JP2011216510A - Electrode for capacitor and capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a capacitor, with low risk of the short-circuit of the electrodes with each other.SOLUTION: In the electrode for the capacitor using a metal porous body as a collector, the peripheral edge part of the electrode is compressed in the thickness direction. It is preferable that the metal porous body is iron, nickel or the alloy or solid solution of iron or nickel and at least one kind of metals among Fe, Ni, Cr, Al and Ti, and the added metal is ≤40 wt.%.

Description

  The present invention relates to a capacitor electrode and a capacitor using the same.

  Electric double layer capacitors have recently attracted attention because of their large capacitance among various capacitors. For example, capacitors are widely used for memory backup of electrical equipment, and in recent years, the use of electric double layer capacitors has been promoted for this purpose as well. Further, it is expected to be used for vehicles such as hybrid vehicles and fuel vehicles.

  There are various types of electric double layer capacitors such as a button type, a cylindrical type, and a square type, and various types of capacitors are known. The button type is, for example, a pair of polarizable electrodes with an activated carbon electrode layer provided on a current collector, and a separator is arranged between the electrodes to form an electric double layer capacitor element, which is stored in a metal case together with an electrolyte. It is manufactured by sealing with a sealing plate and a gasket that insulates both. For the cylindrical type, this pair of polarizable electrodes and separator are overlapped and wound to form an electric double layer capacitor element. The element is covered with an electrolytic solution and stored in an aluminum case, and sealed with a sealing material. It is manufactured by doing. The basic structure of the square type is the same as that of the button type or cylindrical type.

  The electric double layer capacitor used for the above-mentioned applications such as memory backup and automobile is required to have a higher capacity. That is, it is required to increase the capacity per unit volume and reduce the internal resistance. For this reason, various types of current collectors constituting the electrodes have been proposed.

  For example, a metal current collector using aluminum, stainless steel, etc., a stainless steel fiber mat electrically welded to a stainless steel foil, or a porous body made of at least one metal selected from tantalum, aluminum and titanium Is known (patent documents 1 to 3).

  It has also been attempted to make the current collector a porous body (three-dimensional structure) instead of a metal foil. For example, an electrode is prepared by applying an electrode material to foamed nickel (Patent Document 4). For this electrode, cermet is used as a current collector instead of aluminum foil, and the cross section has a two-layer structure. In addition, it is known that a foam metal current collector is immersed in an activated carbon paste, dried and rolled to obtain an electrode (Patent Document 5). The electrode has a thickness of 1.0 mm when the activated carbon paste is filled, and is then rolled and adjusted to have an electrode thickness of 0.5 mm.

  However, the conventional current collector as described above has a high risk that the skeleton of the porous metal body touches the electrode facing through the separator and short-circuits.

Japanese Patent Laid-Open No. 11-274012 JP 09-232190 A Japanese Patent Laid-Open No. 11-150042 Japanese Patent No. 3252868 Japanese Examined Patent Publication No. 62-37807

  In view of the above problems, an object of the present invention is to provide a capacitor electrode that has a low risk of short circuit between electrodes.

  As a result of intensive investigations to solve the above problems, the present inventors have found that the edge of the electrode and the skeleton of the metal porous body at the corner are likely to cause a short circuit due to passing through the separator. And it discovered that it was effective to compress the peripheral part of an electrode in the thickness direction previously, and completed this invention.

The configuration of the present invention is as follows.
(1) An electrode for a capacitor using a metal porous body as a current collector, wherein the peripheral portion of the electrode is compressed in the thickness direction.
(2) The metal porous body is iron, nickel, or an alloy or solid solution of one or more kinds of metals of Fe, Ni, Cr, Al, and Ti with iron or nickel, and the added metal is 40 The capacitor electrode as described in (1) above, which is not more than% by weight.
(3) The capacitor electrode according to (1) or (2) above, wherein the metal basis weight of the porous metal body is 100 g / m ² or more and 450 g / m ² or less.
(4) A capacitor using the capacitor electrode according to any one of (1) to (3) above.

  The main cause of the short circuit is the penetration of the separator at the electrode edge portion. By compressing the peripheral portion of the electrode in the thickness direction in advance, the penetration of the separator at the edge portion can be prevented.

It is a figure showing an example of the structure of the electrode for capacitors concerning this invention.

The capacitor electrode according to the present invention is characterized in that the peripheral edge of the electrode is compressed in the thickness direction. When manufacturing the capacitor, the risk of short-circuiting the capacitor can be eliminated by compressing the peripheral edge of the electrode in the thickness direction.
The capacitor electrode and the capacitor according to the present invention will be described in detail below for each constituent member.

