DE1564405C3 - Electrolytic capacitor - Google Patents

Description

The invention relates to an electrolytic capacitor.

As is well known, an electrolytic capacitor basically consists of a metal electrode with an oxide skin, which is immersed in an electrolyte liquid together with a second electrode, which is usually made of any non-corrosive metal and is called the counter electrode. the Oxide skin, which is usually formed by anodic oxidation of the electrode, is used as a dielectric Capacitor is effective and must therefore have good insulating properties.

The electrolyte fluid not only serves as an electrical conductor, but also allows minor damage to heal the oxide skin as a result of local breakdown during operation of the capacitor.

In comparison, rrit has other types of capacitors the electrolytic capacitor has the advantage that it has a high capacity per unit volume.

A major disadvantage of electrolytic capacitors, which was previously considered inevitable, is their polar nature. The capacitor has rectifying properties, so that it is only applicable as a capacitor in the reverse direction, i.e. i.e., the electrode with that obtained by anodic oxidation

ίο Oxide skin must be positive for the electrolyte.

It is Z. B. possible, an electrolytic capacitor

manufacture, which is in the reverse direction at a formation voltage of z. B. 40 V has a leakage current of less than 1 μΑ / cm ² . In the forward direction

x5 direction, that is, if the electrode in question forms the cathode, such a capacitor has a leakage current of more than 1 mA / cm ² when a voltage of only a few volts is applied, which increases over time because the oxide layer increases damaged. ,

There are also known so-called bipolar electrolytic capacitors whose two metal electrodes with r of such anodic oxide skin are provided; these are housed in a suitable electrolyte liquid. Such a capacitor can be used for both polarities because one of the two electrodes is always in the reverse direction, but on the other hand the capacitance per unit volume is lower than that of a conventional unipolar electrolytic capacitor.

This type of capacitor is therefore not used in practice used.

The invention creates an electrical capacitor which has a leakage current in both directions of less than 1 μΑ / cm ² at a working voltage, the absolute value of which is about 75% of the formation voltage.

The electrolytic capacitor, which consists of an electrode of a metal with an anodic in a known manner Oxidation obtained, dielectric oxide skin, an electrolyte solution and a metallic counter electrode consists, which can also be provided with such an anodic oxide skin, or of any Another metal, preferably a metal, on which no dielectric due to anodic oxidation Oxide skin is formed, that is to say a metal that is chemically inert in this medium, is according to the invention characterized in that the capacitor contains an electrolyte liquid which has a specific Has resistance less than 10,000 ohm · cm and that of a solvent or mixture of solvents that do not contain or split off hydrogen ions, in which Solvent a salt is dissolved as an oxidizing anion and as a cation one of the alkaline earth metals or comprising earth metals, the liquid containing at most 2 percent by weight water.

The dielectric oxide skin can also be produced by means of the electrolyte liquid used in the context of the invention be formed as a forming liquid, but it has been found that this is not necessary. The dielectric oxide skin can be formed using any forming electrolyte. It is special It is advantageous that, for industrial use, the previously customary forming devices and the customary Can use forming fluids.

In addition to calcium, strontium and barium, the aforementioned alkaline earth metals are also said to be magnesium lock in. The earth metals are the elements of the

3. Main group of the periodic system excluding the element boron. These are therefore aluminum, Scandium, Yttrium and the Lanthanides. When the invention came about it has been shown that other metal ions are not suitable for use in the electrolytic capacitor according to the invention. There wander z. B., if the capacitor is switched in the opposite direction to the formation voltage, alkali metal ions through the dielectric oxide skin and consequently cause a high leakage current of the capacitor emerged.

A type particularly suitable for use in an electrolytic capacitor within the scope of the invention of electrolyte fluid consists of a mixture, of pyridine and another, no hydrogen ions containing or releasing solvents.

According to one embodiment, the liquid consists of at least 90 percent by weight pyridine.

According to a preferred embodiment, the electrolyte consists of a salt or a salt mixture, whose cations are calcium ions and in which at least part of the anions or another solute has oxidizing properties.

Calcium nitrate is preferably used, which is preferably used in high concentrations, up to saturation, is used.

The invention will be discussed in more detail with reference to the following exemplary embodiments.

I. The electrolyte liquids described, their solvents various classes of compounds All of them were used in an electrolytic capacitor made as follows would:

An aluminum foil with a degree of purity of 99.99% was chemically pickled in a solution of 5 g of potassium dichromate per liter of a 50% solution of sulfuric acid in water at a temperature of 110 ^{° C. for three minutes.} Anode plates, which had a macroscopically measured surface of 3 cm ^{2 on} both sides, were punched from the thus pickled foil. The plates were formed to 10 V and in some cases to 100 V in an electrolyte solution which contained 7.5 g of borax (Na ₂ B ₄ O ₇ · 1OH ₂ O) and 30 g of boric acid in 1 liter of water until the

ίο leakage current was less than 1 μΑ / cm ² .

