Manufacturing method of a power storage device and an electrode for a power storage device

Abstract

The purpose of the present technology is to provide a power storage device having a large surface area and a method for manufacturing an electrode for a power storage device. An electric double-layer capacitor comprises a positive electrode collector (P1), carbon nanowalls (CNW1, CNW2) on the positive electrode collector (P1), a negative electrode collector (N1), and carbon nanowalls (CNW3, CNW4) on the negative electrode collector (N1). A projection region (PR1) obtained by projecting a carbon nanowall (CNW1(a)) onto the surface of the positive electrode collector (P1) or the negative electrode collector (N1) does not include a carbon nanowall (CNW1(b)) other than the carbon nanowall (CNW1(a)).

Description

Technical Field

[0001] The technical field of this specification relates to an electricity storage device using a carbon material and a method for manufacturing an electrode for an electricity storage device.

Background Art

[0002] Examples of rechargeable electricity storage devices include secondary batteries, electric double layer capacitors, and the like. An electric double layer capacitor generally includes a positive electrode formed by forming a carbon material on a positive electrode current collector, a negative electrode formed by forming a carbon material on a negative electrode current collector, a separator, and an electrolytic solution.

[0003] For example, Patent Document 1 discloses a wound-type electric double layer capacitor. Further, in the electrode 10 thereof, an active material-containing layer 14 is formed on a current collector 12. The active material-containing layer 14 contains an active material such as acetylene black, graphite, graphite, activated carbon, etc. (see paragraph

[0025] of Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, in the electric double layer capacitor of Patent Document 1, the capacitance is 0.1 F or less. If the capacitance is larger, the electric double layer capacitor can be used as an electricity storage device for operating electronic devices, automobiles, etc. Therefore, it is better for the capacitance of the electric double layer capacitor to be larger. This is because electronic devices, automobiles, etc. can operate for a long time. For this purpose, it is preferable to increase the surface area of the carbon material.

[0006] Also, in a lithium-ion secondary battery, it is preferable to increase the surface area of the carbon material. This is because high-speed charging and discharging become possible. That is, this lithium-ion secondary battery can pass a large current.

[0007] The problem to be solved by the technology of this specification is to provide a power storage device with a large surface area and a method for manufacturing an electrode for a power storage device.

Means for Solving the Problem

[0008] The power storage device in the first aspect is Set a conductive body, the Set carbon nanowalls on the conductive body, and the Set amorphous carbon layer between the conductive body and the carbon nanowalls, and the projection area where the carbon nanowalls project onto the Set surface of the conductive body includes carbon nanowalls other than the carbon nanowalls themselves Further, the average angle between the current collector and the carbon nanowall is 89° or more and 90° or less, and the surface area increase rate due to the presence or absence of the carbon nanowall is 4 × H1 / D1, where H1 is the average height of the carbon nanowall and D1 is the average interval of the carbon nanowall, and H1 and D1 are set so that the surface area increase rate is 400 or more.

[0009] The electrode of this power storage device has carbon nanowalls as a carbon material. The surface area of the carbon nanowalls is significantly larger than that of conventional carbon materials such as activated carbon. Therefore, when this power storage device is used as an electric double layer capacitor, this electric double layer capacitor has a very large capacitance. When this power storage device is used as a lithium-ion secondary battery, this lithium-ion secondary battery has excellent charge and discharge characteristics.

Effects of the Invention

[0010] This specification provides a power storage device with a large surface area and a method for manufacturing an electrode for a power storage device.

Brief Description of the Drawings

[0011]

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Best Mode for Carrying Out the Invention

[0012] Hereinafter, specific embodiments will be described with reference to the drawings by taking as an example a method for manufacturing an electric storage device and an electrode for an electric storage device. In this specification, an electric storage device is a device capable of charging and discharging. The electric storage device includes a secondary battery and an electric double layer capacitor.

[0013] (First Embodiment) 1. Electric Double Layer Capacitor FIG. 1 is a diagram showing a schematic configuration of an electric double layer capacitor EDLC1 according to the first embodiment. The electric double layer capacitor EDLC1 includes a positive electrode PE, a negative electrode NE, a separator Sp1, an electrolytic solution ES1, and a container V1.

[0014] The positive electrode PE is the positive electrode of the electric double layer capacitor EDLC1. The positive electrode PE includes a positive electrode current collector P1 and carbon nanotubes CNW1 and CNW2. Carbon nanotubes CNW1 are formed on the surface of the first surface P1a of the positive electrode current collector P1. Carbon nanotubes CNW2 are formed on the surface of the second surface P1b of the positive electrode current collector P1. Thus, carbon nanotubes CNW1 and CNW2 are formed on both surfaces of the positive electrode current collector P1. The positive electrode current collector P1 is, for example, Al or Ti. Or it may be a conductor such as other metals.

[0015] The negative electrode NE is the negative electrode of the electric double layer capacitor EDLC1. The negative electrode NE has a negative electrode current collector N1 and carbon nanotubes CNW3 and CNW4. A carbon nanotube CNW3 is formed on the surface of the third surface N1a of the negative electrode current collector N1. A carbon nanotube CNW4 is formed on the surface of the fourth surface N1b of the negative electrode current collector N1. Thus, carbon nanotubes CNW3 and CNW4 are formed on both surfaces of the negative electrode current collector N1. The negative electrode current collector N1 is, for example, Cu. Or it may be a conductor such as other metals.

