Current collector, intermediate body for manufacturing current collector and method for manufacturing current collector

Abstract

To provide a technique for preventing an electrode applied onto a current collector from coming into contact with a metallic foil, and preventing an electrode from being peeled from the current collector.SOLUTION: A current collector includes a metallic foil, and a resin layer which is composed of a resin containing a plurality of conductive assistants, and is arranged on the metallic foil. The resin layer includes a first layer arranged on the metallic foil, and a second layer arranged on the first layer. The second layer has unevenness on a surface opposite to a surface in contact with the first layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a current collector, an intermediate for producing a current collector, and a method for producing a current collector. [Background technology]

[0002] Current collectors used in secondary batteries have undergone various improvements to enhance their performance. For example, the current collector disclosed in 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, the electrode is disposed on the resin layer when coated on the current collector. Furthermore, the electrode is pressurized when coated on the current collector, and penetrates into the resin layer. By the electrode penetrating into the resin layer, an anchor effect is created between the electrode and the resin layer, making the electrode less likely to peel off from the current collector. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-26192 Summary of the Invention [Problem to be solved by the invention]

[0004] In the current collector of Patent Document 1, when the electrode is applied to the current collector, pressure is applied, causing the electrode to penetrate into the resin layer, creating an anchor effect 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 comes into contact with the metal foil, the metal foil may be damaged. If the metal foil is damaged and penetrated, there is a risk of the electrode coming into contact with the electrode arranged on the opposite side and causing a short circuit. Furthermore, if the rigidity of the resin layer is increased to prevent the electrode from contacting the metal foil (for example, by increasing the amount of conductive additive contained in the resin layer), the electrode will be less likely to penetrate into the resin layer, making the electrode more likely to peel off from the current collector.

[0005] This specification discloses a technique 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. [Means for solving the problem]

[0006] In a first aspect of the present technology, a current collector includes a metal foil and a resin layer made of a resin containing a plurality of conductive additives and disposed on the metal foil. The resin layer includes a first layer disposed on the metal foil and a second layer disposed on the first layer. The second layer has an uneven surface on the side opposite to the surface in contact with the first layer.

[0007] According to this configuration, by providing irregularities on the surface of the second layer that comes into contact with the electrode when coated on the current collector, the electrode can easily fit into the irregularities of the second layer when coated on the current collector. This creates an anchor effect between the electrode and the second layer, making the electrode less likely to peel off from the current collector. Furthermore, by providing the first layer between the second layer and the metal foil, the electrode is less likely to come into contact with the metal foil. Therefore, it is possible to simultaneously make it difficult for the electrode coated on the current collector to come into contact with the metal foil and to make the electrode less likely to peel off from the current collector.

[0008] In a second aspect of the present technology, in the first aspect described above, the plurality of conductive additives may include a plurality of first conductive additives contained in the first layer and a plurality of second conductive additives contained in the second layer. The second layer may include a plurality of conductive additive groups formed by aggregation of some of the plurality of second conductive additives. Each conductive additive group may be arranged with an interval between adjacent conductive additive groups.

[0009] According to this configuration, the second layer has a plurality of conductive additive groups each formed by agglomerating the second conductive additive, which are spaced apart from one another, which tends to increase the area in the second layer where no conductive additive is present between the conductive additive groups, making it easier for irregularities to form on the surface of the second layer.

[0010] In a third aspect of the present technology, in the first aspect, the plurality of conductive additives may include a plurality of first conductive additives contained in the first layer and a plurality of second conductive additives contained in the second layer, and an outer shape of each of the second conductive additives may be larger than an outer shape of each of the first conductive additives.

[0011] With this configuration, because the outer shape of the second conductive additive is large, the area in the second layer where no conductive additive is placed between the second conductive additives tends to be large. This makes it easy for unevenness to occur on the surface of the second layer. On the other hand, because the outer shape of the first conductive additive is small, the area in the first layer where no conductive additive is placed between the first conductive additives tends to be small. This makes it difficult for the electrode to penetrate into the first layer, even if the electrode reaches the first layer when applied to the current collector.

[0012] According to a fourth aspect of the present technology, in the first aspect, a plurality of grooves may be provided on the opposite surface of the second layer.

[0013] According to this configuration, by providing a plurality of grooves, continuously extending recesses and continuously extending protrusions formed between the grooves are provided, thereby making it possible to provide unevenness on the surface of the second layer.

[0014] In a fifth aspect of the present technology, in the fourth aspect, the first layer and the second layer may be made of the same type of resin, and the first layer and the second layer may contain the same type of conductive additive at the same density.

[0015] According to this configuration, the first layer and the second layer have the same composition. This prevents the number of materials required to manufacture the current collector from increasing. Furthermore, for example, when forming a resin layer using a slurry, the slurry prepared for forming the first layer can also be used to form the second layer. In this way, the number of steps required to manufacture the current collector can be reduced.

[0016] In a sixth aspect of the present technology, an intermediate is an intermediate for producing a current collector. The intermediate includes a metal foil and a resin layer made of a resin containing a plurality of conductive additives and disposed on the metal foil. The resin layer includes a first layer disposed on the metal foil and a second layer disposed on the first layer. The second layer includes a thermally decomposable component.

