CN110914942B - Hybrid capacitor - Google Patents

Hybrid capacitor Download PDF

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Publication number
CN110914942B
CN110914942B CN201880046902.5A CN201880046902A CN110914942B CN 110914942 B CN110914942 B CN 110914942B CN 201880046902 A CN201880046902 A CN 201880046902A CN 110914942 B CN110914942 B CN 110914942B
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positive electrode
active material
electrode active
graphite
amorphous carbon
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CN110914942A (en
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芳尾真幸
浅田敏広
石井亮太
小林直哉
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Fang Weizhenxing
TPR Co Ltd
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Fang Weizhenxing
TPR Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/04—Hybrid capacitors
    • H01G11/06—Hybrid capacitors with one of the electrodes allowing ions to be reversibly doped thereinto, e.g. lithium ion capacitors [LIC]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/26—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features
    • H01G11/28—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features arranged or disposed on a current collector; Layers or phases between electrodes and current collectors, e.g. adhesives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/32—Carbon-based
    • H01G11/38—Carbon pastes or blends; Binders or additives therein
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/66—Current collectors
    • H01G11/68—Current collectors characterised by their material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/66—Current collectors
    • H01G11/70—Current collectors characterised by their structure
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/13—Energy storage using capacitors

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Electric Double-Layer Capacitors Or The Like (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)
  • Cell Electrode Carriers And Collectors (AREA)

Abstract

The present invention relates to a hybrid capacitor, which can maintain a discharge capacity retention ratio of 80% or more for 1000 hours or more in a constant current constant voltage continuous charge test at 60 ℃ and 3.5V, and which comprises: a positive electrode containing graphite as a positive electrode active material, and a current collector composed of an aluminum material. The aluminum material is covered with an amorphous carbon coating having a thickness of 60nm to 300nm, and a conductive carbon layer is further provided between the amorphous carbon coating and the positive electrode active material.

Description

Hybrid capacitor
Technical Field
The present invention relates to a hybrid capacitor.
The present application claims priority based on Japanese patent application No. 2017-139522 filed from the sun on 7/18/2017, the contents of which are incorporated herein by reference.
Background
Conventionally, as a technique for storing electric energy, an electric double layer capacitor (see, for example, patent document 1) and a secondary battery are known. An Electric Double Layer Capacitor (EDLC) is excellent in life, safety, and output density compared to a secondary battery. However, the electric double layer capacitor has a problem that the energy density (volumetric 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 using the capacitance (C) of the capacitor and the applied voltage (V)2The energy 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 of increasing the capacitance and applied voltage of the electric double layer capacitor has been proposed.
As a technique for increasing the capacitance of an electric double layer capacitor, a technique for increasing the specific surface area of activated carbon constituting an electrode of an electric double layer capacitor is known. Currently, the known activated carbon has a specific surface area of 1000m2/g～2500m2(ii) in terms of/g. In an electric double layer capacitor using such an activated carbon as an electrode, an organic electrolyte solution obtained by dissolving a quaternary ammonium salt in an organic solvent, an aqueous electrolyte solution such as sulfuric acid, or the like is used as an electrolyte solution.
Since the organic electrolytic solution can be used at a wide voltage range, the applied voltage can be increased, and the energy density can be increased.
As a capacitor for increasing an applied voltage by utilizing the principle of an electric double layer capacitor, a lithium ion capacitor is known. Graphite or carbon capable of intercalating and deintercalating lithium ions is used for the negative electrode, and activated carbon equivalent to an electrode material of an electric double layer capacitor capable of adsorbing and desorbing electrolyte ions is used for the positive electrode, and the device is referred to as a lithium ion capacitor. A device using activated carbon equivalent to an electrode material of an electric double layer capacitor for either the positive electrode or the negative electrode and using a metal oxide or a conductive polymer as an electrode for inducing a faraday reaction for the other electrode is called a Hybrid capacitor (Hybrid capacitor). Among electrodes constituting an electric double layer capacitor, a lithium ion capacitor is an electrode in which a negative electrode is made of graphite, hard carbon, or the like, which is a negative electrode material of a lithium ion secondary battery, and lithium ions are inserted into the graphite or the hard carbon. The lithium ion capacitor has a characteristic of having a larger applied voltage than a general electric double layer capacitor, that is, a capacitor in which both electrodes are made of activated carbon.
However, when graphite is used for the electrode, there is a problem that propylene carbonate (propylene carbonate) known as a solvent of the electrolyte cannot be used. The reason for this is that, when graphite is used as the electrode, propylene carbonate is electrolyzed, and the decomposition product of propylene carbonate adheres to the surface of graphite, and the reversibility of lithium ions is reduced. Propylene carbonate is a solvent that is also operable at low temperatures. In the case of applying the propylene carbonate to an electric double layer capacitor, the electric double layer capacitor can be operated at-40 ℃. Therefore, in the lithium ion capacitor, hard carbon in which propylene carbonate is hard to decompose is used for the electrode material. However, hard carbon has a low capacity per unit volume of the electrode compared to graphite, and the voltage is also lower (reaches a positive potential) compared to graphite. Therefore, there is a problem that the energy density of the lithium ion capacitor is low.
When low temperature characteristics are regarded as important, it is difficult to increase the energy density of a lithium ion capacitor in which high-capacity graphite is difficult to use as a negative electrode. Further, in the lithium ion capacitor, since the copper foil is used for the current collector as in the negative electrode of the lithium ion secondary battery, there is a problem that the copper is eluted to cause a short circuit or to decrease the charge/discharge capacity when overdischarge of 2V or less is performed. Therefore, the lithium ion capacitor has a problem that a use method is limited as compared with an electric double layer capacitor capable of discharging up to 0V.
