Method for manufacturing a non-aqueous electrolyte secondary battery

Abstract

To provide a compact non-aqueous electrolyte secondary battery that is excellent in electrical characteristics such as high output and is excellent in safety.SOLUTION: A non-aqueous electrolyte secondary battery 100 comprises: an exterior body in which a negative electrode can 1 and a positive electrode can 2 are insulated and sealed; and an electrode structure 10 that is accommodated in the external body and includes a negative electrode 6 and a positive electrode 8 electrically connected with the negative electrode can 1 and the positive electrode can 2, respectively. The negative electrode 6 and the positive electrode 8 further include a negative electrode lead tab 5 and a positive electrode lead tab 7 that are electrically connected with the electrodes, respectively, and the negative electrode lead tab 5 and the positive electrode lead tab 7 have a negative electrode connection part 50 and a positive electrode connection part 70, respectively, which are on opposite surfaces to the negative electrode can 1 and the positive electrode can 2. Irregularity parts 4 for connecting to the negative electrode connection part 50 and the positive electrode connection part 70 are formed on an inner surface 1a of the negative electrode can 1 and an inner surface 2a of the positive electrode can 2. Irregularity absorption parts are arranged between the negative electrode connection part 50 and positive electrode connection part 70 and the electrode structure 10.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte secondary battery.

Background Art

[0002] There is known a so-called coin-type (button-type) battery in which an electrode structure as a power generation element is housed in a flat cylindrical metal container. The coin-type (button-type) battery has a structure in which, for example, a metal positive electrode can connected to a positive electrode and a metal negative electrode can connected to a negative electrode are sealed via a gasket (packing) made of an insulator. In such a structure, a metal container such as a positive electrode can and a negative electrode can can be used as current collectors. When using a metal container as a current collector, by making the contact between the electrodes (positive electrode and negative electrode) to be connected and the container good, the internal resistance of the power generation element can be reduced, and electrical characteristics such as the load characteristics of the battery can be improved. As a mode of contact between the metal container and the electrode, for example, it has been proposed to form sharp irregularities with a predetermined surface roughness on the contact surface on the inner bottom surface of the container. (For example, see Patent Document 1.)

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, as the main power source of electronic devices, conventionally, batteries in rectangular or cylindrical containers have been used, but there has been a demand for smaller batteries such as the above-mentioned coin-type (button-type) batteries. Since high output characteristics are required for the battery used as the main power source, for the electrode structure as the power generation element, a flat positive electrode and a negative electrode are laminated so as to face each other with a separator in between, and further integrated by winding, folding, etc. are used. Here, the positive electrode and the negative electrode constituting the electrode structure usually have a structure in which an active material or the like is disposed on a current collector made of a metal thin film such as aluminum or copper. Also, the electrical connection between the electrode structure and the metal container is made by connecting a lead tab extending from the electrode structure and the metal container by welding or the like. This lead tab can be formed by extending the above-mentioned metal thin film or joining a separate metal plate to the metal thin film.

[0005] As in Patent Document 1 described above, when irregularities are formed on the inner bottom surface of the metal container, it is expected that the contact property between the lead tab and the metal container is improved, thereby reducing the resistance of the battery and enhancing the output characteristics. However, when the electrode structure is housed in the metal container at a high density, a high pressure is applied to the electrode structure. In particular, the lead tab and the current collector are usually metal thin films with a thickness of less than 100 μm, and when irregularities are transferred to this, the distance to the adjacent current collector becomes short, which may cause an internal short circuit in the electrode structure. In view of such problems, an object of the present invention is to provide a small non-aqueous electrolyte secondary battery having excellent electrical characteristics such as high output and excellent safety.

Means for Solving the Problems

[0006] The non-aqueous electrolyte secondary battery in the present invention Manufacturing methodIt includes an outer package in which a first container and a second container are hermetically sealed, and an electrode structure including a first electrode and a second electrode that are accommodated in the outer package and electrically connected to the first container and the second container respectively. At least one of the first electrode and the second electrode further includes a lead tab electrically connected to the electrode. The lead tab has a connection portion on the opposing surface with the container on the connection side, and uneven portions having tips for connecting to the connection portion are formed on the inner surface of the container. , before An uneven absorption portion including an insulating uneven absorption material is disposed between the connection portion and the electrode structure. , fixing the connection part of the lead tab to the uneven part by pressure welding connection It is characterized by this.

