Multilayer capacitor electrode and method for manufacturing same

Abstract

[Problem] To develop a multilayer capacitor electrode which has a long life and is high-performing and practical. [Solution] This multilayer capacitor electrode is provided with multiwalled carbon nanotubes vertically oriented on both surfaces of a Cu substrate. The method for manufacturing the multilayer capacitor electrode comprises: coating Fe fine particles on both surfaces of a Cu substrate; arranging the Cu substrate in a thermal CVD apparatus so that the Cu substrate is in an upright position in a gas supply direction; and arranging multiwalled carbon nanotubes vertically oriented on both surfaces of a conductive metal substrate at a temperature of 750–850°C in a mist atmosphere in which a Fe / ethanol mixed liquid is atomized in the thermal CVD apparatus.

Description

Electrode for multilayer capacitor and manufacturing method thereof

[0001] The present invention relates to an electrode for a multilayer capacitor and a method for manufacturing the same.

[0002] Multilayer capacitors are attracting attention as devices that can be charged and discharged rapidly, with little degradation and a long lifespan. Currently, large, high-capacity capacitors are being developed (for electric vehicles, elevators, and automated factories), and small capacitors are also needed for applications such as home appliances, mobile phones, and mobile communications.

[0003] Conventional activated carbon is used as an electrode for multilayer capacitors. However, when powdered activated carbon is formed into an electrode, a conductive adhesive is required. This can be easily deteriorated by impurities and dust on the adhesive or activated carbon surface, shortening the lifespan of the electrode. Therefore, there is a demand for the development of a long-life, high-performance, and practical multilayer capacitor electrode that can replace activated carbon electrodes.

[0004] JP 2012-136362 JP 2005-286247 Republished 2004 / 084244

[0005] Jianhui Zhang, Wei Li, Tetsuo Soga, Takashi Jimbo and Takayoshi Tanji, “Synthesis of High-Density Vertically Aligned Carbon Nanotubes Using Ultrasonic Nebulizer”, Materials Sciences and Applications, Volume 2012, 3, 213-217

[0006] According to the inventor's research, multi-walled carbon nanotubes (MWNTs), which grow vertically aligned, are a material in which six-membered ring networks (graphene sheets) made of carbon are arranged in the form of multiple coaxial tubes. They have high density, high heat resistance, electrical conductivity, high acid resistance and chemical stability, and because they have a fibrous structure, they are electrically conductive, do not require adhesives, have few impurities on the surface, and have an extremely large specific surface area. There are large amounts of "gaps" between the nanotubes, which makes it possible to store large amounts of electrons and protons within them. These properties make them ideal for use as electrodes in multi-layer capacitors, and multi-walled carbon nanotubes (MWNTs) are expected to be used in applications such as multi-layer capacitors.

[0007] However, conventional multi-walled carbon nanotube (MWNT) synthesis methods have not been able to confirm sufficient performance as a multilayer capacitor electrode due to the presence of substances such as impurities and dust on the adhesive or activated carbon surface. As a result of trial and error research, the inventors have developed a synthesis method for vertically aligned multi-walled carbon nanotubes (MWNTs) made of pure carbon containing no impurities, thereby expanding the range of applications for multilayer capacitor electrodes.

[0008] The present invention proposes an electrode for a multilayer capacitor, which comprises a conductive metal substrate having vertically oriented multi-layer carbon nanotubes on both sides thereof.

[0009] Furthermore, the present invention proposes a method for manufacturing an electrode for a multilayer capacitor, in which iron-based metal fine particles are coated on both sides of a conductive metal substrate, the conductive metal substrate is arranged upright in the gas supply direction in a thermal CVD apparatus, and multi-layer carbon nanotubes that are vertically oriented are provided on both sides of the conductive metal substrate at a temperature of 600 to 900°C in a mist atmosphere in which an iron-based metal / alcohol mixed liquid is atomized in the thermal CVD apparatus.

[0010] Here, examples of the conductive metal substrate include substrates made of Cu, aluminum, titanium, and the like.

[0011] Examples of iron-based metals include Fe, Co, and Ni, with a typical example being Fe. A typical example of an iron-based metal / alcohol mixed liquid is an Fe / ethanol mixed liquid.

[0012] Furthermore, the temperature range is 600 to 900°C, preferably 750 to 850°C.

[0013] That is, according to the present invention, a large amount of electrons can be stored in the gaps between the multi-walled carbon nanotubes, and a long-life, high-performance electrode for a multilayer capacitor can be provided.

[0014] Diagram of a multilayer capacitor Schematic diagram of a thermal CVD apparatus with a nebulizer SEM images of synthesized vertically aligned multi-walled carbon nanotubes (MWNTs) SEM images of vertically aligned multi-walled carbon nanotubes (MWNTs) at different synthesis temperatures TEM images of synthesized vertically aligned multi-walled carbon nanotubes (MWNTs) EDS spectra of synthesized vertically aligned multi-walled carbon nanotubes (MWNTs) Diagram of the manufacturing method for a multilayer capacitor

[0015] An electrode for a multilayer capacitor having multi-walled carbon nanotubes aligned vertically on both sides of a Cu substrate, and a method for manufacturing the electrode, involves coating both sides of the Cu substrate with Fe fine particles, placing the Cu substrate upright in a thermal CVD apparatus in the gas supply direction, and then forming multi-walled carbon nanotubes aligned vertically on both sides of the conductive metal substrate at a temperature of 750 to 850°C in a mist atmosphere of atomized Fe / ethanol mixed liquid within the thermal CVD apparatus.