[0017] According to this configuration, since the second layer contains a thermally decomposable component, when the intermediate is heat-treated, the thermally decomposable component contained in the second layer is decomposed. As a result, voids are generated in the second layer, and the surface of the second layer is likely to become uneven. Therefore, by producing a current collector using the above-mentioned intermediate, it is possible to generate unevenness on the surface of the second layer.

[0018] According to a seventh aspect of the present technology, in the sixth aspect, the density of the resin constituting the second layer may be higher than the density of the thermally decomposable component.

[0019] The first and second resin layers are often manufactured by applying and drying a slurry. While the slurry is drying, the components of each layer with higher density tend to move downward. According to the above configuration, the density of the resin in the second layer is higher than the density of the thermally decomposable component, so that the resin with higher density moves downward during the manufacturing of the second layer, and the thermally decomposable component tends to be distributed in large amounts above the second layer. Therefore, when the intermediate is heat-treated, voids tend to form near the surface of the second layer. Therefore, when a current collector is manufactured using the above intermediate, unevenness tends to form on the surface of the second layer.

[0020] In an eighth aspect of the present technology, a method for manufacturing a current collector includes a metal foil and a resin layer made of a resin containing a plurality of conductive additives and disposed on the metal foil. The manufacturing method includes: a disposing step of disposing a slurry containing the plurality of conductive additives and the resin on the metal foil; a groove forming step of inserting a comb-shaped jig into a surface of the slurry disposed on the metal foil opposite to a surface that contacts the metal foil in the disposing step and linearly moving the jig to form a plurality of grooves on the opposite surface; and a drying step of drying the slurry in which the plurality of grooves have been formed on the opposite surface in the groove forming step to form irregularities constituted by the plurality of grooves on the surface of the resin layer opposite to the surface that contacts the metal foil.

[0021] According to this configuration, by using a comb-shaped jig, it is possible to easily form the unevenness composed of a plurality of grooves on the surface of the resin layer. Furthermore, since a plurality of grooves are formed on the surface of the resin layer, it is possible to achieve the same effects as the current collectors of the first and fourth aspects described above.

[0022] In a ninth aspect of the present technology, a method for manufacturing a current collector includes a first arrangement step of arranging a first layer made of a resin containing a plurality of conductive additives on a metal foil, a second arrangement step of arranging a second layer made of a resin containing a plurality of conductive additives and a thermally decomposable component on the first layer, and a heat treatment step of heat-treating an intermediate formed by the first arrangement step and the second arrangement step to form irregularities on a surface of the second layer opposite to a surface that comes into contact with the first layer.

[0023] According to this configuration, by heat-treating an intermediate in which a second layer containing a thermally decomposable component is disposed on a first layer, it is possible to produce a current collector in which irregularities are formed on the surface of the second layer, thereby achieving the same effects as those of the current collector of the first aspect described above. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a current collector according to Example 1. [Figure 2] FIG. 2 is a diagram showing a state in which an electrode is applied to a current collector according to Example 1. [Figure 3] FIG. 10 is a diagram showing a schematic configuration of a current collector according to Example 2. [Figure 4] FIG. 10 is a diagram showing a schematic configuration of a current collector according to a modified example of Example 2. [Figure 5] FIG. 10 is a diagram showing a schematic configuration of an intermediate for producing a current collector in Example 3. [Figure 6] 10 is a flowchart showing an example of a method for producing a current collector using the intermediate of Example 3. [Figure 7] 10A and 10B are diagrams showing a schematic configuration of a current collector according to Example 4, in which (a) is a vertical cross-sectional view and (b) is a top view. [Figure 8] FIG. 10 is a top view showing the flow of electrons in the second layer when a tab lead is connected to the current collector of Example 4. [Figure 9] 10 is a flowchart showing an example of a method for manufacturing a current collector according to a modified example of Example 4. [Figure 10] 1A and 1B are schematic diagrams showing the application of resin slurry to a metal foil using a jig, where (a) is a side view and (b) is a top view. [Figure 11] 1A and 1B are schematic diagrams for explaining the formation of a resin layer using a jig, in which (a) shows the state immediately after the resin slurry is applied to the metal foil, and (b) shows the state after the resin slurry has dried (the state after the resin layer has been formed). [Figure 12] 10A and 10B are schematic diagrams showing other configurations of resin layers formed using a jig. [Figure 13] 10A and 10B are diagrams showing a schematic configuration of a current collector according to Example 5, in which (a) is a vertical cross-sectional view and (b) is a top view. [Figure 14] FIG. 10 is a diagram showing a schematic configuration of a current collector according to a modified example of Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0025] Example 1 The current collector 10 of this example will be described with reference to the drawings. The current collector 10 has an electrode 40 (see FIG. 2) coated on its surface and is used in a secondary battery. As shown in FIG. 1, the current collector 10 includes a metal foil 12 and a resin layer 14.

[0026] The metal foil 12 is made of a conductive metal. In this embodiment, the metal foil 12 is a copper foil. The type of metal constituting the metal foil 12 is not particularly limited, and the metal foil 12 may be made of other metals such as aluminum, nickel, stainless steel, etc.

[0027] 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 plurality of conductive additives 30. The resin layer 14 includes a plurality of layers, and in this embodiment 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.