[0009] The non-aqueous electrolyte secondary battery in the present invention Manufacturing method Preferably, the uneven absorption material includes at least one kind of the group consisting of a resin sponge, a tape, a sheet, and a clip.

Effect of the Invention

[0010] According to the present invention, the inner surface of the positive electrode can or the negative electrode can with uneven portions formed thereon is crimped to the positive electrode connection portion or the negative electrode connection portion, and a good electrical connection can be obtained between the electrode structure and the can. In addition, since the uneven absorption portion is disposed between the positive electrode connection portion or the negative electrode connection portion and the electrode structure, the electrode structure is less affected by the uneven portions on the inner surface of the can. As a result, the lead tab extending from the electrode structure and the container can be favorably conductively connected and short circuit can be prevented, so that a non-aqueous electrolyte secondary battery with high output and excellent safety can be provided.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0012] Hereinafter, each embodiment of the non-aqueous electrolyte secondary battery of the present invention will be given, and each configuration will be described in detail with reference to the drawings.

[0013] (First Embodiment) An example of the non-aqueous electrolyte secondary battery in this embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic cross-sectional view of the state before sealing for explaining each member constituting the non-aqueous electrolyte secondary battery 100. FIG. 2 is a schematic cross-sectional view for explaining the non-aqueous electrolyte secondary battery 100 in the sealed state.

[0014] The non-aqueous electrolyte secondary battery 100 in this embodiment is a so-called coin type (button type) battery in which an electrode structure as a power generation element is housed inside a flat cylindrical metal container. More specifically, as shown in FIGS. 1 and 2, a metal first container (negative electrode can 1) having a flat cylindrical shape with one end open and a metal second container (positive electrode can 2) are insulated from each other via a gasket 3. Then, by overlapping and caulking the opening of the positive electrode can 2 on the negative electrode can 1, a flat cylindrical metal container having a sealed accommodation space formed inside can be formed. And an electrode structure 10 is housed in this accommodation space, and a battery is configured by being electrically connected to each of the negative electrode can 1 and the positive electrode can 2.

[0015] The electrode structure 10 is produced in a structure that can be accommodated in a container by lamination, folding, etc., in addition to the winding structure shown in FIG. 1, in a state where a first electrode (negative electrode 6) and a second electrode (positive electrode 8) are laminated so as to face each other with a separator 9 interposed therebetween. Furthermore, although not shown, an electrolytic solution is sealed in the accommodation space.

[0016] In this embodiment, uneven portions 4 described later are formed on the inner surface 1a of the negative electrode can 1 and the inner surface 2a of the positive electrode can 2, respectively. Then, the negative electrode lead tab 5 and the positive electrode lead tab 7 are fixedly connected by pressure contact to the uneven portions 4 formed on the respective inner surfaces. Here, the negative electrode lead tab 5 is an extension of the negative electrode 6 that constitutes the electrode structure 10. More specifically, for example, the negative electrode lead tab 5 is an extension of a negative electrode current collector made of copper foil that constitutes the negative electrode 6. This negative electrode lead tab 5 is disposed at a position between the electrode structure 10 and the negative electrode can 1 in a state of being folded back and laminated a plurality of times. The negative electrode connection portion 50 of the negative electrode lead tab 5 that faces the negative electrode can 1 is pressure-bonded to the uneven portion 4 formed on the inner surface 1a of the negative electrode can 1, whereby the negative electrode connection portion 50 and the inner surface 1a are connected. Further, the negative electrode lead tab folded portion 51, which is the remaining negative electrode lead tab 5, is disposed between the negative electrode connection portion 50 and the electrode structure 10. Similarly, a positive electrode lead tab 7 extends from the positive electrode 8 (for example, a positive electrode current collector made of aluminum foil that constitutes the positive electrode 8) that constitutes the electrode structure 10. The positive electrode lead tab 7 is disposed at a position between the electrode structure 10 and the positive electrode can 2 in a state of being folded back and laminated a plurality of times. The positive electrode connection portion 70 of the positive electrode lead tab 7 that faces the positive electrode can 2 is pressure-bonded to the uneven portion 4 formed on the inner surface 2a of the positive electrode can 2, whereby the positive electrode connection portion 70 and the inner surface 2a are connected. Further, the positive electrode lead tab folded portion 71, which is the remaining positive electrode lead tab 7, is disposed between the positive electrode connection portion 70 and the electrode structure 10.

