JP2015073015A - Electrode foil, electrolytic capacitor and method of manufacturing electrode foil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode foil that can implements increase of the capacity, reduction of occurrence of short-circuit, and enhancement of repair of damage of a dielectric layer, a method of manufacturing the same and an electrolytic capacitor.SOLUTION: An electrode foil has a base material which is formed of first valve metal or alloy thereof and has many recess portions and a surface having no recess portion on the surface layer portion thereof, and a dielectric layer formed on the inner walls of the recess portions and the surfaces. A protection layer is formed above the dielectric layer provided on the surface and above the dielectric layer in a recess portion upper side area at the upper side of a half position of the depth of the recess portion. The dielectric layer contains the largest amount of the first valve metal at a portion which is formed below at least the protection layer, and secondly largest amount of second valve metal different form the first valve metal. The protection layer contains the largest amount of second valve metal, and also contains secondly largest amount of first valve metal.

Description

  The present invention relates to an electrode foil, an electrolytic capacitor using the electrode foil, and a method for manufacturing the electrode foil.

  Examples of the electrolytic capacitor include a low ESR solid electrolytic capacitor used around a CPU of a personal computer, a high-voltage aluminum electrolytic capacitor used for an inverter power supply for large equipment, an automotive inverter power supply such as a hybrid car, and the like. . These electrolytic capacitors are strongly desired to have a small size and a large capacity.

  In order to increase the capacity of the electrolytic capacitor, it is possible to increase the surface area by forming a large number of concave portions by etching on a base material made of aluminum foil or by forming a plurality of columnar bodies by vapor deposition on the base material. It is valid. It is also effective to form a dielectric film made of titanium oxide having a high dielectric constant on the surface of the substrate.

  For example, Patent Document 1 is known as prior art document information related to the above-described large capacity technology.

JP 2012-124347 A

  In the technique described in Patent Document 1, zirconium or hafnium is sputtered on a base material made of aluminum having a number of concave portions formed on the surface, thereby forming a metal layer (zirconium layer or hafnium layer). Thereafter, a dielectric film is formed by chemical conversion. The content of zirconium or hafnium in the dielectric film gradually decreases from the opening of the recess toward the depth of the recess.

  With such a configuration, an effect of reducing the leakage current can be obtained, but there is a problem that a short circuit occurs when a large voltage is suddenly applied to the electrolytic capacitor.

  In Patent Document 1, since the metal layer is formed by a dry process such as sputtering, the metal layer is easily attached to the inner wall on the opening side of the recess, but the metal layer is attached to the inner wall on the bottom side of the recess. Difficult to attach. Since the content of zirconium in the electrolytic capacitor is small, there is a problem in that there is a limit to the improvement in capacitance.

  Therefore, the present invention realizes an increase in the capacity of an electrolytic capacitor, and an electrode foil capable of avoiding occurrence of a short circuit even when a large voltage is suddenly applied, a manufacturing method thereof, and an electrolysis using the electrode foil The object is to provide a capacitor.

  The first invention of the present invention comprises a base material comprising a first valve metal or an alloy thereof and having a large number of recesses in the surface layer portion and a surface on which the recesses are not formed, an inner wall of the recess, and the surface And a dielectric layer formed on the electrode foil. A protective layer is formed on the dielectric layer provided on the surface and on the dielectric layer in the upper region of the concave portion above ½ of the depth of the concave portion. , At least in the part formed under the protective layer, the first valve metal is most contained, and the second valve metal, which is a valve metal different from the first valve metal, is next contained in the most amount, The protective layer contains the second valve metal most, and the second valve metal next.

  The protective layer may contain at least one of carbon, sulfur, and nitrogen.

  The first valve metal may be aluminum, and the second valve metal may be zirconium or hafnium.

  The protective layer can contain 0.5 to 25 atomic% of aluminum.

  The protective layer can be formed on the dielectric layer also in the lower region of the concave portion that is lower than ½ of the depth of the concave portion.

  The base material may have a columnar body in a surface layer portion thereof, and the recess may be formed by a space between the columnar bodies adjacent to each other.

  A second invention of the present invention includes an anode part, a cathode part, a capacitor element having a dielectric film formed between the anode part and the cathode part, and an anode terminal electrically connected to the anode part. An electrolytic capacitor comprising: a cathode terminal electrically connected to the cathode portion; and an exterior body that houses the capacitor element so that the anode terminal and a part of the cathode terminal are exposed to the outside. At least one of the anode part and the cathode part and the dielectric film are made of the electrode foil according to the first invention.

  According to a third aspect of the present invention, a plurality of concave portions are formed in a surface layer portion of a base material made of the first valve metal or an alloy thereof, and the concave portions and the concave portions are formed in the surface layer portion of the base material. A recess forming step of providing a non-surface, and after the recess forming step, the recess upper region above the half of the depth of the recess and the surface is a valve metal different from the first valve metal. A plating step of forming a protective layer made of an oxide containing the largest amount of the two-valve metal and the second largest amount of the first valve metal by plating, and after the plating step, the protective layer was formed And forming a dielectric layer between the protective layer and the base material by forming the base material.

