Electrode for energy storage device, secondary battery, and method for manufacturing electrode for energy storage device

Abstract

To provide a novel electrode for a power storage device that can improve the performance of a power storage device using carbon as an active material and is easy to mass produce.SOLUTION: An electrodes for a power storage device includes a metal substrate constituting a current collector, and an active material layer formed on the surface of the metal substrate and containing carbon as an active material. The surface of the active material layer has a fine uneven structure in which a plurality of fine granular body are densely arranged, and on the surface layer of the granular body, carbon nanostructures made of graphene and elongated toward the outside of the granular body are arranged over the entire surface layer.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present application relates to an electrode for a power storage device, a secondary battery, and a method for manufacturing an electrode for a power storage device.

Background Art

[0002] As rechargeable power storage devices, for example, secondary batteries, electric double layer capacitors, etc. are known. In these electrodes for power storage devices, carbon may be used as an active material disposed on the surface of a current collector. For example, Patent Documents 1 and 2 below disclose techniques for forming an active material layer of a negative electrode of a lithium ion secondary battery with graphite or carbon nanotubes. When carbon nanotubes are applied to the active material layer, it can be expected that the battery performance of the power storage device, such as the charge capacity and charge rate, will be improved compared to the case where graphite is applied.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, with the conventional techniques as described above, the high battery performance targets required for power storage devices have still not been fully achieved.

[0005] Furthermore, electrodes having a carbon nanowall active material layer are often difficult to handle when rolled up for transportation or storage, because the carbon nanowalls on the electrode surface are destroyed or removed by compressive stress or shear stress. This problem is one of the reasons why mass production of electrodes having a carbon nanowall active material layer is difficult. Thus, there is still room for improvement in the ease of manufacturing and mass production of electrodes for power storage devices that use carbon as the active material. [Means for solving the problem]

[0006] The inventors of the present invention have conducted extensive research into electrodes for power storage devices that use carbon as an active material, and have succeeded in developing an active material layer that has a different shape from conventional graphite or carbon nanowalls and can dramatically improve battery performance. The present invention can be realized, for example, in the following forms.

[0007] A first aspect of the present invention is provided as an electrode for an electricity storage device. This electrode for an electricity storage device includes a metal substrate constituting a current collector, and an active material layer formed on the surface of the metal substrate and containing carbon as an active material, the surface of the active material layer having a fine uneven structure in which a plurality of minute particles are densely arranged, and carbon nanostructures made of graphene extending outward from the particles are arranged throughout the surface layer of the particles.

[0008] According to this configuration of the electrode for an electricity storage device, the surface area of the carbon nanostructures contained in the active material layer can be increased, thereby increasing the charging capacity of the electricity storage device. Furthermore, according to this configuration of the electrode for an electricity storage device, even when rolled up, it is possible to at least suppress the destruction or detachment of the carbon nanostructures present in the recesses of the fine uneven structure of the active material layer. Therefore, it is possible to improve the handleability of the electrode for an electricity storage device and its mass productivity.

[0009] The invention of the present application can be realized in various forms other than the electrodes for power storage devices. For example, it can also be realized in the form of power storage devices such as secondary batteries equipped with electrodes for power storage devices, manufacturing methods for electrodes for power storage devices, manufacturing methods for power storage devices, manufacturing methods for current collectors, manufacturing methods for active material layers, manufacturing apparatuses suitable for executing those manufacturing methods, control programs for controlling those manufacturing apparatuses, recording media on which those control programs are recorded, and the like.

Brief Description of the Drawings

[0010]

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Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the electrode for a power storage device according to the invention of the present application will be described with reference to the drawings. In this specification, the "power storage device" means, for example, a rechargeable power storage body such as a secondary battery or an electric double layer capacitor, and a device including the power storage body.

[0012] 1. Embodiment: 1-1. Configuration of a secondary battery: FIG. 1 is a schematic diagram showing the configuration of a secondary battery 10 including an electrode 20 for a power storage device according to this embodiment. The secondary battery 10 of this embodiment is a lithium ion secondary battery in which lithium ions are involved in charge and discharge. The secondary battery 10 includes a container 11, an electrolytic solution 12, a separator 15, a first electrode 20, and a second electrode 30. In FIG. 1, for convenience, the container 11 is illustrated by a dashed line, and the separator 15 is illustrated by a broken line.

[0013] The container 11 has an internal space filled with the electrolytic solution 12. The container 11 is configured to be liquid-tight with a material that is hardly reactive with the electrolytic solution 12. The electrolytic solution 12 has the property of being able to transmit metal ions involved in charge and discharge between the first electrode 20 and the second electrode 30. In this embodiment, the electrolytic solution 12 is composed of a solution in which a lithium salt is dissolved in an organic solvent, and can transmit lithium ions between the first electrode 20 and the second electrode 30. As the lithium salt of the electrolytic solution 12, for example, lithium hexafluorophosphate (LiPF6) can be used. Further, as the organic solvent, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. can be used.

[0014] Separator 15 divides the internal space of container 11 into a first electrode chamber 16 that houses the first electrode 20 and a second electrode chamber 17 that houses the second electrode 30. Separator 15 has electrical insulation and ion conductivity, electrically insulates the first electrode 20 and the second electrode 30, and allows lithium ions transmitted through the electrolyte 12 to permeate. Separator 15 is composed of, for example, a resin film or non-woven fabric having a porous structure.

[0015] The first electrode 20 corresponds to the electrode for the power storage device of the present embodiment. In the secondary battery 10 of the present embodiment, the first electrode 20 constitutes the negative electrode. The first electrode 20 includes a metal substrate 21 and an active material layer 22.

[0016] The metal substrate 21 constitutes a current collector. In the present embodiment, the metal substrate 21 is composed of a copper (Cu) metal foil. The metal substrate 21 may be composed of a metal other than Cu. The metal substrate 21 may be composed of, for example, any one of a Cu alloy, aluminum (Al), and an Al alloy. Further, the metal substrate 21 does not have to be composed of a metal foil, and may be composed of, for example, a thin metal plate. The metal substrate 21 does not have to be configured in a flat plate shape, and may be bent into various shapes such as a cylindrical shape or a corrugated shape.

[0017] The active material layer 22 is provided on both the first surface 21a and the second surface 21b of the metal substrate 21. The active material layer 22 contains carbon (C) as an active material. Details of the configuration and manufacturing method of the metal substrate 21 and the active material layer 22 of the first electrode 20 will be described later. In the following description, the first electrode 20 is also simply referred to as "electrode 20".

[0018] The second electrode 30 constitutes the positive electrode of the secondary battery 10. The second electrode 30 includes a positive electrode current collector 31 and a positive electrode active material layer 32. The positive electrode current collector 31 is made of, for example, a metal foil such as Al or titanium (Ti). The positive electrode current collector 31 may be made of other metals or may have a form other than a metal foil. The positive electrode current collector 31 does not have to be configured in a flat shape and may be bent into various shapes such as a cylindrical shape or a wavy shape.

[0019] The positive electrode active material layer 32 is formed on each of the first surface 31a and the second surface 31b of the positive electrode current collector 31. The positive electrode active material layer 32 contains a positive electrode active material containing lithium atoms, a conductive auxiliary agent, and a binder. The positive electrode active material layer 32 may contain a thickening agent. As the positive electrode active material, for example, a ternary material can be used, and lithium cobalt oxide (LiCoO2), lithium manganate (LMO), or lithium nickelate (NCA) can be used. As the conductive auxiliary agent, for example, acetylene black or carbon black can be used. As the binder, for example, polyvinylidene fluoride (PVDF) or styrene-butadiene rubber (SBR) can be used. As the thickening agent, for example, carboxymethyl cellulose (CMC) can be used.