[0017] When manufacturing the non-aqueous electrolyte secondary battery 100, first, after manufacturing the electrode structure 10 using the negative electrode 6, the positive electrode 8, and the separator 9, the electrode structure 10 is housed inside the exterior body composed of the negative electrode can 1, the positive electrode can 2, and the gasket 3 in the arrangement shown in FIG. 1. Next, after arranging the negative electrode can 1 with the gasket 3 attached so as to be in contact with the positive electrode can 2, the non-aqueous electrolyte secondary battery 100 as shown in FIG. 2 can be created by caulking and sealing the opening of the positive electrode can 2 toward the negative electrode can 1 side. At this time, the negative electrode connection portion 50 and the positive electrode connection portion 70 are respectively pressure-bonded to the inner surface 1a of the negative electrode can 1 and the inner surface 2a of the positive electrode can 2. In this way, the negative electrode can 1 and the positive electrode can 2 and the electrode structure 10 can be electrically connected.

[0018] Also, before caulking and sealing the negative electrode can 1 and the positive electrode can 2, the negative electrode connection portion 50 of the negative electrode lead tab 5 may be pressure-bonded to the uneven portion 4 formed on the inner surface 1a of the negative electrode can 1, and the positive electrode connection portion 70 of the positive electrode lead tab 7 may be pressure-bonded to the uneven portion 4 formed on the inner surface 2a of the positive electrode can 2. By doing so, the electrical connection between the negative electrode can 1 and the positive electrode can 2 and the electrode structure 10 can be performed more reliably.

[0019] In the present embodiment, the uneven portion 4 is formed on the inner surface 1a of the negative electrode can 1 and the inner surface 2a of the positive electrode can 2. By forming this uneven portion 4, the contact area when the negative electrode connection portion 5 and the positive electrode connection portion 7 are connected to the inner surfaces on their respective sides increases, and the contact resistance can be sufficiently reduced. In the examples shown in FIGS. 1 and 2, the uneven portion 4 is formed on both the negative electrode side and the positive electrode side, but it may be formed on at least one side. As shown in FIGS. 1 and 2, the uneven portion 4 is formed in a protruding shape with a sharp tip. Thereby, it can sufficiently bite into the oxide film on the metal surface at the negative electrode connection portion 5 and the positive electrode connection portion 7, and the contact resistance can be greatly reduced. Further, when the uneven portion 4 is pressure-bonded so as to penetrate the negative electrode connection portion 5 and the positive electrode connection portion 7, the inner surface 1a of the negative electrode can 1 and the negative electrode connection portion 5, or the inner surface 2a of the positive electrode can 2 and the positive electrode connection portion 7 can be firmly fixed.

[0020] The uneven portion 4 may also have a tip formed in a flat shape (not shown). Further, the tip may be rounded. By adopting these shapes, while achieving to a certain extent the effects obtained when the above-described tip is a sharp protrusion, it is possible to more reliably prevent short circuits in combination with the uneven absorption portion described later.

[0021] Also, as shown in FIGS. 1 and 2, in the present embodiment, the negative electrode lead tab 5 and the positive electrode lead tab 7 are folded back, and a plurality of layers are folded back a plurality of times, having a negative electrode lead tab folded portion 51 and a positive electrode lead tab folded portion 71. Thereby, due to the malleability of the negative electrode lead tab 5 and the positive electrode lead tab 7 made of metal, or the gaps between the layers of the negative electrode lead tab 5 and the positive electrode lead tab 7, it is possible to prevent the shape of the uneven portion 4 from spreading to the electrode structure 10. In addition, since the negative electrode lead tab 5 and the positive electrode lead tab 7 have a predetermined length, a space for arranging a crimping jig can be provided when crimping the negative electrode connection portion 50 and the positive electrode connection portion 70 to the can, which is also suitable from the manufacturing aspect.

