JP2005136401A - Electrode for electric double layer capacitor and its manufacturing method, and electric double layer capacitor as well as conductive adhesive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode 10 whose heat resisting adhesion between a polarizable porous sheet 12 and a collector 11 is strong, its internal resistance is low, its continuous production is easy, and the high capacitance can be secured with the internal resistance lower than the customary when using it in the electric double layer capacitor. <P>SOLUTION: In the electric double layer capacitor 10, the polarizable porous sheet 12, which is composed of composition materials including a carbonaceous electric double layer forming material, a carbon material to hold the conductivity, and an adhesive, is united on at least one side of the collector 11 through a conductive intermediate layer 13, and the conductive intermediate layer 13 contains a synthetic rubber and two kinds or more of carbon materials in different diameters of particle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a collector-integrated polarizable electrode used for an electric double layer capacitor, an electric double layer capacitor using the electrode, and a conductive adhesive suitable for the electrode.

  Conventionally, as an electric double layer capacitor (electric double layer capacitor), a separator is interposed between a pair of polarizable electrode bodies, and these are sealed together with an electrolytic solution by a metal case and a gasket (coin or button type). ); A type in which a long electrode sheet and a separator are overlapped and wound to form an electric double layer capacitor unit, which is housed in a metal case, and then impregnated with an electrolyte and sealed (winding type) ); Electrode double layer capacitor unit in which rectangular electrode thin films and separators are alternately stacked to form an electrode laminate, and a positive electrode lead is connected to the positive electrode end of the electrode and a negative electrode lead is connected to the negative electrode end by caulking. Type, which is stored in a metal case and then impregnated with an electrolytic solution in a unit (seal type); It is known.

  Here, a power-oriented electric double layer capacitor such as an electric vehicle is required to have a high energy density and a high output density such as a high electric capacity per unit volume and a low internal resistance. In order to satisfy this requirement, studies have been made on increasing the electrode body area by increasing the opposing area of the electrodes and reducing the thickness of the electrode body. It goes without saying that the electric double layer capacitor needs to be excellent in mass productivity.

  In order to increase the area of the electrode body and reduce the thickness of the electrode body, the sheet-like and thin-film electrode bodies are: (1) a paste-like or ink-like mixture containing an electrode material is applied to the current collector by coating or the like. Then, drying (solvent removal), rolling, etc .; (2) An electrode sheet comprising an electrode material is prepared in advance, and a current collector is superimposed on the surface of the electrode sheet and integrated with a rolling roller or the like. However, since it is difficult to increase the density and capacity of the electrode body in the method (1), at present, the method (2) is generally used. ing.

  In the production method (2), in order to reduce the internal resistance of the electric double layer capacitor, it is important to improve the contact integration between the electrode material and the current collector. Here, as the electrode material, a material obtained by blending a binder with high conductivity carbon-based powder particles such as activated carbon (carbonaceous electric double layer forming material) and acetylene black is generally used. FIG. 7 shows an example of such an electrode 10 ″. The electrode sheet 2 composed of carbon-based particles and a binder is a porous layer having pores 3 and the surface thereof is an uneven surface. . In this case, when a metal foil or metal sheet having a smooth surface is used as the current collector 1, the interface between the current collector 1 and the electrode sheet 2 becomes point contact, and the substantial contact area is reduced. This is because the electrical resistance increases due to the increase in the air part (which becomes a liquid phase part when the electrolyte is injected) 4 interposed between the current collector 1 and the electrode sheet 2. This may cause deterioration of the multilayer capacitor characteristics.

As a polarizable electrode body that can solve such a problem, for example, Patent Document 1 discloses a polarizable electrode in which a porous electrode sheet (polarizable porous sheet) and a current collector are laminated via a conductive intermediate layer. A polarizable electrode body has been proposed in which a part of the conductive intermediate layer has entered a hole portion of the electrode sheet.
JP 11-154630 A (claims, etc.)

  Since the polarizable electrode body disclosed in Patent Document 1 has a lower internal resistance than that of the conventional one, the electric double layer capacitor using this has an excellent electric capacity as compared with the conventional electric double layer capacitor. The electrode body is excellent in productivity.

  By the way, in the electric double layer capacitor, when moisture is adsorbed on the electrode, the moisture adsorbed on the electrode when the capacitor is used is electrolyzed, and this phenomenon contributes to the deterioration of the performance of the capacitor.

  Therefore, the electrode for the electric double layer capacitor is dried before being used in the capacitor, but the electric double layer capacitor is prevented from deterioration in performance to a higher degree, and the electrode, and further, the electric double layer is extended. From the viewpoint of increasing the productivity of the capacitor, it is required to completely remove the moisture in the electrode in a short time, and accordingly, a drying process at a higher temperature is required.

  The present invention has been made in view of the above circumstances, and the purpose thereof is high heat-resistant adhesion between the polarizable porous sheet and the current collector, and can withstand a drying treatment at a higher temperature, and has low internal resistance. , An electrode capable of ensuring high electric capacity with low internal resistance when used in an electric double layer capacitor that is easy to produce continuously, a method for manufacturing the electrode, an electric double layer capacitor using the electrode, and the electrode The object is to provide a suitable conductive adhesive.

  The electric double layer capacitor electrode of the present invention that has achieved the above object comprises a carbonaceous electric double layer forming material (such as activated carbon), a carbon material for ensuring conductivity, and a constituent material including a binder. A polarizable porous sheet is formed by integrating a conductive intermediate layer on at least one surface of a current collector through a conductive intermediate layer, and the conductive intermediate layer is made of synthetic rubber and two or more types having different particle sizes. It has a gist where it contains the carbon material. The “sheet” in this specification is a concept including a so-called “film”.

  The electrode preferably contains flaky graphite and / or carbon black as the carbon material of the conductive intermediate layer.

  The synthetic rubber constituting the conductive intermediate layer is preferably a styrene / butadiene rubber, and the styrene / butadiene rubber preferably has a glass transition temperature of −5 to 30 ° C.

  The conductive intermediate layer is formed using a conductive adhesive containing the carbon material, synthetic rubber, and dispersion medium, and the total carbon material is 3 to 30% by mass in the conductive adhesive. In addition, it is recommended that the synthetic rubber is 7% by mass or less in the conductive adhesive.