[0028] The resin layer 14 is composed of the same type of resin 20. That is, the first layer 16 and the second layer 18 are composed of the same type of resin, and resins 20 having approximately the same composition are disposed at every position within the resin layer 14. The type of resin 20 is not particularly limited, and either non-conductive or conductive resins may be used. The non-conductive resin may be selected from thermoplastic resins and thermosetting resins. The conductive resin may be, for example, polythiophene, but other conductive resins may also be used. For example, when the electrode 40 coated on the current collector 10 is used as a positive electrode, polyvinylidene fluoride (PVdF)-based resins, polyacrylic acid-based resins, etc. may be used, but are not limited to these. When the electrode 40 coated on the current collector 10 is used as a negative electrode, polyacrylic acid-based resins, polyamideimide, polyimide, styrene butadiene rubber, etc. may be used, but are not limited to these.

[0029] The resin layer 14 contains the same type of conductive additive 30. That is, the first layer 16 and the second layer 18 contain the same type of conductive additive 30. In this embodiment, the conductive additive 30 is acetylene black. The type of conductive additive 30 is not particularly limited. For example, the conductive additive 30 may be formed from a carbon material or a metal material. Carbon materials come in various shapes, such as particles (solid, hollow, or porous), fibers, tubes, brushes, and chips (or flattened), and the conductive additive 30 may have any of these shapes. Metal materials come in shapes such as particles and fibers, and the conductive additive 30 may have any of these shapes. The conductive additive 30 can be formed from metals such as aluminum, nickel, copper, and stainless steel, but may also be formed from metal materials other than those listed above. The conductive additive 30 may also be formed from a metal-coated carbon material. In addition, in this embodiment, the resin layer 14 contains one type of conductive additive 30, but may contain multiple types of conductive additives.

[0030] The first layer 16 and the second layer 18 each contain a plurality of conductive additives 30. The plurality of conductive additives 30 in the first layer 16 are dispersed, while the plurality of conductive additives 30 in the second layer 18 are aggregated. Specifically, the plurality of conductive additives 30 in the first layer 16 are arranged so that the contact area between adjacent conductive additives 30 is small. On the other hand, the plurality of conductive additives 30 in the second layer 18 are arranged so that some of the conductive additives 30 aggregate. The second layer 18 contains a plurality of conductive additive groups 32 formed by aggregation of some of the conductive additives 30. In the second layer 18, the plurality of conductive additive groups 32 are arranged with a gap between adjacent conductive additive groups 32. In the second layer 18, some of the conductive additive groups 32 protrude from the surface of the resin 20. This provides unevenness to the surface of the second layer 18.

[0031] Here, a method for manufacturing the current collector 10 will be described. First, a resin slurry containing a conductive additive 30 and a resin 20 (hereinafter also referred to as a first resin slurry) is applied to the surface of the metal foil 12. The first resin slurry contains a plurality of conductive additives 30 in a dispersed state (i.e., in a state in which the conductive additive group 32 is absent). The first resin slurry may contain other substances such as a dispersant or a dispersion medium.

[0032] Next, the first resin slurry applied to the surface of the metal foil 12 is dried. As a result, a first layer 16 is disposed on the surface of the metal foil 12. Because the first resin slurry is dried, the thickness of the first layer 16 becomes thinner than the thickness of the first resin slurry before drying. Since multiple conductive additives 30 are dispersed in the first resin slurry, the multiple conductive additives 30 are also dispersed and disposed in the first layer 16. Because the dimensions of each dispersed conductive additive 30 are smaller than the thickness of the first layer 16 after the first resin slurry has been dried, the multiple conductive additives 30 are contained within the first layer 16.

[0033] Once the first layer 16 is placed on the surface of the metal foil 12, a resin slurry (hereinafter also referred to as the second resin slurry) containing conductive additives 32 and a resin 20 is applied to the surface of the first layer 16. The second resin slurry may also contain other substances such as a dispersant or a dispersion medium. When comparing the particle size distributions of the first and second resin slurries, the conductive additives 32 in the second resin slurry have a larger size than the conductive additives 30 in the first resin slurry. This indicates that, although the same conductive additive 30 is used, the conductive additives 30 are in a more aggregated state in the second resin slurry than in the first resin slurry.

[0034] Next, the second resin slurry applied to the surface of the first layer 16 is dried. As a result, the second layer 18 is disposed on the surface of the first layer 16. Because the second resin slurry is dried, the thickness of the second layer 18 becomes thinner than the thickness of the second resin slurry before drying. When the second resin slurry is dried, the height dimension of the conductive additive groups 32 in the second layer 18 becomes greater than the thickness of the resin 20. As a result, in the second layer 18, the conductive additive groups 32 protrude from the surface of the resin 20, and unevenness is provided on the surface of the second layer 18. Alternatively, a mixture of the conductive additive groups 32, the resin 20, a dispersant, etc. may protrude.

[0035] In the current collector 10 of this embodiment, the presence of the plurality of conductive additive groups 32 provides unevenness on the surface of the second layer 18. As shown in Fig. 2, when the electrode 40 is applied to the surface of the current collector 10, the electrode 40 enters the unevenness (more specifically, the depressions formed by the unevenness) on the surface of the second layer 18. This creates an anchor effect between the electrode 40 and the second layer 18 (i.e., the resin layer 14), making it difficult for the electrode 40 to peel off from the current collector 10.