[0022] Also, in the present embodiment described above, one negative electrode lead tab 5 and one positive electrode lead tab 7 extend from the electrode structure 10 respectively. However, the present invention is not limited to this, and a plurality of each may extend. And instead of the folding structure of one connection portion, a laminated structure of a plurality of connection portions may be used as the uneven absorption portion.

[0023] Known materials can be used for the materials constituting the non-aqueous electrolyte secondary battery in the present embodiment. The negative electrode can 1 is formed in a flat cylindrical shape with one end open. Further, as shown in FIG. 1, the negative electrode can 1 may have a fold formed at the end on the opening side, or may be formed in a multi-stage cylindrical shape. The negative electrode can 1 can be formed by drawing a stainless steel plate or the like. Examples of the stainless steel material include SUS316L, SUS329J4L, or SUS304. Further, as the material of the negative electrode can, for example, a clad material obtained by crimping copper, nickel, or the like to stainless steel may be used.

[0024] The positive electrode can 2 is formed in a flat cylindrical shape with one end open. This positive electrode can 2 can be formed by drawing a stainless steel sheet or the like. Examples of the stainless steel material include SUS316L and SUS329J4L.

[0025] The gasket 3 is made of an annular insulating member, is interposed between the negative electrode can 1 and the positive electrode can 2, and insulates and holds both of them. Examples of the material of the gasket 3 include plastic resins such as polypropylene resin (PP), polyphenylene sulfide (PPS), polyethylene terephthalate (PET), polyamide, liquid crystal polymer (LCP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA), polyether ether ketone resin (PEEK), polyether nitrile resin (PEN), polyether ketone resin (PEK), polyarylate resin, polybutylene terephthalate resin (PBT), polycyclohexane dimethylene terephthalate resin, polyether sulfone resin (PES), polyaminobismaleimide resin, polyetherimide resin, and fluororesin.

[0026] In order to improve the sealing performance of the container, a sealing agent may be further disposed between the negative electrode can 1 or the positive electrode can 2 and the gasket 3. Examples of the sealing agent include asphalt, epoxy resin, polyamide-based resin, and butyl rubber-based adhesive.

[0027] The electrode structure 10 includes a sheet-like negative electrode 6, a positive electrode 8, and a separator 9. This electrode structure 10 can be manufactured into a shape that can be accommodated in a container by laminating the negative electrode 6 and the positive electrode 8 with the separator 9 interposed therebetween and winding, stacking, folding, or the like. For example, when manufacturing the electrode structure 10 by winding, the separator 9 can be sandwiched between both sides of the sheet of the positive electrode 8, and then the negative electrode 6 can be further laminated and flatly wound.

[0028] The negative electrode 6 is formed by applying a negative electrode mixture composed of a negative electrode active material, a conductive assistant, and a binder onto a negative electrode current collector. More specifically, the negative electrode 6 can be obtained by applying a negative electrode mixture diluted with an organic solvent to form a paste onto the negative electrode current collector and then drying the negative electrode current collector to remove the organic solvent.

[0029] The negative electrode current collector is a metal thin film with a thickness of 100 μm or less, and metals such as copper and aluminum can be used. The negative electrode lead tab 5 is composed of a metal thin film that is an extension of this negative electrode current collector. Also, the negative electrode lead tab 5 may be formed by welding copper, nickel, aluminum, etc. to the extension of the negative electrode current collector.

[0030] Known materials used in non-aqueous electrolyte secondary batteries can be used as the negative electrode active material. Examples of the negative electrode active material include carbon materials such as hard carbon, soft carbon, and graphite, silicon oxide represented by SiO x (0 < x < 2), lithium titanate (Li4Ti5O 12 ), Si, WO2, WO3, Li-Al alloy, and various other materials.

[0031] Examples of the conductive assistant contained in the negative electrode mixture include carbonaceous materials such as furnace black, ketjen black, acetylene black, and graphite. In addition, one of the above conductive assistants can be used alone, or two or more can be used in combination.

