Electric double layer capacitor

Abstract

To firmly form 3-D graphene on a Cu substrate surface of a positive electrode and a negative electrode in an electric double layer capacitor.SOLUTION: Hydrogen radicals are introduced into a plasma atmosphere to remove CuO layers formed on surfaces of Cu substrates of a positive electrode and a negative electrode in an electric double layer capacitor, the surfaces of the Cu substrates are sputtered, and hydrogen radicals and CH4 gas are further introduced to form 3-D graphene oriented in a vertical direction on the surfaces of the Cu substrates. As a result, the 3-D graphene grows perpendicularly to the surface of the copper substrate, so that the tip thereof coincides with the flow direction of lithium ions, and an electric double layer capacitor capable of storing a large amount of ions and electrons can be provided.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electric double layer capacitor in which 3-D graphene oriented in the vertical direction is formed on the surface of a Cu substrate. [Background technology]

[0002] Chargeable and dischargeable energy storage devices include primary batteries, secondary batteries, electric double layer capacitors (EDLCs), capacitors, etc. The subject of this research is electric double layer capacitors (EDLCs), which are electronic components that have the ability to store electric charge.

[0003] Because electric double-layer capacitors store electrical energy as static electricity, they can be charged and discharged rapidly, much faster than batteries, which require chemical reactions. Capacitors also have a long cycle life, with little degradation even after tens of thousands of charge-discharge cycles. Furthermore, electric double-layer capacitors have extremely high power density (the amount of energy that can be supplied per unit time), allowing them to supply large currents in a short period of time. Taking advantage of their fast charging and high output, they are used as auxiliary power sources for electric vehicles and for quickly storing energy from solar and wind power plants. They are also used in systems requiring short-term power supply (e.g., UPS systems that compensate for temporary power shortages) and for ensuring a stable supply of power in industrial equipment that requires instantaneous high power. Because electric double-layer capacitors have characteristics different from batteries, they are highly effective in certain applications, and future technological advances are expected to lead to even more applications. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 163464 Summary of the Invention [Problem to be solved by the invention]

[0005] Activated carbon and graphite are often used as electrode materials for electric double-layer capacitors, but they require the use of conductive adhesives, which can lead to the adhesion of adhesives, impurities, and dust to the surfaces of the activated carbon and graphite. Furthermore, during charging and discharging, lithium ions are inserted into or extracted from the crystal lattice (or between layers) of the active material, but the adhesives of activated carbon and graphite hinder this to some extent. Furthermore, because activated carbon and graphite are arranged in a disordered manner on the surface of the Cu substrate, it becomes difficult for lithium ions to fully insert into or extract from the crystal lattice (or between layers). This raises concerns about a shortened lifespan for electric double-layer capacitors.

[0006] To address this issue, a nanostructured material called 3-D graphene has been investigated as a potential electrode material for electric double layer capacitors as an alternative to activated carbon and graphite. Because 3-D graphene has high electrical conductivity, surface area, and chemical stability, it may offer superior performance compared to conventional activated carbon and graphite. A synthesis technique for robust 3-D graphene material made from pure carbon has been developed.

[0007] This three-dimensional graphene, or 3-D graphene, is a wall-like material made up of cyclic graphene sheets with six-membered rings composed of carbon, and is dense, heat-resistant, and has excellent electrical conductivity and chemical stability.

[0008] Meanwhile, it is important to select appropriate metal substrates for the positive and negative electrodes of electric double layer capacitors depending on the specific application and requirements. Cu substrates are used to support the conduction of electrons and are widely used for transmitting electrical signals and conducting heat.

[0009] Therefore, if 3-D graphene can be grown firmly on the surface of a Cu substrate without using an adhesive, the 3-D graphene will grow perpendicular to the surface of the copper substrate, with its tips aligned with the direction of lithium ion flow, making it an ideal material for electric double-layer capacitors that can store large amounts of ions and electrons.

[0010] To solve this problem, the inventors of the present invention conducted extensive research and discovered that by treating the surface of a Cu substrate with hydrogen radicals and plasma, and then introducing CH4 gas, 3-D graphene was formed that was firmly oriented vertically on the Cu substrate surface. [Means for solving the problem]

[0011] The present invention proposes an electric double layer capacitor in which an electrolyte and a separator are provided between the positive and negative electrodes, and in which 3-D graphene is formed that is oriented perpendicularly to the surfaces of the Cu substrates of the positive and negative electrodes.