  By the chemical conversion step, the dielectric layer can contain the first valve metal most and the second valve metal next.

  In the recess forming step, by forming a large number of columnar bodies made of the first valve metal on the base material, spaces between the columnar bodies adjacent to each other can be made the large number of recesses.

Although a short circuit may occur when a large voltage is suddenly applied to the electrolytic capacitor, according to the present invention, the short circuit is prevented by forming a protective layer on the dielectric layer. More specifically, a protective layer is formed at least in the upper region of the concave portion (the region higher than ½ of the depth of the concave portion), which is particularly prone to electric field concentration and high possibility of occurrence of a short circuit. High effect. In particular, the effect becomes higher when the conductivity is 1.0 × 10 ^{−10 to} 50 S / cm.

  In addition, if damage such as cracks occurs in the dielectric layer, it causes problems such as an increase in leakage current. However, according to the present invention, a protective layer exists on the dielectric layer, and among the constituent elements of the protective layer, The element with the largest composition and the element with the second largest number are the same as the elements with the second largest number and the largest number among the constituent elements of the dielectric layer. Therefore, the most or the second most of the constituent elements of the protective layer can be diffused in the damaged portion of the dielectric layer, and the damage can be sufficiently repaired. That is, damage repairability can be improved.

  Since the protective layer contains at least one of carbon, sulfur, and nitrogen, the protective layer is not insulating or conductive, and can be made highly resistant. Therefore, the effect of preventing short circuit can be further enhanced.

  Zirconium oxide and hafnium oxide, like titanium oxide, have a higher dielectric constant than aluminum oxide. Further, since zirconium oxide and hafnium oxide have a binding energy with oxygen closer to that of aluminum than titanium oxide, these metals can be formed simultaneously. On the other hand, aluminum and titanium tend to be preferentially formed into aluminum oxide. Therefore, according to the present invention, the capacity of the electrolytic capacitor can be increased.

  Since the protective layer contains 0.5 to 25 atomic% of aluminum, it has an effect of improving the conductivity of the protective layer.

  Even in the lower region of the concave portion that is lower than ½ of the depth of the concave portion, the short-circuit preventing effect can be further enhanced by forming the protective layer on the dielectric layer. Moreover, even when damage occurs in the lower region of the recess, the repairability of damage can be further improved.

  Rather than etching the base material, the surface area of the base material can be increased by forming a columnar body by vapor deposition and forming a recess by the space between the adjacent columnar bodies. A large capacity can be realized.

  By using the electrode foil according to the first invention of the present invention for at least one of the anode part and cathode part of the electrolytic capacitor and the dielectric film, the capacity of the electrolytic capacitor is increased, and a short circuit occurs when a large voltage is suddenly applied. Avoidance and improvement of damage repairability can be achieved.

  By the way, when a deposited layer (corresponding to a protective layer) is formed by sputtering, a metal layer (for example, a zirconium layer) having high conductivity is formed. Due to the principle of the sputtering process, a metal layer is likely to adhere to the inner wall on the opening side of the recess, but it is difficult to adhere the metal layer to the inner wall on the bottom side of the recess. If the metal layer is not formed on the bottom side of the recess, the content of zirconium in the formed dielectric film is reduced, and there is a problem that the electrostatic capacity cannot be increased.

In the manufacturing method according to the present invention, the protective layer is formed using a solution process (plating method). Although the protective layer is not a metal layer but an oxide layer, it does not have an insulating property and preferably has a high resistance of 1.0 × 10 ^{−10 to} 50 S / cm. Further, the protective layer has a higher conductivity than the dielectric layer. If the protective layer formed by plating is a metal, the protective layer has high conductivity, so that the electroplating current is concentrated in the opening of the relatively projecting recess, resulting in deposits from electroplating. Some protective layers are consistently deposited around the opening and are difficult to deposit on the bottom side of the recess.

  On the other hand, in the manufacturing method according to the present invention, in the initial stage of plating, current concentrates in the opening of the recess, so that a protective layer is formed from the vicinity of the opening. Since it is a characteristic oxide, the plating current hardly flows through the protective layer. Therefore, after the initial stage, a plating current flows on the inner wall of the concave portion of the base material on which the protective layer is not formed or on the surface of the base material, and the protective layer is formed in that portion. Accordingly, the protective layer can be easily formed on the inner wall of the concave portion of the base material or the entire surface of the base material, and the capacity of the electrolytic capacitor can be increased.

  As described above, according to the present invention, it is possible to realize a large capacity, reduce the occurrence of a short circuit, and improve the damage repairability of the dielectric layer.

The perspective view of the electrolytic capacitor in a 1st embodiment of the present invention. Sectional drawing of the electrode foil in 1st Embodiment of this invention The schematic cross section which shows the principal part of the capacitor | condenser element in 1st Embodiment of this invention Sectional drawing which shows the manufacturing process of the electrode foil in 1st Embodiment of this invention. Sectional drawing of the base material for electrode foils in another example of 1st Embodiment of this invention Sectional drawing of the capacitor | condenser element in another example of 1st Embodiment of this invention. The perspective view of the electrolytic capacitor in 2nd Embodiment of this invention Schematic sectional view of the electrode foil in the third embodiment of the present invention The figure which shows the composition of the principal part of the capacitor | condenser element of 1st Embodiment of this invention. The figure which shows the composition of the principal part of the capacitor element of the reference example Photo of TEM image of main part of capacitor element of first embodiment of the present invention

(First embodiment)
Hereinafter, the electrode foil in the first embodiment, the manufacturing method thereof, and the electrolytic capacitor using the electrode foil will be described.