As a capacitor of a new concept, a capacitor has been developed which uses graphite as a positive electrode active material instead of activated carbon and utilizes a reaction of intercalation and deintercalation of electrolyte ions between graphite layers (for example, see patent document 2). Patent document 2 describes that, in a conventional electric double layer capacitor using activated carbon as a positive electrode active material, decomposition of an electrolyte occurs and gas is generated when a voltage of more than 2.5V is applied to a positive electrode, whereas in a capacitor of a new concept using graphite as a positive electrode active material, decomposition of an electrolyte is not caused even at a charging voltage of 3.5V, and operation at a higher voltage is possible as compared with a conventional electric double layer capacitor using activated carbon as a positive electrode active material. The cycle characteristics, low-temperature characteristics, and output characteristics are equal to or more than those of conventional electric double layer capacitors. The specific surface area of graphite is a few hundred times the specific surface area of activated carbon, and the difference in the decomposition effect of the electrolyte results from the large difference in the specific surface area.
It is currently known that: in a capacitor of a new concept using graphite as a positive electrode active material, the durability is insufficient, and therefore, practical use is hindered; however, by using an aluminum material coated with an amorphous carbon coating for the current collector (see patent document 3), the high-temperature durability can be improved to a practical level. Note that the capacitor of this new concept is a capacitor using a reaction of intercalation and deintercalation of electrolyte ions between graphite layers in a positive electrode, and is not strictly an electric double layer capacitor, but is referred to as an "electric double layer capacitor" in a broad sense in patent document 3.
Here, the durability test is generally performed by raising the temperature to accelerate the test (high-temperature durability test, charge/discharge cycle test). This test was carried out by a method according to "durability (high temperature continuous constant voltage application) test" described in JIS D1401: 2009. Some people call: if the temperature is raised by 10 ℃ from room temperature, the deterioration rate is about 2 times. Examples of the high-temperature durability test include the following: the resultant was held at a predetermined voltage (3V or more in the present invention) for 2000 hours in a constant temperature bath at 60 ℃ (continuous charging), and thereafter, returned to room temperature to perform charging and discharging, and the discharge capacity at that time was measured. It is considered desirable to satisfy the requirement that the discharge capacity retention rate after the high-temperature durability test reaches 80% or more with respect to the initial discharge capacity.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open publication No. 2011-046584
Patent document 2: japanese laid-open patent publication No. 2010-040180
Patent document 3: international publication No. 2017/216960
Disclosure of Invention
Problems to be solved by the invention
An electrode produced by directly coating an amorphous carbon coating such as a diamond-like carbon (DLC) film covering an aluminum material with an active material such as graphite or active carbon has a high contact resistance between the amorphous carbon coating and the active material such as graphite or active carbon, and therefore has problems of low discharge rate and low output characteristics.
The hybrid capacitor according to the present invention has been made in view of the above circumstances, and an object thereof is to reduce contact resistance between a current collector and a positive electrode active material, to improve a discharge rate, to improve output characteristics, and to improve high-temperature durability.
Means for solving the problems
In order to solve the above problems, the present invention provides the following means.
(1) One aspect of the present invention relates to a hybrid capacitor in which a discharge capacity retention rate can be maintained at 80% or more for 1000 hours or longer in a constant-current constant-voltage continuous charge test at 60 ℃ and 3.5V, wherein a positive electrode contains graphite as a positive electrode active material, a positive-electrode-side current collector is an aluminum material, the aluminum material is covered with an amorphous carbon coating having a thickness of 60nm or more and 300nm or less, and a conductive carbon layer is further provided between the amorphous carbon coating and the positive electrode active material.
(2) In the hybrid capacitor according to (1) above, the conductive carbon layer may include graphite.
(3) In the hybrid capacitor according to the above (1) or (2), the conductive carbon layer may contain a binder.
(4) The hybrid capacitor according to any one of (1) to (3) above, wherein the binder is selected from the group consisting of: cellulose, acrylic acid, polyvinyl alcohol, thermoplastic resins, rubbers, and organic resins.
(5) The hybrid capacitor according to any one of (1) to (4) above, wherein the negative electrode side current collector is selected from: an aluminum material covered with an amorphous carbon coating and provided with a conductive carbon layer between the amorphous carbon coating and the negative electrode active material, an aluminum material covered with an amorphous carbon coating, etched aluminum, and an aluminum material.
Effects of the invention
According to the hybrid capacitor of the present invention, the conductive carbon layer is provided, so that 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.
Even when a pinhole (pin-hole) is present in the amorphous carbon coating, the conductive carbon layer is provided between the amorphous carbon coating and the positive electrode active material as in the present invention, whereby the pinhole can be sealed.
Drawings
Fig. 1 is a graph showing discharge characteristics (discharge capacity retention ratio at 60 ℃ in a constant current and constant voltage continuous charge test) of the hybrid capacitors according to example 1, comparative example 2, and comparative example 5 of the present invention.
Detailed Description
Hereinafter, a hybrid capacitor according to an 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, a portion to be a feature may be enlarged for convenience in order to facilitate understanding of the feature, and the dimensional ratio of each component is not limited to be actually the same. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to these examples, and can be appropriately modified and implemented within a range in which the effects are achieved.
A hybrid capacitor according to one embodiment of the present invention is a hybrid capacitor capable of maintaining a discharge capacity retention ratio of 80% or more for 1000 hours or more in a constant-current constant-voltage continuous charge test of 3.5V at 60 ℃, and is characterized by comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode contains graphite as a positive electrode active material, the positive electrode-side current collector is an aluminum material, the aluminum material is covered with an amorphous carbon coating, the amorphous carbon coating has a thickness of 60nm or more and 300nm or less, and a conductive carbon layer is further provided between the amorphous carbon coating and the positive electrode active material.
The positive electrode is formed by forming a positive electrode active material layer on a current collector (current collector on the positive electrode side).
The positive electrode active material layer can be formed by applying and drying a paste-like positive electrode material containing a binder and a conductive material in an amount according to need on a positive electrode-side current collector.