[0016] The separator Sp1 is for electrically insulating the positive electrode PE and the negative electrode NE. The separator Sp1 can permeate ions in the electrolytic solution ES1.

[0017] The container V1 houses the positive electrode PE, the negative electrode NE, the separator Sp1, and the electrolytic solution ES1 therein. The container V1 is made of a material that is less reactive to the electrolytic solution ES1.

[0018] The second surface P1b of the positive electrode current collector P1 and the third surface N1a of the negative electrode current collector N1 face each other. Also, since the positive electrode PE and the negative electrode NE are alternately arranged, the first surface P1a of the positive electrode current collector P1 and the fourth surface N1b of the negative electrode current collector N1 face each other.

[0019] 2. Carbon Nanowall In this specification, a carbon nanotube is a conductive nanostructure mainly composed of carbon atoms arranged by growing in a wall shape on a substrate such as the positive electrode current collector P1.

[0020] FIG. 2 is a diagram conceptually showing the structure of the carbon nanotube CNW1 of the electric double layer capacitor EDLC1 of the first embodiment. In FIG. 2, a graphene sheet GS1 is illustrated. However, any carbon nanotube having conductivity may be used. Graphite composed of a plurality of graphene sheets GS1 also has good conductivity and is suitable.

[0021] Carbon nanotube walls are formed on both sides of the positive electrode current collector P1 or the negative electrode current collector N1, but only one side is shown in FIG. 2. The positive electrode PE and the negative electrode NE have the same structure. However, the materials of the positive electrode current collector P1 and the negative electrode current collector N1 are different.

[0022] The positive electrode PE includes a positive electrode current collector P1, an amorphous carbon layer AC1, and carbon nanotube walls CNW1 and CNW2. The carbon nanotube walls CNW1 and CNW2 are positive electrode side carbon nanotube walls. The negative electrode NE includes a negative electrode current collector N1, an amorphous carbon layer AC1, and carbon nanotube walls CNW3 and CNW4. The carbon nanotube walls CNW3 and CNW4 are negative electrode side carbon nanotube walls. Therefore, the explanation will be centered on the carbon nanotube wall CNW1 on the positive electrode current collector P1.

[0023] The carbon nanotube walls CNW1, CNW2, CNW3, and CNW4 have a graphene sheet GS1. The graphene sheet GS1 exists in a graphite state in which about 10 layers are stacked in the thickness direction of the carbon nanotube walls CNW1, CNW2, CNW3, and CNW4. The number of stacked layers may be other than the above. The graphite with the graphene sheet GS1 stacked has a higher electrical conductivity than carbon materials such as activated carbon.

[0024] The amorphous carbon layer AC1 is located between the positive electrode current collector P1 or the negative electrode current collector N1, which is a conductor such as a metal, and the carbon nanotube walls CNW1, CNW2, CNW3, and CNW4. The amorphous carbon layer AC1 can be a layer that serves as a growth starting point for the graphene sheet GS1 that constitutes the carbon nanotube walls CNW1, CNW2, CNW3, and CNW4. The film thickness of the amorphous carbon layer AC1 is, for example, 10 nm or more and 300 nm or less. Preferably, it is 10 nm or more and 100 nm or less. More preferably, it is 12 nm or more and 30 nm or less. Note that depending on the method of growing the carbon nanotube walls, the amorphous carbon layer AC1 may not be necessary.

[0025] In carbon nanowalls CNW1, CNW2, CNW3, and CNW4, there is a root portion R1 on the side of the positive electrode current collector P1, and a tip portion E1 on the side opposite to the positive electrode current collector P1. The root portion R1 is a fixed portion that is often fixed to the positive electrode current collector P1 via an amorphous carbon layer AC1. Further, the root portion R1 is a connection portion that is electrically connected to the positive electrode current collector P1 or the amorphous carbon layer AC1.

[0026] In carbon nanowalls CNW1, CNW2, CNW3, and CNW4, the graphene sheet GS1 is formed in a direction intersecting the surface (the first surface P1a, the second surface P1b, the third surface N1a, the fourth surface N1b) of the positive electrode current collector P1 or the negative electrode current collector N1. In FIG. 2, the graphene sheet GS1 and the positive electrode current collector P1 are substantially perpendicular. Therefore, there is a tip portion E1 at the tip of the graphene sheet GS1. The tip portion E1 is a location located at the tip of the graphene sheet GS1. Note that the carbon atom C1 at the tip portion E1 is bonded to a hydrogen atom. That is, the terminal group of the carbon nanowalls CNW1, CNW2, CNW3, and CNW4 is a hydrogen atom.

[0027] Also, as described above, the carbon nanowalls CNW1, CNW2, CNW3, and CNW4 are graphite in which a large number of graphene sheets GS1 are stacked. Actually, the graphene sheets GS1 do not extend completely parallel to each other. Since the graphene sheets GS1 grow in different directions at each initial growth nucleus, actually, the graphene sheets GS1 are randomly joined and overlapped. As shown in FIG. 2, the distance between adjacent wall-like graphites is referred to as the wall interval D1.