[0020] With reference to FIGS. 2, 3, and 4, the detailed configuration of the electrode 20 of the present embodiment will be described.

[0021] FIG. 2 is a schematic cross-sectional view schematically illustrating the cross-sectional structure of the electrode 20 in an arbitrary cut surface along the thickness direction. In FIG. 2, the configuration of the electrode 20 on the first surface 21a side of the metal substrate 21 is extracted and illustrated. The configuration of the electrode 20 on the second surface 21b side of the metal substrate 21 is the same as the configuration on the first surface 21a side shown in FIG. 2. In FIG. 2, the metal particles 26 to be described later are schematically illustrated as substantially spherical.

[0022] FIG. 3 is a schematic plan view schematically illustrating the state of the surface of the active material layer 22 in an arbitrary region of the electrode 20. In FIG. 3, the outer peripheral contour line of the granular body 23 when facing the surface of the active material layer 22 is shown by a broken line.

[0023] FIG. 4 is a schematic diagram schematically showing the configuration of the carbon nanostructure 25 included in the active material layer 22. In FIG. 4, for convenience, the surface of the metal substrate 21 is illustrated as a plane. Further, in FIG. 4, for convenience, the graphene GS constituting the carbon nanostructure 25 is illustrated in a substantially rectangular sheet shape.

[0024] As shown in FIG. 2, the surface of the active material layer 22 of the electrode 20 has a fine concavo-convex structure CS in which a plurality of minute granular bodies 23 are densely arranged. Here, the “granular body” means a part that can be recognized as having a particle shape when viewed from a certain direction, and is a concept including a convex part that bulges in a substantially spherical shape. Further, in the present specification, the “particle” is a concept meaning a minute lump having various shapes, and does not necessarily have a substantially spherical shape, and includes a shape having a random concavo-convex structure on the surface. As shown in FIG. 3, each granular body 23 of the active material layer 22 has a particle-shaped outer peripheral shape when viewed in the thickness direction of the active material layer 22.

[0025] The average particle diameter of the granular body 23 is preferably 0.1 μm or more and 10.0 μm or less, more preferably 0.5 μm or more and 5.0 μm or less, and still more preferably 1.0 μm or more and 3.0 μm or less. By this average particle diameter of the granular body 23, when the secondary battery 10 is charged, the precipitation of lithium described later is smoothed, and the generation of lithium dendrites can be suppressed.

[0026] Note that the average particle diameter of the granular body 23 is obtained, for example, by measuring the maximum value of the width in a certain measurement direction of each granular body 23 in a plurality of images taken facing an arbitrary region of the active material layer 22 of the electrode 20 using a scanning electron microscope or the like, and averaging the measured values. When the average particle diameter of the granular body 23 varies greatly depending on the measurement direction, it is preferable to calculate by averaging the average particle diameters obtained for a plurality of predetermined measurement directions.

[0027] The height of the granules 23 is preferably 0.5 μm or more and 8.0 μm or less, and more preferably 0.8 μm or more and 6.0 μm or less. The height of the granules 23 can be measured, for example, using a scanning electron microscope or the like, from multiple images taken from a direction perpendicular to the thickness direction of an arbitrary region of the active material layer 22 of the electrode 20. The height of the granules 23 can be measured as the distance from the bottom end to the top end of each granule 23 in the thickness direction of the active material layer 22.

[0028] As shown in FIG. 2, carbon nanostructures 25 made of carbon atoms are disposed all over the surface layer of each granule 23. The carbon nanostructures 25 are electrically conductive. As shown in FIG. 4, the carbon nanostructures 25 have a shape in which graphene GS extends in an elongated shape outward from the granules 23. The carbon nanostructures 25 have a multilayer structure in which multiple graphene GS are stacked in the thickness direction. Graphene GS, also known as a graphene sheet, is a sheet-like substance having a thickness equivalent to one carbon atom and composed of a six-membered carbon ring structure, i.e., a hexagonal lattice structure with carbon atoms as vertices.

[0029] The carbon nanostructures 25 are formed in a needle, plate, or pleat shape. The carbon nanostructures 25 can also be considered to be the same type of structure as carbon nanowalls and similar carbon nanoflakes and carbon nanoflowers. Because the carbon nanostructures 25 are graphite-like substances, they have higher electrical conductivity than carbon materials such as activated carbon.

[0030] The carbon nanostructure 25 does not have to be entirely composed of single crystals of six-membered carbon rings. The graphene GS constituting the carbon nanostructure 25 may not have a complete graphene structure, but may be a thin film mainly composed of carbon with a six-membered ring structure. The graphene GS may have a mosaic structure mainly composed of carbon with a six-membered ring structure. The mosaic structure means a structure in which multiple regions composed of six-membered carbon ring structures are discretely arranged.

[0031] Here, the height H of the carbon nanostructure 25 corresponds to the length from the lower end on the substrate 21 side to the apex of the carbon nanostructure 25. In the present embodiment, the height H of the carbon nanostructure 25 corresponds to the height from the surface of the amorphous carbon layer 29 to the apex of the carbon nanostructure 25.

[0032] The average height H of the carbon nanostructure 25 is preferably 100 nm or more. As will be described later, in the secondary battery 10 using the electrode 20 of the present embodiment, during charging, lithium ions are not occluded in the active material layer 22, but lithium is deposited on the surface of the carbon nanostructure 25. When the average height H of the carbon nanostructure 25 is 100 nm or more, during charging of the secondary battery 10, lithium is likely to be dispersed and deposited over the entire surface of the active material layer 22 starting from the carbon nanostructure 25. As a result, the local growth of lithium dendrites is suppressed, and the separator 15 is prevented from being damaged by the dendrite-grown lithium.

[0033] The average height H of the carbon nanostructure 25 may be 200 nm or more. However, if an attempt is made to form a higher carbon nanostructure 25, the time required to form the carbon nanostructure 25 will be longer accordingly. Therefore, from the viewpoint of enhancing the productivity of the electrode 20, the average height H of the carbon nanostructure 25 is preferably 100×10 3 nm or less. Also, the average height H of the carbon nanostructure 25 is more preferably 20×10 3 nm or less, and even more preferably 5×10 3 nm or less.

[0034] The average thickness W of the carbon nanostructure 25 is preferably, for example, 0.5 nm or more and 100.0 nm or less. The average thickness W is more preferably 1.0 nm or more and 50.0 nm or less, and even more preferably 1.5 nm or more and 30.0 nm or less.

[0035] The average distance D between adjacent carbon nanostructures 25 in the active material layer 22 is preferably 10 nm or more and 500 nm or less. If the average distance D is large, the density of the carbon nanostructures 25 in the active material layer 22 decreases, and the battery performance of the secondary battery 10 may deteriorate. If the average distance D is small, the density of the carbon nanostructures 25 in the active material layer 22 increases. However, increasing the density of the carbon nanostructures 25 may take time and effort to form the carbon nanostructures 25, and the productivity of the electrode 20 may decrease. The average distance D is a value calculated as the average value of the measured lengths of line segments defined by adjacent carbon nanostructures 25 in a certain direction at a plurality of predetermined locations on a captured image obtained by projecting the carbon nanostructures 25 in the height direction.