[0036] In this embodiment, the first layer 16 is disposed between the metal foil 12 and the second layer 18. For example, if the second layer 18 is disposed on the surface of the metal foil 12 (i.e., if the first layer 16 is not disposed and there is no resin layer in which the conductive additive 30 is dispersed), applying pressure when applying the electrode 40 to the surface of the current collector 10 may cause the electrode 40 to penetrate the entire resin layer (i.e., the second layer 18) and reach the metal foil 12. In this embodiment, the first layer 16 is disposed between the metal foil 12 and the second layer 18. Because the conductive additive 30 is dispersed in the first layer 16, the electrode 40 is less likely to penetrate into the first layer 16. In this embodiment, by disposing the first layer 16 between the metal foil 12 and the second layer 18, even if the electrode 40 applied to the surface of the second layer 18 passes through the second layer 18 and reaches the first layer 16, the electrode 40 is less likely to come into contact with the metal foil 12. This makes it possible to simultaneously make it difficult for the electrode 40 coated on the current collector 10 to come into contact with the metal foil 12 and to make it difficult for the electrode 40 to peel off from the current collector 10. Furthermore, in the first layer 16, the conductive additive 30 is dispersed throughout the first layer 16. This makes it possible to ensure the conductivity of the current collector 10.

[0037] In this embodiment, the multiple conductive additives 30 contained in the first layer 16 and the second layer 18 were the same type, but this configuration is not limited to this. For example, the first layer 16 and the second layer 18 may each contain different types of conductive additives with approximately the same outer shape. Furthermore, the multiple conductive additives 30 contained in the first layer 16 and the second layer 18 may have different shapes. For example, the multiple conductive additives arranged in the first layer 16 may be dispersed within the first layer 16 and may have different sizes and outer shapes. Furthermore, the multiple conductive additives arranged in the second layer 18 are not particularly limited in size and outer shape as long as some of them form a conductive additive group and the conductive additive group is arranged at intervals within the second layer 18.

[0038] Example 2 In the above-described Example 1, the conductive additive group 32 is disposed in the second layer 18 to provide the unevenness on the surface of the second layer 18, but the present invention is not limited to such a configuration. For example, as shown in Fig. 3, the conductive additive 34 having a large outer shape may be disposed in the second layer 118 to provide the unevenness on the surface of the second layer 118.

[0039] The current collector 110 of this example includes a metal foil 12 and a resin layer 114. The resin layer 114 is made of a resin 20 containing a plurality of conductive additives 30, 34. In this example, the metal foil 12 and the resin 20 can be the same as the metal foil 12 and the resin 20 of Example 1, and therefore detailed description thereof will be omitted.

[0040] The resin layer 114 includes multiple layers, and in this embodiment includes a first layer 116 disposed on the surface of the metal foil 12, and a second layer 118 disposed on the surface of the first layer 116. The first layer 116 and the second layer 118 contain conductive additives 30, 34 of different sizes. Hereinafter, the conductive additive 30 contained in the first layer 16 may be referred to as the "first conductive additive 30," and the conductive additive 34 contained in the second layer 18 may be referred to as the "second conductive additive 34." The outer shape of the second conductive additive 34 is larger than the outer shape of the first conductive additive 30. The types (materials, etc.) of the first conductive additive 30 and the second conductive additive 34 are not particularly limited.

[0041] In the current collector 110 of this embodiment, when manufacturing the current collector 110, a first layer 116 is disposed on the surface of the metal foil 12, and then a second layer 118 is disposed on the surface of the first layer 116. When disposing the first layer 116, a first resin slurry containing a conductive additive 30 and a resin 20 is applied to the surface of the metal foil 12, and then the first resin slurry is dried. After the first layer 116 is disposed on the surface of the metal foil 12, a second resin slurry containing a second conductive additive 34 and a resin 20 is applied to the surface of the first layer 116. The second conductive additive 34 has a large outer shape. Therefore, when the second resin slurry is dried, the height dimension of the second conductive additive 34 in the second layer 118 becomes larger than the thickness of the resin 20. As a result, in the second layer 118, the second conductive additive 34 protrudes from the surface of the resin 20, and unevenness is provided on the surface of the second layer 118.

[0042] In the current collector 110 of this embodiment, too, the surface of the second layer 118 is provided with irregularities. Therefore, when the electrode 40 is coated on the surface of the current collector 110, the electrode 40 fits into the irregularities on the surface of the second layer 118, thereby creating an anchor effect between the electrode 40 and the second layer 118 (i.e., the resin layer 114), making it difficult for the electrode 40 to peel off from the current collector 110. Furthermore, in the current collector 110 of this embodiment, the first layer 116 is also disposed between the metal foil 12 and the second layer 118. Therefore, even if the electrode 40 coated on the surface of the second layer 118 passes through the second layer 118 and reaches the first layer 116, the electrode 40 is unlikely to come into contact with the metal foil 12. Therefore, it is possible to simultaneously make it difficult for the electrode 40 coated on the current collector 110 to come into contact with the metal foil 12 and to make it difficult for the electrode 40 to peel off from the current collector 110. Furthermore, in this embodiment, the first layer 116 contains the first conductive additive 30, which has a small outer shape, so the area of ​​only the resin 20 surrounded by the first conductive additive 30 (area without the first conductive additive 30) tends to be small in the first layer 116. This makes it possible to ensure the conductivity of the current collector 110.