[0028] The average wall interval, which is the average value of this wall interval D1, is related to the density of the carbon nanowalls CNW1, CNW2, CNW3, and CNW4. That is, the wider the average wall interval, the lower the density of the carbon nanowalls CNW1, CNW2, CNW3, and CNW4. Conversely, the narrower the average wall interval, the higher the density of the carbon nanowalls CNW1, CNW2, CNW3, and CNW4.

[0029] 2-1. Size of the Wall FIG. 3 is a diagram schematically showing a cross section of the carbon nanotube wall CNW1 of the electric double layer capacitor EDLC1 according to the first embodiment. The average height H1 of the graphene sheet GS1 is 0.1 μm or more and 50 μm or less. That is, the average height H1 of the carbon nanotube walls CNW1, CNW2, CNW3, and CNW4 is 0.1 μm or more and 50 μm or less. Preferably, it is 0.5 μm or more and 30 μm. More preferably, it is 1 μm or more and 20 μm.

[0030] The average thickness W1 of the graphene sheet GS1 is on the order of 0.5 nm or more and 100 nm or less. That is, the average thickness W1 of the carbon nanotube walls CNW1, CNW2, CNW3, and CNW4 is 0.5 nm or more and 100 nm or less. Preferably, it is 1 nm or more and 50 nm or less. More preferably, it is 2 nm or more and 30 nm or less.

[0031] The ratio of the height H1 of the carbon nanotube wall CNW1 to the thickness W1 of the carbon nanotube wall CNW1 is 3.3 or more and 40000 or less. Preferably, it is 500 or more and 5000 or less. This numerical range is an example, and numerical values other than the above may also be used.

[0032] 2-2. Wall Spacing The average wall spacing D1 between adjacent carbon nanotube walls CNW1 and CNW1 is, for example, 10 nm or more and 500 nm or less. Preferably, it is 10 nm or more and 100 nm or less. More preferably, it is 10 nm or more and 50 nm or less. These numerical ranges are examples, and numerical values other than the above may also be used. Note that the carbon nanotube walls do not necessarily grow with long walls parallel to each other, but generally grow in a lattice-like pattern (see FIG. 12).

[0033] 2-3. Angle of the Wall FIG. 4 is a diagram schematically showing the inclination of the carbon nanowalls of the electric double layer capacitor EDLC1 according to the first embodiment. FIG. 4 shows a case where the carbon nanowall CNW1 is projected onto the first surface P1a of the positive electrode current collector P1. In FIG. 4, the case of the positive electrode PE is shown, but of course, the same structure holds for the negative electrode NE.

[0034] The projection region PR1 obtained by projecting the carbon nanowall CNW1(a) onto the first surface P1a of the positive electrode current collector P1 does not include the carbon nanowall CNW1(b) other than the carbon nanowall CNW1(a).

[0035] When the tip E1 of the carbon nanowall CNW1(a) is projected onto the first surface P1a of the positive electrode current collector P1, the tip E1 of the carbon nanowall CNW1(a) does not cross the side surface of the adjacent carbon nanowall CNW1(b).

[0036] As shown in FIG. 4, an intermediate region PR2 exists between the projection regions PR1 and PR1. The intermediate region PR2 is a visible region observable by an observer when viewing the positive electrode current collector P1 from the direction of the arrow J1 in FIG. 4. However, a microscope may be required. Here, the direction of the arrow J1 in FIG. 4 is a direction perpendicular to the first surface P1a of the positive electrode current collector P1.

[0037] The average angle θ between the first surface P1a of the positive electrode current collector P1 and the carbon nanowall CNW1 is 80° or more and 90° or less. Here, the average angle θ is the average value of angles of 90° or less. If one angle θ1 of the angle formed by the carbon nanowall and the positive electrode current collector P1 is an acute angle, the other angle θ2 is an obtuse angle. Also, the relationship θ1 + θ2 = 180° holds. Among such angles, the average of the smaller angle θ1 is the average angle θ.

[0038] Since each carbon nanowall is arranged in a state where it grows almost vertically, the upper ends of the carbon nanowalls do not contact each other, and the electrolyte can enter between the carbon nanowalls. Therefore, the entire carbon nanowall can function as an electrode.

[0039] The average angle θ1 is determined by the growth conditions of the carbon nanowalls. Depending on the average angle θ1, it is necessary to set the average height H1 and the average wall spacing D1 of the carbon nanowalls so that the carbon nanowalls do not contact each other at the upper ends of the carbon nanowalls. Depending on the values of these average height H1 and average wall spacing D1, the electrolyte cannot enter the gap between the carbon nanowalls, and only a part of the carbon nanowalls can function as an electrode.

[0040] For example, when the average height H1 of the carbon nanowalls is 5 μm and the average wall spacing D1 is 100 nm, an angle of 88.9° or more is required to avoid contact with adjacent vertical walls. Alternatively, when the average height H1 of the carbon nanowalls is 0.6 μm and the average wall spacing D1 is 100 nm, an angle of 80.4° or more is required to avoid contact with adjacent vertical walls.

[0041] The numerical values showing the structure of these carbon nanowalls CNW1 are shown in Table 1. The same relationship also holds for the other carbon nanowalls CNW2, CNW3, and CNW4.

