JP2005310836A - Electrode for electrochemical element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new electrode for electrochemical element having a large capacity within the liquid, and superior impedance characteristics. <P>SOLUTION: In the electrode for electrochemical element, (1) the etched aluminum and a carbon layer, including the carbon element covering the surface thereof is 85% or higher, (2) the thickness of the carbon layer is 1 μm or smaller, (3) such a carbon layer includes micron-size holes in the narrow diameter of 2 nm or smaller and the maximum value in distribution of the micron-size hole diameter is within the range of 0.5 to 1.5 nm;(4) moreover an activated charcoal layer used for an ordinary electric double-layer capacitor is formed to cover the electrode with the conventional method; and(5) moreover the electric chemical element, such as the cathode of the electric double-layer capacitor and a winding type electrolytic capacitor, is formed by using a non-aqueous system electrolyte. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrode for an electrochemical element, and more particularly, to a highly reliable electrode used as a collector electrode for an electric double layer capacitor, a negative electrode for an electrolytic capacitor, and the like, and a method for producing the electrode.

  An electrochemical element is an element utilizing an electrochemical reaction, and refers to an element used for energy storage, such as a battery, an electrolytic capacitor, an electric double layer capacitor, and a fuel cell.

  An electric double layer capacitor (EDLC: Electric Double Layer Capacitor) is an electrochemical element for electrical storage that uses an electric double layer capacitance generated at the interface between an electrode (polarizable electrode) and an electrolyte when a voltage is applied. There are two types of electrolytes for EDLC: organic electrolytes (non-aqueous electrolytes) and aqueous electrolytes. Since the operating voltage is high and the energy density of the charged state can be increased, the electric double layer using organic electrolytes Capacitors are attracting attention.

Compared to secondary batteries with electrochemical reaction, this EDLC is characterized by (1) fast charge / discharge, (2) high reversibility of charge / discharge, and (3) excellent repeated life characteristics. It is used as a memory backup power source. The disadvantage is that energy density is low, it is only 4WhL ^-1 whereas the energy density of the lithium ion battery is about 200WhL ^-1. For this reason, the characteristic was inadequate for uses, such as a hybrid type vehicle and the auxiliary power supply for fuel cells.

  Since the electric double layer capacity of EDLC is considered to be proportional to the surface area of the electrode, carbon materials such as activated carbon and carbon black whose surface area is increased by activation are generally used to improve the energy density.

  Usually, since these carbon materials are in a powder form, for example, a sheet-like electrode is formed using a fluorine-based resin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride as a binder. These polarizable electrodes are joined to a current collector made of a metal foil such as aluminum or stainless steel or graphite in order to reduce internal resistance and efficiently charge and discharge.

  However, this EDLC electrode has two technical problems. The first is that only a part of the surface area of the activated carbon material is involved in the double layer capacity, and the actual surface area of the activated carbon measured by, for example, the BET method is not necessarily proportional to the double layer capacity. If ions can be adsorbed on all the walls of the pores, an ideal large-capacity electric double layer capacitor should be formed. However, in reality, the size of ions may be increased due to solvent coordination, and it is difficult to insert ions deep into the pores and to smoothly extract them outside the pores.

  For this reason, the device for controlling the pore size of the activated carbon to an appropriate size for taking in and out of ions has been devised, for example, a method of carbonizing a polyvinylidene chloride resin (see Patent Documents 1 to 4) and many others. A method has been proposed. However, it is said that only one ion is coordinated to 60 carbons even when these devices are devised and the battery is charged to the limit of the decomposition voltage.

  The second technical problem is a problem that the internal impedance of the electrode increases when a sheet-like electrode is produced using activated carbon and a fluororesin as a binder. The internal impedance becomes an IR drop at the time of discharge and reduces the capacitance of the element. Therefore, a method such as adding graphite having high electrical conductivity to the activated carbon to reduce internal impedance is taken. However, even if such a method is used, there is a limit to the improvement, and a reduction in capacitance due to internal impedance is inevitable.

  Further, such an electrode has a problem that the bonding strength between the current collector and the sheet electrode is weak. Insufficient bonding strength not only increases the internal impedance of the device, but also adversely affects the stability of the repeated life.

In order to improve the adhesion between an electrode made of a carbon material and a current collector, an electrode body using a highly etched aluminum foil as a current collector is disclosed (Patent Document 5) (Patent Document 6).
When the highly etched aluminum foil is used as a current collector and immersed in a slurry composed of activated carbon, a binder and a solvent, or the slurry is applied and dried to form an electrode body, the degree of adhesion is somewhat Although the strength is improved, the strength of the obtained electrode body is weak and may be damaged in the process of device preparation. Furthermore, aluminum has a problem in that an insulating oxide film is easily formed on the surface thereof, which increases impedance, and such an electrode has not been put into practical use.

