JP2006165522A - Electrode sheet and electric double layer capacitor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adhere a current collector to a polarizable electrode even when a polarizable electrode is easily and firmly formed on the surface of a current collector such as a metal foil, and gas or vibration generated by repeated charge / discharge Provided are an electrode sheet that can hardly maintain strength and maintain performance such as internal resistance for a long period of time and an electric double layer capacitor using the same.
A coating liquid in which a graft polymer obtained by graft polymerization of at least activated carbon and / or carbon black and an organic monomer is dispersed in a solvent is applied to the surface of a current collector, and then dried. An electrode sheet formed by heat treatment and an electric double layer capacitor using the electrode sheet are obtained.
[Selection] Figure 1

Description

  The present invention relates to a power storage medium such as an electric double layer capacitor, and more specifically, an electrode sheet that forms a polarizable electrode by applying a coating liquid to the surface of a current collector such as a metal foil, and The present invention relates to an electric double layer capacitor using the same.

  In recent years, an electric double layer capacitor in which a polarizable electrode such as activated carbon is impregnated with an electrolytic solution and electric energy is accumulated in an electric double layer at the interface has been put into practical use as a power storage medium. As a general configuration of an electric double layer capacitor, an electric sheet having a configuration in which a current collector such as a metal foil and a polarizable electrode such as activated carbon and separators are alternately laminated and impregnated with an electrolytic solution. A multilayer capacitor cell is formed, and the electric double layer capacitor cell is sealed in a container to form an electric double layer capacitor.

  In addition, the electric double layer capacitor is manufactured by forming a laminated body of an electrode sheet and a separator in a sandwich shape in a square electric double layer capacitor and in a roll shape in a cylindrical electric double layer capacitor. After connecting the lead portions of the electric body (positive electrode body and negative electrode body) to each terminal and storing the laminate in a container, the electrolyte is injected from the opening of the container to impregnate the laminate with the electrolyte, Many methods of sealing the container with the tip of the terminal exposed to the outside have been implemented.

  In such an electric double layer capacitor, the electrode sheet is generally produced by forming a polarizable electrode by applying a coating liquid containing activated carbon to the surface of a current collector such as a metal foil and drying. Conventionally, as coating components, there are many coating liquids in which conductive materials such as carbon black, activated carbon, and binders such as polytetrafluoroethylene and cellulose are dispersed in an organic solvent or an aqueous solvent. Although it is used, its constituent components, coating method, and the like are one factor that greatly determines the quality of important performance such as the internal resistance of the electric double layer capacitor. Therefore, with the goal of excellent uniformity, adhesive strength, etc., a number of methods have been developed to date, such as the binder component in the coating liquid or the method of bringing the coating liquid into close contact with the current collector. An application has been filed.

  That is, JP-A-11-162794 discloses a coating liquid comprising a copolymer latex containing an aromatic vinyl unit, a conjugated diene unit, etc., and JP-A-11-329904 discloses an organic solvent dispersion of a carbon material and polytetrafluoroethylene. Japanese Patent Application Laid-Open No. 2002-222741 discloses a coating liquid comprising activated carbon powder, a conductivity imparting agent having a smaller particle diameter, and a water-soluble binder in which a resin is dissolved. Japanese Patent Laid-Open No. 2001-222992 discloses a method of forming a polarizable electrode on the surface of a current collector by evaporating a solvent in a coating liquid by irradiating infrared rays. Japanese Patent Laid-Open No. 2001-345095 discloses a coating liquid. A method of forming a polarizable electrode on the surface of a current collector by evaporating the solvent therein by applying hot air is disclosed.