[0043] In this embodiment, the resin layer 114 contains the first conductive additive 30 and the second conductive additive 34, but this configuration is not limited thereto. For example, as shown in FIG. 4 , if the first layer 116a contains the first conductive additive 30 and the second layer 118a contains the second conductive additive 34, both the first layer 116a and the second layer 118a may further contain a third conductive additive 36 different from the first conductive additive 30 and the second conductive additive 34. The third conductive additive 36 is smaller than the second conductive additive 34. This provides an uneven surface on the second layer 118a even when the second layer 118a contains the third conductive additive 36. This simultaneously makes it difficult for the electrode 40 coated on the current collector 110a to come into contact with the metal foil 12 and for the electrode 40 to peel off from the current collector 110a. Furthermore, since the first layer 116a and the second layer 118a contain a larger amount of the conductive additive, the conductivity of the current collector 110a can be improved. Note that the type (material, etc.) of the third conductive additive 36 is not particularly limited.

[0044] Example 3 In the above-mentioned Example 1, the conductive additive group 32 was disposed in the second layer 18, and in the above-mentioned Example 2, the second conductive additive 34 having a large outer shape was disposed in the second layers 118, 118a, thereby providing irregularities on the surfaces of the second layers 18, 118, 118a, but this is not limitative. For example, the second layer 218 (see FIG. 5) may contain a thermally decomposable component to provide irregularities on the surface of the second layer 218.

[0045] In this example, an intermediate 210 for producing a current collector will be described. The intermediate 210 includes a metal foil 12 and a resin layer 214. The resin layer 214 includes multiple layers, and in this example, includes a first layer 216 disposed on the surface of the metal foil 12 and a second layer 218 disposed on the surface of the first layer 216.

[0046] The first layer 216 is made of a resin 220 (hereinafter also referred to as the first resin 220) containing a plurality of conductive additives 30. The second layer 218 is made of a resin 222 (hereinafter also referred to as the second resin 222) containing a plurality of conductive additives 30 and a thermally decomposable component. In this example, the conductive additive 30 is acetylene black. Note that the conductive additives 30 and the resin 220 can be the same as the conductive additives 30 and the resin 20 in Example 1 above, and therefore detailed description thereof will be omitted.

[0047] The density of second resin 222 is set to be greater than the density of the thermally decomposable component. In this embodiment, second resin 222 is polyimide (density: approximately 1.4 g / cm), and the thermally decomposable component is polyethylene glycol 20000 (density: approximately 1.2 g / cm). Note that the above combination of second resin 222 and thermally decomposable component is one example, and the combination of second resin 222 and thermally decomposable component is not particularly limited as long as the density of second resin 222 is greater than the density of the thermally decomposable component.

[0048] Next, the intermediate 210 and a method for manufacturing a current collector using the intermediate 210 will be described. As shown in Fig. 6, first, a first layer 216 is disposed on the surface of the metal foil 12 (S12). Specifically, a first resin slurry containing a conductive additive 30 and a resin 220 is applied to the surface of the metal foil 12. Next, the first resin slurry applied to the surface of the metal foil 12 is dried. As a result, the first layer 116 is disposed on the surface of the metal foil 12.

[0049] Next, the second layer 218 is disposed on the surface of the first layer 216 (S14). Specifically, a resin slurry (hereinafter also referred to as the second resin slurry) containing a conductive additive 30, a thermally decomposable component, and a resin 222 is applied to the surface of the first layer 216. Next, the second resin slurry applied to the surface of the first layer 216 is dried. As a result, the second layer 218 is disposed on the surface of the first layer 216. The density of the second resin 222 is greater than the density of the thermally decomposable component. Therefore, while the second resin slurry is drying, the second resin 222, which has a higher density, tends to move downward. Therefore, in the second layer 218, the second resin 222 tends to be located at the bottom, and the thermally decomposable component tends to be located at the top. In this embodiment, the conductive additive 30 is acetylene black (density: approximately 1.75 g / cm), which has a higher density than the second resin 222 (polyimide) and the thermally decomposable component (polyethylene glycol 20000). Therefore, the conductive additive 30 is also likely to be located lower in the second layer 218. Therefore, the thermally decomposable component is likely to be located higher in the second layer 218. When the processing of step S14 is completed, the intermediate body 210 is formed.

[0050] Next, the intermediate 210 is heat-treated (S16). The heat treatment is performed at a temperature (e.g., 300 to 400°C) at which the heat-decomposable component (in this embodiment, polyethylene glycol 20000) contained in the intermediate 210 can be thermally decomposed. This decomposes the heat-decomposable component contained in the intermediate 210. The heat-decomposable component is contained in the second layer 218. Therefore, by performing the heat treatment in step S16, the heat-decomposable component is decomposed, and voids are generated in the second layer 218. Furthermore, the heat-decomposable component is contained in large amounts above the second layer 218. Therefore, by performing the heat treatment in step S16, many voids are generated above the second layer 218. As a result, in a current collector manufactured using the intermediate 210, unevenness is provided on the surface of the resin layer (the surface corresponding to the second layer 218 of the intermediate 210).

