TWI670736B - Hybrid capacitor - Google Patents

Abstract

A hybrid capacitor is used in a constant current and constant voltage continuous charging test at 60 ° C and 3.5V, which can maintain a discharge capacity retention rate of at least 80% or more for at least 1000 hours or more, and includes: including graphite as a positive electrode active material Positive electrode; and current collector made of aluminum. The aluminum material is coated with an amorphous carbon film with a thickness of 60 nm to 300 nm, and a conductive carbon layer is further provided between the amorphous carbon film and the positive electrode active material.

Description

   Hybrid capacitor   

The invention relates to a hybrid capacitor.

This application claims priority based on Japanese Patent Application No. 2017-139522 filed in Japan on July 18, 2017, the contents of which are incorporated herein by reference.

Conventionally, as a technique for storing electrical energy, an electric double layer capacitor (for example, refer to Patent Document 1) or a secondary battery is known. The electric double layer capacitor (EDLC: Electric double layer capacitor) has far better life, safety, and output density than secondary batteries. However, the electric double layer capacitor has a lower energy density (volume energy density) than the secondary battery is its subject.

Here, the energy (E) stored in the electric double-layer capacitor is represented by E = 1/2 × C × V ² using the capacitance (C) and applied voltage (V) of the capacitor. The energy system and the capacitance and application The square of the voltage is proportional to. Therefore, in order to improve the energy density of the electric double layer capacitor, a technique to increase the electrostatic capacity or applied voltage of the electric double layer capacitor has been proposed.

As a technique for increasing the electrostatic capacity of an electric double layer capacitor, a technique of increasing the specific surface area of activated carbon constituting the electrode of the electric double layer capacitor is known. Today, the known activated carbon has a specific surface area of 1000 m ² / g to 2500 m ² / g. An electric double layer capacitor using such activated carbon as an electrode uses an organic electrolytic solution in which a quaternary ammonium salt is dissolved in an organic solvent, or an aqueous electrolytic solution such as sulfuric acid as an electrolytic solution.

The wide range of voltages that can be used with organic electrolytes can increase the applied voltage, so the energy density can be increased.

As a person who uses the principle of an electric double layer capacitor to increase the applied voltage of the electric double layer capacitor, a lithium ion capacitor is known. The use of graphite or carbon that can insert and extract lithium ions in the negative electrode, and the use of activated carbon equivalent to the electrode material of the electric double layer capacitor that can absorb and desorb electrolyte ions in the positive electrode are called lithium ion capacitors. In addition, the use of activated carbon equivalent to the electrode material of the electric double layer capacitor for either the positive electrode or the negative electrode, and the use of metal oxides or conductive polymers as the electrode for Faraday reaction at the other electrode is called hybrid capacitor. (Hybrid capacitor). Regarding lithium ion capacitors, the negative electrode of the electrode constituting the electric double layer capacitor is composed of graphite or carbon black of the negative electrode material of the lithium ion secondary battery, and lithium ion is embedded in the graphite or carbon black. Lithium-ion capacitors are characterized by more general electric double-layer capacitors, that is, those whose poles are composed of activated carbon, have a larger applied voltage.

However, when graphite is used as an electrode, it is a problem that propylene carbonate cannot be used as an electrolyte. When graphite is used as an electrode, propylene carbonate is electrolyzed, and the decomposition product of propylene carbonate adheres to the graphite surface, which reduces the reversibility of lithium ions. Propylene carbonate is a solvent that can operate at low temperatures. When propylene carbonate is used as an electric double layer capacitor, the electric double layer capacitor can also operate at -40 ° C. Therefore, in lithium ion capacitors, hard carbon that is not easily decomposed by propylene carbonate is used for the electrode system. However, compared with graphite, hard carbon has a lower capacity per unit volume of electrode, and the voltage is lower than graphite (which becomes an expensive potential). Therefore, lithium ion capacitors have problems such as lower energy density.

When emphasis is placed on low-temperature characteristics, it is difficult to use high-capacity graphite as the negative electrode for lithium-ion capacitors, and it will be difficult to further increase the energy density. In addition, in the lithium ion capacitor, since the copper foil is used for the current collector in the same manner as the negative electrode of the lithium ion secondary battery, when overdischarge of 2 V or less is performed, copper will be eluted to cause a short circuit, and there is a problem that the discharge capacity decreases . Therefore, compared with an electric double layer capacitor capable of discharging to 0V, the method of using the lithium ion capacitor has a problem of being limited.

In the case of capacitors of a new concept, graphite is used as a positive electrode active material instead of activated carbon, and a reaction is developed in which a desorbed electrolyte ion is inserted between graphite layers (for example, refer to Patent Document 2). Patent Document 2 describes that in a conventional electric double-layer capacitor using activated carbon as a positive electrode active material, if a voltage exceeding 2.5 V is applied to the positive electrode, the electrolyte will decompose to generate gas. In contrast, the use of graphite for the positive electrode active material The electric double layer capacitor does not decompose the electrolyte even at a charging voltage of 3.5V, and can operate at a higher voltage than the conventional electric double layer capacitor using activated carbon as the positive electrode active material. Regarding cycle characteristics or low-temperature characteristics, output characteristics are also equal to or higher 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. The difference in the decomposition of the electrolyte results from such a huge difference in specific surface area.

In a new concept capacitor using graphite as a positive electrode active material, its practical application is hindered due to insufficient durability, but it has been found that a technique using an aluminum material covered with an amorphous carbon film as a current collector (see Patent Document 3), can improve the high temperature durability to a practical level. This new concept capacitor is a capacitor that uses a reaction in which electrolyte ions are desorbed between graphite layers on the positive electrode, and strictly speaking this is not an electric double layer capacitor, but in Patent Document 3, it is in a broad sense It is called an electric double layer capacitor.

