Electrode material and method for producing same

Abstract

Provided is an electrode material which can be produced in a short heat treatment time, can exhibit high conductivity, and has excellent adhesion between an aluminum foil as a substrate and a coating layer.　The electrode material is characterized by comprising, on at least one surface of an aluminum foil, a coating layer containing a valve metal oxide and a fibrous carbon material, Wherein the valve metal oxide contains titanium oxide and silicon oxide.

Description

Electrode material and method for manufacturing the same

[0001] The present invention relates to electrode materials and methods for manufacturing the same, and more particularly to electrode materials used as current collectors for electrodes in energy storage devices such as cathodes for capacitors, batteries, and capacitors, and methods for manufacturing the same.

[0002] Conventionally, dielectric materials with high dielectric constants have been widely used in electronic products such as capacitors, semiconductor devices, and light-emitting elements. Aluminum foil is widely used in the energy sector as an electrode material for manufacturing these electronic products because it is inexpensive and can provide high capacitance.

[0003] When aluminum foil is used as is as a material for electrodes or current collectors, the oxide film formed on the surface of the aluminum foil becomes passivated, reducing the surface conductivity and causing it to become an insulator. To solve this problem, a method has been proposed to improve the surface conductivity of aluminum foil by coating the surface with carbon, metal, metal nitride, etc. (see Patent Documents 1 and 2).

[0004] Patent Document 1 proposes an electrode body for an electrolytic capacitor that exhibits stable capacitance even after being subjected to high-temperature environmental stress, in which a carbon layer containing graphite and spherical carbon is formed on a cathode foil made of a valve-acting metal. Patent Document 2 proposes an electrode structure comprising valve-acting metal oxide particles and carbon on an aluminum foil.

[0005] International Publication No. 2020 / 059609, Japanese Patent Publication No. 2024-129543

[0006] However, in the electrode body described in Patent Document 1, resin is used as the binder and dispersant to fix the carbon material. As a result, the binder and dispersant decompose thermally during capacitor reflow, leading to deterioration of capacitor characteristics due to the detachment of carbon material and swelling of the capacitor, resulting in insufficient heat resistance. Furthermore, in order to obtain sufficient conductivity, it is necessary to increase the ratio of material that increases the amount of carbon in the carbon layer. However, as the amount of carbon increases, the strength of the carbon layer decreases, making it easier for carbon to detach, and resulting in insufficient adhesion to the substrate.

[0007] The electrode structure described in Patent Document 2 requires heat treatment at a predetermined temperature for 12 hours or more to obtain high adhesion between the aluminum foil and the coating layer, which presents the problem of a long heat treatment time. A long heat treatment time results in a high environmental burden in terms of the amount of energy required for heat treatment, and also significantly increases production costs. On the other hand, shortening the heat treatment time increases resistance, making it difficult to obtain sufficient conductivity, and also reduces the adhesion between the aluminum foil and the coating layer.

[0008] In view of the above circumstances, the present invention aims to provide an electrode material that can be manufactured in a short heat treatment time, exhibits high conductivity, and has excellent adhesion between the aluminum foil base material and the coating layer.

[0009] As a result of diligent research, the inventors have found that the above objective can be achieved by providing a coating layer containing a valve metal oxide and a fibrous carbon material on at least one side of an aluminum foil, wherein the valve metal oxide is an electrode material containing titanium oxide and silicon oxide, and thus have completed the present invention.

[0010] That is, the present invention relates to the following electrode material and method for manufacturing the electrode material. 1. An electrode material characterized in that an aluminum foil has a coating layer comprising a valve metal oxide and a fibrous carbon material on at least one side thereof, wherein the valve metal oxide comprises titanium oxide and silicon oxide. 2. The electrode material according to claim 1, wherein the fibrous carbon material comprises at least one selected from the group consisting of carbon nanotubes and carbon nanofibers. 3. The titanium oxide comprises TiO x1. An electrode material according to item 1 or 2, comprising a lower-order titanium oxide represented by (where x is 0 < x < 2). 4. An electrode material according to any one of items 1 to 3, wherein the valve metal oxide further comprises a metal oxide of at least one metal selected from the group consisting of tantalum, hafnium, zirconium, niobium, and aluminum. 5. An electrode material according to any one of items 1 to 4, wherein the coating layer comprises amorphous carbon. 6. An electrode material according to any one of items 1 to 5, comprising an intervening layer comprising aluminum and carbon formed on at least a portion of the surface of the aluminum foil between the aluminum foil and the coating layer. 7. An electrode material according to any one of items 1 to 6, used as the cathode of an electrolytic capacitor. 8. A method for producing an electrode material, comprising in order: (1) forming a mixture layer on the surface of an aluminum foil, the mixture layer containing an organometallic compound including an organotitanium compound and an organosilicon compound, and a fibrous carbon material; and (2) heating the aluminum foil on which the mixture layer has been formed in an inert atmosphere for 1 minute to 8 hours. 9. The method for producing an electrode material according to item 8, wherein the mixture layer contains a resin binder. 10. The method for producing an electrode material according to item 8 or 9, wherein the heat treatment step is performed in a temperature range of 450°C to less than 660°C.

[0011] The electrode material of the present invention can be manufactured with a short heat treatment time, exhibits high conductivity, and has excellent adhesion between the aluminum foil base material and the coating layer.

[0012] This is a schematic diagram showing the layer structure of the electrode material of the present invention. This is a schematic diagram showing the layer structure of the electrode material of the present invention. This is a scanning electron microscope (SEM) image of the surface of the intervening layer of the electrode material of Example 11.

[0013] 1. Electrode Material The electrode material of the present invention comprises a coating layer containing a valve metal oxide and a fibrous carbon material on at least one side of an aluminum foil, wherein the valve metal oxide is an electrode material containing titanium oxide and silicon oxide. The electrode material of the present invention having the above features exhibits high conductivity even with a short heat treatment time of, for example, 8 hours or less, and shows excellent adhesion between the aluminum foil substrate and the coating layer, by forming a coating layer containing a valve metal oxide and a fibrous carbon material on the surface of the aluminum foil.

[0014] The layer structure of the electrode material of the present invention will be explained with reference to the figures. Figure 1 is a schematic diagram showing the structure of the electrode material of the present invention. In Figure 1, the electrode material 1 of the present invention comprises a coating layer 12 containing a valve metal oxide and a fibrous carbon material on at least one side of the aluminum foil 11. Alternatively, the electrode material of the present invention may have the layer structure shown in Figure 2. In Figure 2, the electrode material 1 of the present invention comprises a coating layer 12 containing a valve metal oxide and a fibrous carbon material on at least one side of the aluminum foil 11, and an interlayer 13 containing aluminum and carbon formed between the aluminum foil 11 and the coating layer 12 in at least a portion of the surface of the aluminum foil 11. In Figure 2, 131 is aluminum carbide produced by heating during the manufacture of the electrode material. As shown in Figure 2, the interlayer adhesion between the aluminum foil 11 and the coating layer 12 is further improved by comprising the interlayer 13 in the electrode material 1 of the present invention.

[0015] The electrode material of the present invention comprises a coating layer on at least one side of an aluminum foil, the coating layer comprising a valve metal oxide and a fibrous carbon material, wherein the valve metal oxide comprises titanium oxide and silicon oxide.

[0016] In this invention, the term "electrode material" includes not only the electrode material before heat treatment for manufacturing the electrode structure, but also the electrode material after heat treatment. Furthermore, in this invention, "short heat treatment time" specifically refers to a heat treatment time of 1 minute or more and 8 hours or less.

[0017] The following describes each component that constitutes the electrode material of the present invention.

