ELECTRODE FOR ELECTRIC STORAGE DEVICE, SECONDARY BATTERY, AND METHOD FOR MANUFACTURING ELECTRIC STORAGE DEVICE ELECTRODE

Abstract

To provide an electrode for a power storage device comprising an active material layer of a novel configuration that is capable of improving the performance of the power storage device.SOLUTION: An electrode for power storage devices comprises: a metal substrate constituting a collector; a plurality of projections formed on a surface of the metal substrate; and a plurality of carbon nanofibers containing graphene as a main component, linearly extending on the surface of the metal substrate when viewed in a thickness direction of the metal substrate and distributed on the surface of the metal substrate. In the electrode for power storage devices, an active material layer is formed by the plurality of projections on the surface of the metal substrate and linear carbon nano structures disposed therebetween, and the battery performance of the power storage device can be improved.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] Known examples of chargeable and dischargeable electricity storage devices include secondary batteries and electric double layer capacitors. In electrodes for these electricity storage devices, carbon is sometimes used as an active material disposed on the surface of a current collector. For example, Patent Documents 1 and 2 listed below disclose techniques for forming an active material layer of a negative electrode of a lithium ion secondary battery using graphite or carbon nanowalls. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 2668678 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-9980 Summary of the Invention [Problem to be solved by the invention]

[0004] However, electrodes using graphite in the active material layer have yet to fully achieve the high battery performance required for electricity storage devices. Furthermore, electrodes using carbon nanowalls in the active material layer are superior to graphite in terms of improving battery performance, but have yet to be mass-produced. Therefore, in the technical field of electricity storage devices, there is a need for the development of novel active material layers other than those using graphite or carbon nanowalls as the active material. The present application aims to provide an electrode for an electricity storage device having an active material layer with a novel configuration that can improve the performance of the electricity storage device. [Means for solving the problem]

[0005] The inventors of the present invention have been conducting extensive research into electrodes for electricity storage devices that use carbon as an active material, and have succeeded in developing an active material layer with a novel configuration that differs from conventional active material layers that use graphite or carbon nanowalls. The present invention can be realized, for example, in the following aspects.

[0006] A first aspect of the present invention is provided as an electrode for an electricity storage device. The electrode for an electricity storage device of this aspect includes a metal substrate constituting a current collector, a plurality of protrusions formed on the surface of the metal substrate and composed of fine metal particles, and a plurality of carbon nanostructures containing graphene as a main component, extending linearly on the surface of the metal substrate when viewed in the thickness direction of the metal substrate, and distributed on the surface of the metal substrate.

[0007] In this embodiment of the electrode for an electricity storage device, the active material layer is composed of a plurality of protrusions on the surface of the metal substrate and a plurality of linear carbon nanostructures distributed on the surface of the metal substrate, and this active material layer can improve the battery performance of the electricity storage device.

[0008] The present invention can be realized in various forms other than an electrode for an electricity storage device, for example, an electricity storage device such as a secondary battery including an electrode for an electricity storage device, a method for manufacturing an electrode for an electricity storage device, a method for manufacturing an electricity storage device, a method for manufacturing an active material layer, a manufacturing apparatus suitable for carrying out these manufacturing methods, a control program for controlling the manufacturing apparatus, a recording medium on which the control program is recorded, etc. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a secondary battery including an electrode for an electricity storage device. [Figure 2] FIG. 2 is a schematic diagram showing the structure of an active material layer. [Figure 3] FIG. 1 is a process flow diagram showing a manufacturing process of a secondary battery. [Figure 4] FIG. 2 is a schematic diagram showing the configuration of a first processing apparatus. [Figure 5] FIG. 3 is a schematic diagram showing the configuration of a second processing apparatus. [Figure 6] FIG. 10 is an explanatory diagram showing a photographed image in the embodiment. [Figure 7] FIG. 4 is an explanatory diagram showing the particle size distribution of metal particles constituting the convex portions of the example. [Figure 8] FIG. 4 is an explanatory diagram showing the results of an evaluation test of the battery performance of the examples. [Figure 9] FIG. 4 is an explanatory diagram showing the results of an evaluation test of the battery performance of the first comparative example. [Figure 10] FIG. 10 is an explanatory diagram showing the results of an evaluation test of the battery performance of the second comparative example. [Figure 11] FIG. 4 is an explanatory diagram showing the results of an evaluation test of the battery performance of an example and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of an electrode for an electricity storage device according to the present invention will be described with reference to the drawings. In this specification, the term "electricity storage device" refers to a chargeable and dischargeable electricity storage body, such as a secondary battery or an electric double layer capacitor, and an apparatus including such an electricity storage body.

[0011] 1. Embodiment: 1-1. Secondary battery structure: 1 is a schematic diagram showing the configuration of a secondary battery 10 of this embodiment. The secondary battery 10 of this embodiment is a lithium ion secondary battery, and the metal ions involved in its charging and discharging are lithium (Li) ions.

[0012] The secondary battery 10 includes a container 11, an electrolyte 12, a separator 15, a first electrode 20, and a second electrode 30. For convenience, in Fig. 1, the container 11 is shown by a dashed line, and the separator 15 is shown by a broken line.

[0013] Container 11 has an internal space filled with electrolyte solution 12. Container 11 is liquid-tight and made of a material that is not easily reactive with electrolyte solution 12. The internal space of container 11 is partitioned by separator 15 into a first electrode chamber 16 that houses first electrode 20 and a second electrode chamber 17 that houses second electrode 30.