[0051] In this embodiment, too, by manufacturing a current collector using the intermediate 210, unevenness is provided on the surface of the resin layer. Therefore, when the electrode 40 is coated on the surface of the current collector, the electrode 40 penetrates into the unevenness on the surface of the resin layer, creating an anchor effect between the electrode 40 and the resin layer, making the electrode 40 less likely to peel off from the current collector. Furthermore, in the intermediate 210, the first layer 116 is disposed between the metal foil 12 and the second layer 218. Therefore, even if the electrode 40 coated on the surface of the resin layer of the current collector manufactured from the intermediate 210 reaches the first layer 116, the electrode 40 is less likely to come into contact with the metal foil 12. Therefore, it is possible to simultaneously make it difficult for the electrode 40 coated on the current collector to come into contact with the metal foil 12 and to make the electrode 40 less likely to peel off from the current collector.

[0052] Example 4 In the above-described Examples 1 and 2, the conductive additive group 32 and the second conductive additive 34 are protruded from the surface of the resin 20 to provide irregularities on the surface of the second layer 18, 118, and in the above-described Example 3, the irregularities are provided on the second layer 218 by thermally decomposing the pyrolysis component contained in the second layer 218, but the present invention is not limited to such a configuration. For example, as shown in Figures 7(a) and 7(b), the irregularities may be provided on the surface of the second layer 318 by providing a plurality of grooves 24 in the second layer 318.

[0053] As shown in FIG. 7( a), the current collector 310 of this example includes a metal foil 12 and a resin layer 314. The resin layer 314 is composed of a resin 20 containing a plurality of conductive additives 30. The resin layer 314 includes a plurality of layers, and in this example, includes a first layer 316 disposed on the surface of the metal foil 12 and a second layer 318 disposed on the surface of the first layer 316. The first layer 316 and the second layer 318 have the same composition. Specifically, the first layer 316 and the second layer 318 are composed of the same type of resin 20. Furthermore, the first layer 316 and the second layer 318 contain the same type of conductive additive 30 at the same density. Note that in this example, the metal foil 12, resin 20, and conductive additive 30 can be the same as the metal foil 12, resin 20, and conductive additive 30 of Example 1 above, and therefore detailed description thereof will be omitted.

[0054] In this example, the first layer 316 has the same configuration as the first layers 16, 116, and 216 of Examples 1 to 3. On the other hand, the second layer 318 is provided with a plurality of grooves 24, and is configured with a plurality of protrusions 25 located between the plurality of grooves 24.

[0055] As shown in Figure 7(b), the second layer 318 has a plurality of linearly extending grooves 24 formed therein. The grooves 24 are arranged in parallel. Each groove 24 extends with a constant width from the upper surface of the second layer 318 (the surface farthest from the first layer 316) to the upper surface of the first layer 316. In the portions of the second layer 318 where the grooves 24 are formed, the surface of the first layer 316 is exposed.

[0056] A plurality of protrusions 25 extending in parallel are formed between the plurality of grooves 24. The upper surface of each protrusion 25 is approximately flat. As the second layer 318 is composed of the plurality of grooves 24 and the plurality of protrusions 25, striped irregularities are provided on the surface of the resin layer 314 (the surface opposite to the surface that comes into contact with the metal foil 12). In this embodiment, the tip (upper surface) of the second layer 318 is flat, but this configuration is not limited to this. For example, the tip of the second layer 318 may be pointed or semi-rounded.

[0057] In the current collector 310 of this embodiment, when manufacturing the current collector 310, the first layer 316 is disposed on the surface of the metal foil 12, and then the second layer 318 is disposed on the surface of the first layer 316. When disposing the first layer 316, a resin slurry containing a conductive additive 30 and a resin 20 is applied to the surface of the metal foil 12, and then the resin slurry is dried. After the first layer 316 is disposed on the surface of the metal foil 12, the resin slurry used to form the first layer 316 is applied to the surface of the first layer 316. Specifically, the resin slurry is applied to a mold (not shown) that conforms to the shape of the multiple grooves 24 and is then dried. This forms the second layer 318 (i.e., the multiple protrusions 25) in an inverted state within the mold. Then, the mold is inverted and placed on top of the first layer 316, and the second layer 318 is bonded to the first layer 316. This forms the resin layer 314 including the first layer 316 and the second layer 318.

[0058] In the current collector 310 of this embodiment, the surface of the resin layer 314 is also provided with an unevenness formed by a plurality of grooves 24 and a plurality of protrusions 25. Therefore, when the electrode 40 is coated on the surface of the current collector 310, the electrode 40 enters the grooves 24 provided in the second layer 318, thereby creating an anchor effect between the electrode 40 and the resin layer 314, making the electrode 40 less likely to peel off from the current collector 310. Furthermore, in the current collector 310 of this embodiment, the first layer 316 is also disposed between the metal foil 12 and the second layer 318, making it less likely that the electrode 40 coated in the grooves 24 provided in the second layer 318 will come into contact with the metal foil 12. Therefore, it is possible to simultaneously make it difficult for the electrode 40 coated on the current collector 310 to come into contact with the metal foil 12 and to make it difficult for the electrode 40 to peel off from the current collector 310.

[0059] In this embodiment, the first layer 316 and the second layer 318 are made of the same type of resin 20, and the first layer 316 and the second layer 318 contain the same type of conductive additive 30. Therefore, the resin slurry used to form the first layer 316 can also be used to form the second layer 318. Since there is no need to separately prepare the resin slurries for the first layer 316 and the second layer 318, the effort and time required to manufacture the current collector 310 can be reduced. Furthermore, since the first layer 316 and the second layer 318 can be formed from the same type of material (i.e., the same type of resin and conductive additive), an increase in the number of types of materials required to manufacture the current collector 310 can be suppressed.