[0018] (Aluminum foil) Aluminum foil is a component that serves as the base material for the electrode material. In this specification, aluminum foil is not limited to aluminum foil with a thickness of 5 μm or more and 200 μm or less, but also includes aluminum vapor-deposited sheets with a thickness of less than 5 μm and aluminum plates with a thickness of more than 200 μm.

[0019] The aluminum foil is not particularly limited, and foils made of pure aluminum or aluminum alloys, i.e., pure aluminum foil or aluminum alloy foil, can be used. Among these, the use of pure aluminum foil is preferred.

[0020] The aluminum content of the pure aluminum foil is preferably 99.00% by mass or more, more preferably 99.85% by mass or more, and even more preferably 99.99% by mass or more.

[0021] The aluminum alloy forming the aluminum alloy foil may be an aluminum alloy in which at least one metallic element selected from the group consisting of silicon (Si), iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), titanium (Ti), vanadium (V), gallium (Ga), nickel (Ni), and boron (B) is added to aluminum within the necessary range, or it may be an aluminum alloy containing the above elements as unavoidable impurities.

[0022] The thickness of the aluminum foil is not particularly limited, but is preferably 5 μm to 200 μm, more preferably 7 μm to 100 μm, and even more preferably 9 μm to 50 μm. When the thickness of the aluminum foil is within the above range, it is easy to handle when coating the aluminum foil surface with a mixture containing an organometallic compound including a valve metal and a fibrous carbon material, and the capacitance per unit volume can be further improved when the electrode material of the present invention is used as a capacitor electrode.

[0023] (Coating layer) The electrode material of the present invention comprises a coating layer on at least one side of an aluminum foil, the coating layer containing a valve metal oxide and a fibrous carbon material.

[0024] The thickness of the coating layer is preferably 0.01 μm to 5 μm, and more preferably 0.05 μm to 2 μm. When the lower limit of the thickness is within the above range, the coating layer tends to be more uniform, and defects such as gaps are suppressed. When the upper limit of the thickness is within the above range, the occurrence of cracks in the coating layer is suppressed, peeling of the coating layer from the aluminum foil surface is suppressed, and the reliability of the electrode is further improved.

[0025] <Valve Metal Oxide> The coating layer constituting the electrode material of the present invention includes a valve metal oxide and a fibrous carbon material.

[0026] In the electrode material of the present invention, the valve metal oxide contained in the coating layer contains titanium oxide, so the coating layer contains titanium oxide, resulting in lower resistance and higher conductivity.

[0027] Titanium dioxide is TiO x It is preferable to include lower-order titanium oxide represented by (where x represents 0 < x < 2). Such lower-order titanium oxide is conductive and functions as an inorganic binder that fixes the aluminum foil and the coating layer, and also improves the conductivity of the coating layer itself. Therefore, when the electrode material is used as the cathode foil of a capacitor, an electric double-layer capacitor, or a current collector of a battery, the ESR characteristics of the capacitor can be further improved.

[0028] The above-mentioned lower-grade titanium oxides can be used individually or as a mixture of two or more types.

[0029] The titanium oxide content in the valve metal oxide is not particularly limited, but is preferably 50% to 99% by mass, and more preferably 70% to 95% by mass, with the valve metal oxide being 100% by mass. When the titanium oxide content is within the above range, the resistance can be further reduced when combined with a fibrous carbon material.

[0030] The valve metal oxide contains silicon oxide. Because the valve metal oxide contains silicon oxide, the adhesion between the coating layer and the aluminum foil is improved, and the density of the coating layer is also improved, thus improving the reliability of the cathode foil of capacitors, electric double-layer capacitors, and current collectors of batteries.

[0031] The silicon oxide is not particularly limited and examples include silicon dioxide and silicon oxide. Among these, silicon dioxide can be used more preferably.

[0032] The content of silicon oxide in the valve metal oxide is not particularly limited, but is preferably 1% to 50% by mass, and more preferably 5% to 30% by mass, with the valve metal oxide being 100% by mass. When the lower limit of the silicon oxide content is within the above range, the adhesion between the coating layer and the aluminum foil is further improved. When the upper limit of the silicon oxide content is within the above range, the resistance as an electrode is further suppressed.

[0033] Furthermore, the total content of titanium oxide and silicon oxide in the valve metal oxide is 100% by mass or less.

[0034] The valve metal oxide may further contain other valve metal oxides besides the titanium oxide and silicon oxides mentioned above. Examples of other valve metal oxides include tantalum, hafnium, zirconium, niobium, and aluminum.

[0035] The other valve metal oxides mentioned above can be used individually or in combination of two or more.

[0036] The content of valve metal oxide in the coating layer is not particularly limited, but is preferably 25% to 99.9% by mass, and more preferably 45% to 99.5% by mass, with the coating layer being 100% by mass. When the lower limit of the valve metal oxide content is within the above range, the content of valve metal oxide, which also acts as a binder, becomes more sufficient, and the adhesion between the coating layer and the aluminum foil is further improved. When the upper limit of the valve metal oxide content is within the above range, the proportion of fibrous carbon material, which has higher conductivity than valve metal oxide, becomes more sufficient, and the resistance as an electrode can be further suppressed.

[0037] <Fibrous carbon material> In the electrode material of the present invention, the coating layer contains a fibrous carbon material. When the coating layer contains a fibrous carbon material, compared with the case where only particulate carbon such as acetylene black is used, the formation of conductive paths in the coating layer is facilitated, and conductivity can be improved with a small addition amount. As a result, compared with the case where a large amount of only particulate carbon is used, defects such as fine cracks and omissions in the coating layer are suppressed, and the adhesion between the coating layer and the aluminum foil is also improved, so that the reliability of the cathode foil of a capacitor, an electric double layer capacitor, and a current collector of a battery is further improved. In addition, when the coating layer contains titanium oxide and a silicon oxide as valve metal oxides, the silicon oxide and other oxides may inhibit the conductive paths between titanium oxide particles and cause a significant increase in resistance. However, the fibrous carbon material reinforces the conductive paths between titanium oxide particles, and in combination with the excellent conductivity of fibrous carbon, excellent conductivity can be maintained.

[0038] The fibrous carbon material is not particularly limited, and examples thereof include carbon nanotubes and carbon nanofibers.

[0039] The type of carbon nanotube is not particularly limited, and either single-walled carbon nanotubes or multi-walled carbon nanotubes can be used.

[0040] The above fibrous carbon materials may be used alone or as a mixture of two or more thereof.

[0041] The diameter of the fibrous carbon material is preferably 1000 nm or less, more preferably 200 nm or less. When the upper limit of the diameter falls within the above range, the addition amount for imparting conductivity to the coating layer can be reduced, and an increase in defects in the coating layer and a decrease in adhesion between the coating layer and the aluminum foil can be further suppressed. The lower limit of the diameter is not particularly limited, and is preferably 1 nm or more.

[0042] The length of the fibrous carbon material is preferably 0.5 µm or more, more preferably 1 µm or more. When the lower limit of the length falls within the above range, an increased addition amount is obtained for imparting conductivity to the coating layer, the increase of defects such as fine cracks and voids in the coating layer is further suppressed, and a decrease in adhesion between the coating layer and the aluminum foil can be further suppressed. In addition, the upper limit of the length is not particularly limited, and is preferably 1000 µm or less.

[0043] The ratio of the length to the diameter of the fibrous carbon material (length / diameter) is preferably 5 or more, more preferably 20 or more. When the lower limit of the above ratio (length / diameter) falls within the above range, the addition amount for imparting conductivity to the coating layer is suppressed, and an increase in defects such as fine cracks and voids in the coating layer and the adhesion between the coating layer and the aluminum foil are further improved. The upper limit of the above ratio (length / diameter) is not particularly limited, and is preferably 100000 or less.