  The polarizable porous sheet is a porous body, and preferably has an average pore diameter of 0.1 to 5 μm and a porosity of 40 to 90%. The current collector is preferably composed of aluminum, and it is recommended that the surface be roughened.

The electrode for electric double layer capacitor of the present invention,
(A) A carbonaceous electric double layer forming material (activated carbon or the like), a polarizable porous sheet comprising a carbon material for ensuring conductivity and a constituent material containing a binder and / or (B) a current collector (C) Synthetic rubber, two or more types of carbon materials having different particle diameters, and a conductive adhesive containing a dispersion medium are applied to the joint surfaces,
Before the dispersion medium is dried, the current collector and the polarizable porous sheet are bonded together and pressed, so that a part of the non-volatile components of the conductive adhesive is removed from the pores of the polarizable porous sheet. It can be manufactured by press fitting inside.

  Further, the electric double layer capacitor having the electric double layer capacitor electrode of the present invention and the conductive adhesive for forming the conductive intermediate layer are also included in the present invention.

  The electrode for an electric double layer capacitor of the present invention employs the above specific configuration for the conductive intermediate layer interposed between the current collector and the polarizable porous sheet, has an extremely low internal resistance, Excellent bonding strength and durability (heat resistant adhesiveness) between the current collector and the polarizable porous sheet. In addition, since the bonding strength between the polarizable porous sheet and the current collector is high, a long electrode is produced, and can be stored and transported in a state of being wound in a roll shape. Excellent storage and transportability.

  The conductive adhesive of the present invention is suitable for the production of the electric double layer capacitor electrode of the present invention.

  Since the electric double layer capacitor of the present invention uses the electrode for the electric double layer capacitor of the present invention that has achieved low internal resistance, the internal resistance is low, the electric capacity is high, and a high output density can be achieved.

  FIG. 1 shows an example of an embodiment of an electrode for an electric double layer capacitor of the present invention (hereinafter sometimes simply referred to as “electrode”). The electrode 10 has a carbonaceous electric double layer forming material (hereinafter sometimes simply referred to as “electric double layer forming material”), a carbon material and a binder for ensuring conductivity on both sides of the current collector 11. Polarizable porous sheets 12 and 12 made of a constituent material including are bonded via conductive intermediate layers 13 and 13. As shown in FIG. 1, the polarizable porous sheets 12 and 12 made of the above-described constituent materials are porous bodies, and a part of the conductive intermediate layer 13 enters the pores 12a and 12a. .

  As described above, in an electrode for an electric double layer capacitor, it is necessary to perform a drying process for removing adsorbed moisture from the viewpoint of preventing performance deterioration when used for an electric double layer capacitor. In order to achieve this, a drying process at a high temperature is required.

  For example, in the polarizable electrode body described in Patent Document 1, water is bonded to the electrode sheet (polarizable porous sheet) constituting the electrode body and the current collector (that is, the binder constituting the conductive intermediate layer). Glass, cellulose derivatives such as carboxymethyl cellulose, and other thermoplastic resins such as polyvinyl alcohol are applied.

  However, when a thermoplastic resin such as the above cellulose derivative or polyvinyl alcohol is used, it is necessary to control the drying treatment temperature to about 150 ° C. or lower, and when the drying treatment is performed at a temperature exceeding this, Since the adhesion between the polarizable porous sheet and the current collector is impaired, it was difficult to completely remove moisture in a short time.

  On the other hand, water glass has better heat resistance (heat resistant adhesiveness) than thermoplastic resins such as the above cellulose derivatives and polyvinyl alcohol, and even if the drying temperature is increased to some extent, the polarizable porous sheet and the current collector are bonded. However, it is difficult to completely remove the water contained in the water glass itself, and it is not possible to meet the demand for a drying process in a short time.

  In view of such circumstances, the present inventors have focused on synthetic rubber as a binder that is interposed between the polarizable porous sheet and the current collector and constitutes a conductive intermediate layer for joining them. If synthetic rubber is used, good heat-resistant adhesiveness can be ensured. Therefore, even if a drying process is performed at a high temperature (for example, about 230 ° C.), the adhesive property between the polarizable porous sheet and the current collector is sufficient. Since it can be maintained, the adsorbed moisture of the electrode can be completely removed in a shorter time.

  The conductive intermediate layer is formed by applying a liquid conductive adhesive in which a carbon material for securing conductivity and a binder are dispersed (including when partially dissolved) in a dispersion medium. The method of removing is common.

  Therefore, in a conductive adhesive, a synthetic rubber used as a binder is usually applied in a state where it is present as dispersed particles in a dispersion medium. Here, a carbon material such as carbon black is relatively used. When a material having a small particle size and a large specific surface area is applied, the amount of the binder adsorbed on the carbon black surface of the synthetic rubber increases, and when the conductive intermediate layer is formed, sufficient adhesion may not be exhibited.

  On the other hand, if, for example, flaky graphite having a relatively large particle size and a small specific surface area is used as the carbon material, sufficient adhesiveness can be ensured because the amount of synthetic rubber adsorbed on the graphite surface is small. However, flaky graphite is difficult to enter into the pores of the polarizable porous sheet because of its relatively large particle size, and the internal resistance due to the conductive intermediate layer entering into the pores of the polarizable porous sheet. The reduction effect may not be sufficiently secured.

By the way, the loss η (energy loss) due to charging / discharging of the electric double layer capacitor is obtained by the following equation.
η = 2CR / t
Here, C is the capacitance of the entire electric double layer capacitor, R is the internal resistance of the electric double layer capacitor, and t is the charging time. That is, the energy loss of the electric double layer capacitor is proportional to the internal resistance and capacity, and inversely proportional to the charging time. Therefore, for example, when the internal resistance of the electric double layer capacitor is doubled, in order to make the energy loss the same, it is necessary to double the charging time. Recently, since shortening of the charging time is required, the internal resistance needs to be kept as low as possible.

  Although it is known that synthetic rubber is used as a binder for conductive adhesives, when synthetic rubber is used as a binder for conductive adhesives used in electric double layer capacitors, the internal resistance of electric double layer capacitors is a thermoplastic resin. Synthetic rubber has not been adopted as a binder for conductive adhesives used in electric double layer capacitors because it is several times higher than when used as a binder.