Here, the durability test is generally performed by an accelerated test (high temperature durability test, charge-discharge cycle test) to increase the temperature. This test can be performed in accordance with the method of "durability (high temperature continuous rated voltage application) test" described in JIS D 1401: 2009. If the temperature is increased from room temperature by 10 ° C, the rate of deterioration will be approximately doubled. High temperature durability test, for example, a test at a constant temperature bath at 60 ° C (continuous charging) at a predetermined voltage (3 V or more in the present invention) for 2000 hours, and then returning to room temperature for charging and discharging, and measuring the discharge capacity at this time. After the high-temperature durability test, it is preferable that the discharge capacity retention rate with respect to the initial discharge capacity be 80% or more.

[Prior technical literature]

[Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 2011-046584

Patent Document 2: Japanese Patent Laid-Open No. 2010-040180

Patent Literature 3: International Publication No. 2017/216960

An electrode prepared by directly coating an active material such as graphite or activated carbon on an amorphous carbon thin film such as a diamond-like carbon (DLC) film covered with an aluminum material, since the amorphous carbon thin film and active material such as graphite or activated carbon Since the contact resistance between them is high, there is a problem of low discharge rate and low output characteristics.

In view of the above, the hybrid capacitor according to the present invention has been manufactured. The object of the present invention is to reduce the contact resistance between the current collector and the positive electrode active material, increase the discharge rate, enhance the output characteristics, and improve the high-temperature durability.

In order to solve the above-mentioned problems, the present invention provides the following means.

(1): One aspect of the present invention relates to a hybrid capacitor, which is capable of maintaining a discharge capacity retention rate of 80% or more for 1000 hours or more in a continuous charging test at a constant current and constant voltage of 60 ° C and 3.5V , Where: the positive electrode contains graphite as the positive electrode active material; the positive electrode side current collector is made of aluminum material; the aluminum material is coated with an amorphous carbon film; the thickness of the amorphous carbon film is 60 nm or more and 300 nm Less than meters; and a conductive carbon layer is further provided between the amorphous carbon film and the positive electrode active material.

(2): In the hybrid capacitor of the above point (1), the conductive carbon layer may contain graphite.

(3): In the hybrid capacitor of the above point (1) or (2), the conductive carbon layer may contain a binder.

(4): In any of the hybrid capacitors of the above points (1) to (3), the binder may be selected from the group consisting of cellulose, acrylic acid, polyvinyl alcohol, thermoplastic resin, rubber and organic resin An ethnic group.

(5): The hybrid capacitor according to any one of the above points (1) to (4) further includes a negative electrode-side current collector selected from the group consisting of an amorphous carbon film and A group consisting of an aluminum material with a conductive carbon layer between the amorphous carbon film and the negative electrode active material, an aluminum material covered with the amorphous carbon film, etched aluminum, and aluminum material.

According to the hybrid capacitor of the present invention, by providing the conductive carbon layer, the contact resistance between the current collector and the positive electrode active material can be reduced, the discharge rate can be improved, the output characteristics can be improved, and the high-temperature durability can be improved.

Furthermore, even if there are small holes in the amorphous carbon film, by providing a conductive carbon layer between the amorphous carbon film and the positive electrode active material as in the present invention, they can be sealed.

FIG. 1: A graph showing the discharge characteristics (discharge capacity retention rate when a constant current and constant voltage continuous charging test at 60 ° C.) of the hybrid capacitors of Example 1, Comparative Example 2 and Comparative Example 5 of the present invention is performed.

Hereinafter, the structure of the hybrid capacitor to which the present invention is applied will be described using drawings. In the drawings used in the following description, for easy understanding of the features, there are cases where the feature parts are enlarged for convenience, and the dimensional ratio of each component is not always the same as the actual one. In addition, the materials, sizes, etc. exemplified in the following description are only examples, and the present invention is not limited thereto, and can be implemented by appropriately changing within the scope of exerting effects.

The hybrid capacitor of one embodiment of the present invention is a hybrid capacitor capable of maintaining a discharge capacity retention rate of 80% or more for 1000 hours or more in a continuous charging test at a constant current and constant voltage of 60 ° C and 3.5V. It is provided with a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode contains graphite as a positive electrode active material. The positive electrode side current collector is made of aluminum material. The aluminum material is coated with an amorphous carbon film. The thickness of the amorphous carbon film It is 60 nm or more and 300 nm or less, and a conductive carbon layer is further provided between the amorphous carbon thin film and the positive electrode active material.

The positive electrode is formed by forming a positive electrode active material layer on a current collector (collector on the positive electrode side).

The positive electrode active material layer can be formed by applying a paste-like positive electrode material containing a binder and a conductive material in a desired amount to a positive electrode-side current collector and drying it.

As the binder, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propadiene rubber, styrene butadiene, acrylic, olefin, carboxymethyl cellulose (CMC) is a single system or a mixed system of two or more.

The conductive material is not particularly limited as long as the conductivity of the positive electrode active material can be made good, and a well-known conductive material can be used. For example, carbon black, carbon fiber (including carbon nanotubes (CNT), VGCF (registered trademark), etc., not limited to carbon nanotubes) and the like can be used.

The positive electrode side current collector is an aluminum material coated with an amorphous carbon film.

For the aluminum material of the base material, the aluminum material used for general current collector applications can be used.

The shape of the aluminum material can be made into foil, sheet, film, net, etc. For the current collector, aluminum foil is preferably used.

In addition, the aluminum material may be etched aluminum to be described later, in addition to those having a flat surface.

