Current collector

Abstract

To provide a technique which prevents an electrode applied to a current collector from being brought into contact with a metallic foil, and prevents the electrode from being peeled from the current collector.SOLUTION: A current collector is composed of a metallic foil, and a resin layer which is composed of a resin containing a conductive assistant and is arranged on the surface of the metallic foil. The resin layer includes a first layer arranged on the surface of the metallic foil, and a second layer arranged on the first layer. The conductive assistant includes a first conductive assistant contained in the first layer, and a second conductive assistant contained in the second layer. The aspect ratio of the first conductive assistant is larger than the aspect ratio of the second conductive assistant.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The technology disclosed in this specification relates to a current collector.

Background Art

[0002] Current collectors used in secondary batteries have been variously improved to enhance performance. For example, the current collector of Patent Document 1 includes a metal foil and a resin layer disposed on the surface of the metal foil. By disposing the resin layer on the surface of the metal foil, when an electrode is coated on the current collector, the electrode is disposed on the resin layer. Further, when the electrode is coated on the current collector, it is pressed and penetrates into the resin layer. When the electrode penetrates into the resin layer, an anchor effect occurs between the electrode and the resin layer, making it difficult for the electrode to peel off from the current collector.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the current collector of Patent Document 1, when the electrode is coated on the current collector and pressed, the electrode penetrates into the resin layer, and an anchor effect occurs between the electrode and the resin layer. However, when the electrode is pressed against the current collector, the electrode may reach the metal foil. When the electrode contacts the metal foil, the metal foil may be damaged. If the metal foil is damaged and penetrated, the electrode may contact the electrode disposed on the opposite surface and cause a short circuit. Further, if the rigidity of the resin layer is increased to avoid the electrode contacting the metal foil, it becomes difficult for the electrode to penetrate into the resin layer, and the electrode is likely to peel off from the current collector.

[0005] This specification discloses a technique for suppressing contact between the electrode coated on the current collector and the metal foil and making it difficult for the electrode to peel off from the current collector.

Means for Solving the Problem

[0006] In an aspect of the present technology, the current collector comprises a metal foil and a resin containing a conductive aid, and a resin layer disposed on the surface of the metal foil. The resin layer includes a first layer disposed on the surface of the metal foil and a second layer disposed on the first layer. The conductive aid includes a first conductive aid contained in the first layer and a second conductive aid contained in the second layer. The aspect ratio of the first conductive aid is larger than the aspect ratio of the second conductive aid.

[0007] According to this configuration, since the aspect ratio of the first conductive aid contained in the first layer on the metal foil side is large, the contact area between the first conductive aids in the first layer becomes large. Thereby, the rigidity of the first layer is increased. For this reason, when an electrode is applied to the current collector, it becomes difficult for the electrode applied to the current collector to penetrate into the first layer, and contact between the electrode and the metal foil can be suppressed. Further, since the aspect ratio of the second conductive aid contained in the second layer disposed at a position away from the metal foil is small, the contact area between the second conductive aids in the second layer becomes small. Thereby, the rigidity of the second layer is decreased. For this reason, it becomes easy for the electrode applied to the current collector to penetrate into the second layer, and peeling of the electrode from the current collector can be suppressed. Therefore, it is possible to simultaneously make it difficult for the electrode applied to the current collector to contact the metal foil and make it difficult for the electrode to peel off from the current collector.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

[0009] The current collector 10 of the present embodiment will be described with reference to the drawings. An electrode is applied to the surface of the current collector 10, and it is used for a secondary battery. As shown in FIG. 1, the current collector 10 includes a metal foil 12 and a resin layer 14.

[0010] The metal foil 12 is formed of a metal having high conductivity. In this embodiment, the metal foil 12 is a copper foil. Note that the type of metal constituting the metal foil 12 is not particularly limited, and the metal foil 12 may be formed using other metals such as aluminum, nickel, and stainless steel.

[0011] The resin layer 14 is disposed on the surface of the metal foil 12. The resin layer 14 is composed of a resin 20 containing a conductive auxiliary agent 30. The resin layer 14 includes a plurality of layers. In this embodiment, the resin layer 14 includes a first layer 16 disposed on the surface of the metal foil 12 and a second layer 18 disposed on the first layer 16.