  Therefore, in the present invention, two or more types of carbon materials having different particle diameters are employed together with the synthetic rubber as the configuration of the conductive intermediate layer. When the carbon material contains two or more types (for example, two types, three types, four types, etc.) having different particle sizes, the carbon material has a particle size that can enter the pores of the polarizable porous sheet; Although it cannot enter the pores of the polarizable porous sheet, a small amount of synthetic rubber particles can be used together with a carbon material having a particle size that is large enough to allow binding between the carbon material particles. Therefore, by adopting such a configuration, for example, it has been found that the heat-resistant adhesiveness can be enhanced while ensuring a low internal resistance of the same level as the polarizable electrode body disclosed in Patent Document 1, and the present invention. It came to complete. Hereinafter, the present invention will be described in detail.

<Conductive intermediate layer and conductive adhesive>
The polarizable porous sheet used for the electrode of the present invention is a porous body as described above. In the electrode of the present invention, by introducing a part of the conductive intermediate layer containing at least two kinds of carbon materials and synthetic rubber into the pores of the polarizable porous sheet, the joint strength can be improved by the anchor effect, The resistance is reduced.

The synthetic rubber serves as a binder in the conductive intermediate layer. Specific examples of synthetic rubber include isoprene-based rubbers such as isoprene rubber (polyisoprene); butadiene rubber (cis-1,4-polybutadiene), styrene-butadiene rubber (SBR)
Butadiene rubber such as nitrile rubber (NBR), chloroprene rubber, etc .; olefin rubber such as ethylene / propylene rubber, ethylene / propylene / diene rubber, acrylic rubber; hydrin rubber; urethane rubber; fluorine rubber; Is mentioned.

  Among the above synthetic rubbers, SBR having various varieties is inexpensive and suitable. Further, SBR having a glass transition temperature (Tg) of −5 ° C. or higher and 30 ° C. or lower is more preferable. By using such SBR of Tg, it is possible to ensure good adhesion and heat resistant adhesiveness. In addition, when activated carbon is used as the electric double layer forming material in the polarizable porous sheet, the activated carbon has a large surface area because it has many pores, thereby increasing the surface area of the polarizable porous sheet. This contributes to the improvement of the electric capacity per unit volume of the electrode. However, if the Tg is SBR within the above range, it is possible to suppress the clogging of the pores of the activated carbon by the SBR. It is possible to prevent deterioration of the characteristics of the electrode due to

  That is, when the Tg of SBR is less than the above range, the adhesion is improved, but the pores of the activated carbon in the polarizable porous sheet are likely to be blocked, and the electric capacity tends to be reduced. On the other hand, when the Tg of the SBR exceeds the above range, the fluidity of the SBR is lowered, so that the adhesion tends to be lowered. The TBR of SBR is more preferably 0 ° C. or higher and 10 ° C. or lower. The TBR of SBR is a value measured according to JIS K 7121.

  The TBR of SBR can be generally controlled by adjusting the copolymerization ratio of styrene and butadiene. That is, the higher the butadiene ratio, the lower the Tg, whereas the higher the styrene ratio, the higher the Tg. Moreover, although heat resistant adhesiveness becomes so high that there are many styrene ratios, when too much, it turns out that a coating film becomes hard and lacks a softness | flexibility.

  The conductive intermediate layer is formed from a liquid conductive adhesive containing a carbon material described later, the synthetic rubber, and a dispersion medium. The dispersion medium is not particularly limited, but water and lower alcohols (methanol, ethanol, n-propanol, isopropanol, etc.) are preferable. Normally, synthetic rubbers cannot be dissolved or dispersed in these dispersion media as they are, so that a known surfactant or a water-soluble polymer for forming a protective colloid may be added. The conductive intermediate layer forming component is a component obtained by removing a volatile component such as a dispersion medium to be removed in the adhesion between the polarizable porous sheet and the current collector (that is, a non-volatile component). ).

  Of the above synthetic rubbers, it is also preferable to use latex when it is easy to obtain latex. For example, latex such as SBR and NBR is common. In this case, all of the conductive adhesive dispersion medium may be derived from latex, or a dispersion medium may be added separately.

  When such a latex is used, it is preferable that the rubber particles in the latex have an average particle size of 50 to 300 nm. The latex containing rubber particles having such a particle size includes carbon particles having a particle size such as carbon black (for example, acetylene black) described later and particles having a particle size such as flaky graphite described later. When a conductive adhesive is prepared using a material and is used for bonding the polarizable porous sheet and the current collector, a small particle size is formed in the pores of the polarizable porous sheet having a pore diameter described later. Since the synthetic rubber particles can enter well together with the carbon material, the above-described anchor effect and internal resistance reduction effect are excellent.

  As said carbon material, it is a carbon material which can ensure electroconductivity, Comprising: The thing of 2 or more types from which a particle size differs should just be used. Specific examples of carbon materials include graphite having high conductivity due to the presence of delocalized π electrons; carbon black (spherical aggregate in which several layers of graphitic carbon microcrystals gather to form a turbulent structure ( Acetylene black, ketjen black, other furnace blacks, channel blacks, thermal lamp blacks, etc.); hydrocarbons such as methane, propane, acetylene, etc. are vapor-phase pyrolyzed and deposited in a thin film state on the blackboard as a substrate And pyrolytic graphite. Among them, flaky graphite [particularly natural graphite (scaly graphite)] is also a acetylene because it has a relatively small particle size and a relatively good conductivity because it can ensure high conductivity. Black is preferred. Therefore, as the carbon material, a mixture of flaky graphite and acetylene black is a particularly preferable embodiment.

  The case where acetylene black and flaky graphite are used as the carbon material will be described. The particle diameter of acetylene black is usually about 10 to 50 nm as an average particle diameter (primary particle diameter). Moreover, the average particle size of the flake graphite is preferably 0.5 to 20 μm, more preferably 1 to 10 μm. A polarizable porous sheet, which will be described later, while increasing the conductivity of the conductive intermediate layer itself by having a conductive intermediate layer having a carbon material in which flaky graphite having such an average particle diameter and acetylene black are used in combination A part of the conductive intermediate layer can be made to enter the pores to ensure excellent bonding strength and internal resistance reduction effect.

