JP4383226B2 - Solid electrolytic capacitor - Google Patents

Description

  The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same.

Conventionally, a solid electrolytic capacitor using a dielectric layer made of titanium oxide having a dielectric constant approximately 5 times larger than that of aluminum oxide is known (see, for example, Patent Document 1 and Patent Document 2). Here, the dielectric layer made of titanium oxide is formed by anodizing an anode made of a titanium metal plate or a sintered body of titanium powder.
JP-A-5-121275 Japanese Patent Laid-Open No. 11-312628

  However, in the conventional solid electrolytic capacitor in which the dielectric layer made of titanium oxide is formed by anodic oxidation as described above, the titanium oxide is easily crystallized during the anodic oxidation process, thereby reducing the insulating property of the dielectric layer. However, there is a problem that the leakage current between the anode and the cathode layer becomes large.

  In addition, titanium has higher mechanical strength than aluminum, so it is difficult to deform, and the anode cannot be wound in a spiral shape with a small radius of curvature like a conventional solid electrolytic capacitor using an aluminum foil as an anode. There was a bug. As a result, the anode area per volume of the solid electrolytic capacitor cannot be sufficiently increased, so that there is a problem that the capacity of the solid electrolytic capacitor cannot be increased.

The present invention has been made to solve the above problems,
One object of the present invention is to provide a solid electrolytic capacitor capable of reducing a leakage current between an anode and a cathode.

  In order to achieve the above object, a solid electrolytic capacitor according to one aspect of the present invention includes an anode having at least a surface made of titanium carbide, and a dielectric layer formed on the anode and made of titanium oxide.

  In the solid electrolytic capacitor according to this aspect, as described above, oxygen is difficult to diffuse in the titanium carbide on the surface of the anode, so that oxygen in the dielectric layer made of titanium oxide diffuses toward the anode. Can be suppressed. Thereby, since oxygen in the dielectric layer is difficult to decrease, a decrease in the thickness of the dielectric layer can be suppressed. As a result, it is possible to suppress a decrease in insulating properties of the dielectric layer, thereby reducing a leakage current between the anode and the cathode. The entire anode need not be made of titanium carbide, and a thin layer made of titanium carbide may be formed on the surface of a substrate made of a material other than titanium carbide.

  In the solid electrolytic capacitor according to the aforementioned aspect, the atomic ratio (C / Ti) of carbon (C) and titanium (Ti) in the anode is preferably in the range of 0.05-1. More preferably, the atomic ratio (C / Ti) of carbon (C) and titanium (Ti) in the conductor layer is in the range of 0.1 to 0.75. With this configuration, since the diffusion of oxygen from the dielectric layer to the anode can be sufficiently suppressed, it is possible to suppress a decrease in insulating properties of the dielectric layer, and easily between the anode and the cathode. Leakage current can be reduced.

  In the solid electrolytic capacitor according to the above aspect, the thickness of the dielectric layer is preferably in the range of 4 nm to 20 nm. More preferably, the thickness of the dielectric layer is in the range of 6 nm to 15 nm. When the thickness of the dielectric layer is small, sufficient insulation cannot be ensured, and when the thickness of the dielectric layer is large, the anodization time for forming the dielectric layer becomes long, Since the crystallization of titanium oxide easily proceeds during the process of anodizing, the insulating property of the dielectric layer is lowered. Therefore, by setting the thickness of the dielectric layer within the above range, the insulating property of the dielectric layer can be sufficiently increased.

  In the solid electrolytic capacitor according to the above aspect, preferably, the anode has an anode layer made of titanium carbide on a base made of metal foil. If comprised in this way, the dielectric layer which consists of a titanium oxide can be easily formed by anodizing the anode layer which consists of titanium carbide on a base | substrate. Furthermore, the anode can be easily deformed because the base is made of a metal foil. Therefore, for example, a cathode made of a metal foil and this anode can be overlapped with a separator interposed between them, and this can be wound into a roll. Thereby, since the anode area per volume in the solid electrolytic capacitor can be increased, the capacity can be increased.

  Hereinafter, the present invention will be described in more detail based on the embodiments. However, the present invention is not limited to the following embodiments, and can be appropriately modified and implemented without departing from the scope of the present invention. It is a thing.

  FIG. 1 is a partially broken side view of a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 2 is a partially developed perspective view of the capacitor element inside the solid electrolytic capacitor according to the embodiment of the present invention. FIG. 3 is a cross-sectional view of an anode of a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of a cathode of a solid electrolytic capacitor according to an embodiment of the present invention. With reference to FIGS. 1-4, the structure of the solid electrolytic capacitor by one Embodiment of this invention is demonstrated below.

