WO2020262464A1

WO2020262464A1 - Hybrid capacitor

Info

Publication number: WO2020262464A1
Application number: PCT/JP2020/024840
Authority: WO
Inventors: 芳尾　真幸; 直哉小林
Original assignee: Ｔｐｒ株式会社; 芳尾　真幸
Priority date: 2019-06-24
Filing date: 2020-06-24
Publication date: 2020-12-30
Also published as: CN114207756A; JPWO2020262464A1; CN114207756B; JP6967688B2

Abstract

This hybrid capacitor is configured so that: a positive electrode includes graphite as a positive electrode active material; a positive-electrode-side current collector is made of an aluminum material; and the aluminum material is coated by a carbon plating film in which the content ratio sp²/(sp² + sp³) of sp² structures is 80% or higher.

Description

Hybrid capacitor

The present invention relates to a hybrid capacitor.
The present application claims priority based on Japanese Patent Application No. 2019-116704 filed in Japan on June 24, 2019, the contents of which are incorporated herein by reference.

Conventionally, electric double layer capacitors (see, for example, Patent Document 1) and secondary batteries are known as techniques for storing electric energy. Electric double layer capacitors (EDLCs) are significantly superior to secondary batteries in terms of life, safety, and power density. However, the electric double layer capacitor has a problem that the energy density (volume energy density) is lower than that of the secondary battery.
Here, the energy (E) stored in the electric double layer capacitor is expressed as E = 1/2 × C × V ² using the capacitance (C) and the applied voltage (V) of the capacitor, and the energy is It is proportional to the capacitance and the square of the applied voltage. Therefore, in order to improve the energy density of the electric double layer capacitor, a technique for improving the capacitance and the applied voltage of the electric double layer capacitor has been proposed.

As a technique for improving the capacitance of an electric double layer capacitor, a technique for increasing the specific surface area of activated carbon constituting the electrode of the electric double layer capacitor is known. Currently known activated carbons have a specific surface area of 1000 m ² / g to 2500 m ² / g. In the electric double layer capacitor using such activated carbon as an electrode, an organic electrolytic solution in which a quaternary ammonium salt is dissolved in an organic solvent, an aqueous electrolytic solution such as sulfuric acid, or the like is used as the electrolytic solution.
Since the organic electrolyte has a wide usable voltage range, the applied voltage can be increased and the energy density can be improved.

A lithium ion capacitor is known as a capacitor in which the applied voltage is improved by utilizing the principle of an electric double layer capacitor. A lithium ion capacitor is a capacitor that uses graphite or carbon that can intercalate and deintercalate lithium ions for the negative electrode and activated carbon that is equivalent to the electrode material of an electric double layer capacitor that can absorb and desorb electrolyte ions for the positive electrode. ing. For one of the positive electrode and the negative electrode, which uses the same activated carbon as the electrode material of the electric double layer capacitor, and which uses a metal oxide or a conductive polymer as the electrode at which the Faraday reaction occurs on the other electrode, It is called a hybrid capacitor. In the lithium ion capacitor, among the electrodes constituting the electric double layer capacitor, the negative electrode is made of graphite, hard carbon, soft carbon, etc., which are the negative electrode materials of the lithium ion secondary battery, and the inside of the graphite, hard carbon, soft carbon, etc. An electrode into which lithium ions are inserted. A lithium ion capacitor is characterized in that the applied voltage is larger than that of a general electric double layer capacitor, that is, one in which both electrodes are composed of activated carbon.

However, when graphite is used for the electrode, there is a problem that propylene carbonate, which is known as a solvent for the electrolytic solution, cannot be used. This is because when graphite is used for the electrode, propylene carbonate is electrolyzed and the decomposition product of propylene carbonate adheres to the surface of graphite, which reduces the reversibility of lithium ions. Propylene carbonate is a solvent that can operate even at low temperatures. When propylene carbonate is applied to an electric double layer capacitor, the electric double layer capacitor can also operate at −40 ° C. Therefore, in lithium ion capacitors, hard carbon and soft carbon, which are difficult to decompose propylene carbonate, are used as electrode materials. However, hard carbon and soft carbon have a lower capacity per volume of the electrode than graphite, and the voltage is also lower than that of graphite (becomes a noble potential). Therefore, there is a problem that the energy density of the lithium ion capacitor becomes low.