  When using an aluminum foil as a current collector electrode, an attempt to improve the strength of the aluminum foil includes an unroughened portion having a thickness of 8 to 50 μm and a thickness of 0.5 to 5 μm on one or both sides thereof. Technology using an aluminum foil having a roughened surface (Patent Document 7), or having a roughened surface having a thickness of 1 to 5 μm on the surface of the aluminum foil, with a breaking energy of 3 kg. A technique using an aluminum foil that is equal to or greater than mm is disclosed. (Patent Document 8) However, even with these foils, the problem of impedance due to the formation of an insulating oxide film has not been solved.

  On the other hand, as an attempt to prevent deterioration of characteristics due to the formation of an oxide film on an aluminum foil, a technique for embedding carbon particles on the surface of the aluminum foil by pressure bonding to prevent an increase in impedance has been disclosed. (Patent Document 9) (Patent Document 10) Although this method is considered to be effective for flat foils, it is difficult to embed carbon particles in the etching holes with a foil provided with surface irregularities by etching or the like. Even if such a method is taken, the portion where carbon particles are not embedded is covered with an oxide film, so that it is still insufficient as a current collector for electric double layer capacitors and a negative electrode for electrolytic capacitors. I do not get.

As another attempt to reduce the internal resistance of a carbon composite electrode, for example, a method of depositing carbon powder and other conductivity modifiers on an aluminum substrate has been disclosed. (Patent Document 11) Further, a technique is disclosed in which a carbon composite electrode impregnated with a pair of porous aluminum containing a preform of activated carbon fiber having a large surface area impregnated with molten aluminum is disclosed. (Patent Document 12) However, all of these methods have complicated manufacturing methods, and it has been difficult to apply them to double-layer capacitors with strict price requirements.
JP-A-7-249551 JP-A-9-213589 Japanese Patent Laid-Open No. 2001-110689 Japanese Patent Application No. 2000-533380 JP-A-57-60828 JP-A-57-84120 Japanese Patent Laid-Open No. 11-135368 Japanese Patent Laid-Open No. 11-238771 JP 2001-297852 A JP-A-11-288849 US Pat. No. 5,150,283 Japanese National Patent Publication No. 10-509560

  The problem to be solved by the present invention is to provide a novel electrode for an electrochemical device having a large capacity in liquid and excellent impedance characteristics.

  The electrode of the present invention is composed of etched aluminum and a carbonaceous layer containing 85% or more of the carbon component coated on the surface thereof. By using an electrode having such a structure, an electrode having a large capacity and excellent impedance characteristics can be obtained. When the carbon content of the carbonaceous film is 85% or less, the resistance value of the carbonaceous film is extremely high, which is not preferable for the purpose of the present invention.

  The electrode of the present invention comprises a highly etched aluminum foil and a carbonaceous layer having a thickness of 1 μm or less formed on the surface thereof. The surface area of the aluminum foil is remarkably increased by etching, and the carbonaceous film is directly bonded to the surface of the aluminum foil. Since the average thickness of the carbonaceous film is kept to 1 μm or less, the electrode impedance can be kept low even if a carbonaceous film having a relatively high resistance is used, and the holes in the etched aluminum are blocked by the carbonaceous film. There is nothing. The carbonaceous layer formed on the surface of the aluminum foil has a function of preventing the formation of an aluminum oxide film and suppressing an increase in impedance due to the formation of the oxide film.

  Further, such a carbonaceous layer has micropores having a pore diameter of 2 nm or less, and the maximum value of the micropore diameter distribution is in the range of 0.5 to 1.5 nm, whereby the electrode The area can be further increased. In addition to the above micropores, activated carbon is known to have mesopores (pore diameters of 2 nm or more and 50 nm or less) and macropores (pore diameters of 50 nm or more). In activated carbon used for electric double layer capacitors, mesopores and It is believed that macropores are necessary. FIG. 1 shows a conceptual diagram of the presence of macropores, mesopores, and micropores in activated carbon. (1) is macropores, (2) is mesopores, and (3) is micropores.

  However, in the electrode of the present invention, the etched hole of the etched aluminum foil can also serve as a macro hole or, in some cases, a meso hole. The conceptual diagram of the structure of the electrode of this invention is shown in FIG. This figure shows a cross section of etched aluminum, (4) is an aluminum foil, (5) is an etching hole formed in the aluminum foil, and (6) is a carbonaceous layer according to the present invention. The carbonaceous layer is preferably formed so as not to block the etching holes, and preferably contains mesopores and micropores.