When the aluminum material is a foil, sheet, or film, its thickness is not particularly limited, but when the battery itself has the same size, the thinner it is, the more active materials can be enclosed in the battery case, but there is a disadvantage of reduced strength. Therefore, it is preferable to select an appropriate thickness so that the amount of active material put into the battery case can be increased without damaging the strength. The actual thickness is preferably 10 μm to 40 μm , and more preferably 15 μm to 30 μm . When the thickness is less than 10 μm , the aluminum material may be cracked or cracked in the step of roughening the surface of the aluminum material or in other manufacturing steps.

Etched aluminum can also be used for aluminum coated with amorphous carbon film.

The etched aluminum is roughened by etching. For etching, a method of immersing in an acid solution such as hydrochloric acid (chemical etching) or a method of electrolysis (electrochemical etching) using aluminum as an anode in an acid solution such as hydrochloric acid can be used. For electrochemical etching, since the current waveform during electrolysis, the composition of the solution, the temperature, etc. will make the etching shape different, it can be selected from the viewpoint of capacitor performance.

The aluminum material can be used for any one with or without a passivation layer on the surface. When a passivation film of a natural oxide film is formed on the surface of the aluminum material, an amorphous carbon passivation layer may be provided on the natural oxide film, or, for example, the natural oxide layer may be removed by argon sputtering.

The natural oxide film on aluminum is a passivation film, which has the advantage that it is not easily eroded by the electrolyte. On the other hand, it is also related to the increase of the collector resistance. Therefore, from the viewpoint of reducing the collector resistance, Oxide film is better.

In this specification, the amorphous carbon thin film refers to an amorphous carbon film or a hydrogenated carbon film, including a diamond-like carbon (DLC) film, a carbon hard film, an amorphous carbon (aC) film, and hydrogenated amorphous carbon (aC: H) film, etc. As a method for forming the amorphous carbon thin film, a well-known method such as a plasma CVD method using a hydrocarbon-based gas, a sputtering evaporation method, an ion plating method, and a vacuum arc evaporation method can be used. In addition, the amorphous carbon thin film preferably has a degree of conductivity as a current collector.

Among the exemplified materials of the amorphous carbon thin film, the diamond-like carbon is a material having an amorphous structure in which diamond bonds (SP ³ ) and graphite bonds (SP ² ) are mixed, and has high chemical resistance. However, when used as a thin film of a current collector, the conductivity is low, so in order to improve the conductivity, it is preferable to dope with boron or nitrogen.

The thickness of the amorphous carbon thin film is preferably 60 nm or more and 300 nm or less. The thickness of the amorphous carbon thin film is too thin if it is less than 60 nm, so that the coating effect of the amorphous carbon thin film becomes small, and the corrosion of the current collector in the constant current and constant voltage continuous charging test cannot be sufficiently suppressed. If it becomes too thick beyond 300 nm, the amorphous carbon thin film becomes a resistor, and the resistance with the active material layer increases. Therefore, it is preferable to appropriately select an appropriate thickness so that the coating effect of the amorphous carbon coating does not become small, and the resistance between the amorphous carbon thin film and the active material layer does not become large. The thickness of the amorphous carbon thin film is preferably 80 nm or more and 300 nm or less, and more preferably 120 nm or more and 300 nm or less. When the amorphous carbon film is formed by the plasma CVD method using hydrocarbon-based gas, the thickness of the amorphous carbon film can be controlled by the energy injected into the aluminum material, specifically by applying voltage, application time, and temperature control.

A conductive carbon layer is further provided on the amorphous carbon thin film layer. The thickness of the conductive carbon layer is preferably 5000 nm or less, more preferably 3000 nm or less. If the thickness exceeds 5000 nm, the energy density becomes smaller when the battery or electrode is formed. As the material of the conductive carbon layer, any type of carbon having high conductivity can be used, but it is preferable to contain graphite as carbon having high conductivity, and it is more preferable to contain only graphite.

The particle diameter of the material of the conductive carbon layer is preferably 1/10 or less of the size of graphite or activated carbon as an active material. This is because if the particle size falls within this range, the contact performance at the interface where the conductive carbon layer and the active material layer contact increases, and the interface (contact) resistance can be reduced. Specifically, the particle diameter of the carbon material of the conductive carbon layer is preferably 1 μm or less, and more preferably 0.5 μm or less.

In addition, when forming a conductive carbon layer, a binder is added together with a solvent to prepare a coating, and the coating is applied on an aluminum foil coated with DLC (hereinafter may be referred to as "DLC coated aluminum foil"). As the coating method, screen printing, gravure printing, a comma coater (registered trademark), a spin coater, or the like can be used. As the binder, cellulose, acrylic, polyvinyl alcohol, thermoplastic resin, rubber, and organic resin can be used. As the thermoplastic resin, polyethylene, polypropylene, or the like can be used. As the rubber, SBR (styrene-butadiene rubber), EPDM, or the like can be used. As the organic resin, phenol resin, polyimide resin, or the like can be used.

It is preferable that the conductive carbon layer has a small gap and low contact resistance between particles. In addition, as the solvent used to dissolve the binder for forming the conductive carbon layer, there are two kinds of solvents, an aqueous solution and an organic solvent. If the binder used to form the electrode active material layer is soluble in an organic solvent, it is preferable to use a binder soluble in an aqueous solution for the conductive carbon layer. In contrast, when the binder used to form the electrode active material layer is an aqueous solution, it is preferable to use an organic solvent-soluble binder for the conductive carbon layer. This is because, if the same type of solvent is used for the electrode active material layer and the conductive carbon layer, when the electrode active material layer is coated, the binder of the conductive carbon layer easily dissolves and is easily uneven.

