Current collector

Abstract

To provide a technology for preventing an electrode coated on a current collector from coming into contact with a metal foil and for making the electrode less likely to peel off from the current collector.SOLUTION: A current collector includes a metal foil and a resin layer made of a resin containing a conductive additive and 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 volume fraction of the conductive additive in the first layer is greater than the volume fraction of the conductive additive in the second layer.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 pressurized 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 pressurized, the electrode penetrates into the resin layer, and an anchor effect occurs between the electrode and the resin layer. However, when the electrode is pressurized 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 the contact of an electrode coated on a current collector with a metal foil and making it difficult for the electrode to peel off from the current collector.

Means for Solving the Problem

[0006] In the first aspect of the present technology, the current collector is composed of a metal foil and a resin containing a conductive auxiliary agent, and includes 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 volume fraction of the conductive auxiliary agent in the first layer is larger than the volume fraction of the conductive auxiliary agent in the second layer.

[0007] According to this configuration, since the volume fraction of the conductive auxiliary agent in the first layer on the metal foil side is large, when an electrode is coated on the current collector, it becomes difficult for the electrode coated on the current collector to penetrate into the first layer, and it is possible to suppress the electrode from contacting the metal foil. Further, since the volume fraction of the conductive auxiliary agent in the second layer disposed at a position away from the metal foil is small, it becomes easy for the electrode coated on the current collector to penetrate into the second layer, and it is possible to suppress the electrode from peeling off from the current collector. Therefore, it is possible to simultaneously achieve making it difficult for the electrode coated on the current collector to contact the metal foil and making it difficult for the electrode to peel off from the current collector.

[0008] In the second aspect, in the above first aspect, the conductive auxiliary agent may include a first conductive auxiliary agent having a first outer diameter and a second conductive auxiliary agent having a second outer diameter smaller than the first outer diameter. The first conductive auxiliary agent may be included in the first layer and the second layer. The second conductive auxiliary agent may be included in the first layer and may not be included in the second layer.

[0009] According to this configuration, since the second conductive auxiliary agent having an outer diameter smaller than that of the first conductive auxiliary agent is included only in the first layer, in the first layer, the first conductive auxiliary agent and the second conductive auxiliary agent are mixed, and the volume fraction of the conductive auxiliary agent (the total of the first conductive auxiliary agent and the second conductive auxiliary agent) in the first layer increases. Therefore, the volume fraction of the conductive auxiliary agent in the first layer can be made even larger than the volume fraction of the conductive auxiliary agent in the second layer.

[0010] In the third aspect, in the above-described first aspect, the conductive auxiliary agent may include a first conductive auxiliary agent contained in the first layer and a second conductive auxiliary agent contained in the second layer. The density of the first conductive auxiliary agent may be higher than the density of the second conductive auxiliary agent.

[0011] According to this configuration, since the density of the first conductive auxiliary agent is higher than the density of the second conductive auxiliary agent, the volume fraction of the conductive auxiliary agent in the first layer can be made preferably larger than the volume fraction of the conductive auxiliary agent in the second layer.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0013] (Example 1) The current collector 10 of this example 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.

[0014] The metal foil 12 is formed of a metal having high conductivity. In this example, the metal foil 12 is a copper foil. Note that the type of the 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.

[0015] 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.

[0016] The resin layer 14 is composed of the same type of resin 20. That is, the resin 20 having substantially the same composition is disposed at any position within the resin layer 14, and the first layer 16 and the second layer 18 are composed of the same type of resin 20. In this embodiment, the resin 20 is polyacrylic acid. Note that the type of the 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, or the like can be used, but it is not limited thereto. Further, 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, or the like can be used, but it is not limited thereto.