[0042] [Table 1] Wall height 100 nm or more and 50 μm or less Wall thickness 0.5 nm or more and 100 nm or less Wall spacing 10 nm or more and 500 nm or less Wall angle 80° or more and 90° or less

[0043] 2-4. Surface area of carbon nanowalls Here, the surface areas of carbon nanowalls CNW1, CNW2, CNW3, and CNW4 will be described. For simplicity of understanding, assume that the shape of the carbon nanowall is a grid-like shape.

[0044] FIG. 5 is a view of the carbon nanowall of the electric double layer capacitor EDLC1 of the first embodiment as seen from a direction perpendicular to the surface of the positive electrode current collector P1 or the negative electrode current collector N1. In FIG. 5, it is assumed that the shape of the carbon nanowall is a grid-like shape. In reality, the shape of the carbon nanowall deviates from the grid-like shape.

[0045] Assuming the pitch interval I1 of the carbon nanowall, the area SS1 of a square with a side length of the interval I1 is I1 2 which is the surface area of the carbon material when the carbon material is painted solid on the surface of the positive electrode current collector P1 instead of the carbon nanowall. In FIG. 5, the side area SS2 of the carbon nanowall occupying the square with a side length of the interval I1 as the repeating unit is given by the following formula. SS2 = 8 × (D1 / 2) × H1 = 4 × D1 × H1 H1: Average height of the carbon nanowall D1: Wall interval

[0046] The surface area SS3 of the carbon nanowall in the region of a square with a side length of the interval I1 when the carbon nanowall is present is given by the following formula. SS3 = SS1 + SS2

[0047] Therefore, the ratio SS3 / SS1 indicates the increase rate of the surface area due to the presence or absence of the carbon nanowall. SS3 / SS1 = (4×D1×H1+I1 2 ) / I1 2 ≒ 4×D1×H1 / I1 2 ≒ 4×H1 / D1 Here, H1>>I1 and D1≒I1 are used.

[0048] Thus, the higher the height of the carbon nanowalls and the narrower the spacing between the carbon nanowalls, the larger the surface area of the electric double layer capacitor EDLC1.

[0049] Table 2 shows the relationship between the size and angle of the carbon nanowalls and the increase rate of the surface area. The capacitance of the electric double layer capacitor EDLC1 is considered to be proportional to the surface area of the carbon nanowalls. Therefore, the increase rate of the surface area is equal to the increase rate of the capacitance of the electric double layer capacitor EDLC1.

[0050] As shown in Table 2, if the average angle θ between the first surface P1a of the positive electrode current collector P1 and the carbon nanowalls is 80° or more and 90° or less, the increase rate of the capacitance of the electric double layer capacitor EDLC1 can be increased to 20 times or more. The average angle θ is preferably 83° or more. The average angle θ is more preferably 85° or more. The average angle θ is even more preferably 88° or more. Also, when it is 89° or more, the increase rate of the surface area is about 400 times or more.

[0051] [Table 2] Wall height Wall spacing Wall angle Increase rate of surface area (μm) (nm) (°) (times) 1.0 200 78.5 20 1.0 50 87.1 80 2.0 400 78.5 20 2.0 50 88.6 160 5.0 500 84.3 40 5.0 50 89.4 400 10.0 50 89.7 800 10.0 20 89.9 2000 20.0 50 89.9 1600 20.0 20 89.9 4000 30.0 50 89.9 2400 30.0 20 89.9 6000 50.0 50 89.9 4000 50.0 20 89.9 10000

[0052] When the average angle is small between 2 - 5 Here, the case where the average angle θ between the first surface P1a of the positive electrode current collector P1 and the carbon nanotube wall is small will be described.

[0053] FIG. 6 is a diagram for explaining the case where the average angle θ between the first surface P1a of the positive electrode current collector P1 and the carbon nanotube wall is small. As shown in FIG. 6, the projection region PR3 obtained by projecting the carbon nanotube wall CNW1(c) onto the first surface P1a of the positive electrode current collector P1 includes the carbon nanotube wall CNW1(d) other than the carbon nanotube wall CNW1(c).

[0054] When the tip E1 of the carbon nanotube wall CNW1(c) is projected onto the first surface P1a of the positive electrode current collector P1, the tip E1 of the carbon nanotube wall CNW1(c) crosses the side surface of the adjacent carbon nanotube wall CNW1(d).

[0055] Thus, when the average angle θ is small, the electrolyte hardly enters near the root R1 of the carbon nanotube walls CNW1, CNW2, CNW3, and CNW4. When the electrolyte does not cover the entire carbon nanotube wall, the capacitance is reduced accordingly.

[0056] 3. Manufacturing apparatus A manufacturing apparatus for forming a carbon nanotube wall on the surface of the positive electrode current collector P1 or the negative electrode current collector N1 will be described.

[0057] FIG. 7 is a schematic configuration diagram showing the configuration of a manufacturing apparatus 1 for growing a carbon nanotube wall in the electric double - layer capacitor EDLC1 of the first embodiment. The manufacturing apparatus 1 has a plasma generation chamber 46 and a reaction chamber 10. The plasma generation chamber 46 is for generating plasma inside and also generating radicals to be supplied to the reaction chamber 10. The reaction chamber 10 is for forming the carbon nanotube wall CNW1 by using the radicals generated in the plasma generation chamber 46.

[0058] In addition, the manufacturing apparatus 1 includes a waveguide 47, a quartz window 48, and a slot antenna 49. The waveguide 47 is for introducing the microwave 39. The slot antenna 49 is for introducing the microwave 39 from the quartz window 48 into the plasma generation chamber 46.