The positive electrode active material used in the hybrid capacitor of this embodiment contains graphite. As graphite, either artificial graphite or natural graphite can be used. In addition, natural graphite is known to have scales and soils. Natural graphite is obtained by crushing and repeatedly mining the raw ore that has been excavated, which is called a beneficiation method. In addition, artificial graphite is manufactured, for example, by a graphitization step of firing a carbon material at a high temperature. More specifically, for example, a binder such as pitch can be added to the raw coke to form, and the primary firing can be performed by heating to about 1300 ° C, and then the primary firing product can be impregnated with asphalt resin, and then carried out at a high temperature near 3000 ° It is prepared by secondary firing. In addition, a coating of graphite particles coated with carbon can also be used.

Moreover, the crystal structure of graphite can be roughly divided into a hexagonal crystal with a layer structure composed of ABAB and a rhombohedral crystal with a layer structure composed of ABCABC. These conditions depend on whether the structures are in a single or mixed state, but any crystal structure or mixed state can be used. For example, Irisite graphite and carbon Japan ( ‧ ‧ ) The ratio of rhombohedral crystals of graphite of KS-6 (trade name) made by the joint-stock company is 26%. The metastable phase spherical carbon (MCMB) of artificial graphite manufactured by Osaka Gas Chemical Co., Ltd. The ratio is 0%.

Compared with the activated carbon used in the conventional EDLC, the graphite used in this example has a different mechanism for displaying the electrostatic capacity. In the case of activated carbon, with a large specific surface area, electrolyte ions are adsorbed and desorbed on the surface to generate electrostatic capacity. On the other hand, in the case of graphite, the electrostatic capacity is exhibited by the intercalation and deintercalation (intercalation-deintercalation) of anions which are electrolyte ions between graphite layers. Due to this difference, in Patent Document 3, the hybrid capacitor using graphite according to the present embodiment is broadly referred to as an electric double layer capacitor, but is different from the EDLC using activated carbon having an electric double layer.

Since the current collector of the present invention has an amorphous carbon thin film on the surface of the aluminum material, the aluminum material is prevented from coming into contact with the electrolyte, and the current collector can be prevented from being corroded by the electrolyte during high-voltage charging. Furthermore, since the current collector also has a conductive carbon layer, the corrosion resistance is further improved and a more stable hybrid capacitor can be obtained.

The negative electrode is formed by forming a negative electrode active material layer on a current collector (negative electrode-side current collector).

The negative electrode active material layer can be formed by applying a slurry-like negative electrode material mainly containing a negative electrode active material, a binder, and a conductive material in an amount as required to the negative electrode current collector and drying it.

As the negative electrode active material, materials capable of adsorbing and desorbing or intercalating (intercalating-extracting) cations of electrolyte ions can be used. For example, carbon materials such as activated carbon, graphite, hard carbon, and soft carbon, and lithium titanate can be used. , Where lithium titanate is an electrode potential material lower than carbonaceous materials.

A well-known one can be used for the negative electrode current collector. For example, an aluminum material selected from an amorphous carbon film coated with amorphous carbon and having a conductive carbon layer provided between the amorphous carbon film and the negative electrode active material, or an amorphous carbon film can be used. A group consisting of coated aluminum, etched aluminum, and aluminum. Preferably, an aluminum material coated with an amorphous carbon film on the negative electrode side and having a conductive carbon layer between the amorphous carbon film and the negative electrode active material, or an aluminum material coated with amorphous carbon is used When the hybrid capacitor is operated with a high voltage, the high-temperature durability can be improved.

As the binder, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propadiene rubber, styrene butadiene, acrylic, olefin, carboxymethyl cellulose (CMC) is a single system or a mixed system of two or more.

The conductive material is not particularly limited as long as the conductivity of the negative electrode active material layer can be made good, and a well-known conductive material can be used. For example, carbon black, carbon fiber (including carbon nanotubes (CNT), VGCF (registered trademark), etc., not limited to carbon nanotubes) and the like can be used.

As the electrolyte, an organic electrolyte using an organic solvent can be used. The electrolyte contains electrolyte ions that can be adsorbed and desorbed from the electrode. The type of electrolyte ions should be as small as possible. Specifically, an ammonium salt or a phosphorus salt, or an ionic liquid, a lithium salt, or the like can be used.

As the ammonium salt, tetraethylammonium (TEA) salt, triethylammonium (TEMA) salt, etc. can be used. As the phosphorus salt, a spiro compound having two five-membered rings can be used.

The type of ionic liquid is not particularly limited, and considering the ease of movement of electrolyte ions, a material with a viscosity as low as possible or a high conductivity (conductivity) is preferable. Specific 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- propyl-pyrrolizinium) (MPPy) ion, 1-methyl-1-propyl-piperizinium (MPPi) ion, etc. In addition, lithium tetrafluoroborate LiBF ₄ , lithium hexafluorophosphate LiPF ₆ and the like can be used as the lithium salt.

Examples of the pyridinium ion include 1-ethylpyridium ion, 1-buthylpyridnium ion, and the like.

Examples of the anion constituting the ionic liquid include BF ₄ ion, PF ₆ ion, [(CF ₃ SO ₂ ) ₂ N] ion, FSI (bis (fluorosulfonyl) imide; bis (fluorosulfonyl) imide) ion, TFSI ( Bis (trifluoromethanesulfonyl) imide; bis (trifluorosulfonyl) imide) ions, etc.

The solvent can be acetonitrile, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl sulfone, ethyl isopropyl sulfone, ethyl carbonate, fluoroethylene carbonate, γ butyrolactone , Cyclobutane, N, N-dimethylformamide, or dimethyl sulfoxide, alone or in a mixed solvent.

The separator is preferably a cellulose-based paper-like separator, a glass fiber separator, or a microporous membrane such as polyethylene or polypropylene for reasons such as preventing short circuit of the positive electrode and the negative electrode, or ensuring storage stability of the electrolyte.