[0036] As shown in FIG. 2, a plurality of protrusions 28 each composed of a plurality of minute metal particles 26 are formed on the surface of the metal substrate 21. In the example of FIG. 2, the protrusion 28 is composed of a particle aggregate 27 formed by densely gathering metal particles 26. The particle structure 27 is formed as a mass in which a plurality of metal particles 26 gather in a bundle shape. In addition to the particle structure 27 constituting the protrusion 28, single metal particles 26 constituting the protrusion 28 may be present on the surface of the metal substrate 21.

[0037] Each of the above-described granular bodies 23 is configured by arranging carbon nanostructures 25 extending from the surface of the metal particles 26 over the entire surface of the protrusion 28 constituted by the metal particles 26. The active material layer 22 can also be interpreted as having a configuration in which a plurality of granular bodies 23 gather in a bundle shape with the metal particles 26 of the metal substrate 21 as nuclei.

[0038] The average particle diameter of the metal particles 26 constituting the particle structure 27 and the metal particles 26 that individually constitute the protrusion 28 is preferably 0.1 μm or more and 5.0 μm or less, and more preferably 0.5 μm or more and 3.0 μm or less. The average particle diameter of the metal particles 26 can be calculated by the same method as the average particle diameter of the above-described granular bodies 23.

[0039] The metal particles 26 preferably have a shape in which the height is larger than the particle diameter, whether they constitute the particle structure 27 or exist alone. The average height of the metal particles 26 is preferably 0.5 μm or more and 3.0 μm or less. The average height of the metal particles 26 may be 0.6 μm or more and 2.5 μm or less. The height of the metal particles 26 corresponds to the distance between the lowermost end and the uppermost end of each metal particle 26 when the thickness direction of the metal substrate 21 is taken as the height direction in a captured image obtained by photographing the protrusion 28 from a direction orthogonal to the thickness direction of the metal substrate 21 with a scanning electron microscope.

[0040] The average value of the maximum width of the particle structure 27 is preferably 1.0 μm or more and 50.0 μm or less, and may be 1.5 μm or more and 30.0 μm or less. The maximum width of the particle structure 27 is the maximum value among the widths in all directions measured in a captured image obtained by photographing the surface of the metal substrate 21 facing the lens by a scanning electron microscope or the like.

[0041] The lower limit value of the height of the particle structure 27 is preferably 0.5 μm or more, more preferably 0.8 μm or more. Further, the lower limit value of the height of the particle structure 27 is more preferably 1.0 μm or more, and even more preferably 1.2 μm or more. The upper limit value of the height of the particle structure 27 may be 10.0 μm or less, may be 8.0 μm or less. The upper limit value of the height of the particle structure 27 may be 5.0 μm or less. Incidentally, the height of the particle structure 27 corresponds to the distance from the lowermost end portion to the apex of the particle structure 27 in the thickness direction of the metal substrate 21.

[0042] As described above, the protrusions 28 include those composed of single metal particles 26 and those composed of the particle structure 27. The maximum width of each protrusion 28 is preferably 0.1 μm or more and 50.0 μm, and more preferably 0.5 μm or more and 30.0 μm or less. The maximum width of each protrusion 28 is the maximum value among the widths in all directions measured in a captured image taken facing the surface of the metal substrate 21 with a scanning electron microscope or the like.

[0043] The height of each protrusion 28 is preferably 0.5 μm or more and 10.0 μm, and more preferably 0.6 μm or more and 8.0 μm or less. The height of the protrusion 28 corresponds to the distance between the lowermost end and the uppermost end of each protrusion 28 when the height direction is the thickness direction of the metal substrate 21 in a captured image obtained by photographing the protrusion 28 from a direction perpendicular to the thickness direction of the metal substrate 21 with a scanning electron microscope.

[0044] The area of the projection region obtained by projecting each protrusion 28 in the thickness direction of the metal substrate 21 is larger than 0.01 μm 2 and less than or equal to 10000 μm 2 . Further, the density of the projection region of the protrusion 28 when the metal substrate 21 is projected in the thickness direction is 1 piece / mm 2 or more and less than 10 8 pieces / mm 2 . The protrusions 28 with such dimensions can be easily formed by surface treatment by electrolytic deposition on the metal foil. Further, according to the research of the inventors of the present invention, with the metal substrate 21 having the protrusions 28 with such dimensions on its surface, the active material layer 22 having the above-described granular bodies 23 can be easily formed by the CVD method.

[0045] As shown in FIG. 2, in this embodiment, the surface of the metal substrate 21 is covered with an amorphous carbon layer 29. As shown in FIG. 4, the carbon nanostructure 25 extends vertically upward from the amorphous carbon layer 29. The amorphous carbon layer 29 is the starting point for the growth of the carbon nanostructure 25. When the amorphous carbon layer 29 is formed well, the formation state of the carbon nanostructure 25 is improved. The film thickness of the amorphous carbon layer 29 is preferably, for example, 10 nm or more and 300 nm or less. More preferably, the film thickness of the amorphous carbon layer 29 is 10 nm or more and 100 nm or less, and even more preferably 12 nm or more and 30 nm or less.

[0046] 1-2. Battery reaction in a secondary battery: The chemical reaction during charge and discharge in the secondary battery 10 can be represented, for example, by the following reaction formula. When the positive electrode material is LiCoO2, the reaction formula at the second electrode 30 which is the positive electrode is represented by the following formula (1). x represents the ratio of reacting atoms and is a real number greater than 0 and less than 1. Li 1-x CoO2 + xLi + + xe- ⇔ LiCoO2…(1)

[0047] On the other hand, the reaction formula at the electrode 20 which is the negative electrode is represented by the following formula (2). As shown in formula (2), during charging of the secondary battery 10, lithium is deposited on the electrode 20. Li + + e - ⇔ Li …(2)

[0048] Here, in the case of the configuration of a conventional negative electrode in which graphite is disposed as an active material on the surface of a flat metal substrate, during charging, in principle, one lithium ion is occluded per six carbon atoms, and lithium carbide (LiC6) is formed. Therefore, the reaction formula in that conventional configuration as a comparative example is represented as the following formula (3). Reaction formula in the conventional configuration: xLi + + C6 + xe - ⇔ Li xC6…(3)

[0049] As shown in the above formula (3), in the case of an electrode having a conventional configuration using graphite as a negative electrode active material, the number of lithium ions that can be occluded by charging is determined by the number of carbon atoms contained in the active material layer.

[0050] On the other hand, in the case of the electrode 20 used in the secondary battery 10 of the present embodiment, as shown by the above formula (2), theoretically, as long as lithium can be deposited without being limited by the number of carbon atoms in the active material layer 22, charging is possible. That is, according to the electrode 20 of the present embodiment, in one charge or discharge, two or more lithium ions per carbon atom can be involved in the charge-discharge reaction. Therefore, the secondary battery 10 of the present embodiment has an increased charge capacity by including the electrode 20 as a negative electrode.

[0051] According to the electrode 20 of the present embodiment, the precipitation of lithium due to the charge reaction is promoted, and it becomes easy to uniformly form a lithium layer on the surface layer of the active material layer 22, enabling a stable and smooth charge-discharge reaction. In addition, the local generation of lithium dendrites and the deterioration of the secondary battery 10 are suppressed. Based on the consideration according to the nucleation theory, it is presumed that the reason for obtaining such an effect is that lithium is likely to precipitate starting from the convex portions formed by the granular bodies 23 in the electrode 20 of the present embodiment.

[0052] Further, according to the electrode 20 of the present embodiment, since the fine concavo-convex structure CS is formed on the surface of the active material layer 22, for example, even if it is rolled into a roll shape for transportation of the electrode 20, at least the destruction and detachment of the carbon nanostructure 25 located at a position lower than the apex of the concavo-convex structure CS can be suppressed. Therefore, the handling of the electrode 20 in the manufacturing process of the secondary battery 10 becomes easy, and the mass production of the electrode 20 becomes easy. In addition, the manufacturing of the secondary battery 10 using the electrode 20 is facilitated.