[0012] Furthermore, the present invention proposes an electric double layer capacitor in which an electrolyte and a separator are provided between the positive and negative electrodes, in which the positive and negative Cu substrates are placed in a plasma atmosphere, hydrogen radicals are introduced to remove the CuO layer formed on the surfaces, the Cu substrate surface is sputtered, and hydrogen radicals and CH4 gas are further introduced to form 3-D graphene oriented vertically on the Cu substrate surface.

[0013] For the negative electrode and positive electrode of the present invention, a plasma CVD apparatus can be used to form 3-D graphene oriented perpendicular to the surface of the Cu substrate.

[0014] CH4 and H2 radicals are supplied into a plasma CVD apparatus, and 3-D graphene oriented perpendicular to the Cu substrate surface is formed in a carbon atmosphere at a temperature of 300 to 1000°C, preferably 400 to 800°C. [Effects of the Invention]

[0015] The 3-D graphene used in the anode and cathode of the present invention is a carbon-based material created using nanotechnology, which has a very large surface area and a structure suitable for storing electrons, making the electric double layer capacitor of the present invention widely usable as a high-performance, long-life power storage device. [Brief explanation of the drawings]

[0016] [Figure 1] Image of an electric double layer capacitor [Figure 2] Illustration of sputtering on a Cu substrate in a hydrogen radical and plasma atmosphere [Figure 3] SEM image of Cu substrate after sputtering in hydrogen radical and plasma atmosphere [Figure 4] Image of CuC layer formed on Cu substrate in hydrogen radical, CH4 gas and plasma atmosphere [Figure 5] SEM image of CuC layer formed on Cu substrate in hydrogen radical, CH4 gas and plasma atmosphere [Figure 6] Diagram of plasma CVD equipment [Figure 7] Process diagram of 3-D graphene synthesis on Cu substrate [Figure 8] SEM images of 3-D graphene synthesized on a Cu substrate: (a) overhead view; (b) cross-section view [Figure 9] Raman spectroscopy of vertically oriented 3-D graphene DETAILED DESCRIPTION OF THE INVENTION

[0017] In the electric double layer capacitor described above, in which an electrolyte and a separator are provided between the positive and negative electrodes, the positive and negative Cu substrates are placed in a plasma atmosphere, hydrogen radicals are introduced to remove the CuO layer formed on their surfaces, the Cu substrate surface is sputtered, and hydrogen radicals and CH4 gas are further introduced to form 3-D graphene oriented vertically on the Cu substrate surface. [Example]

[0018] The present invention will be described below with reference to illustrative examples. Figure 1 is a schematic diagram of the structure of an electric double layer capacitor using the method of the present invention. The electric double layer capacitor mainly consists of a negative electrode (1) and a positive electrode (2), on which 3-D graphene (7) is synthesized. Between the electrodes is an electrolyte (8) and a separator (6) that separates them. The separator (6) separates the electrolyte (8) from the electrodes (1, 2) to prevent short circuits. [Example]

[0019] (1) A process in which the positive and negative Cu substrates are placed in a plasma atmosphere, hydrogen radicals are introduced to remove the CuO layer formed on the surface, and the Cu substrate surface is sputtered. Figure 2 is an illustration of the Cu substrate surface (1, 2) after hydrogen radicals (4) are introduced into the Cu substrate in a plasma atmosphere. Figure 2 shows numerous Cu particles (5) appearing on the Cu substrate surface. A thin CuO layer (3) is present on the Cu substrate surface. The introduction of hydrogen radicals (4) and irradiation with Plasma-1 (10) removes the CuO layer (3), exposing some Cu particles (5) to the Cu substrate (1, 2), while other Cu particles (5) are knocked out of the Cu substrate (1, 2) and reattached to the surface. In other words, the collision of ions and atoms with the Cu substrate (1, 2) surface sputters oxygen atoms and other impurity atoms adsorbed on the Cu substrate (1, 2), effectively purifying the surface. This refers to the chemical reaction represented by the following equation: CuO + H2 → Cu + H2O

[0020] Figure 3 shows an SEM image of the surface of a Cu substrate (1, 2) after hydrogen radicals (4) were introduced onto the Cu substrate in a plasma atmosphere. Numerous Cu particles (5) are exposed or deposited on the surface of the Cu substrate.