  The electrolytic capacitor 1 according to the first embodiment shown in FIG. 1 includes an anode part 2, a dielectric layer (number 3 in FIG. 3) formed on the surface of the anode part 2, and at least the dielectric layer 3 on the dielectric layer 3. A protective layer (part number 40 in FIG. 3) formed in part, a solid electrolyte layer (polypyrrole) formed on the dielectric layer 3 and the protective layer 40 exposed from the protective layer 40, and the solid electrolyte layer A plurality of capacitor elements 5 each having a cathode portion 4 made of a cathode lead layer (carbon layer, silver layer) formed in the above are laminated. Between the capacitor elements 5 and between the capacitor element 5 and the cathode terminal 6B are fixed with a conductive adhesive (silver paste).

  The electrolytic capacitor 1 has an anode terminal 6A and a cathode terminal 6B for drawing out the electrodes of the anode part 2 and the cathode part 4, respectively, and a capacitor element 5 is molded so that a part of the anode terminal 6A and the cathode terminal 6B is exposed to the outside. And an exterior body 7 to be accommodated.

  FIG. 2 is a cross-sectional view of the electrode foil 2E. In FIG. 2, a dielectric layer 3 and a protective layer 40 described later are omitted. FIG. 3 is a schematic cross-sectional view of the main part of the capacitor element 5 provided with the electrode foil 2E. As shown in FIG. 2 and FIG. 3, the anode portion 2 uses a base material 8 made of aluminum, and the base material 8 has a large number of concave portions 9 and these concave portions 9 formed in the surface layer portion 8S. It has a surface 11 that is not. Dielectric layer 3 is formed on inner wall 12 of recess 9 and surface 11 of substrate 8. The dielectric layer 3 only needs to be formed in a region where the solid electrolyte layer is to be formed, and the dielectric layer 3 is not formed at the bonding portion between the anode portion 2 and the anode terminal 6A, or is removed at the time of bonding.

  A protective layer 40 having high resistance is formed on the dielectric layer 3 in the concave upper region 9U above ½ of the depth d of the concave 9 (on the opening 10 side).

The dielectric layer 3 is composed of an oxide of a first valve metal and an oxide of a second valve metal. For example, when the first valve metal is aluminum and the second valve metal is zirconium, zirconium oxide and aluminum oxide (AlZr _x2 O _y2 , where x2> 0, y2> 0), and the composition (atomic%) in the dielectric layer 3 is the most in aluminum (first valve metal) and zirconium (different from aluminum) The second largest metal is the valve metal.

The protective layer 40 is composed of an oxide of a first valve metal and an oxide of a second valve metal. For example, when the first valve metal is aluminum and the second valve metal is zirconium, zirconium oxide and aluminum oxide (AlZr _x1 O _y1 , where x1> 0, y1> 0), and the composition (atomic%) in the protective layer 40 is zirconium (second valve metal, which is a valve metal different from aluminum). Most of them are aluminum (first valve metal).

  And the protective layer contains 0.01-5.0 atomic% of at least one of carbon, sulfur, and nitrogen. Specifically, it is more preferable to increase the amount of carbon than sulfur or nitrogen. Specifically, sulfur and nitrogen are 0.01 to 1.0 atomic%, and carbon is 0.1 to 5.0 atomic%. Is desirable. By doing in this way, the electroconductivity of a protective layer can be improved.

  In FIG. 3, there is a portion where the protective layer 40 is not formed in the concave portion lower region 9 </ b> D below ½ of the depth d of the concave portion 9 (on the bottom portion 14 side), and the dielectric layer 3 is the protective layer. Although it is exposed from 40, it is preferable to form the protective layer 40 on the dielectric layer 3 in the entire region of the concave upper region 9U and the concave lower region 9D (see FIG. 6).

  Hereinafter, the manufacturing method of the electrode foil 2E will be described with reference to FIG.

  First, a high-purity aluminum foil having a thickness of 30 to 120 μm and a purity of 99.9% or more was prepared as the base material 8. FIG. 4A is a cross-sectional view of the vicinity of the surface layer 8S on one main surface of the main surfaces of the base material 8. FIG.

  Next, as shown in FIG. 4B, the surface layer portion 8S of the base material 8 is roughened to form a large number of concave portions 9A (recessed portion forming step). By this step, the surface layer portion 8S has a large number of concave portions 9A and a surface 11A on which the concave portions 9A are not formed. The recess 9A has a depth d and an inner wall 12A. Moreover, 9 A of recessed parts may be formed in both the main surfaces of the base material 8, and may be formed only in one main surface.

  The recess 9A can be mechanically formed by, for example, blasting, or can be chemically formed (chemical etching) by immersion in a hydrochloric acid solution.