[0014] The electrolyte solution 12 has the property of being able to transfer metal ions involved in charge and discharge between the first electrode 20 and the second electrode 30. In this embodiment, the electrolyte solution 12 is made of a solution in which a lithium salt is dissolved in an organic solvent, and is able to transfer lithium ions between the first electrode 20 and the second electrode 30. For example, lithium hexafluorophosphate (LiPF6) can be used as the lithium salt of the electrolyte solution 12. Furthermore, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. can be used as the organic solvent.

[0015] Separator 15 has electrical insulation and ion conductivity, electrically insulating first electrode 20 from second electrode 30, and allowing lithium ions to pass through via electrolyte solution 12. Separator 15 is made of, for example, a resin film or nonwoven fabric having a porous structure.

[0016] The first electrode 20 corresponds to the power storage device electrode of this embodiment. In the secondary battery 10 of this embodiment, the first electrode 20 constitutes a negative electrode. The first electrode 20 includes a metal substrate 21 that constitutes a current collector. In this embodiment, the metal substrate 21 is made of a metal foil of copper (Cu). The metal substrate 21 may be made of a metal other than Cu. In other embodiments, the metal substrate 21 may be made of, for example, any one of a Cu alloy, aluminum (Al), and an Al alloy. The metal substrate 21 does not have to be made of a metal foil, and may be made 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] A plurality of protrusions 22 are formed on the surface of the metal substrate 21, and carbon nanostructures are arranged between the protrusions 22. The carbon nanostructures are not shown in FIG. 1. The carbon nanostructures contain carbon (C) as an active material, and the protrusions 22 of the metal substrate 21 and the carbon nanostructures 26 form an active material layer 25 of the first electrode 20. In this embodiment, the active material layer 25 is provided on both the first surface 21a and the second surface 21b of the metal substrate 21. The details of the configuration of the active material layer 25 and the manufacturing method will be described later. In the following description, the first electrode 20 will also be simply referred to as "electrode 20."

[0018] The second electrode 30 constitutes the positive electrode of the secondary battery 10. The second electrode 30 has a positive electrode current collector 31 and a positive electrode active material layer 32. The positive electrode current collector 31 is made of 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 made in a flat shape, and may be bent into various shapes such as a cylindrical shape or a corrugated 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 Li atoms, a conductive additive, and a binder. The positive electrode active material layer 32 may also contain a thickener. As the positive electrode active material, for example, a ternary substance can be used, such as lithium cobalt oxide (LiCoO), lithium manganese oxide (LMO), or lithium nickel oxide (NCA). As the conductive additive, 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 thickener, for example, carboxymethyl cellulose (CMC) can be used.

[0020] The configuration of the active material layer 25 of the electrode 20 of this embodiment will be described with reference to Fig. 2. Fig. 2 is a schematic diagram of the active material layer 25 of the metal substrate 21 when viewed in a direction perpendicular to the thickness direction of the metal substrate 21.

[0021] As described above, a plurality of protrusions 22 are formed on the surface of the metal substrate 21. In this embodiment, each protrusion 22 is composed of fine metal particles 22p. In this specification, the term "particle" is a concept meaning minute lumps of various shapes, and is not necessarily limited to a substantially spherical shape, but also includes irregular shapes having a random uneven structure on the surface.

[0022] The protrusions 22 include those formed by a single metal particle 22p and those formed by a plurality of metal particles 22p densely packed together. The metal particles 22p and the protrusions 22 are made of the same metal as the metal substrate 21. On the surface of the metal substrate 21, regions where the protrusions 21 are densely packed and regions where the number of protrusions 21 is small are distributed throughout. In this embodiment, the protrusions 22 are formed by a plasma CVD (chemical vapor deposition) method. The method for forming the protrusions 22 will be described later.

[0023] As will be described later, the protrusions 22 contribute to the generation of carbon nanostructures 26 and also contribute to the battery performance of the secondary battery 10. Therefore, it is preferable that the protrusions 22 are formed with appropriate dimensions and distribution density.

[0024] To obtain protrusions 22 of appropriate dimensions, the particle diameter of metal particles 22p when viewed in the thickness direction of metal substrate 21 is preferably 5 nm or more and 55 nm or less. Also, the average particle diameter of metal particles 22p is preferably 8 nm or more and 30 nm or less. In this specification, "particle diameter" refers to the maximum value of particle diameters in all directions measured in multiple images taken directly facing metal substrate 21 using, for example, a scanning electron microscope or the like.

[0025] In order to realize an appropriate distribution density of the protrusions 22, the distribution density of the metal particles 22p in the active material layer 25 is set to 1 particle / μm 2 More than 1000 pieces / μm 2Here, the "distribution density of metal particles 22p" corresponds to the number of metal particles 22p distributed per unit area of ​​active material layer 25, which can be observed when viewed in the thickness direction of metal substrate 21.

[0026] Furthermore, the height of the protrusions 22 when viewed in a direction perpendicular to the thickness direction of the metal substrate 21 is preferably 5 nm or more and 300 nm or less. The height of the protrusions 22 is measured as the distance from the flat surface at the bottom end of the protrusions 22 to the top end of the protrusions 22 on an image taken from a direction perpendicular to the thickness direction of an arbitrary region of the metal substrate 21 using, for example, a scanning electron microscope or the like.

[0027] On the surface of the metal substrate 21, a plurality of carbon nanostructures 26, each composed mainly of graphene and extending linearly on the surface of the metal substrate 21, are arranged. Here, "linear" may also be referred to as fibrous, thread-like, or string-like, and preferably has a length at least 7 to 8 times greater than its diameter. Furthermore, the "main component" may be, for example, a component whose content ratio in the entire material is 50 mass % or more.