According to the hybrid capacitor of this embodiment, by providing the conductive carbon layer, the contact resistance of the amorphous carbon film covering the current collector and the positive electrode active material can be reduced, the discharge rate can be improved, the output characteristics can be improved, and the high-temperature durability can be improved.

Furthermore, even if there are small holes in the amorphous carbon thin film, by providing a conductive carbon layer between the amorphous carbon thin film and the positive electrode active material as in this embodiment, they can be sealed.

In this embodiment, the graphite positive electrode using an aluminum material coated with an amorphous carbon thin film and provided with a conductive carbon layer between the amorphous carbon thin film and the negative electrode active material is not limited to hybrid capacitors. The graphite positive electrode can also be used as an electrode of a lithium ion capacitor, for example, by using a material alloyed with lithium such as hard carbon, soft carbon, graphite, lithium metal, tin or silicon, or lithium titanate as a negative electrode.

In addition, the aluminum material coated with amorphous carbon and provided with a conductive carbon layer between the amorphous carbon film and the negative electrode active material used in this embodiment exhibits an effect even when activated carbon is used as the positive electrode active material The above-mentioned effects make it possible to increase the voltage compared to the past. However, because the specific surface area of activated carbon is higher than that of graphite by two to three digits, and the reaction area of the electrode becomes larger, the decomposition of the electrolyte, the decomposition of the activated carbon itself, or the decomposition of functional groups on the surface of the activated carbon Etc., and has the effect of gas generation caused by the increase of the internal pressure of the gas. Therefore, only the combination of activated carbon and an aluminum material coated with amorphous carbon and provided with a conductive carbon layer between the amorphous carbon film and the negative electrode active material cannot obtain the effect of this embodiment.

    (Example)    

The effect of the present invention will be made clearer by the following examples. It should be noted that the present invention is not limited to the following embodiments, but can be implemented by appropriate changes within the scope of exerting effects.

[Example 1]

First, the positive electrode-side current collector is a DLC-coated aluminum foil coated with a conductive carbon layer, which is produced as follows. Using a screen printing machine, the graphite conductive paste (trade name: Bunny Height T-602U, cellulose-based resin binder, and aqueous solution) manufactured by Japan Graphite Industry Co., Ltd. was coated on the DLC-coated aluminum foil (thickness 20 μm ) To form a conductive carbon layer, after that, it was dried in a hot air dryer at 100 ° C. for 20 minutes to obtain a current collector. DLC coated aluminum foil is equivalent to an aluminum material coated with an amorphous carbon film. In addition, the DLC-coated aluminum foil covered with a conductive carbon layer is covered with an amorphous carbon film, and the conductive carbon layer corresponds to an aluminum material provided between the amorphous carbon film and the positive electrode active material. The manufacturing method of DLC coated aluminum foil is to remove the natural oxide film on the surface of the aluminum foil by argon sputtering on the aluminum foil with a purity of 99.99%, and then discharge it in the mixed gas of methane, acetylene and nitrogen near the aluminum surface to generate plasma , By applying a negative pulse voltage to the aluminum material to generate a DLC film. The thickness of the DLC film on the DLC-coated aluminum foil was measured with a probe-type surface shape measuring device DektakXT manufactured by BRUKER, and the result was 135 nm.

Next, combine Iris graphite and Carbon Japan ( ‧ ‧ ) Graphite (trade name: KS-6; average particle size 6 microns), acetylene black (conductive material), polyvinylidene fluoride (organic solvent-based binder) manufactured by the joint stock company at a weight percentage concentration of 80:10:10 ( wt%) ratio, and dissolve and mix with N-methylpyrrolidone (organic solvent) to obtain a slurry as a positive electrode active material, and apply the slurry to the current collector prepared previously as a positive electrode using a doctor blade . The positive electrode side current collector was measured using a micrometer, which was 0.08 mm.

Next, the activated carbon (trade name: MSP-20), acetylene black (conductive material), and polyvinylidene fluoride (organic solvent-based binder) manufactured by Kansai Thermochemical Co., Ltd. were concentrated at a weight percentage of 80:10:10. The ratio (wt%) was weighed, and the slurry obtained by dissolving and mixing N-methylpyrrolidone (organic solvent) was applied to an etched aluminum foil (20 μm) manufactured by Nippon Electric Appliance Industry Co., Ltd. using a doctor blade as a negative electrode.

Next, the positive electrode and the negative electrode were punched into a disc shape with a diameter of 16 mm, and vacuum-dried at 150 ° C. for 24 hours, and then moved to an argon glove box. These paper separators manufactured by Japan High Paper Industry Co., Ltd. were laminated and 0.1 mL of electrolyte was added (wherein the electrolyte used 1M TEA-BF ₄ (tetraethylammonium tetrafluoroborate) as the electrolyte, and SL + DMS (Sulfolane + dimethyl sulfide) as a solvent), making a 2032 button-type battery in an argon glove box.

[Example 2]

Except that the positive electrode current collector of the DLC-coated aluminum foil coated with a conductive carbon layer of Example 1 was used as the negative electrode current collector, the same 2032-type button-type battery as Example 1 was produced.

[Example 3]

A 2032 type button battery similar to Example 1 was produced except that artificial graphite (MCMB6-10) manufactured by Osaka Gas Chemical Co., Ltd. was used as the positive electrode active material.

[Example 4]

The preparation was the same as in Example 1 except that lithium titanate Li ₄ Ti ₅ O ₁₂ as a negative electrode active material, and 1M lithium tetrafluoroborate LiBF ₄ electrolyte and propylene carbonate (PC) solvent were used as electrolytes. 2032 type button battery.