As the binder, for example, one kind of a polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, acrylic, olefin, Carboxy Methyl Cellulose (CMC) or a mixed system of two or more kinds can be used.
The conductive material is not particularly limited as long as the positive electrode active material layer has good conductivity, and a known conductive material can be used. For example, carbon black, carbon fiber (including Carbon Nanotube (CNT), VGCF (registered trademark), and the like, not limited to carbon nanotube), and the like may be used.
The current collector on the positive electrode side is an aluminum material covered with an amorphous carbon coating.
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 may be in the form of foil, sheet, film, net, or the like. As the current collector, aluminum foil may be preferably used.
As the aluminum material, etched aluminum described later may be used in addition to a smooth material.
The thickness of the aluminum material in the case of foil, sheet or film is not particularly limited. When the size of the battery (cell) itself is the same, there is an advantage that the thinner the battery, the more the active material can be enclosed in the battery case, but there is a disadvantage that the strength is reduced. Therefore, it is preferable to select an appropriate thickness that allows a large amount of active material to be added to the battery case without impairing the strength. The actual thickness is preferably 10 to 40 μm, and more preferably 15 to 30 μm. When the thickness is less than 10 μm, there is a possibility that fracture or cracking of the aluminum material may occur in the step of roughening the surface of the aluminum material or in other manufacturing steps.
As the aluminum material covered with the amorphous carbon coating, etched aluminum may be used.
The etching aluminum is aluminum subjected to roughening treatment by etching. Etching generally employs a method of immersion in an acid solution such as hydrochloric acid (chemical etching); and a method of performing electrolysis (electrochemical etching) using aluminum as an anode in an acid solution such as hydrochloric acid. In electrochemical etching, the etching shape differs depending on the current waveform at the time of electrolysis, the composition of the solution, the temperature, and the like, and therefore, can be selected from the viewpoint of the performance of the capacitor.
The aluminum material may use a material with or without a passivation layer on the surface. When a passive film, which is a natural oxide film, is formed on the surface of the aluminum material, an amorphous carbon coating layer may be provided on the natural oxide film, or the natural oxide film may be removed by, for example, argon sputtering.
The natural oxide film on the aluminum material is a passive film, which has an advantage of being hardly corroded by the electrolyte, but on the other hand, it is preferable that no natural oxide film is present from the viewpoint of reducing the resistance of the current collector because the resistance of the current collector increases.
In the present specification, the amorphous carbon coating film refers to an amorphous carbon film or a hydrogenated carbon film, and includes a diamond-like carbon (DLC) film, a carbon hard film, an amorphous carbon (a-C) film, a hydrogenated amorphous carbon (a-C: H) film, and the like. As a method for forming the amorphous carbon film, a known method such as a plasma CVD method using a hydrocarbon gas, a sputtering deposition method, an ion plating method, or a vacuum arc deposition method can be used. The amorphous carbon coating preferably has conductivity to the extent that it functions as a current collector.
Among the materials of the amorphous carbon coating film, diamond-like carbon has a diamond bond (sp)3) And graphite bond (sp)2) The mixed amorphous structure material has high chemical reagent resistance. Among them, when used for a coating film of a current collector, boron or nitrogen is preferably doped for the purpose of improving the conductivity because the conductivity is low.
The thickness of the amorphous carbon coating is preferably 60nm or more and 300nm or less. If the film thickness of the amorphous carbon coating is less than 60nm, the film thickness becomes too thin, the effect of covering the amorphous carbon coating is reduced, and corrosion of the current collector in the constant-current constant-voltage continuous charging test cannot be sufficiently suppressed. If the thickness is too large than 300nm, the resistance between the active material layers increases due to the amorphous carbon coating forming the resistor. Therefore, it is preferable to appropriately select an appropriate thickness so that the effect of covering with the amorphous carbon does not decrease and the resistance between the amorphous carbon coating and the active material layer does not increase. The specific thickness of the amorphous carbon coating is more preferably 80nm or more and 300nm or less, and still more preferably 120nm or more and 300nm or less. When an amorphous carbon film is formed by a plasma CVD method using a hydrocarbon-based gas, the energy for injecting the aluminum material, specifically, the applied voltage, the applied time, and the temperature are controlled, whereby the thickness of the amorphous carbon film can be controlled.
And a conductive carbon layer is also arranged on the amorphous carbon coating layer. The thickness of the conductive carbon layer is preferably 5000nm or less, and more preferably 3000nm or less. The reason for this is that if the thickness is more than 5000nm, the energy density becomes small when forming a battery or an electrode. The material of the conductive carbon layer is not limited to a type if it is carbon having high conductivity, but graphite is preferably contained as carbon having high conductivity, and graphite alone is more preferable.
The particle size of the material of the conductive carbon layer is preferably 1/10 or less compared with the size of graphite or activated carbon as an active material. The reason for this is that if the particle diameter is in this range, the contact property at the interface where the conductive carbon layer and the active material layer are in contact with each other becomes high, 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 the conductive carbon layer is formed, a binder is added together with a solvent to prepare a coating material, and the coating material is applied to a DLC-coated aluminum foil (hereinafter, may be referred to as "DLC-coated aluminum foil"). As a coating method, screen printing, gravure printing, comma coater (registered trademark), 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 or polypropylene can be used, as the rubber, SBR (styrene-butadiene rubber) or EPDM can be used, and as the organic resin, phenol resin, polyimide resin, or the like can be used.
The conductive carbon layer preferably has a small interparticle gap and a low contact resistance. As a solvent for dissolving the binder for forming the conductive carbon layer, there are two kinds of solvents, an aqueous solution and an organic solvent. When the binder for forming the electrode active material layer is dissolved in an organic solvent, it is preferable to use a binder dissolved in an aqueous solution in the conductive carbon layer. In contrast, in the case where the binder for forming the electrode active material layer is an aqueous solution, it is preferable to use a binder dissolved in an organic solvent in the conductive carbon layer. The reason for this is that when the same solvent is used for the electrode active material layer and the conductive carbon layer, the binder of the conductive carbon layer is easily dissolved and easily becomes uneven when the electrode active material layer is applied.