Japanese Patent Laid-Open No. 11-162794 JP 11-329904 A JP 2001-216955 A JP 2001-222992 A JP 2001-345095 A JP 2002-222741 A JP 2003-297696 A JP 2004-128145 A

  Among conventionally used coating liquids, a coating liquid with excellent uniformity is a slurry in which activated carbon, carbon black, and the like are uniformly dispersed in a solvent. When such a coating liquid is kept at a low viscosity, it can be relatively well penetrated into the recesses of the metal foil that has an uneven surface and is subjected to an etching process that is preferably used as a current collector. Seem. However, in any coating liquid, activated carbon, carbon black and the like dispersed in the solvent are likely to aggregate with each other, and each particle is in a relatively large lump state. Therefore, when these coating liquids are used as they are, there has been a disadvantage that an electrode sheet excellent in adhesive strength between the current collector and the polarizable electrode cannot be obtained. Furthermore, there is a problem that the current collector and the polarizable electrode are peeled off due to gas generated by repeated charge / discharge or vibration when used in an automobile, and the performance such as internal resistance deteriorates in a short period of time.

  In order to solve such a problem, for example, in Japanese Patent Application Laid-Open No. 2001-216955, a binder powder on the surface of the current collector, preferably a binder powder smaller than the average opening diameter of the irregularities on the surface of the metal foil, There has been proposed a method in which a solvent-free powder is disposed, and then an active material (activated carbon or the like) and a paste (coating liquid) containing a solvent are applied and dried. However, such a coating method has the disadvantage that the number of manufacturing steps increases and it takes time and effort.

  Therefore, the problem to be solved by the present invention is that a polarizable electrode is easily and firmly formed on the surface of a current collector such as a metal foil, and is also collected by gas generated by repeated charge / discharge or vibration. By providing an electrode sheet in which the adhesive strength between an electric body and a polarizable electrode is less likely to be reduced and the performance such as internal resistance can be maintained for a long time in a good state, and an electric double layer capacitor using the electrode sheet is there.

  As a result of intensive studies to solve these problems, the present inventors have found that activated carbon and carbon black can each be graft polymerized with an organic monomer, and the obtained graft polymer is unreacted activated carbon, carbon black, Alternatively, it is difficult to agglomerate with the graft polymers, each particle is finely dispersed in a solvent in the form of small particles, and the coating liquid containing the graft polymer has extremely excellent wettability to the metal foil surface, and The present inventors have found that the adhesive strength between the current collector and the polarizable electrode is greatly improved by using the coating liquid, and have reached the present invention.

That is, the present invention applies a coating solution in which a graft polymer obtained by graft polymerization of at least activated carbon and / or carbon black and an organic monomer in a solvent is applied to the surface of the current collector and then dried. An electrode sheet obtained by heat treatment.
The present invention is also an electric double layer capacitor having a configuration in which the electrode sheet and the separator are laminated and impregnated with an electrolytic solution.

  In the coating liquid of the present invention, the activated carbon and carbon black in the solvent are less likely to aggregate with unreacted activated carbon, carbon black, or graft polymer, and each particle is finely dispersed in the solvent in the form of small particles. Moreover, the wettability with respect to metal surfaces, such as aluminum foil, is very excellent. Therefore, the electrode sheet of the present invention using the coating liquid can easily and sufficiently form a concave portion on the surface of the metal foil even when a current collector made of a metal foil such as an aluminum foil subjected to etching treatment is used. The adhesive strength between the current collector and the polarizable electrode can be significantly improved as compared with the conventional one. In addition, the electric double layer capacitor of the present invention using the electrode sheet is in a good state of performance, such as internal resistance, whether it is used repeatedly or repeatedly for charging or used for vibrations such as automobiles. Can be maintained for a long time.

The electrode sheet of the present invention is an electrode that forms a polarizable electrode by applying it to the surface of a current collector (or electrode) such as a metal foil (or metal) in an electric storage medium such as an electric double layer capacitor or a lithium battery. Applied to the sheet.
The electric double layer capacitor of the present invention is applied to an electric double layer capacitor using an electrode sheet having a configuration in which a polarizable electrode is formed by applying a coating liquid on the surface of a current collector. In particular, the adhesive strength against vibration is high, and it is suitably applied to electric double layer capacitors for automobiles. Moreover, the electric double layer capacitor of the present invention can be applied to both a square electric double layer capacitor and a cylindrical electric double layer capacitor.