[0032] Examples of the binder contained in the negative electrode mixture include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), etc. In addition, one of the above binders can be used alone, or two or more can be used in combination.

[0033] The positive electrode 8 is formed by applying a positive electrode mixture composed of a positive electrode active material, a conductive assistant, and a binder onto a positive electrode current collector. More specifically, the positive electrode 8 can be obtained by applying a positive electrode mixture diluted with an organic solvent to a paste state onto a positive electrode current collector and then drying the positive electrode current collector to remove the organic solvent.

[0034] The positive electrode current collector is a metal thin film with a thickness of 100 μm or less, and aluminum or the like can be used as the metal. The positive electrode lead tab 7 is composed of a metal thin film that is an extension of this positive electrode current collector. Also, the positive electrode lead tab 7 may be formed by welding aluminum or the like to the extension of the positive electrode current collector.

[0035] Known materials used in non-aqueous electrolyte secondary batteries can be used as the positive electrode active material. Examples of the positive electrode active material include various materials such as lithium manganese oxide, molybdenum oxide, lithium iron phosphate compound, lithium cobalt oxide, lithium nickel oxide, and vanadium oxide.

[0036] As the conductive assistant and binder contained in the positive electrode mixture, various materials mentioned above as the conductive assistant and binder contained in the negative electrode mixture can be used.

[0037] The separator 9 is a member having the property of passing lithium ions. The separator 9 is formed, for example, by a resin porous film made of polyolefin, a glass non-woven fabric, a resin non-woven fabric, a laminate of cellulose fibers, or the like.

[0038] As the electrolytic solution, a non-aqueous electrolyte in which a supporting salt is dissolved in a non-aqueous solvent can be used. As the non-aqueous solvent, various compounds such as cyclic carbonates, chain carbonates, chain ethers, etc. can be used. These can be, for example, organic solvents such as γ-butyrolactone (GBL), propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), dioxolane, dimethylformamide (DMF), glyme, sulfolane, acetonitrile, etc., either alone or as a mixed solvent. Also, as the supporting salt, for example, LiClO4, LiPF6, LiBF4, LiCF3SO3, LiN(CF3SO2)2, LiN(SO2F)2, etc. can be adopted.

[0039] As the supporting salt, for example, LiClO4, LiPF6, LiBF4, LiCF3SO3, LiN(CF3SO2)2, LiN(SO2F)2, etc. can be adopted. Also, an ionic liquid may be used as the supporting salt.

[0040] Also, in addition to these solvents and supporting salts, various additives can be added. Furthermore, instead of the electrolytic solution, a gel electrolyte in which these non-aqueous electrolytic solutions are impregnated and occluded in a highly liquid-absorbent porous polymer, a polymer solid electrolyte in which the lithium salt is solid-dissolved in a polymer such as polyethylene oxide or a polyphosphazene crosslinked body, or an inorganic solid electrolyte such as Li3N or LiI can also be used.

[0041] (Second Embodiment) Next, an embodiment different from the first embodiment will be described by taking FIGS. 3 and 4 as examples. The description of the configuration common to the first embodiment will be omitted, and the differences will be described.

[0042] The non-aqueous electrolyte secondary battery 200 is configured such that an electrode structure 10 is accommodated in an accommodation space of an exterior body composed of a positive electrode can 2 and a negative electrode can 1 that is fastened to the positive electrode can 2 via a gasket 3. Similar to the first embodiment, uneven portions 4 are formed on the inner surface 1a of the negative electrode can 1 and the inner surface 2a of the positive electrode can 2, respectively.