  As described above, the use of carbon black such as acetylene black and flaky graphite as the carbon material means that the conductive intermediate layer is exposed by peeling off the polarizable porous sheet or current collector from the electrode. From the diffraction intensity curve obtained by the X-ray diffraction method for the surface, a crystalline diffraction line shape based on flaky graphite and an amorphous diffraction line shape based on carbon black are observed, which can be confirmed.

  The mixing ratio of acetylene black and flaky graphite is preferably 1:10 to 1: 1 by mass ratio, and more preferably 1: 5 to 1: 2. By setting it as such a mixing ratio, sufficient adhesiveness and the high internal resistance reduction effect can be ensured simultaneously.

  In addition, the average particle diameter of flaky graphite is a value measured by a laser type particle size distribution measuring device (“SALD-2000” manufactured by Shimadzu Corporation). Moreover, what is necessary is just to select the acetylene black whose average particle diameter is in the said range according to the nominal value of the manufacturer of acetylene black.

  In addition, as for these carbon materials, it is desirable that ash content is 0.05% or less regardless of the kind. When an electrode using a carbon material having such a low ash content is applied to an electric double layer capacitor, the life of the capacitor can be extended.

  The amount of the total carbon material in the conductive adhesive is preferably 3% by mass or more and 30% by mass or less. More preferably, it is 10 mass% or more and 25 mass% or less. When the amount of the carbon material is less than the above range, the conductivity of the conductive intermediate layer may be insufficient. On the other hand, when the above range is exceeded, the amount balance with the binder (the synthetic rubber) for forming the conductive intermediate layer is lost, and the adhesiveness tends to decrease.

  Further, the amount of the synthetic rubber in the conductive adhesive is preferably 7% by mass or less, and more preferably 5% by mass or less. If the amount of synthetic rubber exceeds the above range, the internal resistance may increase too much. In addition, from the viewpoint of sufficiently securing the adhesiveness due to the conductive intermediate layer, the amount of the synthetic rubber in the conductive adhesive is preferably 0.5% by mass or more, and more preferably 2% by mass or more. .

  In addition, the conductive adhesive of the present invention is a carbon material having a small particle size that can enter the pores of the polarizable porous sheet satisfactorily by adopting a structure containing two or more types of carbon materials having different particle sizes. Along with (for example, carbon black such as acetylene black), a carbon material having a large particle diameter (for example, flaky graphite) may be contained. Therefore, it is possible to form a conductive intermediate layer with good conductivity while reducing the amount of the carbon material having a small particle size, so that the surface of the synthetic rubber particle in the dispersion medium is covered with the carbon material having a small particle size. When the conductive intermediate layer is formed, good heat-resistant adhesiveness can be secured.

  In FIG. 2, the schematic diagram which expanded the cross section of the electrode of this invention is shown. In FIG. 2, 101 is a carbon material having a small particle size (carbon black), 102 is a carbon material having a large particle size (flaky graphite), and 103 is a synthetic rubber particle. In the electrode 10 ′, in the conductive intermediate layer 13, the carbon material 102 having a large particle size and a part of the carbon material 101 having a small particle size are bound to the synthetic rubber particle 103, and the carbon particle having a small particle size is further bonded. A part of the material 101 enters the pores 12 a of the polarizable porous sheet 12 together with the synthetic rubber particles 103. With such a structure, the electrode of the present invention ensures good bonding strength including heat-resistant adhesion and low internal resistance. Note that FIG. 2 shows a mode in which the surface of the current collector 11 ′ is roughened, and the carbon particles having a small particle diameter are also formed in the pits (recesses) formed on the surface of the current collector 11 ′. A part of the material 101 enters with the synthetic rubber particles 103, and can exhibit more excellent bonding strength improvement effect and internal resistance reduction effect.

<Polarizable porous sheet>
Polarized porous sheets are roll-rolled by mixing an electric double layer forming material (carbon electrode material) with a carbon material and a binder for ensuring conductivity, and adding ethanol or oil to this mixture. It is a porous sheet obtained by roll extrusion or the like. That is, the gap between the particulate electric double layer forming material becomes the pores 12a (FIG. 1) to form a porous sheet.

  The electric double layer forming material that is a raw material for the polarizable porous sheet is not particularly limited as long as it is a carbonaceous substance that can form the electric double layer, but activated carbon is typical. As the activated carbon, various activated carbons generally used for carbon electrodes can be used. Specifically, use charcoal, coconut husk charcoal, lignite, uncarburized materials such as sawdust, activated with a gas such as water vapor or carbon dioxide, or activated with chemicals such as zinc chloride Can do. The shape may be powder or granular. As described above, since the specific surface area of activated carbon is significantly increased by activation, an electrode having a large electric capacity per unit volume can be formed.

  The electric double layer forming material may be graphite-like microcrystalline carbon produced by subjecting a carbon material to activation treatment. This microcrystalline carbon forms an electric double layer when ions or the like enter between crystal layers when a voltage is applied, and can be obtained, for example, according to the technique disclosed in JP-A-11-317333.

  The carbon material for ensuring conductivity is not particularly limited, and for example, various carbon materials exemplified for the conductive intermediate layer can be used.

  As the binder, those known in the electric double layer capacitor field can be used. For example, fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and ethylene-tetrafluoroethylene copolymer; cellulose resins such as carboxymethyl cellulose;

  The average pore size of the polarizable porous sheet is preferably 0.1 μm or more and 5 μm or less, and more preferably 0.5 μm or more and 3 μm or less. If the average pore diameter is less than the above range, the conductive intermediate layer forming component may not easily enter the pores of the polarizable porous sheet. On the other hand, if the average pore diameter exceeds the above range, the conductive intermediate layer forming component may be The conductive intermediate layer that penetrates deeply into the pores of the polarizable porous sheet and remains at the interface between the current collector and the polarizable porous sheet may become very thin and the bonding strength may decrease. In addition, when the polarizable porous sheet is made of activated carbon, the pores of the activated carbon are covered with the conductive intermediate layer forming component, so that the capacitor performance may be reduced. In addition, the average pore diameter referred to in the present specification is a value measured using a mercury intrusion porosimeter (“Pore Sizer 9310” manufactured by Micrometrics).