(Current collector)
A porous metal body can be obtained by coating a base material such as urethane foam or nonwoven fabric with a metal, and then heat-treating the resin in a reducing atmosphere after burning out the resin. Metal coating can be coated to a predetermined amount of metal by electroplating after imparting conductivity by applying sputtering or chemical plating to the base material, or applying conductive paint and drying. It is.

  When used for a positive electrode of a non-aqueous capacitor, it is necessary to improve corrosion resistance because it corrodes with a metal such as iron or nickel. In order to give the current collector corrosion resistance, it is preferable to add Al, Cr, Ti or the like. A metal porous body having high corrosion resistance can be obtained by alloying by a powder pack method or a CVD method. At this time, it is preferable that the total amount of the metal added does not exceed 40 wt% by weight ratio after alloying. If the amount added is too large, the electrical resistance of the current collector becomes high, and the current collecting performance is lowered.

  Examples of the structure include a foamed structure and a nonwoven fabric structure, but a foamed structure that is excellent in current collection and active material holding ability is preferable. If the foam structure is fine, the filling capacity of the active material is deteriorated. Conversely, if the foam structure is coarse, the active material holding ability is lowered. Therefore, a foam structure in which the number of cells per inch is about 40 to 100 cells is preferable. . When using a nonwoven fabric structure, it is preferable that the length of the fiber used is sufficiently longer than the thickness of the nonwoven fabric. If a too short fiber is used, a structure in which the skeleton protrudes not only from the edge portion but also from the entire electrode, and the risk of a short circuit is increased.

The porous metal body is iron, nickel, or an alloy or solid solution of one or more of iron, nickel, and Fe, Ni, Cr, Al, or Ti, and the added metal is 40 wt% or less. It is preferable that
When the metal porous body is used as a positive electrode of a non-aqueous capacitor, it corrodes with iron or nickel, so it is necessary to add a different metal to enhance corrosion resistance.

Further, the metal basis weight is greatly related to the electrical resistance and the strength of the base material. If the metal basis weight of the metal porous body is too small, both the current collecting performance and the strength of the base material are remarkably lowered, and the electric resistance is increased and the shape of the electrode cannot be maintained. For this reason, the metal basis weight must be 100 g / m ² or more. However, if the amount of the metal is excessive, the porosity of the base material is lowered and the filling property of the active material is lowered, so that the capacity of the capacitor is lowered and the strength of the skeleton is increased and the short circuit easily occurs. For this reason, the metal basis weight is preferably 450 g / m ² or less.

(Activated carbon paste)
An activated carbon paste was prepared by adding a conductive additive, a thickener (if necessary when the viscosity of the solvent is low), a binder and a solvent to the activated carbon powder and stirring with a mixer.
The activated carbon activation method and the raw material are not particularly limited, but the larger surface area is better, and the specific surface area measured by the nitrogen adsorption BET method is preferably 2000 m ² / g or more. In addition, the smaller the particle size of the activated carbon, the smaller the internal resistance of the capacitor. Therefore, the smaller the particle size, the better. The average particle size is preferably 10 μm or less, more preferably 5 μm or less. Furthermore, in order to increase the capacity of the capacitor, it is better that the amount of activated carbon in the activated carbon paste is large, and it is preferable that the activated carbon is 75 wt% or more in the composition ratio after drying (after solvent removal).

  As the conductive aid, ketjen black, acetylene black, carbon fiber, or a composite material thereof can be used. This is necessary because the internal resistance of the capacitor increases if the conductive additive is small. However, if the added amount is too large, the charged amount of activated carbon decreases and the capacity decreases. Therefore, the added amount is 2 wt% in terms of the composition ratio after drying. % To 15 wt% is preferable.

  As the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, styrene butadiene rubber or the like can be used. Since the binder also causes an increase in internal resistance, the amount is preferably as small as possible. However, if the amount is too small, the activated carbon peels from the current collector, so the amount used is preferably 2 wt% or more and 15 wt% or less.

  As the solvent, water or an organic solvent may be appropriately selected depending on the kind of the binder. In organic solvents, N-methylpyrrolidone is often used. Moreover, when using water for a solvent, you may use surfactant in order to improve a filling property.

  Moreover, when using water for a solvent, it is preferable to add a thickener. Water alone will cause insufficient dispersion of the activated carbon, leading to uneven filling of the electrodes. As the thickener, carboxymethylcellulose, xanthan gum and the like can be used. The amount used is preferably 2 wt% or less after drying.