[0043] In the present embodiment, similar to the first embodiment, a negative electrode lead tab 15 and a positive electrode lead tab 17 extend from a negative electrode 6 and a positive electrode 8 that constitute the electrode structure 10, respectively. On the other hand, the negative electrode lead tab 15 and the positive electrode lead tab 17 do not have a lead tab folding portion as in the first embodiment, and are each composed of only one layer that extends from and is folded back from the electrode structure 10, and serve as a negative electrode connection portion 150 and a positive electrode connection portion 170, respectively. The negative electrode connection portion 150 is pressure-bonded to the uneven portion 4 formed on the inner surface 1a of the negative electrode can 1. Thereby, the negative electrode connection portion 150 and the inner surface 1a of the negative electrode can 1 are connected. Further, the positive electrode connection portion 170 is pressure-bonded to the uneven portion 4 formed on the inner surface 2a of the positive electrode can 2. Thereby, the positive electrode connection portion 170 and the inner surface 2a of the positive electrode can 2 are connected.

[0044] In the present embodiment, in particular, an unevenness absorbing material 11 is disposed between the negative electrode connection portion 150 and the electrode structure 10, and also between the positive electrode connection portion 170 and the electrode structure 10. The unevenness absorbing material 11 is a deformable material, and by being disposed between the positive electrode connection portion 170 and the electrode structure 10, it is possible to prevent the shape of the uneven portion 4 from spreading to the electrode structure 10.

[0045] As shown in FIGS. 3 and 4, the unevenness absorbing material 11 is formed in a sheet shape. The unevenness absorbing material 11 may be of any type such as metal or non-metal as long as it is chemically stable and deformable. In particular, when the unevenness absorbing material 11 is an insulator, in addition to absorbing the shape of the uneven portion 4, insulation between the lead tab and the electrode can be achieved. Thereby, the risk of short circuit of the electrode structure 10 can be further reduced.

[0046] As the material of the specific unevenness absorber 11, for example, in addition to various insulating materials such as resins such as thermosetting resins and thermoplastic resins, elastomers such as rubber, glass, and ceramics, various metal materials of the same type as the materials used for the positive electrode lead tab 17 and the negative electrode lead tab 15 can also be used. In addition to being arranged in a sheet shape, the unevenness absorber 11 can be in various forms such as a sponge, a tape, a U-shaped clip, etc. Among these combinations of materials and shapes, materials such as resin sponge, rubber, polyimide tape, separator, U-shaped clip made of resin, etc. are suitable in terms of ease of use and availability of materials.

[0047] Also, the sheet of the separator 9 made of the above-mentioned resin porous film made of polyolefin, glass non-woven fabric, resin non-woven fabric, laminate of cellulose fibers, etc. may be used as the unevenness absorber 11. In this case, a sheet-shaped separate separator material may be arranged between the negative electrode connection part 150 and the electrode structure 10, or between the positive electrode connection part 170 and the electrode structure 10, or the separator 9 constituting the electrode structure 10 may be extended from the electrode structure 10 and used.

Explanation of symbols

[0048] 100, 200 ··· Non-aqueous electrolyte secondary battery 1 ··· Negative electrode can 1a ··· Inner surface of the negative electrode can 2 ··· Positive electrode can 2a ··· Inner surface of the positive electrode can 3 ··· Gasket 4 ··· Uneven part 10 ··· Electrode structure 5, 15 ··· Negative electrode lead tab 50, 150 ··· Negative electrode connection part 51 ··· Folded part of the negative electrode lead tab 6 ··· Negative electrode 7, 17 ··· Positive electrode lead tab 70, 170 ··· Positive electrode connection part 71 ··· Folded part of the positive electrode lead tab 8 ··· Positive electrode 9 ··· Separator 11 ··· Concavo-convex absorbent

Claims

1. An exterior body in which a first container and a second container are hermetically sealed, and an electrode structure including a first electrode and a second electrode that are accommodated in the exterior body and electrically connected to the first container and the second container, respectively. At least one of the first electrode and the second electrode further includes a lead tab that is electrically connected to the electrode, and the lead tab has a connection portion on a surface facing the container on the connection side. Uneven portions having tips for connecting to the connection portion are formed on the inner surface of the container. An uneven absorption portion including an insulating uneven absorption material is disposed between the connection portion and the electrode structure. Fixing the connection portion of the lead tab to the uneven portion by pressure contact connection. A method for manufacturing a non-aqueous electrolyte secondary battery, characterized by the above.

2. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, wherein the uneven absorption material includes at least one kind selected from the group consisting of a resin sponge, a tape, a sheet, and a clip.

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