  The porosity of the polarizable porous sheet is preferably 40% or more and 90% or less, and more preferably 60% or more and 80% or less. If the porosity is below the above range, a sufficient amount of electrolyte may not be retained when used in a capacitor, and the internal resistance may increase. Moreover, since the amount of the conductive intermediate layer forming component that can enter the pores of the polarizable porous sheet is reduced, the above-described anchor effect and internal resistance reduction effect may not be sufficiently ensured. On the other hand, if the porosity exceeds the above range, if the amount of the conductive adhesive is insufficient, there will be many holes where the conductive intermediate layer has not entered. The anchor effect may be insufficient. In addition, an air layer (in the case of a capacitor, an electrolyte is injected to become a liquid phase portion) is interposed between the current collector and the above-described internal resistance reduction effect cannot be sufficiently ensured. is there. Conversely, when the amount of the conductive adhesive is too large, the conductive intermediate layer enters deeply into the pores of the polarizable porous sheet. Therefore, when activated carbon is used for the polarizable porous sheet, most of the pores of the activated carbon are covered with the component, which reduces the specific surface area of the activated carbon, which causes a decrease in capacitor performance. There is.

Here, the porosity (%) referred to in the present specification is obtained as a ratio [(V ₀ / V) × 100] of the pore volume (V ₀ ) to the volume (V) of the entire polarizable porous sheet. Value. The pore volume can be obtained by the following formula by measuring the true density (ρ) of the polarizable porous sheet and the mass (W) of the polarizable porous sheet.
V ₀ = V− (W / ρ)
The porosity and average pore size of the polarizable porous sheet should be adjusted by the type of the electric double layer forming material that is the constituent material of the polarizable porous sheet, the amount of binder, the roll pressure when making the polarizable porous sheet, etc. Can do. The thickness of the polarizable porous sheet is generally 0.05 to 1 mm, and more preferably 0.08 to 0.5 mm.

  A polarizable porous sheet can be manufactured by the following method, for example. The above-mentioned electric double layer forming material, carbon material for ensuring conductivity, binder, and molding aids [water, alcohol (methanol, ethanol, etc.), oil (petroleum, other oils, etc.) as necessary] Are mixed and formed into a sheet shape by rolling or extruding, and the forming aid is removed to obtain a polarizable porous sheet. For example, when ethanol is used as the molding aid, the mixing ratio is 3 to 15 parts by mass of the carbon material, 5 to 15 parts by mass of the binder, and 100 parts by mass of the electric double layer forming material. : Polarizing porous sheet having the above average pore diameter and porosity can be obtained by roll extrusion at 50 to 300 parts by mass and at a temperature of 50 to 100 ° C.

<Current collector>
For the current collector, metal materials such as aluminum, titanium, tantalum, nickel, iron, stainless steel, and copper can be used. However, aluminum has excellent electrical conductivity and high stability (it does not dissolve and precipitate in the electrolyte). It is particularly preferable because of its low cost. These metals can be used in any shape of foil, plate and sheet. The current collector may have a smooth surface as shown in FIG. 1, for example. Even in this case, a void portion that may exist at the interface due to point contact between the current collector 11 and the polarizable porous sheet 12 Is filled with the conductive intermediate layer 13 so that air can be reduced, and the conductive intermediate layer enters the pores 12a of the polarizable porous sheet 12, thereby improving the bonding strength due to the anchor effect. Can be achieved.

  As a more preferable embodiment of the current collector, one that has been roughened so that irregularities are formed on the surface can be mentioned. An example of an electrode using a current collector whose surface is roughened is shown in FIG. In this electrode 10 ′, a part of the conductive intermediate layer enters not only the pores 12a of the polarizable porous sheet 12, but also the pits of the current collector 11 ′. The bonding strength with the electric body 11 ′ is further improved. Of course, since the conductive intermediate layer forming component that has entered the pits of the current collector 11 ′ can eliminate air in the pits, an increase in electrical resistance due to the presence of the electrolyte in the recesses in the case of a capacitor can be prevented. Can do.

  In addition, in an electrode using a current collector whose surface is roughened, the amount of a conductive adhesive for forming a conductive intermediate layer, or when laminating a current collector and a polarizable porous sheet By adjusting the pressure, a structure as shown in FIG. 3 is possible.

  In the electrode 10 ′ of FIG. 3, the conductive intermediate layer 13 is interposed between the current collector 11 ′ and the polarizable porous sheet 12, but microscopically, the convex portion 11 of the current collector 11 ′. 'b and the convex portion of the polarizable porous sheet 12 are in contact with each other, and the conductive intermediate layer 13 is a discontinuous layer (in FIG. 3, pits formed on the surface of the current collector 11' Is not shown). In such a case, the internal resistance can be further reduced. That is, in the electrode having the structure as shown in FIG. 3, a conductive path from the current collector 11 ′ to the polarizable porous sheet 12 through the conductive intermediate layer 13 (arrow A in FIG. 3), Two types of paths (arrow B in FIG. 3) that conduct directly from the electric body 11 ′ to the polarizable porous sheet 12 are formed. Since the path B has a lower electrical resistance than the path A, the electrical resistance of the electrode as a whole can be reduced. As a result, the internal resistance is low and a higher performance electric double layer capacitor can be formed. Become.

  The method for roughening the surface of the current collector is not particularly limited, and known methods such as sand blasting and etching (electrolytic etching, chemical etching, etc.) can be employed. Among these, chemical etching using chemicals is preferable because the pores and irregularities formed on the surface of the current collector can be easily controlled to a shape suitable for the anchor effect of the adhesive.

  The thickness of the current collector (when the surface is roughened, the thickness before the treatment) is generally 10 to 100 μm, and more preferably 20 to 70 μm.

<Depth of penetration of conductive intermediate layer into pores of polarizable porous sheet (entrance)>
The depth (degree of penetration) at which the conductive intermediate layer has entered the pores of the polarizable porous sheet is 0.15% or more, preferably 0.25% or more with respect to the thickness of the polarizable porous sheet. Therefore, it is recommended that it is 15% or less, preferably 10% or less. If the depth of penetration of the conductive intermediate layer is too small with respect to the thickness of the polarizable porous sheet, the effect of improving the adhesive strength due to the anchor effect may not be sufficient, and the polarizable porous sheet and Air may intervene between the conductive intermediate layer and cause an increase in internal resistance. On the other hand, when the penetration depth of the conductive intermediate layer is too large with respect to the thickness of the polarizable porous sheet, if the polarizable porous sheet is composed of activated carbon, the pores of the activated carbon are electrically conductive. The ratio covered by the conductive intermediate layer forming component is increased, and the specific surface area of the activated carbon is decreased, which may cause deterioration of characteristics when a capacitor is obtained.