The carbon black used in the present invention may be any of furnace black, acetylene black, channel black, thermal black and the like.
Moreover, as activated carbon, coconut shell charcoal activated by steam or carbon dioxide, wood dust charcoal, peat charcoal or the like, or alkali activated charcoal activated by graphitizable carbon with an alkali metal compound can be used. Graphitizable carbon, which is a raw material for alkali activated carbon, is obtained from carbonized synthetic pitch obtained by polymerizing petroleum pitch, coal pitch, condensed polycyclic aromatic hydrocarbons, needle coke, etc. Any activated carbon may be used. In the present invention, those having a specific surface area of usually 10 m ² / g or more, preferably 50 m ² / g or more, more preferably 200 m ² / g or more are used.

The organic monomer is not particularly limited as long as it produces a graft polymer by a graft polymerization reaction with activated carbon or carbon black. For example, an acrylic monomer, an epoxy monomer, a vinyl monomer, and an ester monomer. A monomer, an amide monomer, an ether monomer, etc. can be mentioned. Among these organic monomers, it is preferable to use vinyl monomers. The vinyl monomer has a general formula CH ₂ ═C (R) —COOR ′ (R is a hydrogen atom or a methyl group, R ′ is a hydrogen atom, a C1-C12 hydrocarbon group, or a substituted hydrocarbon group). Saturated carboxylic acids and esters thereof. Specifically, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, butyl acrylate, Examples include butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, octyl acrylate, octyl methacrylate, lauryl acrylate, and lauryl methacrylate.

The coating liquid in the present invention can contain a resin. The resin is not particularly limited as long as the effect of the binder is obtained, but a thermosetting resin is preferable, for example, epoxy resin, phenol resin, polyester resin, melamine resin, urea resin, alkyd resin. , And polyimide resin can be used.
In addition, the coating liquid in the present invention includes a synthetic pitch obtained by polymerizing a condensed polycyclic hydrocarbon or a compound containing the same, and a graft polymer obtained by graft polymerization of an organic monomer in order to enhance the binding property. Can be made. The organic monomer used in this case is the same as the organic monomer described above.
In the present invention, such a resin or graft polymer is usually added.

  In addition, the synthetic pitch is naphthalene, monomethylnaphthalene, dimethylnaphthalene, anthracene, phenanthrene, acenaphthene, acenaphthylene, pyrene, as shown in Japanese Patent No. 2931593, Japanese Patent No. 2621253, or Japanese Patent No. 2526585. Etc., and condensed polycyclic hydrocarbons having these skeletons, mixtures thereof, and pitches obtained by polymerizing substances containing these. In this polymerization, 0.1 to 20 mol of hydrogen fluoride and 0.05 to 1.0 mol of boron trifluoride are used as a polymerization catalyst with respect to 1 mol of pitch raw material, and the temperature is 5 to 30 at a temperature of 100 to 400 ° C. This is done by reacting for a minute. This synthetic pitch exhibits high fluidity and a high residual carbon ratio at the heat treatment range temperature.

  The solvent used in the present invention is not limited as long as it is well dispersed in activated carbon, carbon black, graft polymer and the like, and can be easily volatilized by a drier in the coating machine. For example, fat such as propyl alcohol, isopropyl alcohol, butyl alcohol Aromatic alcohols, ketones such as methyl isobutyl ketone and methyl ethyl ketone, aromatic hydrocarbons such as benzene, toluene and xylene, nitrogen-containing aromatic hydrocarbons such as pyridine, aliphatic hydrocarbons such as pentane and hexane, cyclohexane Such as cycloaliphatic hydrocarbons such as tetrahydrofuran, ethers such as tetrahydrofuran, cellosolves such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether, and the like. These organic solvents may be used alone or in combination. Moreover, it can also be set as the coating liquid which consists of an epoxy emulsion, an acrylic emulsion, etc., using an aqueous solvent.