[0021] (2) Further, hydrogen radicals and CH4 gas are introduced to form 3-D graphene oriented vertically on the Cu substrate surface. The Cu substrates (1, 2) are placed in the reaction chamber of a plasma CVD apparatus under vacuum, and a mixed gas of CH4 (11) and H2 radicals (4) is injected.

[0022] The degree of vacuum is approximately 2000 Pa to 10 Pa. A DC voltage of 200 V is applied, causing a glow discharge in the vacuum, and the potential difference creates a strong electric field gradient on the surface of the Cu substrate. Due to this strong electric field gradient, electrons emitted from the cathode are rapidly accelerated and move toward the anode. As shown in the molecular formula below, H2 and CH4 gas molecules and atoms collide with each other, causing decomposition and plasma generation.

[0023]

number

[0024] In this reaction process, large amounts of hydrogen, carbon, and methane ions and H γ , C γ Active atoms of C are generated. Under the action of the electric field, these ions and atoms collide with the surface of the Cu substrate, which increases the surface temperature of the Cu substrate. This temperature increase promotes the diffusion rate of C atoms and increases the rate of "carburization" on the surface of the Cu substrate.

[0025] When ions and atoms bombard the surface of a Cu substrate, ion implantation and particle formation increase the surface hardness of the Cu substrate. The Cu atoms scattered by the impact bond with C atoms to form CuC(9), creating a highly C-rich layer on the surface of the Cu substrate. During the thermal diffusion process, the C in this surface layer continues to diffuse into the interior of the Cu substrate, forming a uniform CuC layer(9). This CuC layer(9) is the starting layer for the growth of graphene sheets that constitute 3D graphene(7). The thickness of the CuC layer (9) is about 300 nm.

[0026] Figure 5 shows an SEM image of the surface of a CuC particle layer (9) after introducing CH4 gas (11) into a plasma atmosphere on Cu substrates (1, 2). The CuC layer (9) is deposited on the Cu substrates (1, 2) as a growth base for 3-D graphene (7). [Example]

[0027] For the negative and positive electrodes of the present invention, a plasma CVD apparatus is used to form 3-D graphene oriented perpendicular to the surface of a Cu substrate. This will be explained with reference to FIG. 6, which is a schematic diagram of a plasma CVD apparatus for growing 3-D graphene (7) in an electric double layer capacitor. The plasma CVD apparatus has a plasma generation chamber (18) and a reaction chamber (12). The plasma generation chamber (18) generates plasma therein and also generates hydrogen radicals to be supplied to the reaction chamber (12). The reaction chamber (12) is used to form 3-D graphene (7) using the hydrogen radicals generated in the plasma generation chamber (18).

[0028] The plasma CVD apparatus also includes a microwave chamber (19), a quartz window (16), and a slot antenna (20). The microwave chamber (19) is for generating microwaves (17). The slot antenna (20) is for introducing the microwaves (17) through the quartz window (16) into the plasma generation chamber (18).

[0029] The plasma generation chamber (18) is for generating plasma by microwaves (17). The plasma generation chamber (18) is provided with a hydrogen radical supply port (4), through which a radical source gas is supplied into the plasma-1 (10) generated in the plasma generation chamber (18).

[0030] A partition plate (21) is provided between the plasma generation chamber (18) and the reaction chamber (12). The partition plate (21) separates the plasma generation chamber (18) from the reaction chamber (12). A through-hole (22) is formed in the partition plate (21) and is used to supply radicals generated in the plasma generation chamber (18) to the reaction chamber (12).

[0031] The reaction chamber (12) is used to generate plasma. The reaction chamber (12) is also used to form Cu microparticles (5) on the Cu substrate. The reaction chamber (12) is provided with an electrode-1 (23), an electrode-2 (24), a heater (25), a supply port for CH4 gas (11), and an exhaust port for a vacuum pump (15). The electrode-2 (24) is used to apply a voltage between the electrode-2 (24) and the electrode-1 (23). The heater (25) is used to heat the Cu substrates (1, 2) to control the temperature. The exhaust port is connected to the vacuum pump (15), and the vacuum pump (15) is used to adjust the pressure inside the reaction chamber (12).