  Capacitance can be further improved by depositing an activated carbon layer used for a normal electric double layer capacitor on the electrode of the present invention by a conventional method.

  The electrode of the present invention having these structures can exhibit excellent characteristics by using a non-aqueous electrolyte, and can constitute an electrochemical element such as an electric double layer capacitor or a cathode of a wound electrolytic capacitor.

  Examples of the solvent used as the non-aqueous electrolyte include propylene carbonate, ethylene carbonate, diethyl carbonate, acetonitrile, dimethylformamide, sulfolane, nitromethane, and γ-butyllactone. Examples of the salt to be added include tetrafluoroborate of a quaternary ammonium salt or a phosphonium salt. Specific examples include tetraalkylammonium tetrafluoroborate and tetraalkylphosphonium tetrafluoroborate, and more specific alkyl groups include methyl, ethyl, propyl, butyl, and hexyl groups.

  In the electrode having such a structure, a polymer layer having an average thickness of 2 μm or less formed on the surface of an etched aluminum foil is subjected to 400 ° C. or more and 650 ° C. in a vacuum or an inert gas, or in the presence of water vapor or carbon dioxide. It can be obtained by heating and carbonizing at the following temperatures. The carbonization temperature is preferably 500 ° C. or higher.

  In addition, the polymer layer used for such a purpose can be formed by immersing an etching aluminum foil in a polymer solution dissolved in a solvent, and then lifting and drying.

  Furthermore, a carbonaceous layer having pores can be formed by using a polyvinylidene chloride homopolymer or a vinylidene chloride copolymer as the organic polymer layer, and the capacity of the device can be improved.

  Furthermore, it is preferable to form micropores by adding zinc chloride to a polyvinylidene chloride homopolymer or vinylidene chloride copolymer, followed by carbonization and heat treatment.

  According to the present invention, an electrode for an electrochemical element having a large capacity in liquid and excellent impedance characteristics can be obtained. By using this electrode as a current collector electrode for an electric double layer capacitor, it is possible to obtain a capacitor element having a large capacitance density and excellent internal impedance characteristics and repeated stability. Further, by using the electrode of the invention as a cathode of a wound electrolytic capacitor, an element excellent in internal impedance characteristics and repetitive stability can be obtained.

  Initially, the etching aluminum foil used for this invention is demonstrated. Etched aluminum foil is exclusively used as an anode foil for aluminum electrolytic capacitors. For the purposes of the present invention, aluminum or aluminum alloy foil is used. Here, the aluminum alloy refers to an alloy containing one or more elements selected from elements such as iron, silicon, copper, manganese, magnesium, zinc, etc. with aluminum as a main component. By adding these elements, the foil machine Can increase the strength of the target. In the case of an electrolytic capacitor, high-purity aluminum foil is used to form an oxide film serving as a dielectric layer on the surface of the etched aluminum foil. However, since the etched aluminum foil is used as a collector electrode or a cathode in the present invention, the above aluminum alloy can also be used favorably for this purpose.

  There are an AC method and a DC method for forming holes in the foil by etching, and it is known that the shape of the holes formed is greatly different depending on the difference in the methods. For the purpose of the present invention, both an alternating current etching foil and a direct current etching foil can be preferably used. The etched aluminum foil of the present invention preferably has a large surface area as long as the mechanical strength can be maintained.

In general, in order to evaluate the surface area of the etched aluminum foil, an oxide film is formed on the surface at a constant voltage, and the evaluation is performed based on the capacity in liquid at that time. When such evaluation is carried out, for the purpose of the present invention, for example, it is preferable to use an etching foil having an electrostatic capacitance of 80 μF / cm ² or more when formed at 5 V. Actually, since the thickness of the oxide film formed at 1V is 1.3 nm, in the case of 5V conversion, a film having a thickness of 6.5 nm is formed. Therefore, very fine holes are crushed and may not contribute to the surface area. Therefore, in practice, the true surface area of such a foil can be expected to be even greater.

  In the present invention, the surface of the aluminum sample foil is immersed in an acidic aqueous solution and washed with pure water. Further, the surface is etched by dipping in an aqueous alkali solution, washed with pure water, dipped in acetone and then dried to remove the natural oxide film formed on the surface to obtain a sample foil.