[0059] The plasma generation chamber 46 is for generating a surface wave plasma (SWP) by the microwave 39. A radical source inlet 42 is provided in the plasma generation chamber 46. The radical source inlet 42 is for supplying a gas serving as a radical source into the plasma 61 generated in the plasma generation chamber 46.

[0060] A partition wall 44 is provided between the plasma generation chamber 46 and the reaction chamber 10. The partition wall 44 is for partitioning the plasma generation chamber 46 and the reaction chamber 10. The partition wall 44 also serves as an electrode for applying a voltage. A through hole is formed in the partition wall 44. This is for supplying radicals generated in the plasma generation chamber 46 to the reaction chamber 10.

[0061] The reaction chamber 10 is for generating a capacitively coupled plasma (CCP). The reaction chamber 10 is also for forming carbon nanotubes on the positive electrode current collector P1 or the negative electrode current collector N1. The reaction chamber 10 includes a second electrode 24, a heater 25, a raw material inlet 12, and an exhaust port 16. The second electrode 24 is for applying a voltage between the second electrode 24 and the first electrode 22. The heater 25 is for heating the positive electrode current collector P1 or the negative electrode current collector N1 to control the temperature of the positive electrode current collector P1 or the negative electrode current collector N1. The raw material inlet 12 is for supplying a carbon-based gas 32 serving as a raw material for carbon nanotubes. The exhaust port 16 is connected to a vacuum pump or the like. The vacuum pump is for adjusting the pressure inside the reaction chamber 10.

[0062] Here, the partition wall 44 also serves as the first electrode 22 for applying a voltage between it and the second electrode 24. A power supply and a circuit are connected to the first electrode 22, which is for controlling the potential of the first electrode 22 over time. The second electrode 24 is for applying a voltage between it and the first electrode 22. And the second electrode 24 is also a mounting table for mounting the positive electrode current collector P1 or the negative electrode current collector N1. The second electrode 24 is grounded. The distance between the first electrode 22 and the second electrode 24 is about 5 cm. Of course, it is not limited to this value.

[0063] 4. Method for manufacturing an electric double layer capacitor 4-1. Amorphous carbon layer forming step First, place the positive electrode current collector P1 or the negative electrode current collector N1 before forming the carbon nanotube wall CNW1 inside the manufacturing apparatus 1. Next, introduce the microwave 39 into the waveguide 47. The microwave 39 is introduced from the quartz window 48 into the plasma generation chamber 46 by the slot antenna 49. Thereby, a high-density plasma 60 is generated.

[0064] Then, this high-density plasma 60 diffuses inside the plasma generation chamber 46 to become plasma 61. This plasma 61 contains ions of the radical source supplied from the radical source inlet 42. Hydrogen is used as the radical source. Or it may be oxygen, nitrogen, or other gases. Most of the ions in the plasma 61 collide with the partition wall 44 and are neutralized to become radicals. The radicals 38 pass through the through holes of the partition wall 44 and enter the reaction chamber 10.

[0065] Inside the reaction chamber 10, in addition to the radicals 38, the carbon-based gas 32 is supplied from the raw material inlet 12. The carbon-based gas 32 is, for example, CH4 or C2F6. Of course, it may be other substances. And a voltage is applied between the first electrode 22 and the second electrode 24. Thereby, plasma 34 is generated inside the reaction chamber 10.

[0066] In the atmosphere of the plasma 34, the carbon-based gas 32 as a raw material and the radicals 38 are mixed. Then, an amorphous carbon layer AC1 grows on the surface of the positive current collector P1 or the negative current collector N1 in the atmosphere of this plasma 34.

[0067] In this way, the carbon-based gas made into plasma inside the manufacturing apparatus 1 is supplied to the current collector, and the amorphous carbon layer AC1 is formed on the current collector.

[0068] The pressure inside the reaction chamber 10 is within the range of 5 to 2000 mTorr (0.65 Pa to 267 Pa). Also, the temperature of the positive current collector P1 or the negative current collector N1 is within the range of 100 to 800°C. Of course, these are examples and are not limited to these numerical ranges.

[0069] 4-2. Carbon Nanowall Growth Process Subsequently, inside the manufacturing apparatus 1, a carbon nanowall CNW1 is grown on the amorphous carbon layer AC1. Similar to the case of growing the amorphous carbon layer AC1, plasma 61 is generated. Hydrogen gas is used as the radical source of the radicals 38, and for example, CH4 or C2F6 is used as the carbon-based gas 32.

[0070] In this way, the carbon-based gas made into plasma inside the manufacturing apparatus 1 is supplied to the current collector, and a carbon nanowall is grown on the amorphous carbon layer AC1.

[0071] The pressure inside the reaction chamber 10 is within the range of 5 to 2000 mTorr (0.65 Pa to 267 Pa). Also, the temperature of the positive current collector P1 or the negative current collector N1 is within the range of 100 to 800°C. Of course, these are examples and are not limited to these numerical ranges.

[0072] 4-3. Cleaning Process After the growth of the carbon nanowall CNW1 has progressed to a certain extent, the positive current collector P1 or the negative current collector N1 is taken out. The height H1 of the carbon nanowall CNW1 at this time is, for example, 1000 nm.