The positive electrode active material used in the hybrid capacitor of the present embodiment contains graphite. As the graphite, artificial graphite and natural graphite can be used. As natural graphite, flaky graphite and earthy graphite are known. Natural graphite is obtained by pulverizing mined raw ore and repeating mineral separation called flotation. Further, artificial graphite is produced, for example, through a graphitization step of calcining a carbon material by high temperature. More specifically, for example, the resin composition is obtained by adding a binder such as pitch to coke as a raw material, molding the mixture, heating the mixture to around 1300 ℃ to perform primary calcination, impregnating the pitch resin with the primary calcined product, and performing secondary calcination at a high temperature close to 3000 ℃. Further, a substance obtained by coating the surface of graphite particles with carbon may also be used.
Further, the crystal structure of graphite can be roughly classified into hexagonal crystals of a layer structure formed of ABAB and rhombohedral crystals of a layer structure formed of abcabcabc. They are formed into a single state or a mixed state of these structures depending on conditions, and any substance having a crystal structure or a mixed state may be used. For example, the proportion of the rhombohedral crystals of the graphite used in the examples described below and the graphite produced by KS-6 (trade name) manufactured by carbon co., ltd. イメリス, ジーシー, ジャパン was 26%, and the proportion of the rhombohedral crystals of the mesocarbon microbeads (MCMB), which are artificial graphite produced by osaka gas chemical co., ltd.s.was 0%.
The graphite used in the present embodiment has a different mechanism of capacitance expression from the activated carbon used in the conventional EDLC. In the case of activated carbon, the capacitance is exhibited by adsorption and desorption of electrolyte ions on the surface by virtue of its large specific surface area. On the other hand, in the case of graphite, the capacitance is expressed by intercalation and deintercalation (intercalation-deintercalation) of anions, which are electrolyte ions, between graphite layers. From such a difference, the hybrid capacitor using graphite according to the present embodiment is referred to as an electric double layer capacitor in a broad sense in patent document 3, but is distinguished from an EDLC using activated carbon having an electric double layer.
The current collector of the present invention has an amorphous carbon coating on the surface of the aluminum material, thus preventing the aluminum material from contacting with the electrolyte, and preventing the current collector from being corroded by the electrolyte during high voltage charging, and has a conductive carbon layer, thus further improving the corrosion resistance and obtaining a more stable hybrid capacitor.
The negative electrode is formed by forming a negative electrode active material layer on a current collector (a current collector on the negative electrode side).
The negative electrode active material layer can be formed by applying a paste-like negative electrode material mainly containing a negative electrode active material, a binder, and a conductive material in an amount according to need on a current collector on the negative electrode side and drying the same.
As the negative electrode active material, a material capable of adsorbing, desorbing, or intercalating and deintercalating (intercalation-deintercalation) cations as electrolyte ions, for example, a carbonaceous material (activated carbon, graphite, hard carbon, soft carbon) and a material (lithium titanate) having a lower electrode potential than the carbonaceous material can be used.
As the current collector on the negative electrode side, a known material can be used. For example, a compound selected from: an aluminum material covered with an amorphous carbon coating and provided with a conductive carbon layer between the amorphous carbon coating and a negative electrode active material, an aluminum material covered with an amorphous carbon coating, etched aluminum, and a current collector in the aluminum material. When an aluminum material covered with an amorphous carbon film and having a conductive carbon layer provided between the amorphous carbon film and the negative electrode active material, or an aluminum material covered with an amorphous carbon film is used also on the negative electrode side, it is preferable in terms of being able to improve high-temperature durability when the hybrid capacitor is operated at a high voltage.
As the binder, for example, one kind of a polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, acrylic, olefin, Carboxy Methyl Cellulose (CMC) or a mixed system of two or more kinds can be used.
The conductive material is not particularly limited as long as the negative electrode active material layer has good conductivity, and a known conductive material can be used. For example, carbon black, carbon fiber (including Carbon Nanotube (CNT), VGCF (registered trademark), and the like, not limited to carbon nanotube), and the like may be used.
As the electrolytic solution, an organic electrolytic solution using an organic solvent can be used. The electrolyte contains electrolyte ions capable of adsorption and desorption on the electrodes. The electrolyte ions preferably have an ionic radius as small as possible. Specifically, ammonium salts, phosphonium salts (phosphonium salts), ionic liquids, lithium salts, and the like can be used.
As the ammonium salt, Tetraethylammonium (TEA) salt, Triethylammonium (TEMA) salt, or 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 kind of the ionic liquid is not particularly limited, and a material having a viscosity as low as possible and a high conductivity (electric conductivity) is preferable from the viewpoint of facilitating the movement of electrolyte ions. Examples of the cation constituting the ionic liquid include an imidazolium ion and a pyridinium ion. Examples of the imidazolium ion include a 1-ethyl-3-methylimidazolium (EMIm) ion, a 1-methyl-1-propylpyrrolidinium (1-methyl-1-propylpyrrolidinium) (MPPy) ion, and a 1-methyl-1-propylpiperidinium (1-methyl-1-propylpiperidinium) (MPPi) ion. This is achieved byIn addition, as the lithium salt, lithium tetrafluoroborate LiBF can be used4Lithium hexafluorophosphate LiPF6And the like.
Examples of the pyridinium ion include a 1-ethylpyridinium (1-ethylpyridinium) ion and a 1-butylpyridinium (1-butylpyridinium) ion.
As the anion constituting the ionic liquid, BF may be mentioned4Ion, PF6Ion, [ (CF)3SO2)2N]Ions, FSI (bis (fluorosulfonyl) imide, bis (fluorosulfonyl) imide) ions, TFSI (bis (trifluoromethylsulfonyl) imide, bis (trifluoromethylsulfonyl) imide) ions, and the like.