[0028] As shown in the photographed image of the embodiment in Figure 6, which will be referred to later, the carbon nanostructures 26 extend linearly on the surface of the metal substrate 21 when viewed in the thickness direction of the metal substrate 21, and are distributed over the entire surface of the metal substrate 21. The carbon nanostructures 26 are randomly distributed on the surface of the metal substrate 21. The carbon nanostructures 26 can also be interpreted as extending in a manner that threads between the protrusions 22. However, the carbon nanostructures 26 may include those that extend through regions above the protrusions 22.

[0029] The carbon nanostructure 26 preferably includes a carbon nanotube-like structure in which a graphene sheet is rolled into a cylindrical shape. Because the carbon nanostructure 26 is a graphite-like substance, it has higher electrical conductivity than carbon materials such as activated carbon. The carbon nanostructure 26 is produced by the plasma CVD method described below.

[0030] The diameter of the carbon nanostructure 26 may be, for example, 1 nm or more and 15 nm or less. Furthermore, the length of the carbon nanostructure 26 when stretched out straight may be, for example, 100 nm or more and 2000 nm or less. Carbon nanostructures 26 of this size can further improve the battery performance of the secondary battery 10. Furthermore, they can be easily produced by the manufacturing method described below.

[0031] The carbon nanostructures 26 are randomly arranged over the entire area where the protrusions 22 are distributed on the surface of the metal substrate 21. As described above, the carbon nanostructures 26, together with the protrusions 22 of the metal substrate 21, constitute the active material layer 25 of the electrode 20. The battery reaction in the active material layer 25 will be described below.

[0032] 1-2. Battery reaction in secondary batteries: The chemical reactions occurring during charging and discharging of the secondary battery 10 can be expressed, for example, by the following reaction formula: As described above, in the secondary battery 10, the metal ions involved in charging and discharging are lithium ions.

[0033] When the positive electrode material is LiCoO2, the reaction formula at the second electrode 30, which is the positive electrode, is expressed by the following formula (1): x represents the proportion of reacting atoms and is a real number greater than 0 and less than 1. Li 1-x CoO2+ xLi + + xe- ⇔ LiCoO2…(1)

[0034] On the other hand, the reaction at the negative electrode 20 is expressed by the following formula (2). Li + + e - ⇔ Li …(2)

[0035] According to the secondary battery 10 of this embodiment, during charging, lithium is deposited on the surface layer of the active material layer 25 of the electrode 20 by the reaction of the above formula (2), forming a lithium layer. This is because the carbon nanostructures 26 function as an active material, facilitating the deposition of lithium on the surface layer of the electrode 20. In addition, the deposition of Li on the surface of the electrode 20 is also promoted from the protrusions 22 of the metal substrate 21. This is based on knowledge derived by the inventor of the present invention from experimental results based on nucleation theory.

[0036] In the case of a conventional negative electrode structure in which graphite is placed as an active material on the surface of a flat metal substrate, in principle, one lithium ion is absorbed per six carbon atoms during charging, forming lithium carbide (LiC6). Therefore, the reaction formula for this conventional structure, which serves as a comparative example, is expressed as the following formula (3). Reaction formula in conventional configuration: xLi + + C6+ xe - ⇔ Li x C6…(3)

[0037] As shown in the above formula (3), in the case of a conventional electrode that uses graphite as the negative electrode active material, the number of lithium ions that can be absorbed by charging is determined by the number of carbon atoms contained in the active material layer.

[0038] In contrast, in the case of the electrode 20 used in the secondary battery 10 of this embodiment, as shown in the above formula (2), theoretically, charging is possible as long as lithium can be deposited without being limited by the number of carbon atoms in the active material layer 25. In other words, with the electrode 20 of this embodiment, two or more lithium ions per carbon atom can be involved in the charge / discharge reaction in one charge or discharge. Therefore, the secondary battery 10 of this embodiment has an increased charge capacity by including the electrode 20 as the negative electrode.

[0039] Furthermore, according to the secondary battery 10 of this embodiment, since the protrusions 22 and carbon nanostructures 26 are uniformly distributed on the surface of the metal substrate 21, a lithium layer is uniformly formed on the surface of the electrode 20 during charging, enabling stable and smooth charge-discharge reactions. Furthermore, since the amount of lithium deposition is prevented from increasing locally, the generation of dendrites can be suppressed.

[0040] In the manufacturing process of a secondary battery having an active material layer of carbon nanowalls, when an electrode having carbon nanowalls formed on its surface is rolled up for transportation, storage, etc., some of the carbon nanowalls may be damaged or fall off, which has been one of the reasons why mass production of secondary batteries having carbon nanowalls in the active material layer is difficult.

[0041] In contrast, according to the electrode 20 of this embodiment, even if the electrode 20 is rolled up and transported or stored in the manufacturing process of the secondary battery 10, the protrusions 22 are unlikely to be crushed and the carbon nanostructures 26 arranged in the gaps between the protrusions 22 are unlikely to fall off. Therefore, the electrode 20 of this embodiment is easy to handle when assembling it into the secondary battery 10, and mass production of the secondary battery 10 can be facilitated.

[0042] 1-3. Secondary battery manufacturing method: 3 is a process flow diagram showing the manufacturing process of the secondary battery 10. Steps P1 and P2 are steps for manufacturing the electrode 20.

[0043] In step P1, a plurality of protrusions 22 are formed on the surface of the metal substrate 21. As described above, in this embodiment, each protrusion 22 is made of metal particles 22p and is formed by the plasma CVD method.

[0044] 4 is a schematic diagram showing the configuration of the first processing apparatus 40 used in step P1. In this embodiment, the first processing apparatus 40 is a radical-injection plasma-enhanced (RI-PE) CVD apparatus.