[0073] Next, the inside of the manufacturing apparatus 1 is cleaned. The carbon material is scraped off from the inner wall surface. Alternatively, the carbon material on the inner wall surface is removed by hydrogen plasma or the like. In this way, in this step, the growth step is stopped and the inside of the manufacturing apparatus 1 is cleaned.

[0074] Then, the above-described growth step and cleaning step are repeated. Thereby, the carbon nanotube wall CNW1 having a sufficient height H1 is obtained. Similarly, the carbon nanotube wall CNW2 is formed by turning the positive electrode current collector P1 over. Even when the positive electrode current collector P1 is disposed with the carbon nanotube wall CNW1 on the lower side, no problem occurs in the carbon nanotube wall CNW1. Also, the negative electrode NE is manufactured in the same manner as the positive electrode PE.

[0075] 4-4. Electrolyte injection step Next, the positive electrode PE and the negative electrode NE are alternately disposed inside the container V1 with the separator Sp1 therebetween. At this time, the second surface P1b of the positive electrode current collector P1 and the third surface N1a of the negative electrode current collector N1 are made to face each other. Also, the first surface P1a of the positive electrode current collector P1 and the fourth surface N1b of the negative electrode current collector N1 are made to face each other. Then, the electrolyte ES1 is injected into the container V1. Thereafter, the opening of the container V1 may be sealed.

[0076] 5. Effects of the first embodiment The electric double layer capacitor EDLC1 of the first embodiment has a positive electrode PE and a negative electrode NE. The positive electrode PE or the negative electrode NE has an amorphous carbon layer AC1 on the positive electrode current collector P1 or the negative electrode current collector N1, and carbon nanotube walls CNW1, CNW2, CNW3, CNW4 on the amorphous carbon layer AC1. The positive electrode current collector P1 and the negative electrode current collector N1 are metals. The amorphous carbon layer AC1 and the carbon nanotube walls CNW1, CNW2, CNW3, CNW4 are conductive materials.

[0077] Since the carbon nanowalls CNW1, CNW2, CNW3, and CNW4 are composed of the graphene sheet GS1, they have high conductivity. Compared with the graphene sheet GS1, the conductivity of the amorphous carbon layer AC1 is slightly lower. However, since the film thickness of the amorphous carbon layer AC1 is sufficiently thin, the amorphous carbon layer AC1 hardly has an adverse effect on the electric double layer capacitor EDLC1.

[0078] The carbon nanowalls CNW1, CNW2, CNW3, and CNW4 have a structure in which wall-like graphene sheets GS1 are densely packed. Therefore, the surface area of the carbon nanowalls CNW1, CNW2, CNW3, and CNW4 is much larger than that of conventional carbon materials such as activated carbon. Accordingly, the capacitance and energy density of the electric double layer capacitor EDLC1 of the first embodiment are much higher than those of conventional electric double layer capacitors.

[0079] The manufacturing method of the electric double layer capacitor EDLC1 of the first embodiment includes a growth step of growing carbon nanowalls and a cleaning step of stopping the growth and cleaning the inside of the manufacturing apparatus. In order to carry out the cleaning step, suitable plasma can be generated inside the manufacturing apparatus 1.

[0080] 6. Modification 6-1. Stacking of Stacks FIG. 8 is a diagram (part 1) showing a schematic configuration of an electric double layer capacitor EDLC2 in a modification of the first embodiment. The electric double layer capacitor EDLC2 has only a single stack. The stacks are not laminated. This case may also be acceptable.

[0081] 6-2. Conductivity In addition, by supporting metal fine particles on the carbon nanowalls CNW1, CNW2, CNW3, and CNW4, the tip E1 of the graphene sheet can also be made conductive. Further, using the manufacturing apparatus 1, radicals may be implanted into the formed carbon nanowalls CNW1, CNW2, CNW3, and CNW4. Thereby, the carbon nanowalls CNW1, CNW2, CNW3, and CNW4 can also be made into semiconductors. Then, by introducing nitrogen into the inside of the reaction chamber 10 and generating plasma in a nitrogen atmosphere, the carbon nanowalls CNW1, CNW2, CNW3, and CNW4 can also be made into n-type semiconductors.

[0082] 6-3. One side In the first embodiment, the carbon nanowalls are formed on both surfaces of the current collector. However, as shown in FIG. 9, the carbon nanowalls may be formed only on one side of the current collector. FIG. 9 is a diagram (part 2) showing a schematic configuration of the electric double layer capacitor EDLC3 in a modified example of the first embodiment.

[0083] 6-4. Combination The above-described modified examples may be freely combined.

[0084] (Second Embodiment) The second embodiment will be described.

[0085] 1. Lithium ion secondary battery The lithium ion secondary battery of the second embodiment has a positive electrode and a negative electrode. The negative electrode of the lithium ion secondary battery has the same structure as the negative electrode NE of the electric double layer capacitor EDLC1 of the first embodiment.

[0086] Figure 10 is a diagram showing the schematic configuration of the lithium-ion secondary battery LiB1 of the second embodiment. As shown in Figure 10, the positive electrode PE of the lithium-ion secondary battery LiB1 has a positive electrode active material layer P2 on the positive electrode plate P1. The positive electrode active material layer P2 contains a positive electrode active material, a conductive assistant, and a binder. The positive electrode active material layer P2 may contain a thickener or the like. Examples of the positive electrode active material include lithium cobaltate, lithium manganate, lithium nickelate, and a ternary system. Examples of the conductive assistant include carbon black. Examples of the binder include SBR.

