JP4832342B2 - Solid electrolytic capacitor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a winding type solid electrolytic capacitor using a conductive polymer as a solid electrolyte and a solid electrolytic capacitor for surface mounting.

In recent years, with the digitization of electronic devices, electrolytic capacitors are also required to have a large capacity and a small size, and further reduction of impedance in a high frequency region is required.
Solid electrolytic capacitors are attracting attention because of their excellent frequency characteristics among electrolytic capacitors, and are mainly used as anodes by forming a chemical conversion film on valve metals such as aluminum and tantalum.

  As a typical structure of a solid electrolytic capacitor using aluminum as an electrode foil, a monomer element is formed on a capacitor element in which a anodic aluminum conversion foil having a dielectric oxide film formed thereon and a cathode aluminum conversion foil are opposed to each other and wound through a separator paper. And an oxidizing agent impregnated and housed in an aluminum case or a synthetic resin case and sealed.

  The solid electrolytic capacitor is small and can have a large capacity, and is widely used. In addition, polypyrrole, polythiophene, polyaniline, and the like are used as the electrolyte, but polyethylenedioxythiophene is mainly used for the purpose of reducing ESR (equivalent series resistance).

  The above-mentioned solid electrolytic capacitor is small, has a large capacity, has a small ESR, and has characteristics such as being suitable for surface mounting because it can be easily made into a chip. It is indispensable for costing.

  However, in the solid electrolytic capacitor, tan δ (dielectric loss) and ESR are affected by the state of interfacial adhesion between the formed solid electrolyte and the cathode foil. Therefore, when the formation state of the solid electrolyte is not dense, the adhesion area between the solid electrolyte and the cathode foil is reduced, tan δ (dielectric loss) is increased, and the degree of adhesion with the solid electrolyte is also reduced, so that ESR is also reduced. It will rise.

  Further, when a valve metal is used for the cathode foil of the solid electrolytic capacitor, the capacitor capacity is determined by the dielectric constant of the oxide film of the valve metal, the opposing area of the dielectric and the cathode, and the combined capacity of the anode and the cathode. Even when a high-capacity cathode is used, the combined capacity does not exceed the capacity value of the anode, so there is a limit to increasing the capacity. In addition, a capacitor having a high capacity achievement rate cannot be obtained even when a dense and high yielding conductive polymer layer cannot be formed.

  In order to solve these problems, by forming a film made of a metal nitride such as TiN, ZrN, TaN or NbN, a valve metal such as Ti, Zr, Ta or Nb on the cathode foil, the capacity appearance rate is reduced. Improved technology (see Patent Literature 1), (see Patent Literature 2) and technology in which a cathode is coated with a carbon-based material by vacuum deposition (see Patent Literature 3), or applying and drying carbide particles on a cathode foil After that, a technique of generating whiskers on the cathode foil (see Patent Document 4) is also introduced. That is, in these techniques, an oxide film is not formed on the aluminum cathode foil, and the capacitance value of only the cathode foil gradually approaches almost infinite.

(Where C is the combined capacitance of the solid electrolytic capacitor, Cc is the capacitance of the cathode foil, and Ca is the capacitance of the anode foil)
As shown, the capacitance of the solid electrolytic capacitor in this case is the capacitance of only the anode foil, which is drastically improved over the capacitance of the conventional solid electrolytic capacitor.
JP 2000-114108 A JP 2000-114109 A JP 2001-196270 A JP 2006-93347 A

  However, in the techniques of Patent Documents 1 and 2, metal nitrides, valve metals, etc. are expensive, and it is necessary to use a physical vapor deposition (PVD) method, which is a pretreatment to the cathode foil and a complicated operation. For this reason, there is a problem that the cost merit becomes worse. Also, by using PVD, it is extremely difficult to control the thickness of the metal nitride layer on the cathode foil.