[0045] The first processing apparatus 40 includes, at its upper stage, a plasma generation chamber 41, a waveguide 42, a quartz window 43, a slot antenna 44, a microwave generation unit 45, and a radical source supply unit 46. The first processing apparatus 40 also includes, at its lower stage below the plasma generation chamber 41, a reaction chamber 50, a partition wall 51, a raw material gas supply unit 54, a power supply unit 55, a support base 56, a heater 57, and an exhaust unit 58.

[0046] The plasma generation chamber 41 is a space where surface wave plasma (SWP) is generated by microwaves. The waveguide 42 is a space for transmitting microwaves to the plasma generation chamber 41. The waveguide 42 is partitioned by a quartz window 43 at the upper stage of the plasma generation chamber 41. Slot antennas 44 are arranged on the quartz window 43.

[0047] The microwave generating unit 45 introduces microwaves MW into the waveguide 42. The microwave generating unit 45 can generate microwaves with a frequency of 2.00 to 3.00 GHz, for example, with a power of 300 to 500 W. The microwaves MW introduced into the waveguide 42 are introduced into the plasma generation chamber 41 by the slot antenna 44.

[0048] When microwaves MW are introduced into the plasma generation chamber 41, high density plasma (HDP) is generated at the quartz window 43. The high density plasma HDP diffuses into the plasma generation chamber 41 and becomes surface wave plasma SWP.

[0049] The radical source supply unit 46 supplies a gas that serves as a radical source to the plasma generation chamber 41. For example, hydrogen can be used as the radical source. The gas that serves as the radical source is not limited to hydrogen, and may be, for example, oxygen, nitrogen, or other gases. Ions of the radical source gas are mixed into the surface wave plasma SWP of the plasma generation chamber 41.

[0050] The radical source supply unit 46 supplies a reaction contributing gas for promoting ionization of the radical source gas together with the radical source gas. The reaction contributing gas may be, for example, argon.

[0051] The reaction chamber 50 is partitioned below the plasma generation chamber 41 by a metal partition wall 51. The partition wall 51 is provided with a plurality of through holes 52 for allowing the surface wave plasma SWP generated in the plasma generation chamber 41 to flow into the reaction chamber 50.

[0052] As described above, ions of the radical source are mixed into the surface wave plasma SWP in the plasma generation chamber 41. Most of the ions of the radical source collide with the partition wall 51 provided between the plasma generation chamber 41 and the reaction chamber 50 and are neutralized to become radicals, which are then introduced into the reaction chamber 50 together with the surface wave plasma SWP.

[0053] The power supply unit 55 is connected to the partition wall 51 and applies a high-frequency voltage for plasma processing to the partition wall 51. The power supply unit 55 is capable of applying a power of 300 to 400 W and a high-frequency voltage with a frequency of 80 to 120 MHz. The partition wall 51 functions as an electrode for plasma processing.

[0054] The support base 56 is provided below the partition wall 51 and has a mounting surface 56s facing the partition wall 51. The metal substrate 21 is placed on the mounting surface 56s. The support base 56 is grounded and functions as an electrode for plasma processing. The heater 57 is provided inside the support base 56 and heats the metal substrate 21 placed on the mounting surface 56s of the support base 56 to a predetermined temperature.

[0055] The exhaust unit 58 is connected to the reaction chamber 50. The exhaust unit 58 is equipped with a vacuum pump, which controls the pressure inside the reaction chamber 50 to a predetermined level during plasma processing. In addition to the above-mentioned components, the first processing device 40 may also be equipped with measuring units equivalent to the vacuum gauge 81 and thermocouple 82 of the second processing device 60 shown in FIG. 5, which will be referred to later.

[0056] In step P1, first, the metal substrate 21 is placed in the reaction chamber 50 of the first processing apparatus 40. The metal substrate 21 is placed on the mounting surface 56s of the support base 56. The heater 57 heats the metal substrate 21 to a temperature of, for example, about 600 to 800°C.

[0057] In step P1, the microwave generation unit 45 generates microwaves with a frequency of 2.00 to 3.00 GHz, for example, at a power of 300 to 500 W. The microwaves are introduced into the plasma generation chamber 41 through the waveguide 42 and the slot antenna 44. A radical source gas is also supplied to the plasma generation chamber 41 from the radical source supply unit 46. As a result, as described above, surface wave plasma SWP containing radicals is generated in the plasma generation chamber 41 and introduced into the reaction chamber 50 through the through-holes 52 in the partition wall 51. The pressure inside the reaction chamber 50 is controlled by the exhaust unit 58 to, for example, about 1.0 to 3.0 Pa.

[0058] While the source gas is being supplied to the reaction chamber 50, the power supply unit 55 applies a high-frequency voltage to the partition wall 51. The power supply unit 55 applies a high-frequency voltage with a power of, for example, 300 to 500 W and a frequency of, for example, 80 to 120 MHz. The plasma processing in the first processing device 40 continues for, for example, about 5 to 15 minutes.

[0059] In the plasma processing, a capacitively coupled plasma CCP is generated between the partition wall 51 and the metal substrate 21 on the support base 56. Radicals exist in the capacitively coupled plasma CCP. When the capacitively coupled plasma CCP comes into contact with the metal substrate 21, metal particles constituting the metal substrate 21 are scattered and re-adhere to the metal substrate 21. This forms the convex portions 22 composed of the above-mentioned metal particles 22p. Step P1 is performed on each of the first surface 21a and the second surface 21b of the metal substrate 21.

[0060] Referring to Fig. 3, step P2 corresponds to a step of forming carbon nanostructures 26 on the surface of metal substrate 21. Carbon nanostructures 26 are formed by a plasma CVD method. In this embodiment, carbon nanostructures 26 are formed by a capacitively coupled plasma (CPP) CVD method.