[0044] The content of the fibrous carbon material in the coating layer is not particularly limited. Based on 100% by mass of the coating layer, the content is preferably 0.1% by mass or more and 20% by mass or less, more preferably 0.25% by mass or more and 10% by mass or less. When the lower limit of the content of the carbon material falls within the above range, the resistance of the coating layer becomes lower. When the upper limit of the content of the carbon material falls within the above range, defects in the coating layer are further suppressed, and the adhesion between the coating layer and the aluminum foil is further improved.

[0045] In the electrode material of the present invention, the fibrous carbon material is preferably formed to be three-dimensionally distributed in the coating layer. In the electrode material of the present invention having the above characteristics, the valve metal oxide acts as a binder for fixing the coating layer to the aluminum foil and exhibits high heat resistance, so that falling off of the carbon material and gas generation during reflow of the capacitor can be suppressed. In addition, the electrode material of the present invention has high conductivity because the fibrous carbon material is present in the valve metal oxide containing titanium oxide and silicon oxide. When the electrode material of the present invention is used as a cathode foil of a capacitor, or a current collector of an electric double layer capacitor and a battery, a low-resistance capacitor and an electricity storage device can be manufactured.

[0046] The coating layer preferably contains amorphous carbon. By including amorphous carbon in the coating layer, the density and flexibility of the coating layer can be further improved, and the reliability as an electrode is further enhanced. In the electrode material of the present invention, amorphous carbon is more preferably included in the coating layer formed by distributing fibrous carbon material three-dimensionally in a valve metal oxide containing titanium oxide.

[0047] (Intervening layer) The electrode material of the present invention preferably comprises an intervening layer containing aluminum and carbon, formed between the aluminum foil and the coating layer on at least a portion of the surface of the aluminum foil. The intervening layer contains aluminum and carbon, and more preferably contains aluminum carbide.

[0048] The intervening layer can further improve the adhesion between the aluminum foil and the coating layer, and reduce the electrical resistance between the aluminum foil and the coating layer. It is also preferable that the intervening layer comprises aluminum carbides in the form of fibers, filaments, plates, walls, or scales that extend from the intervening layer toward the coating layer. When the electrode structure is used as the cathode foil of a capacitor and a reverse voltage is applied, gas may be generated at the boundary between the aluminum foil surface and the intervening layer, causing the formation of an aluminum oxide film. Therefore, from the viewpoint of adhesion when a reverse voltage is applied, the presence of the intervening layer alone may not be sufficient. However, from the viewpoint of further improving the adhesion between the aluminum foil and the coating layer, it is preferable to include the intervening layer.

[0049] When the electrode material of the present invention includes an intervening layer, it is preferable that the coating layer contains amorphous carbon. When the electrode material of the present invention includes an intervening layer, the inclusion of amorphous carbon in the coating layer can further improve the adhesion between the aluminum foil and the coating layer, and can also further improve the density and flexibility of the coating layer, thereby improving the reliability of the electrode.

[0050] Because of the above-described structure, the electrode material of the present invention can be manufactured with a short heat treatment time, exhibits high conductivity, and has excellent adhesion between the aluminum foil base material and the coating layer. Such an electrode material of the present invention can be suitably used as a current collector for electrodes in energy storage devices such as capacitor cathodes, batteries, and capacitors, and is particularly suitable for use as a cathode in electrolytic capacitors.

[0051] 2. Method for Manufacturing Electrode Materials The method for manufacturing electrode materials of the present invention comprises, in order: (1) a mixture layer formation step of forming a mixture layer containing an organometallic compound including an organotitanium compound and an organosilicon compound, and a fibrous carbon material, on the surface of an aluminum foil; and (2) a heat treatment step of heating the aluminum foil on which the mixture layer has been formed in an inert atmosphere for 1 minute to 8 hours. Each step will be described below.

[0052] (Mixture Layer Formation Process) The mixture layer formation process is a process of forming a mixture layer containing organometallic compounds, including organotitanium compounds and organosilicon compounds, and fibrous carbon material on the surface of aluminum foil. The mixture layer formation process will be described below.

[0053] <Organotitanium Compounds> The organometallic compounds contained in the mixture layer formed by the mixture layer formation process include organotitanium compounds. The organometallic compounds containing organotitanium compounds are subjected to heat treatment in the heat treatment process described later, and TiO x It is easy to form lower-order titanium oxide represented by (where x represents 0 < x < 2), and the conductivity of the coating layer can be improved.

[0054] The organotitanium compound is not particularly limited as long as it contains titanium and carbon and produces titanium oxide upon heat treatment. From the viewpoint of excellent stability, titanium alkoxides and their chelates, peroxotitanic acid and its salts can be suitably used as organotitanium compounds.

[0055] Examples of titanium alkoxides and their chelates include titanium tetraethoxide, titanium tetraisopropoxide, titanium tetran-butoxide, titanium diisopropoxybis(acetylacetonate), titanium tetraacetylacetonate, titanium diisopropoxybis(ethylacetoacetate), titanium lactate, dihydroxybis(ammonium lactate)titanium, and titanium diisopropoxybis(triethanolamine). Salts of these ammonium salts may also be used. Among these, titanium diisopropoxybis(acetylacetonate) and titanium tetraacetylacetonate are more preferably used.

[0056] Commercially available titanium alkoxide compounds and their chelates can be used. Examples of such commercially available products include TC-300: Titanium diisopropoxybis(acetylacetonate) (manufactured by Matsumoto Fine Chemical Co., Ltd.) and TC-401: Titanium tetraacetylacetonate (manufactured by Matsumoto Fine Chemical Co., Ltd.).

[0057] The above-mentioned organotitanium compounds can be used individually or as a mixture of two or more.

[0058] The content of the organic titanium compound in the mixture layer is not particularly limited, but is preferably 40% to 97.5% by mass, and more preferably 60% to 95% by mass, with the mixture layer being 100% by mass. When the upper limit of the organic titanium compound content is within the above range, resistance can be further reduced by using it in combination with fibrous carbon material. When the lower limit of the organic titanium compound content is within the above range, the adhesion between the aluminum foil and the coating layer is further improved.

[0059] <Organosilicon Compounds> The organometallic compounds contained in the mixture layer formed by the mixture layer formation process include organosilicon compounds. The inclusion of organosilicon compounds in the mixture layer improves the adhesion between the mixture layer and the aluminum foil, and suppresses the detachment of the mixture layer during the manufacturing process. Furthermore, since organosilicon compounds change into silicon oxides upon heat treatment and do not decompose with heat like resins, the adhesion between the coating layer after heat treatment and the aluminum foil can also be improved.

[0060] The organosilicon compounds are not particularly limited as long as they contain silicon and carbon and produce silicon oxides upon heat treatment. Examples of organosilicon compounds include silicon alkoxides and their hydrolysis and polycondensate products.

[0061] Examples of silicon alkoxides include tetraethoxysilane, tetramethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, tetraisopropoxysilane, and their hydrolyzates and condensates. Among these, tetraethoxysilane and tetramethoxysilane are preferred from the viewpoint of superior stability, and their hydrolyzates are even more preferred.

[0062] Commercially available silicon alkoxides can be used. Examples of such commercially available products include HAS-10: Silicate Hydrolyzate (manufactured by Colcoat Co., Ltd.).

[0063] The above organosilicon compounds can be used individually or as a mixture of two or more.

[0064] The content of the organosilicon compound in the mixture layer is preferably 2.5% by mass or more and less than 50% by mass, with the mixture layer being 100% by mass. When the upper limit of the organosilicon compound content is within the above range, resistance can be further reduced by using it in combination with fibrous carbon material. When the lower limit of the organosilicon compound content is within the above range, the adhesion between the aluminum foil and the coating layer is further improved.

[0065] Furthermore, the total content of organotitanium compounds and organosilicon compounds in the mixture layer is less than 100% by mass.

