Collector and method for manufacturing collector

Abstract

To provide a technique of making it more difficult for an electrode applied on a collector to peel off from the collector.SOLUTION: The present invention includes a collector, a metal foil, and a porous structure arranged on a surface of the metal foil.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The technology disclosed in this specification relates to a current collector and a method for manufacturing the current collector.

Background Art

[0002] The current collector used in a secondary battery has been variously improved to enhance its performance. For example, in the current collector of Patent Document 1, the surface of the metal foil used for the current collector is roughened. By roughening the surface of the metal foil, when an electrode is coated on the current collector, the electrode penetrates into the roughened portion of the metal foil. As a result, an anchor effect occurs between the electrode that has penetrated into the roughened portion of the metal foil and the current collector, 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, by roughening the metal foil, voids are formed on the surface of the metal foil substantially perpendicular to the surface of the metal foil. When an electrode is coated on the current collector, an anchor effect occurs substantially perpendicular to the surface of the metal foil between the electrode that has penetrated into the roughened portion of the metal foil and the current collector. Therefore, the adhesion in the direction perpendicular to the surface of the metal foil is improved. However, since the adhesion in a direction different from the direction perpendicular to the surface of the metal foil is not improved, for example, when a force in a direction substantially parallel to the surface of the metal foil is applied, the electrode may peel off from the current collector.

[0005] This specification discloses a technology for making it difficult to peel off the electrode coated on the current collector from the current collector.

Means for Solving the Problems

[0006] In a first aspect of the present technology, the current collector includes a metal foil and a porous structure disposed on the surface of the metal foil.

[0007] According to this configuration, by disposing a porous structure on the surface of the metal foil, when an electrode is coated on the current collector, the electrode enters into the porous structure. The porous structure has voids recessed in various directions with respect to the surface of the metal foil. Therefore, an anchor effect in various directions with respect to the surface of the metal foil occurs between the electrode and the porous structure. For this reason, the adhesion between the electrode and the porous structure increases, and it becomes difficult for the electrode to peel off from the current collector.

[0008] In a second aspect, in the above first aspect, the porous structure may be composed of a plurality of conductive particles. The porous structure may include a first layer disposed on the surface of the metal foil and a second layer disposed on the first layer. The conductive particles disposed in the first layer and the conductive particles disposed in the second layer may have substantially the same outer shape.

[0009] According to this configuration, by laminating conductive particles on the surface of the metal foil, voids in various directions with respect to the surface of the metal foil are generated. Therefore, the adhesion between the electrode and the porous structure can be increased. Further, since the conductive particles having substantially the same outer shape are disposed in the first layer and the second layer, the same type of conductive particles can be disposed in the first layer and the second layer. Therefore, a porous structure can be formed without using a plurality of types of conductive particles.

[0010] In a third aspect, in the above-described first aspect, the porous structure may be composed of a plurality of conductive particles. The porous structure may include a first layer disposed on the surface of the metal foil and a second layer disposed on the first layer. The plurality of conductive particles may include first conductive particles having a first diameter and second conductive particles having a second diameter smaller than the first diameter. The first conductive particles may be disposed in the first layer. The second conductive particles may be disposed in the second layer.

[0011] According to this configuration, the diameter of the first conductive particles disposed on the surface side of the metal foil is larger than the diameter of the second conductive particles disposed at a position away from the surface of the metal foil. As a result, the closer to the surface of the metal foil, the larger the gaps between the conductive particles become. For this reason, it becomes easier for many electrodes to enter the vicinity of the metal foil, and the adhesive force between the electrode and the current collector can be improved.

[0012] In a fourth aspect, in the above-described second or third aspect, the plurality of conductive particles disposed in the first layer may be arranged so as to be in contact with adjacent conductive particles within the first layer. The plurality of conductive particles disposed in the second layer may be arranged so as to be in contact with adjacent conductive particles within the second layer.

[0013] According to this configuration, appropriate gaps can be created between the conductive particles in each of the first layer and the second layer. For example, if adjacent conductive particles are separated, the gaps become too large, and the anchor effect generated between the electrode coated on the current collector and the porous structure becomes small. By arranging the adjacent conductive particles to be in contact with each other in each of the first layer and the second layer, a plurality of appropriate gaps can be created between the conductive particles.