[0053] 1-3. Method for manufacturing a secondary battery: FIG. 5 is a process flow diagram showing the manufacturing process of the secondary battery 10. Processes P1 and P2 are the manufacturing processes of the electrode 20. Process P1 corresponds to the process of preparing the metal substrate 21. In the present embodiment, in Process P1, a metal substrate 21 having protrusions 28 formed of minute metal particles 26 on the surface is produced by performing surface treatment by electrolytic deposition on a base material BM having a flat surface. The base material BM is, for example, a metal foil or a metal thin plate. In the present embodiment, the base material BM is a copper foil.

[0054] FIG. 6 is a schematic diagram showing the configuration of the surface treatment apparatus 50 used in Process P1. The surface treatment apparatus 50 includes, as a conveyance unit for the base material BM, a delivery roller 51 around which the base material BM before treatment is wound, a plurality of guide rollers 52 for guiding the conveyance of the base material BM, and a winding roller 53 for winding up the base material BM after surface treatment. Further, the surface treatment apparatus 50 further includes, as an electrolytic deposition execution unit, an electrolytic bath 55 filled with an electrolytic solution 56 and an electrode plate 58 installed in the electrolytic bath 55. Although not shown, the surface treatment apparatus 50 includes a power supply unit for applying electricity to the electrode plate 58 and the base material BM.

[0055] The base material BM is fed out from the delivery roller 51, guided by a plurality of guide rollers 52, and conveyed to the winding roller 53. One of the guide rollers 52 is installed in the electrolytic bath 55. Thereby, the base material BM is conveyed into the electrolytic bath 55, immersed in the electrolytic solution 56 in the electrolytic bath 55, then turned back in the electrolytic bath 55, and conveyed out of the electrolytic bath 55. While the base material BM passes through the electrolytic solution 56 in the electrolytic bath 55, the surface treatment by electrolytic deposition described below is performed on the surface of the base material BM.

[0056] The electrode plate 58 in the electrolytic bath 55 contains metal atoms of the same kind as the metal constituting the base material BM. In the present embodiment, the electrode plate 58 is made of rough copper. The electrode plate 58 is installed so as to face the surface of the base material BM being conveyed in the electrolytic bath 55. The electrode plate 58 is preferably installed substantially parallel to the surface of the base material BM.

[0057] During the conveyance of the base material BM, a voltage is applied by the power supply unit with the electrode plate 58 as the anode and the base material BM as the cathode. As a result, Cu of the electrode plate 58 is oxidized and eluted into the electrolytic solution 56 as Cu ions, moves toward the base material BM, and is reduced and deposited on the surface of the base material BM. On the surface of the base material BM, fine metal particles 26 are successively formed by the deposited Cu. Protrusions 28 are formed by such metal particles 26. When the metal particles 26 locally gather densely, a particle structure 27 is formed as the protrusion 28. The protrusions 28 are formed in a state of being arranged over the entire surface of the base material BM.

[0058] The surface treatment in the process P1 is performed on both surfaces of the base material BM. Thereby, a metal base material BM having a fine uneven structure CS on both surfaces is completed. The treatment conditions such as the type and concentration of the electrolytic solution 56, the energization voltage, and the conveyance speed of the base material BM in the surface treatment apparatus 50 in the process P1 are appropriately adjusted so that metal particles 26 and protrusions 28 of the above-described size are formed.

[0059] Note that the surface treatment apparatus 50 may be configured such that a plurality of guide rollers 52 are arranged in one electrolytic bath 55, and the immersion of the base material BM into the electrolytic solution 56 in one electrolytic bath 55 is repeated a plurality of times. Alternatively, the surface treatment apparatus 50 may include a plurality of electrolytic baths 55, guide rollers 52 may be arranged in each electrolytic bath 55, and the base material BM may be configured to be conveyed so as to repeat immersion into the electrolytic solution 56 in each electrolytic bath 55.

[0060] In the process P2, an active material layer 22 is formed on the surface of the metal substrate 21 by the CVD (chemical vapor deposition) method. In the process P2, by plasma treatment, a carbon nanostructure 25 is generated on the surface of the metal substrate 21, and an active material layer 22 having a fine uneven structure CS in which a plurality of minute granular bodies 23 having the carbon nanostructure 25 arranged densely over the entire surface layer are formed is formed.

[0061] FIG. 7 is a schematic diagram showing the configuration of a manufacturing apparatus 60 suitable for performing the plasma treatment in step P2. The manufacturing apparatus 60 is a capacitively coupled plasma (CCP) CVD apparatus.

[0062] The manufacturing apparatus 60 includes a reaction chamber 61, an exhaust unit 62, a source gas supply unit 65, a substrate support unit 70, an upper electrode 75, and a power supply device 76. The manufacturing apparatus 60 further includes a vacuum gauge 81 and a thermocouple 82 as measurement units.

[0063] The reaction chamber 61 has an airtight structure that can be maintained in a vacuum. The exhaust unit 62 and the source gas supply unit 65 are connected to the reaction chamber 61.

[0064] The exhaust unit 62 includes an exhaust pipe 63 introduced into the reaction chamber 61 and a vacuum pump 64 connected to the exhaust pipe 63. The vacuum pump 64 sucks surplus gas not consumed in the reaction in the reaction chamber 61 through the exhaust pipe 63 during the plasma treatment, and maintains the inside of the reaction chamber 61 at a degree of vacuum within the range of 5 to 2000 mTorr (0.65 to 267 Pa). The degree of vacuum in the reaction chamber 61 is measured by the vacuum gauge 81.

[0065] The source gas supply unit 65 supplies a source gas consumed in the plasma treatment to the reaction chamber 61. The source gas supply unit 65 includes a source gas storage unit 66, a flow rate control unit 67, and a source introduction pipe 68.

[0066] The raw material gas storage unit 66 stores multiple types of gases for each type as the raw material gases used for plasma processing. In the manufacturing apparatus 60, as the raw material gases, a carbon-based gas containing carbon that constitutes the carbon nanostructure 25 and a reaction contributing gas that contributes to the growth of the carbon nanostructure 25 are used. The carbon-based gas is, for example, methane (CH4) or hexafluoroethane (C2F6). The reaction contributing gas promotes the plasma formation of the carbon-based gas by the Penning effect in plasma processing. Further, the reaction contributing gas forms nuclei that serve as the growth starting points of the carbon nanostructure 25 by ionizing and colliding with the metal substrate 21 that is the object to be processed in plasma processing. The reaction contributing gas is, for example, hydrogen (H2) or argon (Ar). In the raw material gas storage unit 66, those multiple types of gases are stored individually in tanks (not shown).

[0067] The flow rate control unit 67 includes a gas delivery device 67a and a flow rate adjustment valve 67b. The gas delivery device 67a and the flow rate adjustment valve 67b are respectively provided in the pipes for each of the multiple types of gases connected to the raw material gas storage unit 66. The gas delivery device 67a is constituted by, for example, an ejector or a pump, and sends out the gas from the raw material gas storage unit 66 at a predetermined pressure. The flow rate of the gas sent out by the gas delivery device 67a is controlled by the flow rate adjustment valve 67b. The various gases whose flow rates are adjusted by the flow rate adjustment valve 67b merge in the raw material introduction pipe 68. The raw material introduction pipe 68 introduces the raw material gas in which those multiple types of gases are mixed at a predetermined ratio into the reaction chamber 61.