  In the present invention, the polymerization initiator used for the graft polymerization of activated carbon and / or carbon black is preferably an azo compound type, particularly an azonitrile type. Organic peroxides are not preferred when carbon black coexists, resulting in a very long induction period. Since carbon black itself acts as a radical polymerization inhibitor, the polymerization initiator needs to have an amount sufficient to counteract this, but the amount of initiator is usually 5 wt% or less based on the weight of carbon black. A chain transfer agent such as dodecyl mercaptan may be used as necessary.

  The coating liquid in the present invention is prepared using the aforementioned activated carbon, carbon black, organic monomer, solvent and the like. For example, after charging activated carbon, carbon black, an organic monomer, and a solvent into a reaction vessel or the like, the coating liquid is added at a temperature of about 50 to 200 ° C. by adding a polymerization initiator in a batch or multiple times. Can be prepared by graft polymerization. Further, when only one component of activated carbon or carbon black is graft-polymerized with an organic monomer, for example, it is performed by adding a component that is not graft-polymerized to the liquid after completion of graft polymerization.

  In addition, when adding resin to the above-mentioned liquid to make a coating liquid, a solvent in which the resin is dissolved (dispersed) is usually added to the liquid after completion of graft polymerization. In addition, when a synthetic pitch obtained by polymerizing a condensed polycyclic hydrocarbon or a compound containing the same and a graft polymer obtained by graft polymerization of an organic monomer are added, after the graft polymerization of activated carbon and / or carbon black is completed. A solvent in which the graft polymer of synthetic pitch is dissolved (dispersed) may be added to the liquid, or the synthetic pitch may be graft polymerized simultaneously with the graft polymerization of activated carbon and / or carbon black.

  In the present invention, the amount of the organic monomer is usually 10 to 200 wt%, preferably 30 to 100 wt% of the total of activated carbon and carbon black. In the preparation of the coating liquid, the graft polymerization rate of the organic monomer to the activated carbon and carbon black is usually 1 to 50% of the whole organic monomer, preferably 2 to 30% of the whole organic monomer. When the graft polymerization rate is less than 1%, there is a possibility that the coating liquid cannot be made into a slurry or a coating liquid having excellent wettability with the metal foil cannot be obtained. Moreover, it is difficult to produce a coating liquid having a graft polymerization rate exceeding 50%. The content of the activated carbon and / or carbon black graft polymer in the coating solution thus prepared is usually about 1 to 50 wt% with respect to the total amount of the coating solution.

  The viscosity of the coating liquid prepared as described above is usually 10 to 1000 mPa · s at room temperature, but activated carbon, carbon black, etc. are finely and finely dispersed in comparison with the coating liquid used conventionally. In addition, the wettability is extremely excellent. This is because an organic monomer is chemically bonded to the surface of activated carbon and / or carbon black (in the present invention, this is referred to as graft polymerization), and the structure is difficult to aggregate. Conceivable. The organic monomer impregnated in the details of the concave portion of the metal foil is heat-treated and carbonized in a subsequent process, and is firmly bonded to the metal foil.

  The electrode sheet of the present invention is obtained by applying the above-mentioned coating liquid to the surface of the metal foil, then drying and heat treatment. In application to the metal foil surface, in order to obtain a desired film thickness, it can be diluted with a solvent such as ethylene glycol monomethyl ether or xylene. An appropriate amount of an antifoaming agent may be added. Application of the coating liquid onto the surface of the metal foil includes, for example, a coating liquid circulation unit including a charge tank 2 of the coating liquid 1, a coating liquid supply pump 3, an overflow return pump 4 and the like as shown in FIG. 6, a tension adjusting S-shaped step roll 7, a coating liquid vat 8, a coating roll 9, a squeeze roll 10, etc., a coating liquid application unit, a hot air inlet 11, an exhaust port 12, etc. It can be carried out by a coating apparatus provided with a winding unit comprising a hot press and line speed control roll 14, a winder 15 and the like. As described above, since the coating liquid has high uniformity and extremely good wettability, the film thickness can be easily and precisely controlled. In the present invention, the wound electrode sheet may be further heat-treated in a heat treatment furnace or the like. The temperature of heat processing is 100-600 degreeC normally.