[0014] In a fifth aspect, in any one of the above-described second to fourth aspects, the plurality of conductive particles may be solid.

[0015] According to this configuration, in a secondary battery in which an electrode is coated on a current collector, the cross-sectional area through which current passes can be increased. Therefore, the resistance value when current passes can be reduced.

[0016] In the sixth aspect, in any one of the second to fourth aspects described above, the plurality of conductive particles may be porous particles.

[0017] According to this configuration, since many voids exist in the conductive particles, more voids can be generated in the entire porous structure due to the voids inside the conductive particles and the voids between the conductive particles. In addition, the shape of the voids becomes complex, and an anchor effect in more directions occurs between the electrode coated on the current collector and the porous structure. Therefore, the adhesion between the electrode and the porous structure can be improved.

[0018] In the seventh aspect, in the first aspect described above, the porous structure may be composed of conductive fibers.

[0019] According to this configuration, by arranging conductive fibers on the surface of the metal foil, many and complex-shaped voids can be generated between the conductive fibers. Therefore, the anchor effect between the electrode and the porous structure can be improved.

[0020] In the eighth aspect, a method for manufacturing a current collector manufactures a current collector having a porous structure on the surface of a metal foil. The method for manufacturing a current collector includes an oxidation step of oxidizing the metal foil with a positive potential, and a reduction step of reducing the metal foil whose surface has been oxidized in the oxidation step with a negative potential.

[0021] According to this configuration, by oxidizing and reducing, a porous structure can be formed on the surface of the metal foil without using a solvent or the like. Therefore, a porous structure can be formed on the surface of the metal foil uniformly. In addition, the porous structure to be formed can be easily adjusted from the current value during the process.

[0022] In the ninth aspect, a method for manufacturing a current collector manufactures a current collector having a porous structure on the surface of a metal foil. The method for manufacturing the current collector includes a first heat treatment step of heat-treating the metal foil in an oxygen atmosphere, and a second heat treatment step of heat-treating the metal foil heat-treated in the first heat treatment step in a hydrogen atmosphere.

[0023] According to this configuration, the surface of the metal foil can be oxidized by heat treatment in an oxygen atmosphere, and a porous structure can be formed on the oxidized metal foil by heat treatment in a hydrogen atmosphere. Therefore, a porous structure can be formed uniformly on the surface of the metal foil without using a solvent or the like. Further, since the porous structure is formed by heat treatment, it is possible to avoid using water during each step or having water adhere to the current collector after each step. Therefore, the step of removing the water adhering to the current collector can be omitted.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

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Figure 10

Figure 11

[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 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 porous film 20.

[0026] 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 metal constituting the metal foil 12 is not particularly limited, and a metal other than copper may be used.

[0027] The porous film 20 is disposed on the surface of the metal foil 12. The porous film 20 is composed of a plurality of conductive particles 22. Specifically, the porous film 20 is formed by disposing the conductive particles 22 on the surface of the metal foil 12. The conductive particles 22 are substantially spherical and have a plurality of pores. That is, the conductive particles 22 are porous conductive particles. As the conductive particles 22, those obtained by imparting pores to solid conductive particles may be used, or commercially available porous conductive particles may be used. The conductive particles 22 are formed of a metal (for example, copper, nickel, etc.), a metal oxide (for example, titanium oxide, tin oxide, etc.) or carbon (for example, carbon, acetylene black, etc.). Note that the conductive particles 22 only need to be formed of a substance having high conductivity and are not limited to the above.

[0028] The conductive particles 22 are fixed to the surface of the metal foil 12 using an adhesive (not shown in FIG. 1). The type of the adhesive is not particularly limited. The adhesive may be an inorganic material or an organic material. As an example of an inorganic material-based adhesive, there is a metal alkoxide. This material is a type of organometallic material and is distinguished as an inorganic-based adhesive because it undergoes a chemical reaction to produce a metal oxide. Any organometallic material other than the metal alkoxide may be used as long as it is a material that produces a metal oxide through a chemical reaction. Also, as an example of an organic material-based adhesive, there is a resin material. The material of the resin is not limited, and a thermoplastic resin or a thermosetting resin may be used. Also, a conductive polymer may be used. Further, other methods for fixing the conductive particles 22 to the metal foil 12 may be used to fix the conductive particles 22 to the metal foil 12 without using an adhesive.