After the recess forming step, as shown in FIG. 4 (c), electrolytic plating is performed on the substrate 8 on which the recess 9A is formed. For example, when the first valve metal is aluminum and the second valve metal is zirconium, the protective layer 40 made of a compound of zirconium oxide and aluminum oxide (AlZr _x1 O _y1 ) is formed (plating step). The maximum thickness of the protective layer 40 is 5 to 300 nm, and it is preferable that the protective layer 40 is formed to have a thickness of 1/50 or more of the average thickness of the dielectric layer 3 after chemical conversion. If the amount is less than this, the effect of reducing the occurrence of short circuits and improving the damage repairability of the dielectric layer can hardly be obtained.

  The protective layer 40 is formed on at least the surface 11A of the substrate 8 and the inner wall 12A of the concave upper region 9UA of the concave 9A. Further, the protective layer 40 is preferably formed also on at least a part of the inner wall 12A of the recess lower region 9DA of the recess 9A.

  Next, as shown in FIG.4 (d), the base material 8 in which the protective layer 40 was formed is formed (chemical conversion process). In the chemical conversion step, the base material 8 is placed in the electrolyte solution as an anode and anodized so that the vicinity of the exposed region of the base material 8 from the protective layer 40 and the vicinity of the contact region of the base material 8 with the protective layer 40 are dielectric layers. 3 That is, the dielectric layer 3 is formed on the inner wall 12 of the concave portion 9 of the base material 8 and on the surface 11 of the surface layer portion 8S of the base material 8 where the concave portion 9 is not formed. Then, the protective layer 40 is formed on the dielectric layer 3 provided on the surface of the substrate 8 and on the dielectric layer 3 in the concave upper region 9U that is higher than ½ of the depth of the concave 9. Will be.

For example, when the first valve metal is aluminum and the second valve metal is zirconium, the dielectric layer 3 is made of a compound of zirconium oxide and aluminum oxide (AlZr _x2 O _y2 ). An aqueous solution of ammonium borate, ammonium phosphate, ammonium adipate or the like is used for the electrolytic solution for chemical conversion.

  As can be seen from FIG. 1 and FIG. 3, the anode portion 2 and the dielectric film of the electrolytic capacitor 1 of FIG. 1 are composed of the electrode foil 2E of FIG.

(Example A)
As Example A according to the first embodiment, a sample A1 was manufactured by the following manufacturing method.

  First, as shown in FIG. 4A, a high-purity aluminum foil having a thickness of 110 μm and a purity of 99.95% was prepared as the base material 8.

(Recess formation process)
Next, as shown in FIG.4 (b), the surface layer part 8S of the base material 8 is roughened, and many recessed parts 9A are formed (recessed part formation process).

  In the present embodiment, a method was used in which the base material 8 was placed between carbon electrode plates in an electrolytic solution mainly composed of hydrochloric acid to perform electrolysis (electrochemical etching). In electrochemical etching, the etching shape varies depending on the current waveform of the electrolysis, the composition of the solution, the temperature, and the like. Therefore, an etching method that matches the performance of the electrolytic capacitor is selected.

  First, by etching the surface layer portion 8S of the substrate 8, fine pits (recessed portions 9A) are formed. In this embodiment, AC etching using a triangular wave is used.

  As the etching solution, an acidic aqueous solution containing chlorine ions and sulfate ions as additives are blended. In the etching step, the base material 8 in a plain (unetched) state is immersed in this etching solution.

The etching process is performed by setting one carbon electrode on each side of the substrate 8 and applying an alternating current to the two carbon electrodes. At this time, the AC power supply conditions are adjusted so that the etching loss per unit area of the substrate 8 is 10 mg / cm ² .

  In order to increase the capacitance, etching is usually performed to a depth of about 30 to 35 μm. By etching to a depth of at least 10 μm or more, a sufficient capacitance can be ensured. In this example, the depth d of the recess 9A from the opening 10A was 30 to 45 μm on average. The sample thus prepared had an average pore diameter (the diameter of the recess 9A) of about 80 to 300 nm. In addition, the protective layer can be easily formed in the subsequent plating step by increasing the porosity in the upper part of the foil in the depth direction of the foil.

  After the etching process, a dechlorination process was performed and dried to produce an etched base material 8, that is, a base material 8 on which a recess 9 </ b> A was formed.

  In addition, when direct current etching is performed, the base material 8 is formed with a relatively straight recess 13A as shown in FIG. Moreover, although the high purity aluminum foil was used for the base material 8, in order to improve foil strength and an electrostatic capacitance, it is also possible to use, for example, an aluminum-zirconium alloy foil and an aluminum-silicon alloy foil.

(Plating process)
After the recess forming step, as shown in FIG. 4 (c), the base material 8 on which the recess 9A is formed is subjected to electrolytic plating to form a protective layer 40 (AlZr _x1 O _y1 , where x1> 0). , Y1> 0) was formed (plating step).