  Next, the carbonaceous film which is the second component of the present invention will be described. The carbonaceous film of the present invention is formed so as to cover the surface of the etched aluminum foil. In the case of an electric double layer capacitor, a double layer capacitance formed between the carbonaceous film and the electrolytic solution is used. The role of the carbonaceous film of the present invention has the role of preventing the formation of a dielectric oxide film on the aluminum surface in addition to the formation of double layer capacitance.

Here, the carbonaceous film refers to a film in which the weight of carbon in the film is 85% or more. In general, when carbonizing a polymer material, the polymer recombines into a carbonaceous film while releasing atoms such as hydrogen and oxygen by thermal decomposition. As the carbonization reaction progresses, its electrical conductivity increases, and its size is generally predicted by the carbon content in the carbonaceous film and its presence (ie, whether it is sp ³ or sp ² carbon). I can do it. In a carbonaceous film, carbon is generally an insulator when the amount of carbon is 85% by weight or less, and when it exceeds 85% by weight, its electrical conductivity increases rapidly. For the purpose of the present invention, it is desirable that the carbonaceous film has as high conductivity as possible. Therefore, the carbonaceous film of the present invention preferably contains 85% by weight or more of carbon, more preferably 90% by weight or more. When the electrode of the present invention is used as an electrode of a double layer capacitor, the carbon content is desirably 85% or more, more preferably 90% or more, in order to form a stable double layer capacity.

  In general, an aluminum hole formed by etching has an entrance diameter of about 1 to 5 μm, and it is not preferable from the object of the present invention that such a hole is blocked by the formed carbonaceous film. In addition, the carbonaceous film formed inside the etching holes is preferably thinner in terms of preventing the carbonaceous film formed from closing the finer etching holes. The thickness is 1 μm or less, and the average thickness is more preferably 0.5 μm or less.

  For the purpose of the present invention, the carbonaceous layer preferably has micropores having a pore diameter of 2 nm or less. When the carbonaceous film has micropores such as activated carbon, the surface area of the micropores is added to the surface area of the carbonaceous film formed on the etched aluminum foil. As already described, it is known that activated carbon has holes of mesopores (pore diameter 2 nm to 50 nm) and macropores (pore diameter 50 nm or more) in addition to micropores. In the electrode structure of the present invention, the role of the macro hole is basically the hole of the etching aluminum, and the macro hole is not necessary in the carbonaceous film. On the other hand, in the present invention, the role of mesopores in the activated carbon can be played by the carbonaceous film itself or the aluminum etching hole, and the role sharing varies depending on the thickness of the carbonaceous film. That is, the presence of mesopores is required when the average thickness of the carbonaceous film is about 500 to 100 nm, but when it is 100 nm or less, the role of the mesopores is that of etching aluminum. Therefore, the presence of mesopores in the carbonaceous film is not always necessary.

  When the aluminum / carbon composite electrode of the present invention is used as an electrode of a double layer capacitor, it is desirable that the maximum value of the optimum micropore diameter distribution existing in the carbonaceous film is in the range of 0.5 to 1.5 nm. . The optimum micropore size varies depending on the size of the solute ions used. Generally, micropores with a diameter of 0.5 nm or less cannot enter solute molecules inside, and in double layer capacitors, Such micropores cannot contribute to the double layer capacity. For example, it is said that the optimum micropore size of activated carbon used in a double layer capacitor using tetraethylammonium tetrafluoroborate as a solute and propylene carbonate as a solvent is 1.0 to 1.3 nm.

A specific method for producing the electrode of the present invention is a method of carbonizing an etched aluminum foil and a polymer film coated on the surface thereof at a temperature of 400 ° C. or higher and 650 ° C. or lower. The melting point of aluminum is 660 ° C., and if it is 650 ° C. or higher, the aluminum foil melts and the etching holes are crushed, which is not preferable. In the thermal decomposition of a polymer, a change from the sp ³ structure to the sp ² structure of carbon occurs at a temperature of 400 ° C. or higher. Therefore, it is preferable to heat-treat even a carbonaceous film having a carbon content of 85% or more in a temperature range of 400 ° C. or less at 400 ° C. or more.

  For the formation of the polymer film, for example, the polymer film is formed on the surface of the aluminum foil by dissolving the polymer in a solvent, immersing etching aluminum in the diluted solution, pulling it up and drying it. Next, the polymer film is carbonized by heating at a temperature of 400 ° C. or higher and 650 ° C. or lower in an inert gas such as nitrogen, argon or helium, or in an acidic gas such as water vapor or carbon dioxide in vacuum, A carbonaceous film is formed on the surface of the aluminum foil.