  Further, even if the technique of Patent Document 3 is used, the ESR can be reduced because the interface resistance between carbon and metal is increased only by coating the carbon-based material without removing the natural oxide film on the cathode metal surface. I can't plan. Furthermore, since the coated carbon-based material is easily peeled off, there is a problem that characteristic deterioration proceeds with long-term use.

  Further, the technique of Patent Document 4 has a problem that the carbide particles held by the whisker are decomposed on the cathode foil holding the carbide particles by a long-term heat test, and the characteristic deterioration is severe. In solid electrolytic capacitors using polyethylenedioxythiophene formed by polymerization reaction of monomer and oxidant as an electrolyte, carbide particles are obtained by vapor phase soldering test (VPS test) performed at a temperature range of 200 to 280 ° C. The decomposition product of the high temperature decomposition of the catalyst promotes the decomposition of the oxidizing agent contained in the polyethylenedioxythiophene, and the characteristic deterioration due to the increase in the internal pressure of the sealed container due to the generated gas or the like occurs.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a solid electrolytic capacitor having high heat resistance and a large capacity.

The solid electrolytic capacitor according to the present invention, viewed contains a capacitor element in which the anode body and the cathode body having a dielectric film is wound through a separator, a conductive high between the cathode body and the anode body in the solid electrolytic capacitor solid electrolyte comprising a molecule or TCNQ complex salt is formed, before Kikage polar body, characterized that you have carbon nanotubes is formed on the surface.

More preferably, the carbon nanotube is characterized that you have made form by chemical vapor deposition on the surface of the cathode body.

More preferably, the conductive polymer is formed by polymerization reaction of a monomer and an oxidizing agent, wherein the oxidizing agent is characterized in that an aromatic sulfonic acid metal salt or alkylsulfonic acid metal salt.

The manufacturing method of solid electrolytic capacitor according to the present invention is a manufacturing method of a solid electrolytic capacitor comprising a step of forming a carbon nanotube in cathode body, forming a carbon nanotube on the cathode body, forming a step of forming a surface anodization to oxide film etching aluminum foil, and forming pores the oxide film by etching, the carbon nanotubes in the pores and in the oxide film surface of said oxide film a step of, characterized in that it comprises a step of removing the oxide film of the cathode body, wherein the carbon nanotubes are formed.

  In the cathode foil of the solid electrolytic capacitor according to the present invention, multi-walled carbon nanotubes (MWCNT) showing high electrical conductivity are grown directly from a valve metal substrate, for example, an aluminum foil. The anchoring effect of the cathode foil on the solid electrolyte layer by the multi-walled carbon nanotube (MWCNT) of the cathode foil strengthens the adhesion at the cathode foil / solid electrolyte layer interface. As a result, the interface resistance between the cathode foil and the solid electrolyte layer is reduced, and tan δ (dielectric loss) and ESR can be reduced.

Hereinafter, the best mode for carrying out the present invention will be described.
The base material used for the cathode foil is not particularly limited as long as it is a valve metal that forms an oxide film by anodic oxidation such as aluminum, tantalum, niobium, etc. It is preferable to use aluminum which is relatively easy to control the growth of the nanotube (MWCNT). In addition, aluminum may be an untreated smooth foil or an etching foil that has been roughened by a chemical polishing treatment, but the latter is preferred in order to increase the number of multi-walled carbon nanotubes (MWCNT) grown. . In this case, the thickness of the cathode foil is preferably about 20 μm to 200 μm.

  As for the multi-walled carbon nanotube (MWCNT) formed on the cathode foil surface, a scanning electron micrograph is shown in FIG. FIG. 5 shows a conceptual diagram of a synthesis and precipitation scheme of multi-walled carbon nanotubes (MWCNT) according to the present invention, which will be described below.

  An etched aluminum foil having a thickness of 50 μm is anodized in 20 wt% sulfuric acid at 20 V for 2 hours to form an anodized film on the surface of the cathode foil as shown in FIG. Next, the aluminum oxide film is removed by immersion in 20 wt% sulfuric acid for 1 hour, whereby an oxide film having a pore diameter of 30 nm and a film thickness of 70 μm can be obtained as shown in FIG.