  First, in a solid electrolytic capacitor 100 according to an embodiment of the present invention, as shown in FIG. 1, a capacitor element 2 is accommodated in a bottomed cylindrical case 1 made of aluminum or the like. The opening of the case 1 is filled with a sealing material 3 made of rubber, epoxy resin, or the like, whereby the opening of the case 1 is sealed. In addition, lead wires 4 and 5 extend from the capacitor element 2 through the sealing material 3.

  Referring to FIG. 2, the capacitor element 2 has a configuration in which a foil-like separator 23 made of paper or the like is sandwiched between an anode foil 21 and a cathode foil 22 and wound in a roll shape. Have. The lead wires 4 and 5 are connected to the anode foil 21 and the cathode foil 22, respectively.

  Referring to FIG. 3, anode foil 21 includes anode layers 21b and 21b made of titanium carbide formed on both surfaces of a base 21a made of aluminum foil or aluminum alloy foil having a thickness of several tens of μm to several hundreds of μm. , Dielectric layers 21c and 21c made of titanium oxide formed on the anode layers 21b and 21b, conductive polymers such as polypyrrole and polythiophene formed on the dielectric layers 21c and 21c, TCNQ (tetracyanoquinodi And electrolyte layers 21d and 21d made of an organic semiconductor such as a (methane) complex or manganese dioxide. Here, the aluminum foil or the aluminum alloy foil is an example of the “metal foil” in the present invention.

  Referring to FIG. 4, in cathode foil 22, a conductive polymer such as polypyrrole or polythiophene, TCNQ is formed on both surfaces of base 22 a made of aluminum foil or aluminum alloy foil having a thickness of several tens μm to several hundreds μm. Electrolyte layers 22d and 22d made of an organic semiconductor such as a (tetracyanoquinodimethane) complex and manganese dioxide are formed.

  Next, the manufacturing method of the solid electrolytic capacitor by one Embodiment of this invention is demonstrated.

  First, referring to FIG. 3, anode layers 21b and 21b made of titanium carbide are formed on both surfaces of a base 21a made of aluminum foil or the like in a vacuum by a method such as vapor deposition, sputtering, or ion plating. To do.

  Next, the anode foil 21 is anodized in an aqueous solution to form dielectric layers 21c and 21c made of titanium oxide on the anode layers 21b and 21b.

  Next, electrolyte layers 21d and 21d made of polypyrrole or the like are formed on the surfaces of the dielectric layers 21c and 21c by various polymerization methods or thermal decomposition methods. Thereby, anode foil 21 in which anode layers 21b and 21b, dielectric layers 21c and 21c, and electrolyte layers 21d and 21d are laminated in this order is formed on both surfaces of base 21a.

  Referring to FIG. 4, electrolyte layers 22d and 22d made of polypyrrole or the like are formed on both surfaces of base 22a made of aluminum foil or the like by various polymerization methods or thermal decomposition methods. Thereby, the cathode foil 22 in which the electrolyte layers 22d and 22d are formed on both surfaces of the base body 22a is formed.

  Next, referring to FIG. 2, after the lead wires 4 and 5 are attached to the anode foil 21 and the cathode foil 22, both sides of the cathode foil 22 are sandwiched with a foil-like separator 23 made of paper or the like. Anode foil 21 is overlaid on top of each other, and these are wound into a roll. Thereby, the capacitor element 2 is formed.

  Finally, referring to FIG. 1, this capacitor element 2 is accommodated in a bottomed cylindrical case 1 made of aluminum or the like, and a sealing material 3 made of rubber, epoxy resin or the like is provided in the opening of the case 1. By filling, the opening of the case 1 is sealed. With the above method, the solid electrolytic capacitor 100 according to one embodiment of the present invention is manufactured.

  In one embodiment of the present invention, since the anode layers 21b and 21b made of titanium carbide are formed on the surface of the base 21a as described above, oxygen in the dielectric layers 21c and 21c made of titanium oxide is the anode. The diffusion toward the layers 21b and 21b can be suppressed. Thereby, since oxygen in the dielectric layers 21c and 21c is difficult to decrease, a decrease in the thickness of the dielectric layers 21c and 21c can be suppressed. As a result, it is possible to suppress a decrease in the insulating properties of the dielectric layers 21c and 21c, so that the leakage current between the anode foil 21 and the cathode foil 22 can be reduced.