[0087] 2. Effects of the Second Embodiment The lithium-ion secondary battery of the second embodiment has a negative electrode with a large reaction cross-sectional area. Therefore, the lithium-ion secondary battery can pass a large current.

[0088] 3. Modifications In the second embodiment, the carbon nanowalls are formed on both sides of the current collector. However, as shown in Figure 11, the carbon nanowalls may be formed on only one side of the current collector. Figure 11 is a diagram showing the schematic configuration of the lithium-ion secondary battery LiB2 in a modification of the second embodiment.

Examples

[0089] (Experiment) 1. Carbon Nanowalls on the Current Collector 1-1. Manufacturing Method Using the manufacturing apparatus 1, carbon nanowalls were grown on a titanium metal plate.

[0090] Figure 12 is a micrograph of the carbon nanowalls viewed from a direction perpendicular to the plate surface of the metal plate. As shown in Figure 12, the carbon nanowalls are growing randomly. And the wall-like walls are growing and merging with each other. However, the intervals are somewhat uniform.

[0091] Figure 13 is a micrograph of carbon nanotubes showing a cross-section perpendicular to the surface of the metal plate. As shown in Figure 13, the carbon nanotubes are formed almost perpendicular to the substrate.

[0092] 2. Discharge characteristics 2-1. Al positive electrode + EDLC electrolyte A positive electrode with carbon nanotubes formed on Al and a negative electrode with carbon nanotubes formed on Cu were used. As the electrolyte, one commonly used in electric double layer capacitors was used.

[0093] Figure 14 is a graph showing the charge-discharge characteristics of an electric double layer capacitor using Al with carbon nanotubes formed as the positive electrode. The horizontal axis of Figure 14 is the measurement time (seconds). The vertical axis of Figure 14 is the voltage (V). As shown in Figure 14, the charge and discharge are completed in about 2 seconds. That is, the charging time and discharging time of this electric double layer capacitor are very short.

[0094] 2-2. Ti positive electrode + EDLC electrolyte A positive electrode with carbon nanotubes formed on Ti and a negative electrode with carbon nanotubes formed on Cu were used. As the electrolyte, one commonly used in electric double layer capacitors was used.

[0095] Figure 15 is a graph showing the charge-discharge characteristics of an electric double layer capacitor using Ti with carbon nanotubes formed as the positive electrode. The horizontal axis of Figure 15 is the measurement time (seconds). The vertical axis of Figure 15 is the voltage (V). As shown in Figure 15, the charge and discharge are completed in about 2 seconds. That is, the charging time and discharging time of this electric double layer capacitor are very short.

[0096] 2-3. Al positive electrode + LiB electrolyte A positive electrode with carbon nanotubes formed on Al and a negative electrode with carbon nanotubes formed on Cu were used. As the electrolyte, one commonly used in lithium ion secondary batteries was used.

[0097] FIG. 16 is a graph showing the charge and discharge characteristics of a lithium ion capacitor using Al on which carbon nanowalls are formed as the positive electrode. The horizontal axis of FIG. 16 is the measurement time (seconds). The vertical axis of FIG. 16 is the voltage (V). As shown in FIG. 16, the charge and discharge are completed in about 2 seconds. That is, the charging time and the discharging time of this electric double layer capacitor are very short.

[0098] 3. Capacitance 3-1. Electric double layer capacitor The capacitance of the electric double layer capacitor using Al on which carbon nanowalls are formed as the positive electrode and Cu on which carbon nanowalls are formed as the negative electrode was about 18 F / g. On the other hand, the capacitance of the electric double layer capacitor using Ti instead of Al was about 22 F / g.

[0099] 3-2. Lithium ion secondary battery A lithium ion secondary battery was fabricated using Li metal as the positive electrode and Cu on which carbon nanowalls are formed as the negative electrode. The electrolyte is the one used in lithium ion secondary batteries. The capacitance of this lithium ion secondary battery was about 3300 F / g.

[0100] 4. Charge and discharge capacity A lithium ion secondary battery was fabricated using Li metal as the positive electrode and Cu on which carbon nanowalls are formed as the negative electrode. The electrolyte is the one used in lithium ion secondary batteries.

[0101] FIG. 17 is a graph showing the relationship between the charge and discharge capacity and the voltage of the lithium ion secondary battery. The horizontal axis of FIG. 17 is the charge and discharge capacity. The vertical axis of FIG. 17 is the voltage. In FIG. 17, the charge and discharge after the second cycle are plotted. As shown in FIG. 17, the discharge voltage decreases as the discharge proceeds. The charge voltage increases as the charge proceeds.

[0102] FIG. 18 is a graph showing the relationship between the capacity and voltage of a lithium-ion secondary battery using carbon nanowalls with a height of 4 μm as the negative electrode. The horizontal axis of FIG. 18 is the charge-discharge capacity. The vertical axis of FIG. 18 is the voltage. The charge current or discharge current was 0.5 mA. As shown in FIG. 18, the discharge capacity of the lithium-ion secondary battery was 9.0 mAh.