The formed electrode was then placed in one of the below-mentioned new electrolyte liquids with a platinum counter electrode, and the capacitor thus obtained was conditioned by connecting it to the formation voltage Vp (10 or 100 V) for 10 minutes, the leakage current i _{a was} measured. The capacitor was then connected to 7.5 or 75 V in the opposite direction and the leakage current (/ *) was measured again. Instead of the above-mentioned boric acid solution, the usual glycol-boric acid-ammonia electrolyte liquid can be used for formation with the same result.
A number of electrolyte fluids according to the invention are given in the table below, the formation voltage Vf used, the leakage current obtained in both directions / «and / j; and the specific resistance of the liquid being given.

The anhydrous salt was obtained in that the salt in question containing water of crystallization, e.g. B. Mg (NO the relevant salt containing water of crystallization, e.g. Mg (NO ₃ ) J · 6H ₂ O, Ca (NO ₃ ) ₂ · 6H ₂ O or Sr (NO ₃ ), 4H ₂ O for a few hours 160 ⁰ C was heated.

Electrolyte fluid Vt (volts) U (μΑ / cm ² ) i _k (μΑ / cm ² ) κ (Ohm ■ cm
at 2O ⁰ C) 1 6 g Ca (NO ₃ ),
36 g pyridine
24 g of N, N-dimethylacetamide 10 0.1 0.25 460 2 2.8 g of Sr (NO ₃ ) ₂
29 g pyridine
19 g of N, N-dimethyl acetamide 10 0.1 0.25 3350 3 1.8 g Ba (NO ₃ ) ₂
40 g pyridine
25 g of N, N-dimethylacetamide 10 0.1 0.30 1080 4th 4 g Mg (NO ₃ ),
29 g pyridine
36 g of N, N-dimethylacetamide 10 - 0.06 0.04 200 5 5.3 g Ca (NO ₃ ) ₂
62 g of N, N-dimethylacetamide 10 0.28 0.23 180 6th 6.15 g Ca (NO ₃ ) ₂
60 g cyclohexanone 100 0.40 2.5 7750 7th 5.3 g Ca (NO ₃ ),
78 g dimethyl sulfoxide 10 0.04 0.03 118 8th 5.7 g Ca (NO ₃ ),
37.1 g of ethyl cyanoacetate
9.8 grams of pyridine 10 0.50 0.30 4760

Electrolyte fluid

V _F (volt) i _a (μΑ cm ² ) i _k (μΑ cm ² ) κ (ohm cm

at 20 "C)

10
11
12th
13th
14th
15th
16
17th

8.2g Ca (NOa) ₂ 10

62.5 g of dimethyl sulfoxide
20.5 g maleic anhydride

5.1 g Ca (NO ₃ ) ₂ 10

11.4 g κ-picoline

32.3 g of Ν, Ν-dimethylacetamide

5.53 g Ca (NOa) ₂ 10

37.18 g quinoline 100

25.87 g of Ν, Ν-dimethylacetamide

7.4 g Ca (NO ₃ ), 10

40.0 g pyridine 100 30.9 g benzonitrile

7.7 g Ca (NOa) ₂ 10

39.5 g pyridine
31.3 g of nitroethane

6.4 g Ca (NOa) ₂ 10

25.2 grams of pyridine

68.8 g of nitromethane

8.3 g Ca (NOa) ₂ 10

37.6 g cyclohexanone 100

27.9 g Ν, Ν-dimethylacetamide

5.0 g Ca (NOa) ₂ 10 38.2 g pyridine 100

36.6 g of nitrobenzene

7.1 g Ca (NOa) ₂ 10

31.7 g pyridine

37.7 g of dimethyl sulfoxide

3.3 g Y (NOa) ₃ 10

55.8 g pyridine

6.6 g Ca (NOa) ₂ 10

35.2 g pyridine

30.3 g cyclohexanone

8.9 g Y (NOa) ₃ 10

59.4 g Ν, Ν-dimethylacetamide

7.9 g Ca (NO ₃ ) ₂ 10

56.4 g of Ν, Ν-dimethylacetamide

7.2 g Ca (NOa) ₂ 10 6.0 g urea

57.1 g pyridine

4.0 g Ca (NOa) ₂ 10

22.7 grams of pyridine
77.7 g Ν, Ν-dimethylacetamide 0.52

0.01

0.03 0.02

0.01 0.01

0.01

0.02

0.01 0.2

0.1 0.03

0.5

0.3

0.01

0.02

0.02

0.02

0.02

0.27

0.08

0.02 0.5

0.04 1

0.10

0.2

0.1 1

0.04 0.1

0.2

0.6

0.3

0.1

0.02

0.02

0.3

174

400

745

9000

710

816

830

8900

182

1750

6250

640

456

1230

238

24 5.9 g Ca (NOa) ₂
67.2 grams of N-methylpyrrolidone 10
100 0.01
0.3 0.2
0.3 348 25th 6 g Ca (NO ₃ I ₂
45 g of methyl ethyl ketone 10
100 0.01
1.5 0.02
1.5. 1650 26th 6 g Ca (NO ₃ ),
45 g of furfural 10 0.02 0.2 2220 27 16.8 g Mg (NOa) ₂
55.4 g of Ν, Ν-dimethylacetamide 100 0.06 0.1 292 28 5.4 g Ca (NOa) ₂
45.8 grams of pyridine
15.1 g of acetamide 10 0.13 0.15 535