When emphasizing low temperature characteristics, it is difficult to use high-capacity graphite for the negative electrode. It is difficult to further increase the energy density of lithium-ion capacitors. Further, in the lithium ion capacitor, a copper foil is used for the current collector as in the negative electrode of the lithium ion secondary battery, so that when an overdischarge of 2 V or less is performed, copper is eluted to cause a short circuit or charge. There are problems such as a decrease in discharge capacity. Therefore, the lithium ion capacitor has a problem that the usable voltage range is limited as compared with the electric double layer capacitor which can discharge up to 0V.

As a new concept capacitor, a capacitor using graphite as the positive electrode active material instead of activated carbon and using a reaction of inserting and removing electrolyte ions between the layers of graphite has been developed (see, for example, Patent Document 2). In Patent Document 2, in the conventional electric double-layer capacitor using activated carbon as the positive electrode active material, when a voltage exceeding 2.5 V is applied to the positive electrode, the electrolytic solution is decomposed and gas is generated, whereas the positive electrode active material is generated. It is described that a capacitor with a new concept that uses graphite does not cause decomposition of the electrolytic solution even at a charging voltage of 3.5 V, and can operate at a higher voltage than a conventional electric double-layer capacitor that uses activated carbon as the positive electrode active material. .. By using this technique, the energy density can be increased by about 2 to 3 times as compared with the conventional electric double layer capacitor. The cycle characteristics, low temperature characteristics, and output characteristics are also equal to or better than those of conventional electric double layer capacitors. The specific surface area of graphite is several hundredths of the specific surface area of activated carbon, and this difference in electrolytic solution decomposition action is due to this large difference in specific surface area.

Capacitors with a new concept that uses graphite as the positive electrode active material have not been put into practical use due to insufficient durability, but a technology that uses an aluminum material coated with an amorphous carbon film for the current collector (patented). (Refer to Reference 3), it is known that the high temperature durability performance can be improved to a practical level. The capacitor of this new concept is a capacitor that uses a reaction of inserting and removing electrolyte ions between layers of graphite on the positive electrode, and is not strictly an electric double layer capacitor, but in Patent Document 3, it is electric in a broad sense. It is called a double layer capacitor.

Here, the durability test is usually performed by raising the temperature and performing an accelerated test (high temperature durability test, charge / discharge cycle test). The test can be performed by a method according to the "durability (high temperature continuous rated voltage application) test" described in JIS D 1401: 2009. It is said that the deterioration rate doubles when the temperature is raised from room temperature by 10 ° C. As a high-temperature durability test, for example, the battery is held (continuously charged) at a predetermined voltage (3 V or more in the present invention) for 2000 hours in a constant temperature bath at 60 ° C., and then returned to room temperature for charging and discharging, and discharging at that time. There is a test to measure capacity. After this high temperature durability test, it is considered desirable that the discharge capacity retention rate satisfies 80% or more with respect to the initial discharge capacity.

Japanese Unexamined Patent Publication No. 2011-046584 Japanese Unexamined Patent Publication No. 2010-040180 Japanese Patent No. 6167243 Japanese Unexamined Patent Publication No. 2015-232171

In the capacitor of the new concept of Patent Document 3, aluminum, which is a current collector, is coated with an amorphous carbon film. The diamond-like carbon (DLC) film is amorphous carbon film, graphite are contained and the sp ³ structure mainly composed of sp ² structure and diamond composed mainly of, containing the sp ² structure the ratio ^sp 2 / Since (sp ² + sp ³ ) is 35 to 55%, it is a hard film. Therefore, when the capacitor is used, when it is consolidated by a roll press or the like in order to increase the electrode density, it may be damaged or peeled off from the aluminum material, and the aluminum dissolution reaction starts in the exposed portion, resulting in durability. There is a concern that the sex will deteriorate. The capacitor is required to further improve the input / output characteristics of the capacitor by preventing such a decrease in durability and reducing the interfacial resistance between the current collector and the electrode active material layer.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hybrid capacitor that suppresses a decrease in durability due to dissolution of a current collector and has excellent input / output characteristics.

In order to solve the above problems, the present invention employs the following means.

(1) In the hybrid capacitor according to one aspect of the present invention, the positive electrode contains graphite as the positive electrode active material, the current collector on the positive electrode side is an aluminum material, and the aluminum material has a sp ² structure content ratio sp ^2. It is coated with a carbon-plated film in which / (sp ² + sp ³ ) is 80% or more.

(2) In the hybrid capacitor according to (1), the thickness of the carbon plating film is preferably 100 nm or more and 5000 nm or less.