[0060] Furthermore, the protrusions 25 constituting the second layer 318 of this embodiment extend continuously in a straight line. As shown in FIG. 8 , when a tab lead 52 is connected to one end of the plurality of protrusions 25 of the current collector 310, electrons move along the linearly extending protrusions 25 in the second layer 318. For example, compared to a case where the protrusions 25 are not arranged continuously (for example, as shown in FIG. 13 described later, where the protrusions 425 are arranged intermittently), the cross-sectional area through which current flows in the current collector 310 can be increased. This reduces the electrical resistance of the current collector 310. Note that, in this embodiment, the grooves 24 and the protrusions 25 are arranged parallel to the side surface of the current collector 310. However, they may be arranged obliquely with respect to the side surface of the current collector 310, for example.

[0061] In this example, the second layer 318 is formed using a mold (not shown), but the present invention is not limited to this configuration. For example, the resin layer 314a (see FIG. 11(b)) may be formed using a comb-shaped jig 50 (see FIGS. 10(a) and 10(b)).

[0062] 9 to 11, a method for manufacturing a current collector 310a having a second layer 318a using a jig 50 will be described. As shown in FIGS. 9, 10(a), and 10(b), first, a resin slurry 26 is applied to the surface of the metal foil 12 (S100). The resin slurry 26 can be the same as that used in manufacturing the current collector 310 shown in FIG. 7 above, and therefore a detailed description thereof will be omitted.

[0063] Next, grooves 27 (see FIG. 11(a)) are formed in the resin slurry 26 using a jig 50 (S110). As shown in FIGS. 10(a) and 10(b), specifically, a comb-shaped jig 50 is inserted into the resin slurry 26 coated on the surface of the metal foil 12. The jig 50 is inserted until its tip (the tip of each tooth of the jig 50) is positioned near the metal foil 12. Then, while the jig 50 is inserted into the resin slurry 26, it is moved linearly (from left to right in FIGS. 10(a) and 10(b)). This simultaneously forms a plurality of parallel grooves 27 and a plurality of protrusions 28 (see FIG. 11(a)) between the grooves 27. As shown in FIG. 11(a), immediately after the grooves 27 are formed in the resin slurry 26, the grooves 27 reach the vicinity of the metal foil 12. Immediately after the grooves 27 are formed in the resin slurry 26, the resin slurry 26 has a shape in which the grooves 27 and the protrusions 28 extend linearly along the comb-shaped shape of the jig 50.

[0064] Next, the resin slurry 26 is dried (S120). As described above, the resin slurry 26 becomes thinner as it dries. Furthermore, while the resin slurry 26 is drying, a portion of the resin slurry 26 that forms the protrusions 28 moves into the grooves 27. That is, a portion of the resin slurry 26 that forms the protrusions 28 flows into the grooves 27 near the metal foil 12. As a result, while the resin slurry 26 is drying, the resin slurry 26 is positioned between the metal foil 12 and the grooves 27, forming the first layer 316a. Furthermore, while the resin slurry 26 becomes thinner while drying, the height of the protrusions 28 becomes smaller, but the protrusions 28 (25a) remain sufficiently even after the resin slurry 26 dries. As a result, a second layer 318a is formed that is disposed on the first layer 316a and is composed of a plurality of grooves 24a and protrusions 25a. 11(b) , similarly to the current collector 310 of FIG. 7 , by forming a plurality of grooves 24a and protrusions 25a (i.e., second layer 318a) on the surface of resin layer 314a, it is possible to simultaneously make it difficult for the electrode 40 coated on current collector 310a to come into contact with the metal foil 12 and to make it difficult for the electrode 40 to peel off from current collector 310a. Furthermore, since first layer 316a is disposed between the metal foil 12 and second layer 318a, it is difficult for the electrode 40 coated in grooves 24a provided in second layer 318a to come into contact with the metal foil 12.

[0065] 11(b), the resin layer 314a is formed using the jig 50, which allows the first layer 316a and the second layer 318a to be formed simultaneously without applying the resin slurry 26 twice, thereby reducing the number of steps required to manufacture the current collector 310a.

[0066] 12, when resin layer 314b is formed using jig 50, protrusions 25b constituting second layer 318b disposed on first layer 316b may have rounded tips. The tips of protrusions 25b may become rounded during the time from when resin slurry 26 is applied to first layer 316 to when it is dried. Current collector 310b of FIG. 12 also forms second layer 318b composed of grooves 24b and protrusions 25b. Therefore, similar to current collector 310a of FIG. 11(b), it is possible to simultaneously make electrode 40 applied to current collector 310b less likely to come into contact with metal foil 12 and to make electrode 40 less likely to peel off from current collector 310b.

[0067] Example 5 In the above-described Example 4, grooves 24, 24a, and 24b are provided in the second layers 318, 318a, and 318b, thereby forming irregularities on the surfaces of the resin layers 314, 314a, and 314b. However, the present invention is not limited to this configuration. For example, as shown in Figures 13(a) and 13(b), a second layer 418 formed of a plurality of cylindrical protrusions 425 may be provided on a first layer 416 of a current collector 410.