  In the embodiment of the present invention, as described above, since the anode foil 21 uses the base body 21a made of a metal foil, the anode foil 21 can be easily deformed. For example, as in the present embodiment, the separator 23 is sandwiched between the anode foil 21 and the cathode foil 22 and can be wound up in a roll shape, so that the anode area per volume in the solid electrolytic capacitor Can be increased. As a result, the capacity of the solid electrolytic capacitor can be increased.

  In the embodiment of the present invention, as described above, the bases 21a and 22a constituting the anode foil 21 and the cathode foil 22 are made of a conductive material such as an aluminum foil or an aluminum alloy foil. The foil 21 and the cathode foil 22 can be used as a current collector.

  In one embodiment of the present invention, a substrate made of a metal foil is used as the substrate 21a. However, the present invention is not limited to this, and a plate-shaped substrate may be used. The base | substrate which becomes may be sufficient. Since these substrates are generally difficult to deform and difficult to wind in a spiral shape with a small radius of curvature, when using a substrate of these shapes, a capacitor element includes an anode and a cathode as separators. A cathode layer formed by applying carbon paste or silver paste or the like on the dielectric layer on the surface of the anode can be formed directly between them.

  In the embodiment of the present invention, the electrolyte layers 21d and 21d are formed on the dielectric layers 21c and 21c in the anode foil 21, but the present invention is not limited to this, and the electrolyte layers 21d and 21d are formed. It may not be used.

  In the embodiment of the present invention, the cathode foil 22 has the electrolyte layers 22d and 22d formed on both surfaces of the foil-like substrate 22a. However, the present invention is not limited to this, and the electrolyte layers 22d and 22d are formed. It may not be used.

  In the following examples, a test electrolytic capacitor was produced, and the anode foil used in the above embodiment was evaluated.

Example 1
FIG. 5 is a structural diagram of a test electrolytic capacitor A according to Example 1 of the present invention. With reference to FIG. 5, the test electrolytic capacitor of Example 1 of the present invention and the manufacturing method thereof will be described below.

First, an anode layer 31b made of titanium carbide (TiC _0.5 ) having a thickness of about 30 nm was formed on the substantially entire surface of the base 31a made of an aluminum foil having a thickness of about 100 μm by sputtering. Thus, the anode 31 was formed. Here, the aluminum foil is an example of the “metal foil” in the present invention.

Next, the substrate 31a is anodized at a constant voltage of about 5 V for about 20 minutes in an aqueous solution of about 1% by weight ammonium adipate maintained at about 60 ° C., and an anode made of titanium carbide (TiC _0.5 ). A dielectric layer 31c having a thickness of about 10 nm and made of titanium oxide was formed on the layer 31b. In this way, the anode foil 31 in which the anode layer 31b made of titanium carbide and the dielectric layer 31c made of titanium oxide were laminated in this order on the surface of the base 31a made of aluminum foil was formed.

  Next, this anode foil 31 was heat-treated in air at about 300 ° C. for about 30 minutes.

  The anode foil 31 was immersed in an about 1 wt% adipic acid aqueous solution 33 held at about 60 ° C. in a stainless steel beaker 32 and the anode foil 31 and the beaker 32 were held so as not to contact each other. And the electrolytic capacitor A for a test of Example 1 was produced by using this beaker 32 as a cathode.

(Comparative Example 1)
In Comparative Example 1, a test electrolytic capacitor X was produced in the same manner as in Example 1 except that an anode layer made of titanium was formed instead of the anode layer 31b made of titanium carbide (TiC _0.5 ) in Example 1. did. That is, in the test electrolytic capacitor X, the anode layer made of titanium and the dielectric layer made of titanium oxide formed by anodic oxidation are formed in this order on the substantially entire surface of the substrate made of aluminum foil.

(Evaluation)
FIG. 6 is a diagram showing measurement results by ESCA (Electron Spectroscopy for Chemical Analysis) of the anode foil 31 used in the test electrolytic capacitor A according to Example 1 of the present invention. In FIG. 6, the vertical axis represents the element content in the anode foil 31, and the horizontal axis represents the sputtering time in ESCA measurement. The sputtering time corresponds to the position in the thickness direction of the capacitor, and the sputtering depth per minute of the sputtering time is about 1 nm.