(3) In the hybrid capacitor according to any one of (1) or (2) above, the current collector on the negative electrode side is an aluminum material coated with a carbon plating film, an amorphous carbon film and a negative electrode active material. It is preferably selected from the group consisting of an aluminum material having a conductive carbon layer formed between them, an aluminum material coated with an amorphous carbon film, etched aluminum, and an aluminum material.

(4) In the hybrid capacitor according to any one of (1) to (3), the graphite preferably contains rhombohedral crystals.

(5) In the hybrid capacitor according to any one of (1) to (4) above, the negative electrode is a carbon substance selected from the group consisting of activated carbon, graphite, hard carbon, and soft carbon as the negative electrode active material. It preferably contains at least one of the materials or lithium titanate.

(6) In the hybrid capacitor according to any one of (1) to (5) above, the carbon plating film is preferably a plating film made from a molten salt as a raw material.

According to the present invention, it is possible to provide a hybrid capacitor that suppresses a decrease in durability due to melting of a current collector and has excellent input / output characteristics.

It is a graph which shows the relationship between the thickness (thickness) of a carbon plating film, the discharge capacity retention rate, and the discharge capacity per electrode volume in the hybrid capacitor which concerns on Example 5 of this invention.

Hereinafter, the hybrid capacitor according to the embodiment to which the present invention is applied will be described in detail with reference to the drawings. In the drawings used in the following description, in order to make the features easier to understand, the featured parts may be enlarged for convenience, and the dimensional ratios of each component may not be the same as the actual ones. Absent. Further, the materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and the present invention can be appropriately modified without changing the gist thereof.

The hybrid capacitor according to the embodiment of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator, the positive electrode contains graphite as a positive electrode active material, the current collector on the positive electrode side is an aluminum material, and the aluminum material is sp ^2. It is characterized in that it is coated with a carbon-plated film having a structure content ratio of sp ² / (sp ² + sp ³ ) of 80% or more.

The positive electrode includes a current collector (current collector on the positive electrode side) and a positive electrode active material layer formed on the current collector. The positive electrode active material layer is formed by applying a paste-like positive electrode material containing a positive electrode active material, a binder, and an required amount of a conductive material on the current collector on the positive electrode side, and drying and drying the positive electrode material. be able to.

As the binder, for example, fluororesin, rubber, acrylic resin, olefin resin, carboxymethyl cellulose (CMC) resin, and natural polymer can be used. Examples of the fluororesin include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Examples of rubber include fluororubber, ethylene propylene diene rubber, and styrene butadiene rubber. Examples of natural polymers include gelatin, chitosan and alginic acid. One of these binders may be used alone, or two or more of these binders may be used in combination.

The conductive material is not particularly limited as long as it improves the conductivity of the positive electrode active material layer, and a known conductive material can be used. For example, carbon black and carbon fiber can be used. Examples of carbon fibers include carbon nanotubes (CNT) and VGCF®. The carbon nanotubes may be single-walled carbon nanotubes or multi-walled carbon nanotubes. One of these conductive materials may be used alone, or two or more of them may be used in combination.

The current collector on the positive electrode side is an aluminum material coated with a carbon plating film. As the aluminum material as the base material, an aluminum material generally used for current collector applications can be used. The shape of the aluminum material can be a foil, a sheet, a film, a mesh, or the like. Aluminum foil can be preferably used as the current collector. Further, in addition to a plain aluminum material, etched aluminum described later may be used.

The thickness when the aluminum material is a foil, sheet or film is not particularly limited, but if the size of the cell itself is the same, the thinner the aluminum material, the more active material can be enclosed in the cell case, but the strength is reduced. Therefore, select an appropriate thickness. The thickness is preferably 10 μm to 50 μm, more preferably 15 μm to 30 μm. If the thickness is less than 10 μm, the aluminum material may be broken or cracked during the step of roughening the surface of the aluminum material or another manufacturing process.

Etched aluminum may be used as the aluminum material. Etched aluminum is roughened by etching. For etching, a method of immersing in an acid solution such as hydrochloric acid (chemical etching) or electrolysis (electrochemical etching) using aluminum as an anode in an acid solution such as hydrochloric acid is generally used. In electrochemical etching, the etching shape differs depending on the current waveform during electrolysis, solution composition, temperature, etc., so it can be selected from the viewpoint of capacitor performance.