  The cathode foil (aluminum foil) obtained as described above is put into a reaction furnace at 800 ° C., and hydrocarbon gas is introduced. At this time, the hydrocarbon gas is decomposed at a high temperature to obtain multi-walled carbon nanotubes (MWCNT) with high electrical conductivity.

  In this case, the types of hydrocarbon gas include, for example, paraffinic hydrocarbons such as methane, ethane, propane, n-butane, isobutane and pentane, olefinic hydrocarbons such as ethylene, propylene, butene and butadiene, and acetylene. Examples thereof include acetylene hydrocarbons and derivatives of these hydrocarbons. Among these hydrocarbons, olefinic hydrocarbons such as ethylene, propylene, butene, and butadiene are preferable because they are gasified at a high temperature to obtain multi-walled carbon nanotubes (MWCNT) having relatively high electrical conductivity.

  More preferable is any one of methane, ethane and propane, and the most preferable hydrocarbon is industrially inexpensive propylene.

  Multi-walled carbon nanotubes (MWCNTs) obtained by chemical vapor deposition as described above are deposited on the outer surface of the oxide film and the inner wall of the pores. The surface of the oxide film has a strong catalytic action on carbon and the like, and therefore, multi-walled carbon nanotubes (MWCNT) can be uniformly deposited on the inner walls of the pores in the nanospace inside the oxide film pores.

  When the multi-walled carbon nanotube (MWCNT) / oxide film / aluminum foil thus formed is immersed in a dilute acid solution such as 0.02% phosphoric acid for 2 hours to remove the oxide film, the multi-walled carbon nanotubes deposited are removed. (MWCNT) will remain. In other words, when the multi-walled carbon nanotubes (MWCNT) are uniformly deposited on the inner walls of the linear pores and the anodized film is removed, the multi-walled carbon nanotubes (SEM) shown in FIG. MWCNT) is deposited on the cathode foil.

  Further, FIG. 4 shows a transmission electron microscope image of the multi-walled carbon nanotube (MWCNT), and the pore diameter is preferably 10 to 500 μm. In addition, the anchor effect of the cathode foil on the solid electrolyte layer by the multi-walled carbon nanotubes (MWCNT) acts effectively, improving the bonding strength between the cathode foil and the solid electrolyte layer and reducing the interface resistance.

  Next, examples of the conductive polymer layer that is a solid electrolyte layer formed between the anode and the cathode include polyethylenedioxythiophene-based, polypyrrole-based conductive polymers, or TCNQ complex salts. Polyethylene dioxythiophene obtained by polymerizing 1,4-ethylenedioxythiophene is more preferable because it can lower the ESR.

Examples of the oxidizing agent for thermal polymerization include aromatic sulfonic acids such as p-toluenesulfonic acid, p-methoxybenzenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, etc. As the transition metal constituting the metal salt portion of the oxidant, the metal salt of the alkyl sulfonic acid of, iron (III), copper (II), chromium (VI), cerium (IV), manganese (VII), zinc In particular, an oxidizing agent solution which is a metal salt of iron (III) is used, such as (II). Furthermore, it is preferable to use a mixed oxidant mixed with an oxidant because the dopant in the conductive polymer is stabilized and the heat resistance is improved.

  The solvent of the oxidizing agent may be ethanol or a mixed solvent of ethanol and an alcohol having 1 or more carbon atoms, but the solute concentration of the oxidizing agent is preferably 40 wt% to 70 wt%. When the solute concentration of the oxidizing agent is less than 40 wt%, a polymer film having sufficient conductivity cannot be obtained in capacitor production. When the solute concentration of the oxidizing agent is larger than 70 wt%, the oxidizing agent is precipitated and precipitated in the solution, which is not preferable as the oxidizing agent solution.