[0061] 5 is a schematic diagram showing the configuration of second processing apparatus 60, which is a CCP-CVD apparatus used in process P2. Second processing apparatus 60 includes a reaction chamber 61, an exhaust unit 62, a source gas supply unit 65, a support base 70, an upper electrode 75, and a power supply unit 76. Second processing apparatus 60 also includes a vacuum gauge 81 and a thermocouple 82 as measuring units.

[0062] The reaction chamber 61 has an airtight structure capable of maintaining a vacuum. The reaction chamber 61 is connected to an exhaust unit 62 and a raw material gas supply unit 65. The exhaust unit 62 is equipped with a vacuum pump, and controls the reaction chamber 61 to a predetermined pressure (degree of vacuum) during plasma processing. The degree of vacuum in the reaction chamber 61 is measured by a vacuum gauge 81.

[0063] The raw material gas supply unit 65 supplies raw material gas to the reaction chamber 61. The raw material gas includes a carbon-based gas containing carbon that constitutes the carbon nanostructures 26, and a reaction contributing gas that contributes to the growth of the carbon nanostructures 26.

[0064] Examples of the carbon-based gas that can be used include methane (CH4) and hexafluoroethane (C2F6). Examples of the reaction-contributing gas that can be used include hydrogen (H2) and argon (Ar). The reaction-contributing gas promotes the formation of plasma from the carbon-based gas due to the Penning effect during plasma processing. Furthermore, the reaction-contributing gas is ionized during plasma processing and collides with the metal substrate 21 to be processed, thereby forming nuclei that serve as growth starting points for the carbon nanostructures 26.

[0065] The source gas supply unit 65 includes a storage unit 66, a flow rate control unit 67, and an introduction pipe 68. In the storage unit 66, a plurality of types of gases constituting the source gas are stored in tanks (not shown) for each type.

[0066] The flow rate control unit 67 includes a gas delivery device 67a and a flow rate adjustment valve 67b, which are respectively provided in pipes connected to the reservoir 66 for the plurality of types of gases.

[0067] The gas delivery device 67a is configured by, for example, an ejector or a pump, and delivers gas at a predetermined pressure from the storage unit 66. The flow rate of the gas delivered by the gas delivery device 67a is controlled by a flow rate adjustment valve 67b.

[0068] The various gases whose flow rates are adjusted by the flow rate adjustment valve 67b join together in the inlet pipe 68. The inlet pipe 68 introduces into the reaction chamber 61 a source gas in which the multiple gases are mixed at a predetermined ratio.

[0069] A support base 70 is provided in the reaction chamber 61. The support base 70 includes a susceptor 71, a quartz cover 72, and a heater 73. The susceptor 71 constitutes a mounting surface for the metal substrate 21. The metal substrate 21 is placed on the susceptor 71. The susceptor 71 is earthed. The susceptor 71 may be floating.

[0070] The susceptor 71 is disposed on a quartz cover 72, and a heater 73 is provided below the quartz cover 72. The quartz cover 72 protects the heater 73. The quartz cover 72 also supports the susceptor 71 and prevents the heater 73 from coming into direct contact with the susceptor 71.

[0071] During plasma processing, the metal substrate 21 is heated by receiving radiant heat from the heater 73 via 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.

[0072] An upper electrode 75 is installed at the top 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 approximately parallel to the metal substrate 21. The distance between the upper electrode 75 and the susceptor 71 is, for example, approximately 1 to 5 cm. The upper electrode 75 is connected to a power supply unit 76 installed outside the reaction chamber 61.

[0073] The power supply unit 76 is a high-frequency power supply device. The power supply unit 76 is capable of applying a high-frequency voltage with a power of 300 to 700 W and a frequency of 12 to 15 MHz to the upper electrode 75. When the source gas is being supplied to the reaction chamber 61 by the reservoir 66, the power supply unit 76 applies the high-frequency voltage to the upper electrode 75 to generate a high-density capacitively coupled plasma in the reaction chamber 61.

[0074] In step P2, first, the metal substrate 21 on which the protrusions 22 have been generated in step P1 is placed on the support base 70 in the reaction chamber 61. The heater 73 heats the metal substrate 21 to a temperature of, for example, 600 to 800°C.

[0075] In step P2, the raw material gas supply unit 65 supplies raw material gas to the reaction chamber 50. The raw material gas supply unit 65 supplies, for example, a carbon-based gas as the raw material gas at a flow rate of 80 to 120 sccm, and also supplies a reaction contributing gas at a flow rate of 40 to 60 sccm.

[0076] The exhaust unit 62 controls the pressure inside the reaction chamber 50. According to findings obtained through experiments by the inventors of the present invention, the pressure inside the reaction chamber 50 during the plasma treatment is important for generating the carbon nanostructures 26 in the linear configuration described above. In step P2, the pressure inside the reaction chamber 50 is controlled to be between 30 Pa and 50 Pa during the plasma treatment. It is more preferable that the pressure inside the reaction chamber 50 be controlled to be between 35 Pa and 45 Pa.

[0077] While the source gas is being supplied to the reaction chamber 61, the power supply unit 76 applies a high-frequency voltage to the upper electrode 75. The power supply unit 76 applies a high-frequency voltage with a power of 300 to 700 W and a frequency of 12 to 15 MHz, for example. The power supply unit 76 gradually increases the power to the target power over a period of several tens of seconds to several minutes.

[0078] The plasma treatment in second processing apparatus 60 continues for, for example, about 5 to 15 minutes. Carbon nanostructures 26 described in FIG. 2 are produced by the plasma treatment in second processing apparatus 60. In the plasma treatment in step P2, convex portions 22 of metal substrate 21 function as starting points for the production of carbon nanostructures 26. Therefore, according to the manufacturing process of this embodiment, it is possible to omit the need to prepare a catalyst separately from metal substrate 21 and place it on metal substrate 21 for growing carbon nanostructures 26 on the surface of metal substrate 21.