  The electrode of the present invention may be activated by a known method if necessary after forming a carbonaceous film by heating and carbonization. Specifically, gas activation treatment in water vapor or carbon dioxide gas, KOH treatment in nitrogen, treatment using phosphoric acid or boric acid, and the like.

  The polymer material is not particularly limited as long as the carbon component becomes 85% by weight or more by heat treatment at 650 ° C. or less. At that time, it is more preferable if the organic polymer forms a film. Polyvinyl alcohol, polyvinylidene chloride, polyvinyl chloride, phenol resin, phenol formaldehyde, furfuryl alcohol, polyvinylidene chloride copolymer, resorcinol and formaldehyde (carbon aerosil), polyacrylonitrile, and the like can be preferably used. Among these, polyvinylidene chloride and a polyvinylidene chloride copolymer are preferable because micropores are formed in the carbon film by chlorine gas generated during the carbonization process.

  Monomers that can co-polymerize with vinylidene chloride are not particularly limited, but typical monomers include vinyl monomers such as vinyl chloride, acrylic acid esters, methacrylic acid esters, vinyl acetate, acrylonitrile, divinylbenzene, itaconic acid and its esters, etc. Of the unsaturated dibasic acid and its monoester or diester. In the formation of pores in these copolymers, the molar ratio of vinylidene chloride is preferably 50% or more, and more preferably 70% or more.

  Taking the polyvinylidene chloride homopolymer as an example, the method for producing the electrode of the present invention will be described more specifically. Since polyvinylidene chloride is dissolved in a chlorinated solvent, it is dissolved in a solvent such as chloroform, chloronaphthalene, or ethyl chloride. The etched aluminum foil is dipped in this polyvinylidene chloride solution and evacuated to allow the solution to penetrate into the etching holes. When the solution penetrates, it is pulled up and dried to remove the solvent, and a vinylidene chloride layer is formed on the surface of the etched aluminum foil.

  At this time, an inorganic metal compound such as zinc chloride, a metal such as iron, cobalt, manganese, an additive such as phosphoric acid, boric acid, sodium sulfate hydroxide, potassium hydroxide, or ferrocene is added to the polymer material in advance. In addition, it is preferable to form micropores by the additive effect or to promote the carbonization reaction. Among them, zinc chloride is a very effective additive for forming micropores in vinylidene chloride. For pore formation, the amount of zinc chloride added is preferably 50% to 150% by weight of vinylidene chloride. When zinc chloride is added, the remaining zinc chloride is removed by washing with acidic water after the carbonization treatment described later. Specifically, residual zinc chloride is removed by washing with 5% hydrochloric acid, followed by washing with water and drying.

  For the formation of micropores, it is also effective to add an organic monomer that decomposes or gasifies by heating. In order to form micropores, it is preferable that the organic monomer used for such a purpose is dispersed in a molecular form in the polymer.

  Zinc chloride and organic monomers can be added to polymers other than vinylidene chloride such as polyvinyl alcohol, polyvinylidene chloride, polyvinyl chloride, phenolic resin, phenol formaldehyde, furfuryl alcohol, polyvinylidene chloride copolymer, resorcinol and formaldehyde (carbon aerobic). It is needless to say that it is also effective as (jil), polyacrylonitrile, and the like.

  As the carbonization method, the vinylidene chloride resin is heat-treated in vacuum, in an inert gas such as nitrogen or argon, in water vapor, in carbon dioxide, in carbon monoxide, or the like. The thermal decomposition temperature is 400 ° C. or higher and 650 ° C. or lower, and the treatment temperature is about 20 minutes to 30 hours.

  In the thermal decomposition of vinylidene chloride resin, an insoluble carbon precursor (char) is obtained by dehydrochlorination in a solid state having a melting point of 130 ° C. to 190 ° C. or lower, and the pore diameter is large even when heated at 600 ° C. Good pores are formed without change. Therefore, even when the heat carbonization is performed at 400 ° C. to 650 ° C., it is preferable to perform a preliminary treatment in the region of 130 ° C. to 190 ° C.

  The aluminum / carbon composite electrode produced by the above method can be used alone or as an electrode of a double layer capacitor. However, for use as an electrode of a double layer capacitor, in order to further improve the capacity, it is preferable to apply activated carbon on the electrode of the present invention and combine it with activated carbon to form a composite electrode.

