Lithium ion capacitor

Abstract

To develop a lithium ion capacitor using carbon nanowalls for the positive and negative electrodes instead of activated carbon.SOLUTION: It is characterized that a lithium ion capacitor consists of a negative electrode formed on carbon nanowalls oriented perpendicular to the conductive substrate surface and a positive electrode formed on carbon nanowalls oriented perpendicularly to the conductive substrate surface and lithium microparticles coded on the carbon nanowalls, and a separator is provided between both electrodes to separate the electrolyte from the electrodes.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a lithium-ion capacitor.

Background Art

[0002] A lithium-ion capacitor (LIC) can be rapidly charged and discharged, and is attracting attention as a device with little deterioration and a long life. It is a device that combines the characteristics of a supercapacitor (also called an ultracapacitor or an ultra-battery), and provides a high energy density and a high power density.

[0003] A lithium-ion capacitor can be charged and discharged very rapidly, and provides a high power density. It is suitable for high-power applications such as electric vehicles and lifting equipment, usually has hundreds of thousands of charge-discharge cycles or more, and has relatively little deterioration, so it is used as a long-life device. Large lithium-ion capacitors are suitable for high-capacity applications such as electric vehicles and automated factories, and are used for energy storage and high-power applications. There are also small lithium-ion capacitors, which are suitable for applications for small devices such as household appliances, mobile phones, and mobile communications. In the future, with further technological progress, the performance of lithium-ion capacitors may be improved and new applications may be developed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] Although activated carbon has been used as the electrode material for conventional LICs, it has been pointed out that a conductive adhesive needs to be used in the manufacturing process, which may lead to a decrease in performance. In particular, there is concern that the lifespan of LICs may be shortened due to the adhesion of adhesives, impurities, dust, etc. to the surface of activated carbon. In the conventional negative electrode synthesis method of capacitors, it has been pointed out that substances such as adhesives, impurities, and dust on the surface of activated carbon exist, which have an adverse effect on the performance of the electrode of the lithium-ion capacitor.

[0006] To solve this problem, as a development of alternative materials for activated carbon, graphene, two-dimensional materials, nanostructured materials, etc. have been studied as candidates for electrode materials. Since these materials have high conductivity, surface area, and chemical stability, they may provide superior performance compared to conventional activated carbon. Furthermore, as a result of trial and error, a synthesis method of carbon nanowalls (CNWs) composed of pure carbon has been developed.

[0007] According to the research of the present inventors, carbon nanowall synthesis (CNWs) is a substance in which graphene sheets of six-membered rings made of carbon form a wall-like shape. It has high density, high heat resistance, conductivity, high acid resistance, and chemical stability, and has a wall-like structure. Therefore, it has conductivity, does not require an adhesive, has few impurities on the surface, and has a very large specific surface area. There are a large number of "gaps" between the nanowalls, so a large number of electrons and protons can be stored therein, and it has ideal characteristics as a lithium-ion capacitor. Carbon nanowalls (CNWs) can be expected to be applied to lithium-ion capacitors and the like.

Means for Solving the Problem

[0008] Therefore, the present invention proposes a lithium-ion capacitor characterized by comprising a negative electrode formed on carbon nanowalls oriented in the vertical direction on the surface of a conductive substrate, and a positive electrode formed on carbon nanowalls oriented in the vertical direction on the surface of a conductive substrate and having lithium fine particles coated on the carbon nanowalls, with an electrolytic solution and a separator for partitioning them provided between the two electrodes.

[0009] The conductive metal substrate is a substrate used to support the conduction of electrons, and various metals such as Cu (copper), aluminum (Al), and titanium (Ti) are used. These metals are widely used to transmit electrical signals and conduct heat, and it is important to select an appropriate conductive metal substrate according to specific applications and requirements.

[0010] In addition, when using an electrolytic copper substrate as the conductive metal substrate, it is necessary to remove the copper oxide on its surface in advance by acid treatment or the like.