As the solvent, acetonitrile, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl sulfone, ethyl isopropyl sulfone, ethyl carbonate, ethylene fluorocarbon, γ -butyrolactone, sulfolane, N-dimethylformamide, dimethyl sulfoxide, or a single or mixed solvent thereof can be used.
The separator is preferably a cellulose-based paper separator, a glass fiber separator, a microporous film of polyethylene or polypropylene, or the like, for the reasons of preventing a short circuit between the positive electrode and the negative electrode, securing the storage stability of the electrolyte solution, and the like.
In the hybrid capacitor according to the present embodiment, the conductive carbon layer is provided, so that the contact resistance between the amorphous carbon coating 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.
Even when the amorphous carbon coating has pinholes, the conductive carbon layer is provided between the amorphous carbon coating and the positive electrode active material as in the present embodiment, and thus the pinholes can be sealed.
In the present embodiment, the graphite positive electrode using the aluminum material covered with the amorphous carbon coating and having the conductive carbon layer provided between the amorphous carbon coating layer and the positive electrode active material is not limited to the use in the hybrid capacitor. The graphite positive electrode can also be used as an electrode of a lithium ion capacitor when a material that is alloyed with lithium, such as hard carbon, soft carbon, graphite, lithium metal, tin, or silicon, or lithium titanate is used for the negative electrode.
In addition, the aluminum material used in the present embodiment, which is covered with the amorphous carbon coating and has the conductive carbon layer provided between the amorphous carbon coating and the positive electrode active material, exhibits the above-described effects even when activated carbon is used for the positive electrode active material, and can be applied with a higher voltage than in the conventional case. However, the specific surface area of activated carbon is two to three digits (2 to 3 orders of magnitude) higher than that of graphite. Therefore, the electrode reaction area is large, and gas is generated due to decomposition of the electrolyte, decomposition of the activated carbon itself, or decomposition of functional groups on the surface of the activated carbon, which has an effect of increasing the internal pressure of the battery. Therefore, only the combination of the activated carbon and the aluminum material covered with the amorphous carbon film and having the conductive carbon layer provided between the amorphous carbon film and the positive electrode active material cannot obtain the same effect as the present embodiment.
Examples
Hereinafter, the technical effects of the present invention will be further clarified by examples. The present invention is not limited to the following examples, and can be implemented by appropriately changing the examples within the scope of achieving the above-described effects.
< example 1 >
First, as a current collector on the positive electrode side, a DLC-coated aluminum foil coated with a conductive carbon layer was produced as follows. A graphite electroconductive paste (trade name: Bunny Height (バニーハイト) T-602U, a cellulose-based resin binder, and an aqueous solution) manufactured by japan graphite industries co ltd (japan black type ) was applied on a DLC-coated aluminum foil (thickness 20 μm) using a screen printer to form an electroconductive carbon layer, and then dried in a hot air dryer at 100 ℃ for 20 minutes to prepare a current collector. DLC-coated aluminum foil corresponds to: an aluminum material covered with an amorphous carbon coating. Furthermore, DLC-coated aluminum foils covered with a conductive carbon layer correspond to: an aluminum material which is covered with an amorphous carbon coating and has a conductive carbon layer provided between the amorphous carbon coating and a positive electrode active material. As a method for producing a DLC-coated aluminum foil, an aluminum foil having a purity of 99.99% is sputtered with argon gas to remove a natural oxide film on the surface of the aluminum foil, and then discharge plasma is generated in a mixed gas of methane, acetylene, and nitrogen gas in the vicinity of the aluminum surface, and a negative bias is applied to the aluminum material, thereby forming a DLC film. The thickness of the DLC film on the DLC-coated (covered) aluminum foil was measured using a stylus profilometer (surface shape measuring instrument) DektakXT manufactured by BRUKER corporation (ブルカー) and found to be 135 nm.
Next, as a positive electrode active material, graphite (trade name: KS-6, average particle diameter 6 μm) manufactured by carbon corporation, acetylene black (conductive material), and polyvinylidene fluoride (organic solvent-based binder) were weighed so that the ratio of the weight percentage concentration (wt%) reached 80:10:10, and were dissolved and mixed in N-methylpyrrolidone (organic solvent), and the paste (slurry) thus obtained was coated on the previously prepared current collector using a doctor blade to prepare a positive electrode. The result of measuring the current collector on the positive electrode side using a micrometer was 0.08 mm.
Next, as a negative electrode active material, activated carbon (trade name: MSP-20) manufactured by seiki chemical co, acetylene black (conductive material), and polyvinylidene fluoride (organic solvent-based binder) were weighed so that the ratio of the weight percentage concentration (wt%) reached 80:10:10, and dissolved and mixed in N-methylpyrrolidone (organic solvent), and the paste thus obtained was coated on an etched aluminum foil (thickness 20 μm) manufactured by japan electric storage device industries co.
Then, the disk-shaped article having a diameter of 16mm obtained by punching the above-mentioned positive electrode and negative electrode was vacuum-dried at 150 ℃ for 24 hours, and then moved into an argon glove box. They were stacked via a paper separator (trade name: TF40-30) manufactured by JAN DENTIAN PAPER INDUSTRIAL (, ニッポン DENTIAN) and 0.1mL of electrolyte solution [ wherein the electrolyte was 1M TEA-BF ] was used4(tetraethylammonium tetrafluoroborate), solvent SL + DMS (Sulfolane) + dimethyl sulfide)]And manufacturing a 2032 type button battery in an argon glove box.
< example 2 >
A 2032 type coin cell was produced in the same manner as in example 1, except that the DLC-coated aluminum foil coated with a conductive carbon layer used as the positive electrode side current collector in example 1 was used as the negative electrode side current collector.
< example 3 >
A 2032 type coin cell was produced in the same manner as in example 1, except that artificial graphite (trade name: MCMB6-10) manufactured by Osaka Gas Chemicals co.