[0032] The partition plate (21) also serves as electrode-1 (23) for applying a voltage between it and electrode-2 (24). A power supply and a circuit are connected to electrode-1 (23) for temporally controlling the potential of electrode-1 (23). Electrode-2 (24) is used to apply a voltage between it and electrode-1 (23). Figure 6 is a schematic diagram of a plasma CVD apparatus for growing 3-D graphene (7) in an electric double layer capacitor. The plasma CVD apparatus has a plasma generation chamber (18) and a reaction chamber (12). The plasma generation chamber (18) generates plasma therein and also generates hydrogen radicals to be supplied to the reaction chamber (12). The reaction chamber (12) uses the hydrogen radicals generated in the plasma generation chamber (18) to form 3-D graphene (7).

[0033] The plasma CVD apparatus also includes a microwave chamber (19), a quartz window (16), and a slot antenna (20). The microwave chamber (19) is for generating microwaves (17). The slot antenna (20) is for introducing the microwaves (17) through the quartz window (16) into the plasma generation chamber (18).

[0034] The plasma generation chamber (18) is for generating plasma by microwaves (17). The plasma generation chamber (18) is provided with a hydrogen radical supply port (4), through which a radical source gas is supplied into the plasma-1 (10) generated in the plasma generation chamber (18).

[0035] A partition plate (21) is provided between the plasma generation chamber (18) and the reaction chamber (12). The partition plate (21) separates the plasma generation chamber (18) from the reaction chamber (12). A through-hole (22) is formed in the partition plate (21) and is used to supply radicals generated in the plasma generation chamber (18) to the reaction chamber (12).

[0036] The reaction chamber (12) is used to generate plasma. The reaction chamber (12) is also used to form Cu microparticles (5) on the Cu substrate. The reaction chamber (12) is provided with an electrode-1 (23), an electrode-2 (24), a heater (25), a supply port for CH4 gas (11), and an exhaust port for a vacuum pump (15). The electrode-2 (24) is used to apply a voltage between the electrode-2 (24) and the electrode-1 (23). The heater (25) is used to heat the Cu substrates (1, 2) to control the temperature. The exhaust port is connected to the vacuum pump (15), and the vacuum pump (15) is used to adjust the pressure inside the reaction chamber (12).

[0037] The partition plate (21) also serves as electrode-1 (23) for applying a voltage between it and electrode-2 (24). A power supply and a circuit are connected to electrode-1 (23) for temporally controlling the potential of electrode-1 (23). Electrode-2 (24) is used to apply a voltage between it and electrode-1 (23). [Example]

[0038] Method for Manufacturing Positive and Negative Electrodes The process for forming Cu fine particles will be described with reference to FIG. <The process shown in Figure 7-a> First, a Cu substrate is placed inside the plasma CVD apparatus. Next, microwaves (17) are introduced into the microwave generation chamber (19). The microwaves (17) are then introduced into the plasma generation chamber (18) through the quartz window (16) via the slot antenna (20). This generates high-density plasma (27).

[0039] <The process shown in Figure 7-b> This high-density plasma (27) diffuses inside the plasma generation chamber (18) to become Plasma-1 (10). This Plasma-1 (10) contains ions of the radical source supplied from the inlet of the radical source (4). A gas containing hydrogen gas is used as the radical source. Most of the ions in Plasma-1 (10) collide with the partition plate (21). The radicals (4) pass through the through holes (22) in the partition plate (21) and enter the reaction chamber (12). A voltage is applied between Electrode-1 (23) and Electrode-2 (24). This generates Plasma-2 (26) inside the reaction chamber (12).