[0029] By disposing the porous conductive particles 22 on the surface of the metal foil 12, a plurality of voids 24 due to the pores of the porous conductive particles 22 are formed in the porous film 20. The orientation of the conductive particles 22 disposed on the surface of the metal foil 12 is random. For this reason, the orientations of the plurality of voids 24 provided in the porous film 20 also become random. That is, the direction in which each void 24 sinks with respect to the surface of the metal foil 12 is not constant, and the plurality of voids 24 sink in various directions with respect to the surface of the metal foil 12.

[0030] The current collector 10 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 voids 24 provided in the porous film 20. When the electrode 40 enters the voids 24, an anchor effect is generated between the electrode 40 and the porous film 20, making it difficult for the electrode 40 to peel off from the current collector 10. Even when only a part of the electrode 40 (for example, the binder) enters the voids 24 instead of all of the electrode active material, conductive assistant, binder, etc. constituting the electrode 40, the electrode 40 is adhered to the current collector 10 by the anchor effect in the same manner.

[0031] Also, in this embodiment, the plurality of voids 24 provided in the porous film 20 are recessed in various directions with respect to the surface of the metal foil 12. An anchor effect occurs in the direction in which the electrode 40 enters the void 24 (the direction indicated by the arrow in FIG. 2) between the electrode 40 and the porous film 20. For example, even when the surface of the metal foil is roughened and an electrode is coated on the surface, the electrode enters the recesses formed by the roughening, and an anchor effect occurs between the electrode and the metal foil (i.e., the current collector). However, when the surface of the metal foil is roughened, the recesses formed by the roughening are substantially perpendicular to the surface of the metal foil, and the anchor effect between the electrode and the metal foil occurs only in substantially the same direction (substantially perpendicular to the surface of the metal foil). In this embodiment, by providing the voids 24 that are recessed in random directions in the porous film 20, an anchor effect occurs in various directions with respect to the surface of the metal foil 12 between the electrode 40 and the porous film 20. Therefore, the electrode 40 coated on the current collector 10 can be made difficult to peel off from the current collector 10.

[0032] (Example 2) In the above-described Example 1, the porous film 20 was composed of the porous conductive particles 22, but it is not limited to such a configuration. For example, as shown in FIG. 3, the porous film 120 may be composed by laminating solid conductive particles 122. In this embodiment, the metal foil 12 and the adhesive 30 can be the same as the metal foil 12 and the adhesive in the above-described Example 1. Therefore, detailed descriptions of the metal foil 12 and the adhesive 30 are omitted.

[0033] The current collector 110 of this embodiment includes a metal foil 12 and a porous film 120. The porous film 120 is composed of a plurality of conductive particles 122. The conductive particles 122 are solid. That is, the conductive particles 122 do not have a plurality of pores like the porous conductive particles 22 of the above-described Example 1. The conductive particles 122 are formed of a material having high conductivity such as, for example, metal, metal oxide, or carbon. The porous film 120 is composed of the same type of conductive particles 122. That is, the plurality of conductive particles 122 constituting the porous film 120 all have substantially the same outer shape. The porous film 120 includes a plurality of layers. In this embodiment, the porous film 120 includes a first layer 120a and a second layer 120b. The same type (that is, substantially the same shape) of conductive particles 122 are arranged in the first layer 120a and the second layer 120b. The plurality of conductive particles 122 arranged in the first layer 120a are in contact with each other. Also, the plurality of conductive particles 122 arranged in the second layer 120b are in contact with each other.

[0034] The porous film 120 is formed, for example, by the following procedure. First, an adhesive 30 is applied to the surface of the metal foil 12. Next, the conductive particles 122 are arranged on the surface of the metal foil 12 to which the adhesive 30 is applied (the upper surface in FIG. 3), and the first layer 120a is formed. Then, the conductive particles 122 are further arranged on the first layer 120a, and the second layer 120b is formed. Note that the coating and drying of a mixture (for example, slurry) of the conductive particles 122 and the adhesive 30 may be repeated to form the first layer 120a and the second layer 120b. Also, in this embodiment, the conductive particles 122 may be fixed to the metal foil 12 without using the adhesive 30. Also, the porous film 120 may include three or more layers. Also, the conductive particles 122 constituting the porous film 120 only need to have substantially the same outer shape and may be of different types (that is, different materials). Also, as long as the structure has voids between the particles, the particles may be stacked regularly or irregularly.