[0068] A substrate support unit 70 is provided in the reaction chamber 61. The substrate support unit 70 supports the metal substrate 21 prepared in step P1. The substrate support unit 70 includes a susceptor 71, a quartz cover 72, and a heater 73. The susceptor 71 constitutes the support base of the metal substrate 21. The metal substrate 21 that is the object to be processed is disposed on the susceptor 71. The susceptor 71 is grounded. As will be described later, since a high-frequency voltage is used during plasma processing, the susceptor 71 may be floating.

[0069] The susceptor 71 is disposed on the quartz cover 72, and a heater 73 is provided under the quartz cover 72. The quartz cover 72 protects the heater 73. Also, the quartz cover 72 supports the susceptor 71 and prevents the heater 73 from directly contacting the susceptor 71.

[0070] During plasma processing, the metal substrate 21 is heated by receiving the radiant heat of the heater 73 through the susceptor 71. The thermocouple 82 measures the heating temperature of the heater 73. During plasma processing, the heating of the metal substrate 21 by the heater 73 is controlled based on the temperature measured by the thermocouple 82. In this embodiment, the heater 73 is controlled at a predetermined heating temperature within the range of room temperature (RT) or higher and 700 ° C or lower. The control with the heating temperature set to RT means the control to stop the driving of the heater 73.

[0071] An upper electrode 75 is installed at the upper part of the reaction chamber 61. The upper electrode 75 is installed on the susceptor 71 so as to face the metal substrate 21 to be processed. The upper electrode 75 is preferably installed so as to be substantially parallel to the metal substrate 21. The distance between the upper electrode 75 and the susceptor 71 is, for example, about 1 to 5 cm. The upper electrode 75 is connected to a power supply device 76 provided outside the reaction chamber 61.

[0072] The power supply device 76 is a high-frequency power supply device. When the raw material gas is supplied to the reaction chamber 61 by the raw material gas storage unit 66, the power supply device 76 applies a high-frequency voltage to the upper electrode 75 to generate a high-density capacitively coupled plasma in the reaction chamber 61. Due to the generation of this high-density plasma, radicals are generated in the reaction chamber 61. In plasma processing, using these radicals, the carbon nanostructure 25 is formed on the entire surface of the metal substrate 21. When the plasma processing is started, first, an amorphous carbon layer 29 is formed so as to cover the entire surface of the metal substrate 21, and then, starting from the metal particles 26 covered by the amorphous carbon layer 29, the carbon nanostructure 25 grows.

[0073] Here, generally, when forming carbon nanotubes on the flat surface of a metal substrate by the CVD method, the heating temperature of the metal substrate is controlled to a high temperature of 700°C or higher. When protrusions such as metal particles 26 are formed on the surface of the metal substrate 21 as in the present embodiment, since the metal particles 26 serve as the growth starting points of the carbon nanostructure 25, the growth of the carbon nanostructure 25 is promoted compared to that on a flat surface. Therefore, even if the heating temperature of the metal substrate 21 is controlled to a relatively low temperature of RT or higher and 700°C or lower by the heater 73 as described above, it is possible to smoothly form the carbon nanostructure 25. Note that the upper limit of the heating temperature of the metal substrate 21 by the heater 73 may be less than 700°C, may be 600°C or lower, or may be 500°C or lower. The heating temperature of the metal substrate 21 by the heater 73 may be controlled to 400°C or lower, or may be controlled to RT.

[0074] In step P2, the metal substrate 21 to be processed is disposed in the reaction chamber 61, and an active material layer 22 having a carbon nanostructure 25 is formed on the surface of the metal substrate 21 by plasma processing in the manufacturing apparatus 60. Although not shown, the metal substrate 21 to be processed in the manufacturing apparatus 60 is installed in a state of being wound around a roll outside the reaction chamber 61. During the execution of the plasma processing, the metal substrate 21 is fed out from the roll into the reaction chamber 61 and conveyed out of the reaction chamber 61 while being supported by the susceptor 71. In the manufacturing apparatus 60, the active material layer 22 is formed on the surface of the metal substrate 21 passing through the reaction chamber 61 by plasma processing.

[0075] In step P3, the second electrode 30 serving as the positive electrode is manufactured. In step P4, as shown in FIG. 1, the first electrode 20 and the second electrode 30 are assembled in the container 11 filled with the electrolytic solution 。By the above steps, the secondary battery 10 is completed.

[0076] As described above, according to the manufacturing process of the present embodiment, in step P1, the metal substrate 21 can be efficiently manufactured by surface treatment by electrolytic deposition. Further, in step P2, due to the presence of the protrusions 28 on the surface of the metal substrate 21, the active material layer 22 having a plurality of granular bodies 23 formed on the surface can be efficiently generated under relatively low temperature conditions. As described above, even when the electrode 20 prepared in steps P1 and P2 is rolled up and conveyed, the destruction and detachment of the carbon nanostructure 25 of the active material layer 22 are suppressed, so that it is easy to handle. Therefore, the mass productivity of the electrode 20 is increased, and the manufacture of the secondary battery 10 using the electrode 20 is facilitated.

Example

[0077] With reference to FIGS. 8, 9, 10, and 11, Examples E1, E2, E3, E4 and Comparative Examples C1, C2 of the electrode 20 of the present embodiment will be described.

[0078] Photographed images of the surface of the metal substrate 21 constituting the current collector of Example E1 are shown in FIGS. 8(a) and 8(b), respectively. Also, photographed images of the surface of the metal substrate 21 constituting the current collector of Example E2 are shown in FIGS. 9(a) and 9(b), respectively. FIGS. 8(a) and 9(a) are images of the protrusions 28 taken by a scanning electron microscope when viewed from a direction orthogonal to the thickness direction of the metal substrate 21. FIGS. 8(b) and 9(b) are images of the surface of the metal substrate 21 taken by a scanning electron microscope in the thickness direction of the metal substrate 21. The images of FIGS. 8(b) and 9(b) correspond to images of the projection regions obtained by projecting the protrusions 28 in the thickness direction of the metal substrate 21.

[0079] The metal substrates 21 of Examples E1 and E2 were fabricated by using a copper foil as a base material and subjecting it to the surface treatment by electrolytic deposition described above. As shown in FIGS. 8(a) and 9(a), the protrusions 28 include a particle structure 27 having a structure in which metal particles 26 are densely aggregated, and those composed of single metal particles 26. In Example E1, as shown in FIG. 8(b), the particle structure 27 was formed so as to be distributed over the entire surface of the metal substrate 21. On the other hand, in Example E2, as shown in FIG. 8(b), the metal particles 26 that individually constitute the protrusions 28 were dispersed and arranged over the entire surface of the metal substrate 21, and between the individual metal particles 26, there was a particle structure 27 that constitutes the protrusions 28.

[0080] As shown in FIG. 8(b), in Example E1, the particle diameter of the metal particles 26 that constitute the particle structure 27 was generally in the range of 0.5 to 5.0 μm. Also, as shown in FIG. 9(b), in Example E2, the particle diameters of the metal particles 26 that individually constitute the protrusions 28 and the metal particles 26 that constitute the particle structure 27 were generally in the range of 0.1 to 5.0 μm.

[0081] As shown in FIG. 8(b), in Example E1, the maximum width of the particle structure 27 was generally in the range of 5.0 to 50.0 μm. Also, as shown in FIG. 9(b), in Example E2, the maximum width of the particle structure 27 was generally in the range of 1.0 to 10.0 μm.