[0066] <Organometallic Compounds> Organometallic compounds include the above-mentioned organotitanium compounds and organosilicon compounds.

[0067] The types and content of organotitanium and organosilicon compounds contained in the organometallic compounds are as described above.

[0068] The organometallic compound may include organometallic compounds of other metals besides the above-mentioned organotitanium compound and organosilicon compound.

[0069] Other metals besides titanium and silicon can be widely used, including valve metals other than titanium and silicon. Examples of such valve metals include tantalum, hafnium, zirconium, niobium, and aluminum, with tantalum, hafnium, niobium, and aluminum being more preferred.

[0070] Examples of organometallic compounds containing the valve metals mentioned above include organotantalum compounds, organohafnium compounds, organoniob compounds, organoaluminum compounds, and the like. Examples of metal alkoxides and chelates containing these valve metals, as well as salts thereof, are also included.

[0071] The organometallic compounds of the other metals mentioned above can be used individually or in combination of two or more.

[0072] The content of other metals in the organometallic compound is not particularly limited, but is preferably 0.1% to 20% by mass, and more preferably 2.5% to 10% by mass, with the organometallic compound being 100% by mass.

[0073] <Fibrous carbon material> The mixture layer contains fibrous carbon material.

[0074] The fibrous carbon material included in the mixture layer is not particularly limited, and carbon nanotubes and carbon nanofibers can be suitably used.

[0075] The types and properties of carbon nanotubes and carbon nanofibers used as fibrous carbon materials are the same as those described in the electrode materials of the present invention.

[0076] To ensure uniform distribution of the fibrous carbon material within the mixture layer, the mixture layer may contain a dispersant. In the manufacturing method of the present invention, a step may be provided in which the fibrous carbon material and the dispersant are pre-dispersed in a solvent before mixing the organometallic compound in the mixture layer formation step. Known dispersion methods can be used, such as ultrasonic homogenizers, high-pressure homogenizers, and bead mills. The dispersant is either thermally decomposed and disappears or remains as carbides after the heat treatment in the heat treatment step described later.

[0077] Commercially available fibrous carbon materials can be used. Examples of such commercially available products include SPC-061: Single-Walled Carbon Nanotube Dispersion (manufactured by Kusumoto Chemical Co., Ltd.).

[0078] The above-mentioned fibrous carbon material can be used alone or as a mixture of two or more types.

[0079] The content of fibrous carbon material in the mixture layer is preferably 0.1% to 20% by mass, and more preferably 0.25% to 10% by mass, based on 100% by mass of the mixture layer. When the upper limit of the fibrous carbon material content is within the above range, the adhesion between the aluminum foil and the coating layer is further improved when used in combination with organometallic compounds. When the lower limit of the fibrous carbon material content is within the above range, the adhesion between the aluminum foil and the coating layer is further improved.

[0080] <Resin Binder> The above mixture layer may contain a resin binder.

[0081] In the manufacturing method of the present invention, by including a resin binder in the mixture layer formation step, the flexibility of the mixture layer can be further improved, and the adhesion between the mixture layer and the aluminum foil can be further improved, thereby suppressing the shedding of the mixture layer during the manufacturing process. Furthermore, by using a resin binder that functions as a dispersant, the dispersibility of fibrous carbon materials can be further improved. In addition, after the heat treatment in the processing step, the resin binder carbonizes and becomes amorphous carbon, which can further improve conductivity. Moreover, the amorphous carbon, which is the carbonized resin binder, can further improve the density and flexibility of the coating layer, thereby improving the reliability as an electrode. Furthermore, because the mixture layer contains a resin binder, an intervening layer containing aluminum and carbon can be formed by the decomposition gas containing carbon generated when the resin binder is thermally decomposed.

[0082] The resin used as a resin binder is not particularly limited, and known resins can be used. Examples of such resins include synthetic resins such as carboxy-modified polyolefin resins, vinyl acetate resins, vinyl chloride resins, vinyl chloride / vinyl acetate copolymer resins, vinyl alcohol resins, butyral resins, vinyl fluoride resins, acrylic resins, polyester resins, urethane resins, epoxy resins, urea resins, phenolic resins, xylene resins, furan resins, acrylonitrile resins, cellulose resins, paraffin wax, and polyethylene wax; natural resins or waxes such as waxes, tars, animal glue, lacquer, pine resin, and beeswax can also be suitably used. Resins that have good adhesion to aluminum foil and that easily carbonize upon thermal decomposition, leaving behind amorphous carbon, are preferred, and specifically polyvinyl alcohol resins, phenolic resins, and furan resins are preferred.

[0083] The resin binder content in the mixture layer is preferably 0.1 to 50% by mass, and more preferably 5 to 30% by mass, based on 100% by mass of the mixture layer.

[0084] The above mixture layer may further contain additives and solvents.

[0085] <Additives> When additives are included in the mixture layer, the additives are not particularly limited and include additives commonly used in electrode materials. Examples of such additives include leveling agents to improve the coating properties of the mixture for forming the mixture layer, defoaming agents, thixotropes, dispersants to improve the dispersibility of fibrous carbon materials, and chelating agents to improve the stability of organometallic compounds.

[0086] <Solvent> When the mixture layer contains a solvent, the solvent is not particularly limited, but a parent solvent of an organometallic compound is preferred. Examples of such parent solvents include solvents that do not cause the organometallic compound to gel or precipitate, and specifically include ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; aromatic solvents such as toluene and xylene; aliphatic solvents such as n-pentane, n-hexane, n-heptane, and n-octane; alcohol solvents such as methanol, ethanol, isopropyl alcohol, and n-butanol; glycol solvents such as ethylene glycol and propylene glycol; glycol ether solvents such as propylene glycol monomethyl ether and dipropylene glycol monomethyl ether; and water.

[0087] In the mixture layer formation process, the thickness of the mixture layer is preferably 0.005 μm or more and 5 μm or less. Furthermore, when the mixture layer is formed on both sides of the aluminum foil, it is preferable that the thickness of the mixture layer on one side is within the above range.

[0088] The method for forming a mixture layer on the surface of aluminum foil is not particularly limited, and examples include applying the mixture for forming the mixture layer by coating methods such as die coating, gravure coating, direct coating, bar coating, roller, brush, spray, dipping, etc., or printing by known printing methods such as silkscreen printing.

[0089] Before forming a mixture layer on the surface of the aluminum foil, the surface of the aluminum foil may be subjected to a pretreatment to improve its wettability. Examples of such pretreatments include solvent cleaning to remove rolling oil adhering to the surface of the aluminum foil when manufacturing it as a sheet or foil, acid / alkali cleaning, heat treatment in air or an inert atmosphere, and corona treatment or plasma treatment for surface modification.

[0090] <Drying Process> The mixture layer formation process may include a drying process in which, after forming a mixture layer on the surface of the aluminum foil, the aluminum foil on which the mixture layer has formed is heated to dry the mixture layer. By including a drying process in the mixture layer formation process, solvents and other substances contained in the mixture layer can be removed.

[0091] The heating temperature in the drying process is preferably between 80°C and 350°C, and the heating time is preferably between 10 seconds and 1 hour.

[0092] Through the mixture layer formation process described above, a mixture layer is formed on the surface of the aluminum foil.

[0093] (Heat treatment process) The heat treatment process involves heating the aluminum foil, which has a mixture layer formed on it, in an inert atmosphere for a period of 1 minute to 8 hours.

[0094] In the heat treatment process, the inert atmosphere is not particularly limited and can include, for example, atmospheres of hydrogen, nitrogen, noble gases (helium, neon, argon, etc.), paraffinic hydrocarbons (methane, ethane, propane, n-butane, isobutane, and pentane, etc.), olefinic hydrocarbons (ethylene, propylene, butene, butadiene, etc.), or derivatives of these hydrocarbons. When forming an intercalated layer containing aluminum and carbon by heat treatment, among these inert atmospheres, an atmosphere of paraffinic hydrocarbons such as methane, ethane, and propane is preferred, an atmosphere of any one of methane, ethane, or propane is more preferred, an atmosphere of methane is even more preferred, and from the viewpoint of ease of handling, argon is preferred.