  As a specific method for producing such a composite electrode, for example, an activated carbon is well kneaded (kneaded) with a mixture of acetylene black, polytetrafluoroethylene, graphite powder, and methanol. It is applied so that the entire electrode is covered, and then heat-treated to remove methanol and form an electrode. In general, etched aluminum or reticulated aluminum is used as a collector electrode of a double layer capacitor. However, in such an electrode, an insulator oxide film is often formed on the aluminum surface, so that the capacitance characteristic is increased due to an increase in internal impedance. to degrade. On the other hand, in the electrode of the present invention, the carbonaceous film formed on the surface prevents the formation of the insulator aluminum oxide, so that the characteristic deterioration can be prevented. Furthermore, a double layer formed on the surface of the carbonaceous film or the micropore surface can also contribute to an increase in device capacity.

  The electrode of the present invention is preferably used for an electrochemical device using a non-aqueous electrolyte. In the case of an electric double layer capacitor, there are two types: a capacitor using an aqueous solvent and a capacitor using a non-aqueous solvent. The electrode of the present invention is preferably used for a capacitor using a non-aqueous solvent such as propylene carbonate, for example, and is particularly preferably used as an electrode for a wound double-layer capacitor for large capacity.

  Furthermore, the electrode of the present invention can be used as a negative electrode of a wound aluminum electrolytic capacitor. In an aluminum electrolytic capacitor, an etching aluminum having an aluminum oxide dielectric layer formed on the surface is used for the anode, and the electrode foil of the present invention is wound through a separator. Also in this case, by using the electrode of the present invention as a cathode, an increase in internal impedance due to the formation of dielectric aluminum oxide on the cathode surface can be prevented.

Example 1

As an etching aluminum foil, a low pressure etched foil manufactured by Nippon Kogyo Paper Industries Co., Ltd., product name U752 was used. The capacitance when this foil is formed at 5 V is 240 μF / cm ² , and the capacitance value at 20.5 V is 57.8 μF / cm ² . The thickness is 70 μm and the tensile strength is ≧ 17.7 N / cm. This etching foil was cut into a strip shape having a width of 1 cm and a length of 2 cm to obtain a sample.

The surface of the aluminum sample foil was immersed in a solution composed of 70% HNO ₃ (15 parts) + 85% H ₃ PO ₄ (85 parts) at 85 ° C. for 2 minutes and washed with pure water. Further, the surface was etched by immersion in a 1N NaOH aqueous solution at room temperature for 10 minutes, washed with pure water, dipped in acetone and dried to remove the natural oxide film formed on the surface to obtain a sample foil.

  Next, a polymer film was formed on the surface of the aluminum foil using a phenol-based resin (Gunei Chemical Industry Co., Ltd., Resist Top PL2407). Specifically, methanol is added to the cash register top to prepare dilute solutions with various concentrations of 10% or less of the non-volatile components. The etched aluminum foil is immersed in this solution, and the solution penetrates into the etching holes by evacuation. I tried to do it. When the solution penetrated, it was pulled up, heated and dried to remove the solvent, and a phenol resin layer was formed on the surface of the etched aluminum foil. The thickness of the formed polymer layer was controlled by the concentration of the dilute solution, and the average thickness was estimated by gravimetry. Five types of samples having different average thicknesses of the polymer layers were prepared.

  The obtained etching aluminum foil coated with a phenolic resin was heated in nitrogen gas from room temperature to a maximum temperature of 600 ° C. at a rate of 5 ° C./min, and kept at 600 ° C. for 1 hour for carbonization. . The thickness of the formed carbonaceous film was approximately 70% of the original polymer layer thickness. Moreover, the carbon content of the formed carbonaceous film was estimated from the elemental analysis value of the phenol-based resin heat-treated under the same conditions. As a result, C: 92.0%, H: 3.8%, and O: 4.2%. When the maximum processing temperature is 500 ° C., C: 89.0%, H: 4.4%, O: 6.6%, and similarly when the maximum processing temperature is 400 ° C., 85.1%, H: It was 5.0% and O: 9.9%.

The specific surface area of the obtained sample was measured using an AUTOSORB-1 measuring apparatus manufactured by Yuasa Ionics Co., Ltd. The measurement results are shown in Table 1. As shown in Table 1, when a carbonaceous film having an average thickness of 0.1 μm is formed, the specific surface area is estimated to be 6.8 m ² / g and the average thickness is estimated to be 0.2 μm. In that case, the specific surface area was 8.6 m ² / g, and when the average thickness was estimated to be 0.5 μm, the specific surface area was 8.9 m ² / g. This is about twice as large as the expected value from the surface area of aluminum, which is about 3.2 m ² / g. The resulting carbonaceous film has a pore structure that contributes to an increase in surface area. It is thought that there is. Also, the increase in surface area accompanying the increase in thickness can be explained by the increase in carbonaceous film.