[0082] Thus, the maximum width of the protrusions 28 in the metal substrates 21 of Examples E1 and E2 was generally in the range of 0.1 to 50.0 μm.

[0083] As shown in FIG. 8(a), in Example E1, the height of the metal particles 26 that constitute the particle structure 27 was generally in the range of 0.5 to 2.5 μm. As shown in FIG. 9(a), in Example E2, the heights of the metal particles 26 that individually constitute the protrusions 28 and the metal particles 26 that constitute the particle structure 27 were generally in the range of 0.5 to 3.0 μm.

[0084] As shown in FIG. 8(a), in Example E1, the height of the particle structure 27 was generally in the range of 3.0 to 10.0 μm or less. Also, as shown in FIG. 9(a), in Example E2, the height of the metal particle 26 that constitutes the protrusion 28 alone was generally in the range of 0.5 to 5.0 μm. Further, in Example E2, the height of the particle structure 27 was generally in the range of 1.0 to 8.0 μm.

[0085] Thus, the height of the protrusion 28 on the metal substrate 21 in Examples E1 and E2 was generally in the range of 0.5 to 10.0 μm.

[0086] In both Examples E1 and E2, the area of the projection region where the protrusion 28 was projected in the thickness direction of the metal substrate 21 was larger than 0.01 μm 2 and less than or equal to 10000 μm 2 . Also, the density of the projection region of the protrusion 28 when the metal substrate 21 was projected in the thickness direction was 1 piece / mm 2 or more and less than 10 8 pieces / mm 2 . Note that the projection region of the protrusion 28 corresponds to the area of the region surrounded by the dark outer peripheral contour line shown in the captured image of FIG. 8(b).

[0087] FIGS. 8(c) and (d) respectively show captured images of the active material layer 22 in Example E1. Also, FIGS. 9(c) and (d) respectively show captured images of the active material layer 22 in Example E2. FIGS. 10(a) and (b) respectively show captured images of the active material layer 22 in Example E3. FIGS. 11(c) and (d) respectively show captured images of the active material layer 22 in Example E4. FIGS. 8(c), 9(c), 10(a), and 10(c) are images of the granular bodies 23 of the active material layer 22 taken by a scanning electron microscope looking from a direction orthogonal to the thickness direction of the electrode 20. FIGS. 8(d), 9(d), 10(b), and 10(d) are images of the granular bodies 23 on the surface of the active material layer 22 taken by a scanning electron microscope in the thickness direction of the electrode 20.

[0088] Examples E1, E3, and E4 were fabricated by forming the active material layer 22 on the surface of the metal substrate 21 shown in FIGS. 8(a) and 8(b) by CVD method under the conditions shown in Table 1 below. Example E2 was fabricated by forming the active material layer 22 on the surface of the metal substrate 21 shown in FIGS. 9(a) and 9(b) by CVD method under the conditions shown in Table 1 below. The distance between the upper electrode 75 and the metal substrate 21 was 3 cm. In Examples E1 and E4, the CCP-CVD method was adopted. In Examples E2 and E3, different from Examples E1 and E4, hydrogen was plasma-treated with a microwave power source.

[0089] In the plasma treatment, the heating temperature of the metal substrate 21 by the heater 73 was controlled to 700 °C for Examples E1 and E2, RT for Example E3, and 400 °C for Example E4 as shown in Table 1. Note that the "heating temperature of the metal substrate" in Table 1 means the measured value of the temperature near the heater 73 by the thermocouple 82, which is different from the temperature of the metal substrate 21. The temperature of the metal substrate 21 is usually higher than RT even when it is not heated by the heater 73 due to the influence of plasma irradiation.

[0090]

Table 1

[0091] As shown in FIGS. 8, 9, and 10, on the surface of the active material layer 22 of Examples E1, E2, E3, and E4, a fine uneven structure CS was formed by densely arranging a plurality of minute granular bodies 23. Each granular body 23 was formed in a state of being three-dimensionally dispersed in the thickness direction and the direction along the surface of the electrode 20.

[0092] In the images shown in FIGS. 8, 9, and 10, the carbon nanostructure 25 appears as white streaks. In any of Examples E1, E2, E3, and E4, the carbon nanostructure 25 was formed over the entire surface layer of the granular body 23.

[0093] As shown in Fig. 8(d), in Example E1, the particle size of each granule 23 was generally in the range of 0.5 μm or more and 5.0 μm or less. As shown in Fig. 9(d), in Example E2, the particle size of each granule 23 was generally in the range of 0.5 μm or more and 5.0 μm or less. As shown in Fig. 10(b), in Example E3, the particle size of each granule 23 was generally in the range of 0.5 μm or more and 5.0 μm or less. As shown in Fig. 10(d), in Example E4, the particle size of each granule 23 was generally in the range of 0.1 μm or more and 2.0 μm or less. The particle size of each granule 23 here is the maximum value of the width of each granule 23 in the width direction of the image.

[0094] As shown in Fig. 8(c), in Example E1, the height of each granule 23 was generally in the range of 0.5 μm or more and 3.0 μm or less. As shown in Fig. 9(c), in Example E2, the height of each granule 23 was generally in the range of 1.5 μm or more and 6.0 μm or less. As shown in Fig. 10(a), in Example E3, the height of each granule 23 was generally in the range of 1.0 μm or more and 4.0 μm or less. As shown in Fig. 10(c), in Example E4, the height of each granule 23 was generally in the range of 0.5 μm or more and 2.0 μm or less.

[0095] The height H of the carbon nanostructure 25 was approximately about 80 to 200 nm in all of Examples E1, E2, E3, and E4. The thickness W of the carbon nanostructure 25 was generally in the range of 1 to 10 nm in any of Examples E1, E2, E3, and E4. Also, the interval D between the carbon nanostructures 25 was generally in the range of 10 nm or more and 500 nm or less in any of Examples E1, E2, E3, and E4.

[0096] Although not visible in the images of Figs. 8, 9, and 10, in Examples E1, E2, E3, and E4, an amorphous carbon layer 29 was formed under the carbon nanostructure 25. The film thickness of the amorphous carbon layer 29 was generally in the range of 10 nm or more and 300 nm or less.

[0097] As shown in Table 1 above, in Examples E3 and E4, the heating temperature of the metal substrate 21 by the heater 73 was controlled to be less than 700°C. Even under this temperature condition, the carbon nanostructure 25 could be formed in the same manner as in Examples E1 and E2. Further, as will be described later, there was no significant difference in the battery performance of the secondary battery between the electrodes of Examples E3 and E4 and those of Examples E1 and E2.

[0098] Photographed images of the active material layer of Comparative Example C1 are shown in FIGS. 11(a) and (b), respectively. FIG. 11(a) is an image obtained by photographing the active material layer of Comparative Example C1 from a direction orthogonal to the thickness direction using a scanning electron microscope. FIG. 11(b) is an image obtained by photographing the surface of the active material layer of Comparative Example C1 from a direction facing the surface using a scanning electron microscope.

[0099] The active material layer of Comparative Example C1 was formed by the CVD method under the conditions shown in Table 1 above using a copper foil having a flat surface that was not subjected to surface treatment by electrolytic deposition as in the examples as the metal substrate. In the CVD method of Comparative Example C1, hydrogen was plasma-treated with a microwave power source in the same manner as in Example E2.

[0100] As shown in FIGS. 11(a) and (b), in Comparative Example C1, the active material layer was composed of carbon nanowalls. As shown in FIG. 11(a), in Comparative Example C1, the carbon nanowalls were formed at a substantially uniform height of about 1.0 μm. As shown in FIG. 11(b), in Comparative Example C1, the carbon nanowalls were formed in a random mesh pattern over the entire surface of the metal substrate.