II. Anode plates, which were produced in a manner similar to the previous example, were formed up to 40 V in the same electrolyte solution as in the previous example until the leakage current was less than 1 μΑ / cm ² . The formed electrode, together with a platinum counter electrode, was then placed in a saturated solution of anhydrous Ca (NO ₃ ) in pure pyridine with a water content of less than 0.1 percent by weight. This electrolyte liquid had a specific resistance value of 800 ohm · cm.

The anhydrous calcium nitrate was obtained by that the commercially available calcium nitrate Ca (NOG) ₂ ■ 6H ₂ O for several hours was heated to 160 ⁰ C long. A small part of the calcium nitrate decomposes into Ca (OH) ₂ by pyrolysis, but this is harmless because Ca (OH) _{2 is} not soluble in pyridine.

The capacitor was then completed by connecting it to the forming voltage (40 V) for ten minutes. The leakage current was then less than 0.3 μΑ / cm ² . The capacitor obtained was then connected to 30 V in the opposite direction. After twelve hours, the leakage current in this direction had decreased to less than 1 μΑ / cm ² .

It was found that when the capacitor was connected in this direction for the next 400 hours the leakage current continued to decrease slowly.

If the aforementioned formation is not in the mentioned borax-boric acid solution, but in a conventional one Glycol-Boric-Acid-Ammonia Electrolyte Fluid gives the same results.

III. Tantalum capacitors were manufactured and tested in the manner described in Example I.

The punched Ta plates were chemically stained in a freshly prepared solution consisting of 10 ml concentrated HNO ₃ , 10 ml HF 40% and 25 ml H ₂ SO ₄ (d = 1.84). The plates were formed in a conventional electrolyte based on borax boric acid, glycol boric acid, in 0.1 molar phosphoric acid or in dilute nitric acid. They were also formed and shaped at 40 V until the leakage current was less than 1 μΑ / cm ² . They were then assembled into a capacitor in the manner described in Example I. When creating the. Formation voltage, the leakage current was also less than 0.3 μΑ / cm ² .

When connecting to 30 V in the opposite direction, the leakage current decreased to less than 3 μΑ / cm ² in that direction and then remained constant.

IV. Al plates formed according to Example I were assembled to a capacitor, the operating electrolyte being a solution of anhydrous Ca (NO ₃ ) ₂ in a mixture with 90% anhydrous pyridine and 10 <anhydrous dimethylformamide with a specific resistance value of 40000hm · cm was used. A capacitor was obtained which had a leakage current of less than 0.1 μΑ / cm ² in the direction of the formation voltage at 30 V and a leakage current of less than 3 μΑ / cm 2 at the same voltage in the opposite direction, which after twelve hours cm ² sank.

609 615/28

Claims (6)

Patent claims: 1. Electrolytic capacitor, which consists of an electrode of a metal with an anodic through Oxidation obtained, dielectric oxide skin, an electrolyte solution and a counter electrode consists, the latter preferably consists of a metal that is also anodic with such Is provided with an oxide skin, or made of a metal that is chemically inert in this medium, characterized in that the capacitor contains an electrolyte liquid which has a resistivity of less than 10,000 ohm-cm and that of a solvent or a mixture of solvents that do not contain hydrogen ions or split off, is composed, in which solvent a salt is dissolved, which is an oxidizing Anion and as a cation one of the alkaline earth metals or the earth metals, and which liquid Contains a maximum of 2 percent by weight of water. 2. electrolytic capacitor according to claim 1, characterized in that the solvent for the anhydrous electrolyte made from a mixture of pyridine and another does not have hydrogen ions containing or splitting off solvent. 3. electrolytic capacitor according to claim 2, characterized in that the solvent to consists of at least 90% pyridine. 4. electrolytic capacitor according to claim 1, characterized in that the electrolyte consists of one Salt or a salt mixture, the cations of which are calcium ions and in which at least one Part of the anions has oxidizing properties, or the electrolyte has another oxidizing property Substance is added. 5. electrolytic capacitor according to claim 4, characterized in that in the electrolyte liquid Calcium nitrate is dissolved. 6. electrolytic capacitor according to claim 5, characterized in that the calcium nitrate in the Electrolyte solution is present in saturation concentration.