[0012] The resin layer 14 is composed of the same type of resin 20. That is, at any position within the resin layer 14, the resin 20 having substantially the same composition is disposed, and the first layer 16 and the second layer 18 are composed of the same type of resin 20. Note that the type of resin 20 is not particularly limited, and a non-conductive resin or a conductive resin may be used. As the non-conductive resin, it may be selected from thermoplastic resins and thermosetting resins and used. The conductive resin is, for example, polythiophene, but other conductive resins may be used. For example, when the electrode coated on the current collector 10 is used as a positive electrode, a polyvinylidene fluoride (PVdF)-based resin, a polyacrylic acid-based resin, etc. can be used, but it is not limited thereto. Also, when the electrode coated on the current collector 10 is used as a negative electrode, a polyacrylic acid-based resin, polyamideimide, polyimide, styrene-butadiene rubber, etc. can be used, but it is not limited thereto.

[0013] The resin layer 14 contains a plurality of types of conductive aids 32 and 34. In this embodiment, two types of conductive aids 32 and 34 (hereinafter also referred to as the first conductive aid 32 and the second conductive aid 34) are included. Specifically, the first layer 16 contains the first conductive aid 32, and the second layer 18 contains the second conductive aid 34. The aspect ratio of the first conductive aid 32 is larger than the aspect ratio of the second conductive aid 34. In this embodiment, the first conductive aid 32 is a conductive fiber, and the second conductive aid 34 is a solid spherical particle. In this embodiment, the "aspect ratio" refers to, for one conductive aid 32 or 34, the ratio of the first length that becomes the longest when disposed in the resin layer 14 to the second length that is the shortest among the lengths orthogonal to the first length. For example, since the second conductive aid 34 is a spherical particle, the first length and the second length are equal, and the aspect ratio is 1. The first conductive aid 32 is a conductive fiber. The conductive fiber is disposed on the surface of the metal foil 12 so as not to apply tension. The longest length (the horizontal length in FIG. 1) when the conductive fiber is disposed in this way becomes the first length of the first conductive aid 32. Also, the length orthogonal to the first length when the conductive fiber is disposed in this way varies depending on the shape and arrangement method of the conductive fiber, resulting in a width. Therefore, the shortest length among the lengths orthogonal to the first length (the vertical or depthwise length in FIG. 1) is taken as the second length of the first conductive aid 32. The aspect ratio of the first conductive aid 32 is greater than 1.

[0014] Note that it is only necessary that the aspect ratio of the first conductive aid 32 is larger than the aspect ratio of the second conductive aid 34, and the types of the first conductive aid 32 and the second conductive aid 34 are not particularly limited. For example, the first conductive aid 32 and the second conductive aid 34 can be selected from various shapes such as spherical particles (solid, hollow, porous), elliptical, fibrous, tubular, brush-shaped, chip-shaped (or flat-shaped), etc., and different combinations of shapes can be selected. A material with a large aspect ratio can be used for the first conductive aid 32, and a material with a small aspect ratio can be used for the second conductive aid 34. Also, the first conductive aid 32 and the second conductive aid 34 may be formed of any of a carbon material, a metal material, or a metal-coated carbon.

[0015] The first layer 16 contains a first conductive aid 32. Since the first conductive aid 32 has a large aspect ratio, the contact area between the first conductive aids 32 in the first layer 16 becomes large. For example, when the first conductive aid 32 is fibrous or chip-shaped, the first conductive aids 32 are in line contact or surface contact depending on the arrangement. On the other hand, the second layer 18 contains a second conductive aid 34. Since the second conductive aid 34 has a small aspect ratio, the contact area between the second conductive aids 34 in the second layer 18 becomes small. For example, when the second conductive aid 34 is spherical particles, the second conductive aids 34 are in point contact and do not have line contact or surface contact. Thus, since the contact area between the first conductive aids 32 contained in the first layer 16 is larger than the contact area between the second conductive aids 34 contained in the second layer 18, the area where the conductive aids interact and attract each other is enlarged. The force by which the conductive aids attract each other serves as a resistance against the action of separating the conductive aids as the resin layer deforms. The first layer 16 containing the first conductive aid 32 with a large aspect ratio has a structure in which the conductive aids are combined that is more likely to remain without being broken as the resin layer deforms than the second layer 18 containing the second conductive aid 34 with a small aspect ratio. Therefore, the rigidity of the first layer 16 is higher than the rigidity of the second layer 18.