[0011] For the negative electrode to the positive electrode, a plasma CVD apparatus can be used to form carbon nanowalls that are oriented in the direction perpendicular to the conductive metal surface.

[0012] CH4 or H2 is sent into the plasma CVD apparatus, and carbon nanowalls that are oriented perpendicular to the surface of the conductive metal substrate are formed at a temperature of 250 to 800 °C, preferably 250 to 500 °C, in a carbon atmosphere.

[0013] For the positive electrode, a pulsed laser deposition apparatus is used as a method for coating the carbon nanowalls with lithium fine particles.

[0014] With the pulsed laser deposition apparatus, a strong pulsed laser is irradiated on the surface of the lithium target, thereby converting lithium into a plasma state and using it to adsorb lithium fine particles onto the carbon nanowalls (CNWs).

Advantages of the Invention

[0015] The carbon nanowalls used for the negative electrode and the positive electrode in the present invention are carbon-based materials created using nanotechnology, which have a very large surface area and a structure suitable for storing electrons. Therefore, the lithium-ion capacitor according to the present invention can be widely used as a power storage device that contributes to the improvement of high performance and long life performance.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0017] A lithium-ion capacitor comprising a negative electrode formed on a carbon nanotube vertically oriented in the vertical direction on the surface of a conductive electrolytic copper, and a positive electrode formed on a carbon nanotube vertically oriented in the vertical direction on the surface of the conductive electrolytic copper and coding lithium fine particles on the carbon nanotube, and an electrolytic solution and a separator for partitioning them are provided between the two electrodes

Examples

[0018] The present invention will be described based on the illustrated embodiments. FIG. 1 is a schematic diagram of the operation of a capacitor by the method of the present invention. The operation access of the present invention will be described along FIG. 3. A specific process regarding the operating principle of the capacitor is illustrated. The capacitor mainly consists of a negative electrode (1) and a positive electrode (2). There is an electrolytic solution (6) and a separator (5) that separates them between these electrodes. The separator separates the electrolytic solution and the electrodes to prevent short circuits. When the capacitor is charged, positive charges (7) are accumulated from the positive electrode to the negative electrode through the electrolytic solution and the separator. At the same time, electrons (9) move to the negative electrode through the wire, enter the carbon nanowall (8), and are charged together with the positive charges. When the capacitor is discharged, the positive charges (7) at the negative electrode are discharged to the negative electrode through the electrolytic solution and the separator (5), the stored energy is released, and current is supplied from the electric field.

[0019] FIG. 2 is an external view image of a lithium-ion capacitor according to the present invention. It is a stacked lithium-ion capacitor structure composed of four single lithium-ion capacitors.