  First, a plating bath was prepared by mixing a first valve metal halide, a second valve metal halide, an organic solvent, and an additive. The valve metal halide is used as a valve metal raw material for forming a protective layer. Suitable valve metal halides include, for example, fluoride, chloride, bromide, iodide and the like. Among these, chloride is more preferable from the viewpoint of easily forming the protective layer and economical efficiency. Therefore, in this example, aluminum chloride was used as the first valve metal halide, and zirconium chloride was used as the second valve metal halide.

  Moreover, as an organic solvent, a dialkyl sulfone is preferable. Examples of the dialkyl sulfone include dimethyl sulfone, diethyl sulfone, and dipropyl sulfone. Moreover, ethyl methyl sulfone and ethyl isopropyl sulfone can also be used, and these organic solvents can also be mixed and used. Here, dimethyl sulfone was used from the viewpoint of plating efficiency. The organic solvent is not limited to these examples, and any organic solvent can be used as long as it can dissolve the valve metal halide and can be efficiently plated.

  As an additive, for example, dimethylamine hydrochloride, ammonium halide, and the like can be used in view of stability of the plating bath, improvement of plating efficiency, and the like.

  As the composition ratio (molar ratio) of the plating bath, a concentration of organic solvent> (first valve metal halide + second valve metal halide)> additive was used.

  Next, the plating process will be described sequentially. A plating bath is placed in the plating bath, and an anode and a cathode (base material 8 with the recess 9A formed therein) are inserted into the plating bath, and both electrodes are energized, thereby charging the first valve metal and the second valve metal. Analyze.

  The anode material is preferably a material made of the first valve metal, the second valve metal, or both. By using such a material, the valve metal compound in the plating bath reduced by plating can be replenished. Alternatively, an inert material can be used, but in this case, it is necessary to replenish the plating bath with a valve metal halide or the like.

  From the viewpoint of electrodeposition efficiency, the plating temperature is preferably not lower than the temperature at which the valve metal halide is dissolved in the organic solvent and not higher than 150 ° C. When dimethyl sulfone is used as the organic solvent as in this embodiment, a plating film (protective layer) with good film quality can be formed at a temperature between 85 and 120 ° C.

When aluminum is used as the first valve metal and zirconium is used as the second valve metal, the current density is preferably between 3 and 120 mA / cm ² from the viewpoint of efficient electrodeposition. More preferably, it is better to set it to 5 to 60 mA / cm ^2, and by doing so, a uniform plating film (protective layer) free from peeling, cracks, etc. can be formed.

For example, when electrolysis was performed at a current density of 30 mA / cm ² , a protective layer of about 175 nm could be formed. At this time, it is possible to arbitrarily form a thin protective layer when the amount of electrolysis is reduced and a thick protective layer when the amount of electrolysis is increased.

  In the description here, both the first valve metal halide and the second valve metal halide are mixed in the plating bath, but it is sufficient that at least the second valve metal halide is dissolved. When the first valve metal halide is not mixed therein, it is supplied by another method. For example, in the case where aluminum is used for the plating anode substrate, the substrate is slightly dissolved after being immersed in the plating bath. This dissolved aluminum compound can be used as the first valve metal raw material of the protective layer. As another method, a material containing the first valve metal can be used for the anode substrate for plating. By doing so, the first valve metal dissolved from the anode substrate during plating is dissolved in the plating bath. Other methods not described may be used.

  In addition, as the first valve metal and the second valve metal, if the valve action metal is selected from Al, Ta, Ti, Nb, Si, Zr, Hf, etc., it is an electrode foil that prevents short circuit and has a large capacitance. be able to. However, (1) the recess 9A can be easily formed by using an Al foil as the substrate, and (2) the dielectric layer 3 can be formed by using Al for the first valve metal and Zr or Hf for the second valve metal. (3) Since Al, Zr, and Hf are close to the Gibbs free energy ΔG ° of oxide generation, the capacitance of the electrolytic capacitor 1 can be increased and the leakage current can be reduced, as will be described later. Therefore, it is preferable to use Al, Zr, and Hf as the first valve metal and the second valve metal. Moreover, although the 1st valve metal and the 2nd valve metal are contained in the protective layer, it may contain the 3rd valve metal which is a valve metal different from the 1st and 2nd valve metal besides this. I do not care.

  In this embodiment, the plating method is used as the method for forming the protective layer. However, if the second valve metal is contained most and the first valve metal is contained next, the method is limited. It is not a thing. For example, the protective layer having the same configuration may be formed by using electroless plating, a coating method, a vacuum process, or the like.

(Chemical conversion process)
Next, the base material 8 on which the protective layer 40 was formed was formed (chemical conversion step).

In the chemical conversion step, the base material 8 is placed in an electrolyte solution as an anode, and anodized to form an oxide film on the opening 10A of the recess 9A, the surface 11A of the base 8 and the inner wall 12A of the recess 9A. This oxide film becomes the dielectric layer 3. In this example, a 7% ammonium adipate aqueous solution was used as the electrolytic solution for chemical conversion. In this example, the applied voltage (formation voltage) at the time of anodic oxidation was formed at a formation voltage of 18 V, a holding time of 30 minutes, 70 ° C., and 0.05 A / cm ² . Through such a chemical conversion step, a dielectric layer 3 (AlZr _x2 O _y2 , where x2> 0, y2> 0) of about 35 nm was formed.