[0101] A photographed image of the active material layer of the electrode of Comparative Example C2 is shown in FIG. 11(c). FIG. 11(c) is an image obtained by photographing the surface of the active material layer of Comparative Example C2 from a direction facing the surface using a scanning electron microscope. Comparative Example C2 has a configuration in which a graphite layer is formed on the surface of the same flat metal substrate as Comparative Example C1.

[0102] Figures 12 to 17 are explanatory diagrams showing the evaluation test results of the battery performance of secondary batteries using the electrodes of the above Examples E1, E2, E3, E4 and Comparative Examples C1, C2 as the negative electrode. In Figures 12 to 15, graphs obtained from the secondary batteries using Examples E1, E2, E3, E4 are shown. Further, in Figures 16 and 17, graphs obtained from the secondary batteries using Comparative Examples C1, C2 are shown, respectively. In Figures 12 to 17, the relationship between the voltage and the charge capacity of the secondary battery is shown by a solid-line graph for charging and a dashed-dotted line graph for discharging. Figure 18 shows the charge capacity and specific capacity of the secondary batteries using Examples E1, E2 and Comparative Examples C1, C2 as bar graphs, respectively. In this evaluation test, both the charging current and the discharging current were 0.5 mA.

[0103] The secondary batteries using Examples E1, E2, E3, E4 and Comparative Examples C1, C2 are lithium-ion secondary batteries and were fabricated with the configurations shown in Table 2 below.

[0104]

Table 2

[0105] As shown in Figures 12 to 18, according to the secondary battery using Comparative Example C2 having a graphite active material layer, the charge capacity was 4.0 [mAh] and the specific capacity was 2.0 [mAh / cm 2 . Also, according to the secondary battery using Comparative Example C1 having a carbon nanotube wall active material layer of uniform thickness, the charge capacity was 12.6 [mAh] and the specific capacity was 9.4 [mAh / cm 2 . Thus, applying carbon nanotube walls to the active material layer of the negative electrode can significantly improve the battery performance of the secondary battery compared to the case of applying graphite to the active material layer.

[0106] However, according to the secondary battery using Example E2, the charge capacity was 14.3 [mAh] and the specific capacity was 11.0 [mAh / cm 2It was. Also, according to the secondary battery using Example E1, the charge capacity was 15.0 [mAh], and the specific capacity was 11.3 [mAh / cm 2 It was. Also in the secondary batteries using Examples E3 and E4, the charge capacity was 14.0 [mAh] or more, and the specific capacity was 11.0 [mAh / cm 2 or more. Thus, for any of Examples E1, E2, E3, and E4, the battery performance was clearly and significantly improved compared to the secondary battery using Comparative Example C2 having the active material layer of carbon nanotubes. Such a result is considered to be because the surface area of the carbon nanostructure 25 in the active material layer 22 of Examples E1, E2, E3, and E4 is significantly larger than the surface area of the carbon nanotubes in the active material layer of Comparative Example C2.

[0107] As described above, it can be seen that according to the electrode for a power storage device according to the present invention, the battery performance of the power storage device can be significantly improved.

[0108] 2. Other Embodiments: The present invention is not limited to the configurations of the above-described embodiments and examples. For example, it can also be realized in the following forms. In the following, all the configurations described as other embodiments are also positioned as one example of implementing the present invention, similar to the above-described embodiments and examples.

[0109] 2-1. Other Embodiment 1: The secondary battery using the electrode 20 of the above embodiment may have a configuration in which metal ions other than lithium ions are involved in charge and discharge. The secondary battery using the electrode 20 of the above embodiment may have a configuration in which, for example, sodium (Na) ions, potassium (K) ions, magnesium (Mg) ions, etc. are involved in charge and discharge.

[0110] 2-2. Other Embodiment 2: The electrode 20 of the above embodiment may be used in an electricity storage device other than a secondary battery. For example, the electrode 20 of the above embodiment may be used in an electric double layer capacitor. In this case, the electrode 20 may be used as both the positive electrode and the negative electrode of the electric double layer capacitor.

[0111] 2-3. Alternative embodiment 3: In the manufacturing method of the electrode 20 described in the above embodiment, in step P1, the base material BM of the metal substrate 21 may be surface-treated by a method other than electrolytic deposition. The protrusions 28 of the metal substrate 21 may be formed, for example, by surface treatment using a CVD method, oxidation treatment of the metal substrate, blasting treatment, or the like. Furthermore, the protrusions 28 of the metal substrate 21 may be formed by a mechanical process of pressing the surface of the metal substrate 21, for example, by pressing a roll having a plurality of protrusions against the surface.

[0112] 2-4. Alternative embodiment 4: In the manufacturing method of the electrode 20 described in the above embodiment, the plasma treatment may be performed by a CVD method other than the CCP-CVD method in step P2. In step P2, the carbon nanostructures 25 may be produced by, for example, the RI-CVD method, the ICP-CVD method, the LIA-CVD method, or the like.

[0113] 3. Example of morphology: The present invention can be realized in the following forms.

[0114] [First form] An electrode for an electricity storage device, comprising: a metal substrate constituting a current collector; and an active material layer formed on the surface of the metal substrate and containing carbon as an active material, wherein the surface of the active material layer has a fine uneven structure in which a plurality of minute granules are densely arranged, and carbon nanostructures composed of graphene extending in elongated shapes outward from the granules are arranged throughout the surface layer of the granules. According to the electrode for a power storage device of the first embodiment, since the surface area of the carbon nanostructure contained in the active material layer can be increased, the charging capacity of the power storage device can be enhanced. Further, according to the electrode for a power storage device of the first embodiment, even when it is rolled up, at least the destruction and detachment of the carbon nanostructure present in the concave portions of the fine uneven structure of the active material layer can be suppressed. Therefore, the handleability of the electrode for a power storage device can be improved, and its mass productivity can be enhanced.

[0115] [Second Embodiment] In the electrode for a power storage device of the first embodiment described above, a plurality of protrusions composed of minute metal particles are formed on the surface of the metal substrate, and the granular body may be configured such that the carbon nanostructure formed so as to extend from the surface of the metal particles is disposed so as to cover the entire surface of the protrusions. According to the electrode for a power storage device of the second embodiment, since it is easy to generate the carbon nanostructure starting from the metal particles of the metal substrate, the granular body of the active material layer can be formed in a more suitable state.

[0116] [Third Embodiment] In the electrode for a power storage device of the second embodiment described above, the protrusion may include an aggregate of particles formed by a dense gathering of a plurality of the metal particles. According to the electrode for a power storage device of the third embodiment, the granular body of the active material layer can be formed more easily and in a more suitable state by the aggregate of particles of the metal substrate.

[0117] [Fourth Embodiment] In the electrode for a power storage device according to the second or third embodiment described above, the area of the projection region obtained by projecting the protrusion in the thickness direction of the metal substrate is larger than 0.01 μm 2 and equal to or less than 10000 μm 2 , and the density of the projection region of the protrusion when the metal substrate is projected in the thickness direction is equal to or more than 1 piece / mm 2 and less than 10 8 pieces / mm 2 and may be. According to the fourth embodiment of the electricity storage device electrode, the metal substrate has protrusions of a more suitable size, so that the granules of the active material layer can be formed in a more suitable state.

[0118] [Fifth Mode] In the electricity storage device electrode of any one of the first, second, third and fourth modes, the average particle size of the granules may be 0.1 μm or more and 10.0 μm or less. According to the electricity storage device electrode of the fifth aspect, it is possible to suppress the generation of dendrites in the electricity storage device.