[0095] The weight ratio of hydrocarbon-containing substance introduced into the space (atmosphere) in which the aluminum foil with the mixture layer formed on its surface is placed is not particularly limited, but it is generally preferable to be in the range of 0.1 parts by mass or more and 50 parts by mass or less in terms of carbon per 100 parts by mass of aluminum foil.

[0096] The heating time in the heat treatment process is between 1 minute and 8 hours. If the heating time is less than 1 minute, the adhesion between the aluminum foil and the coating layer decreases. If the heating time exceeds 8 hours, the environmental burden is high in terms of the amount of energy required for heat treatment, and production costs increase. Preferably, the heating time is between 5 minutes and 7 hours, more preferably between 10 minutes and 6 hours, even more preferably between 15 minutes and 5 hours, and particularly preferably between 20 minutes and 4 hours. When the heating time is within the above range, the amount of energy required for heat treatment can be reduced by more than 30% compared to conventional methods, further reducing the environmental burden and production costs.

[0097] The heating temperature in the heat treatment process is usually preferably in the range of 450°C to less than 660°C. By setting the heating temperature to 450°C or higher, the crystallized aluminum carbides can be sufficiently incorporated into the interlayer containing aluminum and carbon, thereby further improving the adhesion between the aluminum foil and the coating layer. Furthermore, an organometallic compound containing titanium is added. x By using lower-order titanium oxide represented by (where x represents 0 < x < 2), the resistance can be further reduced and higher conductivity can be obtained. However, this does not preclude setting the heating temperature in the heat treatment step to less than 450°C in the manufacturing method of the present invention, and it is preferable that the temperature is at least above 300°C. Furthermore, it is preferable that the heating temperature is less than 660°C from the melting point of aluminum.

[0098] In the heat treatment process, if the heating temperature is 400°C or higher, it is preferable to keep the oxygen concentration in the heating atmosphere at 1.0 volume% or less. If the oxygen concentration in the heating atmosphere exceeds 1.0 volume% under conditions where the heating temperature is 400°C or higher, the oxide film on the surface of the aluminum foil will thicken, increasing the interfacial electrical resistance on the surface of the aluminum foil and potentially increasing the internal resistance of the electrode material. It may also affect the degree of oxidation of the valve metal oxide, increasing the electrical resistance of the valve metal oxide and potentially increasing the internal resistance of the electrode material. Furthermore, the carbon material contained in the coating layer may oxidize and decompose, increasing electrical resistance and potentially causing defects such as fine cracks or voids in the coating layer. By keeping the oxygen concentration in the heating atmosphere at 1.0 volume% or less when the heating temperature is 400°C or higher, the increase in the internal resistance of the electrode material and defects in the coating layer can be further suppressed.

[0099] Through the heat treatment process described above, the electrode material of the present invention can be manufactured by heating the aluminum foil, which has a mixture layer formed on it, in an inert atmosphere for a period of 1 minute to 8 hours.

[0100] (Preheating step) The method for manufacturing the electrode material of the present invention may include a preheating step, which is performed after the mixture layer formation step and before the heat treatment step, in which the aluminum foil on which the mixture layer has been formed on its surface is heated in an atmosphere containing oxygen. By including a preheating step in the manufacturing method of the present invention, if the mixture layer contains a resin binder, the resin binder can be appropriately decomposed, and the amount of carbon material remaining in the coating layer after the heat treatment step can be adjusted. Furthermore, by including a preheating step, the dehydration and condensation reactions of the organometallic compounds are promoted, the bonding strength between the aluminum foil and the coating layer is further improved, and the adhesion between the coating layer and the aluminum foil can be further improved.

[0101] The concentration of oxygen in the atmosphere during the preheating step is not particularly limited, but it is sufficient that oxygen is present in the space where the aluminum foil is placed, and it is preferable that the space contains 2 to 50 volume percent of oxygen. This preheating step can usually be carried out in air.

[0102] The heating temperature in the preheating step is preferably between 100°C and 350°C, and the heating time is preferably between 1 minute and 100 hours.

[0103] The electrode material manufacturing method of the present invention described above allows for continuous processing on a roll at a much higher speed than conventional ion plating, vacuum deposition, chemical vapor deposition, and sputtering methods in the mixture layer formation step, and also allows for continuous processing on a roll or large-lot processing in a roll shape using a large heat treatment furnace in the heat treatment step, resulting in good productivity.

[0104] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples.

[0105] (Example 1) Titanium tetraacetylacetonate (TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) as an organometallic compound, silicate hydrolysis solution (HAS-10, manufactured by Colcoat Co., Ltd.) as an organosilicon compound, and single-walled carbon nanotube dispersion (SPC-061, manufactured by Kusumoto Chemical Co., Ltd.) as a fibrous carbon material were mixed in a weight ratio of 99.5 (titanium tetraacetylacetonate 94.5 + silicate hydrolysis solution 5.0):carbon material 0.5, and the mixture was appropriately diluted with a mixed solvent containing isopropyl alcohol and butyl acetate to prepare a coating solution. Note that the weight of the organometallic compound is the weight assuming that all of the organometallic compound becomes titanium dioxide. Next, the prepared coating solution was applied to both sides of a 20 μm thick aluminum foil (JIS standard alloy number 1085 hard material), one side at a time, and after each side was coated, it was dried in air at 180°C for 1 minute to form a mixed layer. The amount of the mixture layer adhering after drying is 0.2 g / m² on each side. 2 Next, the electrode material was prepared by heating it at a temperature of 600°C for 1 hour in an argon gas atmosphere.

[0106] (Example 2) An electrode material was prepared in the same manner as in Example 1, except that the coating solution was prepared in a weight ratio of 99.5 parts organometallic compound (89.5 parts titanium tetraacetylacetonate + 10.0 parts silicate hydrolysate) to 0.5 parts carbon material.

[0107] (Example 3) An electrode material was prepared in the same manner as in Example 1, except that the coating solution was prepared in a weight ratio of 99.0 parts organometallic compound (79.0 parts titanium tetraacetylacetonate + 20.0 parts silicate hydrolysate) to 1.0 parts carbon material.

[0108] (Example 4) A multi-walled carbon nanotube A with a diameter of 7 to 15 nm and a length of 5 to 15 μm was used as the fibrous carbon material. 200 parts by mass of BYK-ET 3034 (manufactured by Bic Chemie Japan Co., Ltd.) was added to 100 parts by mass of multi-walled carbon nanotube A as a dispersant, and the mixture was dispersed in a mixed solvent containing isopropyl alcohol and butyl acetate using a high-pressure homogenizer to prepare a multi-walled carbon nanotube dispersion. The prepared dispersion was mixed with titanium tetraacetylacetonate (manufactured by Matsumoto Fine Chemical Co., Ltd., TC-401) and silicate hydrolysate (manufactured by Colcoat Co., Ltd., HAS-10) as organometallic compounds in a weight ratio of organometallic compound 99.0 (titanium tetraacetylacetonate 89.0 + silicate hydrolysate 10.0):carbon material 1.0 to prepare a coating solution. The electrode material was prepared in the same manner as in Example 1.