(Thickness of current collector)
The obtained current collector is adjusted to an optimum thickness by a press machine. The press machine is a flat plate press or a roller press. A flat plate press is preferable for suppressing the elongation of the current collector, but is not suitable for mass production, and a roller press capable of continuous processing can also be used.

(Compression of current collector periphery)
In order to prevent a short circuit, the periphery of the current collector is compressed in the thickness direction. The compression width is preferably 5 mm or less because the portion penetrates the separator if it is too long. It is possible to compress it excessively as a space for welding the current collector lead later. The compression may be performed by a flat plate press using a mold matched to the size of the electrode, or may be performed by applying a roller having a width desired to be compressed. Moreover, although the activated carbon paste may be attached to the compressed part, since there is a possibility of peeling in the middle of the process, it is preferable to mask it so that it cannot be filled.
The compressed portion is preferably located near the center of the electrode in the thickness direction. Moreover, it is preferable that the thickness of the compressed part is 0.1 mm or less, 0.08 mm or less is more preferable, and 0.05 mm or less is further more preferable. There is no particular lower limit to the thickness of the compressed portion, but it is preferably 0.01 mm or more because it cannot be compressed beyond the value determined from the density of the material.
In addition, you may perform compression of a peripheral part after preparation of an electrode.

(Production of electrodes)
The activated charcoal paste is filled into the adjusted current collector. It can also be filled by spraying a paste from one side of the current collector, immersing the current collector in the paste, or using a printing machine or roll coater. Next, the solvent is removed with a dryer. The drying temperature is preferably 80 ° C. or higher. However, if the temperature is too high, the current collector may be oxidized or the thickener or binder may be decomposed.

  After drying, the electrode is obtained by compressing in the thickness direction with a press. As a press machine, a flat plate press or a roller press can be used. A flat plate press is preferable for suppressing the elongation of the current collector, but is not suitable for mass production, and a roller press capable of continuous processing can also be used. When using a roller press, you may devise control which suppresses elongation, such as embossing on the surface.

(Capacitor production)
A lead for current collection is welded to the obtained electrode. In order to secure a space for welding, the activated carbon at the welding point may be removed, or the space for welding may be compressed or masked in advance so as not to be filled. The lead material is preferably aluminum.

  When a non-aqueous electrolyte is used, the following operations from here must be performed in a dry atmosphere. When using a dry room or a dry box, the dew point is preferably −65 ° C. or lower. A glove box filled with an inert gas such as argon can also be used.

  Since the activated carbon easily adsorbs moisture, the electrode is further dried. It is preferable to dry at 180 ° C. or more and 250 ° C. or less for 8 hours or more under a reduced pressure environment of 10 kPa or less. Moreover, it is preferable to dry separately also the can used for a separator and an exterior, an aluminum laminate, etc.

  For the separator, a cellulose nonwoven fabric or a resin microporous membrane can be used. If the thickness is large, the internal resistance of the capacitor increases. If it is too thin, the risk of short-circuiting increases, so 30 μm or more and 100 μm or less is preferable. Moreover, since internal resistance becomes large also when porosity is small, it is preferable that there exists a porosity of 40% or more.

  Aluminum and stainless steel cans and aluminum laminate can be used for the exterior. When an aluminum laminate is used for the exterior, it is preferable that the current collecting lead has an insulating / sealing seal in order to prevent a short circuit or leakage at the bonding portion between the current collecting lead and the laminate.

An electrode group is obtained by stacking an electrode and a separator. There are a method in which electrodes and separators are alternately stacked, and a method in which elongated electrodes and separators are stacked and wound. What is necessary is just to take a method suitable for the exterior to be used.
The electrode group is put in the exterior and an electrolyte solution is injected. Thereafter, sealing is performed under a reduced pressure environment of 10 kPa or less.

  The electrolyte can be used for both aqueous and non-aqueous electrolytes, but the non-aqueous electrolyte is preferred because the voltage can be set higher. In an aqueous system, potassium hydroxide or the like can be used as an electrolyte. Many non-aqueous electrolytes are combinations of cations and anions, and lower aliphatic quaternary ammonium, lower aliphatic quaternary phosphonium, imidazolinium, and the like are used as cations. Tetrafluoroboric acid and hexafluorophosphoric acid are used as anions. The solvent of the organic electrolyte is a polar aprotic organic solvent, and specifically, ethylene carbonate, propylene carbonate, γ-butyrolactone, sulfolane and the like are used. Among these, a combination of tetraethylammonium borofluoride and propylene carbonate, which is a combination having low ionic conductivity, is preferable.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these.