[0079] Returning to Fig. 3, in step P3, a second electrode 30, which will serve as a positive electrode, is manufactured. In step P4, as shown in Fig. 1, the first electrode 20 and the second electrode 30 are assembled into a container 11 filled with an electrolytic solution 12. Through these steps, a secondary battery 10 is completed.

[0080] According to the manufacturing process for secondary battery 10 of this embodiment, active material layer 25 composed of multiple protrusions 22 and linear carbon nanostructures 26 can be easily formed on the surface of metal substrate 21. Furthermore, secondary battery 10 including electrode 20 having this active material layer 25 can be obtained. Secondary battery 10 including electrode 20 having active material layer 25 can increase its charge capacity and charge rate, improving its battery performance. As described above, electrode 20 having active material layer 25 is easy to handle, facilitating mass production of secondary batteries 10.

[0081] In the past, an active material layer made of carbon nanotubes included in the negative electrode of a secondary battery was sometimes formed by applying a slurry containing carbon nanotubes that had been processed into a powder after production to the surface of a current collector. In contrast, in the manufacturing process for secondary battery 10 of this embodiment, carbon nanostructures 26 are grown by CVD on the surface of metal substrate 21 on which protrusions 22 have been formed, and then the metal substrate 21 can be assembled as electrode 20 of secondary battery 10. Therefore, a process of processing carbon nanostructures 26 after production to assemble them into secondary battery 10 is not required, thereby simplifying the manufacturing process for secondary battery 10. [Example]

[0082] 1-4. Example E1: Example E1 of the electrode 20 of this embodiment was produced by carrying out the above-described steps P1 and P2 under the conditions shown in the following Table 1. In Example E1, copper foil was used as the metal substrate 21 constituting the current collector.

[0083] [Table 1]

[0084] In step P1, convex portions 22 were formed on the surface of metal substrate 21 by RI-PECVD. In step P2, carbon nanostructures 26 were generated between convex portions 22 on the surface of metal substrate 21 by CCP-CVD. In step P2, the pressure in the reaction chamber during plasma treatment was controlled to 40 Pa.

[0085] Please refer to Figures 6 and 7. Figures 6(a) and (b) show images of the surface of the metal substrate 21 used in Example E1 taken with a scanning electron microscope. The image in Figure 6(a) is an image of the protrusions 22 obtained in step P1, which was carried out under the conditions in Table 1. The image in Figure 6(b) is an image of the carbon nanostructures 26 produced in step P2, which was carried out under the conditions in Table 1. Figure 7 shows a histogram showing the particle size distribution of the metal particles 22p that make up the protrusions 22 of Example E1.

[0086] As shown in the photographed image of FIG. 6(a), a plurality of protrusions 22 were formed on the metal substrate 21 of Example E1 by the step P1 under the above conditions, which were made of Cu metal particles 22p. As shown in FIG. 7, the metal particles 22p of Example E1 were formed with particle diameters in the range of 5 to 55 nm, and the average particle diameter was about 21 nm. The distribution density of the metal particles 22p in Example E1 was 1 particle / μm 2 More than 1000 pieces / μm 2 The height of the protrusions 22 in Example E1 was generally within the range of 5 nm to 200 nm.

[0087] As shown in the photographed image in Figure 6(b), carbon nanostructures 26 extending between the protrusions 22 were produced on the metal substrate 21 of Example E1 by step P2 under the above conditions. The diameter of the carbon nanostructures 26 of Example E1 was generally within the range of 1 nm to 15 nm. The length of the carbon nanostructures 26 of Example E1 was generally within the range of 100 nm to 2000 nm.

[0088] Fig. 8 is an explanatory diagram showing the results of an evaluation test of the battery performance of a secondary battery fabricated using Example E1. In Fig. 8, the relationship between the voltage and charge capacity of the secondary battery is shown by a solid line graph during charging and by a dashed line graph during discharging. The secondary battery had the configuration shown in Table 2 below.

[0089] [Table 2]

[0090] In this evaluation test, both the charge current and the discharge current were set to 0.5 mA. The secondary battery of Example E1 had a charge capacity of 14.6 [mAh] and a specific capacity of 11.0 [mAh / cm 2 ] was.

[0091] 1-5. Comparative examples C1, C2: 9 and 10 are explanatory diagrams showing the results of an evaluation test of the battery performance of secondary batteries fabricated using the electrodes of Comparative Examples C1 and C2 as negative electrodes. The electrode of Comparative Example C1 was fabricated to have substantially the same configuration as Example E1, except that it did not have carbon nanostructures 26. The electrode of Comparative Example C2 was fabricated by forming active material layers in which graphite was densely arranged as an active material on both sides of copper foil constituting a current collector. The secondary batteries of Comparative Examples C1 and C2 had the configurations shown in Table 2 above, similar to the secondary battery of Example E1.

[0092] 9 and 10, similar to FIG. 8 of Example E1, the relationship between the voltage and charge capacity of the secondary battery is shown by a solid line graph during charging and by a dashed line graph during discharging.

[0093] In the evaluation tests of Comparative Examples C1 and C2, the charge current and discharge current were both 0.5 mA, as in the evaluation test of Example E1. The secondary battery of Comparative Example C1 had a charge capacity of 12.8 mAh and a specific capacity of 9.6 mAh / cm 2 In the secondary battery of Comparative Example C2, the charge capacity was 4.0 [mAh] and the specific capacity was 2.0 [mAh / cm 2 ] was.