[0040] <The process shown in Figure 7-c> Radicals (4) are present in the atmosphere of Plasma-2 (26), so Cu particles are formed on the Cu substrates (1, 2) in this atmosphere of Plasma-2 (26). During this process, the CuO layer (3) adhering to the surface of the Cu substrates (1, 2) is removed, and some of the Cu particles (5) are scattered and re-deposited on the surface of the Cu substrates (1, 2). Hydrogen gas is converted into plasma and supplied to the Cu substrates (1, 2), forming a plurality of Cu particles (5) made of the same material as Cu on the Cu substrate surface. <The process shown in Figure 7-d> By introducing CH4 gas (11), carbon atoms decomposed from the CH4 gas (11) react with the formed Cu particles (5), and the carbon atoms penetrate into the Cu particles to form a CuC layer, i.e., Cu + C → CuC. <The process shown in Figure 7-e> During the thermal diffusion process, the carbon in the CuC layer continues to diffuse into the Cu substrate, thereby forming a uniform CuC layer (9), meaning that the entire surface of the Cu substrate (1, 2) plays the role of a catalyst. <The process shown in Figure 7-f> The formation of CuC layers (9) with C atoms leads to a drop in the melting point. Further increasing the carbon concentration leads to a supersaturation of the C concentration, and graphite precipitates to form 3-D graphene. While graphene sheets are known to form on the flat surfaces of Fe, Co, and Ni, 3-D graphene-like materials can also be produced.

[0041] The pressure inside the reaction chamber (12) is in the range of 5 to 2000 mTorr (0.65 Pa to 267 Pa). The temperature of the Cu substrates (1, 2) is in the range of room temperature to 500° C. These are merely examples, and the present invention is not limited to these numerical ranges.

[0042] Figure 8(a) shows a typical SEM image of the synthesized high-density, vertically aligned 3-D graphene. This material has a unique structure in which graphene sheets (sheet-like graphite) grow perpendicular to the Cu substrate. The thickness of the nano-sized graphene sheets is observed to be 200-400 nm.

[0043] The cross-sectional view in Figure 8(b) shows that the height of the 3-D graphene is 0.85 μm, and that it was synthesized in 10 minutes. CuC particles of approximately 200 to 400 nm are visible at the base of the 3-D graphene (CuC particles). It is clear that the 3-D graphene grown from the base (CuC particles) is very strongly bonded to the base and does not easily peel off from the Cu substrate.

[0044] Figure 9 shows the characteristic peak of graphene, the G band, which originates from the in-plane motion of carbon atoms and is located at 1580 cm -1 The D band is known to be a band caused by structural disorder and defects. -1 The presence of this peak at 2700 cm indicates defects in the graphene sample. The 2D band exhibits a strong frequency dependence on the excitation laser due to a double resonance process that relates the phonon wave vector to the electronic band structure. This feature appears at approximately 2700 cm for 514 nm laser excitation. -1 which can also be used to determine the number of graphene layers. [Industrial Applicability]

[0045] The electric double layer capacitor according to the present invention can be widely used as a power storage device, contributing to improved performance with high performance and long life. [Explanation of symbols]

[0046] 1………………Positive electrode Cu substrate 2. Negative electrode Cu substrate 3………………CuO layer 4...Hydrogen radical 5………………Cu fine particles 6………………Separator 7. 3-D graphene synthesized on the anode and cathode 8……………… Electrolyte 9………………Cu C fine particle layer 10………………Plasma-1 11...CH4 gas 12...Reaction chamber 13………………High frequency power supply 14………………Earth wire 15...Vacuum pump 16………………Quartz window 17………………Microwave 18...Plasma generation chamber 19...Microwave room 20...Slot antenna 21………………Partition board 22………………Through hole 23……………………Electrode plate 1 24……………………Electrode plate 2 25………………Heater 26………………Plasma-2 27...High-density plasma

Claims

1. An electric double layer capacitor characterized by having a positive electrode and a negative electrode with 3-D graphene oriented vertically on the surface of a Cu substrate, with an electrolyte and a separator separating the electrodes.

2. In the electric double layer capacitor according to claim 1, in which an electrolyte and a separator are provided between the positive and negative electrodes, the Cu substrates of the positive and negative electrodes are introduced into a plasma atmosphere with hydrogen radicals to remove the CuO layer formed on the surfaces thereof, the Cu substrate surfaces are sputtered, and further hydrogen radicals CH 4 An electric double layer capacitor in which gas is introduced to form 3-D graphene oriented vertically on the Cu substrate surface.

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