[Example]
Urethane sheet (commercially available, number of cells: 55 cells / inch, thickness 1.4 mm, porosity 96%) after the nickel by sputtering 10 g / m ² coating, as the basis weight of the total is 200 g / m ² sulphamic Nickel plating was performed in an acid bath. Thereafter, urethane was incinerated and removed at 800 ° C. in the air, and then heated to 1000 ° C. in a reducing atmosphere (hydrogen) to reduce nickel to obtain foamed nickel. The produced foamed nickel had a cell number of 55 cells / inch, a thickness of 1.4 mm, and a porosity of 95%. Further, Cr was impregnated by a powder pack method in which this foamed nickel was filled with a penetrating material mixed with chromium powder and heated in a reducing atmosphere to finally obtain a Ni-Cr 35 wt% foamed current collector. . The metal basis weight was 330 g / m ² . The obtained current collector was adjusted to a thickness of 0.3 mm by a roller press and cut into 3 cm square.

  In order to prevent short circuit, 2 mm from the end of 3 sides and 5 mm from the end of 1 side were compressed as shown in FIG. 1 using a mold and a flat plate press. The press was weighted at 50 kg. The thickness of the compressed part was 0.045 mm.

2.0 g of activated carbon powder (specific surface area 2500 m ² / g, average particle size of about 3 μm), 0.3 g of ketjen black as a conductive aid, 5.0 g of a 0.5% aqueous solution of carboxymethyl cellulose as a thickener, binder As a mixture, 0.5 g of a 60 wt% aqueous dispersion of polytetrafluoroethylene was mixed, and 4.5 g of water was further added as a solvent, followed by stirring with a mixer to prepare an activated carbon paste. The composition ratio after drying and removing water was 77 wt% activated carbon powder, 11.6 wt% ketjen black, 1.7 wt% carboxymethylcellulose, and 9.7 wt% polytetrafluoroethylene.

  This activated carbon paste was filled in the current collector. Next, after drying with a dryer at 200 ° C. for 1 hour to remove the solvent, it was pressurized with a roller press having a diameter of 500 mm (slit: 100 μm). An Al tab lead was welded to a 5 mm compressed portion to obtain an electrode. The average thickness of the electrode was 0.2 mm, and the packing density of the activated carbon was 0.34 g / cc.

  This electrode was transferred to a dry room having a dew point of -72 ° C., and dried at 200 ° C. for 12 hours in a reduced pressure environment of 6 kPa. Two types of separators with a thickness of 30 μm and 60 μm were prepared. Aluminum laminate was prepared for the exterior. These were dried at 100 ° C. for 12 hours under 6 kPa separately from the electrodes.

  After completion of drying, the separator was sandwiched between electrodes, and the three sides of the laminate were heat-sealed. An electrolyte was injected from the remaining opening, and sealing was performed in a reduced pressure environment of 20 kPa to obtain a capacitor. As the electrolytic solution, 0.3 ml of propylene carbonate in which 1 mol / L tetraethylammonium borofluoride was dissolved was used per cell.

  A similar capacitor was prepared for each of the two types of separators by 20 cells, and the obtained capacitor was charged by applying a voltage of 2.5 V for 2 minutes, and the presence or absence of a short circuit was examined. As a result, no short circuit occurred regardless of the thickness of the separator (30 μm, 60 μm).

[Comparative example]
A capacitor was fabricated in the same manner as in Example, except that compression for preventing a short circuit was not performed and compression was performed with a width of 5 mm on only one side for tab lead welding. As a result of checking for the presence or absence of a short circuit after charging, the voltage of 12/20 cells did not increase at all from the initial stage, and the voltage of 6/20 cells did not increase by about 0.6 V or more. In the separator having a thickness of 60 μm, the voltage of 9/20 cells did not increase at all from the beginning, and the voltage of 4/20 cells did not increase by about 0.6 V or more.

  From the above, it has been clarified that the capacitor electrode of the present invention has an effect of preventing a short circuit.

Claims (4)

  An electrode for a capacitor using a metal porous body as a current collector, wherein the peripheral edge of the electrode is compressed in the thickness direction.   The metal porous body is iron, nickel, or an alloy or a solid solution of one or more of iron, nickel, and Fe, Ni, Cr, Al, or Ti, and the added metal is 40% by weight or less. The capacitor electrode according to claim 1, wherein: 3. The capacitor electrode according to claim 1, wherein a metal basis weight of the metal porous body is 100 g / m ² or more and 450 g / m ² or less.   A capacitor comprising the capacitor electrode according to any one of claims 1 to 3.

Images