  As described above, sample A1 was completed as electrode foil 2E.

  As a comparative example, a sample X1 was also prepared in which the protective layer was not formed by removing the plating process from the manufacturing method of Example A.

(Composition analysis)
The results of the composition analysis in the thickness direction for Sample A1 and Sample X1 are shown in FIGS. In the same figure, the relationship between the depth (distance) converted value (nm) from the surface of the electrode foil and the atomic concentration (atomic%) obtained from the X-ray photoelectron spectroscopy (XPS) analysis result is shown. The depth conversion value from the surface of the electrode foil was calculated by the following method. That is, using a base material on which a silicon dioxide film having a predetermined thickness is formed as a reference, the atomic concentration is measured by XPS analysis while performing argon sputtering. Then, the relationship between the analysis time and the thickness is derived from the time when the silicon atomic concentration suddenly decreases and becomes almost zero and the actual thickness of the silicon dioxide film. And using this relationship, the depth conversion value from the surface of the electrode foil was calculated from the atomic concentration analysis time of the electrode foil of each sample. Hereinafter, the depth from the surface of the electrode foil indicates this depth converted value, and the film thickness is a value calculated from this converted value.

  9 and 10, the vertical axis indicates the atomic concentration (atomic%), and the horizontal axis indicates the depth conversion value (nm) from the surface.

  First, sample A1 will be described. From FIG. 9, the region (i) having a depth of about 100 nm from the surface is a protective layer, and here, more zirconium is contained as the second valve metal than aluminum as the first valve metal. The inner region (ii) having a depth from the surface of about 100 nm to about 180 nm is a dielectric layer, and here, the first valve metal, aluminum, is more contained than the second valve metal, zirconium. Has been. Moreover, it turns out that the area | region (iii) whose depth from the surface is about 180 nm or more is a base material part, and contains much aluminum which is a 1st valve metal. In particular, in the region (i) which is a protective layer, it is found that carbon is contained in the range of 0.1 to 5.0 atomic%, and 0.01 to 1.0 atomic% is also present in sulfur and nitrogen. Contained. In addition, about nitrogen, since there was little content and it overlapped with a horizontal axis when data was plotted, the data plot was abbreviate | omitted. Thus, by including any of carbon, sulfur, and nitrogen derived from the plating solution in the protective layer, the protective layer can be made highly resistant, not insulating or conductive. The effect of the present invention can be exhibited not only when the protective layer but also the dielectric layer contains any of carbon, sulfur, and nitrogen.

  Next, the sample X1 of the comparative example will be described. From FIG. 10, the region (ii) having a depth of about 80 nm from the surface is a dielectric layer, and here, only aluminum which is the first valve metal was observed as the valve metal. Moreover, it turns out that the area | region (iii) of about 80 nm or more in depth from the surface is a base-material part, and contains the aluminum which is a 1st valve metal. Thus, in the sample X1 without the protective layer, the region (i) does not exist and the second valve metal does not exist. In all regions, carbon, sulfur and nitrogen are not observed.

  FIG. 11 is a TEM image obtained by photographing the dielectric layer 3 and the protective layer 40 formed on the surface 11 where the concave portion 9 is not formed in the sample A1. As shown in the figure, a dielectric layer 3, a protective layer 40, and a cathode portion 4 are sequentially formed on a substrate 8.

(Capacitance)
Capacitance was measured for Sample A1 of Example A and Sample X1 of Comparative Example.

  When measuring the capacitance, each electrode foil cut into 1 × 2 cm was used. As a capacity measurement condition, an LCR meter was used, and the measurement was performed at a 15% ammonium adipate aqueous solution, 30 ° C., and a measurement frequency of 120 Hz.

As a result, the sample A1 formed with 18V as in this example increased in capacitance by 1.5% compared to the sample X1 without the protective layer. For example, sample A1 formed with 100V
Was found to increase by 11% and increase in capacity compared to sample X1.

  As described above, the sample A1 of Example A has a larger capacitance than the sample X1 of the comparative example. This is because, among the constituent elements of the dielectric layer 3, zirconium, which is the second valve metal, has an atomic percentage higher than aluminum which is the first valve metal.

  The protective layer contains 0.1 to 5.0 atomic percent of carbon among carbon, sulfur and nitrogen. Since the protective layer contains not only carbon but sulfur or nitrogen, the protective layer 40 is neither insulating nor conductive, and has high resistance.

  The aluminum content in the protective layer 40 is preferably 0.5 to 25 atomic%. This is because the protective layer 40 becomes an insulator when the thickness is smaller than this range, and the corrosion resistance of the protective layer 40 is lowered when the thickness is larger than this range.

In this embodiment, zirconium is contained as the dielectric film 3, but hafnium may be used instead of zirconium. Hafnium is a quaternary transition metal similar to zirconium, has similar chemical characteristics, has a Gibbs free energy ΔG ° of oxide formation of about −270 kJ eq ⁻¹ , and is about −220 kJ eq of titanium oxide. ⁻¹ is closer to about −260 kJ eq ⁻¹ of aluminum oxide and zirconium oxide. Therefore, even when hafnium is used, it is considered that the electrolytic capacitor 1 can be increased in capacity and leakage current can be reduced by the same principle.