[0094] 1-6. Comparison of Example E1 and Comparative Examples C1 and C2: The charge capacities and specific capacities of the secondary batteries of Example E1 and Comparative Examples C1 and C2 are shown in bar graphs in Figure 11. The secondary battery of Example E1 exhibited significantly improved battery performance compared to the secondary battery of Comparative Example C2, which used graphite as the negative electrode active material.

[0095] The secondary battery of Comparative Example C1, in which the negative electrode was formed with a metal substrate 21 having protrusions 22 similar to those of Example E1, also showed a significant improvement in battery performance compared to the secondary battery of Comparative Example C2. This result shows that the protrusions 22 of the metal substrate 21 contribute to the improvement of battery performance.

[0096] Furthermore, the secondary battery of Example E1, which had carbon nanostructures 26 in the negative electrode, had improved battery performance compared to the secondary battery of Comparative Example C1. This result shows that the presence of carbon nanostructures 26 as an active material contributes to the improvement of battery performance. The improvement in battery performance due to carbon nanostructures 26 may be due to a component other than graphene contained in carbon nanostructures 26, such as the carbon nanostructures 26 containing a portion of Cu from the metal substrate 21. The components of carbon nanostructures 26 that contribute to the improvement of battery performance can be analyzed by, for example, Raman spectroscopy or an energy dispersive X-ray fluorescence analyzer (EDX).

[0097] 1-7. Summary: As described above, according to the electrode 20 for the energy storage device of the above-mentioned embodiment and example, the secondary battery using the same, and the manufacturing method thereof, the battery performance of the energy storage device can be improved by the novel active material layer 25 composed of the protrusions 22 and the carbon nanostructures 26.

[0098] 2. Other embodiments: The present invention is not limited to the configurations of the above-described embodiments and examples, and can also be realized in the following forms, for example. All of the configurations described below as other embodiments are positioned as examples of modes for implementing the present invention, just like the above-described embodiments and examples.

[0099] 2-1. Alternative embodiment 1: A secondary battery using the electrode 20 of the above embodiment may be configured so that metal ions other than lithium ions are involved in charging and discharging. A secondary battery using the electrode 20 of the above embodiment may be configured so that sodium (Na) ions, potassium (K) ions, magnesium (Mg) ions, etc. are involved in charging and discharging.

[0100] 2-2. Alternative embodiment 2: The electrode 20 may be used in an electricity storage device other than a secondary battery. The electrode 20 of the above embodiment may be used, for example, 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.

[0101] 2-3. Alternative embodiment 3: The protrusions 22 of the electrode 20 and the metal particles 22p that make up the protrusions 22 may have dimensions and distribution densities outside the preferred ranges described in the above embodiment. Also, the carbon nanostructures 26 may have diameters and lengths outside the preferred ranges described in the above embodiment.

[0102] 2-4. Alternative embodiment 4: The protrusions 22 do not have to be composed of metal particles 22p. The protrusions 22 of the electrode 20 may be formed by a surface treatment such as shot blasting that forms a fine uneven structure on the surface of the metal substrate 21. The protrusions 22 may be formed by a type of plasma PVD method other than the RI-PECVD method. The protrusions 22 may be formed by a CCP-CVD method, for example. The protrusions 22 may also be formed by a surface treatment such as electrolytic deposition, oxidation treatment, or sputtering on the metal substrate 21. The protrusions 22 may also be formed by adhering particles of a metal different from the metal that constitutes the metal substrate 21 to the surface.

[0103] 2-5. Alternative embodiment 5: The carbon nanostructures 26 may be produced by a plasma CVD method other than the CCP-CVD method, for example, the RI-PECVD method.

[0104] 3. Example of morphology: The present invention can be realized in the following forms.

[0105] [First embodiment] The first embodiment is provided as an electrode for an electricity storage device. The electrode for an electricity storage device of the first embodiment includes a metal substrate constituting a current collector, a plurality of protrusions formed on the surface of the metal substrate, the protrusions being composed of fine metal particles, and a plurality of carbon nanostructures containing graphene as a main component, extending linearly on the surface of the metal substrate when viewed in the thickness direction of the metal substrate, and distributed on the surface of the metal substrate. In the first embodiment of the electrode for an electricity storage device, the active material layer is composed of a plurality of protrusions on the surface of the metal substrate and a plurality of linear carbon nanostructures distributed on the surface of the metal substrate, and this active material layer can improve the battery performance of the electricity storage device.

[0106] [Second Mode] In the electrode for an electricity storage device of the first mode, the carbon nanostructure may have a diameter of 1 nm or more and 15 nm or less, and a length of 100 nm or more and 1000 nm or less. According to the second embodiment of the electrode for an electricity storage device, the battery performance of the electricity storage device can be further improved.

[0107] [Third Mode] In the electricity storage device electrode of the first mode or the second mode, the height of the convex portion may be 5 nm or more and 300 nm or less. According to the third embodiment of the electrode for an electricity storage device, the protrusions that function as starting points for depositing metal ions involved in charge and discharge as metal during charging are formed with more appropriate dimensions in the electrode, thereby further improving the battery performance of the electricity storage device. Furthermore, the protrusions are more likely to function as starting points for the production of carbon nanostructures, allowing for more stable production of carbon nanostructures.

[0108] [Fourth Mode] In the electricity storage device electrode of the first, second, and third modes, the protrusions may be made of fine metal particles. According to the electricity storage device electrode of the fourth embodiment, fine protrusions can be more easily formed by, for example, plasma CVD processing.