In the production of the electrode sheet of the present invention, the solvent is volatilized mainly by drying. In addition, the heat treatment decomposes and removes the functional groups (—OH, —COOH, —C═O, etc.) remaining in the activated carbon, carbon black, synthetic pitch, etc. in the coating liquid or generated during the graft polymerization reaction. At the same time, carbon black, activated carbon, and resin are reinforced and carbonized.
In the present invention, the coating solution is usually applied to both surfaces of the metal foil 17 excluding the portion that becomes the lead portion 18, and is finished into an electrode sheet 16 as shown in FIG.

  The electric double layer capacitor of the present invention uses the above electrode sheet. In the present invention, when the electrode sheet and the separator are laminated, the positive electrode body lead portion and the negative electrode body lead portion 18 of the electrode sheet are laminated so that they can be connected to the positive electrode terminal and the negative electrode terminal 21, respectively. Thereafter, the laminate 19 is accommodated in a flat container 20 made of metal foil covered with a plastic film having an opening on at least one side, but is accommodated so that the electrode terminal 21 is on the opening side. In the production of the electric double layer capacitor, usually, the laminate is dried before injecting the electrolytic solution. In the present invention, the electric double layer is continuously produced after the production of the electrode sheet. In the case of manufacturing a capacitor, the drying process time can be shortened or the drying process can be omitted.

In the present invention, the operation of injecting the electrolytic solution into the container and impregnating the electric double layer capacitor cell with the electrolytic solution, and removing the gas adsorbed on the polarizable electrode by reducing the pressure inside the container is performed. It is. By doing in this way, a laminated body can be efficiently impregnated with electrolyte solution. In addition, if necessary, between the injection of the electrolyte and the sealing of the container, the electrode terminal is energized and subjected to electrolytic purification in order to electrolyze and remove moisture and functional groups contained in the polarizable electrode. You can also.
Thereafter, the container is sealed by pressing, for example, two heated heat seal bars in a state where a flat container made of plastic or metal foil is sandwiched, and the book having the structure shown in FIG. The electric double layer capacitor of the invention is obtained. In the present invention, the process from injection of the electrolytic solution to sealing of the container is performed under reduced pressure or in an inert gas atmosphere.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited by these.

(Preparation of coating solution)
In a reaction vessel equipped with a stirrer, 100 parts by weight of activated carbon (activated carbon A-BAC-PW15 manufactured by Kureha Chemical Co., Ltd.), 10 parts by weight of carbon black (Denka Black manufactured by Denki Kagaku Co., Ltd.), synthetic pitch ( Synthetic pitch produced by Mitsubishi Gas Chemical Co., Ltd., synthetic pitch prepared by polymerizing condensed polycyclic hydrocarbons in the presence of hydrogen fluoride and boron trifluoride) 5 parts by weight, butyl acrylate 75 as an organic monomer Part by weight and 150 parts by weight of ethylene glycol monomethyl ether as a solvent were added, and the inside of the container was purged with nitrogen. Then, 5 parts by weight of azobisisobutyronitrile was added in several portions, and azobisisobutyronitrile was added. Was heated above the temperature at which radicals were generated, and the solution was stirred to complete the graft polymerization reaction.