[0035] In this embodiment, by laminating and arranging the conductive particles 122 on the surface of the metal foil 12, a plurality of voids 124 are formed between the conductive particles 122. For example, when the conductive particles 122 are closely packed, the porosity is about 26%. The plurality of voids 124 are recessed in various directions with respect to the surface of the metal foil 12. Therefore, also in this embodiment, an anchor effect occurs between the electrode coated on the surface of the current collector 110 and the porous film 120, making it difficult for the electrode to peel off from the current collector 110.

[0036] Note that in this embodiment, the porous film 120 was composed of solid conductive particles 122, but it is not limited to such a configuration. For example, as shown in FIG. 4, the porous film 220 may be formed by laminating porous conductive particles 22. By forming the porous film 220 by laminating the porous conductive particles 22, a plurality of voids 224 are formed in the porous film 220, which are formed by the spaces between the conductive particles 22 and the pores provided in the conductive particles 22. Therefore, even when the porous conductive particles 22 are laminated, an anchor effect occurs between the electrode coated on the surface of the current collector 210 and the porous film 220, making it difficult for the electrode to peel off from the current collector 210. In addition, as the porosity of the porous film 220 increases, the shape of the voids 224 becomes more complex. When the shape of the voids 224 becomes more complex, an anchor effect in more directions occurs between the electrode and the porous film 220. Therefore, the anchor effect between the electrode and the porous film 220 can be improved. Also, as long as the structure has voids between particles and voids on the particle surface, the particles may be laminated regularly or irregularly.

[0037] (Example 3) In the above Examples 1 and 2, the porous films 20, 120, and 220 were composed of the conductive particles 22 and 122, but it is not limited to such a configuration. For example, as shown in FIG. 5, the porous film 320 may be composed of conductive fibers 26. Note that also in this embodiment, since the metal foil 12 and the adhesive 30 are the same as the metal foil 12 and the adhesive in Examples 1 and 2 above, detailed description thereof is omitted.

[0038] The current collector 310 of this embodiment includes a metal foil 12 and a porous film 320. The porous film 320 is composed of conductive fibers 26. The conductive fibers 26 are in a twisted yarn shape and are formed of metal, metal oxide, or carbon. The porous film 320 is formed, for example, by the following procedure. First, an adhesive 30 is applied to the surface of the metal foil 12. Next, the conductive fibers 26 are arranged on the surface of the metal foil 12 to which the adhesive 30 is applied (the upper surface in FIG. 5). The conductive fibers 26 are arranged on the surface of the metal foil 12 without applying tension. By not applying tension to the conductive fibers 26, the conductive fibers 26 are avoided from being pulled in a certain direction, and many voids 324 are generated between the conductive fibers 26. Note that the porous film 320 may be formed by repeating the coating and drying of a mixture (for example, a slurry) of the conductive fibers 26 and the adhesive 30. Also, in this embodiment, the conductive fibers 26 may be fixed to the metal foil 12 without using the adhesive 30.

[0039] Also in this embodiment, since the porous film 320 is composed of the conductive fibers 26, many voids 324 are generated in the porous film 320. For this reason, an anchor effect occurs between the electrode coated on the surface of the current collector 310 and the porous film 320, and the electrode is less likely to peel off from the current collector 310.

[0040] (Example 4) In the above Examples 1 and 2, the porous films 20, 120, and 220 were composed of the same type (substantially the same shape) of conductive particles 22 and 122, but the configuration is not limited to this. For example, as shown in FIG. 6, the porous film 420 may be composed of a plurality of types of conductive particles 122a and 122b. Also, in this embodiment, since the metal foil 12 and the adhesive 30 are the same as the metal foil 12 and the adhesive in the above Examples 1 to 3, detailed description is omitted.