As the aluminum material, either one having a passivation layer on the surface or one not having a passivation layer can be used. When a passivation film, which is a natural oxide film, is formed on the surface of the aluminum material, a carbon plating film layer may be provided on the natural oxide film, or may be provided after the natural oxide film is removed. Good. The natural oxide film on the aluminum material is a passivation film and has the advantage that it is not easily eroded by the electrolytic solution, but on the other hand, it forms a uniform and strong carbon plating film, and also increases the resistance of the current collector. To prevent it, it is preferable that there is no natural oxide film. As a removing method, electrolytic etching, chemical etching, or the like can be used. By etching by these methods, the surface of the aluminum material is formed with irregularities at the same time as the natural oxide film is removed, which is also preferable in that the adhesion with the subsequent carbon plating film is improved.

The aluminum material is coated with a carbon plating film. The carbon plated layer contains an sp ³ structure mainly composed of sp ² structure and diamond composed mainly of graphite, sp ² structure content ratio ^sp 2 ^{/ (sp} 2 + sp ³⁾ of becomes 80% or more It has a structure similar to that of a graphite film. The content ratios of the sp ² structure and the sp ³ structure can be confirmed, for example, by analyzing XANES (X-ray Absorption Near Edge Structure: structure near the X-ray absorption edge) obtained by X-ray irradiation.

Therefore, this carbon-plated film is softer than the DLC film, which is an amorphous carbon film. Specifically, the Vickers hardness is about 700 to 1000 HV in the case of the DLC film, while it is about 3 to 80 HV in the case of the carbon-plated film.

Further, this carbon-plated film has a lower resistivity and higher conductivity than the DLC film. Specifically, the resistivity in the penetration resistance measurement method using a gold probe is about 0.3 to 1.0 mΩ · cm ^{2 in} the case of a DLC film, whereas it is about 0.3 to 1.0 mΩ · cm ^{2 in} the case of a carbon-plated film. It is about 0.04 to 0.2Ω · cm ² . It should be noted that these values are values when the aluminum foil is coated with each film.

Carbon cannot be plated in an aqueous solution system, but for example, by using a molten salt as described in Patent Document 4, plating is possible, and the above-mentioned carbon plating film can be formed on an aluminum material. .. In this case, a halide is suitable as the molten salt bath, and for example, LiCl, NaCl, KCl, MgCl _2, etc. can be used alone or in combination. CaCl ₂ or the like is added as a carbon source to the molten salt bath to dissolve it. A metal to be plated (here, an aluminum material) can be used for the anode. Classic carbon or the like can be used for the cathode.

The carbon plating film is a plating film using a molten salt as a raw material or a part of the raw material, and is formed, for example, by changing carbon ion C ^2- in the molten salt to C at the anode. At this time, the reaction of C ^2- → C + 2e ⁻ occurs at the anode, and the reaction of Li ⁺ + e ⁻ → Li occurs at the cathode.

The feature of carbon plating is that a dense film can be formed and the thickness of the formed film can be controlled by the amount of electricity. Furthermore, since the carbon produced is graphite or carbon having an sp ² structure similar to graphite, it is also a major feature that it has high conductivity. In the present embodiment, the thickness of the carbon plating film is preferably 100 nm or more and 5000 nm or less.

In addition, instead of carbon plating, there is also a method of applying graphite particles to the aluminum material. In this case, the conductivity of graphite is equal to or higher than that of carbon in the carbon plating film, but since it is made into an ink together with the binder and applied to the aluminum material, there are gaps between the graphite particles, and the electrolytic solution invades through the gaps. As a result, aluminum is likely to elute during charging and discharging. Especially in high temperature durability tests and the like, the problem of aluminum dissolution is more likely to occur. Further, since the binder is composed of an organic substance, it has an adverse effect that the conductivity is lowered and the binder itself is easily decomposed depending on the voltage at the time of charging / discharging.

The positive electrode active material used in the hybrid capacitor of the present invention contains graphite. As the graphite, either artificial graphite or natural graphite can be used. Further, as natural graphite, scaly and earth-like graphite are known. Natural graphite is obtained by crushing the mined raw ore and repeating beneficiation called flotation. Further, artificial graphite is produced, for example, through a graphitization step of calcining a carbon material at a high temperature. More specifically, for example, the raw material coke is molded by adding a binder such as pitch, heated to around 1300 ° C. for primary firing, then the primary fired product is impregnated with the pitch resin, and the temperature is further increased to 3000 ° C. It is obtained by secondary firing at a near high temperature. Further, those in which the surface of graphite particles is coated with carbon can also be used.