In the initial stage of the graft polymerization, the presence of a hard mud was observed, but it became fluid in the middle of the reaction and became a slurry that could be easily stirred. The monomer reaction rate was quantitatively determined by gas chromatography, and the reaction was terminated when the reaction rate was 99% or more. As a result of measuring the total graft polymerization rate of butyl acrylate after the reaction to activated carbon, carbon black, synthetic pitch, and the like, it was about 12%. The calculated nonvolatile content of the slurry was about 55%.
The obtained slurry was a coating solution with extremely good dispersion stability that was free from sedimentation such as activated carbon, carbon black, and pitch even after standing for one day.

  The graft polymerization rate was measured as follows. First, the slurry prepared as described above was heat-treated to lose dispersibility in a solvent such as a graft polymer, and then the homopolymer was extracted with tetrahydrofuran using a Soxhlet extractor. When the extract was exhausted, it was taken out and dried. A portion thereof was weighed and heat-treated at a temperature equal to or higher than the decomposition temperature of butyl acrylate, the residue was weighed, and the ratio used for the grafted product of butyl acrylate was defined as the graft polymerization rate.

(Production of electrode sheet)
The coating liquid prepared as described above was applied to an aluminum foil having a width of 150 mm and a thickness of 30 μm in which a portion to be a lead portion of the electrode sheet was sealed using a coating apparatus as shown in FIG. The unwinding speed and winding speed of the aluminum foil were 0.5 m / min. Moreover, 150 degreeC dry air was introduce | transduced in the drying part from the hot air inlet. Furthermore, after the wound one was heat treated in a heat treatment furnace for 30 minutes, the seal was peeled off and cut into a shape as shown in FIG. 2 to form a polarizable electrode having a thickness of 100 μm on the surface of the current collector A sheet was obtained.

  With respect to the aluminum foil (current collector) and the coating film (polarizable electrode) of this electrode sheet, the adhesive strength was measured according to the mechanical strength measuring method of JIS K 5600-5-6. The application part of the coating solution of the electrode sheet was cut into 6 pieces each in the vertical and horizontal directions, and a peeling test from the aluminum foil with cello tape (registered trademark) was performed on the sample divided into 25 central grids. As a result, none of the samples could peel the coating film (polarizable electrode) from the aluminum foil (current collector).

(Production of electric double layer capacitor)
A total of 30 electrode sheets manufactured as described above and a paper separator (thickness: 50 μm) are stacked so that the lead portions can be alternately connected to the positive and negative electrode terminals, and the lead portions are removed. A square laminate (thickness 10.2 mm) with a side of 100 mm was produced. Next, after the lead part of the positive electrode body and the lead part of the negative electrode body were bonded to the electrode terminals by welding, they were dried under reduced pressure at 160 ° C. for 24 hours using a vacuum dryer.
In addition, a square flat container having a side of 150 mm and having an aluminum foil whose surface was covered with a plastic film as a base material was dried under reduced pressure at 105 ° C. for 15 hours using a vacuum dryer. This flat container has an opening on one side.

After the laminate and the flat container were cooled to room temperature in a nitrogen atmosphere, the laminate was inserted into the container as shown in FIG. Next, 90 ml of an electrolytic solution in which an ammonium salt or the like was dispersed in a propylene carbonate solvent was injected from the opening of a flat container. After completing the injection of the electrolytic solution, the laminate was decompressed by a vacuum pump for 30 minutes, and the laminate was decompressed. During this period, the electrode terminal was energized to perform electrolytic purification. Thereafter, the opening of the container was heat sealed at 150 ° C., and the flat container was sealed to obtain an electric double layer capacitor.
As a result of measuring the electrostatic capacity and the internal resistance of this electric double layer capacitor at 25 ° C. and 2.7 V charge, they were 960 F and 3.0 mΩ, respectively, and it was confirmed that the performance was excellent.

(Preparation of coating solution)
In the same reaction vessel as in Example 1, 100 parts by weight of activated carbon (activated carbon A-BAC-PW15 manufactured by Kureha Chemical Industry Co., Ltd.), 10 parts by weight of carbon black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.), as an organic monomer After adding 75 parts by weight of butyl acrylate and 150 parts by weight of ethylene glycol monomethyl ether as a solvent, the inside of the container was purged with nitrogen, and then 5 parts by weight of azobisisobutyronitrile was added in several portions. While heating above the temperature at which isobutyronitrile generates radicals, the solution was stirred to complete the graft polymerization reaction.