However, when the average thickness is estimated to be 1 μm, the specific surface area decreases to 2.7 m ² / g, and when the average thickness is estimated to be 2 μm, the specific surface area is 0. It decreased sharply to 5m ² / g. This is presumably because the carbonaceous film formed on the surface of the aluminum foil closed the aluminum etching holes, so that the specific surface area was reduced. Therefore, it was found that the optimum thickness of the carbonaceous film of the present invention is 1 μm or less, more preferably 0.5 μm or less.

（実施例２）

(Example 2)

  First, the etching aluminum foil processed by the same method as Example 1 was prepared.

  Next, the polyvinylidene chloride homopolymer was dissolved in a mixed solvent of chloroform and chloronaphthalene. The amount of polyvinylidene chloride dissolved was controlled to 0.5 wt% to 5 wt%, and the etched aluminum foil was immersed in the polyvinylidene chloride solution and evacuated to allow the solution to penetrate into the etching holes. . When the solution penetrated, it was pulled up, dried to remove the solvent, and a vinylidene chloride layer was formed on the surface of the etched aluminum foil. The thickness of the formed vinylidene chloride layer was estimated by observing the cross section of the foil with an electron microscope, and the average thickness of the vinylidene chloride layer was adjusted to about 0.5 μm.

  In the same manner, a sample was prepared by adding zinc chloride to a mixed solvent of vinylidene chloride in chloroform and chloronaphthalene. The amount of zinc chloride added was 100% by weight of vinylidene chloride.

  The obtained etched aluminum foil coated with polyvinylidene chloride was heat-treated at 180 ° C. for 3 hours in nitrogen gas to form a carbon precursor. Next, similarly, the temperature was increased from 180 ° C. to a maximum temperature of 600 ° C. at a rate of 5 ° C./minute in nitrogen gas, and carbonization was performed by holding at 600 ° C. for 1 hour. In the case of a sample to which zinc chloride has been added, the remaining zinc chloride is removed by washing with acidic water after the carbonization treatment described later, washing the remaining zinc chloride with 5% hydrochloric acid, washing with water and drying. It was. The thickness of the formed carbonaceous film was about 0.14 μm for polyvinylidene chloride and about 0.1 μm for the system to which zinc chloride was added. Moreover, as a result of estimating the carbon content of the formed carbonaceous film from the elemental analysis value of the polyvinylidene chloride heat-treated on the same conditions, it was found that the carbon content was 96%. Experiments were also carried out on the (vinylidene chloride + vinyl chloride) copolymer in exactly the same way.

The specific surface area and pore distribution of the obtained sample were measured using an AUTOSORB-1 measuring device manufactured by Yuasa Ionics Co., Ltd. The measurement results are shown in Table 2. When vinyl chloride was used, the specific surface area of the obtained electrode was 19.7 m ² / g. This value is a small value of 1/10 to 1/100 compared to the value of 200 to 2000 m ² / g, which is the BET specific surface area observed with normal activated carbon. However, assuming that the carbonaceous film does not have a pore structure, the carbonaceous film formed is about six times larger than the value expected from the aluminum specific surface area of about 3.2 m ² / g. It is considered that a pore structure that contributes to an increase in specific surface area is formed in the membrane.

The specific surface area of the electrode could be further improved by adding zinc chloride to vinylidene chloride, and similar results could be obtained using a (vinylidene chloride + vinyl chloride) copolymer. When the pore diameter distribution curve is obtained and the pore diameter at which the differential pore diameter volume (cm ³ / g · A) is maximized is obtained, it is 0.8 nm for vinylidene chloride and 1.1 nm for the system to which zinc chloride is added. It was. The (vinylidene chloride + vinyl chloride) copolymer had a slightly larger value than this, but did not exceed 2 nm.

（実施例３）

(Example 3)

  Electrodes were produced by changing the maximum processing temperature in the same manner as in Example 1, and the characteristics were measured. The obtained results are shown in Table 3. As the maximum processing temperature is lowered, the value of the specific surface area is also reduced, and it is understood that a temperature of 300 ° C. or higher is necessary for carbonization. Since the resistance value of the carbon precursor obtained is high at 300 ° C. or lower and the impedance of the electrode is high, a carbonization temperature of 400 ° C. or higher is necessary from this meaning, and it is understood that the carbon precursor temperature is preferably 500 ° C. or higher. .