The crystal structure of graphite is roughly divided into hexagonal crystals with a layered structure consisting of ABAB and rhombohedral crystals with a layered structure consisting of ABCABC. Depending on the conditions, these structures may be in a single state or in a mixed state, but any crystal structure or a mixed state can be used. For example, the graphite of KS-6 (trade name) manufactured by Imerys GC Japan Co., Ltd. used in the examples described later has a rhombohedral crystal ratio of 26%, and is an artificial graphite manufactured by Osaka Gas Chemical Co., Ltd. Carbon microbeads (MCMB) have a ratio of rhombohedral crystals of 0%.

The graphite used in this embodiment has a different capacitance expression mechanism from the activated carbon used in the conventional EDLC. In the case of activated carbon, taking advantage of its large specific surface area, electrolyte ions are adsorbed and desorbed on the surface of the activated carbon to develop capacitance. On the other hand, in the case of graphite, the capacity is developed by inserting and desorbing (intercalation-deintercalation) an anion which is an electrolyte ion between the layers. From such a difference, the hybrid capacitor according to the present embodiment was called an electric double layer capacitor in a broad sense in Patent Document 3, but it can also be called a hybrid capacitor, and activated carbon having an electric double layer is used. It is distinct from EDLC.

The negative electrode includes a current collector (current collector on the negative electrode side) and a negative electrode active material layer formed on the current collector.
The negative electrode active material layer is formed by applying a paste-like negative electrode material containing a negative electrode active material, a binder, and an required amount of a conductive material on the current collector on the negative electrode side, and drying the negative electrode material. be able to.

As the negative electrode active material, materials capable of absorbing / desorbing or inserting / desorbing (intercalation-deintercalation) a cation which is an electrolyte ion, for example, activated carbon, graphite, hard carbon, soft carbon and carbon which are carbonaceous materials. Lithium titanate, which is an electrode potential material that is more noble than the quality material, can be used.

A known collector can be used as the current collector on the negative electrode side, but a conductive carbon layer is formed between the aluminum material coated with the carbon plating film, the amorphous carbon film, and the negative electrode active material. A material selected from the group consisting of an aluminum material, an aluminum material coated with an amorphous carbon film, etched aluminum, and an aluminum material can be used. When an aluminum material coated with a carbon plating film is used on the negative electrode side as well, it is preferable in that high temperature durability performance can be improved when the hybrid capacitor is operated at a high voltage.

As the binder and conductive material, those of the same type as the positive electrode can be used.

As the electrolytic solution, for example, an organic electrolytic solution using an organic solvent can be used. As long as it contains electrolyte ions, it is not limited to the organic electrolyte. Further, for example, a gel may be used. The electrolyte contains electrolyte ions that can be attached to and detached from the electrode. The type of electrolyte ion is preferably one having an ion diameter as small as possible. Specifically, ammonium salts, phosphonium salts, ionic liquids, lithium salts and the like can be used.

As the ammonium salt, tetraethylammonium (TEA) salt, triethylammonium (TEMA) salt and the like can be used. Further, as the phosphonium salt, a spiro compound having two five-membered rings or the like can be used.

The type of ionic liquid is not particularly limited, but a material having a viscosity as low as possible and a high conductivity (conductivity) is preferable from the viewpoint of facilitating the movement of electrolyte ions. Examples of the cation constituting the ionic liquid include imidazolium ion and pyridinium ion. Examples of the imidazolium ion include 1-ethyl-3-methylimidazolium (EMIm) ion and 1-methyl-1-propylpyrrolidinium (1-methyl-1-propylpyrrolidinium). Examples thereof include (MPPy) ion, 1-methyl-1-propylpiperidinium (MPPi) ion and the like. Further, as the lithium salt, lithium tetrafluorobolate LiBF ₄ , lithium hexafluorophosphate LiPF _6, or the like can be used.

Examples of the pyridinium ion include 1-ethylpyridinium ion, 1-butylpyridinium ion and the like.

The anions that make up the ionic liquid include BF ₄ ions, PF ₆ ions, [(CF ₃ SO ₂ ) ₂ N] ions, FSI (bis (fluorosulfonyl) imide, bis (fluorosulfonyl) imide) ions, and TFSI (bis (bis (fluorosulfonyl) imide) ions. Examples thereof include trifluoromethylsulfonyl) imide and bis (trifluoromethyl sulphonyl) ion.

As the solvent, acetonitrile, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl sulfone, ethyl isopropyl sulfone, ethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, sulfolane, N, N-dimethylformamide, dimethyl sulfoxide and the like alone or A mixed solvent can be used.

As the separator, a cellulosic paper-like separator, a glass fiber separator, a microporous polyethylene or polypropylene film, or the like is suitable for the purpose of preventing a short circuit between the positive electrode and the negative electrode and ensuring the electrolyte liquid retention property.