[0017] The resin layer 14 contains the same type of conductive auxiliary agent 30. That is, the first layer 16 and the second layer 18 contain the same type of conductive auxiliary agent 30. In this embodiment, the conductive auxiliary agent 30 is acetylene black. Note that the type of the conductive auxiliary agent 30 is not particularly limited. For example, the conductive auxiliary agent 30 may be formed of a carbon material or a metal material. The carbon material has various shapes such as particulate (solid, hollow, porous), fibrous, tubular, brush-shaped, chip-shaped (or flat-shaped), etc., and the conductive auxiliary agent 30 may have any of these shapes. The metal material has shapes such as particulate and fibrous, and the conductive auxiliary agent 30 may have any of these shapes. Further, the conductive auxiliary agent 30 can be formed of a metal such as aluminum, nickel, copper, stainless steel, etc., but may be formed of a metal material other than the above. Also, the conductive auxiliary agent 30 may be formed of a metal-coated carbon material. Further, in this embodiment, the resin layer 14 contains one type of conductive auxiliary agent 30, but if the formulation of the conductive auxiliary agent 30 contained in the first layer 16 is substantially the same as the formulation of the conductive auxiliary agent 30 contained in the second layer 18, a plurality of types of conductive auxiliary agents may be contained.

[0018] The volume of the conductive auxiliary agent 30 in the first layer 16 is larger than the volume of the conductive auxiliary agent 30 in the second layer 18. When the volume of the conductive auxiliary agent 30 in the resin layer 14 is increased, the volume of the resin 20 in the resin layer 14 becomes smaller. Therefore, the volume of the conductive auxiliary agent 30 in the first layer 16 is larger than the volume of the conductive auxiliary agent 30 in the second layer 18, and the volume of the resin 20 constituting the first layer 16 is smaller than the volume of the resin 20 constituting the second layer 18. In other words, the volume fraction of the conductive auxiliary agent 30 in the first layer 16 is larger than the volume fraction of the conductive auxiliary agent 30 in the second layer 18.

[0019] For example, in the first layer 16, when the mass fraction of polyacrylic acid (resin 20) and acetylene black (conductive assistant 30) is 30:70 (wt%), the volume fraction of polyacrylic acid (resin 20) and acetylene black (conductive assistant 30) can be estimated to be 40:60 (vol%). Also, in the second layer 18, when the mass fraction of polyacrylic acid (resin 20) and acetylene black (conductive assistant 30) is 70:30 (wt%), the volume fraction of polyacrylic acid (resin 20) and acetylene black (conductive assistant 30) can be estimated to be 80:20 (vol%). Thus, when the mass fraction of the conductive assistant 30 in the first layer 16 is made larger than the mass fraction of the conductive assistant 30 in the second layer 18, the volume fraction of the conductive assistant 30 in the first layer 16 becomes larger than the volume fraction of the conductive assistant 30 in the second layer 18. Note that the ratios of the mass fractions and volume fractions of the resin 20 and the conductive assistant 30 in the first layer 16 described above, and the ratios of the mass fractions and volume fractions of the resin 20 and the conductive assistant 30 in the second layer 18 are examples and are not limited to the above ratios.

[0020] 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 due to the application of pressure to the electrode 40. When the electrode 40 enters the resin layer 14, an anchor effect is generated between the electrode 40 and the resin layer 14, making it difficult for the electrode 40 to peel off from the current collector 10.

[0021] Also, in this embodiment, since the volume of the conductive assistant 30 in the first layer 16 is larger than the volume of the conductive assistant 30 in the second layer 18, the volume fraction of the conductive assistant 30 in the first layer 16 is larger than the volume fraction of the conductive assistant 30 in the second layer 18. For example, when the conductive assistant 30 is uniformly contained in the entire resin layer 14, when applying pressure during coating the electrode 40 on the surface of the current collector 10, 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 volume fraction of the conductive assistant 30 in the resin layer 14 is increased as a whole, the rigidity of the resin layer 14 will increase. Therefore, when the electrode 40 is coated on 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 smaller. In this embodiment, by making the volume fraction of the conductive assistant 30 in the first layer 16 larger than the volume fraction of the conductive assistant 30 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 coated on the surface of the current collector 10, the electrode 40 easily penetrates into the second layer 18 on the side of the electrode 40 where the volume fraction of the contained conductive assistant 30 is small. On the other hand, the first layer 16 on the side of the metal foil 12 is difficult for the electrode 40 to penetrate because the volume fraction of the contained conductive assistant 30 is large. Therefore, the electrode 40 easily penetrates into the second layer 18 but hardly penetrates into the first layer 16. Therefore, in the current collector 10 of this embodiment, it becomes difficult for the electrode 40 coated on 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.