[0109] [Fifth Mode] In the electrode for an electric storage device according to any one of the first, second, third, and fourth modes, the particle diameter of the metal particles when viewed in the thickness direction of the metal substrate may be 5 nm or more and 55 nm or less. According to the fifth embodiment of the electrode for an electricity storage device, it is easy to form protrusions of appropriate dimensions, and the battery performance of the electricity storage device can be further improved.

[0110] [Sixth Mode] In the electrode for an electric storage device according to any one of the first, second, third, fourth, and fifth modes, the average particle diameter of the metal particles when viewed in the thickness direction of the metal substrate may be 15 nm or more and 30 nm or less. According to the electricity storage device electrode of the sixth embodiment, the amount of metal particles with appropriate dimensions can be increased, and therefore the battery performance of the electricity storage device can be further improved.

[0111] [Seventh Mode] The seventh mode is provided as a secondary battery. The secondary battery of the seventh mode includes a first electrode configured as the electrode for an electricity storage device according to any one of the first, second, third, fourth, fifth, and sixth modes, and a second electrode containing metal atoms that are ionized and migrate to the first electrode. According to the electricity storage device of the seventh embodiment, the first electrode has an active material layer made up of the protrusions and the carbon nanostructure, and therefore, it is possible to improve the battery performance.

[0112] [Eighth Embodiment] The eighth embodiment provides a method for manufacturing an electrode for an electricity storage device. The manufacturing method of the eighth embodiment includes the steps of: forming a plurality of protrusions composed of fine metal particles on the surface of a metal substrate; and placing the metal substrate in a reaction chamber, supplying a carbon-containing source gas while controlling the pressure in the reaction chamber to 30 Pa or more and 50 Pa or less, and generating a plurality of carbon nanostructures, mainly composed of graphene, that extend linearly on the surface of the metal substrate and are distributed on the surface of the metal substrate when viewed in the thickness direction of the metal substrate by plasma CVD. According to the manufacturing method of the eighth embodiment, it is possible to manufacture an electrode for an electricity storage device having an active material layer with a novel structure composed of protrusions and linear carbon nanostructures. This electrode for an electricity storage device can dramatically improve the battery performance of the electricity storage device. [Explanation of symbols]

[0113] 10... Secondary battery, 11... Container, 12... Electrolyte, 15... Separator, 16... First electrode chamber, 17... Second electrode chamber, 20... First electrode (electrode for electricity storage device) / electrode, 21... Metal substrate, 21a... First surface, 21b... Second surface, 22... Convex portion, 22p... Metal particles, 25... Active material layer, 26... Carbon nanostructure, 30... Second electrode, 31... Positive electrode current collector, 31a... First surface, 31b... Second surface, 32... Positive electrode active material layer, 40... First processing device, 41... Plasma generation chamber, 42... Waveguide, 43... Quartz window, 44... Slot antenna, 45... Micro generator, 46... Radical source supply unit, 50 ...reaction chamber, 51...partition wall, 52...through hole, 55...power supply unit, 56...support base, 56s...mounting surface, 57...heater, 58...exhaust unit, 60...second processing device, 61...reaction chamber, 62...exhaust unit, 65...source gas supply unit, 66...storage unit, 67...flow rate control unit, 67a...gas delivery device, 67b...flow rate adjustment valve, 68...inlet piping, 70...support base, 71...susceptor, 72...quartz cover, 73...heater, 75...upper electrode, 76...power supply unit, 81...vacuum gauge, 82...thermocouple, CCP...capacitively coupled plasma, HDP...high density plasma, MW...microwave, SWP...surface wave plasma

Claims

1. An electrode for an electricity storage device, a metal substrate constituting a current collector; a plurality of protrusions formed so as to be distributed over the entire surface of the metal substrate, the protrusions including a protrusion formed of a single metal particle and a protrusion formed of a plurality of densely packed metal particles; a plurality of carbon nanostructures made of carbon nanotubes, extending linearly along the surface of the metal substrate between the plurality of protrusions and distributed over the entire surface of the metal substrate; An electrode for an electricity storage device comprising:

2. The electrode for an electricity storage device according to claim 1, The carbon nanostructure has a diameter of 1 nm or more and 15 nm or less, and a length of 100 nm or more and 1000 nm or less.

3. The electrode for an electricity storage device according to claim 1, The height of the protrusions is 5 nm or more and 300 nm or less.

4. The electrode for an electricity storage device according to claim 1, The electrode for an electricity storage device, wherein the particle diameter of the metal particles when viewed in the thickness direction of the metal substrate is 5 nm or more and 55 nm or less.

5. The electrode for an electricity storage device according to claim 1, The electrode for an electricity storage device, wherein the metal particles have an average particle diameter of 15 nm or more and 30 nm or less when viewed in the thickness direction of the metal substrate.

6. A secondary battery, A first electrode constituted by the electrode for an electricity storage device according to any one of claims 1 to 5; a second electrode containing metal atoms that ionize and migrate to the first electrode; Equipped with A secondary battery in which, during charging, metal atoms of the second electrode are ionized and move to the first electrode, and a layer in which ions of the metal atoms are precipitated is formed on the surface of the first electrode.

7. A method for manufacturing an electrode for an electricity storage device, comprising: forming a plurality of protrusions, including protrusions made of a single metal particle and protrusions made of a plurality of densely packed metal particles, so as to be distributed over the entire surface of the metal substrate; placing the metal substrate in a reaction chamber, supplying a carbon-containing raw material gas while controlling the pressure in the reaction chamber to 30 Pa or more and 50 Pa or less, and generating, by a plasma CVD method, a plurality of carbon nanostructures made of carbon nanotubes, distributed over the entire surface of the metal substrate, and extending linearly along the surface of the metal substrate between the plurality of convex portions; A manufacturing method comprising:

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