[0020] The manufacturing process of the lithium-ion capacitor will be described according to FIG. 3. <The process shown in FIG. 3A> Two electrolytic copper substrates (1) and (2) are being cut (pressing process). <The process shown in FIG. 3B> The two cut electrolytic copper substrates (1) and (2) are put into a hydrofluoric acid solution for a process of removing the surface layer of copper oxide on the surface of the electrolytic copper in 10 minutes. <The process shown in FIG. 3C> The two electrolytic copper substrates (1) and (2) are left in a plasma CVD apparatus to synthesize carbon nanowalls (CNWs) (8) that are vertically oriented as lithium-ion capacitor electrodes (positive and negative) on the surfaces of the two electrolytic copper substrates (1) and (2). <The process shown in FIG. 3D> The electrolytic copper (1) substrate as the positive electrode refers to a copper substrate used as the positive electrode in capacitor manufacturing. The pulsed laser deposition apparatus (PLD) is a device used to deposit or grow materials using pulsed lasers. The lithium target is a lithium material irradiated with a pulsed laser. Due to the energy of the pulsed laser, lithium changes to a plasma state, and the plasma is in a high-temperature and high-energy state with various particles (atoms, ions, clusters, electrons, photons, etc.) mixed. The fine particles generated from the lithium plasma are deposited on the electrolytic copper substrate, and lithium adheres to the electrolytic copper substrate, which may be used in the manufacturing stage of the positive electrode material. <The process shown in Figure 3E> It is an energy storage device used by laminating a positive electrode and a negative electrode. The positive electrode is composed of carbon nanotubes containing lithium fine particles, which absorb and accumulate lithium ions. On the other hand, the negative electrode is composed of carbon nanotubes with a high surface area, responsible for accepting and supplying electrons, having both high energy density and high power density, and enabling rapid charge and discharge. <The process shown in Figure 3F> The current collector tab welding is a process carried out in capacitor packs and energy storage devices to connect electrode materials such as the positive electrode and the negative electrode to the external circuit of the capacitor. It is a part of the assembly process of the capacitor pack. It is carried out to securely connect the current collector tab and the electrode material and ensure electrical conductivity. The current collector tab is made of a thin metal foil (generally copper or aluminum), connected to the electrode of the battery. The current collector tab functions as the contact point between the electrode and the external circuit of the battery pack, providing a path for the current. The current collector tab welding is carried out to safely and firmly connect this current collector tab to the electrode material. Generally, the current collector tab welding is carried out using various welding techniques such as electron beam welding, laser welding, resistance welding, and ultrasonic welding, so that the electrode material and the current collector tab are firmly connected and the electrical performance is optimized. <The process shown in Figure 3G> Laminating heat welding is a process of joining different materials or thin films. Using a laminating heat welding machine, heat is applied to the joint, melting the materials. After the joint surfaces fuse, pressure is applied to make the joint adhere tightly. The melted materials are evenly distributed, strengthening the joint. Then the joint is cooled to solidify the materials. <Process shown in FIG. 3H> Vacuum drying is a process to remove the humidity inside the capacitor and ensure the stability of the insulating materials and internal structure. It is an important process especially in the manufacturing and maintenance of large-capacity capacitors for high voltage and high frequency applications. The capacitor is placed in a dedicated vacuum chamber, which is equipped with a vacuum pump to evacuate the air around the capacitor, facilitating moisture evaporation and reducing humidity. After drying is completed, the insulation state and capacitance of the capacitor are inspected and corrections are made if necessary. <Process shown in FIG. 3I> The electrolyte generally consists of water and electrolytes (usually ammonium salts or aluminum salts). After the preparation of the electrolyte is completed, the electrolyte is carefully injected into the capacitor with a specific injection point opened. After injection is finished, the injection point is sealed and the seal of the capacitor is checked. <Process shown in FIG. 3J> This is a process carried out to seal the electrodes and insulators inside the capacitor. The laminating heat sealer uses high temperature and pressure to seal the electrodes and insulators, and uses heated rollers or presses around the laminate to seal the periphery of the laminate. This provides insulation to isolate the inside of the capacitor from the air and ensure proper operation. <Process shown in FIG. 3K> To check the performance of a capacitor, it is necessary to examine several important parameters. (1) Capacitance (unit: farad, F) represents the amount of charge stored in the capacitor and is measured using a capacitance meter tester or a multimeter. (2) The allowable voltage (rated voltage, unit: volt, V) indicates the maximum voltage at which it can be operated safely, and care must be taken not to exceed the allowable voltage. (3) ESR (equivalent series resistance, unit: ohm, Ω) represents the internal resistance of the capacitor, and it can be said that the lower the ESR, the better the performance. (4) The loss angle (Dissipation Factor) represents the ratio of the loss to the reactance of the capacitor, and a low loss angle indicates high performance of the capacitor. (5) Inductance (unit: henry, H) may affect the performance at high frequencies, and it is desirable for capacitors for high frequencies to have low inductance. (6) It is important to check the temperature characteristics of the capacitor and use it within an appropriate temperature range.