  The degree of penetration was measured by the following method.

  The epoxy resin is cured in a state where the electrode is immersed in a solution in which the epoxy resin and the curing agent are mixed, and then an arbitrary portion of the electrode solidified with the epoxy resin is cut vertically (in the thickness direction), and the cross section is cut. Polish with sandpaper or alumina powder. Next, the polished cross-section is observed with an optical microscope with a deflection lens, and the average distance between the polarizable porous sheet side tip of the conductive intermediate layer and the conductive intermediate layer side tip of the polarizable porous sheet ( In FIG. 1, the ratio [(t / T) × 100] of t) to the average thickness (T in FIG. 1) of the polarizable porous sheet is determined as the degree of penetration.

  The degree of penetration can be adjusted by the average pore diameter of the polarizable porous sheet, the amount of the conductive intermediate layer forming component, the pressure applied when the polarizable porous sheet and the current collector are laminated, and the like.

<Method for producing electrode for electric double layer capacitor>
First, the conductive adhesive is applied to the polarizable porous sheet and / or the current collector surface (bonding surface). The application surface may be a bonding surface of either the polarizable porous sheet or the current collector, but may be applied to both. More preferably, it is a method of applying to the bonding surface of the current collector. The surface of the polarizable porous sheet is, so to speak, an aggregate of powder, and pores are opened over the entire surface. Therefore, when a conductive adhesive is applied to the bonding surface of the polarizable porous sheet, This is because the conductive adhesive penetrates to a considerably deep position inside the pores of the polar porous sheet, and the degree of penetration may exceed the above-described preferable range. Also, from the viewpoint of productivity (mass productivity), it is preferable to apply to a higher strength current collector.

The coating amount of the conductive adhesive, the amount of dried (i.e., conductive intermediate layer forming component amount) In is preferably to 2 to 15 g / m ^2, and more preferably set to 3 to 10 g / m ² .

  Next, the polarizable porous sheet and the current collector are laminated so that the applied conductive adhesive is interposed before the dispersion medium evaporates. The laminating method may be simply overlapping and bonding, but it is preferable to press and compress after bonding. By making it like the latter, while joining more reliably, a part of conductive adhesive can be reliably press-fitted in the hole of a polarizable porous sheet. Further, since the polarizable porous sheet is compressed and densified, it is possible to increase the capacity of the polarizable porous sheet. Although the pressurization method is not particularly limited, for example, a method of passing between a pair of rolls is relatively simple. At this time, the clearance between the rolls with respect to the total thickness of the laminate is preferably, for example, 30 to 90%, and more preferably 50 to 70%. By setting it as such clearance, while being able to make an approach degree into the said range, the high capacity | capacitance of a polarizable porous sheet can be achieved. When the clearance is less than the above range, the current collector may be deformed and the polarizable porous sheet may be peeled off.

  Next, volatile components (such as a dispersion medium) in the conductive adhesive are removed. Although the removal method is not particularly limited, for example, a hot air drying method is suitable. The hot air temperature is preferably near the boiling point of the dispersion medium. By removing the dispersion medium, a conductive intermediate layer is formed, and the electrode of the present invention as shown in FIGS. 2 and 3 show only one side of the current collector.

<Electric double layer capacitor>
The electric double layer capacitor of the present invention is formed by using the electrode for an electric double layer capacitor of the present invention. Specifically, as shown in FIG. 4, the electrodes 10 and separators 15 of the present invention are alternately arranged. A plurality of such combinations are arranged side by side (FIG. 5), the electrolyte solution is filled between the electrode 10 and the separator 15, and is usually stored in a case (such as a metal case) (FIG. 5). 6). In FIG. 6, 20 is a case, 21 is an upper lid, 22 is an electrolytic solution, and 23 is a current collecting lead.

  As said separator, the well-known thing conventionally used for the electric double layer capacitor can be used. For example, a porous sheet made of PTFE, polyethylene, polypropylene, or the like; a porous sheet obtained from sisal hemp;

  Moreover, the well-known thing conventionally used for the electric double layer capacitor can also be employ | adopted for electrolyte solution. Solvents for the electrolyte include carbonates such as propylene carbonate and butylene carbonate; lactones such as β-butyrolactone and γ-butyrolactone; sulfolanes; amide solvents such as dimethylformamide; nitromethane; 1,2-dimethoxyethane; acetonitrile; Is mentioned. Moreover, as electrolyte of electrolyte solution, fluorine-containing acids such as tetrafluoroboric acid, hexafluorophosphoric acid, hexafluoroarsenic acid, hexafluoroantimonic acid, trifluoroalkylsulfonic acid; perchloric acid, tetrachloride Chlorine-containing acids such as aluminate; acids such as alkali metal salts (sodium salt, potassium salt, etc.), alkaline earth metal salts (magnesium salt, calcium salt, etc.), ammonium salts, tetraalkylammonium salts ( Examples thereof include tetramethylammonium salt and tetraethylammonium salt) and tetraalkylphosphonium salt (tetramethylphosphonium salt, tetraethylphosphonium salt and the like).

  In FIG. 4, reference numeral 9 denotes a current collecting terminal attached to the current collector, and a current collecting lead (not shown) is attached to the current collecting terminal 9. 4 and 5 show examples using the electrodes having the structure shown in FIG. 1, these electrodes may have the structures shown in FIG. 2 and FIG. Moreover, the electrodes arranged in parallel may all have the same structure, or may have different structures. Furthermore, as shown in FIG. 5, for a plurality of electrodes arranged side by side, an electrode in which a polarizable porous sheet is laminated only on one side of the current collector may be used. it can.