< example 4 >
Except for using lithium titanate Li4Ti5O12As a negative electrode active material, and lithium tetrafluoroborate LiBF using an electrolyte of 1M4A 2032 type coin cell was produced in the same manner as in example 1, except that the solvent was an electrolyte solution of Propylene Carbonate (PC).
< example 5 >
A DLC-coated aluminum foil was produced by the same procedure as in example 1, and a graphite conductive paste (trade name: Bunny Height UCC-2, rubber-based adhesive, and toluene solvent) manufactured by Nippon graphite industries, Ltd was applied thereon to prepare a positive electrode-side current collector. Further, as the binder of the positive electrode, 10 wt% of polyacrylic acid (trade name: AZ-9001) manufactured by Nippon Zeon (ゼオン) and 3 wt% of CMC (carboxymethyl cellulose, trade name: BM-400) manufactured by Nippon Zeon corporation were used as aqueous solution binders. Except for this, a 2032 type coin cell was produced in the same manner as in example 1.
The case of using an aluminum foil having a conductive carbon layer with a thickness of 0nm (no conductive carbon layer) as the positive electrode-side current collector corresponds to comparative examples 2, 4 and 5 described later, and is not an example of the present invention.
< comparative example 1 >
A 2032-type coin cell was produced in the same manner as in example 1, except that activated carbon (trade name: MSP-20) used as the negative electrode active material in example 1 was also used as the positive electrode active material (that is, activated carbon was used for both the positive electrode active material and the negative electrode active material).
< comparative example 2 >
A 2032 type coin cell was produced in the same manner as in example 1, except that DLC-coated aluminum foil not covered with a conductive carbon layer was used as the positive electrode-side current collector.
< comparative example 3 >
A 2032 type coin cell was produced in the same manner as in example 1, except that activated carbon (trade name: MSP-20) used as the negative electrode active material in example 1 was used as the positive electrode active material, and polyacrylic acid (trade name: AZ-9001)10 wt% and CMC (trade name: BM-400)3 wt% as the aqueous solution type binder were used as the binder for the positive electrode.
< comparative example 4 >
A 2032 type coin cell was produced in the same manner as in example 5, except that a DLC-coated aluminum foil not covered with a conductive carbon layer was used as the positive electrode-side current collector.
< comparative example 5 >
A 2032 type coin cell was produced in the same manner as in example 1, except that an etched aluminum foil (thickness 20 μm) manufactured by japan electric storage device industries co, used as the negative electrode side current collector in example 1 was used as the positive electrode side current collector (that is, an etched aluminum foil was used for both the positive electrode side current collector and the negative electrode side current collector).
(test 1) evaluation (energy, discharge Capacity)
The batteries of examples 1, 3, 4, 5, 1 and 3 were charged and discharged at 0.4mA/cm in a thermostatic bath at 25 ℃ using a charge and discharge test device BTS2004 manufactured by Nagano corporation (Kagaku corporation, ナガノ)2The current density of (3) and a voltage in the range of 0V to 3.5V. As a result, the energy (Wh) was calculated from the obtained discharge capacity and the average discharge voltage, and the results are shown in table 1. Table 1 shows values obtained by normalizing the energy and discharge capacity of example 1, example 3, example 4, and example 5 with comparative example 1 or comparative example 3, respectively. At this time, the results of comparative example 1 or comparative example 3 were normalized as 100.
In examples 1, 3, 4, and 5 in which graphite was used as the positive electrode active material, up to 3.5V could be applied to the upper limit of the applied voltage, but in comparative examples 1 and 3 in which activated carbon was used as the positive electrode, up to 2.5V was measured.
[ Table 1]
Example/comparative example as reference Energy of Discharge capacity
Example 1/comparative example 1 420 300
Example 3/comparative example 1 310 220
Example 4/comparative example 1 600 350
Example 5/comparative example 3 430 310
The energy (product of discharge capacity and average discharge voltage) of the batteries of examples 1 and 3, in which graphite was used as the positive electrode active material, was 4.2 times and 3.1 times higher than that of comparative example 1, in which activated carbon was used as the positive electrode active material, respectively, and high energy was obtained. The reason for this is considered to be that graphite can cause intercalation and deintercalation of electrolyte ions between layers (interlamination), and can increase the discharge capacity as compared with activated carbon in which only electrolyte ions are adsorbed and desorbed on the pore surfaces. In fact, the discharge capacity was increased 3.0 times in the case of example 1 and 2.2 times in the case of example 3, compared with the battery of comparative example 1. The use of graphite for the positive electrode active material can increase the voltage as compared with the use of activated carbon for the positive electrode active material, which is also a cause of the energy increase.
In example 4 in which lithium titanate was used as a negative electrode active material in addition to graphite, the energy was 6.0 times and the discharge capacity was 3.5 times in comparative example 1 in which activated carbon was used for both the positive electrode active material and the negative electrode active material. In example 4, the discharge potential of the lithium titanate used in the negative electrode active material is flatter than that of example 1 in which graphite is used for the positive electrode active material but activated carbon is used for the negative electrode active material, and therefore the average voltage is higher, and high energy can be achieved, and further, the effect of increasing the discharge capacity is obtained as compared with activated carbon, and thus high capacity can be achieved.
The batteries of example 5 and comparative example 3, in which polyacrylic acid and CMC were used as aqueous solution binders for the positive electrode binder and rubber was used as an organic solvent binder for the conductive carbon layer, were formed in a reverse configuration to example 1, that is, in a configuration in which an aqueous solution binder was used for the positive electrode active material layer binder and an organic solvent binder was used for the conductive carbon layer. As a result of observation of the results, it was found that, similarly to the battery of example 1, the energy and discharge capacity were higher than those of comparative example 3, and the energy and discharge capacity were able to be increased without being affected by the difference in the solvent of the binder.
The difference between example 1 and example 3 is only in the type of graphite of the positive electrode active material, but the energy and discharge capacity are different as shown in table 1.