[Example 5]

DLC-coated aluminum foil was prepared by the same method as in Example 1, and a graphite conductive paste (trade name: Bunny Height UCC-2, rubber-type adhesive, toluene solvent) manufactured by Japan Graphite Industry Co., Ltd. was coated thereon to The positive electrode side current collector is formed. In addition, the binder for the positive electrode is 10 wt% of polyacrylic acid (as an aqueous binder (trade name: AZ-9001)) manufactured by Zeon Corporation of Japan and CMC (carboxymethyl cellulose, a commercial product manufactured by Zeon Corporation of Japan). Name: BM-400) 10wt%. Except for this, a 2032 type button battery similar to Example 1 was produced.

Furthermore, when an aluminum foil (without a conductive carbon layer) with a thickness of the conductive carbon layer of 0 nm is used as the current collector on the positive electrode side, this is not an example of the present invention, but corresponds to Comparative Example 2, Comparative Example 4, and Comparative Example 5 .

[Comparative Example 1]

The activated carbon (trade name: MSP-20) of the negative electrode active material in Example 1 is also used as the positive electrode active material (that is, the activated carbon is used not only for the positive electrode active material but also for the negative electrode active material). Except for this, a 2032 type button battery similar to Example 1 was produced.

[Comparative Example 2]

A 2032 type button battery as in Example 1 was manufactured except that DLC-coated aluminum foil not coated with a conductive carbon layer was used as the positive electrode-side current collector.

[Comparative Example 3]

The activated carbon (trade name: MSP-20) of the negative electrode active material in Example 1 was also used as the positive electrode active material, and the binder of the positive electrode was polyacrylic acid (trade name: AZ-9001) 10wt as an aqueous solution binder % And Japanese CMC (carboxymethyl cellulose, trade name: BM-400) 10wt%. Except for this, a 2032 type button battery similar to Example 1 was produced.

[Comparative Example 4]

A 2032 type button battery similar to that of Example 5 was manufactured except that DLC-coated aluminum foil not coated with a conductive carbon layer was used as the current collector on the positive electrode side.

[Comparative Example 5]

In Example 1, the etched aluminum foil (thickness 20 μm) manufactured by Japan Accumulator Industry Co., Ltd. used as the negative electrode side current collector was also used as the positive electrode active material (that is, the etched aluminum foil was not only used for the positive electrode side current collector It is also used for the negative electrode current collector). Except for this, a 2032 type button battery similar to Example 1 was produced.

(Test 1) <Evaluation (Energy, Discharge Capacity)>

For the fabricated batteries of Example 1, Example 3, Example 4, Example 5, Comparative Example 1, and Comparative Example 3, a charge-discharge test device BTS2004 manufactured by Nagano Co., Ltd. was used in a constant temperature bath at 20 ° C. to The current density of 0.4mA / cm ² is charged and discharged in the voltage range of 0 to 3.5V. As a result, the energy (Wh) was calculated from the obtained discharge capacity and average discharge voltage, and the results are shown in Table 1. Table 1 shows the values of the energy and discharge capacity of Example 1, Example 3, Example 4 and Example 5 after being standardized with Comparative Example 1 and Comparative Example 3, respectively. At this time, the results of Comparative Example 1 and Comparative Example 3 were normalized to 100.

In addition, the upper limit of the applied voltage can be applied to 3.5 V in Examples 1, 3, 4 and 5 using graphite as the active material, but Comparative Examples 1 and 3 using activated carbon in the positive electrode It is measured until 2.5V.

Compared to Comparative Example 1 using activated carbon as the positive electrode active material, the energy (product of the discharge capacity and the average discharge voltage) of Examples 1 and 3 using graphite as the positive electrode active material became 4.2 times and 3.1 times, respectively, which can be achieved High energy. This is presumably because graphite can intercalate and desorb electrolyte ions between its layers (between layers), so that the discharge capacity can be increased compared to activated carbon that adsorbs and desorbs electrolyte ions only on the surface of fine pores. Regarding the actual discharge capacity, the battery of Comparative Example 1 can be tripled in Example 1 and 2.2 times higher in Example 3. In addition, when graphite is used as the positive electrode active material, compared with the use of activated carbon as the positive electrode active material, the voltage can be increased and the main reason for the energy increase.

In addition, in Example 4 where graphite was used as the positive electrode active material and lithium titanate was used as the negative electrode active material, the energy became 6.0 times that of Comparative Example 1 using activated carbon as the positive electrode active material and the negative electrode active material. , The discharge capacity becomes 3.5 times. Although the point of using graphite as the positive electrode active material is the same, compared with Example 1 using activated carbon as the negative electrode active material, the discharge potential of Example 4 using lithium titanate as the negative electrode active material is flatter. Therefore, the average voltage becomes higher, and high energy can be achieved. Furthermore, since the discharge capacity has a greater effect than activated carbon, the capacity can be increased.

In addition, the battery of Example 5 and Comparative Example 3 using polyacrylic acid (as an aqueous solution-type binder) and CMC, and a conductive carbon layer using rubber (as an organic solvent-type binder) for the positive electrode binder, the configuration and The configuration of Example 1 is reversed, that is, it is configured to use an aqueous binder as the binder of the positive electrode active material layer and an organic solvent-type binder for the conductive carbon layer. From these results, it can be seen that, as in the battery of Example 1, the energy and discharge capacity are higher than that of Comparative Example 3, and it is understood that high energy and high capacity can be achieved without the difference of the solvent without the binder.

The difference between Example 1 and Example 3 is that only the type of graphite of the positive electrode active material is different, but the energy and discharge capacity are different as shown in Table 1.