[0022] Note that, in this embodiment, the first layer 16 and the second layer 18 contain the same type of conductive assistant 30, but it is not limited to such a configuration. For example, as shown in FIG. 3, the first layer 116 may contain a conductive assistant 130 having an outer diameter smaller than that of the conductive assistant 30 together with the conductive assistant 30. Hereinafter, the conductive assistant 30 may be simply referred to as "conductive assistant 30", and the conductive assistant 130 may be referred to as "small-diameter conductive assistant 130".

[0023] The current collector 110 shown in Fig. 3 includes a metal foil 12 and a resin layer 114. The resin layer 114 is composed of a resin 20 containing a conductive assistant 30 and a small-diameter conductive assistant 130, and includes a first layer 116 disposed on the surface of the metal foil 12 and a second layer 18 disposed on the first layer 116. The first layer 116 contains a conductive assistant 30 and a small-diameter conductive assistant 130. The second layer 18 contains only the conductive assistant 30 and does not contain the small-diameter conductive assistant 130. For the metal foil 12, the resin 20, and the conductive assistant 30, the same ones as those of the metal foil 12, the resin 20, and the conductive assistant 30 of the current collector 10 described above can be used. Therefore, detailed descriptions of the metal foil 12, the resin 20, and the conductive assistant 30 are omitted. In addition, the small-diameter conductive assistant 130 only needs to have an outer diameter smaller than that of the conductive assistant 30, and the material is not particularly limited. For example, the small-diameter conductive assistant 130 may be composed of any of a carbon material, a metal material, and a metal-coated carbon. Also, the shape of the small-diameter conductive assistant 130 is not particularly limited.

[0024] The small-diameter conductive assistant 130 is included in the first layer 116 but not in the second layer 18. That is, the first layer 116 contains a conductive assistant 30 and a small-diameter conductive assistant 130, and the second layer 18 contains only the conductive assistant 30. Since the outer diameter of the small-diameter conductive assistant 130 is smaller than that of the conductive assistant 30, it is easy to enter between the conductive assistants 30. By including not only the conductive assistant 30 but also the small-diameter conductive assistant 130 in the first layer 116, the volume fraction of the conductive assistants (the conductive assistant 30 and the small-diameter conductive assistant 130) contained in the first layer 116 becomes even larger. That is, the volume fraction of the resin 20 constituting the first layer 116 becomes smaller. As a result, the rigidity of the first layer 116 becomes even greater than the rigidity of the second layer 118. Therefore, in the current collector 110 of Fig. 3, the electrode 40 coated on the current collector 110 is less likely to peel off from the current collector 110, and the electrode 40 is less likely to come into contact with the metal foil 12.

[0025] (Example 2) In the above Example 1, by changing the amount of the conductive assistant 30 contained in the resin 20 between the first layer 16 and the second layer 18, the volume fraction of the conductive assistant 30 in the first layer 16 was made larger than the volume fraction of the conductive assistant 30 in the second layer 18. However, the configuration is not limited to this. For example, as shown in FIG. 4, by using conductive assistants 232 and 234 having different densities, the volume fraction of the conductive assistant 230 in the first layer 216 may be made larger than the volume fraction of the conductive assistant 230 in the second layer 218.

[0026] The current collector 210 of this example includes a metal foil 12 and a resin layer 214. The resin layer 214 is composed of a resin 20 containing a conductive assistant 230. The resin layer 214 includes a plurality of layers. In this example, it includes a first layer 216 disposed on the surface of the metal foil 12 and a second layer 218 disposed on the first layer 216. Note that in this example, the metal foil 12 and the resin 20 can be the same as those of the metal foil 12 and the resin 20 in the above Example 1. Therefore, detailed descriptions of the metal foil 12 and the resin 20 are omitted.