[0103] (Appendix) The power storage device in the first aspect includes a negative electrode current collector and carbon nanowalls on the negative electrode current collector. The projected area of the carbon nanowalls projected onto the surface of the negative electrode current collector does not include carbon nanowalls other than the carbon nanowalls.

[0104] The power storage device in the second aspect includes a negative electrode current collector, carbon nanowalls on the negative electrode current collector, and an amorphous carbon layer between the negative electrode current collector and the carbon nanowalls. The projected area of the carbon nanowalls projected onto the surface of the negative electrode current collector does not include carbon nanowalls other than the carbon nanowalls.

[0105] In the power storage device in the third aspect, the film thickness of the amorphous carbon layer is 10 nm or more and 300 nm or less.

[0106] In the power storage device in the fourth aspect, the average angle between the positive electrode current collector or the negative electrode current collector and the carbon nanowalls is 80° or more and 90° or less.

[0107] In the power storage device in the fifth aspect, the average height of the carbon nanowalls is 0.1 μm or more and 50 μm or less. The average thickness of the carbon nanowalls is 0.5 nm or more and 100 nm or less. The average interval of the carbon nanowalls is 10 nm or more and 500 nm or less.

[0108] In the power storage device in the sixth aspect, the negative electrode current collector is Cu.

[0109] In the power storage device according to the seventh aspect, the average wall interval between two adjacent carbon nanotubes is 10 nm or more and 500 nm or less.

[0110] The power storage device according to the eighth aspect includes a first carbon nanotube on a first surface of a positive electrode current collector, a second carbon nanotube on a second surface of the positive electrode current collector, a third carbon nanotube on a third surface of a negative electrode current collector, and a fourth carbon nanotube on a fourth surface of the negative electrode current collector. The second surface of the positive electrode current collector and the third surface of the negative electrode current collector face each other.

[0111] The power storage device according to the ninth aspect includes a positive electrode current collector and a carbon nanotube on the positive electrode current collector. The projected area of the carbon nanotube projected onto the surface of the positive electrode current collector does not include carbon nanotubes other than that carbon nanotube.

[0112] The method for manufacturing an electrode for a power storage device according to the tenth aspect includes an amorphous carbon layer forming step of supplying a carbon-based gas plasmaized inside a manufacturing apparatus to a current collector to form an amorphous carbon layer on the current collector, and a growth step of supplying a carbon-based gas plasmaized inside the manufacturing apparatus to the current collector to grow carbon nanotubes on the amorphous carbon layer.

[0113] The method for manufacturing an electrode for a power storage device according to the eleventh aspect includes a growth step of plasmaizing a carbon-based gas inside a manufacturing apparatus to grow carbon nanotubes on a current collector, and a cleaning step of stopping the growth step and cleaning the inside of the manufacturing apparatus.

[0114] In the method for manufacturing an electrode for a power storage device according to the twelfth aspect, the growth step and the cleaning step are repeatedly performed.

Description of Reference Numerals

[0115] 1... Manufacturing apparatus EDLC1... Electric double layer capacitor PE... Positive electrode P1... Positive electrode current collector NE…Negative electrode N1…Negative electrode current collector Sp1…Separator ES1…Electrolyte CNW1…First carbon nanotube wall CNW2…Second carbon nanotube wall CNW3…Third carbon nanotube wall CNW4…Fourth carbon nanotube wall E1…Tip R1…Base GS1…Graphene sheet

Claims

1. A current collector, a carbon nanotube wall on the current collector, and an amorphous carbon layer between the current collector and the carbon nanotube wall, wherein a projection area where the carbon nanotube wall is projected onto the surface of the current collector does not include carbon nanotube walls other than the carbon nanotube wall, an average angle between the current collector and the carbon nanotube wall is 89° or more and 90° or less, a rate of increase in surface area due to the presence or absence of the carbon nanotube wall is 4×H1 / D1, where H1 is an average height of the carbon nanotube wall and D1 is an average interval between the carbon nanotube walls, and H1 and D1 are set such that the rate of increase in surface area is 400 or more, A power storage device characterized by the above.

2. In the power storage device according to Claim 1, a film thickness of the amorphous carbon layer is 10 nm or more and 300 nm or less. A power storage device including this.

3. In the power storage device according to Claim 1 or Claim 2, the current collector is a positive electrode current collector and a negative electrode current collector, a first carbon nanotube wall on a first surface of the positive electrode current collector, a second carbon nanotube wall on a second surface of the positive electrode current collector, a third carbon nanotube wall on a third surface of the negative electrode current collector, a fourth carbon nanotube wall on a fourth surface of the negative electrode current collector, and has the second surface of the positive electrode current collector and the third surface of the negative electrode current collector face each other. A power storage device including this.

4. In the power storage device according to Claim 3, the negative electrode current collector is Cu. A power storage device including this.

5. In the power storage device according to any one of Claims 1 to 4, an average height of the carbon nanotube wall is 1 μm or more and 20 μm or less, an average thickness of the carbon nanotube wall is 2 nm or more and 30 nm or less, an average interval between the carbon nanotube walls is 10 nm or more and 50 nm or less. A power storage device including this.

6. In the power storage device according to any one of Claims 1 to 5, a ratio of the average height of the carbon nanotube wall to the average thickness of the carbon nanotube wall is 500 to 5000. A power storage device including this.

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