As described above, in the hybrid capacitor according to the present embodiment, the current collector is coated with a carbon plating film. This carbon-plated film has a denser structure than the films obtained by other manufacturing methods, and the gaps between the particles constituting the film are remarkably small.

Further, since this carbon-plated film has a content ratio of sp ² structure mainly composed of graphite of 80% or more and has a structure close to graphite, it is compared with a film having an amorphous structure such as a DLC film. And soft. Therefore, the adhesion to the current collector and the electrode active material is high, and it is possible to reduce the occurrence of problems such as damage or peeling from the aluminum material when consolidation is performed by a roll press or the like in order to increase the electrode density. ..

Therefore, in the hybrid capacitor according to the present embodiment, it is possible to suppress a decrease in durability due to a part of the aluminum material being exposed and the dissolution reaction starting from there.

Further, since the carbon-plated film covering the current collector of the present invention has higher conductivity than the film having an amorphous structure, the interfacial resistance with the electrode active material layer is low, and the present hybrid capacitor It is possible to reduce the resistance and obtain excellent input / output characteristics.

Hereinafter, the effects of the present invention will be made clearer by the examples. The present invention is not limited to the following examples, and can be appropriately modified and implemented without changing the gist thereof.

<Example 1>
In an argon glove box, 5 mol% of CaC ₂ was added to a solution containing LiCl and KCl at a weight percent concentration (wt%) of 50:50, and the solution was dissolved at 500 ° C. to prepare a molten salt bath. Aluminum foil (thickness 50 μm) was used for the anode, and glassy carbon was used for the cathode. Electrolysis was carried out at a constant current of 3 mA / cm ² for 25 minutes, and carbon was plated on an aluminum foil (thickness 50 μm) having a purity of 99.99% to obtain a current collector on the positive electrode side of this example.
When the thickness (film thickness) of the carbon plating film was measured by observing the cross section of the current collector with an SEM, it was 3 μm. Further, the ratio ^sp 2 ^/ the sp ² structure ^(sp 2 + sp ^3), was measured using a soft X-ray XANES (X-ray absorption near edge structure) was 83%.

Graphite manufactured by Imeris GC Japan Co., Ltd. (trade name: KS-6), acetylene black (conductive material), and vinylidene fluoride (organic solvent-based binder) are used as positive electrode active materials in terms of weight percent concentration (wt%). Weighed so as to be 80:10:10, and the paste obtained by dissolving and mixing with N-methylpyrrolidone (organic solvent) was applied onto the obtained current collector using a doctor blade. An example positive electrode was obtained.

Next, as the negative electrode active material, activated charcoal manufactured by Kansai Thermochemical Co., Ltd. (trade name: MSP-20), acetylene black (conductive material), and polyvinylidene fluoride (organic solvent-based binder) were added in a weight percent concentration (wt%) ratio. Weighed so that the concentration was 80:10:10, and the paste obtained by dissolving and mixing with N-methylpyrrolidone (organic solvent) was placed on an etched aluminum foil (thickness 20 μm) manufactured by Nippon Denki Kogyo Co., Ltd. The coating was applied using a doctor blade to obtain a negative electrode of this example.

Next, the obtained positive electrode was punched into a disk shape having a diameter of 16 mm and the obtained negative electrode having a diameter of 14 mm, and vacuum dried at 150 ° C. for 24 hours. After that, it was moved to the argon glove box. The dried positive electrode and negative electrode are laminated via a paper separator (trade name: TF40-30) manufactured by Nippon Kodoshi Paper Industry Co., Ltd., and 1M TEA-BF ₄ (tetraethylammonium tetrafluoride) is used as an electrolyte and a solvent is used. 0.1 mL of an electrolytic solution using SL + DMS (Sulfolane + dimethyl sulfide) was added to prepare a 2032 type coin cell of this example in an argon glove box.

<Example 2>
Similar to the current collector on the positive electrode side of Example 1, a 2032 type coin cell similar to that of Example 1 was produced as the current collector on the negative electrode side, except that an aluminum foil coated with a carbon plating film was used.

<Example 3>
A 2032 type coin cell similar to that of Example 1 was produced except that artificial graphite (trade name: MCMB6-10) manufactured by Osaka Gas Chemical Co., Ltd. was used as the positive electrode active material.

<Example 4>
Examples except that lithium titanate Li ₄ Ti ₅ O ₁₂ was used as the negative electrode active material, 1 M lithium tetrafluoroborate LiBF ₄ was used as the electrolyte, and an electrolytic solution using propylene carbonate (PC) as the solvent was used. A 2032 type coin cell similar to No. 1 was produced.