[0016] The current collector 10 having the above configuration is used as a secondary battery with an electrode coated on its surface. As shown in FIG. 2, when the electrode 40 is coated on the surface of the current collector 10, the electrode 40 enters the resin layer 14 as the electrode 40 is pressurized. When the electrode 40 enters the resin layer 14, an anchor effect occurs between the electrode 40 and the resin layer 14, making it difficult for the electrode 40 to peel off from the current collector 10.

[0017] In addition, in this embodiment, since the aspect ratio of the first conductive aid 32 included in the first layer 16 is larger than the aspect ratio of the second conductive aid 34 included in the second layer 18, the rigidity of the first layer 16 becomes higher than the rigidity of the second layer 18. For example, when the resin layer 14 contains only conductive aids of the same shape with a small aspect ratio (for example, spherical particle conductive aids), when applying the electrode 40 to the surface of the current collector 10 under pressure, the electrode 40 may penetrate into the entire resin layer 14 and reach the metal foil 12. When the electrode 40 reaches the metal foil 12, the metal foil 12 may be damaged. Also, in order to avoid the electrode 40 reaching the metal foil 12, if the conductive aids contained in the resin layer 14 are only conductive aids of the same shape with a large aspect ratio (for example, fibrous or chip-shaped conductive aids), when the electrode 40 is applied to the surface of the current collector 10, it becomes difficult for the electrode 40 to penetrate into the resin layer 14, and the anchor effect generated between the electrode 40 and the resin layer 14 becomes small. In this embodiment, by making the aspect ratio of the first conductive aid 32 included in the first layer 16 larger than the aspect ratio of the second conductive aid 34 included in the second layer 18, the rigidity of the first layer 16 becomes higher than the rigidity of the second layer 18. Therefore, when the electrode 40 is applied to the surface of the current collector 10, the electrode 40 easily penetrates into the second layer 18 on the side of the electrode 40 with low rigidity. On the other hand, since the first layer 16 on the side of the metal foil 12 has high rigidity, it is difficult for the electrode 40 to penetrate. Therefore, the electrode 40 easily penetrates into the second layer 18 while hardly penetrating into the first layer 16. Thus, in the current collector 10 of this embodiment, it becomes difficult for the electrode 40 applied to the current collector 10 to contact the metal foil 12, and it becomes difficult for the electrode 40 to peel off from the current collector 10.

[0018] The specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. For example, in the first layer 16 and the second layer 18, an intermediate layer in which the respective interfaces are mixed may be formed. Also, the first layer 16 and the second layer 18 may be composed of a plurality of conductive aids. The technology described in the claims includes various modifications and changes of the specific examples exemplified above. The technical elements described in this specification or the drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Further, the technology exemplified in this specification or the drawings can achieve a plurality of purposes simultaneously, and achieving one of these purposes itself has technical utility.

Explanation of Reference Numerals

[0019] 10: Current collector 12: Metal foil 14: Resin layer 16: First layer 18: Second layer 20: Resin 30: Conductive aid 32: First conductive aid 34: Second conductive aid 40: Electrode

Claims

Claim 1 a metal foil, a resin layer made of a resin containing a conductive auxiliary agent and disposed on the surface of the metal foil, and the resin layer includes a first layer disposed on the surface of the metal foil and a second layer disposed on the first layer, the conductive auxiliary agent includes a first conductive auxiliary agent contained in the first layer and a second conductive auxiliary agent contained in the second layer, a current collector in which the aspect ratio of the first conductive auxiliary agent is larger than the aspect ratio of the second conductive auxiliary agent.

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