[0109] (Example 5) A multi-walled carbon nanotube B with a diameter of 20 to 40 nm and a length of 5 to 15 μm was used as the fibrous carbon material. 100 parts by mass of BYK-ET 3034 (manufactured by Bic Chemie Japan Co., Ltd.) was added to 100 parts by mass of multi-walled carbon nanotube B as a dispersant, and the mixture was dispersed in a mixed solvent containing isopropyl alcohol and butyl acetate using a high-pressure homogenizer to prepare a multi-walled carbon nanotube dispersion. The prepared dispersion was mixed with titanium tetraacetylacetonate (manufactured by Matsumoto Fine Chemical Co., Ltd., TC-401) and silicate hydrolysate (manufactured by Colcoat Co., Ltd., HAS-10) as organometallic compounds in a weight ratio of organometallic compound 98.0 (titanium tetraacetylacetonate 88.0 + silicate hydrolysate 10.0):carbon material 2.0 to prepare a coating solution. The electrode material was prepared in the same manner as in Example 1.

[0110] (Example 6) A multilayer carbon nanotube C with a diameter of 60 to 100 nm and a length of 5 μm or more was used as a fibrous carbon material. 100 parts by mass of BYK-ET 3034 (manufactured by Bic Chemie Japan Co., Ltd.) was added to 100 parts by mass of the multilayer carbon nanotube C as a dispersant, and the mixture was dispersed in a mixed solvent containing isopropyl alcohol and butyl acetate using a high-pressure homogenizer to prepare a multilayer carbon nanotube dispersion. The prepared dispersion was mixed with titanium tetraacetylacetonate (manufactured by Matsumoto Fine Chemical Co., Ltd., TC-401) and silicate hydrolysate (manufactured by Colcoat Co., Ltd., HAS-10) as organometallic compounds in a weight ratio of organometallic compound 97.0 (titanium tetraacetylacetonate 87.0 + silicate hydrolysate 10.0):carbon material 3.0 to prepare a coating solution. The electrode material was prepared in the same manner as in Example 1.

[0111] (Example 7) Carbon nanofibers with a diameter of 200 to 800 nm and a length of 1 to 20 μm were used as the fibrous carbon material. 50 parts by mass of BYK-ET 3034 (manufactured by Bic Chemie Japan Co., Ltd.) was added to 100 parts by mass of carbon nanofibers as a dispersant, and the mixture was dispersed in a mixed solvent containing isopropyl alcohol and butyl acetate using a high-pressure homogenizer to prepare a carbon nanofiber dispersion. The prepared dispersion was mixed with titanium tetraacetylacetonate (manufactured by Matsumoto Fine Chemical Co., Ltd., TC-401) and silicate hydrolysate (manufactured by Colcoat Co., Ltd., HAS-10) as organometallic compounds in a weight ratio of organometallic compound 95.0 (titanium tetraacetylacetonate 85.0 + silicate hydrolysate 10.0):carbon material 5.0 to prepare a coating solution. Electrode materials were prepared in the same manner as in Example 1.

[0112] (Example 8) The amount of the mixture layer after drying was 0.4 g / m². 2 Except for the above, the electrode material was prepared in the same manner as in Example 2.

[0113] (Example 9) The amount of the mixture layer after drying was 0.4 g / m². 2 The electrode material was prepared in the same manner as in Example 2, except that the heat treatment was performed in a methane gas atmosphere.

[0114] (Example 10) An electrode material was prepared in the same manner as in Example 8, except that in preparing the coating solution, titanium tetraacetylacetonate (TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) as an organometallic compound, silicate hydrolysate (HAS-10, manufactured by Colcoat Co., Ltd.) as an organosilicon compound, single-walled carbon nanotube dispersion (SPC-061, manufactured by Kusumoto Chemical Co., Ltd.) as a fibrous carbon material, and phenolic resin (Reditop PL-2243, manufactured by Gun-ei Chemical Industry Co., Ltd.) as a resin binder were mixed by weight in the ratio of organometallic compound 94.5 (titanium tetraacetylacetonate 84.5 + silicate hydrolysate 10.0): carbon material 0.5: resin binder 5.0 to prepare the coating solution.

[0115] (Example 11) An electrode material was prepared in the same manner as in Example 10, except that in the preparation of the coating solution, an organometallic compound (titanium tetraacetylacetonate 79.5 + silicate hydrolysate 10.0) was mixed by weight in the ratio of 89.5: carbon material 0.5: resin binder 10.0 to prepare the coating solution.

[0116] (Example 12) An electrode material was prepared in the same manner as in Example 10, except that in the preparation of the coating solution, an organometallic compound (titanium tetraacetylacetonate 69.0 + silicate hydrolysate 10.0) was mixed by weight in the ratio of 79.0:1.0:1.0:resin binder.

[0117] (Example 13) An electrode material was prepared in the same manner as in Example 10, except that in the preparation of the coating solution, an organometallic compound (titanium tetraacetylacetonate 59.0 + silicate hydrolysate 20.0) was mixed by weight in the ratio of 79.0: carbon material 1.0: resin binder 20.0.

[0118] (Comparative Example 1) Titanium oxide particles with a primary particle size of 15 nm (STR-100N, manufactured by Sakai Chemical Industry Co., Ltd.) as the valve metal oxide particles and titanium lactate ammonium salt (TC-300, manufactured by Matsumoto Fine Chemical Co., Ltd.) as the organometallic compound were mixed in a ratio of 95:5 in terms of titanium oxide equivalent. Next, an aqueous coating solution was prepared by mixing and dispersing an aqueous solution of polyvinyl alcohol (Kuraray Poval 3-88, manufactured by Kuraray Co., Ltd.) at a ratio of 25% by mass to 100% by mass of the total of titanium oxide particles (STR-100N) and polyvinyl alcohol. The obtained aqueous coating solution was applied to both sides of a 30 μm thick aluminum foil (soft 1085 material), one side at a time, and dried in air at 180°C for 3 minutes after each side was coated to form a mixed layer. The amount of adhesion of the mixed layer after drying was 1.5 g / m on each side. 2 Next, the dried aluminum foil was heated in air at 200°C for 1 hour. Then, the electrode material was prepared by heating it in a methane gas atmosphere at 615°C for 1 hour.

[0119] (Comparative Example 2) The electrode material for Comparative Example 2 was prepared in the same manner as in Comparative Example 1, except that polyvinyl alcohol was replaced with phenolic resin (Reditop PL-2243, manufactured by Gun-ei Chemical Industry Co., Ltd.) as the resin binder, and titanium lactate ammonium salt (TC-300, manufactured by Matsumoto Fine Chemical Co., Ltd.) was replaced with titanium tetraacetylacetonate (TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) as the organometallic compound.

[0120] (Comparative Example 3) An electrode material was prepared in the same manner as in Example 1, except that titanium tetraacetylacetonate (TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) was used as the organometallic compound in the preparation of the coating solution, and the coating solution was prepared by appropriately diluting it with isopropyl alcohol.

[0121] (Comparative Example 4) In preparing the coating solution, an electrode material was prepared in the same manner as in Example 1, except that titanium tetraacetylacetonate (TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) as an organometallic compound and silicate hydrolysate (HAS-10, manufactured by Colcoat Co., Ltd.) as an organosilicon compound were mixed in a weight ratio of 100.0 (titanium tetraacetylacetonate 90.0 + silicate hydrolysate 10.0):carbon material, and the mixture was diluted appropriately with isopropyl alcohol to prepare the coating solution.

[0122] (Comparative Example 5) In preparing the coating solution, instead of using fibrous carbon material, graphite with an average particle size of 6 μm (UP-5-α, manufactured by Nippon Graphite Co., Ltd.) was used as a flake-type carbon material. 50 parts by mass of BYK-ET 3034 (manufactured by Bic Chemie Japan Co., Ltd.) was added as a dispersant to 100 parts by mass of graphite, and the graphite dispersion was prepared by dispersing it in a mixed solvent containing isopropyl alcohol and butyl acetate using a ball mill. The electrode material was prepared in the same manner as in Example 1, except that the prepared dispersion was mixed with titanium tetraacetylacetonate (TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) and silicate hydrolysate (HAS-10, manufactured by Colcoat Co., Ltd.) as organometallic compounds in a weight ratio of organometallic compound 90.0 (titanium tetraacetylacetonate 80.0 + silicate hydrolysate 10.0):carbon material 10.0 to prepare the coating solution.