[0119] [Sixth Mode] The sixth mode is provided as a secondary battery. The secondary battery of the sixth mode includes a first electrode configured as the electrode for an electricity storage device according to any one of the first, second, third, fourth, and fifth modes, and a second electrode containing metal atoms that ionize and migrate to the first electrode, and during charging, a layer in which the metal atoms are precipitated is formed on the surface of the first electrode. According to the secondary battery of the sixth embodiment, a reaction occurs in which metal atoms are precipitated at the negative electrode during charging, and therefore a high charge capacity can be obtained.

[0120] [Seventh form] A method for manufacturing an electrode for an electricity storage device, comprising: (i) a step of placing a metal substrate having a plurality of protrusions formed on its surface and composed of minute metal particles, into a reaction chamber; and (ii) a step of supplying a raw material gas containing at least a carbon-based gas into the reaction chamber to generate high-density plasma, thereby growing carbon nanostructures composed of graphene extending elongatedly from the surfaces of the protrusions over the entire surfaces of the protrusions, and forming a plurality of minute particulates in which the carbon nanostructures are arranged over the entire surface layer, thereby forming an active material layer on the metal substrate, the surface of which has a fine uneven structure in which the particulates are densely arranged. According to the manufacturing method of the seventh embodiment, an active material layer having a plurality of granules with carbon nanostructures formed over the entire surface layer can be easily formed on the surface of a metal substrate that constitutes a current collector.

[0121] [Embodiment 8] The manufacturing method of the seventh embodiment may further include a step of forming the protrusions by depositing the metal particles on a flat surface of the base material of the metal substrate by electrolytic deposition to prepare the metal substrate. According to the manufacturing method of the eighth embodiment, the protrusions on the surface of the metal substrate can be easily formed by electrolytic deposition on the base material of the metal substrate.

[0122] [Embodiment 9] In the manufacturing method of the eighth embodiment, the protrusions including an aggregate of the metal particles densely gathered may be formed on the flat surface of the base material of the metal substrate by the electrolytic deposition. According to the manufacturing method of the ninth embodiment, the formation of the granular bodies is further facilitated by the aggregate of the particles on the surface of the metal substrate.

[0123] [Embodiment 10] In the manufacturing method according to any one of the seventh, eighth, and ninth embodiments, when forming the carbon nanostructure on the surface of the metal substrate in the reaction chamber, the metal substrate may be controlled at a temperature of room temperature or higher and lower than 700°C. According to the manufacturing method of the tenth embodiment, since the heating temperature for forming the carbon nanostructure can be lowered, the manufacturing efficiency of the electrode for the power storage device can be further improved. [Description of Reference Numerals]

[0124] 10…Secondary battery, 11…Container, 12…Electrolyte, 15…Separator, 16…First electrode chamber, 17…Second electrode chamber, 20…First electrode (electrode for power storage device), 21…Metal substrate, 21a…First surface, 21b…Second surface, 22…Active material layer, 23…Granular body, 25…Carbon nanostructure, 26…Metal particles, 27…Particle structure, 28…Protrusion, 29…Amorphous carbon layer, 30…Second electrode, 31…Positive electrode current collector, 31a…First surface, 31b…Second surface, 32…Positive electrode active material layer, 50…Surface treatment device, 51…Delivery roller, 52…Guide roller, 53…Take-up roller, 55…Electrolytic bath, 56…Electrolyte, 58…Electrode plate, 60…Manufacturing device, 61…Reaction chamber, 62…Exhaust part, 63…Exhaust pipe, 64…Vacuum pump, 65…Raw material gas supply part, 66…Raw material gas storage part, 67…Flow control part, 67a…Gas delivery device, 67b…Flow adjustment valve, 68…Raw material introduction pipe, 70…Substrate support part, 71…Susceptor, 72…Quartz cover, 73…Heater, 75…Upper electrode, 76…Power supply device, 81…Vacuum gauge, 82…Thermocouple, BM…Base material, CS…Convex-concave structure, GS…Graphene

Claims

1. An electrode for a power storage device, comprising: a metal substrate that constitutes a current collector and has a plurality of protrusions formed on its surface; an active material layer formed on the surface of the metal substrate and containing carbon as an active material; and the surface of the active material layer has an uneven structure in which a plurality of granular bodies are arranged, wherein the granular bodies are constituted by carbon nanostructures formed of graphene extending outward from the granular bodies and are arranged over the entire surface of the protrusions, the electrode for a power storage device.

2. The electrode for a power storage device according to Claim 1, wherein the surface of the metal substrate is covered with an amorphous carbon layer, and the carbon nanostructure extends from the amorphous carbon layer, the electrode for a power storage device.

3. An electrode for a power storage device, comprising: a metal substrate that constitutes a current collector; an active material layer formed on the surface of the metal substrate and containing carbon as an active material; and the surface of the active material layer has an uneven structure in which a plurality of granular bodies are arranged, wherein a carbon nanostructure formed of graphene extending outward from the granular bodies is arranged over the entire surface of the granular bodies, a plurality of protrusions constituted by metal particles are formed on the surface of the metal substrate, and the granular bodies are constituted by the carbon nanostructure formed so as to extend from the surface of the metal particles and arranged so as to cover the entire surface of the protrusions, the electrode for a power storage device.

4. The electrode for a power storage device according to Claim 3, wherein the protrusions include an aggregate of particles constituted by a plurality of the metal particles, the electrode for a power storage device.

5. The electrode for a power storage device according to Claim 3, wherein the area of the projection region of each of the protrusions projected in the thickness direction of the metal substrate is 0.01 μm ２ larger than, and 10,000 μm ２ or less, the density of the projection region of the protrusions when the metal substrate is projected in the thickness direction is 1 piece / mm ２ or more, 10 ８ pieces / mm ２ less than, an electrode for a power storage device.

6. The electrode for a power storage device according to Claim 3, wherein the average particle diameter of the granular bodies is 0.1 μm or more and 10.0 μm or less, the electrode for a power storage device.

7. A secondary battery, comprising: a first electrode constituted by the electrode for a power storage device according to any one of Claims 1 to 6; a second electrode containing metal atoms that are ionized and move to the first electrode; and when charging, a layer in which the metal atoms are deposited is formed on the surface layer of the first electrode, the secondary battery.

8. A method for manufacturing an electrode for a storage device, comprising: placing a metal substrate having a plurality of protrusions formed of metal particles disposed on its surface into a reaction chamber; supplying a source gas containing at least a carbon-based gas into the reaction chamber to generate a high-density plasma, growing a carbon nanostructure composed of graphene extending from the surface of the metal particles over the entire surface of the protrusions, and forming a plurality of granular bodies having the carbon nanostructure disposed over the entire surface layer, thereby forming an active material layer having an uneven structure with the granular bodies disposed thereon on the metal substrate; The manufacturing method comprising the above steps.

9. The manufacturing method according to claim 8, further comprising: preparing the metal substrate by forming the protrusions by depositing the metal particles on a flat surface of a base material of the metal substrate by electrolytic deposition.

10. The manufacturing method according to claim 9, wherein: the protrusions including an aggregate of the metal particles gathered and formed on a flat surface of a base material of the metal substrate are formed by the electrolytic deposition.

11. The manufacturing method according to any one of claims 8 to 10, wherein: when forming the carbon nanostructure on the surface of the metal substrate in the reaction chamber, the temperature of the metal substrate is controlled to be equal to or higher than room temperature and lower than 700 °C.

Images