[0041] The current collector 410 of this embodiment includes a metal foil 12 and a porous film 420. The porous film 420 includes a first layer 420a and a second layer 420b. In the first layer 420a, solid conductive particles 122a having substantially the same shape (hereinafter also referred to as first conductive particles 122a) are arranged. In the first layer 420a, adjacent first conductive particles 122a are in contact with each other. Also, in the second layer 420b, solid conductive particles 122b having substantially the same shape (hereinafter also referred to as second conductive particles 122b) are arranged. In the second layer 420b, adjacent second conductive particles 122b are in contact with each other. The diameter of the second conductive particles 122b is smaller than the diameter of the first conductive particles 122a. Note that the second conductive particles 122b only need to have a smaller diameter than the first conductive particles 122a, and the materials of the first conductive particles 122a and the second conductive particles 122b may be the same or different. The first layer 420a may have a structure in which two or more layers of the first conductive particles 122a are laminated, and the second layer 420b may have a structure in which two or more layers of the second conductive particles 122b are laminated.

[0042] The porous film 420 is formed, for example, by the following procedure. First, an adhesive 30 is applied to the surface of the metal foil 12. Next, the first conductive particles 122a are arranged on the surface of the metal foil 12 to which the adhesive 30 is applied (the upper surface in FIG. 6), and the first layer 420a is formed. Note that a mixture of the first conductive particles 122a and the adhesive 30 (for example, a slurry) may be coated and dried to form the first layer 420a, and a mixture of the second conductive particles 122b and the adhesive 30 (for example, a slurry) may be coated and dried to form the second layer 420b. Also, in this embodiment, the first conductive particles 122a may be fixed to the metal foil 12 without using the adhesive 30. Thereafter, the second conductive particles 122b are arranged on the first layer 420a, and the second layer 420b is formed. Also, as long as the structure has voids between the particles, the particles may be regularly laminated or irregularly laminated.

[0043] In this embodiment, the diameter of the second conductive particles 122b disposed in the second layer 420b is smaller than the diameter of the first conductive particles 122a disposed in the first layer 420a. That is, the diameter of the first conductive particles 122a disposed on the metal foil 12 side is larger than the diameter of the second conductive particles 122b disposed at a position away from the metal foil 12. The gap 424a between the first conductive particles 122a with a larger diameter is larger than the gap 424b between the second conductive particles 122b with a smaller diameter. That is, the closer to the metal foil 12, the larger the size of the gap. Therefore, when the electrode is applied to the current collector 410, many electrodes are likely to enter the vicinity of the surface of the metal foil 12, and it becomes difficult for the electrode to peel off from the current collector 110.

[0044] In addition, in this embodiment, the porous film 420 is composed of solid conductive particles 122a and 122b, but it is not limited to such a configuration. For example, as shown in FIG. 7, the porous film 520 may be composed of porous first conductive particles 22a and second conductive particles 22b. The diameter of the first conductive particles 22a is larger than the diameter of the second conductive particles 22b. In the porous film 520, the first conductive particles 22a are disposed on the surface of the metal foil 12, and the second conductive particles 22b are disposed on the first conductive particles 22a. By using the porous first conductive particles 22a and second conductive particles 22b, more gaps 524a and 524b are generated in the porous film 520. Therefore, a higher anchor effect is generated between the electrode applied to the current collector 510 and the porous film 520, and it becomes more difficult for the electrode to peel off from the current collector 510. Also, as long as the structure has gaps between particles and gaps on the particle surface, the particles may be stacked regularly or irregularly.

[0045] (Example 5) In the above Examples 1 to 4, by disposing the conductive particles 22, 22a, 22b, 122, 122a, 122b and the conductive fibers 26 on the surface of the metal foil 12, voids 24, 124, 224, 324, 424a, 424b, 524a, 524b were formed in the porous membranes 20, 120, 220, 320, 420, 520. However, the present invention is not limited to such a configuration. For example, as shown in FIG. 8, the porous membrane 620 may be composed of a metal layer 28 having voids 624 (hereinafter, the metal layer 28 having voids 624 is also simply referred to as "metal layer 28"). In this example as well, since the metal foil 12 is the same as the metal foil 12 in Examples 1 to 4 above, detailed description thereof is omitted.