  According to the electric double layer capacitor of the present invention, since the electrode for the electric double layer capacitor of the present invention that achieves a lower internal resistance than before is used, the internal resistance is low, the electric capacity is high, and the high output density is achieved. Can demonstrate.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

Example 1
[Polarizable porous sheet]
Activated carbon powder (“RP-20” manufactured by Kuraray Chemical Co., Ltd., specific surface area: 2000 m ² / g, average particle size: 8 μm): 85 parts by mass, Ketjen Black (“EC600JD” manufactured by Ketjen Black International): 7 parts by mass , PTFE powder: 8 parts by mass of ethanol: 100 parts by mass of ethanol, kneaded and roll-rolled, width: 100 mm, thickness: 0.3 mm, porosity: 65%, average pore size: 0 A long polarizable porous sheet having a thickness of 8 μm was obtained.

[Current collector]
As the current collector, a high-purity etched aluminum foil (“C513” manufactured by KDK) having a width of 150 mm and a thickness of 50 μm was used.

[Conductive adhesive]
As a carbon material, ash content: 0.02%, average particle size: 4 μm natural flake graphite (“graphite powder” manufactured by Hitachi Powdered Metals) and ash content: 0.02%, average particle size (primary particle size): 35 nm Acetylene black (“Denka Black” manufactured by Denki Kagaku Kogyo) was used. Further, SBR latex (“Grade 0850” manufactured by JSR) was used as a synthetic rubber. These were mixed so that it might become a composition shown in Table 1, and the conductive adhesive was obtained.

[Manufacture of electrodes]
A conductive adhesive was applied to both sides of the current collector using an application roll. The coating amount was 30 g / m ² per side (7 g / m ² after drying). After the application, a long polarizable porous sheet was stacked on the conductive adhesive application surface (both sides) of the current collector, and a laminated sheet was passed through a compression roll (clearance: 70%). The laminated sheet was passed through a continuous hot air dryer set at a temperature of 150 ° C. in 3 minutes, and the dispersion medium was removed from the conductive adhesive to obtain a long electrode.

[Manufacture of electric double layer capacitors]
A plurality of 10 cm square electrodes were punched from the long electrodes, and current collector terminals of 2 cm × 10 cm were attached to the current collectors of the electrodes by welding. Thereafter, 15 combinations of these electrodes and separators as shown in FIG. 4 were stacked. In addition, the separator (Japan Gore-Tex "BSP0102560-2", thickness: 25 micrometers, porosity: 60%) which hydrophilized the expanded porous PTFE membrane was used for the separator. This was vacuum-dried at 150 ° C. for 72 hours and then housed in an aluminum case, and then a current collecting lead was attached to each current collecting terminal, and a positive electrode terminal and a negative electrode terminal were further attached to the current collecting leads. Next, a propylene carbonate solution of tetraethylammonium tetrafluoroborate (concentration: 1 mol / L) was poured into the case as an electrolytic solution, an upper lid was attached, and the case was sealed to obtain a square electric double layer capacitor.

  The following evaluation was performed about said electrode and electric double layer capacitor. The results are shown in Tables 2 and 3.

<Tape peeling test (heat resistance test)>
After the electrode is dried at a predetermined temperature for 24 hours, a cut is made in a grid pattern on the polarizable porous sheet portion (one eye is 5 × 5 mm, 144 pieces), and the cut surface is formed on the surface. Adhesive tape ("Damplon Ace II" manufactured by Nitto Denko Co., Ltd.) is applied and pressed with enough fingers to remove air bubbles between the polarizable porous sheet and the adhesive tape. The peeled state of the sheet portion was observed.

<Capacitance density>
For the electric double layer capacitor, an operation of charging for 1500 seconds under the conditions of 10 mA / cm ² and 2.7 V and discharging until reaching 0 V under the conditions of 10 mA / cm ² is defined as one cycle, and this is repeated for 10 cycles. The discharge curve from the start of the discharge at the 10th cycle to 0 V was integrated to obtain the capacitance of the electric double layer capacitor at the time of the 10th charge, and this was divided by the electrode volume. The capacitance density was calculated.

<DC internal resistance>
It calculated | required by calculating using a formula "V = IR" at the time of the said capacitance density measurement.

<High temperature durability test>
For the electric double layer capacitor, an operation of charging at 100 ° C. for 100 hours under the condition of 10 mA / cm ² and 2.7 V at a temperature of 70 ° C. and discharging until reaching 0 V under the condition of 10 mA / cm ² is one cycle. This operation was repeated. The capacitance at the first cycle and the cycle after 1000 hours is obtained by the above-described method for the capacitance density, and the result is the maintenance of the capacitance after 1000 hours from the start of measurement (first cycle). The rate [100 × (capacitance of the cycle after 1000 hours) / (capacitance at the first cycle)] (%) was evaluated.

Example 2
An electrode and an electric double layer capacitor were produced and evaluated in the same manner as in Example 1 except that the configuration of the conductive adhesive was changed as shown in Table 1. The SBR latex used in Example 2 is “Grade 0597C” manufactured by JSR. The results are shown in Tables 2 and 3.

Example 3
An electrode and an electric double layer capacitor were produced and evaluated in the same manner as in Example 1 except that the configuration of the conductive adhesive was changed as shown in Table 1. The SBR latex used in Example 3 is “Grade 0668” manufactured by JSR. The results are shown in Tables 2 and 3.

Example 4
An electrode and an electric double layer capacitor were produced and evaluated in the same manner as in Example 1 except that the configuration of the conductive adhesive was changed as shown in Table 1. The results are shown in Tables 2 and 3.

Example 5
An electrode and an electric double layer capacitor were produced and evaluated in the same manner as in Example 1 except that the configuration of the conductive adhesive was changed as shown in Table 1. In addition, the carbon material used in Example 5 has an ash content of 0.05%, an average particle size of 10 μm, natural flake graphite (“graphite powder” manufactured by Hitachi Powder Metallurgy), and an ash content of 0.02%, an average particle size. (Primary particle size): 35 nm acetylene black (“Denka Black” manufactured by Denki Kagaku Kogyo). The results are shown in Tables 2 and 3.

Example 6
An electrode and an electric double layer capacitor were produced and evaluated in the same manner as in Example 1 except that the configuration of the conductive adhesive was changed as shown in Table 1. The results are shown in Tables 2 and 3.