[0068] In the current collector 410 of this embodiment, similarly to the manufacturing process of the current collector 310 of FIG. 7 , the second layer 418 can be formed by applying a resin slurry to a mold (not shown) conforming to the shape of the plurality of protrusions 425, drying the mold, and then inverting the mold to adhere the resin slurry to the first layer 416. In the current collector 410 of this embodiment, the arrangement of the plurality of protrusions 425 also provides unevenness on the surface of the resin layer 414. This makes it possible to simultaneously make it difficult for the electrode 40 applied to the current collector 410 to come into contact with the metal foil 12 and to make it difficult for the electrode 40 to peel off from the current collector 410. Furthermore, because the first layer 416 is disposed between the metal foil 12 and the second layer 418, the electrode 40 applied between the protrusions 425 provided on the second layer 418 makes it difficult for the electrode 40 to come into contact with the metal foil 12.

[0069] In this embodiment, the protrusions 425 are cylindrical, but the shape of the protrusions 425 is not particularly limited. For example, the protrusions 425 may be polygonal pillar-shaped, conical, or pyramidal. The multiple protrusions 425 may be arranged in a regular array as shown in FIG. 13(b), or may be arranged randomly.

[0070] Furthermore, as shown in FIG. 14, the protrusions 425a constituting the second layer 418a may be spherical. When manufacturing the current collector 410a shown in FIG. 14, after forming the first layer 416a, a spherical resin slurry is sprayed onto the first layer 416a and supported on the surface of the first layer 416a. This allows the second layer 418a to be formed, which is composed of spherical protrusions 425a. In the current collector 410a, the arrangement of multiple protrusions 425a also provides unevenness on the surface of the resin layer 414a. This simultaneously makes it difficult for the electrode 40 coated on the current collector 410a to come into contact with the metal foil 12 and for the electrode 40 to peel off from the current collector 410a.

[0071] Although specific examples of the technology disclosed in this specification have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or 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. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of those objectives itself has technical utility. [Explanation of symbols]

[0072] 10, 110, 110a, 310, 310a, 310b, 410, 410a: current collector 12: Metal foil 14, 114, 314, 314a, 314b, 414, 414a: Resin layer 16, 116, 116a, 316, 316a, 316b, 416, 416a: 1st layer 18, 118, 318, 318a, 318b, 418, 418a: 2nd layer 20: Resin 24, 24a, 24b: Second layer grooves 25, 25a, 25b, 425, 425a: Second layer protrusions 26: Resin slurry 27: Resin slurry groove 28: Protrusion of resin slurry 30: Conductive additive (first conductive additive) 32: Conductive additive group 34: Second conductive additive 40: Electrode 50: Jig 210: Intermediate 220: First resin 222: Second resin

Claims

1. A metal foil; a resin layer made of a resin containing a plurality of conductive additives and disposed on the metal foil; the resin layer includes a first layer disposed on the metal foil and a second layer disposed on the first layer; The second layer has a surface opposite to the surface in contact with the first layer, and the second layer has a concave-convex shape.

2. The current collector according to claim 1 , the plurality of conductive additives include a plurality of first conductive additives contained in the first layer and a plurality of second conductive additives contained in the second layer, the second layer includes a plurality of conductive assistant groups formed by aggregation of some of the plurality of second conductive assistants, Each of the conductive additive groups is disposed with a gap between adjacent conductive additive groups.

3. The current collector according to claim 1 , the plurality of conductive additives include a plurality of first conductive additives contained in the first layer and a plurality of second conductive additives contained in the second layer, A current collector, wherein the outer dimensions of each of the second conductive additives are larger than the outer dimensions of each of the first conductive additives.

4. The current collector according to claim 1 , a current collector, wherein the opposite surface of the second layer is provided with a plurality of grooves.

5. The current collector according to claim 4, the first layer and the second layer are made of the same type of resin, The current collector, wherein the first layer and the second layer contain the same type of conductive additive at the same density.

6. An intermediate for producing a current collector, A metal foil; a resin layer made of a resin containing a plurality of conductive additives and disposed on the metal foil; the resin layer includes a first layer disposed on the metal foil and a second layer disposed on the first layer; The second layer comprises a thermally decomposable component.

7. 7. The intermediate of claim 6, An intermediate, wherein the density of the resin constituting the second layer is greater than the density of the thermally decomposable component.

8. A method for manufacturing a current collector including a metal foil and a resin layer made of a resin containing a plurality of conductive additives and disposed on the metal foil, comprising: a disposing step of disposing a slurry containing the plurality of conductive additives and the resin on the metal foil; a groove forming step of inserting a comb-shaped jig into a surface of the slurry placed on the metal foil opposite to a surface that contacts the metal foil in the placement step, and linearly moving the jig to form a plurality of grooves on the opposite surface; a drying step of forming an irregularity constituted by a plurality of grooves on the surface of the resin layer opposite to the surface that comes into contact with the metal foil by drying the slurry in which the plurality of grooves have been formed on the opposite surface in the groove forming step.

9. A method for manufacturing a current collector, comprising: a first disposing step of disposing a first layer made of a resin containing a plurality of conductive additives on a metal foil; a second disposing step of disposing a second layer made of a resin containing a plurality of conductive additives and a thermally decomposable component on the first layer; a heat treatment step of heat-treating an intermediate body formed by the first arrangement step and the second arrangement step to form irregularities on a surface of the second layer opposite to a surface that comes into contact with the first layer.

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