[0046] The current collector 610 of this example includes a metal foil 12 and a porous membrane 620. The porous membrane 620 is composed of a metal layer 28 formed by oxidizing and reducing the metal foil 12, and a plurality of voids 624 are provided in the metal layer 28.

[0047] Here, a method for forming the porous membrane 620 will be described. As shown in FIG. 9, first, a metal oxide layer 50 (see FIG. 10(a)) is formed on the surface of the metal foil 12 by electrolysis (S10). Specifically, the metal foil 12 is immersed in an electrolytic solution, and the electrolytic solution is set to a noble potential (positive potential). An aqueous solution of a supporting salt (for example, sodium sulfate or the like) is used as the electrolytic solution. Then, as shown in FIG. 10(a), the surface of the metal foil 12 is oxidized and decomposed, and a metal oxide layer 50 containing a metal oxide 52 is formed on the surface of the metal foil 12. Further, the metal oxide 52 may be scattered in the metal oxide layer 50, or the entire metal oxide layer 50 may be the metal oxide 52. In this example, since the metal foil 12 is a copper foil, when the metal foil 12 (copper foil) is oxidized and decomposed, copper oxide is formed on the surface of the metal foil 12 (copper foil). During electrolysis, the current value is measured. By measuring the current value, the metal oxide layer 50 formed on the metal foil 12 can be adjusted to a desired thickness.

[0048] Next, the metal foil 12 on which the metal oxide layer 50 has been formed in step S10 is reduced by electrolysis (S20). Specifically, while the metal foil 12 is immersed in the electrolytic solution, the electrolytic solution is set to a low potential (negative potential). Then, as shown in FIGS. 10(a) and 10(b), the metal oxide 52 contained in the metal oxide layer 50 formed on the surface of the metal foil 12 is reductively decomposed, voids 624 are formed in the portion where the metal oxide 52 has been reductively decomposed, and a metal layer 28 including a plurality of voids 624 is formed. During electrolysis, the current value is measured. By measuring the current value, the voids 624 formed in the metal layer 28 can be adjusted to a desired thickness or amount. In this way, a porous film 620 (that is, a metal layer 28 having a plurality of voids 624) is formed on the surface of the metal foil 12.

[0049] In this embodiment, the porous film 620 is formed by electrolysis. By using electrolysis, a uniform metal layer 28 can be formed on the surface of the metal foil 12, and a plurality of voids 624 can be uniformly formed in the formed metal layer 28. Further, in electrolysis, an aqueous solution of a supporting salt (for example, sodium sulfate or the like) is used as the electrolytic solution. Therefore, the scale of the apparatus for forming the porous film 620 can be reduced as compared with the case of using a reducing agent such as sodium borohydride. Further, the reactant by electrolysis is only water molecules. Since water molecules have a smaller molecular weight than a reducing agent such as sodium borohydride, they easily penetrate the surface of the metal foil 12. Therefore, the voids 624 can be uniformly formed throughout the metal layer 28. The above-described method of forming the metal oxide layer 50 on the metal foil electrochemically and forming the porous film 620 by reducing the metal oxide layer 50 is an example, and other processing conditions may be used to form a similar structure.

[0050] Note that, in this embodiment, the porous film 620 is formed by electrolysis, but the present invention is not limited to such a configuration. For example, the porous film 620 may be formed by heat treatment.

[0051] A method of forming a porous film 620 by heat treatment will be described. As shown in FIG. 11, first, a metal foil 12 is heat-treated in an oxygen atmosphere (S100). Specifically, the metal foil 12 is heat-treated at 200 to 400 degrees in an atmosphere of air, oxygen, or a mixed gas of 20 vol% oxygen and argon. Thereby, the surface of the metal foil 12 is oxidized, and a metal oxide 52 (for example, copper oxide if the metal foil 12 is a copper foil) is generated on the surface of the metal foil 12.

[0052] Next, the metal foil 12 on which the metal oxide 52 has been generated in step S100 is heat-treated in a hydrogen atmosphere (S200). Specifically, the metal foil 12 on which the metal oxide 52 has been generated is heat-treated at 300 degrees in an atmosphere of hydrogen or a mixed gas of 5 vol% hydrogen and argon. Thereby, the metal oxide 52 contained in the metal oxide layer 50 formed on the surface of the metal foil 12 is reduced, and a metal layer 28 having a plurality of voids 624 is formed. In this way, a porous film 620 (that is, a metal layer 28 having a plurality of voids 624) may be formed on the surface of the metal foil 12.