<Example 5>
In the same procedure as the carbon plating of Example 1, a plurality of current collectors having different thicknesses of the carbon plating film were prepared by changing the electrolysis time at a constant current. Specifically, those having thicknesses of 0 nm, 50 nm, 100 nm, 300 nm, 1000 nm, 2000 nm, 3000 nm, 5000 nm, 7000 nm, and 10000 nm were produced. In each case, a 2032 type coin cell similar to that of Example 1 was produced except that the electrolysis time at a constant current was changed.

<Comparative example 1>
A 2032 type coin cell similar to that of Example 1 was produced except that the activated carbon manufactured by Kansai Coke Chemical Co., Ltd. (trade name: MSP-20) used as the negative electrode active material in Example 1 was also used as the positive electrode active material. ..

<Comparative example 2>
A 2032 type coin cell similar to that of Example 1 was produced except that a DLC-coated aluminum foil (hereinafter, may be referred to as “DLC-coated aluminum foil”) was used as the current collector on the positive electrode side. The DLC coated aluminum foil corresponds to an aluminum material coated with an amorphous carbon film. As a method for producing a DLC-coated aluminum foil, an aluminum foil (thickness 50 μm) having a purity of 99.99% is subjected to argon sputtering to remove a natural oxide film on the surface of the aluminum foil, and then methane and acetylene are present in the vicinity of the aluminum surface. A discharge plasma was generated in a mixed gas of and nitrogen, and a negative bias voltage was applied to the aluminum material to form a DLC film. Here, the thickness of the DLC film on the aluminum foil coated with DLC was measured using a stylus type surface shape measuring instrument DektakXT manufactured by Bruker Co., Ltd. and found to be 135 nm.

A current density of 0.4 mA / cm ² and 0 for the cells of Examples 1, 3, 4 and Comparative Example 1 produced in a constant temperature bath at 25 ° C. using the charge / discharge test device BTS2004 manufactured by Nagano Co., Ltd. A charge / discharge test was performed at a voltage in the range of ~ 3.5V. Table 1 shows the results of calculating the energy (Wh) from the obtained discharge capacity and the average discharge voltage. In Table 1, the energy and discharge capacities of Examples 1, 3 and 4 are shown as standardized values in Comparative Example 1, respectively. At this time, the result of Comparative Example 1 was standardized as 100. Regarding the upper limit of the applied voltage, in Examples 1, 3 and 4 in which graphite was used as the positive electrode active material, up to 3.5 V could be applied, but in Comparative Example 1 in which activated carbon was used as the positive electrode active material, up to 2.5 V. Measured in.

The energy (product of discharge capacity and average discharge voltage) of Examples 1 and 3 using graphite as the positive electrode is 4.4 times and 3.2 times, respectively, as compared with Comparative Example 1 in which the conventional activated carbon is used as the positive electrode. It was found that all of them have high energy. This is because graphite, which can insert and desorb electrolyte ions between layers, can have a larger discharge capacity than activated carbon, which absorbs and desorbs electrolyte ions on the surface of pores. Further, in the case of the graphite positive electrode, the fact that the voltage can be higher than that of the activated carbon positive electrode is also mentioned as a factor of energy improvement.

Further, it was found that the discharge capacities of Examples 1 and 3 were 3.2 times and 2.3 times, respectively, as compared with Comparative Example 1, and the capacity could be increased. Further, in Example 4 in which lithium titanate was used as the negative electrode, the energy was 5.8 times and the discharge capacity was 3.3 times that of Comparative Example 1. This is because the discharge potential of lithium titanate in Example 4 is flatter than that of the activated carbon negative electrode of Example 1, the average voltage is higher, so that the energy is higher and the discharge capacity is also larger than that of activated carbon. It is thought that this is due to the fact.

Current density 0.4mA / cm ² , voltage for cells of Examples 1, 2, 4 and Comparative Examples 1 and 2 produced in a constant temperature bath at 60 ° C. using the charge / discharge test device BTS2004 manufactured by Nagano Co., Ltd. A 2000-hour continuous charging test (constant current constant voltage continuous charging test) was performed at 3.5 V. Table 2 shows the discharge capacity improvement rate obtained as a result. The discharge capacity improvement rate is defined as the charging time when the discharge capacity maintenance rate after the constant current constant voltage continuous charge test is 80% or less of the discharge capacity before the start of the constant current constant voltage continuous charge test. The time at which the life reached in Comparative Example 1 or Comparative Example 3 was standardized as 100, respectively. That is, the case where the activated carbon of Comparative Example 1 was used for both the positive electrode active material and the negative electrode active material and the case where the current collector on the positive electrode side of Comparative Example 2 was DLC coated were standardized as 100.

