent was applied was adhered on the adhesive layer side, a roller having a unevenness with a surface roughness of 320 μm was pressed from the substrate layer side with a linear pressure of 60 kgf/cm, and then the pressed tape was cut to a 10-mm width to produce a fixing tape having an uneven shape on an entire surface on the substrate layer side.
The fixing tape in which the laminated paper was peeled was attached to a side of the negative electrode on which the negative electrode mixture layer was not formed to produce a specimen.
A specimen was produced in the same manner as in Example 1 except that the linear pressure of compressing the flat-plate tape with the roller was changed to 40 kgf/cm.
A specimen was produced in the same manner as in Example 1 except that the linear pressure of compressing the flat-plate tape with the roller was changed to 20 kgf/cm.
A specimen was produced in the same manner as in Example 1 except that the linear pressure of compressing the flat-plate tape with the roller was changed to 5 kgf/cm.
A specimen was produced in the same manner as in Example 1 except that the flat plate tape was not compressed with a roller.
[Measurement of Surface Roughness (SO on Substrate Layer]
Before the fixing tape was attached to the negative electrode, surface roughnesses (Sa) of the fixing tapes produced in Examples 1 to 3 and Comparative Examples 1 to 2 were measured by using VR-3200 manufactured by KEYENCE under a condition of magnification of 25.
[Stress Application Test]
On the specimens of Examples 1 to 3 and Comparative Examples 1 to 2, a stress application test was performed by using a stress applying, apparatus illustrated in
A surface roughness (Sa) of each of the fixing taps used in Examples 1 to 3 and Comparative Examples 1 to 2 and a presence/absence of the breakage of each specimen after the test are shown in Table 1.
In Comparative Examples 1 to 2, which had a small surface roughness (Sa) of the fixing tape, the negative electrode current collector was broken at the breakage evaluating portion. Meanwhile, in Examples 1 to 3, which had a large surface roughness (Sa) of the fixing tape, the negative electrode current collector was not broken. In other words, in Examples 1 to 3, the fixing tape has a small impact to the deformation, such as flexure, of the positive electrode and negative electrode, resulting in a low possibility of occurrence of the deformation of the positive electrode and negative electrode derived from the fixing tape. From the results, it is found that a large surface roughness (Sa) of the fixing tape may prevent the deformation, such as flexure, of the negative electrode and positive electrode even when the contacting pressure occurs between the electrode assembly and the exterior housing body.
10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 12a Winding terminal end part, 13 Separator, 14 Electrode assembly, 15 Exterior housing body, 16 Sealing assembly, 17, 18 Insulating plate, 19 Positive electrode lead, 20 Negative electrode lead, 21 Grooved part, 22 Filter, 23 Lower vent member, 24 Insulating member, 25 Upper vent member, 26 Cap, 26a Opening, 27 Gasket, 30 Positive electrode current collector, 32 Positive electrode mixture layer, 34 Positive electrode current collector exposed part, 40 Negative electrode current collector, 42 Negative electrode mixture layer, 44 Negative electrode current collector exposed part, 50 Fixing tape, 52 Substrate layer, 54 Adhesive layer, 60 Stress applying apparatus, 62 Specimen, 70 Specimen stage, 72 Chloroprene rubber sheet, 74 Indenter, 76 Breakage evaluating portion
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-165303 | Sep 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/033864 | 9/8/2020 | WO |