  As shown in FIG. 6, the anode foil 31 of the test electrolytic capacitor A of Example 1 has a thickness of about 10 nm due to the distribution of oxygen (O), and the dielectric layer 31c made of titanium oxide is an anode foil. It was found that it was formed on the surface of 31. Further, in FIG. 6, the region where oxygen (O) located on the right side of the dielectric layer 31c in the drawing hardly exists and carbon (C) exists is an anode layer 31b made of titanium carbide. FIG. 6 indicates that the atomic ratio (C / Ti) of carbon (C) and titanium (Ti) in the anode layer 31b made of titanium carbide is about 0.5.

  The dielectric layer 31c also contains carbon (C), and the atomic ratio (C / Ti) between carbon (C) and titanium (Ti) in the dielectric layer 31c is about 0.5. I found out. It is considered that carbon (C) in the dielectric layer 31c is diffused from the anode layer 31b made of titanium carbide. It was also found that the concentration of oxygen (O) decreased from the dielectric layer 31c toward the anode layer 31b.

  Similarly, the anode and dielectric layer of the test electrolytic capacitor X of Comparative Example 1 were also measured by ESCA. As a result, it was found that in the test electrolytic capacitor X of Comparative Example 1, the anode and the dielectric layer contained titanium and oxygen, but almost no carbon was observed. From this, it was found that the anode layer made of titanium on the anode of the test electrolytic capacitor X of Comparative Example 1 did not contain carbon, and the dielectric layer did not contain carbon.

  Next, for each test electrolytic capacitor of Example 1 and Comparative Example 1, as shown in FIG. 5, the voltage applied to the anode foil 31 and the beaker 32 is about ½ of the voltage applied during anodization, that is, about 2 The leakage current between the anode foil 31 and the cathode (beaker 32) of the test electrolytic capacitor A of Example 1 was measured by applying a constant voltage of .5V and measuring the leakage current after about 20 seconds. . These results are shown in Table 1. In Table 1, the measurement results of leakage current between the anode and the cathode of each test electrolytic capacitor of Example 1 and Comparative Example 1 were normalized with the measurement result of Example 1 as 100, and the standardized leakage The current value is shown.

As shown in Table 1, it was found that the test electrolytic capacitor X of Comparative Example 1 produced a leakage current five times or more that of the test electrolytic capacitor A of Example 1. Thereby, in the electrolytic capacitor A for a test of Example 1, it became clear that the leakage current was reduced by the anode layer 31b made of titanium carbide in the anode foil 31.

(Example 2)
In Example 2, the correlation between the composition of the anode layer made of titanium carbide of the present invention and the leakage current between the anode foil and the cathode was verified.

Here, in Example 2, carbon (C) and titanium (Ti) in the anode layer were changed by changing the sputtering conditions when forming the anode layer in the production of the test electrolytic capacitor A of Example 1 above. The atomic ratio (C / Ti) of about 0.03, about 0.05, about 0.1, about 0.25, about 0.5, about 0.75, about 0.9, about 1, about 1 1. An anode layer made of titanium carbide (TiC _X ) was prepared, and the other test electrolytic capacitors B1 to B8 were prepared in the same manner as the test electrolytic capacitor A of Example 1 above.

(Evaluation)
For the electrolytic capacitors B1 to B8 for testing of Example 2, the anode foil was measured by ESCA in the same manner as in Example 1. As a result, in the test electrolytic capacitors B1 to B8 of Example 2, a dielectric layer made of titanium oxide is formed on the surface of the anode foil, similarly to the test electrolytic capacitor A of Example 1. all right. It was also found that an anode layer made of titanium carbide (TiC _X ) was formed at the interface between the substrate and the dielectric layer. The atomic ratio (C / Ti) of carbon (C) and titanium (Ti) in the anode layer made of titanium carbide is about 0.03, about 0.05, about 0.1, about 0.25, about 0.5, about 0.75, about 0.9, about 1, and about 1.1). Similarly to the test electrolytic capacitor A of Example 1, the dielectric layer contains carbon and the oxygen concentration decreases from the dielectric layer toward the anode layer. all right.

  Next, as in Example 1, the leakage current between the anode foil and the cathode was also measured for the electrolytic capacitors B1 to B8 for test in Example 2. These results are shown in Table 2. In Table 2, as in Table 1, the measurement result of the leakage current of each test electrolytic capacitor of Example 2 was normalized to 100 as the measurement result of the leakage current of the test electrolytic capacitor A of Example 1, The normalized leakage current value is shown.