[0016] The present invention will be explained below based on the illustrated embodiments. Figure 1 is a schematic diagram of a multilayer capacitor incorporating electrodes according to the present invention. The capacitor is made up of four Cu substrates (1). Heat-resistant insulating resin (3) is inserted into the Cu substrates (1) on which CNTs are present. Vertically aligned multi-walled carbon nanotubes (2) are synthesized on the Cu substrates (1) using a thermal CVD apparatus, and finally wired (12).

[0017] The manufacturing process for a multilayer capacitor is described with reference to Figure 7. <Step shown in Figure 7A> Four Cu substrates (1) are cleaned. <Step shown in Figure 7B> Fe particles (5) are coated on both sides of the four Cu substrates (1) by vacuum deposition. <Step shown in Figure 7C> The four Cu substrates (1) are placed in a thermal CVD apparatus, and vertically aligned multi-walled carbon nanotubes (MWNTs) (2) are synthesized on both sides of the four Cu substrates (1) as multilayer capacitor electrodes. <Step shown in Figure 7D> Two Cu (1) substrates on the right and two Cu (1) substrates on the left are separately arranged, and a heat-resistant insulating resin (3) is attached to assemble the multilayer capacitor. Solder terminals (4) are then attached. <Step shown in Figure 7E> The multilayer capacitor is wired (12).

[0018] Manufacturing Method of Electrodes for Multilayer Capacitors Figure 2 is a schematic diagram of the apparatus used in the method of the present invention. The method of the present invention will be explained using the apparatus in Figure 2. The thermal CVD apparatus has three main parts: an electric furnace (6), a nebulizer device (9), and a nitrogen gas canister (8). In Figure 2, the electric furnace (6), the nebulizer device (9), and the nitrogen gas canister (8) are arranged in this order on the left and right. However, the apparatus used in the method of the present invention is not limited to this.

[0019] Next, we will explain the manufacturing procedure using the equipment shown in Figure 2. (1) Using an ultrasonic cleaning device, the Cu substrate (1) is first cleaned in order with acetone, a methanol solution, and ultrapure water, and then the remaining ultrapure water on the Cu substrate (1) is removed with a nitrogen gun.

[0020] (2) Place the cleaned Cu substrate (1) into the electric furnace (6) of the thermal CVD equipment, open the nitrogen valve (7), set the nitrogen flow rate to 0.1 L / min, and let it flow for about 10 minutes. Turn on the electric furnace (6) of the thermal CVD equipment and let it run for about 600-800 o Heat to C, wait another 10 minutes, and then turn on the nebulizer device (9).

[0021] (3) The nebulizer device (9) (1.65 MHz, Atom Medical Corp., Model 303) described in (2) is a key device in the thermal CVD apparatus of the present invention, capable of atomizing the Fe / ethanol mixed liquid, and feeding the raw material gas to the surface of the Cu substrate (1) in the thermal CVD apparatus via nitrogen gas for synthesis.

[0022] (4) The proportions of the Fe / ethanol mixed liquid described in (1) are 10 wt% and 100 ml, respectively.

[0023] (5) The reaction time was about 1 hour. After the experiment was completed, the electric furnace (6) of the thermal CVD apparatus was turned off, and the temperature of the electric furnace (6) was allowed to drop to room temperature before the Cu substrate (2) was removed.

[0024] (6) A heat-resistant insulating resin material (4) is applied to or inserted onto the Al substrate (1).

[0025] Figure 3 shows a typical SEM image of high-density, vertically aligned multi-walled carbon nanotubes (MWNTs) synthesized at a synthesis temperature of approximately 800°C, where high-density nanotubes with lengths of 10 μm are observed.

[0026] As shown in Figure 4, the SEM in Figure 4(a) shows that nanotubes can be formed in a dense, vertical state with a length of about 3 μm at a synthesis temperature of 750°C. The SEM in Figure 4(b) shows that nanotubes can be formed in a dense, vertical state with a length of about 10 μm at a synthesis temperature of 850°C.

[0027] As shown in Figure 5(a) and (b), it can be clearly observed that the carbon nanotubes have straight morphology, smooth walls, closed ends, and clean surfaces. The outer diameter of carbon nanotubes ranges from 10 to 30 nm, and the inner diameter of carbon nanotubes is usually about 2 to 5 nm.

[0028] Figure 6 shows an EDS spectrum showing three strong peaks representing Cu, Fe, and C. This suggests that the growth of vertically aligned multi-walled carbon nanotubes (MWNTs) originates from Fe or Fe carbide particles on the Cu substrate.

[0029] The present invention can provide a long-life, high-performance and practical multilayer capacitor electrode.

[0030] 1………………Cu substrate 2………………Vertically aligned multi-walled carbon nanotubes (MWNTs) 3………………Heat-resistant insulating resin 4………………Solder terminal 5………………Fe fine particles 6………………Electric furnace 7………………Nitrogen valve 8………………Nitrogen gas canister 9………………Nebulizer device 10………………Supply gas inlet 11………………Exhaust port 12………………Wiring

Claims

1. An electrode for a multilayer capacitor, in which multi-layer carbon nanotubes are vertically oriented on both sides of a conductive metal substrate.

2. A method for manufacturing electrodes for multilayer capacitors, in which iron-based metal particles are coated on both sides of a conductive metal substrate, the conductive metal substrate is placed upright in a thermal CVD apparatus in the gas supply direction, and multi-layer carbon nanotubes are provided that are vertically oriented on both sides of the conductive metal substrate at a temperature of 600-900°C in a mist atmosphere of an iron-based metal / alcohol mixture liquid.

3. The manufacturing method according to claim 2, wherein the iron-based metal is Fe, and the iron-based metal / alcohol mixed liquid is an Fe / ethanol mixed liquid.

4. The method according to claim 2, wherein the temperature is in the range of 750 to 850°C.

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