  A conductive polymer layer made of polypyrrole was formed on the above-described electrode foil by chemical polymerization, electrolytic polymerization, dispersion liquid coating / drying, etc., and a carbon layer and a silver layer were further formed to complete a capacitor element.

  Thereafter, a predetermined number of capacitor elements were laminated, the anode part was fixed to the anode terminal by laser welding, and each cathode part and cathode terminal of the capacitor element were fixed by a conductive adhesive (silver paste). Next, the capacitor element was molded with an exterior body so that part of the anode terminal and the cathode terminal was exposed to the outside, thereby completing the electrolytic capacitor.

  Here, the effect that sample A1 reduces the occurrence of a short circuit when a voltage is applied abruptly as compared with sample X1 without a protective layer was observed.

(Second Embodiment)
In the first embodiment, the electrode foil 2E is used as the anode part 2 and the dielectric film of the chip-type electrolytic capacitor 1. However, the electrode foil 2E is used as the anode foil 16 and the cathode foil 17 of the wound electrolytic capacitor 15 shown in FIG. Can do. As one of the anode foil 16 and the cathode foil 17, the electrode foil 2E of the first embodiment may be used, or may be used for both.

  The winding type electrolytic capacitor 15 was impregnated with a capacitor element 19 in which an anode foil 16 (anode portion) and a cathode foil 17 (cathode portion) were wound with a separator 18 interposed therebetween. A cathode material (not shown) such as an electrolytic solution or a solid electrolyte layer, an anode terminal 20 for extracting the electrode of the anode foil 16, a cathode terminal 21 for extracting the electrode of the cathode foil 17, and one of the anode terminal 20 and the cathode terminal 21 The exterior body 22 which accommodates the capacitor | condenser element 19 so that a part may be exposed outside, and the sealing member 23 which seals this exterior body 22 are provided. Examples of the cathode material include a solid electrolyte made of a conductive polymer and an electrolytic solution, and both of them may be used in combination.

  Also in the electrolytic capacitor of the present embodiment, a large capacity can be realized in the same way as the electrolytic capacitor of the first embodiment, and the occurrence of a short circuit can be reduced and the damage repairability of the dielectric layer can be improved.

(Third embodiment)
The difference of the third embodiment from the first embodiment is the structure and forming method of the electrode foil.

  As shown in FIG. 8, the electrode foil 24 of the third embodiment includes a base material 25 made of aluminum, a plurality of columnar bodies 26 made of aluminum formed on the surface of the base material 25, and a surface of the columnar body 26. And a protective layer (not shown) formed on the dielectric layer. The columnar body 26 may be formed on both surfaces of the base material 25, or may be formed only on one surface. In addition to aluminum, the base material 25 may be made of an aluminum alloy, a valve metal such as titanium or tantalum, or other conductive materials.

  The columnar body 26 may have a simple cylindrical shape or a quadrangular prism shape, but may have a structure such as sea grapes in which a plurality of aluminum fine particles 27 are branched.

  A base material 31 is constituted by the base material 25 and the columnar body 26. That is, the base material 31 has the columnar body 26 in the surface layer portion 31 </ b> S, and the recess 32 is formed by the space between the columnar bodies 26 adjacent to each other. And the part which does not comprise the recessed part 32 among the outer edges of the columnar body 26 comprises the surface 33 in which the recessed part 32 is not formed.

  The dielectric layers formed on these columnar bodies 26 are composed of zirconium oxide and aluminum oxide, and contain the most aluminum oxide and the second most zirconium oxide.

  The columnar body 26 can be formed by etching, plating, vacuum deposition, or the like. The columnar body 26 of the present embodiment was formed by vacuum deposition. A thin oxide film (this oxide film is formed in the chemical conversion step described later) on the surface of the evaporated aluminum fine particles 27 by introducing the mixed gas of active gas and inert gas while keeping the inside of the vacuum chamber at 150 to 300 ° C. And is integrated on the base material 25 while maintaining the particle shape. Further, in the depth direction t of the columnar body, the protective layer to be formed next can be easily formed by increasing the porosity in the upper part rather than the lower part.

  After forming the columnar body 26 as described above, a protective layer containing zirconium is formed from above the columnar body 26 by plating. The protective layer contains the most zirconium oxide and the second most aluminum oxide. The maximum thickness of the protective layer is preferably 1 to 100 nm. This is because if the thickness is smaller than this, the short-circuit suppressing effect at the time of rapid voltage application can hardly be obtained.

  In order to reduce the occurrence of short circuits, the protective layer is preferably formed preferentially at the tip 28 of the columnar body 26. This is because a short circuit is likely to occur near the tip 28 of the columnar body 26. In the present embodiment, the protective layer has an average thickness of 10 nm.

  Next, the base material 31 on which the protective layer is formed is formed in the same manner as in the first embodiment.