[0123] (Comparative Example 6) An electrode material was prepared in the same manner as in Comparative Example 5, except that the coating solution was mixed in a weight ratio of 80.0 parts organometallic compound (70.0 parts titanium tetraacetylacetonate + 10.0 parts silicate hydrolysate) to 20.0 parts carbon material.

[0124] (Comparative Example 7) An electrode material was prepared in the same manner as in Comparative Example 5, except that, in the preparation of the coating solution, acetylene black (Li-400, manufactured by Denka Co., Ltd.) with an average particle size of 48 nm was used as a spherical carbon material instead of a fibrous carbon material.

[0125] (Comparative Example 8) In the preparation of the coating liquid, an electrode material was produced in the same manner as in Comparative Example 6, except that acetylene black (Li-400, manufactured by Denka Company Limited) having an average particle diameter of 48 nm was used as the spherical carbon material in place of the fibrous carbon material.

[0126] (Comparative Example 9) An electrode material was produced in the same manner as in Comparative Example 3, except that the heat treatment was performed in a methane gas atmosphere.

[0127] (Comparative Example 10) In the preparation of the coating liquid, an electrode material was produced in the same manner as in Example 1, except that only a silicate hydrolysis liquid (HAS-10, manufactured by Colcoat Co., Ltd.) was used as the organometallic compound, and the blending ratio by weight was 99.5 parts of organometallic compound (99.5 parts of silicate hydrolysis liquid): 0.5 parts of carbon material.

[0128] (Comparative Example 11) A dispersion liquid, in which single-walled carbon nanotubes having a diameter of 1.6 nm and a length of 5 µm or more as a fibrous carbon material were dispersed in an aqueous solvent (TUBALL BATT H2O 0.2% CMC, manufactured by OCSiAl S.A.), and an aqueous styrene-butadiene rubber dispersion (TRD2001, manufactured by JSR Corporation) as a resin binder were mixed at a weight ratio of 0 part of organometallic compound: 5.0 parts of carbon material: 95.0 parts of resin binder, and appropriately diluted with water to prepare a coating liquid. The prepared coating liquid was applied on both sides of a 20 µm-thick aluminum foil (JIS standard alloy No. 1085 material, hard) one side at a time, and dried in air at 180°C for 1 minute after each single-side coating to form a mixture layer. The adhesion amount of the mixture layer after drying was 0.2 g / m on one side 2 . From the above, an electrode material was produced.

[0129] (Comparative Example 12) In the preparation of the coating liquid, an electrode material was produced in the same manner as in Comparative Example 11, except that an acrylic resin emulsion (Bonron XHS-100, manufactured by Mitsui Chemicals, Inc.) was used as the resin binder.

[0130] (Comparative Example 13) In the preparation of the coating liquid, an electrode material was produced in the same manner as in Comparative Example 11, except that an aqueous solution of polyvinyl alcohol (Poval 3-98, manufactured by Kuraray Co., Ltd.) was used as the resin binder.

[0131] (Comparative Example 14) In preparing the coating solution, multi-walled carbon nanotubes B with a diameter of 20 to 40 nm and a length of 5 to 15 μm were used as the fibrous carbon material. 100 parts by mass of BYK-ET 3034 (manufactured by Bic Chemie Japan Co., Ltd.) was added to 100 parts by mass of multi-walled carbon nanotubes B as a dispersant, and the mixture was dispersed in a mixed solvent containing isopropyl alcohol and butyl acetate using a high-pressure homogenizer to prepare a multi-walled carbon nanotube dispersion. The prepared dispersion was mixed with a phenolic resin (Reditop PL-2243, manufactured by Gun-ei Chemical Industry Co., Ltd.) as a resin binder in a weight ratio of organometallic compound 0:carbon material 20.0:resin binder 80 to prepare the coating solution. The electrode material was prepared in the same manner as in Comparative Example 11.

[0132] (Comparative Example 15) An electrode material was prepared in the same manner as in Comparative Example 14, except that it was heated at a temperature of 600°C for 1 hour in an argon gas atmosphere after drying.

[0133] The properties of the fabricated electrode materials were evaluated using the following method.

[0134] <Adhesion> This was evaluated using the taping method. Specifically, a 24 mm wide adhesive tape (manufactured by Sekisui Chemical Co., Ltd., product name "Sekisui Cellotape (registered trademark) No. 252") was pressed onto the surface of the electrode material sample over a 24 mm x 100 mm area. The adhesive tape was then folded back 180° and peeled off in the direction of the long side to check the degree of peeling of the coating layer. The evaluation was performed according to the following evaluation criteria: ++: The coating layer hardly peeled off, i.e., the coating layer hardly adhered to the adhesive tape. +: The surface of the coating layer peeled off slightly. -: The coating layer peeled off in aggregate or completely peeled off from the aluminum foil interface.

[0135] <Resistance Evaluation> (1) Resistance evaluation using current collectors for electric double layer capacitors (EDLCs) Electric double layer capacitors were fabricated using samples of the fabricated electrode material as current collectors according to the following procedure, and their resistance was evaluated.

[0136] Electrode Fabrication: An activated carbon slurry was prepared by coating one side of the prepared electrode material with activated carbon (YP50F, manufactured by Kuraray Co., Ltd.), acetylene black (Li-400, manufactured by Denka Co., Ltd.), sodium carboxymethylcellulose (1160, manufactured by Daicel Mirise Co., Ltd.), cellulose nanofiber (Reocrista I-2SP, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and acrylic resin emulsion (Bonlon XHS-100, manufactured by Mitsui Chemicals, Inc.) in a mixing ratio (by weight) of 89.5:5.0:2.0:0.5:3.0, and drying it to create an activated carbon electrode.

[0137] - Cell Preparation: After cutting the fabricated activated carbon electrodes into strips, two electrodes were prepared by removing the other coated areas so that the activated carbon slurry coated area was 20 mm x 50 mm. A cellulose-based separator was used as the separator, and 1.5 M triethylmethylammonium tetrafluoroborate / propylene carbonate was used as the electrolyte. Cells were then packed in aluminum laminate film, and AC impedance measurements were performed. AC impedance measurements were performed using an electrochemical measurement system (Hokuto Denko HZ-7000) under the conditions of applied voltage: 20 mVp-P and frequency range: 20 kHz-100 mHz. The results of the AC impedance measurement were analyzed using Cole-Cole plot, and the value of the real component on the X axis when the imaginary component on the Y axis changed from positive to 0 was taken as the resistance value of the cell. Table 1 shows the values ​​of each example and the comparative example, with Comparative Example 1, which served as the standard for conductivity evaluation, set to 100. Furthermore, if the Y-axis value was already negative at a frequency of 20 kHz, that value was used as the cell's resistance.

[0138] (2) Resistance evaluation by conductive polymer coating The conductive polymer was coated onto the prepared electrode material samples according to the following procedure and the resistance was evaluated.

[0139] - A conductive polymer aqueous dispersion of PEDOT / PSS (polyethylenedioxythiophene / polystyrene sulfonic acid) (Organon ICP 1050, manufactured by Agfa-Gevaert NV) was prepared as the conductive polymer for coating. A solution prepared by adding 3% by mass of diethylene glycol to the aqueous dispersion of this conductive polymer relative to 100% by mass of PEDOT / PSS was coated onto one side of the sample and dried at 105°C for 2 minutes to form a conductive polymer layer with a thickness of approximately 100 nm.