（実施例４）

Example 4

  Various polymer materials were used in place of vinylidene chloride in the same manner as in Example 1 (a carbon / aluminum composite electrode was prepared and its characteristics were measured. The results are shown in Table 4. Vinylidene chloride / methyl acrylate In the polymer (9/1) and polyvinyl chloride, a clear increase in specific surface area was observed and the formation of pores was observed, while in phenol / formaldehyde resin, polyvinyl butyral, furfuryl alcohol, polyvinyl alcohol and polyacrylonitrile. Although the increase in specific surface area accompanying the formation of pores could not be observed, the object of the present invention is to prevent the formation of an oxide film on the surface of the aluminum foil by covering the surface of the etched aluminum foil with a carbonaceous film It became a sufficient composite electrode.

（実施例５）

(Example 5)

  Cyclic voltammetry (maximum voltage 2.3 V) was measured using the aluminum / carbon composite electrode prepared in Example 1, and the electric double layer capacity was measured. The solute used was tetraethylammonium tetrafluoroborate, the solvent used was propylene carbonate, and the concentration of the solute was 1 mol / l.

The electric double layer capacity per unit area thus obtained was 18.8 μF / cm ² , and the electric double layer capacity per unit weight was 3.6 F / g. This cyclic voltammetry was very excellent in repeated stability, and a rapid repetition of double layer capacity could be realized.
(Example 6)

  Activated carbon was further laminated on the electrode of the present invention, and an electric double layer capacitor was prototyped and its characteristics were examined.

A mixture of acetylene black (70 parts by weight), polytetrafluoroethylene (15 parts by weight), graphite powder (15 parts by weight), and methanol (150 parts by weight) was well kneaded. The acetylene black used has a specific surface area of 40 m ² / g, and the graphite powder has an average particle diameter of 4 μm and a specific surface area of 20 m ² / g. This kneaded material was applied at a thickness of 20 μm so as to cover the entire current collector of the electrode foil of the present invention produced in Example 6, and then heat-treated at 150 ° C. to obtain an electrode except for methanol.

  The characteristics of the double layer capacitor were measured using the electrodes prepared by the above method. First, charging was performed at a constant current of 1 A in the range of 0 to 2.5V. The initial discharge capacity and internal resistance were measured, and then the internal resistance and discharge capacity after 50,000 cycles were measured to examine the repeated stability. The initial capacity was 8.9 F, the internal resistance was 0.23 Ω, the capacity after 50,000 cycles test was 8.8 F, and the internal resistance was 0.24 Ω.

  As a comparative experiment, activated carbon was laminated in the same manner using an etched aluminum foil as a collector electrode, and the repeated charge / discharge stability was examined. The initial capacity at that time was 7.9 F and the internal resistance was 0.21Ω, but the capacity after the 50,000-cycle test was changed to 7.6 F and the internal resistance was 0.35Ω, and the electrode of the present invention was excellent. I understood that.

The conceptual diagram of the hole in activated carbon. The conceptual diagram which shows the structure of the electrode of this invention.

Explanation of symbols

(1) Macro hole (2) Meso hole (3) Micro hole (4) Aluminum foil (5) Aluminum etching hole (6) Carbonaceous layer

Claims (10)

  An electrode for an electrochemical device comprising an etched aluminum foil and a carbonaceous layer having a carbon component of 85% or more coated on the surface thereof.   The electrode for an electrochemical element according to claim 1, wherein the carbonaceous layer has an average thickness of 1 μm or less.   The electrode for an electrochemical element according to claim 1, wherein the carbonaceous layer has micropores having a pore diameter of 2 nm or less.   4. The electrode for an electrochemical element according to claim 3, wherein the maximum value of the micropore diameter distribution is in the range of 0.5 to 1.5 nm.   An electrode for an electrochemical element, wherein an activated carbon layer is deposited on the electrode according to claim 1, 2, 3, 4.   An electrochemical element comprising at least the electrode according to claim 1 and a non-aqueous electrolyte.   The polymer layer formed on the surface of the etched aluminum foil is heated and carbonized at a temperature of 400 ° C. or higher and 650 ° C. or lower in vacuum, in an inert gas such as nitrogen or argon, in water vapor or in carbon dioxide gas. The method for producing an electrode for an electrochemical element according to claim 1, 2, 3, or 4.   8. The method for producing an electrode for an electrochemical element, wherein the polymer layer according to claim 7 is formed by immersing an etching aluminum foil in a polymer solution dissolved in a solvent, and then pulling and drying.   A method for producing an electrode for an electrochemical element, wherein the polymer layer according to claim 7 is a homopolymer of polyvinylidene chloride or a vinylidene chloride copolymer.   A method for producing an electrode for an electrochemical element, wherein zinc chloride is added to the homopolymer of polyvinylidene chloride or the vinylidene chloride copolymer according to claim 9.

Images