(Example 1)
Examples of the present invention will be described. FIG. 1 is a perspective view of a capacitor element of a solid electrolytic capacitor according to the present invention, and FIG. 2 is a sectional view of the solid electrolytic capacitor according to the present invention.

  As shown in FIG. 1, the anode foil 3 was obtained by subjecting the aluminum foil to an etching treatment and then a chemical conversion treatment at 5 V.

  As shown in FIG. 5, the cathode foil 2 is formed by anodizing an etched aluminum foil having a thickness of 50 μm in 20 wt% sulfuric acid at 20 V for 2 hours, and then dipping in 20 wt% sulfuric acid for 1 hour to form an aluminum oxide film. By removing, an oxide film having a pore diameter of 30 nm and a film thickness of 70 μm can be obtained as shown in FIG.

  The cathode foil (aluminum foil) obtained as described above was put into a reaction furnace at 800 ° C., and hydrocarbon gas was introduced to obtain multi-walled carbon nanotubes (MWCNT) on the cathode foil. .

  At this time, the pore diameter of the multi-walled carbon nanotube (MWCNT) deposited on the cathode foil was 20 μm from the analysis of the transmission electron microscope (TEM) image in FIG.

The anode foil 3 and the cathode foil 2 obtained by the above method are opposed to each other, and the anode foil 3 and the cathode foil 2 are formed in a cylindrical shape via a separator paper 4 made of electrolytic paper mainly composed of Manila hemp. A winding capacitor element 1 was formed.
Here, 6 is a lead tab terminal, 7 is an anode lead wire, and 8 is a cathode lead wire.

  Thereafter, the capacitor element 1 is subjected to cut formation and heat treatment at 280 ° C. with a solution having an ammonium adipate concentration of 1 wt%.

  Next, the capacitor element 1 is impregnated with 3,4-ethylenedioxythiophene as a polymerizable monomer and 50 wt% of p-toluenesulfonic acid ferric ethanol solution as an oxidant solution, and thermally polymerized at 280 ° C. Thus, a conductive polymer layer was formed between both electrodes of the capacitor element 1.

  Next, a rubber packing 10 for sealing shown in FIG. 4 is inserted into the capacitor element 1 and stored and fixed in an aluminum case 9 having a dimension φ8 × 11.5 mm, and then the opening of the aluminum case 9 is curled with a horizontal diaphragm. Sealing is performed, and then an aging process is performed.

  Next, a plastic seat plate 11 was inserted into the curled surface of the capacitor as shown in FIG. 2, and the capacitor lead wires 7 and 8 were pressed and bent as electrode terminals to complete a solid electrolytic capacitor.

  In addition, the nonwoven fabric etc. which have PET (polyethylene terephthalate), vinylon, an aramid fiber as a main component can also be used for a separator.

(Comparative Example 1)
In Comparative Example 1, a solid electrolytic capacitor was produced under the same conditions as in Example 1 except that a low conversion voltage high-magnification etched aluminum foil having a thickness of 50 μm was used as the cathode foil by etching the aluminum foil. .

(Comparative Example 2)
In Comparative Example 2, as a cathode foil, a low conversion voltage high-magnification etched aluminum foil having a thickness of 50 μm is subjected to ion plating, which is a PVD technique, and carbon that becomes a graphite-like carbon (GLC) film on the surface thereof. A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the thickness of the system coating layer was 1.0 μm.
The deposition conditions for ion plating at this time are as follows.
Deposition condition time: 2h
Temperature: 200 ° C
In-apparatus pressure: P = 2 × 10 ⁻² Torr
Target: Amorphous carbon The rated voltage of Example 1 and Comparative Examples 1 and 2 is 4 WV, the capacitance of the solid electrolytic capacitor at a frequency of 120 MHz, the ESR at a frequency of 100 kHz, and the leakage current at 2 minutes after application of the rated voltage. Values are shown in Table 1. 50 solid electrolytic capacitors of Example 1 and Comparative Examples 1 and 2 were prepared, and the average value thereof is shown in Table 1.