[0140] - Resistance Measurement An LCR meter (HIOKI E.E. CORPORATION 3522-50) was used to measure Rs (effective resistance in series equivalent circuit mode) at a frequency of 120 Hz by clamping the conductive polymer coated surface and the opposite uncoated surface of the prepared sample with tweezers probes. The resistance value was measured three times, and the average value was taken as the measured value. Table 1 shows the values ​​for each example and the comparative example, with Comparative Example 1, which serves as the standard for conductivity evaluation, set to 100.

[0141] <Heat Resistance (Adhesion after Heating)> The electrode materials prepared in each example and comparative example were kept in air at 300°C for 10 hours using a high-temperature constant-temperature oven (STPH-101, manufactured by ESPEC Corporation), and the change in adhesion before and after heating was observed to evaluate the heat resistance. The adhesion was evaluated in the same manner as the adhesion evaluation described above.

[0142] <Acid Resistance Evaluation> In addition to adhesion evaluation, resistance evaluation, and heat resistance evaluation of the fabricated electrode material, the acid resistance was evaluated using the following method to confirm that defects in the coating layer were suppressed and the reliability as an electrode was improved. Specifically, the prepared sample was cut into strips of 10 mm x 120 mm, and a 10 mm x 60 mm area was immersed in 1 M hydrochloric acid solution at 80°C, and the time until the coating layer peeled off was measured.

[0143] The results are shown in Table 1.

[0144]

[0145] The following was learned from the results in Table 1.

[0146] Regarding the adhesion evaluation, as shown in Table 1, the coating layer remained largely intact and excellent in all examples. However, a decrease in adhesion was observed in Comparative Examples 1 and 2, which used titanium oxide particles, organometallic compounds, and a resin binder; Comparative Example 6, which used flake-like carbon material; Comparative Example 8, which used spherical carbon material; and Comparative Example 15, which used fibrous carbon and a resin binder.

[0147] Regarding resistance evaluation (EDLC), as shown in Table 1, all examples showed lower resistance than the reference Comparative Example 1. In other words, all examples demonstrated high conductivity despite short heat treatment times, indicating suitability for use as current collectors for electric double-layer capacitors. Comparative Example 4, which combined TC-401 and HAS-10, showed high resistance, as did Comparative Examples 5 and 6, which used flake graphite. Among Comparative Examples 7 and 8, which used spherical carbon materials, only Comparative Example 8, with its extremely low adhesion, showed low resistance. Furthermore, Comparative Example 9, which underwent heat treatment in a methane atmosphere, showed higher resistance than all examples. In addition, Comparative Example 10, a combination of fibrous carbon and HAS-10, also showed high resistance. Comparative Examples 11 to 14, which combined fibrous carbon with a resin binder and were not heat-treated, showed extremely high resistance despite having a higher proportion of fibrous carbon than the examples. This is thought to be because the insulating resin binder coated the surface of the fibrous carbon, inhibiting conductivity.

[0148] Regarding the resistance evaluation (conductive polymer), as shown in Table 1, the trend is similar to that of the evaluation results for current collectors used in EDLCs. In other words, it was found that conductivity was high in all examples.

[0149] From these results, it was found that low-resistance capacitors can be manufactured by using the electrode material of the present invention as the cathode foil for conductive polymer aluminum solid electrolytic capacitors and conductive polymer hybrid aluminum electrolytic capacitors.

[0150] Regarding the evaluation of heat resistance (adhesion after heating), as shown in Table 1, all examples showed no change in adhesion before and after heating, resulting in a ++ rating. On the other hand, in Comparative Examples 3-5, 7, and 9-14, the adhesion before heating was all rated ++, but after heating, a decrease in adhesion was observed in the samples of Comparative Examples 11-14. It is thought that the resin binder melted or decomposed due to heating at 300°C for 10 hours, resulting in a decrease in adhesion.

[0151] Regarding the acid resistance evaluation, as shown in Table 1, in Examples 10 to 13, it was found that as the proportion of resin binder increased while maintaining low resistance, acid resistance improved while maintaining high conductivity, adhesion, and heat resistance. This is thought to be because the phenolic resin, which is the resin binder, carbonizes due to the heat treatment and remains as dense amorphous carbon, thereby suppressing defects in the coating layer and improving the reliability as an electrode. Furthermore, it was found that Example 13, which has a higher proportion of HAS-10, showed even greater acid resistance than Example 12. This is thought to be due to improved adhesion between the coating layer and the aluminum foil by the silicon-containing metal oxide, as well as suppression of defects in the coating layer and further improvement in the reliability as an electrode.

[0152] In addition to the evaluations in Table 1, the following evaluations were also performed.

[0153] <Observation of the back surface> To observe the intercalation layer of the electrode material manufactured in Example 11, the aluminum foil was dissolved using a brom-methylmethanol mixed solution, and the surface of the remaining intercalation layer was directly observed using a scanning electron microscope (SEM). The photograph is shown in Figure 3. Specifically, Figure 3 is a photograph of the back surface of the electrode material, observed from the intercalation layer toward the coating layer, with the aluminum foil removed to expose the intercalation layer. In Figure 3, the magnification of the photograph is 10,000x. As shown in Figure 3, an intercalation layer, which is a plate-like crystalline material, was confirmed between the aluminum foil and the coating layer. Furthermore, X-ray microanalyzer (EPMA) and X-ray diffraction (XRD) confirmed that the above-mentioned intercalation layer contains aluminum and carbon. Similar analysis was also performed on Example 9, and it was confirmed that an intercalation layer containing aluminum and carbon was formed.

[0154] <EPMA / XRD Measurement> EPMA and XRD measurements were performed on the sample obtained in Example 9, and TiO was found in the coating layer. x It was confirmed that the material contains lower-order titanium oxide, represented by (where x represents 0 < x < 2). As shown in the above results, the electrode material of the present invention has high conductivity even with a short heat treatment time, and also exhibits excellent adhesion and heat resistance between the aluminum foil base material and the coating layer.

[0155] 1: Electrode material 11: Aluminum foil 12: Coating layer 13: Interlayer 131: Aluminum carbide

Claims

1. An electrode material characterized by comprising a coating layer on at least one side of an aluminum foil, the coating layer comprising a valve metal oxide and a fibrous carbon material, wherein the valve metal oxide comprises titanium oxide and silicon oxide.

2. The electrode material according to claim 1, wherein the fibrous carbon material comprises at least one selected from the group consisting of carbon nanotubes and carbon nanofibers.

3. The titanium oxide is TiO x The electrode material according to claim 1, comprising lower-order titanium oxide represented by (where x represents 0 < x < 2).

4. The electrode material according to claim 1, wherein the valve metal oxide further comprises a metal oxide of at least one metal selected from the group consisting of tantalum, hafnium, zirconium, niobium, and aluminum.

5. The electrode material according to claim 1, wherein the coating layer comprises amorphous carbon.

6. The electrode material according to claim 5, further comprising an intervening layer containing aluminum and carbon, formed on at least a portion of the surface of the aluminum foil, between the aluminum foil and the coating layer.

7. An electrode material according to any one of claims 1 to 6, used as the cathode of an electrolytic capacitor.

8. A method for manufacturing an electrode material, comprising, in order: (1) a mixture layer formation step of forming a mixture layer containing an organometallic compound including an organotitanium compound and an organosilicon compound, and a fibrous carbon material, on the surface of an aluminum foil; and (2) a heat treatment step of heating the aluminum foil on which the mixture layer has been formed in an inert atmosphere for 1 minute to 8 hours.

9. The method for producing an electrode material according to claim 8, wherein the mixture layer contains a resin binder.

10. The method for manufacturing an electrode material according to claim 8, wherein the heat treatment step is performed in a temperature range of 450°C or more and less than 660°C.

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