  The electrode foil 24 formed as described above and an electrolytic capacitor (whether a chip type or a wound type) using the electrode foil 24 can realize a large capacity as in the first embodiment, reduce the occurrence of short circuit, An improvement in the damage repairability of the dielectric layer can be achieved.

  In Example A described above, an alloy of zirconium and aluminum was used as the protective layer. For example, an alloy of aluminum (first valve metal) and hafnium, which is a valve metal (second valve metal) different from aluminum, is used. May be used. In this case, the dielectric layer contains the most aluminium (first valve metal) and the second largest amount of hafnium (second valve metal) at least in the portion formed below the protective layer. The protective layer contains the most hafnium (second valve metal) and the second most aluminum (first valve metal).

  In the first to third embodiments, a high-purity aluminum foil having a purity of 99.95% was used as the “base material made of a valve metal”, but the invention is not limited to this. For example, an element such as zirconium is 0.1% An aluminum foil (valve metal alloy) contained to some extent can also be used as a substrate.

  In addition to polypyrrole, polyethylenedioxythiophene (PEDOT), polyaniline, and the like can also be used as the cathode portion.

  The electrode foil according to the present invention is particularly useful as an electrode foil of an electrolytic capacitor, particularly an anode foil, which is required to have a large capacity, reduce the occurrence of short circuit, and improve the damage repairability of the dielectric layer. Moreover, according to the manufacturing method of the electrode foil by this invention, such an electrode foil of this invention can be manufactured easily. In addition, the electrolytic capacitor according to the present invention can achieve particularly large capacity, reduction in occurrence of short circuit, and improvement in damage repairability of the dielectric layer, and can be applied to various electronic devices and mechanical devices.

DESCRIPTION OF SYMBOLS 1 Capacitor 2 Anode part 2E Electrode foil 3 Dielectric layer 4 Cathode part 5 Capacitor element 6A Anode terminal 6B Cathode terminal 7 Exterior body 8 Base material 9 Recess 9D Recess lower area 9U Recess upper area 10 Opening 11 Surface 12 Inner wall 13A Recess DESCRIPTION OF SYMBOLS 14 Bottom part 15 Capacitor 16 Anode foil 17 Cathode foil 18 Separator 19 Capacitor element 20 Anode terminal 21 Cathode terminal 22 Exterior body 23 Sealing member 24 Electrode foil 25 Base material 26 Column body 27 Aluminum fine particle 28 Tip 31 Base material 32 Recessed part 33 Surface 40 Protective layer

Claims (10)

A base material made of a first valve metal or an alloy thereof, and having a plurality of concave portions on the surface layer portion and a surface on which the concave portions are not formed,
A dielectric layer formed on the inner wall of the recess and the surface;
An electrode foil comprising:
A protective layer is formed on the dielectric layer provided on the surface and on the dielectric layer in the upper region of the concave portion above a half of the depth of the concave portion;
The dielectric layer contains the largest amount of the first valve metal at least in a portion formed below the protective layer, and the second largest valve metal is a valve metal different from the first valve metal. Contains
The protective foil is an electrode foil that contains the second valve metal most and then contains the first valve metal next. The electrode foil according to claim 1, wherein the protective layer contains at least one of carbon, sulfur, and nitrogen. The first valve metal is aluminum;
The electrode foil according to claim 1 or 2, wherein the second valve metal is zirconium or hafnium. The electrode foil according to claim 1, wherein the protective layer contains 0.5 to 25 atomic% of aluminum. The electrode foil according to any one of claims 1 to 4, wherein the protective layer is formed on the dielectric layer also in a concave portion lower side region that is lower than 1/2 of the depth of the concave portion. The electrode foil according to any one of claims 1 to 5, wherein the base material has a columnar body in a surface layer portion, and the concave portion is formed by a space between the columnar bodies adjacent to each other. A capacitor element having an anode part, a cathode part, and a dielectric film formed between the anode part and the cathode part;
An anode terminal electrically connected to the anode part;
A cathode terminal electrically connected to the cathode portion;
An exterior body that houses the capacitor element such that a part of the anode terminal and the cathode terminal is exposed to the outside;
With
7. An electrolytic capacitor comprising at least one of the anode part and the cathode part and the dielectric film comprising the electrode foil according to claim 1. A recess forming step of forming a plurality of recesses in a surface layer portion of a base material made of a first valve metal or an alloy thereof, and providing the surface layer portion of the base material with the recesses and a surface on which the recesses are not formed; ,
After the recess forming step, the recess upper region above the half of the depth of the recess and the surface contain the second valve metal, which is a valve metal different from the first valve metal, and the most A plating step of forming a protective layer made of an oxide containing the next largest amount of the first valve metal by plating;
After the plating step, the base material on which the protective layer is formed is formed, and a chemical forming step of forming a dielectric layer between the protective layer and the base material;
A method for producing an electrode foil, comprising: By the chemical conversion step,
The method for producing an electrode foil according to claim 8, wherein the dielectric layer contains the first valve metal most and the second valve metal next. The said recessed part formation process WHEREIN: By forming many columnar bodies which consist of 1st valve metals in a base material, the space between the said columnar bodies adjacent to each other is made into the said many recessed parts. Manufacturing method of electrode foil.