Iris graphite and carbon Japan ( ‧ ‧ ) Graphite (trade name: KS-6) made by a joint-stock company contains 26% rhombohedral crystals (hence, hexagonal crystals are 76%). In contrast, metastable phase spherical carbon (MCMB) made by Osaka Gas Chemical Co., Ltd. ) Does not contain rhombohedral crystals.

The rhombohedral crystal is a layer structure composed of ABCABC, and the hexagonal crystal is a layer structure composed of ABAB. It is speculated that the difference in crystal structure will also affect the above properties. That is, rhombohedral crystals are larger than hexagonal crystals due to structural changes caused by ion insertion, which is a factor affecting the difficulty of ion insertion.

From the results shown in Table 1, from the viewpoint of energy and discharge capacity, it is preferable that the graphite of the positive electrode active material contains rhombohedral crystals.

(Test 2) <Evaluation (discharge capacity improvement rate)>

For the fabricated batteries of Example 1, Example 2, Example 4, Example 5, and Comparative Examples 1 to 5, a charge-discharge test device (manufactured by Nagano, BTS2004) was used to charge in a constant temperature bath at 60 ° C. A continuous charging test (constant current and constant voltage continuous charging test) was carried out at a current of 0.4 mA / cm ² and a voltage of 3.5 V for 2000 hours. Specifically, after stopping charging within a predetermined time during the charging period, after transferring the battery to a constant temperature bath at 25 ° C., it was carried out 5 times at a current density of 0.4 mA / cm ² and a voltage range of 0 V to 3.5 V as in Test 1. Charge and discharge test to obtain discharge capacity. After that, return to the thermostat at 60 ° C and restart the continuous charging test, and perform the test until the sum of the continuous charging test time reaches 2000 hours.

The resulting improvement in discharge capacity is shown in Table 2. The discharge capacity improvement rate is defined as the life of the charging time when the discharge capacity maintenance rate after the constant current constant voltage continuous charging test becomes less than 80% with respect to the discharge capacity before the constant current constant voltage continuous charging test is started The life time in Example 1, Comparative Example 2 or Comparative Example 4 is normalized to 100. That is, Comparative Example 1 when activated carbon is used not only as a positive electrode active material but also as a negative electrode active material, and when etched aluminum foil is used for the negative electrode side current collector, or when DLC coated aluminum foil is not coated with a conductive carbon layer Example 2 and Comparative Example 4 are standardized to 100.

Example 1 using graphite as the positive electrode active material, and using DLC coated aluminum foil and coated with a conductive carbon layer as the positive electrode side current collector, the discharge capacity retention rate after a 2000 hour constant current and constant voltage continuous charging test 92%.

In addition, graphite is used as the positive electrode active material, and in addition to using DLC coated aluminum foil and coated with a conductive carbon layer as the positive electrode side current collector, there is Example 4 using lithium titanate as the negative electrode active material. The discharge capacity maintenance rate after the continuous charging test with constant current and voltage at the hour was 83%.

In addition, graphite is used as the positive electrode active material, and in addition to using DLC coated aluminum foil and coated with a conductive carbon layer as the positive electrode side current collector, there is also an organic solvent type rubber binder used in the conductive carbon layer, And in Example 5 using polyacrylic acid and CMC with an aqueous binder in the positive electrode active material layer, the discharge capacity retention rate after a 2000-hour constant current and constant voltage continuous charging test was 93%.

The hybrid capacitor of the present invention can meet the specification of a discharge capacity retention rate of 80% or more after a continuous charging test at a voltage of 3V or more (especially a high voltage of 3.5V or more) and a constant current and constant voltage of 2000 hours at 60 ° C .

In contrast, in Comparative Example 1 or Comparative Example 3 using activated carbon as the positive electrode active material, and using DLC coated aluminum foil and coated with a conductive carbon layer as the positive electrode side current collector, the discharge capacity retention rates were 21 hours and 16 respectively Hours become below 80%. This is because although the corrosion resistance of the current collector itself can be maintained during the continuous charging test, the reason is that since the activated carbon and the electrolyte solution react at a high voltage of 3.5V, the surface of the activated carbon is covered by the decomposition products of the electrolyte .

In addition, Comparative Example 5 using graphite as the positive electrode active material and using etched aluminum foil as the positive electrode side current collector had a discharge capacity retention rate of 80% or less at 65 hours.

In either Example 1 or Example 4, graphite was used as the positive electrode active material, and DLC-coated aluminum foil covered with a conductive carbon layer was used as the positive electrode side current collector. On the other hand, in Comparative Example 1, activated carbon was used as the positive electrode active material, and DLC-coated aluminum foil covered with a conductive carbon layer was used as the positive electrode side current collector. As shown in Table 2, in Examples 1 and 4, compared with Comparative Example 1, the discharge capacity improvement rate was significantly increased to 45 times and 31 times.

This result shows that only by simply combining activated carbon and the DLC-coated aluminum foil covered with the conductive carbon layer of the present invention, the same effect as this embodiment cannot be obtained.

In addition, in Example 2 using graphite as the positive electrode active material and DLC-coated aluminum foil covered with a conductive carbon layer as the positive electrode-side current collector, the discharge capacity retention rate relative to Comparative Example 1 was 49 times, which can be further improved High temperature durability.

This result indicates that corrosion of the current collector is also a major factor hindering the durability of the negative electrode side.

In addition, in Example 1 using DLC-coated aluminum foil covered with the conductive carbon layer of the present invention as the positive electrode-side current collector, compared with Comparative Example 2 using DLC-coated aluminum foil not coated with a conductive carbon layer It can be seen that the discharge capacity maintenance rate increased to 1.06 times. In addition, in contrast to the configuration of Example 1, that is, an aqueous binder is used for the positive electrode active material layer, and an organic solvent-based binder is used for the conductive carbon layer, the discharge capacity retention rate in Example 5 is 1.08 times. The same effect as in Example 1 was confirmed.