As shown in Table 2, it can be seen that all of the test electrolytic capacitors B <b> 1 to B <b> 8 of Example 3 have a smaller leakage current than Comparative Example 1. It can also be seen that the leakage current is relatively large in the test electrolytic capacitors B1 and B8. Thus, for the reduction of the leakage current between the anode foil and the cathode, the atomic ratio (C / Ti) of carbon (C) and titanium (Ti) in the anode layer made of titanium carbide (TiC _X ). ) Is preferably in the range of 0.05 to 1, more preferably 0.1 to 0.75.

(Example 3)
In Example 3, the correlation between the thickness of the dielectric layer of the present invention and the leakage current between the anode foil and the cathode was verified.

  Here, in Example 3, in the production of the test electrolytic capacitor A of Example 1 described above, the voltage during anodization was about 1 V, about 2 V, about 3 V, about 7.5 V, about 10 V, about 12. Other than that, each of the test electrolytic capacitors C1 to C6 was prepared in the same manner as the test electrolytic capacitor A of Example 1 except that the voltage was changed to 5V.

(Evaluation)
For the electrolytic capacitors C1 to C6 for test of Example 3, the anode foil was measured by ESCA in the same manner as in Example 1. As a result, in the test electrolytic capacitors C1 to C6 of Example 3, a dielectric layer made of titanium oxide is formed on the surface of the anode foil, similarly to the test electrolytic capacitor A of Example 1. all right. The thicknesses of the dielectric layers were about 2 nm, about 4 nm, about 6 nm, about 15 nm, about 20 nm, and about 25 nm, respectively. Further, an anode layer made of titanium carbide (TiC _x ) is formed at the interface between the substrate and the dielectric layer, and the atomic ratio (C / C) of carbon (C) and titanium (Ti) in the anode layer. Ti) was about 0.5. Similarly to the test electrolytic capacitor A of Example 1, the dielectric layer contains carbon and the oxygen concentration decreases from the dielectric layer toward the anode layer. all right.

  Next, in the same manner as in Example 1, the electrolytic capacitors C1 to C6 for Example 3 also have a voltage that is about ½ of the applied voltage during anodization between the anode foil and the cathode, that is, about 0. A constant voltage of about 0.5 V, about 1 V, about 3.8 V, about 5 V, and about 6.3 V was applied, and leakage current after about 20 seconds was measured. These results are shown in Table 3. In Table 3, as in Table 1, the measurement result of the leakage current of each test electrolytic capacitor of Example 3 was normalized with the measurement result of the leakage current of the test electrolytic capacitor A of Example 1 as 100, The normalized leakage current value is shown.

As shown in Table 3, it can be seen that all of the test electrolytic capacitors C <b> 1 to C <b> 6 of Example 3 have a leakage current smaller than that of Comparative Example 1. It can also be seen that the leakage current is relatively large in the test electrolytic capacitors C1 and C6. From this, it was found that the thickness of the dielectric layer is preferably in the range of 4 nm to 20 nm, and more preferably in the range of 6 nm to 15 nm.

  From the above results, it was found that all of the anode foils produced in Examples 1 to 3 had good characteristics and could be used for the solid electrolytic capacitor of the above embodiment.

It is a partially broken side view of the solid electrolytic capacitor by one Embodiment of this invention. It is a partial expansion perspective view of the capacitor element inside the solid electrolytic capacitor by one embodiment of the present invention. It is sectional drawing of the anode of the solid electrolytic capacitor by one Embodiment of this invention. It is sectional drawing of the cathode of the solid electrolytic capacitor by one Embodiment of this invention. 1 is a structural diagram of a test electrolytic capacitor according to Example 1 of the present invention. FIG. It is a figure which shows the measurement result by ESCA about the anode and dielectric material layer which were used with the solid electrolytic capacitor by Example 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Case 2 Capacitor element 3 Sealing material 4, 5 Lead wire 21 Anode foil 21a Base body 21b Anode layer 21c Dielectric layer 21d Electrolyte layer 22 Cathode foil 22a Base body 22d Electrolyte layer 23 Separator 100 Solid electrolytic capacitor

Claims (3)

An anode having at least a surface made of titanium carbide;
An anode layer formed on the anode ;
A dielectric layer formed on the anode layer and made of titanium oxide;
The solid electrolytic capacitor, wherein an atomic ratio (C / Ti) of carbon and titanium in the anode layer is in a range of 0.05-1 . 2. The solid electrolytic capacitor according to claim 1, wherein an atomic ratio (C / Ti) of carbon and titanium in the anode layer is in a range of 0.1 to 0.75 . The thickness of the said dielectric material layer is a solid electrolytic capacitor of Claim 1 or 2 which is the range of 4 nm-20 nm.