Graphite Yiruite graphite and graphite manufactured by carbon Kabushiki Kaisha (trade name: KS-6) contained 26% of rhombohedral crystals (accordingly, the hexagonal crystals were 76%), whereas mesocarbon microbeads (MCMB) manufactured by Osaka gas chemical K.K. did not contain rhombohedral crystals.
The rhombohedral crystal is a layer structure formed by ABCABC and the hexagonal crystal is a layer structure formed by ABAB, and it is presumed that the difference in crystal structure affects the above properties. That is, since rhombohedral crystals have a larger structural change due to ion intercalation than hexagonal crystals, it is considered that the influence of ion intercalation is hardly caused.
Based on the results shown in table 1, graphite as the positive electrode active material preferably contains rhombohedral crystals from the viewpoint of energy and discharge capacity.
(test 2) evaluation (discharge Capacity improvement rate)
The batteries of examples 1, 2, 4, 5 and comparative examples 1 to 5 were charged and discharged in a 60 ℃ constant temperature bath at a current density of 0.4mA/cm using a charge and discharge test apparatus (BTS 2004, manufactured by Nagano corporation)2And a continuous charging test (constant current, constant voltage and continuous charging test) was carried out at a voltage of 3.5V for 2000 hours. Specifically, during the charging, the charging was stopped for a predetermined time, and the battery was transferred to a thermostatic bath at 25 ℃ and then charged at 0.4mA/cm in the same manner as in test 12The discharge capacity was obtained by conducting a charge-discharge test 5 times at a voltage in the range of 0V to 3.5V. Thereafter, the temperature was returned to the constant temperature bath at 60 ℃, and the continuous charging test was restarted and carried out until the total continuous charging test time reached 2000 hours.
As a result, the obtained discharge capacity improvement rate is shown in table 2. The discharge capacity improvement rate is normalized by designating a charging time at which a discharge capacity retention rate after a constant current-constant voltage continuous charge test becomes 80% or less with respect to a discharge capacity before a constant current-constant voltage continuous charge test is started as a life, and designating a time to reach the life in comparative example 1, comparative example 2, or comparative example 4 as 100. That is, the case of comparative example 1 in which activated carbon is used for a positive electrode active material and also for a negative electrode active material and an etched aluminum foil is used for a current collector on the negative electrode side, and the cases of comparative examples 2 and 4 in which a DLC-coated aluminum foil not covered with a conductive carbon layer is used are standardized as 100.
[ Table 2]
Example/comparative example as reference Rate of improvement of discharge capacity
Example 1/comparative example 1 4500
Example 2/comparative example 1 4900
Example 4/comparative example 1 3100
Example 1/comparative example 2 106
Example 5/comparative example 4 108
In example 1 in which graphite was used as the positive electrode active material and a DLC-coated aluminum foil covered with a conductive carbon layer was used as the positive electrode-side current collector, the discharge capacity retention rate after a constant-current constant-voltage (3.5V) continuous charge test of 2000 hours was 92%.
In example 4 in which graphite was used as the positive electrode active material, and an aluminum foil coated with DLC coated with a conductive carbon layer was used as the positive electrode-side current collector, and lithium titanate was used as the negative electrode active material, the discharge capacity retention rate after the 2000-hour constant-current constant-voltage continuous charge test was 83%.
Further, in example 5 in which graphite was used as the positive electrode active material, and a DLC-coated aluminum foil covered with a conductive carbon layer was used as the positive electrode-side current collector, and in addition, a rubber-based binder as an organic solvent was used as the conductive carbon layer, and polyacrylic acid and CMC were used as aqueous solution-based binders as the positive electrode active material layer, the discharge capacity retention rate after the constant current and constant voltage continuous charge test was 93% at 2000 hours.
The hybrid capacitor of the present invention can satisfy the standard that the discharge capacity retention ratio after a 2000-hour constant-current constant-voltage continuous charge test at 60 ℃ is 80% or more at a high voltage of 3V or more, particularly 3.5V.
On the other hand, in comparative examples 1 and 3 in which 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, the discharge capacity retention rates were 80% or less at 21 hours and 16 hours, respectively. This is because, in the continuous charging test, although the corrosion resistance of the current collector itself can be maintained, the activated carbon reacts with the electrolyte at a high voltage of 3.5V, and the surface of the activated carbon is covered with the electrolyte decomposition product.
In comparative example 5 in which graphite was used as the positive electrode active material and an etched aluminum foil was used as the positive electrode-side current collector, the discharge capacity retention ratio was 80% or less at 65 hours.
In both examples 1 and 4, graphite was used as the positive electrode active material, and an aluminum foil was coated with DLC coated with a conductive carbon layer as the positive electrode-side current collector. On the other hand, in comparative example 1, an aluminum foil was coated with activated carbon for the positive electrode active material and DLC coated with a conductive carbon layer for the positive electrode-side current collector. As shown in table 2, the discharge capacity improvement rates of example 1 and example 4 were 45 times and 31 times as high as those of comparative example 1, and were significantly improved.
As a result, it was found that the same effect as that of the present embodiment cannot be obtained by simply combining activated carbon with the DLC-coated aluminum foil covered with the conductive carbon layer of the present invention.
In addition, in example 2 in which graphite was used as the positive electrode active material and DLC-coated aluminum foil covered with a conductive carbon layer was used for both the positive electrode-side current collector and the negative electrode-side current collector, the discharge capacity retention ratio was 49 times higher than that in comparative example 1, and the high-temperature durability was further improved.
The results show that corrosion of the current collector in the negative electrode side is also a factor that hinders durability.