[0053] By forming the porous film 620 by heat treatment as described above, the porous film 620 can be formed without using an aqueous solution. The current collector 610 is used in a secondary battery. Therefore, when water adheres to the current collector 610 during the production of the current collector 610, it is necessary to remove the water adhering to the current collector 610. By forming the porous film 620 by heat treatment, it is possible to avoid using water or generating water during the formation of the porous film 620, and the step of removing the water adhering to the current collector 610 can be omitted. Further, in the method by the above heat treatment, the reactant is a hydrogen molecule. Since the hydrogen molecule has a smaller molecular weight than a reducing agent such as sodium borohydride, it easily penetrates the surface of the metal foil 12, and a metal layer 28 having voids 624 can be formed uniformly. Also, generation of harmful waste can be avoided. The above-described method of forming the metal oxide layer 50 on the electrochemical metal foil and forming the porous film 620 by reducing the metal oxide layer 50 is an example, and other processing conditions may be used to form a similar structure.

[0054] Points to note regarding the current collectors 10, 110, 210, 310, 410, 510, 610 described in the embodiments will be described. The porous membranes 20, 120, 220, 320, 420, 520, 620 in the embodiments are an example of a "porous structure".

[0055] As described above, specific examples of the present invention have been described in detail, 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. 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. In addition, the technology illustrated in this specification or the drawings can achieve multiple purposes simultaneously, and achieving one of these purposes itself has technical utility.

Explanation of Reference Numerals

[0056] 10, 110, 210, 310, 410, 510, 610: Current collectors 12: Metal foil 20, 120, 220, 320, 420, 520, 620: Porous membranes 22, 22a, 22b: Porous conductive particles 24, 124, 224, 324, 424a, 424b, 524a, 524b, 624: Void spaces 26: Conductive fibers 28: Metal layer 40: Electrodes 50: Metal oxide layer 52: Metal oxide 120a, 420a: First layer 120b, 420b: Second layer 122, 122a, 122b: Solid conductive particles

Claims

1. Metal foil; a porous structure disposed on a surface of the metal foil; The current collector comprises:

2. The current collector according to claim 1 , the porous structure is constituted by a plurality of conductive particles; the porous structure comprises a first layer disposed on a surface of the metal foil and a second layer disposed on the first layer; The conductive particles arranged in the first layer and the conductive particles arranged in the second layer have substantially the same outer shape.

3. The current collector according to claim 1 , the porous structure is constituted by a plurality of conductive particles; the porous structure comprises a first layer disposed on a surface of the metal foil and a second layer disposed on the first layer; the plurality of conductive particles include first conductive particles having a first diameter and second conductive particles having a second diameter smaller than the first diameter; the first conductive particles are disposed in the first layer; The second conductive particles are disposed in the second layer.

4. The current collector according to claim 2 or 3, the conductive particles disposed in the first layer are disposed so as to contact adjacent conductive particles in the first layer; A current collector, wherein the plurality of conductive particles disposed in the second layer are positioned so as to contact adjacent conductive particles in the second layer.

5. The current collector according to claim 2 or 3, A current collector, wherein the plurality of conductive particles are solid.

6. The current collector according to claim 2 or 3, The current collector, wherein the plurality of conductive particles are porous particles.

7. The current collector according to claim 1 , The current collector, wherein the porous structure is constituted by conductive fibers.

8. A method for producing a current collector having a porous structure on a surface of a metal foil, comprising the steps of: an oxidation step of oxidizing the metal foil by applying a positive potential; a reduction step of reducing the metal foil, the surface of which has been oxidized in the oxidation step, by applying a negative potential to the metal foil.

9. A method for producing a current collector having a porous structure on a surface of a metal foil, comprising the steps of: a first heat treatment step of heat treating the metal foil in an oxygen atmosphere; a second heat treatment step of heat treating the metal foil heat-treated in the first heat treatment step in a hydrogen atmosphere.

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