As in Example 1, the presence of a hard mud was observed in the initial stage of graft polymerization. However, the slurry became fluid in the middle of the reaction and became a slurry that could be easily stirred. The monomer reaction rate was quantitatively determined by gas chromatography, and the reaction was terminated when the reaction rate was 99% or more. As a result of measuring the total graft polymerization ratio of butyl acrylate to activated carbon, carbon black, and the like after completion of the reaction, it was about 11%. The calculated nonvolatile content of the slurry was about 55%.
The obtained slurry was a very good slurry having excellent dispersion stability, such as activated carbon and carbon black, which did not settle even when allowed to stand for 1 day. Further, 5 parts by weight of an epoxy resin (EP815 manufactured by Japan Epoxy Resin Co., Ltd.), a solvent, an antifoaming agent, and the like were added as a binder to the slurry to obtain a coating solution having a desired concentration.

(Production of electrode sheet)
In the production of the electrode sheet of Example 1, an electrode sheet in which a polarizable electrode having a thickness of 100 μm was formed on the surface of the current collector was produced in the same manner as in Example 1 except that the coating liquid was used. .
With respect to the aluminum foil (current collector) and the coating film (polarizable electrode) of this electrode sheet, the adhesive strength was measured according to the mechanical strength measurement method of JIS K 5600-5-6 under the same conditions as in Example 1. It was measured. As a result, none of the samples could peel the coating film (polarizable electrode) from the aluminum foil (current collector).

(Production of electric double layer capacitor)
In the production of the electric double layer capacitor of Example 1, an electric double layer capacitor was produced in the same manner as in Example 1, except that the above electrode sheet was used. As a result of measuring the electrostatic capacity and the internal resistance at 25 ° C. and 2.7 V charge of this electric double layer capacitor, they were 940 F and 3.2 mΩ, respectively, and it was confirmed that the performance was excellent.

[Comparative Example 1]
(Preparation of coating solution)
In the same reaction vessel as in Example 1, 100 parts by weight of activated carbon (activated carbon A-BAC-PW15 manufactured by Kureha Chemical Industry Co., Ltd.), 10 parts by weight of carbon black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.), synthetic pitch (Synthetic pitch produced by Mitsubishi Gas Chemical Co., Ltd., synthetic pitch prepared by polymerizing condensed polycyclic hydrocarbons in the presence of hydrogen fluoride and boron trifluoride) 5 parts by weight, and ethylene glycol monomethyl as a solvent 150 parts by weight of ether was added, and the mixture was heated and stirred. However, a slurry-like coating liquid in which activated carbon, carbon black, synthetic pitch, etc. easily aggregated and settled and had good dispersion could not be obtained.

(Production of electrode sheet)
In the production of the electrode sheet of Example 1, an electrode sheet in which a polarizable electrode having a thickness of 100 μm was formed on the surface of the current collector was produced in the same manner as in Example 1 except that the coating liquid was used. .
With respect to the aluminum foil (current collector) and the coating film (polarizable electrode) of this electrode sheet, the adhesive strength was measured according to the mechanical strength measurement method of JIS K 5600-5-6 under the same conditions as in Example 1. It was measured. As a result, about 11 samples out of 25 samples, the coating film (polarizable electrode) was peeled from the aluminum foil (current collector).

[Comparative Example 2]
(Preparation of coating solution)
In the same reaction vessel as in Example 1, 100 parts by weight of activated carbon (activated carbon A-BAC-PW15 manufactured by Kureha Chemical Co., Ltd.), 10 parts by weight of carbon black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.), and solvent Although 150 parts by weight of ethylene glycol monomethyl ether was added and heated and stirred, activated carbon, carbon black and the like were liable to aggregate and settle, and a slurry-like coating solution with good dispersion could not be obtained.