[0021] Figure 4 shows a model of the reaction at the negative electrode of a lithium-ion capacitor, and this model explains how the capacitor works when it is charged. At the beginning of charging, lithium ions ⁺(7) as positive charges exist in the electrolyte (6), and the lithium ions move through the electrolyte and through the separator (5) towards the negative electrode. Lithium ions ⁺(7) enter the carbon nanotubes (8) synthesized on the negative electrode, and the carbon nanotubes have a special structure and can efficiently take in lithium ions. Lithium ions are adsorbed on the carbon nanotubes, where a chemical reaction occurs, resulting in the state of LiC6(10), a compound of lithium and carbon, and also forming a cluster of positively charged lithium ions (11) outside the carbon nanotubes. At the same time, electrons - (9) move towards the carbon nanotubes synthesized on the negative electrode through the wire (12), and electrons - enter the carbon nanotubes, react with the carbon, and combine with the positively charged (lithium ion) ⁺(7) in the charged state, enabling the negative electrode of the lithium-ion capacitor to be in a charged state.

[0022] Figure 5 illustrates the reaction model at the positive electrode of a lithium-ion capacitor. Lithium fine particles (4) present in the positive electrode (carbon nanowall) receive positive charges (7) from the negative electrode. At the same time, electrons (9) enter the composite carbon nanowall of the positive electrode through the electric wire (12). The lithium fine particles (4) and electrons (9) merge at the positive electrode to form positive charges (lithium ions) (7), and through these processes, discharge access occurs.

[0023] Figures 6(a) and (b) show typical SEM images of the synthesized high-density vertically aligned carbon nanowalls (CNWs), and nanowalls with a high density and a length of 0.9 μm are observed.

[0024] In Figure 6, the G band, which is one of the characteristic peaks of graphene, originates from the in-plane motion of carbon atoms and appears in the vicinity of 1580 - 1600 cm -1 The D band is known as a disorder band caused by structural disorder and defects, and it originates from lattice motion away from the center of the Brillouin zone. If this peak exists at 1270 - 1450 cm -1 (depending on the excitation wavelength), it indicates defects or edges in the graphene sample. The 2D band, also called G'(G prime), is a second-order two-phonon scattering. The 2D band shows a strong frequency dependence on the excitation laser due to a double resonance process that associates the phonon wave number vector with the electronic band structure. This feature appears at approximately 2700 cm -1 and can also be used to determine the number of graphene layers.

Industrial Applicability

[0025] The lithium-ion capacitor according to the present invention can be widely used as a power storage device that contributes to performance improvement with high performance and long life.

Explanation of Symbols

[0026] 1............... Electrolytic copper substrate of the positive electrode 2............... Electrolytic copper substrate of the negative electrode 3………………Carbon nanotubes synthesized on the positive electrode 4………………Lithium microparticles 5………………Separator 6………………Electrolyte 7………………Positive charge (lithium ion) ⁺ 8………………Carbon nanotubes synthesized on the negative electrode 9………………Electrons ‐ 10………………LiC6 11………………Lithium ion cluster 12………………Electric wire

Claims

1. It consists of a negative electrode formed on carbon nanotubes vertically oriented on the surface of a conductive substrate, and a positive electrode formed on carbon nanotubes vertically oriented on the surface of the conductive substrate and coated with lithium fine particles on the carbon nanotubes. An electrolytic solution and a separator for separating them are provided between the two electrodes. The lithium ion capacitor is characterized by this.

2. When an electrolytic copper substrate is used as the conductive metal substrate, the copper oxide on its surface is removed in advance by acid treatment and formed on carbon nanotubes vertically oriented on its surface. The lithium ion capacitor according to Claim 1.

3. The lithium ion capacitor according to Claim 1, wherein a powerful pulsed laser is irradiated on the surface of a lithium target by a pulsed laser deposition apparatus, and the lithium fine particles generated thereby are coated on carbon nanotubes.

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