  In addition, after vapor phase soldering (VPS) test (230 × 75 seconds × 2 times), a voltage of 4V is applied at 125 ° C atmosphere, and the change in the capacitance value after the load heat test after 1000 hours is

(However, C0 is the initial capacitance, C is the capacitance value of the vapor phase soldering test)
Indicated by

 As is clear from Table 1, when Example 1, Comparative Example 1, and Comparative Example 2 are compared, a cathode foil having multilayer carbon nanotubes (MWCNTs) deposited by chemical vapor deposition is used. Compared to Comparative Example 1 (graphite-like carbon (GLC) as the cathode foil) in Comparative Example 1 (cathode foil is etched only), the solid electrolytic capacitor has a significantly larger capacity and higher heat resistance. We were able to.

  Further, in Example 1, when the capacitor element was disassembled after the load heat resistance test, no peeling or dropping of the conductive polymer was observed from the aluminum cathode foil which is the base material of the multi-walled carbon nanotube (MWCNT).

    The present invention makes it possible to provide a high heat resistance and large capacity solid electrolytic capacitor that will be required in the future market.

  In the embodiment of the present invention, an etched aluminum foil is used for the electrode foil, and a polythiophene-based conductive polymer is used for the electrolyte, but a plain (unetched) aluminum foil is used for the electrode foil. The same effect can be obtained by using polypyrrole-based or polyaniline-based conductive polymer or TCNQ complex salt in the electrolyte.

  In this example, the surface mount type winding capacitor is shown. However, since the same effect can be obtained for the radial type and the multilayer type capacitor, the embodiment of the electrolyte and capacitor should not be reduced.

Capacitor element perspective view in a solid electrolytic capacitor according to the present invention Sectional view of a solid electrolytic capacitor according to the present invention Scanning electron microscope image of MWCNT deposited on cathode foil according to the present invention Transmission electron microscope image of MWCNT cross section Schematic diagram of MWCNT synthesis / deposition scheme according to the present invention (a) State of oxide film formation on cathode foil, (b) State after oxide film etching on cathode foil, (c) State of oxide film on cathode foil MWCNT formation state, (d) MWCNT formation state after oxide film removal

Explanation of symbols

1 Capacitor element, 2 Cathode foil, 3 Anode foil, 4 Separator paper, 5 Winding tape, 6 Lead tab terminal, 7 Anode lead wire, 8 Cathode lead wire, 9 Aluminum case, 10 Sealing rubber packing, 11 Seat plate , 12 electrode terminals, 13 oxide film, 14 pores,
15 Multi-walled carbon nanotube (MWCNT)

Claims (4)

Look containing a capacitor element and the anode body and the cathode body having a dielectric film is wound through a separator, solid electrolyte made of a conductive polymer or TCNQ complex salt between the cathode body and the anode body is In the formed solid electrolytic capacitor,
Before Kikage polar body, a solid electrolytic capacitor characterized that you have carbon nanotubes is formed on the surface. The carbon nanotubes, solid electrolytic capacitor according to claim 1, characterized that you have made form by chemical vapor deposition on the surface of the cathode body. The conductive polymer is formed by a polymerization reaction between a monomer and an oxidizing agent ,
The oxidizing agent is a solid electrolytic capacitor according to claim 1 or 2, characterized in that an aromatic sulfonic acid metal salt or alkylsulfonic acid metal salt. A method of manufacturing a solid electrolytic capacitor comprising a step of forming a carbon nanotube in cathode body,
The step of forming carbon nanotubes on the cathode body includes:
Forming an oxide film by anodizing the surface of the etched aluminum foil ;
Etching the oxide film to form pores ;
Forming carbon nanotubes in the pores of the oxide film and on the surface of the oxide film ;
And a step of removing the oxide film of the cathode body on which the carbon nanotubes are formed.

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