The results show that by providing the conductive carbon layer, the contact resistance between the amorphous carbon film and the positive electrode active material can be reduced, and it is not affected by the difference in the solvent of the binder of the electrode layer or the conductive carbon layer.

(Test 3)

Except for the batteries of Example 1, Comparative Example 2, and Comparative Example 5 that were produced, the same continuous charging test (constant current and constant voltage continuous charging test) as in Test 2 was performed. The results are shown in the graph in Figure 1. In this figure, the discharge capacity before the start of the test is 100, and after the start of the test, the discharge capacity after each charging time is displayed in a ratio to the discharge capacity of 100. The horizontal axis of the graph indicates that the constant current and voltage at 60 ° C are continuous. Charging time (h), the vertical axis of the graph represents the discharge capacity retention rate (%).

In Comparative Example 5 using an etched aluminum foil as a current collector, the discharge capacity of 400 hours or more could not be maintained. On the other hand, Example 1 and Comparative Example 2 using DLC-coated aluminum foil as a current collector showed a high discharge capacity retention rate of 80% or more after 1000 hours. This is considered to be because the DLC film prevents the electrolyte from directly contacting the aluminum foil, and can suppress corrosion of the aluminum foil by the electrolyte.

In addition, when comparing Example 1 and Comparative Example 2, Example 1 shows a higher discharge capacity retention rate. This difference is considered to be caused by whether a conductive carbon layer is further provided on the DLC film coated with DLC aluminum foil. Since the particles of the conductive carbon layer have more unevenness and higher conductivity than the DLC film, it is considered that by providing the conductive carbon layer, an increase in contact resistance between the current collector and the positive electrode active material layer can be suppressed.

(Test 4)

In addition to a battery as the object is produced in Example 1 and Example 5 of the battery, and the current density of 0.4mA / cm ² and 4.0mA / cm ^2, to accomplish the same charge and discharge test test 1, thereby obtaining the discharge capacity . About Example 1 and Example 5, is calculated at 4.0mA / cm ² with respect to the discharge capacity to the discharge capacity ratio of 0.4mA / cm ^2, thereby obtaining discharge rate. Table 3 shows the values of the discharge rates of Example 1 and Example 5 after normalization with Comparative Example 2 and Comparative Example 4, respectively. At this time, the results of Comparative Examples 2 and 4 were normalized to 100.

Compared with Comparative Example 2 using a DLC coated aluminum foil not coated with a conductive carbon layer as the positive electrode side current collector, the discharge rate performance of Example 1 of the present invention using a DLC coated aluminum foil coated with a conductive carbon layer is 1.32 times, so the discharge rate performance can be improved. This is considered to be because the graphite in the conductive carbon layer formed on the DLC-coated aluminum foil is submicron particles compared to the case where the graphite active material with an average particle size of 6 μm is directly coated on the DLC-coated aluminum foil Therefore, the adhesion (contact performance) with the DLC-coated aluminum foil increases, the contact resistance between the current collector and the graphite positive electrode active material layer decreases, and the conductive carbon layer has large unevenness compared to the DLC film Therefore, the adhesion to the graphite active material layer formed on the conductive carbon layer increases, and the contact resistance between the current collector and the graphite positive electrode active material layer decreases.

In addition, the structure opposite to that of Example 1, that is, Example 5 using an aqueous binder in the positive electrode active material layer and using an organic solvent type binder in the conductive carbon layer, also has a discharge rate characteristic of 1.42 times, and can obtain a specific performance Example 1 has a higher effect.

According to the above, by using a DLC coated aluminum foil covered with a conductive carbon layer according to an embodiment of the present invention as a current collector, the current collector can be reduced compared to the case where a DLC coated aluminum foil not coated with a conductive carbon layer is used Contact resistance with positive electrode active material, increase discharge rate, improve output characteristics and improve high temperature durability.

[Industrial availability]

It is possible to reduce the contact resistance between the current collector and the positive electrode active material, improve the discharge rate, improve the output characteristics, and improve the high-temperature durability, and it can be used as a means for storing electrical energy in power storage devices and the like.

Claims (5)

A hybrid capacitor, which is capable of maintaining a discharge capacity retention rate of more than 80% for more than 1000 hours in a continuous charging test at a constant current and constant voltage of 60 ° C and 3.5V. The hybrid capacitor includes: a positive electrode, including graphite as a positive electrode Substance; a positive electrode side current collector made of aluminum material; wherein the aluminum material is coated with an amorphous carbon film; the thickness of the amorphous carbon film is 60 nm or more and 300 nm or less; and in A conductive carbon layer is further provided between the amorphous carbon film and the positive electrode active material; the particle size of the material of the conductive carbon layer is less than 1/10 of the size of the size of the positive electrode active material; an electrolytic solution containing electrolyte ions; The electrostatic capacity is exhibited by the intercalation and desorption of anions of the electrolyte ions between the graphite layers. The hybrid capacitor as described in item 1 of the patent application scope, wherein the conductive carbon layer comprises graphite. The hybrid capacitor as described in item 1 or 2 of the patent application, wherein the conductive carbon layer contains a binder. The hybrid capacitor as described in item 1 or 2 of the patent application, wherein the conductive carbon layer contains a binder selected from cellulose, acrylic, polyvinyl alcohol, thermoplastic resin, rubber and organic resin A group of people. The hybrid capacitor as described in item 1 or 2 of the patent application scope further includes a negative electrode side current collector selected from the group consisting of an amorphous carbon film coated with a conductive carbon layer A group consisting of an aluminum material between the amorphous carbon thin film and the negative electrode active material, an aluminum material covered with the amorphous carbon thin film, an etched aluminum, and an aluminum material.