It is further understood that in example 1 in which the DLC-coated aluminum foil covered with the conductive carbon layer of the present invention was used for the positive electrode-side current collector, the discharge capacity retention ratio was improved by 1.06 times as compared with comparative example 2 in which the DLC-coated aluminum foil not covered with the conductive carbon layer was used. In addition, in example 5 in which the configuration opposite to that of example 1, that is, the configuration in which the aqueous solution binder was used for the positive electrode active material layer and the organic solvent binder was used for the conductive carbon layer, was used, the discharge capacity retention ratio was 1.08 times, and the same effect as that of example 1 was confirmed.
The results show that: the contact resistance between the amorphous carbon coating and the positive electrode active material can be reduced by providing the conductive carbon layer without being affected by the difference in the solvent of the binder of the electrode layer and the conductive carbon layer.
(test 3)
The continuous charge test (constant current constant voltage continuous charge test) was performed in the same manner as in test 2 except that the target batteries were the batteries of example 1, comparative example 2, and comparative example 5. The results are shown in the graph of fig. 1. The discharge capacity before the start of the test is shown as 100, the discharge capacity after each charge time after the start of the test is shown as a ratio to the discharge capacity of 100, the horizontal axis of the graph represents the constant current and constant voltage continuous charge time (h) at 60 ℃, and the vertical axis of the graph represents the discharge capacity retention rate (%).
In comparative example 5 in which an etched aluminum foil was used as a current collector, the discharge capacity of 400 hours or more could not be maintained. In contrast, example 1 and comparative example 2, in which DLC-coated aluminum foil was used as a current collector, showed a high discharge capacity retention rate of 80% or more even after 1000 hours or more. This is considered to be because the DLC film prevents the electrolytic solution from directly contacting the aluminum foil, and corrosion of the aluminum foil due to the electrolytic solution can be suppressed.
In addition, if comparing example 1 and comparative example 2, example 1 showed a higher discharge capacity retention rate. This difference is considered to be caused by whether or not a conductive carbon layer is further provided on the DLC film of the DLC-coated aluminum foil. This is because the particles of the conductive carbon layer have more irregularities than the DLC film and are also highly conductive, and therefore, 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)
The target batteries were the batteries of examples 1 and 5, which were fabricated, and the current density was 0.4mA/cm2And 4.0mA/cm2Except for this, the same charge-discharge test as in test 1 was carried out to obtain the discharge capacity. For example 1 and example 5, 4.0mA/cm was calculated2Discharge capacity at a discharge rate of 0.4mA/cm2The discharge capacity was obtained as a ratio of the discharge capacity. The results are shown in Table 3. Table 3 shows the values normalized by comparative example 2 or comparative example 4 for the discharge rates of example 1 and example 5, respectively. At this time, the results of comparative example 2 or comparative example 4 were normalized as 100.
[ Table 3]
Example/comparative example as reference Discharge rate
Example 1/comparative example 2 132
Example 5/comparative example 4 142
The discharge rate performance of example 1 of the present invention using the DLC-coated aluminum foil coated with a conductive carbon layer was 1.32 times higher than that of comparative example 2 using the DLC-coated aluminum foil not coated with a conductive carbon layer for the positive electrode-side current collector, and the discharge rate performance was improved. The reason for this is considered to be that since the graphite in the conductive carbon layer formed on the DLC-coated aluminum foil is submicron fine particles, the adhesion (contact) to the DLC-coated aluminum foil is improved and the contact resistance between the current collector and the graphite positive electrode active material layer is reduced compared to the case where the graphite active material having an average particle diameter of 6 μm is directly coated on the DLC-coated aluminum foil, and the unevenness of the conductive carbon layer is larger compared to the DLC film, so the adhesion to the graphite active material layer formed thereon is improved and the contact resistance between the current collector and the graphite positive electrode active material layer is reduced.
In example 5 in which the configuration opposite to that of example 1, that is, the configuration in which the aqueous solution binder was used for the positive electrode active material layer and the organic solvent binder was used for the conductive carbon layer, was used, the discharge rate characteristics were 1.42 times higher, and higher effects were obtained as compared with the configuration of example 1.
As described above, by using the DLC-coated aluminum foil covered with the conductive carbon layer according to the embodiment of the present invention as the current collector, 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, as compared with the case of using a DLC-coated aluminum foil not covered with the conductive carbon layer.
Industrial applicability
The present invention can reduce contact resistance between the current collector and the positive electrode active material, improve discharge rate, improve output characteristics, and improve high-temperature durability, and can be applied as a means for storing electric energy, such as an electric storage device.

Claims (5)

1. A hybrid capacitor, which has a discharge capacity retention ratio capable of being maintained at 80% or more for 1000 hours or more in a constant-current constant-voltage continuous charge test at 60 ℃ and 3.5V; the hybrid capacitor is characterized in that it is,
the positive electrode contains graphite as a positive electrode active material,
the current collector on the positive electrode side is an aluminum material,
the aluminum material is covered by an amorphous carbon coating film,
the amorphous carbon coating has a thickness of 60nm to 300nm inclusive, and
a conductive carbon layer is further provided between the amorphous carbon coating film and the positive electrode active material;
a particle size of a material of the conductive carbon layer is 1/10 or less as compared with a size of the positive electrode active material;
the electrolyte solution contains electrolyte ions;
capacitance is exhibited by intercalation and deintercalation of anions as the electrolyte ions between the layers of the graphite.
2. The hybrid capacitor of claim 1,
the conductive carbon layer comprises graphite.
3. The hybrid capacitor according to claim 1 or 2,
the conductive carbon layer includes a binder.
4. The hybrid capacitor of claim 1 or 2,
the conductive carbon layer comprises a binder selected from the group consisting of: at least one member selected from the group consisting of cellulose, acrylic acid, polyvinyl alcohol, thermoplastic resin, rubber, and organic resin.
5. The hybrid capacitor of claim 1 or 2,
the current collector on the negative side is selected from: at least one of the group consisting of an aluminum material covered with an amorphous carbon coating and having a conductive carbon layer provided between the amorphous carbon coating and the negative electrode active material, an aluminum material covered with an amorphous carbon coating, etched aluminum, and an aluminum material.
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