[0027] The resin layer 214 contains a plurality of types of conductive assistants 232 and 234. In this example, two types of conductive assistants 232 and 234 (hereinafter also referred to as the first conductive assistant 232 and the second conductive assistant 234) are included. Specifically, the first layer 216 contains the first conductive assistant 232, and the second layer 218 contains the second conductive assistant 234. The density of the first conductive assistant 232 is higher than the density of the second conductive assistant 234. Note that the types of the first conductive assistant 232 and the second conductive assistant 234 are not particularly limited. For example, the first conductive assistant 232 and the second conductive assistant 234 may be formed of any of a carbon material, a metal material, or a metal-coated carbon. Also, the shapes of the first conductive assistant 232 and the second conductive assistant 234 are not particularly limited.

[0028] In this embodiment, the amount of the first conductive auxiliary agent 232 included in the first layer 216 and the amount of the second conductive auxiliary agent 234 included in the second layer 218 are substantially the same. Also, the first conductive auxiliary agent 232 and the second conductive auxiliary agent 234 are formed of the same material, and the second conductive auxiliary agent 234 has more pores formed therein than the first conductive auxiliary agent 232. Specifically, the first conductive auxiliary agent 232 is a solid particle, and the second conductive auxiliary agent 234 is a porous particle. Note that both the first conductive auxiliary agent 232 and the second conductive auxiliary agent 234 may be porous particles, and the second conductive auxiliary agent 234 may have more pores formed therein than the first conductive auxiliary agent 232. Since more pores are formed in the second conductive auxiliary agent 234 than in the first conductive auxiliary agent 232, the density of the first conductive auxiliary agent 232 becomes higher than the density of the second conductive auxiliary agent 234.

[0029] Note that the first conductive auxiliary agent 232 and the second conductive auxiliary agent 234 may be formed of different materials. In this case, different combinations of densities may be selected from carbon materials, metal materials, or metal-coated carbons, and a material with a higher density may be used for the first conductive auxiliary agent 232, while a material with a lower density may be used for the second conductive auxiliary agent 234.

[0030] In this embodiment, the density of the first conductive auxiliary agent 232 included in the first layer 216 is higher than the density of the second conductive auxiliary agent 234 included in the second layer 218. As a result, the rigidity of the first layer 216 becomes higher than the rigidity of the second layer 218. Therefore, also in this embodiment, when the electrode 40 is applied to the surface of the current collector 210, the electrode 40 easily penetrates into the second layer 218 while hardly penetrating into the first layer 216. Accordingly, also in the current collector 210 of Example 2, it becomes difficult for the electrode 40 applied to the current collector 210 to contact the metal foil 12, and it becomes difficult for the electrode 40 to peel off from the current collector 210.

[0031] 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. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. In the above Examples 1 and 2, the same type of resin 20 is used for the first layer (16, 116, 216) and the second layer 18 (18, 118, 218), but different types of resins may be used for the first layer (16, 116, 216) and the second layer (18, 118, 218). Further, an intermediate layer in which the respective interfaces are mixed may be formed between the first layer (16, 116, 216) and the second layer (18, 118, 218). 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. Also, the technology illustrated in this specification or the drawings can achieve multiple purposes simultaneously, and achieving one of those purposes itself has technical utility.

Explanation of Reference Numerals

[0032] 10, 110, 210: Current collector 12: Metal foil 14, 114, 214: Resin layer 16, 116, 216: First layer 18, 218: Second layer 20: Resin 30: Conductive aid 40: Electrode 130: Small-diameter conductive aid 232: First conductive aid 234: Second conductive aid

Claims

1. A metal foil and a resin layer made of a resin containing a conductive aid 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, wherein the volume fraction of the conductive aid in the first layer is larger than the volume fraction of the conductive aid in the second layer. A current collector.

2. The current collector according to claim 1, wherein the conductive aid includes a first conductive aid having a first outer diameter and a second conductive aid having a second outer diameter smaller than the first outer diameter, the first conductive aid is included in the first layer and the second layer, the second conductive aid is included in the first layer and not included in the second layer. A current collector.

3. The current collector according to claim 1, wherein the conductive aid includes a first conductive aid included in the first layer and a second conductive aid included in the second layer, wherein the density of the first conductive aid is higher than the density of the second conductive aid. A current collector.

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