Example 7
An electrode and an electric double layer capacitor were produced and evaluated in the same manner as in Example 1 except that the configuration of the conductive adhesive was changed as shown in Table 1. The results are shown in Tables 2 and 3.

Comparative Example 1
For the conductive adhesive, an electrode and an electric double layer capacitor were produced in the same manner as in Example 1 except that only acetylene black (“DENKA BLACK” manufactured by Denki Kagaku Kogyo) with an average particle diameter of 2 μm was used as the carbon material. And evaluated. The content of acetylene black is 20% by mass with respect to the total amount of the conductive adhesive. The results are shown in Tables 2 and 3.

Comparative Example 2
As for the conductive adhesive, carboxymethyl cellulose (“CMC Daicel” manufactured by Daicel Chemical Industries, Ltd.) was used instead of synthetic rubber (SBR), and natural scaly graphite having an average particle size of 4 μm was used as the carbon material. In the same manner as in Example 1, an electrode and an electric double layer capacitor were produced and evaluated. In addition, content of scaly graphite is 20 mass% with respect to electroconductive adhesive whole quantity. The results are shown in Tables 2 and 3. The comparative example 1 corresponds to the example of the above-mentioned Patent Document 1.

Comparative Example 3
About conductive adhesive, instead of synthetic rubber (SBR), thermosetting polyimide ("U-Vanice" manufactured by Ube Industries) is used, and natural scaly graphite with an average particle size of 4 μm is used for the carbon material. In the same manner as in Example 1, an electrode and an electric double layer capacitor were produced and evaluated. In addition, content of scaly graphite is 20 mass% with respect to electroconductive adhesive whole quantity. The results are shown in Tables 2 and 3.

FIG. 1 is a partially enlarged schematic sectional view showing an example of an electrode for an electric double layer capacitor of the present invention. FIG. 2 is a partially enlarged schematic sectional view showing another example of the electrode for an electric double layer capacitor of the present invention. FIG. 3 is a partially enlarged schematic cross-sectional view showing another example of the electrode for an electric double layer capacitor of the present invention. FIG. 4 is a schematic perspective view showing a configuration in which the electric double layer capacitor electrode of the present invention and a separator are combined. FIG. 5 is a schematic perspective view showing a state in which a plurality of components of the electric double layer capacitor are arranged side by side. FIG. 6 is a partially cutaway schematic perspective view showing the configuration of the electric double layer capacitor produced in the example (example of the present invention). FIG. 7 is a partially enlarged schematic cross-sectional view showing the configuration of a conventional electrode for an electric double layer capacitor.

Explanation of symbols

10, 10 ', 10 "Electric double layer capacitor electrode 11, 11' Current collector 12 Polarized porous sheet 12a Hole 13 Conductive intermediate layer 15 Separator

Claims (19)

A polarizable porous sheet made of a carbonaceous electric double layer forming material, a carbon material for ensuring conductivity and a constituent material containing a binder is disposed on at least one side of the current collector via a conductive intermediate layer. An electrode for an electric double layer capacitor integrated,
The electrode for an electric double layer capacitor, wherein the conductive intermediate layer contains synthetic rubber and two or more kinds of carbon materials having different particle diameters.   2. The electrode for an electric double layer capacitor according to claim 1, wherein the carbon material of the conductive intermediate layer contains flaky graphite.   2. The electrode for an electric double layer capacitor according to claim 1, wherein the carbon material for the conductive intermediate layer contains carbon black.   The electrode for an electric double layer capacitor according to any one of claims 1 to 3, wherein the synthetic rubber of the conductive intermediate layer is styrene-butadiene rubber.   The electrode for an electric double layer capacitor according to claim 4, wherein the styrene-butadiene rubber has a glass transition temperature of -5 to 30 ° C.   The conductive intermediate layer is formed using a conductive adhesive containing the carbon material, the synthetic rubber, and a dispersion medium, and the total carbon material is 3 to 30% by mass in the conductive adhesive. The electric double layer capacitor electrode according to any one of claims 1 to 5.   The electrode for an electric double layer capacitor according to claim 6, wherein the synthetic rubber is 7% by mass or less in the conductive adhesive.   The electrode for an electric double layer capacitor according to any one of claims 1 to 7, wherein the polarizable porous sheet has an average pore diameter of 0.1 to 5 µm and a porosity of 40 to 90%.   The said current collector is comprised from aluminum, The electrode for electric double layer capacitors in any one of Claims 1-8.   The electrode for an electric double layer capacitor according to any one of claims 1 to 9, wherein the current collector has a surface roughened. (A) a carbonaceous electric double layer forming material, a polarizable porous sheet comprising a constituent material including a carbon material and a binder for ensuring conductivity, and / or (B) a bonding surface of a current collector, (C) Applying a conductive adhesive containing synthetic rubber, two or more carbon materials having different particle diameters, and a dispersion medium,
Before the dispersion medium is dried, the current collector and the polarizable porous sheet are bonded together and pressed, so that a part of the non-volatile components of the conductive adhesive is removed from the pores of the polarizable porous sheet. A method for producing an electrode for an electric double layer capacitor, characterized by being press-fitted into the inside.   It has an electrode for electric double layer capacitors in any one of Claims 1-10, The electric double layer capacitor characterized by the above-mentioned. A polarizable porous sheet made of a carbonaceous electric double layer forming material, a carbon material for ensuring conductivity and a constituent material containing a binder is disposed on at least one side of the current collector via a conductive intermediate layer. A conductive adhesive for forming the conductive intermediate layer used in the electrode for an electric double layer capacitor formed by integration,
A conductive adhesive comprising two or more carbon materials having different particle diameters, a synthetic rubber, and a dispersion medium.   The conductive adhesive according to claim 13, wherein the carbon material includes flaky graphite.   The conductive adhesive according to claim 13 or 14, wherein the carbon material contains carbon black.   The conductive adhesive according to any one of claims 13 to 15, wherein the synthetic rubber is styrene-butadiene rubber.   The conductive adhesive according to claim 16, wherein the styrene-butadiene rubber has a glass transition temperature of -5 to 30 ° C.   The conductive adhesive according to any one of claims 13 to 17, wherein the total carbon material is 3 to 30% by mass in the conductive adhesive. The conductive adhesive according to claim 18, wherein the synthetic rubber is 7% by mass or less in the conductive adhesive.