(Production of electrode sheet)
In the production of the electrode sheet of Example 1, an electrode sheet in which a polarizable electrode having a thickness of 100 μm was formed on the surface of the current collector was produced in the same manner as in Example 1 except that the coating liquid was used. .
With respect to the aluminum foil (current collector) and the coating film (polarizable electrode) of this electrode sheet, the adhesive strength was measured according to the mechanical strength measurement method of JIS K 5600-5-6 under the same conditions as in Example 1. It was measured. As a result, for 19 samples out of 25 samples, the coating film (polarizable electrode) was peeled from the aluminum foil (current collector).

  As described above, in the electrode sheet of the example of the present invention, it was confirmed that the current collector and the polarizable electrode were firmly bonded. Moreover, it has confirmed that the electrical double layer capacitor using the electrode sheet of the Example of this invention was excellent in an electrostatic capacitance and internal resistance.

The block diagram which shows an example of the coating apparatus which apply | coats a coating liquid to metal foil in manufacture of the electrode sheet of this invention The top view which shows an example of the application part of a coating liquid in the electrode sheet of this invention Configuration diagram showing an example of an electric double layer capacitor of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coating liquid 2 Charge tank 3 Coating liquid supply pump 4 Overflow return pump 5 Metal foil 6 Unwinder 7 S-shaped level difference roll 8 for tension adjustment 8 Coating liquid bat 9 Application roll 10 Squeeze roll 11 Hot air inlet 12 Exhaust port 13 Thickness measurement Device 14 Heat press and line speed control roll 15 Winding device 16 Electrode sheet 17 Application portion of coating liquid 18 Lead portion 19 Laminate 20 Container 21 Electrode terminal (positive electrode terminal, negative electrode terminal)

Claims (11)

  At least a coating solution in which a graft polymer obtained by graft polymerization of activated carbon and / or carbon black and an organic monomer is dispersed in a solvent is applied to the surface of the current collector, and then dried and heat-treated. An electrode sheet characterized by that.   The electrode sheet according to claim 1, wherein a graft polymerization rate of the organic monomer to the activated carbon is 1 to 50% of the whole organic monomer.   The electrode sheet according to claim 1, wherein a graft polymerization rate of the organic monomer to the carbon black is 1 to 50% of the whole organic monomer.   The electrode sheet according to claim 1, wherein the activated carbon is activated carbon prepared using a synthetic pitch obtained by polymerizing a condensed polycyclic hydrocarbon or a compound containing a condensed polycyclic hydrocarbon as a raw material.   The electrode sheet according to claim 1, wherein the coating liquid further contains a resin.   The electrode sheet according to claim 5, wherein the resin is at least one resin selected from an epoxy resin, a phenol resin, a polyester resin, a melamine resin, a urea resin, an alkyd resin, and a polyimide resin.   The coating liquid further contains a graft polymer obtained by graft polymerization of a synthetic pitch prepared by polymerizing a condensed polycyclic hydrocarbon or a compound containing a condensed polycyclic hydrocarbon and an organic monomer. 2. The electrode sheet according to 1.   The electrode sheet according to claim 1, wherein the organic monomer is at least one monomer selected from an acrylic monomer, an epoxy monomer, a vinyl monomer, an ester monomer, an amide monomer, and an ether monomer.   The solvent is selected from aliphatic alcohols, ketones, aromatic hydrocarbons, nitrogen-containing aromatic hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, and cellosolves. The electrode sheet according to claim 1, wherein the electrode sheet is one or more organic solvents.   The electrode sheet according to claim 1, wherein the content of the graft polymer is 1 to 50 wt% with respect to the total amount of the coating liquid. The electric double layer capacitor which has the structure by which the electrode sheet and separator in any one of Claims 1-10 were laminated | stacked, and the electrolyte solution was impregnated.

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