In Example 1 in which the carbon-plated aluminum foil was used for the current collector on the positive electrode side, the discharge capacity retention rate could be significantly improved to 47 times that of Comparative Example 1. Further, in the case of Example 2 in which the carbon-plated aluminum foil was also used for the current collector on the negative electrode side, it was possible to improve 54 times as much as in Comparative Example 1 and further improve the durability performance. Further, as a result of comparing Example 1 in which the carbon-plated aluminum foil was used for the current collector on the positive side with Comparative Example 2 in which only the DLC-coated aluminum foil was used, the result was 1.12 times improved, and carbon plating was performed. When the aluminum foil was used, the durability performance could be further improved as compared with the case where the DLC coated aluminum foil was used.

A voltage range of 0 to 3.5 V with a current density of 40 mA / cm ² for the cells of Example 1 and Comparative Example 2 produced in a constant temperature bath at 25 ° C. using the charge / discharge test device BTS2004 manufactured by Nagano Co., Ltd. in were charged and discharged, as the discharge rate, shown in Table 3 the result of calculating the ratio of the discharge capacity at 4.0 mA / cm ² to the discharge capacity at 0.4 mA / cm ^2. In Table 3, the discharge rate of Example 1 is shown as a standardized value in Comparative Example 2. At this time, the result of Comparative Example 2 was standardized as 100.

The discharge rate performance of Example 1 could be improved 1.26 times as compared with Comparative Example 2. The results show that the carbon-plated aluminum foil has a high sp ² structure ratio sp ² / (sp ² + sp ³ ) of 83%, which has a structure similar to graphite, and that it has a structure similar to that of graphite particles. It is considered that this is because the contact resistance is reduced, the unevenness of the plated carbon enhances the contact property with the active material particles, and the interfacial resistance between the current collector and the active material layer is reduced.

The graph of FIG. 1 shows the thickness (film thickness) (nm) of the carbon-plated film, the discharge capacity retention rate (%), and the discharge capacity (%) per electrode volume when the cell of Example 5 is used. It is a graph which shows the relationship of. The discharge capacity of the electrode was defined as the discharge capacity per electrode volume including the thickness of the current collector, and the discharge capacity when the thickness of the carbon plating film was 0 nm was standardized as 100.

From FIG. 1, it was found that when the thickness of the carbon plating film was 100 nm, the discharge capacity retention rate was 2890, and the high temperature durability performance was improved. By further increasing the thickness, it showed stable high temperature durability performance of 4600 to 4750 at 1000 nm or more.

In addition, the volume capacity of the electrode including the current collector decreases due to the increase in the thickness of the carbon plating film. From FIG. 1, it can be seen that the discharge capacity is reduced by 7% when the thickness of the carbon plating film is 10000 nm and when it is 0 nm. Since the high temperature durability performance became constant at 1000 nm or more, it is considered that the range of 1000 to 5000 nm is optimal from the viewpoint of the volume capacity of the electrode.

Claims

It ’s a hybrid capacitor,
The positive electrode contains graphite as the positive electrode active material and contains
The current collector on the positive electrode side is made of aluminum.
The aluminum material is a hybrid capacitor characterized in that the aluminum material is coated with a carbon plating film having a sp 2 structure content ratio sp 2 / (sp 2 + sp 3 ) of 80% or more.
The hybrid capacitor according to claim 1, wherein the thickness of the carbon plating film is 100 nm or more and 5000 nm or less.
The current collector on the negative electrode side is coated with an aluminum material coated with a carbon plating film, an aluminum material in which a conductive carbon layer is formed between the amorphous carbon film and the negative electrode active material, and an amorphous carbon film. The hybrid capacitor according to any one of claims 1 or 2, which is selected from the group consisting of aluminum material, etched aluminum, and aluminum material.
The hybrid capacitor according to any one of claims 1 to 3, wherein the graphite contains rhombohedral crystals.
The negative electrode is any one of claims 1 to 4, wherein the negative electrode contains at least one carbonaceous material selected from the group consisting of activated carbon, graphite, hard carbon, and soft carbon as the negative electrode active material, or lithium titanate. The hybrid capacitor described.
The hybrid capacitor according to any one of claims 1 to 5, wherein the carbon plating film is a plating film using a molten salt as a raw material.